JPH0935710A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery in which lithium is not deposited in the surface of a negative electrode and which has large capacity by using a specific composite oxide for the negative electrode of a nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode and a nonaqueous electrolytic solution. SOLUTION: Lix InO2 belongs to a pyramidal quadratic system (a space group I 41/and, a lattice constant a0 , b0 is 4.312Å, Co is 9.342Å), and a movable lithium ion is accommodated in the gap position of an oxide unit formed of oxygen 6 coordination around an In ion at a center. The theoretical capacity obtained from the formula weight of the material is 272mAh/g, assuming two electron reaction and however, since a filling density is as high as approximately 3.55g/cc, it can be expected that capacity per volume is 933mAh/cc, so that the capacity of a negative electrode may be made larger. Also, the detachable reaction of a lithium ion is more precise potential than the dissolution deposition potential of metallic lithium and therefore, lithium is not deposited, so that a large-capacity nonaqueous electrolyte secondary battery may be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a non-aqueous electrolyte secondary battery, especially a negative electrode.

[0002]

2. Description of the Related Art Non-aqueous electrolyte secondary batteries are small and lightweight,
Moreover, since it has a high energy density, its expectations are increasing as the equipment becomes more portable and cordless.

Hitherto, lithium-containing metal oxides such as LiCoO ₂ and LiNiO ₂ have been proposed as positive electrode active materials for non-aqueous electrolyte secondary batteries. On the other hand, as the negative electrode, metallic lithium, a lithium alloy, a graphite material capable of occluding and releasing lithium ions, and the like have been proposed, and some of them have been put to practical use.

[0004]

However, in the conventional negative electrode using metallic lithium, metallic lithium is deposited as needle-like crystals on the surface of the negative electrode plate during charging, and the needle-like crystals pierce the separator, There was a case in which an internal short circuit occurred due to contact with the positive electrode. In order to solve this problem, studies have been made on using a graphite material for the negative electrode. In this case, carbon theoretically occludes Li ions up to C ₆ Li (1 Li atom for 6 carbon atoms), and the theoretical capacity is 37.
It is said that it is 2 mAh / g, but the capacity per volume estimated from the battery configuration is, for example, a packing density of 1.
At 5 g / cm ³ , it is about 558 mAh / cc.
Therefore, it is difficult to increase the capacity further in terms of volume.

The present invention solves such a problem, and prevents metallic lithium from acicularly depositing on the surface of the negative electrode, and has the general formula C ₆ when a graphite material is used as the negative electrode during charging. It is intended to provide a negative electrode capable of exceeding the capacity per volume defined by Li.

[0006]

In order to solve these problems, in the non-aqueous electrolyte secondary battery of the present invention, the negative electrode is represented by the general formula Li _x InO ₂ (0 ≦ x ≦ 2.0). It uses a complex oxide.

[0007]

[Function] Li _x InO ₂ is tetragonal (space group I41 / am
d, the lattice constants a ₀ and b ₀ are 4.312 angstrom c ₀
Is 9.342 angstroms), and movable lithium ions are accommodated in the gap position of the oxide unit composed of oxygen 6-coordination around the central In ion. The theoretical capacity obtained from the formula weight of this material is about 272 mAh / g assuming a two-electron reaction, but since the packing density during electrode plate fabrication is high at about 3.55 g / cc, the capacity per volume is 933 mAh. / Cc can be expected, and the capacity of the negative electrode can be increased.

Further, since the insertion / removal reaction of lithium ions occurs at a potential nobler than the dissolution / deposition potential of metallic lithium, the deposition of lithium does not occur.

From the above, it is possible to provide a high-capacity non-aqueous electrolyte secondary battery in which lithium is not deposited on the negative electrode surface.

