JPH03285273A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To prevent the gas generation by decomposition of an electrolyte at the time of charge by using a specified carbon material having the surfaces preliminarily oxidized in which an active material of light metal is stored. CONSTITUTION:As the carbon material of a negative electrode 4, a carbon material with a face space (d002) of face 002 by X-ray wide angle diffraction method ranging from 3.37Angstrom to 3.50Angstrom , a c-axial crystallite thickness (Lc) ranging from 50Angstrom to 200Angstrom , and an a-axial crystallite thickness (La) ranging from 100Angstrom to 400Angstrom , formed by thermally decomposing hydrocarbon in gas phase and accumulating and growing the carbon on a metal base material, and having the surface preliminarily oxidized is used. It is desirably at least one selected from the group consisting of benzene, methane, and propane. The metal base material is desirably at least one grain or base plate selected from the group consisting of iron, nickel, and cobalt.

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 and lightweight secondary battery.

Conventional technology In recent years, electronic devices have rapidly become portable and cordless, and as a power source for driving these devices, small and lightweight
There is a high demand for secondary batteries with high energy density. In this respect, 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, etc. have been used as positive electrode active materials for lithium secondary batteries, and these positive electrodes, monometallic lithium negative electrodes, and organic electrolytes constitute a battery and are charged and discharged. There is. However, in general, secondary batteries that use lithium metal for the negative electrode have problems such as internal short circuits due to dendrite-like lithium produced during charging and side reactions between the active material and the electrolyte, which are obstacles to practical application.

In addition, it cannot be said that the high-rate charging characteristics and over-discharging characteristics are fully satisfactory.

Recently, intercalation (insertion reaction) of layered compounds
A new type of electrode active material that utilizes has attracted attention.

Graphite intercalation compounds have long been considered as electrode materials for secondary batteries. In particular, ClO4-1PFs-1BF4-
A graphite intercalation compound incorporating anions such as ions is used as a positive electrode, and a graphite intercalation compound incorporating cations such as Mari, L 1 , Na, etc. can be considered as a negative electrode. However, graphite incorporating such cations is used as a negative electrode. Intercalation compounds are extremely unstable, and when a graphite material is used as a negative electrode, it lacks stability as a battery.Also, large amounts of electrolyte decomposition are involved, so it cannot be used as a substitute for lithium negative electrodes.

For example, a cationic insert of a pseudographite material obtained by carbonizing a polymer material (such as some liquid hydrocarbons) is effective as a negative electrode, and has a relatively high utilization rate and stability as a battery. It is reported that a compact, lightweight secondary battery with excellent performance can be provided.

Problems to be Solved by the Invention Generally, 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 C6L i in which one lithium atom is inserted for every six carbon atoms. ing. In that case, the active material is 372 mA
The capacity is h/g. Using the above pseudographite material as an electrode material, the amount of lithium absorbed and released was determined to be 1
Only a capacity of 00 to 150mAh/g carbon can be obtained,
Also, since the polarization of the carbon electrode is large during charging and discharging, for example, LiC.

When combined with a positive electrode such as O2, it has a satisfactory capacity,
It is difficult to obtain batteries with high voltage.

The present invention solves the conventional problems as described above, and
The purpose is to provide a secondary battery with high capacity.

Means for Solving the Problems In order to solve these problems, the present invention provides a negative electrode carbon material with a lattice spacing of 002 planes (d O0
2) is a hydrocarbon whose crystallite thickness in the f-C axis direction (L c) is 50 Å or more and 200 Å or less, and the crystallite thickness in the a-axis direction (La) is 100 Å or more and 400 Å or less A carbon material that is deposited and grown on a metal base material by thermally decomposing it in the gas phase, and whose surface has been oxidized in advance is used.

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 and 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 to absorb and release lithium during charging and discharging in carbon materials with Lc of 200 Å or more. It is.

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, the lithium ink-calated between the layers is extremely unstable and cannot be easily charged and discharged. The accompanying polarization of the carbon electrode increases.

Therefore, it is difficult to obtain high capacity, and high rate charging and discharging is also impossible. From this point of view, as negative electrode carbon materials,
The interplanar spacing (dO02) at the X-ray diffraction peak is 337 Å or more and 3°50 Å or less, and the shape factor K according to Scherrer's equation is 0.
．． 9, a carbon material with an Lc value of 50 Å or more and 200 Å or less, preferably 100 Å or more and 200 Å or less is optimal, but those made by baking a polymer or synthesized from a Bi-Sochi system satisfy the above conditions. However, this is not enough, and there is only one carbon material synthesized from the gas phase that shows good properties. In a carbon material that satisfies this condition, crystallization is relatively advanced and the layered structure is developed to some extent. Therefore, the electrochemically intercalated lithium can stably exist between the layers, and the polarization of the carbon electrode becomes small. In addition, self-discharge is small, and high-rate charging and discharging is also expected to be possible. This is closely related to the value of the thickness La of the crystallites in the a-axis direction of the carbon material. Similarly, when the shape factor K is 1.84 in the N error formula, the La value is 100λ or more and 40
A carbon material with a thickness of 0 Å or less, preferably 200 Å or more and 400 Å or less is suitable.

