Gel electrolyte and gel-electrolyte battery

Abstract: A gel electrolyte and a gel-electrolyte battery are disclosed which have an improved cycle characteristic and preservation easiness at high temperatures. The gel-electrolyte battery incorporates a positive-electrode mix layer (3), a negative-electrode mix layer (5) and a gel-electrolyte layer (6). The gel-electrolyte layer contains a plasticizer which contains lithium salt, a matrix polymer for dispersing the plasticizer and fibrous insolubles. The fibrous insolubles are contained in the gel electrolyte in a quantity not less than 0.1wt% nor more than 50wt%. The ratio of the length and diameter of the fiber is not less than 10 nor more than 3000. The length of the fiber is not less than 10µm nor more than 1cm and the diameter of the fiber is not less than 0.05µm nor more than 50µm.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a gel electrolyte containing fibrous insolubles and a gel-electrolyte battery incorporating the gel electrolyte. Description of the Related Art In recent years, portable electronic apparatuses including camcorders (VTR) portable telephones and portable computers have come on the market. An attempt has been made to reduce the size and weight of the foregoing electronic apparatuses. As the portable power sources for the foregoing electronic apparatuses, batteries, in particular, secondary batteries, and more particularly lithium batteries have energetically researched and developed to reduce the thickness of the battery and realize a foldable structure. As the electrolyte for above-mentioned batteries, solid electrolytes manufactured by solidifying an electrolyte have energetically been studied. In particular, attention is being given to a solid electrolyte (hereinafter called a "gel electrolyte") containing a polymer compound. As a plasticizer adaptable to the gel electrolyte, an electrolyte has been employed which has prepared by dissolving lithium salt, such as LiPF 6 , in non-aqueous carbonate solvent of, for example, propylene carbonate (PC) or γ-butyrolactone. In the foregoing case, a gel electrolyte exhibiting a relatively high conductivity can be obtained. Thus, the foregoing structure has been expected to be put into practical use. The non-aqueous solvent, such as PC or γ-butyrolactone, which is capable of improving ion conductivity, however, deteriorates the mechanical strength of the gel electrolyte depending on the content. Hence it follows that the cycle characteristic and reservation easiness of the lithium-ion battery deteriorate excessively. What is worse, an adverse influence is exerted on the characteristics of the battery including the discharge capacity. Also a gel electrolyte which does not incorporate the non-aqueous solvent, such as PC or γ-butyrolactone, encounters the foregoing problems if the glass transition point or the molecular weight of the matrix polymer contained in the gel electrolyte or the molecular weight is low similar to the plasticizer. SUMMARY OF THE INVENTION In view of the foregoing, an object of the present invention is to provide a gel electrolyte which is capable of improving the cycle characteristic of a lithium-ion battery and preservation easiness at high temperatures and a gel-electrolyte battery incorporating the gel electrolyte. To achieve the foregoing object, according to one aspect of the present invention, there is provided a gel electrolyte comprising: a plasticizer containing lithium salt; matrix polymer for dispersing the plasticizer; and fibrous insolubles according to claim 1. A gel-electrolyte battery comprising: a positive-electrode-mix layer; a negative-electrode-mix layer; and a gel-electrolyte layer, wherein the gel-electrolyte layer is constituted by a gel electrolyte containing a plasticizer which contains lithium salt, a matrix polymer for dispersing the plasticizer and fibrous insolubles according to claim 7. The gel electrolyte and the gel-electrolyte battery according to the present invention has the structure that the gel electrolyte which constitutes the gel electrolyte layer contains the fibrous insolubles. Therefore, the mechanical strength of the gel electrolyte and the gel electrolyte layer constituted by the gel electrolyte can be increased. Moreover, the cycle characteristic and preservation easiness at high temperatures can be improved. Other objects, features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram showing the structure of