JP2011029199A - Positive electrode material for lithium secondary battery, positive electrode for lithium secondary battery, and lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manganese compound which can be used for a lithium ion secondary battery excellent in high temperature characteristics such as high temperature stability and high temperature cycle characteristics.
In a positive electrode material containing manganese oxide and / or lithium manganese composite oxide as a positive electrode active material, the amount of PF ₆ anion decomposed by the following storage test is 1 × 10 μm.
The positive electrode material for lithium secondary batteries which is less than mol.
Storage test a) A mixture of EC and DEC (volume ratio 3) containing 24 mg of a positive electrode material on a current collector, Li metal as a counter electrode, and 1.0 mol / L LiPF ₆ as an electrolyte. : 7) was assembled, and this was charged at a charge current density of 0.2 mA / cm ² and an upper limit voltage of 4.2.
After charging to V, the battery element was then disassembled and the positive electrode was
b) Under an argon gas atmosphere c) In a dried polytetrafluoroethylene container,
d) Immerse in a mixture of 1.5 ml EC and 3.5 ml DEC containing 1.0 mol / L LiPF ₆
e) Store at 80 ° C. for one week, measure the amount of PF ₆ anion in the mixed solution before and after storage, and determine the amount of PF ₆ anion decomposition.
[Selection figure] None

Description

  The present invention relates to a positive electrode material for a lithium secondary battery, and more particularly to a positive electrode material that improves high temperature characteristics of a lithium secondary battery, and further relates to a positive electrode containing the positive electrode material and a battery including the positive electrode as a constituent element. .

As a positive electrode active material of a lithium secondary battery, LiMn ₂ O ₄ having a spinel structure, which is a complex oxide of manganese and lithium, has been proposed and actively researched. In addition to high voltage and high energy density, it also has the advantage of being cheaper and more reserve than cobalt and nickel. In addition, the charge / discharge cycle life at room temperature, which has been regarded as a problem, has been improved to a practical level. However, since such a manganese-based lithium secondary battery has a problem that it is inferior in high-temperature stability, the present situation is that the demand for use in a high-temperature environment has not reached a practical level.

Conventionally, various studies aimed at improving cycle characteristics and storage characteristics under a high temperature environment have been reported and reported for improving high temperature stability. For example, Journalof Power Sources
74 (1998) 228-233 proposed that Mn was partially replaced with Co.
Society Proceedings Volume 97-18.494 discloses that a part of Mn is replaced by Co or a part of oxygen is replaced by F has an effect of improving high-temperature cycle characteristics. Japanese Patent Application Laid-Open No. 8-264183 discloses that a coating made of a metal fluoride is provided on the surface of the active material, and Japanese Patent Application Laid-Open No. 8-213014 performs surface modification such as fluorination treatment of the active material. Therefore, the storage characteristics at high temperature are improved. Japanese Patent Application Laid-Open No. 10-125307 reports that the surface of the positive electrode active material is coated with an organic substance containing an amino group.

  Furthermore, as an example of improving the spinel type lithium manganese composite oxide, a layered lithium cobalt composite oxide, a layered lithium nickel composite oxide, and these other metal substitutes are mixed into the spinel type lithium manganese composite oxide. Examples are known. For example, spinel lithium manganese composite oxide and layered lithium cobalt composite oxide are mixed to improve cycle characteristics (Japanese Patent No. 2751624), or lithium nickel cobalt aluminum composite oxide and lithium manganese composite An example of providing an inexpensive and highly safe battery by mixing an oxide (Japanese Patent Laid-Open No. 11-54120) is known.

  However, a major problem for batteries using manganese-based composite oxides is that the cycle characteristics and storage characteristics under high temperature environment are poor, and whether or not this improvement can be made has not been discussed sufficiently. There was no discussion of what kind of manganese-based composite oxide and what kind of compound was good for improving the cycle characteristics and storage characteristics under the environment.

  In the above-described conventional technology, the cycle characteristics and storage characteristics under a high temperature environment are still insufficient, and further improvement of the high temperature stability and cycle characteristics under a high temperature environment has been strongly desired.

  An object of the present invention is to provide a manganese-based compound that can be used for a lithium ion secondary battery having excellent high-temperature characteristics such as high-temperature stability and high-temperature cycle characteristics.

As a result of intensive studies, the present inventors have promoted the decomposition of LiPF ₆ salt in an electrolyte solution under a higher temperature environment, and the conventional positive electrode containing a lithium manganese composite oxide, thereby allowing the PO ₂ F ₂ anion to migrate. It was found to be generated. It was also found that this decomposition reaction depends on the state of the positive electrode and proceeds remarkably in the charged end state. Further, it has been found that the lithium secondary battery using the positive electrode that causes the decomposition reaction of LiPF ₆ remarkably deteriorates in performance particularly at high temperatures. It has also been found that the decomposition reaction of LiPF ₆ is determined not only by the use of additives and the composition of the positive electrode but also by various factors such as the particle size of the positive electrode. From the above, the present inventors have found that it is possible to as an index ease occur decomposition of LiPF _6, lithium secondary battery degradation with excellent high temperature characteristics With hardly cathode occur LiPF ₆ The present invention has been completed.

That is, the first gist of the present invention resides in the following (1) to (20).
(1) In a positive electrode material for a lithium secondary battery containing manganese oxide and / or lithium manganese composite oxide as a positive electrode active material, a battery element is prepared using the positive electrode material, and the positive electrode material charged with the battery element is stored. A positive electrode material for a lithium secondary battery, wherein the decomposition amount of PF ₆ anion measured by the following storage test (I), which is a test, is 1 × 10 μmol or less.

Storage test (I)
a1) A positive electrode formed by forming 24 mg of a positive electrode material into a circular shape having a diameter of 12 mm, and pressure-bonding to a current collector (a circular aluminum expanded metal having a diameter of 16 mm), Li metal as a counter electrode, and 1.0 mol as an electrolyte / L LiPF ₆ containing ethylene carbonate and diethyl carbonate mixed solution (volume ratio 3: 7) was used to assemble a battery element, which was charged to a maximum voltage of 4.2 V at a charging current density of 0.2 mA / cm ² After charging, then disassemble the battery element,
Take out the positive electrode in the charged state, the positive electrode,
b1) In an argon gas atmosphere with a dew point of −75 ° C. or less c1) In a polytetrafluoroethylene container dried at 80 ° C. for 3 hours,
d1) A mixed solution of 1.5 ml of ethylene carbonate and 3.5 ml of diethyl carbonate containing 1.0 mol / L of LiPF ₆ (acid content: 2.0 mmol / L or less, PO ₂ F ₂ anion: 0.5 mmol / L) And soaking in ethanol: 0.01 mg or less),
e1) Store at 80 ° C. for one week, measure the amount of PF ₆ anion in the mixed solution before and after storage (measurement temperature: 20 ° C.), and determine the amount of PF ₆ anion decomposition from the difference.

(2) The positive electrode material for a lithium secondary battery according to (1), wherein the amount of PO ₂ F ₂ anion contained in the liquid after storage obtained according to the storage test (I) is 1 × 10 μmol or less at 20 ° C.
(3) The positive electrode material for a lithium secondary battery according to (1) or (2), wherein the positive electrode material contains a binder resin.

(4) The positive electrode material for a lithium secondary battery according to any one of claims 1 to 3, wherein a PF ₆ anion decomposition inhibitor is dispersed and mixed in the positive electrode material.
(5) In a positive electrode material for a lithium secondary battery containing a positive electrode active material comprising a manganese oxide and / or a lithium manganese composite oxide and a PF ₆ anion decomposition inhibitor, the following storage is provided as the PF ₆ anion decomposition inhibitor: A positive electrode material for a lithium secondary battery, wherein the PF ₆ anion decomposition amount measured by test (II) is 6 × 10 μmol or less.

Storage test (II)
a2) Lithium manganese equivalent to a fully charged state obtained by extracting lithium from a lithium manganese composite oxide having a spinel structure having a composition of Li _{1 + x} Mn _2−x O ₄ (where 0 ≦ X ≦ 0.05) 160 mg of complex oxide (0.05 ≦ Li / Mn molar ratio ≦ 0.09)
b2) In an argon gas atmosphere with a dew point of −75 ° C. or lower,
c2) In a polytetrafluoroethylene container dried at 80 ° C. for 3 hours,
d2) mixed with 160 mg of the PF ₆ anion degradation inhibitor,
e2) A mixed liquid of ethylene carbonate 2.4 ml diethyl carbonate 5.6 ml containing 1.0 mol / L LiPF ₆ (acid content: 2.0 mmol / L or less, PO ₂ F ₂ anion: 0.5 mmol / L or less, And soaked in ethanol: 0.01 mg or less)
f2) Store at 70 ° C. for one week, measure the amount of PF ₆ anion in the mixed solution before and after storage (measurement temperature: 20 ° C.), and determine the amount of PF ₆ anion decomposition.

(6) The positive electrode for a lithium secondary battery according to (5), wherein the amount of PO ₂ F ₂ anion contained in the liquid after storage obtained according to the storage test (II) is 5 × 10 μmol or less at 20 ° C. material.
(7) The lithium secondary battery according to (5) or (6), wherein the amount of ethanol contained in the liquid after storage when the storage in the storage test (II) is further extended for 2 weeks is 1 mg or less Positive electrode material.

(8) The PF ₆ anion degradation inhibitor is dispersed and mixed, (5) to (7)
) The positive electrode material for a lithium secondary battery according to any one of the above.
(9) The positive electrode material for a lithium secondary battery according to any one of (4) to (8), wherein the PF ₆ anion decomposition inhibitor contains a lithium nickel composite oxide.
(10) A compound in which the PF ₆ anion decomposition inhibitor contains at least one element selected from the group consisting of groups 15 and 16 of the periodic table, and a compound having at least a secondary amino group in the molecule , A compound having at least a tertiary amino group in the molecule, a compound having at least one amide bond in the molecule, a compound having at least one nitrogen-containing heterocyclic ring in the molecule, or having at least one hydroxyl group in the molecule The positive electrode material for a lithium secondary battery according to any one of (4) to (8), which contains a compound.

(11) The addition amount of the PF ₆ anion decomposition inhibitor is 0.0001 to 80 with respect to the positive electrode active material.
The positive electrode material for a lithium secondary battery according to any one of (4) to (10), in the range of wt%.
(12) The positive electrode material for a lithium secondary battery according to (9), wherein the addition amount of the PF ₆ anion decomposition inhibitor is in the range of 1 to 80 wt% with respect to the positive electrode active material.

(13) The addition amount of the PF ₆ anion decomposition inhibitor is 0.0001 to 10 with respect to the positive electrode active material.
The positive electrode material for a lithium secondary battery according to (10), which is in the range of wt%.
(14) The manganese oxide and / or the lithium manganese composite oxide is a lithium manganese composite oxide having a spinel structure, in which a part of the manganese site is substituted with at least one element selected from typical elements. The positive electrode material for a lithium ion secondary battery according to any one of (1) to (13).

(15) The positive electrode material for a lithium ion secondary battery according to (14), wherein the typical element that substitutes a part of the manganese site is aluminum and / or lithium.
(16) The positive electrode material for a lithium ion secondary battery according to (14) or (15), wherein the substitution amount of the typical element is 0.05 mol or more in 2 mol of manganese.

(17) The positive electrode material contains a lithium manganese composite oxide having a spinel structure and a lithium nickel composite oxide having a layered structure, and a part of the manganese site of the lithium manganese composite oxide is substituted with another element. (1) to (9), (11), wherein the other element-substituted lithium-manganese composite oxide has an average voltage measured by the following measurement method (I) of 4.059 V or more. The positive electrode material for a lithium ion secondary battery according to any one of (12) and (14) to (16).

<Measuring method of average voltage (I)>
(1) The composite oxide is weighed at a ratio of 75% by weight, acetylene black 20% by weight, and polytetrafluoroethylene (PTFE) powder 5% by weight, and is made into a thin sheet. After adjusting the total weight to 12.5 mg / cm ² , this sample is further pressure-bonded to an aluminum expanded metal to form a test electrode. The test electrode is dried at 120 ° C. under reduced pressure for 1 hour.
(2) A 25 μm porous polyethylene film as a separator under an argon atmosphere,
Lithium metal foil was used as the counter electrode, and 1 mol / liter lithium hexafluorophosphate (LiPF ₆ ) was added as a non-aqueous electrolyte solution to a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7. A CR2032 type coin-type battery is manufactured using the dissolved solution.
(3) The obtained coin-type battery was subjected to a constant current charge / discharge cycle (charge upper limit 4.35 V, discharge lower limit 3.2 V) at a current density of 0.5 mA / cm ^{2 in} an environment of 25 ° C., and the average voltage Ve = Ve = (average charge voltage in the second cycle + discharge average voltage in the second cycle) / 2
Asking. The charge average voltage or discharge average voltage is calculated by measuring the voltage during charging or discharging at intervals of 2 seconds and dividing the value obtained by integrating the voltage over time by the time required for charging or discharging.
(18) The lithium nickel composite oxide is a lithium nickel composite oxide having an average voltage of 3.830 V or less when measured by the following measurement method (II). The positive electrode material for lithium ion secondary batteries as described in any one.

