JP2005166684A - Non-aqueous secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the energy amount and cycle life of a lithium secondary battery. <P>SOLUTION: The nonaqueous secondary battery comprises a positive pole that contains a positive pole material, comprising a transition metal oxide that is possible to be inserted or discharge lithium, a negative pole that contains a negative pole material, and a non-aqueous electrolyte. The negative pole material is a solid compound, containing silicon atoms that can to be inserted and discharge lithium. The solid compound has a coating comprising a plurality of materials. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a non-aqueous secondary battery, particularly a lithium secondary battery having a high capacity and a long cycle life.

In a lithium secondary battery using a negative electrode material not containing lithium metal and a positive electrode active material containing lithium, first, lithium contained in the positive electrode active material is inserted into the negative electrode material to increase the activity of the negative electrode material. This is a charging reaction, and the reverse reaction is a reaction in which lithium ions are inserted into the positive electrode active material from the negative electrode material. Carbon is used as this type of lithium battery negative electrode material. The theoretical capacity of carbon (C ₆ Li) is 372 mAh / g, and a further high capacity negative electrode material is desired. On the other hand, it is well known that the theoretical capacity of silicon forming an intermetallic compound with lithium exceeds 4000 mAh / g and is larger than that of carbon. For example, Patent Document 1 discloses single crystal silicon, and Patent Document 2 discloses amorphous silicon. Moreover, in the alloy containing silicon, the example which contains silicon in a Li-Al alloy is patent document 3 (silicon is 19 weight%), patent document 4 (silicon is 0.05-1.0 weight%), patent document 5 (1-5% by weight of silicon). However, since these alloy patent applications are mainly composed of lithium, a compound containing no lithium has been used for the positive electrode active material. Patent Document 6 discloses an alloy containing 0.05 to 1.0% by weight of silicon. Patent Document 7 discloses a method of mixing a metal that can be alloyed with lithium and graphite powder. However, both have poor cycle life and have not yet been put to practical use. The reason why the cycle life of silicon is inferior is presumed that its electronic conductivity is low, the volume expands due to lithium insertion, and the particles are pulverized.
JP-A-5-74463 Japanese Patent Laid-Open No. 7-29602 JP-A 63-66369 JP 63-174275 A JP-A 63-285865 JP-A-4-109562 JP 62-226563 A

  An object of the present invention is to increase the energy amount of a lithium secondary battery and increase the cycle life.

  An object of the present invention is to provide a positive electrode having a positive electrode active material that is a transition metal oxide capable of inserting and releasing lithium, a negative electrode having a negative electrode material, and a non-aqueous secondary battery including non-aqueous electrolytes as constituent elements. This was solved by a non-aqueous secondary battery characterized in that the material is a solid of a compound containing a silicon atom capable of inserting and releasing lithium, and the solid has a coating made of a plurality of materials.

  According to the present invention, a nonaqueous secondary battery with improved energy amount and cycle life can be obtained.

Although the aspect of this invention is demonstrated below, this invention is not limited to these.
(1) In a non-aqueous secondary battery including a positive electrode having a positive electrode active material which is a transition metal oxide capable of inserting and releasing lithium, a negative electrode having a negative electrode material, and a non-aqueous electrolyte, the negative electrode material is lithium. A non-aqueous secondary battery characterized in that the solid is a compound containing a silicon atom that can be inserted and released, and the solid has a coating made of a plurality of materials.
(2) A water secondary battery in which the silicon-containing compound of item (1) is a compound in which a metal coating and a ceramic coating are simultaneously applied to the surface of silicon.
(3) A nonaqueous secondary battery in which the silicon-containing compound according to item (1) is a compound in which a metal coating and a thermoplastic resin coating are simultaneously applied to the silicon surface.
(4) A non-aqueous secondary battery in which the silicon-containing compound of item (1) is a compound in which a metal coating, a ceramic coating, and a thermoplastic resin coating are simultaneously applied to the silicon surface.
(5) A nonaqueous secondary battery in which the average particle size of the compound containing silicon of item (1) is 0.01 to 50 μm.
(6) A non-aqueous secondary battery in which the silicon covered in the items (1) to (4) is a silicon simple substance and / or an alloy.
(7) A nonaqueous secondary battery in which the silicon simple substance of item (6) is single crystal, polycrystal, or amorphous.
(8) A nonaqueous secondary battery in which the silicon to be coated according to items (1) to (4) is an alloy.
(9) A non-aqueous secondary battery in which at least one metal other than silicon is an alkaline earth metal, transition metal, or semimetal in the alloy according to item (8).
(10) A nonaqueous secondary battery in which at least one of the metals of item (8) or (9) is Ge, Be, Ag, Al, Au, Cd, Ga, In, Sb, Sn, or Zn.
(11) A nonaqueous secondary battery according to item (10), further comprising at least one selected from Mg, Fe, Ni, Co, Ti, Mo, and W.
(12) A nonaqueous secondary battery in which the atomic ratio of metal to silicon described in item (11) exceeds 0 and is 20% or less.
(13) A non-aqueous secondary battery in which the atomic ratio of the metal to silicon according to items (8) to (12) is 5 to 90%.
(14) A nonaqueous secondary battery obtained by firing the alloy according to items (8) to (13).
(15) The nonaqueous secondary battery according to item (14), wherein the firing temperature is 1000 ° C. or higher and 1800 ° C. or lower.
(16) The nonaqueous secondary battery according to item (14) or (15), wherein the cooling temperature after firing the alloy is 10 ° C./min or more.
(17) A nonaqueous secondary battery in which the silicon according to items (1) to (4) is silicon obtained by removing metal from a metal silicide.
(18) A non-aqueous secondary battery in which the metal silicide according to item (17) is lithium silicide.
(19) The non-aqueous secondary battery in which the lithium content of the lithium silicide according to item (18) is 100 to 420 atomic% with respect to silicon.
(20) A non-aqueous secondary battery which is silicon from which lithium has been removed by treating lithium silicide with an alcohol obtained by dehydration of silicon according to item (17).
(21) A method for producing a non-aqueous secondary battery in which the method of simultaneous coating according to (2) to (4) comprises dispersing a ceramic or a thermoplastic resin in a plating solution of an electroless plating method.
(22) A non-aqueous secondary battery in which the metal covered in (21) is at least one of Ni, Cu, Ag, Co, Fe, Cr, W, Ti, Au, Pt, Pd, Sn, and Zn.
(23) A non-aqueous secondary battery in which the metal to be coated according to items (21) and (22) is at least one of Ni, Cu, and Ag.
(24) A nonaqueous secondary battery in which the specific conductivity of the silicon compound coated with the metal of items (21) to (23) is at least three times the specific conductivity of the uncoated silicon compound.
(25) A nonaqueous secondary battery in which the metal coating amount of items (21) to (24) is 1 to 80 atomic% with respect to silicon.
(26) A nonaqueous secondary battery in which the ceramic according to item (2) or (4) is at least one selected from Al ₂ O ₃ , SiO ₂ , TiO ₂ , SiC, and Si ₃ N ₄ .
(27) A nonaqueous secondary battery in which the ceramic according to item (26) is SiO ₂ .
(28) SiO ₂ according to item (27), colloidal is non-aqueous secondary battery is SiO _2.
(29) A nonaqueous secondary battery in which the weight ratio of the ceramic to silicon according to items (26) to (28) is 2 to 50%.
(30) A method for producing a non-aqueous secondary battery, wherein the method of attaching the ceramic to silicon according to (26) to (29) includes a step of heating at 300 ° C to 1600 ° C.
(31) A non-aqueous secondary battery in which the thermoplastic resin of items (3) and (4) is at least one selected from polyvinylidene fluoride and polytetrafluoroethylene.
(32) A nonaqueous secondary battery in which the weight ratio of the thermoplastic resin to silicon in item (31) is 2 to 30%.
(33) A nonaqueous secondary battery in which the coverage of the thermoplastic resin according to items (31) and (32) is 5 to 95%.
(34) A non-aqueous secondary battery in which carbon is present in an amount of 5 to 1900% by weight with respect to the silicon compound of item (1).
(35) A nonaqueous secondary battery in which carbon is present in an amount of 5 to 400% by weight with respect to the silicon compound of item (1).
(36) A non-aqueous secondary battery in which the carbon in (34) and (35) is scaly natural graphite.
(37) A nonaqueous secondary battery in which the charge / discharge range of the silicon compound of item (1) is represented by Li _x Si as _x equivalent ratio of lithium inserted and released into silicon, and x is in the range of 0 to 4.2 .
(38) A nonaqueous secondary battery in which the charge / discharge range of the silicon compound of item (1) is x in the range of 0 to 3.7 when expressed by Li _x Si.
(39) A non-aqueous secondary battery in which charging of the silicon compound according to item (1) is terminated in a range of 0.1% to 10% of 1 hour rate current.
(40) A non-aqueous secondary battery in which the charging according to item (39) is completed within 15 minutes to 10 hours.
(41) The positive electrode active material of the item (1) is a material containing Li _y MO ₂ (M = Co, Ni, Fe, Mn, y = 0 to 1.2), or Li _z N ₂ O ₄ ( A non-aqueous secondary battery using at least one material having a spinel structure represented by N = Mn z = 0 to 2).
(42) the positive electrode active material is _{Li y M a D 1-a} O 2 (M = Co, Ni, Fe, at least one of Mn in terms (41), D = Co, Ni, Fe, Mn, Al, Zn , Cu, Mo, Ag, W, Ga, In, Sn, Pb, Sb, Sr, B, P, at least one other than M, y = 0 to 1.2, a = 0.5 to 1) material containing or _{Li z (N b E 1-} b) 2 O 4 (N = Mn, E = Co, Ni, Fe, Al, Zn, Cu, Mo, Ag, W,, Ga, In, Sn, Pb , Sb, Sr, B, P, a non-aqueous secondary battery using at least one material having a spinel structure represented by b = 0.2-1 and z = 0-2.
(43) A nonaqueous secondary battery in which the average particle size of silicon used in items (2) to (42) is 0.01 to 50 μm.
(43) A nonaqueous secondary battery in which the average particle size of silicon used in items (2) to (42) is 0.05 to 5 μm.

