SECONDARY BATTERY

Abstract: Disclosed is a non-aqueous secondary battery having a positive electrode composed of a polymer of aniline or an aniline derivative and a negative electrode composed of (i) and alkali metal, (ii) an alkali metal alloy, (iii) an electroconductive polymer or (iv) an alkali metal or alkali metal alloy/electroconductive polymer composite, wherein the polymer of aniline or an aniline derivative is formed by converting a doped polymer obtained by oxidative polymerization to an undoped state.

Description: 1. Field of the Invention The present invention relates to a high-performance non-aqueous secondary battery which has a high energy density, a good reversibility between charging and discharging, a very low self-discharge ratio and an excellent thermal stability. 2. Description of the Related Art A so-called polymer battery comprising an electrode composed of a polymeric compound having a conjugated double bond in the main chain is regarded as a secondary battery having a high energy density. Various reports concerning secondary batteries have been published, for example, by P.J. Nigrey et al, J. Chem. Soc. Chem. Commun., 1979 , 594, J. Electrochem. Soc., 1981 , 1651, and Japanese Unexamined Patent Publications No. 56-136,469, No. 57-121,168, No. 59-3,870, No. 59-3,872, No. 59-3,873, No. 59-196,566, No. 59-196,573, No. 59-203,368 and No. 59-203,369. The use of polyaniline obtained by electrolytic oxidative polymerization of aniline, which is a kind of conjugated polymer, as an electrode of an aqueous solution type or non-aqueous solvent type battery has already been proposed [A.G. MacDiarmid et al, Polymer Preprints, 25 , NO. 2, 248 (1984), Sasaki et al, Lectures at 50th General Meeting of Electrochemical Association, 123 (1983) and Sasaki et al, Lectures at 51st General Meeting of Electrochemical Association, 228 (1984)]. A polymer of aniline or an aniline derivative is generally prepared by electrochemical polymerization or chemical polymerization. In each case, since polymerization is carried out by an oxidative reaction, the process is called an "oxidative polymerization process", and a polymer of aniline or an aniline derivative obtained according to this process is protonated by a protonic acid. Moreover, the polymer is obtained in the state doped with dopant in an amount of several to scores of mole% based on the repeating units. In order to use a polymer of aniline or an aniline derivative obtained according to this process as an active electrode material, the obtained polymer is dried under a reduced pressure, the polymer is washed with water to remove impurities and then dried under a reduced pressure, or the polymer is washed with an organic solvent. These methods can be used in combination. In a non-aqueous secondary battery in which a polymer of aniline or an aniline derivative prepared by the above-mentioned oxidative polymerization process and treated by the above-mentioned method is used as the positive electrode and an alkali metal, an alkali metal alloy, an electroconductive polymer, an electroconductive polymer composite is used as the negative electrode, a good battery performance such as a low self-discharge ratio or a high energy density is difficult to obtain, and the characteristics of such a secondary battery cannot be regarded as epoch-making and excellent over those of a known nickel/cadmium battery or lead battery. From a publication entitled "Polyaniline: A cathode-active material for rechargeable aqueous batteries" published in Abstract No. 622, in 1046B Extended Abstracts, 84(1984) October, No. 2, New Orleans, Louisiana, USA, page 906, it is known that polyaniline can be used as a cathode-active material for rechargeable aqueous batteries. According to this publication, a polyaniline cathode assembled in the battery is used which is in an undoped state and has been prepared by pretreating a doped polyaniline with a methanolic alkali solution. While an aqueous electrolyte is used in the battery according to this prior art, the document is completely silent as to any heat-treatment or specific temperatures or temperature ranges of any such heat-treatment of the polymer in question. Document FR-A-2 554 822 relates to electrochemical charging and discharging of secondary polyaniline in a non-aqueous battery cell. While a reversible interconversion of polyaniline from the undoped to the doped state and vice versa by repetitive treatment with alkaline and acidic solutions is described there, this document is silent as to any alkali-treatment followed by a heat-treatment of the polymer in question. Document FR-A-2 545 494 relates to a method of preparing polyaniline and its application in electrochemical generators. While polyaniline is used as an active cathode material in a non-aqueous secondary battery, the polyaniline is used in the state as made according to this document, in other words, without any alkali-treatment followed by any heat-treatment. SUMMARY OF THE INVENTION The object underlying the present invention is to provide a high-performance non-aqueous secondary battery which has a very low self-discharge ratio, a large electric capacity, a good reversibility between charging and discharging, a high energy density and an excellent thermal stability. According to the present invention, there is provided a non-aqueous