Separator for non-aqueous secondary batteries and non-aqueous secondary batteries

Abstract

To provide a separator for non-aqueous secondary batteries that exhibits excellent adhesion to both the positive and negative electrodes through bonding treatment at relatively low temperatures and pressures. [Solution] The separator for non-aqueous secondary batteries comprises a polyolefin microporous membrane, a surface layer (A) containing an acrylic resin disposed on one side of the polyolefin microporous membrane, and a surface layer (C) containing a polyvinyl chloride resin disposed on the other side of the polyolefin microporous membrane.

Description

[Technical Field]

[0001] This disclosure relates to a separator for non-aqueous secondary batteries and a non-aqueous secondary battery. [Background technology]

[0002] The adhesion of the separator for non-aqueous secondary batteries to the electrodes is important from the following perspectives. (1) To prevent the separator from separating from the electrode due to the expansion and contraction of the electrode active material layer during charging and discharging. (2) By adhering a separator to the electrodes, the rigidity of the battery cell is increased, thereby preventing deformation of the battery cell caused by the expansion and contraction of the electrode active material layer during charging and discharging. (3) Suppress the formation of an electrolyte layer between the electrode and the separator, thereby increasing the energy density of the battery.

[0003] A separator is known that has a surface layer with excellent adhesion to electrodes. For example, Patent Document 1 discloses a separator for a non-aqueous secondary battery comprising a porous substrate, a heat-resistant layer containing barium sulfate particles and a binder resin, and a surface layer consisting of polyvinylidene fluoride resin particles and acrylic resin particles. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2021-192385 [Overview of the project] [Problems that the invention aims to solve]

[0005] Generally, the positive electrode active material layer is a composite layer in which an active material such as a lithium-containing transition metal oxide is bound with a binder resin made of polyvinylidene fluoride resin. A separator surface layer containing polyvinylidene fluoride resin or acrylic resin adheres easily to this composite layer. On the one hand, generally, the negative electrode active material layer is a mixture layer in which an active material such as graphite is bound with a binder resin made of a styrene-butadiene copolymer. In order to adhere a separator surface layer containing a polyvinylidene fluoride-based resin or an acrylic-based resin to this mixture layer to the negative electrode, a relatively high-temperature and high-pressure adhesion treatment is required. When a high-temperature and high-pressure adhesion treatment is performed to adhere the surface layer of the separator to the electrode, there is a problem that the pores of the separator are blocked, the ion mobility deteriorates, and the charge and discharge characteristics of the battery decrease.

[0006] There are also the following problems with the high-temperature and high-pressure adhesion treatment of the separator to the electrode. If a high-temperature and high-pressure adhesion treatment is performed on a large-area battery such as an in-vehicle battery, the equipment required for the implementation will become large-scale. In addition, the form of the exterior material for which a high-temperature and high-pressure adhesion treatment can be performed is limited. If the exterior material is a flat aluminum laminate film pack, it is easy to apply high temperature and pressure, so the electrode and the separator can be accommodated in the exterior material and the adhesion treatment can be performed. On the other hand, it is difficult to effectively apply high temperature and pressure to a metal can without damaging the metal can.

[0007] This disclosure has been made under the above circumstances. An object of this disclosure is to provide a separator for a non-aqueous secondary battery that exhibits excellent adhesion to both the positive electrode and the negative electrode by a relatively low-temperature and low-pressure adhesion treatment.

Means for Solving the Problems

[0008] Specific means for solving the above problems include the following aspects. <1> A polyolefin microporous membrane, A surface layer (A) containing an acrylic-based resin disposed on one surface of the polyolefin microporous membrane, A surface layer (C) containing a polyvinyl chloride-based resin disposed on the other surface of the polyolefin microporous membrane, and A separator for a non-aqueous secondary battery. <2> The acrylic resin is acrylic resin particles. <1> A separator for non-aqueous secondary batteries as described above. <3> A heat-resistant resin layer is further provided between the polyolefin microporous membrane and the surface layer (A), wherein the heat-resistant resin comprises more than 10% by mass. The surface layer (A) is a layer formed by acrylic resin particles adhering to the heat-resistant resin layer. <1> or <2> A separator for non-aqueous secondary batteries as described above. <4> The heat-resistant resin comprises at least one selected from the group consisting of aromatic polyamides, polyimides, and polyamideimides. <3> A separator for non-aqueous secondary batteries as described above. <5> The heat-resistant resin layer further contains inorganic particles. <3> or <4> A separator for non-aqueous secondary batteries as described above. <6> The average primary particle size of the inorganic particles contained in the heat-resistant resin layer is 0.01 μm to 0.3 μm. <5> A separator for non-aqueous secondary batteries as described above. <7> The inorganic particles include barium sulfate particles, <5> or <6> A separator for non-aqueous secondary batteries as described above. <8> Between the polyolefin microporous membrane and the surface layer (A) and / or between the polyolefin microporous membrane and the surface layer (C), there is further an inorganic particle layer containing inorganic particles, wherein the inorganic particles constitute 90% by mass or more. <1> ~ <7> A separator for non-aqueous secondary batteries as described in any one of the following. <9> The average primary particle size of the inorganic particles contained in the inorganic particle layer is 10 nm to 500 nm. <8> A separator for non-aqueous secondary batteries as described above. <10> The inorganic particles include at least one selected from the group consisting of γ-alumina particles, boehmite particles, and barium sulfate particles. <8> or <9> A separator for non-aqueous secondary batteries as described above. <11> The average degree of polymerization of the polyvinyl chloride resin contained in the surface layer (C) is 500 to 1400. <1> ~ <10> A separator for non-aqueous secondary batteries as described in any one of the following. <12> A positive electrode, a negative electrode, and a device disposed between the positive electrode and the negative electrode. <1> ~ <11> A separator for a non-aqueous secondary battery as described in any one of the following, An electromotive force is obtained by doping and dedoping lithium ions. Non-aqueous secondary battery. [Effects of the Invention]

[0009] According to this disclosure, a separator for non-aqueous secondary batteries is provided that exhibits excellent adhesion to both the positive and negative electrodes by bonding at relatively low temperatures and pressures. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic cross-sectional view of an example of the separator of this disclosure. [Figure 2] This is a schematic cross-sectional view of another example of the separator of this disclosure. [Figure 3] This is a schematic cross-sectional view of another example of the separator of this disclosure. [Figure 4] This is a schematic cross-sectional view of another example of the separator of this disclosure. [Figure 5] This is a schematic cross-sectional view of another example of the separator of this disclosure. [Figure 6] This is a schematic cross-sectional view of another example of the separator of this disclosure. [Figure 7] This graph shows the wet adhesion properties of the separator. [Modes for carrying out the invention]

[0011] The embodiments of this disclosure are described below. These descriptions and embodiments are illustrative and do not limit the scope of the embodiments.

[0012] In this disclosure, the numerical range indicated using "~" represents a range that includes the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages within this disclosure, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in numerical ranges described within this disclosure, the upper or lower limit of that range may be replaced with the values ​​shown in the examples.

[0013] In this disclosure, "A and / or B" is synonymous with "at least one of A and B." In other words, "A and / or B" may be A alone, B alone, or a combination of A and B.

[0014] In this disclosure, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, provided that their objectives are achieved.

[0015] When referring to the amount of each component in a composition in this disclosure, if there are multiple substances corresponding to each component in the composition, unless otherwise specified, it refers to the total amount of those multiple substances present in the composition. In this disclosure, each component may contain multiple types of particles. If multiple types of particles corresponding to each component are present in the composition, the particle size of each component refers to the value for a mixture of such multiple types of particles present in the composition, unless otherwise specified.

[0016] In this disclosure, MD (Machine Direction) means the longitudinal direction in a separator manufactured in a long shape, and TD (Transverse Direction) means the direction perpendicular to the MD in the planar direction of the separator. In this disclosure, TD is also referred to as the "width direction".

[0017] In this disclosure, when the stacking relationship of each layer constituting the separator is expressed as "upper layer" and "lower layer," the layer closer to the polyolefin microporous membrane is called the "lower layer," and the layer further away from the polyolefin microporous membrane is called the "upper layer."

[0018] In this disclosure, the volume of the porous layer excluding the voids is referred to as the "solids volume."

[0019] In this disclosure, the process of impregnating a separator with an electrolyte solution and then performing a heat press treatment is referred to as "wet heat press," and the process of performing a heat press treatment without impregnating the separator with an electrolyte solution is referred to as "dry heat press."

[0020] In this disclosure, "monomer unit" of a polymer or resin means a constituent unit of a polymer or resin, which is formed by the polymerization of monomers. In this disclosure, the term "(meth)acrylic" means that either "acrylic" or "methacrylic" may be used.

[0021] <Separator for non-aqueous secondary batteries> The separator for non-aqueous secondary batteries of this disclosure (also simply referred to as "separator" in this disclosure) comprises a polyolefin microporous membrane, a surface layer (A) containing an acrylic resin disposed on one side of the polyolefin microporous membrane, and a surface layer (C) containing a polyvinyl chloride resin disposed on the other side of the polyolefin microporous membrane.

[0022] The separator of this disclosure has one outermost layer which is a surface layer (A) and the other outermost layer which is a surface layer (C).

[0023] The separator of this disclosure has a surface layer (A) containing an acrylic resin that exhibits excellent adhesion to the positive electrode, and a surface layer (C) containing a polyvinyl chloride resin that exhibits excellent adhesion to the negative electrode. The separator of this disclosure exhibits excellent adhesion to both the positive and negative electrodes by bonding treatment at relatively low temperature and low pressure.

[0024] The details of the polyolefin microporous membrane and each layer of the separator of this disclosure are described below.

[0025] [Polyolefin microporous membrane] A polyolefin microporous membrane refers to a microporous membrane containing polyolefin. A microporous membrane is a membrane that has numerous micropores inside, with these micropores interconnected, allowing gas or liquid to pass from one side to the other.

[0026] The separator of this disclosure has a shutdown function by comprising a polyolefin microporous membrane. The shutdown function refers to a function that prevents thermal runaway of the battery by blocking ion movement when the battery temperature rises, as the constituent material of the porous structure melts and the pores of the porous structure become blocked.

[0027] Examples of polyolefin microporous membranes include those used in conventional battery separators, and it is preferable to select one from among these that has sufficient mechanical properties and ion permeability.

[0028] From the viewpoint of exhibiting a shutdown function, a polyethylene-containing microporous membrane (hereinafter referred to as "polyethylene microporous membrane") is preferred as the polyolefin microporous membrane. The polyethylene content is preferably 95% by mass or more relative to the mass of the polyethylene microporous membrane.

[0029] From the viewpoint of possessing heat resistance that prevents the film from easily breaking when exposed to high temperatures, polyolefin microporous membranes containing polypropylene are preferred.

[0030] From the viewpoint of possessing both a shutdown function and heat resistance that prevents easy rupture when exposed to high temperatures, polyolefin microporous membranes containing polyethylene and polypropylene are preferred. Examples of polyolefin microporous membranes containing polyethylene and polypropylene include microporous membranes in which polyethylene and polypropylene are mixed in a single layer. In such microporous membranes, from the viewpoint of achieving both a shutdown function and heat resistance, it is preferable to include 95% by mass or more of polyethylene and 5% by mass or less of polypropylene. From the viewpoint of achieving both a shutdown function and heat resistance, polyolefin microporous membranes having a laminated structure of two or more layers, in which at least one layer contains polyethylene and at least one layer contains polypropylene, are also preferred.