  The positive electrode (or negative electrode) used in the present invention can be prepared by coating and molding a positive electrode mixture (or negative electrode mixture) on a current collector. The positive electrode mixture (or negative electrode mixture) includes a positive electrode active material (or negative electrode material), a conductive agent, a binder, a dispersant, a filler, an ionic conductive agent, a pressure enhancer, and various additives. it can. These electrodes may be disk-shaped or plate-shaped, but are preferably flexible sheets.

  The configuration and materials of the present invention are described in detail below. The compound containing a silicon atom capable of inserting and releasing lithium used in the negative electrode material of the present invention means a silicon simple substance, a silicon alloy, or a silicide. As the silicon compound, any of single crystal, polycrystal, and amorphous can be used. The purity of the simple substance is preferably 85% by weight or more, and particularly preferably 95% by weight or more. Furthermore, 99 weight% or more is especially preferable. Impurities mainly include Fe, Al, Ca, Mn, Mg, Ni, Cr and the like. Their content is from 0 to 0.5% by weight. The average particle size of the silicon compound is preferably 0.01 to 50 μm. In particular, 0.02 to 30 μm is preferable. Furthermore, 0.05-5 micrometers is preferable. Further, it is well known that the surface of silicon is covered with silicon dioxide, and it is considered that the surface of the silicon also serves as an ion conductive film.

  The silicon alloy is considered to be effective because it suppresses pulverization due to expansion and contraction of silicon that occurs when lithium is inserted and released, and improves the low conductivity of silicon. As the alloy, an alloy with an alkaline earth metal, a transition metal, or a metalloid is preferable. In particular, a solid solution alloy or a eutectic alloy is preferable. A solid solution alloy is an alloy that forms a solid solution. For example, an alloy of Ge is a solid solution alloy. An eutectic alloy is an alloy that is eutectic with silicon in any proportion, but the solid obtained by cooling is a mixture of silicon and metal. Be, Ag, Al, Au, Cd, Ga, In, Sb, Sn, and Zn form a eutectic alloy. Among these, alloys of Ge, Be, Ag, Al, Au, Cd, Ga, In, Sb, Sn, and Zn are more preferable. Moreover, these 2 or more types of alloys are also preferable. In particular, an alloy containing Ge, Ag, Al, Cd, In, Sb, Sn, and Zn is preferable. The mixing ratio of these alloys is preferably 5 to 90% by weight with respect to silicon. In particular, 10 to 80% by weight is preferable. Furthermore, 20 to 60% by weight is particularly preferable. In addition to eutectic alloys, Mg, Fe, Co, Ni, Ti, Mo, and W may be included. The content of these metals is preferably 0 to 20% by weight. The mixing ratio of metals other than silicon is not particularly limited. In this case, electrical conductivity is improved, but in terms of battery performance, in particular, discharge capacity, high rate characteristics, and cycle life, the specific conductivity may be 10 times or more that of silicon or a silicon compound before the alloy. preferable.

  As an alloy synthesis method, a firing method or a mechanical milling method is used. As a firing method, raw materials are mixed, transferred to a crucible, heated in an inert gas at a rate of temperature increase of 5 to 100 ° C./min, and a constant temperature of 1000 to 1800 ° C., particularly preferably Is kept at 1300 to 1700 ° C. for 10 minutes to 24 hours, particularly preferably 30 minutes to 5 hours, and cooled at a temperature lowering rate of 10 ° C./min or more. In particular, it is preferable to cool at 100 ° C./min or more. As the inert gas, it is preferable to use a gas such as argon, nitrogen, hydrogen or the like alone or in combination. It is preferable to anneal after cooling. The annealing condition is preferably in the range of 200 ° C. to a temperature at which some alloys do not melt in an inert gas.

  As the mechanical milling method, a method is used in which a plurality of metals are pulverized until they become ultrafine using a pulverizer such as a ball mill, a planetary ball mill, or a vibration mill. The inside of the mill cell is preferably filled with an inert gas, an inert liquid, a reducing gas, or a reducing liquid. As the inert gas, it is preferable to use a gas such as argon, nitrogen, hydrogen or the like alone or in combination. As the inert liquid, deoxygenated water, alcohol or the like is used. As the reducing gas, ammonia, sulfurous acid gas or the like is used. As the reducing liquid, an aqueous solution or dimethyl sulfoxide solution containing sodium sulfite, sodium thiosulfate, hydroxylamine, hydroquinone, or the like can be used. It is particularly preferable to grind with an inert gas. The milling time is preferably 1 hour to 48 hours.

  The average particle size of the alloy is preferably 0.01 to 40 μm. In particular, 0.02 to 20 μm is preferable, and 0.03 to 5 μm is particularly preferable. As a pulverization method, a vibration mill, a ball mill, a planetary ball mill, a jet mill, or an automatic mortar is used. The grinding time is preferably 1 minute to 1 hour. As the atmosphere for pulverization, the method described in the section of mechanical milling is used.

Silicide refers to a compound of silicon and metal. The _{silicide, CaSi, CaSi 2, Mg 2} Si, BaSi 2, SrSi 2, Cu 5 Si, FeSi, FeSi 2, CoSi 2, Ni 2 Si, NiSi 2, MnSi, MnSi 2, MoSi 2, CrSi 2, _{TiSi 2, Ti 5 Si 3,} Cr 3 Si, NbSi 2, NdSi 2, CeSi 2, SmSi 2, DySi 2, ZrSi 2, WSi 2, W 5 Si 3, TaSi 2, Ta 5 Si 3, TmSi 2, TbSi _{2, YbSi 2, YSi 2,} YSi 2, ErSi, ErSi 2, GdSi 2, PtSi, V 3 Si, VSi 2, HfSi 2, PdSi, PrSi 2, HoSi 2, EuSi 2, LaSi, RuSi, ReSi, RhSi etc. Is used.

  As the silicon compound, silicon obtained by removing metal from a metal silicide is preferably used. Examples of the shape of silicon include fine particles having a size of 1 μm or less and porous particles, and fine particles aggregated to form porous secondary particles. The reason why the cycle life is improved when silicon is used is considered to be difficult to pulverize. The metal of the metal silicide is preferably an alkali metal or an alkaline earth metal. Of these, Li, Ca, and Mg are preferable. In particular, Li is preferable. The average particle size of the metal silicide is preferably 0.01 to 300 μm, more preferably 0.01 to 50 μm, and most preferably 0.01 to 10 μm. The lithium content of the lithium silicide is preferably 100 to 420 mol% with respect to silicon. 200 to 420 mol% is particularly preferable. The method of removing alkali metal or alkaline earth metal from the alkali metal or alkaline earth metal silicide is preferably treated with a solvent that reacts with alkali metal or alkaline earth metal. As the solvent, water and alcohols are preferable. In the case of lithium silicide, it is preferable that deoxidized and dehydrated alcohols can suppress oxidation of silicon during the reaction. The degree of dehydration is preferably 1000 ppm or less, preferably 200 ppm or less, and most preferably 50 ppm or less. As a method of deaeration and dehydration, bubbling with an inert gas such as argon while refluxing the alcohol can be mentioned. Examples of the alcohol include methyl alcohol, ethyl alcohol, 1-propyl alcohol, 2-propyl alcohol, 1-butyl alcohol, 2-butyl alcohol, t-butyl alcohol, 1-pentyl alcohol, 2-pentyl alcohol, and 3-pentyl. Alcohol is preferred. In particular, 1-propyl alcohol, 2-propyl alcohol, 1-butyl alcohol, 2-butyl alcohol, and t-butyl alcohol are preferable. The removal of Ca and Mg is preferably water. It is more preferable to use a pH buffering agent that keeps it near neutrality. The solvent amount may be equal to or greater than the reaction equivalent, but is preferably about 10 times. The reaction temperature is not particularly limited, but is preferably room temperature or lower for allowing the reaction to proceed mildly and uniformly.

