JP2017212116A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery which is improved in battery life by preventing a nonaqueous electrolyte solution from being leaked to outside the battery to prevent the liquid depletion of the battery.SOLUTION: A lithium ion secondary battery according to the present invention comprises a power-generating element including a positive electrode, a negative electrode, a separator, and an electrolyte solution in an outer packaging body. The outer packaging body includes a laminate arranged by laminating a metal base material, an acid-modified polypropylene layer, and a polypropylene layer in this order, of which the polypropylene layer includes a lubricant. In the lithium ion battery, the polypropylene layer is disposed to make an inner face of the outer packaging body. The outer packaging body has a heat seal portion and a non-heat seal portion. In the polypropylene layer, the concentration of the lubricant is 100-230 ppm in the heat seal portion.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a non-aqueous electrolyte battery, particularly a lithium ion secondary battery.

  Nonaqueous electrolyte batteries have been put to practical use as automobile batteries including hybrid cars and electric cars. Lithium ion secondary batteries are used as such on-vehicle power supply batteries. Lithium ion secondary batteries are required to have various characteristics such as output characteristics, energy density, capacity, lifetime, and high temperature stability.

  A lithium ion secondary battery includes a wound battery in which a positive electrode, a negative electrode, and a separator are laminated and wound together in a container such as a can together with an electrolytic solution, and a sheet-like material in which the positive electrode, the negative electrode, and the separator are laminated. Are laminated batteries (hereinafter also referred to as “laminate batteries”) encapsulated in a relatively flexible outer package together with the electrolyte. A laminated battery has a high weight energy density and a high degree of freedom in shape, and is suitable for use as a battery for in-vehicle power supply.

  In order to improve the water vapor permeation resistance and the drawability of an outer package of a laminate type battery, it has been proposed that the resin layer contains a specific amount of lubricant (Patent Document 1).

JP 2003-288865 A

  Patent Document 1 discloses a laminated material in which an exterior resin film, a first adhesive layer, a chemical conversion treated aluminum foil, a second adhesive layer, and a sealant film are sequentially laminated, and a lubricant (erucamide) in the sealant film. Or the oleic acid amide) content is 500-2500 ppm, and the laminated material is disclosed. When using such a laminated material as an outer package of a laminated battery, for example, the laminated material is thermally fused on the outer periphery of the battery in a state where the power generation element of the battery is stored from above and below with two laminated materials. An exterior body is formed, and a nonaqueous electrolyte is sealed inside the exterior body. Thus, the heat-adhesive resin layer inside the exterior body comes into contact with the non-aqueous electrolyte. The heat-adhesive resin layer formed of the organic polymer gradually impregnates the non-aqueous electrolyte solution, which is an organic substance, and the impregnated non-aqueous electrolyte solution passes through the heat-adhesive resin layer and the adhesion reinforcing layer and the metal foil. Can reach the layer. At this time, as in Patent Document 1, if the resin layer on the side where the electrolytic solution comes into contact contains a large amount of an oleophilic lubricant such as erucamide, the nonaqueous electrolytic solution has an affinity for the lubricant. Then, it may penetrate into the outer package fusion part and the non-aqueous electrolyte may leak out of the outer package.

  Accordingly, an object of the present invention is to provide a lithium ion secondary battery that prevents leakage of a non-aqueous electrolyte to the outside of the battery and prevents battery drainage, thereby improving battery life.

  The lithium ion secondary battery in the embodiment of the present invention is a lithium ion secondary battery including a power generation element including a positive electrode, a negative electrode, a separator, and an electrolytic solution inside the exterior body. Here, the exterior body is composed of a laminate in which a metal base, an acid-modified polypropylene layer, and a polypropylene layer are laminated in this order, and among these, the polypropylene layer contains a lubricant. In the lithium ion battery, the inner surface of the outer package is arranged to be a polypropylene layer, and the outer package has a heat-fused portion and a non-fused portion. And the density | concentration of the lubricant in a polypropylene layer is 100 ppm or more and 230 ppm or less in a heat-fusion part.

  In the lithium ion secondary battery of the present invention, leakage of the electrolytic solution is suppressed, the electrolytic solution is prevented from withering, and the battery life is improved.