<Measuring method of average voltage (II)>
(1) 75% by weight of lithium nickel composite oxide, 20% by weight of acetylene black and 5% by weight of polytetrafluoroethylene powder are mixed and formed into a thin sheet. After adjusting the total weight to 12.5 mg / cm ² , this sheet is further pressure-bonded to an aluminum expanded metal to form a test electrode. The test electrode is dried at 120 ° C. under reduced pressure for 1 hour.
(2) A 25 μm porous polyethylene film as a separator under an argon atmosphere,
Lithium metal foil was used as the counter electrode, and 1 mol / liter lithium hexafluorophosphate (LiPF ₆ ) was added as a non-aqueous electrolyte solution to a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7. A CR2032 type coin-type battery is manufactured using the dissolved solution.
(3) The obtained coin-type battery was subjected to a constant current charge / discharge cycle (charge upper limit 4.2 V, discharge lower limit 3.2 V) at a current density of 0.2 mA / cm ^{2 in} an environment of 25 ° C., and the average voltage Ve = Ve = (average charge voltage in the second cycle + discharge average voltage in the second cycle) / 2
Asking. The charge average voltage or discharge average voltage is a value obtained by measuring the voltage during charging or discharging at intervals of 2 seconds and dividing the value obtained by integrating the voltage over time by the time required for charging or discharging.

(19) Any one of (14) to (18), wherein the weight ratio of the lithium nickel composite oxide to the total amount of the lithium manganese composite oxide and the lithium nickel composite oxide is 0.7 or less. The positive electrode material for lithium ion secondary batteries as described in 1.
(20) More than 80% of the decomposition product of PF ₆ anion in the liquid after the storage test (I) or (II) is P
The positive electrode material for a lithium secondary battery according to any one of (1) to (25), which is an O ₂ F ₂ anion.

Furthermore, the present inventors use a lithium manganese composite oxide having a spinel structure in which a part of a manganese site is substituted with a specific element and a lithium nickel composite oxide having a layered structure in combination with high temperature characteristics. When the battery characteristics are remarkably improved and the lithium manganese composite oxide having a spinel structure and the lithium nickel composite oxide having a layered structure are used in combination, the lithium manganese composite oxide is relatively higher than usual. It has also been found that battery characteristics including high temperature characteristics are remarkably improved if an average voltage is used.

That is, the second gist of the present invention resides in the following (21) to (26).
(21) A positive electrode material for a lithium ion secondary battery comprising a lithium manganese composite oxide having a spinel structure and a lithium nickel composite oxide having a layered structure, wherein a part of the manganese site of the lithium manganese composite oxide Is substituted with at least one element selected from typical elements. A positive electrode material for a lithium ion secondary battery, wherein

(22) The positive electrode material for a lithium ion secondary battery according to (21), wherein the typical element that substitutes a part of the manganese site is aluminum and / or lithium.
(23) The positive electrode material for a lithium ion secondary battery according to (21) or (22), wherein the substitution amount of the typical element is 0.05 mol or more in 2 mol of manganese.

(24) A positive electrode material for a lithium ion secondary battery comprising a lithium manganese composite oxide having a spinel structure and a lithium nickel composite oxide having a layered structure, wherein one of the manganese sites of the lithium manganese composite oxide Lithium ion secondary battery, characterized in that the average voltage measured by the following measurement method (I) of the other element substituted lithium manganese composite oxide is 4.059 V or more Positive electrode material.

<Measuring method of average voltage (I)>
(1) The composite oxide is weighed at a ratio of 75% by weight, acetylene black 20% by weight, and polytetrafluoroethylene (PTFE) powder 5% by weight, and is made into a thin sheet. After adjusting the total weight to 12.5 mg / cm ² , this sample is further pressure-bonded to an aluminum expanded metal to form a test electrode. The test electrode is dried at 120 ° C. under reduced pressure for 1 hour.
(2) A 25 μm porous polyethylene film as a separator under an argon atmosphere,
Lithium metal foil was used as the counter electrode, and 1 mol / liter lithium hexafluorophosphate (LiPF ₆ ) was added as a non-aqueous electrolyte solution to a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7. A CR2032 type coin-type battery is manufactured using the dissolved solution.
(3) The obtained coin-type battery was subjected to a constant current charge / discharge cycle (charge upper limit 4.35 V, discharge lower limit 3.2 V) at a current density of 0.5 mA / cm ^{2 in} an environment of 25 ° C., and the average voltage Ve = Ve = (average charge voltage in the second cycle + discharge average voltage in the second cycle) / 2
Asking. The charge average voltage or discharge average voltage is calculated by measuring the voltage during charging or discharging at intervals of 2 seconds and dividing the value obtained by integrating the voltage over time by the time required for charging or discharging.

(25) The lithium nickel composite oxide is a lithium nickel composite oxide having an average voltage of 3.830 V or less when measured by the following measurement method (II). (21) to (24) The positive electrode material for lithium ion secondary batteries as described in any one.

<Measuring method of average voltage (II)>
(1) 75% by weight of lithium nickel composite oxide, 20% by weight of acetylene black and 5% by weight of polytetrafluoroethylene powder are mixed and formed into a thin sheet. After adjusting the total weight to 12.5 mg / cm ² , this sheet is further pressure-bonded to an aluminum expanded metal to form a test electrode. The test electrode is dried at 120 ° C. under reduced pressure for 1 hour.
(2) A 25 μm porous polyethylene film as a separator under an argon atmosphere,
Lithium metal foil was used as the counter electrode, and 1 mol / liter lithium hexafluorophosphate (LiPF ₆ ) was added as a non-aqueous electrolyte solution to a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7. A CR2032 type coin-type battery is manufactured using the dissolved solution.
(3) The obtained coin-type battery was subjected to a constant current charge / discharge cycle (charge upper limit 4.2 V, discharge lower limit 3.2 V) at a current density of 0.2 mA / cm ^{2 in} an environment of 25 ° C., and the average voltage Ve = Ve = (average charge voltage in the second cycle + discharge average voltage in the second cycle) / 2
Asking. The charge average voltage or discharge average voltage is a value obtained by measuring the voltage during charging or discharging at intervals of 2 seconds and dividing the value obtained by integrating the voltage over time by the time required for charging or discharging.

(26) The weight ratio of the lithium nickel composite oxide to the total amount of the lithium manganese composite oxide and the lithium nickel composite oxide is 0.7 or less, and any one of (21) to (25) The positive electrode material for lithium ion secondary batteries as described in 1. Moreover, the following (27)-(31) is mentioned as another summary of this invention.

(27) A positive electrode for a lithium ion secondary battery formed by forming an active material layer containing the positive electrode material for a lithium secondary battery according to any one of (1) to (26) on a current collector.
(28) A lithium ion secondary battery containing the positive electrode material for a lithium secondary battery according to any one of (1) to (26) in a positive electrode.
(29) A lithium secondary battery comprising a positive electrode using the positive electrode material for a lithium secondary battery according to any one of (1) to (26), a negative electrode, and an electrolytic solution obtained by dissolving a lithium salt in a solvent. .

(30) The lithium secondary battery according to (28) or (29), wherein the negative electrode contains a carbon material. (31) The lithium according to any one of (28) to (30), wherein the lithium salt is LiPF _6. Secondary battery.

  ADVANTAGE OF THE INVENTION According to this invention, when using as a lithium secondary battery, a positive electrode material with a favorable high temperature characteristic can be provided. Moreover, according to the present invention, a lithium secondary battery having good high-temperature characteristics can be provided. Accordingly, since manganese, which is an inexpensive material, can be used practically as a positive electrode material, a high-performance, safe and inexpensive lithium secondary battery can be supplied to a wide range of applications, and its industrial value is great.

Hereinafter, the present invention will be described in more detail. A feature of the present invention resides in that a manganese compound that suppresses decomposition of LiPF ₆ under a high temperature environment is used as a positive electrode of a lithium secondary battery. That is, the important point in the present invention is to use a material having low reactivity with respect to LiPF ₆ as the positive electrode material.

Specifically, as a first aspect, as a positive electrode material for a lithium secondary battery containing a positive electrode active material made of manganese oxide or lithium manganese composite oxide, PF ₆ anion measured by the following storage test (I) That whose decomposition amount is 1 × 10 μmol or less is used.
When the decomposition amount of the PF ₆ anion is larger than 1 × 10 μmol, the high temperature characteristics such as high temperature stability and high temperature cycle characteristics are poor, which is not preferable. In the case of a conventional positive electrode material, high temperature characteristics such as high temperature stability and high temperature cycle characteristics are not preferable, and the amount of decomposition of the PF ₆ anion is usually larger than 1 × 10 μmol.

Storage test (I)
a1) A positive electrode formed by forming 24 mg of a positive electrode material into a circular shape having a diameter of 12 mm, and pressure-bonding to a current collector (a circular aluminum expanded metal having a diameter of 16 mm), Li metal as a counter electrode, and 1.0 mol as an electrolyte / L LiPF ₆ containing ethylene carbonate and diethyl carbonate mixed solution (volume ratio 3: 7) was used to assemble a battery element, which was charged to a maximum voltage of 4.2 V at a charging current density of 0.2 mA / cm ² After charging, then disassemble the battery element,
Take out the positive electrode in the charged state, the positive electrode,
b1) In an argon gas atmosphere with a dew point of −75 ° C. or less c1) In a polytetrafluoroethylene container dried at 80 ° C. for 3 hours,
d1) A mixed solution of 1.5 ml of ethylene carbonate and 3.5 ml of diethyl carbonate containing 1.0 mol / L of LiPF ₆ (acid content: 2.0 mmol / L or less, PO ₂ F ₂ anion: 0.5 mmol / L) And soaking in ethanol: 0.01 mg or less),
e1) Store at 80 ° C. for one week, measure the amount of PF ₆ anion in the mixed solution before and after storage (measurement temperature: 20 ° C.), and determine the amount of PF ₆ anion decomposition from the difference.

In the present invention, the PF ₆ anion decomposition amount means the decomposition amount of the PF ₆ anion. The PF ₆ anion is considered to be decomposed into, for example, PO ₂ F ₂ ⁻ , PO ₃ F ^{2− and the} like. In the present invention, the PF ₆ anion decomposition inhibitor means an agent that suppresses the decomposition of the PF ₆ anion. In the storage test (I), a circular aluminum expanded metal having a diameter of 16 mm is used as the current collector. The thickness of the current collector is usually 50 to 300 μm, and a current collector of about 200 μm may be used. In the above storage test (I), the press bonding of the positive electrode material to the current collector in a1) is performed by, for example, setting a current collector and a 24 mg positive electrode material formed in a circular shape with a diameter of 12 mm on a tablet molding machine, and pressing do it. The pressure for pressure bonding is usually 80 to 100 MPa, and the pressure may be about 90 MPa.

In the storage test (I), c1) to e1) are performed under the conditions of b1). Regarding e1), the inside of the polytetrafluoroethylene container of c1) in which the positive electrode of a1) is immersed may be in the condition of b1), and the outside of the polytetrafluoroethylene container that does not affect the immersion of the positive electrode. Need not be under the conditions of b1). In d1) of the above storage test (I), “a mixed solution of 1.5 ml of ethylene carbonate and 3.5 ml of diethyl carbonate containing 1.0 mol / L of LiPF ₆ (acid content: 2.0 mmol / L or less, PO 2 F 2 anion "Immerse in 0.5 mmol / L or less and Ethanol: 0.01 mg or less)" means "Immerse in a mixed solution satisfying the following (i) to (iii)".
(I) The acid content is 2.0 mmol / L or less, the PO ₂ F ₂ anion content is 0.5 mmol / L or less, and the ethanol content is 0.01 mg or less.
(Ii) Contains 1.0 mol / L LiPF ₆ .
(Iii) It consists of 1.5 ml ethylene carbonate and 3.5 ml diethyl carbonate.
The condition (i) above is that the acid content and PO ₂ F ₂ anion contained in the ethylene carbonate (EC) and diethyl carbonate (DEC) that are generally commercially available affect the decomposition of the PF ₆ anion. This is a condition specified to eliminate the influence. Under these conditions, the acid content and the PO ₂ F ₂ anion do not affect the decomposition of the PF ₆ anion.