[0031] For polyolefin microporous membranes, polyolefins with a weight-average molecular weight (Mw) of 100,000 to 5,000,000 are preferred. A polyolefin with an Mw of 100,000 or more provides sufficient mechanical properties to the microporous membrane. A polyolefin with an Mw of 5,000,000 or less exhibits good shutdown characteristics and facilitates the molding of the microporous membrane.

[0032] Methods for producing polyolefin microporous membranes include: a method in which molten polyolefin resin is extruded from a T-die to form a sheet, which is then crystallized, stretched, and subsequently heat-treated to form a microporous membrane; and a method in which molten polyolefin resin together with a plasticizer such as liquid paraffin is extruded from a T-die, which is then cooled to form a sheet, stretched, the plasticizer is extracted, and then heat-treated to form a microporous membrane.

[0033] -Properties of polyolefin microporous membranes- From the viewpoint of mechanical strength, the thickness of the polyolefin microporous membrane is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more. From the viewpoint of increasing the energy density of the battery, the thickness of the polyolefin microporous membrane is preferably 10 μm or less, more preferably 9 μm or less, and even more preferably 8 μm or less. The thickness of a polyolefin microporous membrane is determined by measuring 20 points within a 10cm square area using a contact-type length measuring instrument and averaging the results.

[0034] From the viewpoint of excellent electrolyte permeability and ion permeability, the porosity of the polyolefin microporous membrane is preferably 30% to 60%. The porosity ε(%) of a polyolefin microporous membrane can be calculated using the following formula. ε = {1 - Ws / (ds·t)} × 100 Here, Ws is the mass per unit area (i.e., basis weight) (g / m²) of the polyolefin microporous membrane. 2 ), ds is the true density (g / cm³) of the polyolefin microporous membrane. 3 ), where t is the thickness of the polyolefin microporous membrane (μm).

[0035] From the viewpoint of suppressing internal short circuits in the battery, the air permeability of the polyolefin microporous membrane is preferably 80 seconds / 100 mL or more, more preferably 90 seconds / 100 mL or more, and even more preferably 100 seconds / 100 mL or more. From the viewpoint of excellent electrolyte permeability and ion permeability, the air permeability of the polyolefin microporous membrane is preferably 200 seconds / 100 mL or less, more preferably 180 seconds / 100 mL or less, and even more preferably 160 seconds / 100 mL or less. The air permeability of the polyolefin microporous membrane was measured using a Gurley densometer in accordance with JIS P8117:2009 "Paper and cardboard - Test methods for air permeability and air permeability resistance (intermediate region) - Gurley method".

[0036] [Surface layer (A)] The surface layer (A) contains at least an acrylic resin. The surface layer (A) may also contain other components besides the acrylic resin. The surface layer (A) may also contain inorganic particles.

[0037] The surface layer (A) has a porous structure. Examples of the porous structure of the surface layer (A) include the following forms.

[0038] • A structure in which fibrils containing acrylic resin are linked together in a two-dimensional or three-dimensional network. A structure in which fibrils containing acrylic resin are linked together in a two-dimensional or three-dimensional network, and inorganic particles are bound to or trapped in these fibrils. • A mesh-like microporous membrane containing acrylic resin. A structure in which inorganic particles are bound to or trapped in a mesh-like microporous membrane containing acrylic resin. • An acrylic resin forms a layered structure in which numerous inorganic particles are linked together, with voids between the inorganic particles. • A layered structure in which acrylic resin particles are arranged adjacent to each other in two or three dimensions, with voids between the particles. • A layered structure in which acrylic resin particles and inorganic particles are arranged adjacent to each other in two or three dimensions, with voids between the particles. • A layered structure in which acrylic resin particles are scattered on a polyolefin microporous membrane or other layer.

[0039] An example of an embodiment of the surface layer (A) is a layer in which acrylic resin particles are attached to a polyolefin microporous film or another layer. From the viewpoint of ion permeability of the surface layer (A), the average primary particle size of the acrylic resin particles is preferably 50 nm or more, more preferably 100 nm or more, and even more preferably 200 nm or more. The average primary particle size of the acrylic resin particles is preferably 1000 nm or less, more preferably 800 nm or less, and even more preferably 500 nm or less, from the viewpoint of thinning the surface layer (A) and suppressing delamination between the surface layer (A) and the polyolefin microporous film or other layers, and maintaining the adhesion of the separator to the electrode.

[0040] The average primary particle size of acrylic resin particles is determined by measuring the major axis of 100 randomly selected acrylic resin particles observed using a scanning electron microscope (SEM) and averaging the major axes of these 100 particles. The sample used for SEM observation is either acrylic resin particles that form the surface layer (A), or acrylic resin particles extracted from the surface layer (A).

[0041] When the surface layer (A) contains acrylic resin particles, in a separator that is bonded to an electrode, some or all of the acrylic resin particles contained in the surface layer (A) may melt due to the heat applied to bond the separator to the electrode, causing adjacent acrylic resin particles to connect and resulting in some or all of them not maintaining their particle shape.

[0042] -Acrylic resin- Examples of acrylic resins include homopolymers or copolymers of acrylic monomers; and copolymers of acrylic monomers and styrene monomers. Copolymers include alternating copolymers, random copolymers, block copolymers, and graft copolymers. Acrylic resins may be used individually or in mixtures of two or more types.

[0043] Examples of acrylic monomers for acrylic resins include (meth)acrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. Alkyl (meth)acrylate esters are preferred as acrylic monomers. The alkyl group in the ester portion of the alkyl (meth)acrylate ester is preferably a C1-C10 alkyl group, and more preferably a C1-C8 alkyl group. The acrylic monomers may be used individually or in combination of two or more.

[0044] Examples of styrene monomers for acrylic resins include styrene, α-methylstyrene; alkyl-substituted styrenes such as 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, and 4-ethylstyrene; halogen-substituted styrenes such as 2-chlorostyrene, 3-chlorostyrene, and 4-chlorostyrene; and fluorine-substituted styrenes such as 4-fluorostyrene and 2,5-difluorostyrene. Styrene and α-methylstyrene are preferred as styrene monomers, with styrene being more preferred. Styrene monomers may be used individually or in combination of two or more.

[0045] -Other resins- The surface layer (A) may contain resins other than acrylic resins. Examples of other resins include polyvinylidene fluoride resins, butadiene-acrylonitrile resins, fluororubber, homopolymers or copolymers of vinyl nitrile compounds (acrylonitrile, methacrylonitrile, etc.), carboxymethylcellulose, hydroxyalkylcellulose, polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, and polyethers (polyethylene oxide, polypropylene oxide, etc.). These resins may be used individually or in mixtures of two or more.

[0046] The mass percentage of other resins in the total resin of the surface layer (A) is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 1% by mass or less, and particularly preferably substantially absent. The mass percentage of acrylic resin in the total resin of the surface layer (A) is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 99% by mass or more, and particularly preferably 100% by mass.

[0047] -Inorganic particles- The surface layer (A) may contain inorganic particles. From the viewpoint of increasing the rigidity of the separator, it is preferable that the surface layer (A) contains inorganic particles.

[0048] Examples of inorganic particles include metal oxide particles, metal hydroxide particles, metal sulfate particles, metal carbonate particles, metal nitride particles, and clay mineral particles.

[0049] Examples of metal oxides that constitute metal oxide particles include silica (silicon dioxide), alumina (aluminum oxide), boehmite (alumina monohydrate), titania (titanium oxide), zirconia (zirconium oxide), magnesium oxide, and barium oxide, with alumina being preferred. Examples of metal hydroxides that constitute the metal hydroxide particles include magnesium hydroxide, aluminum hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, cerium hydroxide, nickel hydroxide, and boron hydroxide, with magnesium hydroxide being preferred. Examples of metal sulfates constituting the metal sulfate particles include barium sulfate and calcium sulfate, with barium sulfate being preferred. Examples of metal carbonates that make up metal carbonate particles include calcium carbonate, magnesium carbonate, and barium carbonate. Examples of metal nitrides that constitute metal nitride particles include boron nitride and aluminum nitride. Examples of clay mineral particles include calcium silicate and talc.

[0050] The inorganic particles may be inorganic particles whose surface has been modified with a silane coupling agent or the like.

[0051] Inorganic particles may be used individually or in combination of two or more types.

[0052] As inorganic particles, at least one selected from the group consisting of metal oxide particles, metal hydroxide particles, and metal sulfate particles is preferred from the viewpoint of stability with respect to the electrolyte and electrochemical stability. Among these, at least one selected from the group consisting of alumina particles (aluminum oxide particles), magnesium hydroxide particles, and barium sulfate particles is more preferred.

[0053] There are no limitations on the particle shape of the inorganic particles; they may be spherical, elliptical, plate-shaped, needle-shaped, or irregularly shaped. From the viewpoint of suppressing internal short circuits in the battery, the inorganic particles contained in the surface layer (A) are preferably plate-shaped particles or non-aggregated primary particles.

[0054] The average primary particle size of the inorganic particles contained in the surface layer (A) is preferably 0.01 μm to 1 μm, more preferably 0.1 μm to 1 μm, and even more preferably 0.5 μm to 1 μm, from the viewpoint of forming a good porous structure without aggregation and suppressing delamination between the polyolefin microporous membrane or other layers.

[0055] The average primary particle size of inorganic particles is determined by measuring the major axis of 100 randomly selected inorganic particles observed using a scanning electron microscope (SEM) and averaging the major axes of these 100 particles. The sample used for SEM observation is inorganic particles that form the surface layer (A), or inorganic particles extracted from the surface layer (A). There are no restrictions on the method for extracting inorganic particles from the surface layer (A). For example, this method involves immersing the surface layer (A) peeled from the separator in an organic solvent that dissolves acrylic resin to dissolve the acrylic resin and extract the inorganic particles; or heating the surface layer (A) peeled from the separator to about 800°C to remove the acrylic resin and extract the inorganic particles; and so on.

[0056] In a form in which the surface layer (A) contains inorganic particles, the mass ratio of inorganic particles to the surface layer (A) is preferably 40% to 90% by mass, more preferably 50% to 80% by mass, and even more preferably 60% to 70% by mass, from the viewpoint of increasing the rigidity of the separator and the adhesion of the surface layer (A) to the electrode.

[0057] In a form in which the surface layer (A) does not contain inorganic particles, the mass ratio of acrylic resin to the surface layer (A) is preferably 85% to 100% by mass, more preferably 90% to 100% by mass, and even more preferably 95% to 100% by mass.

[0058] In one example of the separator embodiment of this disclosure, the mass ratio of inorganic particles in the surface layer (A) may be 0% to 10% by mass, 0% to 5% by mass, or 0% by mass.

[0059] -Other ingredients- The surface layer (A) may contain additives such as dispersants (including surfactants), wetting agents, defoamers, and pH adjusters. Dispersants are added to the coating solution for forming the surface layer (A) to improve dispersibility, coating properties, or storage stability. Wetting agents, defoamers, and pH adjusters are added to the coating solution for forming the surface layer (A) to improve compatibility with the polyolefin microporous membrane or other layers, to suppress air entrapment in the coating solution, or to adjust the pH.

