JP2015088430A - Nonaqueous electrolyte secondary battery separator, and nonaqueous electrolyte secondary battery having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a non-aqueous electrolyte secondary battery, which can prevent the battery from reaching a higher temperature when the temperature becomes higher. SOLUTION: A separator 2A for a non-aqueous electrolyte secondary battery is formed on one surface of a base material layer 20 which is a microporous film of a thermoplastic resin, and a first surface containing a binder and a filler. A filler layer 21 and a second filler layer 22 formed on the other surface of the base material layer 20 and containing a binder and a filler are provided. The binder weight fraction of the second filler layer 22 is 5 wt% or more, and is higher than the binder weight fraction of the first filler layer 21. The average value of the binder weight fraction of the first filler layer 21 and the binder weight fraction of the second filler layer 22 is lower than 7 wt %. The difference between the binder weight fraction of the second filler layer 22 and the binder weight fraction of the first filler layer 21 is smaller than 10 wt %. [Selection diagram] Fig. 3

Description

  The present invention relates to a separator for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery including the same.

  Conventionally, as a separator for a non-aqueous electrolyte secondary battery, a separator having a so-called shutdown characteristic is known that increases the internal resistance of a battery by closing a hole when the temperature of the battery reaches a predetermined value or more. . As such a separator, a uniaxially or biaxially stretched polyolefin microporous film is used. However, the stretched film is distorted and has a problem of shrinkage due to residual stress when exposed to high temperatures. In order to solve this problem, a separator in which a layer mainly composed of a resin and a layer mainly composed of a filler are laminated has been proposed.

  Japanese Patent Application Laid-Open No. 2008-123988 discloses a porous material mainly composed of a separator layer (I) composed of a microporous film mainly composed of a resin having a melting point of 80 to 130 ° C. and a filler having a heat resistant temperature of 150 ° C. or higher. A separator for an electrochemical device is disclosed, wherein the separator layer (II) and at least one of the separator layer (I) and the separator layer (II) contain plate-like particles. .

  JP 2011-198532 A discloses a base material layer (I) composed of a microporous film mainly composed of a thermoplastic resin between a positive electrode and a negative electrode, and a filler layer (II) mainly composed of an inorganic filler. And a resin layer (III) mainly comprising resin particles having a melting point in the range of 100 to 130 ° C., the filler layer (II) on one side of the base material layer (I), and the resin on the other side A lithium ion secondary battery characterized by laminating layer (III) is disclosed.

JP 2008-123988 A JP 2011-198532 A

  Some non-aqueous electrolyte secondary batteries include a mechanism that discharges internal gas when a part of the exterior body is cleaved when the internal pressure exceeds a predetermined value. When such a gas discharge occurs in the charged nonaqueous electrolyte secondary battery, the negative electrode that occludes lithium ions may come into contact with the outside air. At this time, there is a possibility that moisture contained in the outside air reacts with the negative electrode to generate heat.

  The objective of this invention is providing the separator for non-aqueous-electrolyte secondary batteries which can prevent that it becomes further high temperature, when a battery becomes high temperature. Another object of the present invention is to provide a non-aqueous electrolyte secondary battery that can prevent high temperature.

  A separator for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention includes a base material layer that is a microporous film of a thermoplastic resin, a binder layer and a filler that are formed on one surface of the base material layer. A first filler layer and a second filler layer formed on the other surface of the base material layer and including a binder and a filler are provided. The binder weight fraction of the second filler layer is 5 wt% or more and is higher than the binder weight fraction of the first filler layer. The average value of the binder weight fraction of the first filler layer and the binder weight fraction of the second filler layer is lower than 7 wt%. The difference between the binder weight fraction of the second filler layer and the binder weight fraction of the first filler layer is less than 10 wt%.

  According to the configuration of the separator for a non-aqueous electrolyte secondary battery (hereinafter simply referred to as a separator), the base material layer is a microporous film of a thermoplastic resin. Therefore, the separator has a shutdown characteristic. Filler layers (first filler layer and second filler layer) are formed on both surfaces of the base material layer. Therefore, the separator is excellent in dimensional stability at high temperatures.

  According to said structure, a binder softens the binder of a 2nd filler layer at the time of high temperature, and closely_contact | adheres to the electrode arrange | positioned adjacent to a 2nd filler layer. Thereby, the surface of the electrode is covered with the separator, and the electrode and the outside air can be prevented from contacting each other.

  If the weight fraction of the binder is too low, the above function cannot be obtained. On the other hand, when the weight fraction of the binder is too high, the porosity is lowered and the ionic conductivity is lowered. According to said structure, the weight fraction of the binder of a 2nd filler layer is 5 wt% or more, Comprising: It makes higher than the weight fraction of the binder of a 1st filler layer. The porosity of the entire separator is adjusted by relatively reducing the weight fraction of the binder in the first filler layer. Specifically, the average value of the weight fraction of the binder of the first filler layer and the weight fraction of the binder of the second filler layer is made lower than 7 wt%. Thereby, a predetermined ion conductivity can be ensured.