FIG. 1 is a schematic cross-sectional view showing a lithium ion secondary battery according to an embodiment of the present invention. FIG. 2 is an enlarged view of a heat fusion part and a non-fusion part of the outer package.

  Embodiments of the present invention will be described below. In the embodiment, the lithium ion secondary battery is a lithium ion secondary battery including a power generation element including a positive electrode, a negative electrode, a separator, and an electrolytic solution inside the exterior body. In the embodiment, the positive electrode is a thin plate shape in which a positive electrode active material layer, a binder, and, if necessary, a mixture of a conductive additive are applied to a positive electrode current collector such as a metal foil or rolled and dried to form a positive electrode active material layer. Or it is a sheet-like battery member. The negative electrode is a thin plate-like or sheet-like battery member in which a negative electrode active material layer is formed by applying a mixture of a negative electrode active material, a binder, and, if necessary, a conductive additive to a negative electrode current collector. The separator is a film-like battery member for separating the positive electrode and the negative electrode and ensuring the conductivity of lithium ions between the negative electrode and the positive electrode. The electrolytic solution is an electrically conductive solution in which an ionic substance is dissolved in a solvent. In this embodiment, a nonaqueous electrolytic solution can be used in particular. The power generation element including the positive electrode, the negative electrode, the separator, and the electrolytic solution is a unit of the main constituent member of the battery. Usually, the positive electrode and the negative electrode are stacked (stacked) with the separator interposed therebetween. Is immersed in the electrolyte.

  The lithium ion secondary battery of the present embodiment is configured such that the power generation element is included in the exterior body, and preferably the power generation element is sealed inside the exterior body. The term “sealed” means that the power generation element is encased in an exterior body material, which will be described later, so as not to touch the outside air. The exterior body has a bag shape capable of sealing the power generation element therein, or is formed by fusing the periphery of two exterior body laminate materials. The lithium ion secondary battery of the embodiment is preferably a laminate type battery.

In the lithium ion secondary battery of the embodiment, the positive electrode is a positive electrode active material obtained by applying or rolling and drying a mixture of a positive electrode active material, a binder, and, if necessary, a conductive additive to a positive electrode current collector such as a metal foil. It is a thin plate-like or sheet-like battery member in which a layer is formed. Preferably, the positive electrode has a positive electrode active material layer obtained by applying or rolling a mixture of a positive electrode active material, a binder, and optionally a conductive additive to a positive electrode current collector made of a metal foil such as an aluminum foil, and drying. ing. The positive electrode active material layer preferably contains a lithium / nickel composite oxide as the positive electrode active material. The lithium-nickel based composite oxide is a general formula Li _x Ni _y Me _(1-y) O ₂ (where Me is Al, Mn, Na, Fe, Co, Cr, Cu, Zn, Ca, K, It is a transition metal composite oxide containing lithium and nickel, represented by at least one metal selected from the group consisting of Mg and Pb.

The positive electrode active material layer can further contain a lithium / manganese composite oxide as a positive electrode active material. Examples of the lithium / manganese composite oxide include a zigzag layered structure lithium manganate (LiMnO ₂ ) and spinel type lithium manganate (LiMn ₂ O ₄ ). By using a lithium-manganese composite oxide in combination, the positive electrode can be produced at a lower cost. In particular, it is preferable to use spinel type lithium manganate (LiMn ₂ O ₄ ) which is excellent in terms of stability of the crystal structure in an overcharged state.

In particular, the positive electrode active material layer may include a lithium nickel manganese cobalt composite oxide having a layered crystal structure represented by the general formula Li _x Ni _y Co _z Mn _(1-yz) O ₂ as a positive electrode active material. preferable. Here, x in the general formula is 1 ≦ x ≦ 1.2, y and z are positive numbers that satisfy y + z <1, and the value of y is 0.5 or less. Note that when the proportion of manganese increases, it becomes difficult to synthesize a single-phase composite oxide, so 1-yz ≦ 0.4 is desirable. Further, since the cost increases and the capacity decreases when the proportion of cobalt increases, it is desirable to satisfy z <y and z <1-yz. In order to obtain a high capacity battery, it is particularly preferable to satisfy y> 1-yz and y> z.

