Separator for nonaqueous secondary battery and nonaqueous secondary battery

Abstract

The present application relates to a separator for nonaqueous secondary batteries and a nonaqueous secondary battery. A separator for nonaqueous secondary batteries, which has a porous substrate and a heat-resistant porous layer provided on one side or both sides of the porous substrate, the heat-resistant porous layer containing a polyvinylidene fluoride-based resin A, a polyvinylidene fluoride-based resin B, and a filler, the polyvinylidene fluoride-based resin A being a polyvinylidene fluoride-based resin containing a tetrafluoroethylene unit, the polyvinylidene fluoride-based resin B being a polyvinylidene fluoride-based resin other than the polyvinylidene fluoride-based resin A, the polyvinylidene fluoride-based resin B being a homopolymer of vinylidene fluoride or a copolymer of vinylidene fluoride and a monomer other than tetrafluoroethylene, the average primary particle diameter of the filler included in the heat-resistant porous layer being 0.01 to 0.5 µm.

Description

[0001] This application is a divisional application of the invention application filed on February 13, 2020, with application number 202080021604.8 and title "Separator for Non-Aqueous Secondary Batteries and Non-Aqueous Secondary Batteries". Technical Field

[0002] This invention relates to a separator for non-aqueous secondary batteries and a non-aqueous secondary battery. Background Technology

[0003] For the separator, which is one of the components constituting a non-aqueous secondary battery, heat resistance is required to ensure battery safety; that is, the membrane should not easily break or shrink even when the internal temperature of the battery becomes high. As a separator with improved heat resistance, it is known to have a porous layer containing fillers on a porous substrate. For example, Patent Document 1 discloses a separator having a porous layer containing at least one type of inorganic particles, namely metal oxide particles and metal hydroxide particles, on a porous substrate.

[0004] Furthermore, the diaphragm requires adhesiveness, meaning it should not easily peel off from the electrode even when subjected to external impact or when the electrode expands and contracts during charging and discharging. Diaphragms that improve adhesion to the electrode are known to have a resin layer containing a resin exhibiting adhesiveness to the electrode on a porous substrate. For example, Patent Document 2 discloses a diaphragm having a porous layer containing a polyvinylidene fluoride resin on a porous substrate.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent No. 5757363

[0008] Patent Document 2: Japanese Patent No. 4127989 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] During battery manufacturing, dry hot pressing (a hot pressing process performed without impregnating the separator with electrolyte) is sometimes applied to a laminate formed by placing a separator between the positive and negative electrodes. If the separator and electrodes are well bonded through dry hot pressing, misalignment between the separator and electrodes is less likely to occur during battery manufacturing, thus improving the battery yield. A separator with heat resistance and good adhesion to the electrodes through dry hot pressing is desired.

[0011] The implementation of this disclosure is based on the above circumstances.

[0012] The purpose of this disclosure is to provide a separator for non-aqueous secondary batteries that has heat resistance and excellent adhesion to the electrodes based on dry hot pressing, and to achieve this purpose.

[0013] Methods for solving problems

[0014] The specific means used to solve the aforementioned problems include the following methods.

[0015] [1] A separator for a non-aqueous secondary battery, comprising a porous substrate and a heat-resistant porous layer disposed on one or both sides of the porous substrate, wherein the heat-resistant porous layer contains polyvinylidene fluoride resin A, polyvinylidene fluoride resin B, and filler, wherein the polyvinylidene fluoride resin A is a polyvinylidene fluoride resin containing tetrafluoroethylene units, the polyvinylidene fluoride resin B is a polyvinylidene fluoride resin other than the polyvinylidene fluoride resin A, and the average primary particle size of the filler contained in the heat-resistant porous layer is 0.01 μm to 1.0 μm.

[0016] [2] The non-aqueous secondary battery separator as described in [1], wherein the average primary particle size of the filler contained in the aforementioned heat-resistant porous layer is 0.01 μm to 0.5 μm.

[0017] [3] The non-aqueous secondary battery separator as described in [1] or [2], wherein the aforementioned filler comprises at least one selected from the group consisting of metal sulfate particles, metal hydroxide particles, metal oxide particles and metal nitride particles.

[0018] [4] The non-aqueous secondary battery separator as described in any one of [1] to [3], wherein the volume percentage of the aforementioned filler in the aforementioned heat-resistant porous layer is 30% to 90% by volume.

[0019] [5] A non-aqueous secondary battery separator as described in any one of [1] to [4], wherein the melting point of the aforementioned polyvinylidene fluoride resin A is 120°C to 150°C.

[0020] [6] A non-aqueous secondary battery separator as described in any one of [1] to [5], wherein the weight-average molecular weight of the aforementioned polyvinylidene fluoride resin A is 600,000 to 3,000,000.

[0021] [7] A non-aqueous secondary battery separator as described in any one of [1] to [6], wherein the melting point of the aforementioned polyvinylidene fluoride resin B is 120°C to 173°C.

[0022] [8] A non-aqueous secondary battery separator as described in any one of [1] to [7], wherein the weight-average molecular weight of the aforementioned polyvinylidene fluoride resin B is 300,000 to 3,000,000.

[0023] [9] A non-aqueous secondary battery separator as described in any one of [1] to [8], wherein the aforementioned polyvinylidene fluoride resin B is a polyvinylidene fluoride resin containing hexafluoropropylene units.

[0024]

[10] The separator for non-aqueous secondary batteries as described in any one of [1] to [9], wherein the porosity of the aforementioned heat-resistant porous layer is 30% to 90%.

[0025]

[11] A non-aqueous secondary battery comprising a positive electrode, a negative electrode, and a separator for a non-aqueous secondary battery disposed between the aforementioned positive electrode and the aforementioned negative electrode, wherein the aforementioned non-aqueous secondary battery obtains an electromotive force by lithium doping and dedoping.

[0026] The effects of the invention

[0027] According to this disclosure, a separator for non-aqueous secondary batteries that has heat resistance and excellent adhesion to electrodes based on dry hot pressing can be provided. Detailed Implementation

[0028] The following describes embodiments of this disclosure. These descriptions and examples are illustrative of the embodiments and do not limit the scope of the embodiments.

[0029] In this disclosure, the range of values ​​indicated by “~” represents the range of values ​​before and after “~” as the minimum and maximum values, respectively.

[0030] In this disclosure, the term "process" includes not only independent processes, but also processes that achieve the desired purpose of the process, even if they cannot be clearly distinguished from other processes.

[0031] In this disclosure, when referring to the amount of each component in the composition, if there are multiple substances belonging to each component in the composition, unless otherwise specified, it refers to the total amount of those multiple substances present in the composition.

[0032] In this disclosure, the particles belonging to each component may be of multiple types. In the case where multiple particles belonging to each component are present in the composition, unless otherwise specified, the particle size of each component refers to a value relative to a mixture of the multiple particles present in the composition.

[0033] In this disclosure, the term "MD direction" refers to the longitudinal direction in the manufacture of a long, porous substrate and diaphragm, and the term "TD direction" refers to the direction orthogonal to the "MD direction". In this disclosure, the "MD direction" is also referred to as the "mechanical direction", and the "TD direction" is referred to as the "width direction".

[0034] In this disclosure, when the layering relationship of the layers constituting the diaphragm is presented using "upper" and "lower", the layer closer to the substrate is referred to as "lower" and the layer farther from the substrate is referred to as "upper".

[0035] In this publication, the expression “(meth)propene-” means that it can be any group of “propene-” and “methpropene-”.

[0036] In this disclosure, the term "monomer unit" in copolymers or resins refers to the structural unit of copolymers or resins, which is the structural unit formed by the polymerization of monomers.

[0037] In this disclosure, the term "heat-resistant resin" refers to a resin with a melting point of 200°C or higher, or a resin that does not have a melting point but has a decomposition temperature of 200°C or higher. That is, the heat-resistant resin in this disclosure is a resin that does not melt or decompose in a temperature range below 200°C.

[0038] In this disclosure, the hot pressing process in which the diaphragm is impregnated with electrolyte is referred to as "wet hot pressing," and the hot pressing process in which the diaphragm is not impregnated with electrolyte is referred to as "dry hot pressing."

[0039] In this publication, vinylidene fluoride is referred to as “VDF”, tetrafluoroethylene as “TFE”, and hexafluoropropylene as “HFP”.

[0040] <Separator for non-aqueous secondary batteries>

[0041] The non-aqueous secondary battery separator (also referred to as "separator" in this disclosure) comprises a porous substrate and a heat-resistant porous layer disposed on one or both sides of the porous substrate.

[0042] In the diaphragm of this disclosure, the heat-resistant porous layer contains at least polyvinylidene fluoride (PVDF) resin A and PVDF resin B as binder resins. PVDF resin A is a PVDF resin containing tetrafluoroethylene units, and PVDF resin B is a PVDF resin other than PVDF resin A. In this disclosure, PVDF resin A is also referred to as "PVDF resin A," and PVDF resin B is also referred to as "PVDF resin B."

[0043] PVDF-based resin B is a polyvinylidene fluoride resin other than PVDF-based resin A, that is, a polyvinylidene fluoride resin that does not contain tetrafluoroethylene units.

[0044] In the diaphragm of this disclosure, the heat-resistant porous layer contains filler, and the average primary particle size of the filler contained in the heat-resistant porous layer is 0.01 μm to 1.0 μm.

[0045] For the separator of this disclosure, the heat resistance of the porous layer and the separator is improved by including filler in the porous layer disposed on one or both sides of the porous substrate. From the viewpoints of stability relative to the electrolyte, electrochemical stability, adhesion to the electrode, and heat resistance, polyvinylidene fluoride (PVDF) resins are suitable as binder resins for the porous layer. By using PVDF resins as binder resins for the porous layer, a separator suitable for use in non-aqueous secondary batteries can be obtained.

