JPH034445A - Nonaqueous medium secondary battery - Google Patents

Abstract

PURPOSE:To obtain nonaqueous medium secondary battery of long life and high performance by using lithium or lighium alloy for a negative electrode and using a specific lighium manganic oxide for positive electrode active material. CONSTITUTION:Lithium or lighium alloy is used for a negative electrode 5, and a lighium magnetic oxide, which is obtained by adding lighium salt to a manganic oxide (gamma-MnOOH), having an X-ray fiffraction pattern shown in table I, and heat treating it and which has spinel structure, is used for positive electrode active material. This lithium manganic oxide (LiMn2O4) has, inside the crystal structure, vacant lattice points, which Li ions can invade, in the shape of being different in three dimensions, and it is small in grain degree and is large in specific surface area. Accordingly, during charge, the invasion and emission of Li ions of negative electrode active material into the positive electrode active material of a positive electrode 3 are done smoothly, and the collapse of the crystal structure by repeating charge and discharge can be suppressed. Hereby, a long life of nonaqueous medium secondary battery, wherein the capacity deterioration by a charge/discharge cycle is small, can be obtained.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to a non-aqueous solvent secondary battery with an improved positive electrode active material.

(Prior Art) In recent years, with the development of electronic devices, there has been a demand for the development of secondary batteries that are small, lightweight, have high energy density, and can be repeatedly charged and discharged. This type of secondary battery is known to use lithium (Li) or a lithium alloy as the negative electrode, and to use oxides, sulfides, or selenides of molybdenum, vanadium, titanium, niobium, etc. as the positive electrode active material.

-4. Manganese dioxide (MnOi) has been put to practical use in non-aqueous solvent batteries as a positive electrode active material with high energy density and high voltage, but MnO2 has a tunnel structure. In a secondary battery, as the battery discharges, Li ions invade the 1-channel, thereby expanding the MnO□ crystal structure. Since the I-i ions in this I-tunnel are in a state where they can be easily moved, when this battery is brought into a charged state, the Li ions in the tunnel are released, and the MnOx crystal structure contracts accordingly. In this way, if MnO2, which is used in conventional non-aqueous solvent secondary batteries, is used as it is as a positive electrode active material in secondary batteries, the crystal structure will repeatedly contract and expand as the battery is charged and discharged. This allows M n O
There is a problem in that the tunnel structure of x collapses and the charge/discharge capacity deteriorates significantly as the charge/discharge cycle progresses.

For this reason, lithium compounds (for example, ■,
A non-aqueous solvent secondary battery is known in which a positive electrode active material is lithium manganese oxide produced by adding 12G O3) and heat-treating.

(Problem to be Solved by the Invention) However, even in secondary batteries using lithium manganese oxide produced from such electrolytic manganese dioxide as a positive electrode active material, deterioration in charge/discharge capacity still occurs as the charge/discharge cycle progresses. Due to this problem, it was necessary to improve the positive electrode active material in order to obtain a nonaqueous solvent secondary battery that has a long cycle life and is highly economical.

[Structure of the Invention] (Means for Solving the Problems) The present invention uses lithium or a lithium alloy as a negative electrode, and a manganese oxide (γ-Mn) having the following X-ray diffraction pattern.
A non-aqueous solvent secondary battery characterized by using a lithium manganese oxide mainly having a spinel structure obtained by adding a lithium salt to OOH) and heat-treating it as the positive electrode active material. 3.41±0.02 2.64±0.02 2.4]±0.02 2.27±0.02 2.19±0.02 1,78±0.02 1,69±0.02 1,67±0.02 1,50±0,02 1,44±0.02 Manganese oxide (γ-M
n OOH) can be obtained, for example, by adding hydrogen peroxide and ammonia water to an aqueous manganese sulfate solution.

Furthermore, examples of the lithium salt include notium carbonate (L12Cos) and lithium hydroxide (LiOH). Regardless of which of these lithium salts is used, the product after the heat treatment is mainly spinel-type lithium manganese oxide (LiMn, 04).

The above lithium salt and the above manganese oxide (γ-MnOOH
) The molar ratio of MnLi is preferably in the range of 2:Q, 3 to 2:1.2.

When the ratio of the two is less than 2+0.8, Mn=O= and MnvO4 produced by the decomposition of γ-MnOOH are mixed in the lithium manganese oxide obtained after heat treatment, and on the other hand, when the ratio is less than 2:1, If it exceeds .2, Ll and 0 will be generated and mixed in the lithium manganese oxide obtained after the heat treatment, and in either case, it is not preferable because it causes deterioration of the charge/discharge capacity.

The heat treatment temperature is preferably in a temperature range of 540 to 950°C. If this temperature is lower than 540℃,
Mn is present in the lithium manganese oxide obtained after heat treatment.
When aOs is generated and mixed, and the temperature exceeds 950℃, M
This is not preferable because n+104 may be generated and coexisted, leading to deterioration of charge/discharge capacity.

