SOLID ELECTROCHEMICAL ELEMENT AND PRODUCTION PROCESS THEREOF

Abstract: This invention provides a solid electrochemical element which has high flexibility and good environmental resistance and accordingly is superior to conventional solid electrochemical elements by using (a) solid electrolyte particles surrounded by a plastic resin and (b) electrode material particles surrounded or not surrounded by the plastic resin, as well as a process for producing said solid electrochemical element which uses, as starting materials, (a) solid electrolyte particles coated with a thin layer of a plastic resin and (b) electrode material particles coated with a thin layer of the plastic resin and which includes a step of crushing the solid electrolyte particles by pressing.

Description: The present invention relates to a solid electrochemical element which uses an ion conductor and the constituent members of which are all solid, such as a solid cell, a solid electrical double layer capacitor, a solid electrochromic display or the like, as well as to a process for producing said element. More particularly, the present invention relates to a solid electrochemical element with excellent mechanical strength and excellent environmental resistance which is constituted by (a) an ionic conductor containing an insulating supporting substance for solid electrolyte such as a plastic resin or the like and having flexibility and excellent environmental resistance and (b) electrode material particles, as well as to a process for producing said element. Solid electrochemical elements whose constituent members are all solid are advantageous in that they have no problem of liquid leakage and that they can be easily produced in a small and thin shape. In constituting such an element, there is required a solid ion conductor for moving ions within the element, namely, a solid electrolyte. The solid electrolyte is classified by the type of a movable ion and includes Li⁺-conductive solid electrolyte, Ag⁺-conductive solid electrolyte, Cu⁺-conductive solid electrolyte, H⁺-conductive solid electrolyte, etc. A solid electrochemical element is constituted by combining one of these solid electrolytes with an appropriate electrode material. Not only solid electrolytes but also general electrolytes have no directional property or no anisotropy with respect to the ion conductivity and accordingly have a random ion conductivity. Therefore, a solid electrochemical element is ordinarily constituted by shaping a solid electrolyte powder into a layer by pressing or into a thin film by vapor deposition and providing a pair of electrodes on the both surfaces of the layer or the thin film to form one solid electrochemical element per one solid electrolyte layer. In ordinary electrochemical elements using a liquid electrolyte, the electronic and ionic contact between electrolyte and electrode material can be easily obtained. In contrast, in solid electrochemical elements constituted by solid substances, generally it is not easy to obtain electronic and ionic contact between solid electrolytes, between electrode materials or between solid electrolyte and electrode material. In electrochemical elements using a liquid electrolyte, it is usual to add a foreign matter such as a binder or the like to the electrolyte or the electrode in order to prevent the leakage of the electrolyte or to prevent the excessive penetration of the electrolyte into the electrode and the resulting deformation of the electrode. Meanwhile in solid electrochemical elements, the addition of a foreign matter is ordinarily avoided because it reduces said electronic and ionic contact. Using no foreign matter, the solid electrochemical elements, when produced in a large and thin shape, generally tend to lack in elasticity and consequently are fragile to mechanical impacts and easily destroyed or impaired. Further in the solid electrochemical elements, the solid electrolyte generally comprises a chemically active monovalent cation as a conducting element. This monovalent cation, when exposed to oxygen or moisture in the atmosphere, is converted to a divalent cation by oxidation or immobilized in the electrolyte crystal as an oxide, whereby the conducting function of the electrolyte is lost. Furthermore, when a plurality of solid electrochemical elements are arranged into an element group wherein they are connected in series or in parallel, it is necessary to isolate each constituent element of the element group electronically and ionically. In this case, since the electrolyte used in each element generally has random ion conductivity and has no anisotropy, each element must have an electrolyte layer ionically isolated from other electrolyte layers. Without this isolation, the ionic flow within the electrolyte of one element not only occurs between the electrodes of the element but also spreads into between the electrodes of other elements, whereby the element group fails to exhibit its desired function. This is a problem when a solid electrochemical element is produced in a small or miniature size, which is a feature of solid electrochemical elements, in addition to the above-mentioned problem when a solid electrochemical element is produced in a large and thin shape. The isolation of each element in an element group requires complicated assembly steps including photolithography, etc. as used in an ordinary semiconductor assembly line. From DE-A-3 125 525, which is regarded as the most relevant state of art, it is known to produce a solid electrochemical element by mixing particles of a solid electrolyte material having a given, substantially uniform diameter with a plastic resin and preparing a layer of the mixture having a thickness substantially corresponding to the diameter of the solid electrolyte particles. After drying the layer in which the spaces between the electrolyte particles are filled with the resin, the both opposing surfaces of the layer are ground to lay open the electrolyte particle material in large extent and to increase the electronical contact between the surfaces and corresponding electrodes. Further, from EP-A-0 083 682 it is known to produce a flexible electrochemical