JP2010238588A - Current collector laminate of lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a current collector laminate capable of protecting a current collector from corrosion without impairing battery characteristics even in a high voltage specification and not impairing flexibility of an electrode, and provide a lithium secondary battery. <P>SOLUTION: The current collector laminate is provided with a conductive protecting layer (A) containing a cross-linked fluorine containing elastomer (a) and a conductive filler (b)arranged on a current collector (B). The lithium secondary battery includes the above laminate. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a current collector laminate and an electrode laminate of a lithium secondary battery, and further to a lithium secondary battery.

  A lithium secondary battery is composed of a positive electrode in which a positive electrode mixture layer containing a positive electrode active material such as a lithium-containing composite oxide is provided on a positive electrode current collector such as an aluminum foil, and a negative electrode current collector such as an aluminum foil. A negative electrode provided with a negative electrode mixture layer containing a negative electrode active material such as a carbonaceous material, and a nonaqueous electrolytic solution containing an electrolyte salt such as a lithium salt and an organic solvent are provided.

  In the lithium secondary battery having such a configuration, there is a problem that the current collector is anodized and corroded due to the action of an electrolyte such as a lithium salt contained in the electrolytic solution, and cycle characteristics and battery capacity are deteriorated. is there.

  In order to prevent or suppress such corrosion of the current collector, Patent Document 1 proposes forming a surface protective layer containing a heterocyclic compound on the current collector. Patent Document 2 proposes that a protective layer containing at least one material selected from precious metals, alloys, conductive ceramics, semiconductors, organic semiconductors, and conductive polymers is formed on a current collector. Examples of the conductive polymer include polyaniline, polypyrrole, polyacene, polydisulfide, and polyparaphenylene. One method of forming a protective layer using a conductive polymer is to cast or apply a mixed solution in which a conductive polymer, a binder, and dopan (aromatic sulfonic acid ester) are dissolved in a solvent, and then heat and dry. Illustrated.

Japanese Patent Laid-Open No. 10-162833 JP 2002-203562 A

  However, in recent years, required characteristics for batteries have become stricter, and further higher voltages (for example, 4.35 V or more) are required. At higher voltage specifications, the current collector is further corroded and its protection becomes an important issue.

  Further, as a lithium secondary battery having a small size and a high electric capacity, a method of winding an electrode (winding type or spiral type) is mainly used, and thus high flexibility is required for the electrode.

  From this point of view, the surface protective layer of the heterocyclic compound described in Patent Document 1 is insufficient in terms of oxidation potential, and the material described in Patent Document 2 is hard and lacks flexibility. In addition, the imide salt is effective in corroding the aluminum foil, but is insufficient when used at a high voltage.

  An object of the present invention is to provide a current collector laminate and a lithium secondary battery that can protect a current collector from corrosion without impairing battery characteristics even in high voltage specifications, and that do not impair flexibility of an electrode. .

  The present invention relates to a current collector laminate in which a conductive protective layer (A) containing a cross-linked fluorine-containing elastomer (a) and a conductive filler (b) is provided on a current collector (B).

  In addition, an electrode laminate in which an electrode mixture layer (C) is provided on the conductive protective layer (A) of the current collector laminate of the present invention, and further provided with a positive electrode, a negative electrode, and a non-aqueous electrolyte, The present invention also relates to a lithium secondary battery in which at least one of the negative electrode and the negative electrode is the electrode laminate of the present invention.

  Furthermore, the present invention provides a conductive fluorine-containing elastomer composition for forming a current collector protective layer of a lithium secondary battery, wherein the fluorine-containing elastomer (a) and a conductive filler (b) are crosslinked or not crosslinked. And an organic solvent (c).

  According to the present invention, it is possible to provide a current collector laminate and a lithium secondary battery that can protect a current collector from corrosion without impairing battery characteristics even in a high voltage specification, and that do not impair flexibility of an electrode. .

It is a chart which shows the result of the CV measurement of the current collection laminated body of this invention produced in the Example.

  The present invention relates to a current collector laminate in which a conductive protective layer (A) containing a cross-linked fluorine-containing elastomer (a) and a conductive filler (b) is provided on a current collector (B).

  Such a current-collecting laminate may be produced by any production method, but can be produced mainly by two methods. One method is to mix a fluorine-containing elastomer, a conductive filler, a cross-linking agent, and a cross-linking aid in a dry manner, then form a film by melt extrusion or roll extrusion, and a film obtained by primary cross-linking and secondary cross-linking. This is a method of bonding to (mostly metal film) with a laminate. The second method is to prepare a coating solution by dispersing a fluorine-containing elastomer, a conductive filler, a crosslinking agent, and a crosslinking aid with an organic solvent or water, and then apply the coating solution to a current collector film and then dry it. In this method, primary crosslinking and secondary crosslinking are performed. Of these two manufacturing methods, it is preferable to use a manufacturing method that uses the second coating step because the film can be easily thinned and the process is simple.

  Hereinafter, first, a conductive fluorine-containing elastomer composition for forming a current collector protective layer of a lithium secondary battery will be described.

(A) Crosslinked or non-crosslinked (uncrosslinked) fluorinated elastomer The uncrosslinked fluorinated elastomer (a) can be used without particular limitation as long as it is not susceptible to oxidation, but it must contain a conductive filler. Therefore, a non-perfluoro fluorine-containing elastomer is preferable.

  Non-perfluoro fluorine-containing elastomers include, for example, non-perfluoro fluorine-containing elastomers (a1) mainly composed of vinylidene fluoride (VdF) and tetrafluoroethylene (TFE), thermoplastic fluorine-containing elastomers (a2), and Among these, a non-perfluoro fluorine-containing elastomer (a1) is preferable.

  The non-perfluoro fluorine-containing elastomer (a1) is not particularly limited, but is relatively inexpensive, has good polymerizability, and is excellent in heat resistance, cold resistance, and chemical resistance of the resulting compound. It is preferably composed of at least one of vinylidene fluoride (VdF) units and tetrafluoroethylene (TFE) units and at least one other monomer.

