JP2016018584A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery having a flat wound electrode body and good charge and discharge cycle characteristics with good productivity.SOLUTION: The problem is solved by a nonaqueous electrolyte secondary battery which comprises: a wound electrode body shaped in a flat form in cross section and arranged by put together a positive electrode, a negative electrode appropriately and a separator and winding them like a swirl; a nonaqueous electrolyte; and a battery case in which the wound electrode body and the nonaqueous electrolyte are enclosed. The battery case has a bottomed cylindrical metal outer can and a lid for sealing an opening of the metal outer can; in a particular part of the outer can, the thickness t of metal making up the part is 0.30 mm or smaller. The positive electrode has a metal collector, and a positive electrode mixture layer formed on the collector on each side thereof and including a positive electrode active material, a conductive assistant and a binding agent. The collector of the positive electrode is 11 μm or smaller in thickness, and 2.5 N/mm or larger in tensile strength.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a non-aqueous electrolyte secondary battery having a flat wound electrode body and good charge / discharge cycle characteristics and productivity.

  In recent years, with the development of portable electronic devices such as mobile phones and laptop computers, and the practical application of electric vehicles, small and light non-aqueous electrolyte secondary batteries have become necessary. .

  As such a non-aqueous electrolyte secondary battery that is reduced in size and weight, for example, a positive electrode and a negative electrode are overlapped with a separator interposed therebetween and wound in a spiral shape, and the cross section becomes flattened. A structure in which the formed flat wound electrode body is accommodated in a thin outer casing (battery case) such as a rectangular (square tube) outer can or a laminated film outer casing made of a metal laminate film. Can be mentioned.

  However, in the flat wound electrode body as described above, in the curved portion (particularly, the innermost curved portion), cracks in the positive electrode mixture layer (mixture layer containing the positive electrode active material) or current collector As a result, there is a risk that the production efficiency of the battery may be reduced because a large number of manufactured batteries include those with low reliability due to the above-described cracking or breaking.

  Regarding the breakage of the current collector in the flat wound electrode body, for example, a technique for preventing this by using a current collector having a specific tensile strength has been proposed (for example, Patent Document 1).

JP 2012-28158 A

  By the way, in the nonaqueous electrolyte secondary battery, conventionally, it is required to have excellent charge / discharge cycle characteristics so that a large capacity can be maintained even after repeated charge / discharge. Technology has been developed.

  However, even in cases where the normal usage environment is considered to be normal temperature, such as mobile devices such as mobile phones, there are many cases where the temperature is higher than normal temperature in actual use. Regarding the assumed charge / discharge cycle characteristics of the non-aqueous electrolyte secondary battery, there is still room for improvement.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a non-aqueous electrolyte secondary battery having a flat wound electrode body and good charge / discharge cycle characteristics and productivity. It is in.

  The non-aqueous electrolyte secondary battery of the present invention that has achieved the above object comprises a spirally wound electrode body in which a positive electrode, a negative electrode, and a separator are stacked and wound in a spiral shape, and a non-aqueous electrolyte having a flat cross section. A non-aqueous electrolyte secondary battery housed in a battery case, wherein the battery case has a bottomed cylindrical metal outer can and a lid that seals the opening of the metal outer can The side surface portion of the outer can is opposed to each other and has two wide surfaces wider than the other surfaces in a side view, and the wide surface is projected from the side surface. The shape of the metal that constitutes the outer can in the shape of a quadrangle is t is 0.30 mm or less, where t is the thickness at the location corresponding to the intersection of two diagonal lines in the projected shape of the wide surface. The positive electrode comprises a metal current collector and a positive electrode active material formed on both sides of the current collector; A positive electrode mixture layer containing an electric assistant and a binder, and the positive electrode current collector has a thickness of 11 μm or less and a tensile strength of 2.5 N / mm or more. It is a feature.

  According to the present invention, it is possible to provide a nonaqueous electrolyte secondary battery that has a flat wound electrode body and has good charge / discharge cycle characteristics and good productivity.

It is a perspective view showing typically an example of the nonaqueous electrolyte secondary battery of the present invention. It is a side view of the nonaqueous electrolyte secondary battery of FIG. It is a fragmentary longitudinal cross-sectional view which represents typically an example of the nonaqueous electrolyte secondary battery of this invention.

  The nonaqueous electrolyte secondary battery of the present invention comprises a spirally wound electrode body (hereinafter referred to as “flat spirally wound electrode body”) in which a positive electrode, a negative electrode, and a separator are overlapped and wound in a spiral shape and the cross section is flattened. The nonaqueous electrolyte is contained in a battery case, and the battery case has a bottomed cylindrical metal outer can and a lid that seals the opening of the metal outer can. The side surface of the outer can is opposed to each other and has two wide surfaces wider than the other surfaces in a side view, and the wide surface has a quadrangular projection shape from the side surface. is there. That is, the nonaqueous electrolyte secondary battery of the present invention is a prismatic battery having a so-called rectangular tube-shaped outer can.

  And the positive electrode which concerns on the nonaqueous electrolyte secondary battery of this invention is a positive electrode containing the positive electrode active material, the conductive support agent, and the binder which were formed in the metal collector and the both surfaces of the said collector. And a mixture layer. The positive electrode current collector has a thickness of 11 μm or less and a tensile strength of 2.5 N / mm or more.

  Repeated charge / discharge of the nonaqueous electrolyte secondary battery causes oxidative decomposition of the nonaqueous electrolyte, resulting in a shortage of electrolyte in the positive electrode, which causes decomposition products to deposit on the surface layer of the positive electrode active material contained in the positive electrode. Or the ion conduction path between particles decreases, and these cause deterioration in charge / discharge cycle characteristics.

  However, the positive electrode according to the non-aqueous secondary battery of the present invention includes a thin current collector having a thickness of 11 μm or less, and thus, the positive electrode current collector occupies the internal volume of the non-aqueous electrolyte secondary battery. The ratio of being made is made as small as possible. Therefore, in the non-aqueous electrolyte secondary battery of the present invention, it is possible to increase the amount of non-aqueous electrolyte introduced into the interior, and thereby charge / discharge cycle characteristics (particularly in a slightly high temperature environment of about 45 ° C.). Charging / discharging cycle characteristics) can be improved.