  If the difference between the binder weight fraction of the second filler layer and the binder filler weight fraction of the first filler layer is too large, the separator warps. According to said structure, the difference of the weight fraction of the binder of a 2nd filler layer and the weight fraction of the binder of a 1st filler layer is made smaller than 10 wt%. Thereby, the curvature of a separator can be suppressed.

  A non-aqueous electrolyte secondary battery according to an embodiment of the present invention includes a separator for a non-aqueous electrolyte secondary battery having the above-described configuration, and the first filler layer side of the separator for a non-aqueous electrolyte secondary battery. The positive electrode arrange | positioned and the negative electrode arrange | positioned at the said 2nd filler layer side of the said separator for nonaqueous electrolyte secondary batteries are provided.

  According to the configuration of the above non-aqueous electrolyte secondary battery, the separator automatically has a shutdown characteristic, so that the reaction automatically stops when the temperature becomes high. In addition, since the separator is excellent in dimensional stability at high temperature, the positive electrode and the negative electrode are not easily short-circuited even at a high temperature. Furthermore, when the temperature becomes high, the binder of the second filler layer is softened, so that the negative electrode disposed on the second filler layer side and the separator are in close contact with each other. By covering the surface of the negative electrode with the separator, the negative electrode can be prevented from coming into contact with the outside air.

  ADVANTAGE OF THE INVENTION According to this invention, when a battery becomes high temperature, the separator for nonaqueous electrolyte secondary batteries which can prevent becoming higher temperature is obtained. Moreover, the nonaqueous electrolyte secondary battery which can prevent becoming high temperature is obtained.

FIG. 1 is a perspective view showing a schematic configuration of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing a part of the electrode winding body. FIG. 3 is a cross-sectional view schematically showing the configuration of the separator.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated. In addition, in order to make the explanation easy to understand, in the drawings referred to below, the configuration is shown in a simplified or schematic manner, or some components are omitted. Further, the dimensional ratio between the constituent members shown in each drawing does not necessarily indicate an actual dimensional ratio.

[Configuration of non-aqueous electrolyte secondary battery]
FIG. 1 is a perspective view showing a schematic configuration of a nonaqueous electrolyte secondary battery 1 according to an embodiment of the present invention. The nonaqueous electrolyte secondary battery 1 includes an outer can 11, a lid plate (top cover) 12, a negative electrode terminal 13, an electrode winding body 14, a sealing plug 15, and an electrolyte solution (not shown).

  The outer can 11 has a box shape with an upper side opened, and houses the electrode winding body 14 therein. The opening of the outer can 11 is blocked by the lid plate 12. The outer can 11 and the lid plate 12 are made of, for example, aluminum or an aluminum alloy.

  The negative terminal 13 is disposed at the center of the lid plate 12. The negative terminal 13 passes through the lid plate 12. The negative electrode terminal 13 and the lid plate 12 are electrically insulated by an insulating packing (not shown). The negative electrode terminal 13 is made of, for example, nickel or copper plated with nickel.

  The electrode winding body 14 is obtained by laminating a positive electrode and a negative electrode via a separator, as will be described later. The positive electrode of the electrode winding body 14 is connected to the lid plate 12 by a positive electrode lead tab (not shown). The negative electrode of the electrode winding body 14 is connected to the negative electrode terminal 13 by a negative electrode lead tab (not shown).

  On the side surface of the outer can 11, a substantially S-shaped cleavage groove 11 a constituting a vent is formed. The cleavage groove 11a is configured to be cleaved when the pressure in the outer can 11 becomes larger than a predetermined threshold value. In addition, by forming the cleavage groove 11a in a substantially S shape, the cleavage groove 11a can be formed in a narrow range as compared with the case where the cleavage groove having the same length is formed in a straight line or an arc shape.

  The lid plate 12 has a liquid injection port 12a for injecting an electrolytic solution. The liquid injection port 12 a passes through the lid plate 12. The liquid injection port 12 a is sealed with a sealing plug 15.

The electrolytic solution is a solution in which a lithium salt is dissolved in an organic solvent. As an organic solvent, vinylene carbonate (VC), propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), or γ- Butyrolactone and the like can be used alone or in admixture of two or more. As the lithium salt, LiPF ₆ , LiBF ₄ , LiN (CF ₃ SO ₂ ) _2, or the like can be used.

  FIG. 2 is a cross-sectional view schematically showing a part of the electrode winding body 14. The electrode winding body 14 includes a strip-shaped positive electrode 141, a strip-shaped negative electrode 142, a separator 2A, and a separator 2B. The electrode winding body 14 is formed by laminating the negative electrode 142, the separator 1A, the positive electrode 141, and the separator 2B in this order, winding the negative electrode 142 inside, and then compressing in one direction into a flat shape. .

  The positive electrode 141 is obtained by forming a positive electrode mixture layer on one side or both sides of a belt-like positive electrode current collector. The positive electrode current collector is formed of, for example, a foil such as aluminum or titanium, a plain woven wire net, an expanded metal, a lath net, or a punching metal.

