JPH05190177A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To provide a nonaqueous electrolyte secondary battery which possesses the high voltage, high energy density, and the superior electric charge/discharge cycle life characteristic and storage characteristic. CONSTITUTION:A nonaqueous electrolyte secondary battery is constituted of a positive electrode consisting of the composite oxide of Li which is represented by a general formula LixM1(1-x)M2O2 (M is copper or silver, M2 is one selected from Fe, Ni, and Mn and (x) is 0<x<1), negative electrode consisting of the carbon material which can be doped or dedopeds with Li alloy or Li, and a nonaqueous electrolyte. Accordingly, the decomposition reaction of the electrolyte on a positive electrode activating substance under high voltage or the crystal destruction of the positive electrode activating substance can be prevented, and the electric charge/discharge cycle life characteristic and storage characteristic can be improved.

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, and more particularly to improvement of a lithium composite oxide used for a positive electrode.

[0002]

2. Description of the Related Art In recent years, there has been a great demand for a secondary battery having a high energy density as a power source for driving these electronic devices as they have become portable and cordless. In particular, non-aqueous electrolyte secondary batteries using lithium are It is expected as a secondary battery with high voltage and high energy density.

A layered compound capable of being doped and dedoped with lithium as an active material used for the positive electrode of this battery,
For example, LiCoO ₂ , LiNiO ₂ (US Pat.
No. 02518) and Li _y Ni _x Co _(1-x) O ₂ (0 <
A composite oxide of lithium such as x ≦ 0.75, y ≦ 1) (Japanese Patent Laid-Open No. 63-299056) has been proposed.

By using these compounds as the positive electrode active material, it is possible to realize a secondary battery having a high voltage and a high energy density with a voltage of 4V class.

[0005]

However, in the above-mentioned non-aqueous electrolyte secondary battery, the organic electrolytes such as propylene carbonate and dimethoxyethane used as the electrolyte are decomposed under a high voltage, so that There is a problem that the charge and discharge characteristics are deteriorated.

In order to solve this problem, a technique of substituting a part of cobalt of LiCoO ₂ with another metal element has been proposed. Specifically, a part of the cobalt is nickel (Japanese Patent Laid-Open No. 63- 299056), iron (JP-A-6-6
3-211564), aluminum, tin, and indium (Japanese Patent Laid-Open No. 62-90863).

However, when a composite oxide of lithium in which a part of cobalt is substituted with such a metal element is used for the positive electrode, the discharge voltage of the battery tends to be low.

Further, a battery using a lithium composite oxide containing cobalt such as LiCoO ₂ as a positive electrode active material has a problem that the battery capacity is remarkably reduced when stored at a high temperature in a charged state.

It is considered that this is due to the decomposition reaction of the electrolytic solution on the positive electrode active material and the crystal destruction of the positive electrode active material. The present invention is to solve such a problem, in order to realize a non-aqueous electrolyte secondary battery having a high voltage and high energy density, and excellent in charge-discharge cycle life characteristics and storage characteristics, An object of the present invention is to provide a non-aqueous electrolyte secondary battery using a positive electrode active material capable of preventing the decomposition reaction of the electrolytic solution on the positive electrode active material under voltage and the crystal collapse of the positive electrode active material. ..

[0010]

To solve this problem, the non-aqueous electrolyte secondary battery of the present invention has a general formula Li _x M _1
(1-x) M ₂ O ₂ (wherein M ₁ is copper or silver, M ₂ is any one of iron, nickel and manganese) and a positive electrode made of a composite oxide of lithium and lithium, a lithium alloy or A non-aqueous electrolyte secondary battery composed of a negative electrode made of a carbon material that can be doped and dedoped with lithium and a non-aqueous electrolyte.

[0011]

Function: Li _x M _{1 (1-x)} M ₂ O ₂ which is the positive electrode active material of the non-aqueous electrolyte secondary battery of the present invention (where M ₁ is Cu or A
g and M ₂ are any one of Fe, Ni and Mn, and x is 0
<X <1) belongs to a part of the delafossite-type composite oxide that is a hexagonal crystal.

