JPH0251220B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a battery active material with improved discharge characteristics, which is made of a specific graphite fluoride.

As fluorinated graphite obtained by fluorinating graphite, those represented by the formula (CF) n and those represented by the formula (C ₂ F) n have been confirmed so far, and they can also be used in compositions containing both. It is also known to exist in the form of However, there are still many aspects of its reality that are unclear. It is well known that this fluorinated graphite has excellent properties as a battery active material, as described below.

For example, in Japanese Patent Publication No. 48-25565, solid graphite fluoride (CFx) is used as a positive electrode active material for batteries.
(However, 0.5≦x≦1) In particular, by using graphite fluoride, where x is 1 or close to 1, it has a high utilization rate as an active material, has excellent voltage flatness, and has a high energy density with a good shelf life. It is described that it provides a primary battery.

Furthermore, JP-A _- 53-102893 discloses a novel graphite fluoride (hereinafter referred to as
Simply referred to as (C ₂ F)n) and its manufacturing method are described, and this (C ₂ F)n does not show an increase in fluorine content even after heat treatment in a fluorine atmosphere at 600°C. It has also been suggested that this new (C ₂ F)n can be used as a battery active material. Furthermore, in JP-A No. 55-28246, it is reported that (C ₂ F)n exhibits a higher discharge potential than graphite fluoride (hereinafter simply referred to as (CF)n) represented by the above formula (CF)n. Are listed.

Furthermore, Japanese Patent Application Laid-Open No. 57-84570 discloses that by mixing (CF)n and (C ₂ F)n and using it as a positive electrode active material of a battery, the voltage at the early stage of discharge, which is a problem with (CF)n, can be reduced. It has been proposed that temporary deterioration can be improved, and Japanese Patent Application Laid-Open No. 16468/1983 describes a battery active material whose main component is (C ₂ F)n, which is obtained by reacting artificial graphite with fluorine. In a preferred embodiment, artificial graphite as a raw material is reacted with fluorine until there is no increase in the weight of the product.

Battery active materials based on (C ₂ F)n have been described and have been shown to exhibit high discharge potentials.

The present inventors conducted various studies on the production process of fluorinated graphite, and found that in the fluorination reaction of graphite with fluorine, the first reaction stage in which unreacted graphite remains in the reaction product; a second reaction stage in which the fluorination reaction proceeds despite the absence of unreacted graphite in the product, resulting in an increase in the weight or fluorine content of the reaction product;
There are three reaction stages: and a third reaction stage, in which no increase in weight or fluorine content is observed in the reaction product even if the fluorination reaction is progressed, and the crystallinity is mainly thought to be increased. It was found that all of the fluorinated graphite described in the directions were almost at the third reaction stage. The present inventors further researched the characteristics of the graphite fluoride obtained in each reaction step as a battery active material, and found that the graphite fluoride obtained in the second reaction step was obtained in the third reaction step. We discovered the surprising fact that the discharge potential is 100 to 200 mV higher than that of graphite fluoride, and in particular, in the above-mentioned Japanese Patent Application Laid-Open No. 16468/1983, we discovered the surprising fact that there is a region that shows a higher discharge potential in a range that deviates from the preferred embodiment. The invention was completed.

That is, the present invention provides fluorinated graphite obtained by fluorinating graphite, which (1) contains substantially no unreacted graphite, and (2) when it is refluorinated with fluorine, the product The present invention relates to a battery active material that satisfies the condition that an increase in weight or an increase in fluorine content is observed in the battery active material.

It was discovered for the first time by the present inventors that the graphite fluorination reaction product has a unique fluorinated graphite region such as the second reaction stage that satisfies such conditions. , and the conventional first
It differs from the fluorinated graphite obtained in the reaction step and the third step in the above points (1) and (2).

That is, the battery active material of the present invention is one in which no peak of unreacted graphite (diffraction angle 2θ of the (002) plane is around 26.5 degrees) is observed when analyzed by powder X-ray diffraction. Free fluorine is occluded in the fluorinated graphite of the first reaction stage in which unreacted graphite remains, and although the discharge potential is high, the free fluorine causes damage to the performance of the battery. There are cases where practical problems remain as battery active materials.

Furthermore, when the battery active material of the present invention is subjected to a fluorination reaction with fluorine, an increase in weight or an increase in fluorine content is observed in the product.

Note that in this specification, weight increase is approximately 1%.
(wt%, the same applies hereinafter) or more, preferably 3% or more, and the increase in fluorine content is about 0.5% or more, preferably 1.5% or more.
% or more.

