Separator for non-aqueous secondary battery and non-aqueous secondary battery

Abstract

One embodiment of the present invention provides a separator for a non-aqueous secondary battery, comprising a porous substrate and a heat-resistant porous layer disposed on one or both surfaces of the porous substrate, wherein the heat-resistant porous layer comprises a heat-resistant resin and barium sulfate particles, wherein the average primary particle size of the barium sulfate particles contained in the heat-resistant porous layer is greater than or equal to 0.01 μm and less than 0.30 μm, and the volume ratio of the barium sulfate particles in the solid content of the heat-resistant porous layer is greater than or equal to 5 volume % and less than 30 volume %.

Description

Technical Field

[0001] The present disclosure relates to a separator for a non-aqueous secondary battery and a non-aqueous secondary battery. Background Art

[0002] To ensure battery safety, the separator, a component of non-aqueous secondary batteries, requires heat resistance. This means it should be less susceptible to damage or shrinkage even when the battery interior reaches high temperatures. Separators with improved heat resistance are known, comprising a porous layer containing a heat-resistant resin and / or inorganic particles on a porous substrate.

[0003] For example, Japanese Patent No. 5429811 and International Publication No. 2014 / 148036 disclose a separator including a porous layer containing barium sulfate particles on a porous substrate.

[0004] For example, Japanese Patent Application Laid-Open No. 2012-119224 or Japanese Patent Application Laid-Open No. 2019-216033 discloses a separator including a porous layer containing a resin such as wholly aromatic polyamide and inorganic particles on a porous substrate.

[0005] For example, Japanese Patent No. 6526359 discloses a separator including a porous layer containing a resin such as wholly aromatic polyamide and barium sulfate particles on a porous substrate. Summary of the Invention

[0006] Problems to be solved by the invention

[0007] To ensure battery safety, the separator must adhere well to the electrodes, preventing them from easily peeling off even when subjected to external impact or when the electrodes expand and contract during charging and discharging. To ensure good adhesion of the separator to the electrodes, not only must the separator surface have good adhesion to the electrodes, but it must also ensure that the layers that make up the separator do not easily peel off from each other. This is also important from the perspective of improving battery manufacturing yields.

[0008] The embodiments of the present disclosure are completed based on the above circumstances.

[0009] An object of embodiments of the present disclosure is to provide a non-aqueous secondary battery separator comprising a heat-resistant porous layer on a porous substrate, the separator having excellent heat resistance and the heat-resistant porous layer being less likely to peel from the porous substrate.

[0010] Means for solving problems

[0011] Specific means for solving the aforementioned problems include the following.

[0012] <1> A separator for a non-aqueous secondary battery, comprising:

[0013] a porous substrate; and

[0014] a heat-resistant porous layer provided on one or both sides of the porous substrate and comprising a heat-resistant resin and barium sulfate particles;

[0015] The barium sulfate particles contained in the heat-resistant porous layer have an average primary particle size of 0.01 μm or more and less than 0.30 μm.

[0016] The volume ratio of the barium sulfate particles in the solid content of the heat-resistant porous layer is 5 volume % or more and less than 30 volume %.

[0017] <2> like <1> In the non-aqueous secondary battery separator, the volume ratio of the barium sulfate particles in the solid content of the heat-resistant porous layer is 5 volume % or more and less than 27 volume %.

[0018] <3> like <1> or <2> In the non-aqueous secondary battery separator, the heat-resistant resin comprises at least one selected from the group consisting of wholly aromatic polyamide, polyamideimide, poly-N-vinylacetamide, polyacrylamide, copolyether polyamide, polyimide, and polyetherimide.

[0019] <4> like <1> ~ <3> The non-aqueous secondary battery separator according to any one of the preceding claims, wherein the peel strength between the porous substrate and the heat-resistant porous layer is 0.30 N / 12 mm or more.

[0020] <5> like <1> ~ <4> The non-aqueous secondary battery separator according to any one of the preceding claims, wherein the area shrinkage rate when the non-aqueous secondary battery separator is heat-treated at 135° C. for 1 hour is 30% or less.

[0021] <6> like <1> ~ <5> The non-aqueous secondary battery separator according to any one of the preceding claims, wherein the area shrinkage rate when the non-aqueous secondary battery separator is heat-treated at 150° C. for 1 hour is 45% or less.

[0022] <7> like <1> ~ <6> The non-aqueous secondary battery separator according to any one of the preceding claims, wherein the heat-resistant porous layer has a porosity of 30% to 70%.

[0023] <8> like <1> ~ <7> The non-aqueous secondary battery separator according to any one of the preceding claims, wherein the mass per unit area of the heat-resistant porous layer is 1.0 g / m² in total on both sides. 2 ~30.0g / m 2 .

[0024] <9> like <1> ~ <8> The non-aqueous secondary battery separator according to any one of the preceding claims further comprises an adhesive layer as an outermost layer on one or both surfaces thereof.

[0025] <10> A non-aqueous secondary battery comprising a positive electrode, a negative electrode and a <1> ~ <9> The non-aqueous secondary battery separator according to any one of the preceding claims, wherein the non-aqueous secondary battery generates an electromotive force by doping and dedoping lithium ions.

[0026] Effects of the Invention

[0027] The present disclosure provides a nonaqueous secondary battery separator comprising a heat-resistant porous layer on a porous substrate, the separator having excellent heat resistance and the heat-resistant porous layer being less likely to peel from the porous substrate. DETAILED DESCRIPTION

[0028] Hereinafter, embodiments of the present disclosure will be described. These descriptions and examples are examples of the embodiments and do not limit the scope of the embodiments.

[0029] In the present disclosure, a numerical range expressed using “to” indicates a range including the numerical values described before and after “to” as the minimum value and the maximum value, respectively.

[0030] In the numerical ranges described in stages in this disclosure, the upper limit or lower limit described in one numerical range may be replaced by the upper limit or lower limit of the numerical range described in another stage. In addition, in the numerical ranges described in this disclosure, the upper limit or lower limit of the numerical range may also be replaced by the value shown in the embodiments.

[0031] In the present disclosure, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes as long as the intended purpose of the process can be achieved.

[0032] In the present disclosure, when referring to the amount of each component in a composition, if there are multiple substances belonging to each component in the composition, unless otherwise specified, it refers to the total amount of the multiple substances present in the composition.

[0033] In the present disclosure, particles belonging to each component may contain multiple types. When multiple types of particles belonging to each component are present in a composition, the particle size of each component refers to the value for the mixture of the multiple types of particles present in the composition unless otherwise specified.

[0034] In this disclosure, the term "MD" (machine direction) refers to the longitudinal direction of a porous substrate or separator manufactured in an elongated shape, and the term "TD" (transverse direction) refers to the direction perpendicular to the MD in the plane direction of the porous substrate or separator. In this disclosure, "TD" is also referred to as the "width direction."

[0035] In this disclosure, when the stacking relationship of each layer constituting the separator is expressed as “upper” and “lower”, the layer closer to the porous substrate is referred to as “lower” and the layer farther from the porous substrate is referred to as “upper”.

[0036] <Separator for non-aqueous secondary batteries>

[0037] The non-aqueous secondary battery separator of the present disclosure (also referred to as “separator” in the present disclosure) includes a porous substrate and a heat-resistant porous layer provided on one or both surfaces of the porous substrate.

[0038] In the diaphragm of the present disclosure, the heat-resistant porous layer contains a heat-resistant resin and barium sulfate particles. The average primary particle size of the barium sulfate particles contained in the heat-resistant porous layer is greater than or equal to 0.01 μm and less than 0.30 μm, and the volume ratio of the barium sulfate particles in the solid content of the heat-resistant porous layer is greater than or equal to 5 volume % and less than 30 volume %.

[0039] In this disclosure, a heat-resistant resin refers to a resin having a melting point of 200°C or higher, or a resin having no melting point but a decomposition temperature of 200°C or higher. In other words, a heat-resistant resin in this disclosure is a resin that does not melt or decompose in a temperature range below 200°C.

[0040] From the viewpoint of improving the heat resistance of heat-resistant porous layer, the average primary particle size of the barium sulfate particles included in the heat-resistant porous layer is less than 0.30 μm. If the average primary particle size of the barium sulfate particles is less than 0.30 μm, the heat resistance of the heat-resistant porous layer improves. As its mechanism, it is believed that because the particle diameter of the barium sulfate particles is little, the surface area (that is, specific surface area) of the barium sulfate particles per unit volume becomes large, and therefore, the contact points of the barium sulfate particles and the heat-resistant resin become many, thus suppressing the shrinkage of the heat-resistant porous layer when being exposed to high temperature. In addition, it is speculated that because the barium sulfate particles with little particle diameter are connected to each other in a large number, the heat-resistant porous layer is difficult for shrinkage when being exposed to high temperature.

