JP2000012029A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the elution of manganese and lengthen the life of a nonaqueous electrolyte secondary battery using lithium manganate (LiMn2O4) as the positive active material. SOLUTION: In lithium managanate, an average particle size (D) is set so that 30<=D<=35 μm, 10% particle size (D10) is set as 10<=D10<=20 μm, 50% particle size (D50) is set as 25<=D50<=32 μm, 90% particle size (D90) is set made as 55<=D90<=70 μm, and part of manganese is substituted with a transition metal or an alkali earth metal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery using lithium manganate as a positive electrode active material.

[0002]

2. Description of the Related Art With advances in electronic technology, miniaturization and portability have progressed, and high energy density batteries have been demanded as power sources. Conventional secondary batteries include a lead storage battery, a nickel-cadmium battery, and a nickel-hydrogen battery, but these batteries are still insufficient in terms of energy density. Therefore, as an alternative to these batteries, non-aqueous electrolyte secondary batteries with high energy density (hereinafter referred to as lithium secondary batteries) have been developed and rapidly spread. At present, a battery using LiCoO ₂ as a positive electrode active material has been put into practical use as a 4 V class lithium secondary battery.
Attempts have been made to put NiO ₂ into practical use as a positive electrode active material. However, Co and Ni have a problem in that the amount of resources is scarce and expensive.

On the other hand, use of lithium manganate (LiMn ₂ O ₄ ) having a spinel structure and using manganese, which has abundant resources and is inexpensive, has been proposed. The discharge potential of this LiMn ₂ O ₄ is around 4 V and 2.8.
It has the characteristic of showing a two-step plateau near V. Among them, a technique of using a region near 4 V and repeating charging and discharging in a potential range of 4.5 to 3.0 V is being developed. However, a battery using LiMn ₂ O ₄ , which is a composite oxide of lithium and manganese, for the positive electrode has a problem that manganese in the positive electrode active material is eluted into the electrolytic solution during the charge / discharge cycle and the capacity is reduced. At present, it has not been put to practical use except for some uses.

[0004]

The problem to be solved by the present invention is to suppress the elution of manganese ions from the lithium manganate used as the above-mentioned positive electrode active material into the electrolytic solution to provide a long-life non-aqueous solution. An object of the present invention is to provide an electrolyte secondary battery.

[0005]

According to a first aspect of the present invention, there is provided a non-aqueous electrolyte secondary battery using a positive electrode active material capable of inserting and releasing lithium, as the positive electrode active material. Lithium manganate (LiMn ₂ O ₄ ) having a spinel structure has an average particle diameter (D) of 30 ≦ D
≦ 35 μm and 10% particle diameter (D10) is 10 ≦ D10
≦ 20 μm, 50% particle size (D50) 25 ≦ D50 ≦ 3
2 μm, 90% particle size (D90) is 55 ≦ D90 ≦ 70 μm
In the second invention, a part of the manganese of the lithium manganate is V, Cr, Fe, Co, N
wherein at least one element selected from the group consisting of i, Cu, and Mo is substituted, and in the third invention, a part of manganese of the lithium manganate is Mg, Ca,
At least one selected from the group consisting of Sr, Ba, Mg
It is characterized by having been replaced by various kinds of elements.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have found that the amount of manganese eluted can be suppressed by reducing the contact area between the positive electrode active material and the electrolytic solution, and that the average particle size of the positive electrode active material has an optimum range. It is a thing. Note that Japanese Patent Application Laid-Open
According to Japanese Patent Publication No. -17471, an effect of increasing the discharge capacity by setting the specific surface area of the positive electrode active material to 0.5 m ² / g or less is reported. On the other hand, in the present invention, the contact area between the positive electrode active material and the electrolyte can be reduced by removing fine powder having a predetermined particle size or less from the positive electrode active material, and the discharge capacity can be reduced. And improved cycle life characteristics. In addition, they have found that by substituting a part of manganese of lithium manganate with a transition metal or an alkaline earth metal element, deterioration of charge / discharge characteristics can be further suppressed.