This is different from the hexagonal complex oxide containing cobalt as typified by LiCoO ₂ , because copper and silver exist in a stable state in the crystal, and thus react with the electrolytic solution. It is possible to suppress the catalytic action. Thereby, the decomposition reaction of the electrolytic solution on the positive electrode active material can be prevented. Further, even when a vacancy of lithium occurs during charging, the presence of stable metal atoms stabilizes the crystal, and as a result, it is possible to prevent the crystal from collapsing.

Therefore, by using the lithium composite oxide of the present invention as the positive electrode active material, it is possible to prevent the decomposition reaction of the electrolytic solution and the crystal collapse of the positive electrode active material, and improve the charge / discharge cycle life characteristics and storage characteristics. Can be made

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

A lithium composite oxide, which is a positive electrode active material of the non-aqueous electrolyte secondary battery of the present invention, was produced as follows.

Cuprous oxide (Cu₂O) and iron oxyhydroxide
And lithium oxide (Li₂O) at a constant molar ratio of 1:
1: Weighed to 0.5 and mixed, then 10 wt% of hydroxylation
Add sodium solution and heat them at 700 ℃
did. Then, after washing this with water, heat drying at 110 ℃
And pulverized to obtain Li having a particle size of 2 to 4 μm._0.5Cu_0.5Fe
O ₂Got

In the same manner, by using nickel and manganese oxyhydroxides respectively, the particle size of 2 to
4 μm of Li _0.5 Cu _0.5 NiO ₂ and Li _0.5 Cu _0.5
MnO ₂ was prepared.

Next, after sterilized silver oxide (Ag ₂ O), iron oxyhydroxide and lithium oxide (Li ₂ O) were weighed and mixed at a constant molar ratio of 1: 1: 0.5, A 10 wt% sodium hydroxide solution was added, and these were heat-treated at 500 ° C. Then, this was washed with water, dried by heating at 110 ° C., and pulverized to obtain Li _0.5 Ag _0.5 F having a particle size of 3 to 6 μm.
eO ₂ was obtained.

In a similar manner, L having a particle size of 3 to 6 μm was prepared using nickel and manganese oxyhydroxides, respectively.
i _0.5 Ag _0.5 NiO ₂ and Li _0.5 Ag _0.5 MnO ₂ were obtained.

The positive electrode active material 100 thus obtained
Parts by weight and acetylene black 4 parts by weight, graphite 4
By weight, 7 parts by weight of a fluororesin binder was mixed to prepare a positive electrode mixture, which was suspended in a carboxymethyl cellulose aqueous solution to form a paste. This paste was applied to both sides of an aluminum foil, dried and rolled to obtain a positive electrode plate.

Next, a negative electrode plate was produced as follows. 100 parts by weight of the carbon material obtained by baking the coke was mixed with 10 parts by weight of the fluororesin-based binder and suspended in an aqueous solution of carboxymethyl cellulose to form a paste. This paste was applied to both sides of a copper foil, dried and rolled to obtain a negative electrode plate.

A sealed type non-aqueous electrolyte secondary battery as shown in FIG. 1 is constructed by using the positive electrode, the negative electrode, the polypropylene separator and the non-aqueous electrolytic solution, and the non-aqueous electrolyte secondary battery of the present invention is formed. It was a battery.

Here, the electrolyte is 1 volume of lithium perchlorate in a mixed solvent of equal volume of propylene carbonate and ethylene carbonate.
1 / l dissolved product was used.

In FIG. 1, the positive electrode plate and the negative electrode plate are formed into a spiral electrode plate group 1 with a separator interposed therebetween, and the electrode plate group 1 is a battery case 2 formed by processing a stainless steel plate resistant to organic electrolyte.
It is stored in. The upper portion of the battery case 2 is sealed with a sealing plate 3 having a safety valve.

A positive electrode lead 4 is drawn out from the positive electrode and connected to the sealing plate 3, and a negative electrode lead 5 is drawn out from the negative electrode and connected to the battery case 2. Figure 1
A middle 6 is an insulating packing that insulates between the battery case 2 and the sealing plate 3, 7 is an insulating plate positioned between the inner bottom of the case 2 and the lower part of the electrode plate group 1, and a positive electrode as a comparison battery. A battery similar to the battery of the present invention was constructed except that LiCoO ₂ and LiNi _0.5 Co _0.5 O ₂ were used as the active material.