[0041] From the viewpoint of suppressing aggregation of barium sulfate particles and forming a highly uniform heat-resistant porous layer, the average primary particle size of the barium sulfate particles contained in the heat-resistant porous layer is 0.01 μm or more.

[0042] In the separator of the present disclosure, the volume ratio of the barium sulfate particles in the solid content of the heat-resistant porous layer is 5 volume % or more from the viewpoint of obtaining the heat-resistant function of the barium sulfate particles.

[0043] In the separator of the present disclosure, the volume ratio of the barium sulfate particles in the solid components of the heat-resistant porous layer is less than 30% by volume, so as to prevent the heat-resistant porous layer from being easily peeled off from the porous substrate. If the content of barium sulfate particles having a small particle size, such as an average primary particle size of less than 0.30 μm, is high, the surface of the heat-resistant porous layer becomes flat, and the heat-resistant porous layer is easily peeled off from the porous substrate. To prevent this phenomenon, the volume ratio of the barium sulfate particles in the solid components of the heat-resistant porous layer is less than 30% by volume.

[0044] The above-mentioned components act in synergistic manner, so that the separator of the present disclosure has excellent heat resistance and the heat-resistant porous layer is less likely to be peeled off from the porous substrate.

[0045] Hereinafter, the porous substrate and the heat-resistant porous layer included in the separator of the present disclosure will be described in detail.

[0046] [Porous substrate]

[0047] In this disclosure, the so-called porous substrate refers to a substrate having pores or voids inside. Examples of such substrates include microporous membranes; porous sheets such as non-woven fabrics and paper formed from fibrous materials; composite porous sheets obtained by laminating one or more other porous layers on these microporous membranes and porous sheets; and the like. In this disclosure, from the perspective of thin film and strength of the diaphragm, a microporous membrane is preferred. The so-called microporous membrane refers to a membrane having a structure with a large number of micropores inside, and the micropores are connected, so that gas or liquid can pass from one side of the surface to the other side.

[0048] The material of the porous base material is preferably an electrically insulating material, and may be either an organic material or an inorganic material.

[0049] To impart a shutdown function to the porous substrate, it is preferred that the porous substrate contain a thermoplastic resin. This shutdown function allows the constituent materials to melt when the battery temperature rises, blocking the pores of the porous substrate and thereby preventing ion migration and thermal runaway. Thermoplastic resins with a melting point below 200°C are preferred. Examples of thermoplastic resins include polyesters such as polyethylene terephthalate and polyolefins such as polyethylene and polypropylene, with polyolefins being preferred.

[0050] The porous substrate is preferably a microporous membrane made of polyolefin (referred to as "polyolefin microporous membrane" in this disclosure). Examples of the polyolefin microporous membrane include polyolefin microporous membranes suitable for existing battery separators. It is preferred to select a polyolefin microporous membrane having sufficient mechanical properties and ion permeability.

[0051] From the viewpoint of exhibiting the shutdown function, the polyolefin microporous membrane is preferably a microporous membrane containing polyethylene, and the polyethylene content is preferably 95% by mass or more relative to the total mass of the polyolefin microporous membrane.

[0052] The polyolefin microporous membrane is preferably a microporous membrane made of polypropylene from the viewpoint of having heat resistance such that the membrane is less likely to be damaged when exposed to high temperatures.

[0053] From the viewpoint of having a shutdown function and heat resistance that is not easily damaged when exposed to high temperatures, the polyolefin microporous membrane is preferably a polyolefin microporous membrane comprising polyethylene and polypropylene. As the polyolefin microporous membrane comprising polyethylene and polypropylene, a microporous membrane in which polyethylene and polypropylene are mixed in one layer can be cited. In the microporous membrane, from the viewpoint of simultaneously achieving the shutdown function and heat resistance, it is preferred to include polyethylene of 95% by mass or more and polypropylene of 5% by mass or less. In addition, from the viewpoint of simultaneously achieving the shutdown function and heat resistance, a polyolefin microporous membrane of the following structure is also preferred, which has a laminated structure of more than two layers, at least one layer comprising polyethylene, and at least one layer comprising polypropylene.

[0054] The polyolefin contained in the polyolefin microporous membrane preferably has a weight-average molecular weight (Mw) of 100,000 to 5,000,000. A polyolefin with an Mw of 100,000 or greater can impart sufficient mechanical properties to the microporous membrane. On the other hand, a polyolefin with an Mw of 5,000,000 or less can provide excellent shutdown properties of the microporous membrane, making it easier to form the microporous membrane.

[0055] As methods for producing polyolefin microporous membranes, the following methods can be cited: a method in which a molten polyolefin resin is extruded from a T-die to form a sheet, the sheet is crystallized, then stretched, and then heat-treated to form a microporous membrane; a method in which a molten polyolefin resin is extruded from a T-die together with a plasticizer such as liquid paraffin, the sheet is cooled to form a sheet, the sheet is stretched, the plasticizer is extracted, and the sheet is heat-treated to form a microporous membrane; and the like.

[0056] Examples of porous sheets formed from fibrous materials include non-woven 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 wholly aromatic polyamides, polyamide-imides, polyimides, polyethersulfones, polysulfones, polyetherketones, and polyetherimides; cellulose; and the like.

[0057] Examples of composite porous sheets include sheets obtained by laminating a functional layer on a porous sheet formed of a microporous membrane or a fibrous material. Such composite porous sheets are preferred from the perspective of further adding functions through the functional layer. As functional layers, for example, from the perspective of imparting heat resistance, examples include porous layers formed of a heat-resistant resin, and porous layers formed of a heat-resistant resin and an inorganic filler. Examples of heat-resistant resins include one or more heat-resistant resins selected from wholly aromatic polyamides, polyamide-imides, polyimides, polyethersulfones, polysulfones, polyetherketones, and polyetherimides. Examples of inorganic fillers include metal oxides such as aluminum oxide; metal hydroxides such as magnesium hydroxide; and the like. Examples of composite methods include: coating a functional layer on a microporous membrane or porous sheet; bonding the microporous membrane or porous sheet to the functional layer with an adhesive; and thermocompression bonding the microporous membrane or porous sheet to the functional layer.

[0058] In order to improve the wettability of the coating liquid used to form the heat-resistant porous layer, the surface of the porous substrate may be subjected to various surface treatments within a range that does not damage the properties of the porous substrate. Examples of surface treatments include corona treatment, plasma treatment, flame treatment, and ultraviolet irradiation treatment.

[0059] [Characteristics of porous substrates]

[0060] As for the thickness of the porous substrate, from the perspective of improving the energy density of the battery, it is preferably less than 18 μm, more preferably less than 15 μm, and further preferably less than 12 μm. From the perspective of the manufacturing yield of the diaphragm and the manufacturing yield of the battery, it is preferably more than 4 μm, more preferably more than 6 μm, and further preferably more than 8 μm.

[0061] From the viewpoint of the balance between ion permeability and suppression of battery short circuit, the Gurley value (JIS P8117:2009) of the porous substrate is preferably 40 to 300 sec / 100 mL, more preferably 50 to 200 sec / 100 mL.

[0062] From the viewpoint of obtaining appropriate membrane resistance and shutdown function, the porosity of the porous substrate is preferably 20% to 60%. The porosity ε (%) of the porous substrate is calculated by the following formula.

[0063] ε={1-Ws / (ds·t)}×100

[0064] Here, Ws is the weight per unit area of the porous substrate (g / m 2 ), ds is the true density of the porous substrate (g / cm 3 ), t is the thickness of the porous substrate (μm). The so-called unit area weight is the mass per unit area.

[0065] From the perspective of ion permeability and suppression of battery short circuits, the average pore diameter of the porous substrate is preferably 20 nm to 100 nm. The average pore diameter of the porous substrate is measured using a palm porometer (CFP-1500-A manufactured by PMI) in accordance with ASTM E1294-89.

[0066] From the perspective of the manufacturing yield of the separator and the manufacturing yield of the battery, the puncture strength of the porous substrate is preferably 150 gf or more, more preferably 200 gf or more. The puncture strength of the porous substrate refers to the maximum puncture strength (gf) measured by a puncture test using a KES-G5 handheld compression tester manufactured by Kato Tech, with a needle tip curvature radius of 0.5 mm and a puncture speed of 2 mm / second.

[0067] [Heat-resistant porous layer]

[0068] The heat-resistant porous layer has a structure in which a large number of micropores are formed inside and the micropores are connected, and gas or liquid can pass from one surface to the other surface.

