JP2942911B2 - Non-aqueous electrolyte secondary battery - Google Patents

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, and provides a non-aqueous electrolyte secondary battery using a high capacity carbon negative electrode.

[0002]

2. Description of the Related Art The positive electrode active material of a non-aqueous electrolyte secondary battery includes:
Various compounds such as titanium disulfide, lithium cobalt composite oxide, spinel type lithium manganese oxide, vanadium pentoxide and molybdenum trioxide have been studied. Among them, lithium cobalt composite oxide (LixC
oO ₂ ) and spinel lithium manganese oxide (LixMn
_{Since 2} O ₄ ) charges and discharges lithium at a very noble potential of 4 V or more, a battery having a high discharge voltage can be realized by using it as a positive electrode.

As the non-aqueous electrolyte, a solution in which a metal salt serving as an electrolyte is dissolved in an aprotic organic solvent is used. For example, for lithium salts, LiClO ₄ , LiP
F ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , etc. can be used alone such as propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, γ-butyrolactone, dioxolan, 2-methyltetrahydrofuran, diethyl carbonate, dimethyl carbonate, sulfolane, etc. A solution dissolved in a solvent or a mixed solvent is used. These non-aqueous electrolytes are used by being injected into a battery container, but are impregnated in a porous separator, are made highly viscous by adding a high molecular weight resin, or are gelled to lose fluidity. Sometimes used in.

As a negative electrode active material of a non-aqueous electrolyte secondary battery,
Conventionally, various substances have been studied, but a lithium-based negative electrode has attracted attention as a material expected to have a high energy density.

[0005] Lithium has a high electromotive force and can be expected to have a high energy density. However, due to its high reactivity, there is a problem in the safety of the battery. There is a major problem that it is easy to cause internal short circuit and reduction of charge / discharge efficiency. As a solution to this problem, as a host material holding lithium ions, for example, as described in JP-A-61-111907. A lithium ion type secondary battery using a carbon material capable of inserting and extracting lithium ions between layers of a crystal lattice of a carbon material has been developed.

[0006]

Conventionally, propylene carbonate is mainly used as a cyclic ester as an electrolyte for a non-aqueous electrolyte secondary battery in order to obtain a good electric conductivity, and a chain form such as diethyl carbonate is used. Due to the use of an organic electrolyte solution in which a lithium salt serving as an electrolyte was dissolved in a mixed solvent of esters, it was considered that completely graphitized negative electrode carbon was not preferred due to its reactivity with propylene carbonate. Was. The degree of graphitization is the distance between the lattice planes of the carbon crystal d ₀₀₂ and the length of the crystallite in the C-axis direction
Lc, fully graphitized, d ₀₀₂ = 0.3354n
m, Lc = 100 nm or more, for example, JP-A-62-122066
JP-A-63-26953, JP-A-63-69154, JP-A-63-114056
, JP-A-63-276873, etc., d ₀₀₂ = 0.337 nm or more, Lc = 15
It was said that those having a graphitization of less than nm and not sufficient exhibited more preferable properties. However, these carbon materials
Discharge capacity is 150
Only ~ 200 mAh / g was obtained, and there was a problem in increasing the capacity.

In order to increase the capacity of a carbon material, it is necessary to develop a hexagonal carbon network structure in order to increase the number of lithium intercalation sites. 002) Face spacing
(d ₀₀₂ ) needed to approach 0.3354 nm.

However, when propylene carbonate is used as a cyclic ester of the electrolyte solvent in a highly crystalline carbon material having a carbon hexagonal network structure, a decomposition reaction of the electrolyte occurs on the carbon surface during charging, and lithium intercalation occurs. And the capacity is reduced. For this reason,
The discovery of high capacity carbon materials has been delayed.

Therefore, when the discharge capacity of natural graphite, which has been most crystallized, was measured using ethylene carbonate having low reactivity with carbon, C ₆ Li (372 mAh / g), which is considered to be the theoretical amount of lithium occlusion of graphite, was measured. , The initial discharge capacity was obtained. However, since natural graphite contains many impurities, there is a problem that the discharge capacity decreases as the cycle progresses in the cycle characteristics of repeating charge and discharge.

The present invention solves such a conventional problem and provides a non-aqueous electrolyte secondary battery using a high-capacity carbon negative electrode.

