JPH04112455A - Secondary battery - Google Patents

Abstract

PURPOSE:To provide a secondary battery having less decrease in the capacity due to self-discharging, less decomposition of electrolyte when storing Li, suppressed generation of gas, and excellent cycle characteristics by using a neg. electrode material chiefly containing a carbonic substance which occludes and emits alkali metal ion or alkali earth metal ion. CONSTITUTION:A neg. electrode 1 chiefly containing carbonic substance is contacted by pressure to a neg. electrode electricity collector 3 secured to the inner bottom surface of a neg. electrode can 2. A pos. electrode 4 is made by molding a black mix of a fluoric resin binder and acetylene black conductivity agent with a Mn oxide as active substance being in pressure contact with the inner bottom surface of the pos. electrode can 5. Examples of neg. electrode material are a carbonic substance obtained through heat treatment of alkali metal, alkali earth metal, or salt of these metals and carbonic material, or a carbonic substance obtained through alkali treatment. Thereby a secondary battery is accomplished having less self-discharge and less leakage of solution due to gas generation resulting from decomposition of the electrolytic solution.

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to a negative electrode having an alkali metal such as lithium or an alkaline earth metal as an active material, and manganese dioxide, molybdenum trioxide, vanadium pentoxide. , relates to a secondary battery equipped with a positive electrode made of titanium sulfide or the like as an active material.

(b) Conventional technology This type of battery has an extremely short charge/discharge cycle life because lithium, which is the negative electrode active material, grows in a dendritic manner on the surface of the negative electrode during charging and comes into contact with the positive electrode, causing internal short-term termination. There is a problem.

As a countermeasure against this problem, the negative electrode may be made of a lithium alloy, or a graphite intercalation compound containing lithium in the crystal, which is doped and dedoped by charging and discharging, may be used as the negative electrode material (for example, see Japanese Patent Publication No. 60-23433). ), using an n-doped carbon material having a predetermined crystal thickness and true density (see JP-A-62-90863),
A method using a carbon material such as coke in which lithium is occluded has been proposed (see Japanese Patent Laid-Open No. 62-90863).

In particular, if the negative electrode is made of a compound of carbon material and lithium, the charge/discharge cycle characteristics of the secondary battery will be dramatically improved. On the other hand, in a battery whose negative electrode is a material in which lithium is doped or occluded in a carbon material, if left uncharged, the capacity decreases significantly due to self-discharge, and this decrease in capacity causes the cycle to repeat. However, the problem is that it does not recover. Furthermore, in Notium secondary batteries that use carbon materials as negative electrode materials, the activity of the carbon materials is high;
When lithium is occluded in a carbon material, there are problems such as the electrolyte reacts with the carbon material and decomposes, generating gas, increasing the internal pressure of the battery, and causing leakage.

(c) Problems to be solved by the invention The present invention has been made in view of the above problems, and includes:
It is an object of the present invention to provide a secondary battery with excellent cycle characteristics, in which the capacity decrease due to self-discharge is small, and gas generation is suppressed due to little decomposition of the electrolytic solution when notium is occluded.

(d) Means for Solving the Problems In the secondary battery of the present invention, the negative electrode material is mainly composed of a carbon material that electrochemically absorbs and releases alkali metal ions or alkaline earth metal ions. The carbon material is characterized in that it has been subjected to alkali treatment or heat treatment.

The carbon material is preferably one that has been heat-treated with an alkali metal, an alkaline earth metal, or a salt of these metals.

As this carbon material, carbon black, coke, graphite, etc. can be used.

(E) Function According to the present invention, a carbon material obtained by heat-treating an alkali metal, an alkaline earth metal, or a salt of these metals and a carbon material, or an alkali-treated carbon material can be used as a negative electrode material. By using it as a negative electrode material, it is possible to provide a secondary battery with less self-discharge and less leakage due to gas generation due to decomposition of the electrolytic solution. The reason for this is that carbon generally has a crystal structure in which carbon atoms are mainly bonded in a hexagonal shape, but the hexagonal structure cannot be maintained at the ends of the bonds, and the carbon atoms at the ends are air-filled. It easily combines with oxygen and moisture inside, forming hydroxyl groups (COH) and carbonyl groups (
COOI().

Since these functional groups have high activity, they may react with the electrolyte and decompose it, or the lithium occluded in the carbon material may react with these functional groups during charging, causing self-discharge. . Therefore, it is necessary to reduce the activity of these functional groups in advance. That is, by substituting the hydrogen atom of the functional group with a lithium atom, the activity of the carbon material against decomposition of the electrolytic solution can be lowered, and the decomposition of the electrolytic solution can be suppressed. Furthermore, since the reaction of these functional groups with lithium can be suppressed, a secondary battery with less self-discharge can be provided.

