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

Abstract

A separator for a non-aqueous secondary battery comprises a porous substrate and an adhesive porous layer comprising a polyvinylidene fluoride resin and a filler, wherein the porous substrate contains fluorine atoms and when differential scanning calorimetry is performed using the entire polyvinylidene fluoride resin included in the adhesive porous layer as a sample, two or more endothermic peaks and / or two or more exothermic peaks are observed.

Description

Technology Field

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

[0002] International Publication No. 2013 / 058367, International Publication No. 2013 / 058368, International Publication No. 2013 / 058369, and International Publication No. 2013 / 058370 each disclose a separator for a non-aqueous secondary battery comprising a porous substrate and an adhesive porous layer comprising a polyvinylidene fluoride resin, wherein the polyvinylidene fluoride resin comprises at least two types of polyvinylidene fluoride resins.

[0003] Patent Publication No. 6487130 discloses a separator for a non-aqueous secondary battery comprising a porous substrate and an adhesive porous layer comprising a polyvinylidene fluoride resin, wherein the polyvinylidene fluoride resin comprises a copolymer of vinylidene fluoride, hexafluoropropylene, and a monomer having an acidic group or an ester group. The problem to be solved

[0004] A battery using a separator having an adhesive porous layer containing a polyvinylidene fluoride resin is generally manufactured by producing a laminate of an electrode and a separator, housing the laminate in an outer casing, injecting an electrolyte, and performing a heat press treatment (referred to as "wet heat press" in this disclosure). According to the wet heat press, since the polyvinylidene fluoride resin is heat pressed while swollen in the electrolyte, the adhesion between the electrode and the separator is good, and good battery characteristics are easily obtained. However, if the wet heat press is performed at a relatively high temperature, the electrolyte or the electrolyte may decompose and generate gas within the battery, which causes, for example, a decrease in the cycle characteristics and dimensional stability of the battery.

[0005] Meanwhile, there is a technique for bonding the electrode and the separator by performing a heat press treatment (referred to as "dry heat press" in this disclosure) on a laminate of the electrode and the separator without impregnating it with an electrolyte. If the electrode and the separator are sufficiently bonded by the dry heat press, a wet heat press is not required, and thus, decomposition of the electrolyte and electrolyte does not occur.

[0006] Furthermore, even when performing a wet heat press, if a dry heat press is performed on the laminate prior to bond the electrode and separator, the temperature of the wet heat press can be set to a relatively low temperature, thereby suppressing the decomposition of the electrolyte and electrolyte. Additionally, if the separator is bonded to the electrode by a dry heat press before the laminate is placed in the outer casing, deformation of the laminate that may occur during transport for placement in the outer casing is suppressed.

[0007] Therefore, if the separator can be well adhered to the electrode by a dry heat press, it is expected that the battery will have a larger surface area and better performance.

[0008] However, it is known that when non-aqueous secondary batteries are charged and discharged at high speeds, the interior of the battery can become high, and that non-aqueous secondary batteries exposed to high temperatures undergo changes in the porous structure of the separator, resulting in a decrease in battery performance (e.g., capacity retention rate).

[0009] In addition, it is known that when the inside of the battery becomes high temperature, it becomes difficult to retain the electrolyte, especially in porous substrates, and the ion permeability of the separator decreases, causing the membrane resistance value to increase.

[0010] The present disclosure was made under the above circumstances.

[0011] The present disclosure aims to provide a separator for a non-aqueous secondary battery that has excellent adhesion to an electrode by a dry heat press and adhesion to an electrode by a wet heat press, and is easy to retain an electrolyte within a porous substrate, thereby having a low film resistance value even after exposure to high temperatures and a high capacity retention rate of the battery even after exposure to high temperatures. means of solving the problem

[0012] Specific means for solving the above problem include the following aspects.

[0013] <1> porous substrate and,

[0014] An adhesive porous layer is provided on one or both sides of the above porous substrate and comprises a polyvinylidene fluoride-based resin and a filler.

[0015] The above porous substrate contains fluorine atoms, and

[0016] When differential scanning calorimetry is performed using the entire polyvinylidene fluoride-based resin contained in the above adhesive porous layer as a sample, two or more endothermic peaks and / or two or more exothermic peaks are observed,

[0017] Separator for non-aqueous secondary batteries.

[0018] <2>

[0019] <1> In this regard,

[0020] When differential scanning calorimetry is performed using the entire polyvinylidene fluoride-based resin included in the adhesive porous layer as a sample, at least one endothermic peak is observed in the region between 125°C and 140°C and in the region between 140°C and 190°C,

[0021] Separator for non-aqueous secondary batteries.

[0022] <3>

[0023] <1> or <2> In this regard,

[0024] When differential scanning calorimetry is performed using the entire polyvinylidene fluoride-based resin contained in the adhesive porous layer as a sample, two or more endothermic peaks are observed, and the temperature difference between adjacent endothermic peaks is 10°C or more and 60°C or less,

[0025] Separator for non-aqueous secondary batteries.

[0026] <4>

[0027] <1> ~ <3> In any one of these,

[0028] When differential scanning calorimetry is performed using the entire polyvinylidene fluoride-based resin included in the adhesive porous layer as a sample, at least one exothermic peak is observed in the region between 80°C and 125°C and in the region between 125°C and 190°C,

[0029] Separator for non-aqueous secondary batteries.

[0030] <5>

[0031] <1> ~ <4> In any one of these,

[0032] When differential scanning calorimetry is performed using the entire polyvinylidene fluoride-based resin contained in the adhesive porous layer as a sample, two or more exothermic peaks are observed, and the temperature difference between adjacent exothermic peaks is 10°C or more and 90°C or less,

[0033] Separator for non-aqueous secondary batteries.

[0034] <6> porous substrate and,

[0035] An adhesive porous layer is provided on one or both sides of the above porous substrate and comprises a polyvinylidene fluoride-based resin and a filler.

[0036] The above porous substrate contains fluorine atoms, and

[0037] The above polyvinylidene fluoride resin comprises the following polyvinylidene fluoride resin X and polyvinylidene fluoride resin Y,

[0038] Separator for non-aqueous secondary batteries.

[0039] Polyvinylidene fluoride resin X: comprises constituent units derived from vinylidene fluoride and constituent units derived from hexafluoropropylene, wherein the proportion of constituent units derived from hexafluoropropylene in the total constituent units is greater than 3.5 mol% and less than or equal to 15 mol%, the weight average molecular weight is greater than or equal to 100,000 and less than 1 million, and the melting point is greater than or equal to 125°C and less than 150°C.

[0040] Polyvinylidene fluoride resin Y: contains constituent units derived from vinylidene fluoride, may contain constituent units derived from hexafluoropropylene, and the proportion of constituent units derived from hexafluoropropylene in the total constituent units is 0 mol% or more and 3.5 mol% or less, the weight average molecular weight is 1 million or more and less than 3 million, and the melting point is 150°C or more and less than 180°C.

[0041] <7>

[0042] <6> In this regard,

[0043] When differential scanning calorimetry is performed using the entire polyvinylidene fluoride-based resin contained in the above adhesive porous layer as a sample, two or more endothermic peaks and / or two or more exothermic peaks are observed,

[0044] Separator for non-aqueous secondary batteries.

[0045] <8>

[0046] <6> or <7> In this regard,

[0047] The difference between the melting point of the polyvinylidene fluoride resin X and the melting point of the polyvinylidene fluoride resin Y is 25°C or more and less than 55°C,

[0048] Separator for non-aqueous secondary batteries.

[0049] <9>

[0050] <6> ~ <8> In any one of these,

[0051] The mass ratio of the polyvinylidene fluoride-based resin X and the polyvinylidene fluoride-based resin Y included in the adhesive porous layer is 20:80 to 80:20,

[0052] Separator for non-aqueous secondary batteries.

[0053] <10>

[0054] <6> ~ <9> In any one of these,

[0055] The above polyvinylidene fluoride-based resin X comprises constituent units derived from vinylidene fluoride and constituent units derived from hexafluoropropylene, wherein the proportion of constituent units derived from hexafluoropropylene in the total constituent units is greater than 5.0 mol% and less than or equal to 15 mol%, the weight average molecular weight is 300,000 or more and less than 1,000,000, and the melting point is 125°C or more and less than 140°C.

[0056] Separator for non-aqueous secondary batteries.

[0057] <11>

[0058] <6> ~ <10> In any one of these,

[0059] The above polyvinylidene fluoride-based resin Y may comprise constituent units derived from vinylidene fluoride and may comprise constituent units derived from hexafluoropropylene, wherein the proportion of constituent units derived from hexafluoropropylene in the total constituent units is 0 mol% or more and 2.0 mol% or less, the weight average molecular weight is 1.5 million or more and less than 2 million, and the melting point is 150°C or more and less than 170°C.

[0060] Separator for non-aqueous secondary batteries.

[0061] <12>

[0062] <1> ~ <11> In any one of these,

[0063] The ratio of fluorine atoms to the total atoms contained in the porous substrate is 0.05 atomic% or more and 1.00 atomic% or less,

[0064] Separator for non-aqueous secondary batteries.

[0065] <13>

[0066] <1> ~ <12> In any one of these,

[0067] The above adhesive porous layer comprises a polyvinylidene fluoride resin having a constituent unit derived from a monomer represented by the following formula (1).

[0068] Separator for non-aqueous secondary batteries.

[0069]

[0070] In Equation (1), R 1 , R 2 and R 3 Each independently represents a hydrogen atom, a halogen atom, a C1-5 alkyl group, a carboxyl group, or a derivative of a carboxyl group, where X represents a single bond, a C1-5 alkylene group, or a C1-5 alkylene group having a substituent, and Y represents a hydrogen atom, a C1-5 alkyl group, a C1-5 alkyl group substituted with at least one hydroxyl group, a C1-5 alkyl group substituted with at least one carboxyl group, or -ROC(=O)-(CH2) n -C(=O)-OH (R represents an alkylene group having 1 to 5 carbon atoms, and n represents an integer greater than or equal to 0).

[0071] <14>

[0072] <1> ~ <13> In any one of these,

[0073] The acid value of the entire polyvinylidene fluoride-based resin included in the adhesive porous layer is less than 3.0 mgKOH / g

[0074] Separator for non-aqueous secondary batteries.

[0075] <15>

[0076] <1> ~ <14> In any one of these,

[0077] The total weight average molecular weight of the polyvinylidene fluoride-based resin included in the above adhesive porous layer is 300,000 or more and less than 3 million,

[0078] Separator for non-aqueous secondary batteries.

[0079] <16>

[0080] <1> ~ <15> In any one of these,

[0081] In the entire polyvinylidene fluoride-based resin included in the adhesive porous layer, the ratio of constituent units derived from hexafluoropropylene accounting for the total constituent units is greater than 3.5 mol% and less than or equal to 7.0 mol%.

[0082] Separator for non-aqueous secondary batteries.

[0083] <17>

[0084] <1> ~ <16> In any one of these,

[0085] The ratio of the filler to the volume excluding the pores of the adhesive porous layer is 30 volume% to 90 volume%,

[0086] Separator for non-aqueous secondary batteries.

[0087] <18>

[0088] <1> ~ <17> In any one of these,

[0089] The above filler comprises at least one selected from the group consisting of metal hydroxide particles, metal sulfate particles, and barium titanate particles,

[0090] Separator for non-aqueous secondary batteries.

[0091] <19>

[0092] <1> ~ <18> In any one of these,

[0093] The average primary particle size of the entire filler included in the adhesive porous layer is 0.01㎛ to 1.5㎛,

[0094] Separator for non-aqueous secondary batteries.

[0095] <20>

[0096] A positive electrode, a negative electrode, and a structure disposed between the positive electrode and the negative electrode. <1> ~ <19> A non-aqueous secondary battery having a separator for a non-aqueous secondary battery as described in any one of the above, and obtaining an electromotive force by doping and thawing of lithium ions. Effects of the invention

[0097] According to the present disclosure, a separator for a non-aqueous secondary battery is provided, which has excellent adhesion to an electrode by a dry heat press and adhesion to an electrode by a wet heat press, and is easy to retain an electrolyte within a porous substrate, thereby having a low film resistance value even after exposure to high temperatures and a high capacity retention rate of the battery even after exposure to high temperatures. Specific details for implementing the invention

[0098] Embodiments of the present disclosure are described below. These descriptions and examples are illustrative of embodiments and are not intended to limit the scope of the embodiments.

[0099] In the present disclosure, a numerical range indicated using “~” represents a range that includes the value described immediately after “~” as a minimum value and a maximum value, respectively.

[0100] In the numerical ranges described stepwise in the present disclosure, an upper or lower limit value described in one numerical range may be substituted with an upper or lower limit value of another numerical range described stepwise. Additionally, in the numerical ranges described in the present disclosure, an upper or lower limit value of said numerical range may be substituted with a value indicated in the examples.

[0101] In the present disclosure, the term “process” includes not only independent processes but also cases where the process cannot be clearly distinguished from other processes, provided that the intended purpose of the process is achieved.

[0102] In the present disclosure, when referring to the amount of each component in a composition, if there are multiple types of substances corresponding to each component in the composition, it refers to the total amount of said multiple types of substances present in the composition, unless specifically mentioned otherwise.

[0103] In the present disclosure, particles corresponding to each component may be included in multiple types. If multiple types of particles corresponding to each component exist in the composition, the particle size of each component refers to the value of the mixture of said multiple types of particles existing in the composition, unless specifically mentioned otherwise.

[0104] In the present disclosure, MD (Machine Direction) refers to the long-length direction of a porous substrate and a separator manufactured in a long-length form, and TD (transverse direction) refers to a direction orthogonal to MD in the plane direction of the porous substrate and the separator. In the present disclosure, TD is also referred to as the "width direction."

[0105] In the present disclosure, when the stacking relationship of each layer constituting the separator is expressed as “upper” and “lower,” the layer closer to the porous substrate is called “lower,” and the layer further away from the porous substrate is called “upper.”