  However, if the current collector of the positive electrode is thinned as described above, the strength is reduced, so that when the flat wound electrode body is formed, the current collector is likely to be broken, producing a non-aqueous electrolyte secondary battery. Sex is reduced.

  Therefore, in the non-aqueous electrolyte secondary battery of the present invention, a metal outer can that is at least partly composed of a thin metal is used for the battery case.

  In a square battery using a rectangular battery case, from the viewpoint of increasing capacity, it is common to greatly increase the proportion of the flat wound electrode body in the internal volume of the battery case, It is necessary to strongly tighten the flat wound electrode body when it is wound, or to press it with a large stress when it is flat. Therefore, in such a rectangular battery, stress applied to the flat wound electrode body is increased, and therefore, if the thin current collector having low strength is used for the positive electrode, the battery is easily broken.

  However, when a metal outer can made of a battery case made of a thin metal is used, the inner volume can be increased even in the case of batteries having the same outer size. The rotating electrode body can be used without being tightly wound or pressed with too much stress when flattened. Therefore, the stress applied to the flat wound electrode body in the battery case can be reduced, and the current collector of the positive electrode can be prevented from being broken, and the productivity and reliability of the nonaqueous electrolyte secondary battery can be improved.

  On the other hand, the flat wound electrode body has a large repulsive force to return from the wound state to the original state (the state in which the electrode and the separator are laminated), and therefore an outer can made of a thin metal is used. The outer can is easily deformed by the repulsive force. However, in the nonaqueous electrolyte secondary battery of the present invention, the current collector of the positive electrode is made thin as described above, and thus the repulsive force of the flat wound electrode body is reduced, so that it is made of a thin metal. Even if an outer can is used, the deformation can be suppressed, and productivity can be increased from this viewpoint.

The positive electrode active material of the positive electrode related to the non-aqueous electrolyte secondary battery of the present invention includes those conventionally used as positive electrode active materials for non-aqueous electrolyte secondary batteries, for example, occlusion of lithium ions. An active material that can be released is used. As a specific example of such a positive electrode active material, for example, a layered structure represented by Li _{1 + x} MO ₂ (−0.1 <x <0.1, M: Co, Ni, Mn, Al, Mg, etc.) Lithium-containing transition metal oxide, LiMn ₂ O ₄ and spinel-structured lithium manganese oxide obtained by substituting some of its elements with other elements, LiMPO ₄ (M: Co, Ni, Mn, Fe, etc.) Type compounds. Specific examples of the lithium-containing transition metal oxide having the layered structure include LiCoO ₂ and other oxides including at least Co, Ni, and Mn (LiMn _1/3 Ni _1/3 Co _1/3 O ₂ , LiMn _{5 / 12} Ni _5/12 Co _1/6 O ₂ ) and the like. In particular, in order to increase the stability of the positive electrode active material in a state of being charged at a high voltage, when the non-aqueous electrolyte secondary battery is charged with a higher final voltage than usual before its use. The various active materials exemplified above preferably further contain a stabilizing element. Examples of such stabilizing elements include Mg, Al, Ti, Zr, Mo, and Sn.

  The content of the positive electrode active material in the positive electrode mixture layer is preferably 94 to 98% by mass.

  Examples of the conductive additive for the positive electrode include graphites such as natural graphite (flaky graphite, etc.) and artificial graphite; carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black. Carbon materials such as carbon fibers; conductive fibers such as metal fibers; carbon fluoride; metal powders such as aluminum; zinc oxide; conductive whiskers such as potassium titanate; Conductive metal oxides such as titanium oxide; organic conductive materials such as polyphenylene derivatives; and the like can also be used.

  It is preferable that content of the conductive support agent in a positive mix layer is 1-5 mass%.

  Examples of the binder for the positive electrode include acrylonitrile, acrylic esters (methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, etc.) and methacrylic esters (methyl methacrylate, ethyl methacrylate, butyl methacrylate). A copolymer formed by two or more monomers including at least one monomer selected from the group consisting of: hydrogenated nitrile rubber; PVDF; vinylidene fluoride-tetrafluoroethylene copolymer (VDF-TFE); Vinylidene-hexafluoropropylene-tetrafluoroethylene copolymer (VDF-HFP-TFE); vinylidene fluoride-chlorotrifluoroethylene copolymer (VDF-CTFE); and the like. May be use, it may be used in combination of two or more thereof.

  Among the binders exemplified above, it is preferable to use VDF-CTFE.

  Polyvinylidene fluoride (PVDF) is often used as the binder of the positive electrode mixture layer relating to the positive electrode for the nonaqueous electrolyte secondary battery. This PVDF undergoes deHF reaction in the presence of alkali components (such as unreacted raw materials of the positive electrode active material and by-products during the synthesis of the positive electrode active material) contained in the positive electrode active material to form a crosslink. Therefore, the positive electrode mixture layer tends to be hard. When a flat wound electrode body is formed using a positive electrode having a hard positive electrode mixture layer, the stress applied to the current collector during winding is increased, so a thin and low strength current collector is used. If so, the tears are more likely to occur.

  However, in the case of VDF-CTFE, even if a deHF reaction occurs in the presence of an alkali component, the reaction is stopped by the action of a structural unit derived from chlorotrifluoroethylene. Therefore, since the flexibility of the positive electrode mixture layer is improved by using VDF-CTFE as a binder, the formation of a flat wound electrode body can be achieved even if a thin current collector is used as described above. It is possible to increase the productivity of non-aqueous electrolyte secondary batteries by suppressing current collector breakage at the time, and to suppress deterioration of battery characteristics such as capacity that can occur due to current collector breakage Therefore, the reliability of the non-aqueous electrolyte secondary battery can be improved.

  In addition, when VDF-CTFE and PVDF are used together in the binder of the positive electrode mixture layer, the formation of a crosslinked structure in PVDF is suppressed by the action of the structural unit derived from chlorotrifluoroethylene in VDF-CTFE. Therefore, the flexibility of the positive electrode mixture layer can be maintained.