secondary battery comprising a positive electrode composed of a polymer of aniline or an aniline derivative, and a negative electrode composed of (i) an alkali metal, (ii) an alkali metal alloy, (iii)an electroconductive polymer or (iv) an alkali metal/electroconductive polymer composit or an alkali metal alloy/electroconductive polymer composite, wherein the polymer of an aniline or an aniline derivative is formed by converting a doped polymer prepared by oxidative polymerization to an undoped state prior to electrode implementation in the battery, the conversion of the doped polymer to an undoped state being effected by treating the doped polymer with an aqueous solution of an alkali and then heat-treating the polymer at a temperature of 100° C to 300° C. According to a specific embodiment of the secondary battery according to the invention, the polymer of aniline or an aniline derivative is a homopolymer of a compound represented by the following general formula (1) or (2) or a copolymer comprising at least 50 mole % of units derived from a compound represented by the following general formula (1) or (2): wherein R₁ through R₆ independently represent a hydrogen atom or an alkyl group or alkoxy group having 1 to 5 carbon atoms, and X and Y independently represent a hydrogen atom or a phenyl group. According to a further development of the secondary battery according to the invention the doped polymer of aniline or an aniline derivative is obtained by subjecting aniline or an aniline derivative to electrochemical oxidative polymerization in a solvent capable of dissolving aniline or the aniline derivative therein at a current density of 0,01 to 50 mA/cm² and an electric field voltage of 1 to 300 V in the presence of a complexing agent represented by the following general formula: M⁺A⁻ wherein M⁺ is a cation selected from the group consisting of a proton, a quaternary ammonium cation, a lithium cation, a sodium cation and a potassium cation and A⁻ is an anion selected from the group consisting of BF₄⁻, AsF₄⁻, AsF₆⁻, SbF₆⁻, SbCl₆⁻, PF₆⁻, ClO₄⁻, HSO₄⁻, HSO₄⁻, SO₄²⁻, Cl⁻, Br⁻, and F⁻. According to a further development of the secondary battery according to the invention, the polymer of aniline or an aniline derivative is obtained by subjecting aniline or an aniline derivative to chemical oxidative polymerization in the presence of a strong acid exerting an oxidative action in the water-dissolved state or in the presence of a strong acid and an oxidant. According to a further development of the secondary battery according to the invention, the alkali is selected from the group consisting of alkali metal hydroxides, alkali earth metal hydroxides, ammonia and amines. In a preferred embodiment of the secondary battery according to the invention, the heat treatment is carried out in an inert gas or in vacuum. According to a further development of the secondary battery according to the invention, a supporting electrolyte of an electrolytic solution of the secondary battery is an alkali metal salt. The invention will be explained in more detail below with reference to specific embodiments and in connection with the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram illustrating a cross-section of an experimental glass cell for a sealed lid secondary battery according to one embodiment of the present invention; and Fig. 2 is a schematic diagram illustrating a cross-section of a battery cell for measuring the characteristics of a secondary battery according to one embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS The polymer of aniline or an aniline derivative used as the positive electrode of the secondary battery of the present invention is obtained by oxidative polymerization of a compound represented by the following general formula (1) or (2), and the polymer may be a homopolymer or a copolymer: wherein R₁ through R₆ independently represent a hydrogen atom or an alkyl group or alkoxy group having 1 to 5 carbon atoms, and X and Y independently represent a hydrogen atom or a phenyl group. As typical examples of the aniline compounds represented by the general formulae (1) and (2), there can be mentioned aniline, 2-methylaniline, 2,5-dimethylaniline, 2-methoxyaniline, 2,5-dimethoxyaniline, o-phenylene-diamine, 3-methyl-1,2-diaminobenzene, diphenylamine and triphenylamine. Of these aniline compounds represented by the general formulae (1) and (2), aniline, o-phenylene-diamine and triphenylamine are preferred and aniline is especially preferred. The copolymer comprises at least 50 mole% of units derived from the compound represented by the general formula (1) or (2). As the comonomer, there can be mentioned benzene, thiophene and pyrrole. The polymer of the aniline compound can be prepared according to either the electrochemical oxidative polymerization process or the chemical oxidative polymerization process. An example of the electrochemical polymerization process is disclosed in Journal of Japanese Chemical Society, No. 11, page 1801 (1984). According to the electrochemical oxidative polymerization process, polymerization of aniline or its derivative is accomplished by anodic oxidation. For this anodic oxidation, a current density of about 0,01 to about 50 mA/cm², preferably 2 to 20 mA/cm², and an electric field voltage of 1 to 300 V, preferably 10 to 300 V, are adopted. The