element by mixing particles of a lithium compound with an elastical binding material with or without a solvent and shaping a thin electrolyte film from the mixture which is highly flexible after drying. Finally, from GB-A-2 034 103 it is known to produce electrochemical cells from a solid electrolyte material, in which electrode material particles and solid electrolyte particles are mixed to reduce contact resistance of the electrodes. The object of the present invention is to provide for a solid electrochemical element which has excellent properties in view of mechanical strength, environmental resistance and flexibility, in which the electronic and ionic contact between the electrolyte and the electrode material can be easily obtained and which can be produced in a large and thin shape. According to a first aspect of the present invention there is provided a process for producing a solid electrochemical element, which comprises dispersing and mixing solid electrolyte particles including particles of a given particle diameter in a solvent containing a plastic resin to form powdery particles coated with the plastic resin, shaping the mixture to produce a shaped material of solid electrolyte particles, and providing electrodes on the two opposing surfaces of the shaped solid electrolyte material to form an integral body, wherein the step of forming the shaped solid electrolyte particle material includes forming a layer of the mixture of the coated solid electrolyte particles having a first thickness of substantially said given particle diameter and then pressing the resulting layer into a layer having a second thickness smaller than said first thickness, such that the surfaces of the solid electrolyte particles are not coated with the plastic resin in the two opposing surfaces of the shaped solid electrolyte material. According to a second aspect of the invention there is provided a process for producing a solid electrochemical element, which comprises mixing solid electrolyte particles including particles of a given particle diameter with a plastic resin powder or grain, shaping the resulting mixture to produce a shaped material of solid electrolyte particles, and providing a shaped electrode material on the two opposing surfaces of the shaped material of solid electrolyte particles to form an integral body, wherein the step of forming the shaped solid electrolyte particle material includes forming a layer of the mixture of the coated solid electrolyte particles having a first thickness of substantially said given particle diameter and then pressing the resulting layer into a layer having a second thickness smaller than said first thickness, such that the surfaces of the solid electrolyte particles are not coated with the plastic resin in the two opposing surfaces of the shaped solid electrolyte material. According to another aspect of the present invention, there is provided a solid electrochemical element comprising a shaped solid electrolyte material of a layer made from a mixture of said electrolyte particles, including particles of a given particle diameter, and a plastic resin, and comprising electrodes on each of the opposing surfaces of the solid electrolyte material, wherein the solid electrolyte particles extend from one of the opposing surfaces of the solid electrolyte material to the other, the solid electrolyte particles being coated with the plastic resin except the surfaces of the solid electrolyte particles lying in the two opposing surfaces of the solid electrolyte material, which are not coated with the plastic resin to provide for an electrical contact with the electrodes, wherein the uncoated surfaces of the solid electrolyte particles are formed by pressing a layer of the mixture of the solid electrolyte particles and the plastic resin having a first thickness of substantially the given particle diameter into a layer having a second thickness smaller than said first thickness, wherein the resulting pressed surfaces of the solid electrolyte particles from the uncoated surfaces lying in the two opposing surfaces of the solid electrolyte material. The present invention has been achieved in order to solve the above mentioned problems of conventional solid electrochemical elements. According to the present invention, there is provided a flexible, environment-resistant ion conductor by constituting it with a solid electrolyte and an insulating supporting substance for solid electrolyte surrounding the solid electrolyte, preferably with a solid electrolyte and a plastic substance. There is further provided an ion conductor having an anisotropic ion conductivity by allowing the plastic resin to have a thickness approximately same as the particle diameter of the solid electrolyte particles or by alternately stacking in layers a sheet of a solid electrolyte and a sheet of a supporting substance for solid electrolyte such as a plastic resin or the like and cutting the resulting laminate in the thickness direction. Such an ion conductor is produced by a process including a step of crushing solid electrolyte particles by pressing. Preferably, solid electrolyte particles and a plastic resin podwer or grain are mixed in a solvent or under heating and the mixture or its melt is shaped by rolling to obtain an ion conductor. According to the present invention there is furthermore provided a solid electrochemical element with flexibility and environmental resistance by surrounding solid electrolyte particles and electrode material particles with a plastic resin. This solid electrochemical element is produced by separately or jointly mixing solid electrolyte particles and electrode material particles with a plastic resin in a solvent or mixing these particles directly with a plastic resin powder or grain to obtain the particles coated with said plastic resin, shaping these coated particles to produce a shaped material of solid electrolyte particles and a shaped electrode material, and shaping these two materials into one integral body. Preferably, the solid electrochemical element is produced by a process including a step of crushing solid electrolyte particles by pressing. Fig. 1 is a schematic view showing