[0069] The heat-resistant porous layer may be present only on one side of the porous substrate or on both sides of the porous substrate. If the heat-resistant porous layer is present on both sides of the porous substrate, the heat resistance of the separator is further improved, which can further improve the safety of the battery. In addition, curling is not easy to occur in the separator, and the operability during battery manufacturing is excellent. If the heat-resistant porous layer is present only on one side of the porous substrate, the ion permeability of the separator is further improved. In addition, the thickness of the entire separator can be suppressed, and a battery with a higher energy density can be manufactured.

[0070] The heat-resistant porous layer contains at least a heat-resistant resin and barium sulfate particles. The heat-resistant porous layer may also contain resins other than the heat-resistant resin. The heat-resistant porous layer may also contain inorganic particles other than the barium sulfate particles. The heat-resistant porous layer may also contain an organic filler.

[0071] -Heat-resistant resin-

[0072] The heat-resistant resin is not limited in type, as long as it does not melt or decompose in a temperature range below 200°C. Examples of the heat-resistant resin include wholly aromatic polyamides, polyamide-imides, poly-N-vinylacetamides, polyacrylamides, copolyether polyamides, polyimides, and polyetherimides. The heat-resistant resins may be used alone or in combination of two or more.

[0073] Among heat-resistant resins, fully aromatic polyamides are preferred from the perspective of durability. A fully aromatic polyamide is a polyamide whose main chain consists solely of benzene rings and amide bonds. A small amount of aliphatic monomers may also be copolymerized in a fully aromatic polyamide. Fully aromatic polyamides are also known as aramids.

[0074] Wholly aromatic polyamides may be of the meta or para type. Among wholly aromatic polyamides, meta-type wholly aromatic polyamides are preferred due to their ease of forming a porous layer and excellent redox resistance during electrode reactions. Specifically, the wholly aromatic polyamide is preferably poly(m-phenylene isophthalamide), copoly(p-phenylene-3,4'-oxydiphenylene-terephthalamide), or poly(p-phenylene terephthalamide). As the meta-type wholly aromatic polyamide, poly(m-phenylene isophthalamide) is more preferred.

[0075] In addition, para-type wholly aromatic polyamides are preferred due to their excellent heat resistance at relatively high temperatures. Para-type wholly aromatic polyamides are preferably copolymerized paraphenylene, 3,4'-oxydiphenylene, and terephthalamide. The heat resistance of heat-resistant resins can be evaluated, for example, by a spot heating test in the presence of an electrolyte.

[0076] When the heat-resistant porous layer is present on both surfaces of the porous substrate, the type of heat-resistant resin contained in one heat-resistant porous layer may be the same as or different from the type of heat-resistant resin contained in the other heat-resistant porous layer.

[0077] The content of the heat-resistant resin in the heat-resistant porous layer is preferably 85 to 100 mass %, more preferably 90 to 100 mass %, and even more preferably 95 to 100 mass %, relative to the total amount of the resin in the heat-resistant porous layer.

[0078] -Other resins-

[0079] The heat-resistant porous layer may contain a resin other than the heat-resistant resin, that is, a resin that melts or decomposes in a temperature range below 200° C. Examples of the other resin include polyvinylidene fluoride resins, acrylic resins, fluororubbers, styrene-butadiene copolymers, homopolymers or copolymers of vinyl nitrile compounds (acrylonitrile, methacrylonitrile, etc.), carboxymethyl cellulose, hydroxyalkyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, polyethers (polyethylene oxide, polypropylene oxide, etc.), polysulfones, polyketones, polyetherketones, polyethersulfones, and mixtures thereof.

[0080] The type and content of other resins can be selected from the viewpoints of improving the adhesion between the heat-resistant porous layer and the electrode, the function of binding the barium sulfate particles, the moldability of the heat-resistant porous layer, and the like.

[0081] The content of other resins in the heat-resistant porous layer is preferably 0 to 15 mass %, more preferably 0 to 10 mass %, and even more preferably 0 to 5 mass %, based on the total amount of resins in the heat-resistant porous layer.

[0082] -Barium sulfate particles-

[0083] Barium sulfate is less likely to decompose electrolytes or electrolytes, and therefore less likely to cause gas generation. Therefore, by using barium sulfate particles as the inorganic filler in the heat-resistant porous layer, gas generation is less likely to occur, and a separator that is less likely to swell or deform in the battery can be obtained.

[0084] The barium sulfate particles may be those whose surfaces have been modified with a silane coupling agent or the like.

[0085] The shape of the barium sulfate particles is not limited and may be any of spherical, plate-like, needle-like, or irregular shapes. From the perspective of suppressing battery short circuits or forming a highly uniform heat-resistant porous layer, the barium sulfate particles are preferably spherical or plate-like.

[0086] From the perspective of improving the heat resistance of the heat-resistant porous layer, the average primary particle size of the barium sulfate particles contained in the heat-resistant porous layer is less than 0.30 μm, preferably 0.28 μm or less, and more preferably 0.27 μm or less. From the perspective of suppressing aggregation of the barium sulfate particles and forming a highly uniform heat-resistant porous layer, the average primary particle size of the barium sulfate particles contained in the heat-resistant porous layer is 0.01 μm or more, preferably 0.03 μm or more, and more preferably 0.04 μm or more.

[0087] The average primary particle size of the barium sulfate particles was determined by measuring the major diameters of 100 randomly selected barium sulfate particles observed using a scanning electron microscope (SEM) and averaging the major diameters. The sample used for SEM observation was barium sulfate particles used as a material for forming the heat-resistant porous layer, or barium sulfate particles removed from the heat-resistant porous layer of a separator.

[0088] There are no specific limitations on the method for removing the barium sulfate particles from the heat-resistant porous layer of the separator. Examples of such methods include immersing the heat-resistant porous layer peeled from the separator in an organic solvent capable of dissolving the resin, thereby removing the barium sulfate particles; heating the heat-resistant porous layer peeled from the separator to approximately 800°C, thereby dissolving the resin and removing the barium sulfate particles; and the like.

[0089] When the heat-resistant porous layer exists on both surfaces of the porous substrate, the average primary particle size of the barium sulfate particles contained in one heat-resistant porous layer may be the same as or different from the average primary particle size of the barium sulfate particles contained in the other heat-resistant porous layer.

[0090] From the perspective of heat resistance of the separator, the volume ratio of the barium sulfate particles in the solid components of the heat-resistant porous layer is 5 volume % or more, preferably 8 volume % or more, and more preferably 10 volume % or more. From the perspective of preventing the heat-resistant porous layer from being easily peeled off from the porous substrate, the volume ratio of the barium sulfate particles in the solid components of the heat-resistant porous layer is less than 30 volume %, preferably less than 27 volume %, and more preferably less than 24 volume %.

[0091] The volume ratio Va (volume %) of the barium sulfate particles in the solid content of the heat-resistant porous layer can be determined by the following formula.

[0092] Va={(Xa / Da) / (Xa / Da+Xb / Db+Xc / Dc+…+Xn / Dn)}×100

[0093] Here, among the constituent materials of the heat-resistant porous layer, the barium sulfate particles are a, and the other constituent materials are b, c, ..., n. The mass of each constituent material contained in a predetermined area of the heat-resistant porous layer is Xa, Xb, Xc, ..., Xn (g), and the true density of each constituent material is Da, Db, Dc, ..., Dn (g / cm 3 ).

[0094] Xa and the like substituted into the above formula are the mass (g) of the constituent material used to form the heat-resistant porous layer of a predetermined area, or the mass (g) of the constituent material removed from the heat-resistant porous layer of a predetermined area.

[0095] Da, etc., substituted into the above formula, is the true density (g / cm 3 ), or the true density (g / cm2) of the constituent material taken out from the heat-resistant porous layer 3 ).

[0096] When the heat-resistant porous layer exists on both surfaces of the porous substrate, the volume ratio of the barium sulfate particles in the solid content of one heat-resistant porous layer and the volume ratio of the barium sulfate particles in the solid content of the other heat-resistant porous layer may be the same or different.

[0097] The content of the barium sulfate particles in the heat-resistant porous layer is preferably 50 to 100 volume %, more preferably 60 to 100 volume %, and even more preferably 70 to 100 volume %, relative to the total amount of the inorganic particles in the heat-resistant porous layer.