[0106] In the present disclosure, performing a heat press treatment by impregnating a separator with an electrolyte is called a "wet heat press," and performing a heat press treatment without impregnating a separator with an electrolyte is called a "dry heat press."

[0107] In the present disclosure, the term "constituent unit" of a copolymer or resin is synonymous with a monomer unit.

[0108] In the present disclosure, the volume excluding the voids of the adhesive porous layer is referred to as the “solid volume.”

[0109] Separator for Non-Aqueous Secondary Batteries

[0110] A separator for a non-aqueous secondary battery according to the present disclosure (also simply referred to as "separator" in the present disclosure) comprises a porous substrate and an adhesive porous layer provided on one or both sides of the porous substrate. The adhesive porous layer of the separator according to the present disclosure comprises a polyvinylidene fluoride-based resin and a filler.

[0111] The description of the adhesive porous layer in the present disclosure is a description of the adhesive porous layer on each side of the porous substrate. The separator of the present disclosure may have the adhesive porous layer of the present disclosure on at least one side of the porous substrate. As examples of embodiments of the separator of the present disclosure, the following examples (1) to (3) may be given.

[0112] (1) A separator having adhesive porous layers of the present disclosure on both sides of a porous substrate. In the separator, the adhesive porous layer on one side and the adhesive porous layer on the other side may be the same or different in terms of composition, thermal properties, etc.

[0113] (2) A separator having an adhesive porous layer of the present disclosure on one side of a porous substrate and another layer on the other side of a porous substrate.

[0114] (3) A separator having an adhesive porous layer of the present disclosure on one side of a porous substrate and not having a layer on the other side of the porous substrate (i.e., the surface of the porous substrate is exposed).

[0115] The porous substrate in the separator of the present disclosure comprises fluorine atoms. The porous substrate comprising fluorine atoms is easy to retain the electrolyte within the porous substrate, and the film resistance value is difficult to increase even when the inside of the battery becomes high temperature.

[0116] The proportion of fluorine atoms in the total atoms included in the porous substrate is preferably 0.05 atomic% or more, more preferably 0.06 atomic% or more, and more preferably 0.07 atomic% or more, from the perspective of suppressing the increase in membrane resistance value by retaining the electrolyte inside the porous substrate.

[0117] The proportion of fluorine atoms in the total atoms included in the porous substrate is preferably 1.00 atomic% or less, more preferably 0.50 atomic% or less, and more preferably 0.35 atomic% or less in terms of ion permeability.

[0118] The fact that the porous substrate contains fluorine atoms, and the proportion of fluorine atoms in the total atoms contained in the porous substrate, are determined by performing elemental analysis using SEM-EDX (Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy).

[0119] A cross-section of the separator is fabricated by the Cryo BIB method, and a platinum coating is applied by the ion sputtering method to perform a conductive treatment. Elemental analysis is performed on an area of ​​6 μm in the thickness direction × 12 μm in the plane direction within the region of the porous substrate in the cross-section of the separator, specifically in the center of the porous substrate in the thickness direction.

[0120] A porous substrate containing fluorine atoms is obtained, for example, by coating the porous surface of the porous substrate with a part of the coating solution and attaching the polyvinylidene fluoride resin to the porous substrate when coating the porous substrate with a coating solution for forming an adhesive porous layer (the coating solution contains a polyvinylidene fluoride resin).

[0121] The proportion of fluorine atoms in the total atoms contained in the porous substrate is controlled, for example, by impregnating the porous substrate with a solvent of polyvinylidene fluoride resin in advance to adjust the amount of penetration of the coating solution into the porous substrate; by adjusting the viscosity of the coating solution according to the molecular weight of the polyvinylidene fluoride resin to adjust the amount of penetration of the coating solution into the porous substrate; and by adjusting the concentration of the polyvinylidene fluoride resin in the coating solution to adjust the amount of polyvinylidene fluoride resin attached to the porous surface of the porous substrate.

[0122] In addition, as another method for controlling the proportion of fluorine atoms in the total atoms contained in the porous substrate, there is also a method of impregnating the porous substrate with a solution in which a fluorine atom-containing compound is dissolved in both solvents in advance, thereby supporting the fluorine atom-containing compound inside the porous substrate before coating with a polyvinylidene fluoride-based resin. In this method, the proportion of fluorine atoms in the total atoms contained in the porous substrate can be controlled by selecting a compound while considering its solubility in the solvent so that the fluorine atom content in the fluorine atom-containing compound becomes appropriate; adjusting the concentration of the fluorine atom-containing compound in the solution dissolved in both solvents; and adjusting the amount of the solution dissolved in both solvents impregnated into the porous substrate.

[0123] As for the fluorine atom-containing compound, low molecular weight fluorine atom-containing compounds, fluorine atom-containing high molecular weight compounds, etc., may be selected. Preferably, it is a polyolefin containing fluorine atoms, more preferably a polyvinylidene fluoride resin, and even more preferably a polyvinylidene fluoride resin having the same chemical composition as the polyvinylidene fluoride resin forming the adhesive porous layer. The solvent for dissolving the fluorine atom-containing compound is not specifically limited as long as it is a solvent capable of uniformly dissolving the fluorine atom-containing compound, but examples include polar amide solvents such as N-methylpyrrolidone, dimethylacetamide, and dimethylformamide. Preferably, a solvent of the same type as the coating solution for forming the adhesive porous layer is used.

[0124] When differential scanning calorimetry (DSC) is performed on the entire polyvinylidene fluoride-based resin contained in the adhesive porous layer of the separator of the present disclosure, two or more endothermic peaks and / or two or more exothermic peaks are observed.

[0125] Endothermic peaks and exothermic peaks may be observed with at least two of each, or with two or more of each. If two or more endothermic peaks are observed, there may be two or three or more endothermic peaks. If two or more exothermic peaks are observed, there may be two or three or more exothermic peaks.

[0126] When DSC is performed using the entire polyvinylidene fluoride resin contained in the adhesive porous layer as a sample, if two or more endothermic peaks or two or more exothermic peaks are observed in the DSC curve with heat flow on the vertical axis and time or temperature on the horizontal axis, it means that the adhesive porous layer contains polyvinylidene fluoride resin in which polymer chains move due to heating at a relatively low temperature (in other words, polyvinylidene fluoride resin in which polymer chains are easy to move) and polyvinylidene fluoride resin in which polymer chains move due to heating at a relatively high temperature (in other words, polyvinylidene fluoride resin in which polymer chains are difficult to move).

[0127] Since a polyvinylidene fluoride resin, in which polymer chains are easily movable, is included in the adhesive porous layer, the adhesive porous layer exhibits adhesion even when the polyvinylidene fluoride resin is not swollen in the electrolyte or when the heat press is at a relatively low temperature. Furthermore, since a polyvinylidene fluoride resin, in which polymer chains are difficult to move, is included in the adhesive porous layer, it is presumed that clogging of the adhesive porous layer is suppressed even when the polyvinylidene fluoride resin is swollen in the electrolyte or when the heat press is at a relatively high temperature, thereby maintaining the performance of the separator.

[0128] In addition, it is presumed that the clogging of the adhesive porous layer is suppressed even when the inside of the battery reaches a high temperature, as a polyvinylidene fluoride-based resin, in which polymer chains are difficult to move, is included in the adhesive porous layer.

[0129] Therefore, it is presumed that the separator of the present disclosure maintains the performance of the separator, exhibits excellent adhesion to the electrode by either a dry heat press or a wet heat press, and also has a high capacity retention rate of the battery even after exposure to high temperatures.

[0130] The separator of the present disclosure preferably exhibits at least one of the following (a) to (d) in order to achieve both adhesion with the electrode by heat pressing and maintenance of the separator's performance after heat pressing.

[0131] (a) When DSC is performed on the entire polyvinylidene fluoride resin included in the adhesive porous layer, two or more endothermic peaks are observed, at least one endothermic peak is observed in the region between 125°C and 140°C, and at least one endothermic peak is observed in the region between 140°C and 190°C.

[0132] In this case, an additional endothermic peak may be observed in a region other than the two regions mentioned above.

[0133] (b) When DSC is performed on the entire polyvinylidene fluoride resin contained in the adhesive porous layer, two or more endothermic peaks are observed, and the temperature difference between adjacent endothermic peaks is 10°C or more and 60°C or less.

[0134] The above temperature difference is preferably 15°C or more, and more preferably 20°C or more. The above temperature difference is preferably 50°C or less, and more preferably 40°C or less.

[0135] (c) When DSC is performed on the entire polyvinylidene fluoride resin included in the adhesive porous layer, two or more exothermic peaks are observed, at least one exothermic peak is observed in the region between 80°C and 125°C, and at least one exothermic peak is observed in the region between 125°C and 190°C.

[0136] In this case, additional heat peaks may be observed in regions other than the two regions mentioned above.

[0137] (d) When DSC is performed on the entire polyvinylidene fluoride resin included in the adhesive porous layer, two or more exothermic peaks are observed, and the temperature difference between adjacent exothermic peaks is 10°C or more and 90°C or less.

[0138] The above temperature difference is preferably 15°C or higher, more preferably 18°C ​​or higher, and more preferably 20°C or higher. The above temperature difference is preferably 80°C or lower, more preferably 50°C or lower, and more preferably 40°C or lower.

[0139] As a method for controlling the endothermic and exothermic peaks of a DSC with respect to a polyvinylidene fluoride-based resin included in an adhesive porous layer, examples include (I) and (II) below.

[0140] (I) In forming a polyvinylidene fluoride resin, two or more types of polyvinylidene fluoride resins that differ in the type or amount of polymerization components, molecular weight, or melting point are used, and the mixing ratio is adjusted.

[0141] (II) The degree of crystallization of the polyvinylidene fluoride resin included in the adhesive porous layer is controlled by the thermal conditions when forming the adhesive porous layer, the type or amount of filler, or the formulation of the crystallization control agent.

[0142] This explains the method for observing DSC and endothermic and exothermic peaks using the entire polyvinylidene fluoride-based resin contained in the adhesive porous layer as the sample.

[0143] -Sample-

[0144] The adhesive porous layer is peeled off from the separator, the peeled adhesive porous layer is immersed in dimethylacetamide, and heated to about 50°C to obtain a resin solution in which the polyvinylidene fluoride resin is dissolved. The resin solution is centrifuged using a centrifuge to precipitate the insoluble matter. The rotational speed of the centrifuge is set to an effective speed for precipitating the insoluble matter, depending on the radius of the rotor. The supernatant of the resin solution from which the insoluble matter has precipitated is removed, and centrifugation is repeated to remove the insoluble matter. The resin solution from which the insoluble matter has been removed is added dropwise to water to solidify the polyvinylidene fluoride resin. The solidified material is removed from water and dried, and the solid after drying is used as a sample.

[0145] If the separator has an adhesive porous layer (or a similar layer) on both sides, the adhesive porous layer (or a similar layer) is peeled off from one side at a time, and each side is treated as a different sample.

[0146] Differential Scanning Calorimetry (DSC)

[0147] Place a sample of 5.0 mg ± 0.3 mg into an aluminum sample pan and set it in a measuring device. Under a nitrogen atmosphere, perform the following three steps in succession and perform thermal analysis of the sample.

[0148] · Step 1: Increase the temperature from 30℃ to 200℃ at a rate of 5℃ / min.

[0149] · Step 2: Decrease temperature from 200℃ to 30℃ at a rate of 5℃ / min.

[0150] · Step 3: Increase the temperature from 30℃ to 200℃ at a rate of 5℃ / min.

[0151] -Observation of Endothermic and Exothermic Peaks-

[0152] Based on the thermal analysis results of the DSC, a DSC curve is plotted with temperature (°C) on the horizontal axis and heat flow (W / g) on ​​the vertical axis.

[0153] In Step 2, the upwardly convex portion in the temperature range from 180°C to 60°C is defined as the exothermic peak. The temperature of the maximum point of the exothermic peak, that is, the temperature at which the slope of the tangent line changes from negative to positive as it moves from a high temperature to a low temperature in the DSC curve of Step 2, is defined as the exothermic peak temperature.

[0154] In Step 3, the downwardly convex portion in the temperature range from 60°C to 180°C is defined as the endothermic peak. The temperature of the minimum point of the endothermic peak, that is, the temperature at which the slope of the tangent line changes from negative to positive as it moves from low to high temperature in the DSC curve of Step 3, is defined as the endothermic peak temperature.

[0155] Hereinafter, details of the porous substrate and adhesive porous layer having the separator of the present disclosure will be described.

[0156] [Porous substrate]

[0157] In the present disclosure, a porous substrate refers to a substrate having pores or voids within. Examples of such substrates include microporous membranes; porous sheets made of fibrous materials, such as nonwoven fabrics or paper; and composite porous sheets in which one or more other porous layers are laminated onto these microporous membranes or porous sheets. In the present disclosure, microporous membranes are preferred from the perspective of thinning and strength of the separator. A microporous membrane refers to a membrane having a plurality of micropores within it and a structure in which the micropores are connected, allowing gas or liquid to pass from one side to the other.

[0158] As for the porous substrate material, a material having electrical insulating properties is preferred, and it may be either an organic material or an inorganic material.

[0159] It is preferable that the porous substrate includes a thermoplastic resin to impart a shutdown function to the porous substrate. The shutdown function refers to a function that prevents thermal runaway of the battery by blocking the movement of ions through the melting of the constituent material and the blocking of the pores of the porous substrate when the battery temperature rises. As for the thermoplastic resin, a thermoplastic resin with a melting point of less than 200°C is preferred. Examples of thermoplastic resins include polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; among these, polyolefins are preferred.

[0160] As a porous substrate, a microporous membrane containing polyolefin (referred to as "polyolefin microporous membrane" in this disclosure) is preferred. As for the polyolefin microporous membrane, for example, a polyolefin microporous membrane applied to a conventional battery separator may be cited, and among these, it is preferable to select one that has sufficient mechanical properties and ion permeability.