  Carbon fibers such as carbon nanofibers, carbon blacks such as acetylene black and ketjen black, activated carbon, graphite, mesoporous carbon, fullerenes, carbon nanotubes and other carbon materials as conductive aids optionally used in the positive electrode active material layer Is mentioned. In addition, electrode additives generally used for electrode formation, such as thickeners, dispersants, and stabilizers, can be appropriately used for the positive electrode active material layer.

  As a binder used for the positive electrode active material layer, fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyvinyl fluoride (PVF), and conductive materials such as polyanilines, polythiophenes, polyacetylenes, and polypyrroles. Polymer, synthetic rubber such as styrene butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), isoprene rubber (IR), acrylonitrile butadiene rubber (NBR), or carboxymethyl cellulose (CMC), xanthan gum, guar gum, Polysaccharides such as pectin can be used.

  In the embodiment, the positive electrode active material layer is formed by mixing a lithium composite oxide, a binder, and a conductive additive, which are positive electrode active materials, with a solvent (N-methylpyrrolidone (NMP), water, etc.) in an appropriate ratio. And it can form by apply | coating or rolling this to the positive electrode electrical power collector which consists of metal foil (aluminum foil etc.), and evaporating a solvent by heating.

  In the lithium ion secondary battery of the embodiment, the negative electrode is a negative electrode active material obtained by applying or rolling and drying a mixture of a negative electrode active material, a binder, and, if necessary, a conductive additive to a negative electrode current collector such as a metal foil. It is a thin plate-like or sheet-like battery member in which a layer is formed. Preferably, the negative electrode has a negative electrode active material layer obtained by applying or rolling a mixture of a negative electrode active material, a binder, and optionally a conductive additive to a negative electrode current collector made of a metal foil such as copper foil, and drying. ing. A carbon material is preferably used as the negative electrode active material.

  In each embodiment, the carbon material includes graphite. In particular, when graphite is contained in the negative electrode active material layer, there is an advantage that the output of the battery can be improved even when the remaining capacity (SOC) of the battery is low. Graphite is a carbon material of hexagonal hexagonal plate crystal, and is sometimes referred to as graphite or graphite. The graphite is preferably in the form of particles.

  Graphite includes natural graphite and artificial graphite. Natural graphite can be obtained in large quantities at low cost, has a stable structure and is excellent in durability. Artificial graphite is artificially produced graphite that has high purity (contains almost no impurities such as allotropes) and has low electrical resistance. As the carbon material in the embodiment, both natural graphite and artificial graphite can be suitably used. Natural graphite having a coating with amorphous carbon or artificial graphite having a coating with amorphous carbon can also be used.

  Amorphous carbon is a carbon material that has a structure in which microcrystals are randomly networked, and may be partially similar to graphite. is there. Examples of the amorphous carbon include carbon black, coke, activated carbon, carbon fiber, hard carbon, soft carbon, and mesoporous carbon. When natural graphite particles having a coating with amorphous carbon or artificial graphite having a coating with amorphous carbon is used as the carbon material of the negative electrode active material, the decomposition of the electrolytic solution is suppressed and the durability of the negative electrode is improved.

When artificial graphite is used, the interlayer distance d value (d ₀₀₂ ) is preferably 0.337 nm or more. The crystal structure of artificial graphite is generally thinner than natural graphite. When artificial graphite is used as a negative electrode active material for a lithium ion secondary battery, it is necessary to have an interlayer distance into which lithium ions can be inserted. The interlayer distance at which lithium ions can be inserted / removed can be estimated by a d value (d ₀₀₂ ). If the d value is 0.337 nm or more, lithium ions can be inserted / removed without any problem.

  The binder contained in the negative electrode active material layer plays a role of bonding the particles of the carbon material, which is the negative electrode active material, or the negative electrode active material layer and the metal foil. For example, when PVDF is used as a binder, not water but N-methylpyrrolidone (NMP) can be used as a solvent, so that generation of gas due to residual moisture can be prevented. In particular, the binder content is preferably 4 to 7% by weight based on the weight of the whole negative electrode active material layer. When the binder content is within the above range, the binding force of the negative electrode material can be secured and the negative electrode resistance can be kept low. As a binder, in addition to PVDF, fluoropolymers such as polytetrafluoroethylene (PTFE) and polyvinyl fluoride (PVF), conductive polymers such as polyanilines, polythiophenes, polyacetylenes, polypyrroles, and styrene butadiene rubber (SBR). ), Butadiene rubber (BR), chloroprene rubber (CR), isoprene rubber (IR), acrylonitrile butadiene rubber (NBR), and other synthetic rubbers, or saccharides such as carboxymethyl cellulose (CMC), xanthan gum, guar gum, pectin, etc. A binder can also be used.