  The positive electrode mixture layer is formed by mixing a positive electrode active material, a conductive additive, and a binder. As the positive electrode active material, lithium manganate, lithium nickel composite oxide, lithium cobalt composite oxide, lithium nickel cobalt composite oxide, vanadium oxide, molybdenum oxide, or the like can be used. As the conductive assistant, graphite, carbon black, acetylene black, or the like can be used. As the binder, polyimide, polyamideimide, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), or the like can be used alone or in combination.

  The negative electrode 142 is obtained by forming a negative electrode mixture layer on one side or both sides of a strip-shaped negative electrode current collector. The negative electrode current collector is formed of, for example, a foil such as copper, nickel, or stainless steel, a plain woven wire net, an expanded metal, a lath net, or a punching metal.

  The negative electrode mixture layer is formed by mixing a negative electrode active material and a binder. As the negative electrode active material, natural graphite, mesophase carbon, amorphous carbon, or the like can be used. As the binder, celluloses such as carboxymethyl cellulose (CMC) and hydroxypropyl cellulose (HPC), rubber binders such as styrene butadiene rubber (SBR) and acrylic rubber, PTFE, PVDF and the like can be used alone or in combination.

[Configuration of separator for non-aqueous electrolyte secondary battery]
FIG. 3 is a cross-sectional view schematically showing the configuration of the separator 2A. Since the configuration of the separator 2B is the same as that of the separator 2A, illustration and detailed description are omitted. The separator 2A includes a base material layer 20, a filler layer (first filler layer) 21 formed on one surface of the base material layer 20, and a filler layer (second material) formed on the other surface of the base material layer 20. Filler layer) 22.

  The thickness of the base material layer 20 is preferably 8 μm or more and more preferably 12 μm or more from the viewpoint of ensuring a better shutdown function. However, if the base material layer is too thick, the load characteristics and energy density of the battery may be reduced. Therefore, the thickness is preferably 30 μm or less, and more preferably 20 μm or less. The thickness of the filler layer 21 and the filler layer 22 is, for example, preferably 1 μm or more, more preferably 3 μm or more, and preferably 10 μm or less, more preferably 6 μm or less. The thickness of the filler layer 21 and the thickness of the filler layer 22 may be the same or different.

  The base material layer 20 is a microporous film of a thermoplastic resin. The melting point of the thermoplastic resin constituting the base material layer 20 (hereinafter simply referred to as a thermoplastic resin) is preferably 80 to 130 ° C. The melting point of the thermoplastic resin can be determined by, for example, the melting temperature measured using a differential scanning calorimeter (DSC) in accordance with JIS K 7121.

  The thermoplastic resin preferably has electrical insulation and is stable with respect to the electrolyte solution of the nonaqueous electrolyte secondary battery. The thermoplastic resin is preferably an electrochemically stable material that is not easily oxidized or reduced in the battery operating voltage range.

  Specific examples of the thermoplastic resin include polyethylene (PE), copolymerized polyolefin, or polyolefin derivatives (such as chlorinated polyethylene), polyolefin wax, petroleum wax, and carnauba wax. Examples of the copolymer polyolefin include an ethylene-vinyl monomer copolymer, more specifically, an ethylene-propylene copolymer, an ethylene-vinyl acetate copolymer (EVA), an ethylene-methyl acrylate copolymer, and ethylene. An ethylene-acrylic acid copolymer such as an ethyl acrylate copolymer can be exemplified. The ethylene-derived structural unit in the copolymerized polyolefin is desirably 85 mol% or more. Moreover, polycycloolefin etc. can also be used. As the thermoplastic resin, the above exemplified resins may be used alone or in combination of two or more.

  Among the above-described materials, PE, polyolefin wax, or EVA having a structural unit derived from ethylene of 85 mol% or more is suitably used as the thermoplastic resin. The thermoplastic resin may contain various additives (for example, antioxidant etc.).

  The base material layer 20 may contain components other than the thermoplastic resin. The base material layer 20 may include, for example, an inorganic material or a fibrous material.

  The filler layer 21 and the filler layer 22 contain a filler and a binder. In the filler layer 21 and the filler layer 22, the same filler may be used, or different fillers may be used. Similarly, in the filler layer 21 and the filler layer 22, the same binder may be used, or different binders may be used.

  The filler to be contained in the filler layer 21 and the filler layer 22 (hereinafter simply referred to as filler) has heat resistance and electrical insulation and is stable with respect to the solvent used in the production of the electrolytic solution and the separator. Is preferred. The filler preferably has a heat resistance of 150 ° C. or higher. That is, it is preferable that the filler does not undergo deformation such as softening at least at 150 ° C. The filler is preferably an electrochemically stable filler that is not easily oxidized and reduced in the operating voltage range of the battery.

  The filler may be organic particles or inorganic particles. The filler is preferably fine particles from the viewpoint of dispersion and the like, and inorganic fine particles are more preferably used from the viewpoint of stability and the like.