[0046] From the above perspective, the heat-resistant porous layer of the diaphragm in this disclosure contains polyvinylidene fluoride (PVDF) resin and fillers. Furthermore, the PVDF resin in the heat-resistant porous layer of the diaphragm in this disclosure is either PVDF resin A or PVDF resin B, and the average primary particle size of the fillers contained in the heat-resistant porous layer is 0.01 μm to 1.0 μm. The diaphragm constructed in this way exhibits heat resistance and excellent adhesion to the electrodes based on dry hot pressing. The mechanism is speculated as follows.

[0047] It is speculated that by making the average primary particle size of the filler less than 1.0 μm, i.e., the particle size of the filler is small, the surface area (specific surface area) of the filler per unit volume increases. Therefore, the number of contact points between the filler and the binder resin increases, thereby suppressing the shrinkage of the heat-resistant porous layer when exposed to high temperatures. It is also speculated that by densely filling the porous layer with small-particle-size fillers, the shrinkage of the heat-resistant porous layer when exposed to high temperatures is also suppressed.

[0048] It is speculated that by making the average primary particle size of the filler less than 1.0 μm, there are fewer protrusions on the surface of the heat-resistant porous layer, resulting in excellent adhesion between the heat-resistant porous layer and the electrode and the porous substrate.

[0049] By ensuring that the average primary particle size of the filler is above 0.01 μm, the aggregation of the filler particles is suppressed, resulting in high uniformity of the surface properties of the heat-resistant porous layer. It is speculated that the heat-resistant porous layer with high surface uniformity exhibits excellent adhesion to the electrode and the porous substrate.

[0050] Furthermore, although the detailed mechanism is unclear, the heat-resistant porous layer containing PVDF-based resin A and PVDF-based resin B exhibits superior adhesion to the electrode based on dry hot pressing compared to the heat-resistant porous layer containing a single type of polyvinylidene fluoride resin. The heat-resistant porous layer containing PVDF-based resin A and PVDF-based resin B demonstrates superior adhesion to the electrode based on dry hot pressing not only for electrodes formed using slurries obtained by dissolving binder resins (e.g., polyvinylidene fluoride resins) in solvents, but also for electrodes formed using slurries obtained by dispersing particulate binders (e.g., styrene-butadiene copolymer particles, polyvinylidene fluoride resin particles) in water.

[0051] It is speculated that the above effects complement each other, thereby giving the diaphragm of this disclosure heat resistance and excellent adhesion to the electrodes based on dry hot pressing.

[0052] The following describes in detail the porous substrate and heat-resistant porous layer of the diaphragm in this disclosure.

[0053] [Porous Substrate]

[0054] In this disclosure, the term "porous substrate" refers to a substrate having pores or voids internally. Examples of such substrates include microporous membranes; porous sheets such as nonwoven fabrics and paper formed from fibrous materials; composite porous sheets obtained by laminating one or more other porous layers on these microporous membranes or porous sheets; and so on. In this disclosure, from the viewpoint of membrane thinning and strength, microporous membranes are preferred. A microporous membrane is defined as a membrane that has a structure with a large number of interconnected micropores internally, allowing gas or liquid to pass through from one side to the other.

[0055] The preferred material for a porous substrate is one that is electrically insulating; either organic or inorganic materials are acceptable.

[0056] To impart a shut-off function to the porous substrate, the porous substrate preferably comprises a thermoplastic resin. The shut-off function refers to the function that, when the battery temperature rises, the constituent material melts and blocks the pores of the porous substrate, thereby blocking ion movement and preventing thermal runaway of the battery. As a thermoplastic resin, a thermoplastic resin with a melting point below 200°C is preferred. Examples of thermoplastic resins include polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; etc., with polyolefins being preferred.

[0057] As a porous substrate, a microporous membrane comprising polyolefin (referred to as "polyolefin microporous membrane" in this disclosure) is preferred. Examples of polyolefin microporous membranes suitable for existing battery separators can be cited as examples, and polyolefin microporous membranes having sufficient mechanical properties and ion permeability are preferred.

[0058] From the viewpoint of presenting a shut-off function, the polyolefin microporous membrane is preferably a microporous membrane containing polyethylene, and the content of polyethylene is preferably 95% by mass or more relative to the overall mass of the polyolefin microporous membrane.

[0059] From the viewpoint of possessing heat resistance that makes the membrane less prone to damage when exposed to high temperatures, polyolefin microporous membranes are preferably microporous membranes containing polypropylene.

[0060] From the viewpoint of possessing both a shut-off function and heat resistance that prevents membrane rupture when exposed to high temperatures, polyolefin microporous membranes are preferably polyolefin microporous membranes comprising polyethylene and polypropylene. Examples of polyolefin microporous membranes comprising polyethylene and polypropylene include microporous membranes in which polyethylene and polypropylene are mixed in a single layer. From the viewpoint of simultaneously achieving a shut-off function and heat resistance, it is preferable that such a microporous membrane contains 95% or more of polyethylene and 5% or less of polypropylene by mass. Furthermore, from the viewpoint of simultaneously achieving a shut-off function and heat resistance, polyolefin microporous membranes with a structure having a laminated structure of two or more layers, with at least one layer comprising polyethylene and at least one layer comprising polypropylene, are also preferred.

[0061] The polyolefin included in the polyolefin microporous membrane is preferably a polyolefin with a weight-average molecular weight (Mw) of 100,000 to 5,000,000. If the Mw of the polyolefin is 100,000 or more, sufficient mechanical properties can be imparted to the microporous membrane. On the other hand, if the Mw of the polyolefin is 5,000,000 or less, the microporous membrane has good shut-off properties and is easy to form.

[0062] Examples of methods for manufacturing polyolefin microporous membranes include: extruding molten polyolefin resin from a T-die to form a sheet, crystallizing it, stretching it, and then heat-treating it to form a microporous membrane; extruding molten polyolefin resin together with plasticizers such as liquid paraffin from a T-die, cooling it to form a sheet, stretching it, extracting the plasticizer, and heat-treating it to form a microporous membrane; and so on.

[0063] Examples of porous sheets formed from fibrous materials include nonwoven fabrics, paper, and other porous sheets formed from fibrous materials of the following substances: polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; heat-resistant resins such as fully aromatic polyamides, polyamide-imides, polyimides, polyethersulfones, polysulfones, polyetherketones, and polyetherimides; cellulose; etc.

[0064] Examples of composite porous sheets include sheets obtained by laminating functional layers onto microporous membranes or porous sheets formed of fibrous materials. From the viewpoint that further functionalization can be achieved through the functional layers, such composite porous sheets are preferred. As functional layers, from the viewpoint of imparting heat resistance, examples include porous layers formed of heat-resistant resins and porous layers formed of heat-resistant resins and inorganic fillers. Examples of heat-resistant resins include one or more selected from fully aromatic polyamides, polyamide-imides, polyimides, polyethersulfones, polysulfones, polyetherketones, and polyetherimides. Examples of inorganic fillers include metal oxides such as alumina; metal hydroxides such as magnesium hydroxide; and so on. Examples of composite methods include: coating a functional layer onto a microporous membrane or porous sheet; bonding a microporous membrane or porous sheet to a functional layer using an adhesive; hot-pressing a microporous membrane or porous sheet to a functional layer; and so on.

[0065] To improve the wettability of the coating liquid used to form a heat-resistant porous layer, various surface treatments can be applied to the surface of the porous substrate without impairing its properties. Examples of surface treatments include corona treatment, plasma treatment, flame treatment, and ultraviolet irradiation treatment.

[0066] [Characteristics of porous substrates]

[0067] Regarding the thickness of the porous substrate, from the viewpoint of improving the energy density of the battery, it is preferably 25 μm or less, more preferably 20 μm or less, and even more preferably 15 μm or less. From the viewpoint of the manufacturing yield of the separator and the manufacturing yield of the battery, it is preferably 3 μm or more, and more preferably 5 μm or more.

[0068] From the viewpoint of ion permeability or suppression of battery short circuits, the Gurley value (JISP8117:2009) of the porous substrate is preferably 50 s / 100 mL to 800 s / 100 mL, more preferably 50 s / 100 mL to 400 s / 100 mL.

[0069] From the viewpoint of obtaining appropriate thin-film resistance and shut-off function, the porosity of the porous substrate is preferably 20% to 60%. The porosity ε (%) of the porous substrate is calculated using the following formula.

[0070] ε={1-(Wa / da+Wb / db+Wc / dc+…+Wn / dn) / t}×100

[0071] Here, the constituent materials of the porous substrate are a, b, c, ..., n, and the masses of each constituent material are Wa, Wb, Wc, ..., Wn (g / cm³). 2The true densities of each constituent material are da, db, dc, ..., dn (g / cm³). 3 The thickness of the porous substrate is t (cm).

[0072] From the perspective of the manufacturing yield of the separator and the battery, the puncture strength of the porous substrate is preferably 160 gf (1.6 N) or higher, and more preferably 200 gf (2.0 N) or higher. The puncture strength of the porous substrate refers to the maximum puncture strength (gf) measured by puncture testing using a KatoTech KES-G5 handheld compression tester under the conditions of a needle tip curvature radius of 0.5 mm and a puncture speed of 2 mm / s.

