JP2017162699A - Wound type secondary battery separator, method for manufacturing wound type secondary battery separator, flat wound device, wound type secondary battery, and method for manufacturing wound type secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel improved wound type secondary battery separator and others which enable the improvement in the adhesion between a separator and each electrode.SOLUTION: To solve the above problem, a wound type secondary battery separator is provided according to an aspect of the present invention, which comprises: a base material layer; and an adhesive layer formed on at least one surface of the base material layer. In a thermomechanical analysis performed on the wound type secondary battery separator, a positive change in thickness is found. The thermomechanical analysis includes the steps of: immersing the wound type secondary battery separator in an electrolytic solution for evaluation, which is arranged by dissolving 1 M of LiBFin propylene carbonate; and heating the wound type secondary battery separator to at lowest 125°C at a temperature rising rate 5°C/min and measuring a quantity of displacement of the depressing member at each temperature with a fixed load of 0.5 MPa put on a depressing member for depressing the wound type secondary battery separator.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a separator for a wound secondary battery, a method for manufacturing a separator for a wound secondary battery, a flat winding element, a wound secondary battery, and a method for manufacturing a wound secondary battery.

  As a kind of nonaqueous electrolyte secondary battery, a wound secondary battery is known. The wound secondary battery is manufactured by the following steps. First, an electrode laminate is prepared by sequentially laminating a positive electrode, a negative electrode, and a separator. Here, a current collecting tab (tab) (also referred to as a current collecting lead) is welded to the positive electrode and the negative electrode before lamination. Some separators have a porous substrate and an adhesive layer formed on both surfaces or one surface of the substrate. Next, the pre-compression winding element is manufactured by winding the electrode laminate in a flat shape. Here, the current collecting tab is disposed in the innermost peripheral portion of the winding element. Next, the pre-compression winding element is crushed. Through the above steps, a flat winding element is produced. Next, the flat winding element and the electrolytic solution are sealed in the exterior material. Through the above steps, a wound secondary battery is manufactured.

  Here, a wound type secondary battery using a laminate as an exterior material, that is, a laminate type secondary battery, has advantages such as being thin and light and easy to change dimensions. For this reason, the application field of the laminate-type secondary battery is expanding to mobile phones, smart phones, automobile batteries, and the like. In addition, since the laminate type secondary battery has a soft exterior material, it is necessary to stabilize the shape of the flat electrode element inside. For this reason, flat winding elements are often integrated. Here, as a method of integrating the flat electrode elements, a method of applying pressure while heating the wound secondary battery has been proposed. According to this method, the adhesive layer is bound to the positive electrode or the negative electrode that contacts the adhesive layer. That is, the separator is bonded to the positive electrode and the negative electrode. Through the above steps, the flat winding element is integrated. As another method of integrating the flat winding elements, a method of crushing the pre-compression winding elements while heating has been proposed. In the following description, the integrated flat winding element is also referred to as “integrated winding element”.

JP 2005-209474 A JP 2011-0504502 A Japanese Patent Laying-Open No. 2015-053118

  By the way, since the current collecting tab described above is a thick member, a large space is formed around the current collecting tab, particularly between the current collecting tabs. For this reason, when flattened winding elements are integrated, it is difficult to apply pressure to a portion (hereinafter, also referred to as “space holding portion”) that sandwiches this space from the front and rear in the pressurizing direction. Of the space clamping portion, the portion adjacent to the space is particularly difficult to apply pressure. Therefore, there may be a case where a sufficient adhesion interface is not formed between the adhesive layer and each electrode in the space clamping portion. Specifically, a gap may be formed between the adhesive layer and each electrode. For this reason, the adhesive layer may not be sufficiently bonded to each electrode in the space clamping portion. Each electrode may be formed with an uncoated portion of the active material. A space is also formed around the uncoated portion, although not as large as the space formed between the current collecting tabs. Therefore, it is difficult for pressure to be applied to a portion that sandwiches the space from the front and rear in the pressing direction.

  Therefore, there is a problem that the integrated winding element is dotted with portions where the adhesive strength between the separator and each electrode is not sufficient. And when the winding type secondary battery incorporating such an integrated winding element is charged and discharged, the separator and each electrode may be released from these portions, and a gap may be formed. And if a clearance gap is formed between a separator and each electrode, the movement path | route of lithium ion will become long. As a result, the resistance value increases, and as a result, the life characteristics are deteriorated. In addition, when a space is formed between the separator and each electrode, the integrated winding element may be distorted due to a residual stress (or expansion / contraction pressure generated by charging / discharging). . And in a laminated type secondary battery, the whole battery will deform | transform with the deformation | transformation of an integrated winding element.

  For this reason, the technique which adhere | attaches a separator and each electrode more firmly was calculated | required strongly. As a method for solving this problem, there is a method of increasing the pressure at the time of integrating the flat winding element, but in this method, a portion other than the space clamping portion (that is, a sufficient adhesion interface is formed) Therefore, there is a problem in that the life characteristics of the secondary battery are deteriorated.

  On the other hand, Patent Documents 1 to 3 disclose techniques relating to separators. In the technique disclosed in Patent Document 1, in order to improve the adhesion between the separator and each electrode, the thickness reduction behavior of the separator by thermomechanical analysis is defined. In the techniques disclosed in Patent Documents 2 and 3, the separator and each electrode are integrated. However, none of the techniques can sufficiently solve the above-described problem.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a novel and improved winding type capable of improving the adhesion between the separator and each electrode. To provide a separator for a secondary battery, a method for manufacturing a separator for a wound secondary battery, a flat wound element, a wound secondary battery, and a method for manufacturing a wound secondary battery. .

In order to solve the above-described problems, according to one aspect of the present invention, there is provided a separator for a wound secondary battery including a base material layer and an adhesive layer formed on at least one surface of the base material layer. A step of immersing a separator for a wound secondary battery in an electrolyte for evaluation in which 1M LiBF ₄ is dissolved in propylene carbonate, and a pressing member for pressing the separator for the wound secondary battery is 0.5 MPa. Heating the separator for a wound secondary battery to a temperature of at least 125 ° C. at a rate of 5 ° C./min under a constant load and measuring the amount of displacement of the pressing member at each temperature. When mechanical analysis is performed, there is a positive thickness change of 0.1 to 1.0 μm with respect to the base line connecting the displacement amount of the pressing member at 75 ° C. and the displacement amount of the pressing member at 125 ° C. A separator for a wound type secondary battery is characterized by It is subjected.

  According to this aspect, when the flat winding element is integrated, the material constituting the adhesive layer absorbs the electrolyte and swells to fill the gap formed between the adhesive layer and each electrode. . That is, the material constituting the adhesive layer forms a sufficient adhesive interface with each electrode. Thus, the wound secondary battery separator is firmly bonded to each electrode. Therefore, according to this aspect, it becomes possible to improve the adhesiveness between the separator for a wound secondary battery and each electrode.

  Here, the adhesive layer may contain a PVDF polymer material.

  According to this viewpoint, the PVDF polymer material exhibits the behavior described above. For this reason, it becomes possible to improve the adhesiveness between the separator for a wound secondary battery and each electrode.

  PVDF polymer materials include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and Any one or more selected from the group consisting of these modified products may be used.

  According to this viewpoint, it becomes possible to improve the adhesiveness between the separator for a wound secondary battery and each electrode.

  The PVDF polymer material may be in the form of particles.

  According to this viewpoint, it becomes possible to improve the adhesiveness between the separator for a wound secondary battery and each electrode.

  The adhesive layer may further include heat resistant particles, and the total volume of the heat resistant particles may be 100 to 250% by volume with respect to the total volume of the PVDF polymer material.

  According to this aspect, it is possible to improve the adhesiveness between the separator for a wound secondary battery and each electrode while improving the heat resistance of the wound secondary battery.

  The porosity of the adhesive layer may be 45% by volume or less.