The conditions for the fluorination reaction with fluorine to observe the weight increase or increase in fluorine content are the same reaction temperature, pressure, and fluorine concentration as those used in the production of fluorinated graphite in the present invention. be done.

One possible reason why an increase in weight or fluorine content is observed when the battery active material of the present invention is re-fluorinated is due to the conventionally known so-called stabilization state (C ₂ F). This is presumed to be due to the presence of a new (C ₂ F) n in a so-called transition state that can change from (C ₂ F) n to (CF) n, unlike n. Further, the improvement in the discharge potential in the present invention is achieved by (C ₂ F) in the transition state.
This is thought to be due to the presence of n, and the reason why the discharge potential of conventional graphite fluoride is lower than that of the present invention is thought to be that the (C ₂ F)n contained therein is in a stabilized state. .

The battery active material of the present invention has a fluorine content of 48 to 58%,
In particular, 50 to 56% of the fluorinated graphite is preferred. Although the lower limit of fluorine content of 48% is not an important limit in relation to the discharge voltage,
When it is less than %, it is generally undesirable because free fluorine is occluded in the reaction product. When it exceeds 58%, the desired effect of improving the discharge voltage cannot be obtained.

The battery active material of the present invention has a diffraction angle (2θ) of the (001) plane in powder X-ray diffraction based on the graphite fluoride portion.
A peak appears at 9.9 to 14.5 degrees, and in some cases a peak or shoulder indicating (C ₂ F)n may appear around 10 degrees.

Examples of the raw material graphite used in the present invention include natural graphite, artificial graphite, and artificial scaly graphite (for example, XS series, T series, etc. manufactured by Rozan Co., Ltd.).

The battery active material of the present invention is usually produced by fluorinating raw material graphite with fluorine gas (the fluorine gas is mixed with a diluent gas if necessary), but is not particularly limited thereto.

Fluorine gas or a mixed gas of fluorine gas and diluent gas is introduced into the reactor at room temperature so that the partial pressure of fluorine gas is 0.1 to 1 atm. The temperature is gradually raised from room temperature until the desired reaction temperature, i.e.
Store at 300-500°C, preferably 300-450°C.

The fluorination reaction for producing the battery active material of the present invention is carried out in advance under the same conditions, and the reaction time from the start of the reaction until the time when unreacted graphite ceases to exist and the amount of graphite produced is determined. Check the reaction time until no increase in the fluorine content or weight of the product occurs, and either stop the reaction during the re-reaction time or sample the product at regular intervals. The sample should be separately examined for the presence of unreacted graphite by powder X-ray diffraction, and the fluorination reaction can be performed under the same conditions to check for an increase in weight and fluorine content, and then the reaction can be stopped. .

The reaction time varies depending on the crystallinity of the raw material graphite, particle size, fluorine gas pressure, reaction temperature, etc., but is usually 15 to 100 hours at a reaction temperature of 380°C. This reaction time is 1/2 to 1/10 of the conventional reaction time of 100 to 200 hours at the same temperature when producing fluorinated graphite, and production efficiency can be greatly improved.

The raw material graphite is preferably degassed at the normal reaction temperature to remove moisture.

As the diluent gas to be mixed with the fluorine gas, a gas that does not react with fluorine and graphite is used. Specific examples include nitrogen gas, perfluorocarbon, rare gas, and the like.

An electrode material can be obtained by blending a binder and a conductive material with the battery active material of the present invention. Their blending ratio is 10 parts of fluorinated graphite (by weight, the same applies hereinafter), 1 part of binder.
-4 parts, preferably 0.5-2 parts of the conductive material.

Examples of the binder include polytetrafluoroethylene (PTFE), and examples of the conductive material include highly conductive carbon black such as acetylene black and Kettien black, or natural graphite.

When the battery active material of the present invention is used in a battery, it is preferable to use the battery active material of the present invention as a positive electrode and to use, for example, lithium, magnesium, calcium, aluminum alone or an alloy containing these as main components for the negative electrode. Although it depends on the type of negative electrode used as the electrolyte, a non-aqueous electrolyte is usually used.

Next, the battery active material of the present invention will be explained with reference to Examples, but the present invention is not limited to these Examples.

Example 1 and Comparative Example 1 10.0 g of artificial graphite (average particle size 15μ) was placed in a reactor and degassed at 380°C for 30 minutes to remove water.
Cooled to room temperature.