[0161] In terms of exhibiting a shutdown function, a polyolefin microporous membrane containing polyethylene is preferred, and the polyethylene content is preferably 95 mass% or more with respect to the total mass of the polyolefin microporous membrane.

[0162] A polyolefin microporous membrane is preferably a microporous membrane containing polypropylene in terms of having heat resistance that prevents it from easily rupturing when exposed to high temperatures.

[0163] A polyolefin microporous membrane comprising polyethylene and polypropylene is preferred from the perspective of having a shutdown function and heat resistance that prevents easy rupture when exposed to high temperatures. Examples of polyolefin microporous membranes comprising polyethylene and polypropylene include a microporous membrane in which polyethylene and polypropylene are mixed in a single layer. In the microporous membrane, it is preferable to include 95 mass% or more of polyethylene and 5 mass% or less of polypropylene from the perspective of achieving both a shutdown function and heat resistance. Furthermore, from the perspective of achieving both a shutdown function and heat resistance, a polyolefin microporous membrane having a laminated structure of two or more layers, wherein at least one layer comprises polyethylene and at least one layer comprises polypropylene, is also preferred.

[0164] As for the polyolefin included in the polyolefin microporous membrane, a polyolefin with a weight-average molecular weight (Mw) of 100,000 to 5 million is preferred. If the Mw of the polyolefin is 100,000 or higher, sufficient mechanical properties can be imparted to the microporous membrane. On the other hand, if the Mw of the polyolefin is 5 million or lower, the shutdown characteristics of the microporous membrane are good, and the microporous membrane is easy to mold.

[0165] Examples of methods for manufacturing a polyolefin microporous membrane include: a method of extruding a molten polyolefin resin through a T-die to form a sheet, then crystallizing and stretching it, and subsequently heat treating it to form a microporous membrane; and a method of extruding a molten polyolefin resin together with a plasticizer such as liquid paraffin through a T-die, cooling it to form a sheet, stretching it, extracting the plasticizer, and then heat treating it to form a microporous membrane.

[0166] Examples of porous sheets made of fibrous materials include polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; heat-resistant resins such as all-aromatic polyamides, polyamideimide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide; and porous sheets such as nonwoven fabrics and paper made of fibrous materials such as cellulose.

[0167] In the present disclosure, a heat-resistant resin refers to a resin having a melting point of 200°C or higher, or a resin having no melting point and a decomposition temperature of 200°C or higher. That is, a heat-resistant resin in the present disclosure is a resin that does not melt or decompose in a temperature range of less than 200°C.

[0168] Examples of composite porous sheets include a sheet in which a functional layer is laminated onto a porous sheet composed of a microporous membrane or a fibrous material. Such composite porous sheets are desirable from the perspective that additional functions can be added by the functional layer. As for the functional layer, for example, from the perspective of imparting heat resistance, examples include a porous layer composed of a heat-resistant resin or a porous layer composed of a heat-resistant resin and an inorganic filler. As for the heat-resistant resin, one or more types of heat-resistant resins selected from all-aromatic polyamides, polyamideimide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide may be used. As for the inorganic filler, examples include metal oxides such as alumina; metal hydroxides such as magnesium hydroxide, etc. Methods for composite formation include coating a functional layer onto a microporous membrane or porous sheet, bonding the functional layer of the microporous membrane or porous sheet with an adhesive, and heat-pressing the microporous membrane or porous sheet with the functional layer.

[0169] Various surface treatments may be performed on the surface of the porous substrate to improve wettability with the coating solution for forming an adhesive porous layer, provided that the properties of the porous substrate are not damaged. Examples of surface treatments include corona treatment, plasma treatment, flame treatment, and ultraviolet irradiation treatment.

[0170] [Characteristics of porous substrates]

[0171] The thickness of the porous substrate is preferably 25㎛ or less, more preferably 20㎛ or less, and more preferably 15㎛ or less from the perspective of increasing the energy density of the battery, and is preferably 3㎛ or more, more preferably 5㎛ or more, and more preferably 8㎛ or more from the perspective of the manufacturing yield of the separator and the manufacturing yield of the battery.

[0172] The gully value (JIS P8117:2009) of the porous substrate is preferably 20 seconds / 100 mL or more, more preferably 25 seconds / 100 mL or more, more preferably 60 seconds / 100 mL or more, and more preferably 65 seconds / 100 mL or more from the perspective of suppressing short circuits in the battery.

[0173] The gully value (JIS P8117:2009) of the porous substrate is preferably 220 sec / 100mL or less, more preferably 200 sec / 100mL or less, more preferably 190 sec / 100mL or less, and more preferably 150 sec / 100mL or less, from the perspective of ion permeability and suppression of clogging of the porous structure at the boundary between the porous substrate and the adhesive porous layer when exposed to high temperature.

[0174] The porosity of the porous substrate is preferably 20% to 60% from the perspective of obtaining appropriate membrane resistance or shutdown function. The porosity ε(%) of the porous substrate is calculated by the following formula.

[0175] ε={1-Ws / (ds·t)}×100

[0176] Here, Ws is the basis weight of the porous substrate (g / m²), ds is the true density of the porous substrate (g / cm³), and t is the thickness of the porous substrate (μm). Basis weight is the mass per unit area.

[0177] The average pore size of the porous substrate is preferably 15 nm to 100 nm in terms of ion permeability or suppression of short circuits in the battery. The average pore size of the porous substrate is measured according to ASTM E1294-89 using a pump phorometer (PMI CFP-1500-A).

[0178] [Adhesive porous layer]

[0179] An adhesive porous layer is a layer that has a number of micropores inside and a structure in which the micropores are connected, allowing gas or liquid to pass from one side to the other.

[0180] The adhesive porous layer may be located on only one side of the porous substrate or on both sides of the porous substrate. If the adhesive porous layer is located on both sides of the porous substrate, curling is less likely to occur in the separator, resulting in excellent handling performance during battery manufacturing. If the adhesive porous layer is located on only one side of the porous substrate, the ion permeability of the separator is superior. Furthermore, the overall thickness of the separator can be reduced, enabling the manufacture of batteries with higher energy density.

[0181] The adhesive porous layer contains at least a polyvinylidene fluoride-based resin and a filler. The adhesive porous layer may contain a resin other than the polyvinylidene fluoride-based resin. The filler included in the adhesive porous layer may be either an inorganic filler or an organic filler.

[0182] -Polyvinylidene fluoride resin-

[0183] The content of the polyvinylidene fluoride resin included in the adhesive porous layer is preferably 85% to 100% by mass with respect to the total amount of resin included in the adhesive porous layer, more preferably 90% to 100% by mass, and even more preferably 95% to 100% by mass.

[0184] When adhesive porous layers are present on both sides of a porous substrate, the type or amount of polyvinylidene fluoride resin included in one adhesive porous layer and the type or amount of polyvinylidene fluoride resin included in the other adhesive porous layer may be the same or different.

[0185] Examples of polyvinylidene fluoride resins include a homopolymer of vinylidene fluoride (i.e., polyvinylidene fluoride); a copolymer of vinylidene fluoride with a halogen-containing monomer such as hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, vinyl fluoride, or trichloroethylene; a copolymer of vinylidene fluoride with a monomer other than a halogen-containing monomer; a copolymer of vinylidene fluoride with a halogen-containing monomer and a monomer other than a halogen-containing monomer; and mixtures thereof. Polyvinylidene fluoride resins may be used as a single type or in combination of two or more types.

[0186] As a polyvinylidene fluoride-based resin, a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) (VDF-HFP copolymer) is preferred in terms of adhesion to the electrode. In the present disclosure, the VDF-HFP copolymer includes either a copolymer formed by polymerizing only VDF and HFP, or a copolymer formed by polymerizing VDF, HFP, and other monomers. By increasing or decreasing the content of HFP units, the crystallinity, heat resistance, and solubility in an electrolyte of the VDF-HFP copolymer can be controlled within an appropriate range.

[0187] In the entire polyvinylidene fluoride-based resin included in the adhesive porous layer, it is preferable that the proportion of HFP-derived constituent units in the total constituent units be greater than 3.5 mol% and less than or equal to 7.0 mol%.

[0188] If the proportion of constituent units derived from HFP in the total constituent units of the polyvinylidene fluoride resin exceeds 3.5 mol%, the polymer chains of the polyvinylidene fluoride resin are easily movable, and the adhesion to the electrode is excellent even when heat pressing is performed in a state where the polyvinylidene fluoride resin does not swell in the electrolyte or when heat pressing is performed at a relatively low temperature. From this perspective, the proportion of constituent units derived from HFP is more preferably greater than 4.0 mol%, and more preferably greater than 4.5 mol%.

[0189] If the proportion of HFP-derived constituent units in the total constituent units of the polyvinylidene fluoride resin is 7.0 mol% or less, the solubility in electrolytes is excellent. From this perspective, the proportion of HFP-derived constituent units is more preferably 6.8 mol% or less, and more preferably 6.5 mol% or less.

[0190] It is preferable that the polyvinylidene fluoride resin comprises a polyvinylidene fluoride resin having a constituent unit derived from a monomer represented by the following formula (1) (referred to as "polyvinylidene fluoride resin (1)" in the present disclosure).

[0191]

[0192] In Equation (1), R 1 , R 2 and R 3 Each independently represents a hydrogen atom, a halogen atom, a C1-5 alkyl group, a carboxyl group, or a derivative of a carboxyl group, where X represents a single bond, a C1-5 alkylene group, or a C1-5 alkylene group having a substituent, and Y represents a hydrogen atom, a C1-5 alkyl group, a C1-5 alkyl group substituted with at least one hydroxyl group, a C1-5 alkyl group substituted with at least one carboxyl group, or -ROC(=O)-(CH2) n -C(=O)-OH (R represents an alkylene group having 1 to 5 carbon atoms, and n represents an integer greater than or equal to 0).

[0193] In Equation (1), R 1 , R 2 and R 3 As the halogen atom represented by, it may be any of a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, and a fluorine atom is preferred.

[0194] In Equation (1), R 1 , R 2 and R 3Examples of the alkyl groups having 1 to 5 carbon atoms represented by α include straight-chain alkyl groups such as methyl, ethyl, n-propyl, n-butyl, and n-pentyl groups; and branched alkyl groups such as isopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl, neopentyl, and tert-pentyl groups. 1 , R 2 and R 3 As for the alkyl group having 1 to 5 carbon atoms, an alkyl group having 1 to 4 carbon atoms is preferred, and an alkyl group having 1 to 3 carbon atoms is more preferred.

[0195] In Equation (1), R 1 , R 2 and R 3 As a derivative of the carboxyl group represented by, for example, -C(=O)-OR 4 (R 4 (represents an alkyl group.) can be cited as an example. R 4 Examples include straight-chain alkyl groups such as methyl, ethyl, n-propyl, n-butyl, and n-pentyl groups; and branched alkyl groups such as isopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl, neopentyl, and tert-pentyl groups. R 4 As for the alkyl group, a carbon atom 1 to 5 is preferred, a carbon atom 1 to 4 is more preferred, and a carbon atom 1 to 3 is more preferred.

[0196] In Formula (1), the alkylene group having 1 to 5 carbon atoms represented by X may be, for example, a straight-chain alkylene group such as a methylene group, an ethylene group, an n-propylene group, an n-butylene group, or an n-pentylene group; or a branched alkylene group such as an isopropylene group, an isobutylene group, a sec-butylene group, a tert-butylene group, an isopentylene group, a neopentylene group, or a tert-pentylene group. As for the alkylene group having 1 to 5 carbon atoms in X, an alkylene group having 1 to 4 carbon atoms is preferred, and an alkylene group having 1 to 3 carbon atoms is more preferred.

[0197] In Formula (1), the substituent for the alkylene group having 1 to 5 carbon atoms having the substituent represented by X may be, for example, a halogen atom, or any of a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom. The substituted alkylene group having 1 to 5 carbon atoms in X may be, for example, a straight-chain alkylene group such as a methylene group, an ethylene group, an n-propylene group, an n-butylene group, or an n-pentylene group; or a branched alkylene group such as an isopropylene group, an isobutylene group, a sec-butylene group, a tert-butylene group, an isopentylene group, a neopentylene group, or a tert-pentylene group. The substituted alkylene group having 1 to 5 carbon atoms in X is preferably an alkylene group having 1 to 4 carbon atoms, and more preferably an alkylene group having 1 to 3 carbon atoms.

[0198] In Formula (1), the alkyl group having 1 to 5 carbon atoms represented by Y may include, for example, straight-chain alkyl groups such as methyl, ethyl, n-propyl, n-butyl, and n-pentyl groups; and branched alkyl groups such as isopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl, neopentyl, and tert-pentyl groups. As for the alkyl group having 1 to 5 carbon atoms in Y, an alkyl group having 1 to 4 carbon atoms is preferred, and an alkyl group having 1 to 3 carbon atoms is more preferred.

[0199] In Formula (1), for the alkyl group having 1 to 5 carbon atoms substituted with at least one hydroxyl group represented by Y, the substituted alkyl group having 1 to 5 carbon atoms may be, for example, a straight-chain alkyl group such as a methyl group, an ethyl group, an n-propyl group, an n-butyl group, or an n-pentyl group; or a branched alkyl group such as an isopropyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an isopentyl group, a neopentyl group, or a tert-pentyl group. For the substituted alkyl group having 1 to 5 carbon atoms in Y, an alkyl group having 1 to 4 carbon atoms is preferred, and an alkyl group having 1 to 3 carbon atoms is more preferred. The number of substituted hydroxyl groups is preferably 1 or 2, and more preferably 1.

[0200] In Formula (1), the alkyl group having 1 to 5 carbon atoms substituted with at least one hydroxyl group represented by Y can be, for example, a 2-hydroxyethyl group, a 2-hydroxypropyl group, or a 4-hydroxybutyl group.