the structure of an embodiment of the ion conductor of the present invention. In Fig. 1, solid electrolyte particles 1 are surrounded by a supporting substance 2 for solid electrolyte, except for the upper and lower surfaces which are necessary for formation of an ion-conductive path. Fig. 2 is a view showing steps of producing an ion conductor according to the present invention. A mixture 4 consisting of solid electrolyte particles, a supporting substance for solid electrolyte and a solvent is printed on a substrate 3 with a spatula 6, dried and then rolled by rollers 7 and 8, whereby an ion conductor is produced. Fig. 3 is a view showing the structure of an ion conductor having an anisotropy with respect to the ion conductivity which is obtained by stacking in layers a solid electrolyte sheet and a sheet of a supporting substance for solid electrolyte such as a plastic resin or the like and then cutting the resulting laminate. Fig. 4 is a view showing the structure of a laminated film battery using an ion conductor. In conventional ion conductors consisting of a solid electrolyte or conventional solid electrochemical elements using a solid electrolyte, the use of a foreign substance has been avoided usually. However, in the ion conductor or solid electrochemical element of the present invention, there is used a foreign substance, namely, an insulating material which supports and surrounds a solid electrolyte. That is, the solid electrolyte material or the electrode material is surrounded by an insulating supporting material for solid electrolyte, preferably a plastic resin material, except for the portions which form an ion- or electron-conductive path optionally having a particular directionality. Accordingly, the insulating supporting substance for solid electrolyte is pushed into the gaps between the solid electrolyte particles or between the electrode material particles in forming an ion conductor (a shaped material of solid electrolyte) or a shaped electrode material or in assembling a solid electrochemical element, whereby an aggregate of particles is formed in which the neighbouring particles are in direct contact with one another and each particle is surrounded by the insulating supporting substance for solid electrolyte. As a result, the particles as a constituent member of the ion conductor, the electrode or the solid electrochemical element can keep a shape as an aggregate, can secure an electrical and ionic contact, and are not directly exposed to oxygen and moisture in the air and become unlikely to undergo deterioration. These merits can be obtained more effectively by employing a step of crushing the solid electrolyte particles by pressing, in a process for producing an ion conductor (a shaped material of solid electrolyte), a shaped electrode material or a solid electrochemical element. When the solid electrolyte particles coated with a plastic resin (an insulating supporting substance for solid electrolyte) are crushed by pressing, there appear the surfaces thereof not coated with the plastic resin and, through these surfaces, there occurs a direct contact between the solid electrolyte particles or between these particles and electrode particles. Thus, there can be obtained a sheet type ion conductor (a shaped material of solid electrolyte) with flexibility and excellent ion conductivity, as well as a shaped electrode material, and as a result there can be obtained a solid electrochemical element having an excellent mechanical strength and an excellent environmental resistance and capable of generating a large current. The ion conductor of the present invention can also be formed in a sheet shape wherein surfaces of solid electrolyte particles are coated with an insulating supporting substance for solid electrolyte (e.g. a plastic resin) except for the particular surfaces, for example, the upper and lower surfaces. When two or more pairs of electrodes are provided on the upper and lower surfaces of the ion conductor, the electrodes cover and are contacted with the upper and lower portions of the solid electrolyte particles not coated with the insulating supporting substance, and thus the electrodes and the ion conductor are connected ionically. Within the ion conductor sheet, the ion does not move in the lateral direction but only in the vertical direction of the sheet, whereby no ionic flow occurs between the two neighbouring electrodes or between the two neighbouring but opposing electrodes. Thus, it is possible to constitute, using only one ion conductor sheet, a solid electrochemical element group consisting of a plurality of solid electrochemical elements which are electrically independent from one another, by providing two or more pairs of opposing electrodes on the two opposing surfaces of an ion conductor sheet. In the present invention there is used an ion conductor consisting of solid electrolyte particles coated with an insulating supporting substance for solid electrolyte. When this ion conductor is used in a solid electrochemical element, the upper and lower surfaces of the ion conductor are provided with electrodes. Therefore, the ion conductor may be produced in such a manner that the upper and lower surface on which electrodes are to be provided, may be coated very thinly or may not be coated substantially with an insulating supporting substance for solid electrolyte in order to obtain a good ionic contact between the ion conductor and the electrodes. The insulating supporting substance for solid electrolyte according to the present invention can be any substance as long as it can surround solid electrolyte particles and can form a flexible aggregate of the solid electrolyte particles. Particularly, a plastic resin is preferred. As the plastic resin, there can be preferably used those which can be stably mixed with a solid electrolyte containing a high concentration of a chemically active monovalent cation such as Na⁺, Li⁺, Ag⁺, Cu⁺, H⁺ or the like or with an electrode material as a strong oxidizing agent or a strong reducing agent. Such plastic resins are, for example, polyethylene, polypropylene, synthetic rubbers (e.g., styrene-butadiene rubber, Neoprene rubber), silicone