  Other monomers include, for example, hexafluoropropylene (HFP), fluoroalkyl vinyl ether, perfluoro (alkyl vinyl ether) (PAVE), chlorotrifluoroethylene (CTFE), trifluoroethylene, trifluoropropylene, tetrafluoropropylene, penta Fluorine-containing monomers such as fluoropropylene, trifluorobutene, tetrafluoroisobutene, vinyl fluoride, iodine-containing fluorinated vinyl ether; fluorine-free monomers such as ethylene (Et), propylene (Pr), alkyl vinyl ether, etc. These fluorine-containing monomers and non-fluorine-containing monomers can be used alone or in combination of two or more.

The PAVE has the general formula (1):
_{CF 2 = CFO (CF 2 CFY} 2 O) p - (CF 2 CF 2 CF 2 O) q -R f 1 (1)
(Wherein Y ² is a fluorine atom or —CF ₃ ; R _f ¹ is a perfluoroalkyl group having 1 to 5 carbon atoms; p is an integer of 0 to 5; q is an integer of 0 to 5) Can be used alone or in combination of two or more. Among those represented by the general formula (1), perfluoro (methyl vinyl ether) and perfluoro (propyl vinyl ether) are preferable, and perfluoro (methyl vinyl ether) is particularly preferable.

  Specifically, VdF / HFP copolymer, VdF / HFP / TFE copolymer, VdF / CTFE copolymer, VdF / CTFE / TFE copolymer, VdF / PFE copolymer, VdF / TFE / PAVE copolymer. Polymer, VdF / HFP / PAVE copolymer, VdF / HFP / TFE / PAVE copolymer, VdF / TFE / Pr copolymer, VdF / Et / HFP copolymer, TFE / Pr copolymer are preferred, In particular, a VdF / HFP copolymer and a VdF / HFP / TFE copolymer are preferable.

  The VdF / HFP copolymer preferably has a VdF / HFP composition of 45 to 85/55 to 15 mol%, more preferably 50 to 80/50 to 20 mol%, and still more preferably, 60 to 80/40 to 20 mol%.

  The VdF / HFP / TFE copolymer preferably has a VdF / HFP / TFE composition of 40 to 80/10 to 35/10 to 25 mol%.

  The VdF / PAVE copolymer preferably has a VdF / PAVE composition of 65 to 90/10 to 35 mol%.

  As a VdF / TFE / PAVE copolymer, the composition of VdF / TFE / PAVE is preferably 40 to 80/3 to 40/15 to 35 mol%.

  The VdF / HFP / PAVE copolymer preferably has a VdF / HFP / PAVE composition of 65 to 90/3 to 25/3 to 25 mol%.

  As VdF / HFP / TFE / PAVE copolymer, the composition of VdF / HFP / TFE / PAVE is preferably 40 to 90/0 to 25/0 to 40/3 to 35, preferably 40 to 80/3 to 25 More preferred are those of / 3 to 40/3 to 25 mol%.

  The TFE / Pr copolymer preferably has a TFE / Pr composition of 40 to 70/60 to 30 mol%, and more preferably 50 to 60/50 to 40 mol%.

  The non-perfluoro fluorine-containing elastomer (a1) can be crosslinked by a known method such as peroxide crosslinking, polyol crosslinking or amine crosslinking. Further, it may have a crosslinking site capable of crosslinking reaction. Such a cross-linked site may be introduced into the fluorine-containing elastomer by a polymer reaction, but in addition to the copolymer exemplified above as a non-perfluoro fluororubber, as another monomer, It is preferable to use a monomer that imparts the above because it is easy to produce. The monomer that gives a crosslinking site is preferably 0.1 mol% or more, based on the total amount of monomers (including the monomer that gives the crosslinking site) constituting the non-perfluoro fluororubber. Preferably it is 0.3 mol% or more, preferably 5 mol% or less, more preferably 2 mol% or less.

（Ｒ⁶は前記と同じ）
で示される基を有するものである。 As a monomer that gives a crosslinking site, it has an ethylenically unsaturated bond, and as a functional group, a cyano group (—CN group), a carboxyl group (—COOH group), an alkoxycarbonyl group (—COOR ⁶ group (R ⁶ Is an alkyl group), an acid halide group (—COX ³ group (X ³ is a halogen atom such as iodine atom, chlorine atom, bromine atom)) or

(R ⁶ is the same as above)
It has group shown by these.

As the non-perfluoro fluorine-containing elastomer (a1), specifically,
(A1-1) Fluorine-containing compound comprising a VdF structural unit and / or a TFE structural unit and a structural unit derived from at least one other monomer, and having a Mooney viscosity (ML _{1 + 10 at} 100 ° C.) of 2 to 30 Elastomer,
(A1-2) VdF structural unit and / or TFE structural unit and a structural unit derived from at least one other monomer, Mooney viscosity (ML _{1 + 10 at} 100 ° C.) is 80 or less, 30 Exceeding fluorine-containing elastomer is preferred.

  The fluorine-containing elastomer (a1-1) is derived from the fluorine-containing elastomer described in International Publication No. 2006/011547, that is, a VdF structural unit and / or a TFE structural unit and at least one other monomer. A fluorine-containing elastomer comprising structural units and having a number average molecular weight (Mn) of 30,000 to 70,000 g / mol and an iodine content of 0.3 to 1.0% by weight has outstanding fluidity. It can illustrate preferably from the point which is carrying out.