The reason why the high-temperature cycle characteristics deteriorate when a positive electrode material that causes decomposition of LiPF _{6 in} a high-temperature environment is used as the positive electrode of a lithium secondary battery is not yet clear, but it is a positive electrode material that causes decomposition of LiPF ₆ It is inferred that the surface easily reacts with the solvent of the electrolytic solution, lithium salt, and the like, and as a result, a compound having an adverse effect on the charge and discharge of the lithium secondary battery is generated on the surface of the positive electrode. Moreover, such a positive electrode surface also has a bad influence also on an internal positive electrode active material, and it is thought that it will also have a bad influence on charging / discharging.

The means for suppressing the decomposition of LiPF ₆ in the storage test (I) is not particularly limited. For example, a PF ₆ anion decomposition inhibitor is present in the positive electrode material. Specifically, a positive electrode containing manganese oxide or / and lithium manganese composite oxide contains a PF ₆ anion decomposition inhibitor such as an inorganic compound, an organic compound, an organic metal compound, or an organic ion, other metal elements, Examples include a method of substituting some elements of the positive electrode active material with inorganic ions such as groups 15 to 17 of the periodic table.

If the inclusion of PF ₆ anion decomposition inhibitor for the positive electrode material, as the PF ₆ anion decomposition inhibitor, decomposition amount is 6 × 10 [mu] m of PF ₆ anions as determined by the following storage test (II)
It is preferable to use one that is less than or equal to ol. If a PF ₆ anion decomposition inhibitor having a decomposition amount of PF ₆ anion measured by the following storage test (II) of 6 × 10 μmol or less is used, high temperature characteristics such as high temperature stability and high temperature cycle characteristics can be improved.

Storage test (II)
a2) Li _{1 + x} Mn _2−x O ₄ (where 0 ≦ X ≦ 0.05) Lithium manganese equivalent to a fully charged state obtained by extracting lithium from a lithium manganese composite oxide having a spinel structure 160 mg of composite oxide (0.05 ≦ Li / Mn molar ratio ≦ 0.09)
b2) In an argon gas atmosphere with a dew point of −75 ° C. or lower,
c2) In a polytetrafluoroethylene container dried at 80 ° C. for 3 hours,
d2) mixed with 160 mg of the PF ₆ anion degradation inhibitor,
e2) A mixed liquid of ethylene carbonate 2.4 ml diethyl carbonate 5.6 ml containing 1.0 mol / L LiPF ₆ (acid content: 2.0 mmol / L or less, PO ₂ F ₂ anion: 0.5 mmol / L or less, And soaked in ethanol: 0.01 mg or less)
f2) Store at 70 ° C. for one week, measure the amount of PF ₆ anion in the mixed solution before and after storage (measurement temperature: 20 ° C.), and determine the amount of PF ₆ anion decomposition.

“Li _{1 + x} Mn _2−x O ₄ (where 0 ≦ X ≦ 0.0)” in the storage test (II) a2).
5) Lithium manganese composite oxide corresponding to a fully charged state (0.05 ≦ Li / Mn molar ratio ≦ 0.09) extracted from lithium of the lithium manganese composite oxide having a spinel structure having the composition “ It is obtained by treating a lithium manganese composite oxide having a spinel structure having a composition of _{1 + x} Mn _2−x O ₄ (where 0 ≦ X ≦ 0.05) with an acid. Specifically, a lithium manganese composite oxide having a spinel structure having a composition of Li _{1 + x} Mn _2−x O ₄ (where 0 ≦ X ≦ 0.05) is added to water and stirred at room temperature. However, it is obtained by dropping the acid until the pH is stable at 0.8 to 1.2. Usually, it may be stabilized at pH1. As the acid, sulfuric acid or the like may be used. Whether or not the pH is stable at 0.8 to 1.2 may be confirmed by continuing stirring for a while (about 6 hours) and no fluctuation in pH. If it can be confirmed that the pH is stable at 0.8 to 1.2, it is obtained by repeating washing with water several times while performing suction filtration, for example, drying at 90 ° C.

“Li _{1 + x} Mn _2−x O ₄ (where 0 ≦ X ≦ 0.05) lithium manganese composite oxide having a spinel structure extracted from lithium and corresponding to a fully charged lithium manganese composite Oxide (0.05 ≦ Li / Mn molar ratio ≦ 0.09) ”means“ Li _Y Mn _2−x O ₄ (where 0 ≦ X ≦ 0.05, 0.10 ≦ y ≦ 0). .18).

“Li _{1 + x} Mn _2−x O ₄ (where 0 ≦ X ≦ 0.0)” in the storage test (II) a2).
5) Lithium manganese composite oxide corresponding to a fully charged state (0.05 ≦ Li / Mn molar ratio ≦ 0.09) extracted from lithium of the lithium manganese composite oxide having a spinel structure having the following composition: The lithium manganese oxide having a spinel structure (Li _{1 + x} Mn _2−x O ₄ (where 0 ≦ X ≦ 0.05)) used as the positive electrode active material of the present invention is shown in a fully charged state. The fluctuation of the / Mn molar ratio is in a range where there is almost no influence on the decomposition amount of the PF ₆ anion in the storage test (II).

In the storage test (II), c2) to f2) are performed under the conditions of b2). F2
), A mixture of a lithium manganese composite oxide corresponding to the fully charged state of a2) and a PF ₆ anion decomposition inhibitor of d2) is immersed in the polytetrafluoroethylene container of c2) under the conditions of b2) The outside of the polytetrafluoroethylene container that does not affect the immersion of the positive electrode need not be under the condition of b2).

In e2) of the above storage test (II), “a mixed solution of ethylene carbonate 2.4 ml diethyl carbonate 5.6 ml containing 1.0 mol / L LiPF ₆ (acid content: 2.0 mmol / L or less, PO ₂ F ₂ “Immerse in anion: 0.5 mmol / L or less and ethanol: 0.01 mg or less)” means “soak in a mixed solution satisfying the following (iv) to (vi)”.
(Iv) The acid content is 2.0 mmol / L or less, the PO ₂ F ₂ anion content is 0.5 mmol / L or less, and the ethanol content is 0.01 mg or less.
(V) Contains 1.0 mol / L LiPF ₆ .
(Vi) It consists of 2.4 ml of ethylene carbonate and 5.6 ml of diethyl carbonate. The condition (iv) is for the same reason as described in (i) above.

In the present invention, the ability of the PF ₆ anion degradation inhibitor is not determined by the composition of the substance or the specific physicochemical properties. This is also a compound of the same composition, preparation, grinding method, a storage method or the like, its structure, surface area, acidity, basicity, different physicochemical properties of the average voltage and the like, mutual and results LiPF ₆ This is because the strength of the action is different.

The composition of the PF ₆ anion decomposition inhibitor used in the present invention includes an inorganic compound, an organic compound,
An organometallic compound etc. can be mentioned. A plurality of types of PF ₆ anion degradation inhibitors may be used. Specific examples of the PF ₆ anion degradation inhibitor are shown below, but it is noted that whether or not the PF ₆ anion degradation inhibitor of the present invention is satisfied is not uniquely determined by the composition alone as described above. There is a need to.

Examples of the inorganic compound that can be used as the PF ₆ anion decomposition inhibitor include 2 to 5 in the periodic table of elements.
Examples include oxides, composite oxides, nitrides, sulfides, and the like of various metals belonging to Group 14, and preferred are oxides or composite oxides of various metals belonging to Groups 2-14. Specific examples of the metal element include Sr, Ca, Ba, Mg, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, B, Al, and Sn. A compound capable of reversibly occluding and releasing lithium ions can also be suitably used as the PF ₆ anion degradation inhibitor. For example, a lithium iron composite oxide, a lithium cobalt composite oxide, and a lithium nickel composite oxide can be mentioned, preferably a lithium nickel composite oxide, particularly preferably a lithium nickel composite oxide having a layered structure. . Of course, those obtained by replacing some of these metals with other metal elements can also be used.

Examples of the organic compound and organometallic compound that can be used as the PF ₆ anion decomposition inhibitor include chelating agents, that is, those having the property of forming a complex with a heavy metal (chelating action). Among these, a compound containing at least one element selected from the group consisting of at least group 15 and group 16 of the periodic table is preferable. Specifically, a compound having at least one amino group in the molecule, a compound having at least one amide bond in the molecule, a compound having at least a hydroxyl group in the molecule, or at least one nitrogen-containing heterocyclic ring in the molecule. The compound which has is mentioned. Moreover, the metal salt of these compounds can also be used suitably,
Examples of the metal element used for the metal salt include at least one metal element selected from the group consisting of Group 1, Group 2 and Group 13 of the Periodic Table of Elements. Specifically, bisbenzylidene hydrazide oxalate, bis (cyclohexanone) oxalyl dihydrazone, N, N′-bis {
2- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxyl] ethyl} oxamide, 3- (N-salicyloyl) amino-1,2,4-triazole, decanedicarboxylic acid dissari Tyroyl hydrazide, N, N′-bis [3-3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine, bis [2-phenoxypropionylhydrazide] isophthalate, pyrrole, pyrazole, imidazole, benzo Examples thereof include imidazole, 1,2,4-triazole, 3- (N-salicyloyl) amino-1,2,4-triazole, and lithium, sodium, magnesium, and aluminum salts thereof.

When using a compound having an amino group as a PF ₆ anion degradation inhibitor, secondary or 3
Compounds having a secondary amino group are preferred. In particular, this tendency is remarkable when an electrolytic solution containing LiPF ₆ is used. This is considered to be due to the following reasons. That is, when a compound having an amino group is used as the PF ₆ anion degradation inhibitor, if a hydrogen atom is bonded to the nitrogen atom of the amino group, this hydrogen atom functions as an active proton, and this compound is converted to LiPF ₆ and As a result of the reaction to generate an acid such as HF, it is presumed that this further reacts with the electrode and may deteriorate the performance as a battery. This tendency is remarkable for primary amines with many active protons. On the other hand, tertiary amine does not have an active proton, so LiPF ₆
However, from the viewpoint of interaction with manganese oxide, primary or secondary amines are generally stronger in interaction. There is a tendency. Compared with primary or secondary amines that can form ionic or covalent bonds with manganese oxides, tertiary amines have less interaction with manganese oxides (coordination bonds). Therefore, it seems that the tertiary amine once interacted easily dissociates easily. Therefore, it is considered that the ability as a PF ₆ anion decomposition inhibitor contained in the positive electrode material is determined by the above two balances. As a result, it is presumed that a compound having a secondary or tertiary amine is preferable to a primary amine. However, by using an amine having a bulky substituent, the reaction between itself and LiPF ₆ can be suppressed, so that a primary amine can also be used.

The presence state of the PF ₆ anion decomposition inhibitor in the positive electrode material is usually a state where the surface of the positive electrode active material is uniformly covered, or a state where it is localized or dispersed in the positive electrode material. In the former case, direct contact between LiPF ₆ and manganese can be prevented. In the latter case, Li
By allowing the PF ₆ decomposition inhibitor to coexist, the interaction of LiPF _{6 with} the positive electrode active material can be inhibited. In order to allow the LiPF ₆ decomposition inhibitor used in the present invention to be present in the positive electrode material, for example, dispersion mixing may be mentioned. In addition, a LiPF ₆ decomposition inhibitor film may be formed on the surface of the active material particles by vapor deposition, sol-gel coating, heat treatment or the like. A forming method can be adopted.
However, the coating by heat treatment, etc. Depending on the type of PF ₆ anion decomposition inhibitor, there are cases where PF ₆ anion decomposition inhibitor or loss, altered, which may lose the aimed effects. On the other hand, dispersive mixing is preferable because it is a simple addition method, has no influence of alteration, and can sufficiently exhibit its original effect. In addition, the dispersive mixing in the present invention means simply mixing a plurality of substances, and means mixing without heat treatment or the like at such a high temperature that the mixture chemically changes. A substance obtained by mixing a plurality of substances and dispersing the PF ₆ anion decomposition inhibitor used in the present invention in the positive electrode material is preferable, and it is preferable that the substance is uniformly dispersed. The dispersion mixing may be dry mixing or wet mixing. A mortar, a ball mill, a jet mill, a Redige mixer, etc. can be used for physical mixing. Moreover, in order to remain in a positive electrode material effectively, what is hard to melt | dissolve in electrolyte solution is preferable.

As the PF ₆ anion decomposition inhibitor to be used, a compound having low solubility in the electrolyte used is desirable. In addition, PF ₆ anion degradation inhibitors often do not pose a major problem when using inorganic compounds. However, physical or physicochemical trends include low average voltage, large surface area, and lattice defects. Some are preferred compounds. However, since these are not unambiguous and are determined by the combination of the factors, not all compounds necessarily follow the respective tendencies described above.

