JPS58133764A - Manufacture of positive electrode for organic electrolyte battery - Google Patents

Abstract

PURPOSE:To obtain a battery with improved electric-discharge characteristic and preservation characteristic by using a carbon fluoride as a main active material, and mixing a specified carbon into said main active material. CONSTITUTION:A thin battery is constituted by using a negative lithium electrode 2, a separator 3 made of a non-woven polypropylene fabric, and a resin gasket 4. A positive pellet 5 for such a battery is prepared by mixing carbon with a specific surface area of over 500m<2>/g into a carbon fluoride containing a large amount of fluorine with a weak binding strength, and subjecting the mixture to heat treatment at 200-400 deg.C. As a result, the electric-discharge voltage of the battery can be maintained high, and the preservation characteristic of the battery can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a positive electrode for an organic electrolyte battery in which carbon fluoride is used as the main active material and carbon is mixed therein.
The purpose is to provide FM batteries with good discharge and storage characteristics. Carbon heptide, which is produced by directly fluorinating a carbon cylinder, is (11 Polycarbon monofluoride).
(OF)n(21Po1yt@tracarb
onmonofluoride (04F)n 21
4 was known, but recently, a new formula % has been discovered (Japanese Patent Application Laid-Open No. 102893/1983). This (02F)n, like (CF)n and (04F)n, is known to be useful as a positive electrode active material for organic electrolyte batteries (Japanese Unexamined Patent Publication No. 66-28246).

(02F)n has various properties compared to (OF)n. For example, (02F)n is a 2nd stage compound, and the interlayer distance is (OF)n. It has a larger value of about 9 mu0 compared to about 6 mu0, and its electrochemical properties are also different. In general, (02F)n has a feature that the discharge voltage is higher than that of (OF)n, but the flatness of the voltage tends to be slightly inferior compared to (CF)n.

Carbon fluoride, both (CF)n and ((lj2F)n, has different characteristics as a positive electrode active material for lithium batteries depending on the raw material carbon and manufacturing conditions. Although the voltage at the initial stage of discharge is high, the flatness of the voltage is Unfortunately, the voltage may gradually drop due to discharge.In this case, the utilization rate of discharge is also poor, and the capacity deterioration after high temperature storage is also poor.The high voltage part at the beginning of this discharge is mainly caused by fluoride. This is thought to be due to a discharge reaction of fluorine, which has a weak bonding force, contained in carbon.Fluorine, which has a weak bonding force, is not only caused by adsorption and occlusion of fluorine molecules or atoms, but also by chemical and electrical reactions. It is considered to be chemically active fluorine.For example, when activated carbon with a large specific surface area is brought into contact with fluorine at room temperature, fluorinated activated carbon can be obtained by chemical adsorption.If this is combined with lithium, fluorinated activated carbon can be obtained. Although a high discharge voltage can be obtained by constructing a battery, the flatness of the voltage is poor, and furthermore, if it is stored in an organic solution, the discharge capacity will be greatly reduced due to self-discharge.Also, if it is left in the air, Similarly, fluorine is liberated. However, if activated carbon is reacted with fluorine at an appropriate temperature range, stable fluorinated carbon containing almost no fluorine, which has a weak bonding force as described above, can be obtained.

The present inventors mixed carbon with a specific surface area of 500rn"7g or more, such as activated carbon or carbon black, into fluorinated carbon containing a large amount of fluorine, which has a weak bonding force, and thereby maintained a high discharge voltage. It was discovered that the storage properties could be improved.

Hereinafter, fluorocarbon ((32F)n) will be taken as an example and explained in detail with reference to Examples.

FIG. 1 shows a flat battery used for evaluation. 1 is a sealing plate, 2 is a lithium negative electrode, 3 is a separator made of polypropylene nonwoven fabric, and 4 is a resin gasket. 5 is a positive electrode mixture pellet with a diameter of 14 mm and a thickness of 0.60 mm;
6 is a positive electrode current collector, and 7 is a case. The electrolyte has a volume ratio of propylene carbonate and dimethoxyethane of 1:1.
Lithium fluoroborate was dissolved at a concentration of 1 mol/l in a mixed solvent.

The positive electrode pellet 6 is made of fluorocarbon (CI) n1o.