[0098] -Other inorganic particles-

[0099] The heat-resistant porous layer may also contain other inorganic particles besides barium sulfate particles. Examples of other inorganic particles include metal sulfate particles such as strontium sulfate, calcium sulfate, calcium sulfate dihydrate, alunite, and jarosite; metal hydroxide particles such as magnesium hydroxide, aluminum hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, cerium hydroxide, nickel hydroxide, and boron hydroxide; metal oxide particles such as magnesium oxide, aluminum oxide (Al2O3), boehmite (aluminum oxide monohydrate), titanium dioxide (TiO2), silicon dioxide (SiO2), zirconium oxide (ZrO2), barium titanate (BaTiO3), and zinc oxide; metal carbonate particles such as calcium carbonate and magnesium carbonate; metal nitride particles such as magnesium nitride, aluminum nitride, calcium nitride, and titanium nitride; metal fluoride particles such as magnesium fluoride and calcium fluoride; and clay mineral particles such as calcium silicate, calcium phosphate, apatite, and talc. As other inorganic particles, from the viewpoint of stability in the electrolyte and electrochemical stability, preferably particles of metal hydroxide or metal oxide.Other inorganic particles can also be inorganic particles surface-modified using silane coupling agents etc.Other inorganic particles can be used alone or in combination of two or more.

[0100] When the heat-resistant porous layer exists on both surfaces of the porous substrate, the type of other inorganic particles contained in one heat-resistant porous layer may be the same as or different from the type of other inorganic particles contained in the other heat-resistant porous layer.

[0101] The average primary particle size of the other inorganic particles is preferably 0.01 to 5 μm, more preferably 0.05 to 3 μm, and even more preferably 0.1 to 1 μm. The average primary particle size of the other inorganic particles is measured in the same manner as that of the barium sulfate particles.

[0102] The particle shape of the other inorganic particles is not limited and can be any of spherical, plate-like, needle-like, and irregular shapes. From the perspective of suppressing battery short circuits or forming a highly uniform heat-resistant porous layer, the other inorganic particles are preferably spherical or plate-like particles.

[0103] The content of other inorganic particles contained in the heat-resistant porous layer is preferably 0 to 50 volume %, more preferably 0 to 40 volume %, and even more preferably 0 to 30 volume %, based on the total amount of inorganic particles contained in the heat-resistant porous layer.

[0104] When the heat-resistant porous layer exists on both sides of the porous substrate, the volume ratio of the other inorganic particles in the solid content of one heat-resistant porous layer and the volume ratio of the other inorganic particles in the solid content of the other heat-resistant porous layer may be the same or different.

[0105] From the perspective of preventing the heat-resistant porous layer from being easily peeled off from the porous substrate, the volume ratio of the inorganic particles as a whole in the solid content of the heat-resistant porous layer is preferably less than 50 volume %, more preferably less than 45 volume %, further preferably less than 40 volume %, and further preferably less than 35 volume %.

[0106] From the viewpoint of heat resistance of the separator, the volume ratio of the entire inorganic particles in the solid content of the heat-resistant porous layer is preferably 5 volume % or more, more preferably 10 volume % or more, and even more preferably 15 volume % or more.

[0107] The volume ratio Va0 (volume %) of the inorganic particles in the solid content of the heat-resistant porous layer can be determined by the following formula.

[0108] Va0={(Xa0 / Da0) / (Xa0 / Da0+Xb / Db+Xc / Dc+…+Xn / Dn)}×100

[0109] Here, among the constituent materials of the heat-resistant porous layer, the inorganic particles are a0, and the other constituent materials are b, c, ..., n. The mass of each constituent material contained in a given area of the heat-resistant porous layer is Xa0, Xb, Xc, ..., Xn (g), and the true density of each constituent material is Da0, Db, Dc, ..., Dn (g / cm 3 ).

[0110] Xa0 etc. substituted into the above formula is the mass (g) of the constituent material used to form the heat-resistant porous layer of a predetermined area, or the mass (g) of the constituent material removed from the heat-resistant porous layer of a predetermined area.

[0111] Da0, etc. substituted into the above formula is the true density (g / cm 3 ), or the true density (g / cm2) of the constituent material taken out from the heat-resistant porous layer 3 ).

[0112] -Organic fillers-

[0113] The heat-resistant porous layer may also contain an organic filler. Examples of the organic filler include: particles formed from cross-linked polymers such as cross-linked poly(meth)acrylic acid, cross-linked poly(meth)acrylate, cross-linked polystyrene, cross-linked polysiloxane, cross-linked polydivinylbenzene, styrene-divinylbenzene copolymer cross-linked products, melamine resins, phenolic resins, and benzoguanamine-formaldehyde condensates; particles formed from heat-resistant polymers such as polysulfone, polyacrylonitrile, aromatic polyamide, and polyacetal; and the like. These organic fillers may be used alone or in combination of two or more. In this disclosure, the expression "(meth)acrylic-" means that it can be either "acrylic-" or "methacrylic-".

[0114] -Other ingredients-

[0115] The heat-resistant porous layer may contain additives such as dispersants such as surfactants, wetting agents, defoaming agents, and pH adjusters. Dispersants are added to the coating liquid used to form the heat-resistant porous layer to improve dispersibility, coating properties, or storage stability. Wetting agents, defoaming agents, and pH adjusters are added to the coating liquid used to form the heat-resistant porous layer, for example, to improve affinity with the porous substrate, to suppress air ingestion into the coating liquid, or to adjust the pH.

[0116] [Characteristics of the heat-resistant porous layer]

[0117] As for the thickness of the heat-resistant porous layer, from the perspective of the heat resistance or operability of the diaphragm, it is preferably 0.5 μm or more on one side, more preferably 1.0 μm or more on one side, and further preferably 1.5 μm or more on one side. From the perspective of ion permeability and battery energy density, it is preferably 8.0 μm or less on one side, more preferably 6.0 μm or less on one side, and further preferably 4.0 μm or less on one side.

[0118] Regarding the thickness of the heat-resistant porous layer, when the heat-resistant porous layer exists on both sides of the porous substrate, the total thickness of both sides is preferably 1.0 μm or more, more preferably 2.0 μm or more, further preferably 3.0 μm or more, preferably 16.0 μm or less, more preferably 12.0 μm or less, further preferably 8.0 μm or less, and further more preferably 6.0 μm or less.

[0119] When the heat-resistant porous layer exists on both sides of the porous substrate, the difference (μm) between the thickness of one heat-resistant porous layer and the thickness of the other heat-resistant porous layer is preferably as small as possible, and is preferably 20% or less of the total thickness (μm) of both sides.

[0120] The mass per unit area of the heat-resistant porous layer is as follows: In terms of heat resistance and operability of the separator, the total mass of both surfaces is preferably 1.0 g / m2. 2 More than 2.0 g / m 2 More preferably, 3.0 g / m 2 From the viewpoint of ion permeability and battery energy density, the total of both sides is preferably 30.0 g / m 2 Below, more preferably 20.0g / m 2 Below, more preferably 10.0 g / m 2 Below, further more preferably 6.0g / m 2 the following.

[0121] When the heat-resistant porous layer is present on both sides of the porous substrate, from the viewpoint of suppressing curling of the separator or improving the cycle characteristics of the battery, the difference (g / m2) between the mass per unit area of one heat-resistant porous layer and the mass per unit area of the other heat-resistant porous layer is preferably calculated. 2 ) is smaller, the better, preferably the total amount of both sides (g / m 2 ) is less than 20%.

[0122] The porosity of the heat-resistant porous layer is preferably 30% or greater, more preferably 35% or greater, and even more preferably 40% or greater from the perspective of ion permeability. From the perspective of the mechanical strength and heat resistance of the heat-resistant porous layer, it is preferably 70% or less, more preferably 65% or less, and even more preferably 60% or less. The porosity ε (%) of the heat-resistant porous layer is calculated by the following formula.

[0123] ε={1-(Wa / da+Wb / db+Wc / dc+…+Wn / dn) / t}×100

[0124] Here, the constituent materials of the heat-resistant porous layer are a, b, c, ..., n, and the mass per unit area of each constituent material is Wa, Wb, Wc, ..., Wn (g / cm 2 ), the true density of each constituent material is da, db, dc, ..., dn (g / cm 3 ), the thickness of the heat-resistant porous layer is t (cm).

[0125] The average pore diameter of the heat-resistant porous layer is preferably 10 nm to 200 nm. When the average pore diameter is 10 nm or greater, even if the resin contained in the heat-resistant porous layer swells during impregnation with an electrolyte, pore clogging is less likely to occur. When the average pore diameter is 200 nm or less, ion migration in the heat-resistant porous layer is highly uniform, resulting in excellent battery cycle and load characteristics.

[0126] The average pore diameter (nm) of the heat-resistant porous layer was calculated from the following formula assuming that all pores were cylindrical.

[0127] d=4V / S

[0128] Wherein, 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 1m 2 Pore surface area of the heat-resistant porous layer.