  The number average molecular weight (Mn) of the fluorine-containing elastomer (a1-1) is 30,000 to 70,000 g / mol, a more preferable lower limit is 35,000 g / mol, and a further preferable lower limit is 40,000 g / mol. A more preferred upper limit is 65,000 g / mol, and a more preferred upper limit is 60,000 g / mol. When the number average molecular weight (Mn) of the fluorine-containing elastomer (a1-1) is too small, it becomes liquid and easily flows during heating from drying to crosslinking, and a conductive auxiliary agent is contained or immobilized. It becomes difficult. In addition, the number average molecular weight (Mn) of the fluorine-containing elastomer (a1-1) exceeds 70,000 g / mol (such as the fluorine-containing elastomer (a1-2) described later) and the content of the conductive filler is elastic. Will be inferior. However, it may be eliminated by appropriately adjusting the type and content of the conductive filler. Further, the molecular weight distribution (weight average molecular weight Mw / number average molecular weight Mn) of the fluorine-containing elastomer (a1-1) is not particularly limited, but it is 1.3 or more and less than 4.0. It is preferable in terms of balance between ease and workability. Further, the viscosity is preferably less than 3.0 because the viscosity can be kept low.

  The fluorine-containing elastomer (a1-1) used in the present invention can be produced by the method described in International Publication No. 2006/011547.

  Examples of the fluorine-containing elastomer (a1-2) include elastomers obtained by copolymerizing the same monomers as the fluorine-containing elastomer (a1-1), but the number average molecular weight (Mn) exceeds 70,000 g / mol. 400,000 g / mol or less. Examples of the fluorine-containing elastomer (a1-2) include fluorine-containing elastomers having relatively high viscosity described in, for example, JP-A Nos. 53-125491 and 62-12734. When the number average molecular weight (Mn) exceeds 400,000 g / mol, the solution viscosity of the coating solution increases, making it difficult to obtain a solution with good coating properties.

  As the thermoplastic fluorine-containing elastomer (a2), for example, a resin comprising a fluorine-containing elastomeric polymer chain segment and a fluorine-containing non-elastomeric segment described in the development of fluorine-based materials (CMC Publishing Co., Ltd. 1997) Examples that have both properties and elastomeric properties.

  These uncrosslinked fluorine-containing elastomers are crosslinked to improve mechanical strength and flexibility and constitute one component of the composition.

  There are mainly three types of cross-linking, amine cross-linking, polyol cross-linking, and peroxide cross-linking. Among them, polyol cross-linking or peroxide cross-linking is preferable.

  In the case of polyol crosslinking, a base component that induces deHF from the main chain, such as calcium oxide or magnesium oxide, is exemplified as a crosslinking aid, and a polyol component that is added to the formed double bond, such as bisphenol, is shown below. Compounds are mentioned as suitable crosslinking agents.

  When using peroxide crosslinking, it is preferable to crosslink by blending an organic peroxide crosslinking agent. Furthermore, a polyfunctional crosslinking aid may be included.

  The organic peroxide crosslinking agent may be a peroxide crosslinking crosslinking agent, such as α, α′-bis (t-butylperoxy) diisopropylbenzene, 2,5-dimethyl-2,5-di (t -Butylperoxy) hexane, dicumyl peroxide, benzoyl peroxide, 1,1-bis (t-butylperoxy) -2-methylcyclohexane, 1,1-bis (t-hexylperoxy) -3,3 , 5-trimethylcyclohexane, 1,1-bis (t-hexylperoxy) cyclohexane, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t- Butylperoxy) cyclohexane, 1,1-bis (t-butylperoxy) cyclododecane, t-hexylperoxybenzoate, 2,5-silane Til-2,5-di (benzoylperoxy) hexane, t-butylperoxyacetate, 2,2-bis (t-butylperoxy) butane, t-butylperoxybenzoate, n-butyl-4,4- Bis (t-butylperoxy) valerate, di-t-butylperoxyisophthalate, t-butylcumyl peroxide, di-t-butylperoxide, p-methanehydroperoxide, 2,5-dimethyl-2, An organic peroxide such as 5-di (t-butylperoxy) hexane-3 or diisopropylbenzene hydroperoxide may be used. As the organic peroxide crosslinking agent, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane is preferable from the viewpoint of good crosslinkability and handleability.

  It is preferable that the compounding quantity of an organic peroxide crosslinking agent is 0.01-10 mass parts with respect to 100 mass parts of fluorine-containing elastomer (a), More preferably, it is 0.1-5 mass parts. When the crosslinking agent is less than 0.01 parts by mass, the crosslinking density is insufficient, so that the performance of the protective film tends to be impaired, and a crosslinking agent exceeding 10 parts by mass is usually unnecessary. However, when highly blending the conductive filler (b), the blending amount of the organic peroxide crosslinking agent is preferably 0.5 to 10 parts by mass in order to reduce the viscosity of the composition.

  Examples of multifunctional crosslinking aids include triallyl cyanurate, triallyl isocyanurate (TAIC), tris (diallylamine-s-triazine), triallyl phosphite, N, N-diallylacrylamide, hexaallylphosphoramide, N , N, N ′, N′-tetraallyltetraphthalamide, N, N, N ′, N′-tetraallylmalonamide, trivinyl isocyanurate, 2,4,6-trivinylmethyltrisiloxane, tri (5 -Norbornene-2-methylene) cyanurate and the like. Among these, triallyl isocyanurate (TAIC) is preferable from the viewpoint of good crosslinkability and physical properties of the crosslinked product.

  The compounding amount of the polyfunctional crosslinking aid is preferably 0.01 to 20 parts by mass, more preferably 0.05 to 10 parts by mass, with respect to 100 parts by mass of the fluorine-containing elastomer (a). -5.0 mass parts is more preferable. When the polyfunctional crosslinking aid is less than 0.01 parts by mass, the time required for crosslinking tends to be long, and when it exceeds 20 parts by mass, it becomes difficult to form a smooth film. However, when highly blending the conductive filler (b), in order to reduce the viscosity of the composition, the blending amount of the polyfunctional crosslinking aid is preferably 1.0 to 20 parts by mass.

(B) Conductive filler The conductive filler (b) used in the present invention refers to a filler having a volume resistivity of 1 × 10 ⁻⁹ to 1 Ω · cm. A preferred volume resistivity is 1 × 10 ⁻⁸ to 1 × 10 ⁻¹ Ω · cm.

