JP2001266879A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

[PROBLEMS] To provide a non-aqueous electrolyte secondary battery which realizes high energy density and has excellent safety. SOLUTION: This non-aqueous electrolyte secondary battery includes a positive electrode 4 containing a lithium-containing compound, a negative electrode 5, and a non-aqueous electrolyte, wherein the conductive agent contained in the positive electrode is represented by formula (A) _3.
An oxide having a perovskite structure represented by
(B) Formula A ₂ BO ₄ (where A is 2
B is at least one member selected from the group consisting of a typical element having a valency, a lanthanoid element, and a combination thereof.
Oxide having a K ₂ NiF _4- type structure, which is at least one selected from transition elements of Group Va, Group Va, Group VIa, Group VIIa, Group VIII and Group Ib);
₂ (where M is Va group, VIa group, VIIa group, VI
And (d) a mixture of (a), (b) and (c). A non-aqueous electrolyte secondary battery comprising an oxide and a conductive oxide having free electrons.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a secondary battery,
In particular, the present invention relates to a nonaqueous electrolyte secondary battery provided with a positive electrode containing a lithium-containing compound as an active material.

[0002]

2. Description of the Related Art In recent years, non-aqueous electrolyte secondary batteries have attracted attention. This is considered to be largely due to the successful development of a relatively safe anode material and the realization of a high voltage battery by increasing the decomposition voltage of the non-aqueous electrolyte. Among such non-aqueous electrolyte secondary batteries, a secondary battery using lithium ions has a particularly high discharge potential, and thus is expected to realize a battery having a high energy density. The positive electrode of the nonaqueous electrolyte secondary battery using lithium ions is composed of an oxide of a transition metal called an active material, a binder, and a conductive agent for imparting necessary conductivity to the active material in general. I have.

[0003] In this case, the conductive agent is required to have, in addition to high electrical conductivity, oxidation resistance which is not easily oxidized by contact with the active material, and furthermore, the active material is effectively electrically connected to each other. A structure for contacting, for example, a fibrous structure is required. In addition to the above conditions, in consideration of lighter weight and cost, conventionally, carbon-based acetylene black or the like has been used as a conductive agent. In fact, in a secondary battery using LiCoO ₂ as a positive electrode active material, relatively satisfactory characteristics are obtained by using the above-described conductive agent.

[0004]

By the way, recently, Co
In view of the increase in material costs and the pursuit of batteries with higher energy density, search for active materials using substances other than Co-based materials and research and development have been promoted. Some of these new active materials have high energy densities, but may not have sufficient thermal stability after charging compared to Co-based active materials, and may have problems such as relatively high oxidizing power. It is becoming clear.

Accordingly, it is an object of the present invention to provide a non-aqueous electrolyte secondary battery which realizes high energy density and is excellent in safety.

[0006]

In order to achieve the above object, a nonaqueous electrolyte secondary battery according to the present invention comprises a nonaqueous electrolyte comprising a positive electrode containing a lithium-containing compound, a negative electrode, and a nonaqueous electrolyte. A liquid secondary battery, wherein the surface of the active material particles contained in the positive electrode is coated with a conductive oxide shown in (a), (b), and (c) below. . (A) The following formula ABO ₃ (where A is at least one selected from the group consisting of a divalent typical element, a lanthanoid element, and a combination thereof)
B is a species of group IVa, Va, VIa, VIIa
An oxide having a perovskite structure represented by at least one selected from the group consisting of transition elements of Group III, Group VIII and Group Ib), (B) the following formula A ₂ BO ₄ (where A is a divalent typical element) , At least one selected from the group consisting of lanthanoid elements or a combination thereof
B is a species of group IVa, Va, VIa, VIIa
Having a K ₂ NiF ₄ type structure represented by (C) a mixture of (A) and (B). A conductive oxide having free electrons selected from the group consisting of:

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A non-aqueous electrolyte secondary battery according to the present invention will be described below based on one embodiment (cylindrical non-aqueous electrolyte secondary battery) shown in FIG.

In the cylindrical non-aqueous electrolyte secondary battery shown in FIG. 1, an insulator 2 is disposed at the bottom of a cylindrical container 1 made of, for example, stainless steel. The electrode group 3 is housed in the container 1.

