JP2010086658A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

Disclosed is a non-aqueous electrolyte secondary battery capable of suppressing deterioration due to a decrease in charge / discharge capacity even when charged / discharged with a large current.
A negative electrode, the nonaqueous electrolyte secondary battery in which a cathode having a lithium-containing compound is immersed in the non-aqueous electrolyte, a lithium-containing compound of the positive _{electrode, LiFe x M1 y M2 z PO} 4 M1 is one or more elements selected from V, Cr, Cu, Zn, In, Sn, Mo, Ti and Mn, and M2 is Bi, Zr, Cd, Pd, Nb and Ag. A non-aqueous electrolyte secondary battery comprising one or more elements selected from the group consisting of lithium iron phosphate compounds having an olivine structure of 0.01 ≦ x, y, z ≦ 1.00.
[Selection] Figure 1

Description

  In particular, the present invention relates to an improvement in the performance of a lithium iron phosphate compound having an olivine structure that is attracting attention as a novel positive electrode material in a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery.

Although LiCoO ₂ and LiNiO ₂ are widely used as the positive electrode material of the lithium ion secondary battery, these LiCoO ₂ and LiNiO ₂ are unstable because their crystal structure has a layered structure, and are deteriorated by overcharge. Or the charge capacity is significantly reduced by repeated charge / discharge cycles.

Therefore, in recent years, as shown in Patent Documents 1 to 3, a lithium ion phosphate compound having a stable olivine structure with a crystal structure, which is a novel positive electrode material, is used as a positive electrode active material for new next-generation automobiles and large stationary batteries. Is also attracting attention.
Since this lithium iron phosphate compound has a stable crystal structure as described above, it is possible to prevent deterioration due to overcharge and reduction in charge / discharge capacity due to repeated charge / discharge cycles.

Furthermore, this lithium iron phosphate compound can reduce the amount of rare metals used in recent years, such as Co and Ni, which have experienced rapid price increases, compared to LiCoO ₂ and LiNiO _2. This makes it possible to manufacture an inexpensive lithium ion secondary battery without using the battery.

Japanese Patent Application Laid-Open No. 2004-514639 JP 2003-338992 A JP 2001-110414 A

However, the lithium iron phosphate compound having an olivine structure used as the positive electrode active material described above is composed of a negative electrode made of graphite and a lithium ion dilute in an electrolyte solution in which LiPF ₆ is dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate. As a secondary battery, when a repeated charge / discharge cycle test is performed under a high temperature condition of around 60 ° C., there is a problem that iron is eluted and the charge / discharge capacity of the lithium ion secondary battery is reduced. This means that when a large battery or high-power battery is constructed using this lithium iron phosphate compound as the positive electrode active material, charging / discharging the battery with a large current causes an increase in battery temperature, thus reducing the charge / discharge capacity. This means that the lithium ion secondary battery is deteriorated.

  This invention is made | formed in view of this situation, and makes it a subject to provide the nonaqueous electrolyte secondary battery which can suppress degradation by the reduction | decrease in charging / discharging capacity | capacitance, even when it charges / discharges with a large current.

That is, the non-aqueous electrolyte secondary battery according to the invention of claim 1 is a non-aqueous electrolyte secondary battery in which a negative electrode and a positive electrode including a lithium-containing compound are immersed in the non-aqueous electrolyte. the lithium-containing compound of the positive electrode, a _{LiFe x M1 y M2 z PO 4} , M1 is V, Cr, Cu, Zn, in, Sn, Mo, one or more elements selected from among Ti and Mn In addition, M2 is one or more elements selected from Bi, Zr, Cd, Pd, Nb, and Ag, and lithium iron having an olivine structure of 0.01 ≦ x, y, z ≦ 1.00 It consists of a phosphoric acid compound.

  The invention described in claim 2 is the nonaqueous electrolyte secondary battery according to claim 1, wherein the lithium-containing compound of the positive electrode has an average particle size of 0.9 μm or more and 4 μm or less. .

The invention according to claim 3 is the nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the lithium-containing compound of the positive electrode has a BET specific surface area of 17 m ² / g or more and 49 m ² / g or less. It is characterized by being.