  According to this viewpoint, it becomes possible to improve the adhesiveness between the separator for a wound secondary battery and each electrode.

  The layer thickness of the adhesive layer may be 0.5 to 1.5 μm.

  According to this viewpoint, it becomes possible to improve the adhesiveness between the separator for a wound secondary battery and each electrode. Furthermore, the energy density of the wound secondary battery can be improved.

According to another aspect of the present invention, a winding die including a step of forming an adhesive layer on a base material layer by applying a slurry containing a material constituting the adhesive layer onto the base material layer and drying the slurry. A method for manufacturing a separator for a secondary battery, wherein the separator for a wound secondary battery includes a step of immersing the separator for a wound secondary battery in an evaluation electrolytic solution in which 1M LiBF ₄ is dissolved in propylene carbonate. The winding type secondary battery separator is heated to at least 125 ° C. at a rate of 5 ° C./min with a constant load of 0.5 MPa applied to the pressing member for pressing the winding type secondary battery separator. A base for connecting the displacement amount of the pressing member at 75 ° C. and the displacement amount of the pressing member at 125 ° C. when performing a thermomechanical analysis comprising measuring the displacement amount of the pressing member at each temperature 0.1 to 1.0 μm positive thickness variation with respect to the line Characterized in that there is, the manufacturing method of a separator for a winding type rechargeable battery is provided.

  According to this viewpoint, it becomes possible to improve the adhesiveness between the separator for a wound secondary battery and each electrode.

  According to another aspect of the present invention, there is provided a flat winding element comprising: a positive electrode; a negative electrode; and the separator for a wound secondary battery interposed between the positive electrode and the negative electrode. Provided.

  According to this viewpoint, it becomes possible to improve the adhesiveness between the separator for a wound secondary battery and each electrode.

  According to another aspect of the present invention, the flat winding element and a secondary battery electrolyte in which the flat winding element is immersed are included, and the adhesive layer includes the secondary battery electrolyte and the secondary battery electrolyte. A secondary battery electrolyte and a secondary battery separator having the same mass as a secondary battery are enclosed in a sealed container, and the secondary battery electrolyte and the secondary battery separator are heated at a rate of 5 ° C./min. When a differential thermal analysis of the mixture is performed, a wound type secondary battery having an endothermic peak in the range of 80 to 105 ° C. is provided.

  According to this viewpoint, it becomes possible to improve the adhesiveness between the separator for a wound secondary battery and each electrode.

  According to another aspect of the present invention, there is provided a method for manufacturing the above-described wound type secondary battery, wherein the flat wound element and the electrolytic solution for the secondary battery are enclosed in an exterior material, so that the secondary battery before press bonding is provided. And a step of producing a wound secondary battery by compressing the secondary battery before crimping while heating at a temperature of ± 10 ° C. at which the endothermic peak is obtained. A method for manufacturing a wound secondary battery is provided.

  According to this viewpoint, it becomes possible to improve the adhesiveness between the separator for a wound secondary battery and each electrode.

  As described above, according to the present invention, it is possible to improve the adhesion between the separator for a wound secondary battery and each electrode.

It is a plane sectional view showing a schematic structure of a flat winding element concerning an embodiment of the present invention. It is a plane sectional view showing a schematic structure of an electrode layered product concerning the embodiment. It is a graph which compares and shows the thermomechanical analysis result of an Example and a comparative example. It is a graph which compares and shows the thermomechanical analysis result after the baseline correction | amendment of an Example and a comparative example. 4 is a graph showing the results of differential thermal analysis of Example 1.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

<1. Overall configuration of flat winding element>
First, based on FIG.1 and FIG.2, the whole structure of the flat winding element 100 which concerns on this embodiment is demonstrated. In addition, the left figure in FIG. 1 is a plane sectional view which shows the whole structure of the flat winding element 100, and the right figure is an enlarged view of the region A in the left figure. Further, the flat winding element 100 is a winding element before integration. The flat winding element 100 includes two separators 10, a positive electrode 20, and a negative electrode 30. The two separators 10, the positive electrode 20, and the negative electrode 30 are laminated in the order of the separator 10, the negative electrode 30, the separator 10, and the positive electrode 20. Further, the separator 10, the positive electrode 20, and the negative electrode 30 are wound in a flat shape and a spiral shape. Therefore, the separator 10 is interposed between the positive electrode 20 and the negative electrode 30. Moreover, although mentioned later for details, the separator 10 is provided with the base material layer 10a and the contact bonding layer 10b. A positive electrode tab 50 is provided on the innermost peripheral portion of the positive electrode 20, and a negative electrode tab 60 is provided on the innermost peripheral portion of the negative electrode 30. A space C is formed between the positive electrode tab 50 and the negative electrode tab 60.

  For this reason, when integrating the flat winding element 100, it becomes difficult to apply pressure to the space clamping part D in the flat winding element 100. Here, the space clamping portion D is a portion that sandwiches the space C from the front and rear in the pressurizing direction, and the pressurizing direction is a pressurizing direction when the flat winding element 100 is integrated. Arrow B shows an example of the pressing direction. In addition, this pressurization direction corresponds with the pressurization direction at the time of pressurizing the winding element before compression. Of the space clamping portion D, the portion D1 adjacent to the space C is particularly difficult to apply pressure. Therefore, in the space clamping portion D, there may be a case where a sufficient adhesive interface is not formed between the adhesive layer 10b and each electrode. Specifically, a gap may be formed between the adhesive layer 10b and each electrode. For this reason, in the space clamping portion D, when the flat winding element 100 is integrated, the adhesive layer 10b may not be sufficiently bound to each electrode. Each electrode may be formed with an uncoated portion of the active material. A space is formed around the uncoated portion, although not as much as the space C. Therefore, it is difficult for pressure to be applied to a portion that sandwiches the space from the front and rear in the pressing direction.

  In the conventional adhesive layer, when the adhesive interface is not sufficiently formed, the adhesive strength with each electrode cannot be sufficiently increased. On the other hand, the adhesive layer 10b according to the present embodiment includes, for example, a specific thermoreversible physical gel material. This thermoreversible physical gel material absorbs the electrolyte solution by heating and swells, and fills the gap formed between the adhesive layer 10b and each electrode. That is, the thermoreversible physical gel material forms a sufficient adhesive interface with each electrode. Thereafter, the thermoreversible physical gel material is completely dissolved (ie, solated) in the electrolyte. Thereafter, the sol-formed thermoreversible physical gel material returns to the gel by cooling and is firmly bound to each electrode. Thereby, the separator 10 is firmly bonded to each electrode.

<2. Separator configuration>
Next, each component of the flat winding element 100 will be described in detail. First, the separator 10 will be described. The separator 10 is interposed between the positive electrode 20 and the negative electrode 30. The separator 10 is wound in a flat and spiral shape.

Moreover, the separator 10 has the following thermomechanical characteristics. That is, the separator 10 is immersed in an electrolytic solution for evaluation in which 1M LiBF ₄ is dissolved in propylene carbonate. Here, the evaluation electrolytic solution is used for the evaluation of thermomechanical properties in the case of an electrolytic solution used for a normal secondary battery because the electrolyte solvent is volatilized or the electrolyte salt is thermally decomposed during the measurement of the thermomechanical properties. This is because there is a case where it ends up. Next, the separator 10 is heated to at least 125 ° C. at a temperature increase rate of 5 ° C./min with a constant load of 0.5 MPa applied to the pressing member that presses the separator 10, and the displacement amount of the pressing member at each temperature is determined. taking measurement. When such a thermomechanical analysis is performed, the separator 10 has a thickness of 0.1 to 1.0 μm with respect to the base line connecting the displacement amount of the pressing member at 75 ° C. and the displacement amount of the pressing member at 125 ° C. There is a positive thickness change. Here, the positive thickness change means that the separator 10 expands and pushes back the pressing member. That is, the separator 10 has a characteristic of swelling when heated in an electrolytic electrolyte for evaluation having the same composition as or close to that of the wound secondary battery. The pressure during pressurization was 0.5 MPa. This is because it is often appropriate that the pressure at the time of integrating the flat winding element 100 is about 0.5 MPa. Although details will be described later, “there is a positive thickness change of 0.1 to 1.0 μm with respect to the baseline” means that the maximum value of the displacement after the baseline correction is 0.1 to 1.0 μm. Means that A preferable range of the thickness change is 0.1 to 0.2 μm.