The electrode group 3 has a structure in which a strip formed by laminating a positive electrode 4, a separator 5 and a negative electrode 6 in this order is spirally wound so that the negative electrode 6 is located outside. The separator 5 is formed of, for example, a synthetic resin nonwoven fabric, a porous polyethylene film, or a porous porobylene film. The container 1 contains an electrolytic solution. The insulating paper 7 having a central portion opened is placed above the electrode group 3 in the container 1. The insulating sealing plate 8 is disposed at the upper opening of the container 1 and the vicinity of the upper opening is caulked inward to fix the sealing plate 8 to the container 1 in a liquid-tight manner. The positive electrode terminal 9 is fitted in the center of the insulating sealing plate 8. One end of the positive electrode lead 10 is connected to the positive electrode 4, and the other end is connected to the positive electrode terminal 9. The negative electrode 6
Is connected to the container 1 serving as a negative electrode terminal via a negative electrode lead (not shown). Next, the configurations of the positive electrode 4, the negative electrode 6, and the non-aqueous electrolyte will be described more specifically. (1) Configuration of Positive Electrode 4 The positive electrode 4 is made of, for example, a lithium-containing cobalt oxide (LiCoO ₂ ), a lithium-containing nickel oxide (LiNiO ₂ ), or a lithium-containing manganese oxide (Li
Mn ₂ O ₄ ) or a material in which another element is added or partially substituted in the crystal of the active material can be used.

In the present invention, as the conductive agent coated on the surface of the active material, a conductive oxide containing a transition metal element and a conductive composite oxide containing both a typical element and a transition metal element can be used.

That is, in the present invention, a preferred conductive agent to be coated on the surface of the active material is (A) the following formula ABO ₃ (where A is a divalent typical element, a lanthanoid element, or a combination thereof) At least one
B is a species of group IVa, Va, VIa, VIIa
An oxide having a perovskite structure represented by at least one selected from the group consisting of transition elements of Group III, Group VIII and Group Ib), (B) the following formula A ₂ BO ₄ (where A is a divalent typical element) , At least one selected from the group consisting of lanthanoid elements or a combination thereof
B is a species of group IVa, Va, VIa, VIIa
Having a K ₂ NiF ₄ type structure represented by (C) a mixture of (A) and (B). A conductive oxide having free electrons selected from the group consisting of lanthanum nickel composite oxide (LaNi
O ₃ ), strontium vanadate (SrVO ₃ ), calcium vanadate (CaVO ₃ ), strontium ferrate (SrFeO ₃ ), lanthanum titanate (LaTi)
O ₃ ), lanthanum strontium nickel composite oxide (LaSrNiO ₄ ) strontium chromate (SrC
and rO _3), calcium chromate (CaCrO _3), calcium ruthenate (CaRuO _3), strontium ruthenate (SrRuO _3), a conductive composite oxide such as iridium strontium (SrIrO ₃₎ can be preferably used.

Among the above, SrVO ₃ , SrFe
O ₃ , SrCrO ₃ , La _1-x Sr _x MnO ₃ (0.
15 ≦ x ≦ 0.6), LaNiO ₃ , LaSrNiO ₄
And LaCuO ₃ are particularly preferred.

The thickness of the film is preferably in the range of 0.3 nm to 50 nm. This is for the following reason. When the thickness of the film is less than 0.3 nm, it is difficult to form a low-resistance film due to mutual diffusion of the active material and the material of the film. On the other hand, when the thickness of the film exceeds 59 nm or more, the transfer resistance of lithium at the time of insertion and extraction of lithium ions becomes excessive, which causes cycle deterioration. Further, a more preferable film thickness as a range in which the film can be formed more stably and has high mass productivity is in a range of 1 nm to 5 nm.

A method of preparing a positive electrode by suspending the active material, a conductive agent such as acetylene black, and a binder in a suitable solvent, applying the suspension to a current collector, and drying to form a thin plate. Can be.

In the present invention, the specific resistance of the conductive agent coated on the surface is not particularly limited to a specific value.
In general, when the specific resistance of the conductive agent is 1 × 10 ⁻³ (Ωm) or more, the electron conductivity of the positive electrode is insufficient, which tends to cause an increase in overvoltage and internal stress during charging and discharging,
As a result, a reduction in discharge voltage and capacity and a reduction in cycle life are caused, which is not desirable. Further, the lower limit of the specific resistance of the conductive agent is not particularly limited, and in the present invention, the ratio realized by a superconducting material (for example, La _1.85 Sr _0.15 CuO ₄ ) in a low temperature state. Zero resistance is also included.

On the other hand, the reason why the conductive oxide is limited to the compound containing the specific transition metal element as described above is as follows. In other words, oxides of typical elements are essentially semiconductors, and the electrical conductivity is caused by a slight deviation of the ratio of elements from the stoichiometric ratio. In addition to this, when a strong oxidizing agent, which is a positive electrode active material, comes into contact, oxidation proceeds from the contact surface, resulting in a tendency to further reduce the conductivity.