  The negative electrode active material layer may optionally contain a conductive additive. Examples of the conductive aid include carbon fibers such as carbon nanofibers, carbon blacks such as acetylene black and ketjen black, carbon materials such as activated carbon, mesoporous carbon, fullerenes, and carbon nanotubes. In addition, electrode additives generally used for electrode formation, such as a thickener, a dispersant, and a stabilizer, can be appropriately used for the negative electrode active material layer.

  In the embodiment, the negative electrode active material layer is formed by mixing a carbon material that is a negative electrode active material, a binder, and a conductive additive in a solvent (N-methylpyrrolidone (NMP), water, etc.) at an appropriate ratio to form a slurry. It can be formed by applying or rolling this onto a negative electrode current collector made of a metal foil (copper foil or the like) and heating to evaporate the solvent.

  In the lithium ion secondary battery of the embodiment, the separator is a film-shaped battery member that separates the positive electrode and the negative electrode and ensures the conductivity of lithium ions between the negative electrode and the positive electrode. The separator used in the embodiment is composed of an olefin resin layer. The olefin resin layer is a layer composed of polyolefin obtained by polymerizing or copolymerizing α-olefin such as ethylene, propylene, butene, pentene, hexene and the like. In the embodiment, a structure having pores that are closed when the battery temperature rises, that is, a layer composed of a porous or microporous polyolefin is preferable. Since the olefin resin layer has such a structure, even if the battery temperature rises, the separator is closed (shuts down), and the ion flow can be cut off. In order to exert a shutdown effect, it is very preferable to use a porous polyethylene film. The separator may optionally have a heat-resistant fine particle layer. At this time, the heat-resistant fine particle layer provided for preventing abnormal heat generation of the battery is composed of inorganic fine particles having a heat-resistant temperature of 150 ° C. or more and stable in electrochemical reaction. Examples of such inorganic fine particles include inorganic oxides such as silica, alumina (α-alumina, β-alumina, θ-alumina), iron oxide, titanium oxide, barium titanate, zirconium oxide; boehmite, zeolite, apatite, kaolin, Mention may be made of minerals such as spinel, mica and mullite. Thus, a ceramic separator having a heat resistant resin layer can also be used.

  In the lithium ion secondary battery of the embodiment, the electrolytic solution is an electrically conductive solution in which an ionic substance is dissolved in a solvent. In the embodiment, a nonaqueous electrolytic solution can be used. The power generation element including the positive electrode, the negative electrode, the separator, and the electrolytic solution is a unit of the main constituent member of the battery. Usually, the positive electrode and the negative electrode are laminated via the separator, and this laminate is immersed in the electrolytic solution. Has been.

The electrolytic solution used in the embodiment of the present specification is a non-aqueous electrolytic solution, which is dimethyl carbonate (hereinafter referred to as “DMC”), diethyl carbonate (hereinafter referred to as “DEC”), ethyl methyl carbonate (hereinafter referred to as “ EMC ”), linear carbonates such as di-n-propyl carbonate, di-t-propyl carbonate, di-n-butyl carbonate, di-isobutyl carbonate, or di-t-butyl carbonate, and propylene carbonate ( PC) and a cyclic carbonate such as ethylene carbonate (hereinafter referred to as “EC”) are preferable. The electrolytic solution is obtained by dissolving a lithium salt such as lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), or lithium perchlorate (LiClO ₄ ) in such a carbonate mixture.