  When the present inventor made the flat wound element 100 using the separator 10 having the thermomechanical characteristics and selected a specific electrolyte, the life characteristics and the like of the wound secondary battery were dramatically improved. Succeeded in improving. The separator 10 having such characteristics is realized by controlling the structure of the adhesive layer 10b. Hereinafter, a specific configuration of the separator 10 will be described.

  The separator 10 includes a base material layer 10a and an adhesive layer 10b. The base material layer 10a is a so-called band-shaped porous film. The base material layer 10a is not particularly limited, and may be any material as long as it is used as a separator of a lithium ion secondary battery, for example. As the base material layer 10a, it is preferable to use a porous film or a non-woven fabric exhibiting excellent high rate discharge performance alone or in combination. Examples of the resin constituting the base layer 10a include polyolefin resins represented by polyethylene, polypropylene, and the like, polyethylene terephthalate, and polybutylene terephthalate. Polyester resin, PVDF, vinylidene fluoride (VDF) -hexafluoropropylene (HFP) copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoro Ethylene (tetrafluorethylene) e) Copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride-hexafluoroacetone copolymer, vinylidene fluoride -Ethylene copolymer, vinylidene fluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene (Hexafluoropropylene) copolymer, vinylidene fluoride-ethylene (eth) lene) - can be exemplified tetrafluoroethylene (tetrafluoroethylene) copolymers.

  The adhesive layer 10b is formed on at least one surface, preferably both surfaces, of the base material layer 10a. The adhesive layer 10b preferably contains a specific thermoreversible physical gel material, specifically, a PVDF polymer material. By including the PVDF polymer material in the adhesive layer 10b, the separator 10 can have the above-described thermomechanical characteristics. That is, the adhesive layer 10b containing the PVDF polymer material absorbs the evaluation electrolytic solution at a temperature of 125 ° C. or lower and swells, and exhibits a positive thickness change. As a result, it is presumed that the PVDF polymer material exhibits the following behavior when the flat winding element 100 is integrated. That is, the PVDF polymer material swells by absorbing the electrolytic solution of the wound secondary battery, and fills the gaps formed between the adhesive layer 10b and each electrode. That is, the PVDF polymer material forms a sufficient adhesive interface with each electrode. Thereafter, the PVDF polymer material is completely dissolved (that is, made into a sol) in the electrolytic solution. Therefore, the PVDF polymer material swells before completely dissolving in the electrolytic solution. Thereafter, the sol-formed PVDF polymer material returns to gel by cooling and is firmly bound to each electrode. Thereby, the separator 10 is firmly bonded to each electrode.

  Here, the PVDF polymer material is a polymer material containing at least vinylidene fluoride (VDF) as a monomer. PVDF polymer materials include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene (VDF-HFP) copolymer, vinylidene fluoride-tetrafluoroethylene (VDF-TFE) copolymer, vinylidene fluoride- It is preferably at least one selected from the group consisting of hexafluoropropylene-tetrafluoroethylene copolymers and modified products thereof. When the PVDF polymer material is composed of these materials, the separator 10 can have the thermomechanical characteristics described above. The PVDF polymer material may be modified with a polar group such as carboxylic acid as long as the effects of the present invention are not impaired.

  Moreover, it is preferable that the PVDF polymer material has a particle shape. By making the PVDF polymer material into a particle shape, the porosity of the adhesive layer 10b can be easily reduced, and the above-described thermomechanical characteristics can be obtained. The particle size of the PVDF polymer material particles (the diameter when the PVDF polymer material particles are regarded as spheres) is not particularly limited, and the particles can be dispersed to the PVDF polymer material particles in the adhesive layer 10b. Any value can be used as long as it is a diameter, but if it is larger than ½ of the film thickness of the adhesive layer, it may be difficult to obtain a uniform film thickness. There is a case where the porosity is greatly lost by entering the pores. For this reason, the particle size of the PVDF polymer material particles is preferably 50 nm or more and ½ or less of the film thickness of the adhesive layer.

  The PVDF polymer material particles are produced (synthesized) by, for example, emulsion polymerization of a monomer (for example, VDF) constituting the PVDF polymer. The PVDF polymer material particles may be produced by suspension polymerization of monomers constituting the PVDF polymer and pulverizing coarse particles obtained thereby.

  The PVDF polymer material particles are particularly preferably spherical particles. Spherical PVDF polymer material particles can be produced, for example, by the emulsion polymerization method described above. The shape of the PVDF polymer material particles can be confirmed by, for example, SEM (scanning electron microscope).

  Further, the melting point of the PVDF polymer material is preferably 140 ° C. or higher and lower than 160 ° C., more preferably 145 to 150 ° C. When the melting point of the PVDF polymer material is a value within this range, the separator 10 can have the thermomechanical characteristics described above.

  The adhesive layer 10b may further contain heat-resistant particles in order to improve the heat resistance of the adhesive layer 10b. Here, the heat-resistant particles applicable to the present embodiment are not particularly limited. For example, the heat resistant particles may be organic particles, inorganic particles, or a mixture thereof. However, inorganic particles are more preferable because they often have better heat resistance than organic particles.

  Examples of the organic particles include cross-linked polystyrene (cross-linked PS), cross-linked polymethyl methacrylate (cross-linked PMMA), silicone resin, epoxy cured product, polyethersulfone, polyamidoimide (polyimide), Examples thereof include fine particles of a polyimide, a melamine resin, and a polyphenylene sulfide resin. The organic particle may be comprised by 1 type among these, and may be comprised by 2 or more types. The inorganic particles are, for example, ceramic particles, and more specifically metal oxide particles. Examples of the metal oxide particles include fine particles such as alumina, boehmite, titania, zirconia, magnesia, zinc oxide, aluminum hydroxide, and magnesium hydroxide.

  However, the total volume of the heat-resistant particles is preferably 100 to 250% by volume with respect to the total volume of the PVDF polymer material. In this case, the separator 10 can have the thermomechanical characteristics described above.

  Moreover, it is preferable that the average particle diameter of a heat resistant particle is 0.2-0.6 micrometer. In this case, the separator 10 can have the thermomechanical characteristics described above. The average particle diameter of the heat-resistant particles is measured by, for example, laser diffraction (laser diffractometry). Specifically, the particle size distribution of the heat-resistant particles may be measured by a laser diffraction method, and the arithmetic average value of the particle sizes may be calculated based on this particle size distribution. The average particle diameter of other particles can be measured by the same method.

In addition, the larger the porosity of the adhesive layer 10b, the more electrolytic solution penetrates into the adhesive layer 10b during the manufacture of the wound secondary battery. For this reason, the larger the porosity, the lower the resistance of the separator. However, the porosity is disadvantageous in forming the interface for adhesion with the electrode. Specifically, the larger the porosity, the more electrode solution penetrates into the adhesive layer 10b and the gel strength decreases. That is, the adhesive strength of the adhesive layer 10b is reduced. For this reason, the porosity is preferably 60% by volume or less, and more preferably 45% by volume or less. In this case, the separator 10 can have the thermomechanical characteristics described above. Here, the porosity of the adhesive layer 10b is the volume% of the voids in the total volume of the adhesive layer 10b. The porosity is the mass of the adhesive layer coated on the substrate, the so-called coating amount (g / m ² ), the measured coating thickness (m), and the respective material density and adhesive layer composition (mass ratio) used. ) From the composite material density (g / m ³ ) calculated from Specifically, it is calculated by the following mathematical formula. The composite material density means the true density of the composite material (density when the porosity is 0% by volume).