  Examples of the conductive filler (b) include a conductive carbon filler.

  These conductive fillers may be particulate fillers, fibrous fillers, or combinations thereof.

  Examples of the particulate carbon filler include ketjen black, acetylene black, nanoporous carbon, graphite (natural graphite, artificial graphite), furnace black, channel black, etc. Among them, the chemical resistance and conductivity are good, and the composition From the viewpoint of good fluidity, nanoporous carbon and graphite are preferred, and from the viewpoint of good chemical resistance and electrical conductivity, ketjen black and acetylene black are preferred. The average primary particle diameter is preferably 0.02 to 50 nm, and more preferably 0.025 to 40 nm from the viewpoint of good conductivity.

  Examples of the fibrous carbon filler include carbon fibers, carbon nanotubes, and carbon nanofibers. Among them, carbon nanotubes and carbon nanofibers are preferable from the viewpoint of good conductivity, and carbon fibers are preferable from the viewpoint of cost performance. preferable. The diameter of the fibrous carbon is preferably 50 nm or less, preferably 0.1 to 200 nm, more preferably 1 to 200 nm, from the viewpoint of good conductivity. Further, the ratio of average fiber length / average fiber diameter is preferably 5 or more, and more preferably 10 or more from the viewpoint of good conductivity. Moreover, it is preferable that it is 1000 or less, Furthermore, 500 or less from the point which preparation of a composition is easy.

  In particular, the filler to be blended is preferably a filler that is at least one selected from the group consisting of ketjen black, acetylene black, nanoporous carbon, graphite, carbon fiber, carbon nanotube, and carbon nanofiber.

  The particulate carbon filler and the fibrous carbon filler may be used in combination. When used in combination, for example, it becomes easier to control the aspect ratio of the conductivity of the protective film, which will be described later, and the conductivity of the protective film is further improved than when it is used alone. The mixing ratio (mass ratio) of the particulate carbon filler / fibrous carbon filler is preferably 10/90 or more, and more preferably 20/80 or more from the viewpoint of giving good fluidity to the composition. Further, it is preferably 90/10 or less, and more preferably 80/20 or less from the viewpoint of easy control of the conductive aspect ratio in the protective film.

  The compounding quantity of an electroconductive filler (b) is 5-300 mass parts with respect to 100 mass parts of fluorine-containing elastomer (a). When less than 5 mass parts, the electroconductivity of a protective film becomes inadequate and is unpreferable. On the other hand, when the amount exceeds 300 parts by mass, the preparation of the composition becomes difficult, which is not preferable. A preferred lower limit is 5 parts by mass from the viewpoint of good conductivity of the protective film. A preferable upper limit is 200 parts by mass from the viewpoint of good stability during molding, and 100 parts by mass from the viewpoint of easy preparation of the composition. Within this range, a conductive carbon filler and a metal filler may be used in combination. These combinations are particulate carbon filler and particulate and / or fibrous metal filler, fibrous carbon filler and particulate and / or fibrous metal filler, and are appropriately selected according to the required performance. . The mixing ratio may be appropriately selected in consideration of the degree and weight of conductivity of each filler, the elasticity and flexibility of the generated conductive layer, and the like.

  In addition to or in place of the conductive filler (b), a nonconductive filler (volume resistivity exceeds 1 Ω · cm) may be used in combination. Examples of the nonconductive filler include a nonconductive carbon filler, a nonconductive inorganic oxide filler, and a nonconductive resin filler. Specifically, non-conductive carbon black, non-conductive Austin black, non-conductive graphite (natural graphite, artificial graphite), non-conductive carbon nanotube, non-conductive graphitized carbon black, etc. Carbon filler: non-conductive such as silica, silicate, clay, diatomaceous earth, montmorillonite, talc, calcium carbonate, calcium silicate, barium sulfate, fatty acid calcium, titanium oxide, bengara, boron nitride, aluminum nitride, magnesium oxide, alumina Inorganic oxide filler; polyethylene, heat-resistant engineering plastics, PTFE-based tetrafluoroethylene and ethylene-tetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVdF), etc. Rimmer, such as a non-conductive resin filler such as polyimide and the like. The blending amount may be appropriately selected in consideration of the effect of blending and the degree and weight of conductivity of the conductive filler (b), the elasticity and flexibility of the generated conductive layer, and the like.

  The conductive protective layer (A) in the present invention is formed by applying a protective layer forming composition containing a fluorine-containing elastomer (a) and a conductive filler (b) to the current collector (B).

  The protective layer forming composition may be a coating composition or a molding composition.

  In the case of the coating composition, the solvent (c) is contained in addition to the fluorine-containing elastomer (a) and the conductive filler (b). The solvent (c) may be an organic solvent (c1) or an aqueous solvent (c2).

  Examples of the organic solvent (c1) include ketones such as methyl ethyl ketone, acetone, cyclohexanone, and dibutyl ketone; amides such as N-methylpyrrolidone, dimethylacetamide, and dimethylformamide; butyl acetate, amyl acetate, butyl propionate, ethyl cellolbu, methyl cellolrub Examples thereof include polar solvents such as ethers such as tetrahydrofuran, diglyme and triglyme.

  The aqueous solvent (c2) is typically water, but alcohols and ketones may be used in combination. In this case, an emulsion-type coating composition is obtained.

  The blending ratio of the fluorine-containing elastomer (a) and the conductive filler (b) in the coating composition is the ratio described in the protective layer. Moreover, the quantity of a solvent (c) should just be an quantity used as the density | concentration suitable for coating.

  The composition for forming a protective film further includes other resins or rubbers (for example, PTFE or other resins having a high oxidation potential or rubbers other than fluorine-containing elastomers), processing aids, and adhesives that cure by crosslinking (silane coupling agents). , Epoxy, phenol resin) and the like may be used as long as the object of the present invention is not impaired.