The content of the PF ₆ anion decomposition inhibitor may be arbitrary, but it is usually 0.
It is the range of 0001-80 wt%. If the amount is too small, only an insufficient effect can be obtained, and the high temperature stabilization effect is hardly exhibited. Conversely, if the amount is too large, resistance may increase, and other characteristics such as a decrease in capacity may occur. come. When a compound capable of occluding and releasing lithium is used as the PF ₆ anion decomposition inhibitor, there is an advantage that the capacity of the positive electrode does not decrease even if the addition amount is large. The amount of additive used in this case is usually 1 wt% or more, preferably 5 wt% or more, more preferably 10 wt% or more, and usually 80 wt% or less, preferably with respect to manganese oxide and lithium manganese oxide. 60 wt% or less, more preferably 35 wt% or less. On the other hand, when using a compound containing at least one element selected from the group consisting of Group 15 and Group 16 of the Periodic Table of Elements and does not occlude and release lithium, The amount used is usually 0.0001 wt% or more, preferably 0.001 wt% or more, more preferably 0.01 wt% or more, and usually 10 wt% or less, preferably based on manganese oxide and lithium manganese oxide. Is 5 wt% or less, more preferably 1 wt% or less.

In the present invention, the positive electrode active material used may be the PF ₆ anion decomposition inhibitor itself. That is, one compound may be a positive electrode active material and a PF ₆ anion decomposition inhibitor. As a means for suppressing the decomposition of the PF ₆ anion, a method of substituting some elements of the positive electrode active material with other metal elements or inorganic ions such as groups 15 to 17 of the periodic table of elements is also preferable. In this case, as the positive electrode active material, hardly oxygen release at high temperatures, but preferably those having the properties of structural changes with occlusion and release of lattice defects is small or lithium ion is small or the like, also these, PF ₆ anion As in the case of the decomposition inhibitor, the degree of suppressing the decomposition of the PF ₆ anion is not uniquely determined by each factor alone.

In the present invention, the amount of PF ₆ anion decomposed when the above storage test (I) is performed is 1 ×
It is 10 μmol or less, preferably 6 μmol or less. However, since it is not practical to suppress the decomposition amount too much, the lower limit of the decomposition amount is usually about 1 × 10 ⁻² μmol. On the other hand, the amount of PF ₆ anion decomposed when the above storage test (II) was performed was 6 × 1.
It is 0 μmol or less, preferably 55 μmol or less, more preferably 5 × 10 μmol or less. In this case as well, it is not practical to suppress the decomposition amount too much, so the lower limit of the decomposition amount is usually about 1 × 10 ⁻² μmol.

In the present invention, the decomposition product of PF ₆ anion of LiPF _{6 in} the above storage test is usually mainly PO ₂ F ₂ anion. Therefore, the performance of the positive electrode evaluated in the storage test (I) and the performance of the PF ₆ anion degradation inhibitor evaluated in the storage test (II) are as follows.
The production amount of O ₂ F ₂ can also be evaluated as a parameter. In the present invention, the amount of PO ₂ F ₂ anion contained in the storage solution at 20 ° C. when the above storage test is performed is usually 1 × 10 μmol or less, preferably 5 μmol or less in the storage test condition (I). is there. On the other hand, the storage test condition (II) is usually 5 × 10 μmol or less, preferably 4 × 10 μmol or less. Here, the amount of “at 20 ° C.” is limited because the generated PO ₂ F ₂ anion is often contained in the precipitate. Therefore, the state of the preservation solution at 20 ° C. is a state in which the content of PO ₂ F ₂ anion in the preservation solution becomes constant at 20 ° C. regardless of time.

In the present invention, it is preferable that 80% or more, particularly 95% or more of the decomposition product of PF ₆ anion when the above storage test (I) or (II) is performed is PO ₂ F ₂ anion. Furthermore, in the present invention, when the storage test is performed by the method of the storage test (II), ethanol is generated with the generation of PO ₂ F ₂ anion. The preferable amount of ethanol produced in the solution after storage when the storage test (II) was further extended for 2 weeks, that is, when the storage test (II) was performed with a storage time of 3 weeks. The amount of ethanol contained in 1 mg or less, further 0.5 mg or less. When a large amount of ethanol is produced in the storage test (II), the PF ₆ anion degradation inhibitor cannot achieve sufficient improvement in high temperature characteristics. In addition, although the production | generation of ethanol may be confirmed also in the case of said preservation | save test (I), the production amount is very trace amount. The amount of ethanol contained in the preservation solution after the preservation test according to the method of preservation condition (I) is usually 0.1 mg or less.

The amount of PF ₆ anion and PO ₂ F ₂ anion contained in the above preservation solution can be determined by various known analytical methods. Examples thereof include ion chromatographic analysis, F-NMR or P-NMR. In this case, an important point is that, when these analyzes are performed, measurement is performed under a condition in which LiPF ₆ is not decomposed even if a liquid containing 1.0 mol / L LiPF ₆ before storage is used as a blank. is there. In addition, when the amount of PO ₂ F ₂ anion in the preservation solution is small, if necessary, the anion is analyzed by performing an operation such as concentration under conditions that do not change the composition of the anion in the preservation solution. May be.

For the measurement of ethanol, various known analytical methods may be used. For example, gas chromatography, liquid chromatography, NMR and the like can be mentioned. Specifically, measurement can be performed using the measurement method in the examples of the present invention. In the present invention, manganese oxide and / or lithium manganese composite oxide is used as an active material. In the present invention, the active material is a main material that causes the electromotive reaction of the battery, and means a material that can occlude and release Li ions. The manganese oxide and / or lithium manganese composite oxide is not particularly limited as long as it can reversibly absorb and release Li as an active material, and is preferably a lithium manganese composite oxide, and particularly a lithium manganese composite oxide having a spinel structure. Things are preferred. The composition of the lithium manganese composite oxide having a spinel structure is generally represented by LiMn ₂ O ₄ , but those in which a part of Mn is substituted with another metal or those in which oxygen deficiency occurs can be used. It is included in the lithium manganese composite oxide having a spinel structure. Examples of the metal that substitutes a part of Mn include Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, B, and Ge.

  As a preferred embodiment of the first embodiment of the present invention and a second embodiment of the present invention, a positive electrode for a lithium ion secondary battery comprising a lithium manganese composite oxide having a spinel structure and a lithium nickel composite oxide having a layered structure And a positive electrode material for a lithium ion secondary battery in which a part of a manganese site of the lithium manganese composite oxide is substituted with at least one element selected from typical elements. In the present invention, the lithium nickel composite oxide having a layered structure is contained, and a part of the manganese site of the lithium manganese composite oxide is replaced with at least one element selected from typical elements, whereby high temperature stability and high temperature are achieved. Improved high-temperature characteristics such as cycle characteristics.

The lithium manganese composite oxide having a spinel structure used above is, for example, a mixture of a lithium compound, a manganese compound, and a compound of at least one typical element that substitutes a part of the manganese site, and is fired in the atmosphere. Or it can obtain by mixing a lithium compound and a manganese compound, baking in air | atmosphere, manufacturing a spinel type lithium manganese complex oxide, and making it react with the compound of at least 1 type or more of typical elements then. Examples of typical elements that replace Mn sites include Li, B, Mg, Al, Ca, Zn, Ga, and G.
Etc. Of course, it is possible to replace the manganese site with a plurality of elements. Li, Mg, Al, and Ga are preferable as manganese site substitution elements, and aluminum and / or lithium are particularly preferable. The substitution amount of the typical element is preferably 0.05 mol or more of 2 mol of manganese, more preferably 0.06 or more, and most preferably 0.08 mol or more.

  As a preferred embodiment of the first embodiment of the present invention and a third embodiment of the present invention, for a lithium ion secondary battery comprising a lithium manganese composite oxide having a spinel structure and a lithium nickel composite oxide having a layered structure 4. A positive electrode material, wherein a part of the manganese site of the lithium manganese composite oxide is substituted with another element, and the average voltage measured by the following measurement method (I) of the lithium manganese composite oxide is 4. A positive electrode material for a lithium ion secondary battery characterized by having a voltage of 059 V or more can be given. Here, the following measurement method (I) is a measurement method for determining a preferable lithium manganese composite oxide used as the positive electrode material. The lithium manganese composite oxide in which a part of the manganese site whose average voltage measured by the following measuring method (I) is 4.059 V or more is substituted with other elements is high temperature characteristics such as high temperature stability and high temperature cycle characteristics. It is preferable in terms of improvement.

<Measuring method of average voltage (I)>
(1) The composite oxide is weighed at a ratio of 75% by weight, acetylene black 20% by weight, and polytetrafluoroethylene (PTFE) powder 5% by weight, and is made into a thin sheet. After adjusting the total weight to 12.5 mg / cm ² , this sample is further pressure-bonded to an aluminum expanded metal to form a test electrode. The test electrode is dried at 120 ° C. under reduced pressure for 1 hour.
(2) A 25 μm porous polyethylene film as a separator under an argon atmosphere,
Lithium metal foil was used as the counter electrode, and 1 mol / liter lithium hexafluorophosphate (LiPF ₆ ) was added as a non-aqueous electrolyte solution to a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7. A CR2032 type coin-type battery is manufactured using the dissolved solution.
(3) The obtained coin-type battery was subjected to a constant current charge / discharge cycle (charge upper limit 4.35 V, discharge lower limit 3.2 V) at a current density of 0.5 mA / cm ^{2 in} an environment of 25 ° C., and the average voltage Ve = Ve = (average charge voltage in the second cycle + discharge average voltage in the second cycle) / 2
Asking. The charge average voltage or discharge average voltage is calculated by measuring the voltage during charging or discharging at intervals of 2 seconds and dividing the value obtained by integrating the voltage over time by the time required for charging or discharging.

In the measurement method (I) (1), the sample is pressed against the expanded metal by, for example, applying (1) aluminum expanded metal and (2) the composite oxide to 75% by weight and acetylene black 20% by weight in a tablet molding machine. , Polytetrafluoroethylene (PTFE) powder weighed at a ratio of 5% by weight, mixed into a thin sheet, adjusted to a total weight of 12.5 mg / cm ² , stacked and set. That's fine. The pressure for pressure bonding is usually 80 to 100 MPa, and the pressure may be about 90 MPa.

  The thickness of the expanded metal is usually 50 to 300 μm, and a thickness of about 200 μm may be used. The spinel type lithium manganese oxide used as the active material has an average voltage of 4.059 V or higher, preferably an average voltage of 4.060 V or higher, more preferably 4.060 V or higher, and most preferably 4.070 V or higher. However, since an extremely high voltage is difficult to manufacture, the average voltage is usually 4.3 V or less. Here, the average voltage is measured according to the above (1) to (3).

If the method is strictly defined in this way, the average voltage can be uniquely determined. The lithium manganese composite oxide having the spinel structure used above, in which a part of the manganese site is substituted with another element, for example, is obtained by substituting a part of the manganese site with at least one element. Can do. As such an element that replaces the Mn site, as a metal that replaces a part of Mn, Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, B, Ge and the like can be mentioned, and typical elements such as Li, B, Mg, Al, Ca, Zn, Ga and Ge are preferable. Of course, it is possible to replace the manganese site with a plurality of elements. As the manganese site substitution element, aluminum and / or lithium are particularly preferable because the average voltage of the spinel type lithium manganese composite oxide can be increased with a small amount.

In the preferred embodiment of the first embodiment, the second embodiment of the present invention, and the third embodiment of the present invention, a lithium manganese composite oxide having a spinel structure to be used "hereinafter referred to as" composite oxide (A) "is also used. Among them, preferred is a general formula Li [Mn _(2-x) Al _y Li _z ] O ₄ (where x, y and z are each a number of 0 or more, and x = y + z, where y And z are not 0 at the same time.)
It can be expressed as Here, y is usually 0.5 or less, preferably 0.25 or less, and usually 0.1 or more. Z is usually 0.1 or less, preferably 0.08 or less, and usually 0.02 or more. If y and z are too small, the high temperature characteristics may be deteriorated. On the other hand, if y and z are too large, the capacity tends to decrease.

In the above, the oxygen atom of the composite oxide (A) may have nonstoichiometry, and a part of the oxygen atom may be substituted with a halogen element such as fluorine. As a preferred embodiment of the first embodiment, a lithium nickel composite oxide (hereinafter sometimes referred to as “composite oxide (B)”) having a layered structure used in the second embodiment of the present invention and the third embodiment of the present invention. In general, those having the basic composition formula LiNiO _2. Among them, the average voltage is preferably 3.830 V or less, particularly 3.820 V or less, further 3.810 V or less, more preferably 3.800 V or less. Since the potential difference with the composite oxide (A) is widened by lowering the average voltage of the composite oxide (B), mutual interaction between the composite oxide (A) and (B) as described in the section of action is preferable. The effect is expected to increase, and as a result, it is possible to improve the characteristics at a high temperature, etc. However, it is difficult to manufacture a product having an extremely low average voltage, so that the average voltage is usually 3.5 V or more.