a gel-electrolyte battery. DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the gel electrolyte and a gel-electrolyte battery according to the present invention will now be described. The gel electrolyte incorporates fibrous insolubles, plasticizer containing lithium salt and matrix polymer in a quantity not less than 10 wt% nor more than 50 wt%. When the insolubles contained in the gel electrolyte are fibrous insolubles as described above, the mechanical strength of the gel electrolyte can be maintained at a lower concentration as compared with spherical insolubles. The fibrous insolubles is insoluble or swollen when the fibrous insolubles is, at 100°C for 24 hours, immersed in an electrolytic solution for use when the gel electrolyte is prepared. Moreover, the ratio of the length of the fiber and the diameter of the fiber is 10 or higher. The content of the fibrous insolubles employed to serve as a component of the gel electrolyte is not less than 0.1 wt% nor more than 50 wt% of the gel electrolyte. If the quantity of the fibrous insolubles contained in the gel electrolyte is too small, the mechanical strength cannot be maintained in spite of a permitted high ion conductivity. If the quantity of the fibrous insolubles contained in the gel electrolyte is too large, the ion conductivity is lowered in spite of the maintained high mechanical strength. When the content of the fibrous insolubles in the gel electrolyte is not less than 0.1 wt% nor more than 50 wt%, both of the required ion conductivity and mechanical strength can be realized. The fibrous insolubles have a structure that a ratio of the length and diameter of the fiber satisfies a range not less than 10 nor more than 3000. The length of fibers of the fibrous insolubles satisfying the foregoing ratio of the length and the diameter of the fiber is 10 µm to 1 cm and the diameter of the same is 0.05 µm to 50 µm. In particular, it is preferable that the fibrous insolubles are short fibers exhibiting excellent dispersing characteristic. The fibrous insolubles of the foregoing type are exemplified by inorganic oxide, such as Al 2 O 3 , SiO 2 , ZrO, BaO or ITO; an inorganic substance, such as TiN, WC, B 4 C or SiC; hydrocarbon polymer, such as polyethylene or polypropylene; acrylic polymer, such as polyethylene-acrylic acid copolymer; aromatic ester polymer, such as polyethylene terephthalate; polyamide, such as nylon; aromatic polyamide, such as poly-p-phenylene terephthalamide; cellulose; a crosslinked material of polyethylene oxide or acrylic polymer. The lithium salt which is contained in the plasticizer may be known lithium salt for use in a usual electrolyte of a battery. It is preferable that any one of the following materials is employed: LiPF 6 , LiBF 4 , LiAsF 6 , LiClO 4 , LiCF 3 SO 3 , LiN (SO 2 CF 3 ) 2 , LiC (SO 2 CF 3 ) 3 , LiAlCl 4 and LiSiF 6 . In particular, it is preferable that LiPF 6 or LiBF 4 is employed from a viewpoint of stability of oxidation. It is preferable that the lithium salt, such as LiPF 6 , of the plasticizer satisfies a range from 0.1 mol/l to 3.0 mol/l, more preferably a range not less than 0.5 mol/l nor more than 2.0 mol/l. The matrix polymer for gelling the plasticizer may be any one of a variety of polymers for use to constitute the gel electrolyte when the gel electrolyte is prepared. For example, any one of the following materials may be employed: fluorine polymer, such as vinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer; ether polymer, such as ethylene oxide or its crosslinked material; and acrylonitrile. In particular, the fluorine polymer, such as vinylidene fluoride or fluoride-hexafluoropropylene copolymer is employed from a viewpoint of stability of oxidation and reduction. A gel-electrolyte battery 1 incorporating the gel electrolyte layer composed of the foregoing gel electrolyte will now be described. As shown in Fig. 1, the gel-electrolyte battery 1 incorporates a positive-electrode mix layer 3 formed on a positive-electrode collector 2; a negative-electrode mix layer 5 formed on a negative-electrode collector 4; and a gel-electrolyte layer 6 formed between the positive-electrode mix layer 3 and the negative-electrode mix layer 5. The positive-electrode mix layer 3 incorporates an active material of the positive electrode which is metal oxide, metal sulfide or specific polymer to be adaptable to the type of a required battery. When, for example, a lithium-ion battery is constituted, metal