JPH0428174A - Nonaqueous electrolytic liquid secondary battery - Google Patents

Abstract

PURPOSE:To prevent the generation of gas at the time of electric charging, by using as a negative pole material a carbon material whose carbonated hydrogen is disintegrated thermally by means of a phase of air and which is grown in accumulation on a metal base material and whose surface is treated with plasma under an oxygen atmosphere and which is absorbed and stored with a light metal active substance. CONSTITUTION:A carbon material is grown in accumulation on a metal base material by disintegrating thermally by means of a phase of air carbonated hydrogen whose, surface interval (d 002) an X ray 002, is more than 3.37Angstrom but less than 3.50Angstrom , (c) axial crystalizer thickness (Lc) is more than 50Angstrom but less than 200Angstrom , (a) axial crystalizer thickness (La) is more than 100Angstrom but less than 400Angstrom , and is treated in oxidization, and then is used as a negative pole 4 carbon material. As the carbon material is treated with plasma under an oxygen atmosphere, the electrolysis of an electrolytic liquid does not occur even if electric charging is made. As a result, a secondary battery which has a high voltage and a high capacity and in addition, is superior in the stability of the electrolytic liquid, can be obtained.

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 the battery is composed of this positive electrode, a metallic lithium negative electrode, and an organic electrolyte, and is charged and discharged. . However, in general, secondary batteries that use lithium metal for the negative electrode have problems such as dendrite-like internal short circuits caused by the lithium 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 also satisfactory.

Recently, a new type of electrode active material that utilizes intercalation (insertion reaction) of layered compounds has been attracting attention.
Graphite intercalation compounds have long been considered as electrode materials for secondary batteries.

Especially CI! A graphite intercalation compound incorporating anions such as O4-1PF6-1BF4- ions is used as a positive electrode, and a graphite intercalation compound incorporating cations such as Ll and Na+ can be considered as a negative electrode. 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 and also involve large amounts of electrolyte decomposition, making it difficult to replace lithium negative electrodes. It was not something that could have happened.

In this case, cationic inserts of pseudographite materials obtained by carbonizing certain liquid hydrocarbons or polymeric materials are effective as negative electrodes, and have a relatively high utilization rate and excellent stability as batteries. It is reported that a small and lightweight secondary battery can be provided.

Problems to be Solved by the Invention Generally, it has been reported that the upper limit of the amount of lithium that can be calated between graphite layers is the first stage graphite intercalation compound 2C6L1 in which one lithium atom is inserted for every six carbon atoms. In that case, the active material is 372mAh/g
The capacity will be . Using the above pseudographite material as an electrode material, the amount of lithium intercalation and release was determined to be 100 to 150.
For example, LICO0
When combined with a positive electrode such as No. 2, it is difficult to obtain a battery with satisfactory capacity and voltage.

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 high capacity and excellent electrolyte stability.

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 Å or more and 3.50 Å or less, the crystallite thickness in the a-axis force direction (L c) is 50 Å or more and 200 Å or less, and the crystallite thickness in the a-axis direction (L a) is 100 Å or more and 400 A or less, This carbon material is made by thermally decomposing hydrocarbons in the gas phase and depositing them on a metal substrate, and the surface of the carbon material has been oxidized in advance.

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

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 (L c) in the a-axis force direction of the graphite material, and in carbon materials where (L c ) is approximately 200 Å or more, lithium occlusion occurs during charging and discharging.・Release is not possible.

On the other hand, in carbon materials with (L c ) values of 50 Å or less, intercalation of lithium is possible, but lithium intercalated between layers is extremely unstable due to insufficient crystallization. , the polarization of the carbon electrode increases with 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 has a lattice spacing d 002 of 3.37 Å at the X-ray diffraction peak.
3.50 Å or less, and the shape factor K according to Scherrer's equation
When is 0.9, carbon materials with a value of (Lc) of 50 Å or more and 200 Å or less, preferably 100 Å or more and 200 Å or less, are optimal, but those made by firing polymers or synthesized from pitch-based materials satisfy the above conditions. However, the only carbon material synthesized from the gas phase 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 ink-calated lithium can exist stably 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 thought to be possible.