  The electrolytic solution preferably includes a combination of PC and / or EC, which is a cyclic carbonate, and DMC and / or EMC, which is a chain carbonate, as appropriate. PC is a solvent having a low freezing point, and is used for improving the output of the battery at a low temperature. However, it is known that PC has a slightly low compatibility with graphite used as a negative electrode. EC is a solvent having a high polarity and a high dielectric constant, and is used as a constituent component of an electrolytic solution for a lithium ion secondary battery. However, since EC has a high melting point (freezing point) and is a solid at room temperature, it may be solidified and precipitated at a low temperature even if it is used as a mixed solvent. DMC is a solvent having a large diffusion coefficient and low viscosity. However, since DMC has a high melting point (freezing point), the electrolyte may solidify at a low temperature. Similarly to DMC, EMC is a solvent having a large diffusion coefficient and low viscosity. Thus, the constituent components of the electrolytic solution have different characteristics. For example, in order to improve the output of the battery at a low temperature, it is important to consider these balances. By adjusting the content ratio of the cyclic carbonate and the chain carbonate, it is possible to obtain an electrolytic solution that has a low viscosity at normal temperature and does not lose its performance even at low temperatures.

  In addition to this, the electrolytic solution may contain a cyclic carbonate compound as an additive. Examples of the cyclic carbonate used as the additive include vinylene carbonate (hereinafter referred to as “VC”). Moreover, you may use the cyclic carbonate compound which has a halogen as an additive. These cyclic carbonates are also compounds that form a protective film for the positive electrode and the negative electrode during the charge / discharge process of the battery. In particular, it is a compound that can prevent attack on the positive electrode active material containing a lithium / nickel composite oxide by a sulfur-containing compound such as the above-described disulfonic acid compound or disulfonic acid ester compound. Examples of the cyclic carbonate compound having a halogen include fluoroethylene carbonate (hereinafter referred to as “FEC”), difluoroethylene carbonate, trifluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, trichloroethylene carbonate, and the like. Fluoroethylene carbonate, which is a cyclic carbonate compound having a halogen and an unsaturated bond, is particularly preferably used.

  The electrolytic solution may further contain a disulfonic acid compound as an additive. The disulfonic acid compound is a compound having two sulfo groups in one molecule, and includes a disulfonate compound in which the sulfo group forms a salt with a metal ion, or a disulfonate compound in which the sulfo group forms an ester. . One or two of the sulfo groups of the disulfonic acid compound may form a salt with the metal ion or may be in an anionic state. Examples of disulfonic acid compounds include methanedisulfonic acid, 1,2-ethanedisulfonic acid, 1,3-propanedisulfonic acid, 1,4-butanedisulfonic acid, benzenedisulfonic acid, naphthalenedisulfonic acid, biphenyldisulfonic acid, and these And salts (lithium methanedisulfonate, lithium 1,3-ethanedisulfonate, etc.) and anions thereof (methanedisulfonate anion, 1,3-ethanedisulfonate anion, etc.). Examples of the disulfonic acid compound include disulfonic acid ester compounds, such as methanedisulfonic acid, 1,2-ethanedisulfonic acid, 1,3-propanedisulfonic acid, 1,4-butanedisulfonic acid, benzenedisulfonic acid, naphthalenedisulfonic acid, Alternatively, chain disulfonic acid esters such as alkyl diesters or aryl diesters of biphenyl disulfonic acid; and cyclic disulfonic acid esters such as methylenemethane disulfonic acid ester, ethylenemethane disulfonic acid ester, and propylene methane disulfonic acid ester are preferably used. Methylenemethane disulfonate (hereinafter referred to as “MMDS”) is particularly preferably used.

  The exterior body is comprised from the laminated body by which the metal base material, the acid-modified polypropylene layer, and the polypropylene layer were laminated | stacked in this order. A coating layer such as a nylon layer or a polyethylene terephthalate layer may be further formed on the surface of the metal substrate of the laminate. The exterior body is formed so that the polypropylene layer of the laminate is on the inner surface side of the exterior body.

  The metal substrate constituting the laminate is a substrate suitably used as a battery outer film, preferably a metal foil, such as aluminum, nickel, iron, copper, stainless steel, and tin foil. A metal base material has a function which seals the nonaqueous electrolyte inside an exterior body as an exterior body. A laminated body is bent and three sides other than the bent portion are heat-sealed, or two laminated bodies are overlapped and four sides are heat-sealed to form an exterior body. Inside this, a positive electrode, a negative electrode, and a separator And a power generation element composed of the electrolytic solution. Therefore, the exterior body includes a heat-sealed portion and a portion that is not heat-fused (hereinafter referred to as “non-fused portion”).