(Function) The lithium manganese oxide (LiMnzO4) mainly having a spinel structure obtained by adding a lithium salt to γ-MnOOH of the present invention and heating it has vacancies in its crystal structure that allow Li ions to enter. It has a three-dimensional series. Furthermore, compared to spinel-type lithium-manganese oxide using electrolytic manganese dioxide as a starting material, the spinel-type lithium-manganese oxide of the present invention has a smaller particle size and a larger specific surface area, as described in Examples. Therefore, in a non-aqueous solvent secondary battery incorporating a positive electrode obtained by blending the spinel-type lithium manganese oxide of the present invention with a conductive material and a binder, during charging and discharging, the negative electrode active material Li Ions can smoothly enter and release the positive electrode active material of the positive electrode, and furthermore, the collapse of the crystal structure due to repeated charging and discharging can be suppressed. As a result, it is possible to obtain a non-aqueous solvent secondary battery with little capacity deterioration due to charge/discharge cycles and a long life.

(Example) Hereinafter, the present invention will be explained in detail using examples.

Example 1 FIG. 1 is a longitudinal sectional view of a button-shaped non-aqueous solvent secondary battery according to the present invention. 1 in the figure is a positive electrode container made of stainless steel, and in this container 1, a positive electrode 3 manufactured by a method described later is housed via a current collector 2. On this positive electrode 3, a separator 4 made of a boropropylene nonwoven fabric and a negative electrode 5 made of metallic lithium are placed. The separator 4 is impregnated with an electrolytic solution in which lithium perchlorate is dissolved at a concentration of 0.5 mol/I2 in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane (l:l in weight ratio). There is. A negative electrode container 7 is provided at the opening of the positive electrode container 1 via a backing 6,
By caulking the negative electrode container 7, the positive electrode 3° separator 4 and the negative electrode 5 are sealed inside the positive electrode container I and the negative electrode container 7. The above positive electrode was produced by the following method.

A positive electrode mixture was prepared by mixing 490 parts by weight of LiMnzO as a positive electrode active material, 10 parts by weight of acetylene black as a conductive agent, and 5 parts by weight of polytetrafluoroethylene as a binder, and this mixture was heated under a pressure of about 2 tons. /cn+'' conditions, and was further dried in a vacuum at 200°C.

In addition, manganese oxide (γ
-MnOOH) was produced by the following method.

A solution of 15 g of manganese sulfate tetrahydrate dissolved in II2 water was mixed vigorously with 3% hydrogen peroxide solution 150-
0.2mol/i in a row! , ammonia water 200
Tt11 was added to each. The resulting dark brown or black suspension was boiled for a few minutes and then allowed to drain. The solids separated by furnace were washed with 1.5 J2 of hot water and then dried in a vacuum desiccator containing niline pentoxide. × of the obtained substance! 1
When the diffraction pattern was examined, it was as shown in FIG. 2, and it was confirmed that this substance was γ-MnOOH. Moreover, it was confirmed by electron microscopy that the substance had needle-like crystals.

30 g of γ-MnOOH obtained by the above method and 6.3 g of lithium carbonate were mixed in a 1 molar ratio Mn:Li=2:
1) - Grind, heat treat in air at 850°C for 1 hour, cool, then grind again, heat treat in air at 850°C again.
Heat treatment was performed for C12 hours. When the X-ray diffraction pattern of this reaction product was examined, it was as shown in Figure 3. ASTM
It was consistent with the L i M nz Oa data of Na18-736.

Example 2 30 g of γ-M n OOH obtained by the same method as Example 1
and 5.0 g of lithium carbonate (mole ratio Mn:
Li=2 + 0.8) ・Crush and 600 ml in air
After being heat-treated at 600°C for 3 hours and cooled, it was ground again and heat-treated again in air at 600°C for 5 hours. This reaction product has a diffraction pattern similar to that shown in FIG.
It was confirmed that i M n *04 was the main component.

This reaction product was subjected to the same treatment as in Example 1, and a button-type nonaqueous solvent secondary battery having the same structure as in Example 1 was assembled.

Example 3 30 g of γ-MnOOH obtained by the same method as Example 1 and 4.1 g of lithium hydroxide were mixed C molar ratio Mn:L
i = 2: L) ・Crush and heat at 550°C in air
After being heat-treated for 13 hours and cooled, it was ground again and heat-treated again in air at 550°C for 21 hours. The X-ray diffraction pattern of this reaction product is shown in Figure 4, and LiM
It was confirmed that n x O4 was the main component. This reaction product was subjected to the same treatment as in Example 1, and Example 1
A button-type non-aqueous solvent secondary battery with the same structure was assembled.