[0129] Every 1m 2 The pore volume V of the heat-resistant porous layer is calculated from the porosity of the heat-resistant porous layer.

[0130] Every 1m 2 The pore surface area S of the heat-resistant porous layer is determined by the following method.

[0131] First, the specific surface area (m2) of the porous substrate was calculated from the amount of nitrogen adsorption by applying the BET formula in the nitrogen adsorption method. 2 / g) and the specific surface area of the membrane (m 2 / g). Their specific surface area (m 2 / g) multiplied by their respective weight per unit area (g / m 2 ), calculate each 1m 2 Then, from every 1m 2 The pore surface area of the diaphragm is reduced by 2 The pore surface area of the porous substrate is calculated per 1m 2 The heat-resistant porous layer has a pore surface area S. The so-called basis weight is the mass per unit area.

[0132] From the viewpoint of the bonding strength between the diaphragm and the electrode, the peel strength between the porous substrate and the heat-resistant porous layer is preferably more than 0.30N / 12mm, more preferably more than 0.40N / 12mm, further preferably more than 0.50N / 12mm. From the above-mentioned viewpoint, the higher the peel strength between the porous substrate and the heat-resistant porous layer, the more preferred, but usually the peel strength is less than 2.00N / 12mm. When the diaphragm has a heat-resistant porous layer on both sides of the porous substrate, the peel strength between the porous substrate and the heat-resistant porous layer is preferably in the above-mentioned range on both sides of the porous substrate.

[0133] The peel strength (N / 12 mm) between the porous substrate and the heat-resistant porous layer was determined by a T-peel test in which the separator was peeled in the MD direction. The test piece was a rectangular piece with a MD of 70 mm and a TD of 12 mm. The tensile speed for the T-peel test was 300 mm / min.

[0134] [Adhesive layer]

[0135] The separator of the present disclosure may further include other layers in addition to the porous substrate and the heat-resistant porous layer. Examples of such other layers include an adhesive layer. The adhesive layer is provided as the outermost layer of the separator and is bonded to the electrode when the separator and the electrode are superimposed and pressurized or hot-pressed.

[0136] Examples of materials constituting the adhesive layer include resins, inorganic fillers, and organic fillers. Examples of the adhesive layer include: a porous layer having numerous micropores within, allowing gas or liquid to pass from one surface to the other; a porous film having numerous micropores; and a layer having numerous particles arranged in a planar direction, allowing gas or liquid to pass from one surface to the other via the gaps between the particles.

[0137] Examples of the form of the resin constituting the adhesive layer include fibril-shaped resins, film-shaped resins, and particulate-shaped resins. Using these forms of resins, inorganic fillers or organic fillers can be connected and contained in the adhesive layer.

[0138] Examples of the resin constituting the adhesive layer include polyvinylidene fluoride resins, acrylic resins, fluororubbers, styrene-butadiene copolymers, homopolymers or copolymers of vinyl nitrile compounds (acrylonitrile, methacrylonitrile, etc.), carboxymethyl cellulose, hydroxyalkyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, polyethers (polyethylene oxide, polypropylene oxide, etc.), polysulfones, polyketones, polyether ketones, polyether sulfones, and mixtures thereof.

[0139] When the adhesive layer contains an inorganic filler, examples of the inorganic filler include: metal sulfate particles such as barium sulfate, strontium sulfate, calcium sulfate, calcium sulfate dihydrate, alunite, and jarosite; metal hydroxide particles such as magnesium hydroxide, aluminum hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, cerium hydroxide, nickel hydroxide, and boron hydroxide; metal oxide particles such as magnesium oxide, aluminum oxide (Al2O3), boehmite (aluminum oxide monohydrate), titanium dioxide (TiO2), silicon dioxide (SiO2), zirconium oxide (ZrO2), barium titanate (BaTiO3), and zinc oxide; metal carbonate particles such as calcium carbonate and magnesium carbonate; metal nitride particles such as magnesium nitride, aluminum nitride, calcium nitride, and titanium nitride; metal fluoride particles such as magnesium fluoride and calcium fluoride; and clay mineral particles such as calcium silicate, calcium phosphate, apatite, and talc. These inorganic fillers may also be surface-modified with a silane coupling agent or the like. These inorganic fillers may be used alone or in combination of two or more.

[0140] When the adhesive layer contains an organic filler, examples of the organic filler include particles formed from crosslinked polymers such as crosslinked poly(meth)acrylic acid, crosslinked poly(meth)acrylate, crosslinked polystyrene, crosslinked polysiloxane, crosslinked polydivinylbenzene, styrene-divinylbenzene copolymer crosslinked products, melamine resins, phenolic resins, and benzoguanamine-formaldehyde condensates; and particles formed from heat-resistant polymers such as polysulfone, polyacrylonitrile, aromatic polyamide, and polyacetal. These organic fillers may be used alone or in combination of two or more.

[0141] As the diaphragm having an adhesive layer, for example, there can be mentioned: a diaphragm having a heat-resistant porous layer on both sides of a porous substrate and an adhesive layer on each of the two heat-resistant porous layers; a diaphragm having a heat-resistant porous layer on both sides of a porous substrate and an adhesive layer on one heat-resistant porous layer; a diaphragm having a heat-resistant porous layer on one side of a porous substrate and an adhesive layer on the other side of the porous substrate; a diaphragm having a heat-resistant porous layer on one side of a porous substrate and an adhesive layer on the heat-resistant porous layer; a diaphragm having a heat-resistant porous layer on one side of a porous substrate and an adhesive layer on the heat-resistant porous layer.

[0142] [Characteristics of diaphragm]

[0143] As for the thickness of the separator, from the viewpoint of the mechanical strength of the separator, it is preferably 8 μm or more, more preferably 10 μm or more, and further preferably 12 μm or more. From the viewpoint of the energy density of the battery, it is preferably 25 μm or less, more preferably 22 μm or less, and further preferably 20 μm or less.

[0144] From the perspective of the mechanical strength of the separator and the short-circuit resistance of the battery, the puncture strength of the separator is preferably 150 gf to 1000 gf, more preferably 200 gf to 600 gf. The puncture strength of the separator is measured using the same method as that of the porous substrate.

[0145] From the viewpoint of adhesion to the electrode, operability of the separator, ion permeability, and mechanical strength, the porosity of the separator is preferably 30% to 70%, more preferably 35% to 65%, and even more preferably 40% to 60%.

[0146] From the viewpoint of mechanical strength and ion permeability of the separator, the Gurley value (JIS P8117:2009) of the separator is preferably 80 to 400 sec / 100 mL, more preferably 120 to 300 sec / 100 mL, and even more preferably 150 to 250 sec / 100 mL.

[0147] The area shrinkage of the separator when heat-treated at 135° C. for 1 hour is preferably 30% or less, more preferably 20% or less, further preferably 15% or less, and even more preferably 11% or less.

[0148] The separator preferably has an area shrinkage ratio of 45% or less, more preferably 30% or less, and even more preferably 20% or less when subjected to a heat treatment at 150°C for 1 hour.

[0149] The area shrinkage ratio when the separator is heat-treated at 135° C. or 150° C. for 1 hour is determined by the following measuring method.

[0150] The diaphragm is cut into a rectangle with MD180mm and TD60mm to make a test piece. For this test piece, marks are marked on the line that bisects TD and is 20mm and 170mm away from the end of one side (referred to as point A and point B respectively). Furthermore, marks are marked on the line that bisects MD and is 10mm and 50mm away from the end of one side (referred to as point C and point D respectively). A fixture is installed on the marked test piece (the location of the fixture is between the end closest to point A and point A.), and it is suspended in an oven with the temperature inside the box adjusted to 135°C or 150°C, and heat treated for 1 hour in a tension-free state. The lengths between AB and CD are measured before and after heat treatment, and the area shrinkage rate is calculated by the following formula.

[0151] Area shrinkage (%) = {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

[0152] The area shrinkage rate during heat treatment of the separator can be controlled by the volume ratio of the barium sulfate particles in the heat-resistant porous layer, the thickness of the heat-resistant porous layer, the porosity of the heat-resistant porous layer, and the like.

[0153] [Method for manufacturing diaphragm]

[0154] The separator of the present disclosure 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 the present disclosure, the wet coating method involves curing the coating layer in a coagulation solution, while the dry coating method involves curing the coating layer by drying. An example embodiment of the wet coating method is described below.

[0155] The wet coating method is a method in which a coating liquid containing a heat-resistant resin and barium sulfate particles is applied to a porous substrate, the substrate is immersed in a coagulation liquid to solidify the coating layer, the substrate is pulled out of the coagulation liquid, washed with water, and dried.