polymerization is carried out in the presence of an auxiliary liquid in which aniline or its derivative is soluble. Water or a polar organic solvent can be used. When a water-miscible solvent is used, a small amount of water may be incorporated. As the solvent giving good results, there can be mentioned alcohols, ethers (such as dioxane and tetrahydrofuran), acetone, acetonirile, dimethylformamide and N-methlpyrrolidone. The polymerization is carried out in the presence of a complexing agent. By the complexing agent is meant a salt having as an anion a group BF₄⁻, AsF₄⁻, AsF₆⁻, SbF₆⁻, SbCl₆⁻, PF₆⁻, ClO₄⁻, HSO₄⁻, SO₄²⁻ Cl⁻, Br⁻ or F⁻. The obtained polyaniline compound is in the state doped with the corresponding anion (complex compound). The salt contains as a cation, a proton, a quaternary ammonium cation, a lithium cation, a sodium cation or a potassium cation. An example of the chemical polymerization process is disclosed in A.G. Green and A.E. Woodhead, J. Chem. Soc., 2388 (1910). According to the chemical polymerization process, oxidative polymerization is accomplished by an oxidative strong acid or a combination of a strong acid and an inorganic oxidant in an aqueous solution containing aniline or its derivative. The polymer obtained according to this polymerization (oxidation polymer) can be in the form of powder. Accordingly, the obtained powdery polymer may be separated and then dried before use. Also in this process, since an anion is present, the polyaniline compound is in the state doped with the corresponding anion (complex compound). The inorganic oxidant used in the chemical oxidative polymerization process is not particularly critical, so long as the inorganic oxidant is soluble in an aqueous solution of a strong acid. As typical instances, there can be mentioned ammonium persulfate, potassium persulfate, hydrogen peroxide, an ammonium persulfate/Fe (II) ion redox system, a hydrogen peroxide/Fe (II) ion redox system, potassium dichromate, potassium permanganate and sodium chlorate. In order to obtain a secondary battery having a good battery performance, ammonium persulfate, an ammonium persulfate/Fe (II) ion redox system and a hydrogen peroxide/Fe (II) ion redox system are preferred. In each of the polymerization processes, other additives such as carbon black, Teflon powder, polyethylene glycol and polyethylene can be incorporated in the polymerization electrolyte. The doped polymer obtained by the oxidative polymerization is converted to an undoped state by treating the doped polymer with an aqueous solution of an alkali and then heat-treating the polymer at a temperature of 100 to 300°C. This method for converting the doped polymer to an undoped polymer will now be described. First, the alkali treatment method will be described. The polymer of aniline or an aniline derivative obtained according to the oxidative polymerization process is protonated by a protonic acid, and the polymer is often obtained in the state containing the electrolyte, oxidizing agent and additive in the polymerization liquid, impurities in the electrolytic solution, by-products formed by the polymerization and oligomers. By the alkali treatment, the polymer is converted to an undoped state and in addition, these impurities, by-products and the like can be removed. As the alkali treatment method, there can be mentioned a method in which the polymer is washed several times with an aqueous solution of an alkali directly or after water washing, and a method in which alkali washing and water washing are alternately repeated several times and finally, the polymer is washed with water. Water washing is conducted until the pH value of the washing water is 5 to 9, preferably 6 to 8. The kind of aqueous solution of the alkali is not particularly critical, so long as the pH value exceeds 12, but in order to increase the treatment efficiency, use of an aqueous solution having a higher pH value is preferred. As the alkali species, either inorganic alkalis or organic alkalis can be used, so long as they are soluble in water. However, it is preferred that general-purpose alkali species be used. For example, there can be mentioned alkali metal hydroxides such as KOH and NaOH, alkaline earth metal hydroxides such as Mg(OH)₂ and Ca(OH)₂ , ammonia and amines such as triethylamine and tributylamin. Aqueous solutions of KOH, NaOH and ammonia are preferred, and aqueous ammonia is especially preferred because the residual alkali or neutralization salt can be simply removed by the water washing treatment after the neutralization treatment and by the drying treatment of the polymer under reduced pressure. The frequency of the alkali treatment of the polymer depends on the quantity or shape of the polymer to be treated, the polymer-preparing process, the concentration and quantity of the treating solution and the size and shape of the treatment vessel. However, washing is ordinarily conducted one time to several times. At the alkali treatment of the polymer, a sufficient effect can be attained merely by immersing the polymer in an aqueous solution of an alkali, but in order to perform washing promptly and effectively, a method may be adopted in which in the state where an aqueous solution of an alkali is circulated or the polymer is immersed in the aqueous solution of the alkali, the entire system is stirred, and