JP2008004562A - Nonaqueous secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve an amount of energy of a lithium secondary battery, and improve its cycle life. <P>SOLUTION: In the nonaqueous secondary battery provided with a cathode having a cathode active material, an anode having an anode material and a nonaqueous electrolyte as its structuring elements, the cathode active material is a lithium-containing transition metal oxide, the anode material is a compound containing silicon atoms capable of inserting/releasing lithium, a collector of the anode is a metal foil supporter having an average surface roughness of 0.03 μm or more and 1 μm or less, and a thickness of 5 μm or more and 100 μm or less. <P>COPYRIGHT: (C)2008,JPO&INPIT

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. On the other hand, aluminum or copper foil is usually used as the current collector for the negative electrode. However, even with batteries using these materials, the cycle life is not sufficient. One of the causes of insufficient cycle life is estimated to be increased conduction between the current collector and the electrode mixture layer.

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 a positive electrode having a positive electrode active material, a negative electrode having a negative electrode material, and a non-aqueous secondary battery comprising a non-aqueous electrolyte, wherein the positive electrode active material is a lithium-containing transition metal oxide, The negative electrode material is a compound containing a silicon atom capable of inserting and releasing lithium, and the current collector of the negative electrode is a metal foil support having an average surface roughness of 0.03 μm to 1 μm and a thickness of 5 μm to 100 μm. It can be solved by a non-aqueous secondary battery that is characterized.

  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 comprising a positive electrode having a positive electrode active material, a negative electrode having a negative electrode material, and a non-aqueous electrolyte, the positive electrode active material is a lithium-containing transition metal oxide, and the negative electrode material Is a compound containing a silicon atom capable of inserting and releasing lithium, and the current collector of the negative electrode is a metal foil support having an average surface roughness of 0.03 μm to 1 μm and a thickness of 5 μm to 100 μm. Non-aqueous secondary battery characterized.
(2) A nonaqueous secondary battery in which the current collector according to item (1) is copper, nickel, titanium, an alloy thereof, or stainless steel.
(3) A non-aqueous secondary battery in which the current collector according to item (1) or (2) is a metal foil having an average surface roughness of 0.05 μm or more and 0.5 μm or less.
(4) A nonaqueous secondary battery in which the average particle size of the silicon compound according to items (1) to (3) is 0.01 to 100 μm.
(5) A non-aqueous secondary battery in which the silicon compound according to the items (1) to (3) is an alloy.
(6) The alloy according to item (5), wherein at least one of the metals other than silicon is an alkaline earth metal, a transition metal, or a semimetal.
(7) A nonaqueous secondary battery in which at least one of the metals described in item (5) or (6) is Ge, Be, Ag, Al, Au, Cd, Ga, In, Sb, Sn, or Zn.
(8) A nonaqueous secondary battery in which the weight ratio of the metal to silicon according to items (5) to (7) is 5 to 90%.
(9) A nonaqueous secondary battery in which the silicon compound according to item (1) is silicon obtained by removing a metal from a metal silicide.
(10) A nonaqueous secondary battery in which the metal silicide according to item (9) is lithium silicide.
(11) A nonaqueous secondary battery in which the lithium content of the lithium silicide according to item (10) is 100 to 420 atomic% with respect to silicon.
(12) A nonaqueous secondary battery in which the silicon compound according to item (1) is a silicon compound adhered to a ceramic that does not react with lithium.
(13) A nonaqueous secondary battery in which the ceramic according to item (12) is at least one ceramic selected from Al ₂ O ₃ , SiO ₂ , TiO ₂ , SiC, and Si ₃ N ₄ .
(14) A nonaqueous secondary battery in which the weight ratio of the ceramic to the silicon compound according to item (12) or (13) is 2 to 50%.
(15) A method for producing a negative electrode material, wherein the method of attaching the ceramic to the silicon compound according to the items (12) to (14) includes a step of heating to 300 to 1300 ° C.
(16) A nonaqueous secondary battery in which the silicon compound according to item (1) is coated with at least a metal.
(17) A method for producing a negative electrode material, wherein the method of coating with a metal according to item (16) is an electroless plating method, a vapor deposition method, a sputtering method, or a chemical vapor deposition method.
(18) At least one of the metals to be coated described in the item (16) or (17) is Ni, Cu, Ag, Co, Fe, Cr, W, Ti, Au, Pt, Pd, Sn, Zn Non-aqueous secondary battery.
(19) A nonaqueous secondary battery in which the specific conductivity of the silicon compound coated with the metal according to items (16) to (18) is 10 times or more the specific conductivity of the uncoated silicon compound.
(20) A nonaqueous secondary battery in which the silicon compound according to item (1) is previously coated with a thermoplastic resin.
(21) A nonaqueous secondary battery in which the thermoplastic resin according to item (20) is polyvinylidene fluoride or polytetrafluoroethylene.

