JPS6240165A - Secondary battery - Google Patents

Abstract

PURPOSE:To increase the mechanical strength and current collecting ability of electrode by specifying the mixing amount of thermoplastic resin in a secondary battery using a complex comprising a conductive polymer having no conjugated double bond in its principal chain, and thermoplastic resin and conductive material in positive electrode and/or negative electrode. CONSTITUTION:In a secondary battery using a complex comprising conductive polymer having no conjugated double bond in its principal chain, and thermoplastic resin and conductive material in positive electrde and/or negative electrode, the content of the thermoplastic resin is preferably limited to 0.05-0.1 in the weight ratio to the conductive polymer. By specifying the mixing amount of the thermoplastic resin, the mechanical strength of the electrode is increased without sacrifice of conductivity drop before doping. By forming the complex with conductive material, the electrode strength is further increased and current collecting ability is improved.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a secondary battery, and more particularly, to a non-aqueous electrolyte secondary battery using a conductive polymer as an electrode material.

<Prior Art> In recent years, secondary batteries using conductive polymers as electrode materials have been proposed.

Conductive/Hypo1 Tsuma, which is the electrode monthly rate of this type of secondary battery.
usually has little electrical conductivity, or can be doped and doped with various dopants,
Doping dramatically increases conductivity. and,
Conductive polymers doped with anions are used as positive electrode materials, and conductive polymers doped with cations are used as negative electrode materials.
By electrochemically and reversibly performing pinging, a battery that can be charged and discharged is constructed.

Such conductive polymers include those having a conjugated double bond in the main chain, such as polyacetylene, polythiophene,
Polypyrrole and the like have been conventionally known. However, such polymers with conjugated double bonds in their main chains, such as polyacetylene, are very easily oxidized by oxygen in the air, and are susceptible to thermal denaturation and thermal decomposition at temperatures above 300'C. Because of this,
There are drawbacks such as the control of the electrode production environment is important and extremely difficult, the electrode production work is complicated, and the electrode itself has poor storage stability. In addition, when incorporated into a battery, even the slightest presence of moisture can cause denaturation, degrading battery characteristics, and overcharging can cause denaturation of the polymer itself. There are many disadvantages, and there are many problems as a material for battery electrodes.

By the way, recently, conductive polymers that do not have conjugated double bonds in their main chains have been discovered, and their application to electrode materials is being studied. This type of conductive polymer has characteristics such as being stable in the air and not being oxidized, and not being thermally decomposed even at temperatures of 300°C or higher, which makes it difficult to control the environment for electrode production. It is not critical, the manufacturing work is easy, and the electrode itself has a very good shelf life. Therefore, when incorporated into a battery, the polymer is unlikely to deteriorate in the presence of trace amounts of oxygen or moisture, and even if overcharged, there will be almost no alteration and decomposition of the polymer. It has the advantage that there is no performance deterioration and charging and discharging can be repeated over a long period of time.

<Problems to be Solved by the Invention> By the way, as a method for manufacturing practical molded articles of this type of conductive polymer, a method of press-molding a powdered polymer has conventionally been common, but this method does not require mechanical processing. Only molded products with low physical strength can be obtained, and when such molded products are used as electrodes, the cycle life cannot be long, resulting in poor charge-discharge cycle characteristics, and the charge-discharge capacity cannot be increased, resulting in low energy density. , there are problems such as poor voltage flatness during discharge.

In the case of a conductive polymer having a conjugated double bond in the main chain such as polyacetylene, the polymer is made into a composite with a thermoplastic resin or a conductive member as disclosed in JP-A-60-10569. There is a known method for improving characteristics by this method, and it is conceivable to apply this technique to the case where a conductive polymer having no double bond in the main chain is used as an electrode material. However, such conductive raw polymers that do not have conjugated double bonds in their main chains generally have lower conductivity than conductive polymers that have conjugated double bonds in their main chains when undoped or at a low doping rate. Therefore, when adding or mixing thermoplastic resin to increase the mechanical strength of the electrode, if the amount of thermoplastic resin is too large, the conductivity of one electrode will decrease significantly, which will have a major impact on battery performance. There is a strong tendency to .