Add 10 parts by weight of carbon having a known specific surface area to the parts by weight, mix well, leave the mixture as it is, add 6 parts by weight, knead well, and then dry.

It is molded.

All battery characteristics evaluations were conducted at 2'O'C and 6 Ω constant resistance discharge, and the discharge capacity was calculated with a final voltage of 2.4V.

Figure 2 shows a mixture of (02F)n and carbon at 200%
The relationship between the discharge capacity and the specific surface area of carbon in this mixture when heat treated for 2 hours at
This is shown after storage at 0'C and 1 month.

Carbon with a specific surface area of 80 mVg is the one used in the conventional example, acetylene black, but the discharge capacity immediately after battery assembly is also greater when using carbon (activated carbon, etc.) with a specific surface area of 500 mVg or more. When stored at 1go℃ for 1 month, the conventional example shows a large degree of deterioration in volume, but when carbon with a specific surface area of 6oom2/g or more is used, the deterioration in volume is small, and most of the time, immediately after assembly. Similar capacity is obtained.

As is clear from FIG. 2, there is a correlation between the discharge capacity and the specific surface area of the mixed carbon, and #1, which has a large specific surface area, has a large discharge capacity. Moreover, this tendency becomes more pronounced after storage at 60° C. for 1 month.

Examples of carbon that have a similar specific surface area include activated carbon and carbon black.In particular, Furnace Black manufactured by Akzo Corporation in the United States has a large specific surface area of 700 to 1000mVg, and its conductivity is higher than that of acetylene black, a conventional conductive material for dry batteries. This is about the same level, which is preferable as an embodiment of the present invention.

Figure 3 shows fluorocarbon (CzF)n and specific surface area 700m
After mixing the carbon of zog, the heat treatment temperature of this mixture and 2
The relationship between the terminal voltage after 60 hours of sKΩ discharge at 0°C is shown immediately after assembly and after storage at 60°C for 1 month. Immediately after assembly, the terminal voltage was around 2.86V in all cases, and there was no difference due to the treatment temperature, but after storage at 60℃ for 1 month, the terminal voltage was 2.86V for the mixtures heat-treated at 200℃ or higher. The difference is small compared to .83 to 2.84V immediately after assembly, but when the mixture was left at room temperature (26°C) and 110°C, it was 2.78V, respectively.

It can be seen that the voltage has dropped significantly compared to 2.8V immediately after assembly, indicating that the deterioration due to storage has been significant.

FIG. 4 shows one of the embodiments of the present invention and a conventional battery of 20
A comparison was made by discharging at 5Ω at ℃. After mixing carbon with a specific surface area of 700 m''7g with (CzF)n,
This is a discharge curve of a battery in which the positive electrode mixture was heat-treated at 00'C for 2 hours and a binder was added thereto. B is a discharge curve of a battery of a conventional example in which acetylene black was mixed with (02F)n and then a binder was immediately added to prepare a positive electrode mixture.

In addition, the 60"l of the batteries Mu' and B't1, respectively,
: is a discharge curve after storage for one month.

As is clear from Figure 4, both M and A' are B.

The discharge voltage is higher than that of B', the voltage flatness is also good, and the discharge capacity is also comparable. Furthermore, conventional example Bit, 6
While the degree of deterioration after storage at 0°C and one force (B') was large, the degree of deterioration after storage at 0°C was 60'C.

Even after 1 Rikizuki's existence (A'), there are almost the same special provisions as at the beginning.
It can be seen that the storage properties at high temperatures are also greatly improved.

As described above, according to the present invention, carbon fluoride (CzF)
The discharge N voltage of a battery using n as the main active material for the positive electrode is:

In addition, fluorocarbon (OF)n and (OF)n and (CzF
)n mixtures also provide similar effects for the following reasons.

That is, as can be seen from Figure 2, by mixing carbon with a specific surface area of s o Orn''/g or more into (02F)n, the discharge capacity is increased and the storage characteristics are improved, and as can be seen from Figure 3 ( Improvement in storage properties by heat treatment at a temperature of 200° C. or higher after mixing 02F)n and carbon having a large specific surface area can be considered as follows.