This is closely related to the value of the crystallite thickness (La) in the a-axis direction of the carbon material, and similarly, when the shape factor K is 1.84 in Scherrer's equation, the (La) value is 100 Å or more. A carbon material having a thickness of 400 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 microstructure exists near the surface of the carbon material, and this portion decomposes the electrolyte. Therefore, by subjecting the carbon material to plasma treatment in an oxygen atmosphere, the highly reactive microstructures mentioned above are thought to selectively react and become inert to the electrolyte and deactivated, allowing the material to be charged. It was confirmed that no decomposition of the electrolyte occurred even when the electrolyte was heated.

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, we will use a reverse configuration in which the carbon electrode is the positive electrode and the metallic lithium is the negative electrode. A coin-shaped battery 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/l in a mixed solvent of equal volume of propylene carbonate and 1,2-dimethoxyethane. The evaluation test consisted of a charge/discharge current density of 0.3 mA/ci,
End-of-charge voltage (discharge when viewed from the carbon material) 2.5V
, end-of-discharge voltage (same as charging from the perspective of carbon material)
A constant current charge/discharge test was conducted under OV conditions.

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, the same carbon material was
A battery was constructed by performing plasma treatment at a predetermined voltage while flowing an equal volume mixed gas of argon and oxygen at 5 cc per minute under a reduced pressure of 10-2 mmHg.

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

From Table 1 and Figure 2, the materials for the negative electrode include batteries B-D.
and B゛~D°, that is, d 002 is 3.37~3.4
6, Lc is 91-195. La is preferably a carbon material having a physical property value in the range of 132 to 404, and in addition, a material whose surface has been previously plasma-treated in an oxygen atmosphere is 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, the same carbon material was
A battery was constructed by performing plasma treatment at a predetermined voltage while flowing an equal volume mixed gas of argon and oxygen at a rate of 5 cc per minute under a reduced pressure of X 10 mmHg.

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

Table 2 shows various physical property values and 10
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 materials for the negative electrode include batteries E-H.
and E°~H゛, that is, d002 is 3.38~3.51
, Lc is 52-173. La is preferably a carbon material having physical property values in the range of 103 to 370, and in addition, a carbon material that has been previously subjected to plasma treatment in an oxygen atmosphere 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 d 002 of 3.37λ or more as determined by X-ray wide-angle diffraction. ．．
50 Å or less, the crystallite thickness Lc in the a-axis force direction is 50 Å or more and 200 Å or less, and the crystallite thickness La in the a-axis direction is 100λ
A light metal active material is occluded in a carbon material having a thickness of 40 (1 Å or less), which is grown by thermally decomposing hydrocarbons in the gas phase and deposited on the metal substrate, and whose surface has been previously plasma-treated in an oxygen atmosphere. By using such a battery, the inconvenience of the electrolyte decomposing and generating gas during charging can be eliminated.

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 the problems of conventional batteries using metallic lithium, such as inability to over-discharge and internal short-circuiting due to the formation of dendrites.

In addition, although benzene was used as the hydrocarbon in the examples,
Methane gas or propane gas may also be used. Furthermore, 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.

Further, although iron and nickel are used for the metal catalyst particles or the substrate in the embodiment, cobalt or a mixture thereof may be used. Furthermore, it goes without saying that the carbon material may be either fibrous or powdery.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a coin-shaped battery according to an embodiment 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. 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 is formed by thermally decomposing hydrocarbons in the gas phase to form a metal base. The interplanar spacing of the 002 plane (
d002) 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 or less, a
Crystallite thickness (La) in the axial direction is 100 Å or more and 400 Å
1. A non-aqueous electrolyte secondary battery, characterized in that it is made of the following carbon material, the surface of which has been subjected to plasma treatment in an oxygen atmosphere, and further has 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 of at least one selected from the group consisting of iron, nickel, and cobalt.