  The lower limit value of the porosity is not particularly limited, but may be 40% or more, for example. When the porosity is less than 40%, the air permeability of the separator 10 may be reduced. And when the air permeability of the separator 10 falls, the movement of the electrolyte ion in a winding secondary battery may be inhibited, and the performance of a winding secondary battery may fall.

  Moreover, it is preferable that the layer thickness (layer thickness per one side of the base material layer 10a) of the contact bonding layer 10b is 0.5-1.5 micrometers. In this case, the energy density of the wound secondary battery can be improved.

  When the adhesive layer 10b has the above-described structure, the separator 10 can have the above-described thermomechanical characteristics. As a result, the PVDF polymer material constituting the adhesive layer 10b absorbs the electrolyte and swells when the flat winding element 100 is integrated, and is formed between the adhesive layer 10b and each electrode. Fill the gaps. Thereafter, the PVDF polymer material is completely dissolved (that is, made into a sol) in the electrolytic solution. Thereafter, the sol-formed PVDF polymer material returns to gel by cooling and is firmly bound to each electrode. Thereby, the separator 10 is firmly bonded to each electrode.

  However, as described above, the PVDF polymer material swells with the electrolytic solution when the flat winding element 100 is integrated. Therefore, in order for the PVDF polymer material to exhibit the above-described characteristics, the composition of the electrolytic solution and the heating temperature during integration are very important. These parameters will be described later.

  The adhesive layer 10b may contain another binder, for example, a binder that holds the PVDF polymer material in the adhesive layer 10b as long as the effects of the present invention are not impaired. Examples of such a binder include, for example, an ionic water-insoluble binder, a nonionic water-insoluble binder, a nonionic water-soluble binder, and an ionic water-soluble binder. Of these, at least one kind may be included.

  The ionic water-insoluble binder that can be applied to the present embodiment is not particularly limited. Examples of the binder constituting the ionic water-insoluble binder include, for example, carboxylic acid-modified acrylic ester, polyolefin ionomer, and carboxylic acid-modified styrene-budadiene copolymer. The ionic water-insoluble binder may be composed of one of these, or may be composed of two or more.

  The nonionic water-insoluble binder that can be applied to the present embodiment is not particularly limited. Examples of the binder constituting the nonionic water-insoluble binder include non-ionic water-insoluble binders such as a radical polymerizable monomer such as butyl acrylate and an anion such as sodium lauryl sulfate. Examples thereof include a polybutyl acrylate aqueous dispersion obtained by emulsion polymerization from a water-soluble initiator such as a system surfactant and potassium persulfate. A monomer containing a hydroxyl group such as 2-hydroxyethyl acrylate may be appropriately copolymerized to improve the dispersion stability in water. A nonionic water-insoluble binder may be comprised by 1 type among these, and may be comprised by 2 or more types.

  The nonionic water-soluble binder applicable to the present embodiment is not particularly limited. Examples of the binder constituting the nonionic water-soluble binder include poly-N-vinylacetamide (PNVA), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), hydroxyethyl cellulose, methyl cellulose, hydroxypropyl cellulose, Examples include hydroxypropyl gar gum, locust bean gum, and polyoxyethylene. A nonionic water-soluble binder may be comprised by 1 type among these, and may be comprised by 2 or more types.

  The ionic water-soluble binder applicable to this embodiment is not particularly limited. Examples of the binder constituting the ionic water-soluble binder include polyacrylic acid, carboxymethyl cellulose (CMC), styrene-maleic acid copolymer, isobutylene-maleic acid copolymer, and N-vinylacrylamide-acrylic. Examples include acid copolymers, alkali metal salts thereof, and ammonium salts thereof. The ionic water-soluble binder may be composed of one of these, or may be composed of two or more.

  It is preferable that the content rate of another binder is 15 volume% or less with respect to the total volume of solid content of the contact bonding layer 10b, for example. In this case, the separator 10 can have the thermomechanical characteristics described above, and can suppress a decrease in porosity due to the binder. Various additives such as a thickener may be added to the adhesive layer 10b.

<3. Configuration of positive electrode>
The positive electrode 20 includes a positive electrode current collector 20a, a positive electrode active material layer 20b formed on both surfaces of the positive electrode current collector 20a, and a positive electrode tab 50.

  The positive electrode current collector 20a may be any conductor as long as it is a conductor, and is made of, for example, aluminum, stainless steel, nickel-plated steel, or the like. A positive electrode tab 50 is connected to the positive electrode current collector 20a. The positive electrode current collector 20a is a so-called band-shaped current collector.

  The positive electrode active material layer 20b includes at least a positive electrode active material, and may further include a conductive agent and a binder. The positive electrode active material is not particularly limited as long as it is a material capable of reversibly occluding and releasing lithium ions. For example, lithium cobalt oxide (LCO), lithium nickelate, lithium nickel cobaltate, nickel cobalt aluminum acid Lithium (hereinafter also referred to as “NCA”), nickel cobalt lithium manganate (hereinafter also referred to as “NCM”), lithium manganate, lithium iron phosphate, nickel sulfide, copper sulfide, sulfur , Iron oxide, vanadium oxide and the like. These positive electrode active materials may be used independently and 2 or more types may be used together.

The positive electrode active material is preferably a lithium salt of a transition metal oxide having a layered rock salt type structure, among the examples of the positive electrode active materials listed above. As a lithium salt of a transition metal oxide having such a layered rock salt structure, for example, Li _1-x-yz Ni _x Co _y Al _z O ₂ (NCA) or Li _1-x-yz Ni _x Co _y Mn _z O ₂ (NCM) (0 <x <1, 0 <y <1, 0 <z <1, and x + y + z <1) is represented by a lithium salt of a ternary transition metal oxide. Can be mentioned.

  Examples of the conductive agent include carbon black such as ketjen black and acetylene black, fibrous carbon such as carbon fiber and carbon nanotube, natural graphite, artificial graphite, and the like, which increase the conductivity of the positive electrode. If it is for, it will not be restrict | limited in particular.

  The binder bonds the positive electrode active materials to each other and bonds the positive electrode active material and the positive electrode current collector 20a. The type of the binder is not particularly limited, and any binder can be used as long as it is used for the positive electrode active material layer of the conventional lithium ion secondary battery. For example, polyvinylidene fluoride, vinylidene fluoride (VDF) -hexafluoropropylene (HFP) copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene (polyvinylidene fluoride) tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, ethylene-propylene-diene terpolymer, styrene-butadiene rubber butadiene rubber, butadiene rubber acrylonitrile-butadie erubber, fluororubber, polyvinyl acetate, polymethylmethacrylate, polyethylene, cellulosic nitrate, and the like. There is no particular limitation as long as it can be bound on the electric body 20a. Moreover, you may further add a well-known additive etc. to the positive electrode active material layer 20b.

<4. Structure of negative electrode>
The negative electrode 30 includes a negative electrode current collector 30a, a negative electrode active material layer 30b formed on both surfaces of the negative electrode current collector 30a, and a negative electrode tab 60. The negative electrode 30 may be a so-called aqueous negative electrode.

  The negative electrode current collector 30a may be any material as long as it is a conductor, and is composed of, for example, copper, stainless steel, nickel-plated steel, or the like. A negative electrode tab 60 is connected to the negative electrode current collector 30a. The negative electrode current collector 30a is a so-called band-shaped current collector.

The negative electrode active material layer 30b includes at least a negative electrode active material, and may further include a thickener and a binder. The negative electrode active material constituting the negative electrode active material layer 30b is not particularly limited as long as it is a material capable of alloying with lithium or reversibly occluding and releasing lithium (Li). For example, lithium, indium (In), tin (Sn), aluminum (Al), silicon (Si) and other metals and alloys and oxides thereof, transition metal oxides such as Li _4/3 Ti _5/3 O ₄ and SnO, and artificial Graphite, natural graphite, mixture of artificial graphite and natural graphite, natural graphite coated with artificial graphite, non-graphitizable carbon, graphite carbon fiber, resin-fired carbon, pyrolytic vapor-grown carbon, coke, mesocarbon Carbon such as microbeads (MCMB), furfuryl alcohol resin-fired carbon, polyacene, pitch-based carbon fiber, etc. Materials and the like. These negative electrode active materials may be used independently and 2 or more types may be used together. Among these, it is preferable to use a graphite-based material as a main material.