  Preparation of a coating composition should just mix each component with the normal mixing method employ | adopted as the coating composition using an elastomer.

  The method for forming the coating film may be a conventionally known method. For example, by applying to the substrate by roller coating method, brush coating method, dip coating method, spray coating method, gravure coating method, coil coating method, curtain flow coating method, etc., and then naturally drying or heating drying at ambient temperature Form a coating film. Although it depends on the type of crosslinking agent, the coating amount, the type of solvent used, etc., it is usually desirable to carry out heat crosslinking at about 50 to 200 ° C. for about 1 to 180 minutes.

  When the protective film-forming composition is in the form of a molding composition, the fluorine-containing elastomer (a) and the conductive filler (b), and if necessary, a crosslinking agent (d) and a multifunctional crosslinking aid (e ) And a solvent may be slurried by a usual method.

  The blending ratio of the fluorine-containing elastomer (a) and the conductive filler (b), and the crosslinking agent (d) and the multifunctional crosslinking aid (e) in the molding composition is the same as that of the protective layer or coating composition. It is the explained ratio.

  The conductive protective layer (A) thus obtained can control the volume resistivity in the range of 0.001 to 50 Ω · cm, and if necessary, 0.001 to 10 Ω · cm, further 1 Ω · cm or less. A highly conductive protective film can be provided.

  The thickness of the conductive protective layer may be appropriately selected in the range of 0.5 to 50 μm. For example, from the viewpoint of reducing resistance, it is 0.5 μm or more, more preferably 1.0 μm or more. To 50 μm or less, more preferably 10 μm or less.

(B) Current collector The present invention is particularly effective for a material that is corroded by a lithium salt in an electrolytic solution. As a material constituting such a current collector, for example, aluminum or an alloy thereof, stainless steel, nickel or an alloy thereof, titanium or an alloy thereof, a material obtained by treating carbon or titanium on the surface of aluminum or stainless steel, or the like is used. Among these, aluminum and aluminum alloys are mentioned as current collectors that are particularly protected. These materials can also be used after oxidizing the surface. Further, it is preferable that the surface of the current collector is roughened to improve the adhesion. The thickness of the current collector is usually in the range of 5 to 30 μm.

  The current collecting laminate of the present invention may be used for a positive electrode or a negative electrode. In particular, a great effect is exhibited when used for a positive electrode in which the current collector is severely corroded.

  The present invention also relates to an electrode laminate in which an electrode mixture layer (C) is provided on the conductive protective layer (A) of the current collector laminate of the present invention.

  The electrode mixture forming the electrode mixture layer (C) contains an electrode active material and a binder, and if necessary, is prepared by blending other materials. In the present invention, a conventionally known positive electrode mixture and negative electrode mixture can be used, but this is particularly effective in the case of an electrode mixture having a high voltage specification.

As the positive electrode active material, a lithium-containing transition metal composite oxide that produces a high voltage is particularly preferable. For example, Formula (2): Li _a Mn _{2 -b} M ¹ _b O ₄ (where 0.9 ≦ a; 0 ≦ b ≦ 1.5; M ¹ is selected from the group consisting of Fe, Co, Ni, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si and Ge Lithium-manganese spinel composite oxide represented by the formula (3): LiNi _1-c M ² _c O ₂ (where 0 ≦ c ≦ 0.5; M ² is Fe, Lithium represented by at least one metal selected from the group consisting of Co, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge) nickel composite oxide, or LiCo in ^{_{1-d M 3 d O 2}} ( wherein, 0 ≦ d ≦ 0.5; M 3 At least one metal selected from the group consisting of Fe, Ni, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge) Lithium-cobalt composite oxide is preferable.

Specifically, LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , or LiNi _1/3 Co _1/3 Mn _1/3 O ₂ has an energy density. It is preferable in that a high and high output lithium secondary battery can be provided.

In addition, a positive electrode active material such as LiFePO ₄ , LiNi _0.8 Co _0.2 O ₂ , Li _1.2 Fe _0.4 Mn _0.4 O ₂ , LiNi _0.5 Mn _0.5 O ₂ , LiV ₃ O ₆ may be used.

  The compounding amount of the positive electrode active material is preferably 50 to 99% by mass, more preferably 80 to 99% by mass of the positive electrode mixture, from the viewpoint of high battery capacity.

Examples of the negative electrode active material include carbon materials, and also include metal oxides and metal nitrides capable of inserting lithium ions. Examples of carbon materials include natural graphite, artificial graphite, pyrolytic carbons, cokes, mesocarbon microbeads, carbon fibers, activated carbon, and pitch-coated graphite. Metal oxides capable of inserting lithium ions include tin and Examples of the metal compound include silicon and titanium, such as tin oxide, silicon oxide, and lithium titanate. Examples of the metal nitride include Li _2.6 Co _0.4 N.

  The compounding amount of the negative electrode active material is preferably 50 to 99% by mass, more preferably 80 to 99% by mass of the negative electrode mixture, from the viewpoint of high battery capacity.

  Examples of the binder include fluorine resin, non-fluorine resin, rubber and the like.

  Examples of the fluorine resin include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF). The PTFE may be a tetrafluoroethylene homopolymer or a modified PTFE obtained by copolymerizing a small amount of other monomers such as HFP and PAVE.

  Examples of non-fluorinated resins include polyacrylic acid. Examples of the rubber include ethylene / propylene / diene copolymer rubber (EPDM) and styrene / butadiene copolymer rubber (SBR).

  The blending amount of the binder is preferably 0.5 to 15% by mass, more preferably 0.5 to 10% by mass of the electrode mixture from the viewpoint of high battery capacity.