[0010]

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

FIG. 1 shows a vertical sectional view of an evaluation battery for evaluating the negative electrode of the present invention. In FIG. 1, 1 is a battery case formed by processing an organic electrolyte resistant stainless steel plate, 2 is a sealing plate made of the same material, and 3 is a current collector made of the same material, which is spot-welded to the inner surface of the battery case 1. 4 is metallic lithium,
It is crimped inside the sealing plate 2. 5 is a negative electrode of the present invention, 6 is a microporous polypropylene separator, 7
Is an insulating gasket made of polypropylene. The dimensions of the battery for evaluation are 20 mm in diameter and 1.6 mm in total battery height.

The negative electrode active material was obtained by dry-mixing indium oxide and lithium carbonate in a molar ratio of 1: 1 and firing the mixture at 1150 ° C. for 1 hour under air flow. Acetylene black 5 as a conductive material based on 90 parts by weight of the complex oxide.
Parts by weight, and a predetermined amount of a mixture obtained by mixing 10 parts by weight of polyvinylidene fluoride as a binder is molded on the current collector 3 to form an electrode, which is then dried under reduced pressure at 110 ° C. and then used as a negative electrode. It was assembled into a battery. Electrolyte is ethylene carbonate, 1, 3
Lithium hexafluorophosphate was used as a solute dissolved in a mixed solvent of equal volumes of dimethoxyethane at a concentration of 1 mol / liter. After the battery is assembled, the above-mentioned negative electrode is charged with lithium ions electrochemically by charging to obtain the compound of the general formula L
i _x InO ₂ (0 ≦ x ≦ 2.0).

A charging / discharging test was carried out at a voltage of 2.0 V to 0 V with these evaluation batteries at 0.5 mA / cm ² at room temperature (20 ° C.), and the discharge capacity and cycle characteristics were examined. FIG. 2 shows the discharge capacities of the batteries of the present invention and the conventional battery with respect to cycles. As can be seen from FIG. 2, assuming that the capacity of the conventional graphite material is 100, the capacity of the composite oxide of the present invention is about 1.2 times higher, and the subsequent cycle test is performed. The deterioration rate is similar to that of the conventional product, and it can be seen that the characteristics with higher capacity than the conventional product are maintained. Theoretically, about twice the capacity should be obtained, but when we look at the potential range of a single electrode that can be used practically as a battery, the capacity increase is about 1.2 times that of conventional graphite. It was

When the lithium content was examined,
When the electrolytic reduction reaction is performed up to 0 V (lithium standard), lithium is contained until the x value of Li _x InO ₂ is about 2.0 at the initial stage of charging, but the x value does not return to 0 and is about 0.2 at the time of discharging. Lithium remains in the negative electrode active material. This initial remaining of lithium in the negative electrode also occurs when graphite is used. Therefore, although the capacity deteriorates slightly from the second cycle, the x value is about 0.2.
A discharge capacity of 0.3 to 2.0 can be obtained, and higher capacity characteristics than conventional graphite materials can be obtained. Therefore, when the amount of movable lithium when the composite oxide of the present invention is used as a negative electrode is expressed by an x value, it is defined as 0 ≦ x ≦ 2.0. In addition, needle-like lithium was not observed from the electrode surface of the negative electrode using this composite oxide.

The effect of the present invention is that LiCoO
_{The same} is observed when ₂ , ₂ , LiNiO ₂ , LiMn ₂ O ₄ or the like is used, or when an organic electrolytic solution for a lithium ion battery other than that used in this example is used.

[0016]

As described above, in the present invention, the general formula Li _x
Since the composite oxide represented by InO ₂ (0 ≦ x ≦ 2.0) is used as the negative electrode, it has a high capacity and is capable of suppressing needle-like crystals on the electrode surface of the negative electrode due to charge / discharge reaction. An electrolyte secondary battery can be provided.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of an evaluation battery.

FIG. 2 is a diagram showing cycle characteristics.

[Explanation of symbols]

 1 Battery Case 2 Sealing Plate 3 Current Collector 4 Metal Lithium 5 Negative Electrode 6 Separator 7 Gasket

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhiro Okamura 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (1)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the negative electrode has the general formula Li _x In.
A non-aqueous electrolyte secondary battery comprising a composite oxide represented by O ₂ (0 ≦ x ≦ 2.0).