  The thickener adjusts the negative electrode mixture slurry to a viscosity suitable for coating and functions as a binder in the negative electrode active material layer 30b. As the thickener, a water-soluble polymer is preferably used, and examples thereof include a cellulose-based polymer, a polyacrylic acid-based polymer, polyvinyl alcohol, polyethylene oxide, and the like. Examples of the cellulosic polymer include metal derivatives or ammonium salts of carboxymethyl cellulose (CMC), cellulose derivatives such as methyl cellulose, ethyl cellulose, and hydroxyalkyl cellulose. . Other examples include polyvinylpyrrolidone (PVP), starch, starch phosphate, casein, various modified starches, chitin, chitosan derivatives and the like. These thickeners can be used alone or in combination of two or more. Among these, cellulose polymers are preferable, and alkali metal salts of carboxymethyl cellulose are particularly preferable.

  The binder binds the negative electrode active materials to each other. The binder is not particularly limited as long as it can be used as a binder for the negative electrode. Examples of the binder usable in this embodiment include fine particles of an elastomeric polymer. Elastomer polymers include SBR (styrene butadiene rubber), BR (butadiene rubber), NBR (nitrile butadiene rubber), NR (natural rubber), IR (isoprene rubber), EPDM (ethylene-propylene-diene ternary copolymer) Coalesced), CR (chloroprene rubber), CSM (chlorosulfonated polyethylene), acrylic acid ester, methacrylic acid ester copolymer, and partially hydride or complete hydride, acrylic acid ester copolymer, etc. Is mentioned. These may be modified with a monomer having a polar functional group such as carboxylic acid, sulfonic acid, phosphoric acid, or hydroxyl group in order to improve binding properties. Further, the negative electrode active material layer 30b may include fluororesin-containing fine particles as a binder. As for the fluororesin-containing fine particles, the powder may be dispersed later in the slurry, or the aqueous dispersion may be added to the slurry. Therefore, water can be used as a solvent for the slurry for forming the negative electrode active material layer 30b.

  The content ratio of the thickener and the binder in the negative electrode active material layer 30b is not particularly limited as long as it is a content ratio applicable to the conventional negative electrode active material layer. Moreover, you may further add a well-known additive etc. to the negative electrode active material layer 30b.

<5. Manufacturing method of flat wound element>
Next, a method for manufacturing a flat wound element will be described. First, the separator 10, the positive electrode 20, and the negative electrode 30 are produced.

(5-1. Manufacturing method of separator)
An adhesive layer slurry is prepared by dispersing the material of the adhesive layer 10b in a solvent. Next, the coating layer is formed by coating the adhesive layer slurry on at least one surface of both surfaces of the base material layer 10a. Subsequently, this coating layer is dried. Thereby, the separator 10 is produced.

(5-2. Method for producing positive electrode)
A positive electrode mixture slurry is formed by dispersing the material of the positive electrode active material layer 20b in a solvent, and this positive electrode mixture slurry is applied onto the positive electrode current collector 20a. Thereby, a coating layer is formed. Next, the coating layer is dried. Next, the dried coating layer is rolled together with the positive electrode current collector 20a. Next, the positive electrode tab 50 is fixed to the end of the positive electrode current collector 20a by welding or the like. Thereby, the positive electrode 20 is produced.

(5-3. Method for producing negative electrode)
A negative electrode mixture slurry is formed by dispersing the material of the negative electrode active material layer 30b in a solvent, and this negative electrode mixture slurry is applied onto the negative electrode current collector 30a. Thereby, a coating layer is formed. Next, the coating layer is dried. Next, the dried coating layer is rolled together with the negative electrode current collector 30a. Next, the negative electrode tab 60 is fixed to the end of the negative electrode current collector 30a by welding or the like. Thereby, the negative electrode 30 is produced.

(5-4. Manufacturing method of flat wound element)
Next, the separator 10, the negative electrode 30, the separator 10, and the positive electrode 20 are laminated in this order, so that the electrode laminate 100 a shown in FIG. 2 is produced. Next, the electrode laminate 100a is wound in a flat shape. Thereby, the back surface (namely, separator 10) of the other part of electrode laminated body 100a contacts the surface (namely, positive electrode 20) of a part with electrode laminated body 100a. Thereby, a pre-compression winding element is produced. Subsequently, the flat winding element 100 is produced by crushing the pre-compression winding element. Here, the pressing direction when the pre-compression winding element is crushed is, for example, the arrow B direction shown in FIG.

<6. Manufacturing method of wound secondary battery>
Next, a method for manufacturing a wound secondary battery using the flat wound element 100 will be described. First, the secondary battery before press bonding is manufactured by enclosing the flat wound element 100 and the electrolyte in an exterior material. Here, the positive electrode tab 50 and the negative electrode tab 60 are drawn out of the exterior material. The exterior material is, for example, a laminate, but may be a metal exterior material. Next, the flat winding element 100 is integrated by applying pressure while heating the pre-compression secondary battery. The pressing direction is, for example, the arrow B direction shown in FIG. Through the above process, a wound secondary battery is manufactured.

  Thus, in this embodiment, the flat winding element 100 is integrated by pressurizing the flat winding element 100 while heating. Through this step, the PVDF polymer material in the adhesive layer 10b swells by absorbing the electrolytic solution, and fills the gaps formed between the adhesive layer 10b and each electrode. Thereafter, the PVDF polymer material is completely dissolved (that is, made into a sol) in the electrolytic solution. Thereafter, the sol-formed PVDF polymer material returns to gel by cooling and is firmly bound to each electrode. Thereby, the separator 10 is firmly bonded to each electrode.

  Therefore, in order for the PVDF polymer material to exhibit the above-described characteristics, the composition of the electrolytic solution and the heating temperature during integration are very important.

  Specifically, the PVDF polymer material according to the present embodiment has the following differential thermal characteristics. That is, an electrolytic solution, an electrolytic solution (electrolytic solution for a secondary battery) and a separator 10 having the same mass are sealed in a sealed container, and a differential thermal analysis of a mixture of the electrolytic solution and the separator 10 at a temperature rising rate of 5 ° C./min. I do. In this case, an endothermic peak is observed in the range of 80 to 105 ° C. This endothermic peak indicates an endothermic reaction when the PVDF polymer material constituting the adhesive layer 10b is dissolved in the electrolytic solution. More specifically, it shows an endothermic reaction when the crystal component of the PVDF polymer material is dissolved in the electrolytic solution. When the PVDF polymer material has such differential thermal characteristics, the PVDF polymer material can exhibit the above-described characteristics. That is, the PVDF polymer material can swell by absorbing the electrolytic solution and can be completely dissolved in the electrolytic solution. As a result, since the gel strength at room temperature (that is, the strength of the adhesive layer 10b) is increased, the adhesive force is improved. Therefore, the PVDF polymer material can firmly adhere the separator 10 to each electrode.