Additionally, there is a known technique that increases the mechanical strength of an electrode by adding and mixing a thermoplastic resin to an electrode using a metal oxide or metal sulfide, and it is conceivable that this could be applied in the same way as above. Since such intermetallic compounds have higher electrical conductivity than conductive polymers that do not have conjugated double bonds in their main chains, the amount of thermoplastic resin mixed will be different as described above, so this technology cannot be applied as is.

<Means for Solving the Problems> The present inventor has solved the above-mentioned problems, and has improved the cycle characteristics of a conductive polymer that does not have a conjugated double bond in its main chain.
As a result of research aimed at increasing energy density and improving voltage flatness during discharge, it was discovered that the intended purpose could be achieved by using the following means.

That is, the secondary battery of the present invention is a secondary battery in which at least one of the positive electrode and the negative electrode is a composite composed of a conductive polymer having no conjugated double bond in its main chain, a thermoplastic resin, and a conductive member. The battery includes a thermoplastic resin mixed in an amount of 0.005 to 0.005 in terms of ff1M ratio to conductive Bommer.
2, preferably 0.05 to 0.1.

The molecular weight of conductive polymers that do not have conjugated double bonds in the main chain is generally about 10,000 to 500,000,
For example, acenaphthylene polymers such as those having a structural unit represented by the following formula may be mentioned.

In the formula, R1 and R2 represent a water M atom; a halogen atom, such as chlorine, bromine, or iodine; an alkyl group, such as a carbon number of 1 to
6, preferably an alkyl group having 1 to 3 carbon atoms; an alkoxy group, for example, an alkyl group having 1 to 6 carbon atoms, preferably 1 to 3 carbon atoms;
3 alkoxy group; aryl group, for example, phenyl group,
Tolyl group: represents an allyloxy group, such as a phenoxy group, a methylphenoxy group; a nitro group; a cyano group.

Specifically, for example, polyacenaphthylene.

Polybromoacenaphthylene, polychloroacenaphthylene, polyethylacenaphthylene, polydimethylacenaphthylene 2polymethoxyacenaphthylene, polydiphenylacenaphthylene, polyphenoxyacenaphthylene, borini-1 to loacenaphthylene, poly-1-no Examples include cyanoacenaphthylene.

The cough polymer used as the negative electrode in the present invention has, for example, the following general formula (2), where R and R2 have the same meanings as in general formula (1). > by a known method, that is, a method of radical polymerization (Chemical Abstract 55)
Vol., p. 12911 (1961), Method for Cationic Polymerization (Kobunshi Kagaku Vol. 15, 1\o, p. 158.388 (1958), Method for Anionic Polymerization (Polymer Communication Vol. 25, p. 108 (1984))
You can do 1q according to '6.

Furthermore, after obtaining a polymer in which R and/or R2 are hydrogen in the general formula (1) by the above polymerization method, the side chains of the polymer can be prepared by a known method (Journal of Organic Chemistry Vol. 1-48, 2949). Page (1983
) A polymer having a structural unit represented by the general formula (1) in which R1 and/or R2 has a substituent other than hydrogen can be obtained by carrying out a polymer reaction according to (1).

In the radical polymerization reaction of the acenaphthylene compound represented by the general formula (2) described above, an ordinary radical polymerization initiator is used as an initiator, preferably benzoyl peroxide, azobisisobutyro Nitrile, ammonium persulfate, potassium persulfate, etc. are used, and the use of initiators for acenaphthylene compounds is 1
The molar ratio is preferably 0 to 10<-1>. The reaction is carried out without solvent or with benzene.