[0201] In Formula (1), for the alkyl group having 1 to 5 carbon atoms substituted with at least one hydroxyl group represented by Y, the substituted alkyl group having 1 to 5 carbon atoms may be, for example, a straight-chain alkyl group such as a methyl group, an ethyl group, an n-propyl group, an n-butyl group, or an n-pentyl group; or a branched alkyl group such as an isopropyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an isopentyl group, a neopentyl group, or a tert-pentyl group. For the substituted alkyl group having 1 to 5 carbon atoms in Y, an alkyl group having 1 to 4 carbon atoms is preferred, and an alkyl group having 1 to 3 carbon atoms is more preferred. The number of substituted carboxyl groups is preferably 1 or 2, and more preferably 1.

[0202] In Formula (1), the alkyl group having 1 to 5 carbon atoms substituted with at least one carboxyl group represented by Y can be, for example, a 2-carboxyethyl group, a 2-carboxypropyl group, or a 4-carboxybutyl group.

[0203] In Equation (1), -ROC(=O)-(CH2) represented by Y n In -C(=O)-OH, R represents an alkylene group having 1 to 5 carbon atoms, and n represents an integer greater than or equal to 0.

[0204] As R, examples include straight-chain alkylene groups such as methylene, ethylene, n-propylene, n-butylene, and n-pentylene; and branched alkylene groups such as isopropylene, isobutylene, sec-butylene, tert-butylene, isopentylene, neopentylene, and tert-pentylene. As R, an alkylene group having 1 to 4 carbon atoms is preferred, and an alkylene group having 1 to 3 carbon atoms is more preferred.

[0205] As for n, an integer from 0 to 5 is preferred, an integer from 1 to 4 is more preferred, and 2 or 3 is more preferred.

[0206] Specific examples of the said group include, for instance, -(CH2)2-OC(=O)-(CH2)2-C(=O)-OH.

[0207] As a monomer represented by formula (1), for example, R 1 , R 2 and R 3 Examples of monomers include each independently being a hydrogen atom or a carbon-1 to carbon-4 alkyl group, where X is a single bond and Y is a carbon-1 to carbon-3 alkyl group substituted with a carbon-1 to carbon-4 alkyl group or at least one hydroxyl group.

[0208] Examples of monomers represented by formula (1) include acrylic monomers, unsaturated dibasic acids, monoesters of unsaturated dibasic acids, etc.

[0209] Examples of acrylic monomers include (meth)acrylic acid, (meth)acrylate methyl, (meth)acrylate ethyl, (meth)acrylate isopropyl, (meth)acrylate n-butyl, (meth)acrylate isobutyl, (meth)acrylate tert-butyl, (meth)acrylate pentyl, (meth)acrylate 2-hydroxyethyl, (meth)acrylate 2-hydroxypropyl, (meth)acrylate 4-hydroxybutyl, (meth)acrylate 2-carboxyethyl, (meth)acrylate 2-carboxypropyl, (meth)acrylate 4-carboxybutyl, butyric acid, pentene acid, hexenoic acid, (meth)acryloyloxyethyl succinic acid, etc. The notation "(Meta)acryl" means that either "acryl" or "methacryl" is acceptable.

[0210] Examples of unsaturated dibasic acids include unsaturated dicarboxylic acids, and more specifically, maleic acid, maleic anhydride, citraconic acid, itaconic acid, etc.

[0211] Examples of monoesters of unsaturated dibasic acids include maleic acid monomethyl ester, maleic acid monoethyl ester, citraconic acid monomethyl ester, citraconic acid monoethyl ester, itaconic acid monomethyl ester, and itaconic acid monoethyl ester, among which maleic acid monomethyl ester and citraconic acid monomethyl ester are preferred.

[0212] In the polyvinylidene fluoride resin (1), the proportion of the monomer-derived constituent unit represented by formula (1) in the total constituent unit is preferably 0.005 mol% or more, more preferably 0.01 mol% or more, and more preferably 0.02 mol% or more in terms of adhesion to the electrode.

[0213] In the polyvinylidene fluoride resin (1), the proportion of the monomer-derived constituent unit represented by formula (1) in the total constituent unit is preferably 3.0 mol% or less, more preferably 2.0 mol% or less, and more preferably 1.0 mol% or less, from the perspective of having a low influence on the active material included in the electrode.

[0214] The polyvinylidene fluoride resin (1) may include constituent units derived from monomers other than vinylidene fluoride (VDF) and the monomer represented by formula (1). Examples of other monomers include halogen-containing monomers such as hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, vinyl fluoride, and trichloroethylene.

[0215] The polyvinylidene fluoride resin (1) preferably contains a constituent unit derived from hexafluoropropylene (HFP). By increasing or decreasing the proportion of HFP in the total polymerization components of the polyvinylidene fluoride resin (1), the crystallinity of the resin, adhesion to the electrode, and solubility in the electrolyte can be controlled within an appropriate range.

[0216] As a polyvinylidene fluoride resin (1), a terpolymer composed of VDF, HFP, and a monomer represented by formula (1) is preferred. As the terpolymer, a VDF-HFP-acrylic acid terpolymer is preferred.

[0217] The proportion of polyvinylidene fluoride resin (1) in the total polyvinylidene fluoride resin included in the adhesive porous layer is preferably 20 mass% to 80 mass%, more preferably 30 mass% to 70 mass%, and more preferably 40 mass% to 60 mass%, from the perspective of making the acid value of the total polyvinylidene fluoride resin appropriate.

[0218] The acid value (mgKOH / g) of the entire polyvinylidene fluoride resin included in the adhesive porous layer is preferably less than 3.0, more preferably 2.8 or lower, and more preferably 2.6 or lower, from the perspective of having a low effect on the active material included in the electrode.

[0219] The acid value (mgKOH / g) of the total polyvinylidene fluoride resin included in the adhesive porous layer is preferably 0.5 or higher, more preferably 0.8 or higher, and more preferably 1.0 or higher in terms of adhesion to the electrode.

[0220] The acid value (mgKOH / g) of the total polyvinylidene fluoride resin contained in the adhesive porous layer is determined by extracting the polyvinylidene fluoride resin contained in the adhesive porous layer and measuring its acid value by potentiometric titration (JIS K1557-5:2007). Alternatively, the acid value (mgKOH / g) of the polyvinylidene fluoride resin used to form the adhesive porous layer is determined by measuring it by potentiometric titration (JIS K1557-5:2007).

[0221] The weight average molecular weight (Mw) of the entire polyvinylidene fluoride-based resin included in the adhesive porous layer is preferably 300,000 or more, more preferably 500,000 or more, more preferably 650,000 or more, and more preferably 850,000 or more, from the perspective that it is difficult for the pores of the adhesive porous layer to become clogged when heat is applied to the adhesive porous layer during the manufacture of the battery.

[0222] The total Mw of the polyvinylidene fluoride resin included in the adhesive porous layer is preferably less than 3 million, more preferably less than 2.5 million, more preferably less than 2.3 million, and more preferably less than 2 million, from the perspective that the polyvinylidene fluoride resin softens appropriately and the adhesive porous layer and the electrode adhere well when heat is applied to the adhesive porous layer during the manufacture of the battery.

[0223] The total Mw of the polyvinylidene fluoride resin contained in the adhesive porous layer is the molecular weight equivalent to polystyrene, measured by gel permeation chromatography (GPC). The polyvinylidene fluoride resin extracted from the adhesive porous layer or the polyvinylidene fluoride resin used to form the adhesive porous layer is used as a sample.

[0224] In terms of controlling the endothermic peak temperature and exothermic peak temperature in the DSC curve of a polyvinylidene fluoride-based resin included in an adhesive porous layer to a desired range, it is preferable that the adhesive porous layer comprises the polyvinylidene fluoride-based resin X and the polyvinylidene fluoride-based resin Y described below.

[0225] The total amount of polyvinylidene fluoride resin X and polyvinylidene fluoride resin Y included in the adhesive porous layer is preferably 85% to 100% by mass with respect to the total polyvinylidene fluoride resin included in the adhesive porous layer, more preferably 90% to 100% by mass, and even more preferably 95% to 100% by mass.

[0226] -Polyvinylidene fluoride resin X-

[0227] Polyvinylidene fluoride resin X comprises constituent units derived from vinylidene fluoride (VDF) and constituent units derived from hexafluoropropylene (HFP), wherein the proportion of constituent units derived from HFP in the total constituent units is greater than 3.5 mol% and less than or equal to 15 mol%, the weight average molecular weight (Mw) is greater than or equal to 100,000 and less than 1 million, and the melting point is greater than or equal to 125°C and less than 150°C.

[0228] In polyvinylidene fluoride resin X, the proportion of HFP-derived constituent units in the total constituent units is greater than 3.5 mol%, is preferably greater than 4.0 mol%, is more preferably greater than 4.5 mol%, and is more preferably greater than 5.0 mol%, from the perspective that the polymer chains of the resin are easy to move by heat pressing and adhesion to the electrode is excellent.

[0229] In polyvinylidene fluoride resin X, the proportion of HFP-derived constituent units in the total constituent units is 15 mol% or less, 12 mol% or less is preferred, 10 mol% or less is more preferred, and 8.0 mol% or less is more preferred because of the excellent solubility in electrolytes.

[0230] The Mw of polyvinylidene fluoride resin X is 100,000 or more, preferably 150,000 or more, more preferably 200,000 or more, and more preferably 250,000 or more, from the perspective that it is difficult for the cavities of the adhesive porous layer to become clogged when heat is applied to the adhesive porous layer during the manufacture of the battery.

[0231] The Mw of polyvinylidene fluoride resin X is less than 1 million, preferably less than 900,000, more preferably less than 600,000, and more preferably less than 400,000, from the perspective that the resin softens and the adhesive porous layer and the electrode adhere well when heat is applied to the adhesive porous layer during the manufacture of the battery.

[0232] The Mw of polyvinylidene fluoride resin X is the molecular weight equivalent to polystyrene, measured by GPC. Polyvinylidene fluoride resin X, used for forming an adhesive porous layer, is used as a sample.

[0233] The melting point of polyvinylidene fluoride resin X is 125°C or higher, preferably 128°C or higher, and more preferably 130°C or higher, from the perspective that it is difficult for cavities in the adhesive porous layer to become blocked when heat is applied to the adhesive porous layer during the manufacture of a battery.

[0234] The melting point of polyvinylidene fluoride resin X is less than 150°C, preferably less than 145°C, and more preferably less than 140°C, from the perspective that the resin softens and the adhesive porous layer and the electrode adhere well when heat is applied to the adhesive porous layer during the manufacture of the battery.

[0235] The melting point of polyvinylidene fluoride resin X is determined from a DSC curve obtained by performing Differential Scanning Calorimetry (DSC). Polyvinylidene fluoride resin X, used for forming an adhesive porous layer, is used as a sample. The sample is placed in an aluminum sample pan, set in a measuring device, and the following three steps are performed in succession under a nitrogen atmosphere to perform thermal analysis of the sample.

[0236] · Step 1: Increase the temperature from 30℃ to 200℃ at a rate of 5℃ / min.

[0237] · Step 2: Decrease temperature from 200℃ to 30℃ at a rate of 5℃ / min.

[0238] · Step 3: Increase the temperature from 30℃ to 200℃ at a rate of 5℃ / min.

[0239] In Step 3 above, the temperature of the endothermic peak indicated on the DSC curve is set as the melting point of polyvinylidene fluoride resin X. If there are multiple endothermic peaks, the temperature of the endothermic peak on the lowest temperature side is set as the melting point.

[0240] As a preferred form of polyvinylidene fluoride resin X, the proportion of HFP-derived constituent units in the total constituent units is greater than 5.0 mol% and less than or equal to 15 mol%, the Mw is greater than or equal to 300,000 and less than 1 million, and the melting point is greater than or equal to 125°C and less than 140°C.

[0241] -Polyvinylidene fluoride resin Y-

[0242] Polyvinylidene fluoride resin Y contains constituent units derived from vinylidene fluoride (VDF) and may contain constituent units derived from hexafluoropropylene (HFP), and the proportion of constituent units derived from HFP in the total constituent units is 0 mol% or more and 3.5 mol% or less, the weight average molecular weight (Mw) is 1 million or more and less than 3 million, and the melting point is 150°C or more and less than 180°C.

[0243] In polyvinylidene fluoride resin Y, the proportion of HFP-derived constituent units in the total constituent units is 3.5 mol% or less, preferably 3.0 mol% or less, more preferably 2.5 mol% or less, and even more preferably 2.0 mol% or less, as it has excellent solubility in electrolytes.

[0244] In polyvinylidene fluoride resin Y, the proportion of HFP-derived constituent units in the total constituent units is preferably greater than 0 mol%, more preferably 0.2 mol% or more, more preferably 0.5 mol% or more, and more preferably 0.7 mol% or more, from the perspective that the polymer chains of the resin are easy to move by heat pressing and adhesion to the electrode is excellent.

[0245] The Mw of the polyvinylidene fluoride resin Y is 1 million or more, preferably 1.2 million or more, more preferably 1.5 million or more, and more preferably 1.6 million or more, from the perspective that it is difficult for the pores of the adhesive porous layer to become clogged when heat is applied to the adhesive porous layer during the manufacture of the battery.

[0246] The Mw of the polyvinylidene fluoride resin Y is less than 3 million, preferably less than 2.5 million, more preferably less than 2.3 million, and even more preferably less than 2 million, from the perspective that the resin softens appropriately and the adhesive porous layer and the electrode adhere well when heat is applied to the adhesive porous layer during the manufacture of the battery.

[0247] Mw of polyvinylidene fluoride resin Y is the molecular weight equivalent to polystyrene, measured by GPC. Polyvinylidene fluoride resin Y, used for forming an adhesive porous layer, is used as a sample.

[0248] The melting point of polyvinylidene fluoride resin Y is 150°C or higher, preferably 155°C or higher, and more preferably 160°C or higher, from the perspective that it is difficult for occlusion of the pores in the adhesive porous layer to occur when heat is applied to the adhesive porous layer during the manufacture of a battery.

