JPH0770329B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery having an improved positive electrode active material.

2. Description of the Related Art Non-aqueous electrolyte secondary batteries using lithium, a lithium alloy or a lithium compound as a negative electrode are expected to have high energy density at high voltage, and many studies have been conducted.

In particular, MnO ₂ and TiS ₂ have been well studied as a positive electrode active material for these batteries. Recently, Tuckley et al. Reported that LiMn ₂ O ₄ serves as a positive electrode active material. (Material Research Bulletin 1983 Vol. 18, pp. 461-472) LiMn ₂ O ₄
Is a cubic crystal structure having a spinel structure, and when used as a positive electrode active material of a battery, the discharge voltage of the battery becomes a high voltage of about 4 V and is considered to be promising as the positive electrode active material.

The relationship between the X value and the open circuit potential in the Li _X Mn ₂ O ₄ positive electrode active material is shown in FIG. It has a two-step potential curve near 4 volts and around 2.8 volts.

Up to now, focusing on the second stage near the potential curve of 2.8 V, a charging voltage of about 4 V and a charging / discharging cycle of discharging up to about 2 V were performed to obtain a battery with good cycle characteristics. Has been done.

However, in order to obtain a higher energy density, the charge / discharge cycle that uses the first stage of the potential curve that charges to 4.5 V and discharges to 3 V, that is, charge until the X value is 1 or less, preferably 0.7 or less. However, it is more advantageous to discharge until the X value becomes 1 or 1.85. However, the cycle characteristics of the first-stage charging / discharging for charging until the X value was 0.7 or less were poor, and the discharge capacity decreased to half in about 50 cycles. The degree of this deterioration is extremely large as compared with the sirq using the second-stage potential curve.

Further, when the battery is charged to an X value exceeding 0.7, a sufficient discharge capacity cannot be obtained.

Therefore, it is represented by the formula Li _X M _Y Mn _(2-Y) O ₄ , where M is Co, Cr, N
At least one of i, Ta and Zn, and 0.85 ≦
Improvements have been made by using a positive electrode active material in which X ≦ 1.15 and 0.02 ≦ Y ≦ 0.3 to improve cycle characteristics.

Problems to be Solved by the Invention By using the positive electrode active material described above, a significant improvement in cycle characteristics can be realized, but since the charging voltage exceeds 4V,
There is a problem that the self-discharge characteristics of the battery after charging are insufficient. The self-discharge of a non-aqueous electrolyte secondary battery is caused by the decomposition of a small amount of water inside the battery and the solvent of the electrolyte solution, which causes problems such as an increase in internal resistance of the battery and a decrease in charge / discharge capacity. In particular, these phenomena become more remarkable as the battery voltage becomes higher, and become more remarkable when stored at high temperature.

The present invention solves such a problem, and an object thereof is to provide a non-aqueous electrolyte secondary battery having improved self-discharge characteristics.

Means for Solving the Problem In order to solve this problem, the non-aqueous electrolyte secondary battery of the present invention is lithium, a lithium alloy or a lithium compound as a negative electrode, LiMn _2-X Me _X O ₄ (Me: Co, Cr, In a non-aqueous electrolyte secondary battery having a positive electrode mixture containing a manganese-based complex oxide represented by at least one of Ni, Ta, and Zn) as an active material and a non-aqueous electrolyte, the positive electrode mixture is hydroxylated. Lithium LiOH, potassium hydroxide KOH, sodium hydroxide NaO
At least one alkali metal hydroxide such as H is added.

Further, the amount of the alkali metal hydroxide added to the positive electrode mixture is preferably 0.05 to 0.1 mol per 100 g of the positive electrode active material.

Action With this configuration, in the non-aqueous electrolyte secondary battery of the present invention, the action of the alkali metal hydroxide in the secondary battery is not clear, but the action is to suppress the decomposition of the organic electrolyte or to decompose products. And the like. As a result, it is considered that the deterioration of the battery performance, which is considered to be caused by the solvent decomposition product, can be reduced.