[0073] The average pore size of the porous substrate is preferably between 15 nm and 100 nm. If the average pore size of the porous substrate is 15 nm or more, ions can easily move, resulting in good battery performance. From this perspective, the average pore size of the porous substrate is more preferably 25 nm or more, and even more preferably 30 nm or more. If the average pore size of the porous substrate is 100 nm or less, the peel strength between the porous substrate and the heat-resistant porous layer can be improved, and good shut-off function can also be exhibited. From this perspective, the average pore size of the porous substrate is more preferably 90 nm or less, and even more preferably 80 nm or less. The average pore size of the porous substrate is measured using a perm pore size analyzer, according to ASTM E1294-89, using a perm pore size analyzer (PMI CFP-1500-A).

[0074] [Heat-resistant porous layer]

[0075] In the diaphragm disclosed herein, a heat-resistant porous layer is disposed as the outermost layer of the diaphragm on one or both sides of a porous substrate and is bonded to the electrodes when the diaphragm is overlapped with the electrodes and subjected to pressure or hot pressing. The heat-resistant porous layer is a layer that has a structure with a large number of micropores inside, and these micropores are interconnected, allowing gas or liquid to pass through from one side to the other side.

[0076] In the separator disclosed herein, the heat-resistant porous layer may exist only on one side of the porous substrate or on both sides of the porous substrate. When the heat-resistant porous layer exists on both sides of the porous substrate, the separator exhibits superior heat resistance. Furthermore, it is less prone to curling within the separator, resulting in excellent maneuverability during battery manufacturing. When the heat-resistant porous layer exists only on one side of the porous substrate, the separator exhibits superior ion permeability. Additionally, the overall thickness of the separator can be suppressed, enabling the manufacture of batteries with higher energy density.

[0077] In the diaphragm of this disclosure, the heat-resistant porous layer contains at least PVDF-based resin A, PVDF-based resin B, and fillers. In the diaphragm of this disclosure, the heat-resistant porous layer may contain resins other than polyvinylidene fluoride-based resins, organic fillers, etc.

[0078] The following is a detailed description of the components contained in the heat-resistant porous layer of the diaphragm of this disclosure.

[0079] -PVDF-based resins A-

[0080] PVDF-based resin A includes any copolymers obtained by polymerizing only VDF (vinylidene fluoride) and TFE (tetrafluoroethylene), as well as copolymers obtained by polymerizing VDF, TFE and other monomers other than them.

[0081] Other monomers besides VDF and TFE that can constitute PVDF-based resin A include, for example, halogenated monomers such as trifluoroethylene, trifluorochloroethylene, fluoroethylene, trichloroethylene, and hexafluoropropylene; monomers with carboxyl groups (e.g., (meth)acrylic acid, (meth)acrylate, maleic acid, maleic anhydride, maleic esters, and their fluorinated derivatives); and so on. PVDF-based resin A may contain one or more monomer units derived from these monomers.

[0082] The preferred melting point of PVDF-based resin A is 120℃ to 150℃. If the melting point of PVDF-based resin A is below 150℃, its flexibility is easily improved during dry hot pressing, which is beneficial to the adhesion between the heat-resistant porous layer and the electrode. If the melting point of PVDF-based resin A is above 120℃, the heat resistance of the diaphragm is easily ensured.

[0083] The melting point of polyvinylidene fluoride (PVDF) resins is determined by differential scanning calorimetry (DSC) curves. Specifically, the PVDF resin is placed in the sample chamber of a DSC meter, and under a nitrogen atmosphere, the temperature is increased at a rate of 5°C / min within a range of 30°C to 200°C to obtain the DSC curve. The temperature of the endothermic peak appearing in the DSC curve is taken as the melting point of the PVDF resin. If multiple endothermic peaks exist, the temperature of the lowest endothermic peak is taken as the melting point. For the PVDF resin sample, the porous layer is peeled off from the porous substrate, and the filler is removed from the peeled porous layer.

[0084] The weight-average molecular weight (Mw) of PVDF-based resin A is preferably between 600,000 and 3,000,000. If the Mw of PVDF-based resin A is 3,000,000 or less, the viscosity of the coating liquid used to form a heat-resistant porous layer will not become excessively high, making it easier to form a heat-resistant porous layer with a highly uniform porous structure. Furthermore, under mild conditions of dry hot pressing, the flexibility of PVDF-based resin A is easily improved, which is beneficial to the adhesion between the heat-resistant porous layer and the electrode. From these perspectives, the Mw of PVDF-based resin A is preferably 3,000,000 or less, more preferably 2,500,000 or less, and even more preferably 2,300,000 or less. If the Mw of PVDF-based resin A is 600,000 or more, it is possible to impart mechanical properties to the heat-resistant porous layer that can withstand adhesion treatment with the electrode. From this perspective, the Mw of PVDF-based resin A is preferably 600,000 or more, more preferably 650,000 or more, and even more preferably 700,000 or more.

[0085] -PVDF-based resins B-

[0086] Examples of PVDF-based resin B include homopolymers of VDF (i.e., polyvinylidene fluoride); copolymers of VDF with monomers other than TFE (polyvinylidene fluoride copolymers); and mixtures thereof. Examples of monomers other than TFE that can copolymerize with VDF include hexafluoropropylene, trifluoroethylene, trifluorochloroethylene, fluoroethylene, trichloroethylene, etc., and one or more of these monomers may be used.

[0087] The preferred melting point of PVDF-based resin B is 120℃ to 173℃. If the melting point of PVDF-based resin B is below 173℃, its flexibility is easily improved during dry hot pressing, which is beneficial to the adhesion between the heat-resistant porous layer and the electrode. If the melting point of PVDF-based resin B is above 120℃, the heat resistance of the diaphragm is easily ensured.

[0088] The weight-average molecular weight (Mw) of PVDF-based resin B is preferably between 300,000 and 3,000,000. If the Mw of PVDF-based resin B is 3,000,000 or less, the viscosity of the coating liquid used to form a heat-resistant porous layer will not become excessively high, making it easier to form a heat-resistant porous layer with a highly uniform porous structure. Furthermore, under mild conditions of dry hot pressing, the flexibility of PVDF-based resin B is easily improved, which is beneficial to the adhesion between the heat-resistant porous layer and the electrode. From these perspectives, the Mw of PVDF-based resin B is preferably 3,000,000 or less, more preferably 2,000,000 or less, and even more preferably 1,800,000 or less. If the Mw of PVDF-based resin B is 300,000 or more, it is possible to impart mechanical properties to the heat-resistant porous layer that can withstand adhesion treatment with the electrode. From this perspective, the Mw of PVDF-based resin B is preferably 300,000 or more, more preferably 350,000 or more, and even more preferably 400,000 or more. If the Mw of PVDF resin A is high, it can impart mechanical properties that can withstand the bonding treatment with the electrode. Therefore, it is sometimes preferable for the Mw of PVDF resin B to be less than 300,000.

[0089] From the viewpoint of adhesion to the electrode, a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) (VDF-HFP copolymer) is preferred as PVDF-based resin B. In this disclosure, the VDF-HFP copolymer as PVDF-based resin B includes any copolymer obtained by polymerizing only VDF and HFP, and copolymers obtained by polymerizing VDF, HFP, and other monomers (excluding TFE). For the VDF-HFP copolymer, by increasing or decreasing the content of HFP units, the crystallinity, heat resistance, and solubility relative to the electrolyte of the copolymer can be controlled within a suitable range.

[0090] Other monomers besides VDF, HFP, and TFE that can constitute VDF-HFP copolymers include halogenated monomers such as trifluoroethylene, trifluorochloroethylene, fluoroethylene, and trichloroethylene; monomers with carboxyl groups (e.g., (meth)acrylic acid, (meth)acrylate, maleic acid, maleic anhydride, maleic esters, and their fluorinated derivatives); and so on. VDF-HFP copolymers may contain one or more monomer units derived from these monomers.

[0091] The VDF-HFP copolymer, which is PVDF-based resin B, may contain monomer units other than VDF, HFP, and TFE, but preferably the content of other monomer units is less than the content of HFP units. The content of other monomer units is preferably less than 8 mol% relative to all monomer units, more preferably less than 5 mol%.

[0092] The total content of PVDF resin A and PVDF resin B in the heat-resistant porous layer is preferably 85% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 100% by mass, relative to the total amount of binder resin contained in the heat-resistant porous layer.

[0093] The total content of PVDF resin A and PVDF resin B in the heat-resistant porous layer is preferably 10% to 90% by volume, more preferably 20% to 80% by volume, and even more preferably 30% to 70% by volume, relative to the total amount of solid components contained in the heat-resistant porous layer.

[0094] The mass ratio of PVDF resin A to PVDF resin B contained in the heat-resistant porous layer (PVDF resin A: PVDF resin B) is preferably 5:95 to 95:5, more preferably 15:85 to 85:15, and even more preferably 25:75 to 75:25.

[0095] The content of PVDF resin A in the heat-resistant porous layer is preferably 5% to 95% by mass, more preferably 15% to 85% by mass, and even more preferably 25% to 75% by mass, relative to the total amount of binder resin contained in the heat-resistant porous layer.

[0096] The content of PVDF resin A in the heat-resistant porous layer is preferably 1 vol% to 70 vol% relative to the total amount of solid components contained in the heat-resistant porous layer, more preferably 5 vol% to 65 vol%, and even more preferably 10 vol% to 60 vol%.

[0097] The content of PVDF-based resin B in the heat-resistant porous layer is preferably 5% to 95% by mass, more preferably 15% to 85% by mass, and even more preferably 25% to 75% by mass, relative to the total amount of binder resin contained in the heat-resistant porous layer.

[0098] The content of PVDF resin B in the heat-resistant porous layer is preferably 1 vol% to 70 vol% relative to the total amount of solid components contained in the heat-resistant porous layer, more preferably 5 vol% to 65 vol%, and even more preferably 10 vol% to 60 vol%.

