Battery separator winding

Abstract

To provide a resin sheet used for transporting a separator, and a wound-round body or a lamination body of the separator and the resin sheet, capable of suppressing or preventing a blocking over a long time in a storage and transportation, maintaining a quality at a slit, and having a secondary battery characteristic.SOLUTION: The present invention provides a separator for a secondary battery device and a wound-round body to which a resin sheet is wound. The separator for the secondary battery device, includes: a polyolefin porous base material; and a thermoplastic polymer layer containing a thermoplastic polymer in at least one part of at least one surface of the polyolefin porous base material. A MD tensile elastic modulus of the resin sheet is 1000 kgf / cm2 or more and 15000 kgf / cm2 or less, and a ratio of the MD tensile elastic modulus of the separator for the secondary battery device against the MD tensile elastic modulus of the resin sheet is 0.35 or more and 10.0 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to separators for energy storage devices (hereinafter also simply referred to as "separators") and wound resin sheets, etc. More specifically, the present invention relates to resin sheets, separators, and wound or laminated resin sheets used when storing and transporting separators having a thermoplastic polymer layer containing a thermoplastic polymer on at least a portion of at least one side of a polyolefin porous substrate. [Background technology]

[0002] The development of non-aqueous electrolyte batteries, primarily lithium-ion batteries, is actively underway. Typically, non-aqueous electrolyte batteries have a separator between the positive and negative electrodes, which is made of a porous material, such as a microporous membrane, as the substrate. Such a separator prevents direct contact between the positive and negative electrodes and allows ions to pass through the electrolyte held in the micropores.

[0003] In recent years, the miniaturization and thinning of portable devices have led to a demand for smaller and thinner energy storage devices such as lithium-ion secondary batteries. At the same time, efforts are being made to increase the capacity of these devices by improving their volumetric energy density, in order to enable them to be carried for extended periods.

[0004] Traditionally, separators have been required to possess safety-related properties, such as the ability to quickly stop the battery reaction in the event of abnormal overheating (fuse properties) and the ability to maintain their shape even at high temperatures to prevent the dangerous situation of the positive and negative electrode materials directly reacting (short-circuit properties). In recent years, in addition to these safety properties, there has been a demand for improved adhesion between the separator and the electrodes from the perspective of uniformizing the charge and discharge current and suppressing lithium dendrite formation.

[0005] To improve the cycle characteristics or safety of non-aqueous electrolyte batteries, as well as the adhesion between the separator and the electrode, separators have been proposed that impart adhesion or functionality by supporting an adhesive on a porous film or by arranging a functional porous layer such as an adhesive polymer layer or a thermoplastic polymer layer. Further improvements are being considered for the formation and winding of adhesive or functional separators (Patent Documents 1, 2).

[0006] When manufacturing a separator winding, as the number of windings on the separator core increases, the pressure on the separator located in the inner layer of the winding increases, which can cause the thermoplastic polymers to stick together and / or to the substrate. This phenomenon is generally called "blocking." Blocking can make it difficult to unwind the separator on the inner layer of the winding, significantly impairing handling.

[0007] For example, Patent Document 1 describes a laminated wound body obtained by laminating and winding a separator having a fluororesin-containing porous layer on at least one side of a polyolefin microporous membrane, and a film containing inorganic particles and a thermoplastic resin, in order to avoid physically damaging the porous layer by blocking of the adhesive separator and to possess both wet and dry adhesion, wherein the amount of linear oligomers derived from the thermoplastic resin on the film surface is 30 μg / m². 2 The following steps are described.

[0008] Furthermore, Patent Document 2 proposes a laminate for non-aqueous secondary batteries comprising a release substrate and a binder-containing functional layer formed in a dot pattern on one surface of the release substrate, from the viewpoint of being able to easily peel the functional layer from the release substrate while adhering it well to the separator substrate when transferring the functional layer onto the separator substrate, from the viewpoint of winding the laminate for non-aqueous secondary batteries obtained in this way, and from the viewpoint of adhesion between the separator and other battery components. Patent Document 2 also describes a method in which, in the manufacture of a component for non-aqueous secondary batteries, the binder-containing functional layer side of the laminate for non-aqueous secondary batteries is adhered to another battery substrate, and then the release substrate is peeled off from the laminate for non-aqueous secondary batteries. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] International Publication No. 2018 / 021398 [Patent Document 2] International Publication No. 2019 / 039357 [Overview of the project] [Problems that the invention aims to solve]

[0010] However, the laminated winding body containing a separator as described in Patent Document 1, and the laminated body for non-aqueous secondary batteries having a binder-containing functional layer formed in a dot pattern on the surface of a release substrate as described in Patent Document 2, did not possess the ability to suppress or prevent blocking over long periods during storage and transportation, maintain the quality of the separator and film during slitting (e.g., degree of foreign matter contamination, runability, presence or absence of wrinkles), and possess the device characteristics of an energy storage device including a separator.

[0011] In view of the above problems, the present invention aims to provide a resin sheet for use during separator transport, as well as a wound or laminate of separators and resin sheets, which can suppress or prevent blocking over long periods during storage and transport, maintain quality during slitting, and possess the characteristics of an energy storage device. [Means for solving the problem]

[0012] The above problems can be solved by the following technical means. (1) A winding body in which a separator and a resin sheet for an energy storage device are wound, The separator for the energy storage device comprises a polyolefin porous substrate and a thermoplastic polymer layer containing a thermoplastic polymer on at least a portion of at least one side of the polyolefin porous substrate. The MD tensile modulus of the aforementioned resin sheet is 1000 kgf / cm². 2 More than 15000kgf / cm 2 The following and A wound body in which the ratio of the MD tensile modulus of the separator for the energy storage device to the MD tensile modulus of the resin sheet is 0.35 or more and 10.0 or less. (2) The winding body according to item (1), wherein the peel strength between the separator for the energy storage device and the resin sheet is 0.1 N / m or more and 10.0 N / m or less, and the adhesive strength between the separator and the electrode in a dry state is 1.0 N / m or more. (3) The puncture strength of the resin sheet, calculated by basis weight, is 50 gf / g / m². 2 The above is the winding body described in item (1) or (2). (4) The winding body described in any one of items (1) to (3), wherein the internal pressure in the direction of the roll center in the inner 10% of the inner layer is 5 MPa or less. (5) Of the surface free energies of the back surface of the resin sheet, the highest value of the surface free energy is 40 mJ / m 2 A coiled body as described in any one of the following items (1) to (4). (6) Of the smoothness of the back surface of the resin sheet, the minimum value of smoothness is 2000 seconds / 10 cm3 The wound body according to any one of items (1) to (5) above. (7) Among the smoothness of the back surface of the separator for the power storage device, the minimum value of the smoothness is 10,000 seconds / 10 cm 3 The wound body according to any one of items (1) to (6) above. (8) The ratio of the puncture strength of the separator for the power storage device to the puncture strength of the resin sheet is 0.12 or more and 2.0 or less, and the wound body according to any one of items (1) to (7) above. (9) The main component of the thermoplastic polymer layer is an acrylic resin, and the wound body according to any one of items (1) to (8) above. (10) The air permeability of the separator for the power storage device is 200 seconds / 100 cm 3 The wound body according to any one of items (1) to (9) above. (11) The thermoplastic polymer layer is attached to the polyolefin porous substrate without using a transfer method, and the wound body according to any one of items (1) to (10) above. (12) A resin sheet used when transporting a separator for a power storage device, The separator for the power storage device has a polyolefin porous substrate and a thermoplastic polymer layer containing a thermoplastic polymer on at least a part of at least one side of the polyolefin porous substrate, The MD tensile elastic modulus of the resin sheet is 1,000 kgf / cm 2 15,000 kgf / cm or more 2 Less than or equal to The resin sheet having a relationship such that the ratio of the MD tensile elastic modulus of the separator to the MD tensile elastic modulus of the resin sheet is 0.35 or more and 10.0 or less. (13) The resin sheet according to item (12), wherein the peel strength between the separator for the power storage device and the resin sheet is in the relationship of 0.1 N / m or more and 10.0 N / m or less. (14) A laminate obtained by laminating a separator for a power storage device and a resin sheet, The separator for the energy storage device comprises a polyolefin porous substrate and a thermoplastic polymer layer containing a thermoplastic polymer on at least a portion of at least one side of the polyolefin porous substrate. The MD tensile modulus of the aforementioned resin sheet is 1000 kgf / cm². 2 More than 15000kgf / cm 2 The following: A laminate in which the ratio of the MD tensile modulus of the separator for the energy storage device to the MD tensile modulus of the resin sheet is 0.35 or more and 10.0 or less. [Effects of the Invention]

[0013] According to the present invention, blocking can be suppressed or prevented for a long period of time during storage and transportation of separators for energy storage devices, the quality of the separator can be maintained when the separator is slit, and the device characteristics of the energy storage device including the separator can be ensured. [Modes for carrying out the invention]

[0014] The following describes in detail embodiments for carrying out the present invention (hereinafter abbreviated as "embodiments"). It should be noted that the present invention is not limited to the following embodiments, and can be implemented in various modifications within the scope of its essence.

[0015] One aspect of the present disclosure relates to a laminate or wound body comprising a separator for an energy storage device and a resin sheet, and / or a wound body comprising a laminate and / or a wound body of a resin sheet. In a first embodiment, a wound body of a separator for an energy storage device and a resin sheet is provided, and in a second embodiment, a laminate of a separator for an energy storage device and a resin sheet is provided.

[0016] Another embodiment relates to the transport and / or storage of separators for energy storage devices. In a third embodiment, a resin sheet is provided for use when transporting separators for energy storage devices, and in a fourth embodiment, a method for transporting and / or storing separators for energy storage devices using the same is provided.

[0017] In this disclosure, MD means a direction parallel to the mechanical direction of the polyolefin porous substrate. TD means a direction that intersects the MD at a 90° angle.

[0018] In this disclosure, "main component" refers to a component that makes up 50% or more by mass.