(f) Example FIG. 1 shows a longitudinal sectional view of the battery of the present invention. In FIG. 1, reference numeral 1 denotes a negative electrode mainly composed of a carbon material, which is the gist of the present invention (specific examples of fabrication will be described later), and a negative electrode current collector 3 fixed to the inner bottom surface of a negative electrode can 2. It is crimped. 4 is a positive electrode, which is made by molding a mixture of manganese oxide as an active material, an acetylene black conductive agent, and a fluororesin binder in a ratio of 8:10:10 (weight ratio), respectively. It is pressed against the inner bottom surface of the positive electrode can 5. 6 is a separator made of polypropylene nonwoven fabric, and this separator 6 is composed of propylene carbonate and 1
．． A non-aqueous electrolytic solution containing 1 mol/l of lithium perchlorate dissolved in an equal volume mixed solvent with 2-dimethoxyethane is impregnated. 7 is an insulating backing that insulates the positive and negative electrode cans, and the battery dimensions are 25 mm in diameter and 3.0 mm in thickness.

Next, an example of producing a negative electrode will be described in detail.

(Preparation example 1) Lithium hydroxide and coal-based pitch coke in a weight ratio of 1
:99 and calcined at the temperature shown in Table 1 to produce a composite powder of carbon and lithium salt.

Infrared spectroscopy analysis of this starting material, coal-based pitch coke, and the powder produced by firing at 400°C using the above method revealed that hydrogen in the hydroxyl and carbonyl groups in carbon had been replaced with lithium. That's what I found out.

Furthermore, when the ratio of carbon to hydrogen to lithium in these carbon materials was measured, it was found that most of the hydrogen in the carbon was replaced by lithium.

A mixture prepared by mixing ethylene rubber as a binder at a ratio of 90:10 (volume ratio) to the composite material of carbon material and lithium salt prepared in this way was applied at a pressure of 1.5 t/cm''. Pressure molded. Diameter 20mm, thickness 1.0
An electrode made of a carbon material with a diameter of 1 mm was obtained.

A battery prepared using the electrode obtained in this way as a negative electrode,
Batteries of the present invention A1 to A6 and comparative batteries X1 and X2.

Table 1 shows the invention battery Al-A6, comparative batteries X1 and X2.
The heat treatment temperature is shown below.

(Margins below) Table 1 The battery characteristics of the batteries 1 to A6, Xl, and X2 produced in this way were compared.

Figure 2 shows batteries A1 to A6 of the present invention, comparative batteries X1 and X2.
FIG. 3 is a diagram showing the cycle characteristics of the battery and the remaining capacity of the battery after being stored at room temperature for one month. Here, the battery charging and discharging conditions are: discharge to 2V at a discharge current of 3mA, and charge at 3mA to 3V.
．． The end was 5V.

In addition, Table 2 shows the battery A of the present invention after storage at 60°C for one month.
1 to A6, and the occurrence of leakage in comparative batteries X1 and X2.

Table 2 I found out that

Batteries of the present invention B1 to B
5. Comparative batteries Yl and Y2.

Table 3 (Preparation Example 2) Coal-based needle coke is immersed in a potassium hydroxide aqueous solution of various concentrations, treated with alkali, passed through a r-filter, and dried thoroughly to replace hydrogen in hydroxyl groups and carbonyl groups with potassium. A carbon material was obtained. When this carbon material was dispersed in water and its pH value was measured, the values shown in Table 3 were obtained.

In addition, when the carbon material of pi (8) was analyzed by infrared spectroscopy, it was found that the hydrogen of the hydroxyl group and carbonyl group in the carbon material was replaced with potassium. The battery characteristics of the two were compared.

Figure 3 shows the batteries B1 to B5 of the present invention and comparative batteries Y1 and Y2.
FIG. 3 is a diagram showing the cycle characteristics of the battery and the remaining capacity of the battery after being stored at room temperature for one month.

In addition, Table 4 shows the battery B of the present invention after storage at 60°C for one month.
]~B5 shows the occurrence of leakage in comparative batteries Y1 and Y2.

Table 4 Table 5 (Production Example 3) Lithium hydroxide was mixed with coal-based needle coke as shown in Table 5, and then fired at 400°C to produce carbon materials containing lithium at various concentrations. Batteries produced in the same manner as in Production Example 1 except for using this carbon material were used as inventive batteries C1 to C5 and comparative batteries Z1 and Z.
Set it to 2.