[0060] -Properties of the surface layer (A)- The thickness of the surface layer (A) is preferably 0.5 μm or more, more preferably 0.8 μm or more, and even more preferably 1 μm or more, from the viewpoint of adhesion to the electrode. The thickness of the surface layer (A) is preferably 3 μm or less, more preferably 2.5 μm or less, and even more preferably 2 μm or less, from the viewpoint of the energy density of the battery.

[0061] The thickness of the surface layer (A) is the thickness of the separator minus the thickness of the flat film after removing the surface layer (A). The thicknesses of the separator and the flat film are determined by measuring 20 points within a 10 cm square area using a contact-type length measuring instrument and averaging the results.

[0062] The mass per unit area (i.e., basis weight) of the surface layer (A) is 0.1 g / m² from the viewpoint of adhesion to the electrode. 2 Preferably, it is 0.2 g / m 2 The above is more preferable, 0.3 g / m 2 The above is even more preferable. The mass per unit area (i.e., basis weight) of the surface layer (A) is 0.8 g / m², from the perspective of the battery's energy density. 2 Preferably, it is 0.5 g / m 2 The following is more preferable: 0.3 g / m2 The following is even more preferable.

[0063] The mass per unit area (i.e., basis weight) of the surface layer (A) is calculated by subtracting the mass of the flat film with the surface layer (A) removed from the mass of a separator cut to 20 cm × 20 cm, and then dividing the difference in mass by the area.

[0064] [Surface layer (C)] The surface layer (C) contains at least a polyvinyl chloride resin. The surface layer (C) may also contain other components besides the polyvinyl chloride resin. The surface layer (C) may also contain inorganic particles.

[0065] The surface layer (C) has a porous structure. Examples of the porous structure of the surface layer (C) include the following forms.

[0066] • A structure in which fibrils containing polyvinyl chloride resin are linked together in a two-dimensional or three-dimensional network. A structure in which fibrils containing polyvinyl chloride resin are linked together in a two-dimensional or three-dimensional network, and inorganic particles are bound to or trapped in these fibrils. • A mesh-like microporous membrane containing polyvinyl chloride resin. A structure in which inorganic particles are bound to or trapped in a mesh-like microporous membrane containing polyvinyl chloride resin. • A layered structure in which polyvinyl chloride resin connects numerous inorganic particles, with voids between the inorganic particles. • A layered structure in which polyvinyl chloride resin particles are arranged adjacent to each other in two or three dimensions, with voids between the particles. • A layered structure in which polyvinyl chloride resin particles and inorganic particles are arranged adjacent to each other in two or three dimensions, with voids between the particles. • A layered structure in which polyvinyl chloride resin particles are scattered on a polyolefin microporous membrane or other layer.

[0067] An example of an embodiment of the surface layer (C) is a layer in which polyvinyl chloride resin particles are attached to a polyolefin microporous membrane or another layer. From the viewpoint of ion permeability of the surface layer (C), the average primary particle size of the polyvinyl chloride resin particles is preferably 50 nm or more, more preferably 100 nm or more, and even more preferably 200 nm or more. The average primary particle size of the polyvinyl chloride resin particles is preferably 1000 nm or less, more preferably 800 nm or less, and even more preferably 500 nm or less, from the viewpoint of thinning the surface layer (C) and suppressing delamination between the surface layer (C) and the polyolefin microporous film or other layers, and maintaining the adhesion of the separator to the electrode.

[0068] The average primary particle size of polyvinyl chloride (PVC) resin particles is determined by measuring the major axis of 100 randomly selected PVC resin particles observed using a scanning electron microscope (SEM) and averaging the major axes of these 100 particles. The sample used for SEM observation is either PVC resin particles that form the surface layer (C), or PVC resin particles extracted from the surface layer (C).

[0069] When the surface layer (C) contains polyvinyl chloride resin particles, in a separator that is bonded to an electrode, some or all of the polyvinyl chloride resin particles contained in the surface layer (C) may melt due to the heat applied to bond the separator to the electrode, causing adjacent polyvinyl chloride resin particles to connect, and some or all of them may not maintain their particle shape.

[0070] -Polyvinyl chloride resin- Polyvinyl chloride resins include homopolymers of vinyl chloride (also known as chloroethylene) (i.e., polyvinyl chloride) and copolymers of vinyl chloride with other monomers. Copolymers include alternating copolymers, random copolymers, block copolymers, and graft copolymers. In this disclosure, polyvinyl chloride resin means a resin in which the number proportion of vinyl chloride is the largest among the monomers that make up the resin.

[0071] Examples of monomers other than vinyl chloride that constitute polyvinyl chloride resins include vinyl acetate, alkenes (e.g., ethene, propene, butene, pentene, hexene, etc.), dienes (e.g., butadiene, isoprene, etc.), styrene, α-methylstyrene, alkyl-substituted styrenes (e.g., 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4-ethylstyrene, etc.), vinylidene chloride, acrylonitrile, (meth)acrylic acid, (meth)acrylic acid esters, urethane monomers, and the like.

[0072] From the viewpoint of adhesion of the surface layer (C) to the electrode, the polyvinyl chloride resin preferably has a polyvinyl chloride content of 50% to 100% of the total monomers constituting the polyvinyl chloride resin, more preferably 70% to 100%, and even more preferably 90% to 100%.

[0073] The polyvinyl chloride resin contained in the surface layer (C) may be one type or two or more types.

[0074] The polyvinyl chloride resin contained in the surface layer (C) preferably has an average degree of polymerization of 500 to 1400, more preferably 550 to 1200, and even more preferably 600 to 1000. When the average degree of polymerization of the polyvinyl chloride resin is 500 or higher, the surface layer (C) has excellent mechanical strength and is less likely to peel off from the electrode. From this viewpoint, it is more preferable that the average degree of polymerization of the polyvinyl chloride resin be 550 or higher, and even more preferable that it be 600 or higher. When the average degree of polymerization of the polyvinyl chloride resin is 1400 or less, a porous structure is easily formed in the surface layer (C), resulting in excellent permeability of the electrolyte and ion permeability in the surface layer (C). Furthermore, when the average degree of polymerization of the polyvinyl chloride resin is 1400 or less, high mobility of the polymer chains when heated and ease of swelling in the electrolyte are ensured, so the surface layer (C) adheres easily to the electrode by both dry heat pressing and wet heat pressing. In addition, when the average degree of polymerization of the polyvinyl chloride resin is 1400 or less, the viscosity of the coating liquid used to form the surface layer (C) is relatively low, resulting in excellent coating properties. From these viewpoints, the average degree of polymerization of the polyvinyl chloride resin is more preferably 1200 or less, and even more preferably 1000 or less.

[0075] -Other resins- The surface layer (C) may contain resins other than polyvinyl chloride resins. Examples of other resins include acrylic resins, butadiene-acrylonitrile resins, fluororubber, homopolymers or copolymers of vinyl nitrile compounds (acrylonitrile, methacrylonitrile, etc.), carboxymethylcellulose, hydroxyalkylcellulose, polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, and polyethers (polyethylene oxide, polypropylene oxide, etc.). These resins may be used individually or in mixtures of two or more.

[0076] The mass percentage of other resins in the total resin of the surface layer (C) is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 1% by mass or less, and particularly preferably substantially absent. The mass percentage of polyvinyl chloride resin in the total resin of the surface layer (C) is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 99% by mass or more, and particularly preferably 100% by mass.

[0077] -Inorganic particles- The surface layer (C) may contain inorganic particles. From the viewpoint of increasing the rigidity of the separator, it is preferable that the surface layer (C) contains inorganic particles.

[0078] The embodiments of inorganic particles contained in surface layer (C) are the same as the embodiments of inorganic particles contained in surface layer (A). The description of inorganic particles relating to surface layer (A) is applied to surface layer (C) by replacing "surface layer (A)" with "surface layer (C)".

[0079] As inorganic particles, at least one selected from the group consisting of metal oxide particles, metal hydroxide particles, and metal sulfate particles is preferred from the viewpoint of stability with respect to the electrolyte and electrochemical stability. Among these, at least one selected from the group consisting of alumina particles (aluminum oxide particles), magnesium hydroxide particles, and barium sulfate particles is more preferred.

[0080] The average primary particle size of the inorganic particles contained in the surface layer (C) is preferably 0.01 μm to 1 μm, more preferably 0.1 μm to 1 μm, and even more preferably 0.5 μm to 1 μm, from the viewpoint of forming a good porous structure without aggregation and suppressing delamination between the polyolefin microporous membrane or other layers.

[0081] The average primary particle size of inorganic particles is determined by measuring the major axis of 100 randomly selected inorganic particles observed using a scanning electron microscope (SEM) and averaging the major axes of these 100 particles. The sample used for SEM observation is inorganic particles that form the surface layer (C), or inorganic particles extracted from the surface layer (C). There are no restrictions on the method for extracting inorganic particles from the surface layer (C). For example, this method involves immersing the surface layer (C) peeled from the separator in an organic solvent that dissolves polyvinyl chloride resin to dissolve the polyvinyl chloride resin and extract the inorganic particles; or heating the surface layer (C) peeled from the separator to about 800°C to remove the polyvinyl chloride resin and extract the inorganic particles; and so on.

[0082] In a form in which the surface layer (C) contains inorganic particles, the mass ratio of inorganic particles to the surface layer (C) is preferably 40% to 90% by mass, more preferably 50% to 80% by mass, and even more preferably 60% to 70% by mass, from the viewpoint of increasing the rigidity of the separator and the adhesion of the surface layer (C) to the electrode.

[0083] In a form in which the surface layer (C) does not contain inorganic particles, the mass ratio of polyvinyl chloride resin to the surface layer (C) is preferably 85% to 100% by mass, more preferably 90% to 100% by mass, and even more preferably 95% to 100% by mass.

[0084] In one example of the separator embodiment of the present disclosure, the mass ratio of inorganic particles in the surface layer (C) may be 0% to 10% by mass, 0% to 5% by mass, or 0% by mass.

[0085] -Other ingredients- The surface layer (C) may contain additives such as dispersants (including surfactants), wetting agents, defoamers, and pH adjusters. Dispersants are added to the coating solution for forming the surface layer (C) to improve dispersibility, coating properties, or storage stability. Wetting agents, defoamers, and pH adjusters are added to the coating solution for forming the surface layer (C) to improve compatibility with the polyolefin microporous membrane or other layers, to suppress air entrapment in the coating solution, or to adjust the pH.

[0086] -Properties of the surface layer (C)- From the viewpoint of adhesion to the electrode, the thickness of the surface layer (C) is preferably 0.5 μm or more, more preferably 0.8 μm or more, and even more preferably 1 μm or more. The thickness of the surface layer (C) is preferably 3 μm or less, more preferably 2.5 μm or less, and even more preferably 2 μm or less, from the viewpoint of the energy density of the battery.

[0087] The thickness of the surface layer (C) is the value obtained by subtracting the thickness of the flat film from which the surface layer (C) has been removed from the thickness of the separator. The thicknesses of the separator and the flat film are determined by measuring 20 points within a 10 cm square using a contact type length measuring instrument and averaging them.

[0088] The mass per unit area (i.e., basis weight) of the surface layer (C) is preferably 0.8 g / m 2 or more from the viewpoint of adhesion to the electrode, more preferably 1.0 g / m 2 or more, and still more preferably 1.2 g / m 2 or more. The mass per unit area (i.e., basis weight) of the surface layer (C) is preferably 2.5 g / m 2 or less from the viewpoint of the energy density of the battery, more preferably 2.0 g / m 2 or less, and still more preferably 1.8 g / m 2 or less.