  The content of the binder in the positive electrode mixture layer is such that the positive electrode active material and the conductive additive in the positive electrode mixture layer can be satisfactorily bound to prevent desorption from these positive electrode mixture layers. From the viewpoint of improving the reliability of the battery in which the positive electrode is used more preferably, it is preferably 1% by mass or more. However, when the amount of the binder in the positive electrode mixture layer is too large, the amount of the positive electrode active material and the amount of the conductive auxiliary agent are decreased, and the effect of increasing the capacity may be reduced. Therefore, the content of the binder in the positive electrode mixture layer is preferably 1.6% by mass or less.

  Moreover, when using together VDF-CTEF and another binder for the binder which concerns on a positive electrode, from a viewpoint of ensuring the said effect by use of VDF-CTFE more favorably, in binder total quantity. The ratio of VDF-CTFE is preferably 20% by mass or more, and more preferably 50% by mass or more. In addition, since only VDF-CTFE may be used for the binder of the positive electrode mixture layer, the preferable upper limit of the ratio of VDF-CTFE in the total amount of the binder is 100% by mass.

  In producing the positive electrode, a paste in which the positive electrode mixture containing the positive electrode active material, the conductive auxiliary agent and the binder is uniformly dispersed using a solvent such as N-methyl-2-pyrrolidone (NMP). A composition in the form of a slurry or slurry (the binder may be dissolved in a solvent) is applied to the surface of the positive electrode current collector and dried. A method of adjusting the thickness and density of the agent layer can be employed. However, the method for producing the positive electrode of the present invention is not limited to the above method, and other methods may be adopted.

  As described above, the positive electrode current collector has a thickness of 11 μm or less, preferably 10 μm or less. As described above, in the present invention, by adjusting the thickness of the metal constituting the outer can according to the battery case, even a positive electrode having a current collector with such a thickness is a flat wound electrode body. The current collector can be prevented from being broken. However, if the strength of the current collector of the positive electrode is too small, there is a possibility that the action of suppressing breakage due to the use of VDF-CTFE will be insufficient. Therefore, the current collector is broken when a flat wound electrode body is formed by using a positive electrode current collector having a tensile strength of 2.5 N / mm or more, preferably 2.7 N / mm or more. Is better controlled. The tensile strength of the positive electrode current collector is preferably 3.9 N / mm or less.

  The tensile strength of the current collector referred to in this specification is a pre-treatment where the current collector is cut into a 15 mm × 250 mm rectangle to form a test piece. It is a value obtained by conducting a test at a crosshead speed of 10 mm / min using “SDT-52 type”).

  Examples of the current collector having the tensile strength as described above include the following.

  As a material of the positive electrode current collector, an aluminum alloy whose main component is aluminum is desirable. The aluminum alloy has an aluminum purity of 99.0% by mass or more, and as other additive components, for example, Si ≦ 0.6% by mass, Fe ≦ 0.7% by mass, Cu ≦ 0.25% by mass, Mn ≦ 1. It is desirable to contain 5% by mass, Mg ≦ 1.3% by mass, and Zn ≦ 0.25% by mass. A foil or film made of such a material can be used as a current collector.

  In addition, since it will become difficult to ensure the said tensile strength when a collector is too thin, it is preferable that the thickness is 6 micrometers or more.

  The thickness of the positive electrode mixture layer is preferably 30 to 80 μm per one side of the current collector. In the positive electrode mixture layer, the filling rate is preferably 75% or more from the viewpoint of higher capacity. However, when the filling rate of the positive electrode mixture layer is too high, the number of pores in the positive electrode mixture layer becomes too small, and the permeability of the nonaqueous electrolyte (nonaqueous electrolyte solution) into the positive electrode mixture layer decreases. Since there exists a possibility, it is preferable that the filling rate is 83% or less. The filling rate of the positive electrode mixture layer is determined by the following formula.

    Filling rate (%) = 100 × (actual density of positive electrode mixture layer / theoretical density of positive electrode mixture layer)

The “theoretical density of the positive electrode mixture layer” in the above formula for calculating the filling rate of the positive electrode mixture layer is a density (positive electrode mixture) calculated from the density and content of each component of the positive electrode mixture layer. The density obtained by assuming that there are no vacancies in the layer), and the “actual density of the positive electrode mixture layer” is measured by the following method. First, it cuts a positive electrode to a size of 1 cm × 1 cm, a thickness micrometer _{(l 1),} measuring the mass _{(m 1)} a precision balance. Next, the positive electrode material mixture layer is scraped off, and only the current collector is taken out, and the thickness (l _c ) and mass (m _c ) of the current collector are measured in the same manner as the positive electrode. From the obtained thickness and mass, the actual density (d _ca ) of the positive electrode mixture layer is determined by the following formula (the unit of thickness is cm, and the unit of mass is g).
d _ca = (m ₁ −m _c ) / (l ₁ −l _c )

  As a negative electrode which concerns on the nonaqueous electrolyte secondary battery of this invention, what formed the negative mix layer containing a negative electrode active material in the single side | surface or both surfaces of a collector is mentioned, for example. The negative electrode mixture layer contains, in addition to the negative electrode active material, a binder and, if necessary, a conductive aid, and includes, for example, a negative electrode active material and a binder (further, a conductive aid). A negative electrode mixture-containing composition (slurry etc.) obtained by adding a suitable solvent to the mixture (negative electrode mixture) and kneading thoroughly is applied to the surface of the current collector and dried to obtain a desired thickness. Can be formed.

  Examples of the negative electrode active material include graphite materials such as natural graphite (flaky graphite), artificial graphite, and expanded graphite; graphitizable carbonaceous materials such as coke obtained by calcining pitch; furfuryl alcohol resin ( Non-graphitizable carbonaceous material such as amorphous carbon obtained by low-temperature firing of PFA), polyparaphenylene (PPP) and phenolic resin; amorphous carbon or resin is supported on the surface of graphite material And carbon materials such as surface treated carbon materials. In addition to the carbon material, lithium or a lithium-containing compound can also be used as the negative electrode active material. Examples of the lithium-containing compound include lithium alloys such as Li—Al, and alloys containing elements that can be alloyed with lithium such as Si and Sn. Furthermore, oxide-based materials such as Sn oxide and Si oxide can also be used. The content of the negative electrode active material in the negative electrode mixture layer is preferably 97 to 99% by mass, for example.