  The residual silicon powder after completion of the reaction is preferably washed after being taken out by filtration or decantation. As the cleaning liquid, the aforementioned water and alcohols are preferable. The amount of metal remaining in the powder thus obtained is preferably 1% by weight or less, and more preferably 0.1% by weight or less. In order to reduce the amount of remaining metal, it is preferable to reduce the particle size of the silicide during the reaction. Specifically, 0.01 to 300 μm is preferable, 0.01 to 50 μm is more preferable, and 0.01 to 10 μm is most preferable. As another method, it is also preferable to pulverize the powder obtained after completion of the reaction to reduce the particle size and then add it again to the reaction solvent. Moreover, it is also preferable to repeat the said grinding | pulverization and reaction as needed. Covering the silicon powder thus obtained with a metal, which will be described later, is preferable in that the discharge capacity and cycle life can be further improved.

As a method of simultaneously coating metal, ceramic and / or thermoplastic resin on silicon of the present invention, ceramic and / or thermoplastic resin is dispersed in a plating solution of an electroless plating method, and silicon solid is added to the plating solution. Can be obtained. The electroless plating method is described in Nikkan Kogyo Shimbun (1994) edited by “Electroless Plating Basics and Applications”, Electroplating Research Group. The reducing agent is preferably a phosphinate, phosphonate, borohydride, aldehyde, saccharide, amine, or metal salt. Sodium hydrogen phosphinate, sodium hydrogen phosphonate, sodium borohydride, dimethylamine borane, formaldehyde, sucrose, dextrin, hydroxylamine, hydrazine, ascorbic acid, and titanium chloride are preferred. In addition to the reducing agent, the plating solution preferably contains a pH adjusting agent and a complexing agent. Also for these, the compounds described in “Electroless plating basics and applications” are used. The plating solution composition is also described in the book. The concentration of the reducing agent is preferably 10 to 500 g per liter of water. The pH of the plating solution is not particularly limited, but 4 to 13 is preferable. The temperature of the liquid is preferably 10 ° C to 100 ° C, but 20 ° C to 95 ° C is particularly preferable. In addition to the plating bath, an activation bath composed of an aqueous SnCl ₂ hydrochloric acid solution, a nucleation bath composed of an aqueous PdCl ₂ hydrochloric acid solution, a filtration step, a water washing step, a pulverization step, and a drying step are used.

  Further, as the form of silicon to be coated, any of powder, lump, plate and the like is used. The metal to be coated may be anything as long as it is a highly conductive metal, but Ni, Cu, Ag, Co, Fe, Cr, W, Ti, Au, Pt, Pd, Sn, and Zn are particularly preferable. In particular, Ni, Cu, Ag, Co, Fe, Cr, Au, Pt, Pd, Sn, and Zn are preferable, and Ni, Cu, Ag, Pd, Sn, and Zn are particularly preferable. The amount of the metal to be coated is not particularly limited, but it is preferable to coat so that the specific conductivity is 3 times or more of the specific conductivity of the silicon compound as the base. The metal coating amount is preferably 1 to 80% by weight, particularly 1 to 50% by weight, and more preferably 1 to 30% by weight, based on silicon.

It is considered that the ceramic coated with silicon is effective in suppressing silicon micronization. As the ceramic, a compound which does not react with lithium in principle is preferable. In particular, Al ₂ O ₃ , SiO ₂ , TiO ₂ , SiC, and Si ₃ N ₄ are preferable. After coating by the electroless plating method, heating is preferably performed in the range of 300 ° C. to 1600 ° C. in an inert gas, particularly 400 ° C. to 1500 ° C., more preferably 500 ° C. to 1300 ° C. The heating time is preferably 0.5 to 24 hours. Examples of the inert gas include argon, nitrogen, and hydrogen. These mixed gases are also used. Well-known methods such as a ball mill, a vibration mill, a planetary ball mill, a jet mill, and an automatic mortar are used for the pulverization method. This pulverization is also preferably performed in the environment described in the mechanical milling, but is preferably performed in an inert gas. The mixing ratio of ceramics to silicon is preferably in the range of 2 to 50% by weight, particularly 3 to 40%. The average particle size determined from the electron microscope observation of silicon is preferably 0.01 to 40 μm. In particular, 0.5 to 20 μm is preferable, and 1 to 10 μm is more preferable.

As the thermoplastic resin used in the present invention, fluorine-containing polymer compounds, imide polymers, vinyl polymers, acrylate polymers, ester polymers, polyacrylonitrile and the like are used. In particular, the thermoplastic resin is preferably a resin that does not easily swell in the electrolytic solution. Specific examples include water-soluble polymers such as polyacrylic acid, polyacrylic acid Na, polyvinyl phenol, polyvinyl methyl ether, polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylamide, polyhydroxy (meth) acrylate, styrene-maleic acid copolymer, Polyvinyl chloride, polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, polyvinyl acetal resin, methyl methacrylate, and (meth) acrylic acid esters such as 2-ethylhexyl acrylate (Meth) acrylic acid ester copolymer, (meth) acrylic acid ester-acrylonitrile copolymer, polyvinyl ester copolymer containing vinyl ester such as vinyl acetate, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer Examples thereof include emulsions (latex) or suspensions of coalesced polybutadiene, neoprene rubber, fluoro rubber, polyethylene oxide, polyester polyurethane resin, polyether polyurethane resin, polycarbonate polyurethane resin, polyester resin, phenol resin, epoxy resin and the like. In particular, polyacrylate ester latex, carboxymethyl cellulose, polytetrafluoroethylene, and polyvinylidene fluoride are exemplified. These compounds can be used alone or in combination. Of these compounds, fluorine-containing polymer compounds are preferred. Of these, polytetrafluoroethylene and polyvinylidene fluoride are preferred. As for the thermoplastic resin shown above, the usage method as a binder at the time of comprising a negative mix layer is generally known. Whereas the usage as a binder is a method in which the active material, a conductive agent and the like are uniformly mixed, the usage as a coating agent of the present invention localizes the thermoplastic resin on the surface of the active material. It is different in point. Although it has been known that the cycle life is improved by increasing the amount of thermoplastic resin used as a binder, the method of coating the active material surface of the present invention is more effective in improving the cycle performance. Is big.

  As a usage-amount of the synthetic resin with respect to silicon, 2 to 30 weight% is preferable. In particular, 3 to 20% by weight is preferable. In the present invention, the synthetic resin is preferably partially coated. The coverage is preferably 5 to 95%, and particularly preferably 5 to 90%. Here, the coverage is defined as a percentage of the area of the portion coated with the thermoplastic resin to the total surface area of the silicon compound particles.

  In the present invention, it is preferable to use a mixture of a silicon compound and a carbonaceous compound. As the carbonaceous material, a material used for a conductive agent or a negative electrode material is used. Examples of the carbonaceous material include non-graphitizable carbon materials and graphite-based carbon materials. Specifically, carbon materials having surface spacing, density, and crystallite size described in JP-A-62-122066, JP-A-2-66856, JP-A-3-245473, etc. A mixture of natural graphite and artificial graphite described in Japanese Patent No. -290844, and vapor-grown carbon materials described in Japanese Patent Laid-Open Nos. 63-24555, 63-13282, 63-58763, and Japanese Patent Laid-Open No. 6-212617 A material obtained by heating and baking non-graphitizable carbon described in JP-A-5-182664 at a temperature exceeding 2400 ° C. and having a peak of X-ray diffraction corresponding to a plurality of 002 planes, No. 307957, JP-A-5-307958, JP-A-7-85862, and JP-A-8-315820, a mesophase carbon material synthesized by pitch firing described in JP-A-6-84516 Graphite with the above coating layer, various granular materials, microspheres, flat bodies, microfibers, whisker-shaped carbon materials, phenolic resins, acrylonitrile resins, furfuryl alcohol resin fired bodies, hydrogen atoms Examples thereof include carbon materials such as polyacene material. Furthermore, specific examples of the conductive agent include natural graphite such as scaly graphite, scaly graphite, and earthy graphite, high-temperature fired bodies such as petroleum coke, coal coke, celluloses, saccharides, and mesophase pitch, and vapor-grown graphite. Graphite such as artificial graphite, carbon black such as acetylene black, furnace black, ketjen black, channel black, lamp black, thermal black, carbon materials such as asphalt pitch, coal tar, activated carbon, mesofuse pitch, polyacene preferable. These may be used singly or as a mixture.