[0099] Methods for manufacturing polyvinylidene fluoride (PVDF) resins include emulsion polymerization and suspension polymerization. Alternatively, commercially available PVDF resins can also be used.

[0100] -Other Resins-

[0101] The heat-resistant porous layer may contain resins other than polyvinylidene fluoride resins.

[0102] Other examples of resins include fluorinated rubbers, styrene-butadiene copolymers, acrylic resins, styrene-acrylic resins, homopolymers or copolymers of vinyl nitrile compounds (acrylonitrile, methacrylonitrile, etc.), carboxymethyl cellulose, hydroxyalkyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, and polyethers (ethylene oxide, propylene oxide, etc.).

[0103] The content of resins other than polyvinylidene fluoride resins in the heat-resistant porous layer is preferably 50% by mass or less, more preferably 30% by mass or less, and even more preferably 10% by mass or less, relative to the total amount of binder resin contained in the heat-resistant porous layer.

[0104] -filler-

[0105] The diaphragm of this disclosure contains filler in a heat-resistant porous layer. The average primary particle size of the filler contained in the heat-resistant porous layer is 0.01 μm to 1.0 μm.

[0106] From the viewpoint of suppressing the shrinkage of the heat-resistant porous layer when exposed to high temperatures and from the viewpoint of being beneficial to the thin film formation of the heat-resistant porous layer, the average primary particle size of the filler contained in the heat-resistant porous layer is 1.0 μm or less, more preferably 0.8 μm or less, and even more preferably 0.5 μm or less.

[0107] From the viewpoint of suppressing the aggregation of fillers to form a highly uniform heat-resistant porous layer, the average primary particle size of the fillers contained in the heat-resistant porous layer is 0.01 μm or more, more preferably 0.02 μm or more, and even more preferably 0.03 μm or more.

[0108] The average primary particle size of the packing material can be determined by measuring the major diameter of 100 randomly selected packing materials observed using a scanning electron microscope (SEM) and averaging these 100 major diameters. In cases where the primary particle size of the packing material is small and the major diameter is difficult to determine, or where significant agglomeration of the packing material makes it impossible to determine the major diameter, the BET specific surface area (m²) of the packing material can be measured. 2 / g), assuming the filler is a sphere, calculate the average primary particle size using the following formula.

[0109] Average primary particle size (μm) = 6 ÷ [specific gravity (g / cm³)] 3 )×BET specific surface area (m 2 / g)]

[0110] BET specific surface area (m²) 2The nitrogen content (g) was determined using the BET multi-point method, which is a gas adsorption method using nitrogen. In the gas adsorption method, nitrogen is adsorbed onto the packing material at the boiling point of liquid nitrogen (-196°C).

[0111] The samples used for SEM-based observation or BET surface area determination are either fillers used as materials forming the heat-resistant porous layer or fillers removed from the heat-resistant porous layer of the diaphragm. There are no limitations on the method for removing the filler from the heat-resistant porous layer of the diaphragm; examples include immersing the heat-resistant porous layer peeled from the diaphragm in an organic solvent that dissolves the polyvinylidene fluoride resin but not the organic filler, dissolving the polyvinylidene fluoride resin with the organic solvent, and then removing both the inorganic and organic fillers. If the filler is only inorganic, the heat-resistant porous layer peeled from the diaphragm can also be heated to approximately 800°C to remove the binder resin and thus remove the filler.

[0112] The particle shape of the filler is not limited; spherical, elliptical, plate-like, needle-like, and amorphous particles are all acceptable. From the viewpoint of suppressing battery short circuits or easily achieving dense filling of the filler, the filler contained in the heat-resistant porous layer is preferably plate-like or spherical particles, or non-agglomerated primary particles.

[0113] From the viewpoint of the heat resistance of the diaphragm, the volume percentage of the filler in the heat-resistant porous layer is preferably 30% by volume or more, more preferably 40% by volume or more, and even more preferably 50% by volume or more. From the viewpoint of the formability of the heat-resistant porous layer and the viewpoint that the heat-resistant porous layer is not easily peeled off from the porous substrate, the volume percentage of the filler in the heat-resistant porous layer is preferably 90% by volume or less, more preferably 80% by volume or less, and even more preferably 75% by volume or less.

[0114] The volume ratio of polyvinylidene fluoride resin to filler in the heat-resistant porous layer is preferably 10:90 to 70:30, more preferably 15:85 to 65:35, and even more preferably 20:80 to 60:40.

[0115] The filler contained in the heat-resistant porous layer can be any of the following: inorganic filler, organic filler, or a mixture of inorganic and organic fillers. A single filler can be used, or two or more can be used in combination.

[0116] As a filler included in a heat-resistant porous layer, a filler that is stable in the electrolyte and electrochemically stable is preferred.

[0117] Examples of inorganic fillers include particles of metal hydroxides such as magnesium hydroxide, aluminum hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, cerium hydroxide, nickel hydroxide, and boron hydroxide; particles of metal oxides such as magnesium oxide, aluminum oxide, boehmite (alumina monohydrate), titanium dioxide, silicon dioxide, zirconium oxide, barium titanate, and zinc oxide; particles of metal carbonates such as magnesium carbonate and calcium carbonate; particles of metal sulfates such as barium sulfate, magnesium sulfate, and calcium sulfate; particles of metal nitrides such as magnesium nitride, aluminum nitride, calcium nitride, and titanium nitride; metal fluorides such as magnesium fluoride and calcium fluoride; clay minerals such as calcium phosphate, apatite, calcium silicate, and talc; and so on. Inorganic fillers can also be obtained by surface modification using silane coupling agents, etc. These inorganic fillers can be used alone or in combination of two or more.

[0118] From the viewpoint of stability relative to the electrolyte and electrochemical stability, at least one inorganic filler selected from the group consisting of metal sulfate particles, metal hydroxide particles, metal oxide particles, and metal nitride particles is preferred. Furthermore, from the viewpoint of minimizing the decomposition of the electrolyte or electrolyte solution and thus minimizing the generation of gas inside the battery, metal sulfate particles are preferred.

[0119] Examples of metal sulfate particles include barium sulfate (BaSO4) particles, strontium sulfate (SrSO4) particles, calcium sulfate (CaSO4) particles, calcium sulfate dihydrate (CaSO4·2H2O) particles, alunite (KAl3(SO4)2(OH)6) particles, and potassium ferrous sulfate (KFe3(SO4)2(OH)6) particles. Among these, barium sulfate (BaSO4) particles are the most preferred. A single type of metal sulfate particle can be used, or two or more can be used in combination.

[0120] -Organic fillers-

[0121] Examples of organic fillers include particles formed from cross-linked polymers such as cross-linked poly(meth)acrylic acid, cross-linked poly(meth)acrylate, cross-linked polysiloxane, cross-linked polystyrene, cross-linked divinylbenzene, styrene-divinylbenzene copolymer cross-links, melamine resin, phenolic resin, and benzoguanamine-formaldehyde condensate; particles formed from heat-resistant polymers such as polysulfone, polyacrylonitrile, aromatic polyamide, and polyacetal; and so on. These organic fillers can be used individually or in combination of two or more.

[0122] -Other ingredients-

[0123] In the diaphragm disclosed herein, the heat-resistant porous layer may contain additives such as dispersants (e.g., surfactants), wetting agents, defoamers, and pH adjusters. In the coating solution used to form the heat-resistant porous layer, dispersants are added for the purpose of improving dispersibility, coatability, or storage stability. In the coating solution used to form the heat-resistant porous layer, wetting agents, defoamers, and pH adjusters are added, for example, for the purpose of improving affinity with the porous substrate, inhibiting air intake into the coating solution, or adjusting the pH.

[0124] [Characteristics of heat-resistant porous layers]

[0125] From the viewpoint of the heat resistance of the separator and its adhesion to the electrode, the thickness of the heat-resistant porous layer is preferably 0.5 μm or more on one side, more preferably 1.0 μm or more on one side. From the viewpoint of ion permeability and battery energy density, it is preferably 5.0 μm or less on one side, more preferably 4.0 μm or less on one side.

[0126] Regarding the thickness of the heat-resistant porous layer, whether the heat-resistant porous layer exists only on one side of the porous substrate or on both sides, the total thickness of both sides is preferably 1.0 μm or more, more preferably 2.0 μm or more, preferably 10.0 μm or less, and more preferably 8.0 μm or less.

[0127] When a heat-resistant porous layer is disposed on both sides of a porous substrate, the difference between the thickness of the heat-resistant porous layer on one side and the thickness of the heat-resistant porous layer on the other side is preferably less than 25% of the total thickness of both sides, and the smaller the difference, the better.

[0128] For the mass of the heat-resistant porous layer per unit area, considering both the heat resistance of the diaphragm and its adhesion to the electrode, the preferred mass, totaling 1.0 g / m², is 1.0 g / m². 2 The above, more preferably 2.0 g / m 2 The above is further preferred to be 3.5g / m 2 The above is further preferred to be 4.0 g / m 2 The above is further preferred to be 4.5 g / m 2 Considering both ion permeability and battery energy density, the preferred value is 30.0 g / m². 2 The following is more preferably 20.0 g / m 2 The following is a further preferred value of 10.0 g / m 2 The following is a further preferred value: 8.0 g / m 2 the following.

[0129] When a heat-resistant porous layer is provided on both sides of a porous substrate, from the viewpoint of suppressing membrane curling or improving the cycle characteristics of the battery, the mass difference between the heat-resistant porous layers on one side and the other side is preferably 25% by mass or less relative to the total mass of both sides.