[0089] The mass per unit area (i.e., basis weight) of the surface layer (C) is determined by subtracting the mass of the flat film from which the surface layer (C) has been removed from the mass of the separator cut out into a 20 cm × 20 cm square, and dividing the mass difference by the area.

[0090] [Inorganic particle layer] The separator of the present disclosure may include an inorganic particle layer containing inorganic particles between the polyolefin microporous membrane and the surface layer (A) and / or between the polyolefin microporous membrane and the surface layer (C).

[0091] In the separator of the present disclosure, the inorganic particle layer is a porous layer in which the mass ratio of the inorganic particles in the total mass of the layer is 90% by mass or more. In the present disclosure, the porous layer has a structure in which a large number of fine pores are formed inside and the fine pores are connected, and a layer through which gas or liquid can pass from one surface to the other surface.

[0092] Examples of embodiments of the separator provided with an inorganic particle layer include the following forms (1) to (3).

[0093] Form (1): A separator having an inorganic particle layer between a polyolefin microporous membrane and a surface layer (A), and having an inorganic particle layer between a polyolefin microporous membrane and a surface layer (C). In this separator, one inorganic particle layer and the other inorganic particle layer may be the same or different in terms of components and / or composition.

[0094] Morphology (2): A separator having an inorganic particle layer between the polyolefin microporous membrane and the surface layer (A), and not having an inorganic particle layer between the polyolefin microporous membrane and the surface layer (C).

[0095] Morphology (3): A separator having an inorganic particle layer between the polyolefin microporous membrane and the surface layer (C), and not having an inorganic particle layer between the polyolefin microporous membrane and the surface layer (A).

[0096] The inorganic particle layer contains at least inorganic particles and optionally a binder resin.

[0097] From the viewpoint of improving the impact resistance of the battery, the mass ratio of inorganic particles in the inorganic particle layer is 90% by mass or more, preferably 92% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more. The mass ratio of inorganic particles in the inorganic particle layer may be 100% by mass.

[0098] The inorganic particle layer may contain a binder resin to form the layer and maintain its structure. The mass percentage of inorganic particles in the inorganic particle layer is, for example, 10% by mass or more, 8% by mass or more, or 5% by mass or more.

[0099] -Inorganic particles- Examples of inorganic particles include metal oxide particles, metal hydroxide particles, metal sulfate particles, metal carbonate particles, metal nitride particles, and clay mineral particles.

[0100] Examples of metal oxides that constitute metal oxide particles include silica (silicon dioxide), alumina (aluminum oxide), boehmite (alumina monohydrate), titania (titanium oxide), zirconia (zirconium oxide), magnesium oxide, and barium oxide, with alumina being preferred. Examples of metal hydroxides that constitute the metal hydroxide particles include magnesium hydroxide, aluminum hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, cerium hydroxide, nickel hydroxide, and boron hydroxide, with magnesium hydroxide being preferred. Examples of metal sulfates constituting the metal sulfate particles include barium sulfate and calcium sulfate, with barium sulfate being preferred. Examples of metal carbonates that make up metal carbonate particles include calcium carbonate, magnesium carbonate, and barium carbonate. Examples of metal nitrides that constitute metal nitride particles include boron nitride and aluminum nitride. Examples of clay mineral particles include calcium silicate and talc.

[0101] The inorganic particles may be inorganic particles whose surface has been modified with a silane coupling agent or the like.

[0102] Inorganic particles may be used individually or in combination of two or more types.

[0103] As inorganic particles, at least one selected from the group consisting of metal oxide particles, metal hydroxide particles, and metal sulfate particles is preferred from the viewpoint of stability with respect to the electrolyte and electrochemical stability. Among these, at least one selected from the group consisting of alumina particles (aluminum oxide particles), magnesium hydroxide particles, and barium sulfate particles is more preferred.

[0104] From the viewpoint of being able to obtain relatively small particle sizes inexpensively as inorganic particles, at least one selected from the group consisting of γ-alumina particles, boehmite particles, and barium sulfate particles is more preferable.

[0105] There are no limitations on the particle shape of the inorganic particles; they may be spherical, elliptical, plate-shaped, needle-shaped, or irregularly shaped. From the viewpoint of suppressing internal short circuits in the battery, the inorganic particles contained in the inorganic particle layer are preferably plate-shaped particles or non-aggregated primary particles.

[0106] The average primary particle size of the inorganic particles contained in the inorganic particle layer is preferably 10 nm to 500 nm, more preferably 10 nm to 300 nm, even more preferably 20 nm to 200 nm, and still more preferably 30 nm to 100 nm, from the viewpoint of forming a good porous structure without aggregation and suppressing delamination between the inorganic particles and the polyolefin microporous membrane or other layers.

[0107] The average primary particle size of inorganic particles is determined by measuring the major axis of 100 randomly selected inorganic particles observed using a scanning electron microscope (SEM) and averaging the major axes of these 100 particles. The sample used for SEM observation is inorganic particles that form the inorganic particle layer, or inorganic particles extracted from the inorganic particle layer. There are no restrictions on the method for extracting inorganic particles from the inorganic particle layer. For example, this method involves immersing the inorganic particle layer peeled from the separator in an organic solvent that dissolves the binder resin, thereby dissolving the binder resin and extracting the inorganic particles; or heating the inorganic particle layer peeled from the separator to approximately 800°C to remove the binder resin and extract the inorganic particles.

[0108] -Binding resin- The binder resin has the function of binding inorganic particles contained in the inorganic particle layer together, as well as adhering the inorganic particle layer to a polyolefin microporous membrane or other layers. The binder resin contained in the inorganic particle layer may have a particle shape, or it may not have a specific shape, and any form is acceptable as long as it can bind the inorganic particles together.

[0109] The binder resin may be a heat-resistant resin or a non-heat-resistant resin. Examples of heat-resistant resins include aromatic polyamides, polyimides, polyamide-imides, polyethersulfones, polysulfones, polyetherketones, and polyetherimides. Examples of non-heat-resistant resins include butadiene polymers (e.g., butadiene homopolymers, styrene-butadiene copolymers) and acrylic resins (e.g., acrylic monomer homopolymers or copolymers, copolymers of acrylic monomers and styrene monomers). These resins may be used individually or in mixtures of two or more.

[0110] -Other ingredients- The inorganic particle layer may contain additives such as dispersants (including surfactants), wetting agents, defoamers, and pH adjusters. Dispersants are added to the coating solution for forming the inorganic particle layer to improve dispersibility, coating properties, or storage stability. Wetting agents, defoamers, and pH adjusters are added to the coating solution for forming the inorganic particle layer to improve compatibility with the polyolefin microporous membrane or other layers, to suppress air entrapment in the coating solution, or to adjust the pH.

[0111] -Characteristics of the inorganic particle layer- In a configuration where the inorganic particle layer is present on only one side of the polyolefin microporous membrane, the thickness of the inorganic particle layer is preferably 0.5 μm to 3 μm, more preferably 0.8 μm to 2.5 μm, and even more preferably 1 μm to 2 μm, from the viewpoint of the battery's impact resistance and the permeability of the electrolyte.

[0112] In a configuration where the inorganic particle layer is present on both sides of the polyolefin microporous membrane, the total thickness of the inorganic particle layer on both sides is preferably 0.5 μm to 5 μm, more preferably 0.8 μm to 4 μm, and even more preferably 1 μm to 3 μm, from the viewpoint of the battery's impact resistance and the permeability of the electrolyte.

[0113] The thickness of the inorganic particle layer is obtained by subtracting the thickness of the flat film after removing the inorganic particle layer from the thickness of the flat film obtained by removing the upper layer from the separator to expose the inorganic particle layer. The thickness of the flat film is determined by measuring 20 points within a 10 cm square area using a contact-type length measuring instrument and averaging the results.

[0114] [Heat-resistant resin layer] The separator of this disclosure may include a heat-resistant resin layer containing a heat-resistant resin between the polyolefin microporous membrane and the surface layer (A), and / or between the polyolefin microporous membrane and the surface layer (C).

[0115] In the separator of this disclosure, the heat-resistant resin layer is a porous layer in which the mass ratio of the heat-resistant resin to the total mass of the layer is greater than 10% by mass. In this disclosure, a porous layer is a layer having a large number of micropores inside, with a structure in which the micropores are connected, and through which gas or liquid can pass from one surface to the other.

[0116] In this disclosure, a 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 thermal 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 the temperature range below 200°C.

[0117] Examples of embodiments of a separator equipped with a heat-resistant resin layer include the following embodiments (11) to (13).

[0118] Form (11): A separator having a heat-resistant resin layer between a polyolefin microporous membrane and a surface layer (A), and having a heat-resistant resin layer between a polyolefin microporous membrane and a surface layer (C). In this separator, one heat-resistant resin layer and the other heat-resistant resin layer may be the same or different in terms of components and / or composition.

[0119] Morphology (12): A separator having a heat-resistant resin layer between the polyolefin microporous membrane and the surface layer (A), and not having a heat-resistant resin layer between the polyolefin microporous membrane and the surface layer (C).

[0120] Morphology (13): A separator having a heat-resistant resin layer between the polyolefin microporous membrane and the surface layer (C), and not having a heat-resistant resin layer between the polyolefin microporous membrane and the surface layer (A).

[0121] As an example of an embodiment of the separator of this disclosure, there is a form (11) or form (12) in which the surface layer (A) is a layer in which acrylic resin particles are attached to a heat-resistant resin layer. This embodiment is preferred from the viewpoint that the surface layer (A) has excellent ion permeability and that the surface layer (A) is easy to maintain as a layer.

[0122] The heat-resistant resin layer contains at least a heat-resistant resin and may also contain other components.

[0123] The mass ratio of heat-resistant resin to the heat-resistant resin layer is more than 10% by mass, preferably 15% by mass or more, and more preferably 20% by mass or more, from the viewpoint of improving the heat resistance of the separator and suppressing internal short circuits in the battery. The mass ratio of heat-resistant resin to the heat-resistant resin layer may be 100% by mass.

[0124] The heat-resistant resin layer may contain inorganic particles from the viewpoint of increasing the rigidity of the separator or from the viewpoint of easily making the layer porous. In a form in which the heat-resistant resin layer contains inorganic particles, the mass ratio of inorganic particles to the heat-resistant resin layer is preferably 50% by mass or more and less than 90% by mass, more preferably 60% by mass to 85% by mass, and even more preferably 70% by mass to 85% by mass.

[0125] -Heat-resistant resin- Examples of heat-resistant resins include aromatic polyamides, polyimides, polyamide-imides, polyethersulfones, polysulfones, polyetherketones, and polyetherimides. The heat-resistant resin may be used individually or in combination of two or more types.

[0126] As for the heat-resistant resin, at least one selected from the group consisting of aromatic polyamides, polyimides, and polyamide-imides is preferred from the viewpoint of durability and heat resistance.

[0127] As a heat-resistant resin, all-aromatic polyamides (also known as aramids) are more preferred from the viewpoint of durability and heat resistance. All-aromatic polyamides may be meta-type or para-type. Among all-aromatic polyamides, meta-type all-aromatic polyamides are preferred from the viewpoint of easily forming porous layers and having excellent oxidation-reduction resistance in electrode reactions. Specifically, polymetaphenylene isophthalamide or polyparaphenylene terephthalamide are preferred as all-aromatic polyamides, and polymetaphenylene isophthalamide is more preferred.