  In particular, carbon materials described in JP-A-5-182664, various granular materials, microspheres, flat plate bodies, fibers, whisker-shaped carbon materials, and mesophase pitch, phenol resin, acrylonitrile resin fired bodies, Furthermore, a polyacene material containing a hydrogen atom is preferable. Of these, scaly natural graphite is preferable because it makes the mixture film strong. The mixing ratio is preferably 5 to 1900% by weight with respect to the silicon compound. In particular, 20 to 500% by weight is preferable. Furthermore, 30 to 400% by weight is preferable. Although various things can be used as an average particle size of a carbonaceous material, 0.01-50 micrometers is preferable, 0.02-30 micrometers is more preferable, 0.05-5 micrometers is the most preferable.

As the conductive agent, other materials of carbon can be used as described below. The charge / discharge range of the silicon compound negative electrode material is preferably x = 0 to 4.2 when the ratio of lithium and silicon atoms that can be inserted and released is represented by Li _x Si. As a result of intensive studies on improving the cycle life of silicon, it was found that the cycle life is greatly improved when x is kept in the range of 0 to 3.7. The charge potential was 0.0 V, including overvoltage, at x = 4.2 against the lithium metal counter electrode, whereas it was about 0.05 V at x = 3.7. At this time, the shape of the discharge curve changes, and a flat discharge curve is obtained in the vicinity of 0.5 V (vs. lithium metal) at 0.0 V charge folding, whereas it is 0.05 V or more, particularly 0.08 V or more (x = 3.6), a gentle curve with an average voltage of about 0.4V is obtained. In other words, a unique phenomenon was found in which the discharge potential decreased with increasing voltage throughout charging. We also found a phenomenon in which the reversibility of the charge / discharge reaction was improved.

  As the charging start method in the present invention, a method such as a combination of open circuit constant voltage, closed circuit constant voltage, current, time, large current charging and small current charging is used. A method of setting the charging time is also preferable. The constant voltage value is set within the above range. It is preferable to stop charging when the current value falls within a range of 0.1 to 10% of the hourly current in the constant voltage region.

  Although methods having the effect of improving the cycle life while maintaining the high capacity of the silicon compound have been individually described, it has been found that a more preferable embodiment obtains a higher improvement effect by a combination of the above methods.

  In the present invention, as the negative electrode material, in addition to the silicon compound of the present invention, a carbonaceous material, oxide material, nitride material, sulfide material, lithium metal, lithium alloy and other compounds capable of inserting and releasing lithium can be combined. In particular, when a transition metal oxide is used as the positive electrode material, it is used in combination with lithium metal or a lithium alloy.

As the positive electrode material used in the present invention, a transition metal oxide capable of inserting and releasing lithium is used, and a lithium-containing transition metal oxide is particularly preferable. Preferably, it is an oxide mainly containing at least one transition metal element selected from Ti, V, Cr, Mn, Fe, Co, Ni, Mo, W and lithium, and the molar ratio of lithium to transition metal is It is a compound of 0.3 to 2.2. More preferably, the oxide mainly contains at least one transition metal element selected from V, Cr, Mn, Fe, Co, and Ni and lithium, and the molar ratio of lithium to transition metal is 0.3 to 0.3. It is the compound of 2.2. In addition, Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, B, or the like may be contained within a range of less than 30 mole percent with respect to the transition metal present mainly. Among the above positive electrode active materials, the general formula Li _x MO ₂ (M = Co, Ni, Fe, at least one of Mn x = 0 to 1.2), or Li _y N ₂ O ₄ (N = Mn y) It is preferable to use at least one material having a spinel structure represented by = 0-2). _{Specifically, Li x CoO 2, Li x} NiO 2, Li x MnO 2, Li x Co a Ni 1-a O 2, Li x Co b V 1-b O z, Li x Co b Fe 1-b _{O 2, Li x Mn 2 O} 4, Li x Mn c Co 2-c O 4, Li x Mn c Ni 2-c O 4, Li x Mn c V 2-c O 4, Li x Mn c Fe 2- _c O ₄ (where x = 0.02 to 1.2, a = 0.1 to 0.9, b = 0.8 to 0.98, c = 1.6 to 1.96, z = 2. 01-2.3).

Further, the positive electrode active material _{Li y M a D 1-a} O 2 (M = Co, Ni, Fe, at least one D = Co of Mn, Ni, Fe, Mn, Al, Zn, Cu, Mo, Ag, A material containing at least one of W, Ga, In, Sn, Pb, Sb, Sr, B, and P other than M, y = 0 to 1.2, a = 0.5 to 1), or Li _z ( _{N b E 1-b) 2} O 4 (N = Mn E = Co, Ni, Fe, Mn, Al, Zn, Cu, Mo, Ag, W, Ga, In, Sn, Pb, Sb, Sr, B, It is particularly preferable to use at least one kind of material having a spinel structure represented by at least one kind of PE b = 1 to 0.2 z = 0 to 2). The most preferred lithium-containing transition metal _{oxides, Li x CoO 2, Li x} NiO 2, Li x MnO 2, Li x Co a Ni 1-a O 2, Li x Mn 2 O 4, Li x Co b V 1 _-b O _z (x = 0.02 to 1.2, a = 0.1 to 0.9, b = 0.9 to 0.98, z = 2.01 to 2.3). In addition, the value of x is a value before the start of charging / discharging and increases / decreases by charging / discharging. The positive electrode active material used in the present invention can be synthesized by a method in which a lithium compound and a transition metal compound are mixed and fired, or by a solution reaction, and a firing method is particularly preferable. Details for firing are described in paragraph 35 of JP-A-6-60,867, JP-A-7-14,579, and the like, and these methods can be used. The positive electrode active material obtained by firing may be used after being washed with water, an acidic aqueous solution, an alkaline aqueous solution, or an organic solvent. Further, as a method of chemically inserting lithium ions into the transition metal oxide, a method of synthesis by reacting lithium metal, a lithium alloy or butyl lithium with a transition metal oxide may be used.

The average particle size of the positive electrode active material used in the present invention is not particularly limited, but is preferably 0.1 to 50 μm. The volume of particles of 0.5 to 30 μm is preferably 95% or more. More preferably, the volume occupied by a particle group having a particle size of 3 μm or less is 18% or less of the total volume, and the volume occupied by a particle group of 15 μm or more and 25 μm or less is 18% or less of the total volume. No particular limitation is imposed on the specific surface area is preferably 0.01 to 50 m ² / g by the BET method, particularly preferably 0.2m ² / g~1m ² / g. The pH of the supernatant when 5 g of the positive electrode active material is dissolved in 100 ml of distilled water is preferably 7 or more and 12 or less.

  When the positive electrode active material of the present invention is obtained by firing, the firing temperature is preferably 500 to 1500 ° C, more preferably 700 to 1200 ° C, and particularly preferably 750 to 1000 ° C. The firing time is preferably 4 to 30 hours, more preferably 6 to 20 hours, and particularly preferably 6 to 15 hours.

  The conductive agent used in the mixture of the present invention may be anything as long as it is an electron conductive material that does not cause a chemical change in the constructed battery. Specific examples include natural graphite such as scaly graphite, scaly graphite, earthy graphite, high-temperature fired bodies such as petroleum coke, coal coke, celluloses, saccharides and mesophase pitch, and graphite such as artificial graphite such as vapor-grown graphite. , Carbon blacks such as acetylene black, furnace black, ketjen black, channel black, lamp black, thermal black, etc., carbon materials such as asphalt pitch, coal tar, activated carbon, mesofuse pitch, polyacene, conductivity of metal fibers, etc. Examples thereof include fibers, metal powders such as copper, nickel, aluminum and silver, conductive whiskers such as zinc oxide and potassium titanate, and conductive metal oxides such as titanium oxide. It is preferable to use a graphite plate having an aspect ratio of 5 or more. Among these, graphite and carbon black are preferable, and the particle size is preferably 0.01 μm or more and 20 μm or less, and more preferably 0.02 μm or more and 10 μm or less. These may be used alone or in combination of two or more. When using together, it is preferable to use together carbon blacks, such as acetylene black, and a 1-15 micrometers graphite particle. The addition amount of the conductive agent to the mixture layer is preferably 1 to 50% by weight, particularly 2 to 30% by weight, based on the negative electrode material or the positive electrode material. In the case of carbon black or graphite, the content is particularly preferably 3 to 20% by weight.