However, this is still insufficient, and if used as is, the electrolyte will decompose during charging and generate gas. The reason for this is thought to be that a highly reactive amorphous microstructure exists near the surface of the carbon material, and this portion decomposes the electrolyte.

Therefore, by heating the carbon material in an oxidizing atmosphere, the highly reactive amorphous microstructure is thought to selectively react and turn into a substance that is inert to the electrolyte and is deactivated.
It was confirmed that the electrolyte did not decompose even when this material was charged.

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, carbon A coin-shaped battery with a positive electrode and metal lithium as a negative electrode 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 an 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 the 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 a mixture of 85 parts by weight of carbon fiber powder shown below and 15 parts by weight of a fluororesin binder.
mg was filled onto a current collector 3 and molded. 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/i in an equal volume mixed solvent of propylene carbonate and 1,2-dimethoxyethane. The evaluation test was conducted at a charge/discharge current density of 0. 3mA/ca
r, end-of-charge voltage (discharge when viewed from the carbon material)2.
A constant current charge/discharge test was conducted under the conditions of 5 V and a discharge end voltage (also considered as charging from the carbon material's perspective) of OV.

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

Table 1 shows the physical properties of the fibrous carbon material used in this example, obtained by thermally decomposing a mixture of benzene and hydrogen in the gas phase and depositing it on iron catalyst particles, and the discharge at the 10th cycle. The specific capacity is shown. For comparison, a battery was constructed by heat-treating the same carbon material at 300° C. under a predetermined oxygen concentration.

FIG. 2 shows charging curves of the first cycle of batteries using each of the carbon materials shown in Table 1.

Table 1 From Table 1 and Figure 2, the materials for the negative electrode include batteries B-D.
and B°~D° exactly d002 is 3.37~3.46
．． Lc is 91-195. La is preferably a carbon material having a physical property value in the range of 132 to 404, and among them, one whose surface has been previously oxidized is particularly suitable.

Example 2 The coin-shaped battery used in Example 1 was used, and the structure was exactly the same as Example 1, except that a carbon material obtained by thermally decomposing benzene in an argon atmosphere and depositing it on a nickel substrate was used. . Similarly, for comparison, a battery was constructed using the same carbon material heat-treated at 300° C. under a predetermined oxygen concentration.

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

Table 2 shows the physical property values and lO of the carbon material used in this example.
The discharge specific capacity of the cycle is shown. FIG. 3 shows charging curves of the first cycle of batteries using each carbon material shown in Table 2.

From Table 2 and Figure 3, the negative electrode materials include battery F-H.
and F゛~H' or d002 is 3.38~3.51
．． Lc is 52-173. La is preferably a carbon material having a physical property value in the range of 103 to 370, and among them, one whose surface has been oxidized in advance is suitable.

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 3.37λ or more as measured by X-ray wide-angle diffraction. 3
．． 50λ 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 carbon material with a diameter of Å or more and 400λ or less, which is made by thermally decomposing a hydrocarbon in the gas phase and depositing it on a metal substrate, and whose surface has been oxidized in advance and which has a light metal active material occluded therein, is used. This eliminates the problem of electrolyte decomposition and gas generation during charging.

Furthermore, by adopting a configuration in which the potential of the negative electrode is raised, for example, Ov overdischarge is possible, and dendrite formation of lithium metal due to charging is basically eliminated. Therefore, it is possible to solve problems that conventional batteries using metallic lithium have, such as inability to over-discharge and internal short circuits due to dendrite formation.

In addition, although benzene was used as the hydrocarbon in the examples,
Methane gas or propane gas may also be used. Further, in the examples, hydrogen gas was mixed when synthesizing the carbon material, but the synthesis may also be carried out simply in an inert gas atmosphere such as argon.

Furthermore, although iron and nickel were used for the metal catalyst particles or the substrate in the examples, cobalt or a mixture thereof may be used. Furthermore, it goes without saying that the carbon material may be in the form of fibers or powder.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of a coin-shaped battery used in an example of the present invention, and FIG. 2 is a diagram showing a comparison of charging characteristics in the first cycle.
FIG. 3 is a diagram showing a comparison of charging characteristics in the first cycle of another example of batteries. 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 interplanar spacing (d002) of the 002 plane is 3.37 Å or more and 3.50 Å or less, c
The crystallite thickness in the axial direction (Lc) is 50 Å or more and 200 Å or less, and the crystallite thickness in the a-axis direction (La) is 100 Å or more4
1. A non-aqueous electrolyte secondary battery comprising a carbon material having a thickness of 00 Å or less, the surface of which has been previously oxidized, and a light metal active material occluded in the carbon material. (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 base material is a particle or a substrate that is at least one selected from the group consisting of iron, nickel, and cobalt.