[0007] 1. Positive electrode A lithium manganese composite oxide having a particle diameter to be described later, carbon powder having an average particle diameter of 3 μm as a conductive additive, and polyvinylidene fluoride (hereinafter abbreviated as PVdF) as a binder.
Mix at 5: 9: 6 wt%. There, N-methyl-
2-Pyrrolidone is charged and mixed to prepare a slurry-like solution. This mixed solution was applied to both sides of an aluminum foil having a thickness of 20 μm, and after drying the solvent, it was rolled by a roller press to produce a short positive electrode by cutting it to a width of 54 mm and a length of 450 mm. did.

[0008] 2. Negative Electrode As a negative electrode active material, a carbon material having an average particle diameter of 20 μm and a binder of polyvinylidene fluoride (PVdF) were mixed at a weight ratio of 92: 8, and N-methyl-2-pyrrolidone was added and mixed to form a slurry. To prepare a solution. This slurry was applied to both sides of a copper foil having a thickness of 10 μm, and after drying the solvent,
Rolled with a roller press to produce a negative electrode mixture electrode,
Thereafter, the strip was cut into a width of 56 mm and a length of 490 mm to prepare a strip-shaped negative electrode. Examples of the negative electrode active material that can be used in the present invention include pitch coke, petroleum coke, graphite, carbon fiber, activated carbon, and the like, and mixtures thereof.

3. Battery The positive electrode and the negative electrode produced by the above-described method were 40 μm thick,
It is wound through a separator made of a microporous polyethylene film having a width of 58 mm to form a spiral wound group. The wound group is inserted into a battery can, and a nickel tab terminal previously welded to the copper foil of the negative electrode current collector is welded to the bottom of the battery can.
Next, 1 mol / liter of LiPF ₆ was added to a solution obtained by mixing ethylene carbonate and dimethyl carbonate at a volume ratio of 1: 2.
5 ml of the electrolytic solution dissolved at a concentration of 1 was injected into the battery container. Next, an aluminum tab terminal previously welded to the aluminum foil of the positive electrode current collector was welded to the lid, and the lid was placed on the top of the battery can via an insulating gasket. A cylindrical battery having a size of 18 mm and a height of 65 mm was produced. In addition, as an organic solvent used for the electrolytic solution, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyl carbonate, γ-butyl lactone, tetrahydrofuran, diethyl ether, sulfolane, acetonitrile and the like Or a mixed solvent of two or more of these can be used, and the electrolyte is LiClO ₄ , LiPF ₆ , LiPF
_{4, LiBF 4, LiCl, LiBr} , CH 3 SO 3 Li,
Li (SO ₂ CF ₃ ) ₂ N, Li (SO ₂ C ₂ F ₅ ) ₂ N, L
iAsF ₆ or the like can be used.

[0010] 4. Leaving test and cycle life test The prepared battery was charged at 25 ° C at a charge / discharge current of 300 m.
A, charge end voltage 4.3V, discharge end voltage 3.0V
The charge / discharge test is performed for 5 cycles under the conditions described above. Thereafter, the charged battery is stored in an atmosphere at 50 ° C. for 3 days. Then, disassemble the battery and measure the amount of manganese eluted in the electrolyte by IC
Measured at P. At 25 ° C., the charge / discharge current is 300
mA, charge end voltage 4.3 V, discharge end voltage 3.0
A charge / discharge cycle test was performed under the condition of V, and the ratio of the discharge capacity at the 10th cycle to the discharge capacity at the 300th cycle (hereinafter, referred to as capacity retention ratio) was measured.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail. However, the present invention is not limited to these. Commercially available lithium manganate was classified to produce five types of powders (a to e) having different particle diameters as shown in Table 1. In addition,
The particle size of the powder was measured with a laser diffraction type particle size distribution analyzer. Then, as measurement conditions, an average particle diameter (D),
The comparison was made between a 10% particle size (hereinafter, referred to as D10), a 50% particle size (hereinafter, referred to as D50), and a 90% particle size (hereinafter, referred to as D90). Using these powders having different particle diameters as the active material for the positive electrode, a battery was prepared, and the amount of manganese eluted into the electrolyte was measured by ICP. FIG. 1 shows the result. As shown in FIG. 1, in the cases of a and b having a small average particle size, although the amount of manganese eluted into the electrolytic solution is large, the average particle size is 30 to 35 μm
It can be seen that in the cases of c and d, the elution of manganese is reduced. Even in e having a large average particle size, c
Manganese elution is suppressed as in the cases of (a) and (d). However, in the case of e having a large average particle size, there was a problem that the above-mentioned slurry was difficult to apply.