  In the present invention, a binder is used to hold the electrode mixture. Examples of the binder include polysaccharides, thermoplastic resins, and polymers having rubber elasticity. Preferred binders include starch, carboxymethyl cellulose, cellulose, diacetyl cellulose, methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, sodium alginate, polyacrylic acid, polyacrylic acid Na, polyvinyl phenol, polyvinyl methyl ether, polyvinyl alcohol, polyvinyl pyrrolidone. , Polyacrylamide, polyhydroxy (meth) acrylate, water-soluble polymers such as styrene-maleic acid copolymer, polyvinyl chloride, polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene furo Ride-tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene, polypropylene, ethylene-propylene (Meth) acrylic acid ester copolymer containing (meth) acrylic acid ester such as di-diene terpolymer (EPDM), sulfonated EPDM, polyvinyl acetal resin, methyl methacrylate, 2-ethylhexyl acrylate, (meth) acrylic Acid ester-acrylonitrile copolymer, polyvinyl ester copolymer containing vinyl ester such as vinyl acetate, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, polybutadiene, neoprene rubber, fluoro rubber, polyethylene oxide, polyester polyurethane Resin, polyether polyurethane resin, polycarbonate polyurethane resin, polyester resin, phenol resin, epoxy resin emulsion (latex) or suspension It can be cited. In particular, polyacrylate ester latex, carboxymethyl cellulose, polytetrafluoroethylene, and polyvinylidene fluoride are exemplified. These binders are preferably those obtained by dispersing fine powders in water, more preferably those having an average particle size of 0.01 to 5 μm in the dispersion, and 0.05 to 1 μm. It is particularly preferable to use one. These binders can be used alone or in combination. When the amount of the binder added is small, the holding power and cohesion of the electrode mixture is weak. If the amount is too large, the electrode volume increases and the capacity per electrode unit volume or unit weight decreases. For this reason, the addition amount of the binder is preferably 1 to 30% by weight, and particularly preferably 2 to 10% by weight.

  Any filler can be used as long as it is a fibrous material that does not cause a chemical change in the constructed battery. Usually, olefin polymers such as polypropylene and polyethylene, fibers such as glass and carbon are used. Although the addition amount of a filler is not specifically limited, 0 to 30 weight% is preferable. As the ionic conductive agent, those known as inorganic and organic solid electrolytes can be used, and details are described in the section of the electrolytic solution. A pressure enhancer is a compound that increases the internal pressure of a battery, and carbonates such as lithium carbonate are typical examples.

  In the current collector that can be used in the present invention, the positive electrode is aluminum, stainless steel, nickel, titanium, or an alloy thereof, and the negative electrode is copper, stainless steel, nickel, titanium, or an alloy thereof. The form of the current collector is foil, expanded metal, punching metal, or wire mesh. In particular, an aluminum foil is preferable for the positive electrode and a copper foil is preferable for the negative electrode. The thickness of the foil is preferably 7 μm to 100 μm, more preferably 7 μm to 50 μm, and particularly preferably 7 μm to 20 μm. The thickness of the expanded metal, punching metal, and wire mesh is preferably 7 μm to 200 μm, more preferably 7 μm to 150 μm, and particularly preferably 7 μm to 100 μm. The purity of the current collector is preferably 98% or more, more preferably 99% or more, and particularly preferably 99.3% or more. The surface of the current collector may be washed with an acid, alkali, organic solvent or the like.

  The current collector is more preferably one in which metal layers are formed on both sides of a plastic sheet in order to reduce the thickness. The plastic is preferably excellent in stretchability and heat resistance, for example, polyethylene terephthalate. Metal alone has little elasticity and is vulnerable to external forces. If a metal layer is formed on plastic, it will be resistant to impact. More specifically, the current collector may be a composite current collector in which a base material such as a synthetic resin film or paper is covered with an electron conductive substance. Examples of the synthetic resin film serving as the substrate include fluororesin, polyethylene terephthalate, polycarbonate, polyvinyl chloride, polystyrene, polyethylene, polypropylene, polyimide, polyamide, cellulose dielectric, and polysulfone. Examples of the electron conductive substance that covers the base material include carbonaceous materials such as graphite and carbon black, metal elements such as aluminum, copper, nickel, chromium, iron, molybdenum, gold, and silver, and alloys thereof. it can. Particularly preferred electron conductive materials are metals, such as aluminum, copper, nickel, and stainless steel. The composite current collector may have a form in which a base sheet and a metal sheet are bonded together, or a metal layer may be formed by vapor deposition or the like.

  Next, the configuration of the positive and negative electrodes in the present invention will be described. The positive and negative electrodes are preferably in a form in which an electrode mixture is applied to both sides of the current collector. In this case, the number of layers per side may be one or may be composed of two or more layers. When the number of layers per side is 2 or more, the positive electrode active material (or negative electrode material) -containing layer may be 2 or more. A more preferable configuration is a case where the layer is composed of a layer containing a positive electrode active material (or negative electrode material) and a layer not containing a positive electrode active material (or negative electrode material). The layer that does not contain the positive electrode active material (or the negative electrode material) includes a protective layer for protecting the layer containing the positive electrode active material (or the negative electrode material) and a divided positive electrode active material (or negative electrode material) containing layer. And an undercoat layer between the positive electrode active material (or negative electrode material) -containing layer and the current collector. These are collectively referred to as an auxiliary layer in the present invention.

  The protective layer is preferably on both the positive and negative electrodes or on the positive and negative electrodes. In the negative electrode, when lithium is inserted into the negative electrode material in the battery, the negative electrode preferably has a protective layer. The protective layer is composed of at least one layer, and may be composed of a plurality of layers of the same type or different types. Moreover, the form which has a protective layer only in the single side | surface of the mixture layers of both surfaces of a collector may be sufficient. These protective layers are composed of water-insoluble particles and a binder. The binder used when forming the above-mentioned electrode mixture can be used as the binder. As the water-insoluble particles, various kinds of conductive particles and organic and inorganic particles having substantially no conductivity can be used. The solubility of water-insoluble particles in water is 100 PPM or less, preferably insoluble. The proportion of particles contained in the protective layer is preferably 2.5% by weight or more and 96% by weight or less, more preferably 5% by weight or more and 95% by weight or less, and particularly preferably 10% by weight or more and 93% by weight or less.

Examples of water-insoluble conductive particles include carbon particles such as metals, metal oxides, metal fibers, carbon fibers, carbon black, and graphite. Among these water-insoluble conductive particles, those having low reactivity with alkali metals, particularly lithium, are preferable, and metal powders and carbon particles are more preferable. The electrical resistivity at 20 ° C. of the elements constituting the particles is preferably 5 × 10 ⁹ Ω · m or less.

  The metal powder is preferably a metal having low reactivity with lithium, that is, a metal that is difficult to form a lithium alloy. Specifically, copper, nickel, iron, chromium, molybdenum, titanium, tungsten, and tantalum are preferable. The shape of these metal powders may be any of acicular, columnar, plate-like, and massive shapes, and the maximum diameter is preferably 0.02 μm or more and 20 μm or less, more preferably 0.1 μm or more and 10 μm or less. These metal powders are preferably those whose surfaces are not excessively oxidized, and when oxidized, heat treatment is preferably performed in a reducing atmosphere.

  As the carbon particles, a known carbon material used as a conductive material used in combination when the electrode active material is not conductive can be used. Specifically, a conductive agent used for making an electrode mixture is used.

  Examples of the water-insoluble particles having substantially no conductivity include fine powder of Teflon (registered trademark), SiC, aluminum nitride, alumina, zirconia, magnesia, mullite, forsterite, and steatite. These particles may be used in combination with conductive particles, and are preferably used in an amount of 0.01 to 10 times that of the conductive particles.

  The positive (negative) electrode sheet can be prepared by applying a positive (negative) electrode mixture onto a current collector, drying, and compressing. The mixture is prepared by mixing a positive electrode active material (or negative electrode material) and a conductive agent, adding a binder (suspension or emulsion of resin powder) and a dispersion medium, kneading and mixing, It can be carried out by dispersing with a mixer / disperser such as a mixer, homogenizer, dissolver, planetary mixer, paint shaker or sand mill. As the dispersion medium, water or an organic solvent is used, but water is preferable. In addition, additives such as a filler, an ionic conductive agent, and a pressure enhancer may be added as appropriate. The pH of the dispersion is preferably 5 to 10 for the negative electrode and 7 to 12 for the positive electrode.

Application can be performed by various methods, for example, reverse roll method, direct roll method, blade method, knife method, extrusion method, slide method, curtain method, gravure method, bar method, dip method and squeeze method. I can list them. A method using an extrusion die and a method using a slide coater are particularly preferred. The application is preferably performed at a speed of 0.1 to 100 m / min. Under the present circumstances, the surface state of a favorable coating layer can be obtained by selecting the said application | coating method according to the liquid physical property of a mixture paste, and drying property. When the electrode layer is a plurality of layers, it is preferable to apply the plurality of layers at the same time from the viewpoint of uniform electrode production, production cost, and the like. The thickness, length and width of the coating layer are determined by the size of the battery. The thickness of a typical coating layer is 10 to 1000 μm in a compressed state after drying. The electrode sheet after application is dried and dehydrated by the action of hot air, vacuum, infrared rays, far infrared rays, electron beams and low-humidity air. These methods can be used alone or in combination. The drying temperature is preferably in the range of 80 to 350 ° C, particularly preferably in the range of 100 to 260 ° C. The water content after drying is preferably 2000 ppm or less, and more preferably 500 ppm or less. For the compression of the electrode sheet, a generally employed pressing method can be used, but a die pressing method and a calendar pressing method are particularly preferable. The press pressure is not particularly limited, but is preferably 10 kg / cm ^{2 to 3} t / cm ² . The press speed of the calendar press method is preferably 0.1 to 50 m / min. The pressing temperature is preferably room temperature to 200 ° C.