[0019] The wound body according to the first embodiment comprises a separator for an energy storage device and a resin sheet wound together, and the structure of the separator, the MD tensile modulus of the resin sheet, and the ratio of the MD tensile modulus of the separator for the energy storage device to the MD tensile modulus of the resin sheet are specified.

[0020] The winding body according to the first embodiment has a separator comprising a polyolefin porous substrate and a thermoplastic polymer layer containing a thermoplastic polymer disposed on at least a portion of at least one side of the polyolefin porous substrate, and the MD tensile modulus of the resin sheet is 1000 kgf / cm². 2 More than 15000kgf / cm 2 The following conditions apply, and the ratio of the MD tensile modulus of the separator to the MD tensile modulus of the resin sheet (MD tensile modulus) セパレータ / MD Tensile Modulus 樹脂シート By having a value of 0.35 or more and 10.0 or less, blocking can be suppressed or prevented for a long period of time during storage and transportation of separators having a thermoplastic polymer layer, and the quality of the wound body or the separator unwound therefrom can be maintained during slitting, thereby enabling the securing or improvement of the characteristics of energy storage devices equipped with separators.

[0021] In the first embodiment, the storage time and / or transport time of the separator is preferably 1 hour or more and 1000 days or less, and more preferably 365 days or less, from the viewpoint of appropriately achieving the effects of the present invention. The temperature during storage and transport is preferably 60°C or less, and more preferably 40°C or less. The relative humidity during storage and transport is preferably 95 rh% or less, and more preferably 90 rh% or less. The quality at the time of slitting is, for example, the degree of foreign matter contamination in the slitting roll or the slit separator, the runability of the separator during feeding and / or slitting, and the presence or absence of wrinkles in the separator after slitting.

[0022] The winding body according to the first embodiment may optionally include a core (also called a "winding core") for winding the separator and resin sheet. When at least the separator is wound onto the core in any number of turns in an MD manner, the number of turns of the separator in the resulting winding body is preferably 50 or more, more preferably 500 or more, and even more preferably 1,000 to 20,000. By having 50 or more turns, blocking can be suppressed or prevented even in long separators that are prone to deformation due to winding tightness, etc.

[0023] In a wound material, the peel strength between the separator and the resin sheet is preferably 0.1 N / m or more and 10.0 N / m or less, more preferably 0.4 N / m or more and 9.0 N / m or less, and even more preferably 0.6 N / m or more and 8.0 N / m or less, from the viewpoint of ease of unwinding the separator from the wound material and the quality of the separator when slit.

[0024] In a wound material, the internal pressure in the inner 10% of the material towards the roll center is preferably 5 MPa or less, more preferably 4 MPa or less, and even more preferably 0 MPa or more and 4 MPa or less, from the viewpoint of storage or transportation under conditions where blocking is less likely to occur. Here, "inner 10%" refers to the region up to 10% in the winding thickness direction from the center of the wound material, or from the innermost layer in contact with the core if a core is present, toward the outermost layer, when the wound material is observed from the side. Furthermore, "internal pressure towards the roll center" refers to the internal pressure from the inner 10% region of the wound material toward the center or toward the innermost layer when the wound material is observed from the side.

[0025] In a wound body, the ratio of the puncture strength of the separator to the puncture strength of the resin sheet (puncture strength) セパレータ / Puncture strength 樹脂シート The ratio (puncture strength) in a wound body is preferably 0.12 or more and 2.0 or less, and more preferably 0.14 or more and 1.8 or less. セパレータ / Puncture strength 樹脂シート When the above values ​​are within the specified range, the stiffness of the resin sheet and the separator are appropriately balanced during slitting of the wound material, and wrinkles tend to form in the separator.

[0026] <Laminate made of a separator and resin sheet for energy storage devices> The laminate according to the second embodiment comprises a separator for an energy storage device and a resin sheet, and the structure of the separator, the MD tensile modulus of the resin sheet, and the ratio of the MD tensile modulus of the separator for the energy storage device to the MD tensile modulus of the resin sheet are specified.

[0027] The laminate according to the second embodiment has a separator comprising a polyolefin porous substrate and a thermoplastic polymer layer containing a thermoplastic polymer disposed on at least a portion of at least one side of the polyolefin porous substrate, and the MD tensile modulus of the resin sheet is 1000 kgf / cm². 2 More than 15000kgf / cm 2 The following is true, and the ratio (MD tensile modulus) セパレータ / MD Tensile Modulus 樹脂シートBy having a value of 0.35 or more and 10.0 or less, blocking can be suppressed or prevented for a long period of time during storage and transportation of separators having a thermoplastic polymer layer, and the quality of the separator can be maintained during winding, unwinding, and slitting, and consequently, the characteristics of energy storage devices equipped with the separator can be ensured or improved.

[0028] In the second embodiment, the storage time and / or transport time of the separator is preferably 1 hour or more and 1000 days or less, and more preferably 365 days or less, from the viewpoint of appropriately achieving the effects of the present invention. The temperature during storage and transport is preferably 60°C or less, and more preferably 40°C or less. The relative humidity during storage and transport is preferably 95 rh% or less, and more preferably 90 rh% or less. The quality during winding, unwinding, slitting, etc., includes, for example, the degree of foreign matter contamination in the winded body formed by winding the laminate, the degree of foreign matter contamination in the slitting roll or the slit separator, the runability of the separator when peeling the separator or resin sheet from the laminate, the runability of the separator when slitting the separator, and the presence or absence of wrinkles in the separator after slitting.

[0029] In the laminate, the peel strength between the separator and the resin sheet is preferably 0.1 N / m or more and 10.0 N / m or less, more preferably 0.4 N / m or more and 9.0 N / m or less, and even more preferably 0.6 N / m or more and 8.0 N / m or less, from the viewpoint of the peelability of the separator from the laminate and the quality of the separator when slit.

[0030] In a laminate, the ratio (puncture strength) セパレータ / Puncture strength 樹脂シート The ratio (puncture strength) in the laminate is preferably 0.12 or more and 2.0 or less, and more preferably 0.14 or more and 1.8 or less. セパレータ / Puncture strength 樹脂シート When the above values ​​are within the specified range, the stiffness of the resin sheet and the separator are appropriately balanced during slitting of the laminate, and wrinkles tend to form in the separator.

[0031] The manufacturing methods, common configurations, and preferred configurations of the wound body according to the first embodiment and the laminate according to the second embodiment will be described below.

[0032] (Method for laminating and / or winding separators and resin sheets for energy storage devices) A method for manufacturing a wound body according to the first embodiment includes the steps of: obtaining a separator by attaching a thermoplastic polymer layer to at least a portion of at least one side of a polyolefin porous substrate; a lamination step of laminating the separator and a resin sheet; and a winding step of winding the separator and the resin sheet.

[0033] From the viewpoint of suppressing or preventing foreign matter contamination of the separator and resin sheet and / or winding method, it is preferable not to use a transfer method, and it is even more preferable not to use a transfer method in any or all of the separator acquisition process, lamination process and winding process. Here, a transfer method means one used to attach a thermoplastic polymer layer to a polyolefin porous substrate, and includes, for example, a method in which only the thermoplastic polymer layer is formed in advance on the resin sheet or on another component, and the thermoplastic polymer layer is transferred from the resin sheet or other component to the polyolefin porous substrate.

[0034] The separator acquisition process may be described later as a separator manufacturing method, which includes a method for manufacturing a polyolefin porous substrate, a method for forming a thermoplastic polymer layer, and a method for forming a porous layer.

[0035] The lamination process between the separator and the resin sheet may be carried out by known methods, such as overlapping, bonding, compression, adhesion, lamination, interlocking, or joining via another component, and it is preferable not to use a transfer method. The laminate according to the second embodiment can also be manufactured by carrying out the lamination process.

[0036] The lamination process and the winding process can be performed simultaneously, individually, or sequentially. For example, a roll-to-roll method may be used to form a wound body by winding individually dispensed separators and resin sheets onto a core while laminating them. Alternatively, a laminate may be formed by laminating sheet-like separators and resin sheets, and then, if desired, the laminate may be wound to form a wound body.

[0037] The winding process of the separator and resin sheet can generally be carried out by winding them together along the MD (Metal Modulus) for, for example, 50 to 20,000 turns. The tension of the separator during the winding process is preferably 10 N / m to 100 N / m, and more preferably 20 N / m to 70 N / m. A winding tension of 10 N / m or more allows for appropriate adhesive force to be generated within the winding body, suppressing winding misalignment during the production of the winding body and reducing the occurrence of wrinkles in the wound separator. Furthermore, a winding tension of 100 N / m or less allows for smooth unwinding of the separator from the winding body when producing the electrode-separator laminate.

[0038] The winding process can be performed between the time a thermoplastic polymer layer is attached to at least a portion of at least one side of the polyolefin porous substrate and the time before the electrode-separator laminate is fabricated.

[0039] In the winding process, the separator may be further unwound from the winding body containing the separator and resin sheet and wound onto the core to obtain a winding body consisting only of the separator.

[0040] The core for winding up the separator, or the core for winding up the separator and the resin sheet, is not particularly limited in terms of its material. Examples of core materials include paper, resin, metal, and combinations thereof. The core's shape is only required to allow winding up the separator and / or the resin sheet, and is typically cylindrical. The outer diameter of the core is not particularly limited, but may be 3 inches (i.e., 76.2 mm), 6 inches, 8 inches, 10 inches, etc. Similarly, the inner diameter of the core is not particularly limited, but may be 3 inches, 6 inches, 8 inches, 10 inches, etc. The space between the outer and inner circumferences may be filled with the core material, or it may have a partial space, such as a spoke structure. The width of the core is not particularly limited, as long as it is greater than or equal to the width of the separator or resin sheet.

[0041] The separator winding can be subjected to slitting as needed, and then wound onto a predetermined core to manufacture a slitting roll. The separator unwound from the separator winding can also be used in the manufacture of laminates or batteries.

[0042] (Separator for energy storage devices) Separators for energy storage devices are: A polyolefin porous substrate (hereinafter sometimes abbreviated as "substrate") and; A thermoplastic polymer layer containing a thermoplastic polymer is disposed on at least a portion of at least one side of the substrate; A porous layer and; Includes.