  It is preferable to use a surface-treated carbon material as the negative electrode active material because excessive reaction with the nonaqueous electrolyte can be prevented.

  As the negative electrode active material, in particular, when a carbon material having amorphous particles supported on the surface of a graphite material and having an average particle diameter of 8 to 18 μm and relatively small particles is used, the permeability of the nonaqueous electrolyte into the negative electrode mixture layer Is preferable. The reason is not clear, but if the carbon material is relatively small particles, the pores formed in the negative electrode mixture layer are uniformed when the negative electrode is pressed. It is thought that the electrolyte easily penetrates. In addition, this type of graphite has a high lithium ion acceptability (ratio of constant current charge capacity to total charge capacity), and by using this graphite as a negative electrode active material, a non-aqueous electrolyte having more excellent charge / discharge cycle characteristics. A secondary battery can be provided.

In addition, the average particle diameter of the carbon material referred to in the present specification is obtained by, for example, dissolving the carbon material using a laser scattering particle size distribution meter (for example, Microtrack particle size distribution measuring device “HRA9320” manufactured by Nikkiso Co., Ltd.) The value of 50% diameter (d ₅₀ ) median diameter in the volume-based integrated fraction when the integrated volume is obtained from particles having a small particle size distribution measured by dispersing the carbon material in a medium that does not swell.

  The conductive aid is not particularly limited as long as it is an electron conductive material, and may not be used. Specific examples of conductive aids include acetylene black; ketjen black; carbon blacks such as channel black, furnace black, lamp black, and thermal black; carbon materials such as carbon fibers; and conductive fibers such as metal fibers. Carbon fluoride, metal powders such as copper and nickel, organic conductive materials such as polyphenylene derivatives, and the like. These may be used alone or in combination of two or more. . Among these, acetylene black, ketjen black and carbon fiber are particularly preferable. However, when a conductive additive is used for the negative electrode, the content of the conductive additive in the negative electrode mixture layer is preferably 10% by mass or less in order to increase the capacity.

As a binder concerning a negative mix layer, any of a thermoplastic resin and a thermosetting resin may be sufficient. Specifically, for example, the same material as the binder according to the positive electrode of the present invention, a styrene butadiene rubber (SBR), an ethylene-acrylic acid copolymer, or a Na ⁺ ion crosslinked product of the copolymer, ethylene-methacrylic Acid copolymer or Na ⁺ ion crosslinked product of the copolymer, ethylene-methyl acrylate copolymer, Na ⁺ ion crosslinked product of the copolymer, ethylene-methyl methacrylate copolymer or the copolymer Na ⁺ ion crosslinked body etc. can be used, These materials may be used individually by 1 type, and may use 2 or more types together.

Among these, PVDF, SBR, ethylene-acrylic acid copolymer or Na ⁺ ion crosslinked product of the copolymer, ethylene-methacrylic acid copolymer or Na ⁺ ion crosslinked product of the copolymer, ethylene-acrylic acid A methyl copolymer or a Na ⁺ ion crosslinked product of the copolymer, an ethylene-methyl methacrylate copolymer or a Na ⁺ ion crosslinked product of the copolymer is particularly preferable. The content of the binder in the negative electrode mixture layer is preferably 1 to 5% by mass, for example.

  The thickness of the negative electrode mixture layer (when the negative electrode mixture layer is formed on both sides of the current collector, the thickness per one surface thereof) is preferably 30 to 80 μm.

  The current collector used for the negative electrode is not particularly limited as long as it is an electron conductor that is substantially chemically stable in the nonaqueous electrolyte secondary battery. Examples of the material constituting the current collector include stainless steel, nickel or an alloy thereof, copper or an alloy thereof, titanium or an alloy thereof, carbon, conductive resin, carbon, or the like on the surface of copper or stainless steel. A material obtained by treating titanium is used. Among these, copper and copper alloys are particularly preferable. These materials can also be used after oxidizing the surface. Moreover, it is preferable to give an unevenness | corrugation to the collector surface by surface treatment. Examples of the shape of the current collector include films, sheets, nets, punched materials, lath bodies, porous bodies, foamed bodies, and molded bodies of fiber groups, in addition to foils. Although the thickness of a collector is not specifically limited, For example, it is preferable that it is 5-50 micrometers.

  As the non-aqueous electrolyte, for example, a solution (non-aqueous electrolyte) prepared by dissolving a lithium salt in the following non-aqueous solvent can be used.

Examples of the solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), γ-butyrolactone (γ-
BL), 1,2-dimethoxyethane (DME), tetrahydrofuran (THF), 2-methyltetrahydrofuran, dimethyl sulfoxide (DMSO), 1,3-dioxolane, formamide, dimethylformamide (DMF), dioxolane, acetonitrile, nitromethane , Aprotic such as methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivative, sulfolane, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, diethyl ether, 1,3-propane sultone The organic solvent can be used alone or as a mixed solvent in which two or more are mixed.

The lithium salt according to the non-aqueous electrolyte solution, for _{example, LiClO 4, LiPF 6, LiBF} 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiCF 3 CO 2, Li 2 C 2 F 4 (SO 3) 2, LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO 3 (n ≧ 2), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] At least one selected from the above. The concentration of these lithium salts in the non-aqueous electrolyte is preferably 0.6 to 1.8 mol / l, and more preferably 0.9 to 1.6 mol / l.

  Non-aqueous electrolytes used in non-aqueous electrolyte secondary batteries include vinylene carbonate, vinyl ethylene carbonate, anhydrous water for the purpose of further improving charge / discharge cycle characteristics and improving safety such as high-temperature storage and prevention of overcharge. Additives (including these derivatives) such as acid, sulfonic acid ester, dinitrile, 1,3-propane sultone, diphenyl disulfide, cyclohexyl benzene, biphenyl, fluorobenzene, and t-butyl benzene may be added as appropriate.