The measurement method of the average voltage of the composite oxide (B) is almost the same as the measurement method of the composite oxide (A), but in the step (3), the current density is set to 0.2 mA / cm ² and charging is performed. The difference is that the upper limit is 4.2V. Such a composite oxide (B) having a reduced average voltage can be obtained by replacing a part of nickel with another element. It can also be obtained by making lithium in and out easy by reducing the particle size of the composite oxide (B).

Examples of elements that can substitute a part of nickel include metal elements such as B, Al, Fe, Sn, Cr, Cu, Ti, Zn, Co, and Mn. Of course, it is also possible to replace nickel sites with multiple elements. In particular, aluminum and / or cobalt is preferable. A particularly preferable composite oxide (B) is a general formula Li [Ni _(1-x) Co _y Al _z ] O ₂ (where x, y and z are each a number of 0 or more, and x = y + z). However, y and z are not 0 at the same time.) Here, y and z are each independently usually 0.5 or less, preferably 0.25 or less, and usually 0.1 or more. Z is usually 0.1 or less, preferably 0.08 or less, and usually 0.02 or more. If y and z are too small, the high temperature characteristics tend to be poor, while if too large, the capacity tends to decrease.

  In the above, the oxygen atom of the composite oxide (B) may have nonstoichiometry, and part of the oxygen atom may be substituted with a halogen element such as fluorine. In the preferred embodiment of the first embodiment, the second embodiment of the present invention and the third embodiment of the present invention, the composite oxide (A) and the composite oxide (B) are in the form of a mixture thereof. It may also be a complex with chemical bonding.

  In the preferred embodiment of the first embodiment, the second embodiment of the present invention, and the third embodiment of the present invention, the composite oxidation relative to the total amount of the composite oxide (A) and the composite oxide (B) in the active material The weight ratio R of the product (B) is usually 0.7 or less, preferably 0.6 or less, more preferably 0.3 or less. Moreover, it is 0.05 or more normally, Preferably it is 0.1 or more. This is because if the mixing ratio of the lithium nickel composite oxide is too small, the effect of improving the high temperature characteristics tends to be small, and conversely if too large, problems may occur in terms of cost increase and safety.

The particle size of the composite oxide (A) or (B) or these composites is usually 0.1 μm or more, preferably 0.2 μm or more, more preferably 0.3 μm or more, and usually 30 μm or less. Preferably it is 10 micrometers or less, More preferably, it is 5 micrometers or less. The specific surface area of these nitrogen adsorption method is usually 0.3 m ² / g or more, and usually less than 15 m ² / g. If the particle size is too small or the specific surface area is large, the cycle deterioration of the battery may become large, and a safety problem may occur. If the particle size is too large or the specific surface area is too small, the internal resistance of the battery may be large and it may be difficult to output.

  The present invention also relates to a positive electrode and a battery for a lithium ion secondary battery using the positive electrode material for a lithium secondary battery as described above. That is, the positive electrode for a lithium ion secondary battery of the present invention is formed by forming an active material layer containing the positive electrode material on a current collector. The positive electrode is usually formed by forming an active material layer containing an active material and a binder on a current collector. The active material layer can be usually obtained by preparing a slurry containing the above components and applying and drying the slurry on a current collector.

  The ratio of the active material of the present invention in the active material layer is usually 10% by weight or more, preferably 30% by weight or more, more preferably 50% by weight or more, and usually 99.9% by weight or less, preferably 99% by weight. It is as follows. Examples of the binder used for the positive electrode include polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, EPDM (ethylene-propylene-diene terpolymer), SBR (styrene-butadiene rubber), NBR ( Acrylonitrile-butadiene rubber), fluoro rubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose and the like. The ratio of the binder in the active material layer is usually 0.1% by weight or more, preferably 1% by weight or more, more preferably 5% by weight or more, and usually 80% by weight or less, preferably 60% by weight or less, more preferably. Is 40% by weight or less, most preferably 10% by weight or less. If the proportion of the binder is too low, the active material cannot be sufficiently retained, and the mechanical strength of the positive electrode may be insufficient, and battery performance such as cycle characteristics may be deteriorated. On the other hand, if it is too high, the battery capacity and conductivity will be reduced. Sometimes.

  The active material layer usually contains a conductive agent in order to increase conductivity. Examples of the conductive agent include graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, and amorphous carbon such as needle coke. The proportion of the conductive agent in the active material layer is usually 0.01% by weight or more, preferably 0.1% by weight or more, more preferably 1% by weight or more, and usually 50% by weight or less, preferably 30% by weight or less. More preferably, it is 15% by weight or less. If the proportion of the conductive agent is too low, the conductivity may be insufficient, and conversely if it is too high, the battery capacity may be reduced.

  As the slurry solvent, an organic solvent that dissolves or disperses the binder is usually used. Examples thereof include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N, N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran. Moreover, a dispersing agent, a thickener, etc. can be added to water, and an active material can also be slurried with latex, such as SBR.

  The thickness of the active material layer is usually about 10 to 200 μm. As the material of the current collector used for the positive electrode, aluminum, stainless steel, nickel-plated steel or the like is used, and preferably aluminum. Note that the active material layer obtained by coating and drying is preferably consolidated by a roller press or the like in order to increase the packing density of the active material.

  It can be set as a lithium ion secondary battery using the active material and positive electrode of this invention. The lithium ion secondary battery of the present invention contains the active material in a positive electrode, but usually has the positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode active material used for the negative electrode of the secondary battery of the present invention may be a lithium alloy such as lithium or a lithium aluminum alloy, but is preferably a carbon material that can occlude and release more safe lithium. The carbon materials include natural or artificial graphite, petroleum coke, coal coke, petroleum pitch carbide, coal pitch carbide, phenolic resin / crystalline cellulose resin carbide, and charcoal partially carbonized. Examples thereof include carbon black such as raw materials, furnace black and acetylene black, pitch-based carbon fibers, PAN-based carbon fibers, or a mixture of two or more of these.

  The negative electrode is usually formed by forming an active material layer on a current collector as in the case of the positive electrode. As the binder used at this time, the conductive agent and the slurry solvent used as necessary, the same ones used for the positive electrode can be used. In addition, as the negative electrode current collector, copper, nickel, stainless steel, nickel-plated steel, or the like is used, and copper is preferably used.

  Examples of the non-aqueous electrolyte solution that can be used in the lithium secondary battery of the present invention include those in which various electrolyte salts are dissolved in a non-aqueous solvent. As the non-aqueous solvent, for example, carbonates, ethers, ketones, sulfolane compounds, lactones, nitriles, halogenated hydrocarbons, amines, esters, amides, phosphate ester compounds, etc. may be used. it can. Typical examples of these are propylene carbonate, ethylene carbonate, chloroethylene carbonate, trifluoropropylene carbonate, diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, vinylene carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane. 4-methyl-2-pentanone, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methyl Sulfolane, acetonitrile, propionitrile, benzonitrile, butyronitrile, valeronitrile, 1,2-dichloroethane, dimethylformamide, dimethyl sulfoxide, phosphate Methyl, alone or a mixture of two or more solvents such as triethyl phosphate may be used.

  The above non-aqueous solvent preferably contains a high dielectric constant solvent in order to dissociate the electrolyte. Here, the high dielectric constant solvent means a solvent having a relative dielectric constant of 20 or more at 25 ° C. Among the high dielectric constant solvents, it is preferable that the electrolyte solution contains ethylene carbonate, propylene carbonate, and compounds in which hydrogen atoms thereof are substituted with other elements such as halogen or alkyl groups. The proportion of the high dielectric constant solvent in the electrolytic solution is preferably 20% by weight or more, more preferably 30% by weight or more, and most preferably 40% by weight or more. This is because if the content of the high dielectric constant solvent is small, desired battery characteristics may not be obtained.

As the electrolyte salt, any conventionally known electrolyte salt can be used. LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , LiCl, LiBr, LiCH ₃ SO ₃ Li, L
iCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC (SO ₂ CF ₃
) ₃ , and lithium salts such as LiN (SO ₃ CF ₃ ) ₂ .

Addition that produces a good film that enables efficient charge and discharge of lithium ions on the negative electrode surface, such as gas such as CO ₂ , N ₂ O, CO, SO ₂ , polysulfide S _x ²⁻ , vinylene carbonate, catechol carbonate, etc. You may add an agent to the said single or mixed solvent in arbitrary ratios. A polymer solid electrolyte that is a conductor of an alkali metal cation such as lithium ion can also be used. In this case, a conventionally known polymer can be used as the polymer, but a polymer having high ion conductivity with respect to lithium ions is preferably used. Examples of such a polymer include polyethylene oxide, polypropylene oxide, and polyethyleneimine. Usually, the polymer solid electrolyte contains the polymer and the lithium salt, but it can also be used as a gel electrolyte by adding the solvent. That is, in this case, the electrolytic solution made into a matrix with a polymer is used.

Even when an inorganic solid electrolyte is used, a known crystalline or amorphous solid electrolyte can be used for this inorganic substance. Examples of the crystalline solid electrolyte include LiI, Li ₃ N, Li _{1 + x} M _x Ti _2-x (PO ₄ ) ₃ (M = Al, Sc, Y, La), Li _0.5-3x RE _{0.5; x} Examples thereof include TiO ₃ (RE = La, Pr, Nd, Sm) and the like. As an amorphous solid electrolyte, for example, 4.9
_{LiI-34.1Li 2 O-61B 2} O 5, 33.3Li 2 O-66.7SiO oxide glass or 0.45LiI-0.37Li ₂ such as _{2 S-0.26B 2 S 3,} 0.30LiI-0.42Li 2 S-0.28SiS _{2 and the} like. Among these, a plurality of types can be used.

  Usually, a separator is provided between the positive electrode and the negative electrode. As the separator, a microporous polymer film is used. Polyamide-based polymers such as polyamide, polyester, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, polytetrafluoroethylene, polypropylene, polyethylene, polybutene, etc. A molecule can be used. Moreover, a nonwoven fabric filter such as glass fiber, or a composite nonwoven fabric filter of glass fiber and polymer fiber can be used. The chemical and electrochemical stability of the separator is an important factor. In this respect, a polyolefin-based polymer is preferable, and polyethylene is preferable from the viewpoint of the self-occluding temperature, which is one of the purposes of the battery separator.

  In the case of a polyethylene separator, ultrahigh molecular weight polyethylene is preferable from the viewpoint of maintaining high-temperature shape, and the lower limit of the molecular weight is preferably 500,000, more preferably 1,000,000, and most preferably 1.5 million. On the other hand, the upper limit of the molecular weight is preferably 5 million, more preferably 4 million, and most preferably 3 million. This is because if the molecular weight is too large, the pores of the separator may not close when heated because the fluidity is too low.

Hereinafter, the present invention will be described more specifically with reference to examples.
[Preparation of lithium manganese composite oxide]
Preparation Example 1 Preparation of Li [Mn _1.96 Li _0.04 ] O ₄ Spinel type lithium manganese composite oxide Li [Mn _1.96 Li _0.04 ] O ₄ was prepared as follows.

Manganese trioxide (Mn ₂ O ₃ ) and lithium hydroxide (LiOH.H ₂ O) were used as starting materials, and each compound was blended so that the molar ratio of the compound was 1: 1.04. Ethanol was added to this blend and ground well in a mortar to make a uniform mixture. The obtained mixture was calcined in the atmosphere at 500 ° C. (temperature increase rate: 5 ° C./min) for 24 hours, and then in the air at 780 ° C. (temperature increase rate: 5 ° C./min) for 24 hours. Then, it was cooled to 450 ° C. (cooling rate: 0.2 ° C./min) and held for 24 hours, and then slowly cooled to room temperature by natural cooling and taken out. As a result of elemental analysis, Li [Mn _1.96 Li _0.04 ] O ₄ was obtained. The obtained spinel type lithium manganese composite oxide was designated as lithium manganese composite oxide (A).

Preparation Example 2
Preparation of Li [Mn _1.85 Al _0.11 Li _0.04 ] O ₄ A spinel-type lithium manganese composite oxide Li [Mn _1.85 Al _0.11 Li _0.04 ] O ₄ was prepared as follows. Starting from dimanganese trioxide (Mn ₂ O ₃ ), lithium carbonate (Li ₂ CO ₃ ), and alumina hydrate (AlOOH), the molar ratio of each compound is 0.94: 1.04: 0. 10 was added. Ethanol was added to this blend and ground well in a mortar to make a uniform mixture. The resulting mixture was heated in the atmosphere at 500 ° C. (temperature increase rate: 5 ° C./min), 600 ° C. (temperature increase rate: 5 ° C./min), 700 ° C. (temperature increase rate: 5 ° C./min), 800 ° C. Preliminarily calcined for 6 hours each at a heating rate of 5 ° C./min), then calcined in the atmosphere at 900 ° C. (heating rate: 5 ° C./min) for 24 hours, and then cooled to 300 ° C. : Cooled at 0.2 ° C./min, then slowly cooled to room temperature by natural cooling and taken out. As a result of elemental analysis, Li [Mn _1.96 Li _0.04 ] O ₄ was obtained. The obtained spinel type lithium manganese composite oxide was designated as lithium manganese composite oxide (B).