  Other components include fluorine resins such as TFE / HFP copolymer resins and ETFE and VdF copolymer resins for improving the adhesion of electrode mixtures and for improving the utilization of active materials; Fluororubber and acrylic rubber for improving; Cellulosic resin such as cellulose acetate for improving withstand voltage; Additives used for manufacturing electrodes of lithium secondary batteries, for example, conductive materials and thickeners for electrode preparation , Other polymers, surfactants and the like. Examples of the conductive material include conductive carbon black such as acetylene black and ketjen black; and carbonaceous materials such as graphite and carbon fiber.

  When these components are required, the electrode mixture layer (C) is appropriately mixed using an appropriate solvent to prepare an electrode mixture forming composition as a uniform mixture, and the conductivity of the current collecting laminate. On the protective layer (A), it can be carried out by a method such as spin coating, blade coating, roll coating or dip coating.

  The electrode subjected to the drying treatment is usually further subjected to a rolling treatment, if necessary, and then cut and processed into a predetermined thickness and size to obtain an electrode for a lithium secondary battery. The rolling process and the cutting process may be ordinary methods.

  In the electrode laminate of the present invention, the current collector is protected from the lithium salt in the electrolytic solution by a protective layer, so that corrosion of the current collector can be suppressed even at a high operating voltage, and deterioration of battery characteristics such as cycle characteristics can be suppressed. In addition, since the fluorine-containing elastomer is used, the flexibility of the electrode is improved, and cracking and dropping do not occur even when wound like a wound type lithium secondary battery.

  The present invention also relates to a lithium secondary battery. The lithium secondary battery of the present invention includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, and uses the electrode laminate of the present invention as the positive electrode and / or the negative electrode.

  In addition, when using electrodes other than the electrode of this invention for one of a positive electrode or a negative electrode, those positive electrodes or negative electrodes can use a conventionally well-known electrode. However, it is preferable to use the electrode of the present invention for the positive electrode, which has a large flexibility problem.

  The non-aqueous electrolyte is not particularly limited as long as it is an electrolyte containing an electrolyte salt and an organic solvent for dissolving the electrolyte salt and is used in a lithium secondary battery.

Examples of the electrolyte include known electrolyte salts such as LiPF ₆ , LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ , and LiN (SO ₂ C ₂ F ₅ ) _2. Examples of the organic solvent include ethylene carbonate and dimethyl Hydrocarbon solvents such as carbonate, methyl ethyl carbonate, diethyl carbonate, and propylene carbonate; fluorinated solvents such as HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H, CF ₃ COOCF ₃ , CF ₃ COOCH ₂ CF ₃ , and mixtures thereof Although a solvent etc. can be illustrated, it is not limited only to these.

  A separator may be disposed in the lithium secondary battery of the present invention. There is no restriction | limiting in particular as a separator, A microporous polyethylene film, a microporous polypropylene film, a microporous ethylene propylene copolymer film, a microporous polypropylene / polyethylene two-layer film, a microporous polypropylene / polyethylene / polypropylene three-layer film Etc. In addition, a film in which an aramid resin is coated on a separator made for the purpose of improving safety such as a short circuit caused by Li dentrite, or a film in which a resin containing polyamideimide and an alumina filler is coated on a separator can be given (for example, JP, 2007-299612, A, JP, 2007-324073, A).

  The lithium secondary battery of the present invention is useful as a large-sized lithium secondary battery for a hybrid vehicle or a distributed power source, a small-sized lithium secondary battery such as a mobile phone or a personal digital assistant.

  EXAMPLES Next, the present invention will be described with reference to examples, but the present invention is not limited to these examples.

  The measurement method and evaluation method employed in the present invention are as follows.

(Mooney viscosity)
Using a Mooney viscometer (SMV-200) manufactured by Shimadzu Corporation, preheating at 100 ° C. for 1 minute and then measuring for 10 minutes to measure the Mooney viscosity (ML _{1 + 10} , 100 ° C.) of the rubber.

(Film thickness measurement)
It measures using quick macro MDQ-30M made from Mitutoyo Corporation.

Example 1
As fluorine-containing elastomer (a), 50 g of VdF / HFP (78/22 mol%) copolymer (Mooney viscosity (ML _{1 + 10} at 100 ° C.) 13) 13 g was used, and this was used as organic solvent (c) 50 g of methyl ethyl ketone. Into this, 50 g of acetylene black (average particle size 35 nm) as a conductive filler (b), 3 g of Perhexa 25B (manufactured by NOF Corporation) as a crosslinking agent, and triallyl isocyan as a crosslinking accelerator 8 g of nurate was added and stirred for 24 hours to prepare a coating composition. Next, this coating composition was uniformly applied on the positive electrode current collector (15 μm thick aluminum foil), and a conductive fluorine-containing elastomer layer (thickness 5 μm) for forming a current collector protective layer was formed on one side. Formed and dried in a hot air dryer at 60 ° C. for 15 minutes. Also, the coating composition prepared in the same manner was applied to the opposite (back) side and dried to produce a conductive fluorine-containing elastomer layer (total thickness: 10 μm) on both sides. Next, after vacuuming with a vacuum dryer, primary crosslinking is performed at 160 ° C. for 4 hours, and after vacuuming again with a vacuum dryer, secondary crosslinking is performed at 180 ° C. for 4 hours under crosslinking conditions. A conductive protective film was prepared.

  About the obtained positive electrode plate, the oxidation potential was measured in the following manner. As a control, the oxidation potential was also measured for an aluminum foil on which no conductive protective film was formed. The results are shown in FIG.

  As is apparent from FIG. 1, Comparative Example 1 with only the aluminum foil has a large peak around 4.7 V and is considered to be oxidized at this stage, but in Example 1 in which the conductive protective film is formed, 5 No large peak is seen up to 3V. This shows that the aluminum foil is not oxidized by forming a conductive protective film.

(Oxidation potential measurement)
The electrode plate is cut to a size of 0.5 × 0.7 cm, and a nickel wire is welded by resistance welding to produce an electrode for CV. In addition, as an electrolytic solution for measurement, LiPF ₆ as an electrolyte salt in an electrolyte salt dissolving solvent of ethylene carbonate (EC) / methyl ethyl carbonate (MEC) (= 30/70 vol%) is 1.0 mol / liter. Use electrolyte added to achieve concentration.