  Further, as the non-aqueous electrolyte of the non-aqueous electrolyte secondary battery, a gel (gel electrolyte) obtained by adding a known gelling agent such as a polymer to the non-aqueous electrolyte can be used.

  In the non-aqueous electrolyte secondary battery of the present invention, a separator containing the non-aqueous electrolyte is disposed between the positive electrode and the negative electrode. As the separator, an insulating microporous thin film having a large ion permeability and a predetermined mechanical strength is used. Moreover, what has a function which a hole is obstruct | occluded by fusion | melting of a structural material above a fixed temperature (for example, 100-140 degreeC), and raises resistance (namely, what has a shutdown function) is preferable.

  Specific examples of such a separator include a sheet (porous sheet), a nonwoven fabric or a woven fabric composed of a material such as polyethylene solvent, hydrophobic polymer such as polyethylene, polypropylene, or glass fiber having organic solvent resistance and hydrophobicity; And a porous material in which fine particles of the exemplified polyolefin polymer are fixed with an adhesive.

  The pore diameter of the separator is preferably such that the active material of the positive and negative electrodes, the conductive auxiliary agent, the binder and the like detached from the positive and negative electrodes do not pass through, and is preferably 0.01 to 1 μm, for example. The thickness of the separator is generally 8-30 μm, but is preferably 10-20 μm in the present invention. Further, the porosity of the separator is determined according to the constituent material and thickness, but is generally 30 to 80%.

  In the non-aqueous electrolyte secondary battery of the present invention, as described above, the positive electrode and the negative electrode are overlapped via the separator, wound into a spiral shape, and crushed to make the cross section flat. A flat wound electrode body is used.

  And the said flat winding electrode body is enclosed with a non-aqueous electrolyte in a battery case, and the non-aqueous electrolyte secondary battery of this invention is formed.

  In FIG. 1, the perspective view which represents typically the external appearance of an example of the nonaqueous electrolyte secondary battery of this invention is shown. A battery case 10 according to the nonaqueous electrolyte secondary battery 1 shown in FIG. 1 is hollow, and accommodates therein a flat wound electrode body formed of a positive electrode, a negative electrode, and a separator, a nonaqueous electrolyte, and the like.

  The battery case 10 includes an outer can 11 and a lid 20, and the outer can 11 has a bottomed cylindrical shape (square tube shape), and the lid 20 is covered on the opening end portion thereof. It is integrated with the lid 20 by welding. The outer can 11 and the lid 20 are made of, for example, an aluminum alloy.

  A terminal 21 made of stainless steel or the like protrudes from the lid 20, and an insulating packing 22 made of PP or the like is interposed between the terminal 21 and the lid 20. The terminal 21 is connected to, for example, a negative electrode in the battery case 10. In this case, the terminal 21 functions as a negative electrode terminal, and the outer can 11 and the lid 20 function as a positive electrode terminal. However, depending on the material of the battery case 10, the terminal 21 may be connected to the positive electrode in the battery case 10 to function as a positive electrode terminal, and the outer can 11 and the lid 20 may function as a negative electrode terminal. Further, the lid 20 is provided with a nonaqueous electrolyte injection port, and after the nonaqueous electrolyte is injected into the battery case 10, the lid 20 is sealed with a sealing member 23.

  The side surface portion of the battery case 10, that is, the side surface portion of the outer can 11 has two wide surfaces 111 and 111 that are opposed to each other and wider than the other surfaces (surfaces 112 and 112 in the drawing). doing.

  FIG. 2 shows a side view of the nonaqueous electrolyte secondary battery shown in FIG. 1 as viewed from the wide surface 111 side of the outer can 11. As shown in FIG. 2, the wide surfaces 111, 111 are quadrangular when projected from the side, that is, when the wide surface is viewed from the side as a two-dimensional shape. And the metal which comprises the armored can 11 is the thickness in the location equivalent to the intersection of two diagonal lines (it shows with the dashed-dotted line in the figure) of the wide surfaces 111 and 111 in the said projection shape (the said square). Where t is 0.30 mm or less, preferably 0.28 mm or less.

  A rectangular tube-shaped outer can for forming a nonaqueous electrolyte secondary battery is generally manufactured by drawing (deep drawing), but when manufactured by such a method, the outer can Among the constituent metals, the portion corresponding to the intersection of the two diagonals and the vicinity thereof are most likely to be thinnest (however, as described later, when the outer can is provided with a cleavage groove, Excluding forming part). As described above, by reducing the thickness of the metal constituting the outer can at the location as described above, it is possible to suppress the breaking of the thin positive electrode current collector, and to improve the productivity and reliability of the nonaqueous electrolyte secondary battery. Can be increased.

  Further, the ratio of the area of the portion where the thickness of the metal constituting the outer can is equal to or less than the value t in the total area of the projected shape (the square) per one wide surface (for example, the t is 0). In the case of .30 mm, the ratio of the area of the portion having a thickness of 0.30 mm or less) is preferably 50% or more, more preferably 80% or more, whereby the non-aqueous electrolyte secondary The productivity and reliability of the battery can be improved more favorably. The ratio of the area of the portion where the thickness of the metal constituting the outer can is equal to or less than the value of t in the entire area of the projected shape (the square) per one wide surface may be 100%. .

  The ratio of the area of the portion where the thickness of the metal constituting the outer can in the entire area of the projected shape (the square) per one wide surface referred to in this specification is equal to or less than the value of t is the projected shape. Centered from the intersection of two diagonals in the above (rectangle), the center and each vertex to the center are connected by a straight line, and the center is from the middle point between the vertex that is equidistant from the vertex and the vertex Is obtained by dividing the number of points measured with a micrometer below the value of t by the total number of measurement points. Value.

  However, if the metal constituting the outer can is too thin, the reliability of the battery will be lowered, or the battery can easily be swollen with the charging / discharging of the battery. The thickness t at a location corresponding to the intersection of two diagonal lines in the projected shape (the square) is preferably 0.10 mm or more, and more preferably 0.16 mm or more.