The electrolytic solution is a solution in which an electrolyte is dissolved in an organic solvent. Examples of the electrolyte that satisfies the above characteristics include LiBF ₄ , LiPF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ). _{(C 4 F 9 SO 2)} , LiC (CF 3 SO 2) 3, LiC (C 2 F 5 SO 2) 3, (CH 3) 4 NBF 4, (CH 3) 4 NBr, (C 2 H 5) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (n-C ₄ H ₉ ) ₄ NClO ₄ , (n-C ₄ H ₉ ) ₄ NI, (C ₂ H _{5 ) 4 N-maleate, (C} 2 H 5) 4 N-benzoate, (C 2 H 5) 4 N-phtalate, lithium stearyl sulfonate (stearyl sulfonic acid lith um), lithium octyl sulfonate (octyl sulfonic acid), organic ion salts such as lithium dodecyl benzene sulfonate (dodecyl benzene sulphonic acid) and the like. Examples of the organic solvent include ethylene carbonate (EC) / ethyl propionate, propylene carbonate, ethylene carbonate, butylene carbonate, and chloroethylene carbonate. ), Cyclic carbonates such as vinylene carbonate; cyclic esters such as γ-butyrolactone, γ-valerolactone; dimethyl carbonate, diethyl carbonate Chain carbonates such as diethyl carbonate and ethyl methyl carbonate; methyl formate, methyl acetate, butyric acid methyl, ethyl acetate Chain esters such as propyl acetate, ethyl propionate, propyl propionate, etc .; Tetrahydrofuran or its derivatives; 1,3-dioxane, 1,4 -Dioxane, 1,2-dimethoxyethane ethers such as dimethyl ether, 1,4-dibutoxy ethane, methyl diglyme; nitriles such as acetonitrile, benzonitrile, and dioxolanes; ) Or a derivative thereof; ethylene sulfide, sulfolane, sultone, or a derivative thereof alone or a mixture of two or more thereof.

  Further, the heating temperature at the time of integration is a temperature at which the endothermic peak of the electrolyte is obtained, that is, a value within a range of ± 10 ° C. of the endothermic peak temperature. The heating temperature is preferably a value within a range of ± 3 ° C. of the endothermic peak temperature. That is, in this embodiment, the flat winding element 100 is integrated by pressurizing the secondary battery before pressure bonding while heating it at an endothermic peak temperature of ± 10 ° C. Thus, in this embodiment, the separator 10 and each electrode can be sufficiently bonded even when the heating temperature is equal to or lower than the decomposition temperature of the electrolytic solution component or the boiling point of the low boiling point solvent. That is, in the present embodiment, it is possible to achieve both suppression of decomposition of the electrolytic solution and the like and expression of strong adhesive force. By setting the electrolytic solution and the heating temperature as described above, the PVDF polymer material can exhibit the above-described characteristics. That is, the PVDF polymer material can swell by absorbing the electrolytic solution and can be completely dissolved in the electrolytic solution.

<Configuration of wound secondary battery>
The wound secondary battery according to this embodiment includes an integrated flat winding element 100, that is, an integrated winding element, an electrolytic solution, and an exterior material that encloses these. As described above, in the present embodiment, the separator 10 is firmly bonded to each electrode. That is, the adhesiveness between the separator 10 and each electrode is improved. For this reason, battery characteristics, specifically, life characteristics are greatly improved. Furthermore, even when a laminate is used as the exterior material, deformation of the wound secondary battery is suppressed.

Next, examples of the present invention will be described.
Example 1
(Preparation of positive electrode)
A positive electrode mixture slurry was prepared by dissolving and dispersing lithium cobaltate, carbon black, and polyvinylidene fluoride (PVDF) in N-methylpyrrolidone in a mass ratio of solids of 96: 2: 2. Next, the positive electrode mixture slurry was applied to both surfaces of a 12 μm thick aluminum foil current collector and then dried. The positive electrode active material layer was produced by rolling the coating layer after drying. The total thickness of the current collector and the positive electrode active material layer was 120 μm. Next, an aluminum lead wire (positive electrode tab) was welded to the end of the current collector to obtain a positive electrode.

(Preparation of negative electrode)
A negative electrode mixture slurry was prepared by dissolving and dispersing graphite, an aqueous dispersion of modified SBR fine particles, and a sodium salt of carboxymethyl cellulose in an aqueous solvent at a solid mass ratio of 97.5: 1.5: 1. Next, this negative electrode mixture slurry was applied to both sides of a 10 μm thick copper foil current collector and then dried. The negative electrode active material layer was obtained by rolling the coating layer after drying. The total thickness of the current collector and the negative electrode active material layer was 120 μm. Thereafter, a nickel negative wire (negative electrode tab) was welded to the end of the current collector to obtain a strip-shaped negative electrode.

(Preparation of separator)
PVDF-based aqueous dispersion in which PVDF polymer material particles having a melting point of 145 ° C. are dispersed in water, carboxylic acid-modified polybutyl acrylate aqueous dispersion in which carboxylic acid-modified polybutyl acrylate particles are dispersed in water, and average particle diameter An adhesive layer slurry was prepared by dissolving and dispersing 0.5 μm of alumina particles in an aqueous solvent at a solid volume ratio of 30:10:60. Here, the composition of the PVDF polymer material was a vinylidene fluoride-hexafluoropropylene copolymer.

Next, this adhesive layer slurry was coated on both sides of a corona-treated porous polyethylene separator film (base material layer) and dried to give a thickness of 1.9 μm (per side) A separator having an adhesive layer of 0.95 μm was obtained. Since the coating amount (surface density of the adhesive layer) was 3.32 g / m ² , the porosity of the adhesive layer was 42% by volume.

Here, the porosity was calculated as follows. First, Example PVdF polymer materials were used in 1, carboxylic acid-modified poly butyl acrylate, and the respective density of the alumina is ^{1.7g / cm 3, 1.2g / cm} 3, 4.0g / cm 3 met It was. Since these volume ratios are 30:10:60, the true density of these composite materials (volume density when the porosity is 0% by volume) is 3.03 g / cm ³ (= 1). .7 * 0.3 + 1.2 * 0.1 + 4.0 * 0.6).

On the other hand, the coating amount is 3.32 g / m ² , and the thickness of the adhesive layer is 1.9 μm for both surfaces. Therefore, the density of the coating amount is 1.75 g / cm ³ (= 3.32 (g / M ² ) /1.9 (μm)). Since (density of coating layer) = (true density of composite material) * (1−porosity), porosity = 1− (density of coating layer) / (true density of composite material). . Therefore, the porosity is 42% by volume (= 1-1.75 / 3.03).

(Thermomechanical analysis of separator)
A sample for thermomechanical analysis was prepared by stacking 32 separators and punching them into a diameter of 4 mm. Then, the container penetration (penetration) of the thermomechanical analyzer (Netzsch Inc. TMA4000SE), place the sample for thermomechanical analysis, evaluation electrolyte solution 100μL a (propylene carbonate solution of a LiBF ₄ of 1M) It was dripped at the sample for thermomechanical analysis. Subsequently, the penetration container was introduced into the vacuum chamber, and the electrolyte solution was infiltrated into the thermomechanical analysis sample by repeating the vacuum / normal pressure three times. Thereafter, excess electrolyte in the penetration container was removed with a syringe, and the penetration container was set in a thermomechanical analyzer. Further, a penetration detection rod having a diameter of 1 mm was prepared as a pressing member for pressing the thermomechanical analysis sample.

  Next, a constant load of 0.5 MPa (40 gf) was applied to the detection rod at a constant temperature of 25 ° C. This state was held for 1 hour, and the thickness change amount of the separator before and after holding was measured. Next, this amount of change was set to zero. That is, the position of the detection rod at this time was set as the initial position. Next, in the state where a constant load of 0.5 MPa was applied to the detection rod (that is, a constant load of 0.5 MPa was applied to the sample for thermomechanical analysis), the temperature increase rate of the thermomechanical analysis sample was 5 ° C./min. To 125 ° C. Subsequently, the displacement amount of the pressing member at each temperature was measured. Here, regarding the amount of change, the direction in which the detection rod was pushed into the sample for thermomechanical analysis was defined as the negative direction, and the opposite direction was defined as the positive direction.

  The measurement results are shown in FIG. The horizontal axis of FIG. 3 shows the temperature of the sample for thermomechanical analysis, and the vertical axis shows the displacement (μm) of the detection rod. The value on the vertical axis is a value for one separator, that is, a value obtained by dividing the measured displacement amount by 32. Graph L11 shows the measurement results of Example 1.