[0156] The coating liquid for forming a heat-resistant porous layer is prepared by dissolving or dispersing a heat-resistant resin and barium sulfate particles in a solvent. Other components other than the heat-resistant resin and inorganic particles are dissolved or dispersed in the coating liquid as needed.

[0157] The solvent used in the preparation of the coating liquid includes a solvent capable of dissolving the heat-resistant resin (hereinafter also referred to as a "good solvent"). Examples of the good solvent include polar amide solvents such as N-methylpyrrolidone, dimethylacetamide, and dimethylformamide.

[0158] From the perspective of forming a porous layer with a good porous structure, the solvent used in preparing the coating liquid may contain a phase separation agent that induces phase separation. Therefore, the solvent used in preparing the coating liquid may also be a mixed solvent of a good solvent and a phase separation agent. The phase separation agent is preferably mixed with the good solvent in an amount that ensures a viscosity within a range suitable for coating. Examples of the phase separation agent include water, methanol, ethanol, propanol, butanol, butanediol, ethylene glycol, propylene glycol, and tripropylene glycol.

[0159] When the solvent used in preparing the coating liquid is a mixed solvent of a good solvent and a phase separation agent, from the viewpoint of forming a good porous structure, the mixed solvent preferably contains 60% by mass or more of the good solvent and 5% to 40% by mass of the phase separation agent.

[0160] From the viewpoint of forming a good porous structure, the resin concentration of the coating liquid is preferably 1% to 20% by mass. From the viewpoint of forming a good porous structure, the inorganic particle concentration of the coating liquid is preferably 0.5% to 50% by mass.

[0161] The coating liquid may contain dispersants such as surfactants, wetting agents, defoaming agents, pH adjusters, etc. These additives may remain in the heat-resistant porous layer as long as they are electrochemically stable within the operating range of the non-aqueous secondary battery and do not inhibit the reaction within the battery.

[0162] As a means for applying the coating liquid to the porous substrate, there can be mentioned a Meyer rod, a die coater, a reverse roll coater, a roll coater, a gravure coater, etc. When forming a heat-resistant porous layer on both sides of the porous substrate, it is preferable to apply the coating liquid to both sides of the porous substrate simultaneously from the viewpoint of productivity.

[0163] The coating layer can be cured by immersing the porous substrate with the coating layer formed thereon in a coagulation solution to induce phase separation in the coating layer while curing the resin, thereby obtaining a laminate composed of the porous substrate and the heat-resistant porous layer.

[0164] The coagulation liquid typically contains the good solvent and phase separation agent used in the preparation of the coating liquid, as well as water. From a production perspective, the mixing ratio of the good solvent and phase separation agent is preferably consistent with the mixing ratio of the mixed solvent used in the preparation of the coating liquid. From the perspective of porous structure formation and productivity, the water content in the coagulation liquid is preferably 40% to 90% by mass. The temperature of the coagulation liquid is, for example, 20°C to 50°C.

[0165] After the coating layer is cured in the coagulation liquid, the laminate is removed from the coagulation liquid and washed with water. The coagulation liquid is removed from the laminate by washing with water. The laminate is then dried to remove water. Washing can be performed, for example, by transporting the laminate in a water bath. Drying can be performed, for example, by transporting the laminate in a high-temperature environment, blowing air over the laminate, or contacting the laminate with heated rollers. The drying temperature is preferably 40°C to 80°C.

[0166] The separator of the present disclosure can also be produced by a dry coating method. The dry coating method is a method in which a coating liquid is applied to a porous substrate, and the coating layer is dried to volatilize and remove the solvent, thereby forming a heat-resistant porous layer on the porous substrate.

[0167] The separator of the present disclosure can also be manufactured by forming a heat-resistant porous layer as a separate sheet, laminating the heat-resistant porous layer with a porous substrate, and forming a composite using thermocompression bonding or an adhesive. Examples of methods for forming the heat-resistant porous layer as a separate sheet include forming the heat-resistant porous layer on a release sheet using the aforementioned wet coating method or dry coating method.

[0168] When the diaphragm of the present disclosure has an adhesive layer, the adhesive layer can be formed by a wet coating method or a dry coating method. The wet coating method of the adhesive layer is the same method as the wet coating method of the heat-resistant porous layer. The dry coating method of the adhesive layer can be the same method as the dry coating method of the heat-resistant porous layer, or it can be a method of applying and drying an aqueous dispersion containing the constituent materials. The adhesive layer formed on the release sheet can also be overlapped with the porous substrate or the heat-resistant porous layer and composited by thermal compression bonding or an adhesive.

[0169] The adhesive layer may be formed after the heat-resistant porous layer is formed on the porous substrate. Alternatively, the adhesive layer may be provided on one side of the porous substrate, and then the heat-resistant porous layer may be formed on the other side of the porous substrate. Alternatively, multiple layers of multiple coating liquids may be applied to the porous substrate, thereby simultaneously forming the heat-resistant porous layer and the adhesive layer on the porous substrate.

[0170] <Non-aqueous Secondary Battery>

[0171] The non-aqueous secondary battery disclosed herein generates electromotive force through the doping and dedoping of lithium ions. The battery comprises a positive electrode, a negative electrode, and a separator for the non-aqueous secondary battery disclosed herein. Doping refers to the absorption, loading, adsorption, or insertion of lithium ions into the active material of an electrode, such as a positive electrode.

[0172] The non-aqueous secondary battery disclosed herein has a structure in which a battery element (composed of a negative electrode and a positive electrode facing each other with a separator interposed therebetween) is enclosed in an outer packaging material along with an electrolyte solution. The non-aqueous secondary battery disclosed herein is suitable for non-aqueous electrolyte secondary batteries, particularly lithium-ion secondary batteries.

[0173] Hereinafter, examples of the positive electrode, negative electrode, electrolyte solution, and outer casing material included in the non-aqueous secondary battery of the present disclosure will be described.

[0174] As an embodiment of the positive electrode, an active material layer containing a positive electrode active material and a binder resin is formed on a current collector. The active material layer may further contain a conductive additive. As the positive electrode active material, for example, a transition metal oxide containing lithium can be cited, specifically, LiCoO2, LiNiO2, LiMn 1 / 2 Ni 1 / 2 O2、LiCo 1 / 3Mn 1 / 3 Ni 1 / 3 O2, LiMn2O4, LiFePO4, LiCo 1 / 2 Ni 1 / 2 O2、LiAl 1 / 4 Ni 3 / 4O2, etc. Examples of binder 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 5 to 20 μm.

[0175] As an embodiment of the negative electrode, there can be mentioned a structure in which an active material layer containing a negative electrode active material and a binder resin is formed on a current collector. The active material layer may further contain a conductive additive. As the negative electrode active material, there can be mentioned materials that can electrochemically absorb lithium ions, specifically, for example, carbon materials; alloys of silicon, tin, aluminum, etc. with lithium; Wood's metal; etc. As binder resins, there can be mentioned, for example, polyvinylidene fluoride resins, styrene-butadiene copolymers, etc. As conductive additives, there can be mentioned carbon materials such as acetylene black, Ketjen black, graphite powder, ultrafine carbon fibers, etc. As current collectors, there can be mentioned, for example, copper foil, nickel foil, stainless steel foil, etc. with a thickness of 5μm to 20μm. In addition, metal lithium foil can also be used as the negative electrode instead of the above-mentioned negative electrode.

[0176] 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, ethyl methyl carbonate, and their fluorinated derivatives; and cyclic esters such as γ-butyrolactone and γ-valerolactone. These can be used alone or in combination. A suitable electrolyte solution is one in which a cyclic carbonate and a chain carbonate are mixed at a mass ratio of 20:80 to 40:60 (cyclic carbonate:chain carbonate), and a lithium salt is dissolved in a concentration of 0.5 mol / L to 1.5 mol / L.

[0177] Examples of the outer packaging material include metal cases, aluminum laminated film packaging, etc. The shape of the battery includes rectangular, cylindrical, button-shaped, etc. The separator of the present disclosure is suitable for any shape.

[0178] The non-aqueous secondary battery of the present disclosure can be manufactured by, for example, using any of the following methods (1) to (3) after manufacturing a laminated body in which the separator of the present disclosure is disposed between the positive electrode and the negative electrode. Hereinafter, the process of hot pressing the separator while impregnating it with an electrolyte is referred to as "wet hot pressing," and the process of hot pressing the separator while not impregnating it with an electrolyte is referred to as "dry hot pressing."