In the non-aqueous electrolyte secondary battery of the present invention, the internal volume of the battery case is A (cm ³ ), and the total volume of the positive electrode, the negative electrode, and the separator (the volume including these pores) is B (cm ³ ). The ratio A / B is preferably 1.14 or more, more preferably 1.15 or more. In this case, the inner volume of the battery case has a sufficient margin with respect to the total volume of the positive electrode, the negative electrode, and the separator accommodated in the battery case with respect to the inner volume of the battery case. It is possible to use a flat wound electrode body formed by pressing, and it is possible to better suppress cracking of the positive electrode current collector and the positive electrode mixture layer, and to introduce a nonaqueous electrolyte Since the amount can be increased, the charge / discharge cycle characteristics of the battery can be further improved.

  However, if the ratio A / B is too large, the battery capacity may be reduced. Therefore, the ratio A / B is preferably 1.50 or less, and more preferably 1.40 or less. .

  The non-aqueous electrolyte secondary battery shown in FIG. 1 and FIG. 2 is used for cleaving when the internal pressure becomes larger than the threshold value on the wide surface 111 of the outer can 11 in order to increase the safety. A cleavage groove 12 is provided. In addition, the nonaqueous electrolyte secondary battery may have a cleavage vent in the lid body for cleaving when the internal pressure becomes larger than the threshold value, instead of the cleavage groove.

  The shape of the battery case (the shape of the outer can) may be a shape (for example, a shape that is a hexahedron) between the wide surface and the other surface in the side surface portion, as shown in FIG. , The width between the wide surface and the other surface is curved (for example, the portion corresponding to the other surface of the lid and the bottom surface, which is the top surface, is arcuate, and the other surface is curved. Shape).

  The non-aqueous electrolyte secondary battery of the present invention can be applied to the same applications as conventionally known non-aqueous electrolyte secondary batteries.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

Example 1
<Preparation of positive electrode>
LiCoO _{2 as a} positive electrode active material: 97.3 parts by mass, acetylene black as a conductive auxiliary agent: 1.5 parts by mass and PVDF as a binder: 1.2 parts by mass are mixed to form a positive electrode mixture. NMP, a solvent, is added to the positive electrode mixture and treated with “Clearmix CLM0.8 (trade name)” manufactured by M Technique Co., Ltd. for 30 minutes at a rotation speed of 10,000 min ⁻¹ to obtain a paste-like mixture It was. NMP which is a solvent was further added to this mixture, and the mixture was treated at a rotational speed of 10000 min ⁻¹ for 15 minutes to prepare a positive electrode mixture-containing composition.

The positive electrode mixture-containing composition is applied to both sides of an aluminum alloy foil (1100, thickness: 10.0 μm, tensile strength: 2.5 N / mm) as a current collector, and vacuum-dried at 80 ° C. for 12 hours. Then, press treatment was further performed to produce a positive electrode having a positive electrode mixture layer having a thickness of 59 μm on both sides of the current collector. The density (actual density) of the positive electrode mixture layer after the press treatment determined by the above method was 3.83 g / cm ³ , and the filling rate was 76.4%.

<Production of negative electrode>
Natural graphite (average particle size: 19.3 μm) and a surface-treated carbon material having an average particle size of 10 μm carrying amorphous carbon on the surface of natural graphite are mixed at a mass ratio of 1: 1 to obtain a mixture. Obtained. This mixture (negative electrode active material): 97.5% by mass, SBR: 1.5% by mass, and carboxymethylcellulose (thickener): 1% by mass are mixed with water to form a slurry-like negative electrode mixture A composition was prepared. This negative electrode mixture-containing composition was applied to both sides of a copper foil (thickness: 8 μm) as a current collector, vacuum-dried at 120 ° C. for 12 hours, and further subjected to a press treatment to form both sides of the current collector. A negative electrode having a negative electrode mixture layer having a thickness of 71 μm was prepared.

<Production of electrode body>
The positive electrode and the negative electrode are overlapped via a separator (a polyethylene porous film having a thickness of 17 μm and an air permeability of 300 seconds / 100 cm ³ ), wound in a spiral shape, and then the cross section becomes flat. In this way, a flat wound electrode body was produced. The total volume B of the positive electrode, the negative electrode, and the separator constituting the flat wound electrode body was 8.3 cm ³ .

<Preparation of non-aqueous electrolyte>
LiPF ₆ was dissolved at a concentration of 1.2 mol / l in a mixed solvent of methyl ethyl carbonate, diethyl carbonate and ethylene carbonate (volume ratio 2: 1: 3), and vinylene carbonate: 2% by mass, vinyl ethylene carbonate. 1% by mass was added to prepare a non-aqueous electrolyte (non-aqueous electrolyte).

<Battery assembly>
The electrode body is inserted into a rectangular outer can made of aluminum alloy having an outer dimension of thickness 3.75 mm, width 52.8 mm, and height 61.3 mm, the lead body is welded, and an aluminum alloy lid The plate was welded to the open end of the battery case. Thereafter, 3.65 g of the non-aqueous electrolyte solution was injected from the inlet provided in the cover plate, and after standing for 1 hour, the inlet was sealed, and the appearance shown in FIG. A square nonaqueous electrolyte secondary battery was prepared. The outer can used for the non-aqueous electrolyte secondary battery has an internal volume A of 9.73 cm ³ and corresponds to the intersection of two diagonal lines in the projected shape of the wide surface of the metal constituting the outer can. The thickness was 0.30 mm (the proportion of the area of the portion having a thickness of 0.30 mm or less in the total area in the projected shape of one wide surface was 66%).

  Here, the nonaqueous electrolyte secondary battery will be described with reference to FIGS. 1 and 3. FIG. 3 is a partial longitudinal sectional view schematically showing a nonaqueous electrolyte secondary battery. In the nonaqueous electrolyte secondary battery 1, the positive electrode 31 and the negative electrode 32 are spirally wound via the separator 33, and then pressed so as to be flattened to form a flat wound electrode body 30 with a rectangular shape ( It is housed in a rectangular tube-shaped outer can 11 together with a non-aqueous electrolyte. However, in FIG. 3, in order to avoid complication, a metal foil, a non-aqueous electrolyte, or the like as a current collector used for manufacturing the positive electrode 31 and the negative electrode 32 is not illustrated. Moreover, in FIG. 3, the part of the inner peripheral side of the flat winding electrode body 30 is not made into the cross section.