Preparation Example 3
Under Preparation air acid treatment lithium manganese oxide Li _x Mn _y O _4, in 300ml beaker at room temperature, distilled water (180 ml) suspension of the lithium-manganese composite oxide (A) 6.60 g, suspension pH is a 4.5N sulfuric acid was added until a 1.00, after stirring for 6 hours, the resulting suspension was filtered to give the crude Li _x Mn _y O ₄ as a dark red-brown powder. This was washed 6 times with distilled water (20 ml), then air-dried overnight, and further dried at 90 ° C. for 1 hour under normal pressure. An acid-treated lithium manganese composite oxide was obtained. The acid-treated lithium manganese composite oxide had a Li / Mn molar ratio of 0.07. Further, it was confirmed by X-ray diffraction measurement that the cubic spinel structure was maintained, and it was confirmed by IR that water was not contained.

[Example 1]
Preparation and capacity confirmation of positive electrode Lithium manganese composite oxide (A), layered lithium nickel oxide (hereinafter referred to as PF ₆ anion decomposition inhibitor (a) and commercially available composition Li _1.05 Ni _0.80 Co _0.15 Al _0.05 O ₂ May be added) and mixed so that the lithium manganese composite oxide (A) / additive = 3/1 by weight ratio.

  A mixture obtained by weighing 75% by weight of the obtained mixture, 20% by weight of acetylene black, and 5% by weight of polytetrafluoroethylene powder was thoroughly mixed in a mortar to form a positive electrode material. Punched with a punch. At this time, the total weight was adjusted to about 18 mg. This was crimped to an aluminum expanded metal to form a positive electrode.

Next, a battery element was assembled using the obtained positive electrode as a test electrode and Li metal as a counter electrode, and a constant current charge of 0.2 mA / cm ² , that is, a reaction for desorbing Li ions from the positive electrode was 4.2 V to 4.35 V. Further, a test of constant current discharge of 0.2 mA / cm ² , that is, insertion of Li ions into the positive electrode was performed at a lower limit of 3.2 V, and the initial desorption capacity per unit weight of the positive electrode active material at this time was expressed as Qs (C) mAh / g and the initial insertion capacity were Qs (D) mAh / g.

Preparation and Capacity Confirmation of Negative Electrode Graphite powder (d002 = 3.35 Å) having an average particle diameter of about 8 to 10 μm was used as a negative electrode active material, and polyvinylidene fluoride (hereinafter sometimes abbreviated as PVdF) was added to a weight ratio of 92 .5: 7.5 A mixture of N-methylpyrrolidone (hereinafter sometimes abbreviated as NMP) in a ratio to prepare a negative electrode mixture slurry. This slurry was applied to one side of a 20 μm thick copper foil, dried at 120 ° C. to evaporate the solvent, then punched out to 12 mmφ, 0.5 ton / cm ²
The negative electrode was pressed.
A battery element was assembled with this negative electrode as the test electrode and Li metal as the counter electrode, and 0.2 mA / cm ² was assembled.
A test for inserting Li ions into the negative electrode at a constant current of 0 V was performed at a lower limit of 0 V, and the initial insertion capacity per unit weight of the negative electrode active material at this time was defined as Qf mAh / g.

Assembling the battery element A positive electrode was placed on the positive electrode can, a 25 μm porous polyethylene film was placed on it as a separator, and after pressing with polypropylene BR> steal gasket, the negative electrode was placed and a spacer for adjusting the thickness was placed. Thereafter, a non-aqueous electrolyte solution (1 mol of LiPF ₆ dissolved in 1 liter of a mixed solvent of EC / DEC = 3/7) was added into the battery and sufficiently impregnated. Then, the negative electrode can was placed on the battery, and the battery was sealed. A coin-type battery was used. At this time, the balance between the weight of the positive electrode active material and the weight of the negative electrode active material is approximately positive electrode active material amount [g] / negative electrode active material amount [g] = (Qf / 1.2) / Qs (C)
Was set to be.

Test Method The obtained battery element was evaluated as follows. In order to compare the high-temperature characteristics of the batteries thus obtained, first, a constant current 0.2 C charge / discharge cycle and a constant current 1 C charge / discharge cycle were performed at room temperature, and then a constant current 0.2 C at a high temperature of 50 ° C. A cycle test of 1 cycle of charge / discharge and further 100 cycles of constant current 1C charge / discharge was performed. The upper limit of charging was 4.1 V, and the lower limit voltage was 3.0 V.

At this time, the ratio of the discharge capacity Qh (100) of the 100th cycle to the discharge capacity Qh (1) of the 100th cycle in the 1C charge / discharge 100 cycle test at 50 ° C. is the high temperature cycle capacity maintenance rate P, that is,
P [%] = {Qh (100) / Qh (1)} x 100
The high temperature characteristics of the battery were evaluated with this value. At this time, the hourly rate current value of the battery, that is, 1C,
1C [mA] = Qs (D) × amount of positive electrode active material [g]
Was set. The results are shown in Table-1.

[Example 2]
A battery was prepared and evaluated in the same manner as in Example 1 except that the lithium manganese composite oxide (B) was used instead of the lithium manganese composite oxide (A) as the lithium manganese composite oxide. The results are shown in Table-1.
[Example 3]
The lithium manganese composite oxide (B) was used in place of the lithium manganese composite oxide (A) as the lithium manganese composite oxide, and the weight ratio of the lithium manganese composite oxide to the layered lithium nickel oxide was 9 A battery was prepared and evaluated in the same manner as in Example 1 except that it was set to 1. The results are shown in Table-1.

[Example 4]
As the lithium manganese composite oxide, the lithium manganese composite oxide (B) was used instead of the lithium manganese composite oxide (A), and a PF ₆ anion decomposition inhibitor (
A battery was produced in the same manner as in Example 1 except that a powder obtained by further jet milling in nitrogen (hereinafter sometimes referred to as LiPF ₆ decomposition inhibitor (b)) was used instead of a). evaluated. The results are shown in Table-1.

[Example 5]
As a mixture of lithium manganese composite oxide and PF ₆ anion decomposition inhibitor, lithium manganese composite oxide (B) and 3- (N-salicyloyl) amino-1,2,4- as PF ₆ anion decomposition inhibitor are used. Triazole (hereinafter sometimes referred to as PF ₆ anion decomposition inhibitor (c)) was added to 0.6 wt% with respect to the total amount of the lithium manganese composite oxide and mixed with ethanol. A battery was produced and evaluated in the same manner as in Example 1 except that a vacuum-dried one hour was used and that the upper limit of charge during the cycle test was 4.2 V. The results are shown in Table-1.

[Example 6]
As a PF ₆ anion decomposition inhibitor, the total amount with the lithium manganese composite oxide is 1
. A battery was prepared and evaluated in the same manner as in Example 5 except that 6 wt% of bis (cyclohexanone) oxalyl dihydrazone (hereinafter sometimes referred to as PF ₆ anion degradation inhibitor (d)) was used. The results are shown in Table-1.

[Comparative Example 1]
A battery was produced in the same manner as in Example 1, except that the lithium manganese composite oxide (A) was used alone as a positive electrode active material, and the upper limit of charge during the cycle test was 4.2 V. evaluated. The results are shown in Table-1.
[Comparative Example 2]
A battery was produced in the same manner as in Example 1 except that the lithium manganese composite oxide (B) was used as it was as a positive electrode active material, and the upper limit of charge during the cycle test was 4.2 V. evaluated. The results are shown in Table-1.

[Preservation test]
Storage test (I)
The tablet molding machine is overlaid with a round aluminum expanded metal (current collector) having a thickness of 200 μm and a diameter of 16 mm, and 24 mg of the same positive electrode material used in the above-mentioned examples and comparative examples formed into a circular shape of 12 mm in diameter. set Te, a positive electrode and pressed to Tsu positive electrode material in expanded metal aluminum at a pressure of 90 MPa, between which, and Li metal as a counter electrode, ethylene carbonate and diethyl carbonate containing LiPF ₆ of 1.0 mol / L The battery element used with the mixed electrolyte (volume ratio 3: 7) was produced. After charging this to a charging current density of 0.2 mA / cm ² and an upper limit voltage of 4.2 V, the battery was disassembled so as not to cause a short circuit, and a positive electrode material in a charged state was obtained.

The battery element was a CR2032-type coin battery. That is, a positive electrode is placed on a positive electrode can, a 25 μm porous polyethylene film is placed thereon as a separator, pressed with a polypropylene gasket, a counter electrode is placed, a spacer for adjusting the thickness is placed, and non-aqueous electrolysis is then placed. As a liquid, a mixed solution of ethylene carbonate and diethyl carbonate having a LiPF ₆ concentration of 1 mol / L and having a volume fraction of 3: 7 was added to the battery and sufficiently impregnated. Then, a negative electrode can was placed and the battery was sealed.

In a sealed polytetrafluoroethylene container having an internal volume of about 7 ml dried at 80 ° C. for 3 hours under an argon gas atmosphere having a dew point of −75 ° C. or less, the positive electrode material in a charged state obtained as described above was used. 1.5 ml of ethylene carbonate containing 1.0 mol / L LiPF ₆
And diethyl carbonate 3.5 ml (acid content: 2.0 mmol / L or less, PO ₂
F ₂ anion: 0.5 mmol / L or less and ethanol: detection limit or less), 80 ° C.
And stored for a week.

The analysis of the decomposition amount of PF ₆ anion and the content of PO ₂ F ₂ anion and ethanol in the preservation solution was conducted by cooling the temperature from 80 ° C. to 20 ° C. and then the argon gas atmosphere having a dew point of −75 ° C. or less. The storage container was opened below, and only the solution part was collected and the method described below was performed. Table of results
It is shown in 1. In addition, about the analysis of ethanol, it performed with respect to the thing after a 3-week preservation | save at 80 degreeC.
The same storage test was conducted even at a storage temperature of 20 ° C. In this case, no significant difference in the decomposition of PF ₆ anion and generation of PO ₂ F ₂ anion was observed, and the generation of PF ₆ anion was brought into water. It was confirmed that it does not depend on

Storage test (II)
In a sealed polytetrafluoroethylene container having an internal volume of about 15 ml, which was dried at 80 ° C. for 3 hours under an argon gas atmosphere having a dew point of −75 ° C. or less, 160 mg of the acid-treated lithium manganese composite oxide and PF ₆ anion 160 mg of a decomposition inhibitor, and the contents of acid content and PO ₂ F ₂ anion are 2.0 mmol / L or less and 0.5 mmol / L or less, respectively, and the ethanol content is below the detection limit (0.01 mg). It was stored at 70 ° C. for one week in an ethylene carbonate / diethyl carbonate mixed solution (ethylene carbonate 2.4 ml and diethyl carbonate 5.6 ml) containing 0.0 mol / L LiPF ₆ .

The analysis of the decomposition amount of PF ₆ anion and the content of PO ₂ F ₂ anion and the ethanol content in the preservation solution was conducted in an argon gas atmosphere having a dew point of −75 ° C. or lower after cooling the temperature from 70 ° C. to 20 ° C. The storage container was opened below, and only the solution part was collected and the method described below was performed. The results are shown in Table-1. In addition, about the analysis of ethanol, it performed with respect to the thing after a 3-week preservation | save at 80 degreeC.

The same storage test was conducted even at a storage temperature of 20 ° C. In this case, no significant difference in the decomposition of PF ₆ anion and generation of PO ₂ F ₂ anion was observed, and the generation of PF ₆ anion was brought into water. It was confirmed that it does not depend on
[Analysis method]
Analysis of the anion contained in the preservation solution After collecting the preservation solution in an argon gas atmosphere, the concentration of the PF ₆ anion and PO ₂ F ₂ anion in the approximate solution was determined using a DX-120 ion chromatograph analyzer manufactured by Dionex. did. In addition, by measuring the anion amount of the electrolyte solution containing 1.0 mol / L LiPF ₆ before storage in the same analysis as a blank, it was confirmed that the decomposition of LiPF ₆ by this analysis method did not occur.