a method in which an external energy such as ultrasonic vibration is applied. The alkali treatment time depends on the quantity and shape of the polymer, the concentration and quantity of the treating solution and the size and shape of the treatment vessel as well as the frequency of the alkali treatment, and the alkali treatment time cannot be simply specified. The method for heat-treating the polymer to convert it to an undoped state will be described. The temperature for the heat treatment of the polymer is 100 to 300°C. If the heat treatment temperature is lower than 100°C, a secondary battery having a long cycle life and a low self-discharge ratio cannot be obtained. If the heat treatment temperature is higher than 300°C, the oxidation polymer of the aniline type compound is deteriorated to some extent and therefore, a secondary battery having a good performance is difficult to obtain. The heat treatment can be carried out in air, but preferably the heat treatment is carried out in an atmosphere of an inert gas such as nitrogen or argon or especially in vacuo. The heat treatment time depends on the kind of the oxidation polymer of the aniline type compound and the heat treatment temperature and cannot be simply specified, but preferably the heat treatment is conducted for 5 to 20 hours. It is preferred that the thus-obtained undoped polymer be complexed with a protonic acid. The undoped polymer can be directly complexed with a protonic acid. However, it is preferred that components soluble in the electrolyte used for the secondary battery of the present invention be removed before or after the polymer is complexed with a protonic acid. The method for removing components soluble in the electrolyte is not particularly critical. In general, however, there are used a method in which the polymer is washed with the electrolyte, a method in which the polymer is washed with an organic solvent, and an extraction method using an organic solvent. In the washing method using the electrolyte or organic solvent, the presence or absence of stirring, the washing frequency and the washing time are not particularly critical, so long as washing can be effected to such an extent that the electrolyte or organic solvent is not colored. The washing temperature is in the range of from the solidification point of the organic solvent used for washing or the organic solvent in the electrolyte to the boiling point thereof. As the extraction method using an organic solvent, there can be adopted a well-known Soxhlet extraction method. The extraction conditions are not particularly critical, if the extract is not colored. However, it is generally preferred that the extraction be carried out in an atmosphere of an inert gas such as nitrogen or argon. The electrolyte used for washing the polymer is not particularly critical, and for example, an electrolyte used for the secondary battery of the present invention, described below, can be used. The organic solvent used for washing or extraction of the polymer is not particularly critical, and any organic solvents capable of removing the components soluble in the electrolyte of the secondary battery of the present invention can be used. Namely, the organic solvent used for the electrolyte of the secondary battery of the present invention can be used for washing or extraction, or organic solvents having a solubility parameter close to that of the polyaniline compound, for example, carbonyl compounds such as acetone, nitrile compounds such as acetonitrile, chlorinated compounds such as dichloroethane, carboxylic acid compounds such as acetic acid and amide compounds such as dimethylformamide, may be used for washing or extraction. The method for complexing the polymer with a protonic acid is not particularly critical, but a method is generally adopted in which the polymer is immersed or stirred in an acidic aqueous solution having a pH value smaller than 3. As the anion of the protonic acid used for the complexing, there can be mentioned halogens such as Cl⁻, F⁻ and Br⁻, halides of elements of the Group IIIa such as BF₄⁻, halides of elements of the Group Va such as PF₈⁻⁴ and AsF₆⁻, and ClO₄⁻, HSO₄⁻ and SO₄²⁻. Among them, Cl⁻, BF₄⁻ and ClO₄⁻ are preferred, and BF₄⁻ is especially preferred. These anions may be the same as or different from the anion used for the electrolyte of the battery, but preferably the anion of the protonic acid used for the complexing be the same as the anion of the electrolyte of the battery. The doped polymer to be converted to an undoped state or the undoped polymer to be complexed with a protonic acid may be powdery, granular or filmy, or the polymer may be molded in the form of an electrode. The molded body that can be used as an electrode can be obtained according to various methods. For example, in the case of the powdery polymer, a molded body can be obtained by compression-molding the powder according to a known method. In many cases, a temperature ranging from room temperature to 300°C and a pressure ranging from 10 to 10 000 kg/cm² are used. The negative electrode used for the secondary battery of the present invention is composed of (i) an alkali metal, (ii) an alkali metal alloy, (iii) an electroconductive polymer or (iv) an alkali metal or alkali metal alloy/electroconductive polymer composite. As the alkali metal (i), there