[0128] In a form in which the heat-resistant resin layer contains a total aromatic polyamide, the mass percentage of the total aromatic polyamide in the total resin of the heat-resistant resin layer is preferably 85% to 100% by mass, more preferably 90% to 100% by mass, and even more preferably 95% to 100% by mass.

[0129] -Inorganic particles- The heat-resistant resin layer may contain inorganic particles. It is preferable that the heat-resistant resin layer contains inorganic particles from the viewpoint of increasing the rigidity of the separator.

[0130] Examples of embodiments of inorganic particles contained in the heat-resistant resin layer are the same as examples of embodiments of inorganic particles contained in the inorganic particle layer. The description of inorganic particles relating to the inorganic particle layer is applied to the heat-resistant resin layer by replacing "inorganic particle layer" with "heat-resistant resin layer".

[0131] As inorganic particles, at least one selected from the group consisting of metal oxide particles, metal hydroxide particles, and metal sulfate particles is preferred from the viewpoint of stability with respect to the electrolyte and electrochemical stability. Among these, at least one selected from the group consisting of alumina particles (aluminum oxide particles), magnesium hydroxide particles, and barium sulfate particles is more preferred.

[0132] From the viewpoint of being able to obtain relatively small particle sizes inexpensively as inorganic particles, and from the viewpoint of not generating gas inside the battery, metal sulfate particles are preferred, and barium sulfate particles are more preferred.

[0133] The average primary particle size of the inorganic particles contained in the heat-resistant resin layer is preferably 0.01 μm to 1 μm, more preferably 0.02 μm to 1 μm, and even more preferably 0.03 μm to 1 μm, from the viewpoint of forming a good porous structure without aggregation and suppressing delamination between the polyolefin microporous membrane or other layers.

[0134] In a configuration where the surface layer (A) is a layer in which acrylic resin particles are attached to a heat-resistant resin layer, or where the surface layer (C) is a layer in which polyvinyl chloride resin particles are attached to a heat-resistant resin layer, the average primary particle size of the inorganic particles contained in the heat-resistant resin layer is preferably 0.3 μm or less, more preferably 0.1 μm or less, and even more preferably 0.08 μm or less, from the viewpoint of suppressing the peeling of the surface layer (A) or surface layer (C) from the heat-resistant resin layer. From the viewpoint of forming a good porous structure without aggregation, the average primary particle size of the inorganic particles contained in the heat-resistant resin layer is preferably 0.01 μm or larger, more preferably 0.02 μm or larger, and even more preferably 0.03 μm or larger.

[0135] The average primary particle size of inorganic particles is determined by measuring the major axis of 100 randomly selected inorganic particles observed using a scanning electron microscope (SEM) and averaging the major axes of these 100 particles. The sample used for SEM observation is inorganic particles that form the heat-resistant resin layer, or inorganic particles extracted from the heat-resistant resin layer. There are no restrictions on the method for extracting inorganic particles from the heat-resistant resin layer. For example, this method involves immersing the heat-resistant resin layer peeled from the separator in an organic solvent that dissolves the heat-resistant resin, thereby dissolving the resin and extracting the inorganic particles; or heating the heat-resistant resin layer peeled from the separator to approximately 800°C to remove the heat-resistant resin and extract the inorganic particles.

[0136] -Other ingredients- The heat-resistant resin layer may contain additives such as dispersants (including surfactants), wetting agents, defoamers, and pH adjusters. Dispersants are added to the coating solution for forming the heat-resistant resin layer to improve dispersibility, coating properties, or storage stability. Wetting agents, defoamers, and pH adjusters are added to the coating solution for forming the heat-resistant resin layer to improve compatibility with the polyolefin microporous membrane or other layers, to suppress air entrapment in the coating solution, or to adjust the pH.

[0137] -Properties of the heat-resistant resin layer- In a configuration where the heat-resistant resin layer is present on only one side of the polyolefin microporous film, the thickness of the heat-resistant resin layer is preferably 0.5 μm to 4 μm, more preferably 1 μm to 3.5 μm, and even more preferably 1.5 μm to 3 μm, from the viewpoint of balancing the heat resistance and energy density of the battery.

[0138] In a configuration where the heat-resistant resin layer is present on both sides of the polyolefin microporous film, the thickness of the heat-resistant resin layer is preferably 1 μm to 5 μm in total on both sides, more preferably 1.5 μm to 4 μm, and even more preferably 2 μm to 3 μm, from the viewpoint of balancing the heat resistance and energy density of the battery.

[0139] The thickness of the heat-resistant resin layer is obtained by subtracting the thickness of the flat film after removing the heat-resistant resin layer from the thickness of the flat film obtained by removing the upper layer from the separator to expose the heat-resistant resin layer. The thickness of the flat film is determined by measuring 20 points within a 10 cm square area using a contact-type length measuring instrument and averaging the results.

[0140] In a configuration where the heat-resistant resin layer is present on only one side of the polyolefin microporous membrane, the mass per unit area (i.e., basis weight) of the heat-resistant resin layer is 0.8 g / m², from the viewpoint of balancing the heat resistance and energy density of the battery. 2 ~2.5g / m 2 Preferably, it is 1.0 g / m 2 ~2.0g / m 2 More preferably, 1.2 g / m 2 ~1.8g / m 2 That is even more preferable.

[0141] In a configuration where the heat-resistant resin layer is present on both sides of the polyolefin microporous film, the mass per unit area (i.e., basis weight) of the heat-resistant resin layer should be 0.8 g / m² in total for both sides, from the viewpoint of balancing the heat resistance and energy density of the battery. 2 ~4.0g / m 2 Preferably, it is 1.0 g / m 2 ~3.0g / m 2 More preferably, 1.2 g / m 2 ~2.0g / m 2 That is even more preferable.

[0142] The mass per unit area (i.e., basis weight) of the heat-resistant resin layer is calculated by subtracting the mass of the flat film obtained by removing the heat-resistant resin layer from the mass of the flat film obtained by removing the heat-resistant resin layer from a separator cut to 20 cm x 20 cm, and then dividing the difference in mass by the area.

[0143] [Separator characteristics] From the viewpoint of mechanical strength, the thickness of the separator is preferably 5 μm or more, more preferably 7 μm or more, and even more preferably 9 μm or more. From the viewpoint of the battery's energy density, the separator thickness is preferably 15 μm or less, more preferably 14 μm or less, and even more preferably 13 μm or less.

[0144] The thickness of the separator is determined by measuring 20 points within a 10cm square area using a contact-type length measuring device and averaging the results.

[0145] From the viewpoint of ion permeability, the porosity of the separator is preferably 30% to 60%. The porosity ε(%) of the separator is calculated using the following formula.

[0146]

number

[0147] Here, for the constituent materials 1, 2, 3, ..., n of the separator, the mass per unit area of ​​each constituent material is W1, W2、 W3, ..., W n (g / cm 2 ) and the true density of each constituent material is d1, d2, d3, ..., d n (g / cm 3 ) and the thickness of the separator is t (cm).

[0148] From the viewpoint of suppressing internal short circuits in the battery, the air permeability of the separator is preferably 80 seconds / 100 mL or more, more preferably 90 seconds / 100 mL or more, and even more preferably 100 seconds / 100 mL or more. From the viewpoint of ion permeability, the air permeability of the separator is preferably 260 seconds / 100 mL or less, more preferably 250 seconds / 100 mL or less, and even more preferably 240 seconds / 100 mL or less.

[0149] The air permeability of the separator was measured using a Gurley densometer in accordance with JIS P8117:2009 "Paper and cardboard - Test methods for air permeability and air permeability resistance (intermediate region) - Gurley method".

[0150] In a configuration in which an inorganic particle layer and / or a heat-resistant resin layer are arranged on the separator, it is preferable to set the thickness and mass per unit area (i.e., basis weight) of these layers using the thermal shrinkage rate of the separator as an indicator. When a separator having an inorganic particle layer and / or a heat-resistant resin layer is heat-treated at 130°C for 60 minutes, the thermal shrinkage rates of MD and TD are preferably 10% or less, respectively.

[0151] The thermal shrinkage rate of the separator is measured by the following method. Cut the separator into a rectangle measuring TD60mm x MD180mm to create a test specimen. Mark the specimen at points 20mm and 170mm from one end on the line that bisects TD (referred to as points A and B, respectively). Additionally, mark points at points 10mm and 50mm from one end on the line that bisects MD (referred to as points C and D, respectively). Attach a clip to the specimen (the clip should be placed between the end closest to point A and point A), and suspend it in an oven at 130°C for 60 minutes under no tension to perform heat treatment. Measure the lengths between A and B and between C and D before and after heat treatment, and calculate the thermal shrinkage rate using the following formula.

[0152] MD thermal shrinkage rate (%) = {(length of AB before heat treatment - length of AB after heat treatment) ÷ length of AB before heat treatment} × 100 TD thermal shrinkage rate (%) = {(length of CD before heat treatment - length of CD after heat treatment) ÷ length of CD before heat treatment} × 100

[0153] [Layering configuration of separators] The stacking configuration of the separators of this disclosure will be described with reference to the drawings. Figures 1 to 6 are schematic cross-sectional views of embodiments of the separator of this disclosure. Figures 1 to 6 are schematic cross-sectional views mainly for illustrating the stacking order of the layers, and the structure of each layer is abstracted or simplified. In Figures 1 to 6, layers having similar functions are denoted by the same reference numerals and described accordingly.

[0154] Figure 1 is a schematic cross-sectional view of a separator that does not have an inorganic particle layer and a heat-resistant resin layer. The separator shown in Figure 1 is a separator in which a surface layer (A) 70, a polyolefin microporous membrane 20, and a surface layer (C) 90 are stacked in that order.

[0155] Figures 2 and 3 are schematic cross-sectional views of a separator having an inorganic particle layer on one side of a polyolefin microporous membrane. The separator shown in Figure 2 is a separator in which a surface layer (A) 70, an inorganic particle layer 30, a polyolefin microporous film 20, and a surface layer (C) 90 are stacked in this order. The separator shown in Figure 3 is a separator in which a surface layer (A) 70, a polyolefin microporous film 20, an inorganic particle layer 30, and a surface layer (C) 90 are stacked in this order.

[0156] Figure 4 is a schematic cross-sectional view of a separator having inorganic particle layers on both sides of a polyolefin microporous membrane. The separator shown in Figure 4 is a separator in which a surface layer (A) 70, an inorganic particle layer 30, a polyolefin microporous film 20, another inorganic particle layer 30, and a surface layer (C) 90 are stacked in this order. In the separator shown in Figure 4, one inorganic particle layer 30 and the other inorganic particle layer 30 may be the same or different in terms of components and / or composition.

[0157] Figure 5 is a schematic cross-sectional view of a separator having a heat-resistant resin layer on one side of a polyolefin microporous membrane. The separator shown in Figure 5 is a separator in which a surface layer (A) 70, a heat-resistant resin layer 60, a polyolefin microporous film 20, and a surface layer (C) 90 are laminated in this order. In the example shown in Figure 5, the heat-resistant resin layer 60 is positioned between the polyolefin microporous membrane 20 and the surface layer (A) 70, but the heat-resistant resin layer 60 may also be positioned between the polyolefin microporous membrane 20 and the surface layer (C) 90.