resins, acrylic resins, etc. When a polyethylene, polypropylene or acrylic resin is used, the fine powder of the resin is dry-blended with a solid electrolyte powder or grain or with an electrode material powder or grain. The particle diameter of the resin is preferably 1/10 to 1/10,000 time the particle diameter of each powder or grain. During the blending, the particles of the polyethylene, polypropylene or acrylic resin coat the surface of each particle of the powers or grains owing to the static electricity generated between the particles. When a synthetic rubber such as styrene-butadiene rubber, Neoprene rubber or the like, a silicone resin or an acrylic resin is used, wet blending is conducted using an organic solvent such as toluene, xylene or the like. That is, a synthetic rubber, an acrylic resin or a silicone resin is dissolved in an organic solvent in an amount of 5 to 20% by weight; to the solution is added a solid electrolyte powder or grain or an electrode material powder or grain; they are mixed and dispersed to obtain a slurry; the slurry is casted on a Teflon sheet; and the solvent is removed under vacuum, if necessary with heating, whereby a shaped body can be obtained. Alternatively, the slurry itself can be treated under vaccum to remove the solvent and then shaped by pressing. The solid electrolyte used in the present invention includes Li⁺-conductive solid electrolytes such as LiI, LiI·H₂O, Li₃N, Li₄SiO₄-Li₃-Li₃PO₄, polyethylene oxide-LiCF₃SO₃ and the like; Ag⁺-conductive solid electrolytes such as RbAg₄I₅, Ag₃SI, AgI-Ag₂O-MoO₃ glass and the like; Cu⁺-conductive solid electrolytes such as RbCu₄I 1.5 Cl 3.5 , RbCu₄I 1.25 Cl 3.75 , K 0.2 Rb 0.8 Cu₄I 1.5 Cl 3.5 , CuI-Cu₂O-MoO₃ glass and the like; H⁺-conductive solid electrolytes such as H₃Mo₁₂PO₄₀·29H₂O, H₃W₁₂PO₄₀·H₂O and the like; and Na⁺-conductive solid electrolytes represented by Na-β-Al₂O₃ (sodium β-alumina) or Na 1+x Zr₂P 3-x Si x O₁₂ (0 ≦ x ≦ 3). As the electrode material of the present invention, there can be used, for example, carbon materials such as graphite, acetylene black, active carbon and the like; sulfides such as titanium sulfide, niobium sulfide, cuprous sulfide, silver sulfide, lead sulfide, iron sulfide and the like; oxides such as tungsten oxide, vanadium oxide, chromium oxide, molybdenum oxide, titanium oxide, iron oxide, silver oxide, copper oxide and the like; halides such as silver chloride, lead iodide, cuprous iodide and the like; and metal materials such as copper, silver, lithium, gold, platinum, titanium and their alloys. A solid electrolyte cell or battery can be constituted by combining an ion conductor (a shaped material of solid electrolyte particles) and an electrode material which can give ion to the ion conductor or receive ion therefrom, such as titanium disulfide or the like. A solid electrochemical display element (a solid electrochromic display) can be constituted by using an ion conductor and an electrode material which can give or receive ion and simultaneosuly causes an optical change, such as tungsten oxide or the like. A solid electrical double layer capacitor can be constituted by using an ion conductor and an electrode material which does not give or receive ion but can form an electrical double layer at the interface with the ion conductor, such as active carbon or the like. All of these solid electrochemical elements according to the present invention have a sufficient flexibility , an excellent mechanical strength and an excellent environmental resistance. A solid electrolyte, for example, a powder of RbCu₄I 1.5 Cl 3.5 of 200 mesh pass through 100% is dispersed in a toluene solution of a styrene-butadiene copolymer so that the volume fraction of the powder after drying becomes 85%. The resulting slurry is spread on a Teflon sheet using an applicator bar and they are placed in dry air to remove toluene, whereby a flexible sheet type ion conductor (a shaped material of solid electrolyte particles) having no fluidity is obtained. This ion conductor can be used as it is for constitution of a solid electrochemical element but, by rolling it with a roller press so as to have a thickness of about 2/3 or less of the original thickness, can be made into a sheet type ion conductor with improved ion conductivity wherein the solid electrolyte particles have been crushed by pressing. A shaped electrode material can also be formed in a similar manner. In forming a shaped electrode material using, for example, copper as an electrode material, a copper powder having particle diameters of 0,005 mm (5 microns) or less and a RbCu₄I 1.5 Cl 3.5 powder having particle diameters of 200 mesh pass through 100% are mixed at a weight ratio of 90 : 10. The mixed powder is dispersed in a toluene solution of a styrene-butadiene copolymer so that the volume fraction of the mixed powder after drying becomes 90%. The resulting slurry is spread on a Teflon sheet using an applicator bar and they are placed in dry air to remove toluene, whereby a flexible sheet type shaped electrode material is obtained. It can be rolled by a roller press to have a thickness of about 2/3 or less of the original thickness, whereby an electrode having an excellent electrical conductivity and an excellent ionic conductivity can be obtained. By press-molding the ion conductor interposed between the shaped electrode materials thus obtained together with, if necessary, other constituent members such as a current collector into one integral body, a solid electrochemical element can be obtained. Production of a solid electrochemical element can be conducted as above by making a shaped ion conductor and a shaped electrode material into one integral body. Alternatively, it can be conducted by directly shaping the respective powders or grains coated with a plastic resin into one integral body. The present invention will be described in detail below by way of Examples and Comparative Examples. Example 1 Fig. 1 shows the structure of an ion conductor according to the present invention. Fig. 1(a) is a plane view of the ion conductor and Fig. 1(b) is a sectional view obtained by cutting the ion conductor of Fig. 1(a) at a line C. In Figs. 1(a) and 