can be mentioned Li, Na and K, and as the alkali metal alloy (ii), there can be mentioned an Li/Al alloy, an Li/Hg alloy, an Li/Zn alloy, an Li/Cd alloy, an Li/Sn alloy and an Li/Pb alloy, and alloys of at least three metals used for these alloys, inclusive of the alkali metal, such as Li/Al/Mg, Li/Al/Sn, Li/Al/Pb, Li/Al/Zn and Li/Al/Hg. These alloys can be prepared according to the electrochemical method or the chemical method, but an alloy prepared according to the electrochemical method is preferred. As the electroconductive polymer (iii), there can be mentioned polypyrrole, polypyrrole derivatives, polythiophene, polythiophene derivatives, polyquionoline, polyacene, poly-p-phenylene, poly-p-phenylene derivative and polyacetylene. As the alkali metal or alkali metal alloy/electroconductive polymer composite (iv), there can be mentioned a composite of an Li/Al alloy and an electroconductive polymer as mentioned above, such as poly-p-phenylene or polyacetylene. As preferred examples, there can be mentioned polyacetylene, poly-p-phenylene, an Li/Al alloy, an Li/Al/Mg alloy and a composite of an Li/Al alloy and poly-p-phenylene. By the composite referred to herein is meant a homogeneous mixture or laminate of an alkali metal or alkali metal alloy and an electroconductive polymer, or a modification product formed by modifying the component of the substrate with another component. The polymer of aniline or the aniline derivative and the electroconductive polymer, which are used as the electrodes of the secondary battery of the present invention, may be mixed with an appropriate electroconductive material such as carbon black, acetylene black, a metal powder, a metal fiber or a carbon fiber, as is well-known to persons with ordinary skill in the art. Furthermore, the electrodes may be reinforced with a thermoplastic resin such as polyethylene, modified polyethylene, polypropylene, poly(tetrafluoroethylene), an ethylene/propylene/diene terpolymer (EPDM) or sulfonated EPDM. The supporting electrolyte of the electrolytic solution of the secondary battery of the present invention is an alkali metal salt. As the alkali metal of the alkali metal salt, there can be mentioned Li, Na and K, and Li is preferred. As typical instances of the anion component of the supporting electrolyte, there can be mentioned ClO₄⁻, PF₆⁻, AsF₆⁻, AsF₄⁻, SO₃CF₃⁻, BF₄⁻ and BR₄⁻ (R represents an alkyl group having 1 to 10 carbon atoms or aryl group having 6 to 10 carbon atoms). As specific examples of the alkali metal salt as the supporting electrolyte, there can be mentioned LiPF₆ , LiSbF₆ , LiClO₄ , LiAsF₆ , CF₃SO₃Li, LiBF₄ , LiB(Bu)₄ , LiB(Et)₂(Bu)₂ , NaPF₆ , NaBF₄ , NaAsF₆ , NaB(Bu)₄ , KB(Bu)₄ and KAsF₆ , through the alkali metal salt is not limited to these compounds. These alkali metal salts may be used singly or in the form of mixture of two or more thereof. The concentration of the alkali metal salt depends on the kind of the polymer used for the positive electrode, the kind of the negative electrode, the charging conditions, the operating temperature, the kind of the supporting electrolyte and the kind of the organic solvent, and the concentration cannot be simply specified. However, it is generally preferred that the concentration of the alkali metal salt be 0,5 to 10 moles per liter. The electrolytic solution may be homogeneous or heterogeneous. As the organic solvents that can be used singly or in the form of a mixture as the solvent of the electrolytic solution of the secondary battery of the present invention, there can be mentioned: alkylene nitriles such as crotononitrile (liquid at - 51,1 to 120°C), trialkyl borates such as trimethyl borate (CH₃O)₃B (liquid at - 29,3 to 67°C), tetraalkyl silicates such as tetramethyl silicate (CH₃O)₄Si (boiling at 121°C), nitroalkanes such as nitromethane CH₃NO₂ (liquid at - 17 to 100,8°C), alkylnitriles such as acetonitrile CH₃CN (liquid at - 45 to 81,6°C), dialkylamides such as dimethylformamide HCON(CH₃)₂ (liquid at - 60,48 to 149°C), lactams such as N-methylpyrrolidone (liquid at - 16 to 202°C), monocarboxylic acid esters such as ethyl acetate (liquid at - 83,6 to 77,06°C), ortho-esters such as trimethyl orthoformate HC(OCH₃)₃ (boiling at 103°C), lactones such as γ-butyrolactone CH₂-CH₂-CH₂-O-CO (liquid at - 42 to 206°C), dialkyl carbonates such as dimethyl carbonate OC(OCH₃)₂ (liquid at 2 to 90°C), alkylene carbonates such as propylene carbonate (liquid at - 48 to 242°C), monoethers such as diethyl ether (liquid at - 116 to 34,5°C), polyethers such as 1,1-dimethoxyethane (liquid at - 113,2 to 64,5°C) and 1,2-dimethoxyethane (liquid at - 58 to 83°C), cyclic ethers such as tetrahydrofuran (liquid at - 65 to 67°C) and 1,3-dioxolane (liquid at - 95 to 78°C), nitro aromatic hydrocarbons such as nitrobenzene (liquid at 5,7 to 210,8°C), aromatic carboxylic acid halides such as benzoyl chloride (liquid at 0 to 197°C) and benzoyl bromide (liquid at - 24 to 218°C), aromatic sulfonic acid halides such as benzene sulfonyl chloride (liquid at 14,5 to 251°C), aromatic phosphonic acid dihalides such as benzene phosphonyl dichloride (boiling at 258°C), aromatic thiophosphonic acid dihalides such as benzene thiophosphonyl dichloride (boiling at 124°C under 5 mmHg), cyclic sulfones such as sulfolane (melting at 22°C) and 3-methylsulfolane (melting at -1°C), alkylsulfonic