The binder is not particularly limited. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR) Etc. can be used.

As the current collector, for example, aluminum foil, stainless steel foil, titanium foil and the like are preferably used. 2) Configuration of Negative Electrode 6 As the negative electrode 6, for example, a substance capable of inserting and extracting lithium ions (for example, a carbonaceous substance or a chalcogen compound)
, And those made of light metal can be used. Above all, a negative electrode containing a carbonaceous substance or a chalcogen compound that stores and desorbs lithium ions is preferable in terms of improving battery characteristics such as the cycle life of the secondary battery.

Examples of the carbonaceous material for absorbing and desorbing lithium ions include coke, carbon fiber, pyrolytic vapor-grown carbon material, graphite, resin fired body, mesoface pitch-based carbon fiber and mesophase spherical carbon. And the like. Of these, mesoface pitch-based carbon fibers or mesophase spherical carbons graphitized at 2500 ° C. or higher are particularly preferable because of their high electrode capacity.

The above-mentioned carbonaceous material is particularly 70% by differential thermal analysis.
Exothermic peak at a temperature of 0 ° C or higher, more preferably 800 ° C
An exothermic peak is described above, and the intensity ratio P101 / P100 of the (101) diffraction peak (P101) and the (100) diffraction peak (P100) of the graphite structure by X-ray diffraction is 0.7.
-2.2. Since the negative electrode containing such a carbonaceous substance can rapidly insert and extract lithium ions, the rapid charge and discharge performance of the secondary battery can be significantly improved. Further, the negative electrode containing such a carbonaceous substance is excellent in that the possibility of ignition of the negative electrode during overheating can be significantly reduced.

The chalcogen compounds that occlude and desorb lithium ions include titanium disulfide (TiS ₂ ), molybdenum disulfide (MoS ₂ ), and niobium selenide (NbSe).
₂ ) and the like. When such a chalcogen compound is used for the negative electrode, although the voltage of the secondary battery may decrease, the capacity of the negative electrode significantly increases, so that the capacity characteristics of the secondary battery can be improved. Further, since such a negative electrode has a high diffusion rate of lithium ions, the rapid charge / discharge performance of the secondary battery is improved.

Preferred examples of the light metal include aluminum, aluminum alloy, magnesium alloy, lithium metal, lithium alloy and the like.

A negative electrode containing a substance capable of absorbing and desorbing lithium ions is prepared by suspending, for example, the above-described substance and a binder in a suitable solvent, applying the suspension to a current collector, and drying.
It can be made by pressing.

Examples of the binder in this case include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene-propylene-diene copolymer (EPDM), and styrene-butadiene rubber (SB
R), carboxymethyl cellulose (CMC) and the like can be used.

As the current collector of the negative electrode, it is preferable to use, for example, a copper foil, a stainless steel foil, a nickel foil or the like. 3) Configuration of Nonaqueous Electrolyte Solution As the nonaqueous electrolyte solution, a solution in which an electrolyte (lithium salt) is dissolved in a nonaqueous solvent is preferably used.

Specific examples of preferable non-aqueous solvents in this case include cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC) such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate. Carbonate (DE
Chain carbonates such as C), dimethoxyethane (DM
E), chain ethers such as diethoxyethane (DEE) and ethoxymethoxyethane, and tetrahydrofuran (TH
F) and 2-methyltetrahydrofuran (2-MeTH
Cyclic ethers such as F), crown ethers, fatty acid esters such as γ-butyrolactone (γ-BL), nitrogen compounds such as acetonitrile (AN), sulfolane (S
L) and sulfur compounds such as dimethylsulfoxide (DMSO). The non-aqueous solvents may be used alone or in combination of two or more. Among them, one composed of at least one selected from EC, PC and γ-BL, and at least one selected from EC, PC and γ-BL and DMC, EMC, DEC, DM
It is particularly desirable to use a mixed solvent comprising at least one selected from E, DEE, THF, 2-MeTHF and AN. Further, when using a negative electrode containing a carbonaceous material that occludes and desorbs lithium ions, from the viewpoint of improving the cycle life of a secondary battery including the negative electrode, EC, PC, γ-BL, EC and PC and EMC, EC and PC and DEC, EC and PC and DEE, E
C and AN, EC and EMC, PC and DMC, PC and DE
It is desirable to use a mixed solvent composed of C, EC and DEC.