(22) A nonaqueous secondary battery in which the weight ratio of the thermoplastic resin to the silicon compound according to item (20) or (21) is 2 to 30%.
(23) A nonaqueous secondary battery in which the coverage of the thermoplastic resin according to the items (20) to (22) is 5 to 100%.
(24) A nonaqueous secondary battery using a negative electrode in which 5 to 1900% by weight of carbon is allowed to coexist with the silicon compound according to item (1).
(25) A nonaqueous secondary battery in which the carbon according to item (24) is scaly natural graphite.
(26) When the charge / discharge range of the silicon compound according to item (1) is expressed as Li _x Si as an equivalent ratio of lithium inserted into and released from silicon, x is in the range of 0 to 4.2. Next battery.
(27) The non-aqueous secondary battery in which the charge / discharge range of the silicon compound according to item (1) is x in the range of 0 to 3.7 in Li _x Si.
(28) the positive electrode active material comprises _{Li y MO 2 (M = Co} , Ni, Fe, Mn y = 0~1.2) the material according to claim (1) or _{Li z N 2 O 4, (} N = A non-aqueous secondary battery using at least one material having a spinel structure represented by Mn z = 0 to 2).
(29) A nonaqueous secondary battery in which the average particle size of silicon according to items (3) to (27) is 0.01 to 50 μm. The term “silicon” as used herein refers to a silicon simple substance, a silicon alloy, or a silicide that can react with lithium.
(30) A non-aqueous secondary battery in which the alloy according to item (5) to (8) is an alloy to which the ceramic according to item (9) to (15) is attached.
(31) A non-aqueous secondary battery in which the alloy according to items (5) to (8) is an alloy coated with the metal according to items (16) to (19).
(32) A non-aqueous secondary battery, wherein the material according to item (30) is an alloy coated with the metal according to items (16) to (19).
(33) A non-aqueous secondary battery in which the alloy according to items (5) to (8) is an alloy coated with the thermoplastic resin according to items (20) to (23).
(34) A non-aqueous secondary battery in which the material according to item (30) to (32) is a material coated with the thermoplastic resin according to item (20) to (23).
(35) A non-aqueous secondary battery in which the carbon according to item (24) or (25) coexists in the alloy according to item (5) to (8).
(36) A non-aqueous secondary battery in which the carbon according to item (24) or (25) coexists with the material according to items (30) to (34).
(37) A non-aqueous secondary battery using the alloy according to item (5) to (8) in the charge / discharge range of item (26) or (27).
(38) A non-aqueous secondary battery using the material according to items (30) to (34) in the charge / discharge range of item (26) or (27).
(39) A nonaqueous secondary battery using the compound of item (28) as the positive electrode active material of the alloy negative electrode according to items (5) to (8).
(40) A nonaqueous secondary battery using the compound of item (28) as the positive electrode active material of the material according to items (30) to (36). (41) A non-aqueous secondary battery in which the silicon according to the items (9) to (11) is silicon to which the ceramic according to the items (12) to (15) is attached.
(42) A nonaqueous secondary battery in which the silicon according to items (9) to (11) is silicon coated with the metal according to items (16) to (19).
(43) A nonaqueous secondary battery, wherein the material according to item (41) is a material coated with the metal according to items (16) to (19).
(44) A non-aqueous secondary battery in which the silicon described in the items (9) to (11) is silicon coated with the thermoplastic resin described in the items (20) to (23).
(45) A non-aqueous secondary battery in which the material of items (41) to (43) is a material coated with the thermoplastic resin according to items (20) to (23).
(46) A non-aqueous secondary battery, wherein the silicon according to items (9) to (11) is silicon in which the carbon of item (24) or (25) coexists.
(47) A non-aqueous secondary battery, wherein the material according to item (41) to (45) is a material in which the carbon according to item (24) or (25) coexists.
(48) A non-aqueous secondary battery using the silicon described in items (9) to (11) in the charge / discharge range described in item (26) or (27).
(49) A nonaqueous secondary battery using the material according to (41) to (47) in the charge / discharge range according to (26) or (27).
(50) A nonaqueous secondary battery using the compound of item (28) as the positive electrode active material of the silicon negative electrode according to items (9) to (11).
(51) A non-aqueous secondary battery using the compound of item (28) as the positive electrode active material of the negative electrode according to items (41) to (47).
(52) A nonaqueous secondary battery, wherein the silicon compound according to items (12) to (15) is a silicon compound coated with the metal according to items (16) to (19).
(53) A nonaqueous secondary battery in which the silicon compound according to items (12) to (15) is a silicon compound coated with the thermoplastic resin according to items (20) to (23).
(54) A nonaqueous secondary battery, wherein the material according to item (52) is a material coated with the thermoplastic resin according to items (20) to (23).
(55) A non-aqueous secondary battery in which the silicon compound according to item (12) to (15) is allowed to coexist with the carbon according to item (24) or (25).
(56) A non-aqueous secondary battery in which the carbon according to item (24) or (25) coexists with the material according to items (52) to (54).
(57) A nonaqueous secondary battery using the silicon compound according to item (12) to (15) in the charge / discharge range according to item (26) or (27).
(58) A non-aqueous secondary battery using the material according to (52) to (54) in the charge / discharge range according to (26) or (27).
(59) A nonaqueous secondary battery using the compound of item (28) as the positive electrode active material of the silicon compound negative electrode according to items (12) to (15).
(60) A nonaqueous secondary battery using the compound of item (28) as the positive electrode active material of the material negative electrode according to items (52) to (54).
(61) A nonaqueous secondary battery in which the material according to items (16) to (19) is a material to which the ceramic according to items (9) to (15) is attached.
(62) A nonaqueous secondary battery in which the material according to items (16) to (19) is a material coated with the thermoplastic resin according to items (20) to (23).
(63) A nonaqueous secondary battery, wherein the material according to item (61) is a material coated with the thermoplastic resin according to items (20) to (23).
(64) A nonaqueous secondary battery in which the carbon according to item (24) or (25) is coexistent with the material according to items (16) to (19) and (61) to (63).
(65) A nonaqueous secondary battery using the material according to (16) to (19) or (61) to (63) in the charge / discharge range of (26) or (27).
(66) A nonaqueous secondary battery using the compound of item (28) as the positive electrode active material of the material negative electrode according to items (16) to (19) and (61) to (63).
(67) A nonaqueous secondary battery in which the material according to items (20) to (23) is a material to which the ceramic according to items (9) to (15) is attached.
(68) A nonaqueous secondary battery in which the material according to items (20) to (23) and (67) is coated with the metal according to items (16) to (19).
(69) A nonaqueous secondary battery in which the material described in (20) to (23), (67), or (68) is a material in which the carbon described in item (24) or (25) coexists.
(70) A nonaqueous secondary battery using the material described in (20) to (23), (68), (69) in the charge / discharge range described in (26) or (27).
(71) A nonaqueous secondary battery using the compound of item (28) as the positive electrode active material of the material negative electrode according to items (20) to (23), (68), and (69).
(72) A nonaqueous secondary battery using the compound according to item (28) as a positive electrode active material of the negative electrode according to item (24) or (25).