  Next, a base line L12 connecting the displacement amount of the detection rod at 75 ° C. and the displacement amount of the detection rod at 125 ° C. is set. Next, the amount of displacement at each temperature is corrected to the amount of displacement from the baseline L12. That is, baseline correction is performed. The result is shown in FIG. The horizontal axis of FIG. 4 shows the temperature of the sample for thermomechanical analysis, and the vertical axis shows the displacement (μm) after baseline correction. A graph L13 shows the measurement result after baseline correction in the first embodiment. As is apparent from the graph L13, in Example 1, there is a maximum value of displacement near 100 ° C., and this maximum value is about 0.13 μm, that is, a value in the range of 0.1 to 1.0 μm. . Therefore, it can be said that the separator of Example 1 has a positive thickness change of 0.1 to 1.0 μm with respect to the baseline.

  As a reference example, a porous polyethylene separator film without an adhesive layer was prepared, and the same thermomechanical analysis as described above was performed. The results are shown in FIGS. A graph L51 in FIG. 3 shows a measurement result before baseline correction, and a graph L52 shows a baseline. Graph L53 shows the measurement results after baseline correction. As is apparent from the measurement results of the reference example, the normal porous film itself does not exhibit an increase in thickness in the temperature range of 125 ° C. or lower. Therefore, the thickness change in Example 1 indicates that the thickness is changed by the adhesive layer.

(Differential thermal analysis of separator and electrolyte)
64 separators were stacked on the bottom surface of the SUS sealed container of the differential thermal analyzer (xDSC7000 SII Nanotechnology Co., Ltd.) so as to be in close contact with the bottom surface without any gaps. Next, the total mass of the separator was measured. Next, an electrolytic solution prepared by dissolving 1M LiPF ₆ in ethylene carbonate / ethyl propionate (volume ratio 3/7) was prepared as an electrolytic solution. Next, an electrolytic solution having the same mass as the separator was dropped into the SUS sealed container using a micropipette. Next, the lid of the SUS sealed container was caulked to seal it. Then, the SUS sealed container was left at room temperature for 1 day. Next, the SUS sealed container was set in a differential thermal analyzer, and the mixture of the electrolytic solution and the separator was subjected to differential thermal analysis at a heating rate of 5 ° C./min. The result is shown in FIG. The horizontal axis in FIG. 5 is the temperature of the mixture, and the vertical axis is the heat flow (μW). As is clear from FIG. 5, in Example 1, an endothermic peak E was observed at around 99 ° C. The endothermic peak E indicates an endothermic reaction when the crystal component of the PVDF polymer material is dissolved in a high-temperature electrolytic solution.

(Production of a wound secondary battery)
The electrode laminate was produced by laminating the separator, the negative electrode, the separator, and the positive electrode in this order. Next, the electrode laminate was wound around a flat core. That is, the electrode laminate was wound. Here, the end on the positive electrode tab and negative electrode tab side was set to start winding. This produced the pre-compression winding element. The end of the outermost peripheral part of the pre-compression winding element was fixed with tape, and then the winding core was removed. Next, the pre-compression winding element was crushed by sandwiching the pre-compression winding element between the two metal plates. Thereby, a flat electrode winding element was obtained.

The flat electrode winding element and the electrolytic solution were sealed in a laminate film (exterior material) composed of three layers of polypropylene / aluminum / nylon. Here, the two lead wires were pulled out of the laminate film. Further, the electrolytic solution was used which was dissolved LiPF ₆ in 1M ethylene carbonate / ethyl propionate in a solvent were mixed in a 3: 7 (volume ratio). Through the above steps, a secondary battery before pressure bonding was produced.

  Subsequently, the secondary battery before pressure bonding was sandwiched between two 3 cm thick metal plates heated to 100 ° C. and held at a pressure of 0.5 MPa for 2 minutes. By this step, the flat winding element was integrated. In this step, the PVDF polymer material is estimated to exhibit the following behavior. The PVDF polymer material absorbs the electrolytic solution and swells to fill the gap between the adhesive layer and each electrode. Thereafter, the PVDF polymer material is dissolved in the electrolytic solution. Thereafter, the PVDF polymer material is gelled by cooling, and firmly bonds the separator and each electrode. The secondary battery before the initial charge was produced by the above process.

  Next, the secondary battery before the initial charge was charged at a constant current of 1/10 CA of the designed capacity (1 CA is a discharge rate for 1 hour) to 4.35 V, and then charged at a constant voltage of 4.35 V to 1/20 CA. . Thereafter, constant current discharge was performed to 3.0 V at 1/2 CA. Through this process, a wound secondary battery was produced. The discharge capacity at this time was defined as the initial discharge capacity. Two wound type secondary batteries were produced. Subsequently, one winding type secondary battery was disassembled, and the adhesion state of the electrode and the separator in the space C inside the flat winding element was confirmed. “○” indicates that the bonding state of this portion is not different from the bonding state of the other flat portion, “△” indicates that the separator is weaker than the flat portion but is adhered to each electrode, and “△”. Was determined to be “x”. In Example 1, it was “◯”. In addition, a life test in which the wound secondary battery that was not disassembled was charged at 0.66 CA and discharged at 0.5 CA at a temperature of 25 ° C. was performed 300 cycles. Then, the capacity retention rate was measured by dividing the discharge capacity after 300 cycles by the initial discharge capacity. The capacity retention rate was 88%, and the appearance of the battery after the life test was not changed from the state before the start of the life test.

(Example 2)
The same treatment as in Example 1 was performed except that a separator was produced in the following steps. Adhesive layer by dissolving and dispersing carboxylic acid-modified vinylidene fluoride-hexafluoropropylene copolymer (melting point 150 ° C.) and alumina particles used in Example 1 in N-methyl-2-pyrrolidone (NMP) A slurry was prepared. The volume ratio of the carboxylic acid-modified vinylidene fluoride-hexafluoropropylene copolymer and alumina particles was 44:56. Subsequently, the adhesive layer slurry was applied to both surfaces of the porous polyethylene separator film used in Example 1, thereby forming a coating layer. Next, the NMP was removed by immersing the base material layer on which the coating layer was formed in water, and then the attached water was dried. This produced the separator by which the porous contact bonding layer was formed in both surfaces of the base material layer. The adhesive layer had a thickness of 3.0 μm on both sides, a coating amount of 3.44 g / m ² , and a porosity of 59% by volume. Here, the density of the carboxylic acid-modified vinylidene fluoride-hexafluoropropylene copolymer was set to 1.7 g / cm ³ . Next, after the separator was washed with water and dried, thermomechanical analysis and the like were performed.

  The thermomechanical analysis results of the separator are shown in FIGS. A graph L21 in FIG. 3 shows a measurement result before baseline correction, and a graph L22 shows a baseline. A graph L23 shown in FIG. 4 shows the measurement result after baseline correction. As is apparent from the graph L23, in Example 2, there was a maximum value of displacement near 100 ° C., and this maximum value was about 0.15 μm, that is, a value in the range of 0.1 to 1.0 μm. Therefore, it can be said that the separator of Example 2 has a positive thickness change of 0.1 to 1.0 μm with respect to the baseline. Further, when differential thermal analysis of the electrolytic solution and the separator was performed, an endothermic peak was observed at around 90 ° C. Moreover, the heating temperature at the time of heat-pressing the secondary battery before pressure bonding was set to 85 ° C. When the wound type secondary battery was disassembled and the adhesion state of the space C was confirmed, it was confirmed that the adhesion state was maintained although it was weak compared to Example 1. That is, the evaluation of adhesiveness was “Δ”. The capacity retention rate after the life test was 86%, and the appearance of the battery after the life test did not change from the state before the start of the life test. The effect of Example 2 is slightly lower than that of Example 1. One reason for this is that the porosity is larger than that of Example 1. In Example 2, since the porosity is large, it is considered that the gel strength of the adhesive layer was lowered. Another reason is that the difference between the heating temperature and the endothermic peak temperature is a little as large as 5 ° C. In this respect as well, the gel strength is considered to have decreased.