[0179] (1) After the stack is hot-pressed (dry hot-pressing) to bond the electrodes to the diaphragm, it is placed in an outer packaging material (e.g., aluminum laminate film packaging. The same applies hereinafter), and an electrolyte is injected into it to make the outer packaging material into a vacuum state. The stack is then further hot-pressed (wet hot-pressing) from above the outer packaging material to bond the electrodes to the diaphragm and seal the outer packaging material.

[0180] (2) The stack is placed in an outer packaging material, an electrolyte is injected into the stack, and the outer packaging material is made into a vacuum state. The stack is then hot-pressed (wet hot-pressed) from above the outer packaging material to bond the electrode and the separator and seal the outer packaging material.

[0181] (3) After the stacked body is hot-pressed (dry hot-pressing) to bond the electrodes and separators, it is placed in an outer packaging material, an electrolyte is injected therein, and after the outer packaging material is vacuumed, the outer packaging material is sealed.

[0182] The conditions for wet hot pressing in the above-mentioned production method are preferably a pressing temperature of 70°C to 110°C and a pressing pressure of 0.5 MPa to 2 MPa. The conditions for dry hot pressing in the above-mentioned production method are preferably a pressing temperature of 20°C to 100°C and a pressing pressure of 0.5 MPa to 9 MPa. The pressing time is preferably adjusted according to the pressing temperature and pressure, for example, within a range of 0.5 to 60 minutes.

[0183] When manufacturing a laminated body in which a separator is arranged between a positive electrode and a negative electrode, the method of arranging the separator between the positive electrode and the negative electrode can be a method in which the positive electrode, the separator, and the negative electrode are stacked in sequence in at least one layer (the so-called stacking method), or a method in which the positive electrode, the separator, the negative electrode, and the separator are overlapped in sequence and wound along the length direction.

[0184] Example

[0185] The following examples provide a more detailed description of the separator and non-aqueous secondary battery of the present disclosure. The materials, amounts, ratios, and processing steps shown in the following examples may be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the separator and non-aqueous secondary battery of the present disclosure should not be construed as being limited based on the specific examples shown below.

[0186] <Measurement Method, Evaluation Method>

[0187] The measurement methods and evaluation methods used in Examples and Comparative Examples are as follows.

[0188] [Average primary particle size of barium sulfate particles]

[0189] Before adding barium sulfate particles to the coating solution for forming the heat-resistant porous layer, the major diameters of 100 randomly selected particles were measured under a scanning electron microscope (SEM) and the average value was calculated as the average primary particle size (μm) of the barium sulfate particles. The SEM magnification was 50,000 to 300,000 times.

[0190] [Content of barium sulfate particles]

[0191] The volume ratio Va (volume %) of the barium sulfate particles is determined from the following formula based on the amounts and true densities of the barium sulfate particles and the heat-resistant resin used in the coating solution for forming the heat-resistant porous layer.

[0192] Va={(Xa / Da) / (Xa / Da+Xb / Db)}×100

[0193] Here, the barium sulfate particles are a, the heat-resistant resin is b, the usage of each component material is Xa, Xb (g), and the true density of each component material is Da, Db (g / cm 3 ).

[0194] [Thickness of porous substrate and separator]

[0195] The thickness (μm) of the porous substrate and separator was measured at 20 points within a 10 cm square using a contact thickness gauge (Mitutoyo Co., Ltd., LITEMATIC VL-50S) and the averaged results were obtained. A spherical probe with a 10 mm radius (Mitutoyo Co., Ltd., Superhard Spherical Probe φ10.5) was used as the measurement terminal, and a load of 0.19 N was applied during the measurement.

[0196] [Thickness of heat-resistant porous layer]

[0197] The thickness of the heat-resistant porous layer (total of both surfaces, μm) was determined by subtracting the thickness (μm) of the porous substrate from the thickness (μm) of the separator.

[0198] [Mass of the heat-resistant porous layer]

[0199] The separator was cut into 10 cm × 10 cm pieces, and the mass was measured. The mass was divided by the area to obtain the weight per unit area of the separator (g / m 2 The porous substrate used in the manufacture of the separator was cut into 10 cm × 10 cm pieces, the mass was measured, and the weight per unit area of the porous substrate (g / m2) was obtained by dividing the mass by the area. 2 The mass per unit area of the heat-resistant porous layer (total of both sides, g / m2) was calculated by subtracting the mass per unit area of the porous substrate from the mass per unit area of the separator. 2).

[0200] [Porosity of porous substrate]

[0201] The porosity ε (%) of the porous substrate is determined by the following formula.

[0202] ε={1-Ws / (ds·t)}×100

[0203] Here, Ws is the weight per unit area of the porous substrate (g / m 2 ), ds is the true density of the porous substrate (g / cm 3 ), t is the thickness of the porous substrate (μm).

[0204] [Porosity of heat-resistant porous layer]

[0205] The porosity ε (%) of the heat-resistant porous layer can be determined from the following formula.

[0206] ε={1-(Wa / da+Wb / db+Wc / dc+…+Wn / dn) / t}×100

[0207] Here, the constituent materials of the heat-resistant porous layer are a, b, c, ..., n, and the mass per unit area of each constituent material is Wa, Wb, Wc, ..., Wn (g / cm 2 ), the true density of each constituent material is da, db, dc, ..., dn (g / cm 3 ), the thickness of the heat-resistant porous layer is t (cm).

[0208] [Gurley value]

[0209] The Gurley values (seconds / 100 mL) of the porous substrate and the separator were measured using a Gurley densometer (G-B2C, Toyo Seiki Co., Ltd.) in accordance with JIS P8117:2009.

[0210] [Peel Strength between Porous Base Material and Heat-Resistant Porous Layer]

[0211] The diaphragm was subjected to a T-peel test. Specifically, an adhesive tape (3M, #550, 12 mm wide) was attached to the surface of one side of the diaphragm (when attached, the length direction of the adhesive tape was aligned with the MD of the diaphragm.), and the diaphragm was cut into a rectangle with MD70 mm and TD12 mm together with the adhesive tape. The adhesive tape was peeled off a little together with the heat-resistant porous layer immediately below it, and the end portion separated into two parts was grasped with Tensilon (Orientec Co., Ltd., RTC-1210A) to perform a T-peel test. It should be noted that the adhesive tape was used as a support for peeling the heat-resistant porous layer from the porous substrate. The tensile speed of the T-peel test was 300 mm / min, and the load (N / 12 mm) from 10 mm to 40 mm was collected at intervals of 0.4 mm after the start of the measurement, and the average value was calculated. Furthermore, the loads (N / 12 mm) of the ten test pieces were averaged.

[0212] [Area shrinkage due to heat treatment]

[0213] Cut the diaphragm into a rectangle with MD180mm and TD60mm to make a test piece. For this test piece, mark the parts 20mm and 170mm away from the end of one side on the line that divides TD into two equal parts (referred to as point A and point B respectively). Furthermore, mark the parts 10mm and 50mm away from the end of one side on the line that divides MD into two equal parts (referred to as point C and point D respectively). Install a fixture on it (the position of the fixture is between the end closest to point A and point A), hang it in an oven with the temperature inside the box adjusted to 135℃ or 150℃, and implement a heat treatment for 1 hour under tension-free conditions. Measure the length between AB and CD before and after heat treatment, calculate the area shrinkage rate by the following formula, and average the area shrinkage rates of 10 test pieces.

[0214] Area shrinkage (%) = {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

[0215] [Spot Heating Test in the Presence of Electrolyte (Wet Spot Heating Test)]

[0216] Cut the separator into a 50 mm MD x 50 mm TD test piece. Soak the test piece in electrolyte for 1 minute, then remove and wipe away any excess. The electrolyte used was 1 mol / L LiBF4-ethylene carbonate:ethyl methyl carbonate (3:7 by volume).

[0217] The test piece impregnated with electrolyte was placed on a horizontal platform. A soldering iron with a tip diameter of 2 mm was heated. The tip of the soldering iron was brought into point contact with the diaphragm surface for 60 seconds while the tip temperature was kept at 260°C or 400°C. The area of the hole formed in the diaphragm by the point contact was measured (mm 2 ), and the areas of the holes of the 10 test pieces were averaged. The higher the heat resistance of the separator, the smaller the area of the holes produced in the separator.

[0218] <Production of diaphragm>

[0219] [Example 1]

[0220] Meta-type wholly aromatic polyamide (trade name: CONEX (manufactured by Teijin Limited)) and barium sulfate particles were prepared as materials for the heat-resistant porous layer.

[0221] Meta-type wholly aromatic polyamide was dissolved in dimethylacetamide (DMAc) so as to have a resin concentration of 6.5% by mass, and barium sulfate particles were further stirred and mixed to obtain a coating liquid (1).