  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 material of the current collector used in the negative electrode of the present invention is copper, nickel, titanium alone or an alloy thereof, or stainless steel. One of the preferred negative electrode current collector materials used in the present invention is copper or an alloy thereof. Preferred metals that can be alloyed with copper include Zn, Ni, Sn, Al, etc. In addition, Fe, P, Pb, Mn, Ti, Cr, Si, As, and the like may be added in small amounts. Another preferred negative electrode current collector material used in the present invention is titanium or an alloy thereof. Since titanium has a stable oxide film, titanium is completely corrosion resistant to oxidizing environments, and can prevent dissolution during deep discharge or overdischarge in this embodiment. Further, in order to further improve the corrosion resistance, an alloy with Ta, Pd, Mo, Ni, Zr or the like may be used. Other metals to be alloyed include Al, Cr, Sn, Fe, Si, Mn, Cu, V, and Bi. Another material of the preferred negative electrode current collector used in the present invention is nickel or an alloy thereof. A nickel oxide film is dense, has a large protective effect, and is excellent in electrical conductivity, and therefore is preferable as a current collector for the negative electrode active material of the present invention. An alloy mainly composed of nickel can also be used. For example, an alloy with Cu, Cr, Fe, Mo, Si, W or Ta is preferable. In addition, an alloy with Al, Nb, Mn, Co, or the like may be used.