[0130] Regarding the porosity of the heat-resistant porous layer, from the viewpoint of ion permeability, it is preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more. From the viewpoint of the mechanical strength of the heat-resistant porous layer and its adhesion to the electrode, it is preferably 90% or less, more preferably 80% or less, and even more preferably 70% or less. The porosity ε (%) of the heat-resistant porous layer is calculated using the following formula.

[0131] ε={1-(Wa / da+Wb / db+Wc / dc+…+Wn / dn) / t}×100

[0132] Here, the constituent materials of the heat-resistant porous layer are a, b, c, ..., n, and the masses of each constituent material are Wa, Wb, Wc, ..., Wn (g / cm³). 2 The true densities of each constituent material are da, db, dc, ..., dn (g / cm³). 3 The thickness of the heat-resistant porous layer is t (cm).

[0133] Regarding the average pore size of the heat-resistant porous layer, from the viewpoint that even when the heat-resistant porous layer is impregnated with electrolyte, the resin contained in the heat-resistant porous layer does not easily cause pore blockage, it is preferably 10 nm or more, more preferably 20 nm or more. From the viewpoint of the adhesion between the heat-resistant porous layer and the electrode or the viewpoint of excellent cycle characteristics and load characteristics of the battery, it is preferably 300 nm or less, more preferably 200 nm or less.

[0134] For the average pore size (nm) of the heat-resistant porous layer, assuming that all pores are cylindrical, it can be calculated using the following formula.

[0135] d = 4V / S

[0136] In the formula, d represents the average pore size (diameter) of the heat-resistant porous layer, and V represents the average pore size per 1m. 2 The pore volume of the heat-resistant porous layer, S represents the pore volume per 1m³. 2 Pore ​​surface area of ​​heat-resistant porous layers.

[0137] per 1m 2 The pore volume V of the heat-resistant porous layer is calculated from the porosity of the heat-resistant porous layer.

[0138] per 1m 2 The pore surface area S of the heat-resistant porous layer is determined by the following method.

[0139] First, by applying the BET formula in the nitrogen adsorption method, the specific surface area (m²) of the porous substrate is calculated from the amount of nitrogen adsorbed. 2 / g) and the specific surface area of ​​the membrane (m²) 2 / g). Their specific surface area (m²) 2 / g) multiplied by their respective unit area weight (g / m²) 2 ), calculate each of them per 1m 2 The pore surface area. Then, from every 1m 2 The pore surface area of ​​the diaphragm minus the area per 1m 2 The pore surface area of ​​the porous substrate is calculated per 1m². 2 The pore surface area S of the heat-resistant porous layer.

[0140] [Properties of the diaphragm]

[0141] Regarding the thickness of the separator in this disclosure, from the viewpoint of the mechanical strength of the separator, it is preferably 5 μm or more, more preferably 10 μm or more, and from the viewpoint of the energy density of the battery, it is preferably 35 μm or less, more preferably 30 μm or less, further preferably 25 μm or less, and even more preferably 20 μm or less.

[0142] From the viewpoint of the mechanical strength of the separator or the short-circuit withstand capability of the battery, the puncture strength of the separator in this disclosure is preferably 160 gf (1.6 N) to 1000 gf (9.8 N), more preferably 200 gf (2.0 N) to 600 gf (5.9 N). The method for measuring the puncture strength of the separator is the same as the method for measuring the puncture strength of porous substrates.

[0143] From the viewpoint of adhesion to the electrode, operability of the diaphragm, ion permeability, or mechanical strength, the porosity of the diaphragm in this disclosure is preferably 30% to 65%, more preferably 30% to 60%.

[0144] From the viewpoint of mechanical strength and battery load characteristics, the Gurley value (JISP8117:2009) of the separator in this disclosure is preferably 50 seconds / 100 mL to 800 seconds / 100 mL, more preferably 50 seconds / 100 mL to 450 seconds / 100 mL.

[0145] For the diaphragm of this disclosure, from the viewpoint of ion permeability, the value obtained by subtracting the Gurley value of the porous substrate from the Gurley value of the diaphragm is preferably 300 seconds / 100 mL or less, more preferably 150 seconds / 100 mL or less, and even more preferably 100 seconds / 100 mL or less. The lower limit of the value obtained by subtracting the Gurley value of the porous substrate from the Gurley value of the diaphragm is not particularly limited, but in the diaphragm of this disclosure, it is generally 10 seconds / 100 mL or more.

[0146] From the viewpoint of battery load characteristics, the thin-film resistance of the separator in this disclosure is preferably 1 Ω·cm. 2 ~10Ω·cm 2 Here, the membrane resistance, referred to as the membrane film resistance, is the resistance value when the membrane is impregnated with electrolyte. It is measured by an alternating current method at 20°C using a 1 mol / L LiBF4-propylene carbonate:ethylene carbonate (mass ratio 1:1) as the electrolyte. The lower the membrane film resistance, the better the ion permeability of the membrane.

[0147] From the viewpoint of ion permeability, the tortuosity of the diaphragm in this disclosure is preferably 1.2 to 2.8.

[0148] The water content (by mass) in the separator of this disclosure is preferably 1000 ppm or less. The lower the water content of the separator, the better the reaction between the electrolyte and water can be suppressed when the battery is formed, thus suppressing gas generation within the battery and improving the battery's cycle characteristics. From this viewpoint, the water content in the separator is more preferably 800 ppm or less, and even more preferably 500 ppm or less.

[0149] For the diaphragm of this disclosure, from the viewpoint of balancing shape stability and closing characteristics, the shrinkage rate during heat treatment at 120°C is preferably 12% or less in both the MD and TD directions.

[0150] For the diaphragm of this disclosure, the shrinkage rate in the MD direction during heat treatment at 135°C for 1 hour is preferably 40% or less, more preferably 30% or less, even more preferably 20% or less, even more preferably 15% or less, even more preferably 10% or less, and particularly preferably 0%.

[0151] For the diaphragm of this disclosure, the shrinkage rate in the TD direction during heat treatment at 135°C for 1 hour is preferably 40% or less, more preferably 30% or less, even more preferably 20% or less, even more preferably 15% or less, even more preferably 10% or less, and particularly preferably 0%.

[0152] For the diaphragm of this disclosure, the area shrinkage rate during heat treatment at 135°C for 1 hour is preferably 40% or less, more preferably 30% or less, even more preferably 20% or less, even more preferably 15% or less, even more preferably 10% or less, and particularly preferably 0%.

[0153] For the diaphragm of this disclosure, the shrinkage rate in the MD direction during heat treatment at 150°C for 1 hour is preferably 70% or less, more preferably 55% or less, even more preferably 45% or less, even more preferably 20% or less, and even more preferably 10% or less.

[0154] For the diaphragm of this disclosure, the shrinkage rate in the TD direction during heat treatment at 150°C for 1 hour is preferably 70% or less, more preferably 55% or less, even more preferably 45% or less, even more preferably 20% or less, and even more preferably 10% or less.

[0155] For the diaphragm of this disclosure, the area shrinkage rate during heat treatment at 150°C for 1 hour is preferably 70% or less, more preferably 55% or less, even more preferably 45% or less, even more preferably 20% or less, and even more preferably 10% or less.

[0156] The area shrinkage rate of the diaphragm after heat treatment at 135°C or 150°C for 1 hour was determined by the following method.

[0157] The diaphragm was cut into rectangles measuring 180mm in the MD direction and 60mm in the TD direction to prepare test pieces. Markings (points A and B, respectively) were made on the lines bisecting the TD direction, at points 20mm and 170mm from one end. Further markings (points C and D, respectively) were made on the lines bisecting the MD direction, at points 10mm and 50mm from one end. A clamp was installed on the marked test pieces (the clamp was positioned between the end closest to point A and point A), and the pieces were suspended in an oven with the temperature adjusted to 135℃ or 150℃. Heat treatment was performed for 1 hour under tension-free conditions. The lengths between points A and B and between points C and D were measured before and after heat treatment, and the area shrinkage rate was calculated using the following formula.

[0158] Area shrinkage rate (%) = {1 - (length of AB after heat treatment ÷ length of AB before heat treatment) × (length of CD after heat treatment ÷ length of CD before heat treatment)} × 100

[0159] The shrinkage rate of the diaphragm of this disclosure during heat treatment can be controlled, for example, by the content of filler in the heat-resistant porous layer, the thickness of the heat-resistant porous layer, and the porosity of the heat-resistant porous layer.

[0160] The diaphragm of this disclosure may also have other layers besides the porous substrate and the heat-resistant porous layer. Examples of having other layers include, for instance, having a heat-resistant porous layer on one side of the porous substrate and an adhesive porous layer on the other side of the porous substrate, primarily for bonding with the electrodes.

[0161] [Measuring method of the diaphragm]

[0162] The diaphragm disclosed herein can be manufactured, for example, by forming a heat-resistant porous layer on a porous substrate using a wet coating method or a dry coating method. In this disclosure, the wet coating method is a method of curing the coating layer in a coagulating liquid, and the dry coating method is a method of drying and curing the coating layer.

[0163] The following describes an example of a wet coating method. In the following description, PVDF-based resin A and PVDF-based resin B will be collectively referred to as adhesive resins.

[0164] The wet coating method is as follows: a coating liquid containing binder resin and filler is applied to a porous substrate, the coating layer is immersed in a coagulation liquid to cure, and then lifted out of the coagulation liquid for washing and drying.

[0165] For coating solutions used to form heat-resistant porous layers, the binder resin and filler are dissolved or dispersed in a solvent. Other components besides the binder resin and filler are dissolved or dispersed in the coating solution as needed.

[0166] The solvent used in the preparation of the coating solution includes a solvent that dissolves the adhesive resin (hereinafter also referred to as a "good solvent"). Examples of good solvents include polar amide solvents such as N-methylpyrrolidone, dimethylacetamide, and dimethylformamide.