[0043] The separator has excellent adhesion to the electrode or electrode active material by having a thermoplastic polymer layer containing a thermoplastic polymer on at least a portion of at least one side of the substrate.Optionally, the separator may have a configuration in which a porous layer is present on at least a portion of at least one side of a polyolefin porous substrate, and a thermoplastic polymer layer is present on the porous layer.

[0044] In separators, it is preferable that the thermoplastic polymer layer is attached to the substrate without using a transfer method, from the viewpoint of suppressing or preventing blocking during transport and / or storage, maintaining quality during slitting, and the characteristics of the energy storage device.

[0045] The substrate, thermoplastic polymer layer, and porous layer are described below.

[0046] (Polyolefin porous substrate) The polyolefin porous substrate is not particularly limited, but is preferably a microporous film composed of a polyolefin resin composition containing a polyolefin resin, and more preferably a microporous film mainly composed of a polyolefin resin. The polyolefin resin content in the polyolefin porous substrate is not particularly limited, but from the viewpoint of shutdown performance when used as a separator for energy storage devices, it is preferable that the porous substrate is composed of a polyolefin resin composition in which polyolefin resin accounts for 50% to 100% of the mass fraction of all components constituting the substrate. The proportion of polyolefin resin in the substrate is more preferably 60% to 100% by mass, and even more preferably 70% to 100% by mass.

[0047] (Polyolefin resin) The polyolefin resin is not particularly limited, but can be any polyolefin resin used in conventional extrusion, injection, inflation, and blow molding, such as homopolymers and copolymers of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene, or multi-stage polymers. Furthermore, polyolefins selected from the group consisting of these homopolymers, copolymers, and multi-stage polymers can be used individually or in combination.

[0048] Polyethylene is preferable as a base material for forming separators for energy storage devices because it has a low melting point and high strength; therefore, a resin mainly composed of polyethylene is preferable.

[0049] Typical examples of polyolefin resins, though not particularly limited, include low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ultra-high molecular weight polyethylene, isotactic polypropylene, atactic polypropylene, ethylene-propylene random copolymer, polybutene, and ethylene-propylene rubber.

[0050] Here, there are no limitations on the three-dimensional structure of the polypropylene; it may be isotactic polypropylene, syndiotactic polypropylene, or attactic polypropylene.

[0051] The proportion of polypropylene to total polyolefin in the polyolefin resin composition is not particularly limited, but from the viewpoint of achieving both heat resistance and good shutdown function, it is preferably 0 to 35% by mass, more preferably 3 to 20% by mass, and even more preferably 4 to 10% by mass.

[0052] In this case, polyolefin resins other than polypropylene are not limited to, but examples include homopolymers or copolymers of olefin hydrocarbons such as ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene. Specifically, examples include polyethylene, polybutene, and ethylene-propylene random copolymer.

[0053] From the viewpoint of shutdown characteristics where the pores of the porous substrate are closed by thermal melting, it is preferable to use polyethylene other than polypropylene as the polyolefin resin, such as low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, and ultra-high molecular weight polyethylene. Among these, from the viewpoint of strength, polyethylene with a density of 0.93 g / cm³ as measured according to JIS K 7112 is preferable. 3 It is more preferable to use polyethylene as described above.

[0054] The viscosity-average molecular weight of the polyolefin resin constituting the porous polyolefin substrate is not particularly limited, but is preferably 30,000 to 12,000,000, more preferably 50,000 to less than 2,000,000, and even more preferably 100,000 to less than 1,000,000. A viscosity-average molecular weight of 30,000 or more is preferable because it increases the melt tension during melt molding, resulting in good moldability, and tends to result in high strength due to the entanglement of polymers. On the other hand, a viscosity-average molecular weight of 12,000,000 or less is preferable because it facilitates uniform melt-kneading, and tends to result in excellent sheet moldability, particularly thickness stability. Furthermore, a viscosity-average molecular weight of less than 1,000,000 is preferable because it tends to easily close the pores when the temperature rises, resulting in good shutdown function. For example, instead of using a polyolefin with a viscosity-average molecular weight of less than 1,000,000 alone, a mixture of a polyolefin with a viscosity-average molecular weight of 2,000,000 and a polyolefin with a viscosity-average molecular weight of 270,000, in which the viscosity-average molecular weight is less than 1,000,000, may be used.

[0055] Polyolefin porous substrates may contain any additives. Such additives are not particularly limited and include, for example, polymers other than polyolefins; inorganic particles; antioxidants such as phenolic, phosphorus-based, and sulfur-based agents; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorbers; light stabilizers; antistatic agents; antifogging agents; coloring pigments, etc.

[0056] The total content of these additives is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, per 100 parts by mass of the polyolefin resin composition.

[0057] (Physical properties of porous polyolefin substrates) The basis weight of the polyolefin porous substrate is not particularly limited, but preferably 0.5 g / m² at the lower limit. 2 The above is preferable, and more preferably 1.0 g / m 2 The above, and more preferably 1.5 g / m² 2 The above applies, and the upper limit is preferably 10.0 g / m².2 The following, and more preferably 8.0 g / m² 2 The following, and more preferably 6.5 g / m² 2 The following applies: The basis weight is 0.5 g / m². 2 The above is preferable from the viewpoint of providing sufficient shutdown functionality when used as a battery. On the other hand, a basis weight of 10.0 g / m² is preferable. 2 The following conditions are preferable from the viewpoint of improving the mass energy density of the energy storage device and enhancing its performance, such as cycle characteristics. The above basis weight can be adjusted by adjusting the mass fraction of plasticizer, the die lip spacing, the stretching ratio, etc.

[0058] The film thickness of the polyolefin porous substrate is not particularly limited, but the lower limit is preferably 0.5 μm or more, more preferably 1.0 μm or more, and even more preferably 3.0 μm or more, and the upper limit is preferably 30.0 μm or less, more preferably 20.0 μm or less, and even more preferably 15.0 μm or less. A film thickness of 0.5 μm or more is preferable from the viewpoint of suppressing concerns about short circuits due to irregularities in the active material of the positive electrode and / or negative electrode. On the other hand, a film thickness of 30.0 μm or less is preferable from the viewpoint of increasing the volumetric energy density of the energy storage device. The above film thickness can be adjusted by adjusting the mass fraction of the plasticizer, the die lip spacing, the stretching ratio, etc.

[0059] The puncture strength of the polyolefin porous substrate is not particularly limited, but is preferably 50 gf or more, more preferably 100 gf or more, and even more preferably 130 gf or more, and preferably 1000 gf or less, more preferably 800 gf or less, and even more preferably 600 gf or less. A puncture strength of 50 gf or more is preferable from the viewpoint of suppressing film rupture due to detached active material during battery winding, and also from the viewpoint of suppressing concerns about short circuits due to the expansion and contraction of electrodes accompanying charging and discharging. On the other hand, a puncture strength of 1000 gf or less is preferable from the viewpoint of reducing width shrinkage due to orientation relaxation during heating. The puncture strength mentioned above can be adjusted by controlling the stretching ratio, stretching temperature, etc.

[0060] The basis weight strength of the porous polyolefin substrate is not particularly limited, but the lower limit is preferably 30 gf / g / m². 2 The above is preferable to 40 gf / g / m³. 2 The above is preferable to 50 gf / g / m 2 The above applies, and the upper limit is preferably 200 gf / g / m³. 2 The following, and more preferably 150 gf / g / m³ 2 The following, and more preferably 120 gf / g / m³ 2 The following applies: The equivalent strength per unit area is 30 gf / g / m². 2 The above is preferable from the viewpoint of suppressing film rupture due to detached active material during battery winding, and also from the viewpoint of suppressing concerns about short circuits due to the expansion and contraction of electrodes during charging and discharging. On the other hand, the basis weight equivalent strength is 200 gfg / m 2 The following is preferable from the viewpoint of reducing width shrinkage due to orientation relaxation during heating. Furthermore, the above-mentioned puncture strength equivalent to the base weight can be adjusted by adjusting the mass fraction of the plasticizer, the die lip spacing, the stretching ratio, the stretching temperature, etc.

[0061] The porosity of the polyolefin porous substrate is not particularly limited, but is preferably 20% or more, more preferably 35% or more, preferably 90% or less, more preferably 80% or less, and even more preferably 70% or less. A porosity of 20% or more is preferable from the viewpoint of ensuring the permeability of the separator. On the other hand, a porosity of 90% or less is preferable from the viewpoint of ensuring puncture resistance. Here, the porosity is measured by the method described in the examples below. Furthermore, the porosity can be adjusted by changing the stretching ratio, etc.

[0062] The air permeability of the polyolefin porous substrate is not particularly limited, but preferably, at the lower limit, it is 10 seconds / 100 cm. 3 Above, a comfortable 50 seconds / 100cm 3The above applies, and regarding the upper limit, preferably 500 seconds / 100cm. 3 Below, more comfortably, 300 seconds / 100cm 3 More preferably, 150 seconds / 100cm 3 The air permeability is 10 seconds / 100cm. 3 The above is preferable from the viewpoint of suppressing self-discharge of the energy storage device. On the other hand, the air permeability is 500 seconds / 100 cm. 3 The following is preferable from the viewpoint of obtaining good charge-discharge characteristics. Here, the air permeability is measured by the method described in the examples below. The above air permeability can be adjusted by changing the stretching temperature, stretching ratio, etc.

[0063] The average pore size of the polyolefin porous substrate is preferably 0.15 μm or less, more preferably 0.1 μm or less, and preferably 0.01 μm or more as the lower limit. Setting the average pore size to 0.15 μm or less is preferable when used as a separator for energy storage devices, from the viewpoint of suppressing self-discharge of the energy storage device, suppressing capacity degradation, and improving cycle characteristics. The average pore size can be adjusted by changing the stretching ratio when manufacturing the polyolefin porous substrate.