  Another material of the preferred negative electrode current collector used in the present invention is stainless steel. Stainless steel is an Fe—Cr steel containing about 11% or more of chromium and excellent in weather resistance and corrosion resistance. This alloy produces a very thin passive film on its surface in the atmosphere with little subsequent corrosion. Stainless steel is classified into martensite, ferrite, austenite, ferrite-austenite, and semi-austenite according to its metal structure. An austenitic stainless steel belongs to the Fe-Cr-Ni system or Fe-Cr-Mn system and exhibits an austenitic structure, and has high strength and excellent ductility in a wide temperature range from low temperature to high temperature. A solid solution heat treatment rapidly cooled from a temperature of about 1000 degrees Celsius or higher results in a nonmagnetic complete austenite structure, which provides excellent corrosion resistance and maximum ductility. Examples of the preferred composition of the stainless steel used in the present invention include JIS standard SUS304, SUS316, SUS316L, SUS430, and the like. Particularly preferred is an austenitic stainless steel containing Mo such as SUS316 or SUS316L. The molybdenum content is preferably 1 to 7% by weight, more preferably 1.2 to 6% by weight, and most preferably 1.7 to 4% by weight. The nickel content is preferably 8 to 18% by weight, more preferably 9 to 16% by weight, most preferably 10 to 15% by weight. The chromium content is preferably 11 to 26% by weight, more preferably 15 to 20% by weight, most preferably 16 to 19% by weight. The combination of the contents of nickel, chromium and molybdenum is described in this order, preferably 8 to 18 wt%, 11 to 26 wt%, 1 to 7 wt%, more preferably 9 to 16 wt%, 15 to 20 wt% 1.2 to 6 wt%, most preferably 10 to 15 wt%, 16 to 19 wt%, 1.7 to 4 wt%.

  The current collector described in the present invention can be used as an electrode support or a lead terminal. The shape of the current collector when used as an electrode support is preferably a foil shape, an expanded metal shape, a punching metal shape, a foamed metal shape, or a net shape, and most preferably a foil shape. The thickness of the current collector used in the present invention is preferably thin so as to increase the filling amount of the active material. Specifically, the thickness is preferably 5 μ to 100 μ, and more preferably 10 μ to 50 μ. When the current collector used in the present invention is a continuous material such as a foil, the surface may be physically or chemically treated to change the surface roughness, the thickness of the oxide film may be adjusted, A coating film may be applied or coated with silver, gold, TiC, TiN or the like.

  Examples of the roughening treatment include, but are not limited to, methods such as etching treatment (acid treatment, etc.), laser treatment, electrolytic plating, electroless plating, sand blasting and the like on metal foil. The surface roughness is preferably rough from the viewpoint of the affinity with the active material-containing layer. However, if the surface is too rough, it is not preferable because it causes cutting of the metal foil during the steps of coating and pressing. The average surface roughness is preferably in the range of 0.03 μm or more and 1 μm or less. More preferably, it is the range of 0.05 micrometer or more and 0.5 micrometer or less.

  The current collector may have a metal layer 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 is a composite current collector in which a base material such as a synthetic resin film or paper is coated with the above-described metal or alloy having electron conductivity. 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. As the electron conductive substance for coating the substrate, it is preferable to use the above copper, nickel, titanium alone or an alloy thereof, or stainless steel. These composite current collectors 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.

  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 simple substance, 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. The average particle size is preferably 0.01 to 100 μm. Furthermore, 0.05 to 50 μm is more preferable, and 0.1 to 5 μm is particularly preferable.

  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. Two or more of these alloys are also preferred. 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 70% by weight with respect to silicon. 10 to 60 weight% is especially preferable. 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. The average particle size of the alloy is preferably 0.01 to 40 μm. In particular, 0.03 to 5 μm is preferable.

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 can be 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 lithium content of the lithium silicide is preferably 100 to 420 mol% with respect to silicon. 200-420 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 the alkali metal or alkaline earth metal and dissolves the reaction product. . As the solvent, water and alcohols are preferable. In particular, degassed and dehydrated alcohols are preferred. Examples of alcohols 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.