  The separator that can be used in the present invention is only required to be an insulating thin film having a large ion permeability, a predetermined mechanical strength, and an olefin polymer, a fluorine polymer, a cellulose polymer, polyimide, nylon, Glass fiber and alumina fiber are used, and as a form, a nonwoven fabric, a woven fabric, and a microporous film are used. In particular, the material is preferably polypropylene, polyethylene, a mixture of polypropylene and polyethylene, a mixture of polypropylene and Teflon (registered trademark), or a mixture of polyethylene and Teflon (registered trademark), and the form is a microporous film. preferable. In particular, a microporous film having a pore diameter of 0.01 to 1 μm and a thickness of 5 to 50 μm is preferable. These microporous films may be a single film or a composite film composed of two or more layers having different properties such as the shape, density, and material of the micropores. For example, the composite film which bonded the polyethylene film and the polypropylene film can be mentioned.

The electrolytic solution is generally composed of a supporting salt and a solvent. Lithium salt is mainly used as the supporting salt in the lithium secondary battery. The lithium salt can be used in the present invention, for _{example, LiClO 4, LiBF 4, LiPF} 6, LiCF 3 CO 2, LiAsF 6, LiSbF 6, fluorosulfonic represented by _{LiB 10 Cl 10, LiOSO 2 Cn} F 2n + 1 An imide salt represented by an acid (n is a positive integer of 6 or less), LiN (SO ₂ C _n F _{2n + 1} ) (SO ₂ C _m F _{2m + 1} ) (m and n are each a positive integer of 6 or less) Integers), LiC (SO ₂ C _p F _{2p + 1} ) (SO ₂ C _q F _{2q + 1} ) (SO ₂ C _r F _{2r + 1} ) methide salts (p, q: r are 6 or less, respectively) Positive aliphatic integers), lithium salts such as lower aliphatic lithium carboxylates, LiAlCl ₄ , LiCl, LiBr, LiI, chloroborane lithium, lithium tetraphenylborate, etc., and one or more of these may be mixed Can be used. Of these, a solution in which LiBF ₄ and / or LiPF ₆ is dissolved is preferable. The concentration of the supporting salt is not particularly limited, but is preferably 0.2 to 3 mol per liter of the electrolytic solution.

Solvents that can be used in the present invention include propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, trifluoromethyl ethylene carbonate, difluoromethyl ethylene carbonate, monofluoromethyl ethylene carbonate, hexafluoromethyl acetate, and methyl trifluoride acetate. , Dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, methyl formate, methyl acetate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, 2,2-bis ( Trifluoromethyl) -1,3-dioxolane, formamide, dimethylformamide, dioxolane, dioxane, acetonitrile, nitromethane, ethyl Glyme, phosphoric acid triester, boric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, 3-methyl-2-oxazolidinone, 3-alkylsydnone (alkyl group is propyl, isopropyl, butyl group, etc.), propylene carbonate derivative And aprotic organic solvents such as tetrahydrofuran derivatives, ethyl ether, and 1,3-propane sultone. These may be used alone or in combination. Among these, carbonate-based solvents are preferable, and it is particularly preferable to use a mixture of a cyclic carbonate and an acyclic carbonate. As the cyclic carbonate, ethylene carbonate and propylene carbonate are preferable. Moreover, as an acyclic carbonate, diethyl carbonate, dimethyl carbonate, and methyl ethyl carbonate are preferable. Examples of the electrolyte solution that can be used in the present invention include LiCF ₃ SO ₃ , LiClO ₄ , LiBF ₄ and / or LiPF ₆ in a solvent in which ethylene carbonate, propylene carbonate, 1,2-dimethoxyethane, dimethyl carbonate or diethyl carbonate is appropriately mixed. The electrolytic solution containing is preferable. In particular, an electrolysis containing at least one salt selected from LiCF ₃ SO ₃ , LiClO ₄ , or LiBF ₄ and LiPF ₆ in a mixed solvent of at least one of propylene carbonate or ethylene carbonate and at least one of dimethyl carbonate or diethyl carbonate. Liquid is preferred. The amount of the electrolyte added to the battery is not particularly limited, and can be used depending on the amount of the positive electrode material or the negative electrode material or the size of the battery.

In addition to the electrolytic solution, the following solid electrolyte can be used in combination. The solid electrolyte is classified into an inorganic solid electrolyte and an organic solid electrolyte. Well-known inorganic solid electrolytes include Li nitrides, halides, oxyacid salts, and the like. Among _{them, Li 3 N, LiI, Li} 5 NI 2, Li 3 N-LiI-LiOH, Li 4 SiO 4, Li 4 SiO 4 -LiI-LiOH, x Li 3 PO 4 - (1-x) Li 4 SiO ₄ , Li ₂ SiS ₃ , phosphorus sulfide compounds and the like are effective.

  In the organic solid electrolyte, a polyethylene oxide derivative or a polymer containing the derivative, a polypropylene oxide derivative or a polymer containing the derivative, a polymer containing an ion dissociation group, a mixture of a polymer containing an ion dissociation group and the above aprotic electrolyte, phosphoric acid A polymer matrix material containing an ester polymer and an aprotic polar solvent is effective. Furthermore, there is a method of adding polyacrylonitrile to the electrolytic solution. A method of using an inorganic and organic solid electrolyte in combination is also known.

Further, other compounds may be added to the electrolyte for the purpose of improving discharge and charge / discharge characteristics. For example, pyridine, pyrroline, pyrrole, triphenylamine, phenylcarbazole, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone and N , N-substituted imidazolidinone, ethylene glycol dialkyl ether, quaternary ammonium salt, polyethylene glycol, pyrrole, 2-methoxyethanol, AlCl ₃ , monomer of conductive polymer electrode active material, triethylene phosphoramide, trialkylphosphine, morpholine , Aryl compounds having a carbonyl group, crown ethers such as 12-crown-4, hexamethylphosphoric triamide and 4-alkylmorpholine Bicyclic tertiary amines, oils, quaternary phosphonium salts, and the like tertiary sulfonium salt. Particularly preferred is a case where triphenylamine and phenylcarbazole are used alone or in combination.

  In order to make the electrolyte nonflammable, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride chloride can be contained in the electrolyte. In addition, carbon dioxide gas can be included in the electrolyte in order to make it suitable for high-temperature storage.

  It is desirable that the electrolytic solution contains as little water and free acid as possible. For this reason, the raw material of the electrolytic solution is preferably one that has been sufficiently dehydrated and purified. The electrolyte solution is preferably adjusted in dry air or an inert gas with a dew point of minus 30 ° C. or less. The amount of water and free acid content in the electrolytic solution is 0.1 to 500 ppm, more preferably 0.2 to 100 ppm.

  The entire amount of the electrolytic solution may be injected once, but it is preferable to inject it in two or more times. When injecting in two or more times, each solution may have the same composition but a different composition (for example, a non-aqueous solvent or a non-aqueous solvent having a higher viscosity than the solvent after injecting a solution in which a lithium salt is dissolved in the non-aqueous solvent). Or a solution in which a lithium salt is dissolved in a solvent or a non-aqueous solvent may be injected). In order to shorten the time for injecting the electrolyte, etc., the battery can may be decompressed, or centrifugal force or ultrasonic waves may be applied to the battery can.

  Battery cans and battery lids that can be used in the present invention are nickel steel plated steel plates, stainless steel plates (SUS304, SUS304L, SUS304N, SUS316, SUS316L, SUS430, SUS444, etc.), nickel plated stainless steel plates (same as above) , Aluminum or an alloy thereof, nickel, titanium, and copper, and the shapes are a true circular cylinder, an elliptical cylinder, a square cylinder, and a rectangular cylinder. In particular, when the outer can also serves as the negative electrode terminal, a stainless steel plate and a nickel-plated steel plate are preferable, and when the outer can also serves as the positive electrode terminal, a stainless steel plate, aluminum, or an alloy thereof is preferable. The shape of the battery can may be any of buttons, coins, sheets, cylinders, and corners. A safety valve can be used for the sealing plate as a countermeasure against an increase in the internal pressure of the battery can. In addition, a method of cutting a member such as a battery can or a gasket can be used. In addition, various conventionally known safety elements (for example, fuses, bimetals, PTC elements, etc. as overcurrent prevention elements) may be provided.