According to the non-aqueous electrolyte secondary battery according to claim 1 to 3, the M1 of _{LiFe x M1 y M2 z PO 4} V, Cr, Cu, Zn, In, Sn, Mo, from among Ti and Mn And at least one element selected, and M2 is at least one element selected from Bi, Zr, Cd, Pd, Nb and Ag, and 0.01 ≦ x, y, z ≦ 1.00 As a result, the ionic conductivity in the particles can be remarkably improved, and as a result, the charge / discharge capacity can be reduced even when charged / discharged with a large current as confirmed experimentally in Examples described later. Deterioration due to decrease can be suppressed.
The reason why the ionic conductivity is improved in this way is presumed to be that the crystal structure of the lithium-containing compound particles is distorted by the M1, and the strain formation is further promoted by the M2.

In particular, according to the non-aqueous electrolyte secondary battery according to claim 2, by making the average particle diameter of the lithium-containing compound 4 μm or less, the electron conductivity between the particles can be improved, and the average particle By setting the diameter to 0.9 μm or more, it is possible to suppress the occurrence of agglomeration when producing the positive electrode and perform stable slurry preparation.
In addition to this, according to the non-aqueous electrolyte secondary battery according to claim 2, when the BET specific surface area of the lithium-containing compound is 17 m ² / g or more and 49 m ² / g or less, the ion conductivity is further improved. It can be improved, and deterioration due to a decrease in charge / discharge capacity can be suppressed more reliably.

Hereinafter, a lithium ion secondary battery according to the present invention will be described with reference to FIG.
As shown in FIG. 1, the lithium ion secondary battery of this embodiment includes a positive electrode 1 in which a positive electrode mixture layer 11 is formed on the front and back surfaces of a rectangular thin plate-like positive electrode current collector 10, and a negative electrode mixture layer 21. The negative electrodes 2 formed on the front and back surfaces of the rectangular thin plate-shaped negative electrode current collector 20 are alternately arranged in plural (four in the present embodiment, with the separators 3 interposed therebetween with the plate surfaces facing each other. ) Are stacked.

The positive electrode 1 and the negative electrode 2 are immersed in a non-aqueous electrolyte and accommodated in a sealed container 4, and the non-aqueous electrolyte contains an organic solvent inert to the positive electrode 1 and the negative electrode 2. obtained by dissolving a lithium salt such as LiBF _4, LiPF ₆ is used.

Also, the positive electrode mixture layer 11 of the positive electrode 1 is contained a positive electrode active material, the positive electrode active material, the composition formula is a _{LiFe x M1 y M2 z PO 4} , M1 is V, Cr, Cu And one or more elements selected from Zn, In, Sn, Mo, Ti and Mn, and M2 is one or more elements selected from Bi, Zr, Cd, Pd, Nb and Ag. It is made of a lithium iron phosphate compound having an olivine structure of 0 ≦ x, y, z ≦ 0.99. The positive electrode active material is prepared such that the average particle size is 0.9 μm or more and 4 μm or less and the BET specific surface area is 17 m ² / g or more and 49 m ² / g or less.

Such a positive electrode active material is a mixture of LiFe _x M1 _y M2 _z PO ₄ Li source compound, Fe source compound, M1 source compound, M2 source compound and PO ₄ source compound. Obtained by firing.
Then, the positive electrode mixture layer 11 in which the positive electrode active material is mixed with a conductive agent and a binder to form a slurry is applied onto a metal foil as the positive electrode current collector 10. The positive electrode 1 is obtained by attaching the tab 12.

  In the negative electrode 2, carbon capable of occluding and releasing lithium ions, preferably graphite, is used for the negative electrode active material of the negative electrode mixture layer 21. A negative electrode obtained by adding a binder or the like to this negative electrode bulk material to form a slurry. The mixture layer 21 is obtained by coating a metal foil as the negative electrode current collector 20 and attaching a tab 22 to the negative electrode current collector 20.

  Then, the plurality of positive electrodes 1 and negative electrodes 2 described above are alternately stacked such that the tabs 12 of the positive electrode 1 and the tabs 22 of the negative electrode 2 are alternately arranged on one side and the other end of the opposite side. The sealed container 4 is formed by inserting the non-aqueous electrolyte into the outer package and then sealing the opening of the outer package after being inserted into the bag-shaped outer package made of an aluminum laminate film. A lithium ion secondary battery in which the positive electrode 1 and the negative electrode 2 are immersed in a nonaqueous electrolytic solution and accommodated in the sealed container 4 is assembled.

Lithium-ion secondary battery configured as described above, in the positive electrode active material is LiFe _x M1 _y M2 _z PO ₄ of M1 of V, Cr, Cu, Zn, In, Sn, Mo, Ti and Mn And at least one element selected from Bi, Zr, Cd, Pd, Nb, and Ag, and 0.01 ≦ x, y, z ≦ 1. By setting it to 00, the ionic conductivity in the particles can be remarkably improved. As a result, even when charged / discharged with a large current as experimentally confirmed, deterioration due to a decrease in charge / discharge capacity is suppressed. it can.