As shown in Table 1, when only the electrolyte solution was stored at 70 ° C. for 1 week as a blank test of the storage test, significant decomposition of PF ₆ anion and generation of PO ₂ F ₂ anion could be confirmed. There wasn't.
Analysis of ethanol contained in the preservation solution After collecting the preservation solution under an argon gas atmosphere, all volatile components were collected under dry nitrogen by a known method (trap totrap condensation) to determine the amount of ethanol contained in the preservation solution. Quantified by gas chromatography.

  In addition, as shown in Table 1, as a result of storing only the electrolytic solution at 70 ° C. for 3 weeks as a blank test of the storage test, no ethanol was confirmed.

From Table 1, it can be seen that in the examples satisfying the provisions of the present invention, the high-temperature cycle characteristics are greatly improved. Above examples, Comparative Examples, since the high-temperature cycle characteristics Using PF ₆ anion decomposition inhibitor to a particular lithium manganese oxide was found to be improved, the present inventors have PF ₆ anion decomposition inhibition Focusing on one of the lithium nickel oxides, the following investigation was further conducted.

<1. Measurement of average voltage of complex oxide>
(1) Thoroughly mix in a mortar a mixture of 75% by weight of the complex oxide to be measured, 20% by weight of acetylene black, and 5% by weight of polytetrafluoroethylene (PTFE) powder. Punched in a circle with a punch. At this time, the total weight was adjusted to 12.5 mg / cm ² to make the thickness substantially constant. This sample was further pressure-bonded to an aluminum expanded metal to obtain a test electrode. The test electrode was dried at 120 ° C. under reduced pressure for 1 hour.

(2) A CR2032-type coin-type battery was prepared in a dry box in an argon atmosphere. That is, a test electrode was placed on the positive electrode can, a 25 μm porous polyethylene film was placed thereon as a separator, pressed with a polypropylene gasket, a 15 mmφ lithium metal foil was placed as a counter electrode, and a thickness adjusting spacer was placed. After that, a solution obtained by dissolving 1 mol of lithium hexafluorophosphate (LiPF ₆ ) in 1 liter of a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 3: 7 was used as a non-aqueous electrolyte solution. This was added to the battery and sufficiently impregnated, and then the negative electrode can was placed to seal the battery.

(3) in an environment of 25 ° C. The cells created above, a constant current charge-discharge cycle (charging upper limit 4.35V, discharge lower limit 3.2 V) current density 0.5 mA / cm ² in the case of compound oxide (A) and In the case of the composite oxide (B), a constant current charge / discharge cycle (charge upper limit 4.20 V, discharge lower limit 3.2 V) with a current density of 0.2 mA / cm ² was performed, and the average voltage Ve was calculated by the following equation.
Ve = (average charge voltage in the second cycle + average discharge voltage in the second cycle) / 2
The charge average voltage or discharge average voltage of the above formula was calculated by measuring the voltage during charging or discharging at intervals of 2 seconds and dividing the value obtained by integrating the voltage over time by the time required for charging or discharging. .
The initial charge capacity of the composite oxide (A) conducted in this test is Qc (A) mAh / g, the initial discharge capacity is Qd (A) mAh / g, and the initial charge capacity of the composite oxide (B) is Qc ( B) mAh / g and initial discharge capacity were set to Qd (B) mAh / g.

<2. High-temperature cycle test>
(Preparation of positive electrode) A mixture of the composite oxide (A) and the composite oxide (B) was used as a positive electrode active material. The positive electrode active material was 75% by weight, acetylene black 20% by weight, polytetrafluoroethylene powder 5% by weight. A positive electrode was prepared in the same manner as in Example 1 except that the sample was weighed at a ratio of

(Creation of negative electrode)
A negative electrode was produced in the same manner as in Example 1. As in Example 1, this negative electrode was used as a test electrode, Li metal was used as a counter electrode, and a coin-type battery was assembled in the same manner as when the average voltage of the composite oxide was measured. Q (F) mAh / g was defined as the initial insertion capacity when a test for inserting Li ions (lower limit 0 V) and desorption (upper limit 1.5 V) was performed.

(Assembly of battery element)
A battery element was assembled in the same manner as in Example 1. At this time, the balance between the weight of the positive electrode active material and the weight of the negative electrode active material is the weight ratio of the composite oxide (B) in the mixture of the positive electrode active material, that is, the composite oxide (A) and the composite oxide (B). R is obtained from the following formula,
R = (weight of composite oxide (B)) / {(weight of composite oxide (A)) + (composite oxide (B
) Weight)}
Using this, the following formula was set.
Positive electrode active material amount [g] / Negative electrode active material amount [g] = Q (F) / {Qc (A). (1-R) + Qc (B) .R}
/1.2

(Test method)
In order to compare the high temperature characteristics of the obtained batteries, the 1 hour rate current value of the batteries, that is, 1C, was set as follows for the sake of convenience, and the following tests were performed.
1C [mA] = {Qd (A) · (1-R) + Qd (B) · R} × (amount of positive electrode active material [g])
First, perform two constant current 0.2C charge / discharge cycles and one constant current 1C charge / discharge cycle at room temperature, then one constant current 0.2C charge / discharge cycle at a high temperature of 50 ° C. A test was conducted. The upper limit of charging was 4.1V and the lower limit voltage was 3.0V.

At this time, the ratio of the discharge capacity Qh (100) at the 100th cycle to the discharge capacity Qh (100) at the 100th cycle of the 1C charge / discharge cycle test at 50 ° C is the high temperature cycle capacity maintenance rate P [%] The high temperature characteristics of the batteries were compared using the value of P obtained by the equation.
P [%] = {Qh (100) / Qh (1)} × 100 (v)

Example 7
As a lithium-manganese composite oxide having a spinel structure, spinel-type LiMn ₂ O ₄ in which Li was substituted at the Mn site by 0.04 mol, that is, Li [Mn _1.96 Li _0.04 ] O ₄ was prepared in the same manner as in Preparation Example 1. The average particle diameter of the obtained lithium manganese composite oxide was 4.2 μm. It was 4.060V when the average voltage was measured by the said method.

On the other hand, as a lithium nickel composite oxide having a layered structure, a layered LiNiO ₂ in which a part of Ni sites is replaced with cobalt and aluminum, that is, a composition of commercially available Li [Ni _0.80 Co _0.15 Al _0.05 ] O ₂ ( An average particle size of 6.2 μm) was used. The average voltage was measured by the above method and found to be 3.809V. Next, the weight mixing ratio R of the composite oxide (B) in the positive electrode active material is set to 0.5.
As a positive electrode, a high-temperature cycle test was conducted by the above method, and a capacity retention rate after 100 cycles was obtained. The results are shown in Table-2.

Example 8
As the lithium manganese composite oxide having a spinel structure, spinel type LiMn ₂ O ₄ in which _{0.04 and 0.11} mol of lithium and aluminum are substituted at Mn sites, that is, Li [Mn _1.85 Al _0.11 Li _0.04 ] O ₄ is prepared in the above Preparation Example 2. Created in the same way. The average particle diameter of the obtained lithium manganese composite oxide was 7.4 μm. The average voltage was measured by the above method and found to be 4.071V.
The composite oxide (B) is the same as in Example 1, and the composite oxide (B) in the positive electrode active material is used.
A positive electrode was prepared with a weight mixing ratio R of 0.5 and a high-temperature cycle test was conducted by the above method. The results are shown in Table-2.

Example 9
A high-temperature cycle test was conducted in the same manner as in Example 2 except that the weight mixing ratio R of the composite oxide (B) in the positive electrode active material was 0.25. The results are shown in Table-2.

Example 10
The composite oxide (B) used in Examples 7 to 9 was further pulverized in a nitrogen atmosphere, and this was newly used as the composite oxide (B) (average particle size 0.55 μm). The average voltage of this composite oxide (B) was 3.786V. Other conditions were the same as in Example 9 to prepare a positive electrode, and a high-temperature cycle test was conducted by the above method. The results are shown in Table-2.

Comparative Example 3
A high-temperature cycle test was conducted in the same manner as in Example 7 except that the composite oxide (A) used in Example 7 was used alone as the positive electrode active material. The results are shown in Table-2.
Example 11
(Comparative Example 4 for the third aspect of the present invention)
As lithium manganese composite oxide with spinel structure, lithium and cobalt are
Spinel-type LiMn ₂ O ₄ substituted at _{0.04 and 0.10} mol respectively at the Mn site, that is, Li [Mn _1.86 Co _0.10 Li _0.04 ] O ₄ was prepared by the following method.

Manganese trioxide (Mn ₂ O ₃ ), lithium carbonate (Li ₂ CO ₃ ), cobalt carbonate (CoCO ₃
) Was used as a starting material, and the compound was blended so that the molar ratio of each compound was about 0.93: 0.52: 0.10. Ethanol was added to this blend, and it was well ground in a mortar to obtain a uniform mixture and then dried. The resulting mixture was calcined in the air at 500 ° C. for 6 hours, 600 ° C. for 6 hours, 700 ° C. for 6 hours and 800 ° C. for 6 hours, and then in the air at 850 ° C. for 24 hours. Baked and slowly cooled to room temperature at 0.2 ° C./min. The average particle diameter of the obtained lithium manganese composite oxide was 5.2 μm. The average voltage was measured by the above method and found to be 4.081V.
The composite oxide (B) is the same as in Example 1, and the composite oxide (B) in the positive electrode active material is used.
A positive electrode was prepared with a weight mixing ratio R of 0.5 and a high-temperature cycle test was conducted by the above method. The results are shown in Table-2.

Example 12
(Comparative Example 5 for the third aspect of the present invention)
A commercially available unsubstituted LiMn ₂ O ₄ (
Elemental analysis value: Li _1.00 Mn _2.00 O ₄ was used. The average voltage was measured by the above method and found to be 4.052V.

The composite oxide (B) is the same as in Example 7, and the composite oxide (B) in the positive electrode active material is used.
A positive electrode was prepared with a weight mixing ratio R of 0.5 and a high-temperature cycle test was conducted by the above method. The results are shown in Table-2.

It can be seen that Example 7 using a composite oxide in which a part of the manganese site is substituted with lithium as the composite oxide (A) exhibits a very good high temperature characteristic with a maintenance rate of 85% in a high temperature 100 cycle test. In Example 8, the high temperature cycle retention rate is further increased by substituting aluminum and using the composite oxide (A) having a high average voltage. Moreover, when the mixing ratio of the composite oxide (B) is reduced as in Example 9, the high-temperature cycle retention rate is slightly reduced, but the average voltage of the composite oxide (B) is lowered as in Example 10. It can be seen that the maintenance rate is also improved by using.

When the composite oxide (A) is used alone as in Comparative Example 3, the high-temperature cycle retention is very low. In addition, when a PF ₆ anion degradation inhibitor is used as in Examples 11 and 12, the cycle retention rate is clearly better than that of a comparative example in which no PF ₆ anion degradation inhibitor is added. However, in Examples 11 and 12, since the composite oxide (A) having an average potential lower than 4.059 V is used, it is compared with Examples 7 to 10 using the composite oxide (A) having an average voltage higher than 4.059 V. It can also be seen that the high temperature cycle maintenance rate is slightly low.