1(b), 1 is a particulate solid electrolyte and 2 is an insulating supporting substance for solid electrolyte. The slant line portions are the portions of the particulate solid electrolyte hidden by the insulating supporting substance for solid electrolyte. RbCu₄I 1.5 Cl 3.5 as a particulate solid electrolyte was ground with a ball mill under dry air, and only the solid electrolyte having particle diameters of 0,080 to 0,100 mm (80 to 100 microns) was used by sieving. A silicone rubber was used as a supporting substance for solid electrolyte. Preparation of an ion conductor was conducted according to Fig. 2. Firstly, the above two materials were mixed at a ratio of 1 : 1 by weight. Mixing was conducted thoroughly using toluene as a solvent in order to sufficiently disperse the particulate solid electrolyte in the silicone rubber. The resulting mixture 4 was screen-printed on a stainless steel substrate 3 with a spatula 6 using a stainless steel screen 5 of 100 mesh through [see Fig. 2(a)]. Then, toluene was vaporized [see Fig. 2(b)]. Subsequently, the particulate solid electrolyte supported by the silicone rubber was rolled together with a silicone rubber 9 between two rollers 7 and 8 whose gaps had been adjusted to 0,100 mm (100 microns) to obtain an ion conductor sheet having a thickness of 0,100 mm (100 microns) [see Fig. 2(c)]. This ion conductor sheet showed an anisotropy with respect to the ion conductivity. The ion conductivity at 25°C was 4.5 x 10⁻² Ω⁻¹cm⁻¹ in the thickness direction and 7.3 x 10⁻¹² Ω⁻¹cm⁻¹ in the lateral direction. Examples 2 to 4 Using other particulate solid electrolytes and supporting substances for solid electrolyte, ion conductors were prepared in the same manner as in Example 1. Each ion conductor showed an anisotropy with respect to the ion conductivity. The results are shown in Table 1. Example 5 NASICON (Na-super ion conductor), a Na⁺-conductive solid electrolyte represented by Na 1+x Zr₂P 3-x Si x O₁₂ (0 ≦ x ≦ 3) was ground so as to have particle diameters of 0,100 ± 0,010 mm (100 ± 10 microns), and these particles were used as a particulate solid electrolyte. A polyethylene powder having a particle diameter of 100 µm (microns) was used as a supporting substance for solid electrolyte. In order to prepare an ion conductor sheet, the particulate solid electrolyte and the polyethylene powder were mixed; the mixture was melted at 200°C; and the melt was rolled between hot rollers whose gaps had been adjusted to 100 µm (microns) to obtain a sheet. The temperature of the hot rollers was set at 30°C. The sheet had ion conductivities of 7.3 x 10⁻⁵ Ω⁻¹cm⁻¹ in the thickness direction and 2.6 x 10⁻¹³ Ω⁻¹cm⁻¹ in the lateral direction. By melting, the polyethylene could effectively surround each solid electrolyte particle. Example 6 An ion conductor sheet was prepared in the same manner as in Example 5 except that the polyethylene as a supporting substance for solid electrolyte was changed to a polypropylene resin. The sheet had ion conductivities of 5.4 x 10⁻⁵ Ω⁻¹cm⁻¹ in the thickness direction and 2.1 x 10⁻¹³ Ω⁻¹cm⁻¹ in the lateral direction. Example 7 Another embodiment of the ion conductor according to the present invention is shown in Fig. 3. A sheet 10 of a polyethylene oxide (PEO)-LiCF₃SO₃ polymer electrolyte having a thickness of 100 µm (microns) was used as a solid electrolyte. The sheet was prepared by mixing LiCF₃SO₃ and a PEO having a molecular weight of 750,000, dissolving the mixture in acetonitrile, casting the solution on a stainless steel plate, and vaporizing the solvent at 70°C. Separately, a sheet 11 of the PEO alone was prepared in a similar manner. The two sheets were stacked alternately [see Fig. 3(a)], and the laminate was cut at a line B to prepare a zebra-patterned sheet [see Fig. 3(b)]. The sheet was measured for ion conductivities regarding the surfaces a, b and c. They were 3.4 x 10⁻⁶ Ω⁻¹cm⁻¹ between the surfaces a and b and 7.1 x 10⁻¹³ Ω⁻¹cm⁻¹ between the surfaces b and c. Example 8 An ion conductor sheet was prepared in the same manner as in Example 1 except that 60% by weight of white insulating particles of TiO₂ (70 µm (microns) in particle diameter) had been added to the silicone rubber of Example 1. The sheet had ion conductivities of 5.7 x 10⁻³ Ω⁻¹cm⁻¹ in the thickness direction and 2.2 x 10⁻¹³ Ω⁻¹cm⁻¹ in the lateral direction. A laminate type thin film battery was prepared using an ion conductor prepared as above. The preparation process is shown in Fig. 4. The positive electrode group of the battery is shown in Fig. 4(a) and the negative electrode group is shown in Fig. 4(b). The positive electrode group was prepared by vapor-depositing stainless steel on a glass substrate through a mask to form stainless steel portions 13, 15 and 17 and then vapor-depositing thereon CuI through a mask to form CuI portions 14 in a thickness of 0,3 µm (3,000 Å)[see Fig. 4(a)]. The portions 15 and 17 later become a positive electrode terminal and a negative electrode terminal, respectively. In a similar manner, the negative electrode group was prepared by vapor-depositing stainless steel on a glass substrate 12 through a mask to form stainless steel portions 13 and then vapor-depositing thereon copper through a mask to form copper portions 16 [see Fig. 4(b)]. The above mentioned ion conductor sheet consisting of a particulate solid electrolyte 1 and a supporting substance 2 for solid electrolyte was put between the positive electrode group and the negative electrode group so that the electrode groups faced each other, and the circumference of the resulting laminate was coated with an epoxy adhesive 18, whereby a battery was prepared [see Fig. 4(d)]. The connection of the electrode groups was conducted using indium metal 19. The resulting battery was measured for electromotive force, and a voltage of 1.8 V existed between the positive electrode terminal 15 and the negative electrode terminal 17. Since the electromotive force of this battery was 0.6 V per single cell, it was found that the use of an ion conductor sheet according to this invention makes it unnecessary to divide the electrolyte into each single cell portion. Further, in order to examine an effect when a