It is considered that the ceramic adhered to the silicon compound is effective for suppressing silicon fine powder. 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. As a method for adhering silicon and ceramic, mixing, heating, vapor deposition, and CVD are used, but the combined use of mixing and heating is particularly preferable. In particular, after Al ₂ O ₃ or SiO ₂ sol and silicon are dispersed and mixed, the mixture is heated and the solid solution mass is pulverized to obtain a deposit of silicon and Al ₂ O ₃ or SiO ₂ . In this case, the Al ₂ O ₃ and SiO ₂ deposits, or as Al ₂ O ₃ and the surface of SiO ₂ or the like is covered with the silicon powder, trapped inside the mass, such as Al ₂ O ₃ or SiO ₂ Or the condition that the surface of silicon is covered. Mixing and dispersing can be achieved by mechanical stirring, ultrasonic waves, and kneading. Heating is preferably performed in the range of 300 ° C to 1300 ° C in an inert gas, but 500 ° C to 1200 ° C is particularly preferable. Examples of the inert gas include argon and nitrogen. These mixed gases are also used. As the pulverization method, well-known methods such as a ball mill, a vibration mill, a planetary ball mill, and a jet mill are used. This pulverization is also 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, 0.03 to 5 μm is preferable.

The metal coating of the silicon compound of the present invention includes electroplating, displacement plating, electroless plating, resistance heating vapor deposition, electron beam vapor deposition, cluster ion vapor deposition and other vapor deposition methods, sputtering methods, and chemical vapor deposition methods. (CVD method). In particular, an electroless plating method, a resistance heating vapor deposition method, an electron beam vapor deposition method, a cluster ion vapor deposition method or the like, a sputtering method, or a CVD method is preferable. Furthermore, an electroless plating method is particularly preferable. 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 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.

  Moreover, as a form of the silicon compound to be coated, any of powder, block, 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 metal to be coated is not particularly limited, but it is preferable to coat so that the specific conductivity is 10 times or more of the specific conductivity of the silicon compound as the base.

  The silicon compound used in the present invention is preferably coated with a thermoplastic resin. As the thermoplastic resin, a fluorine-containing polymer compound, an imide polymer, a vinyl polymer, an acrylate polymer, an ester polymer, polyacrylonitrile, or the like is 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, fluororubber, 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. In particular, a fluorine-containing polymer compound is preferable. Of these, polytetrafluoroethylene and polyvinylidene fluoride are preferred. As a method of coating in advance, a thermoplastic resin is dissolved in a solvent, and a silicon compound is mixed and kneaded in the solution. A method of drying the solution and pulverizing the obtained solid is preferred. As a usage-amount of the thermoplastic resin with respect to a silicon compound, 2 to 30 weight% is preferable. In particular, 3 to 20% by weight is preferable. The coverage is preferably 5 to 100%, and particularly preferably 5 to 90%. The average size of the coated particles is preferably 0.01 μm to 40 μm. In particular, 0.03 to 5 μm is preferable.

  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 2000% by weight or less with respect to the silicon compound. Furthermore, 10 to 1000% by weight is more preferable, and 20 to 500% by weight is particularly preferable. As the conductive agent, a metal other than carbon can be used. Ni, Cu, Ag, and Fe are preferable.

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. That is, it shows that a specific phenomenon in which the discharge potential is lowered when the voltage at the end of charging is increased and a reversibility of the charge / discharge reaction is also found.

  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.

The positive electrode material used in the present invention is a lithium-containing transition metal oxide. 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, Mnx = 0 to 1.2), or Li _y N ₂ O ₄ (N = Mny y = 0 to 2) It is preferable to use at least one material having a spinel structure represented by: _{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). 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.

  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. 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, fluoro represented by _{LiClO 4, LiBF 4, LiPF 6} , LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiB 10 Cl 10, LiOSO 2 C n F 2n + 1 Imide salts represented by sulfonic 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 6 or less positive) ), A metide salt represented by LiC (SO ₂ C _p F _{2p + 1} ) (SO ₂ C _q F _{2q + 1} ) (SO ₂ C _r F _{2r + 1} ) (p, q and r are each 6). The following positive integers), Li aliphatic salts such as lithium lithium carboxylate, LiAlCl ₄ , LiCl, LiBr, LiI, chloroborane lithium, lithium tetraphenylborate, etc. can be raised, and one or more of these can 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 an electrolyte solution obtained by appropriately mixing ethylene carbonate, propylene carbonate, 1,2-dimethoxyethane, dimethyl carbonate, or diethyl carbonate. Alternatively, an electrolytic solution containing LiPF ₆ 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 N I2, 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 , conductive polymer electrode active material monomer, 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-plated steel and 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, temperature 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. However, the present invention is not limited to the examples unless it exceeds the gist of the invention.

