JPH03289068A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To provide a nonaqueous solvent secondary battery with high voltage and capacity performance and also excellent in its high rate charge-discharge performance by using a negative material which is formed in a manner where an active material of light metal is stored in a specified carbon-based fiberous material or its crushed material. CONSTITUTION:As a material for the negative of nonaqueous electrolyte secondary battery, carbon fiber or the crushed thereof, which is obtained by heat- dissolving in gas phase a mixture of hydrogen carbonate and hydrogen having the distance of 002 face by the X-ray wide anglo diffraction method which is 3.37Angstrom to 3.50Angstrom and the thickness Lc of crystal element in the direction (c) which is 100Angstrom to 400Angstrom , and deposition-developed on metal catalyst particles, is used. An active material of light metal is stored therein. It is thus possible to realize the provision of a negative electrode carbon material capable of charging/discharging at a high rate as well as having high voltage and capacity performance and less self-discharge performance.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a novel compact, lightweight secondary battery.

Conventional technology In recent years, consumer electronic devices have rapidly become portable and cordless, and there is an increasing demand for small, lightweight, and high-energy-density secondary batteries that serve as the power source for driving these devices. . From this point of view, non-aqueous secondary batteries, especially lithium secondary batteries, have high expectations as batteries with particularly high voltage and high energy density.

Conventionally, manganese dioxide, vanadium pentoxide, and titanium disulfide have been used as positive electrode active materials for lithium secondary batteries. A battery is made up of such a positive electrode, a metallic lithium negative electrode, and an organic electrolyte, and is repeatedly charged and discharged.

However, in general, secondary batteries that use lithium metal for the negative electrode have problems such as internal short circuits caused by dendrite-like lithium produced during charging and side reactions between the active material and the electrolyte, which are major obstacles to practical application. Furthermore, no material has been found that satisfies high-rate charging characteristics or over-discharge characteristics.

On the other hand, intercalation (insertion reaction) of layered compounds
A new type of electrode active material that utilizes is attracting attention, and graphite intercalation compounds have been used as electrode materials for secondary batteries for a long time. In particular, ClO4-PF6-1BF4
- Graphite intercalation compounds incorporating anions such as ions are used as positive electrodes. Further, graphite intercalation compounds incorporating cations such as Li+ and Na+ are considered as negative electrodes.

However, graphite intercalation compounds that incorporate such cations are extremely unstable, and when graphite materials are used as negative electrodes, they lack stability as a battery, have low capacity, and are accompanied by a large amount of electrolyte decomposition. However, it could not be used as a substitute for lithium negative electrodes.

Recently, cation-doped pseudographite materials obtained by carbonizing certain liquid hydrocarbons or polymer materials have been found to be effective as negative electrodes, and have a relatively high utilization rate and stability as batteries. It is reported that an excellent, compact, and lightweight secondary battery can be provided.

In general, it is reported that the upper limit of the amount of lithium that can be intercalated between graphite layers is the first stage graphite intercalation compound CaLi in which one lithium atom is inserted for every six carbon atoms. ing. In that case, the active material is 372mAh/H
It will have a capacity of

Using the above pseudographite material as an electrode material, the amount of lithium absorbed and released was determined to be 100 to 150 mA h.
/gh-l, and since the polarization of the carbon electrode is large during charging and discharging, it is difficult to obtain a satisfactory capacity and voltage when combined with a positive electrode such as LiCoO2.

The present invention solves the conventional problems as described above, and
The object of the present invention is to provide a non-aqueous solvent secondary battery that has a high capacity and also has excellent high-rate charge/discharge characteristics.

Means for Solving the Problems In order to solve these problems, the present invention provides a negative electrode carbon material with a 002 plane spacing (d 00
2) is 3.37 A or more and 3.50 λ or less, the crystallite thickness (Lc) in the C-axis direction is 50 Å or more and 200 Å or less, and the crystallite thickness (La) in the a-axis direction is 100 A or more and 400 Å or less. This method uses carbon fibers or pulverized products thereof, which are grown by thermally decomposing a hydrogen mixture in the gas phase and deposited on metal catalyst particles.