[0064] From the viewpoint of safety when used in batteries, the shutdown temperature of the polyolefin porous substrate is preferably 120°C or higher and 200°C or lower, more preferably 165°C or lower, and even more preferably 140°C or lower.

[0065] The short-circuit temperature, an indicator of the heat resistance of the polyolefin porous substrate, is preferably 140°C or higher, more preferably 150°C or higher, and even more preferably 160°C or higher. Setting the short-circuit temperature to 140°C or higher is preferable from the viewpoint of safety of the energy storage device when used as a separator for an energy storage device.

[0066] (Method for manufacturing a porous polyolefin substrate) The method for producing a porous polyolefin substrate is not particularly limited, and known production methods can be employed. Examples include: a method in which a polyolefin resin composition and a plasticizer are melt-kneaded together to form a sheet, which is then optionally stretched, and the plasticizer is extracted to create porosity; a method in which a polyolefin resin composition is melt-kneaded together and extruded at a high draw ratio, and then the polyolefin crystal interface is peeled off by heat treatment and stretching to create porosity; a method in which a polyolefin resin composition and an inorganic filler are melt-kneaded together to form a sheet, which is then peeled off by stretching to create porosity; and a method in which a polyolefin resin composition is dissolved, immersed in a poor solvent for polyolefin, and the polyolefin is solidified while the solvent is removed to create porosity.

[0067] The following describes an example of a method for producing a porous polyolefin substrate, which involves melt-kneading a polyolefin resin composition and a plasticizer to form a sheet, followed by the extraction of the plasticizer.

[0068] First, the polyolefin resin composition and the plasticizer are melt-kneaded. A melt-kneading method involves, for example, introducing the polyolefin resin and, if necessary, other additives into a resin mixing device such as an extruder, kneader, laboplast mill, kneading roll, or Banbury mixer, and mixing the resin components while introducing the plasticizer in a desired ratio. In this case, it is preferable to pre-mix the polyolefin resin, other additives, and plasticizer in a predetermined ratio using a Henschel mixer or the like before introducing them into the resin mixing device. More preferably, only a portion of the plasticizer is introduced during the pre-kneading, and the remaining plasticizer is mixed while feeding it to the side of the resin mixing device. This improves the dispersibility of the plasticizer, allowing the sheet-like molded product of the melt-kneaded resin composition and plasticizer to be stretched at a high magnification without film breakage during subsequent stretching processes.

[0069] As a plasticizer, a non-volatile solvent capable of forming a uniform solution above the melting point of the polyolefin can be used. Specific examples of such non-volatile solvents include hydrocarbons such as liquid paraffin and paraffin wax; esters such as dioctyl phthalate and dibutyl phthalate; and higher alcohols such as oleyl alcohol and stearyl alcohol. Among these, liquid paraffin is preferred because it has high compatibility with polyethylene or polypropylene, and interfacial delamination between the resin and plasticizer is less likely to occur even when the molten mixture is stretched, thus facilitating uniform stretching.

[0070] The ratio of polyolefin resin composition to plasticizer is not particularly limited as long as they can be uniformly melt-mixed and molded into a sheet. For example, the mass fraction of plasticizer in a composition consisting of polyolefin resin composition and plasticizer is preferably 20 to 80% by mass, more preferably 30 to 70% by mass. When the mass fraction of plasticizer is 80% by mass or less, the melt tension during melt molding is less likely to be insufficient, and moldability tends to improve. On the other hand, when the mass fraction of plasticizer is 20% by mass or more, even if the mixture of polyolefin resin composition and plasticizer is stretched at a high magnification, the polyolefin chains do not break, forming a uniform and fine pore structure and increasing strength.

[0071] Next, the molten mixture is formed into a sheet. One method for producing a sheet-shaped molded product is to extrude the molten mixture into a sheet through a T-die or the like, and then cool and solidify it by contacting it with a heat conductor to a temperature sufficiently lower than the crystallization temperature of the resin components. As the heat conductor used for cooling and solidification, metal, water, air, or the plasticizer itself can be used, but a metal roll is preferred because it has high heat conduction efficiency. In this case, when contacting the metal roll, sandwiching the mixture between the rolls is even more preferable because it further increases the efficiency of heat conduction, orients the sheet, increases film strength, and improves the surface smoothness of the sheet. The die lip spacing when extruding the mixture into a sheet from the T-die is preferably 400 μm to 3000 μm, and more preferably 500 μm to 2500 μm. When the die lip spacing is 400 μm or more, die residue and other defects that affect film quality (e.g., streaks) are reduced, and there is a tendency to prevent film breakage in the subsequent stretching process. On the other hand, when the die lip spacing is 3000 μm or less, the cooling rate is faster, uneven cooling can be prevented, and the sheet thickness stability tends to be maintained.

[0072] It is preferable to stretch the sheet-like molded article obtained in this manner. While either uniaxial stretching or biaxial stretching can be suitably used for the stretching process, biaxial stretching is preferred from the viewpoint of the strength of the resulting porous film. When the sheet-like molded article is stretched at high magnification in the biaxial direction, the molecules become oriented in the planar direction, resulting in a porous film that is less prone to tearing and possesses high puncture strength. Examples of stretching methods include simultaneous biaxial stretching, sequential biaxial stretching, multi-stage stretching, and multiple-pass stretching. Simultaneous biaxial stretching is preferred from the viewpoint of improving puncture strength, stretching uniformity, and shutdown properties.

[0073] Simultaneous biaxial stretching refers to a stretching method in which stretching in the MD direction and stretching in the TD direction are performed at the same time, and the stretching ratios in each direction may be different. Sequential biaxial stretching refers to a stretching method in which stretching in the MD direction or the TD direction is performed independently, and when stretching is performed in the MD direction or the TD direction, the other direction is in an unconstrained state or fixed to a fixed length.

[0074] The stretching ratio is preferably in the range of 20 to 100 times in terms of surface magnification, and more preferably in the range of 25 to 50 times. The stretching ratio in each axial direction is preferably in the range of 4 to 10 times in the MD direction and 4 to 10 times in the TD direction, and more preferably in the range of 5 to 8 times in the MD direction and 5 to 8 times in the TD direction. When the total area magnification is 20 times or more, the resulting porous film tends to be given sufficient strength, while when the total area magnification is 100 times or less, film breakage during the stretching process is prevented, and high productivity tends to be obtained.

[0075] The sheet-like molded body may also be rolled. Rolling can be carried out, for example, by a pressing method using a double-belt press. Rolling can particularly increase the orientation of the surface layer. The rolling surface ratio is preferably greater than 1 and 3 or less, and more preferably greater than 1 and 2 or less. When the rolling surface ratio is greater than 1, the surface orientation increases and the film strength of the resulting porous film tends to increase. On the other hand, when the rolling surface ratio is 3 or less, the difference in orientation between the surface layer and the central interior is small, and it tends to form a uniform porous structure in the thickness direction of the film, which is preferable.

[0076] Next, the plasticizer is removed from the sheet-like molded body to form a porous film. Methods for removing the plasticizer include, for example, immersing the sheet-like molded body in an extraction solvent to extract the plasticizer and then thoroughly drying it. The extraction method can be either batch or continuous. To suppress shrinkage of the porous film, it is preferable to restrain the edges of the sheet-like molded body during the immersion and drying process. Furthermore, it is preferable that the amount of plasticizer remaining in the porous film be less than 1% by mass.

[0077] It is preferable to use an extraction solvent that is a poor solvent for polyolefin resins and a good solvent for plasticizers, and whose boiling point is lower than the melting point of the polyolefin resin. Examples of such extraction solvents include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; non-chlorinated halogenated solvents such as hydrofluoroethers and hydrofluorocarbons; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; and ketones such as acetone and methyl ethyl ketone. These extraction solvents may be recovered and reused by operations such as distillation.

[0078] To suppress shrinkage of the porous membrane, heat treatment such as thermal fixation or thermal relaxation may be performed after the stretching process or after the formation of the porous membrane. Furthermore, the porous membrane may be subjected to post-treatment such as hydrophilization with surfactants or crosslinking with ionizing radiation. Post-treatment such as crosslinking with radiation may also be performed.

[0079] (Thermoplastic polymer layer) The thermoplastic polymer layer preferably has adhesive properties so that it can bond the electrode and the separator through a hot pressing process. In other words, the thermoplastic polymer layer preferably functions as an adhesive layer between the electrode and the separator.

[0080] The amount of thermoplastic polymer layer supported on the substrate (also called "coating weight") is preferably 0.02 g / m² as solid content. 2 More than 2.00g / m 2 More preferably 0.02 g / m 2 More than 1.50g / m 2 More preferably, 0.02 g / m 2 More than 1.00g / m 2 The following applies: The amount of thermoplastic polymer layer supported on the substrate is 0.02 g / m². 2 More than 2.00g / m 2Controlling the temperature within the following range is preferable from the viewpoint of suppressing a decrease in cycle characteristics (permeability) due to blockage of pores in the substrate, while further improving the adhesion between the thermoplastic polymer layer and the substrate.

[0081] The amount of thermoplastic polymer layer supported on the substrate can be adjusted, for example, by changing the thermoplastic polymer content in the coating solution or the amount of thermoplastic polymer solution applied. However, the method for adjusting the support amount is not limited to the above.

[0082] The thermoplastic polymer layer is preferably present on the surface of the substrate with a surface coverage rate of 100% or less per surface of the total surface area of ​​the substrate, more preferably 70% or less, and even more preferably 60% or less, on at least one surface of the substrate. It is also preferable that the thermoplastic polymer layer is present on the substrate with a surface coverage rate of 5% or more. Setting the surface coverage rate of the thermoplastic polymer layer to 80% or less is preferable from the viewpoint of further suppressing blockage of pores in the substrate by the thermoplastic polymer and improving the permeability of the separator. On the other hand, setting the surface coverage rate to 5% or more is preferable from the viewpoint of further improving adhesion to the electrode.