sulfide or metal oxide, such as TiS 2 , MoS 2 , NbSe 2 or V 2 O 5 , which does not contain lithium; or a lithium composite oxide mainly composed of Li x MO 2 (where M is one or more types of transition metal and x, which varies depending on the duration of charge/discharge of the battery, is not less than 0.05 nor more than 1.10). It is preferable that the transition metal M which constitutes the lithium composite oxide in the positive-electrode mix layer 3 is Co, Ni or Mn. The lithium composite oxide is exemplified by LiCoO 2 , LiNiO 2 , LiNi y Co 1-y O 2 (where 0 < y < 1) and LiMn 2 O 4 . The foregoing Lithium composite oxide is an active material for the positive electrode which is capable of generating high voltage and which exhibits a satisfactorily high energy density. The positive-electrode mix layer 3 may contain one or more types of the foregoing active material of the positive electrode. When the positive-electrode mix layer 3 is constituted by using the foregoing active material of the positive electrode, a known conductive material and a binder may be added. The negative-electrode mix layer 5 is made of a material into which lithium can be doped and from which lithium can be dedoped. The material of the foregoing negative-electrode mix layer 5 may be a carbon material, for example, non-graphitizable carbon material or a graphite material. Specifically, any one of the following materials may be employed: a sintered material of organic polymer compound obtained by baking, at a proper temperature, and baking pyrocarbon, cokes, such as pitch cokes, needle cokes, petroleum cokes, graphite, vitreous carbon, phenol resin or furan resin; carbon fiber and active carbon. As a material of the negative-electrode mix layer 5 which permits doping/dedoping lithium, polymer, such as polyacetylene or polypyrrole or oxide, such as SnO 2 , may be employed. When the negative-electrode mix layer 5 is constituted by using the foregoing material, a known binder may be added. The gel-electrolyte layer 6 is formed by applying the gel electrolyte having the above-mentioned composition to the positive-electrode mix layer 3 and the negative-electrode mix layer 5 and by joining and contact-bonding the surfaces applied with the gel electrolyte to each other. The shape of the gel-electrolyte battery having the above-mentioned structure is not limited. The gel-electrolyte battery may variously be formed into a cylindrical shape, a square shape, a coin shape or a button shape. Also the size of the gel-electrolyte battery may have a large size, a small size or a thin structure. Examples Examples and comparative examples of the gel-electrolyte battery according to the present invention will now be described. Gel-electrolyte batteries according to Examples 1 to 50 and Comparative Examples 1 to 14 were manufactured as follows. Example 1 Initially, a positive electrode was manufactured as follows. To obtain LiCoO 2 , which was the active material of the positive electrode, lithium carbonate and cobalt carbonate were mixed with each other at a molar ratio of 0.5:1. Then, the mixed materials were baked at 900°C at 5 hours in air. Then, 85 parts by weight of obtained LiCoO 2 , 10 parts by weight of graphite serving as the conductive material and 3 parts by weight of vinylidene fluoride serving as the binder were mixed with one another so that a positive-electrode mix was prepared. Then, the mixed materials were dispersed in N-methyl-2-pyrolidone so that slurry was obtained. The positive-electrode mix in the form of slurry was uniformly applied to either surface of elongated aluminum foil which was a positive-electrode collector and which had a thickness of 20 µm. Then, the surface of aluminum foil was dried. Then, the aluminum foil was compression-molded by a roll pressing machine so that a positive-electrode mix layer was formed. As a result, the positive electrode composed of the positive-electrode mix layer and the positive-electrode collector was manufactured. Then, a negative electrode was manufactured. Pulverized powder of cokes in a quantity of 90 parts by weight and 10 parts by weight vinylidene fluoride serving as a binder were mixed so that a negative-electrode mix was prepared. Then, the negative-electrode mix was dispersed in N-methyl-2-pyrolidone so that a slurry material was prepared. The negative-electrode mix in the form of the slurry was uniformly applied to either surface of elongated copper foil serving