[0167] From the viewpoint of forming a porous layer with a good porous structure, the solvent used in the preparation of the coating solution preferably contains a phase-separating agent that induces phase separation. Therefore, the solvent used in the preparation of the coating solution is preferably a mixture of a good solvent and a phase-separating agent. The phase-separating agent is preferably mixed with the good solvent in an amount that ensures a viscosity range suitable for coating. Examples of phase-separating agents include water, methanol, ethanol, propanol, butanol, butanediol, ethylene glycol, propylene glycol, and tripropylene glycol.

[0168] From the viewpoint of forming a good porous structure, the solvent used in the preparation of the coating liquid is preferably a mixed solvent of a good solvent and a phase separating agent, which contains more than 60% by mass of a good solvent and 5% to 40% by mass of a phase separating agent.

[0169] From the viewpoint of forming a good porous structure, the binder resin concentration of the coating liquid is preferably 3% to 10% by mass. From the viewpoint of forming a good porous structure, the filler concentration of the coating liquid is preferably 2% to 50% by mass.

[0170] The coating solution may contain dispersants such as surfactants, wetting agents, defoamers, pH adjusters, etc. As long as these additives are electrochemically stable within the operating range of non-aqueous secondary batteries and do not hinder the reaction within the battery, they can remain in the heat-resistant porous layer.

[0171] Examples of coating methods for applying coating liquid to porous substrates include Mayer rods, die coaters, reverse roller coaters, roller coaters, and gravure coaters. From a productivity standpoint, it is preferable to simultaneously apply the coating liquid to both sides of the porous substrate when a heat-resistant porous layer is formed on both sides of the substrate.

[0172] The coating layer can be cured by immersing a porous substrate with the coating layer in a coagulating liquid, inducing phase separation within the coating layer while simultaneously curing the binder resin. This yields a laminate consisting of a porous substrate and a heat-resistant porous layer.

[0173] The coagulation solution typically contains a good solvent and a phase-separating agent used in the preparation of the coating solution, and water. From a production perspective, the mixing ratio of the good solvent and the phase-separating agent is preferably consistent with the mixing ratio of the mixed solvent used in the preparation of the coating solution. From the viewpoint of porous structure formation and productivity, the water content in the coagulation solution is preferably 40% to 90% by mass. The temperature of the coagulation solution is, for example, 20°C to 50°C.

[0174] After the coating layer is cured in the coagulating liquid, the laminate is lifted from the coagulating liquid and washed with water. Washing removes the coagulating liquid from the laminate. Then, drying removes water from the laminate. Washing can be performed, for example, by conveying the laminate in a water bath. Drying can be performed, for example, by conveying the laminate in a high-temperature environment, blowing air onto the laminate, or contacting the laminate with hot rollers. The drying temperature is preferably 40°C to 80°C.

[0175] The diaphragm of this disclosure can also be manufactured using a dry coating method. The dry coating method involves applying a coating liquid to a porous substrate, allowing the coating layer to dry and the solvent to evaporate, thereby forming a heat-resistant porous layer on the porous substrate. Compared to wet coating, the porous layer tends to become denser with dry coating; therefore, from the viewpoint of obtaining a good porous structure, wet coating is preferred.

[0176] The diaphragm of this disclosure can also be manufactured by: forming a heat-resistant porous layer in the form of an independent sheet, overlapping the heat-resistant porous layer with a porous substrate, and then composited using hot pressing and an adhesive. As a method for forming the heat-resistant porous layer in the form of an independent sheet, the following method can be used: applying the aforementioned wet coating method or dry coating method to form the heat-resistant porous layer on a release sheet.

[0177] <Non-aqueous secondary batteries>

[0178] The non-aqueous secondary battery disclosed herein is a non-aqueous secondary battery that obtains its electromotive force through lithium doping and dedoping, and it includes a positive electrode, a negative electrode, and a separator for the non-aqueous secondary battery of this disclosure. Doping refers to the phenomenon of lithium ions entering the active material of electrodes such as the positive electrode, through processes such as storage, loading, adsorption, or insertion.

[0179] The non-aqueous secondary battery disclosed herein has, for example, a structure in which battery elements (which are arranged such that the negative and positive electrodes are separated by a separator) and the electrolyte are encapsulated together within an outer packaging material. The non-aqueous secondary battery of this disclosure is suitable for non-aqueous electrolyte secondary batteries, particularly lithium-ion secondary batteries.

[0180] For the non-aqueous secondary batteries of this disclosure, the excellent adhesion of the separator to the electrodes based on dry hot pressing can improve the manufacturing yield.

[0181] Regarding the active material layer of the electrode, from the viewpoint of adhesion to the separator, it is preferable to contain a large amount of binder resin; from the viewpoint of improving the energy density of the battery, it is preferable to contain a large amount of active material, while a relatively small amount of binder resin is preferred. The separator of this disclosure exhibits excellent adhesion to the electrode, thus reducing the amount of binder resin in the active material layer and increasing the mass of the active material, thereby improving the energy density of the battery.

[0182] The following describes examples of the positive electrode, negative electrode, electrolyte, and outer packaging materials of the non-aqueous secondary battery disclosed herein.

[0183] As an example of a positive electrode embodiment, a structure can be provided in which an active material layer comprising a positive electrode active material and a binder resin is formed on a current collector. The active material layer may further comprise a conductive additive. Examples of positive electrode active materials include, for example, transition metal oxides containing lithium, specifically, LiCoO2, LiNiO2, and LiMn. 1 / 2 Ni 1 / 2 O2, LiCo 1 / 3Mn 1 / 3 Ni 1 / 3 O2, LiMn2O4, LiFePO4, LiCo 1 / 2Ni 1 / 2 O2, LiAl 1 / 4 Ni 3 / 4 O2, etc. Examples of adhesive resins include polyvinylidene fluoride resins and styrene-butadiene copolymers. Examples of conductive additives include carbon materials such as acetylene black, Ketjen black, and graphite powder. Examples of current collectors include aluminum foil, titanium foil, and stainless steel foil with a thickness of 5μm to 20μm.

[0184] In the non-aqueous secondary battery of this disclosure, the polyvinylidene fluoride resin contained in the heat-resistant porous layer of the separator exhibits excellent oxidation resistance. Therefore, by configuring the heat-resistant porous layer to contact the positive electrode of the non-aqueous secondary battery, it is easy to apply LiMn, which can operate at high voltages above 4.2V. 1 / 2 Ni 1 / 2 O2, LiCo 1 / 3 Mn 1 / 3Ni 1 / 3 O2 and other substances are used as positive electrode active materials.

[0185] Examples of embodiments of the negative electrode include a structure in which an active material layer comprising a negative electrode active material and a binder resin is formed on a current collector. The active material layer may also include a conductive additive. Examples of negative electrode active materials include materials capable of electrochemically absorbing lithium; specifically, examples include carbon materials; alloys of lithium with silicon, tin, aluminum, etc.; Wood's alloy; etc. Examples of binder resins include, for example, polyvinylidene fluoride resins, styrene-butadiene copolymers, etc. Examples of conductive additives include, for example, acetylene black, Ketjen black, graphite powder, ultrafine carbon fibers, etc. Examples of current collectors include, for example, copper foil, nickel foil, stainless steel foil, etc., with a thickness of 5μm to 20μm. Alternatively, lithium metal foil may be used as the negative electrode instead of the above-mentioned negative electrode.

[0186] The electrolyte is a solution obtained by dissolving a lithium salt in a non-aqueous solvent. Examples of lithium salts include LiPF6, LiBF4, and LiClO4. Examples of non-aqueous solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and their fluorinated derivatives; cyclic esters such as γ-butyrolactone and γ-valerolactone; etc. They can be used alone or in combination. As an electrolyte, a suitable solution is obtained by mixing cyclic carbonates and chain carbonates in a mass ratio of 20:80 to 40:60 (cyclic carbonate: chain carbonate) and dissolving the lithium salt in a concentration range of 0.5 mol / L to 1.5 mol / L.

[0187] Examples of suitable outer packaging materials include metal casings and aluminum laminated film packaging. Battery shapes include square, cylindrical, and button-shaped, and the separator described in this disclosure is suitable for any shape.

[0188] As a method for manufacturing a non-aqueous secondary battery as disclosed herein, a manufacturing method may include the following steps: a step of performing dry hot pressing to bond the separator to the electrode; and a sealing step of sealing the bonded electrode and separator together with the electrolyte inside an outer packaging material.

[0189] More specifically, the above-described manufacturing method includes the following steps: a lamination step of manufacturing a laminate formed by disposing of the diaphragm of this disclosure between the positive and negative electrodes; a dry bonding step of dry hot pressing the laminate to bond at least one of the positive and negative electrodes to the diaphragm; and a sealing step of sealing the laminate that has undergone the dry bonding step together with the electrolyte inside an outer packaging material.

[0190] The lamination process is, for example, a process of placing the diaphragm of this disclosure between the positive electrode and the negative electrode and winding it along the length direction to manufacture a wound body; or a process of sequentially laminating the positive electrode, the diaphragm, and the negative electrode at least one layer each.

[0191] The dry bonding process can be performed before or after the laminate is placed in the outer packaging material (e.g., aluminum laminate packaging). That is, the laminate, which is formed by bonding the electrodes and the diaphragm by dry hot pressing, can be placed in the outer packaging material, or the electrodes and the diaphragm can be bonded by dry hot pressing from above the outer packaging material after the laminate is placed in the outer packaging material.