  Using a closed cell for voltammetry (VC-4) manufactured by BAS, the electrode for CV prepared above is placed on the working electrode, Li is used for the counter electrode and the reference electrode, and 3 ml of the above electrolyte is put into the measuring cell. Make it. The produced cell is scanned at 5 mV / sec from 3 V to 5.3 V at 25 ° C. (constant) using a potentio-galvanostat (Solartron 1287 type), and the current change is measured.

Example 2
50 g of the VdF / HFP copolymer used in Example 1 was used as the fluorine-containing elastomer (a), and this was sufficiently dissolved in 50 g of methyl ethyl ketone. 8 g of isocyanurate was added and stirred for 24 hours to prepare a coating composition. Next, the composition for coating is uniformly coated on a PET film (10 μm), and a conductive fluorine-containing elastomer layer (thickness: 5 μm) for forming a current collector protective layer is formed on one surface. Dry at 60 ° C. for 15 minutes. Next, after vacuuming with a vacuum dryer, primary crosslinking is performed at 160 ° C. for 4 hours, and after vacuuming again with a vacuum dryer, secondary crosslinking is performed at 180 ° C. for 4 hours under crosslinking conditions. A conductive protective film was prepared. The volume resistivity was measured about the obtained laminated body. The results are shown in Table 1.

(Measurement of volume resistivity)
The volume resistivity is measured by the 4-terminal method using Loresta-GP manufactured by Mitsubishi Chemical Analytech Co., Ltd.

Example 3
In Example 2, a VdF / HFP / TFE (50/30/20 mol%) copolymer (Mooney viscosity (ML _{1 + 10} at 100 ° C.) 49) was used instead of the VdF / HFP copolymer. Prepared a coating composition by the same method, applied to a PET film in the same manner as in Example 2, crosslinked, and produced a conductive protective film. The volume resistivity was measured about the obtained laminated body. The results are shown in Table 1.

Example 4
In Example 2, a coating composition was prepared in the same manner except that ketjen black was used instead of acetylene black, applied to a PET film in the same manner as in Example 2, cross-linked, and conductive protection A membrane was prepared. The volume resistivity was measured about the obtained laminated body. The results are shown in Table 1.

Example 5
In Example 2, a coating composition was prepared in the same manner as in Example 2 except that VGCF (gas phase method carbon fiber VGCF @ manufactured by Showa Denko KK) was used instead of acetylene black. Then, it was applied to a PET film and crosslinked to produce a conductive protective film. The volume resistivity was measured about the obtained laminated body. The results are shown in Table 1.

Example 6
A coating composition was prepared in the same manner as in Example 2 except that the amount of acetylene black was changed to 150 g. The coating composition was applied to a PET film and crosslinked in the same manner as in Example 2. Was made. The volume resistivity was measured about the obtained laminated body. The results are shown in Table 1.

Example 7
In Example 2, except that the amount of acetylene black was changed to 2.5 g, a coating composition was prepared in the same manner, applied to a PET film in the same manner as in Example 2, cross-linked, and conductive. A protective film was produced. The volume resistivity was measured about the obtained laminated body. The results are shown in Table 1.

  From Table 1, it can be seen that all of the obtained conductive protective films are high-conductive protective films of 50 Ω · cm or less.

Example 8
Subsequently, LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , carbon black, and polyvinylidene fluoride (manufactured by Kureha Chemical Co., Ltd., trade name KF) were formed on the positive electrode current-collecting laminate of the present invention produced in Example 1. -1000) is mixed at 90/3/7 (mass% ratio), N-methyl-2-pyrrolidone is dispersed in N-methyl-2-pyrrolidone to uniformly apply a slurry of the positive electrode mixture, and then dried to form a positive electrode A mixture layer (thickness: 50 μm) was formed, and then compression molded by a roller press to produce a positive electrode laminate.

  Using the obtained positive electrode laminate, a coin-type lithium secondary battery was produced in the following manner, and the discharge capacity and cycle characteristics were examined. The results are shown in Table 2.

(Create coin-type battery)
The positive electrode laminate is punched into a diameter of 1.6 mm with a punching machine to produce a circular positive electrode.

  Separately, styrene-butadiene rubber dispersed with distilled water is added to artificial graphite powder (manufactured by Hitachi Chemical Co., Ltd., trade name MAG-D) so that the solid content becomes 6% by mass, and mixed with a disperser. The slurry is uniformly applied on a negative electrode current collector (copper foil having a thickness of 10 μm), dried, and a negative electrode mixture layer is formed, and then compression-molded with a roller press, and the diameter is obtained with a punching machine. A circular negative electrode is produced by punching to a size of 1.6 mm.

The above-mentioned circular positive electrode is opposed to the positive electrode and the negative electrode with a microporous polyethylene film (separator) having a thickness of 20 μm, and an electrolytic solution (EC / MEC = 30/70 vol% electrolyte salt dissolving solvent is LiPF _6. Is added to a concentration of 1.0 mol / liter), and after the electrolyte has sufficiently penetrated the separator, etc., it is sealed, precharged and aged, and then a coin-type lithium secondary A battery is produced.

(Measurement of battery characteristics)
The discharge capacity and cycle characteristics of the coin-type lithium secondary battery were examined as follows.

(Discharge capacity)
When the charge / discharge current is indicated by C, measurement is performed under the following charge / discharge measurement conditions with 5 mA as 1C. The evaluation is performed using an index with the result of the discharge capacity of Comparative Example 1 as 100.