Claims (31)

In a positive electrode material for a lithium secondary battery containing manganese oxide and / or lithium manganese composite oxide as a positive electrode active material, a battery element is created using the positive electrode material, and this is a storage test of a positive electrode material charged with the battery element. A positive electrode material for a lithium secondary battery, wherein the decomposition amount of PF ₆ anion measured by the following storage test (I) is 1 × 10 μmol or less.
Storage test (I)
a1) A positive electrode formed by forming 24 mg of a positive electrode material into a circular shape having a diameter of 12 mm, and pressure-bonding to a current collector (a circular aluminum expanded metal having a diameter of 16 mm), Li metal as a counter electrode, and 1.0 mol as an electrolyte / L LiPF ₆ containing ethylene carbonate and diethyl carbonate mixed solution (volume ratio 3: 7) was used to assemble a battery element, which was charged to a maximum voltage of 4.2 V at a charging current density of 0.2 mA / cm ² After charging, then disassemble the battery element,
Take out the positive electrode in the charged state, the positive electrode,
b1) In an argon gas atmosphere with a dew point of −75 ° C. or less c1) In a polytetrafluoroethylene container dried at 80 ° C. for 3 hours,
d1) A mixed solution of 1.5 ml of ethylene carbonate and 3.5 ml of diethyl carbonate containing 1.0 mol / L of LiPF ₆ (acid content: 2.0 mmol / L or less, PO ₂ F ₂ anion: 0.5 mmol / L) And soaking in ethanol: 0.01 mg or less),
e1) Store at 80 ° C. for one week, measure the amount of PF ₆ anion in the mixed solution before and after storage (measurement temperature: 20 ° C.), and determine the amount of PF ₆ anion decomposition from the difference. _{2. The} positive electrode material for a lithium secondary battery according to claim 1, wherein the amount of PO ₂ F ₂ anion contained in the liquid after storage obtained according to the storage test (I) is 1 × 10 μmol or less at 20 ° C. 3.   The positive electrode material for a lithium secondary battery according to claim 1 or 2, wherein the positive electrode material contains a binder resin. The positive electrode material for a lithium secondary battery according to any one of claims 1 to 3, wherein a PF ₆ anion degradation inhibitor is dispersed and mixed in the positive electrode material. In manganese oxide and / or a positive electrode active material and a positive electrode material for a lithium secondary battery containing a PF ₆ anion decomposition inhibitor comprising a lithium-manganese composite oxide, as the PF ₆ anion decomposition inhibitor, following storage test (II ) The amount of decomposition of PF ₆ anion measured by
A positive electrode material for a lithium secondary battery, characterized by using a material having a size of × 10 μmol or less.
Storage test (II)
a2) Lithium manganese equivalent to a fully charged state obtained by extracting lithium from a lithium manganese composite oxide having a spinel structure having a composition of Li _{1 + x} Mn _2−x O ₄ (where 0 ≦ X ≦ 0.05) 160 mg of complex oxide (0.05 ≦ Li / Mn molar ratio ≦ 0.09)
b2) In an argon gas atmosphere with a dew point of −75 ° C. or lower,
c2) In a polytetrafluoroethylene container dried at 80 ° C. for 3 hours,
d2) mixed with 160 mg of the PF ₆ anion degradation inhibitor,
e2) A mixed liquid of ethylene carbonate 2.4 ml diethyl carbonate 5.6 ml containing 1.0 mol / L LiPF ₆ (acid content: 2.0 mmol / L or less, PO ₂ F ₂ anion: 0.5 mmol / L or less, And soaked in ethanol: 0.01 mg or less)
f2) Store at 70 ° C. for one week, measure the amount of PF ₆ anion in the mixed solution before and after storage (measurement temperature: 20 ° C.), and determine the amount of PF ₆ anion decomposition. The positive electrode material for a lithium secondary battery according to claim 5, wherein the amount of PO ₂ F ₂ anion contained in the liquid after storage obtained according to the storage test (II) is 5 × 10 μmol or less at 20 ° C.   The positive electrode material for a lithium secondary battery according to claim 5 or 6, wherein the amount of ethanol contained in the liquid after storage when the storage in the storage test (II) is further extended for 2 weeks is 1 mg or less. The positive electrode material for a lithium secondary battery according to any one of claims 5 to 7, wherein a PF ₆ anion decomposition inhibitor is dispersed and mixed. The PF ₆ anion decomposition inhibitor contains a lithium nickel composite oxide.
The positive electrode material for lithium secondary batteries as described in any one of these. PF ₆ anion decomposition inhibitor is a compound containing at least one element selected from the group consisting of groups 15 and 16 of the periodic table, compound having at least a secondary amino group in the molecule, A compound having at least a tertiary amino group, a compound having at least one amide bond in the molecule, a compound having at least one nitrogen-containing heterocyclic ring in the molecule, or a compound having at least one hydroxyl group in the molecule The positive electrode material for a lithium secondary battery according to any one of claims 4 to 8. The addition amount of the PF ₆ anion decomposition inhibitor is 0.0001 to 80 wt% with respect to the positive electrode active material.
The positive electrode material for a lithium secondary battery according to any one of claims 4 to 10, which is in a range of The positive electrode material for a lithium secondary battery according to claim 9, wherein the addition amount of the PF ₆ anion decomposition inhibitor is in the range of 1 to 80 wt% with respect to the positive electrode active material. The addition amount of the PF ₆ anion decomposition inhibitor is 0.0001 to 10 wt% with respect to the positive electrode active material.
The positive electrode material for a lithium secondary battery according to claim 10, which is in the range described above.   2. The manganese oxide and / or lithium manganese composite oxide is a lithium manganese composite oxide having a spinel structure, wherein a part of the manganese site is substituted with at least one element selected from typical elements. The positive electrode material for lithium ion secondary batteries as described in any one of thru | or 13.   15. The positive electrode material for a lithium ion secondary battery according to claim 14, wherein the typical element that substitutes a part of the manganese site is aluminum and / or lithium.   The positive electrode material for a lithium ion secondary battery according to claim 14 or 15, wherein the substitution amount of the typical element is 0.05 mol or more in 2 mol of manganese. The positive electrode material contains a lithium manganese composite oxide having a spinel structure and a lithium nickel composite oxide having a layered structure, and a part of the manganese site of the lithium manganese composite oxide is substituted with another element, The average voltage measured by the following measurement method (I) of the other element-substituted lithium manganese composite oxide is 4.059 V or more, any one of claims 1 to 9, 11, 12, and 14 to 16 The positive electrode material for lithium ion secondary batteries as described in any one.
<Measuring method of average voltage (I)>
(1) The composite oxide is weighed at a ratio of 75% by weight, acetylene black 20% by weight, and polytetrafluoroethylene (PTFE) powder 5% by weight, and is made into a thin sheet. After adjusting the total weight to 12.5 mg / cm ² , this sample is further pressure-bonded to an aluminum expanded metal to form a test electrode. The test electrode is dried at 120 ° C. under reduced pressure for 1 hour.
(2) A 25 μm porous polyethylene film as a separator under an argon atmosphere,
Lithium metal foil was used as the counter electrode, and 1 mol / liter lithium hexafluorophosphate (LiPF ₆ ) was added as a non-aqueous electrolyte solution to a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7. A CR2032 type coin-type battery is manufactured using the dissolved solution.
(3) The obtained coin-type battery was subjected to a constant current charge / discharge cycle (charge upper limit 4.35 V, discharge lower limit 3.2 V) at a current density of 0.5 mA / cm ^{2 in} an environment of 25 ° C., and the average voltage Ve = Ve = (average charge voltage in the second cycle + discharge average voltage in the second cycle) / 2
Asking. The charge average voltage or discharge average voltage is calculated by measuring the voltage during charging or discharging at intervals of 2 seconds and dividing the value obtained by integrating the voltage over time by the time required for charging or discharging. The lithium nickel composite oxide is a lithium nickel composite oxide having an average voltage of 3.830 V or less when measured by the following measurement method (II). The positive electrode material for lithium ion secondary batteries as described.
<Measuring method of average voltage (II)>
(1) 75% by weight of lithium nickel composite oxide, 20% by weight of acetylene black and 5% by weight of polytetrafluoroethylene powder are mixed and formed into a thin sheet. After adjusting the total weight to 12.5 mg / cm ² , this sheet is further pressure-bonded to an aluminum expanded metal to form a test electrode. The test electrode is dried at 120 ° C. under reduced pressure for 1 hour.
(2) A 25 μm porous polyethylene film as a separator under an argon atmosphere,
Lithium metal foil was used as the counter electrode, and 1 mol / liter lithium hexafluorophosphate (LiPF ₆ ) was added as a non-aqueous electrolyte solution to a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7. A CR2032 type coin-type battery is manufactured using the dissolved solution.
(3) The obtained coin-type battery was subjected to a constant current charge / discharge cycle (charge upper limit 4.2 V, discharge lower limit 3.2 V) at a current density of 0.2 mA / cm ^{2 in} an environment of 25 ° C., and the average voltage Ve = Ve = (average charge voltage in the second cycle + discharge average voltage in the second cycle) / 2
Asking. The charge average voltage or discharge average voltage is a value obtained by measuring the voltage during charging or discharging at intervals of 2 seconds and dividing the value obtained by integrating the voltage over time by the time required for charging or discharging.   19. The lithium according to claim 14, wherein a weight ratio of the lithium nickel composite oxide to the total amount of the lithium manganese composite oxide and the lithium nickel composite oxide is 0.7 or less. Positive electrode material for ion secondary battery. More than 80% of the degradation product of PF ₆ anion in the liquid after the storage test (I) or (II) is PO ₂ F ₂
The positive electrode material for a lithium secondary battery according to claim 1, wherein the positive electrode material is an anion.   A positive electrode material for a lithium ion secondary battery comprising a lithium manganese composite oxide having a spinel structure and a lithium nickel composite oxide having a layered structure, wherein a part of the manganese site of the lithium manganese composite oxide is a typical element A positive electrode material for a lithium ion secondary battery, wherein the positive electrode material is substituted with at least one element selected from:   The positive electrode material for a lithium ion secondary battery according to claim 21, wherein the typical element that substitutes a part of the manganese site is aluminum and / or lithium.   23. The positive electrode material for a lithium ion secondary battery according to claim 21 or 22, wherein the substitution amount of the typical element is 0.05 mol or more in 2 mol of manganese. A positive electrode material for a lithium ion secondary battery comprising a lithium manganese composite oxide having a spinel structure and a lithium nickel composite oxide having a layered structure, wherein a part of the manganese site of the lithium manganese composite oxide is other A positive electrode material for a lithium ion secondary battery, characterized in that an average voltage measured by the following measurement method (I) of the other element-substituted lithium-manganese composite oxide is 4.059 V or more. .
<Measuring method of average voltage (I)>
(1) The composite oxide is weighed at a ratio of 75% by weight, acetylene black 20% by weight, and polytetrafluoroethylene (PTFE) powder 5% by weight, and is made into a thin sheet. After adjusting the total weight to 12.5 mg / cm ² , this sample is further pressure-bonded to an aluminum expanded metal to form a test electrode. The test electrode is dried at 120 ° C. under reduced pressure for 1 hour.
(2) A 25 μm porous polyethylene film as a separator under an argon atmosphere,
Lithium metal foil was used as the counter electrode, and 1 mol / liter lithium hexafluorophosphate (LiPF ₆ ) was added as a non-aqueous electrolyte solution to a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7. A CR2032 type coin-type battery is manufactured using the dissolved solution.
(3) The obtained coin-type battery was subjected to a constant current charge / discharge cycle (charge upper limit 4.35 V, discharge lower limit 3.2 V) at a current density of 0.5 mA / cm ^{2 in} an environment of 25 ° C., and the average voltage Ve = Ve = (average charge voltage in the second cycle + discharge average voltage in the second cycle) / 2
Asking. The charge average voltage or discharge average voltage is calculated by measuring the voltage during charging or discharging at intervals of 2 seconds and dividing the value obtained by integrating the voltage over time by the time required for charging or discharging. 25. The lithium nickel composite oxide according to claim 21, wherein the lithium nickel composite oxide is a lithium nickel composite oxide having an average voltage of 3.830 V or less when measured by the following measurement method (II). The positive electrode material for lithium ion secondary batteries as described.
<Measuring method of average voltage (II)>
(1) 75% by weight of lithium nickel composite oxide, 20% by weight of acetylene black and 5% by weight of polytetrafluoroethylene powder are mixed and formed into a thin sheet. After adjusting the total weight to 12.5 mg / cm ² , this sheet is further pressure-bonded to an aluminum expanded metal to form a test electrode. The test electrode is dried at 120 ° C. under reduced pressure for 1 hour.
(2) A 25 μm porous polyethylene film as a separator under an argon atmosphere,
Lithium metal foil was used as the counter electrode, and 1 mol / liter lithium hexafluorophosphate (LiPF ₆ ) was added as a non-aqueous electrolyte solution to a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7. A CR2032 type coin-type battery is manufactured using the dissolved solution.
(3) The obtained coin-type battery was subjected to a constant current charge / discharge cycle (charge upper limit 4.2 V, discharge lower limit 3.2 V) at a current density of 0.2 mA / cm ^{2 in} an environment of 25 ° C., and the average voltage Ve = Ve = (average charge voltage in the second cycle + discharge average voltage in the second cycle) / 2
Asking. The charge average voltage or discharge average voltage is a value obtained by measuring the voltage during charging or discharging at intervals of 2 seconds and dividing the value obtained by integrating the voltage over time by the time required for charging or discharging.   26. The lithium according to claim 21, wherein the weight ratio of the lithium nickel composite oxide to the total amount of the lithium manganese composite oxide and the lithium nickel composite oxide is 0.7 or less. Positive electrode material for ion secondary battery.   A positive electrode for a lithium ion secondary battery, wherein an active material layer containing the positive electrode material for a lithium secondary battery according to any one of claims 1 to 26 is formed on a current collector.   A lithium ion secondary battery comprising the positive electrode material for a lithium secondary battery according to any one of claims 1 to 26 in a positive electrode.   A lithium secondary battery comprising a positive electrode using the positive electrode material for a lithium secondary battery according to any one of claims 1 to 26, a negative electrode, and an electrolytic solution obtained by dissolving a lithium salt in a solvent.   30. The lithium secondary battery according to claim 28 or 29, wherein the negative electrode contains a carbon material. The lithium secondary battery according to the lithium salt is one either of claims 28 or 30 which is LiPF _6.