[0249] The melting point of polyvinylidene fluoride resin Y is less than 180°C, preferably less than 175°C, and more preferably less than 170°C, from the perspective that the resin softens appropriately and the adhesive porous layer and the electrode adhere well when heat is applied to the adhesive porous layer during the manufacture of the battery.

[0250] The melting point of polyvinylidene fluoride resin Y is determined from a DSC curve obtained by performing Differential Scanning Calorimetry (DSC). Polyvinylidene fluoride resin Y, used for forming an adhesive porous layer, is used as a sample. The sample is placed in an aluminum sample pan, set in a measuring device, and the following three steps are performed in succession under a nitrogen atmosphere to perform thermal analysis of the sample.

[0251] · Step 1: Increase the temperature from 30℃ to 200℃ at a rate of 5℃ / min.

[0252] · Step 2: Decrease temperature from 200℃ to 30℃ at a rate of 5℃ / min.

[0253] · Step 3: Increase the temperature from 30℃ to 200℃ at a rate of 5℃ / min.

[0254] In Step 3 above, the temperature of the endothermic peak indicated on the DSC curve is set as the melting point of polyvinylidene fluoride resin Y. If there are multiple endothermic peaks, the temperature of the endothermic peak on the lowest temperature side is set as the melting point.

[0255] As a preferred form of polyvinylidene fluoride resin Y, the proportion of HFP-derived constituent units in the total constituent units is 0 mol% or more (preferably greater than 0 mol%, more preferably 0.2 mol% or more) and 2.0 mol% or less, Mw is 1.5 million or more and less than 2 million, and the melting point is 150°C or more and less than 170°C.

[0256] It is preferable that the polyvinylidene fluoride resin Y is a polyvinylidene fluoride resin having a constituent unit derived from the monomer represented by the formula (1) above. That is, it is preferable that the polyvinylidene fluoride resin Y is the polyvinylidene fluoride resin (1). That is, it is preferable that the polyvinylidene fluoride resin Y is a terpolymer composed of VDF, HFP, and the monomer represented by the formula (1). As the terpolymer, a VDF-HFP-acrylic acid terpolymer is preferred.

[0257] In polyvinylidene fluoride resin Y, the proportion of the monomer-derived constituent unit represented by formula (1) in the total constituent unit is preferably 0.05 mol% or more, more preferably 0.08 mol% or more, and more preferably 0.1 mol% or more in terms of adhesion to the electrode.

[0258] In polyvinylidene fluoride resin Y, the proportion of the monomer-derived constituent unit represented by formula (1) in the total constituent unit is preferably 5.0 mol% or less, more preferably 4.0 mol% or less, and more preferably 3.0 mol% or less, from the perspective of having a low influence on the active material included in the electrode.

[0259] The mass ratio of polyvinylidene fluoride resin X and polyvinylidene fluoride resin Y included in the adhesive porous layer is preferably polyvinylidene fluoride resin X:polyvinylidene fluoride resin Y = 20:80 to 80:20 in terms of controlling the endothermic peak temperature and exothermic peak temperature in the DSC curve of the polyvinylidene fluoride resin included in the adhesive porous layer to a desired range, more preferably 30:70 to 70:30, more preferably 35:65 to 65:35, and more preferably 40:60 to 60:40.

[0260] The difference between the melting point of polyvinylidene fluoride resin X included in the adhesive porous layer and the melting point of polyvinylidene fluoride resin Y is preferably 25°C or higher, more preferably 27°C or higher, more preferably 28°C or higher, and more preferably 29°C or higher, from the perspective of achieving compatibility between adhesion with the electrode by dry heat press and wet heat press and a high capacity retention rate of the battery even after exposure to high temperature.

[0261] The difference between the melting point of polyvinylidene fluoride resin X included in the adhesive porous layer and the melting point of polyvinylidene fluoride resin Y is preferably less than 55°C, more preferably less than 50°C, more preferably less than 45°C, and more preferably less than 40°C, from the perspective of forming a porous structure with high uniformity for the adhesive porous layer.

[0262] -Other Suji-

[0263] The adhesive porous layer may include resins other than polyvinylidene fluoride resins. Examples of other resins include acrylic resins, fluororubber, styrene-butadiene copolymers, homopolymers or copolymers of vinylnitrile compounds (acrylonitrile, methacrylonitrile, etc.), carboxymethylcellulose, hydroxyalkylcellulose, polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, polyethers (polyethylene oxide, polypropylene oxide, etc.), polyamides, fully aromatic polyamides, polyimides, polyamideimides, polysulfones, polyketones, polyetherketones, polyethersulfones, polyetherimides, and mixtures thereof.

[0264] The content of resin other than polyvinylidene fluoride resin included in the adhesive porous layer is preferably 0% to 15% by mass with respect to the total amount of resin included in the adhesive porous layer, more preferably 0% to 10% by mass, and even more preferably 0% to 5% by mass.

[0265] -Weapon Filler-

[0266] Examples of inorganic fillers include metal hydroxide particles, metal sulfate particles, metal oxide particles, metal carbonate particles, metal nitride particles, metal fluoride particles, and clay mineral particles. One type of inorganic filler may be used alone, or two or more types may be used in combination.

[0267] Examples of metal hydroxides constituting metal hydroxide particles include magnesium hydroxide, aluminum hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, cerium hydroxide, and nickel hydroxide.

[0268] Examples of metal sulfates constituting metal sulfate particles include barium sulfate, strontium sulfate, calcium sulfate, calcium sulfate dihydrate, alunite, and jarosite.

[0269] Examples of metal oxides constituting metal oxide particles include barium titanate (BaTiO3), magnesium oxide, alumina (Al2O3), boehmite (alumina monohydrate), titania (TiO2), silica (SiO2), zirconia (ZrO2), and zinc oxide.

[0270] Examples of metal carbonates constituting metal carbonate particles include calcium carbonate and magnesium carbonate.

[0271] Examples of metal nitrides constituting metal nitride particles include magnesium nitride, aluminum nitride, calcium nitride, and titanium nitride.

[0272] Examples of metal fluorides constituting metal fluoride particles include magnesium fluoride and calcium fluoride.

[0273] Examples of clay minerals that make up clay mineral particles include calcium silicate, calcium phosphate, apatite, and talc.

[0274] The inorganic filler may be an inorganic filler whose surface is modified by a silane coupling agent, etc.

[0275] As for the inorganic filler, at least one type selected from the group consisting of metal hydroxide particles, metal sulfate particles, and barium titanate particles is preferred in that it is difficult to decompose the electrolyte or electrolyte and thus difficult to cause gas generation.

[0276] The total amount of metal hydroxide particles, metal sulfate particles, and barium titanate particles in the total inorganic filler included in the adhesive porous layer is preferably 80 mass% or more, more preferably 85 mass% or more, more preferably 90 mass% or more, more preferably 95 mass% or more, and most preferably 100 mass% from the perspective of suppressing gas generation.

[0277] When adhesive porous layers are present on both sides of a porous substrate, the type of inorganic filler included in one adhesive porous layer and the type of inorganic filler included in the other adhesive porous layer may be the same or different.

[0278] There are no limitations on the particle shape of the inorganic filler, and it may be spherical, plate-shaped, needle-shaped, or irregular in shape. From the perspective of suppressing short circuits in the battery or forming an adhesive porous layer with high uniformity, it is preferable that the inorganic filler be spherical or plate-shaped particles.

[0279] The average primary particle size of the entire inorganic filler included in the adhesive porous layer is preferably 1.5㎛ or less, more preferably 1.2㎛ or less, and more preferably 1.0㎛ or less from the perspective of increasing the heat resistance of the adhesive porous layer.

[0280] The average primary particle size of all inorganic fillers included in the adhesive porous layer is preferably 0.01 μm or more, more preferably 0.05 μm or more, more preferably 0.08 μm or more, and more preferably 0.1 μm or more, from the perspective of suppressing aggregation of inorganic fillers and forming an adhesive porous layer with high uniformity.

[0281] The average primary particle size of all inorganic fillers included in the adhesive porous layer is determined by measuring the major axes of 100 randomly selected inorganic fillers during observation by scanning electron microscope (SEM) and averaging the major axes of the 100. The sample provided for SEM observation is an inorganic filler that is a material forming the adhesive porous layer, or an inorganic filler extracted from the adhesive porous layer of the separator. There are no restrictions on the method of extracting the inorganic filler from the adhesive porous layer of the separator. The method is, for example, a method of extracting the inorganic filler by immersing the adhesive porous layer peeled from the separator in an organic solvent that dissolves the resin and dissolving the resin with the organic solvent; a method of extracting the inorganic filler by heating the adhesive porous layer peeled from the separator to about 800°C to remove the resin.

[0282] When adhesive porous layers are present on both sides of a porous substrate, the average primary particle size of the inorganic filler in one adhesive porous layer and the average primary particle size of the inorganic filler in the other adhesive porous layer may be the same or different.

[0283] The proportion of inorganic filler in the solid volume of the adhesive porous layer is preferably 30 volume% or more, more preferably 35 volume% or more, more preferably 40 volume% or more, and more preferably 45 volume% or more from the perspective of the heat resistance of the separator.

[0284] The proportion of inorganic filler in the solid volume of the adhesive porous layer is preferably 90 volume% or less, more preferably 85 volume% or less, more preferably 80 volume% or less, and more preferably 75 volume% or less, from the perspective that the adhesive porous layer is difficult to peel off from the porous substrate.

[0285] The ratio V (volume %) of inorganic filler to the solid volume of the adhesive porous layer is calculated by the following formula.

[0286] V={(Xa / Da) / (Xa / Da+Xb / Db+Xc / Dc+…+Xn / Dn)}×100

[0287] Here, among the constituent materials of the adhesive porous layer, the inorganic filler is a, and the other constituent materials are b, c, … , n, and the mass of each constituent material included in the adhesive porous layer of a predetermined area is Xa, Xb, Xc, … , Xn(g), and the true density of each constituent material is Da, Db, Dc, … , Dn(g / cm³).

[0288] Xa, etc., substituted into the above formula is the mass (g) of the constituent material used to form an adhesive porous layer of a predetermined area, or the mass (g) of the constituent material extracted from an adhesive porous layer of a predetermined area.

[0289] Da, etc., substituted into the above formula is the true density (g / cm³) of the constituent material used to form the adhesive porous layer, or the true density (g / cm³) of the constituent material extracted from the adhesive porous layer.

[0290] When adhesive porous layers are present on both sides of a porous substrate, the volume ratio of inorganic filler to the solid volume of one adhesive porous layer and the volume ratio of inorganic filler to the solid volume of the other adhesive porous layer may be the same or different.

[0291] The proportion of inorganic filler in the total amount of filler included in the adhesive porous layer (i.e., the total amount of inorganic filler and organic filler) is preferably 90 mass% or more, more preferably 95 mass% or more, and more preferably 100 mass% from the perspective of the heat resistance of the separator.

[0292] -Organic Filler-

[0293] Examples of organic fillers include particles composed of cross-linked polymers such as cross-linked poly(meth)acrylic acid, cross-linked poly(meth)acrylic acid ester, cross-linked polysilicon, cross-linked polystyrene, cross-linked polydivinylbenzene, styrene-divinylbenzene copolymer crosslinker, polyimide, melamine resin, phenolic resin, benzoguanamine-formaldehyde condensate; and particles composed of heat-resistant polymers such as polysulfone, polyacrylonitrile, aramid, polyacetal, and thermoplastic polyimide. The notation "(meth)acrylic" implies that it may be either "acrylic" or "methacrylic."

[0294] The resin constituting the organic filler may be a mixture, modified agent, derivative, copolymer (random copolymer, alternating copolymer, block copolymer, graft copolymer), or crosslinker of the above-mentioned exemplary materials.

[0295] Organic fillers may be used as a single type or in combination of two or more types.

[0296] The proportion of the total filler (i.e., the combined proportion of inorganic and organic fillers) in the solid volume of the adhesive porous layer is preferably 30 volume% or more, more preferably 35 volume% or more, more preferably 40 volume% or more, and more preferably 45 volume% or more from the perspective of the heat resistance of the separator.

[0297] The proportion of the total filler in the solid volume of the adhesive porous layer is preferably 90 volume% or less, more preferably 85 volume% or less, more preferably 80 volume% or less, and more preferably 75 volume% or less, from the perspective that the adhesive porous layer is difficult to peel off from the porous substrate.

[0298] The ratio V (volume %) of the total filler to the solid volume of the adhesive porous layer is calculated by the following formula.

[0299] V={(Xa / Da) / (Xa / Da+Xb / Db+Xc / Dc+…+Xn / Dn)}×100

[0300] Here, among the constituent materials of the adhesive porous layer, the filler is a, and the other constituent materials are b, c, … , n, and the mass of each constituent material included in the adhesive porous layer of a predetermined area is Xa, Xb, Xc, … , Xn(g), and the true density of each constituent material is Da, Db, Dc, … , Dn(g / cm³).

[0301] Xa, etc., substituted into the above formula is the mass (g) of the constituent material used to form an adhesive porous layer of a predetermined area, or the mass (g) of the constituent material extracted from an adhesive porous layer of a predetermined area.

[0302] Da, etc., substituted into the above formula is the true density (g / cm³) of the constituent material used to form the adhesive porous layer, or the true density (g / cm³) of the constituent material extracted from the adhesive porous layer.

[0303] -Other ingredients-

[0304] The adhesive porous layer may include additives such as dispersants, such as surfactants, wetting agents, defoaming agents, and pH adjusters. Dispersants are added to the coating solution for forming the adhesive porous layer for the purpose of improving dispersibility, coating properties, or storage stability. Wetting agents, defoaming agents, and pH adjusters are added to the coating solution for forming the adhesive porous layer for the purpose of, for example, improving affinity with the porous substrate, suppressing air entrapment into the coating solution, or adjusting the pH.