[0158] Figure 6 is a schematic cross-sectional view of a separator having an inorganic particle layer and a heat-resistant resin layer on one side of a polyolefin microporous membrane. The separator shown in Figure 6 is a separator in which a surface layer (A) 70, a heat-resistant resin layer 60, an inorganic particle layer 30, a polyolefin microporous film 20, and a surface layer (C) 90 are laminated in this order. In the example shown in Figure 6, the inorganic particle layer 30 and the heat-resistant resin layer 60 are arranged between the polyolefin microporous membrane 20 and the surface layer (A) 70, but the inorganic particle layer 30 and the heat-resistant resin layer 60 may also be arranged between the polyolefin microporous membrane 20 and the surface layer (C) 90. In the example shown in Figure 6, the inorganic particle layer 30 and the heat-resistant resin layer 60 are arranged on the same surface of the polyolefin microporous membrane 20, but the inorganic particle layer 30 and the heat-resistant resin layer 60 may be arranged on separate surfaces of the polyolefin microporous membrane 20.

[0159] The stacking configuration of the separators in this disclosure is not limited to the configurations shown in Figures 1 to 6. Other examples of the separator of this disclosure include: an example in which an inorganic particle layer and a heat-resistant resin layer are arranged on both sides of a polyolefin microporous membrane; an example in which an inorganic particle layer is arranged on both sides of a polyolefin microporous membrane and a heat-resistant resin layer is arranged on one side of the polyolefin microporous membrane; and an example in which an inorganic particle layer is arranged on one side of a polyolefin microporous membrane and heat-resistant resin layers are arranged on both sides of the polyolefin microporous membrane.

[0160] In a form in which the separator has an inorganic particle layer and a heat-resistant resin layer, there are no restrictions on the stacking order of the inorganic particle layer and the heat-resistant resin layer. From the viewpoint of ease of manufacturing the separator and excellent ion permeability of the separator, it is preferable that the inorganic particle layer is the lower layer and the heat-resistant resin layer is the upper layer.

[0161] [Method of manufacturing a separator] The separator of this disclosure can be manufactured by forming each layer on a polyolefin microporous membrane using a wet coating method or a dry coating method. In this disclosure, a wet coating method is a method of solidifying the coating layer in a solidifying liquid, and a dry coating method is a method of solidifying the coating layer by drying.

[0162] Examples of wet coating and dry coating methods are described below. In the following description, layers other than the polyolefin microporous membrane of the separator are collectively referred to as "porous layers."

[0163] -Wet coating method- An example of a wet coating method includes the steps of: applying a coating liquid to one or both sides of a substrate to form a coating layer; immersing the substrate having the coating layer in a solidifying solution to solidify the coating layer and form a porous layer; and removing the laminate consisting of the substrate and the porous layer from the solidifying solution and washing and drying it.

[0164] The coating solution is prepared by dissolving or dispersing the porous layer material in a solvent.

[0165] The solvent used in preparing the coating solution includes a solvent that dissolves the resin contained in the porous layer (hereinafter also referred to as the "good solvent"). Polar amide solvents are examples of good solvents common to acrylic resins, polyvinyl chloride resins, and polyamides. Examples of polar amide solvents include dimethylacetamide, dimethylformamide, and N-methylpyrrolidone.

[0166] The solvent used in preparing the coating solution preferably contains a phase-separating agent that induces phase separation, from the viewpoint of forming a good porous structure in the porous layer. Therefore, the solvent used in preparing the coating solution is preferably a mixed solvent 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 suitable for coating. Examples of phase-separating agents common to acrylic resins, polyvinyl chloride resins, and polyamides include water, methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, and tripropylene glycol.

[0167] The solvent used in preparing the coating solution is preferably a mixed solvent of a good solvent and a phase separating agent, from the viewpoint of forming a good porous structure in the porous layer, and is preferably a mixed solvent containing 60% by mass or more of the good solvent and 5% to 40% by mass of the phase separating agent.

[0168] The resin concentration of the coating solution is preferably 1% to 20% by mass, from the viewpoint of forming a good porous structure in the porous layer. If the coating solution contains inorganic particles, the inorganic particle concentration of the coating solution is preferably 0.5% to 50% by mass, from the viewpoint of forming a good porous structure in the porous layer.

[0169] The coating solution may contain dispersants such as surfactants, wetting agents, defoamers, pH adjusters, etc. These additives may remain in the porous layer as long as they are electrochemically stable within the operating range of non-aqueous secondary batteries and do not inhibit reactions within the battery.

[0170] Methods for applying the coating liquid to the substrate include Meyer bar, die coater, reverse roll coater, roll coater, and gravure coater. When forming a porous layer on both sides of the substrate, it is preferable from a productivity standpoint to apply the coating liquid to both sides of the substrate simultaneously.

[0171] The coating layer is solidified by immersing the substrate on which the coating layer is formed in a solidifying solution, thereby inducing phase separation in the coating layer and solidifying the resin. This results in a laminate consisting of the substrate and the porous layer.

[0172] The solidification solution generally contains the good solvent and phase separating agent used in the preparation of the coating solution, along with water. From a production standpoint, it is preferable that the mixing ratio of the good solvent and the phase separating agent match the mixing ratio of the mixed solvent used in the preparation of the coating solution. From the viewpoint of forming a porous structure and productivity, the water content in the solidification solution is preferably 40% to 90% by mass. The temperature of the solidification solution is, for example, 20°C to 50°C.

[0173] After the coating layer is solidified in the solidification solution, the laminate is removed from the solidification solution and washed with water. Washing removes the solidification solution from the laminate. Further drying removes water from the laminate. Washing is performed, for example, by transporting the laminate in a water bath. Drying is performed, for example, by transporting the laminate in a high-temperature environment, blowing air on the laminate, or bringing the laminate into contact with a heat roll. In one embodiment, the drying temperature is set to a temperature that does not melt the resin (for example, a temperature of (glass transition temperature of the resin) or lower).

[0174] -Dry coating method- An example of a dry coating method includes the steps of applying a coating liquid to one or both sides of a substrate to form a coating layer, and drying and solidifying the coating layer on the substrate to form a porous layer.

[0175] The coating solution is prepared by dissolving or dispersing the porous layer material in a solvent.

[0176] Water is an example of a solvent used in the preparation of coating solutions. Water is preferred because it is easily removed by drying and has no toxicity to humans or the environment.

[0177] The resin concentration of the coating solution is preferably 1% to 20% by mass, from the viewpoint of coating properties and productivity of the porous layer. If the coating solution contains inorganic particles, the inorganic particle concentration of the coating solution is preferably 0.5% to 50% by mass, from the viewpoint of coating properties and productivity of the porous layer.

[0178] The coating solution may contain dispersants such as surfactants, wetting agents, defoamers, pH adjusters, etc. These additives may remain in the resin particle layer as long as they are electrochemically stable within the operating range of non-aqueous secondary batteries and do not inhibit reactions within the battery.

[0179] Methods for applying the coating liquid to the substrate include Meyer bar, die coater, reverse roll coater, roll coater, and gravure coater. When forming a porous layer on both sides of the substrate, it is preferable from a productivity standpoint to apply the coating liquid to both sides of the substrate simultaneously.

[0180] The coating layer solidifies by drying (i.e., removing the solvent). Drying is performed, for example, by transporting the substrate with the coating layer in a high-temperature environment, by blowing air onto the substrate with the coating layer, or by bringing the substrate with the coating layer into contact with a heat roll. In one embodiment, the drying temperature is set to a temperature that does not melt the resin (for example, a temperature of (glass transition temperature of the resin + 20°C) or lower).

[0181] All porous layers of the separator may be formed by a wet coating method or by a dry coating method. Alternatively, some porous layers of the separator may be formed by a wet coating method and some porous layers by a dry coating method.

[0182] The separator can also be manufactured by preparing the porous layer as an independent sheet and then combining it with a substrate by heat compression or adhesive. One method for preparing the porous layer as an independent sheet is to apply the wet coating method or dry coating method described above to form the porous layer on a release sheet.

[0183] The method for manufacturing the separator may be a discontinuous method or a continuous method.

[0184] • Discontinuous manufacturing method: A lower layer is formed on a substrate unwound from a roll to obtain a laminate of the substrate and the lower layer, and then the laminate is wound onto another roll. Next, an upper layer is formed on the laminate unwound from the roll to obtain a separator, and the resulting separator is wound onto another roll.

[0185] • Continuous manufacturing method: A lower layer is formed on the substrate unwound from a roll to obtain a laminate of the substrate and the lower layer, then an upper layer is formed on the laminate to obtain a separator, and the finished separator is wound onto another roll.

[0186] <Non-aqueous secondary battery> The non-aqueous secondary battery of this disclosure is a non-aqueous secondary battery that obtains electromotive force by doping and dedoping lithium ions, and comprises a positive electrode, a negative electrode, and a separator of this disclosure. Doping means absorption, support, adsorption, or insertion, and refers to the phenomenon in which lithium ions enter the active material of the electrode.

[0187] The non-aqueous secondary battery of this disclosure has a structure in which, for example, a battery element in which a negative electrode and a positive electrode face each other via a separator is sealed together with an electrolyte in an outer casing. The non-aqueous secondary battery of this disclosure is suitable for non-aqueous electrolyte secondary batteries, particularly lithium-ion secondary batteries.

[0188] The non-aqueous secondary battery of this disclosure exhibits excellent adhesion to both the positive and negative electrodes through a relatively low-temperature, low-pressure bonding process, which ensures that the pores of the separator remain open during battery manufacturing, resulting in superior charge-discharge characteristics (e.g., cycle characteristics, rate characteristics).

[0189] The following describes examples of the forms of the positive electrode, negative electrode, electrolyte, and outer casing material of the non-aqueous secondary battery of this disclosure.

[0190] An example of a positive electrode embodiment is a configuration in which an active material layer containing a positive electrode active material and a binder resin is arranged on a current collector. The active material layer may further contain a conductive additive. Examples of positive electrode active materials include lithium-containing transition metal oxides. Examples of lithium-containing transition metal oxides include LiCoO2, LiNiO2, and LiMn 1 / 2 Ni 1 / 2 O2, LiCo 1 / 3 Mn 1 / 3 Ni 1 / 3 O2, LiMn2O4, LiFePO4, LiCo 1 / 2 Ni 1 / 2 O2, Lial 1 / 4 Ni3 / 4 Examples include O2. Examples of binder resins include polyvinylidene fluoride resins and styrene-butadiene copolymers. Examples of conductive additives include acetylene black, Ketjen black, graphite powder, and carbon materials such as ultrafine carbon fibers. Examples of current collectors include aluminum foil, titanium foil, and stainless steel foil with a thickness of 5 μm to 20 μm.

[0191] An example of a negative electrode embodiment is a configuration in which an active material layer containing a negative electrode active material and a binder resin is arranged on a current collector. The active material layer may further contain a conductive additive. Examples of negative electrode active materials include materials that can electrochemically absorb lithium ions. Examples of such materials include carbon materials; alloys of silicon, tin, aluminum, etc. with lithium; Wood's alloys; 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, graphite powder, and ultrafine carbon fibers. Examples of current collectors include copper foil, nickel foil, and stainless steel foil with a thickness of 5 μm to 20 μm. Instead of the above negative electrode, metallic lithium foil may be used as the negative electrode.

[0192] The electrolyte is preferably a solution of a lithium salt dissolved 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; linear carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and their fluorine-substituted derivatives; and cyclic esters such as γ-butyrolactone and γ-valerolactone. The non-aqueous solvent may be used alone or in a mixture of two or more.