Preferred examples of the electrolyte include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), and lithium borofluoride (L
iBF ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ),
Lithium triple olometasulfonate (LiCF ₃ SO
₃ ) and lithium salts such as pistrifluoromethylsulfonylimitolithium (LiN (CF ₃ SO ₂ ) ₂ ). Among them, LiPF ₆ , Li
It is preferable to use BF ₄ or LiN (CF ₃ SO ₂ ) ₂ because conductivity and safety are improved. The amount of the electrolyte dissolved in the nonaqueous solvent is 0.1 mol / 1-3. Omol /
It is preferred to be within the range of 1.

By coating the conductive oxide as described above on the surface of the positive electrode active material, high safety can be realized even in a secondary battery having a high capacity.
Actually, as shown in the results of Examples and Comparative Examples to be described later, the secondary battery according to the present invention in which the conductive oxide is coated on the surface of the positive electrode active material is used in a nail penetration test of the charged battery. While the heat generation is suppressed, it is recognized that the conventional battery has a high heat generation temperature or ignition at a certain temperature. (Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the results shown in the accompanying drawings and the like. It should be noted that the present invention is not limited to the following embodiments at all, and can be implemented with appropriate changes within a scope that does not change the gist of the present invention. Example 1 <Preparation of positive electrode> Li _1.075 Ni as active material
_{The 0.755} Co _0.17 O _1.9 F _0.1 powder is carefully crushed and appropriately measured with a dragon degree distribution meter, and the crushing is continued until no agglomerates are present. Thereafter, the active material powder is added and the mixture is heated with stirring to evaporate. This was further heated to 400 ° C. in oxygen to remove the nitric acid component and to apply LaN
A thin film of iO ₃ is formed. The active material powder and acetylene black powder and graphite powder to be a conductive agent
The mixture was dispersed in an N-methyl-2-pyrrolidone solvent containing PVDF as a binder to prepare a positive electrode mixture slurry. The slurry was applied on an aluminum foil, dried, rolled and cut to prepare a positive electrode. <Preparation of negative electrode> A negative electrode active material, graphite powder as a conductive agent and styrene butadiene rubber as a binder are mixed in an appropriate ratio, and water is carefully dispersed to form a negative electrode mixture slurry, which is coated on a copper foil. After drying, rolling and cutting were performed to produce a negative electrode. <Preparation of non-aqueous electrolyte> Li as an electrolyte in a mixed solvent composed of propylene carbonate and dimethoxyethane
ClO ₄ was dissolved to a concentration of 1 mol / l to prepare a non-aqueous electrolyte. <Preparation of electrode for evaluation> After the obtained positive electrode sheet, negative electrode sheet, and separator were sufficiently dried, the positive electrode and the negative electrode were wound face-to-face through the separator, inserted into a stainless steel battery can, and placed in an argon atmosphere. An electrolyte was injected and sealed to prepare a battery for evaluation. Example 2 The above-described positive electrode evaluation battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that the conductive agent shown below was used as the surface coating of the positive electrode active material. Strontium vanadate (SrVO ₃ ) powder was used as a conductive agent for coating the active material surface. Example 3 The above-described positive electrode evaluation battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that the conductive agent shown below was used as the surface coating of the positive electrode active material. The conductive agent to be coated on the surface of the active _material, using La _{0.5 Sr 0.5} MnO ₃ powder. Example 4 The above-described positive electrode evaluation battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that the conductive agent shown below was used as the surface coating of the positive electrode active material. Strontium chromate (SrCrO ₃ ) powder was used as a conductive agent for coating the active material surface. Example 5 The above-described positive electrode evaluation battery shown in FIG. 1 was assembled in the same manner as in Example 1 except that the active material shown below was used.

As a positive electrode active material, Li _1.075 Ni
_0.755 Al _0.17 O _1.9 F _{0 . One} powder was used. Example 6 The above-described positive electrode evaluation battery shown in FIG. 1 was assembled with the same configuration as in Example 1 except that the active material shown below was used.

As a positive electrode active material, Li _1.075 Ni
_0.705 Al _0.22 O _1.9 F _{0 . One} powder was used. Comparative Example 1 The positive electrode evaluation battery shown in FIG. 1 described above was assembled in the same configuration as in Example 1 except that the conductive agent shown below was used as the surface coating material of the positive electrode active material. Iron tetroxide (Fe ₃ O ₄ ) powder was used as a conductive agent for coating the active material surface. Comparative Example 2 The above-described positive electrode evaluation battery shown in FIG. 1 was assembled with the same configuration as in Example 1 except that the surface of the positive electrode active material was not coated. Comparative Example 3 The above-described positive electrode evaluation battery shown in FIG. 1 was assembled in the same manner as in Example 1, except that a material containing an aggregate of about 100 μm was used as the positive electrode active material.