[0083] The average thickness of the thermoplastic polymer layer is preferably 0.1 to 4.0 μm or less on one side, more preferably 0.1 to 2.0 μm or less, and even more preferably 0.1 to 1.0 μm or less. An average thickness of 4.0 μm or less of the thermoplastic polymer layer is preferable from the viewpoint of suppressing the decrease in permeability due to the thermoplastic polymer and effectively suppressing adhesion between thermoplastic polymer layers or to the substrate when the separator is stored as a wound body. Furthermore, from the viewpoint of achieving both adhesion and permeability, it is preferable that the thickness corresponds to the particle size of the thermoplastic polymer used. An average thickness of 0.1 μm or more of the thermoplastic polymer layer is preferable because it easily conforms to the unevenness of the electrode active material. The average thickness of the thermoplastic polymer layer can be adjusted, for example, by changing the thermoplastic polymer content in the coating solution applied to the substrate, the amount of coating solution applied, and the coating method and conditions. However, the method for adjusting the average thickness of the thermoplastic polymer layer is not limited to these.

[0084] The thermoplastic polymer in the thermoplastic polymer layer preferably contains granular thermoplastic polymer, and more preferably substantially all of the thermoplastic polymer is granular thermoplastic polymer. The granular nature of the thermoplastic polymer tends to improve the adhesion between the separator and the electrode, as well as the handling properties of the separator.

[0085] Optionally, the thermoplastic polymer layer may contain inorganic particles in addition to the thermoplastic polymer, and may further contain a dispersant. The inorganic particles are not particularly limited, but may include, for example, inorganic fillers contained in the porous layer described later.

[0086] (Thermoplastic polymer) The thermoplastic polymer is not particularly limited, but examples include polyolefin resins such as polyethylene, polypropylene, and α-polyolefin; fluorine-based polymers such as polyvinylidene fluoride and polytetrafluoroethylene and copolymers containing these; conjugated diene polymers containing conjugated dienes such as butadiene and isoprene as monomer units, or copolymers containing these and their hydrides; acrylic resins containing acrylic acid esters, methacrylic acid esters, etc. as monomer units, or copolymers containing these and their hydrides; rubbers such as ethylene propylene rubber, polyvinyl alcohol, and polyvinyl acetate; cellulose derivatives such as ethylcellulose, methylcellulose, hydroxyethylcellulose, and carboxymethylcellulose; resins with a melting point and / or glass transition temperature of 180°C or higher, such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester, and mixtures thereof. Furthermore, monomers having a hydroxyl group, sulfonic acid group, carboxyl group, amide group, or cyano group can also be used as monomers when synthesizing thermoplastic polymers.

[0087] Of these thermoplastic polymers, at least one selected from the group consisting of conjugated diene polymers, acrylic resins, and fluoropolymers is preferred because it exhibits excellent bonding properties with electrode active materials and superior strength or flexibility. Among these, the thermoplastic polymer included as the main component of the thermoplastic polymer layer is preferably an acrylic resin, from the viewpoint of adhesion and release properties between the separator and the resin sheet, adhesion between the separator and the electrode, and bending stress of the laminate-type energy storage device.

[0088] (Diene polymer) The diene polymer is not particularly limited, but examples include polymers containing monomer units formed by polymerizing conjugated dienes having two conjugated double bonds, such as butadiene and isoprene. The conjugated diene monomer is not particularly limited, but examples include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-phenyl-1,3-butadiene, 1,3-pentadiene, 2-methyl-1,3-pentadiene, 1,3-hexadiene, 4,5-diethyl-1,3-octadiene, and 3-butyl-1,3-octadiene. These may be polymerized individually or copolymerized.

[0089] The proportion of monomer units composed of conjugated dienes in the diene polymer is not particularly limited, but for example, it is 40% by mass or more, preferably 50% by mass or more, and more preferably 60% by mass or more of the total diene polymer.

[0090] The diene polymer is not particularly limited, but examples include homopolymers of conjugated dienes such as polybutadiene and polyisoprene, and copolymers of conjugated dienes with copolymerizable monomers. The copolymerizable monomer is not particularly limited, but examples include the (meth)acrylate monomers described later, or the monomers listed below (hereinafter also referred to as "other monomers").

[0091] "Other monomers" are not particularly limited, but include, for example, α,β-unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, and fumaric acid; styrene monomers such as styrene, chlorostyrene, vinyltoluene, t-butylstyrene, vinylbenzoic acid, methyl vinylbenzoate, vinylnaphthalene, chloromethylstyrene, hydroxymethylstyrene, α-methylstyrene, and divinylbenzene; olefins such as ethylene and propylene; halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl benzoate; methyl vinyl ether and ethyl vinyl ether Examples include vinyl ethers such as butyl vinyl ether; vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; heterocyclic vinyl compounds such as N-vinylpyrrolidone, vinylpyridine, and vinylimidazole; acrylic acid esters and / or methacrylic acid ester compounds such as methyl acrylate and methyl methacrylate; hydroxyalkyl group-containing compounds such as β-hydroxyethyl acrylate and β-hydroxyethyl methacrylate; and amide monomers such as acrylamide, N-methylolacrylamide, and acrylamide-2-methylpropanesulfonic acid. These may be used individually or in combination of two or more.

[0092] (Acrylic resin) The acrylic resin is not particularly limited, but is preferably a copolymer containing monomer units composed of (meth)acrylate monomers.

[0093] In this specification, "(meth)acrylic acid" refers to "acrylic acid or methacrylic acid," and "(meth)acrylate" refers to "acrylate or methacrylate."

[0094] (Meth)acrylate monomers are not particularly limited, but examples include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate. Examples include alkyl(meth)acrylates such as acrylate, lauryl(meth)acrylate, n-tetradecyl(meth)acrylate, and stearyl(meth)acrylate; hydroxyl group-containing(meth)acrylates such as hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate, and hydroxybutyl(meth)acrylate; amino group-containing(meth)acrylates such as aminoethyl(meth)acrylate; and epoxy group-containing(meth)acrylates such as glycidyl(meth)acrylate.

[0095] The proportion of monomer units composed of (meth)acrylate monomers is not particularly limited, but is, for example, 40% by mass or more, preferably 50% by mass or more, and more preferably 60% by mass or more, based on the mass of the total acrylic polymer. Examples of acrylic polymers include homopolymers of (meth)acrylate monomers and copolymers of these with copolymerizable monomers.

[0096] Examples of copolymerizable monomers include the "other monomers" listed in the section on diene polymers above, and these may be used individually or in combination of two or more.

[0097] (Fluorine-based polymer) The fluorinated polymer is not particularly limited, but examples include homopolymers of vinylidene fluoride and copolymers of vinylidene fluoride and monomers copolymerizable therewith. Fluorinated polymers are preferred from the viewpoint of electrochemical stability.

[0098] The proportion of monomer units composed of vinylidene fluoride is not particularly limited, but is, for example, 40% by mass or more, preferably 50% by mass or more, and more preferably 60% by mass or more, based on the total mass of monomers forming the fluorine-based polymer.

[0099] Monomers copolymerizable with vinylidene fluoride are not particularly limited, but examples include fluorine-containing ethylenically unsaturated compounds such as vinyl fluoride, tetrafluoroethylene, trifluorochloroethylene, hexafluoropropylene, hexafluoroisobutylene, perfluoroacrylic acid, perfluoromethacrylic acid, and fluoroalkyl esters of acrylic acid or methacrylic acid; fluorine-free ethylenically unsaturated compounds such as cyclohexyl vinyl ether and hydroxyethyl vinyl ether; and fluorine-free diene compounds such as butadiene, isoprene, and chloroprene.

[0100] Among fluorinated polymers, homopolymers of vinylidene fluoride, vinylidene fluoride / tetrafluoroethylene copolymers, and vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymers are preferred. Particularly preferred fluorinated polymers are vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymers, whose monomer composition is typically 30-90% by mass of vinylidene fluoride, 9-50% by mass of tetrafluoroethylene, and 1-20% by mass of hexafluoropropylene. These fluororesin particles may be used individually or in mixtures of two or more types.

[0101] Furthermore, monomers having a hydroxyl group, carboxyl group, amino group, sulfonic acid group, amide group, or cyano group can also be used as monomers when synthesizing the above thermoplastic polymer.

[0102] The monomer having a hydroxyl group is not particularly limited, but examples include vinyl monomers such as pentenol.

[0103] The monomers having a carboxyl group are not particularly limited, but examples include unsaturated carboxylic acids having an ethylenic double bond, such as (meth)acrylic acid and itaconic acid, and vinyl monomers such as pentenoic acid.

[0104] The monomer having an amino group is not particularly limited, but examples include 2-aminoethyl methacrylate.

[0105] The monomers having a sulfonic acid group are not particularly limited, but examples include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)alisulfonic acid, styrene sulfonic acid, ethyl (meth)acrylate-2-sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, and 3-alyloxy-2-hydroxypropanesulfonic acid.

[0106] The monomer having an amide group is not particularly limited, but examples include acrylamide, methacrylamide, N-methylolacrylamide, and N-methylolmethacrylamide.

[0107] The monomer having a cyano group is not particularly limited, but examples include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, and α-cyanoethyl acrylate.

[0108] Thermoplastic polymers may be used individually or as a mixture of two or more polymers, but it is preferable that they contain two or more polymers.

[0109] Thermoplastic polymers have a glass transition temperature of less than 100°C, and this glass transition temperature is preferably 40°C or higher from the viewpoint of suppressing the blocking phenomenon between separators. Here, the glass transition temperature is determined from the DSC curve obtained by differential scanning calorimetry (DSC). In this specification, the glass transition temperature may also be expressed as Tg. Specifically, it is determined by the intersection of a straight line extending the baseline on the low-temperature side of the DSC curve toward the high-temperature side, and a tangent line at the inflection point of the stepwise transition portion of the glass transition. For more details, refer to the method described in the examples.

[0110] Here, "glass transition" refers to the endothermic change in heat energy associated with the state change of the polymer specimen in DSC. Such a heat energy change is observed in the DSC curve as a step-like change or a shape that combines a step-like change with a peak.

[0111] A "step-like change" in a DSC curve refers to the portion where the curve deviates from the previous baseline and transitions to a new baseline. This also includes shapes that combine peaks and step-like changes.