[0193] As the electrolyte, a solution is preferred in which cyclic carbonate and linear carbonate are mixed in a mass ratio (cyclic carbonate:linear carbonate) of 20:80 to 40:60, and a lithium salt is dissolved in it at a concentration of 0.5 mol / L to 1.5 mol / L.

[0194] Examples of exterior materials include aluminum laminate film packs and metal cans. Examples of battery shapes include rectangular, cylindrical, and coin-shaped batteries. The separator of this disclosure is suitable for any of the exterior materials and shapes.

[0195] The non-aqueous secondary battery of this disclosure can be manufactured, for example, by manufacturing a laminate in which the separator of this disclosure is placed between the positive electrode and the negative electrode, and then subjecting this laminate to a wet heat press. Dry heat pressing may be performed in the process of manufacturing the laminate for the purpose of integrating the laminate. Integrating the laminate by dry heat pressing is preferable from the viewpoint of the manufacturing yield and transportability of the separator.

[0196] The non-aqueous secondary battery of this disclosure can be manufactured by first creating a laminate in which the separator of this disclosure is placed between the positive electrode and the negative electrode, and then using this laminate by, for example, the following manufacturing method (1) or manufacturing method (2).

[0197] Manufacturing method (1): After temporarily bonding the electrodes and separators by dry heat pressing the laminate, it is placed in an outer casing and electrolyte is injected. Next, the laminate is wet heat pressed from above the outer casing to bond the electrodes and separators and seal the outer casing.

[0198] Manufacturing method (2): The laminate is placed in an outer material and the electrolyte is injected. Next, the laminate is wet heat pressed from above the outer material to bond the electrodes to the separator and seal the outer material.

[0199] In manufacturing methods (1) and (2), the press temperature, press pressure, and press time for the wet heat press should be set according to the type of exterior material, the size and application of the battery, etc.

[0200] When the outer casing is a metal can, it is generally difficult to implement a wet heat press process. When the outer casing is a metal can, the pressure naturally applied from the metal can is used to bond the electrodes and separator. This pressure is approximately 40kPa to 200kPa. After inserting the laminate into the metal can, adding the electrolyte, and sealing it, the electrodes and separator can be bonded by leaving it at 50°C to 80°C for 3 to 20 hours. During the above-mentioned period, the battery may be in any charged state, or it may be charging or discharging. During the above-mentioned period, a part of the outer casing may be opened to release the gas generated inside.

[0201] When manufacturing a laminate with a separator placed between the positive electrode and the negative electrode, the method of placing the separator between the positive electrode and the negative electrode may be a method in which the positive electrode, separator, and negative electrode are stacked in that order in at least one layer each (the so-called stack method), or a method in which the positive electrode, separator, negative electrode, and separator are stacked in that order and wound in the length direction. [Examples]

[0202] The separator and non-aqueous secondary battery of this disclosure will be described in more detail below with reference to examples. The materials, amounts used, proportions, processing procedures, etc., shown in the following examples can be modified as appropriate without departing from the spirit of this disclosure. Therefore, the scope of the separator and non-aqueous secondary battery of this disclosure should not be interpreted as being limited by the specific examples shown below.

[0203] In the following descriptions, synthesis, processing, and manufacturing were carried out at room temperature (25°C ± 3°C) unless otherwise specified.

[0204] <Measurement methods, evaluation methods> The measurement and evaluation methods applied to the examples and comparative examples are as follows.

[0205] [Average primary particle size of inorganic particles] The average primary particle size of inorganic particles was determined by performing SEM observation on inorganic particles used to form a porous layer, measuring the major axis of 100 randomly selected inorganic particles, and averaging the major axes of these 100 particles.

[0206] [Thickness of polyolefin microporous membrane and separator] The thickness (μm) of the polyolefin microporous membrane and separator was determined by measuring 20 points within a 10cm square area using a contact-type length measuring instrument (Mitutoyo Corporation, LITEMATIC VL-50S) and averaging the results. A spherical measuring probe with a radius of 10mm (Mitutoyo Corporation) was used, and a load of 0.19N was applied during measurement.

[0207] [Porosity of polyolefin microporous membranes] The porosity ε(%) of the polyolefin microporous membrane was determined by the following formula. ε = {1 - Ws / (ds·t)} × 100 Here, Ws is the basis weight (g / m²) of the polyolefin microporous membrane. 2 ), ds is the true density (g / cm³) of the polyolefin microporous membrane. 3 ), where t is the thickness of the polyolefin microporous membrane (μm).

[0208] [Air permeability of polyolefin microporous membranes and separators] The air permeability (seconds / 100mL) of the polyolefin microporous membrane and separator was measured using a Gaale densometer (Toyo Seiki Co., Ltd., G-B2C) in accordance with JIS P8117:2009.

[0209] [Porosity of the separator] The porosity ε(%) of the separator was calculated using the following formula.

[0210]

number

[0211] Here, for the constituent materials 1, 2, 3, ..., n of the separator, the mass per unit area of ​​each constituent material is W1, W 2、W3, ..., W n (g / cm 2 ) and the true density of each constituent material is d1, d2, d3, ..., d n (g / cm 3 ) and the thickness of the separator is t (cm).

[0212] [Thermal shrinkage rate of separators] A rectangle measuring TD60mm x MD180mm was cut from the separator to form a test specimen. Marks were made on the specimen at points 20mm and 170mm from one end along the line that bisects TD (referred to as points A and B, respectively). Furthermore, marks were made at points 10mm and 50mm from one end along the line that bisects MD (referred to as points C and D, respectively). A clip was attached to the specimen (the clip was placed between the end closest to point A and point A), and the specimen was suspended in an oven at 130°C and heat-treated for 60 minutes under no tension. The lengths between A and B and between C and D were measured before and after the heat treatment, and the thermal shrinkage rate was calculated using the following formula. The thermal shrinkage rates of the three specimens were then averaged.

[0213] MD thermal shrinkage rate (%) = {(length of AB before heat treatment - length of AB after heat treatment) ÷ length of AB before heat treatment} × 100 TD thermal shrinkage rate (%) = {(length of CD before heat treatment - length of CD after heat treatment) ÷ length of CD before heat treatment} × 100

[0214] [Dry adhesion to electrodes] A slurry for the positive electrode was prepared by stirring and mixing 94 parts by mass of lithium cobalt oxide powder, which is the positive electrode active material, 3 parts by mass of acetylene black, which is a conductive additive, 3 parts by mass of polyvinylidene fluoride, which is a binder resin, and an appropriate amount of N-methyl-2-pyrrolidone in a double-arm mixer. The slurry for the positive electrode was applied to one or both sides of a 20 μm thick aluminum foil, dried, and then pressed to obtain a positive electrode having a positive electrode active material layer on one side.

[0215] A slurry for the negative electrode was prepared by mixing 96.2 parts by mass of artificial graphite, which is the negative electrode active material, 7 parts by mass of a water-soluble dispersion containing 40% by mass of a modified styrene-butadiene copolymer, which is the binder resin, 1 part by mass of carboxymethylcellulose, which is the thickener, and an appropriate amount of water using a double-arm mixer. The slurry for the negative electrode was applied to one or both sides of a 10 μm thick copper foil, dried, and then pressed to obtain a negative electrode having a negative electrode active material layer on both or one side.

[0216] The electrodes (positive and negative) were cut into rectangles measuring 15 mm wide x 70 mm long. The separator was cut into a rectangle measuring TD 18 mm x MD 74 mm. Release paper measuring 15 mm wide x 70 mm long was prepared. The separator was placed on top of the active material layer of the electrode (positive or negative), and then the release paper was placed on top of the separator to create a laminate. For the positive electrode, the separator was placed so that the surface layer (A) was in contact with the positive electrode, and for the negative electrode, the separator was placed so that the surface layer (C) was in contact with the negative electrode. The laminate was inserted into an aluminum laminate film pack, and the pack was heat-pressed (dry heat press) in the direction of the laminate using a heat press machine to bond the electrodes (positive or negative electrode) to the separator. The heat pressing conditions were a temperature of 85°C, a pressure of 2 MPa, and a time of 5 minutes. After heat pressing, the laminate was removed from the pack, the release paper was peeled off, and a dry adhesion test specimen was obtained.

[0217] The uncoated surface of the electrode of the test specimen was fixed to a metal plate with double-sided tape, and the metal plate was fixed to the lower chuck of a Tensilon (A&D Company, Ltd., STB-1225S). At this time, the metal plate was fixed to the Tensilon so that the length direction of the test specimen (i.e., the MD of the separator) was in the direction of gravity. The separator was peeled off the electrode by about 2 cm from the lower end, and that end was fixed to the upper chuck, and a 180° peel test was performed. The tensile speed of the 180° peel test was set to 20 mm / min, and the load (N) from 10 mm to 40 mm after the start of measurement was taken at 0.4 mm intervals, and the average was calculated. Furthermore, the load of 10 test specimens was averaged to obtain the adhesive strength (N / 15 mm) between the electrode and the separator.

[0218] [Wet adhesion to electrodes] A secondary battery for testing described below was prepared. A compression bending test (three-point bending test) was performed on the battery. The measurement was carried out by attaching a compression bending test jig to a tensilon (A&D Company, Ltd., STB-1225S). The distance between the support bases was set to 4 cm, and the battery was placed on the support bases such that the short side direction of the battery was parallel to the longitudinal direction of the indenter and the compression position during measurement was at the center of the longitudinal direction of the internal electrode of the battery. The displacement when the indenter was lowered until a load of 0.1 N was applied was set to 0, and the measurement was started. The compression speed during measurement was set to 2 mm / min, and the measurement was carried out up to a displacement of 4 mm.

[0219] [Impact resistance (compression fracture strength) of battery] Ten secondary batteries for testing described below were prepared. At room temperature, the batteries were charged at a constant current and constant voltage of 0.1 C and 4.2 V and held at 4.2 V for 3 hours. Next, the batteries were placed on a horizontal table with the positive electrode side facing up and fixed with adhesive tape. A spherical terminal with a diameter of 5 mm was placed at the center of the top of the battery and lowered at a speed of 100 mm / min to apply a load to the battery. The load (unit: N) at the time when the voltage of the battery decreased and reached 3.5 V was determined, and the average of the ten batteries was calculated.

[0220] [[ID=ll]]<Separator and battery manufacturing> [Example 1] [Separator manufacturing] Meta-type aramid was dissolved in a mixed solvent of dimethylacetamide (DMAc) and tripropylene glycol (TPG) (DMAc:TPG = 80:20 [mass ratio]), and further barium sulfate particles (average primary particle size 0.05 μm) were dispersed to obtain a coating solution (1). The coating solution (1) had a meta-type aramid concentration of 4.5 mass%, and the mass ratio of meta-type aramid to barium sulfate particles was meta-type aramid:barium sulfate particles = 20:80.

[0221] Polyvinyl chloride (average degree of polymerization 700, homopolymer) was dissolved in a mixed solvent of DMAc and TPG (DMAc:TPG = 80:20 [mass ratio]), and magnesium hydroxide particles (average primary particle size 0.8 μm) were further dispersed to obtain coating solution (2). Coating solution (2) had a polyvinyl chloride concentration of 6% by mass, and the mass ratio of polyvinyl chloride to magnesium hydroxide particles was polyvinyl chloride:magnesium hydroxide particles = 35:65.