Charging / discharging conditions Charging: Holds until the charging current becomes 1 / 10C at 1.0C, 4.7V (CC / CV charging)
Discharge: 1C 3.0Vcut (CC discharge)

(Cycle characteristics)
Regarding the cycle characteristics, the charge / discharge cycle performed under the above-mentioned charge / discharge conditions (charging at 1.0 C at 4.7 V until the charging current becomes 1/10 C and discharging to 3.0 V at a current equivalent to 1 C) is 1 The discharge capacity after the first cycle and the discharge capacity after 100 cycles are measured. For the cycle characteristics, the value obtained by the following calculation formula is used as the cycle maintenance ratio value.
Cycle maintenance ratio (%) = 100 cycle discharge capacity (mAh) / 1 cycle discharge capacity (mAh) × 100

Example 9
As fluorine-containing elastomer (a), VdF / HFP / TFE (50/30/20 mol%) copolymer elastomer (Mooney viscosity (ML _{1 + 10} at 100 ° C.) 50) instead of VdF / HFP copolymer A conductive fluorine-containing elastomer composition for forming a current collector protective layer, a positive electrode current collector laminate, a positive electrode laminate, and a coin-type lithium secondary battery were produced in the same manner as in Example 8 except that The battery characteristics (discharge capacity, cycle characteristics) were examined in the same manner as in Example 8. The results are shown in Table 2.

Example 10
Preparation of a conductive fluorine-containing elastomer composition for forming a current collector protective layer in the same manner as in Example 8 except that ketjen black was used instead of acetylene black as the conductive filler (b), and a positive electrode current collector laminate Then, a positive electrode laminate and a coin-type lithium secondary battery were produced, and the battery characteristics (discharge capacity, cycle characteristics) were examined in the same manner as in Example 8. The results are shown in Table 2.

Example 11
Conductivity for forming a current collector protective layer in the same manner as in Example 8 except that VGCF (vapor phase carbon fiber VGCF @ manufactured by Showa Denko KK) was used instead of acetylene black as the conductive filler (b). Of a porous fluorine-containing elastomer composition, a positive electrode current collector laminate, a positive electrode laminate, and a coin-type lithium secondary battery were produced, and battery characteristics (discharge capacity, cycle characteristics) were examined in the same manner as in Example 8. The results are shown in Table 2.

Example 12
Preparation of a conductive fluorine-containing elastomer composition for forming a current collector protective layer, positive electrode current collector laminate, positive electrode laminate, and coin-type lithium secondary battery as in Example 8 except that the amount of acetylene black was changed to 150 g A secondary battery was manufactured, and battery characteristics (discharge capacity, cycle characteristics) were examined in the same manner as in Example 8. The results are shown in Table 2.

Example 13
Preparation of conductive fluorine-containing elastomer composition for forming current collector protective layer, positive electrode current collector laminate, positive electrode laminate, and coin type in the same manner as in Example 8 except that the amount of acetylene black was changed to 2.5 g A lithium secondary battery was produced, and the battery characteristics (discharge capacity, cycle characteristics) were examined in the same manner as in Example 8. The results are shown in Table 2.

Comparative Example 1
A positive electrode laminate and a coin-type lithium secondary battery were produced in the same manner as in Example 8 except that an aluminum foil without a conductive protective layer was used. Battery characteristics (discharge capacity, Cycle characteristics were investigated. The results are shown in Table 2.

Comparative Example 2
A solution in which 0.03 mol · dm ⁻³ of 1,2,4-triazole was dissolved in a mixed solvent of ethylene carbonate / dimethoxyethane (50/50% by volume) was prepared. Then, after immersing the positive electrode produced in Comparative Example 1 in the solution, the coin-type lithium secondary battery was manufactured using the positive electrode in the same manner as in Example 8, and the same as in Example 8. The battery characteristics (discharge capacity, cycle characteristics) were investigated. The results are shown in Table 2.

Comparative Example 3
A polyparaphenylene protective layer having a thickness of 10 μm was formed on both surfaces of the aluminum foil current collector by low-temperature firing. The positive electrode mixture slurry of Example 8 was applied on the aluminum foil current collector on which the protective layer was formed, and a coin-type lithium secondary battery was produced in the same manner as in Example 8. The battery characteristics (discharge capacity, cycle characteristics) were investigated. The results are shown in Table 2.

  From Table 2, the target discharge capacity was obtained even when the battery of Example 8 was charged and discharged at 4.7 V, but the target discharge capacity was not obtained with the battery of Comparative Example 1, and It can be seen that the cycle deterioration is also large. Thus, it can be seen that the current collector can be protected from oxidative degradation by providing the conductive protection layer of the present invention on the aluminum foil.

Claims (9)

A current collecting laminate comprising a conductive protective layer (A) comprising a cross-linked fluorine-containing elastomer (a) and a conductive filler (b) provided on a current collector (B). The fluorine-containing elastomer (a) is a fluorine-containing elastomer comprising a structural unit derived from vinylidene fluoride and / or a structural unit derived from tetrafluoroethylene and a structural unit derived from at least one additional monomer. 1. The current collecting laminate according to 1. The current collecting laminate according to claim 1 or 2, wherein the conductive filler (b) is a particulate filler, a fibrous filler, or a combination thereof. The current collecting laminate according to any one of claims 1 to 3, wherein the conductive filler (b) is a conductive carbon filler. The current collecting laminate according to claim 1, wherein the conductive protective layer (A) has a volume resistivity of 0.001 to 50 Ω · cm. The current collecting laminate according to any one of claims 1 to 5, wherein 5 to 300 parts by mass of a conductive filler (b) is contained with respect to 100 parts by mass of the fluorine-containing elastomer (a). The electrode laminated body by which an electrode mixture layer (C) is provided on the electroconductive protective layer (A) of the current collection laminated body in any one of Claims 1-6. A lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein at least one of the positive electrode and the negative electrode is an electrode laminate according to claim 7. A conductive inclusion for forming a protective layer for a current collector of a lithium secondary battery comprising a cross-linked or non-cross-linked fluorine-containing elastomer (a), a conductive filler (b), and an organic solvent (c). Fluoroelastomer composition.

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