[0011]

In order to solve these problems, the present invention provides a positive electrode which can be repeatedly charged and discharged, a non-aqueous electrolyte containing an alkali metal ion, and an occlusion / release of an alkali metal ion. In a non-aqueous electrolyte secondary battery provided with a negative electrode made of a carbon material capable of being used, the carbon material has a (002) plane spacing (d0) determined by X-ray wide-angle diffraction.
02) is 0.3355 nm or more and 0.3358 nm or less, the average particle diameter is 5 μm to 50 μm, and the surface area is 4 to 20 μm.
An object of the present invention is to provide a non-aqueous electrolyte secondary battery using m ² / g artificial graphite for a carbon negative electrode.

[0012]

In order to improve the cycle characteristics of natural graphite which can provide a high capacity, high crystallinity artificial graphite with few impurities was examined. The plane spacing (d002) of the (002) plane by the X-ray wide-angle diffraction method was determined. 0.3355 nm or more, 0.335
8 nm or less , average particle diameter of 5 μm to 50 μm, surface area
In the range of 4 to ²⁰ m ² / g , a discharge capacity equivalent to natural graphite was obtained, and good cycle characteristics superior to natural graphite were obtained.

As a result of analyzing the impurities of the natural graphite and the artificial graphite of the present invention, the natural graphite contained 700 p
pm, iron: 500ppm, silicon: 3000ppm, magnesium: 30pp
m, but the artificial graphite of the present invention contained aluminum: 6 ppm, iron: 40 ppm, silicon: 90 ppm, and magnesium:
It was 1 ppm. Although the reason is not clear, it is considered that this difference in the amount of impurities affects the cycle performance.

The artificial graphite has a crystallite length (Lc) in the C-axis direction of 100 nm or more and a true density of 2.24 to 2.26 g / cm 2.
It was cm ^3.

Next, considering a negative electrode in which the artificial graphite of the present invention is applied in the form of a paste with a binder and an organic solvent as shown in the examples, the particle diameter and the surface area of the carbon particles are required for uniform high-density application. Is an important factor. When the surface area of the carbon material is large and the particle diameter is small, the bulk density of the carbon material is low, and the packing density of the electrode is low. If the particle size is too large, it becomes difficult to apply the particles uniformly. The carbon material preferably has an average particle size of 5 μm to 50 μm and a surface area of 4 to 20 m ² / g.

[0016]

The present invention will be described below with reference to preferred embodiments. [Example 1] A negative electrode plate was produced by the following method using artificial graphite obtained from a petroleum-based material as the highly crystalline carbon material of the example and low crystalline carbon and natural graphite as a comparative example.

88 parts by weight of a carbon material, 12 parts of polyvinylidene fluoride as a binder, and N-methyl-2-pyrrolidone 15 as a solvent
0 parts were kneaded to form a paste, applied to a copper foil having a thickness of 20 μm, and then dried to produce an electrode substrate having a thickness of 0.60 mm. This electrode was punched out to form a strip having a width of 14 mm and a length of 52 mm.

The monopolar characteristics of the negative electrode plate were measured. Using lithium as a counter electrode, a charge / discharge test was carried out in a mixed solution of ethylene carbonate and diethyl carbonate in which 1 mol of LiPF ₆ was dissolved. After charging to 0 V with respect to lithium potential at a current of 3 mA, the battery was discharged to 1.2 V at the same current of 3 mA. Table 1 shows the measurement results of the physical properties and unipolar characteristics of the carbon material. The carbon material of the example obtained a high discharge capacity equivalent to that of natural graphite.

[0019]

[Table 1] [Embodiment 2] FIG. 1 is a sectional view of a main part of a prismatic battery according to an embodiment of the present invention. Reference numeral 1 denotes a rectangular container made of stainless steel, in which a negative electrode 2, a separator 3, and a positive electrode 4 are housed. The negative electrode 2 was prepared by applying a carbon material to a copper foil in the same manner as in Example 1. LiCoO ₂ cathodes are alternately inserted through a porous separator 3 made of polypropylene impregnated with a non-aqueous electrolyte. Reference numeral 5 denotes a container lid, which is welded to the opening of the container 1 at the periphery. At the center of the container lid 5, a fitting 7 is fixed via a gasket 6, and a positive electrode terminal 9 is welded. Reference numeral 8 denotes a safety valve fixed inside the positive electrode terminal 9, and seals an opening of the eyelet 7. Reference numeral 10 denotes an exhaust port when the internal pressure increases when the battery is abnormal and the safety valve 8 operates. 11 is
A negative electrode lead provided on the upper part of the negative electrode 2 is connected to the inner surface of the battery cover 5. Reference numeral 12 denotes a positive electrode lead provided above the positive electrode 4, and is connected to the fitting 7 via a positive electrode connecting piece 13.