  For the lead plate used in the present invention, a metal having electrical conductivity (for example, iron, nickel, titanium, chromium, molybdenum, copper, aluminum, etc.) or an alloy thereof can be used. As a welding method for the battery lid, battery can, electrode sheet, and lead plate, a known method (eg, direct current or alternating current electric welding, laser welding, ultrasonic welding) can be used. As the sealing agent for sealing, a conventionally known compound or mixture such as asphalt can be used.

  Gaskets that can be used in the present invention are olefin polymers, fluoropolymers, cellulosic polymers, polyimides, and polyamides as materials. Olefin polymers are preferred from the viewpoint of organic solvent resistance and low moisture permeability, and are mainly composed of propylene. Polymers are preferred. Furthermore, a block copolymer of propylene and ethylene is preferable.

  The battery assembled as described above is preferably subjected to an aging treatment. The aging treatment includes pre-treatment, activation treatment, post-treatment, and the like, whereby a battery with high charge / discharge capacity and excellent cycleability can be produced. The pretreatment is a treatment for homogenizing the distribution of lithium in the electrode. For example, control of lithium dissolution, temperature control to make the lithium distribution uniform, oscillation and / or rotation treatment, optional charging / discharging A combination is made. The activation process is a process for inserting lithium into the negative electrode of the battery body, and it is preferable to insert 50 to 120% of the amount of lithium inserted during actual use charging of the battery. The post-processing is processing for sufficient activation processing, and includes storage processing for uniform battery reaction and charge / discharge processing for determination, which can be arbitrarily combined.

  Preferred aging conditions (pretreatment conditions) before activation of the present invention are as follows. The temperature is preferably 30 ° C. or higher and 70 ° C. or lower, more preferably 30 ° C. or higher and 60 ° C. or lower, and further preferably 40 ° C. or higher and 60 ° C. or lower. The open circuit voltage is preferably 2.5 V or more and 3.8 V or less, more preferably 2.5 V or more and 3.5 V or less, and further preferably 2.8 V or more and 3.3 V or less. The aging period is preferably 1 day or more and 20 days or less, and particularly preferably 1 day or more and 15 days or less. The charging voltage for activation is preferably 4.0 V or higher, more preferably 4.05 V or higher and 4.3 V or lower, and still more preferably 4.1 V or higher and 4.2 V or lower. As the aging conditions after activation, the open circuit voltage is preferably 3.9 V or more and 4.3 V or less, particularly preferably 4.0 V or more and 4.2 V or less, and the temperature is preferably 30 ° C. or more and 70 ° C. or less, and 40 ° C. or more and 60 or less. A temperature of not higher than ° C is particularly preferred. The aging period is preferably from 0.2 days to 20 days, particularly preferably from 0.5 days to 5 days.

  The battery of the present invention is covered with an exterior material as necessary. Examples of the exterior material include a heat-shrinkable tube, an adhesive tape, a metal film, paper, cloth, paint, and a plastic case. Further, at least a part of the exterior may be provided with a portion that changes color by heat so that the heat history during use can be known.

  A plurality of the batteries of the present invention are assembled in series and / or in parallel as needed, and stored in a battery pack. In addition to safety elements such as positive temperature coefficient resistors, thermal fuses, fuses and / or current interrupting elements, the battery pack also requires safety circuits (monitoring the voltage, temperature, current, etc. of each battery and / or the entire battery pack) In this case, a circuit having a function of interrupting current may be provided. In addition to the positive and negative terminals of the entire assembled battery, the battery pack should be provided with the positive and negative terminals of each battery, the entire assembled battery, the temperature detection terminal of each battery, the current detection terminal of the entire assembled battery, etc. as external terminals. You can also. The battery pack may incorporate a voltage conversion circuit (such as a DC-DC converter). The connection of each battery may be fixed by welding a lead plate, or may be fixed so that it can be easily attached and detached with a socket or the like. Further, the battery pack may be provided with display functions such as the remaining battery capacity, the presence / absence of charging, and the number of uses.

  The battery of the present invention is used in various devices. In particular, video movies, portable video decks with built-in monitors, movie cameras with built-in monitors, digital cameras, compact cameras, single-lens reflex cameras, film with lenses, notebook computers, notebook word processors, electronic notebooks, mobile phones, cordless phones, bearded scorpions, It is preferably used for electric tools, electric mixers, automobiles and the like.

  Hereinafter, the present invention will be described in more detail with reference to specific examples, but the present invention is not limited to the examples.

Example 1
Polycrystalline silicon alone (compound-1) as the silicon compound, and the following alloy compounds synthesized metallurgically include Si-Ag alloy (compound-2 atomic ratio 60-40), Si-Al (compound-3 atomic ratio 60). -40), Si-Ag-Cd (compound-4 atomic ratio 60-30-10), Si-Zn (compound-5 atomic ratio 60-40), Si-Ge (compound-6 atomic ratio 60-40), Si-Ag-Sn (compound-7 atomic ratio 60-30-10), Si-Ag-Ni (compound-8 atomic ratio 60-30-10), isopropyl alcohol from metallurgically synthesized Li ₄ Si was used. Then, silicon (compound-9) obtained by pulverizing silicon from which 100% of Li was eluted in argon gas was prepared. The average particle size of the powder of these compounds was adjusted to 1 to 5 μm. Disperse SiO ₂ having an average particle size of 20 nm in a nickel plating bath.

After coating the silicon compound with SiO ₂ and nickel, heating was performed at 1000 ° C. in an argon gas atmosphere for 30 minutes to prepare negative electrode materials 1 to 9 of the present invention.

  Next, 190 g of the powder obtained by sufficiently mixing the negative electrode material (1-9) and an equal weight of scaly natural graphite, 10 g of polyvinylidene fluoride as a binder, and 500 ml of N-methyl-2-pyrrolidone. To prepare a negative electrode mixture paste.

200 g of the positive electrode active material LiCoO ₂ and 10 g of acetylene black are mixed with a homogenizer, then 5 g of polyvinylidene fluoride is mixed as a binder, and 500 ml of N-methyl-2-pyrrolidone is added and kneaded and mixed. Created a paste.

  The positive electrode mixture paste prepared above was applied to both sides of an aluminum foil current collector with a thickness of 30 μm with a blade coater, dried at 150 ° C., compression-molded with a roller press, and cut into a predetermined size. Created. Furthermore, it was sufficiently dehydrated and dried with a far-infrared heater in a dry box (dew point: dry air of −50 ° C. or lower) to prepare a positive electrode sheet. Similarly, a negative electrode mixture paste was applied to a 20 μm copper foil current collector, and a negative electrode sheet was prepared in the same manner as the above positive electrode sheet. The coating amount of the positive and negative electrodes is such that the charge capacity of the first cycle where the positive electrode active material is 4.2 V with respect to lithium metal and the charge capacity of the first cycle where the negative electrode material is 0.0 V are matched. The coating amount of the mixture was adjusted.

Next, the electrolytic solution was prepared as follows. In an argon atmosphere, 65.3 g of diethyl carbonate was placed in a 200 cc narrow-neck polypropylene container, and 22.2 g of ethylene carbonate was dissolved little by little while taking care not to exceed a liquid temperature of 30 ° C. Next, a small amount of 0.4 g of LiBF ₄ and 12.1 g of LiPF ₆ were dissolved in the polypropylene container in order while paying attention not to exceed 30 ° C. The obtained electrolyte was a colorless and transparent liquid with a specific gravity of 1.135. Moisture is 18 ppm (measured with a trade name, MKC-210, Karl Fischer moisture measuring device, manufactured by Kyoto Electronics Co., Ltd.), free acid content is 24 ppm (measured by neutralization titration with 0.1 N NaOH aqueous solution using bromthymol blue as an indicator) )Met.

  The cylinder battery was prepared as follows. A method of making a battery will be described with reference to FIG. The positive electrode sheet prepared above, a separator made of a microporous polyethylene film, a negative electrode sheet, and a separator were sequentially laminated, and this was wound in a spiral shape. The wound electrode group (2) was housed in an iron-bottomed cylindrical battery can (1) plated with nickel which also serves as a negative electrode terminal, and an upper insulating plate (3) was further inserted. After injecting the electrolyte into the battery can, a laminate of a positive electrode terminal (6), an insulating ring, a PTC element (63), a current interrupter (62), and a pressure sensitive valve element (61) is laminated (5). ) To form a cylindrical battery.

  The cylindrical battery is charged at 1.5A. In this case, charging was performed at a constant current up to 4.2 V, and the charging current was controlled so as to be kept constant at 4.2 V until 2.5 hours had elapsed from the start of charging. Discharging was carried out at a constant current up to 3.0 V at 0.2 C current. Table 1 shows the discharge capacity, average discharge voltage, energy amount (discharge capacity, average discharge voltage) of the first cycle, and the capacity retention rate at the 30th cycle after repeated charge / discharge.