Comparative Example 1 Electrolytic manganese dioxide obtained by electrolytically oxidizing manganese sulfate and lithium carbonate were mixed and pulverized at a molar ratio of Mn:Li=2:1, and heat treated in air at 850°C for 1 hour.
After cooling, it was ground again and heat-treated again in air at 850°C for 2 hours. The X-ray diffraction pattern of this reaction product was as shown in FIG. 5, and it was confirmed that the main component was L i M n x 04.

A button-type non-aqueous solvent secondary battery having the same structure as in Example 1 was assembled by performing the same treatment as in Example 1 except that this reaction product was used as the positive electrode active material.

Comparative Example 2 The same electrolytic manganese dioxide and lithium carbonate as in Comparative Example 1 were mixed at a molar ratio of Mn:Li=2:0.5.
It was crushed, heat treated in air at 600°C for 3 hours, cooled, crushed again, and heat treated again in air at 600°C for 15 hours. A button-type non-aqueous solvent secondary battery having the same structure as in Example 1 was assembled by performing the same treatment as in Example 1 except that this reaction product was used as the positive electrode active material.

For the batteries of Examples 1 to 3 and Comparative Examples 1 and 2, 3.5
V~2. The 6th
The characteristic diagram shown in the figure was obtained. Note that A in FIG. 6 represents Example 1.
B is the characteristic line for the battery of Example 2, C is the characteristic line for the battery of Example 3, D is the characteristic line for the battery of Comparative Example 1, and E is the characteristic line for the battery of Comparative Example 2. be.

As is clear from FIG. 6, the battery of the present invention has an extremely high capacity retention rate in a charge/discharge cycle and has excellent performance compared to the comparative battery.

The reason for this is that L i produced from γ-M n OOH
This is because, as shown in the table below, M n *04 has a smaller particle size and a larger specific surface area than L i M n 204 produced from electrolytic manganese dioxide.

In addition, although FIGS. 3 and 5 show the X-ray diffraction patterns of Example 1 and Comparative Example 1, respectively, the Li
It can be seen that M n 204 has higher peak intensity and sharper peak. From the above,
It is thought that the lithium manganese oxide having a spinel structure obtained by the present invention has developed crystallinity of the spinel structure. A solution of lithium perchlorate was used, but γ-butyrolactone, tetrahydrofuran, 2-methylte!・Li in non-aqueous solvents such as lahydrofuran and ethylene carbonate
Cε04. LiPF5, LiAsFs,
Electrolyte such as L I B F 4 at 0.2 to 1.5 mol/
You may also use a solution of ρ.

Furthermore, although polytetrafluoroethylene was used as the binder in the above embodiments, polyacrylic acid or its salts may also be used.

In the above embodiments, a button-type non-aqueous solvent secondary battery has been described as an example, but the present invention can be similarly applied to a cylindrical non-aqueous solvent secondary battery, etc. in which the electrodes have a spiral structure.

[Effects of the Invention] As detailed above, the present invention has a tunnel structure, and after being incorporated into a non-aqueous solvent secondary battery, charging and discharging, that is, L
It is possible to produce a positive electrode active material made of manganese lithium oxide whose crystal structure is less likely to collapse due to the entry and release of i-ions,
Furthermore, by using the positive electrode active material, remarkable effects such as being able to obtain a long-life, high-performance non-aqueous solvent secondary battery with little capacity deterioration in charge/discharge cycles can be achieved.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a button-type non-aqueous solvent secondary battery showing one embodiment of the present invention, FIG. 2 is an X-ray diffraction pattern diagram of manganese oxide (γ-MnOOH) used in the present invention, and FIG. The figure shows an X-ray diffraction pattern of lithium manganese oxide obtained in Example 1, FIG. 4 shows an X-ray diffraction pattern of lithium manganese oxide obtained in Example 3, and FIG. 5 shows Comparative Example 1.
FIG. 6 shows the Xli diffraction pattern of lithium manganese oxide obtained by Example 1.2.3 and Comparative Example 1.
2 is a characteristic diagram showing the capacity retention rate with respect to the number of charge/discharge cycles in the battery No. 2. 1. Positive electrode container 3. Positive electrode 4. Separator 5, negative electrode 7
．． negative electrode container

Claims (1)

[Claims] Lithium manganese mainly having a spinel structure obtained by using lithium or a lithium alloy as a negative electrode, adding lithium salt to manganese oxide (γ-MnOOH) having the following X-ray diffraction pattern, and heat-treating the mixture. A non-aqueous solvent secondary battery characterized by using an oxide as a positive electrode active material. Plane spacing (Å) 3.41±0.02 2.64±0.02 2.41±0.02 2.27±0.02 2.19±0.02 1.78±0.02 1.69 ±0.02 1.67±0.02 1.50±0.02 1.44±0.02