The carbonaceous material used as the working negative electrode material is generally a pseudographite material having a certain degree of turbostratic structure.

When graphite materials with highly developed graphite crystallization, such as those found in natural graphite or artificial graphite, are used, no intercalation reaction of lithium is observed during charging and discharging, and it is thought that the decomposition reaction of the electrolyte proceeds primarily. It will be done.

This seems to be closely related to the value of the crystallite thickness Lc in the C-axis direction of the graphite material, and it is generally impossible for carbon materials with Lc of 200 Å or more to absorb and release lithium during charging and discharging. . On the other hand, in carbon materials with an Lc value of 50 Å or less,
Intercalation of lithium is possible, but due to insufficient crystallization, lithium intercalated between layers is very unstable, and the polarization of the carbon electrode increases during charging and discharging. Therefore, it is difficult to obtain high capacity, and high rate charging and discharging is also impossible. From this point of view, the negative electrode carbon material should have a lattice spacing d002 of 3 at the X-ray diffraction peak.
．． A carbon material having an Lc value of 50 A or more and 200 Å or less, preferably 100 A or more and 200 λ or less when the shape factor K is 09 in Scherrer's equation and is 37 A or more and 3.50 A or less is optimal. However, carbon fibers made by firing polymers or synthesized from a pinch system are not sufficient even if they satisfy the above conditions, and only carbon fibers synthesized from a hydrogen-containing gas phase exhibit good properties. There is. In the carbon material in this region, crystallization is relatively advanced, and the layered structure is in a state of being developed to some extent. Therefore, electrochemically intercalated lithium can stably exist between the layers, and the polarization of the carbon electrode becomes small. In addition, self-discharge is small, making it a negative electrode carbon material that can be charged and discharged at a high rate.

This is closely related to the value of the crystallite thickness La in the a-axis direction of the carbon material, and the shape factor K
is 1.84, the La value is 100 Å or more 400
A carbon material having a thickness of Å or less, preferably 200 Å or more and 400 A or less is optimal.

Example Hereinafter, the present invention will be explained in detail with reference to Examples.

Example 1 In this example, as a method for examining the amount of lithium that can be occluded and released by the carbon material for the negative electrode and the polarization characteristics of the carbon electrode, a coin-shaped battery with the carbon electrode as the positive electrode and metallic lithium as the negative electrode was constructed. The system was constructed and evaluated.

FIG. 1 shows a longitudinal cross-sectional view of the coin-shaped battery.

In the figure, 1 is a battery case made of organic electrolyte-resistant stainless steel plate, 2 is a sealing plate made of the same material, and 3 is a positive electrode current collector made of stainless steel, which is spot welded to the inner surface of case 1. 4 is a metallic lithium negative electrode which is pressed onto the sealing plate 2. 5 is a positive electrode mixture, which is prepared by mixing 85 parts by weight of the powder obtained by pulverizing the carbon fiber shown below with 15 parts by weight of a fluororesin binder, and filling 50 mg of the mixture onto the current collector 3 and molding it. .

6 is a microporous polypropylene separator, and 7 is a polypropylene insulating backing. The electrolytic solution used was one in which lithium perchlorate was dissolved at a ratio of 1 mol/l in a mixed solvent of equal volumes of propylene carbonate and 1,2-dimethquinethane. The evaluation test was conducted at a charge/discharge current density of 0.3 mA/c.
nr, end-of-charge voltage (discharge when viewed from the carbon material) 2
．． A constant current charging/discharging test was conducted under the conditions of 5V and a discharge end voltage (also considered as charging from the viewpoint of the carbon material) of 2.0V.

The dimensions of this battery are 20mm in diameter and 1.6mm in total height.
It is.

Table 1 shows the physical properties and specific discharge capacity of the fibrous carbon material used in this example, which was obtained by thermally decomposing a mixture of benzene and hydrogen in the gas phase and depositing it on iron catalyst particles. Ta.