In addition to this, by making the average particle diameter of the lithium iron phosphate compound 4 μm or less, the electron conductivity between the particles can be improved, and by making the average particle diameter 0.9 μm or more, the positive electrode 1 is produced, the occurrence of aggregation is suppressed, and a stable slurry can be prepared. Furthermore, by setting the BET specific surface area of the lithium-containing compound to 17 m ² / g or more and 49 m ² / g or less, ion conductivity can be further improved, and deterioration due to a decrease in charge / discharge capacity can be suppressed more reliably. .

The present invention is not in any way limited to the embodiments described above, other than the lithium-ion secondary battery, i.e., large by providing the LiFe _x M1 _y M2 _z lithium iron phosphate compound of PO ₄ in the positive electrode 1 The present invention can also be applied to other nonaqueous electrolyte secondary batteries that are expected to have an effect of suppressing the decrease in charge / discharge capacity even when charged and discharged with current.

LiFe _x M1 _y M2 _z PO ₄ of M1 and performance change of the lithium ion secondary battery according element M2 as a cathode active material, M1 and performance change of the lithium ion secondary battery according to the ratio of M2, the average particle of the positive electrode active material The performance change of the lithium ion secondary battery due to the diameter and the performance change of the lithium ion secondary battery due to the BET specific surface area were experimentally confirmed as follows.

<Production of lithium ion secondary battery>
First, the lithium ion secondary batteries of Examples 1 to 84 for confirming the above-described performance change were manufactured as follows.

(Preparation of positive electrode active material)
LiFe _x M1 _y M2 _z iron source iron oxalate dihydrate _{(FeC 2 O 4 · 2H 2} O) as a PO _4, metal oxalate hydrate as M1 source (M1C ₂ O ₄ H ₂ O of the positive electrode active material ), Metal oxalate hydrate (M2C ₂ O ₄ H ₂ O) as the M2 source, ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) as the phosphate source and lithium carbonate (Li ₂ CO ₃ ) as the lithium source the respective tables 1 to 4 show M1, M2 and x, weighed in a predetermined molar ratio to synthesize LiFe _x M1 _y M2 _z PO ₄ having y, and z, allowed to mix for sucrose.

Next, a mixture obtained by adding 2-propanol as a solvent to this mixture was pulverized and mixed with a ball mill for 10 hours, and then vacuum-dried to remove 2-propanol, whereby the positive electrode active material precursors of Examples 1 to 84 were obtained. Obtained.
Each of the precursors of Examples 1 to 84 was put in an aluminum incense bowl, and after calcining at 300 ° C. for 5 hours under an argon flow of 0.5 L / min in a firing furnace, the temperature was kept as it was. The cathode active material of Examples 1 to 84 made of LiFe _x M1 _y M2 _z PO ₄ powder coated with carbon on the surface was synthesized by raising the temperature and firing at 650 ° C. for 20 hours. Next, the average particle diameter (μm) and the BET specific surface area (cm ² / g) of each positive electrode active material of Examples 1 to 84 were measured and shown in Tables 1 to 4, respectively.

(Preparation of positive electrode 1)
Next, acetylene black as a conductive agent and polyvinylidene fluoride as a binder were mixed with each of the positive electrode active materials in Examples 1 to 84, and N-methylpyrrolidone was added to the mixture to form a slurry. The positive electrode slurries of Examples 1 to 84 were synthesized. At that time, the positive electrode active material, the conductive agent, and the binder were prepared in a mass ratio of 90: 5: 5.

  Next, each of the positive electrode slurries of Examples 1 to 84 was applied onto an aluminum foil as the positive electrode current collector 10 and dried, and then rolled using a rolling roller. The positive electrode 1 of Examples 1-84 in which the positive electrode mixture layer 11 was formed was prepared.

(Preparation of negative electrode 2)
A negative electrode slurry was synthesized by mixing graphite as a negative electrode active material and polyvinylidene fluoride as a binder, and further adding N-methylpyrrolidone as a thickener to these mixtures. At that time, the negative electrode active material, the binder, and the thickener were prepared so as to have a mass ratio of 95: 3: 2.