acid halides such as methanesulfonyl chloride (boiling at 161°C), alkylcarboxylic acid halides such as acetyl chloride (liquid at - 112 to 50,9°C), acetyl bromide (liquid at - 96 to 76°C) and propionyl chloride (liquid at - 94 to 80°C), saturated heterocyclic compounds such as tetrahyothiophene (liquid at - 96 to 121°C) and 3-methyl-2-oxazolidone (melting at 15,9°C), dialkylsulfamic acid halides such as dimethylsulfamyl chloride (boiling at 80°C under 16 mmHg), alkyl halosulfonates such as ethyl chlorosulfonate (boiling at 151°C), unsaturated heterocyclic carboxylic acid halides such as 2-furoyl chloride (liquid at - 2 to 173°C), 5-membered unsaturated heterocyclic compounds such as 1-methylpyrrole (boiling at 114°C), 2,4-dimethylthiazole (boiling at 144°C) and furane (liquid at - 85,65-31,36°C), dibasic carboxylic acid esters and halides such as ethyl oxalyl chloride (boiling at 135°C), mixed alkylsulfonic acid halide/carboxylic acid halide such as chlorosulfonyl acetyl chloride (boiling at 98°C under 10 mmHg), dialkylsulfoxides such as dimethylsulfoxide (liquid at 18,4 to 189°C), dialkyl sulfites such as dimethyl sulfite (liquid at - 31,75 to 188,5°C), dialkyl sulfates such as dimethyl sulfate (boiling at 126°C), alkylene sulfites such as ethylene glycol sulfite (liquid at - 11 to 173°C), and halogenated alkanes such as methylene chloride (liquid at - 95 to 40°C) and 1,3-dichloropropane (liquid at - 99,5 to 120,4°C). Among these organic solvents, there are preferably used sulfolane, crotononitrile, nitrobenzene, tetrahydrofuran, methyl-substituted tetrahydrofuran, 1,3-dioxolane, 3-methyl-2-oxazolidone, propylene carbonate, ethylene carbonate, γ-butyrolactone, ethylene glycol sulfite, dimethyl sulfite, dimethyl sulfoxide, 1,1-dimethoxyethane and 1,2-dimethoxyethane, and a mixed solvent of propylene carbonate and 1,2-dimethoxyethane and a mixed solvent of sulfolane and 1,2-dimethoxyethane are especially preferred because they are considered to be chemically most inactive to the battery components and they are liquid within a broad temperature range and because they make it possible to utilize the positive electrode substance most efficiently. In the secondary battery of the present invention, the amount of the dopant to be doped in the polymer of aniline or the aniline derivative is 0,2 to 1,0 mole, preferably 0,2 to 0,8 mole, per nitrogen atom in the polymer. The amount of the dopant doped can be freely controlled by measuring the quantity of coulomb flowing at the electrolysis. The doping can be carried out at a constant current or voltage or under conditions where the current and voltage vary. In the present invention, a porous membrane of a synthetic resin such as polyethylene or polypropylene or a natural fiber paper may be used as a separator according to need. Some of the electrodes used for the secondary battery of the present invention react with oxygen or water to degrade the performance of the battery. Accordingly, it is preferred that the battery be closed to maintain a substantially oxygen-free and anhydrous state. The non-aqueous secondary battery of the present invention is advantageous over the known Ni/Cd battery or lead battery in that the energy density is high, the reversibility between charging and discharging is good, the self-discharge ratio is very low and the performance characteristics are very good. The non-aqueous secondary battery of the present invention is advantageous over the non-aqueous secondary battery comprising a positive electrode of the polymer of aniline or the aniline derivative not converted to an undoped state in that the self-discharge ratio is very low, the electric capacity is large and the energy density is high. Moreover, since the secondary battery of the present invention has a light weight and a small size, the secondary battery of the present invention is very suitable as a battery for a portable device, an electric car or a gasoline car or as a power storage battery. The present invention will now be described in detail with reference to the following examples and comparative examples. Example 1 Preparation of Polyaniline A glass vessel was charged with distilled water, from which oxygen had been sufficiently removed, HBF₄ and aniline, and the concentrations of HBF₄ and aniline were adjusted to 1,5 mole/l and 0,35 mole/l, respectively. Two platinum electrodes having a surface area of 6 cm² were arranged in the aqueous solution while a distance of 2 cm was taken between the platinum electrodes. Electrolysis was carried out with stirring at a current flow rate of 120 A. A dense-green polymer was precipitated on the positive electrode. The covered positive electrode was washed with distilled water three times and air-dried, and the formed polyaniline film was separated from the platinum plate. Alkali Treatment and Heat Treatment of Polyaniline The separated polymer was immersed in 28% aqueous ammonia and allowed to stand overnight, and the polymer was washed with distilled water three times repeatedly and dried in vacuo at 250°C for 15 hours. The elementary analysis values of the thus-treated polyaniline were 79,38% by weight for C, 5,10% by weight for H and 15,30% by weight for N, and the C/H/N atomic ratio was 6,05/4,63/1.00. Thus, it was confirmed that the purity was considerably high. Preparation of Filmy Acetylene High Polymer