[0222] An appropriate amount of coating liquid (1) was loaded onto a Meyer rod and applied to both sides of a polyethylene microporous membrane (thickness 10 μm, porosity 48%, Gurley value 72 seconds / 100 mL). The coating was applied so that the amount of coating on the front and back sides of the polyethylene microporous membrane was equal. The membrane was immersed in a coagulation solution (DMAc:water = 50:50 [mass ratio], liquid temperature 40°C) to solidify the coating layer, and then washed in a water washing tank at a water temperature of 40°C and dried. As described above, a diaphragm having a heat-resistant porous layer formed on both sides of the polyethylene microporous membrane was obtained.

[0223] [Examples 2 to 8, Comparative Examples 1 to 4]

[0224] Each separator was produced in the same manner as in Example 1, except that the particle size of the barium sulfate particles contained in the heat-resistant porous layer and / or the volume ratio of the barium sulfate particles were changed to the specifications described in Table 1.

[0225] [Example 9]

[0226] A separator was produced in the same manner as in Example 1 except that the meta-type wholly aromatic polyamide contained in the heat-resistant porous layer was replaced with a para-type wholly aromatic polyamide (trade name: Technora (manufactured by Teijin Limited)).

[0227] [Example 10]

[0228] A separator was produced in the same manner as in Example 1 except that the meta-type wholly aromatic polyamide contained in the heat-resistant porous layer was changed to polyamideimide (trade name: 4000T HV (manufactured by Solvay)).

[0229] The composition, physical properties, and evaluation results of each separator of Examples 1 to 10 and Comparative Examples 1 to 4 are shown in Table 1. In Table 1, the meta-type wholly aromatic polyamide used for forming the heat-resistant porous layer is described as "meta-type aromatic polyamide."

[0230] In Table 1, the para-type wholly aromatic polyamide of Example 9 used for forming the heat-resistant porous layer is described as “para-type aromatic polyamide”.

[0231] In Table 1, the polyamideimide used in Example 10 for forming the heat-resistant porous layer is described as “PAI”.

[0232] [Table 1]

[0233]

[0234] Wet spot heating tests were performed on the separators of Comparative Example 1, Example 1, and Example 9. In the case of the separator of Comparative Example 1, the pore areas at the time of the tests at 260°C and 400°C were 8.6 mm and 8.6 mm, respectively. 2 、14.0mm 2 In the case of the diaphragm of Example 1, the pore areas are 4.3 mm 2 , 11.9mm 2 , which is smaller than that of Comparative Example 1. In the case of the diaphragm of Example 9, the pore areas are 0 mm 2 , 0mm 2 , no holes are opened.

[0235] [Example 11]

[0236] Adhesive layers were provided on both surfaces of the separator of Example 1 by the following method to produce a separator of Example 11.

[0237] An aqueous dispersion (solids concentration: 7% by mass) was prepared by dispersing polyvinylidene fluoride resin particles (melting point 140°C, volume average particle size 0.2 μm) and acrylic resin particles (glass transition temperature 59°C, volume average particle size 0.5 μm) in water at a mass ratio of 70:30. The separator of Example 1 was passed between a pair of bar coaters loaded with an appropriate amount of this aqueous dispersion. Equal amounts of the aqueous dispersion were applied to both surfaces of the separator, followed by drying. This produced a separator having a heat-resistant porous layer and an adhesive layer formed on both surfaces of a polyethylene microporous membrane.

[0238] [Example 12]

[0239] Adhesive layers were provided on both surfaces of the separator of Example 9 by the same method as in Example 11, thereby producing a separator of Example 12.

[0240] [Example 13]

[0241] Adhesive layers were provided on both surfaces of the separator of Example 10 by the same method as in Example 11, thereby producing a separator of Example 13.

[0242] The adhesive strength between the separator of Example 1 and the separators of Examples 11 to 13 and the electrodes was measured. The adhesive strength between the separators of Examples 11 to 13 and the electrodes was higher than that of the separator of Example 1. The electrodes used in the measurement of the adhesive strength between the electrodes and the measurement method are as follows.

[0243] -Making the positive electrode-

[0244] 94 parts by mass of lithium cobalt oxide powder, 3 parts by mass of acetylene black, 3 parts by mass of polyvinylidene fluoride resin, and an appropriate amount of N-methyl-2-pyrrolidone were mixed in a double-arm mixer to prepare a slurry with a polyvinylidene fluoride resin concentration of 5% by mass. This slurry was applied to one side of a 20 μm thick aluminum foil, dried, and then pressed to obtain a positive electrode.

[0245] - Fabrication of the negative electrode -

[0246] A double-arm mixer was used to mix 300 parts by mass of artificial graphite, 7.5 parts by mass of an aqueous dispersion containing 40% by mass of a modified styrene-butadiene copolymer, 3 parts by mass of carboxymethyl cellulose, and an appropriate amount of water to prepare a slurry. This slurry was applied to one side of a 10 μm thick copper foil, dried, and then pressed to produce a negative electrode.

[0247] The positive and negative electrodes were cut into rectangles measuring 70 mm and 15 mm, respectively. The separator was cut into a rectangle measuring 72 mm in diameter and 18 mm in depth. The positive electrode, separator, and negative electrode were stacked in this order and hot-pressed (85°C, 1 MPa, 30 seconds) to bond the electrodes and separator to obtain test pieces.

[0248] The test piece is fixed to the lower chuck of Tensilon (A&D company, STB-1225S). At this time, the test piece is fixed to Tensilon in such a way that the length direction of the test piece (i.e., the MD of the diaphragm) becomes the direction of gravity. The positive electrode is peeled off from the diaphragm from one end of the bottom by about 2 cm, and the end is fixed to the upper chuck for a 180 ° peel test. The tensile speed of the 180 ° peel test is 300 mm / min, and the load (N) from 10 mm to 40 mm is collected at intervals of 0.4 mm after the start of the measurement, and the average value is calculated. The loads of the three test pieces are further averaged as the bonding strength (N / 15 mm) between the electrode and the diaphragm.

[0249] The entire disclosure of Japanese Patent Application No. 2020-130639 filed on July 31, 2020 is incorporated into this specification by reference.

[0250] All documents, patent applications, and technical standards described in this specification are incorporated herein by reference to the same extent as if each document, patent application, and technical standard were specifically and individually indicated.

Claims

1. A separator for a non-aqueous secondary battery, comprising: a porous substrate; and a heat-resistant porous layer provided on one or both surfaces of the porous substrate and comprising a heat-resistant resin and barium sulfate particles; The heat-resistant resin is at least one selected from the group consisting of wholly aromatic polyamide, polyamideimide, poly-N-vinylacetamide, polyacrylamide, copolymerized polyether polyamide, polyimide, and polyetherimide. The content of the heat-resistant resin contained in the heat-resistant porous layer is 85% by mass to 100% by mass relative to the total amount of the resin contained in the heat-resistant porous layer. The average primary particle size of the barium sulfate particles contained in the heat-resistant porous layer is 0.01 μm or more and less than 0.30 μm. The volume ratio of the barium sulfate particles in the solid content of the heat-resistant porous layer is 5 volume % or more and less than 30 volume %.

2. The non-aqueous secondary battery separator according to claim 1, wherein The volume ratio of the barium sulfate particles in the solid content of the heat-resistant porous layer is 5 volume % or more and less than 27 volume %.

3. The non-aqueous secondary battery separator according to claim 1 or claim 2, wherein: The peel strength between the porous substrate and the heat-resistant porous layer is 0.30 N / 12 mm or more.

4. The non-aqueous secondary battery separator according to claim 1 or claim 2, wherein: When the non-aqueous secondary battery separator is heat-treated at 135° C. for 1 hour, the area shrinkage is 30% or less.

5. The non-aqueous secondary battery separator according to claim 1 or claim 2, wherein When the non-aqueous secondary battery separator is heat-treated at 150° C. for 1 hour, the area shrinkage is 45% or less.

6. The non-aqueous secondary battery separator according to claim 1 or claim 2, wherein: The porosity of the heat-resistant porous layer is 30% to 70%.

7. The non-aqueous secondary battery separator according to claim 1 or claim 2, wherein: The mass per unit area of the heat-resistant porous layer is 1.0 g / m2 in total for both sides. 2 ~30.0g / m 2 . 8 . The non-aqueous secondary battery separator according to claim 1 , further comprising an adhesive layer as an outermost layer on one or both surfaces thereof.

9. A non-aqueous secondary battery comprising a positive electrode, a negative electrode, and the non-aqueous secondary battery separator according to any one of claims 1 to 8 disposed between the positive electrode and the negative electrode, wherein the non-aqueous secondary battery generates an electromotive force by doping and dedoping lithium ions.

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