  The outer can 11 is made of an aluminum alloy and also serves as a positive electrode terminal. And the insulator 40 which consists of a polyethylene sheet is arrange | positioned at the bottom part of the armored can 11, and it connects to each one end of the positive electrode 31 and the negative electrode 32 from the flat wound electrode body 30 which consists of the positive electrode 31, the negative electrode 32, and the separator 33. The positive electrode lead body 51 and the negative electrode lead body 52 are drawn out. A stainless steel terminal 21 is attached to an aluminum alloy cover plate 20 that seals the opening of the outer can 11 via a polypropylene insulating packing 22, and an insulator 24 is connected to the terminal 21. A stainless steel lead plate 25 is attached.

  And this cover plate 20 is inserted in the opening part of the armored can 11, and the opening part of the armored can 11 is sealed by welding the junction part of both, and the inside of a battery is sealed. Further, in the battery of FIG. 3, the lid plate 20 is provided with a non-aqueous electrolyte inlet 23, and a sealing member is inserted into the non-aqueous electrolyte inlet 23, for example, laser welding or the like. As a result, the battery is sealed by welding.

  In the battery of Example 1, the outer can 11 and the cover plate 20 function as a positive electrode terminal by directly welding the positive electrode lead body 51 to the lid plate 20, and the negative electrode lead body 52 is welded to the lead plate 25. By connecting the negative electrode lead body 52 and the terminal 21 through the lead plate 25, the terminal 21 functions as a negative electrode terminal.

  In the battery of Example 1, as shown in FIG. 1, the wide groove 111 of the outer can 11 is provided with a cleavage groove 12 for cleaving when the internal pressure becomes larger than a threshold value.

Example 2
The outer can has an inner volume A of 10.1 cm ³ , and the metal constituting the outer can has a thickness of 0.25 mm (one wide width) at a location corresponding to the intersection of two diagonal lines in the projected shape of the wide surface. The ratio of the area of the portion having a thickness of 0.25 mm or less in the total area of the projected shape of the surface is changed to 66%), and the amount of the nonaqueous electrolyte to be injected is changed to 4.02 g. A square nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1.

Example 3
The outer can has an inner volume A of 10.3 cm ³ , and the metal constituting the outer can has a thickness of 0.22 mm (one wide width) at a location corresponding to the intersection of two diagonal lines in the projected shape of the wide surface. The ratio of the area of the portion having a thickness of 0.22 mm or less in the total area in the projected shape of the surface is changed to 66%), and the amount of the nonaqueous electrolyte to be injected is changed to 4.14 g, A square nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1.

Example 4
The outer can has an inner volume A of 10.4 cm ³ , and the metal constituting the outer can has a thickness of 0.20 mm (one wide width) at a point corresponding to the intersection of two diagonal lines in the projected shape of the wide surface. The ratio of the area of the portion having a thickness of 0.20 mm or less in the total area of the projected shape of the surface is changed to 66%), and the amount of the nonaqueous electrolyte to be injected is changed to 4.28 g, A square nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1.

Example 5
The outer can has an internal volume A of 10.5 cm ³ , and the metal constituting the outer can has a thickness of 0.18 mm (one wide width) at a location corresponding to the intersection of two diagonal lines in the projected shape of the wide surface. Except that the ratio of the area of the portion having a thickness of 0.18 mm or less in the total area of the projected shape of the surface is 66%), and the amount of the nonaqueous electrolyte to be injected is changed to 4.43 g. A square nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1.

Example 6
A positive electrode was produced in the same manner as in Example 1 except that an aluminum alloy foil (3003) having a thickness of 8.0 μm and a tensile strength of 2.5 N / mm was used as the current collector. And, using this positive electrode, the metal constituting the outer can has a thickness of 0.16 mm at the point corresponding to the intersection of two diagonal lines in the projected shape of the wide surface (the total area in the projected shape of one wide surface) The ratio of the area of the portion with a thickness of 0.16 mm or less is changed to 66%), and the amount of the nonaqueous electrolyte to be injected is changed to 4.70 g. A square nonaqueous electrolyte secondary battery was produced.

Example 7
A positive electrode was produced in the same manner as in Example 1 except that the binder was changed to VDF-CTFE. A square nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

Comparative Example 1
The outer can has an inner volume A of 9.4 cm ³ , and the metal constituting the outer can has a thickness of 0.35 mm (one wide width) at a location corresponding to the intersection of two diagonal lines in the projected shape of the wide surface. The ratio of the area of the portion having a thickness of 0.35 mm or less in the total area of the projected shape of the surface is changed to 66%), and the amount of the nonaqueous electrolyte to be injected is changed to 3.28 g, A square nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1.

Comparative Example 2
A positive electrode was produced in the same manner as in Example 1 except that the thickness of the current collector was changed to 15.0 μm, and this positive electrode was used, except that the amount of nonaqueous electrolyte to be injected was changed to 3.48 g. A square nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1.

Comparative Example 3
A positive electrode was produced in the same manner as in Example 1 except that the current collector was changed to an aluminum alloy foil (A1N30) having a thickness of 10.0 μm and a tensile strength of 2.2 N / mm, and this positive electrode was used and injected. A square nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the amount of the nonaqueous electrolyte was changed to 3.65 g.

  The structure of the positive electrode current collector used in the non-aqueous electrolyte secondary batteries of Examples and Comparative Examples, the thickness of the metal constituting the outer can at the location corresponding to the intersection of two diagonal lines in the projected shape of the wide surface Table 1 shows the ratio A / B and the amount of the non-aqueous electrolyte injected into these non-aqueous electrolyte secondary batteries.

  The following evaluation was performed about the nonaqueous electrolyte secondary battery of an Example and a comparative example, and the positive electrode used for these batteries.