1 to an organic solvent such as toluene or heptane, or an aqueous solvent based on a water-emulsifier system. If a solvent is used, the acenaphthylene compound is preferably used at a concentration of 10 to 102 molar. The reaction temperature is in the range of 0 to 150'C,
It is preferably carried out at 10 to 100'C. In the cationic polymerization reaction, an ordinary cationic polymerization reaction initiator is used as an initiator, preferably boron trifluoride Nieteller i~, aluminum chloride, aluminum bromide, phosphorus pentafluoride, trifluoromethanesulfonic acid ester, etc. The initiator used for the acenaphthylene compound is preferably carried out in a molar ratio of 10-6 to 1. The reaction is carried out using methylene chloride, carbon tetrachloride, and nitromethane.

1o-2 to 10 in an organic solvent such as dichloroethane
``It is preferable to work within a molar concentration range.

The reaction temperature is 178-100'C, preferably 178-100'C.
It is done at 0'C. In the anionic polymerization reaction, a normal anionic polymerization initiator is used as an initiator, preferably n-butyllithium, 5ec-butyllithium, phenylmagnesium bromide, etc.
The use of initiators for acenaphthylene compounds is 1o-
The molar ratio is preferably 6 to 10<-1>. The reaction is carried out using an ether solvent, preferably diethyl ether, dibutyl ether, or tetrahydrofuran.

It is preferably carried out in dioxane, diphenyl ether, etc., and the acenaphthylene compound is preferably carried out in a range of 10 -2 to 102 molar Q degrees. Reaction temperature is -78~150'C
, preferably at -78 to 100°C.

As the thermoplastic resin, any thermoplastic resin can be used without particular limitation as long as it is substantially insoluble in the electrolyte of the battery.

Generally, materials with a molecular length of 10,000 or more are used, and a specific example is polyethylene.

Polypropylene, ethylene-propylene copolymer, ethylenetetrafluoroethylene copolymer.

Polytetrafluoroethylene, poly1 to reflow ethylene, polydifluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene.

Copolymers, polytrifluorochloroethylene, polyvinylidene fluoride, tetrafluoroethylene-ethylene copolymers, chloro 1-1 nofluoroethylene-ethylene copolymers, polyamides, polyesters, polycarbonate-1 and modified Examples include polyolefins.

In addition, there are no particular restrictions on conductive members if they are made of metals such as stainless steel, gold, platinum, nickel, copper, molybdenum, titanium, etc., carbon, carbon fiber, etc., which do not dissolve even after repeated charging and discharging. However, it is particularly preferable to use a material that is light in weight and highly conductive. Specifically, metal nets made from such metals or metal-plated fibers.

Examples include net woven fabrics and nonwoven fabrics made of metal-deposited fibers, metal-containing synthetic fibers, carbon fibers, carbon composite fibers, and the like.

The amount of the conductive polymer and thermoplastic resin used in the present invention is usually 100 to 5000 parts by weight of the conductive polymer and 1 to 100 parts by weight of the thermoplastic resin per 100 parts by weight of the conductive member.
, selected from the IH Department.

<Function> In this way, by adding the thermoplastic resin mixture No. 2 above to a conductive polymer that does not have a conjugated double bond in its main chain, the electrode strength can be improved without causing a decrease in conductivity when undoped. 8. A conductive member can be combined with these to form a composite; By doing so, the electrode strength can be further improved and the current collecting property of the electrode can be made extremely good.

<Example> Capacity Q 500m, l! Acenaphthylene in a four-sided round bottom flask 20. Take Oq (0,131 mol), 2.0 g of sodium dotesyl sulfate, and 100 mg of demineralized water, replace the system with nitrogen, and add 6.1 nl of ammonium persulfate (]
Add. After maintaining the reaction temperature at 95° C. for 4 hours while stirring, the reaction solution was cooled and added to a saturated aqueous solution of sodium sulfate to precipitate the produced polyacenaphthylene. Next, after repeated washing with methanol and water and filtration, the obtained pale yellow solid was dissolved in 1 to 1 to 1 toluene, poured into a large amount of methanol, and purified by reprecipitation to obtain a 12.9 CJ pale yellow polymer (polymer). acenaphthylene)
I got it. This polymer was prepared using Te1-G using lahydrofuran.
When subjected to molecular pressure measurement using PC, the weight average molecular weight was found to be 1.5×105.