[0192] The pressurization temperature in the dry bonding process is preferably 30°C to 100°C. Within this temperature range, the adhesion between the electrode and the separator is good, and the separator can expand moderately in the width direction, thus reducing the likelihood of short circuits in the battery. The pressurization pressure in the dry bonding process is preferably 0.2 MPa to 9 MPa. The pressurization time is preferably adjusted according to the pressurization temperature and pressure, for example, within the range of 0.1 minutes to 60 minutes.

[0193] After the lamination process and before the dry bonding process, the laminate can be temporarily bonded by applying pressure at room temperature.

[0194] The sealing process involves injecting electrolyte into the outer packaging material containing the laminated body and then sealing the opening of the outer packaging material. The sealing of the opening of the outer packaging material can be achieved, for example, by bonding the opening of the outer packaging material with an adhesive; or by heat-pressuring the opening of the outer packaging material. Before sealing the opening of the outer packaging material, it is preferable to create a vacuum inside the outer packaging.

[0195] In the sealing process, it is preferable to perform heat pressing on the opening of the outer packaging material while simultaneously heat-pressing the laminate from above the outer packaging material. By performing heat pressing (wet heat pressing) with the laminate and electrolyte present, the adhesion between the electrode and the diaphragm is stronger.

[0196] For wet hot pressing, the preferred pressing temperature is 60℃~90℃, and the preferred pressing pressure is 0.2MPa~2MPa. The pressing time is preferably adjusted according to the pressing temperature and pressing pressure, for example, within the range of 0.5 minutes to 60 minutes.

[0197] Example

[0198] The following examples illustrate the separator and non-aqueous secondary battery of this disclosure in more detail. The materials, amounts, proportions, processing steps, etc., shown in the following examples may be appropriately modified without departing from the spirit of the invention. Therefore, the scope of the separator and non-aqueous secondary battery of this disclosure should not be interpreted as limiting based on the specific examples shown below.

[0199] <Measurement Methods, Evaluation Methods>

[0200] The measurement and evaluation methods used in the examples and comparative examples are described below.

[0201] Melting point of polyvinylidene fluoride resins

[0202] The melting point of polyvinylidene fluoride (PVDF) resins is determined by differential scanning calorimetry (DSC) curves. Specifically, the porous layer is peeled off from a porous substrate, and the filler is removed from the peeled porous layer to obtain the PVDF resin. The PVDF resin is placed in the sample chamber of a differential scanning calorimeter (TA Instruments Q series), and heated at a rate of 5°C / min within a nitrogen atmosphere over a range of 30°C to 200°C to obtain the DSC curve. The temperature of the endothermic peak appearing in the DSC curve is taken as the melting point of the PVDF resin. In the case of multiple endothermic peaks, the temperature of the lowest endothermic peak is taken as the melting point.

[0203] [Weight-average molecular weight of polyvinylidene fluoride resins]

[0204] The weight-average molecular weight (Mw) of polyvinylidene fluoride (PVDF) resins was determined using gel permeation chromatography (GPC). For GPC-based molecular weight determination, a GPC-900 apparatus (Japan Spectrophotometer Co., Ltd.) was used, with two Tosoh TSKgel SUPER AWM-H columns and N,N-dimethylformamide as the solvent. The determination was performed at 40°C and a flow rate of 0.6 mL / min to obtain the molecular weight converted to polystyrene.

[0205] [Average primary particle size of the packing material]

[0206] The inorganic filler was added to the coating solution used to form the heat-resistant porous layer as a sample.

[0207] The average primary diameter of magnesium hydroxide particles is determined by averaging the major diameters of 100 randomly selected magnesium hydroxide particles observed using a scanning electron microscope (SEM).

[0208] The prepared barium sulfate particles were difficult to measure the major diameter of the primary particles using SEM. Therefore, for the average primary particle size of the barium sulfate particles, the specific gravity (g / cm³) was determined. 3 ) and BET specific surface area (m 2 / g), assuming the barium sulfate particles are spherical, the specific surface area is calculated according to the following formula. The Micromeritics ASAP2020 was used as the apparatus for measuring the BET specific surface area.

[0209] Average primary particle size (μm) = 6 ÷ [specific gravity (g / cm³)] 3 )×BET specific surface area (m 2 / g)]

[0210] [Volume proportion of filler in the heat-resistant porous layer]

[0211] The volume percentage Va (%) of the filler in the heat-resistant porous layer is calculated using the following formula.

[0212] Va={(Xa / Da) / (Xa / Da+Xb / Db+Xc / Dc+…+Xn-1 / Dn-1+Xn / Dn)}×100

[0213] Here, the fillers in the heat-resistant porous layer are a, b, c, ..., and the other constituent materials (such as PVDF resin) are n-1, n. The masses of each constituent material are Xa, Xb, Xc, ..., Xn-1, Xn (g), and the true densities of each constituent material are Da, Db, Dc, ..., Dn-1, Dn (g / cm³).3 ).

[0214] [Thickness of porous substrate and membrane]

[0215] For the thickness (μm) of the porous substrate and diaphragm, a contact thickness gauge (Mitutoyo, LITEMATIC VL-50) was used to measure 20 points within a 10cm square, and the average values ​​were then calculated. Cylindrical terminals with a diameter of 5mm were used for measurement, and adjustments were made to apply a load of 0.01N during the measurement.

[0216] [Thickness of the heat-resistant porous layer]

[0217] For the thickness (μm) of the heat-resistant porous layer, the total thickness of both sides is obtained by subtracting the thickness (μm) of the porous substrate from the thickness (μm) of the diaphragm.

[0218] [Coating amount of heat-resistant porous layer]

[0219] The diaphragm was cut into 10cm x 10cm squares and its mass was measured. This mass was divided by the area to determine the weight per unit area of ​​the diaphragm. Similarly, the porous substrate used in the diaphragm fabrication was cut into 10cm x 10cm squares and its mass was measured. This mass was divided by the area to determine the weight per unit area of ​​the porous substrate. The total coating amount on both sides of the heat-resistant porous layer was then calculated by subtracting the weight per unit area of ​​the diaphragm from the weight per unit area of ​​the porous substrate.

[0220] [Gurley value]

[0221] For the Gurley value (seconds / 100mL) of porous substrates and diaphragms, it is measured using a Gurley permeability tester (Toyo Seiki Co., Ltd.) in accordance with JIS P8117:2009.

[0222] Porosity of porous substrates

[0223] The porosity ε (%) of the porous substrate is calculated using the following formula.

[0224] ε={1-(Wa / da+Wb / db+Wc / dc+…+Wn / dn) / t}×100

[0225] Here, the constituent materials of the porous substrate are a, b, c, ..., n, and the masses of each constituent material are Wa, Wb, Wc, ..., Wn (g / cm³). 2 The true densities of each constituent material are da, db, dc, ..., dn (g / cm³). 3 The thickness of the porous substrate is t (cm).

[0226] [Porosity of heat-resistant porous layers]

[0227] The porosity ε (%) of the heat-resistant porous layer is calculated using the following formula.

[0228] ε={1-(Wa / da+Wb / db+Wc / dc+…+Wn / dn) / t}×100

[0229] Here, the constituent materials of the heat-resistant porous layer are a, b, c, ..., n, and the masses of each constituent material are Wa, Wb, Wc, ..., Wn (g / cm³). 2 The true densities of each constituent material are da, db, dc, ..., dn (g / cm³). 3 The thickness of the heat-resistant porous layer is t (cm).

[0230] [Area shrinkage rate based on heat treatment]

[0231] The diaphragm was cut into rectangles measuring 180mm in the MD direction and 60mm in the TD direction to prepare test pieces. Markings (points A and B, respectively) were made on the lines bisecting the TD direction, at points 20mm and 170mm from one end. Further markings (points C and D, respectively) were made on the lines bisecting the MD direction, at points 10mm and 50mm from one end. A clamp was installed on the marked test pieces (the clamp was positioned between the end closest to point A and point A), and the pieces were suspended in an oven with the temperature adjusted to 135°C. Heat treatment was performed for 1 hour under tension-free conditions. The lengths between A and B and between C and D were measured before and after heat treatment. The area shrinkage rate was calculated using the following formula, and the area shrinkage rate of the 10 test pieces was averaged.

[0232] Area shrinkage rate (%) = {1 - (length of AB after heat treatment ÷ length of AB before heat treatment) × (length of CD after heat treatment ÷ length of CD before heat treatment)} × 100

[0233] [Adhesion strength to electrodes during dry hot pressing]

[0234] Using a twin-arm mixer, 300g of artificial graphite (as the negative electrode active material), 7.5g of an aqueous dispersion containing 40% by mass of a modified styrene-butadiene copolymer as a binder, 3g of carboxymethyl cellulose (as a thickener), and an appropriate amount of water were stirred and mixed to prepare a negative electrode slurry. This negative electrode slurry was coated onto one side of a 10μm thick copper foil, dried, and then pressurized to obtain a negative electrode with a layer of negative electrode active material.

[0235] The negative electrode obtained above was cut into a 15mm wide and 70mm long piece, and the separator was cut into a rectangle with a TD direction of 18mm × MD direction of 74mm. A release paper with a 15mm wide and 70mm long piece was prepared. A laminate of the negative electrode, separator, and release paper was inserted into an aluminum laminated film package. Using a hot press, the laminate, along with the package, was hot-pressed in the lamination direction to bond the negative electrode and separator. The hot-pressing conditions were set to a temperature of 90℃, a pressure of 9MPa, and a time of 10 seconds. Afterward, the laminate was removed from the package, the release paper was peeled off, and it was used as a test piece.