(Comparative Example 1)
The same treatment as in Example 1 was performed except that a separator was produced in the following steps. The acrylic resin aqueous dispersion in which the carboxylic acid-modified ethyl methacrylate particles are dispersed in water, the carboxylic acid-modified polybutyl acrylate aqueous dispersion used in Example 1, and the alumina particles are mixed in a volume ratio of solids of 30:10. : An adhesive layer slurry was prepared by dissolving and dispersing in a water solvent at a ratio of 60. Next, this adhesive layer slurry is applied to both surfaces of the porous polyethylene separator film (base material layer) used in Example 1 and dried, so that the adhesive layer having a thickness of 2.0 μm is formed on both surfaces of the base material layer. A formed separator was obtained. The coating amount was 3.12 g / m ² , and the porosity was 46% by volume. Here, the density of the carboxylic acid-modified ethyl methacrylate particles was set to 1.2 g / cm ³ . After the separator was washed with water and dried, thermomechanical analysis and the like were performed.

  The thermomechanical analysis results of the separator are shown in FIGS. A graph L31 in FIG. 3 shows a measurement result before baseline correction, and a graph L32 shows a baseline. A graph L33 shown in FIG. 4 shows the measurement result after baseline correction. As is clear from the graph L33, a slight increase in thickness was also observed in Comparative Example 1, but the value was 0.06 μm, which was less than 0.1 μm. Moreover, when the differential thermal analysis of the electrolyte solution and the separator was performed, no endothermic peak was observed. Therefore, it can be said that the acrylic resin according to Comparative Example 1 is an amorphous polymer material. When the wound secondary battery was disassembled and the adhesion state of the space C was confirmed, the separator was not adhered to the electrode in the space C at all. Therefore, the evaluation of adhesiveness was “x”. It was confirmed that the capacity retention rate after the life test was 82%, and the appearance of the wound secondary battery after the life test was slightly bent and distorted from the center line passing between the current collecting tabs.

(Comparative Example 2)
The same treatment as in Example 1 was performed except that a separator was produced in the following steps. Adhesive layer by dissolving and dispersing carboxylic acid-modified vinylidene fluoride-hexafluoropropylene copolymer (melting point 150 ° C.) and alumina particles used in Example 1 in N-methyl-2-pyrrolidone (NMP) A slurry was prepared. The volume ratio of the carboxylic acid-modified vinylidene fluoride-hexafluoropropylene copolymer and alumina particles was 20:80. Subsequently, the adhesive layer slurry was applied to both surfaces of the porous polyethylene separator film used in Example 1, thereby forming a coating layer. Next, NMP was removed by immersing the base material layer on which the coating layer was formed in water. This produced the separator by which the contact bonding layer was formed on both surfaces of the base material layer. The adhesive layer had a thickness of 2.8 μm on both sides, a coating amount of 4.10 g / m ² , and a porosity of 51% by volume. After the separator was washed with water and dried, thermomechanical analysis and the like were performed.

  The thermomechanical analysis results of the separator are shown in FIGS. A graph L41 in FIG. 3 shows a measurement result before baseline correction, and a graph L42 shows a baseline. A graph L43 shown in FIG. 4 shows the measurement result after baseline correction. As is clear from the graph L43, in Comparative Example 2, the separator showed a behavior in which the thickness decreased consistently with heating. The minimum value of the displacement amount was 0.27 μm. Moreover, when the differential thermal analysis of the electrolyte solution and the separator was performed, an endothermic peak was observed at around 85 ° C. Moreover, the heating temperature at the time of heat-pressing the secondary battery before pressure bonding was set to 85 ° C. When the wound secondary battery was disassembled and the adhesion state of the space C was confirmed, the separator was not adhered to the electrode in the space C at all. Therefore, the evaluation of adhesiveness was “x”. The capacity retention rate after the life test was 83%, and it was confirmed that the appearance of the wound secondary battery after the life test was slightly bent and distorted from the center line passing between the current collecting tabs.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Separator 10a Base material layer 10b Adhesive layer 20 Positive electrode 20a Positive electrode collector 20b Positive electrode active material layer 30 Negative electrode 30a Negative electrode collector 30b Negative electrode active material layer 50 Positive electrode tab 60 Negative electrode tab

Claims (11)

A base material layer;
An adhesive layer formed on at least one surface of the base material layer, and a separator for a wound secondary battery,
Immersing the wound secondary battery separator in an electrolytic electrolyte for evaluation in which 1M LiBF ₄ is dissolved in propylene carbonate;
The winding type secondary battery separator is heated to at least 125 ° C. at a rate of 5 ° C./min with a constant load of 0.5 MPa applied to the pressing member for pressing the winding type secondary battery separator. And a step of measuring the displacement amount of the pressing member at each temperature, and when performing a thermomechanical analysis, the displacement amount of the pressing member at 75 ° C. and the displacement amount of the pressing member at 125 ° C. A separator for a wound secondary battery, characterized in that there is a positive thickness change of 0.1 to 1.0 μm with respect to a base line connecting the two.   The separator for a wound secondary battery according to claim 1, wherein the adhesive layer includes a PVDF polymer material.   The PVDF polymer material includes polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and The separator for a wound secondary battery according to claim 2, wherein the separator is one or more selected from the group consisting of those modified products.   The separator for a wound secondary battery according to claim 2 or 3, wherein the PVDF polymer material has a particle shape.   The adhesive layer further includes heat-resistant particles, and the total volume of the heat-resistant particles is 100 to 250% by volume with respect to the total volume of the PVDF polymer material. The separator for wound secondary batteries according to any one of the above.   The separator for a wound secondary battery according to any one of claims 2 to 5, wherein a porosity of the adhesive layer is 45% by volume or less.   The separator for a wound secondary battery according to any one of claims 2 to 6, wherein the adhesive layer has a thickness of 0.5 to 1.5 µm. The manufacturing method of the separator for winding type secondary batteries including the process of forming the said adhesive layer on the said base material layer by applying the slurry containing the material which comprises an adhesive layer on a base material layer, and making it dry Because
The separator for a wound type secondary battery is:
Immersing the wound secondary battery separator in an electrolytic electrolyte for evaluation in which 1M LiBF ₄ is dissolved in propylene carbonate;
The winding type secondary battery separator is heated to at least 125 ° C. at a rate of 5 ° C./min with a constant load of 0.5 MPa applied to the pressing member for pressing the winding type secondary battery separator. And a step of measuring the displacement amount of the pressing member at each temperature, and when performing a thermomechanical analysis, the displacement amount of the pressing member at 75 ° C. and the displacement amount of the pressing member at 125 ° C. A method for producing a separator for a wound secondary battery, wherein there is a positive thickness change of 0.1 to 1.0 μm with respect to a base line connecting the two. A positive electrode;
A negative electrode,
A flat wound element comprising: the wound secondary battery separator according to any one of claims 1 to 7 interposed between the positive electrode and the negative electrode. The flat winding element according to claim 9,
An electrolyte for a secondary battery in which the flat winding element is immersed,
The adhesive layer is
The secondary battery electrolyte and the wound secondary battery separator having the same mass as the secondary battery electrolyte are sealed in a sealed container, and the secondary battery is heated at a rate of 5 ° C./min. A wound secondary battery having an endothermic peak in a range of 80 to 105 ° C when differential thermal analysis of a mixture of an electrolytic solution and a separator for a wound secondary battery is performed. It is a manufacturing method of the winding type rechargeable battery according to claim 10,
A step of producing a secondary battery before pressure bonding by enclosing the flat wound element and the electrolyte for a secondary battery in an exterior material;
A step of producing a wound secondary battery by compressing the pre-crimped secondary battery while heating at a temperature of ± 10 ° C. at which the endothermic peak is obtained, A method for manufacturing a wound secondary battery.

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