[0305] [Characteristics of the adhesive porous layer]

[0306] The thickness of the adhesive porous layer is preferably 0.5 μm or more on one side, more preferably 1.0 μm or more on one side, and more preferably 1.5 μm or more on one side, in terms of adhesion to the electrode or handling properties, and is preferably 10.0 μm or less on one side, more preferably 8.0 μm or less on one side, and more preferably 6.0 μm or less on one side, in terms of ion permeability and energy density of the battery.

[0307] When the adhesive porous layer is on both sides of a porous substrate, the thickness of the adhesive porous layer is preferably 1.0 μm or more, more preferably 2.0 μm or more, more preferably 3.0 μm or more, preferably 20.0 μm or less, more preferably 16.0 μm or less, and more preferably 12.0 μm or less.

[0308] When adhesive porous layers are present on both sides of a porous substrate, the difference (μm) between the thickness of one adhesive porous layer and the thickness of the other adhesive porous layer is preferably smaller, and preferably 20% or less of the total thickness (μm) of both sides.

[0309] The mass per unit area of ​​the adhesive porous layer is preferably 1.0 g / m² or more, more preferably 2.0 g / m² or more, and more preferably 3.0 g / m² or more, as a total of both sides, whether the adhesive porous layer is on one side or on both sides of the porous substrate, from the perspective of adhesion to the electrode or handling properties, and from the perspective of ion permeability and energy density of the battery, it is preferably 30.0 g / m² or less, more preferably 20.0 g / m² or less, and more preferably 10.0 g / m² or less, as a total of both sides.

[0310] When adhesive porous layers are present on both sides of a porous substrate, the difference (g / m²) between the mass per unit area of ​​one adhesive porous layer and the mass per unit area of ​​the other adhesive porous layer is preferably smaller from the perspective of suppressing curling of the separator or improving the cycle characteristics of the battery, and is preferably 20% or less of the total amount (g / m²) of both sides.

[0311] The porosity of the adhesive porous layer is preferably 30% or more, more preferably 35% or more, and more preferably 40% or more in terms of ion permeability, and is preferably 70% or less, more preferably 65% ​​or less, and more preferably 60% or less in terms of the mechanical strength and adhesion to the electrode of the adhesive porous layer. The porosity ε(%) of the adhesive porous layer is calculated by the following formula.

[0312]

[0313] Here, for constituent materials 1, 2, 3, … , n of the adhesive porous layer, the mass per unit area of ​​each constituent material is W1, W2, W3, … , W n (g / cm²) and the true densities of each constituent material are d1, d2, d3, … , d n (g / cm³) and the thickness of the adhesive porous layer is t (cm).

[0314] The average pore size of the adhesive porous layer is preferably 10 nm to 200 nm. If the average pore size is 10 nm or more, it is difficult for the pores to become clogged even if the resin contained in the adhesive porous layer swells when the electrolyte is impregnated into the adhesive porous layer. If the average pore size is 200 nm or less, the uniformity of ion movement in the adhesive porous layer is high, and the cycle characteristics and load characteristics of the battery are excellent.

[0315] The average pore size (nm) of the adhesive porous layer is calculated by the following formula, assuming that all holes are cylindrical.

[0316] d=4V / S

[0317] In the formula, d represents the average pore size (diameter) of the adhesive porous layer, V represents the pore volume per 1 m² of the adhesive porous layer, and S represents the pore surface area per 1 m² of the adhesive porous layer.

[0318] The volume of pores V per 1 m² of the adhesive porous layer is calculated from the porosity of the adhesive porous layer.

[0319] The porous surface area S per 1 m² of the adhesive porous layer is determined by the following method.

[0320] First, the specific surface area (m² / g) of the porous substrate and the specific surface area (m² / g) of the separator are calculated from the nitrogen gas adsorption amount by applying the BET equation to the nitrogen gas adsorption method. The respective basis weights (g / m²) are multiplied by their specific surface areas (m² / g) to calculate the respective pore surface area per 1 m². Then, the pore surface area S of the adhesive porous layer is calculated by subtracting the pore surface area per 1 m² of the porous substrate from the pore surface area per 1 m² of the separator. Basis weight is the mass per unit area.

[0321] [Characteristics of Separators]

[0322] The thickness of the separator is preferably 8㎛ or more, more preferably 10㎛ or more, and more preferably 12㎛ or more, in terms of the mechanical strength of the separator, and is preferably 25㎛ or less, more preferably 22㎛ or less, and more preferably 20㎛ or less in terms of the energy density of the battery.

[0323] The gully value of the separator (JIS P8117:2009) is preferably 50 seconds / 100 mL or more, more preferably 60 seconds / 100 mL or more, more preferably 70 seconds / 100 mL or more, and more preferably 80 seconds / 100 mL or more from the perspective of suppressing short circuits in the battery.

[0324] The gully value of the separator (JIS P8117:2009) is preferably 200 sec / 100 mL or less in terms of ion permeability, more preferably 180 sec / 100 mL or less, more preferably 150 sec / 100 mL or less, and more preferably 130 sec / 100 mL or less.

[0325] The membrane resistance of the separator is preferably 1 Ω·cm² to 10 Ω·cm² from the perspective of the battery's load characteristics. The membrane resistance of the separator is the resistance value when the separator is impregnated with an electrolyte, and is a value measured by the AC method at a temperature of 20°C using 1 mol / L LiBF4-propylene carbonate:ethylene carbonate (mass ratio 1:1) as the electrolyte. The lower the membrane resistance of the separator, the better the ion permeability of the separator.

[0326] [Method for manufacturing a separator]

[0327] The separator of the present disclosure can be manufactured, for example, by forming an adhesive porous layer on a porous substrate by a wet coating method or a dry coating method. In the present disclosure, a wet coating method is a method of solidifying a coating layer in a coagulation liquid, and a dry coating method is a method of solidifying a coating layer by drying it. An example of an embodiment of the wet coating method is described below.

[0328] The wet coating method is a method of coating a porous substrate with a coating solution containing polyvinylidene fluoride resin and a filler, immersing the substrate in a coagulation solution to solidify the coating layer, and then removing the substrate from the coagulation solution to perform washing and drying.

[0329] A coating solution for forming an adhesive porous layer is prepared by dissolving or dispersing a polyvinylidene fluoride-based resin and a filler in a solvent. If necessary, other components other than the polyvinylidene fluoride-based resin and the filler are dissolved or dispersed in the coating solution.

[0330] The solvent used in the preparation of the coating solution includes a solvent that dissolves polyvinylidene fluoride resin (hereinafter also referred to as "both solvents"). Examples of both solvents include polar amide solvents such as N-methylpyrrolidone, dimethylacetamide, and dimethylformamide.

[0331] The solvent used to prepare the coating solution may include a phase separation agent that induces phase separation from the perspective of forming a porous layer having a good porous structure. Therefore, the solvent used to prepare the coating solution may be a mixed solvent of both solvents and a phase separation agent. It is preferable to mix the phase separation agent with both solvents in an amount that can secure a viscosity suitable for coating. Examples of phase separation agents include water, methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, tripropylene glycol, etc.

[0332] When the solvent used to prepare the coating solution is a mixed solvent of a solvent and a phase separation agent, a mixed solvent containing 60 mass% or more of the solvent and 5 mass% to 40 mass% of the phase separation agent is preferred from the perspective of forming a good porous structure.

[0333] The resin concentration of the coating solution is preferably 1 mass% to 20 mass% in terms of forming a good porous structure. The filler concentration of the coating solution is preferably 0.5 mass% to 50 mass% in terms of forming a good porous structure.

[0334] The coating solution may contain dispersants such as surfactants, wetting agents, defoaming agents, pH adjusters, etc. These additives may remain in the adhesive porous layer as long as they are electrochemically stable within the usage range of the non-aqueous secondary battery and do not inhibit reactions within the battery.

[0335] Examples of means for applying a coating solution to a porous substrate include Meyer bars, die coaters, reverse roll coaters, roll coaters, gravure coaters, etc. When forming an adhesive porous layer on both sides of a porous substrate, it is desirable from the perspective of productivity to apply the coating solution to both sides of the porous substrate simultaneously.

[0336] The solidification of the coating layer is achieved by immersing a porous substrate forming the coating layer in a coagulation solution and solidifying a polyvinylidene fluoride-based resin while inducing phase separation in the coating layer. As a result, a laminate consisting of a porous substrate and an adhesive porous layer is obtained.

[0337] The coagulation solution generally comprises the two solvents and phase separator used in the preparation of the coating solution, and water. For production purposes, it is desirable to match the mixing ratio of the two solvents and the phase separator to the mixing ratio of the mixed solvent used in the preparation of the coating solution. It is desirable for the water content in the coagulation solution to be 40% to 90% by mass, from the perspective of forming a porous structure and productivity. The temperature of the coagulation solution is, for example, 20°C to 50°C.

[0338] After solidifying the coating layer in the coagulation liquid, the laminate is lifted from the coagulation liquid and washed with water. By washing with water, the coagulation liquid is removed from the laminate. Additionally, water is removed from the laminate by drying. Washing with water is performed, for example, by conveying the laminate in a water bath. Drying is performed, for example, by conveying the laminate in a high-temperature environment, by blowing air on the laminate, or by contacting the laminate with a heat roll. The drying temperature is preferably 40°C to 80°C.

[0339] The separator of the present disclosure can also be manufactured by a dry coating method. The dry coating method is a method of forming an adhesive porous layer on a porous substrate by coating a coating solution onto a porous substrate and drying the coating layer to volatilize and remove the solvent.

[0340] The separator of the present disclosure can also be manufactured by a method in which an adhesive porous layer is produced as an independent sheet, and the adhesive porous layer is overlapped with a porous substrate and composited by heat pressing or an adhesive. As a method for producing an adhesive porous layer as an independent sheet, a method of forming an adhesive porous layer on a release sheet by applying the wet coating method or dry coating method described above may be cited.

[0341] Non-aqueous secondary batteries

[0342] The non-aqueous secondary battery of the present disclosure is a non-aqueous secondary battery that obtains an electromotive force through the doping and undoping of lithium ions, and comprises a positive electrode, a negative electrode, and a separator for the non-aqueous secondary battery of the present disclosure. Doping means absorption, storage, adsorption, or insertion, and refers to the phenomenon in which lithium ions enter the active material of an electrode such as a positive electrode.

[0343] The non-aqueous secondary battery of the present disclosure has a structure in which, for example, a battery element in which a negative electrode and a positive electrode face each other with a separator is enclosed within an outer casing together with an electrolyte. The non-aqueous secondary battery of the present disclosure is suitable for non-aqueous electrolyte secondary batteries, particularly lithium-ion secondary batteries.

[0344] Hereinafter, examples of the forms of the positive electrode, negative electrode, electrolyte, and outer casing material provided by the non-aqueous secondary battery of the present disclosure will be described.

[0345] As an example of an embodiment of the positive electrode, a structure in which an active material layer comprising a positive electrode active material and a binder resin is formed on a current collector may be provided. The active material layer may further include a conductive additive. As an example of a positive electrode active material, a lithium-containing transition metal oxide may be provided, specifically 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 Ni 3 / 4 Examples include O2. Examples of binder resins include polyvinylidene fluoride resins and styrene-butadiene copolymers. Examples of conductive aids include carbon materials such as acetylene black, Ketjen black, and graphite powder. Examples of current collectors include aluminum foil, titanium foil, and stainless steel foil with a thickness of 5 μm to 20 μm.

[0346] As an example of an embodiment of the negative electrode, a structure in which an active material layer comprising a negative electrode active material and a binder resin is formed on a current collector may be provided. The active material layer may further include a conductive agent. As the negative electrode active material, a material capable of electrochemically absorbing lithium ions may be provided, specifically, examples include carbon materials; alloys of silicon, tin, aluminum, etc., with lithium; and wood alloys. As the binder resin, examples include polyvinylidene fluoride-based resins and styrene-butadiene copolymers. As the conductive agent, carbon materials such as acetylene black, ketjen black, graphite powder, and ultrafine carbon fibers may be provided. As the current collector, examples include copper foil, nickel foil, stainless steel foil, etc., with a thickness of 5 μm to 20 μm. In addition, a metallic lithium foil may be used as the negative electrode instead of the above-mentioned negative electrode.

[0347] The electrolyte is a solution in which a lithium salt is dissolved in a non-aqueous solvent. Examples of lithium salts include LiPF6, LiBF4, LiClO4, etc. Examples of non-aqueous solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, and their fluorine substituents; and cyclic esters such as γ-butyrolactone and γ-valerolactone, etc., and these may be used alone or in combination. As an electrolyte, a solution in which a cyclic carbonate and a chain carbonate are mixed in a mass ratio (cyclic carbonate:chain carbonate) of 20:80 to 40:60 and a lithium salt is dissolved in a solution in the range of 0.5 mol / L to 1.5 mol / L is suitable.

[0348] Examples of exterior materials include metal cans and aluminum laminate film packs. The battery shape may be prismatic, cylindrical, coin-shaped, etc., but the separator of the present disclosure is suitable for any shape.

[0349] A non-aqueous secondary battery of the present disclosure can be manufactured by first preparing a laminate in which a separator of the present disclosure is placed between a positive electrode and a negative electrode, and then using the laminate, for example, by any one of (1) to (3) below.

[0350] (1) After dry heat pressing the laminate to bond the electrode and separator, the laminate is placed in an outer material (e.g., an aluminum laminate film pack. The same applies hereinafter), an electrolyte is mixed in, and the inside of the outer material is vacuumed. Then, the laminate is further wet heat pressed from the top of the outer material to bond the electrode and separator and seal the outer material.

[0351] (2) The laminate is placed in an outer casing, an electrolyte is injected into it, and the inside of the outer casing is vacuumed. Then, the laminate is wet-heat pressed from the top of the outer casing to bond the electrode and the separator and to seal the outer casing.