[0112] An "inflection point" is the point in the stepwise transition section where the gradient of the DSC curve is at its maximum. It can also be described as the point in the stepwise transition section where an upward-convex curve changes to a downward-convex curve.

[0113] A "peak" in a DSC curve refers to the portion of the curve that moves away from the baseline and then returns to the baseline.

[0114] "Baseline" refers to the DSC curve in the temperature range where no transitions or reactions occur in the test specimen.

[0115] When the thermoplastic polymer is granular, it is preferable that at least one of the glass transition temperatures of the granular thermoplastic polymer is in the region of 40°C or higher when measured by differential scanning calorimetry.

[0116] In order to suppress the blocking phenomenon between separators, it is preferable that the glass transition temperature, which exists in the region above 40°C, exists only in the region between 45°C and 100°C.

[0117] The glass transition temperature of the thermoplastic polymer may be in the range below 40°C or in the range above 40°C. A glass transition temperature of 40°C or higher results in superior adhesion and handling between the separator and the electrode. Furthermore, it can enhance the adhesion between the electrode and the separator that develops under pressure during battery fabrication.

[0118] A thermoplastic polymer may have two glass transition temperatures, one below 40°C and the other above 40°C. This can be achieved by methods such as blending two or more thermoplastic polymers, or by using a thermoplastic polymer having a core-shell structure. A core-shell structure is a polymer in the form of a double structure, where the composition of the polymer belonging to the central part and the polymer belonging to the outer shell are different.

[0119] Polymer blends or core-shell structures allow for control of the overall glass transition temperature of a thermoplastic polymer by combining polymers with high and low glass transition temperatures, and also allow for the imparting of multiple functions to the thermoplastic polymer as a whole. For example, in the case of polymer blends, blending two or more polymers, particularly those with glass transition temperatures above 40°C and those with glass transition temperatures below 40°C, is preferable from the viewpoint of achieving both resistance to stickiness and wettability to polyolefin porous substrates. In the case of core-shell structures, the adhesion or compatibility to other materials such as polyolefin porous substrates can be adjusted by changing the composition of the outer shell polymer, and by adjusting the polymer belonging to the central part, for example, adhesion to electrodes after hot pressing can be improved. Furthermore, viscoelasticity can be controlled by combining highly viscous polymers with highly elastic polymers.

[0120] The glass transition temperature (Tg) of a thermoplastic polymer can be adjusted as appropriate, for example, by changing the monomer components used to produce the thermoplastic polymer and the input ratio of each monomer. That is, it can be roughly estimated from the Tg of the homopolymer of each monomer used in the production of the thermoplastic polymer (for example, as described in "Polymer Handbook" (A WILEY-INTERSCIENCE PUBLICATION)) and the blending ratio of the monomers. For example, copolymers blended in high proportions of monomers such as styrene, methyl methacrylate, and acrylonitrile, which give polymers with a Tg of about 100°C, have a high Tg. For example, copolymers blended in high proportions of monomers such as butadiene, which gives polymers with a Tg of about -80°C, and n-butyl acrylate and 2-ethylhexyl acrylate, which give polymers with a Tg of about -50°C, have a low Tg.

[0121] The Tg of a polymer can be estimated using FOX's formula (Equation (1) below). The glass transition temperature of the thermoplastic polymer in this application is determined by the method using DSC described above. 1 / Tg = W1 / Tg1 + W2 / Tg2 + ... + W i / Tg i +‥‥W n / Tg n (1) (In formula (1), Tg(K) is the Tg of the copolymer, Tg i (K) is the Tg and W of the homopolymer of each monomer i. i (These figures represent the mass fraction of each monomer.)

[0122] The thermoplastic polymer is preferably a granular thermoplastic polymer in which at least a portion of the polymer is in the form of granules.

[0123] One method for producing granular thermoplastic polymers involves first synthesizing a thermoplastic polymer, using it as a seed, and then adding monomers, initiators, etc. This allows the thermoplastic polymer to be formed into granules, and also increases the particle size of the thermoplastic polymer. Using such granular thermoplastic polymers tends to improve the adhesion between the separator and the electrode, as well as the handling properties of the separator. Here, the area of ​​the granular thermoplastic polymer is measured by observing the outermost surface of the separator with a scanning electron microscope (magnification 30,000x), as described in the examples below.

[0124] The average particle size of the granular thermoplastic polymer is preferably 10 nm or more and less than 10,000 nm, and more preferably 100 nm or more and less than 2,000 nm. A particle size of 10 nm or more is preferable because it ensures a particle size that prevents the thermoplastic polymer from penetrating the pores of the substrate when the granular thermoplastic polymer is coated onto the polyolefin porous film substrate, while a particle size of less than 10,000 nm is preferable from the viewpoint of adhesion between the separator and the electrode.

[0125] (Method for forming a thermoplastic polymer layer) The method for forming a thermoplastic polymer layer on a polyolefin porous substrate is not particularly limited, and known methods may be employed. Examples of methods for forming the thermoplastic polymer layer include applying a coating solution containing a thermoplastic polymer to the polyolefin porous substrate, and co-extrusion lamination of a resin composition for constituting the polyolefin porous substrate and a thermoplastic polymer-containing resin composition. From the viewpoint of suppressing or preventing foreign matter contamination of the separator and thereby reducing manufacturing costs, it is preferable not to use a transfer method.

[0126] The method for applying a coating solution containing a thermoplastic polymer to a porous film is not particularly limited as long as it can achieve the required layer thickness or coating area. Examples include gravure coater, small-diameter gravure coater, reverse roll coater, transfer roll coater, kiss coater, dip coater, knife coater, air doctor coater, blade coater, rod coater, squeeze coater, cast coater, die coater, screen printing, spray coating, spray coater coating, and inkjet coating. Of these, the gravure coater or spray coating method is preferred because it offers a high degree of freedom in the coating shape of the thermoplastic polymer and allows for easy acquisition of a desirable area ratio.

[0127] A poor solvent for a thermoplastic polymer is preferred as the medium for the coating solution. When a poor solvent for a thermoplastic polymer is used as the medium for the coating solution, it is possible to effectively prevent the coating solution from penetrating into the interior of a porous polyolefin substrate and filling the surface and interior of the pores with the thermoplastic polymer, thereby reducing permeability. Water is preferred as such a medium. Other media that can be used in combination with water are not particularly limited, but examples include ethanol and methanol. The coating solution or thermoplastic polymer-containing resin composition may optionally contain inorganic particles, dispersants, etc., in addition to the thermoplastic polymer and medium.

[0128] Prior to coating, surface treatment of the porous film surface is preferable because it facilitates the application of the coating solution and improves the adhesion between the porous layer and the adhesive polymer. The surface treatment method is not particularly limited as long as it does not significantly impair the porous structure of the porous film, and examples include corona discharge treatment, plasma treatment, mechanical roughening, solvent treatment, acid treatment, and ultraviolet oxidation.

[0129] Regarding the method for removing the solvent from the coated film after coating, there are no particular limitations as long as it does not adversely affect the porous film. For example, methods include drying at a temperature below the melting point while fixing the porous film, drying under reduced pressure at low temperatures, and immersing the adhesive polymer in a poor solvent to solidify the adhesive polymer while simultaneously extracting the solvent.

[0130] (porous layer) The separator for the energy storage device may include, in addition to the polyolefin porous substrate and thermoplastic polymer layer, a porous layer containing an inorganic or organic filler and a resin binder. The location of the porous layer may be at least a portion of the surface of the polyolefin porous substrate, at least a portion of the surface of the thermoplastic polymer layer, and / or between the polyolefin porous substrate and the thermoplastic polymer layer. The porous layer may be provided on one side or both sides of the polyolefin porous substrate.

[0131] (Inorganic filler) While there are no particular limitations on the inorganic filler used in the porous layer, it is preferable to use one that has a melting point of 200°C or higher, high electrical insulation properties, and is electrochemically stable within the operating range of lithium-ion secondary batteries.

[0132] Inorganic fillers are not particularly limited, but examples include oxide ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; nitride ceramics such as silicon nitride, titanium nitride, and boron nitride; silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum hydroxide oxide, potassium titanate, talc, kaolinite, decite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, silica sand, and glass fibers. These may be used individually or in combination.

[0133] Among the above, aluminum oxide compounds such as alumina and aluminum hydroxide oxide; or aluminum silicate compounds that do not have ion exchange capacity, such as kaolinite, decite, nacrite, halloysite, and pyrophyllite, are preferred from the viewpoint of improving electrochemical stability and the heat resistance of multilayer porous films. Among the aluminum oxide compounds, aluminum hydroxide oxide is particularly preferred. As for aluminum silicate compounds that do not have ion exchange capacity, kaolin, which is mainly composed of kaolin minerals, is more preferred because it is inexpensive and readily available. Kaolin includes wet kaolin and calcined kaolin obtained by calcining wet kaolin, but calcined kaolin is particularly preferred in terms of electrochemical stability because crystal water is released during the calcination process and impurities are removed.

[0134] (Organic filler) Examples of organic fillers include various cross-linked polymer microparticles such as cross-linked polyacrylic acid, cross-linked polyacrylic acid esters, cross-linked polymethacrylic acid, cross-linked polymethacrylic acid esters, cross-linked polymethyl methacrylate, cross-linked polysilicone (polymethylsilsesquioxane, etc.), cross-linked polystyrene, cross-linked polydivinylbenzene, styrene-divinylbenzene copolymer cross-linked products, polyimide, polyamide-imide, melamine resin, phenol resin, and benzoguanamine-formaldehyde condensate; and heat-resistant polymer microparticles such as polysulfone, polyacrylonitrile, aramid, polyacetal, and thermoplastic polyimide. Furthermore, the organic resin (polymer) constituting these organic microparticles may be a mixture of the above-mentioned materials, a modified product, a derivative, a copolymer (random copolymer, alternating copolymer, block copolymer, graft copolymer), or a cross-linked product (in the case of the heat-resistant polymer mentioned above). Among these, it is preferable that the resin is one or more resins selected from the group consisting of cross-linked polyacrylic acid, cross-linked polyacrylic acid ester, cross-linked polymethacrylic acid, cross-linked polymethacrylic acid ester, cross-linked polymethyl methacrylate, and cross-linked polysilicone (such as polymethylsilsesquioxane), polyimide, polyamideimide, and aramid.