[0236] The uncoated side of the negative electrode of the test piece was fixed to the metal plate using double-sided tape, and the metal plate was then fixed to the lower chuck of a Tensilon (A&D Company, STB-1225S). The metal plate was then fixed to the Tensilon with the length of the test piece (i.e., the MD direction of the diaphragm) as the direction of gravity. The diaphragm was peeled approximately 2 cm from the negative electrode starting from the lower end, and the end was fixed to the upper chuck for a 180° peel test. The tensile speed of the 180° peel test was 20 mm / min, and the load (N) was measured at 0.4 mm intervals from 10 mm to 40 mm after the start of the test, and the average value was calculated. The loads of 10 test pieces were then averaged to obtain the electrode-diaphragm adhesion strength (N / 15 mm).

[0237] <Septum Production>

[0238] [Example 1]

[0239] As PVDF-based resin A, a VDF-TFE copolymer with a melting point (Tm) of 132℃ and a weight-average molecular weight (Mw) of 1.3 million is prepared.

[0240] As PVDF-based resin B, a VDF-HFP copolymer with a melting point (Tm) of 152℃ and a weight-average molecular weight (Mw) of 1.13 million was prepared.

[0241] PVDF resin A and PVDF resin B were dissolved in a mixed solvent of dimethylacetamide (DMAc) and tripropylene glycol (TPG) (DMAc:TPG = 80:20 [mass ratio]), and the inorganic filler (barium sulfate particles, average primary particle size of 0.05 μm) was further dispersed to obtain coating solution (1). In coating solution (1), the mass ratio of PVDF resin A to PVDF resin B (PVDF resin A:PVDF resin B) was 50:50, the concentration of polyvinylidene fluoride resin was 5% by mass, and the volume ratio of polyvinylidene fluoride resin to filler (polyvinylidene fluoride resin:filler) was 39:61.

[0242] Coating solution (1) was applied to both sides of a polyethylene microporous membrane (thickness 9.1 μm, Gurley value 157 s / 100 mL, porosity 36%) (the coating amount was equal on both sides). The membrane was then immersed in a curing solution (water:DMAc:TPG = 62:30:8 [mass ratio], liquid temperature 40°C) to cure the coating layer. Following this, the membrane was washed with water and dried. As described above, a membrane with a heat-resistant porous layer formed on both sides of the polyethylene microporous membrane was obtained. The coating amount of the heat-resistant porous layer was approximately 6 g / m² on both sides. 2 .

[0243] [Example 2]

[0244] The same procedure as in Example 1 was followed, but the amount of heat-resistant porous layer coating was varied as described in Table 1, thereby creating a diaphragm.

[0245] [Examples 3-4]

[0246] The procedure was the same as in Example 1, except that the PVDF-based resin B was replaced with another PVDF-based resin B (VDF-HFP copolymer. Tm and Mw are as described in Table 1) to produce a diaphragm.

[0247] [Examples 5-6]

[0248] The same procedure as in Example 1 was followed, except that the barium sulfate particles were replaced with other barium sulfate particles (average primary particle size as described in Table 1) to produce a diaphragm.

[0249] [Examples 7-10]

[0250] The procedure was the same as in Example 1, except that the PVDF-based resin A was replaced with another PVDF-based resin A (VDF-TFE copolymer. Tm and Mw are as described in Table 1) to produce a diaphragm.

[0251] [Example 11]

[0252] The procedure was the same as in Example 1, except that the PVDF-based resin B was replaced with another PVDF-based resin B (VDF homopolymer. Tm and Mw are as described in Table 1) to produce a diaphragm.

[0253] [Comparative Example 1]

[0254] The same procedure as in Example 1 was followed, but instead of using PVDF resin A, the amount of PVDF resin B was increased accordingly to produce a diaphragm.

[0255] [Example 12]

[0256] As PVDF-based resin A, a VDF-TFE copolymer with a melting point (Tm) of 132℃ and a weight-average molecular weight (Mw) of 1.3 million is prepared.

[0257] As PVDF-based resin B, a VDF-HFP copolymer with a melting point (Tm) of 131℃ and a weight-average molecular weight (Mw) of 340,000 was prepared.

[0258] PVDF-based resin A and PVDF-based resin B were dissolved in a mixed solvent of DMAc and TPG (DMAc:TPG = 80:20 [mass ratio]), and the inorganic filler (magnesium hydroxide particles, average primary particle size of 0.8 μm) was further dispersed to obtain coating solution (12). In coating solution (12), the mass ratio of PVDF-based resin A to PVDF-based resin B (PVDF-based resin A:PVDF-based resin B) was 50:50, the concentration of polyvinylidene fluoride resin was 5% by mass, and the volume ratio of polyvinylidene fluoride resin to filler (polyvinylidene fluoride resin: filler) was 47:53.

[0259] The coating solution (12) was applied to both sides of a polyethylene microporous membrane (thickness 9.1 μm, Gurley value 157 s / 100 mL, porosity 36%) (the coating amount was equal on both sides). The membrane was then immersed in a curing solution (water:DMAc:TPG = 62:30:8 [mass ratio], liquid temperature 40°C) to cure the coating layer. It was then washed with water and dried. As described above, a membrane with a heat-resistant porous layer formed on both sides of the polyethylene microporous membrane was obtained. The coating amount of the heat-resistant porous layer was approximately 3 g / m² on both sides. 2 .

[0260] [Examples 13-14]

[0261] The same procedure was followed as in Example 12, but the mass ratio of PVDF resin A to PVDF resin B was changed as described in Table 1 to produce a diaphragm.

[0262] [Examples 15-16]

[0263] The procedure was the same as in Example 12, except that the PVDF-based resin B was replaced with another PVDF-based resin B (VDF-HFP copolymer. Tm and Mw are as described in Table 1) to produce a diaphragm.

[0264] [Example 17]

[0265] The same procedure was followed as in Example 12, except that the magnesium hydroxide particles were replaced with other magnesium hydroxide particles (average primary particle size as described in Table 1) to produce a diaphragm.

[0266] [Comparative Example 2]

[0267] The same procedure as in Example 12 was followed, but instead of using PVDF resin B, the amount of PVDF resin A was increased accordingly to produce a diaphragm.

[0268] [Comparative Example 3]

[0269] The same procedure as in Example 15 was followed, but instead of using PVDF resin A, the amount of PVDF resin B was increased accordingly to produce a diaphragm.

[0270] [Comparative Example 4]

[0271] The same procedure was followed as in Example 16, but instead of using PVDF resin A, the amount of PVDF resin B was increased accordingly to produce a diaphragm.

[0272] [Comparative Example 5]

[0273] The same procedure as in Example 12 was followed, but instead of using PVDF resin A, the amount of PVDF resin B was increased accordingly to produce a diaphragm.

[0274] The composition, physical properties, and evaluation results of the diaphragms of Examples 1-17 and Comparative Examples 1-5 are shown in Table 1.

[0275] [Table 1]

[0276]

[0277] The entire contents of Japanese Patent Application No. 2019-049545, filed on March 18, 2019, are incorporated herein by reference.

[0278] All documents, patent applications and technical standards described in this specification are incorporated herein by reference to the extent that each document, patent application and technical standard is incorporated by reference to the extent that it is specifically and separately described.

Claims

1. A separator for non-aqueous secondary batteries, which has the following characteristics: Porous substrates; and A heat-resistant porous layer is disposed on one or both sides of the porous substrate. The heat-resistant porous layer contains polyvinylidene fluoride resin A, polyvinylidene fluoride resin B, and filler. The polyvinylidene fluoride resin A is a polyvinylidene fluoride resin containing tetrafluoroethylene units, and the polyvinylidene fluoride resin B is a polyvinylidene fluoride resin other than polyvinylidene fluoride resin A. The polyvinylidene fluoride resin B is a homopolymer of vinylidene fluoride, or a copolymer of vinylidene fluoride with monomers other than tetrafluoroethylene. The average primary particle size of the filler contained in the heat-resistant porous layer is 0.02 μm to 0.5 μm.

2. The separator for non-aqueous secondary batteries as described in claim 1, wherein, The average primary particle size of the filler contained in the heat-resistant porous layer is 0.03 μm to 0.5 μm.

3. The separator for non-aqueous secondary batteries as described in claim 1 or claim 2, wherein, The filler comprises at least one selected from the group consisting of metal sulfate particles, metal hydroxide particles, metal oxide particles, and metal nitride particles.

4. The separator for non-aqueous secondary batteries as described in claim 1 or claim 2, wherein, The filler occupies 30% to 90% of the volume in the heat-resistant porous layer.

5. The separator for non-aqueous secondary batteries as described in claim 1 or claim 2, wherein, The melting point of the polyvinylidene fluoride resin A is 120℃~150℃.

6. The separator for non-aqueous secondary batteries as described in claim 1 or claim 2, wherein, The weight-average molecular weight of the polyvinylidene fluoride resin A is 600,000 to 3,000,000.

7. The separator for non-aqueous secondary batteries as described in claim 1 or claim 2, wherein, The melting point of the polyvinylidene fluoride resin B is 120℃~173℃.

8. The separator for non-aqueous secondary batteries as described in claim 1 or claim 2, wherein, The weight-average molecular weight of the polyvinylidene fluoride resin B is 300,000 to 3,000,000.

9. The separator for non-aqueous secondary batteries as described in claim 1 or claim 2, wherein, The polyvinylidene fluoride resin B is a polyvinylidene fluoride resin containing hexafluoropropylene units.

10. The separator for non-aqueous secondary batteries as described in claim 1 or claim 2, wherein, The porosity of the heat-resistant porous layer is 30% to 90%.

11. A non-aqueous secondary battery comprising a positive electrode, a negative electrode, and a separator for a non-aqueous secondary battery as described in any one of claims 1 to 10 disposed between the positive electrode and the negative electrode, wherein the non-aqueous secondary battery obtains an electromotive force by lithium doping and dedoping.

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