<Bending strength of positive electrode>
Each non-aqueous electrolyte secondary battery of Example and Comparative Example was disassembled and the positive electrode was taken out, and the portion where the positive electrode mixture layer was formed on both sides of the current collector was cut out to 5 cm in the longitudinal direction and 4 cm in the width direction for testing. A piece 15 mm from the end on the long side of the test piece was bent in the same direction as the bending direction when the wound electrode body was produced. After applying a load of 200 gf uniformly to the bent part of the test piece, set both ends of the test piece opened with a jig of a tensile tester (“SDT-52 type” manufactured by Imada Seisakusho Co., Ltd.). A tensile test was performed at a speed of 50 mm / min, and the strength when the bent portion of the test piece was broken was defined as the bending strength. The greater the bending strength, the better the positive electrode current collector breakage in the flat wound electrode body in the non-aqueous electrolyte secondary battery, and thus the productivity and reliability of the non-aqueous electrolyte secondary battery. It can be evaluated that the property is better.

<Evaluation of degree of deformation of nonaqueous electrolyte secondary battery>
About each battery of an Example and a comparative example, charge capacity (capacity when carrying out constant voltage charge until the total charge time will be 2.5 hours after charging with a constant current of 1.0C to 4.35V under the environment of room temperature ) Was charged at a constant current of 1.0 C up to 50%, and the thickness of the intersection of two diagonal lines in the projected shape of the wide surface of the outer can was measured with calipers to evaluate the degree of deformation. The smaller the thickness required at this time, the smaller the repulsive force to return from the wound state to the original state (the state in which the electrode and the separator are laminated), and the use of an outer can made of a thin metal. It is possible to suppress deformation, and it can be evaluated that the productivity and reliability of the nonaqueous electrolyte secondary battery are better.

<Evaluation of initial discharge capacity of nonaqueous electrolyte secondary battery>
About each battery of an Example and a comparative example, after charging with a constant current of 1.0C to 4.35V, it was charged with a constant voltage until the total charging time was 2.5 hours, and then the battery voltage was 2 at 1.0C. A constant current discharge was performed up to .75 V, and the discharge capacity at that time was determined.

<45 ° C. charge / discharge cycle characteristics evaluation of non-aqueous electrolyte secondary battery>
Each battery of the example and the comparative example was charged at a constant current of 1.0 C up to 4.35 V in an environment of 45 ° C., and then charged at a constant voltage until the total charging time was 2.5 hours. A series of operations for performing constant current discharge at 0.0 C to a battery voltage of 3.3 V was taken as one cycle, and these were repeated many times, and the number of cycles in which the discharge capacity was 60% or more of the discharge capacity in the first cycle was determined.

  The evaluation results are shown in Table 2. In Table 2, the discharge capacity of each non-aqueous electrolyte secondary battery and the number of cycles at the time of 45 ° C. charge / discharge cycle characteristics evaluation are expressed as relative values when the result of the battery of Comparative Example 2 is taken as 100.

  As shown in Table 2, the non-aqueous electrolyte secondary batteries of Examples 1 to 7 using an outer can having a thin constituent metal and a positive electrode current collector having a specific strength and being thin are bent positive electrodes taken from the inside. The strength was high, the occurrence of defects in the positive electrode, such as the breakage of the current collector, was suppressed, and the deformation of the outer can at the time of manufacture was also suppressed, thus providing excellent productivity and reliability. In addition, the nonaqueous electrolyte secondary batteries of Examples 1 to 7 had a large amount of nonaqueous electrolyte that could be injected, and charge / discharge cycle characteristics at high temperatures were also good.

  On the other hand, in the battery of Comparative Example 1 using an outer can with a thick constituent metal, the bending strength of the positive electrode taken out from the inside is small, and the positive electrode defect such as the breaking of the current collector occurs at the innermost bent portion. Productivity and reliability were inferior. In addition, the battery of Comparative Example 2 using a thick positive electrode current collector was inferior in productivity because the outer can was deformed during production. Furthermore, in the battery of Comparative Example 3 using the positive electrode current collector having low strength, the current collector was completely broken at the innermost bent portion, and a reduction in discharge capacity was observed. And the battery of the comparative example 1 and the battery of the comparative example 2 were inferior also in the charging / discharging cycling characteristics in high temperature.

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 10 Battery case 11 Exterior can 111 Wide surface of exterior can side surface 12 Cleavage groove 20 Lid 21 Terminal portion 30 Flat wound electrode body 31 Positive electrode 32 Negative electrode 33 Separator

Claims (4)

A non-aqueous electrolyte secondary battery in which a positive electrode, a negative electrode, and a separator are overlapped and wound in a spiral shape, and a wound electrode body having a flat cross section and a non-aqueous electrolyte are accommodated in a battery case. ,
The battery case has a bottomed cylindrical metal outer can and a lid for sealing the opening of the metal outer can,
The side portions of the outer can have two wide surfaces that are opposed to each other and wider than the other surfaces in a side view,
The wide surface has a quadrangular projection shape from the side surface,
The metal constituting the outer can, when the thickness at a location corresponding to the intersection of two diagonal lines in the projected shape of the wide surface is t, the t is 0.30 mm or less,
The positive electrode has a metal current collector and a positive electrode mixture layer formed on both surfaces of the current collector, the positive electrode active material, a conductive additive and a binder,
The positive electrode current collector has a thickness of 11 μm or less and a tensile strength of 2.5 N / mm or more.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode mixture layer contains a vinylidene fluoride-chlorotrifluoroethylene copolymer as the binder. When the internal volume of the battery case is A (cm ³ ) and the total volume of the positive electrode, the negative electrode and the separator is B (cm ³ ), the ratio A / B is 1.14 to 1.50. Item 3. The nonaqueous electrolyte secondary battery according to Item 1 or 2.   The nonaqueous electrolyte according to any one of claims 1 to 3, wherein the negative electrode contains a carbon material having an average particle diameter of 8 to 18 µm and supporting amorphous carbon on the surface of graphite as a negative electrode active material. Secondary battery.

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