Next, fluorine gas (90%) was introduced into the reactor at 1 atm, the temperature was raised to 380°C, and the reaction was carried out for 16 hours. The product was a dark brown powder with a fluorine content of 52.8% and a weight of 21.1 g. When this material was analyzed by powder X-ray diffraction, no diffraction lines based on graphite were observed, and the diffraction angle of the (001) plane was
A peak appeared at 10.54 degrees at 2θ (hereinafter simply referred to as θ).

Furthermore, 10.00 g of this product was taken and subjected to the fluorine modification reaction again under the same conditions, and the weight was 10.33 g 114 hours after the start of the fluorine modification reaction.
A product with a fluorine content of 54.5% (weight increase of 3.3%) and a peak at 10.90 degrees of 2θ was obtained. No increase in weight or fluorine content was observed even when fluorination reactions were carried out thereafter. The product obtained after 114 hours is referred to as the fluorinated graphite of Comparative Example 1.

Then, 10 parts of these products, 3 parts of PTFE, and 1 part of acetylene black were thoroughly kneaded and pressed onto a nickel mesh to prepare a positive electrode with a surface area of 1.57 cm ² . The negative electrode used was a lithium block cut out with a surface area of 1 cm ² and a thickness of 1 mm and held in a nickel mesh, and the electrolyte was a 1 mol/gamma-butyrolactone solution of lithium borofluoride. The discharge voltage was measured at 25°C with a constant resistance discharge of 10KΩ. Figure 1 shows the change in terminal voltage obtained over time.

Example 2 and Comparative Example 2 Artificial graphite (average particle size 20μ) 10.0 as raw material graphite
The fluorination reaction was carried out under the same conditions as in Example 1 except that g was used, and the reaction was stopped after 16 hours to obtain a battery active material of the present invention. This product was a blackish brown powder, no unreacted graphite was observed, the fluorine content was 51.8%, and the weight was 20.7g. When this material was analyzed by powder X-ray diffraction method, no diffraction lines based on graphite were observed, and at 2θ, 11.41
A peak appeared.

Furthermore, when 10.00 g of this was taken and the fluorination reaction was carried out again under the same conditions, the weight was 10.30 g (3.0% weight increase) 113 hours after the start of the re-fluorination reaction.
The fluorine content is 54.0% (the fluorine content increases by 2.2
%) and having a peak at 11.59 degrees 2θ was obtained. No increase in weight or fluorine content was observed even when fluorination reactions were carried out thereafter. The product obtained after the 113 hours was referred to as fluorinated graphite of Comparative Example 2.

Batteries were produced in the same manner as in Example 1 using the products obtained in Example 2 and Comparative Example 2, and changes in terminal voltage over time were measured. The results are shown in Figure 2.

Example 3 and Comparative Example 3 Natural graphite (average particle size 10μ) 10.0 as raw material graphite
The fluorination reaction was carried out under the same conditions as in Example 1 except that g was used, and the reaction was stopped after 17 hours to obtain a battery active material of the present invention. This product was in the form of a blackish brown powder, no unreacted graphite was observed, the fluorine content was 49.5%, and the weight was 19.8g. When this material was analyzed by powder X-ray diffraction, no graphite-based diffraction lines were observed, and 10.41
A peak appeared.

Further, 10.00 g of this was taken and the fluorination reaction was carried out again under the same conditions. 110 hours after the start of the reaction, the weight was 10.36 g (3.6% increase in weight) and the fluorine content was 51.5% (increase in fluorine content. 2.0%) and a peak at 10.10 degrees 2θ was obtained. No increase in weight or fluorine content was observed even when fluorination reactions were carried out thereafter. The product obtained after the 110 hours was referred to as fluorinated graphite of Comparative Example 3.

Batteries were produced in the same manner as in Example 1 using the products obtained in Example 3 and Comparative Example 3, and changes in their terminal voltages over time were measured. The results are shown in Figure 3.

As is clear from FIGS. 1 to 3, the battery active material of the present invention exhibits a higher discharge potential than that obtained in the third reaction stage.

[Brief explanation of drawings]

Figures 1 to 3 show changes over time in terminal voltage of batteries using the battery active materials obtained in Example 1 and Comparative Example 1, Example 2 and Comparative Example 2, and Example 3 and Comparative Example 3, respectively. It is a graph.

Claims (1)

[Scope of Claims] 1. Fluorinated graphite with a fluorine content of 48 to 58% by weight, which is obtained by fluorinating graphite with fluorine, and (1) it does not substantially contain unreacted graphite. (2) satisfies the condition that when it is fluorinated again under the same reaction temperature, pressure, and fluorine concentration conditions as in the fluorination, an increase in weight or fluorine content is observed in the product; Characteristic battery active materials.