Table 5 shows the batteries C1 to C5 of the present invention and comparative batteries Z1 and Z2.
The mixing ratio of lithium hydroxide and carbon material used in is shown below.

The battery characteristics of the batteries C1 to C6, Zl, and Z2 produced in this way were compared.

Figure 4 shows the batteries 01 to C5 of the present invention and comparative batteries Z1 and Z2.
FIG. 3 is a diagram showing the cycle characteristics of the battery and the remaining capacity of the battery after being stored at room temperature for one month.

In addition, Table 6 shows the battery of the present invention after storage at 60°C for 1 month.
1 to C5, which shows the occurrence of leakage in comparative batteries Z1 and Z2.

(Margin below) Table 6 (Summary) As is clear from these Figures 2 to 4, Table 2, Table 4, and Table 6, batteries A1 to A6, B1-B of the present invention
It can be seen that Samples No. 5 and C1 to C5 have excellent cycle characteristics and less occurrence of self-discharge and leakage. The reason for this is that hydrogen in hydroxyl groups and carbonyl groups in the carbon material is replaced with lithium, potassium, etc., and the activity of these parts decreases. As a result, decomposition of the electrolyte can be suppressed, so gas generation due to decomposition of the electrolyte and leakage of the battery caused by this can be suppressed. In addition, charging makes it difficult for the lithium occluded in the carbon material to react with these functional groups.
Decrease in capacity due to self-discharge can also be suppressed.

Furthermore, it can be seen that in Preparation Example 1, the firing temperature of the lithium salt and carbon material is preferably 150° C. or more and 1500° C. or less. The reason for this is that at temperatures lower than 150°C, the reaction between the lithium salt and the carbon material does not proceed sufficiently, and the hydrogens in the hydroxyl and carbonyl groups in the carbon material are not replaced with alkali metals, which reduces the activity of these functional groups. It is considered that it cannot be lowered. On the other hand, if the temperature exceeds 1500°C, the crystal structure of the carbon material itself changes, and it is considered that it becomes difficult to absorb lithium electrochemically.

In addition, from Preparation Example 2, the pH when dispersed in water was
It can be seen that carbon materials having a value of 6 or more and 10 or less have excellent performance as negative electrode materials for secondary batteries. The reason for this is that when the pH value is low, the hydrogens of the hydroxyl groups and carbonyl groups in the carbon material are not sufficiently substituted with alkali metals, and therefore the activity of these functional groups cannot be reduced. On the other hand, in a carbon material having a high pH value, there is a large amount of unreacted alkali metal salt attached to the carbon material, which is thought to cause decomposition of the electrolytic solution and deteriorate the characteristics.

Furthermore, for the same reason, the weight ratio of the carbon material and the lithium salt was 0.05:99.95.8 in Preparation Example 3.
:92 is considered good.

In this example, a flat battery was used as an example, but it goes without saying that similar effects can be obtained with a cylindrical battery.

Further, in this example, coal-based pitch coke and coal-based needle coke are exemplified as carbon materials, but other carbon materials such as petroleum-based coke, activated carbon, graphite, expanded graphite, carbon black, and various organic compounds may also be used. Any carbon material such as a thermal decomposition product or carbon fiber may be used.

(G) Effects of the Invention As detailed above, according to the present invention, a secondary battery is provided which has a small capacity loss due to self-discharge, less electrolyte decomposition, suppresses gas generation, and has excellent cycle characteristics. The industrial value is extremely large.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of a battery of the present invention, and FIG. 2 is a battery A of the present invention.
Figure 3 is a diagram showing a comparison of the cycle characteristics and capacity remaining rate after storage of the battery B1 of the present invention and the comparative batteries X1 and X2.
Figure 4 shows a comparison of the cycle characteristics and capacity remaining rate after storage of ~B5 and comparative batteries Y1 and Y2.
FIG. 3 is a diagram showing a comparison of cycle characteristics and capacity remaining rate after storage of C5 and comparative batteries Z1 and z2. 1... Negative electrode, 2... Negative electrode needle, 3... Negative electrode current collector, 4... Positive electrode, 5... Positive electrode can, 6...
Separator, 7...Insulating backing.

Claims (3)

[Claims] (1) The negative electrode material electrochemically contains alkali metal ions,
Alternatively, a secondary battery comprising as a main component a carbon material that absorbs and releases alkaline earth metal ions, the carbon material being subjected to alkali treatment or heat treatment. (2) The secondary battery according to claim 1, wherein the carbon material is heat-treated with an alkali metal, an alkaline earth metal, or a salt of these metals. (3) The carbon material is carbon black, coke,
The secondary battery according to claim 1, wherein the secondary battery is made of graphite or the like.