  The “acid-modified polypropylene” forming the acid-modified polypropylene layer means a polypropylene into which an acid has been introduced by a graft reaction. In this specification, a propylene / ethylene copolymer, a propylene / ethylene / butene copolymer, a polypropylene / polypropylene layer is used. A product obtained by introducing an acid into a copolymer in which propylene is introduced as a copolymerization component, such as a butene copolymer, is also referred to as “acid-modified polypropylene”. Examples of the acid introduced by the graft reaction include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride and the like. Representative maleic anhydride-modified polypropylene, maleic anhydride-modified propylene / ethylene copolymer, maleic anhydride-modified propylene / ethylene / butene copolymer, and maleic anhydride-modified polypropylene / butene copolymer introduced with maleic anhydride “Acid-modified polypropylene”. The acid-modified polypropylene layer has a function of bonding a metal substrate and a polypropylene layer described later.

  In this specification, “polypropylene” that forms a polypropylene layer is a propylene homopolymer, propylene / ethylene copolymer, propylene / ethylene / butene copolymer, polypropylene / butene copolymer, propylene / 4 -It includes all copolymers of propylene and other olefins such as methylpentene-1 copolymer and propylene / hexene copolymer, and may be a mixture thereof. A polypropylene layer plays the role which gives a softness | flexibility to a laminated body. The polypropylene layer preferably contains a lubricant. The lubricant provides ease of molding when forming the polypropylene layer. As the lubricant, it is preferable to use a higher fatty acid amide containing 18 or more carbon atoms. Examples of higher fatty acid amides containing 18 or more carbon atoms are oleic acid amide, behenic acid amide, erucic acid amide and the like.

  The concentration of the lubricant in the polypropylene layer is at least 100 ppm and not more than 230 ppm at least in the heat-sealed portion of the outer package. That the concentration of the lubricant is 100 ppm or more and 230 ppm or less in the heat-sealed portion of the exterior body does not mean that the lubricant is contained only in the heat-fused portion. The lubricant is desirably contained in the entire polypropylene layer in the laminate constituting the exterior body. When the laminate is heat-sealed to form an exterior body, the lubricant concentration in the polypropylene layer of the heat-sealed portion can change. Therefore, it is preferable that the concentration of the lubricant in at least the heat-sealed portion is in a specific range. If the lubricant concentration in the heat-sealed portion is 230 ppm or less, the lipophilic lubricant is less effective to attract the non-aqueous electrolyte, so that the non-aqueous electrolyte leaks to the outside through the heat-sealed portion. Can be prevented. Further, considering the ease of molding at the time of forming the polypropylene layer, the lubricant is preferably contained in an amount of 100 ppm or more. In addition, it is preferable that the lubricant concentration in the polypropylene layer in the heat-sealed portion is smaller than the lubricant concentration in the polypropylene layer in the non-fused portion. The electrolytic solution is attracted to the oleophilic lubricant, but the electrolytic solution attracted particularly to the heat-sealed portion is likely to leak. Such an inconvenience hardly occurs in the non-fused portion.

  Note that the lubricant may be contained in the acid-modified polypropylene layer. It is preferable that the acid-modified polypropylene layer contains a lubricant because the moldability such as layer formation is improved.