Next, the battery of the present invention and the comparative battery were charged, lithium in the positive electrode was moved into the carbon material of the negative electrode to dope, and then a constant current charge / discharge cycle test and a high temperature charge storage test were performed using these batteries. went.

In the constant current charge / discharge cycle test, charging was performed at a current of 100 mA up to a voltage of 4.1 V, and discharging was performed at a current of 100
It was carried out at room temperature under the conditions of mA and a final voltage of 3.0V.
The high temperature charge storage test was carried out by repeating the above charge / discharge cycle 100 times and then storing the battery in a charged state at 60 ° C. for 20 days.

The relationship between the number of charge / discharge cycles and the discharge capacity retention rate [(capacity after cycle / initial capacity) × 100] in the charge / discharge cycle life test of the battery of the present invention and the comparative battery is shown in (Table 1).

The capacity retention of the battery after the high temperature charge storage test [(capacity after storage / capacity before storage) × 100] is shown in (Table 2).

[0030]

[Table 1]

[0031]

[Table 2]

As can be seen from (Table 1), in the comparative battery using the lithium-containing composite oxide containing cobalt as the positive electrode active material, the capacity retention ratio after 300 cycles was 52% of the initial value.
%, The capacity decreased to about half of the initial capacity, but in the battery of the present invention using the lithium composite oxide containing copper and silver, the capacity retention rate after 300 cycles was about 80%, The capacity retention rate was good even after the cycle.

Further, as can be seen from (Table 2), in the comparative battery in which the lithium-containing composite oxide containing cobalt was used as the positive electrode active material, the capacity retention rate after high temperature charge storage was 53%. In the battery of the present invention using the lithium composite oxide containing silver and silver, the capacity retention was about 80%, and the storage stability after high temperature charging was good.

From these results, it is possible to improve the charge / discharge cycle life characteristics and storage characteristics of the battery by using the lithium composite oxide containing copper and silver as the positive electrode active material.

In this embodiment, the general formula Li _x M _{1 (1-x)}
Although the value of x of M ₂ O ₂ was set to 0.5, substantially the same effect was obtained in the range of 0 <x <1.

In this embodiment, a carbon material which can be doped with lithium and dedoped is used as the negative electrode, but other than this, lithium metal or lithium alloy may be used. Also,
In the present embodiment, as the electrolytic solution, the one obtained by dissolving lithium perchlorate in the mixed solvent of equal volume of propylene carbonate and ethylene carbonate was used, but it may be one obtained by dissolving the lithium salt as a solute in another organic solvent.

[0037]

As described above, in the non-aqueous electrolyte secondary battery of the present invention, the positive electrode active material has the general formula Li _x M _{1 (1- x)} M ₂ O ₂ (where M ₁ is copper or silver, M ₂ is any one of iron, nickel and manganese, and since the lithium complex oxide represented by 0 <x <1) is used, the decomposition reaction of the electrolytic solution on the positive electrode active material under high voltage and the positive electrode activity are performed. It is possible to prevent crystal collapse of the substance and improve charge / discharge cycle life characteristics and storage characteristics.

[Brief description of drawings]

FIG. 1 is a sectional view of a non-aqueous electrolyte secondary battery of the present invention.

[Explanation of symbols]

 1 electrode plate group 2 battery case 3 sealing plate 4 positive electrode lead 5 negative electrode lead 6 insulating packing 7 insulating ring

Claims (1)

[Claims] 1. A general formula Li _x M _{1 (1-x)} M ₂ O ₂ (where M ₁
Is copper or silver, M ₂ is one of iron, nickel and manganese, and x is a positive electrode made of a lithium composite oxide represented by 0 <x <1), and is doped with lithium, a lithium alloy or lithium. A non-aqueous electrolyte secondary battery including a negative electrode made of a carbon material that can be dedoped and a non-aqueous electrolyte.