Volite 1 to Lafluoroethylene were used as thermoplastic resins in the polymer obtained as described above, and the weight ratio of this thermoplastic resin to the polymer was 0.007 (Battery A), 0.0
5 (Battery B), 0.11 (Battery C), 0.18
(Battery D) and mixed uniformly. Using stainless steel as a conductive member, each of the above mixtures was press-molded together with the stainless steel to produce various composite electrodes. Each of these electrodes is used as a positive electrode, and as shown in FIG. 1, a positive electrode 1, a separator 2, a negative electrode 3 made of known lithium metal, an insulating backing 4,
Batteries A-D were prepared by combining the positive electrode can 5, the positive electrode current collector 6, the negative electrode 7, the negative electrode current collector 8, etc., and using propylene carbonate as the electrolyte solvent and lithium fluoroborate as the electrolyte.
were prepared respectively.

In addition, the weight ratio of the thermoplastic resin to the polymer was 0.03 (Battery E), 0.22 (Battery F), O
(Battery G) and a composite electrode prepared in the same manner as above was used as a positive electrode to prepare batteries E-G having the same structure as above.

When these batteries A to G are each charged with a current of 1 mA for 5 hours and then discharged with a current of 1 mA to a battery voltage of 2.0 V, the cycle is repeated. The characteristics at this time are shown in Figure 2.

As is clear from FIG. 2, Batteries A to D exhibited fairly good characteristics, and in particular, the flatness of the discharge voltage was excellent. On the other hand, batteries E and F have poor characteristics, and battery G
is the worst.

In addition, FIG. 3 shows the cycle characteristics of discharge efficiency, and from this figure, it can be seen that batteries A to D according to the present invention have not only cycle characteristics but also discharge efficiency compared to conventional batteries G or comparative batteries E and F. It can be seen that it has also been significantly improved.

Figure 4 also shows the cycle life of batteries A- and -G with different amounts of thermoplastic resin mixed as described above.
The amount of raw resin mixed is shown as a parameter, and it can be seen from the figure that by setting the amount of thermoplastic resin mixed within the range of the present invention, the battery life can be increased to 150 cycles or more.

The above means that the amount of thermoplastic resin mixed into the electrode is particularly important for electrodes made of conductive polymers that do not have conjugated double bonds in the main chain, and that This means that it is possible to improve the performance for the first time.If the amount of thermoplastic resin mixed in the electrode is small, the electrode strength will be insufficient and satisfactory battery characteristics cannot be obtained, and if there are too many mixed layers, the electrode Since the conductivity becomes insufficient, the battery characteristics deteriorate.

It is clear that the same effect can be obtained by applying this invention to the negative electrode.

<Effects of the Invention> According to the secondary battery of the present invention configured as described above,
A conductive polymer that does not have a conjugated double bond in its main chain is used as the electrode material because it can improve the strength of the electrode without causing a decrease in conductivity when undoped, and the conductivity of the electrode can be made extremely good. This has effects such as improving the cycle characteristics and energy density of the secondary battery, and improving the flatness of the discharge voltage.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the battery structure of an embodiment of the present invention;
Figure 2 is a graph showing changes in battery voltage over time during charging and discharging of various batteries, Figure 3 is a graph showing cycle characteristics of various batteries, and Figure 4 is the relationship between cycle life and the amount of thermoplastic resin mixed. This is a graph showing the following. 1... Positive electrode, 3... Negative electrode, 5... Positive electrode can, 7...
・Negative polarity. Patent applicant Mitsubishi Chemical Industries, Ltd. Sanyo Electric Co., Ltd.

Claims (1)

[Claims] 1. A secondary battery in which at least one of the positive electrode and the negative electrode is a composite consisting of a conductive polymer that does not have a conjugated double bond in its main chain, a thermoplastic resin, and a conductive member, the thermoplastic resin A secondary battery characterized in that the mixing amount of is 0.005 to 0.2 in weight ratio to the conductive polymer.