  Here, the structural example of the lithium ion secondary battery concerning this embodiment is demonstrated using drawing. FIG. 1 shows an example of a cross-sectional view of a lithium ion secondary battery. The lithium ion secondary battery 10 includes a negative electrode current collector 11, a negative electrode active material layer 13, a separator 17, a positive electrode current collector 12, and a positive electrode active material layer 15 as main components. In FIG. 1, the negative electrode active material layer 13 is provided on both surfaces of the negative electrode current collector 11 and the positive electrode active material layer 15 is provided on both surfaces of the positive electrode current collector 12, but only on one side of each current collector. An active material layer can also be formed. The negative electrode current collector 11, the positive electrode current collector 12, the negative electrode active material layer 13, the positive electrode active material layer 15, and the separator 17 are constituent units of one battery, that is, a power generation element (unit cell 19 in the figure). The separator 17 may be composed of a heat-resistant fine particle layer and an olefin resin film (both not shown). A plurality of such unit cells 19 are stacked via the separator 17. The extending portion extending from each negative electrode current collector 11 is collectively bonded onto the negative electrode lead 25, and the extending portion extending from each positive electrode current collector 12 is collectively bonded to the positive electrode lead 27. An aluminum plate is preferably used as the positive electrode lead, and a copper plate is preferably used as the negative electrode lead, and in some cases, it may have a partial coating with another metal (for example, nickel, tin, solder) or a polymer material. The positive electrode lead and the negative electrode lead are welded to the positive electrode and the negative electrode, respectively. A battery formed by laminating a plurality of single cells in this manner is packaged by an outer package 29 so that the welded negative electrode lead 25 and positive electrode lead 27 are drawn out to the outside. An electrolytic solution 31 is injected into the exterior body 29. The exterior body 29 has a shape in which two laminated bodies are overlapped and the peripheral portion is heat-sealed. In FIG. 1, the negative electrode lead 25 and the positive electrode lead 27 are respectively provided on opposite sides of the exterior body 29 (referred to as “both tabs”), but the negative electrode lead 25 and the positive electrode lead 27 are connected to the exterior body 29. (Ie, the negative electrode lead 25 and the positive electrode lead 27 are pulled out from one side of the outer package 29. This is referred to as “one-tab type”).

  Reference is now made to FIG. FIG. 2 is an enlarged view of the vicinity of the heat fusion part of the lithium ion secondary battery of the present embodiment. The exterior body 29 in the present embodiment can be formed by stacking laminated bodies 291 and 292 having appropriate sizes and thermally fusing the periphery thereof. The laminate 291 is formed by laminating a coating layer 41, a metal base 51, an acid-modified polypropylene layer 61, and a polypropylene layer 71. Similarly, the laminate 292 is formed by laminating a coating layer 42, a metal substrate 52, an acid-modified polypropylene layer 62, and a polypropylene layer 72. The exterior body 29 is formed by heat-sealing the polypropylene layer 71 of the laminated body 291 and the polypropylene layer 72 of the laminated body 292 together. That is, the exterior body 29 includes a heat-sealed portion 100 that is a portion where the laminated bodies are heat-sealed and a non-fused portion 200 that is a portion that is not fused. In the heat fusion part 100, the polypropylene layer 71 of one laminated body (291) and the polypropylene layer 72 of the other laminated body (292) are fused and integrated. Here, in the heat fusion part 100, the concentration of the lubricant in the polypropylene layer (the part where 71 and 72 are fused together) is 100 ppm or more and 230 ppm or less.

  Since the heat fusion part 100 is formed by superposing the laminates 291 and 292 and pressing (heat-sealing) them while applying heat, the laminate in that part is more than the laminate in the non-fused part 200 part. Slightly crushed and deformed. It is preferable that the lubricant concentration in the polypropylene layer in the heat-sealed portion 100 is smaller than the lubricant concentration in the polypropylene layer in the non-fused portion 200.

  In addition, it is preferable that the ratio (W / Wh) of the output and capacity | capacitance of the lithium ion secondary battery concerning embodiment is 25 or more. A lithium ion battery having an output capacity ratio in such a range is conveniently used particularly as a vehicle-mounted battery or a stationary battery. Since these batteries are required to have a high capacity retention rate, it is particularly useful to apply the battery of this embodiment.

<Production of model exterior body>
A model of a lithium ion secondary battery outer package was produced. Two aluminum laminates having a thickness of about 150 μm in which a size 86 mm × 56 mm, a coating layer, an aluminum foil, an acid-modified polypropylene layer, and a polypropylene layer were laminated in this order were prepared. These were overlapped so that the polypropylene layer was on the inside, and first, the three sides were heat-sealed at 170 ° C. so as to have a sealing width of 3 mm to produce a bag shape. Next, 3 mL of diethyl carbonate (DEC) as a model non-aqueous electrolyte was put into the bag from one side not thermally fused. And one side was heat-sealed so that it might become 3 mm of sealing widths at 170 degreeC, and the model exterior body was produced.