plastic supporting substance for solid electrolyte is used, a battery was constituted by using, as a substrate 12 for each electrode group, a polyimide film having a thickness of 0.4 mm. As a result, it was found that the battery had an excellent elasticity. Therefore, this battery was found to be suitable for use as an electric source for IC cards requiring an elasticity. It was further found that the ion conductor sheet containing insulating particles, prepared in Example 8, when put between transparent electrodes, produced a sharp pink color on a white background due to the precipitation of copper when a voltage was applied between the transparent electrodes and accordingly is suitable for use as an electrolyte for electrochromic display. Example 9 A powder of 5 µm (5 microns) or less as particulate solid electrolyte was sufficiently mixed with a toluene solution containing 10% of a styrene-butadiene copolymer, in a volume ratio of 85 (solid electrolyte) to 15 (copolymer). In mixing, a suitable amount of toluene was used as a diluent. The mixture thus prepared was a slurry having slight fluidity. The slurry was extended on a Teflon sheet in a thickness of 0.1 mm (100 microns) using an applicator bar. Toluene was vaporized in dry air and then the dried film was rolled into a film thickness of 70 µm microns using a roller press to crush the solid electrolyte particles, whereby a desired ion conductor was obtained. In order to measure the ion conductivity, the ion conductor was cut into specimen of 1 cm². On the two surfaces of the specimen were provided two copper electrodes each having the same size as the specimen, in a sandwich form. This was done by wetting the ion conductor surfaces with toluene and then pressing the electrodes thereon. Subsequently, an AC having a voltage of 10 mV and a frequency of 1 KHz was applied between the two electrodes and the resulting AC resistance was measured. It was 1.5 x 10⁻⁴ S/cm². In a comparative test for examining the effect of crushing by pressing, an ion conductor sheet was prepared according to the following manner. As a particulate solid electrolyte, there was used a powder having particle diameters of 1 µm (1 micron) or less which was difficult to be crushed by rolling, and an ion conductor sheet was prepared in the same manner as in Example 9. The resulting ion conductor showed a low ion conductivity of 9.5 x 10⁻⁶ S/cm². An ion conductor sheet was prepared in the same manner as in the sheet of Example 9 except that crushing and rolling was conducted using an ordinary press in place of the roller press. That is, the ion conductor sheet before crushing and rolling was sandwiched between two stainless steel plates (in the form of a square of 10 cm x 10 cm having a thickness of 1 cm); using spacers of 70 µm (70 microns) in thickness, a pressure of 100 MPa (1 ton/cm²) was applied by a press to crush the solid electrolyte particles. The resulting ion conductor sheet had an ion conductivity of 9.7 x 10⁻⁵ S/cm². The reason is not clear yet but roller pressing, as compared with ordinary pressing by a press, can crush solid electrolyte particles more effectively and can provide an ion conductor with superior ion conductivity. Example 10 100 parts by weight of a solid electrolyte, namely, a powder of a Cu⁺-conductive solid electrolyte represented by RbCu₄I 1.5 Cl 3.5 , having an average particle diameter of 0,010 mm (10 microns) was mixed with 20 parts by weight of a polyethylene powder having an average particle diameter of 0.1 µm (0.1 micron) in a dry nitrogen atmosphere. The mixture was formed into a shaped solid electrolyte material of 5 mm x 20 mm x 0.100 mm (100 microns) (thickness) using a roller press at a pressure of 20 MPa (200 kg/cm²). In a similar manner, there was obtained a shaped positive electrode material of 5 mm x 20 mm x 0.200 mm (200 microns) (thickness) consisting of 50 parts by weight of a powder of a positive electrode active substance represented by Cu 0.1 NbS₂, having an average particle diameter of 0.015 mm (15 microns), 50 parts by weight of the above mentioned solid electrolyte powder and 15 parts by weight of the above mentioned polyethylene powder. Also in a similar manner, there was obtained a shaped negative electrode material of 5 mm x 20 mm x 0,120 mm (120 microns) (thickness) consisting of 50 parts by weight of a powder of a negative electrode active substance (metallic copper) having an average particle diameter of 8 µm (8 microns), 50 parts by weight of the above mentioned solid electrolyte powder and 25 parts by weight of the above mentioned polyethylene powder. These shaped materials were stacked in three layers and a pressure of 25 MPa (250 kg/cm²) was applied thereto, whereby a copper type solid cell A was obtained as an integral body. Example 11 A copper type solid cell B was obtained in the same manner as in Example 10 except that a polypropylene powder having an average particle diameter of 0.1 µm (0.1 micron) was used in place of the polyethylene powder. Comparative Example 1 A copper type solid cell C was obtained in the same manner as in Example 10 except that no polyethylene powder was used. Example 12 An Ag type solid cell D was obtained in the same manner as in Example 10 except that there were used, as a solid electrolyte, a powder of an Ag⁺-conductive solid electrolyte represented by RbAg₄I₅, having an average particle diameter of 8 µm (8 microns), as a positive electrode active substance, a powder of Ag 0.1 NbS₂ having an average particle diameter of 15 µm (15 microns), and as a negative electrode active substance, a powder of metallic silver having an average particle diameter of 8 µm (8 microns). Comparative Example 2 An Ag type solid cell E was obtained in the same manner as in Example 12 except that no polyethylene powder was used. Example 13 A Li type solid cell F was obtained in the same manner as in Example 10 except that there were used, as a solid electrolyte, a powder of a Li⁺-conductive solid electrolyte represented by LiI, having an average particle diameter of 15 µm (15 microns), as a positive electrode active substance, a powder of WO₃ having an average particle diameter of 12 µm (12 microns), and as a negative