Example 1
From the polycrystalline silicon simple substance (compound-1) as the negative electrode material, the following alloy compound synthesized metallurgically, Si-Ag alloy (compound-2 weight ratio 40-60), from the metallurgically synthesized Li ₄ Si Solid obtained by mixing silicon eluting Li using isopropyl alcohol in argon gas (compound-3), polycrystalline silicon and colloidal silica, and heating at 1000 ° C. the Si-SiO ₂ was the powder with a vibration mill in an argon gas (compound -4 weight ratio 90-10), Si was Ag plated as compound plated polycrystalline silicon surface at an electroless plating method (compound - 5 Si-Ag weight ratio 40-60), 30 g of silicon was added to a solution obtained by dissolving 3 g of polyvinylidene fluoride in 50 g of N-methylpyrrolidone, mixed and kneaded, and then dried. The powder (compound-6) pulverized in an automatic mortar was used. As the average particle size of the negative electrode materials (compounds 1 to 6), particles in the range of 0.05 to 4 μm were used. Next, 190 g of a powder obtained by sufficiently mixing silicon and an equal weight of scaly natural graphite, 10 g of polyvinylidene fluoride as a binder are dispersed in 500 ml of N-methyl-2-pyrrolidone, and a negative electrode paste is prepared. Created.

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

  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, the negative electrode mixture paste was applied to a metal foil current collector (copper, nickel, titanium, stainless steel) having a surface roughness of 20 μm and a surface roughness of 0.07 μm, 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-necked 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 was 18ppm (measured by Kyoto Electronics, trade name MKC-210 type Karl Fischer moisture measuring device), free acid content was 24ppm (measured by neutralization titration with 0.1N 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 with a gasket (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. The discharge capacity, average discharge voltage, energy amount (discharge capacity × average discharge voltage) of the first cycle at that time, and the capacity retention rate at the 30th cycle after repeated charge and discharge are shown in Table 1.

Example-2
Batteries 25 to 28 were produced in the same manner as the battery 1 except that the surface roughness of the copper foil of the negative electrode current collector of the battery 1 of Example-1 was 0.03 μm, 0.05 μm, 0.1 μm, and 1 μm. . Next, a comparative battery was made as follows. Except for changing the negative electrode current collector of the battery 1 to a copper foil having a thickness of 20 μm and a surface roughness of 0.01 μm, the comparative battery 29 was made exactly the same as the battery 1, and the negative electrode current collector of the battery 1 was 20 μm thick. A comparative battery 30 was made in exactly the same manner as battery 1 except that the surface roughness was changed to aluminum foil having a surface roughness of 0.1 μm. Using these batteries 25 to 30, the same test as in Example 1 was performed and the results shown in Table 2 were obtained.

  Furthermore, a negative electrode sheet for comparison was prepared in the same manner as the negative electrode of battery 1 except that a copper foil having a thickness of 20 μm and a surface roughness of 2 μm was used for the negative electrode current collector of battery 1. It was found that this negative electrode sheet causes a cutting failure in the coating process and has no process stability.

Comparing the batteries 1 to 28 using the current collector of the present invention with the comparative battery 30, the cycle life is improved by using copper, titanium, nickel, and stainless steel foils compared to the case of using aluminum foils. . Further, from comparison between the batteries 25 to 28 and the batteries 29 and 31, it was found that the surface roughness is suitably 0.03 μm or more and 1 μm or less. Further, the same effects as in Examples 1 and 2 were obtained even when the positive electrode active material LiCoO ₂ used in the examples was changed to LiNiO ₂ or LiMn ₂ O ₄ .

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 element 62 Current interruption element (switch)
63 PTC element

Claims (2)

  In a non-aqueous secondary battery including a positive electrode having a positive electrode active material, a negative electrode having a negative electrode material, and a non-aqueous electrolyte, the positive electrode active material is a lithium-containing transition metal oxide, and the negative electrode material is made of lithium. It is a compound containing silicon atoms that can be inserted and released, and the current collector of the negative electrode is a metal foil support having an average surface roughness of 0.03 μm to 1 μm and a thickness of 5 μm to 100 μm. Non-aqueous secondary battery.   The non-aqueous secondary battery according to claim 1, wherein the current collector of the negative electrode is made of copper, nickel, titanium, an alloy thereof, or stainless steel.

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