Examples of inorganic particles include inorganic oxides such as iron oxide, SiO ₂ , Al ₂ O ₃ , TiO ₂ , BaTiO ₂ and ZrO ₂ , inorganic nitrides such as aluminum nitride and silicon nitride, calcium fluoride, barium fluoride, and sulfuric acid. Examples include hardly soluble ion crystals such as barium, covalent bonds such as silicon and diamond, and clays such as montmorillonite. Here, the inorganic oxide may be a material derived from mineral resources such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, mica, or an artificial product thereof. Further, the surface of a conductive material exemplified by a metal, SnO ₂ , a conductive oxide such as tin-indium oxide (ITO), a carbonaceous material such as carbon black, graphite, or the like is used as a material having electrical insulation ( For example, the particles may be electrically insulating by coating with the above-described inorganic oxide or the like. Among the above inorganic oxides, Al ₂ O ₃ , SiO ₂ and boehmite are particularly preferably used.

  As organic particles, crosslinked polymethyl methacrylate, crosslinked polystyrene, crosslinked polydivinylbenzene, crosslinked styrene-divinylbenzene copolymer, various crosslinked polymer fine particles such as polyimide, melamine resin, phenol resin, benzoguanamine-formaldehyde condensate, polypropylene Examples thereof include heat-resistant polymer fine particles such as (PP), polysulfone, polyacrylonitrile, polyaramid, polyacetal, and thermoplastic polyimide. The organic resin (polymer) constituting these organic fine particles is a mixture, modified body, derivative, or copolymer (random copolymer, alternating copolymer, block copolymer, graft copolymer) of the materials exemplified above. Polymer) or a crosslinked product (in the case of the above heat-resistant polymer).

The shape of the filler may be, for example, a nearly spherical shape or a plate shape. The shape of the filler is preferably a plate-like particle from the viewpoint of short circuit prevention. Typical examples of the plate-like particles include plate-like Al ₂ O ₃ and plate-like boehmite.

  Specific examples of the binder (hereinafter simply referred to as the binder) contained in the filler layer 21 and the filler layer 22 include, for example, an ethylene-vinyl acetate copolymer (EVA, vinyl acetate-derived structural unit of 20 to 35 mol%) ); (Meth) acrylic acid copolymers such as ethylene-ethyl acrylate copolymer, ethylene-ethyl methacrylate copolymer; fluorinated rubber; styrene-butadiene rubber (SBR); polyvinyl alcohol (PVA); polyvinyl butyral (PVB) ); Polyvinylpyrrolidone (PVP); poly N-vinylacetamide; cross-linked acrylic resin; polyurethane; epoxy resin; As the binder, those exemplified above may be used alone or in combination of two or more. The binder is preferably softened at 150 ° C. or lower as compared with room temperature and has heat resistance of 150 ° C. or higher. [In the present specification, “(meth) acrylic acid” means both acrylic acid and methacrylic acid. ]

  The filler layer 21 and the filler layer 22 may contain a fibrous material in addition to the filler and the binder. Specific constituent materials of the fibrous material include, for example, cellulose and its modified products, polyolefin, polyester, polyacrylonitrile (PAN), polyaramid, polyamideimide, polyimide, and other inorganic materials such as glass, alumina, zirconia, and silica. An oxide etc. can be mentioned.

  The filler layer 21 and the filler layer 22 have different binder ratios. Specifically, the binder weight fraction of the filler layer 22 ((weight of the binder of the filler layer 22) / (total weight of the filler layer 22) × 100) is the weight fraction of the binder of the filler layer 21 (( Binder weight of filler layer 21) / (total weight of filler layer 21) × 100). The weight fraction of the binder of the filler layer 22 is 5 wt% or more.

  Also, the average value of the binder weight fraction of the filler layer 21 and the binder weight fraction of the filler layer 22 (((the binder weight fraction of the filler layer 21) + (the binder weight fraction of the filler layer 22))) / 2) is 7 wt% or less. Furthermore, the difference between the binder weight fraction of the filler layer 22 and the binder weight fraction of the filler layer 21 is 10 wt% or less.

  The binder weight fraction of the filler layer 21 is preferably 2 to 3 wt%. The binder weight fraction of the filler layer 22 is preferably 5 to 10 wt%.

  As shown in FIG. 2, both the separator 2A and the separator 2B are arranged such that the filler layer 21 is on the positive electrode 141 side and the filler layer 22 is on the negative electrode 142 side. The separator 2A and the separator 2B have an area larger than the areas of the positive electrode 141 and the negative electrode 142, and are disposed so that the positive electrode 141 and the negative electrode 142 do not protrude from the end sides of the separator 2A and the separator 2B.

[Method for producing non-aqueous electrolyte secondary battery]
The nonaqueous electrolyte secondary battery 1 can be manufactured, for example, as follows.