Example A non-aqueous electrolyte secondary battery according to an example of the present invention will be described below with reference to the drawings.

(Example 1) A battery was manufactured as follows. That is, as positive electrode active material, 100 g of LiMn ₁ .8 CO _0.2 O ₄ was mixed with 3.0 g of acetylene black as a conductive agent, and further 1.5 g of lithium hydroxide LiOH as an alkali metal hydroxide was added and mixed as an aqueous solution. This mixture was dried at 80 ° C. for 10 hours, and then 4.0 g of polyfluorinated ethylene resin as a binder was mixed to prepare a positive electrode mixture. 0.1 g of the positive electrode mixture was press-molded to a diameter of 17.5 mm at 1 ton / cm ² to obtain a positive electrode. A cross-sectional view of the manufactured battery is shown in FIG. The molded positive electrode 1 is placed in the case 2. A porous polypropylene film as the separator 3 was placed on the positive electrode 1. Diameter 17.5mm thickness as negative electrode 4
0.3mm lithium plate, polypropylene gasket 6
It was pressure-bonded to the sealing plate 5 attached with. As the non-aqueous electrolyte, a propylene carbonate solution in which 1 mol / 1 lithium perchlorate was dissolved was used, and this was added onto the separator 3 and the negative electrode 4. After that, the battery was sealed. The battery obtained as described above is designated as A.

By the same method, B is a battery using a positive electrode to which potassium hydroxide KOH is added, C is a battery using a positive electrode to which sodium hydroxide NaOH is added, and a positive electrode to which 0.75 g each of potassium hydroxide KOH and sodium hydroxide NaOH is added. Let B be a battery using E, and let E be a battery using a positive electrode to which 0.50 g of lithium hydroxide LiOH, potassium hydroxide KOH, and sodium hydroxide NaOH was added.

As a comparative example, as a battery without adding an alkali metal hydroxide, LiMn ₁ .8 CO _0.2 O ₄ 100, acetylene black 3.0
g and 4.0 g of polytetrafluoroethylene resin were mixed and used as a positive electrode mixture, and a battery was constructed in the same manner. This battery is designated as F.

The self-discharge test of each of the batteries A to F was conducted as follows. That is, for the battery obtained by the above method, 2 mA
The battery was charged to a constant voltage of 4.5 V and discharged to 3 V. After 10 cycles of this charging and discharging, after the 11th cycle of charging, the battery was stored at 60 ° C. for 4 weeks. After storage, it was discharged under the same conditions. Here, the self-discharge rate is defined as follows.

Self-discharge rate = (Discharged electricity quantity at 10th cycle−Discharged electricity quantity at 11th cycle) / 10 Discharged electricity quantity at 10th cycle FIG. 2 shows the change in the internal resistance of the above batteries due to storage at 60 ° C.

In the battery F having the conventional configuration, a rapid increase in the internal resistance of the battery was observed immediately after storage, and after 4 weeks, it became 40Ω or more. On the other hand, in the batteries A to E of this example, the increase in the internal resistance of the battery is small, which is about 1/5 of that of the battery F.

In addition, Table 1 shows the self-discharge rate of each battery after 4 weeks.

The battery F has a very large self-discharge rate, but in the batteries A to E of this example, it is suppressed within 10%. In this way, adding an alkali metal hydroxide to the positive electrode mixture has an effect of suppressing self-discharge due to high temperature storage, and any of potassium hydroxide KOH, sodium hydroxide, or lithium hydroxide is added. effective.

Further, similar effects are observed when these alkali metal hydroxides are mixed and added.

(Example 2) Furthermore, the amount of lithium hydroxide added to the positive electrode mixture was examined.

FIG. 1 shows the relationship between the added amount of sodium hydroxide (the number of moles relative to 100 g of the active material) and the internal resistance of the battery using these positive electrodes after storage at 60 ° C. for 4 weeks. From the results, it can be seen that when the amount of lithium hydroxide added to the positive electrode mixture is in the range of 0.05 mol to 0.1 mol with respect to 100 g of the positive electrode active material, an increase in internal resistance of the battery is suppressed. Therefore, the amount of lithium hydroxide added to the positive electrode is preferably in the range of 0.05 mol to 0.1 mol with respect to 100 g of the active material.