as a negative-electrode collector and having a thickness of 10 µm. Then, the copper foil was dried, and then compression-molded so that a negative-electrode-mix layer was formed. Thus, the negative electrode composed of the negative-electrode-mix layer and the negative-electrode collector was manufactured. A gel electrolyte was obtained as follows. Initially, 30 g of plasticizer (the composition of the plasticizer was such that the weight ratio of EC and PC was 2:1) containing 15 parts by weight of LiPF 6 , 10 g of vinylidene fluoride-hexafluoropropylene copolymer, 0.04 g (the percentage contents was 0.0999 %) of short fiber of Al 2 O 3 (the fiber diameter was 0.1 µm and the fiber length was 100 µm) and 60 g of dimethyl carbonate were mixed and dissolved so that a gel electrolyte solution was prepared. The gel electrolyte solution was uniformly applied to the surface of the positive-electrode mix layer and the negative-electrode mix layer formed on each collector by coating operations. Then, the formed structure was allowed to stand at room temperature for 8 hours to vaporize and remove dimethyl carbonate so that the gel electrolyte was obtained. Then, the surfaces applied with the gel electrolyte for the positive electrode and that for the negative electrode were joined and contact-bonded to each other so that a gel electrolyte layer was formed. Thus, a 2.5 cm × 4.0 cm flat gel-electrolyte battery having a thickness of 0.3 mm was manufactured. Examples 2 to 13 A process similar to that according to Example 1 was performed except for the contents, the percentage contents, the length of the fiber and the diameter of the same of the Al 2 O 3 in the form of short fiber contained in the gel electrolyte which were as shown in Table 1. Thus, gel-electrolyte batteries were manufactured. Examples 14 to 21 A process similar to that according to Example 1 was performed except for SiO 2 employed as the fibrous insolubles contained in the gel electrolyte and the contents, the percentage contents, the length of the fiber and the diameter of the same of the Al 2 O 3 which were as shown in Table 1. Thus, gel-electrolyte batteries were manufactured. Examples 22 to 25 A process similar to that according to Example 1 was performed except for SiC employed as the fibrous insolubles contained in the gel electrolyte and the contents, the percentage contents, the length of the fiber and the diameter of the same of the Al 2 O 3 which were as shown in Table 1. Thus, gel-electrolyte batteries were manufactured. Comparative Example 1 A process similar to that according to Example 1 was performed except for a gel electrolyte which did not contain the fibrous insolubles which was employed in this comparative example. Thus, a gel-electrolyte battery was manufactured. Comparative Example 2 A process similar to that according to Example 1 was performed except for the contents, the percentage contents, the length of the fiber and the diameter of the same of the Al 2 O 3 in the form of short fiber contained in the gel electrolyte which were as shown in Table 1. Thus, gel-electrolyte batteries were manufactured. Comparative Examples 3 to 6 A process similar to that according to Example 1 was performed except for SiO 2 employed as the fibrous insolubles contained in the gel electrolyte and the contents, the percentage contents, the length of the fiber and the diameter of the same of the SiO 2 which were as shown in Table 1. Thus, gel-electrolyte batteries were manufactured. Name of Substance Contents (g) Percentage Contents (%) Example 1 Al 2 O 3 0.04 0.0999 Example 2 Al 2 O 3 0.5 1.2346 Example 3 Al 2 O 3 1 2.439 Example 4 Al 2 O 3 10 20 Example 5 Al 2 O 3 40 50 Example 6 Al 2 O 3 0.5 1.2346 Example 7 Al 2 O 3 0.5 1.2346 Example 8 Al 2 O 3 0.5 1.2346 Example 9 Al 2 O 3 0.5 1.2346 Example 10 Al 2 O 3 0.5 1.2346 Example 11 Al 2 O 3 0.5 1.2346 Example 12 Al 2 O 3 0.5 1.2346 Example 13 Al 2 O 3 0.5 1.2346 Example 14 SiO 2 0.04 0.0999 Example 15 SiO 2 40 50 Example 16 SiO 2 0.5 1.2346 Example 17 SiO 2 0.5 1.2346 Example 18 SiO 2 0.5 1.2346 Example 19 SiO 2 0.5 1.2346 Example 20 SiO 2 0.5 1.2346 Example 21 SiO 2 0.5 1.2346 Example 22 SiC 0.5 1.2346 Example 23 SiC 0.5 1.2346 Example 24 SiC 0.5 1.2346 Example 25 SiC 0.5 1.2346 Comparative Example 1 - 0 0 Comparative Example 2 Al 2 O 3 50 55.556 Comparative Example 3 SiO 2 0.5 1.2346 Comparative Example 4 SiO 2 0.5 1.2346 Comparative Example 5 SiO 2 0.5 1.2346 Comparative Example 6 SiO 2 