In general, it is known that the structure, physical properties, and electrochemical properties of fluorocarbon vary greatly depending on its raw material carbon and manufacturing conditions. In some cases. (02
F)n tends to contain a relatively large amount of adsorbed and occluded fluorine, as well as chemically and electrochemically active fluorine, that is, fluorine with weak binding strength. This means that the amount of fluorine, which has the oxidizing power to liberate iodine from potassium iodide, is determined by iodometry to be
It is clear from the fact that there are many cases where the number is one to several times higher than 1.
By the way, the 7 atoms with weak bonding strength contained in this strong fluorocarbon not only react with the IF electrode current collector or electrolyte in a self-discharge manner during discharge and storage, and are also consumed. It is conceivable that the internal resistance of the battery will increase, and therefore the discharge capacity will also decrease.

However, for example, when (02F,)n is mixed with carbon having a large specific surface area, the weakly bonding fluorine contained in (C2F)n reacts with potassium iodide. Since it is adsorbed and fixed, it is in a more stable state and has good conductivity, so +l': It is thought that the discharge capacity increases because it is constantly discharged. Furthermore, assuming that the mixing ratio of fluorocarbon and carbon is constant, it is naturally desirable that carbon has a large specific surface area and a large absorption capacity; as is clear from the above, the specific surface area is so
H) It is useful to mix t7g or more of carbon.

Further, it is desirable that the carbon to be mixed has good conductivity, but even carbon with poor conductivity can be solved by mixing it with carbon having good conductivity, as long as it has a large specific surface area.

Next, by heat-treating the mixture of (02F)n and carbon at a temperature of 200°C or higher, the storage properties are improved.By heat-treating the fluorine adsorbed and fixed on carbon, it becomes more stable and strong. At the same time, it is thought that this is to more completely adsorb and fix fluorine contained in (02F)n, which has a weak bonding force, to carbon, thereby stabilizing it. If the fluorine is simply mixed, the fluorine adsorbed and fixed on carbon will be liberated again during storage and react with the positive electrode current collector and electrolyte, increasing the internal resistance of the battery and deteriorating the discharge characteristics. It is thought that by heat-treating a mixture of carbon and carbon at 200° C. or higher, fluorine in carbon can be further stabilized and deterioration due to storage can be reduced. Alternatively, it is also possible that part of the carbon, such as activated carbon or carbon black, which has a large specific surface area, is fluorinated using fluorine, which has a weak bonding force and is contained in fluorinated carbon, as a fluorine source.

Therefore, the temperature range for heat treatment of the mixture must be within a range in which fluorocarbon made from activated ash or the like is stable.

The temperature at which fluorocarbon starts to decompose using activated carbon, etc. as a raw material is:
Since the temperature is approximately 350 to 400°C, the processing temperature range of the mixture is preferably 200°C or higher (400'C Lido 75), more specifically, the temperature at which the fluorocarbon starts to decompose from the carbon to be mixed is the starting temperature.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal cross-sectional view of a flat battery according to an embodiment of the present invention, and Fig. 2 shows the relationship between the specific surface area of the positive electrode mixed carbon and the discharge capacity I11°, immediately after assembly and after storage at 60 liters for one month. later! 1; Figure 3 is a graph showing the relationship between processing temperature and terminal voltage after mixing carbon and (CzF)n, immediately after assembly and after 1 month at 60°C. Figure 4 is a graph showing the relationship between the processing temperature and terminal voltage after mixing carbon and (CzF)n. 1 is a graph showing a comparison of discharge characteristics of batteries according to an embodiment of the invention and a conventional example. 1... Sealing plate, 2... 9 poles, 3...
...Separator, 6...Positive electrode, 7...
·Case. Name of agent: Patent attorney Toshio Nakao and 1 other person11
Figure 2 Specific surface area of the Ministry of Industry and Trade (Layer Shiba 3) I envy! L c-c> No. 41Xl Poem 4ft-1187IQ (&s>

Claims (1)

[Claims] A method for producing a positive electrode containing carbon using fluorocarbon as a living material, in which carbon has a specific surface area of 500 rn'/g or more, and a mixture of this carbon and fluorocarbon is
A method for producing a positive electrode for an organic electrolyte battery, characterized by comprising a step of heat treatment at a temperature of 00°C.