In a nitrogen atmosphere, a glass reaction vessel having an inner capacity of 500 ml was charged with 1,7 ml of titanium tetrabutoxide, and 30 ml of anisole was further added to form a solution. Then, 2,7 ml of triethylaluminum was added to the solution with stirring to form a catalyst solution. The reaction vessel was cooled with liquid nitrogen and the nitrogen gas in the reaction vessel was discharged by a vacuum pump. Then, the reaction vessel was cooled to -78°C and purified acetylene gas under a pressure of 1 atmosphere was then blown into the reaction vessel while keeping the catalyst solution stationary. Immediately, the polymerization occurred on the surface of the catalyst solution to form a filmy acetylene high polymer. When 30 minutes had passed from the initiation of introduction of acetylene, the acetylene gas was discharged to stop the polymerization. In a nitrogen atmosphere, the catalyst solution was discharged by a syringe, and the formed polymer was washed with 100 ml of refined toluene 5 times repeatedly while maintaining the temperature at -78°C. The filmy acetylene high polymer swollen with toluene was a uniform swollen film composed of fibrils densely entangled with one another. The swollen film was dried in vacuo to obtain a reddish violet filmy acetylene high polymer having a metallic luster, a thickness of 180 µm and a cis content of 98%. The bulk density of this filmy acetylene high polymer was 0,30 g/cm³ and the electric conductivity was 10⁻⁹ Ω⁻¹-cm⁻¹ as determined at 20°C according to the direct current four-terminal method. Battery Test Discs having a diameter of 20 mm were cut out from the treated polyaniline film and the filmy acetylene high polymer, and a cell as shown in Fig. 2 was constructed by using them as active material of positive and negative electrodes. More specifically, a collector 13 of a platinum net for the positive electrode was placed in the lower portion of the recess of a Teflon® vessel 15, and a positive electrode 12 was placed on the platinum net collector 13 for the positive electrode and a porous polypropylene separator 11 was piled on the collector 13 and sufficiently impregnated with an electrolytic solution. A negative electrode 10 was piled on the separator 11 and a collector 9 of a platinum net for the negative electrode was piled on the negative electrode 10. The Teflon® vessel 15 was clamped to construct a battery. A solution of 1 mole/l of LiPF₆ in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane (volume ratio = 1/1), which was sufficiently dehydrated by distillation according to customary procedures, was used as the electrolytic solution. In an argon atmosphere, the thus-constructed battery was charged under a constant electric current (1,5 mA/cm²) while supplying electricity in such an amount that the doping quantities to the positive and negative electrodes were 50 mole% and 6 mole%, respectively. After completion of the charging, the battery was discharged under a constant current (2,0 mA/cm²) and when the battery voltage was reduced to 1,0 V, the charging was carried out again under the same conditions as described above. In this manner, the charging-discharging operation was repeated. This operation could be repeated 1210 times before the charging-discharging efficiency was reduced to 70%. At the 5th repetition cycle, the energy density was 136 W·h /kg and the maximum charging-discharging efficiency was 100%. When the battery was allowed to stand in the charged state for 63 hours, the self-discharge ratio was 1,8%. Example 2 Preparation of Polyaniline A 1-liter three-neck flask was charged with 400 ml of sufficiently oxygen-removed distilled water and 100 ml of a 42% aqueous solution of HBF₄ , and the solution was bubbled with a nitrogen gas for about 1 hour with stirring. Then, the inner atmosphere of the reaction vessel was substituted by a nitrogen gas, a thermometer and a condenser were attached to the flask and the solution was maintained at 49°C by warm water. Then, 20 g of aniline was added to the solution, and a solution of 46 g of ammonium persulfate in 200 cm³ of a 1N aqueous solution of HBF₄ was dropped to the aqueous solution of aniline over a period of about 2 hours with starring. Then, reaction was advanced at 49°C for 3 hours. After the reaction, the liquid reaction mixture having a dense green color was filtered to obtain polyaniline having a dense green color. Alkali Treatment and Heat Treatment of Polyaniline The polyaniline was immersed in 500 ml of 28% aqueous ammonia and was allowed to stand overnight. After filtration, the polymer was washed with 200 ml of distilled water 3 times repeatedly and dried in vacuo at 250°C for 15 hours. The elementary analysis values of the obtained treated polymer were 79,36% by weight for C, 5,20% by weight for H and 15,28% by weight for N, and the C/H/N atomic ratio was 6,06/4,73/1.00. Battery Test The battery test was carried out in the same manner as described in Example 1 except that a molded body (compression vacuum molding under 100 kg/cm² for 5 minutes; containing 10% of carbon black) of the treated polymer obtained according to the above-mentioned procedures was used as the positive electrode. The charging-discharging operation could be repeated 1081 times before the charging-discharging efficiency was reduced to 70%. The energy density