Table 1
Battery Anode Material Discharge Capacity Average Discharge Energy Amount Cycle Life Number Number (mAh) Voltage (V) (Wh) (30 cycle%)
1 1 2200 3.5 7.6 84
2 2 2000 3.5 7.0 88
3 3 2000 3.5 7.0 88
4 4 2000 3.5 7.0 90
5 5 2000 3.5 7.0 89
6 6 2000 3.5 7.0 88
7 7 2000 3.5 7.0 89
8 8 2000 3.5 7.0 89
9 9 2200 3.5 7.6 83

Example 2
As in Example 1, except that compounds 1 to 9 were used as the silicon compound and polyvinylidene fluoride having an average particle size of 0.2 μm was dispersed in a nickel plating bath, the same as in Example 1, except that Negative electrode materials 10-18 coated with vinylidene chloride and nickel were prepared. The same test as in Example 1 was performed to obtain the results shown in Table 2.

Table 2
Battery Anode Material Discharge Capacity Average Discharge Energy Amount Cycle Life Number Number (mAh) Voltage (V) (Wh) (30 cycle%)
10 10 2200 3.5 7.6 82
11 11 2000 3.5 7.0 86
12 12 2000 3.5 7.0 85
13 13 2000 3.5 7.0 88
14 14 2000 3.5 7.0 86
15 15 2000 3.5 7.0 86
16 16 2000 3.5 7.0 86
17 17 2000 3.5 7.0 86
18 18 2200 3.5 7.6 81

Example 3
The silicon was coated with SiO ₂ , polyvinylidene fluoride and nickel in the same manner as in Example 1 except that SiO ₂ having an average particle size of 20 nm and polyvinylidene fluoride having an average particle size of 0.1 μm were dispersed in a nickel plating bath. Then, negative electrode materials 19 to 27 of the present invention were produced, and the same test as in Example 1 was performed to obtain the results shown in Table 3.

Table 3
Battery Anode Material Discharge Capacity Average Discharge Energy Amount Cycle Life Number Number (mAh) Voltage (V) (Wh) (30 cycle%)
19 19 2100 3.5 7.3 88
20 20 1900 3.5 6.6 92
21 21 1900 3.5 6.6 92
22 22 1900 3.5 6.6 94
23 23 1900 3.5 6.6 93
24 24 1900 3.5 6.6 93
25 25 1900 3.5 6.6 93
26 26 1900 3.5 6.6 93
27 27 2100 3.5 7.3 86

Example 4
Water was used in place of the N-methylpyrrolidone used in Example 3 to prepare the positive and negative electrode mixture paste. Specifically, the negative electrode sheet was prepared as follows. Water was added to a mixture of 95% of an equal weight mixture of negative electrode material and flake graphite and 4% by weight of an aqueous dispersion of polyvinylidene fluoride as a binder and 1% by weight of carboxymethylcellulose, and kneaded at 10,000 rpm for 10 minutes or more with a homogenizer. A negative electrode mixture slurry was prepared. The obtained slurry was applied to both sides of a 18 μm thick copper film to prepare a negative electrode sheet. The positive electrode sheet was produced as follows. Positive electrode active material LiCoO ₂ 90% by weight, acetylene black 6% by weight, and as a binder, water is added to a mixture of 3% by weight polyvinylidene fluoride aqueous dispersion and 1% by weight sodium polyacrylate, and the mixture is kneaded. A mixture slurry was prepared. The obtained slurry was applied to both surfaces of an aluminum film having a thickness of 30 μm to produce a positive electrode sheet. Next, a protective layer (average thickness of 5 μm) made of a 1: 4 (weight ratio) mixture of scaly graphite and aluminum oxide (average particle size of 2 μm) was applied to the surface of the active material layer of the negative electrode sheet. The charge / discharge test was performed under the same conditions as in Example 1.

Table 4
Battery Anode Material Discharge Capacity Average Discharge Energy Amount Cycle Life Number Number (mAh) Voltage (V) (Wh) (30 cycle%)
28 19 2100 3.5 7.3 88
29 20 1900 3.5 6.6 92
30 21 1900 3.5 6.6 92
31 22 1900 3.5 6.6 95
32 23 1900 3.5 6.6 93
33 24 1900 3.5 6.6 93
34 25 1900 3.5 6.6 93
35 26 1900 3.5 6.6 93
36 27 2100 3.5 7.6 88

Comparative Example 1
Negative electrode materials 28 to 36 were prepared in the same manner as in Example 1 except that the silicon compounds 1 to 9 of Example 1 were used without being coated with SiO ₂ , polyvinylidene fluoride, or the like. The battery preparation method and battery test method are the same as those in Example 1.

Table 5
Battery Anode Material Discharge Capacity Average Discharge Energy Amount Cycle Life Number Number (mAh) Voltage (V) (Wh) (30 cycle%)
37 28 2300 3.5 8.0 70
38 29 2100 3.5 7.3 75
39 30 2100 3.5 7.3 75
40 31 2100 3.5 7.3 77
41 32 2100 3.5 7.3 76
42 33 2100 3.5 7.3 76
43 34 2100 3.5 7.3 76
44 35 2100 3.5 7.3 76
45 36 2300 3.5 8.0 68

Comparative Example 2
A negative electrode material 37 is Si-SiO ₂ (weight ratio 90-10) obtained by mixing polycrystalline silicon and colloidal silica and heating at 1000 ° C. to obtain a solid in powder form using a vibration mill in argon gas. Using. Further, 30 g of polycrystalline silicon of silicon compound-1 was added to a solution obtained by dissolving 3 g of polyvinylidene fluoride in 50 g of N-methylpyrrolidone, mixed and kneaded, dried, and powder obtained by grinding in an automatic mortar was used as the negative electrode material 38. Used as. A negative electrode material 39 was made in the same manner as the negative electrode material 38 except that polycrystalline silicon was replaced with the above compound Si—SiO ₂ . Using these negative electrode materials 37 to 39, batteries 46 to 48 were produced in the same manner as in Example 1. Further, a battery 49 was produced in the same manner as in Example 1 except that mesophase pitch coke was used as the negative electrode material 40 and 2% by weight of acetylene black was added as a conductive auxiliary agent. Using these batteries, the same charge / discharge test as in Example 1 was performed.

Table 5
Battery Anode Material Discharge Capacity Average Discharge Energy Amount Cycle Life Number Number (mAh) Voltage (V) (Wh) (30 cycle%)
46 37 2200 3.5 7.6 80
47 38 2200 3.5 7.6 80
48 39 2100 3.5 7.3 83
49 40 1400 3.7 5.0 94

When comparing the battery performances of the batteries 1 to 36 of Examples 1 to 4 with the compounds of the present invention, the batteries 37 to 45 of Comparative Example 1 and the batteries 46 to 48 of Comparative Example 2, the negative electrode material of the present invention was used. It can be seen that the battery had excellent cycle life while maintaining high capacity. In addition, the battery using the negative electrode material of the present invention is a battery having the same cycle life, high discharge capacity, and high energy amount as compared with the comparative battery 49 using a carbonaceous material as the negative electrode material. all right. From the above results, the same effect was obtained even when a positive electrode in which LiCoO ₂ was changed to LiNiO ₂ or LiMn ₂ O ₄ as the positive electrode active material was used. Further, similar results were obtained even when these positive electrode active materials were substituted with nickel or manganese with other metals.

1 is a cross-sectional view of a cylinder battery used in Examples.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Battery can which also serves as a negative electrode 2 Winding electrode group 3 Upper insulating plate 4 Positive electrode lead 5 Gasket 6 Battery cover which also serves as a positive electrode terminal 61 Pressure sensitive valve body 62 Current interruption element (switch)
63 PTC element

Claims (4)

  In a non-aqueous secondary battery comprising a positive electrode having a positive electrode active material that is a transition metal oxide capable of insertion and release of lithium, a negative electrode having a negative electrode material, and a non-aqueous electrolyte, the negative electrode material is inserted and released of lithium. A non-aqueous secondary battery characterized in that it is a solid of a compound containing possible silicon atoms, and the solid has a coating made of a plurality of materials.   2. The nonaqueous secondary battery according to claim 1, wherein the compound containing silicon atoms is a compound in which a metal coating and a ceramic coating are simultaneously applied to the surface of silicon.   The non-aqueous secondary battery according to claim 1 or 2, wherein the compound containing silicon atoms is a compound in which a metal coating and a thermoplastic resin coating are simultaneously applied to a silicon surface. The nonaqueous secondary according to any one of claims 1 to 3, wherein the compound containing a silicon atom is a compound obtained by simultaneously applying a metal coating, a ceramic coating, and a thermoplastic resin coating on a silicon surface. battery.

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