(Preparation of positive electrode)
A positive electrode active material, a conductive additive, and a binder are sufficiently mixed in pure water or an organic solvent to prepare a slurry. The slurry is applied to one side or both sides of the positive electrode current collector using a die coater, slit coater, dip coater or the like. After coating, the slurry is dried, and the thickness and density are adjusted by calendering. Thereby, the positive electrode 141 is obtained. A positive electrode lead tab is attached to the positive electrode 141 by welding or a conductive adhesive.

(Preparation of negative electrode)
The negative electrode active material and the binder are sufficiently mixed in pure water or an organic solvent to prepare a slurry. The slurry is applied to one side or both sides of the negative electrode current collector using a die coater, slit coater, dip coater or the like. After coating, the slurry is dried, and the thickness and density are adjusted by calendering. Thereby, the negative electrode 142 is obtained. A negative electrode lead tab is attached to the negative electrode 142 by welding or a conductive adhesive.

(Preparation of separator)
The base material layer 20 is prepared. As the base material layer 20, for example, a polyolefin microporous film conventionally used as a separator for a non-aqueous electrolyte secondary battery may be used.

  The base material layer 20 can also be produced as follows. The above-described thermoplastic resin and hole forming resin are mixed at a predetermined ratio to form a film or sheet. The formed film or sheet is immersed in a solvent that dissolves only the hole forming resin. As a result, a thermoplastic resin film or sheet in which pores are formed is obtained.

  A slurry of the precursor of the filler layer 21 is prepared. First, the binder described above is dissolved in a solvent. The filler described above is put into a solvent in which the binder is dissolved. The solvent charged with the filler is stirred to disperse the filler.

  As the solvent, organic solvents such as aromatic hydrocarbons such as toluene, furans such as tetrahydrofuran, ketones such as methyl ethyl ketone and methyl isobutyl ketone are preferably used. In order to control the interfacial tension, alcohols (ethylene glycol, propylene glycol, etc.) or various propylene oxide glycol ethers such as monomethyl acetate may be appropriately added to these solvents. Further, when the organic binder is water-soluble, when used as an emulsion, water may be used as a solvent, and alcohols (methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol, etc.) may be added as appropriate. It is also possible to control the interfacial tension.

  The slurry is applied to one surface of the base material layer 20. The applied slurry is dried to remove the solvent. Thereby, the filler layer 21 is formed on one surface of the base material layer 20.

  Similarly, a precursor slurry of the filler layer 22 is prepared and applied to the other surface of the base material layer 20. The applied slurry is dried to remove the solvent. Thereby, the filler layer 22 is formed on the other surface of the base material layer 20. In addition, before drying the precursor slurry of the filler layer 21, the precursor slurry of the filler layer 22 is applied, and the precursor slurry of the filler layer 21 and the precursor slurry of the filler layer 22 are simultaneously dried. Also good.

(Production of electrode winding body)
The positive electrode 141, the negative electrode 142, the separator 2 </ b> A, and the separator 2 </ b> B are wound using a winding core having a circular, elliptical, or rhomboid cross-sectional shape, and then the winding core is removed and compressed in one direction to a flat shape. . Alternatively, the positive electrode 141, the negative electrode 142, the separator 2A, and the separator 2B may be wound using a winding core having a flat cross-sectional shape to form a flat wound body. Thereby, the electrode winding body 14 is obtained.

(Assembly of non-aqueous electrolyte secondary battery)
An outer can 11 and a lid plate 12 are prepared. The outer can 11 is manufactured, for example, by deep drawing a plate of aluminum or aluminum alloy. The lid plate 12 is manufactured, for example, by punching a plate of aluminum or aluminum alloy.

  The positive electrode lead tab and the lid plate 12 are welded, and the negative electrode lead tab and the negative electrode terminal 13 are welded. The electrode winding body 14 is accommodated in the outer can 11, and the lid plate 12 is fitted into the opening of the outer can 11. In this state, the inner periphery of the opening of the outer can 11 and the outer periphery of the lid plate 12 are welded.

  An electrolytic solution is injected from the injection port 12a, and preliminary charging is performed as necessary. Thereafter, the sealing plug 15 is fitted into the liquid injection port 12a, and the inner periphery of the liquid injection port 12a and the outer periphery of the sealing plug 15 are welded to seal the liquid injection port 12a. Then, the nonaqueous electrolyte secondary battery 1 is manufactured by charging to a predetermined capacity.

[Effects of separator for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery]
Base material layer 20 of separator 2A and separator 2B is a microporous film of a thermoplastic resin. When the separator 2A and the separator 2B are heated to near the melting point of the thermoplastic resin, the thermoplastic resin is melted and the pores of the base material layer 20 are closed. That is, the separator 2A and the separator 2B have shutdown characteristics.

  A filler layer 21 and a filler layer 22 are formed on both surfaces of the base material layer 20. Even when the base material layer 20 is easily deformed by heat, the filler layer 21 and the filler layer 22 suppress deformation of the separator 2A and the separator 2B. That is, the separator 2A and the separator 2B are excellent in dimensional stability at high temperatures.