electrode active substance, a powder of Li 1.5 WO₃ having an average particle diameter of 10 µm (10 microns). Comparative Example 3 A Li type solid cell G was obtained in the same manner as in Example 13 except that no polyethylene powder was used. Example 14 An H type solid cell H was obtained in the same manner as in Example 10 except that there were used, as a solid electrolyte, a powder of a H⁺-conductive solid electrolyte represented by H₃Mo₁₂PO₄₀·29H₂O, having an average particle diameter of 20 µm (20 microns), as a positive electrode active substance, a powder of WO₃ having an average particle diameter of 8 µm (8 microns), and as a negative electrode active substance, a powder of HWO₃ having an average particle diameter of 8 µm (8 microns), and the polyethylene powder was changed to an acrylic resin powder having an average particle diameter of 0.2 µm (0.2 micron). Comparative Example 4 An H type solid cell I was obtained in the same manner as in Example 14 except that no acrylic resin powder was used. Example 15 100 parts by weight of a solid electrolyte, namely, a powder of a Cu⁺-conductive solid electrolyte represented by RbCu₄I 1.25 Cl 3.75 , having an average particle diameter of 2 µm (microns) was mixed with 30 parts by weight of a toluene solution containing 10% by weight of a styrene-butadiene rubber to obtain a solid electrolyte slurry. The slurry was extended on a fluoresin plate using a bar coater in a thickness (when dried) of 20 µm (20 microns) and then dried for 3 hours at 50°C under a reduced pressure of 1 Torr, whereby a solid electrolyte thin film of 60 mm (width) x 800 mm (length) x 0.020 mm (20 microns) (thickness) was obtained. Separately, 50 parts by weight of a graphite powder having an average particle diameter of 0.5 µm (0.5 micron) and 50 parts by weight of the above mentioned solid electrolyte powder were mixed with 35 parts by weight of the above mentioned toluene solution to obtain a positive electrode slurry. In a similar manner and using this slurry, there was obtained a positive electrode thin film of 60 mm (width) x 800 mm (length) x 0.030 mm (30 microns) (thickness). Separately, 50 parts by weight of a metallic copper powder having an average particle diameter of 2 µm (2 microns), 50 parts by weight of the above mentioned solid electrolyte powder and 18 parts by weight of the above mentioned toluene solution were mixed to obtain a negative electrode slurry. In a similar manner and using this slurry, there was obtained a negative electrode thin film of 60 mm (width) x 800 mm (length) x 0.020 mm (20 microns) (thickness). Then, the positive electrode thin film was provided on one surface of the solid electrolyte thin film and the negative electrode thin film was provided on the other surface of the solid electrolyte thin film. They were shaped into one integral body at a pressure of 2 MPa (20 kg/cm²) using a roller press of 130° to 150°C to obtain a thin film of 65 mm (width) x 1,000 mm (length) x 55 to 65 µm [microns) (thickness). This thin film was cut into pieces of 5 mm x 20 mm to obtain a solid cell J. Example 16 A solid cell K was obtained in the same manner as in Example 15 except that the styrene-butadiene rubber was changed to a silicone resin. Example 17 A solid cell L was obtained in the same manner as in Example 15 except that the styrene-butadiene rubber was changed to an acrylic resin. Example 18 On the two surfaces of a solid electrolyte film having a thickness of 0,020 mm (20 microns), obtained in the same manner as in Example 15, were provided an electrode film having a thickness of 0,030 mm (30 microns) and consisting of a graphite powder, a solid electrolyte powder and a styrene-butadiene rubber, obtained in the same manner as in Example 15. They were shaped into one integral body at a pressure of 2 MPa (20 kg/cm²) and at 130° to 150°C using a roller press to obtain a sheet of 65 mm (width) x 1,000 mm (length) x 60 to 65 µm (microns) (thickness). The sheet was cut into pieces of 5 mm x 20 mm to obtain a solid electrical double layer capacitor M. Example 19 50 parts by weight of a solid electrolyte, namely, a powder of a H⁺-conductive solid electrolyte represented by H₃Mo₁₂PO₄₀·29H₂O, having an average particle diameter of 20 microns, 20 parts by weight of an acrylic resin powder having an average particle diameter of 0.2 µm (micron) and a graphite powder having an average particle diameter of 0.5 µm micron were mixed and shaped in the same manner as in Example 10 to prepare a graphite electrode of 5 mm x 20 mm x 30 µm (microns) (thickness). Three layers comprising in the following order (a) the above electrode, (b) a solid electrolyte film of 5 mm x 20 mm x 50 µm (microns) (thickness) consisting of a H⁺-conductive solid electrolyte and an acrylic resin and (c) a display electrode of 5 mm x 20 mm x 10 µm (microns) (thickness) containing tungsten trioxide (WO₃), prepared in the same manner as in Example 14 were pressed into one body, whereby a solid electrochromic display element N of 5 mm x 20 mm x 85 µm (microns) (thickness) was assembled. The above prepared solid cells A to L, solid electrical double layer capacitor M and solid electrochromic display element N were subjected to repeated bending test (30° bending in the longitudinal direction). The number of times of bending until breakage occured in each test is shown in Table 2. Also shown in Table 2 is the ratio of R₁/R₀ of each of the elements A to N wherein R₁ is the internal resistance of an element when the element has been allowed to stand for 48 hours in an atmosphere of 45°C and 60% humidity and R₀ is the initial internal resistance of the element. All of the solid electrochemical elements A, B, D, F, H, J, K, L, M and N according to the present invention can withstand bending of several hundred times to several thousand times, and any of them does not show a noticeable increase in the internal resistance, when allowed to stand in the atmosphere. Meanwhile, the solid electrochemical elements C, E, G and I for comparison have no flexibility at all and are broken in bending of only one time and, when allowed to stand in the atmosphere, show a significant increase in the internal resistance.