[0352] (3) After attaching the electrode and separator to the laminate by dry heat pressing, the electrode is placed in the outer casing, the electrolyte is injected into it, the inside of the outer casing is made into a vacuum, and then the outer casing is sealed.

[0353] In the above manufacturing method, the conditions for the wet heat press are preferably a press temperature of 70°C to 110°C and a press pressure of 0.5 MPa to 2 MPa. In the above manufacturing method, the conditions for the dry heat press are preferably a press temperature of 20°C to 100°C and a press pressure of 0.5 MPa to 9 MPa. The press time is preferably adjusted according to the press temperature and press pressure, for example, within a range of 0.5 minutes to 60 minutes.

[0354] When manufacturing a laminate in which a separator is placed between an anode and a cathode, the method of placing the separator between the anode and the cathode may be a method of stacking at least one layer of an anode, a separator, and a cathode in this order (so-called stack method), or a method of stacking an anode, a separator, a cathode, and a separator in this order and winding them in the longitudinal direction.

[0355] [Example]

[0356] The separator and non-aqueous secondary battery of the present disclosure will be described in more detail below with reference to examples. The materials, usage amounts, ratios, processing procedures, etc., shown in the following examples may be appropriately modified without departing from the spirit of the present disclosure. Accordingly, the scope of the separator and non-aqueous secondary battery of the present disclosure should not be interpreted as being limited by the specific examples shown below.

[0357] In the following description, synthesis, processing, manufacturing, etc. were performed at room temperature (25℃±3℃) unless specifically mentioned otherwise.

[0358] Measurement Methods, Evaluation Methods

[0359] The measurement and evaluation methods applied to the examples and comparative examples are as follows.

[0360] [Quantitative determination of fluorine atoms in porous substrates]

[0361] As measurement devices, a field emission scanning electron microscope S-4800 (Hitachi High-Technology Corporation) and a QUANTAX Flat QUAD System Xflash 5060FQ (Bruker AXS Corporation) were used. The acceleration voltage during SEM observation was set to 1.5 kV, and the acceleration voltage during EDX analysis was set to 3.5 kV.

[0362] [Analysis of Constituent Units of Polyvinylidene Fluoride Resin]

[0363] A polyvinylidene fluoride-based resin used for forming an adhesive porous layer was used as a sample. 20 mg of the polyvinylidene fluoride-based resin was dissolved in 0.6 mL of dimethyl sulfoxide at 100°C, and at 100°C 19 F-NMR spectra were measured. From the obtained NMR spectra, the proportion of constituent units derived from HFP (mol%) and the proportion of constituent units derived from monomers represented by Equation (1) (mol%) were determined.

[0364] [Weight Average Molecular Weight (Mw) of Polyvinylidene Fluoride Resin]

[0365] A polyvinylidene fluoride-based resin used for forming an adhesive porous layer was used as a sample, and its molecular weight was measured by GPC. For the molecular weight measurement by GPC, a GPC device GPC-900 manufactured by Nihon Bunkosha was used, two TSKgel SUPER AWM-H columns manufactured by Toshosha were used, N,N-dimethylformamide was used as the solvent, and measurements were taken under conditions of a temperature of 40°C and a flow rate of 0.6 mL / min to obtain the molecular weight equivalent to polystyrene.

[0366] [Melting point of polyvinylidene fluoride resin]

[0367] A polyvinylidene fluoride-based resin used to form an adhesive porous layer was used as a sample, and differential scanning calorimetry was performed to determine the melting point. As the measuring device, the product name: DSC Q20 (TA Instruments) was used.

[0368] [Acid value of polyvinylidene fluoride resin]

[0369] A polyvinylidene fluoride-based resin used for forming an adhesive porous layer was used as a sample, and the acid value (mgKOH / g) was measured by the potentiometric titration method (JIS K1557-5:2007).

[0370] [Average primary particle size of inorganic filler]

[0371] The average primary particle size was determined by using an inorganic filler used to form an adhesive porous layer as a sample and performing SEM observation.

[0372] [Volume Ratio of Inorganic Filler]

[0373] The ratio V (volume %) of inorganic filler to the solid volume of the adhesive porous layer was calculated by the following formula.

[0374] V={(Xa / Da) / (Xa / Da+Xb / Db+Xc / Dc+…+Xn / Dn)}×100

[0375] Here, among the constituent materials of the adhesive porous layer, the inorganic filler is a, and the other constituent materials are b, c, …, n, and the mass of each constituent material included in the adhesive porous layer of a predetermined area is Xa, Xb, Xc, …, Xn(g), and the true density of each constituent material is Da, Db, Dc, …, Dn(g / cm³). Xa, etc., substituted into the above formula is the mass (g) of the constituent material used to form the adhesive porous layer of a predetermined area. Da, etc., substituted into the above formula is the true density (g / cm³) of the constituent material used to form the adhesive porous layer.

[0376] [Differential Scanning Calorimetry of Polyvinylidene Fluoride Resin Included in Adhesive Porous Layer]

[0377] In the examples and comparative examples, since an adhesive porous layer was formed by applying an equal amount of the same coating solution to both sides of a porous substrate, it was inferred that the adhesive porous layers on both sides have the same thermal properties.

[0378] One adhesive porous layer was peeled off from a separator, the adhesive porous layer was immersed in dimethylacetamide, and heated to about 50°C to obtain a resin solution in which polyvinylidene fluoride resin was dissolved. The resin solution was centrifuged with a centrifuge to precipitate the insoluble matter. The supernatant of the resin solution from which the insoluble matter had precipitated was removed, and centrifugation was repeated to remove the insoluble matter. The resin solution from which the insoluble matter had been removed was added dropwise to water to solidify the polyvinylidene fluoride resin. The solidified material was removed from water and dried, and the solid after drying was used as a sample.

[0379] 5 mg of the sample was placed in an aluminum sample pan (TA Instruments, part number 900786.901), covered with a lid (TA Instruments, part number 900779.901), and set in a measuring device. As the measuring device, the product name: DSC Q20 (TA Instruments) was used. Thermal analysis was performed by varying the sample temperature according to the three steps described above while flowing nitrogen gas at a flow rate of 50 ml / min.

[0380] [Dry Adhesion]

[0381] A cathode slurry was prepared by stirring and mixing 300 parts by mass of artificial graphite as a cathode active material, 7.5 parts by mass of an aqueous dispersion containing 40% by mass of a modified styrene-butadiene copolymer as a binder resin, 3 parts by mass of carboxymethylcellulose as a thickener, and an appropriate amount of water using a twin-arm mixer. The cathode slurry was applied to one side of a copper foil with a thickness of 10 μm, dried, and then pressed to obtain a cathode having a cathode active material layer.

[0382] The above cathode was cut into a rectangular shape of 15mm × 70mm.

[0383] The separator was cut into a rectangular shape measuring TD 20mm × MD 75mm.

[0384] I prepared a rectangular release liner measuring 15mm × 70mm.

[0385] A laminate in which a cathode, a separator, and a release liner were stacked in this order was inserted into a pack made of aluminum laminate film, and for each pack, a heat press was performed using a heat press machine in the stacking direction of the laminate (dry heat press) to bond the cathode and the separator. The heat press conditions were a temperature of 90°C, a load of 30 kg per 1 cm² of electrode, and a pressing time of 30 seconds. Afterward, the laminate was removed from the pack, the release liner was peeled off, and this was used as a test specimen.

[0386] The uncoated surface of the cathode 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, STB-1225S). At this time, the metal plate was fixed to the Tensilon so that the longitudinal direction of the test specimen (i.e., the MD of the separator) was in the direction of gravity. The separator was peeled from the cathode by about 2 cm from the lower end, the 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 300 mm / min, and loads (N) were collected at 0.4 mm intervals from 10 mm to 40 mm after the start of measurement, and the average was calculated. In addition, the loads of 10 test specimens were averaged.

[0387] [Wet Adhesion]

[0388] A cathode slurry was prepared by stirring and mixing 89.5 parts by mass of lithium cobaltate powder as a cathode active material, 4.5 parts by mass of acetylene black as a conductive additive, 6 parts by mass of polyvinylidene fluoride as a binder resin, and an appropriate amount of N-methyl-2-pyrrolidone using a twin-arm mixer. The cathode slurry was applied to both sides of an aluminum foil with a thickness of 20 μm, dried, and then pressed to obtain a double-sided cathode having cathode active material layers on both sides.

[0389] A cathode slurry was prepared by stirring and mixing 300 parts by mass of artificial graphite as a cathode active material, 7.5 parts by mass of an aqueous dispersion containing 40% by mass of a modified styrene-butadiene copolymer as a binder resin, 3 parts by mass of carboxymethylcellulose as a thickener, and an appropriate amount of water using a twin-arm mixer. The cathode slurry was applied to both sides of a copper foil with a thickness of 10 μm, and after drying, pressed to obtain a double-sided cathode having cathode active material layers on both sides.

[0390] The above anode and cathode were each cut into rectangular shapes of 30mm × 70mm.

[0391] The separator was cut into a rectangular shape measuring TD35mm × MD75mm.

[0392] These were stacked so that the positive and negative electrodes alternately and a separator was inserted between the positive and negative electrodes, thereby fabricating a laminate consisting of 3 positive electrodes, 3 negative electrodes, and 5 separators. The laminate was inserted into a pack made of aluminum laminate film, 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. Subsequently, a heat press was performed on each pack in the stacking direction of the laminate using a heat press machine (wet heat press) to bond the electrodes and separators. The heat press conditions were set to a temperature of 90°C, a load of 10 kg per 1 cm² of electrode, and a pressing time of 2 minutes, and this was used as a cell for measuring wet adhesion.

[0393] A compression bending test (3-point bending measurement) was performed on the above cell. The measurement was carried out by attaching a compression bending test jig to a Tensilon (A&D, STB-1225S). The distance between supports was set to 4 cm, and the cell was installed on the supports such that the shorter direction of the cell was parallel to the length direction of the indenter and the compression position during measurement was the center of the length direction of the electrode inside the cell. The measurement was initiated by setting the displacement to 0 when the indenter was lowered until a load of 0.1 N was applied. The compression speed during measurement was set to 2 mm / min, and measurements were performed up to a displacement of 2 mm. The yield point load in the load-displacement curve obtained from the result was defined as the wet adhesion strength. If the yield point load could not be observed, the maximum load was defined as the wet adhesion strength.

[0394] [Film resistance value after heat treatment]

[0395] A separator was cut into a 6cm × 4cm rectangular shape and impregnated with 1 mol / L LiBF4-propylene carbonate:ethylene carbonate (mass ratio 1:1) as the electrolyte. This was then fitted onto an aluminum foil electrode with a lead tab and sealed in an aluminum pack to serve as a test cell. The test cell was placed at a temperature of 100°C for 30 minutes. Subsequently, at a temperature of 20°C, the resistance value of the test cell was measured by the AC impedance method (measurement frequency 100 kHz). The average value of 10 test cells was calculated and used as the film resistance value (Ω·cm²) after heat treatment.

[0396] [Discharge Capacity Retention Rate]

[0397] Twenty test cells were prepared. Ten of them were not heat-treated and were used as standard cells. The remaining 10 were left standing at a temperature of 100°C for 30 minutes and were used as heat-treated cells.

[0398] The following charge and discharge cycles were performed on 10 standard batteries and 10 heat-treated batteries. The charging was performed using a constant current and constant voltage charge of 0.2C and 4.2V, and the discharging was performed using a constant current and constant voltage discharge of 0.2C and 2.5V cutoff, for 5 cycles of charge and discharge. Subsequently, the charging was performed using a constant current and constant voltage charge of 0.2C and 4.2V, and the discharging was performed using a constant current and constant voltage discharge of 10C and 2.5V cutoff. The discharge capacities at this time were recorded, and the average discharge capacities of 10 standard batteries and 10 heat-treated batteries were calculated. The ratio of the discharge capacity of the heat-treated batteries to the discharge capacity of the standard batteries was defined as the discharge capacity retention rate (%) of the batteries exposed to high temperatures and was calculated using the following formula.

[0399] Discharge capacity retention rate = Discharge capacity of heat-treated battery ÷ Discharge capacity of standard battery × 100

[0400] Fabrication of Separators and Batteries

[0401] [Example 1]

[0402] -Production of Separator-

[0403] As materials for the adhesive porous layer, two types of polyvinylidene fluoride-based resins and magnesium hydroxide particles were prepared. Their physical properties are as described in Table 1.

[0404] Two types of polyvinylidene fluoride resins were mixed in a mass ratio of 40:60 and dissolved in dimethylacetamide (DMAc) so that the resin concentration was 5.0 mass%, and magnesium hydroxide particles were further stirred and dispersed to obtain a coating solution (1).

[0405] A polyethylene microporous membrane (thickness 7㎛, porosity 45%, gully value 80 sec / 100mL) was immersed in DMAc, and DMAc was impregnated into the pores of the polyethylene microporous membrane. Hereinafter, this process is referred to as "pretreatment of a porous substrate."

[0406] An appropriate amount of coating solution (1) was placed on a Meyer bar, and the coating solution (1) was applied to both sides of a pretreated polyethylene microporous membrane. At that time, the coating was applied so that the coating amount on the front and back of the polyethylene microporous membrane was equal. This was immersed in a coagulation solution (DMAc:water = 50:50 [mass ratio], liquid temperature 40°C) to solidify the coating layer, and then washed in a washing bath at a water temperature of 40°C and dried. In this way, a separator with an adhesive porous layer formed on both sides of a polyethylene microporous membrane was obtained. The thickness of the adhesive porous layer was set to approximately 3 μm per side.

[0407] -Production of the Cathode-

[0408] A cathode slurry was prepared by stirring and mixing 300 parts by mass of artificial graphite as a cathode active material, 7.5 parts by mass of an aqueous dispersion containing 40% by mass of a modified styrene-butadiene copolymer as a binder resin, 3 parts by mass of carboxymethylcellulose as a thickener, and an appropriate amount of water using a twin-arm mixer. The cathode slurry was applied to one side of a copper foil with a thickness of 10 μm, dried, and then pressed to obtain a cathode having a cathode active material layer.