<Measurement of lubricant concentration>
Three model exterior bodies were produced by the same method, and each one heat-sealed part was peeled off, and the concentration of erucamide in the polypropylene layer of each heat-fused part was measured. The concentration of erucic acid amide was measured by the following procedure.
(1) Collect and weigh an appropriate amount of polypropylene in the heat-sealed part, and immerse and heat in a chloroform solution.
(2) Polypropylene is separated by a Soxhlet extraction method to prepare a chloroform solution in which a lubricant is dissolved.
(3) The chloroform solution is analyzed by gas chromatography to confirm that it is erucic acid amide.
(4) The solvent of this chloroform solution is evaporated, erucic acid amide is taken out and weighed, and the concentration is calculated based on the amount of polypropylene collected first.

<Electrolytic solution permeability test>
After measuring the weight of the model exterior body produced as described above, it was placed in a thermostatic bath. The temperature of the thermostatic layer was set to 55 ° C., and the model exterior body was stored. The model exterior body was taken out of the thermostat and the weight was measured. The amount of decrease compared to the initial weight was calculated as the electrolyte permeation amount. The model outer body whose weight was measured was returned to the thermostat and stored, and weight measurement was repeated periodically. The amount of electrolyte permeation after 20 days from the start of weight measurement was as shown in Table 1. The electrolytic solution permeability in Table 1 is a relative value when the electrolytic solution permeation amount of Comparative Example 1 is 100. This electrolyte permeability test is an accelerated test.

  By setting the concentration of the lubricant in the polypropylene layer of the exterior body to 230 ppm or less, the permeation of the electrolytic solution could be suppressed. It is thought that by reducing the lubricant concentration in the polypropylene layer in the heat fusion part of the exterior body, the non-aqueous electrolyte was prevented from being attracted to the heat fusion part and leaching from the heat fusion part. .

  As mentioned above, although the Example of this invention was described, the said Example was only an example of Embodiment of this invention, and in the meaning which limits the technical scope of this invention to specific embodiment or a specific structure. Absent.

DESCRIPTION OF SYMBOLS 1 Negative electrode 101 for lithium ion secondary batteries Negative electrode current collector 102 Negative electrode active material 103 Conductive support agent 104 Binder 10 Lithium ion secondary battery 11 Negative electrode current collector 12 Positive electrode current collector 13 Negative electrode active material layer 15 Positive electrode active material layer 17 Separator 25 Negative electrode lead 27 Positive electrode lead 29 Exterior body 31 Electrolytic solution 100 Thermal fusion part 200 Non-fusion part 300 Boundary part 291, 292 Laminate body 41, 42 Coating layer 51, 52 Metal base material 61, 62 Acid-modified polypropylene layer 71 72 Polypropylene layer

Claims (5)

A positive electrode;
A negative electrode, a separator,
An electrolyte,
A lithium ion secondary battery including a power generation element including
The exterior body is composed of a laminate in which a metal substrate, an acid-modified polypropylene layer, and a polypropylene layer are laminated in this order, and the polypropylene layer contains a lubricant,
The outer surface of the exterior body is the polypropylene layer,
The exterior body has a heat fusion part and a non-fusion part,
The said lithium ion secondary battery whose density | concentration of this lubricant in this polypropylene layer is 100 ppm or more and 230 ppm or less in this heat-fusion part.   2. The lithium ion secondary battery according to claim 1, wherein a concentration of the lubricant in the polypropylene layer in the heat fusion part is smaller than a concentration of the lubricant in the polypropylene layer in the non-fusion part.   The thickness value of one layer of the acid-modified polypropylene layer in the heat-sealed portion of the outer package is smaller than the thickness value of the polypropylene layer in the heat-sealed portion of the outer package. The lithium ion secondary battery according to 1 or 2.   The electrolyte is selected from dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, di-n-propyl carbonate, di-t-propyl carbonate, di-n-butyl carbonate, di-isobutyl carbonate, and di-t-butyl carbonate The lithium ion secondary battery as described in any one of Claims 1-3 which is a mixture containing the linear carbonate selected, and the cyclic carbonate selected from a propylene carbonate and ethylene carbonate.   The lithium ion secondary battery according to any one of claims 1 to 4, wherein the lubricant is a higher fatty acid amide containing 18 or more carbon atoms.

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