  Next, the negative electrode slurry is applied on a copper foil as the negative electrode current collector 20 and dried, and then rolled using a rolling roller. Further, a tab 22 is attached to the copper foil, whereby a negative electrode mixture is obtained. The negative electrode 2 in which the layer 21 was formed was produced.

(Preparation of electrolyte)
1 mol / L LiPF ₆ was dissolved in a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 3: 7, and vinylene carbonate was further added to prepare an electrolytic solution.

(Battery assembly)
First, the positive electrode 1 and the negative electrode 2 were laminated | stacked alternately so that the plate | board surface might oppose and the separator 3 might interpose each other like the above-mentioned best embodiment, and the electrode body was comprised. In addition, about Examples 1-84, each electrode body is comprised so that the positive electrode 1 and the negative electrode 2 may become the same number.
Next, after this electrode body was dried at 105 ° C. for 20 hours in a vacuum, it was inserted into a package body in which an aluminum laminate film having a thickness of 0.11 mm was formed in a bag shape in a glove box under an argon atmosphere, Then, the said electrolyte solution was inject | poured in this exterior body, the opening of the exterior body was sealed, and the lithium ion secondary battery of Examples 1-84 was assembled.
Therefore, the lithium ion secondary batteries of Examples 1 to 84 have the same configuration except for the positive electrode active material.

(Comparative example / conventional example / production of lithium ion secondary battery)
Next, in the preparation of the positive electrode active material in the above-described Examples, metal oxalic acid hydrate (M1C ₂ O ₄ H ₂ O) is used as the M1 source, and metal oxalic acid hydrate (M2C ₂ O ₄ H is used as the M2 source. _The positive electrode 1 produced by preparing the positive electrode active material in the same manner as in the example except that ₂ O) was not measured or added to a predetermined molar ratio, and the same negative electrode 2 and electrolyte as in the example The lithium ion secondary batteries of Comparative Examples 1 to 8 and Conventional Example 1 shown in Tables 1 and 2 were assembled.

<Performance test>
Next, the output characteristics and temperature characteristics of the lithium ion secondary batteries of Examples 1 to 84, Comparative Examples 1 to 8, and Conventional Example 1 were measured as follows.

(Output characteristics)
All lithium ion secondary batteries were subjected to a charge / discharge test in an operating voltage range of 3 to 4 V under a temperature condition of 25 ° C. at a current density of 0.5 mA / cm ² per unit area of the positive electrode 1 to perform initial discharge. After measuring the capacity, the current density per unit area of the positive electrode 1 is increased to 5 mA / cm ² and the discharge capacity is measured in the same manner. The initial discharge capacity of the discharge capacity measured at this current density of 5 mA / cm ² is measured. The ratio when the value is 100 was determined. Subsequently, the ratio of the discharge capacity of each lithium ion secondary battery when the ratio of the discharge capacity of the lithium ion secondary battery of Conventional Example 1 was set to 100 was shown in Tables 1 to 4, respectively.

(Temperature characteristics)
All the lithium ion secondary batteries are charged at a low current of 600 mA when heated to 60 ° C. until the battery voltage reaches 4.0 V, and the battery voltage becomes 2.5 V at 600 mA when heated to 60 ° C. By measuring the charge / discharge capacity at the time of charge / discharge after 50 cycles of repeated charge / discharge, the ratio of the charge / discharge capacity when the initial discharge capacity is 100, that is, the charge / discharge capacity maintenance rate is Calculated. Furthermore, the charge / discharge capacity maintenance ratio of each lithium ion secondary battery when the charge / discharge capacity maintenance ratio of Conventional Example 1 was set to 100 was obtained and shown in Table 1.

As can be seen the positive electrode active material shown in Table 1 by LiFe _x M1 _y M2 constituent elements of _z PO ₄ of M1 and M2 from the performance change of the lithium ion secondary battery, the conventional example using the LiFePO ₄ as the positive electrode active material even compared, and further, even when compared with Comparative example 2 using Comparative example 1 and LiFeMn using LiFeMo, V to M1 in LiFe _x M1 _y M2 _z PO ₄ of the positive electrode active material, Cr, Cu, Example in which one or more elements selected from Zn, In, Sn, Mo, Ti and Mn and one or more elements selected from Bi, Zr, Cd, Pd, Nb and Ag are selected as M2 The lithium ion secondary batteries 1 to 54 have remarkably improved output characteristics and temperature characteristics.