Claims: A process for producing a solid electrochemical element, which comprises dispersing and mixing solid electrolyte particles including particles of a given particle diameter in a solvent containing a plastic resin, to form powdery particles coated with the plastic resin, forming the mixture to produce a shaped material of solid electrolyte particles, and providing electrodes on the two opposing surfaces of the shaped solid electrolyte material to form an integral body, characterized in that the step of forming the shaped solid electrolyte particle material includes forming a layer of the mixture of the coated solid electrolyte particles having a first thickness of substantially said given particle diameter and then pressing the resulting layer into a layer having a second thickness smaller than said first thickness, such that the surfaces of the solid electrolyte particles are not coated with the plastic resin in the two opposing surfaces of the shaped solid electrolyte material. A process for producing a solid electrochemical element, which comprises mixing solid electrolyte particles including particles of a given particle diameter with a plastic resin powder or grain, forming the resulting mixture to produce a shaped material of solid electrolyte particles, and providing electrodes on the two opposing surfaces of the shaped material of solid electrolyte particles to form an integral body, characterized in that the step of forming the shaped solid electrolyte particle material includes forming a layer of the mixture of the coated solid electrolyte particles having a first thickness of substantially said given particle diameter and then pressing the resulting layer into a layer having a second thickness smaller than said first thickness, such that the surfaces of the solid electrolyte particles are not coated with the plastic resin in the two opposing surfaces of the shaped solid electrolyte material. A process for producing a solid electrochemical element according to claim 1 or 2, characterized in that the solid electrolyte particles are monovalent cation-conductive solid electrolyte particles. A process for producing a solid electrochemical element according to claim 1 or 3, characterized in that the plastic resin is selected from polyethylene, polypropylene, synthetic rubbers such as styrene-butadiene rubber, neoprene rubber or silicone rubber, silicone resin, acrylic resin and their mixtures. A process for producing a solid electrochemical element according to claim 2 or 3, characterized in that the plastic resin is selected from polyethylene, polypropylene, acrylic resin and their mixtures. A process for producing a solid electrochemical element according to one of claims 1 to 5, characterized in that the step of forming shaped electrode material includes dispersing and mixing electrode material particles, alone or preferably under addition of solid electrolyte particles, the particles including particles of given particle diameters, in a solvent containing a plastic resin to form powdery particles coated with the plastic resin, and shaping the mixture of the coated particles to produce a shaped electrode material, and the step of forming the shaped electrode material includes forming a layer of the mixture of the coated particles having a first thickness of substantially said given particle diameter and then pressing the resulting layer into a layer having a second thickness smaller than said first thickness, such that the surfaces of the particles are not coated with the plastic resin in the surface contacting the shaped solid electrolyte material. A process for producing a solid electrochemical element according to one of claims 1 to 5, characterized in that the step of providing the shaped electrode material includes mixing electrode material particles, alone or preferably under addition of solid electrolyte particles, the particles including particles of a given particle diameter, with a plastic resin powder or grain, shaping the resulting mixture to produce a shaped electrode material, and the step of forming the shaped electrode material includes forming a layer of the mixture of the coated particles having a first thickness of substantially said given particle diameter and then pressing the resulting layer into a layer having a second thickness smaller than said first thickness, such that the surfaces of the particles are not coated with the plastic resin in the surface contacting the shaped solid electrolyte material. A process for producing a solid electrochemical element according to claim 6 or 7, characterized in that at least either one of the electrode material particles and the solid electrolyte particles constituting the shaped electrode material are coated with a plastic resin. A process for producing a solid electrochemical element acccording to claim 6 or 8, characterized in that the plastic resin is selected from polyethylene, polypropylene, synthetic rubbers such as styrene-butadiene rubber, neoprene rubber or silicone rubber, silicone resin, acrylic resin and their mixtures. A process for producing a solid electrochemical element according to claim 7 or 8, characterized in that the plastic resin is selected from polyethylene, polypropylene, acrylic resin and their mixtures. A solid electrochemical element comprising a shaped solid electrolyte material of a layer made from a mixture of solid electrolyte particles (1), including particles of a given particle diameter, and a plastic resin (2), and comprising electrodes (14,16) on each of the opposing surfaces of the solid electrolyte material, wherein the solid electrolyte particles (1) extend from one of the opposing surfaces of the solid electrolyte material to the other, the solid electrolyte particles (1) being coated with the plastic resin except the surfaces of the solid electrolyte particles (1) lying in the two opposing surfaces of the solid electrolyte material, which are not coated with the plastic resin to provide for an electrical contact with the electrodes (14,16), characterized in that the uncoated surfaces of the solid electrolyte particles (1) are formed by pressing a layer (5) of the mixture of the solid electrolyte particles (1) and the plastic resin (2) having a first thickness of substantially the given particle diameter into a layer having a second thickness smaller than said first thickness, the resulting pressed surfaces of the solid electrolyte particles (1) form the uncoated surfaces lying in the two opposing surfaces of the solid electrolyte material. A solid electrochemical element according to claim 11, characterized in that the shaped electrode material is a mixture of electrode material particles and solid electrolyte particles. A solid electrochemical element according to claim 11 or 12, characterized in that at least either one of the electrode material particles and the solid electrolyte particles constituting the shaped electrode material are coated with a plastic resin. A solid electrochemical element according to anyone of claims 11 to 13, characterized in that the solid electrolyte particles are monovalent cation-conductive solid electrolyte particles. A solid electrochemical element according to anyone of claims 11 to 14, characterized in that the plastic resin is selected from polyethylene, polypropylene, synthetic rubbers such as styrene-butadiene rubber, neoprene rubber, and silicone rubber, silicone resin, acrylic resin and their mixtures.

Inventors: KONDO, SHIGEO, SOTOMURA, TADASHI
Applicants: MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1987
Main classification: H01M6
IPC codes: H01M4, G02F1, H01M6, H01G9, H01M12