0.5 1.2346 Diameter (d/µm) Length (L/µm) L/d Example 1 0.1 100 1000 Example 2 0.1 100 1000 Example 3 0.1 100 1000 Example 4 0.1 100 1000 Example 5 0.1 100 1000 Example 6 0.05 0.5 10 Example 7 3 30 10 Example 8 50 500 10 Example 9 0.05 50 1000 Example 10 3 3000 1000 Example 11 50 50000 1000 Example 12 0.05 150 3000 Example 13 3 9000 3000 Example 14 0.05 100 2000 Example 15 0.05 100 2000 Example 16 0.05 0.5 10 Example 17 3 30 10 Example 18 50 500 10 Example 19 0.05 150 3000 Example 20 3 9000 3000 Example 21 50 150000 3000 Example 22 3 30 10 Example 23 30 300 10 Example 24 3 1500 500 Example 25 30 15000 500 Comparative Example 1 - - - Comparative Example 2 0.1 100 1000 Comparative Example 3 200 2000 10 Comparative Example 4 200 100000 500 Comparative Example 5 5 5 1 Comparative Example 6 5 25000 5000 Discharge Capacity Retention Ratio After 400 Cycles (%) Discharge Capacity Retention Ratio After Preservation at High Temperature (%) Recovery Ratio (%) Example 1 80.1 79 92 Example 2 82.3 80.1 91.2 Example 3 81.9 82 93.5 Example 4 80.5 82.6 89.4 Example 5 79.3 81.9 90.5 Example 6 80.6 82 92.7 Example 7 80.4 82.4 89.9 Example 8 79.7 81.2 89.7 Example 9 80.1 81.6 90.5 Example 10 80.6 82.3 91.5 Example 11 79.9 81.9 88 Example 12 81.3 81.9 89.5 Example 13 82 78.4 88.1 Example 14 84.5 81.2 90.4 Example 15 80.9 81.1 91 Example 16 79.6 80 89.4 Example 17 79.2 80 90.6 Example 18 78.9 80.6 90.1 Example 19 81.2 81 88.8 Example 20 81.3 80.4 89.9 Example 21 83.1 79.2 90 Example 22 78.5 79.6 85.1 Example 23 78.5 80.1 87.3 Example 24 79.7 81 87.9 Example 25 78.9 81.6 88.6 Comparative Example 1 41.6 40.5 52.3 Comparative Example 2 75.1 78.1 74.1 Comparative Example 3 59.8 56 62.8 Comparative Example 4 67.1 43.5 59.9 Comparative Example 5 63.7 49.1 63.1 Comparative Example 6 58.2 77.7 68 Examples 26 to 38 A process similar to that according to Example 1 was performed except for poly-p-phenylene terephthalamide (PPTA) employed as the fibrous insolubles contained in the gel electrolyte and the contents, the percentage contents, the length of the fiber and the diameter of the same of the poly-p-phenylene terephthalamide (PPTA) which were as shown in Table 2. Thus, gel-electrolyte batteries were manufactured. Example 39 to 46 A process similar to that according to Example 1 was performed except for polyethylene (PE) employed as the fibrous insolubles contained in the gel electrolyte and the contents, the percentage contents, the length of the fiber and the diameter of the same of the PE (PE) which were as shown in Table 2. Thus, gel-electrolyte batteries were manufactured. Examples 47 and 48 A process similar to that according to Example 1 was performed except for (n-PEO) obtained by three-dimensional crosslinking polyethylene oxide (PEO) with toluidine triisocyanate and employed as the fibrous insolubles contained in the gel electrolyte and the contents, the percentage contents, the length of the fiber and the diameter of the same of the (n-PEO) which were as shown in Table 2. Thus, gel-electrolyte batteries were manufactured. Example 49 and 50 A process similar to that according to Example 1 was performed except for (n-PMMA) obtained by three-dimensional crosslinking methyl polymethacrylate (PMMA) with polyethylene glycol diacrylate and employed as the fibrous insolubles contained in the gel electrolyte and the contents, the percentage contents, the length of the fiber and the diameter of the same of the (n-PMMA) which were as shown in Table 2. Thus, gel-electrolyte batteries were manufactured. Comparative Example 7 and 10 to 12 A process similar to that according to Example 1 was performed except for polyethylene (PE) employed as the fibrous insolubles contained in the gel electrolyte and the contents, the percentage contents, the length of the fiber and the diameter of the same of polyethylene (PE) which were as shown in Table 2. Thus, gel-electrolyte batteries were manufactured. Comparative Examples 8 and 9 A process similar to that according to Example 1 was performed except for poly-p-phenylene terephthalamide (PPTA) employed as the fibrous insolubles contained in the gel electrolyte and the contents, the percentage contents, the length of the fiber and the diameter of the same of poly-p-phenylene terephthalamide (PPTA) which were as shown in Table 2. Thus, gel-electrolyte batteries were manufactured. Comparative Example 13 A process similar to that according to Example 1 was performed except for polyethylene oxide (PEO) which was not three-dimensional crosslinked with toluidine triisocyanate and which was employed as the fibrous insolubles contained in the gel electrolyte and the contents, the percentage contents, the length of the fiber and the diameter of the same of polyethylene oxide (PEO) which were as shown in Table 2. Thus, a gel-electrolyte batteries was manufactured. Comparative Example 14 A process similar to that according to Example 1 was performed except for methyl polymethacrylate (PMMA) which was not three-dimensional crosslinked with polyethylene glycol diacrylate and which was employed as the fibrous insolubles contained in the gel electrolyte and the contents, the percentage contents, the length of the fiber and the diameter of the same of methyl polymethacrylate (PMMA) which were as shown in Table 2. Thus, a gel-electrolyte batteries was manufactured. Name of Substance Contents (g) Percentage Contents (%) Example 26 PPTA 0.04 0.0999 Example 27 PPTA 0.5 1.234568 Example 28 PPTA 1 2.439024 Example 29 PPTA 10 20 Example 30 PPTA 40 50 Example 31 PPTA 0.5 1.234568 Example 32 PPTA 0.5 1.234568 Example 33 PPTA 0.5 1.234568 Example 34 PPTA 0.5 1.234568 Example 35 PPTA 0.5 1.234568 Example 36 PPTA 0.5 1.234568 Example 37 PPTA 0.5 1.234568 Example 38 PPTA 0.5 1.234568 Example 39 PE 0.04 0.0999 Example 40 PE 40 50 Example 41 PE 0.5 1.234568 Example 42 PE 0.5 1.234568 Example 43 PE 0.5 1.234568 Example 44 PE 0.5 1.234568 Example 45 PE 0.5 1.234568 Example 46 PE 0.5 1.234568 Example 47 n-PEO 0.5 1.234568 Example 48 n-PEO 0.5 1.234568 Example 49 n-PMMA 0.5 1.234568 Example 50 n-PMMA 0.5 1.234568 Comparative Example 7 PE 50 55.55556 Comparative Example 8 PPTA 50 55.55556 Comparative Example 9 PPTA 0.5 1.234568 Comparative Example 10 PE 0.5 1.234568 Comparative Example 11 PE 0.5 1.234568 Comparative Example 12 PE 0.5 1.234568 Comparative Example 13 PEO 0.5 1.234568 Comparative Example 14 PMMA 0.5 1.234568 Diameter (d/µm) Length (L/µm) L/d Example 26 2 1500 750 Example 27 2 1500 750 Example 28 2 1500 750 Example 29 2 1500 750 Example 30 2 1500 750 Example 31 0.05 0.5 10 Example 32 5 50 10 Example 33 50 500 10 Example 34 0.05 50 1000 Example 35 5 5000 1000 Example 36 50 50000 1000 Example 37 0.05 150 3000 Example 38 50 150000 3000 Example 39 0.05 100 2000 Example 40 0.05 100 2000 Example 41 0.05 0.5 10 Example 42 4 40 10 Example 43 50 500 10 Example 44 0.05 150 3000 Example 45 4 12000 3000 Example 46 50 150000 3000 Example 47 10 10000 1000 Example 48 50 50000 1000 Example 49 10 10000 1000 Example 50 50 50000 1000 Comparative Example 7 4 12000 3000 Comparative Example 8 2 1500 1000 Comparative Example 9 150 1500 10 Comparative Example 10 250 125000 500 Comparative Example 11 12 12 1 Comparative Example 12 50 250000 5000 Comparative Example 13 50 500 10 Comparative Example 14 50 15000 500 Discharge Capacity Retention Ratio After 400 Cycles (%) Discharge Capacity Retention Ratio After Preservation at High Temperature (%) Recovery Ratio (%) Example 26 81 80.1 90 Example 27 83.2 80.1 91.5 Example 28 81.2 80.6 91.5 Example 29 83.1 79.2 90.6 Example 30 80.1 80.9 90 Example 31 79.9 81.6 91 Example 32 80.3 81.9 91.2 Example 33 80.5 80.9 91.3 Example 34 80.6 80.8 92 Example 35 81 80.7 91.5 Example 36 79.5 79.2 89 Example 37 82 80.6 90 Example 38 79.1 80.8 90.5 Example 39 85 80 89.7 Example 40 83 80.8 88.8 Example 41 84 81 90.5 Example 42 83.1 82 90.6 Example 43 84.4 80.6 91 Example 44 81 81.2 89.6 Example 45 84.8 82 90.4 Example 46 82.3 80 89.4 Example 47 79.1 79.9 89.5 Example 48 79.9 79.2 90 Example 49 84.2 81 89.6 Example 50 83.2 80.7 89 Comparative Example 7 77.9 70.5 64.5 Comparative Example 8 76 78.1 70.1 Comparative Example 9 61.3 55.6 63.8 Comparative Example 10 59.9 44.4 61 Comparative Example 11 63.7 50 74 Comparative Example 12 66 78.3 70.5 Comparative Example 13 48.2 52.6 50 Comparative Example 14 50.3 60.4 49.7 Evaluation The cycle characteristic and the preservation characteristic at high temperatures of the thus-manufactured gel-electrolyte batteries according to Examples 1 to 50 and Comparative Examples 1 to 14 were evaluated as follows. Each gel-electrolyte battery was charged for 5 hours with constant voltage and electric current of 30 mA at 23°C such that the upper limit of the charge with the electric current was 4.2 V. Then, each gel-electrolyte battery was discharged with a constant electric current of 30 mA such that the end voltage was 2.5 V. The initial discharge capacity was determined as described