[0222] A resin particle dispersion (1) was prepared in which acrylic resin particles were dispersed in water. The resin particle dispersion (1) had a resin particle concentration of 10% by mass. Acrylic resin particles are copolymer particles of acrylic monomers and styrene monomers, with a polymerization ratio (mass ratio) of acrylic monomers to styrene monomers = 38:62, a glass transition temperature of 52°C, and an average primary particle size of 500 nm.

[0223] A polyethylene microporous membrane (thickness 8 μm, porosity 38%, air permeability 163 seconds / 100 mL) was coated with coating liquid (1) on one side and with coating liquid (2) on the other side using a gravure coater. The coated polyethylene microporous membrane was then immersed in a solidification solution (DMAc:TPG:water = 34:9:57 [mass ratio], liquid temperature 40°C) to solidify the coating layer. Next, it was washed in a water washing tank at a water temperature of 40°C and dried. Then, resin particle dispersion (1) was applied onto the porous layer formed with coating liquid (1) and dried to solidify the coating layer. Thus, the separator of Example 1 was obtained.

[0224] - Manufacturing of positive electrodes - A slurry for the positive electrode was prepared by stirring and mixing 94 parts by mass of lithium cobalt oxide powder, which is the positive electrode active material, 3 parts by mass of acetylene black, which is a conductive additive, 3 parts by mass of polyvinylidene fluoride, which is a binder resin, and an appropriate amount of N-methyl-2-pyrrolidone in a double-arm mixer. The slurry for the positive electrode was applied to one or both sides of a 20 μm thick aluminum foil, dried, and then pressed to obtain a positive electrode having a positive electrode active material layer on one or both sides.

[0225] -Manufacturing of negative electrodes- A slurry for the negative electrode was prepared by mixing 96.2 parts by mass of artificial graphite, which is the negative electrode active material, 7 parts by mass of a water-soluble dispersion containing 40% by mass of a modified styrene-butadiene copolymer, which is the binder resin, 1 part by mass of carboxymethylcellulose, which is the thickener, and an appropriate amount of water using a double-arm mixer. The slurry for the negative electrode was applied to one or both sides of a 10 μm thick copper foil, dried, and then pressed to obtain a negative electrode having a negative electrode active material layer on both or one side.

[0226] -Manufacturing of secondary batteries for wet adhesion testing- The double-sided positive electrode and double-sided negative electrode were each cut into rectangles measuring 30 mm x 70 mm. The separator was cut into a rectangle measuring TD 35 mm x MD 75 mm. These were stacked so that the positive and negative electrodes were alternated and a separator was placed between them, creating a laminate consisting of 3 positive electrodes, 3 negative electrodes, and 5 separators. The separators were arranged so that surface layer (A) was in contact with the positive electrode and surface layer (C) was in contact with the negative electrode. The laminate was placed in an aluminum laminate film pack, and an electrolyte (1 mol / L LiPF6-ethylene carbonate:ethyl methyl carbonate [mass ratio 3:7]) was injected into the pack to allow the electrolyte to permeate the laminate. Next, the pack and the laminate were heat-pressed in the direction of the laminate using a hot press (wet heat press) to bond the electrodes to the separator. The heat-pressing conditions were a press temperature of 70°C, a press pressure of 100 kPa, and a press time of 7 hours. The resulting test secondary battery was used to evaluate the wet adhesion between the electrodes and the battery.

[0227] -Manufacturing of rechargeable batteries for impact resistance testing- A single-sided positive electrode was cut into a rectangle measuring 30 mm x 50 mm. A single-sided negative electrode was cut into a rectangle measuring 31 mm x 51 mm. A separator was cut into a rectangle measuring TD 32 mm x MD 52 mm. These were stacked so that the positive electrode active material layer and the negative electrode active material layer faced each other, and the separator was sandwiched between the positive and negative electrodes, to create a laminate consisting of one positive electrode, one negative electrode, and one separator. The separator was positioned so that its surface layer (A) was in contact with the positive electrode and its surface layer (C) was in contact with the negative electrode. The laminate was placed in an aluminum laminate film pack, and an electrolyte (1 mol / L LiPF6-ethylene carbonate:ethyl methyl carbonate [mass ratio 3:7]) was injected into the pack to allow the electrolyte to permeate the laminate. Next, the pack and the laminate were heat-pressed in the direction of the laminate using a hot press (wet heat press) to bond the electrodes to the separator. The heat-pressing conditions were a press temperature of 70°C, a press pressure of 100 kPa, and a press time of 7 hours. The resulting test secondary battery was used to evaluate the battery's cycle characteristics and shock resistance.

[0228] [Comparative Example 1] -Separator manufacturing- Meta-aramid was dissolved in a mixed solvent of DMAc and TPG (DMAc:TPG = 80:20 [mass ratio]), and magnesium hydroxide particles (average primary particle size 0.8 μm) were further dispersed to obtain coating solution (3). Coating solution (3) had a meta-aramid concentration of 5% by mass, and the mass ratio of meta-aramid to magnesium hydroxide particles was meta-aramid:magnesium hydroxide particles = 20:80.

[0229] A resin particle dispersion (2) was prepared in which acrylic resin particles and polyvinylidene fluoride resin particles were dispersed in water. The resin particle dispersion (2) had a mass ratio of acrylic resin particles to polyvinylidene fluoride resin particles of 30:70, and a resin particle concentration of 10% by mass. Acrylic resin particles are particles of acrylic resin with a glass transition temperature of 59°C and an average primary particle size of 500 nm. The polyvinylidene fluoride resin particles have a melting point of 140°C and an average primary particle size of 250 nm.

[0230] Equal amounts of coating solution (3) were applied to both sides of a polyethylene microporous membrane (thickness 8 μm, porosity 38%, air permeability 163 seconds / 100 mL) using a gravure coater. The coated polyethylene microporous membrane was then immersed in a solidification solution (DMAc:TPG:water = 34:9:57 [mass ratio], liquid temperature 40°C) to solidify the coating layer. Next, it was washed in a water washing tank at 40°C and dried. Then, equal amounts of resin particle dispersion (2) were applied to both sides and dried to solidify the coating layer. Thus, the separator of Comparative Example 1 was obtained.

[0231] -Battery Manufacturing- Using the separator described above, a test secondary battery was manufactured in the same manner as in Example 1.

[0232] [Comparative Example 2] -Separator manufacturing- Polyvinyl chloride (average degree of polymerization 700, homopolymer) was dissolved in DMAc, and magnesium hydroxide particles (average primary particle size 0.8 μm) were further dispersed to obtain coating solution (4). Coating solution (4) had a polyvinyl chloride concentration of 6% by mass, and the mass ratio of polyvinyl chloride to magnesium hydroxide particles was polyvinyl chloride:magnesium hydroxide particles = 35:65.

[0233] Equal amounts of coating solution (4) were applied to both sides of a polyethylene microporous membrane (thickness 8 μm, porosity 38%, air permeability 163 seconds / 100 mL) using a gravure coater. The coated polyethylene microporous membrane was then immersed in a solidification solution (DMAc:water = 50:50 [mass ratio], liquid temperature 40°C) to solidify the coating layer. Next, it was washed in a water washing tank at a water temperature of 40°C and dried. Thus, the separator of Comparative Example 2 was obtained.

[0234] -Battery Manufacturing- Using the separator described above, a test secondary battery was manufactured in the same manner as in Example 1.

[0235] Table 1 shows the structure of the polyolefin microporous membrane and the heat-resistant resin layer, Table 2 shows the structure of the surface layer, and Table 3 shows the physical properties and evaluation results of the separator. The abbreviations in Tables 1 and 2 have the following meanings. • PE: Polyethylene ·AC: Acrylic resin ·PVC: Polyvinyl chloride ·PVDF: Polyvinylidene fluoride resin

[0236]

Table 1

[0237]

Table 2

[0238]

Table 3

[0239] [Wet adhesiveness to the electrode] Fig. 7 shows a graph (measurement result of a three-point bending test) regarding the wet adhesiveness between the separator and the electrode. In Fig. 7, (1) is the load-displacement curve of Example 1, (2) is the load-displacement curve of Comparative Example 1, and (3) is the load-displacement curve of Comparative Example 2. (4) in Fig. 7 is the load-displacement curve when the separator and the electrode are not adhered to each other.

[0240] As can be seen from Fig. 7, in Example 1, the gradient corresponding to the elastic modulus from when deformation is applied to the cell until yielding is large, and the yielding is also large. On the other hand, in Comparative Example 1, since the gradient corresponding to the elastic modulus is small, it is determined that the electrode and the separator are not adhered, and in Comparative Example 2, since the load at the time of yielding is small, it is determined that the adhesive force between the electrode and the separator is weak. From this, it can be seen that the separator of Example 1 showed excellent adhesiveness to both the positive electrode and the negative electrode by a wet adhesion treatment at a relatively low temperature and low pressure.

[0241] All documents, patent applications, and technical standards described in this specification are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually stated to be incorporated by reference.

Explanation of symbols

[0242] 20 Polyolefin microporous membrane 30 Inorganic particle layer 60 Heat-resistant resin layer 70 Surface layer (A) 90 Surface layer (C)

Claims

1. Polyolefin microporous membrane and A surface layer (A) containing an acrylic resin is disposed on one side of the polyolefin microporous membrane, The polyolefin microporous membrane comprises a surface layer (C) containing a polyvinyl chloride resin, which is disposed on the other side of the polyolefin microporous membrane. Separator for non-aqueous secondary batteries.

2. The separator for a non-aqueous secondary battery according to claim 1, wherein the acrylic resin is acrylic resin particles.

3. A heat-resistant resin layer is further provided between the polyolefin microporous membrane and the surface layer (A), wherein the heat-resistant resin comprises more than 10% by mass. The surface layer (A) is a layer in which acrylic resin particles are attached to the heat-resistant resin layer. A separator for a non-aqueous secondary battery according to claim 1.

4. The separator for a non-aqueous secondary battery according to claim 3, wherein the heat-resistant resin comprises at least one selected from the group consisting of aromatic polyamides, polyimides, and polyamideimides.

5. The separator for a non-aqueous secondary battery according to claim 3, wherein the heat-resistant resin layer further contains inorganic particles.

6. The separator for a non-aqueous secondary battery according to claim 5, wherein the average primary particle size of the inorganic particles contained in the heat-resistant resin layer is 0.01 μm to 0.3 μm.

7. The separator for a non-aqueous secondary battery according to claim 5, wherein the inorganic particles include barium sulfate particles.

8. The separator for a non-aqueous secondary battery according to claim 1, further comprising an inorganic particle layer containing inorganic particles, wherein the inorganic particles constitute 90% by mass or more, between the polyolefin microporous membrane and the surface layer (A) and / or between the polyolefin microporous membrane and the surface layer (C).

9. The separator for a non-aqueous secondary battery according to claim 8, wherein the average primary particle size of the inorganic particles contained in the inorganic particle layer is 10 nm to 500 nm.

10. The separator for a non-aqueous secondary battery according to claim 8, wherein the inorganic particles include at least one selected from the group consisting of γ-alumina particles, boehmite particles, and barium sulfate particles.

11. The separator for a non-aqueous secondary battery according to claim 1, wherein the average degree of polymerization of the polyvinyl chloride resin contained in the surface layer (C) is 500 to 1400.

12. A non-aqueous secondary battery separator according to any one of claims 1 to 11, comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, An electromotive force is obtained by doping and dedoping lithium ions. Non-aqueous secondary battery.

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