JPH08106900A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE: To prevent the precipitation of needle metal lithium on the surface of a negative electrode and enhance the capacity by using an aluminum carbonate represented by a prescribed formula and capable of storing and releasing lithium as the negative electrode. CONSTITUTION: For example, a pitch carbon material and aluminum chloride of a prescribed mole ratio are baked under inert atmosphere to synthesize a carbon material represented by the formula II. This carbon material is mixed with a binder of a prescribed weight ratio, and molded on a current collector followed by drying to form a negative electrode. After assembling a battery, the negative electrode is substantially changed to a carbon material represented by the formula II, and no needle lithium precipitate from the negative electrode surface is observed. The lithium ion is housed between the wide layers of the aluminum carbide represented by the formula II, and the housing quantity of lithium ion is increased by the defect of electron on P-orbit. Therefore, a high capacity exceeding an absolute capacity regulated by the formula C6 Li can be provided at charge. (In the formulae I and II, 0<=x<=1.2).

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 negative electrode active material.

[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.

Conventionally, 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 inserting and extracting lithium, and the like have been proposed and partially put into 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 electrode plate during charging, and the needle-like crystals break through 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 to use a graphite material for the negative electrode. In this case, carbon theoretically absorbs Li ions up to C ₆ Li (6 Li atoms to 1 Li atom). It is said that it is difficult to increase the capacity further.

The present invention solves such a problem by preventing metallic lithium from acicularly depositing on the surface of the negative electrode and exceeding the absolute capacity defined by the general formula C ₆ Li during charging. The present invention provides an active material for a negative electrode that can be obtained.

[0006]

In order to solve these problems, the non-aqueous electrolyte secondary battery of the present invention has a negative electrode of the general formula Li
It uses aluminum carbide capable of inserting and extracting lithium represented by xAl ₄ C ₃ (0 ≦ x ≦ 1.2).

[0007]

The aluminum carbide of the present invention is a layered material whose crystal system belongs to the hexagonal system and which has the symmetry of the space group R-3m. The a-axis of the crystal orientation has a lattice parameter of about 3 angstroms while the c-axis has a lattice parameter of about 25 angstroms, and lithium ions can be accommodated between wide layers. Further, in the bond between carbon and metal, since the electron on the P orbital is more deficient than the carbon material alone, the amount of lithium ions accommodated is larger than in the interlayer formed of the carbon material. As a result, the capacity of the negative electrode active material can be increased, and a high capacity non-aqueous electrolyte secondary battery can be provided.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.
You. FIG. 1 shows a coin type non-aqueous electrolyte solution 2 for evaluating a negative electrode of the present invention.
The longitudinal cross-sectional view of the following battery is shown. In the figure, 1 is an organic electrolytic solution
Battery case made of flexible stainless steel plate, 2 is the same material
The sealing plates 3 and 3 are current collectors made of the same material and are attached to the inner surface of the case 1.
It is pot welded. 4 is metallic lithium, sealing plate 2
Is crimped inside. 5 is the negative electrode of the present invention, the pitch
Make sure that the carbonaceous material and aluminum chloride are in the specified molar ratio.
Including, it was synthesized by firing in an inert atmosphere at 1100 ° C.
General formula Al_FourC₃Carbon material represented by (0 ≦ x ≦ 1.2)
Is used. The crystal structure of the sample thus obtained is spatial
Belongs to group R-3m and has a lattice parameter a ₀3.33 Oh
Ngstrom, c₀Is 24.97 angstroms
there were. When making electrodes, 90 parts by weight of the carbon material
In contrast, 10 parts by weight of polyvinylidene fluoride as a binder
Mold a predetermined amount of the mixture obtained by mixing
did. Then, after drying the electrode under reduced pressure at 150 ° C., the battery
Used for assembly. 6 is a microporous polypropylene separator
And 7 are polypropylene insulating gaskets.
The electrolyte is ethylene carbonate, 1,3-dimethoxyethane, etc.
Lithium perchlorate as a solute in the volume mixed solvent 1 mol /
It was used by dissolving it at a concentration of 1 liter. The dimensions of this battery are
The diameter is 20 and the total height of the battery is 1.6 mm.

Using this battery, a current density of 0.5 mA / c
A charge / discharge test was performed in the range of m ² and voltage of 3.0V to 0V. The result is shown in FIG. 460mAh at initial charge
/ G, the initial discharge was 440 mAh / g, but after 2 cycles, a charge / discharge capacity of about 435 mAh / g was obtained, and the charge / discharge efficiency was almost 99% or more. During this charging / discharging, the X value of the general formula LixAl ₄ C ₃ is 0 to about 1.22.
It is considered that the x value changed reversibly between 0.05 and 1.20 even when the cycle was stable. In addition, in the carbon material containing no Al evaluated as a comparison, the x value reversibly changes between 0.05 and 0.95 even when the cycle is stable, and the absolute capacity at the time of charging / discharging is the same as that of the carbon material of the present invention. About 78
It was about%.

The amount of mobile lithium ions in these carbon materials was calculated by electrochemical occlusion / release, and it was found that x = 0 at the end of the synthesis and x = 1.2 at the maximum. In the negative electrode material thus obtained, needle-like lithium deposits were not observed on the electrode surface even during charging.

The effect of the present invention is that LiCoO ₂ , L
It is also effective for positive electrode active materials such as iNiO ₂ and LiMn ₂ O ₄ and other organic electrolytes for lithium batteries.

[0012]

As described above, the general formula Lix is used in the present invention.
Since aluminum carbide represented by Al ₄ C ₃ (0 ≦ x ≦ 1.2) capable of inserting and extracting lithium is used as the negative electrode active material, it has a high capacity and is a needle on the surface of the electrode due to charge / discharge reaction. It is possible to provide a non-aqueous electrolyte secondary battery capable of suppressing crystal-like crystals.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a coin battery.

FIG. 2 is a graph showing charge / discharge electricity quantity at 20 ° C. of a battery using the negative electrode of the present invention.

[Explanation of symbols]

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

Claims (1)

[Claims] 1. A nonaqueous electrolytic solution, a positive electrode, and a general formula LixAl.
A non-aqueous electrolyte secondary battery comprising a negative electrode using aluminum carbide capable of inserting and extracting lithium represented by ₄ C ₃ (0 ≦ x ≦ 1.2).