[0012]

[Table 1]

FIG. 2 shows the capacity retention ratio of batteries using LiMn ₂ O ₄ (a to e) having different particle diameters. From FIG. 2, for a and b having small average particle diameters, the initial discharge capacity is small,
The rate of capacity decrease accompanying the charge / discharge cycle also increases,
At the time of the 00 cycle, it is 65% or less of the initial capacity. In the cases of c and d having an average particle diameter of 30 to 35 μm, the rate of decrease in capacity due to charge / discharge cycles is small, and
At the time of the 00 cycle, 85% or more of the initial capacity is maintained. When e has a large average particle size, the initial discharge capacity increases, but the rate of capacity decrease accompanying the charge / discharge cycle further increases, and becomes about 80% or less of the initial capacity at 300 cycles.

Although an example using lithium manganate (LiMn ₂ O ₄ ) having a spinel structure as the positive electrode active material has been described, a case where a part of manganese is replaced by another transition metal or an alkaline earth metal element is shown. A similar effect was also observed. Further, as the negative electrode, a lithium metal, a lithium alloy, and another material capable of inserting and extracting lithium may be used. Also, a mixture of ethylene carbonate and dimethyl carbonate in a volume ratio of 1: 2 as an electrolytic solution,
Although a solution in which lithium hexafluorophosphate was dissolved at 1.0 mol / dm3 was used, the same applies to an electrolytic solution in which a lithium salt was dissolved in another solvent as described above. In this embodiment, a cylindrical battery is described as an example. However, the present invention can be applied to batteries having various shapes such as a square battery and a coin battery.

[0015]

According to the non-aqueous electrolyte secondary battery of the present invention,
Fine powder of lithium manganate is cut, and part of manganese is removed from V, Cr, Fe, Co, Ni, C
transition metals such as u, Mo, Mg, Ca, Sr, Ba, M
By substituting with an alkaline earth metal element such as g, elution of manganese into the electrolytic solution is suppressed, and a battery having excellent charge / discharge characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 shows the relationship between the average particle size of a positive electrode active material and the amount of manganese eluted.

FIG. 2 shows the relationship between the average particle size of the positive electrode active material and the discharge capacity.

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Claims (3)

[Claims] In a non-aqueous electrolyte secondary battery using a positive electrode active material capable of inserting and releasing lithium, an average particle size of lithium manganate (LiMn ₂ O ₄ ) having a spinel structure used as the positive electrode active material. (D) is 30 ≦ D ≦ 35
μm, and the 10% particle diameter (D10) is 10 ≦ D10 ≦ 20.
μm, 50% particle diameter (D50) is 25 ≦ D50 ≦ 32 μm,
A nonaqueous electrolyte secondary battery having a 90% particle size (D90) of 55 ≦ D90 ≦ 70 μm. 2. The non-aqueous solution according to claim 1, wherein a part of manganese of said lithium manganate is replaced with at least one element selected from the group consisting of V, Cr, Fe, Co, Ni, Cu and Mo. Electrolyte secondary battery. 3. The non-aqueous solution according to claim 1, wherein a part of manganese of said lithium manganate is substituted with at least one element selected from the group consisting of Mg, Ca, Sr, Ba, and Mg. Electrolyte secondary battery.