of the battery was 132 W·h /kg and the maximum charging-discharging efficiency was 100%. When the battery was allowed to stand in the charged state for 63 hours, the self-discharge ratio was 2,1%. Example 3 The battery test was carried out in the same manner as described in Example 1 except that poly-p-phenylene prepared according to the process disclosed in Bull. Chem. Soc. Japan, 51 , 2091 (1978) was used instead of the acetylene high polymer used as the negative electrode in Example 1 and a disc having a diameter of 20 mm, which was formed by molding the poly-p-phenylene under a pressure of 1 ton/cm², was used as the negative electrode. The charging-discharging operation could be repeated 1481 times before the charging-discharging efficiency was reduced to 70%. The energy density of the battery was 143 W·h /kg and the maximum charging-discharging efficiency was 100%. When the battery was allowed to stand in the charged state for 63 hours, the self-discharge ratio was 1,6%. Example 4 The battery test was carried out in the same manner as described in Example 1 except that an Li-Al alloy (atomic ratio = 1/1) was used as the negative electrode instead of the acetylene high polymer used as the negative electrode in Example 1. The charging-discharging operation could be repeated 1018 times before the charging-discharging efficiency was reduced to 70%. The energy density of the battery was 210 W·h /kg and the maximum charging-discharging efficiency was 100%. When the battery was allowed to stand in the charged state for 63 hours, the self-discharge ratio was 1,4%. Example 5 and 6 and Comparative Examples 1 and 2 The battery test was carried out in the same manner as described in Example 1 except that the temperature of the heat treatment of the polyaniline used as the positive electrode was changed as indicated in Table 1. The frequency (times) of repetition that could be conducted before the charging-discharging efficiency was reduced to 70%, the energy density, the maximum charging-discharging efficiency and the self-discharge ratio after 63 hours' standing after charging were determined. The obtained results are shown in Table 1.

Claims: A non-aqueous secondary battery comprising a positive electrode (3, 12) composed of a polymer of aniline or an aniline derivative and a negative electrode (4, 10) composed of (i) an alkali metal, (ii) an alkali metal alloy, (iii) an electroconductive polymer or (iv) an alkali metal/electroconductive polymer composite or an alkali metal alloy/electroconductive polymer composite, wherein the polymer of an aniline or an aniline derivative is formed by converting a doped polymer prepared by oxidative polymerization to an undoped state prior to electrode implementation in the battery, the conversion of the doped polymer to an undoped state being effected by treating the doped polymer with an aqueous solution of an alkali and then heat-treating the polymer at a temperature of 100 to 300°C. A secondary battery as set forth in claim 1, wherein the polymer of aniline or an aniline derivative is a homopolymer of a compound represented by the following general formula (1) or (2) or a copolymer comprising at least 50 mole% of units derived from a compound represented by the following general formula (1) or (2): wherein R₁ through R₆ independently represent a hydrogen atom or an alkyl group or alkoxy group having 1 to 5 carbon atoms, and X and Y independently represent a hydrogen atom or a phenyl group. A secondary battery as set forth in claim 1 or 2, wherein the doped polymer of aniline or an aniline derivative is obtained by subjecting aniline or an aniline derivative to electrochemical oxidative polymerization in a solvent capable of dissolving aniline or the aniline derivative therein at a current density of 0,01 to 50 mA/cm² and an electric field voltage of 1 to 300 V in the presence of a complexing agent represented by the following general formula: M⁺A⁻ wherein M⁺ is a cation selected from the group consisting of a proton, a quaternary ammonium cation, a lithium cation, a sodium cation and a potassium cation and A⁻ is an anion selected from the group consisting of BF₄⁻, AsF₄⁻, AsF₆⁻, SbF₆⁻, SbCl₆⁻, PF₆⁻, ClO₄⁻, HSO₄⁻, HSO₄⁻, SO₄²⁻, Cl⁻, Br⁻, and F⁻. A secondary battery as set forth in any of claims 1 to 3, wherein the polymer of aniline or an aniline derivative is obtained by subjecting aniline or an aniline derivative to chemical oxidative polymerization in the presence of a strong acid exerting an oxidative action in the water-dissolved state or in the presence of a strong acid and an oxidant. A secondary battery as set forth in any of claims 1 to 4, wherein the alkali is selected from the group consisting of alkali metal hydroxides, alkaline earth metal hydroxides, ammonia and amines. A secondary battery as set forth in any of claims 1 to 5, wherein the heat treatment is carried out in an inert gas or in vacuum. A secondary battery as set forth in any of claims 1 to 6, wherein a supporting electrolyte of an electrolytic solution of the secondary battery is an alkali metal salt.

Inventors: KOBAYASHI, YUKIO, KONUMA, HIROSHI, NAKAMURA, HIDENORI, SAKAI, TOSHIYUKI, SHISHIKURA, TOSHIKAZU, TAKEUCHI, MASATAKA
Applicants: HITACHI, LTD., SHOWA DENKO KABUSHIKI KAISHA
Application year: 1986
Main classification: H01M10
IPC codes: H01B1, C08G73, H01M10, H01M4