The obtained Examples 1-6 and Comparative Examples 1-3
After the battery reaches 4.2V at a current value of 0.5C,
The current is kept flowing so as to maintain the voltage, and the current is stopped when the total charging time reaches 5 hours. Thereafter, the thermal stability of the battery is measured as follows. A thermocouple was attached to the battery that had been subjected to the charging process, a nail was pierced from the side of the battery, and the temperature change of the battery over time was measured, and the heat generation peak temperature was measured. At the same time, the cycle characteristics of the battery prepared under the same conditions were also measured. The results are shown in Table 1 below and FIG.
Shown in

As is evident from Table 1, the batteries of Examples 1-6 have a low exothermic peak temperature, and in particular, Examples 1 and 6 show little heat generation. On the other hand, it can be seen that the electrode of Comparative Example 1 has a poor cycle conductivity due to insufficient conductivity of the conductive agent. Comparative Example 2
Although the battery of the above was not ruptured, the ultimate temperature was high, which is not preferable. The battery of Comparative Example 3 had a higher exothermic peak temperature, causing burst ignition. As a result of the comprehensive judgment, all of the examples were judged to be superior to the comparative examples. (In the table, ◎:
Very good, ：: good, Δ: almost good, ×: bad. )

[Table 1]

[0033]

As described in detail above, according to the nonaqueous electrolyte secondary battery of the present invention, by using a specific conductive oxide as a conductive agent for the positive electrode, the thermal stability of the charged battery can be improved. A more reliable secondary battery having high energy density and excellent safety can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a positive electrode evaluation battery used in an example of the present invention.

FIG. 2 is a graph showing cycle characteristics of non-aqueous electrolyte secondary batteries according to Examples and Comparative Examples of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Container 3 Electrode group 4 Positive electrode 5 Negative electrode 6 Separator 8 Sealing plate

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Moto Kanda 1 Tokoba R & D Center, Komukai Toshiba-cho, Saisaki-ku, Kawasaki-shi, Kanagawa F-term (reference) 5H029 AJ12 AK03 AL06 AL07 AL08 AM02 AM03 AM04 AM05 AM07 BJ02 BJ13 BJ14 CJ22 CJ25 DJ15 DJ16 DJ17 EJ05 5H050 AA15 BA17 CA08 CA09 CB07 CB08 CB09 DA02 DA09 EA12 FA16 FA17 FA18 FA19 GA25

Claims (4)

[Claims] 1. A nonaqueous electrolyte secondary battery comprising a positive electrode containing a lithium-containing compound, a negative electrode, and a nonaqueous electrolyte, wherein the surface of active material particles contained in the positive electrode is as follows: (B) A non-aqueous electrolyte secondary battery, which is coated with the conductive oxide shown in (c). (A) The following formula ABO ₃ (where A is at least one selected from the group consisting of a divalent typical element, a lanthanoid element, and a combination thereof)
B is a species of group IVa, Va, VIa, VIIa
An oxide having a perovskite structure represented by at least one selected from the group consisting of transition elements of Group III, Group VIII and Group Ib), (B) the following formula A ₂ BO ₄ (where A is a divalent typical element) , At least one selected from the group consisting of lanthanoid elements or a combination thereof
B is a species of group IVa, Va, VIa, VIIa
Having a K ₂ NiF ₄ type structure represented by (C) a mixture of (A) and (B). An oxide selected from the group consisting of: a conductive oxide having free electrons. 2. The method according to claim 1, wherein the conductive oxide is SrVO.₃, Sr
FeO₃, SrCrO ₃, La_1-xSr_xMnO
₃(0.15 ≦ x ≦ 0.6), LaNiO₃, LaSr
NiO₄, And LaCuO₃Selected from the group consisting of
The non-aqueous electrolyte secondary battery according to claim 1, comprising:
pond. 3. The non-aqueous electrolyte solution according to claim 1, wherein the active material particles are primary particles formed by crystal growth or particles having a smooth surface without any gap. Next battery. 4. The non-aqueous electrolyte secondary battery according to claim 1, wherein a fibrous or plate-like conductive agent is present between the active material particles, and the positive electrode has a structure in which the active materials are not in direct contact with each other.