  When the separator 2A and the separator 2B are heated to near the melting point of the binder of the filler layer 21 and the filler layer 22, these binders are softened. As a result, the separator 2A and the separator 2B have a function of being in close contact with an electrode disposed adjacent to the filler layer 22 at a high temperature.

  If the weight fraction of the binder is too low, the above function cannot be obtained. On the other hand, when the weight fraction of the binder is too high, the porosity of the filler layer 21 and the filler layer 22 decreases, and the ionic conductivity of the separator 2A and the separator 2B decreases. In the present embodiment, the binder weight fraction of the filler layer 22 is 5 wt% or more, and is higher than the binder weight fraction of the filler layer 21. In other words, the porosity of the separator 2A and the separator 2B as a whole is adjusted by relatively reducing the binder weight fraction of the filler layer 21. Specifically, the average value of the binder weight fraction of the filler layer 21 and the binder weight fraction of the filler layer 22 is made lower than 7 wt%. Thereby, a predetermined ion conductivity can be ensured.

  When the difference between the binder weight fraction of the filler layer 22 and the binder weight fraction of the filler layer 21 is too large, warpage occurs in the separator 2A and the separator 2B. In the present embodiment, the difference between the binder weight fraction of the filler layer 22 and the binder weight fraction of the filler layer 21 is made smaller than 10 wt%. Thereby, the curvature of separator 2A and separator 2B can be suppressed.

  As described above, the separator 2A and the separator 2B have shutdown characteristics and dimensional stability at high temperatures, and further have a function of preventing the electrodes and the outside air from coming into close contact with each other at high temperatures. Therefore, the separator 2A and the separator 2B can be prevented from becoming further hot when the battery becomes hot.

  In the non-aqueous electrolyte secondary battery 1 according to the present embodiment, since the separator 2A and the separator 2B have shutdown characteristics, the reaction automatically stops when the temperature becomes high. Further, since the separator 2A and the separator 2B are excellent in dimensional stability at a high temperature, the positive electrode 141 and the negative electrode 142 are not easily short-circuited even at a high temperature.

  The nonaqueous electrolyte secondary battery 1 includes a cleavage groove 11a. In the nonaqueous electrolyte secondary battery 1, when the pressure in the outer can 11 becomes larger than a predetermined threshold, the cleavage groove 11 a is cleaved, and the gas in the outer can 11 is discharged to lower the pressure.

  On the other hand, when the cleavage groove 11a is cleaved and the electrolytic solution further evaporates, the negative electrode 142 may be exposed to the outside air. When the nonaqueous electrolyte secondary battery 1 is in a charged state, the negative electrode 142 that occludes lithium ions may come into contact with the outside air. At this time, moisture contained in the outside air and the negative electrode 142 may react to generate heat.

  According to the present embodiment, the negative electrode 142 is disposed on the filler layer 22 side of the separator 2A and the separator 2B. When the nonaqueous electrolyte secondary battery 1 reaches a high temperature, the binder of the filler layer 22 of the separator 2A and the separator 2B is softened, and the separator 2A and the separator 2B are in close contact with the negative electrode 142. By covering the surface of the negative electrode 142 with the separator 2A and the separator 2B, the negative electrode 142 can be prevented from coming into contact with the outside air.

  As described above, the nonaqueous electrolyte secondary battery 1 according to the present embodiment can be prevented from becoming a high temperature.

  Furthermore, since the separator 2A and the separator 2B have a predetermined ionic conductivity as described above, the load characteristics of the non-aqueous electrolyte secondary battery 1 are the non-aqueous electrolyte using a polyolefin microporous membrane as a separator. Compared to the load characteristics of secondary batteries, there is no inferiority. In addition, since the warpage of the separator 2A and the separator 2B is suppressed as described above, the nonaqueous electrolyte secondary battery 1 can be produced with a high yield.

[Other Embodiments]
As mentioned above, although embodiment about this invention was described, this invention is not limited only to the above-mentioned embodiment, A various change is possible within the scope of the invention.

  In the above-described embodiment, the case where the non-aqueous electrolyte secondary battery includes the electrode winding body in which the belt-like positive electrode and the negative electrode are laminated with the separator interposed therebetween is described. However, the non-aqueous electrolyte secondary battery may include an electrode laminate in which strip-like positive and negative electrodes are laminated with a separator interposed therebetween, instead of the electrode winding body. In the above-described embodiment, the case where the nonaqueous electrolyte secondary battery includes a metal outer can is described. However, the nonaqueous electrolyte secondary battery may be a laminated battery in which an electrode body is laminated. The nonaqueous electrolyte secondary battery may include a vent mechanism other than the cleavage groove or may not include a vent mechanism.

  Hereinafter, based on an Example, this invention is demonstrated more concretely. In addition, this Example does not limit this invention.

  A plurality of separators were produced by changing the binder weight fraction of the filler layers on the front and back sides. Furthermore, a separator having no filler layer was prepared for reference. Using each separator, 10 nonaqueous electrolyte secondary batteries were produced for each type of separator. The produced separator and the nonaqueous electrolyte secondary battery were evaluated.