above. Then, the foregoing charge/discharge were performed 400 cycles under the foregoing charge/discharge conditions. Then, a capacity retention ratio after 400 cycles in a state where the initial discharge capacity was 100 % was determined. Each gel-electrolyte battery was charged/discharged under the foregoing charge/discharge conditions, and then the gel-electrolyte batteries were preserved at an environmental temperature of 80°C for 21 days. The discharge capacity after the preservation and the discharge-capacity retention ratio realized after charge and discharge were performed in a state where the initial capacity was 100 % were determined. As can be understood from Tables 1 and 2, the gel-electrolyte batteries according to Examples 1 to 50 in which the gel electrolyte layer constituted by the gel electrolyte containing fibrous insolubles exhibited satisfactory cycle characteristic and preservation easiness at high temperatures. The results were superior to those of the gel-electrolyte battery according to Comparative Example 1 in which the gel electrolyte layer was constituted by the gel electrolyte which did not contain the fibrous insolubles. Also the gel-electrolyte batteries according to Examples 1 to 50 had the structure that the gel electrolyte layer was constituted by the gel electrolyte which contained the fibrous insolubles having the structure that the ratio L/d of the fiber length L and the fiber diameter d was not less than 10 nor more than 3000 in a quantity not less than 0.1 wt% nor more than 50 wt%. The foregoing gel-electrolyte batteries exhibited a satisfactory cycle characteristic. The gel-electrolyte battery according to Examples 1 to 50 had the structure that the gel electrolyte layer was constituted by the gel electrolyte containing the fibrous insolubles having the structure that the fiber length L was not less than 10 µm nor more than 1 cm and the fiber diameter was not less than 0.05 µm nor more than 50 µm. The foregoing gel-electrolyte batteries exhibited further satisfactory preservation easiness at high temperatures. As can be understood from Table 1, Comparative Example 2 had the structure that the percentage contents of fibrous insolubles Al 2 O 3 were high than 50 wt%. Comparative Examples 3 and 4 had the structure that the fiber diameter d of the fibrous insolubles SiO 2 was larger than 50 µm. Comparative Example 5 had the structure that the ratio L/d of the fiber length L and the fiber diameter d of the fibrous insolubles SiO 2 was not higher than 10. Comparative Example 6 had the structure that the ratio L/d of the fiber length L and the fiber diameter d of the fibrous insolubles SiO 2 was not lower than 3000. The foregoing gel-electrolyte batteries were unsatisfactory from the viewpoint of the cycle characteristic and the preservation easiness at high temperatures as compared with Examples 1 to 25. As can be understood from Table 2, Comparative Examples 7 and 8 had the structure that the contents percentage of fibrous insolubles PE or PPTA were higher than 50 wt%. Comparative Examples 9 and 10 had the structure that the fiber direction d of fibrous insolubles PE or PPTA was larger than 50 m. Comparative Example 11 had the structure that the ratio L/d of the fiber length L and the fiber diameter d of the fibrous insolubles PE was not higher than 10. Comparative Example 12 had the structure that the ratio L/d of the fiber length L and the fiber diameter d of the fibrous insolubles PE was not lower than 3000. Comparative Examples 13 and 14 had the structure that the fibrous insolubles PEO or PMMA was not three-dimensionally crosslinked. The foregoing gel-electrolyte batteries were unsatisfactory from the viewpoints of the cycle characteristic and the preservation easiness at high temperatures as compared with Examples 26 to 50. As described above, the gel electrolyte and the gel-electrolyte battery according to the present invention have the structure that the gel electrolyte contains the fibrous insolubles. As a result, the cycle characteristic and the preservation easiness at high temperatures can be improved. Although the invention has been described in its preferred form and structure with a certain degree of particularity, it is understood that the present disclosure of the preferred form can be changed in the details of construction and in the combination and arrangement of parts without departing from the scope of the invention as hereinafter claimed.