[0409] -Production of the bipolar system-

[0410] A cathode slurry was prepared by stirring and mixing 89.5 parts by mass of lithium cobaltate powder as a cathode active material, 4.5 parts by mass of acetylene black as a conductive additive, 6 parts by mass of polyvinylidene fluoride as a binder resin, and an appropriate amount of N-methyl-2-pyrrolidone using a twin-arm mixer. The cathode slurry was applied to one side of an aluminum foil with a thickness of 20 μm, dried, and then pressed to obtain a cathode having a cathode active material layer.

[0411] -Battery Production-

[0412] The positive electrode was cut into a 3cm × 5cm rectangle, the negative electrode into a 3.2cm × 5.2cm rectangle, and lead tabs were welded to each. The separator was cut into a 3.4cm × 5.4cm rectangle.

[0413] The electrodes were laminated in the order of anode, separator, and cathode. A heat press was performed using a heat press machine in the lamination direction of the laminate (dry heat press), and the electrodes and separator were temporarily bonded. The heat press conditions were a temperature of 90°C, a load of 30 kg per 1 cm² of electrode, and a pressing time of 30 seconds.

[0414] The pre-bonded laminate was inserted into a pack made of aluminum laminate film, 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. Subsequently, a heat press was performed on each pack in the lamination direction using a heat press machine (wet heat press), and the electrode and separator were bonded. The heat press conditions were a temperature of 90°C, a load of 10 kg per 1 cm² of electrode, and a pressing time of 2 minutes.

[0415] Next, the inside of the pack was sealed under vacuum using a vacuum sealer, and a test battery was obtained.

[0416] [Examples 2–4, Comparative Examples 1–4]

[0417] Each separator was prepared in the same manner as in Example 1, provided that the presence or absence of pretreatment of the porous substrate, and the type and amount of polyvinylidene fluoride resin and filler, which are the materials of the adhesive porous layer, were changed to the specifications listed in Table 1. The thickness of the adhesive porous layer was set to approximately 3 μm per side.

[0418] Then, a test battery was fabricated using each separator in the same manner as in Example 1.

[0419] "PVDF-based resin X" in Table 1 is a resin corresponding to polyvinylidene fluoride resin X or a polyvinylidene fluoride resin for comparison therewith. PVDF-based resin X is a binary copolymer composed of VDF and HFP.

[0420] "PVDF-based resin Y" in Table 1 is a resin corresponding to polyvinylidene fluoride resin Y or a polyvinylidene fluoride resin for comparison therewith. PVDF-based resin Y is a terpolymer composed of VDF, HFP, and a monomer represented by formula (1). In all cases, the monomer represented by formula (1) in PVDF-based resin Y is acrylic acid.

[0421] The composition, physical properties, and evaluation results of each separator in Examples 1 to 4 and Comparative Examples 1 to 4 are shown in Tables 1 and 2.

[0422] [Table 1]

[0423]

[0424] [Table 2]

[0425]

[0426] [Reference Example 1]

[0427] The two types of polyvinylidene fluoride resins used in Examples 1 and 2 were mixed in a mass ratio of 50:50. This mixed resin was used as a sample for DSC analysis, and its thermal properties were analyzed. The analysis results are shown in Table 3.

[0428] [Reference Example 2]

[0429] The two types of polyvinylidene fluoride-based resins used in Example 3 were mixed in a mass ratio of 50:50. This mixed resin was used as a sample for DSC analysis, and its thermal properties were analyzed. The analysis results are shown in Table 3.

[0430] [Table 3]

[0431]

[0432] Reference Example 1 and Reference Example 2 are cases where the mixing ratio of two types of polyvinylidene fluoride resins is the same, and among the two types, the low-melting point polyvinylidene fluoride resin (corresponding to polyvinylidene fluoride resin X) is of a different type and the high-melting point polyvinylidene fluoride resin (corresponding to polyvinylidene fluoride resin Y) is of the same type.

[0433] By comparing Reference Example 1 and Reference Example 2, it can be seen that the endothermic peak temperature and exothermic peak temperature on the low-temperature side change by changing the type of low-melting point polyvinylidene fluoride resin.

[0434] Reference Example 1 and Example 2 use two types of polyvinylidene fluoride resins of the same type and have the same mixing ratio. However, in Example 2, the sample provided to the DSC is a polyvinylidene fluoride resin extracted from an adhesive porous layer, so it is a polyvinylidene fluoride resin that has undergone a process of forming an adhesive porous layer.

[0435] Comparing Reference Example 1 and Example 2, it can be seen that the temperature difference between the endothermic peak and the temperature difference between the exothermic peak of the two types of polyvinylidene fluoride resins decreases when the mixture undergoes a process of forming an adhesive porous layer. That is, when the process of forming an adhesive porous layer is performed, the endothermic peak and the exothermic peak on the low-temperature side shift to the high-temperature side, and the endothermic peak and the exothermic peak on the high-temperature side shift to the low-temperature side.

[0436] From this, it is presumed that in the process of forming an adhesive porous layer, two types of polyvinylidene fluoride resins are partially incompatible, and there exist regions where the high-melting-point polyvinylidene fluoride resin is slightly dissolved in the low-melting-point polyvinylidene fluoride resin and regions where the low-melting-point polyvinylidene fluoride resin is slightly dissolved in the high-melting-point polyvinylidene fluoride resin. As a result, it is presumed that the endothermic and exothermic peaks on the low-temperature side shift to the high-temperature side, and the endothermic and exothermic peaks on the high-temperature side shift to the low-temperature side.

[0437] In Comparative Example 1, the difference in melting points between the two types of polyvinylidene fluoride resins is 22°C, but in the DSC curve of the polyvinylidene fluoride resin extracted from the adhesive porous layer, one endothermic peak and one exothermic peak were observed instead of two each.

[0438] As described above, it is presumed that two types of polyvinylidene fluoride resins are at least partially compatible in the process of forming an adhesive porous layer. At this time, if the characteristics of the two types of polyvinylidene fluoride resins (these characteristics are defined by the HFP ratio, molecular weight, and melting point) are approximate, it is presumed that the two types of polyvinylidene fluoride resins are completely compatible and that there is one endothermic peak and one exothermic peak observed in the DSC curve.

[0439] The disclosure of Japanese Patent Application 2021-118147 filed on July 16, 2021, is incorporated herein by reference in its entirety.

[0440] All documents, patent applications, and technical specifications described in this specification are introduced by reference within this specification to the same extent that individual documents, patent applications, and technical specifications are introduced by reference as they are described individually.

Claims

Claim 1 A separator for a non-aqueous secondary battery, comprising a porous substrate and an adhesive porous layer provided on one or both sides of the porous substrate and comprising a polyvinylidene fluoride-based resin and a filler, wherein the porous substrate comprises fluorine atoms, and the fluorine atoms are fluorine atoms contained in a fluorine atom-containing compound that is attached as a coating to the surface of the porous substrate or supported inside the porous substrate, and when differential scanning calorimetry is performed using the entire polyvinylidene fluoride-based resin included in the adhesive porous layer as a sample, at least two endothermic peaks and / or at least two exothermic peaks are observed, wherein at least one endothermic peak is observed in the region of 125°C or higher and less than 140°C and at least one exothermic peak is observed in the region of 140°C or higher and less than 190°C, and at least one exothermic peak is observed in the region of 80°C or higher and less than 125°C and at least one exothermic peak is observed in the region of 125°C or higher and less than 190°C. Claim 2 delete Claim 3 A separator for a non-aqueous secondary battery according to claim 1, wherein when differential scanning calorimetry is performed using the entire polyvinylidene fluoride-based resin included in the adhesive porous layer as a sample, two or more endothermic peaks are observed, and the temperature difference between adjacent endothermic peaks is 10°C or more and 60°C or less. Claim 4 delete Claim 5 A separator for a non-aqueous secondary battery according to claim 1, wherein when differential scanning calorimetry is performed using the entire polyvinylidene fluoride-based resin included in the adhesive porous layer as a sample, two or more exothermic peaks are observed, and the temperature difference between adjacent exothermic peaks is 10°C or more and 90°C or less. Claim 6 A separator for a non-aqueous secondary battery, comprising a porous substrate and an adhesive porous layer provided on one or both sides of the porous substrate and comprising a polyvinylidene fluoride-based resin and a filler, wherein the porous substrate comprises fluorine atoms, and the fluorine atoms are fluorine atoms contained in a fluorine atom-containing compound that is attached as a coating to the surface of a void of the porous substrate or supported inside the porous substrate, and the polyvinylidene fluoride-based resin comprises the following polyvinylidene fluoride-based resin X and polyvinylidene fluoride-based resin Y. Polyvinylidene fluoride-based resin X: comprises constituent units derived from vinylidene fluoride and constituent units derived from hexafluoropropylene, wherein the ratio of constituent units derived from hexafluoropropylene to total constituent units is greater than 3.5 mol% and less than or equal to 15 mol%, the weight average molecular weight is 100,000 or more and less than 1,000,000, and the melting point is 125°C or higher. It is less than 150℃. Polyvinylidene fluoride resin Y: It contains constituent units derived from vinylidene fluoride and may also contain constituent units derived from hexafluoropropylene, and the proportion of constituent units derived from hexafluoropropylene in the total constituent units is 0 mol% or more and 3.5 mol% or less, the weight average molecular weight is 1 million or more and less than 3 million, and the melting point is 150℃ or more and less than 180℃. Claim 7 A separator for a non-aqueous secondary battery according to claim 6, wherein at least two endothermic peaks and / or at least two exothermic peaks are observed when differential scanning calorimetry is performed using the entire polyvinylidene fluoride-based resin included in the adhesive porous layer as a sample. Claim 8 A separator for a non-aqueous secondary battery according to claim 6, wherein the difference between the melting point of the polyvinylidene fluoride resin X and the melting point of the polyvinylidene fluoride resin Y is 25°C or more and less than 55°C. Claim 9 A separator for a non-aqueous secondary battery according to claim 6, wherein the mass ratio of the polyvinylidene fluoride-based resin X and the polyvinylidene fluoride-based resin Y included in the adhesive porous layer is 20:80 to 80:

20. Claim 10 A separator for a non-aqueous secondary battery according to claim 6, wherein the polyvinylidene fluoride-based resin X comprises constituent units derived from vinylidene fluoride and constituent units derived from hexafluoropropylene, wherein the ratio of constituent units derived from hexafluoropropylene to total constituent units is greater than 5.0 mol% and less than or equal to 15 mol%, the weight average molecular weight is greater than or equal to 300,000 and less than 1,000,000, and the melting point is greater than or equal to 125°C and less than 140°C. Claim 11 A separator for a non-aqueous secondary battery according to claim 6, wherein the polyvinylidene fluoride-based resin Y comprises constituent units derived from vinylidene fluoride and may comprise constituent units derived from hexafluoropropylene, wherein the ratio of constituent units derived from hexafluoropropylene to the total constituent units is 0 mol% or more and 2.0 mol% or less, the weight average molecular weight is 1.5 million or more and less than 2 million, and the melting point is 150°C or more and less than 170°C. Claim 12 A separator for a non-aqueous secondary battery according to claim 1 or 6, wherein the ratio of fluorine atoms to the total atoms contained in the porous substrate is 0.05 atomic% or more and 1.00 atomic% or less. Claim 13 A separator for a non-aqueous secondary battery according to claim 1 or 6, wherein the adhesive porous layer comprises a polyvinylidene fluoride-based resin having a constituent unit derived from a monomer represented by the following formula (1). In Equation (1), R 1 , R 2 and R 3 Each independently represents a hydrogen atom, a halogen atom, a C1-5 alkyl group, a carboxyl group, or a derivative of a carboxyl group, where X represents a single bond, a C1-5 alkylene group, or a C1-5 alkylene group having a substituent, and Y represents a hydrogen atom, a C1-5 alkyl group, a C1-5 alkyl group substituted with at least one hydroxyl group, a C1-5 alkyl group substituted with at least one carboxyl group, or -ROC(=O)-(CH2) n -C(=O)-OH (R represents an alkylene group having 1 to 5 carbon atoms, and n represents an integer greater than or equal to 0). Claim 14 A separator for a non-aqueous secondary battery according to claim 1 or 6, wherein the acid value of the entire polyvinylidene fluoride-based resin included in the adhesive porous layer is less than 3.0 mgKOH / g. Claim 15 A separator for a non-aqueous secondary battery according to claim 1 or 6, wherein the total weight average molecular weight of the polyvinylidene fluoride-based resin included in the adhesive porous layer is 300,000 or more and less than 3,000,000. Claim 16 A separator for a non-aqueous secondary battery according to claim 1 or 6, wherein, in the entire polyvinylidene fluoride-based resin included in the adhesive porous layer, the ratio of constituent units derived from hexafluoropropylene in the total constituent units is greater than 3.5 mol% and less than or equal to 7.0 mol%. Claim 17 A separator for a non-aqueous secondary battery according to claim 1 or 6, wherein the ratio of the filler to the volume excluding the pores of the adhesive porous layer is 30 volume% to 90 volume%. Claim 18 A separator for a non-aqueous secondary battery according to claim 1 or 6, wherein the filler comprises at least one selected from the group consisting of metal hydroxide particles, metal sulfate particles, and barium titanate particles. Claim 19 A separator for a non-aqueous secondary battery according to claim 1 or 6, wherein the average primary particle size of the entire filler included in the adhesive porous layer is 0.01㎛ to 1.5㎛. Claim 20 A non-aqueous secondary battery comprising a positive electrode, a negative electrode, and a separator for a non-aqueous secondary battery described in claim 1 or 6 disposed between the positive electrode and the negative electrode, and obtaining an electromotive force by doping and thawing of lithium ions.

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