As can be seen from the performance change of the lithium ion secondary battery according to the percentage of M1 and M2 shown in Table 2, V to M1 in LiFe _x M1 _y M2 _z PO ₄ of the positive electrode active material, Cr, Cu, Zn, In , Sn, Even if one or more elements selected from Mo, Ti, and Mn and one or more elements selected from Bi, Zr, Cd, Pd, Nb, and Ag are selected for M2, the ratio is y. In the lithium ion secondary batteries of Comparative Examples 3 to 8 where z and z are out of the range of 0.01 ≦ y and z ≦ 1.00, the output characteristics and the temperature characteristics are degraded. On the other hand, the lithium ion secondary batteries of Examples 55 to 60 in the range of 0.01 ≦ x, y, z ≦ 1.00 are excellent in both output characteristics and temperature characteristics.

As can be seen from the performance change of the lithium ion secondary battery according to the average particle diameter of the positive electrode active material shown in Table _{3, LiFe x M1 y M2 z} PO A ₄ 0.01 ≦ x as a positive electrode active material, y, z ≦ Since the batteries in the range of 1.00 are used, all of the lithium ion secondary batteries of Examples 61 to 72 are excellent in both output characteristics and temperature characteristics. However, when examined in detail, the lithium ion secondary batteries of Examples 63, 64, 67, 68, 71, and 72 have an average particle diameter of the positive electrode active material of less than 0.9 μm or more than 4 μm. The output characteristics and temperature characteristics tend to decrease. On the other hand, the lithium ion secondary batteries of Examples 61, 62, 65, 66, 69, and 70 in which the average particle diameter of the positive electrode active material is 0.9 μm or more and 4 μm or less have lower output characteristics and temperature characteristics. And excellent performance characteristics.

As can be seen from the performance change of the lithium ion secondary battery according to a BET specific surface area shown in Table 4, as a positive electrode active material LiFe _x M1 _y M2 _z PO A ₄ 0.01 ≦ x, y, a z ≦ 1.00 Since the batteries within the range are used, the lithium ion secondary batteries of Examples 73 to 84 are both excellent in output characteristics and temperature characteristics. However, when examined in detail, in the lithium ion secondary batteries of Examples 75, 76, 79, 80, 83, and 84, the positive electrode active material had a BET specific surface area of less than 17 m ² / g or more than 49 m ² / g. Therefore, the output characteristics and temperature characteristics tend to decrease. On the other hand, the lithium ion secondary batteries of Examples 73, 74, 77, 78, 81, and 82 having a BET specific surface area of 17 m ² / g or more and 49 m ² / g or less are not deteriorated in output characteristics and temperature characteristics. Excellent performance characteristics.

Therefore, LiFe _x M1 _y M2 _z the M1 of _{PO 4 V, Cr, Cu,} Zn, In, Sn, Mo, as well as with one or more elements selected from among Ti and Mn, the M2 Bi, Zr, A lithium ion secondary battery using one or more elements selected from Cd, Pd, Nb, and Ag and using a positive electrode active material satisfying 0.01 ≦ x, y, z ≦ 1.00 is 60 ° C. Even if charging / discharging is repeated in a heated state, the decrease in charge / discharge capacity is limited, and therefore, even if the current is charged / discharged with a large current, the decrease in charge / discharge capacity due to temperature rise can be prevented.

It is an external appearance perspective view which shows the lithium ion secondary battery of this embodiment. FIG. 2 is a cross-sectional view showing a laminated structure of a positive electrode 1 and a negative electrode 2 in the lithium ion secondary battery of FIG. FIG. 3 is a view taken along line III-III in FIG. 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Sealed container 10 Positive electrode collector 11 Positive electrode mixture layer 12 Positive electrode tab 20 Negative electrode collector 21 Negative electrode mixture layer 22 Negative electrode tab

Claims (3)

In a non-aqueous electrolyte secondary battery in which a negative electrode and a positive electrode provided with a lithium-containing compound are immersed in a non-aqueous electrolyte,
The lithium-containing compound of the positive electrode, a _{LiFe x M1 y M2 z PO 4} , M1 is V, Cr, Cu, Zn, In, Sn, Mo, one or more elements selected from among Ti and Mn In addition, M2 is one or more elements selected from Bi, Zr, Cd, Pd, Nb, and Ag, and lithium iron having an olivine structure of 0.01 ≦ x, y, z ≦ 1.00 A non-aqueous electrolyte secondary battery comprising a phosphoric acid compound.   2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the lithium-containing compound of the positive electrode has an average particle size of 0.9 μm or more and 4 μm or less. The non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium-containing compound of the positive electrode has a BET specific surface area of 17 m ² / g or more and 49 m ² / g or less.

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