[0135] The average particle size of the filler is preferably greater than 0.1 μm and 4.0 μm or less, more preferably greater than 0.2 μm and 3.5 μm or less, and even more preferably greater than 0.4 μm and 3.0 μm or less. Adjusting the average particle size of the filler to the above range is preferable from the viewpoint of suppressing thermal shrinkage at high temperatures, even when the thickness of the porous layer is thin (for example, 7 μm or less).

[0136] In the filler, the proportion of particles having a particle size greater than 0.2 μm and less than or equal to 1.4 μm in the total filler is preferably 2 volume% or more, more preferably 3 volume% or more, and even more preferably 5 volume% or more, with an upper limit of preferably 90 volume% or less, and more preferably 80 volume% or less.

[0137] In the filler, the proportion of particles having a particle size greater than 0.2 μm and less than or equal to 1.0 μm in the total inorganic filler is preferably 1 volume% or more, more preferably 2 volume% or more, and the upper limit is preferably 80 volume% or less, more preferably 70 volume% or less.

[0138] In the filler, the proportion of particles having a particle size greater than 0.5 μm and less than or equal to 2.0 μm in the total filler is preferably 8 volume% or more, more preferably 10 volume% or more, and the upper limit is preferably 60 volume% or less, more preferably 50 volume% or less.

[0139] Furthermore, in the filler, the proportion of particles having a particle size greater than 0.6 μm and less than or equal to 1.4 μm in the total filler is preferably 1 volume% or more, more preferably 3 volume% or more, and the upper limit is preferably 40 volume% or less, more preferably 30 volume% or less.

[0140] Adjusting the particle size distribution of the filler to the above range is preferable from the viewpoint of suppressing thermal shrinkage at high temperatures, even when the thickness of the porous layer is thin (for example, 7 μm or less). As a method for adjusting the proportion of filler particle sizes, for example, one can reduce the particle size by crushing the inorganic filler using a ball mill, bead mill, jet mill, etc.

[0141] The filler can take various shapes, including plate-like, flake-like, needle-like, columnar, spherical, polyhedral, and lumpy forms, and multiple types of fillers having these shapes may be used in combination. When a multilayer porous membrane is formed, the shape of the filler is not particularly limited as long as it is possible to suppress the 150°C thermal shrinkage described later to 10% or less, but from the viewpoint of improving permeability, polyhedral, columnar, and spindle-shaped fillers consisting of multiple faces are preferred.

[0142] The proportion of filler in the porous layer can be appropriately determined from the viewpoint of filler binding properties, permeability and heat resistance of the multilayer porous film, and is preferably 50% by mass or more and less than 100% by mass, more preferably 70% by mass or more and 99.99% by mass or less, even more preferably 80% by mass or more and 99.9% by mass or less, and particularly preferably 90% by mass or more and 99% by mass or less.

[0143] (Resin binder) While there are no particular limitations on the type of resin binder, when using a separator for energy storage devices as a separator for lithium-ion secondary batteries, it is preferable to use one that is insoluble in the electrolyte of the lithium-ion secondary battery and electrochemically stable within the operating range of the lithium-ion secondary battery.

[0144] Specific examples of resin binders include, for example, polyolefins such as polyethylene and polypropylene; fluororesins such as polyvinylidene fluoride and polytetrafluoroethylene; fluororubbers such as vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer; rubbers such as styrene-butadiene copolymer and its hydride, acrylonitrile-butadiene copolymer and its hydride, acrylonitrile-butadiene-styrene copolymer and its hydride, methacrylic acid ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer, ethylene propylene rubber, polyvinyl alcohol, and polyvinyl acetate; cellulose derivatives such as ethylcellulose, methylcellulose, hydroxyethylcellulose, and carboxymethylcellulose; and resins with a melting point and / or glass transition temperature of 180°C or higher, such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester.

[0145] When polyvinyl alcohol is used as a resin binder, its degree of saponification is preferably 85% to 100%. A degree of saponification of 85% or higher is preferable because, when the multilayer porous membrane is used as a battery separator, the short-circuit temperature is improved, and better safety performance tends to be obtained. More preferably, the degree of saponification is 90% to 100%, even more preferably 95% to 100%, and particularly preferably 99% to 100%. Furthermore, the degree of polymerization of the polyvinyl alcohol is preferably 200 to 5000, more preferably 300 to 4000, and even more preferably 500 to 3500. A degree of polymerization of 200 or higher is preferable because, with a small amount of polyvinyl alcohol, inorganic fillers such as calcined kaolin can be firmly bonded to the porous membrane, and the increase in air permeability of the multilayer porous membrane due to the formation of the porous layer tends to be suppressed while maintaining the mechanical strength of the porous layer. Furthermore, a degree of polymerization of 5000 or less is preferable because it tends to prevent gelation and other issues when preparing the coating solution.

[0146] As the resin binder, a resin latex binder is preferred. When a resin latex binder is used, if a porous layer containing the filler and binder is laminated on at least one side of a polyolefin porous membrane, the ion permeability tends to decrease less and high power characteristics tend to be easier to obtain compared to the case where part or all of the resin binder is dissolved in a solvent, the resulting solution is laminated on at least one side of the polyolefin porous membrane, and the resin binder is bound to the porous membrane by solvent removal such as immersion in a poor solvent or drying. In addition, even when the temperature rises rapidly during abnormal heat generation, it tends to exhibit smooth shutdown characteristics and a high level of safety tends to be easily obtained.

[0147] As for the resin latex binder, from the viewpoint of improving electrochemical stability and binding properties, it is preferable to obtain one obtained by emulsion polymerization of aliphatic conjugated diene monomers, unsaturated carboxylic acid monomers, and other monomers copolymerizable with these. There are no particular restrictions on the emulsion polymerization method, and conventionally known methods can be used. There are no particular restrictions on the method of adding monomers and other components, and any of the methods such as batch addition, divided addition, or continuous addition can be employed, and any of the methods such as one-step polymerization, two-step polymerization, or multi-step polymerization can be employed.

[0148] The aliphatic conjugated diene monomers are not particularly limited and include, for example, 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chlor-1,3-butadiene, substituted linear conjugated pentadienes, substituted and side-chain conjugated hexadienes, etc. These may be used individually or in combination of two or more. Among the above, 1,3-butadiene is particularly preferred.

[0149] The unsaturated carboxylic acid monomer is not particularly limited and includes, for example, mono- or dicarboxylic acids (anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid. These may be used individually or in combination of two or more. Among the above, acrylic acid and methacrylic acid are particularly preferred.

[0150] Other monomers copolymerizable with these are not particularly limited and include, for example, aromatic vinyl monomers, vinyl cyanide monomers, unsaturated carboxylate alkyl ester monomers, unsaturated monomers containing hydroxyalkyl groups, and unsaturated carboxylate amide monomers. These may be used individually or in combination of two or more. Among these, unsaturated carboxylate alkyl ester monomers are particularly preferred. Unsaturated carboxylate alkyl ester monomers are not particularly limited and include, for example, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate, monomethyl fumarate, monoethyl fumarate, and 2-ethylhexyl acrylate. These may be used individually or in combination of two or more. Among these, methyl methacrylate is particularly preferred.

[0151] In addition to these monomers, other monomer components may be used to further improve various qualities and physical properties.

[0152] The average particle size of the resin binder is preferably 50 to 500 nm, more preferably 60 to 460 nm, and even more preferably 80 to 250 nm. When the average particle size of the resin binder is 50 nm or more, when a porous layer containing inorganic filler and binder is laminated on at least one side of a polyolefin porous film, ion permeability does not easily decrease, and high power characteristics are easily obtained. In addition, even when the temperature rises rapidly during abnormal heat generation, it exhibits smooth shutdown characteristics, and high safety is easily obtained. When the average particle size of the resin binder is 500 nm or less, good bonding properties are observed, and when a multilayer porous film is formed, thermal shrinkage is good, and safety tends to be superior.

[0153] The average particle size of a resin binder can be controlled by adjusting the polymerization time, polymerization temperature, raw material composition ratio, raw material input order, pH, etc.

[0154] The thickness of the porous layer is preferably 1 μm or more from the viewpoint of improving heat resistance and insulation, and preferably 50 μm or less from the viewpoint of increasing the battery capacity and improving permeability. More preferably, the thickness of the porous layer is 1.5 μm to 20 μm, even more preferably 2 μm to 10 μm, even more preferably 3 μm to 10 μm, and particularly preferably 3 μm to 7 μm.

[0155] The layer density of the porous layer is 0.5 to 2.0 g / cm³. 3 Preferably, 0.7 to 1.5 cm 3 It is more preferable that the layer density of the porous layer be 0.5 g / cm³. 3 If the value is above this, the thermal shrinkage rate at high temperatures tends to be good, and 2.0 g / cm² is the standard. 3 The following conditions tend to result in decreased air permeability.

[0156] (Method for forming a porous layer) One method for forming a porous layer is to apply a coating solution containing an inorganic filler and a resin binder to at least one side of a porous substrate mainly composed of polyolefin resin to form a porous layer.

[0157] The solvent for the coating solution is preferably one that can uniformly and stably disperse the inorganic filler and resin binder. Examples include N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, water, ethanol, toluene, hot xylene, methylene chloride, and hexane.

[0158] Various additives such as dispersants (including surfactants), thickeners, wetting agents, defoamers, and pH adjusters (including acids and alkalis) may be added to the coating solution to stabilize dispersion or improve coating properties. While it is preferable that these additives can be removed during solvent removal, they may remain in the porous layer if they are electrochemically stable within the operating range of lithium-ion secondary batteries, do not inhibit the battery reaction, and are stable up to approximately 200°C.