The positive electrode was manufactured as follows. 87 parts by weight of LiCoO ₂ as a positive electrode active material, 1.5 parts of acetylene black as a conductive additive, and 1 part of polyvinylidene fluoride 1 as a binder
1.5 parts of a solvent, 100 parts of N-methyl-2-pyrrolidone, is kneaded into a paste, applied to a 20-μm-thick aluminum foil, dried and rolled to obtain a 0.40-mm-thick positive electrode substrate. Produced. Punch this board, width 14mm, length
A 52 mm strip-shaped positive electrode was obtained. A single positive electrode can discharge 75 mAh.

A secondary battery was composed of six positive electrodes and seven negative electrodes. A positive electrode plate was coated using a nonwoven polypropylene fabric having a thickness of 0.10 mm and a basis weight of 50 g / m ² as a separator, and the periphery thereof was heat sealed. As a non-aqueous electrolyte, LiPF in a 1: 1 mixed solvent of ethylene carbonate and diethyl carbonate
_{6 A} solution dissolved at a rate of 1 mol / liter was used.
The dimensions of the battery of the example were 6 mm in thickness, 16 mm in width, and 65 mm in height.

The battery was operated at a current of 80 mA and a terminal voltage of 4.1 V.
And then discharged at a current of 80 mA.
Table 2 shows the discharge capacity and energy density in the initial first cycle of the prototype battery, and FIG. 2 shows the cycle characteristics under the above charging and discharging conditions.

[0023]

[Table 2] The battery of the present invention has a high energy density, does not show a decrease in discharge capacity as the cycle proceeds, and has an excellent cycle life.

[0024]

According to the present invention, a non-aqueous battery comprising a positive electrode which can be repeatedly charged and discharged, a non-aqueous electrolyte containing alkali metal ions, and a negative electrode made of a carbon material capable of inserting and extracting alkali metal ions. In the aqueous electrolyte secondary battery, the carbon material has a (002) plane spacing (d002) of 0.3355 nm or more and 0.3358 by X-ray wide-angle diffraction.
nm or less , the average particle diameter is 5 μm to 50 μm, and the surface area is 4
By using artificial graphite having a capacity of ２０20 m ² / g for a carbon negative electrode, a high-capacity nonaqueous electrolyte secondary battery can be provided.

Although a copper foil was used for the negative electrode current collector in the embodiment, any metal having corrosion resistance to the alkali metal used, such as nickel or a nickel-copper alloy, silver, iron, stainless steel, etc., can be used. The shape is not limited to a foil, and a foam metal, a metal fiber felt, a perforated plate, or the like can be used.

[Brief description of the drawings]

FIG. 1 is a sectional view showing the structure of a battery according to an embodiment of the present invention.

FIG. 2 is a cycle characteristic diagram of a battery according to an example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Container 2 Negative electrode 3 Separator 4 Positive electrode 5 Container lid 6 Gasket 7 Stopper 8 Safety valve 9 Positive electrode terminal 10 Exhaust hole 11 Negative lead 12 Positive electrode lead 13 Positive electrode connection piece

Claims (1)

(57) [Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode that can be repeatedly charged and discharged, a non-aqueous electrolyte containing alkali metal ions, and a negative electrode made of a carbon material capable of inserting and extracting alkali metal ions. In the above, the plane spacing (d002) of the (002) plane of the carbon material measured by the X-ray wide angle diffraction method is 0.3355 nm or more and 0.3358 nm or less ,
A non-aqueous electrolyte secondary battery characterized in that artificial graphite having a diameter of 5 μm to 50 μm and a surface area of 4 to ²⁰ m ² / g is used for a negative electrode.