[Preparation of separator]
A PE microporous film having a thickness of 9 μm was used as the base material layer.

  A filler (plate boehmite (average particle size 1 μm, aspect ratio 10)) and a binder (emulsion of a self-crosslinking acrylic acid copolymer obtained by using butyl acrylate as a main component of a monomer) are dispersed in pure water. The slurry was adjusted. The prepared slurry was applied to one surface of the base material layer by a blade coater. Thereafter, the slurry was dried to form a first filler layer having a thickness of 3 μm.

  Using the same filler and binder as the first filler layer, a slurry was prepared in which only the binder weight fraction was changed. The prepared slurry was applied to the other surface of the base material layer by a blade coater. Thereafter, the slurry was dried to form a second filler layer having a thickness of 3 μm.

[Preparation of non-aqueous electrolyte secondary battery]
90 parts by weight of LiCoO ₂ , 7 parts by weight of acetylene black and 3 parts by weight of PVDF were mixed uniformly in N-methyl-2-pyrrolidone (NMP) to prepare a slurry. The adjusted slurry was applied to both sides of the aluminum foil. The slurry was dried to remove the solvent, and a positive electrode mixture layer was obtained. Calendar treatment was performed to adjust the density of the positive electrode mixture layer.

Specific conductivity of 98 parts by mass of graphite, 1.0 part by mass of a 1% by mass carboxymethylcellulose aqueous solution having a viscosity adjusted to the range of 1500 to 5000 mPa · s, and 1.0 part by mass of styrene-butadiene rubber Ion exchange water having a degree of 2.0 × 10 ⁵ Ω / cm or more was mixed as a solvent to prepare a water-based negative electrode mixture-containing slurry. The adjusted slurry was applied to both sides of the copper foil. The slurry was dried to remove the solvent, and a negative electrode mixture layer was obtained. Calendar treatment was performed to adjust the density of the negative electrode mixture layer.

The electrolytic solution was prepared by dissolving LiPF ₆ at a concentration of 1.2 mol / liter in a solvent in which EC and MEC were mixed at a volume ratio of 1: 2.

  The positive electrode and the negative electrode were laminated via a separator and wound, and further compressed in one direction to produce a flat electrode wound body. At this time, the separator was disposed so that the first filler layer was on the positive electrode side and the second filler layer was on the negative electrode side. The electrode winding body was inserted into a rectangular battery case made of aluminum alloy. An electrolyte solution was injected into the battery case to produce a non-aqueous electrolyte secondary battery.

[Heating test]
A non-aqueous electrolyte secondary battery is charged with a constant current at a current value of 1.0 C until the battery voltage reaches 4.35 V, and then a constant current-constant voltage charge is performed with constant voltage charging at 4.35 V It was. The total charging time until the end of charging was 2.5 hours. Each battery charged under the above conditions was placed in a thermostatic bath, heated from 30 ° C. to 150 ° C. at a rate of 5 ° C. per minute, and then allowed to stand at 150 ° C. for 1 hour, and the surface temperature of the battery was measured. Of the five non-aqueous electrolyte secondary batteries, even if one battery whose battery surface temperature rose to 200 ° C. or higher was included, the battery was rejected.

[Curl test]
The produced separator was cut out 30 cm in the longitudinal direction. After 24 hours, the case where the edge was wound more than 1 turn was regarded as unacceptable.

[Low temperature discharge characteristics test]
After charging at the rated current (1C charging) at room temperature, the sample was left in an environment of −10 ° C. for 4 hours. Thereafter, while maintaining the environment at −10 ° C., discharge at a rated current (1C discharge) was performed, and the discharge capacity was measured.

[Test results]
Table 1 shows the binder weight fraction of each separator and the test results.

  In Table 1, in the column of “first filler layer”, the weight fraction of the binder of the first filler layer is described. In the “second filler layer” column, the weight fraction of the binder of the second filler layer is described.

  In Table 1, the result of the heating test is described in the column of “heating test”, and the result of the curling test is described in the column of “curl test”. In both columns, “◯” indicates that the test was successful, and “x” indicates that the test was not successful.

  In Table 1, the result of the low temperature discharge characteristic test is described in the “low temperature discharge characteristic” column. In the same column, values normalized with the discharge capacity of the non-aqueous electrolyte secondary battery using the separator (test number 9) having no filler layer as 100 are described. In addition, the value described in the same column is an average value of values measured for five nonaqueous electrolyte secondary batteries.

  As shown in Table 1, the nonaqueous electrolyte secondary battery using the separators of test numbers 1 to 3 passed the heating test. When the nonaqueous electrolyte secondary battery was disassembled and confirmed after the test, all the separators were in close contact with the negative electrode. When these separators were peeled off from the negative electrode, they were not peeled off even when pulled with a force of 4N.

  The separators with test numbers 1 to 3 passed the curl test. Further, the low-temperature discharge characteristics of the nonaqueous electrolyte secondary battery using the separators of Test Nos. 1 to 3 were comparable to Test No. 9.