Claims: A gel electrolyte comprising: a plasticizer containing lithium salt; matrix polymer for dispersing said plasticizer; and fibrous insolubles, wherein said fibrous insolubles are contained in a quantity not less than 0.1 wt% nor more than 50 wt%; have a structure that a ratio of the length of fiber and the diameter of the fiber satisfies a value not less than 10 nor more than 3000; and have a length of fiber which is not less than 10 µm nor more than 1 cm and a diameter of the fiber which is not less than 0.05 µm nor more than 50 µm. A gel electrolyte according to claim 1, wherein said fibrous insolubles are made of an organic polymer material. A gel electrolyte according to claim 1, wherein said fibrous insolubles are made of a polymer material having a crosslinked structure. A gel electrolyte according to claim 1, wherein said fibrous insolubles have a characteristic that said fibrous insolubles are swollen when said fibrous insolubles are immersed in an electrolytic solution. A gel electrolyte according to claim 1, wherein at least one type of said matrix polymers is fluorine polymer. A gel electrolyte according to claim 5, wherein said fluorine polymer is vinylidene fluoride or vinylidene fluoride-hexafluoropropylene copolymer. A gel-electrolyte battery comprising: a positive-electrode-mix layer; a negative-electrode-mix layer; and a gel-electrolyte layer, wherein said gel-electrolyte layer is constituted by a gel electrolyte containing a plasticizer which contains lithium salt, a matrix polymer for dispersing said plasticizer and fibrous insolubles, wherein said fibrous insolubles are contained in a quantity not less than 0.1 wt% nor more than 50 wt%; have a structure that a ratio of the length of fiber and the diameter of the fiber satisfies a value not less than 10 nor more than 3000; and have a length of fiber which is not less than 10 µm nor more than 1 cm and a diameter of the fiber which is not less than 0.05 µm nor more than 50 µm. A gel-electrolyte battery according to claim 7, wherein said fibrous insolubles are made of an organic polymer material. A gel-electrolyte battery according to claim 7, wherein said fibrous insolubles are made of a polymer material having a crosslinked structure. A gel-electrolyte battery according to claim 7, wherein said fibrous insolubles have a characteristic that said fibrous insolubles are swollen when said fibrous insolubles are immersed in an electrolytic solution. A gel-electrolyte battery according to claim 7, wherein at least one type of said matrix polymers is fluorine polymer. A gel-electrolyte battery according to claim 11, wherein said fluorine polymer is vinylidene fluoride or vinylidene fluoride-hexafluoropropylene copolymer. A gel-electrolyte battery according to claim 7, wherein said negative electrode contains a material to which lithium can be doped and from which lithium can be dedoped. A gel-electrolyte battery according to claim 13, wherein said material to which lithium can be doped and from which lithium can be dedoped is a carbon material. A gel-electrolyte battery according to claim 7, wherein said positive electrode is mainly composed of a composite oxide of lithium and transition metal.

Inventors: KEZUKA KOICHIRO, KEZUKA, KOICHIRO
Applicants: SONY CORP, SONY CORPORATION
Application year: 1999
Main classification: H01M6
IPC codes: H01M6, H01M4, H01M10, H01B1