FIG. 2 shows discharge curves corresponding to the discharge specific capacities in Table 1 for batteries using each carbon material. These are all from the 10th cycle.

Example 2 The coin-shaped battery used in Example 1 was used, except that the same fibrous carbon material obtained by thermally decomposing a mixture of benzene and hydrogen in the gas phase and depositing it on nickel catalyst particles was used. was constructed in exactly the same manner as in Example 1.

A charge/discharge test was also conducted in exactly the same manner as in Example 1.

Table 1 Table 2 From Table 1 and Figure 2, negative electrode materials include batteries B to D,
In other words, do02 or 3.37~3.45°Lc is 91~1
92. It can be said that a carbon material having a physical property value of La in the range of 132 to 400 is preferable.

Table 2 shows the physical property values and discharge specific capacity of the carbon material at this time. FIG. 3 shows the charging curve of each battery in the first cycle. Note that, for comparison, FIG. 3 shows the charging curve of the battery C in the first cycle as a representative of Example 1. As seen in FIG. 3, the use of a nickel catalyst is more preferable since there is no voltage behavior corresponding to the decomposition of the electrolyte. Also, from the discharge specific capacity, battery F-H, that is, the negative electrode material has d002 of 3.39 to 3.50. Lc is 50-170. La is 11
It can be said that carbon materials having physical property values in the range of 0 to 360 are preferable.

Effects of the Invention As is clear from the above explanation, Examples 1 and 2 show that the negative electrode material of the non-aqueous electrolyte secondary battery has a 002 plane spacing (d002) of 3.37 Å or more as measured by X-ray wide-angle diffraction. 3
．． 50A or less, the crystallite thickness Lc in the C-axis direction is 50A or more and 200Å or less, the crystallite thickness La in the a-axis direction is 100
By using carbon fibers or pulverized products thereof, which are made by thermally decomposing a mixture of hydrocarbon and hydrogen in the gas phase and depositing and growing on metal catalyst particles, with a size of Å or more and 400λ or less, and by occluding a light metal active material into this. This solves the problems of conventional batteries using metallic lithium, such as the inability to over-discharge and concerns about internal short circuits due to the formation of dendrites. In the examples, Hensen was used as the hydrocarbon, but methane gas or propane gas may also be used.

Furthermore, although iron and nickel were used as the metal catalyst particles in the examples, cobalt or a mixture thereof may also be used.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a coin-shaped battery in an example of the present invention, FIG. 2 is a diagram showing a comparison of discharge characteristics at the 10th cycle, and FIG. 3 is a diagram showing charging characteristics. DESCRIPTION OF SYMBOLS 1... Case, 2... Sealing plate, 3... Positive electrode current collector, 4... Negative electrode, 5... Positive electrode, 6... Separator,
7...Insulating backing.

Claims (3)

[Claims] (1) In a non-aqueous electrolyte secondary battery comprising a chargeable/dischargeable positive electrode, a non-aqueous electrolyte, and a chargeable/dischargeable negative electrode; the negative electrode heats a mixture of hydrocarbon and hydrogen in the gas phase. Consisting of carbonaceous fibers that have been decomposed and deposited on metal catalyst particles or their pulverized products, the interplanar spacing (d002) of the 002 plane measured by X-ray wide-angle diffraction is 3.37 Å or more and 3.50 Å or less,
The crystallite thickness (Lc) in the c-axis direction is 50 Å or more and 200 Å
Hereinafter, a non-aqueous electrolyte secondary battery is characterized in that a light metal active material is occluded in a material having a crystallite thickness (La) of 100 Å or more and 400 Å or less in the a-axis direction. (2) The nonaqueous electrolyte secondary battery according to claim 1, wherein the hydrocarbon is at least one selected from the group consisting of benzene, methane, and propane. (3) The nonaqueous electrolyte secondary battery according to claim 1, wherein the metal catalyst particles are at least one selected from the group consisting of iron, nickel, and cobalt.