  The non-aqueous electrolyte secondary battery using the separator of test number 4 was inferior in 10% or more in low-temperature discharge characteristics as compared to test number 9. This is considered because the weight fraction of the binder as the whole separator was too high, and the ionic conductivity of the separator was low.

  The nonaqueous electrolyte secondary battery using the separator of test number 5 did not pass the heating test. That is, the non-aqueous electrolyte secondary battery produced using the separator of test number 5 contained a battery surface temperature of 200 ° C. or higher during heating at 150 ° C. for 1 hour. Further, in the non-aqueous electrolyte secondary battery whose battery surface temperature did not become 200 ° C. or higher, the separator was not in close contact with the negative electrode. More specifically, when the nonaqueous electrolyte secondary battery was disassembled and confirmed after the test, the separator was attached to the negative electrode, but was easily peeled off when pulled with a force of 4N. This is considered because the weight fraction of the binder of the second filler layer was low.

  The separator of test number 6 is one in which the binder amount of the second filler layer is zero. However, when the binder amount was 0, the filler layer could not be formed.

  The nonaqueous electrolyte secondary battery using the separator of Test No. 7 was inferior by 10% or more in low temperature discharge characteristics as compared with Test No. 9. This is considered because the weight fraction of the binder as the whole separator was too high, and the ionic conductivity of the separator was low. Furthermore, the separator of test number 7 did not pass the curl test. This is presumably because the difference between the binder weight fraction of the second filler layer and the binder filler weight fraction of the first filler layer was too large.

  The separator of test number 8 did not pass the curl test. This is presumably because the difference between the binder weight fraction of the second filler layer and the binder filler weight fraction of the first filler layer was too large.

  The non-aqueous electrolyte secondary battery using the separator of test number 9 did not pass the heating test. When the nonaqueous electrolyte secondary battery was disassembled and confirmed after the test, the separator was contracted.

  The effects of the present invention were confirmed by the above examples.

  That is, in order to obtain the effect of the present invention, a separator for a non-aqueous electrolyte secondary battery is formed on a base layer that is a microporous film of a thermoplastic resin and one surface of the base layer, and a binder and What is necessary is just to provide the 1st filler layer containing a filler and the 2nd filler layer formed in the other surface of a base material layer and containing a binder and a filler. However, the weight fraction of the binder of the second filler layer is 5 wt% or more and higher than the weight fraction of the binder of the first filler layer. The average value of the binder weight fraction of the first filler layer and the binder weight fraction of the second filler layer is lower than 7 wt%. The difference between the binder weight fraction of the second filler layer and the binder filler weight fraction of the first filler layer is less than 10 wt%.

  More preferably, the binder weight fraction of the first filler layer is 2 to 3 wt%, and the binder weight fraction of the second filler layer is 5 to 10 wt%.

  More preferably, at least one of the filler of the first filler layer and the filler of the second filler layer is boehmite.

  More preferably, the first filler layer and the second filler layer contain the same filler.

  A non-aqueous electrolyte secondary battery includes a separator for a non-aqueous electrolyte secondary battery having the above-described configuration, a positive electrode disposed on the first filler layer side of the separator for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte. What is necessary is just to provide the negative electrode arrange | positioned at the 2nd filler layer side of the separator for secondary batteries.

  DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery, 11 Outer can, 12 Cover plate, 13 Negative electrode terminal, 14 Electrode winding body, 141 Positive electrode, 142, Negative electrode, 2A, 2B Separator, 20 Base material layer, 21 1st filler layer, 22 Second filler layer, 15 Seal plug

Claims (5)

A base material layer that is a microporous film of a thermoplastic resin;
A first filler layer formed on one surface of the base material layer and containing a binder and a filler;
Formed on the other surface of the base material layer, and comprising a second filler layer containing a binder and a filler,
The binder weight fraction of the second filler layer is 5 wt% or more and higher than the binder weight fraction of the first filler layer,
The average value of the binder weight fraction of the first filler layer and the binder weight fraction of the second filler layer is lower than 7 wt%,
A separator for a non-aqueous electrolyte secondary battery, wherein a difference between a binder weight fraction of the second filler layer and a binder weight fraction of the first filler layer is less than 10 wt%. The binder weight fraction of the first filler layer is 2 to 3 wt%,
The separator for a non-aqueous electrolyte secondary battery according to claim 1, wherein the binder has a weight fraction of 5 to 10 wt% in the second filler layer.   The separator for a nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein at least one of the filler of the first filler layer and the filler of the second filler layer is boehmite.   The said 1st filler layer and the said 2nd filler layer are the separators for nonaqueous electrolyte secondary batteries as described in any one of Claims 1-3 containing the same filler. A separator for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4,
A positive electrode disposed on the first filler layer side of the non-aqueous electrolyte secondary battery separator;
A non-aqueous electrolyte secondary battery comprising: a negative electrode disposed on the second filler layer side of the non-aqueous electrolyte secondary battery separator.

Images