Similar results were obtained with potassium hydroxide KOH and sodium hydroxide, and LiMn ₁ .8 Ni was used as the positive electrode active material.
_{0 ・ 2} O ₄ , LiMn _{1 ・ 8} Cr _{0 ・ 2} O ₄ , LiMn _{1 ・ 8} Ta _{0 ・ 2} O ₄ , LiMn _{1 ・ 8} Zn
_The same effect was observed when 0.2 O ₄ Co was used.

As described above, the _{LiMn 1 · 8 Co 0 · 2} O 4 in a non-aqueous electrolyte battery that a positive electrode active material, by adding an alkali metal hydroxide in the positive electrode mixture, the self-discharge characteristics superior non-aqueous An electrolyte secondary battery can be obtained.

In the above examples, the results were obtained when a propylene carbonate solution in which 1 mol / l lithium perchlorate was dissolved was used as the electrolytic solution. However, in addition to this as the electrolytic solution, lithium perchlorate as a solute and 6 fluorine were used. An electrolytic solution using lithium phosphated phosphate, lithium trifluoromethanesulfonate, lithium borofluoride, carbonates such as propylene carbonate and ethylene carbonate as a solvent, and esters such as gamma-butyrolactone and methyl acetate was good. However, when ethers such as dimethoxyethane and tetrahydrofuran were used, the self-discharge characteristics were poor and no improvement in the self-discharge characteristics due to the addition of alkali metal hydroxide in the positive electrode was observed. It was about twice as much as when the propylene carbonate shown was used. In this example, it is considered that the positive electrode has a voltage of 4 V or higher, and the ethers are oxidized.

EFFECTS OF THE INVENTION According to the non-aqueous electrolyte secondary battery of the present invention as is clear from the description of the above examples, lithium, a lithium alloy or a lithium compound is used as the negative electrode, and LiMn _2-X Me _X O ₄ (Me: Co , Cr, Ni, T
a, a positive electrode mixture containing a manganese-based composite oxide represented by (at least one of Zn) as an active material, and a non-aqueous electrolyte solution, and the positive electrode mixture contains an alkali metal hydroxide as a positive electrode active material. By adding 0.05 to 0.1 mol per 100 g, a non-aqueous electrolyte secondary battery having good self-discharge characteristics can be obtained, which has great industrial significance.

[Brief description of drawings]

FIG. 1 shows the amount of lithium hydroxide added to the positive electrode mixture (the number of moles per 100 g of the positive electrode active material) in one example of the present invention and a conventional non-aqueous electrolyte secondary battery, and these positive electrodes were used. A graph showing the relationship between the internal resistance of the battery after storage at 60 ° C for 4 weeks, Fig. 2 is a graph showing the change in internal resistance of the battery during storage at 60 ° C, and Fig. 3 was used for the same test. FIG. 4 is a longitudinal sectional view of the battery, and FIG. 4 is a graph showing the relationship between the X value in the active material of the Li _X Mn ₂ O ₄ positive electrode active material and the open circuit potential.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toyoguchi ▲ Yoshi ▼ Tokoku 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference JP-A-2-199770 (JP, A) JP-A 2-54865 (JP, A)

Claims (2)

[Claims] 1. A lithium or lithium compound as a negative electrode, Li
A positive electrode mixture containing a manganese-based composite oxide represented by Mn _2-X Me _X O ₄ (Me: Co, Cr, Ni, Ta, Zn) as an active material,
And a non-aqueous electrolyte, wherein an alkali metal hydroxide is added to the positive electrode mixture, a non-aqueous electrolyte secondary battery. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the amount of the alkali metal hydroxide added to the positive electrode mixture is 0.005 to 0.1 mol per 100 g of the positive electrode active material.