[0159] The method for dispersing the filler and resin binder in the solvent of the coating solution is not particularly limited as long as it can achieve the dispersion characteristics of the coating solution required for the coating process. Examples include ball mills, bead mills, planetary ball mills, vibrating ball mills, sand mills, colloid mills, attritors, roll mills, high-speed impeller dispersion, dispersers, homogenizers, high-speed impact mills, ultrasonic dispersion, and mechanical stirring using stirring blades, etc.

[0160] The method for applying the coating solution to the porous film is not particularly limited as long as it can achieve the required layer thickness or coating area. Examples include gravure coater, small-diameter gravure coater, reverse roll coater, transfer roll coater, kiss coater, dip coater, knife coater, air doctor coater, blade coater, rod coater, squeeze coater, cast coater, die coater, screen printing, and spray coating.

[0161] Applying a surface treatment to the porous film surface prior to applying the coating solution is preferable because it facilitates the application of the coating solution and improves the adhesion between the inorganic filler-containing porous layer and the porous film surface after coating. The surface treatment method is not particularly limited as long as it does not significantly impair the porous structure of the porous film, and examples include corona discharge treatment, mechanical roughening, solvent treatment, acid treatment, and ultraviolet oxidation.

[0162] Regarding the method for removing the solvent from the coated film after coating, there are no particular limitations as long as it does not adversely affect the porous film. Examples include drying the porous film at a temperature below its melting point while fixing it in place, or drying it under reduced pressure at a low temperature. From the viewpoint of controlling the shrinkage stress in the MD direction of the porous film and multilayer porous film, it is preferable to appropriately adjust the drying temperature, winding tension, etc.

[0163] (Physical properties and applications of separators) From the viewpoint of the characteristics of an energy storage device including a separator for energy storage devices, the adhesive strength between the separator and the electrode in a dry state is preferably 1.0 N / m or more, more preferably 2.0 N / m or more, even more preferably 5.0 N / m or more, and particularly preferably 9.8 N / m or more. The dry electrode used to measure the adhesive strength may be the positive or negative electrode of the energy storage device as described later, and the side of the electrode with the active material layer may be used for measurement, or a current collector such as aluminum foil or copper foil may be used as a substitute. It is preferable to measure the adhesive strength between the outermost surface where the thermoplastic polymer layer of the separator exists and the electrode in a dry state. The adhesive strength in a dry state here refers to the peel strength between the separator and the electrode or its substitute after the separator and electrode are laminated or pressed together and maintained for 3 minutes under conditions of 80°C and 1 MPa pressure.

[0164] The minimum smoothness value of the back surface of the separator for energy storage devices is 10000. seconds It is preferable that the separator is in the upper position. When the separator is laminated or wound together with the resin sheet, it is clear from the sheet form that the separator has a front surface and a back surface. Although we do not wish to be bound by theory, it can be inferred that if the smoothness of the separator satisfies the above conditions, air will escape more easily from the wound or laminate of the separator and resin sheet, and wrinkles will be less likely to remain on the separator. Here, the back surface refers to one side of the separator (for example, the side that is exposed on the outside in the form of the wound body) and the other side (for example, the side that is facing inward in the form of the wound body).

[0165] The thickness of the separator for energy storage devices (i.e., the total thickness of the separator including the polyolefin porous substrate, thermoplastic polymer layer, and any porous layer) is preferably 2 μm or more, more preferably 5 μm or more, with an upper limit of preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 30 μm or less. A thickness of 2 μm or more is preferable from the viewpoint of ensuring the strength of the separator for energy storage devices. On the other hand, a thickness of 100 μm or less is preferable from the viewpoint of obtaining good charge and discharge characteristics.

[0166] The upper limit of the air permeability of separators for energy storage devices is 200 seconds / 100 cm. 3 The following is preferable. Although we do not wish to be bound by theory, if the air permeability of the separator is within the above numerical range, air will escape more easily from the rolled or laminated body of the separator and resin sheet, and wrinkles will be less likely to remain in the separator, thus improving the quality of the separator and, consequently, the characteristics of the energy storage device including the separator. The lower limit of the air permeability of the separator is preferably 10 seconds / 100 cm from the viewpoint of suppressing self-discharge of the energy storage device including the separator. 3 Above, a comfortable 50 seconds / 100cm 3 That concludes the explanation. The air permeability of the separator can be adjusted by changing the stretching temperature and stretching ratio during the production of the polyolefin porous substrate, the area ratio of the thermoplastic polymer, its form, etc.

[0167] The puncture strength of the separator for energy storage devices is not particularly limited, but the lower limit is preferably 50 gf or more, more preferably 100 gf or more, and even more preferably 130 gf or more, and the upper limit is preferably 1000 gf or less, more preferably 800 gf or less, and even more preferably 600 gf or less. A puncture strength of 50 gf or more is preferable from the viewpoint of suppressing film rupture due to detached active material during battery winding, and also from the viewpoint of suppressing concerns about short circuits due to the expansion and contraction of electrodes accompanying charging and discharging. On the other hand, a puncture strength of 1000 gf or less is preferable from the viewpoint of reducing width shrinkage due to orientation relaxation during heating. The puncture strength mentioned above can be adjusted by controlling the stretching temperature and stretching ratio during the manufacturing of the porous polyolefin substrate.

[0168] The MD tensile modulus of the separator for energy storage devices is not particularly limited, but from the viewpoint of stabilizing the feed rate when the separator is slit, 1000 kgf / cm² is preferred. 2 More than 20000kgf / cm 2 Preferably, it is 1200 kgf / cm². 2More than 15000kgf / cm 2 It is more preferable that the following conditions are met: 1500 kgf / cm² 2 More than 10000kgf / cm 2 The following is even more preferable: Furthermore, the above-mentioned MD tensile modulus can be adjusted by adjusting the stretching temperature and stretching ratio when manufacturing the porous polyolefin substrate.

[0169] The MD and TD thermal shrinkage rates of the separator for energy storage devices at 120°C are not particularly limited, but from the viewpoint of suppressing the shrinkage of the separator and short-circuiting when the battery heats up, which can lead to thermal runaway of the battery, and from the viewpoint of suppressing the deformation and blocking of the separator laminate and winding body having a thermoplastic polymer layer over time during storage and transport, it is preferable that both the MD and TD are 20% or less and 0% or more, more preferably 18% or less and 0% or more, and even more preferably 15% or less and 0% or more. Furthermore, the MD and TD heat shrinkage rates at 120°C can be adjusted by controlling the stretching temperature, stretching ratio, and heat-fixing temperature during the manufacturing of the polyolefin porous substrate.

[0170] The separator for energy storage devices has a short-circuit temperature, which is an indicator of heat resistance, preferably 140°C or higher, more preferably 150°C or higher, and even more preferably 160°C or higher. A short-circuit temperature of 160°C or higher is preferable from the viewpoint of safety of the energy storage device when used as a separator for energy storage devices.

[0171] The separator for energy storage devices offers excellent handling during winding and rate characteristics for energy storage devices, as well as superior adhesion and permeability between the thermoplastic polymer and the polyolefin porous substrate. Therefore, while the applications of the separator for energy storage devices are not particularly limited, it can be suitably used, for example, as a separator for batteries such as non-aqueous electrolyte secondary batteries, or for energy storage devices such as capacitors, and for separating substances.

[0172] <Resin sheet> The resin sheet contains resin as the main component and has an MD tensile modulus of 1000 kgf / cm 2 or more and 15000 kgf / cm 2 or less. The resin sheet can partially constitute the wound body according to the first embodiment and the laminate according to the second embodiment, or can be provided as the resin sheet according to the third embodiment, or can be used for the transportation and / or storage method of the separator for the power storage device according to the fourth embodiment.

[0173] The resin sheet according to the third embodiment is used when transporting a separator having a thermoplastic polymer layer containing a thermoplastic polymer disposed on at least a part of at least one side of a base material. The MD tensile modulus of the resin sheet is 1000 kgf / cm 2 or more and 15000 kgf / cm 2 or less, and is configured such that the ratio (MD tensile modulus セパレータ / MD tensile modulus 樹脂シート ) is in the relationship of 0.35 or more and 10.0 or less.

[0174] When the MD tensile modulus of the resin sheet is 1000 kgf / cm 2 or more and 15000 kgf / cm 2 or less, and the ratio (MD tensile modulus セパレータ / MD tensile modulus 樹脂シート ) is in the relationship of 0.35 or more and 10.0 or less, when winding the resin sheet and the separator, the influence of TD shrinkage (Poisson deformation) of the resin sheet due to tension can be eliminated or reduced.

[0175] The resin sheet according to the third embodiment has 1000 kgf / cm 2 ≤ MD tensile modulus 樹脂シート ≤ 15000 kgf / cm 2 , and 0.35 ≤ MD tensile modulus セパレータ / MD tensile modulus 樹脂シートSince it is configured to satisfy the relationship of ≦10.0, blocking can be suppressed or prevented during the transportation of the separator having adhesiveness by the thermoplastic polymer layer over a long period of time, for example, over a period of 1 hour or more and 1000 days or less, preferably 365 days or less. As a result, the quality of the separator can be maintained when the separator is slit, and the device characteristics of the power storage device including the separator can be ensured or improved.

[0176] In addition to the above viewpoints, from the viewpoint of stabilizing the unwindability when the separator is slit, the MD tensile modulus of the resin sheet is 1100 kgf / cm 2 or more and 14000 kgf / cm 2 or less, preferably 1200 kgf / cm 2 or more and 13000 kgf / cm 2 or less, and / or the ratio (MD tensile modulus セパレータ / MD tensile modulus 樹脂シート ) preferably satisfies the relationship of 0.40 or more and 9.5 or less, and more preferably 0.45 or more and 9.0 or less.

[0177] From the viewpoint of peeling the separator from the wound body or laminate of the separator and the resin sheet after the transportation and / or storage of the separator, a resin sheet having a peel strength between the separator for the power storage device and the resin sheet of 0.1 N / m or more and 10.0 N / m or less is preferable.

[0178] The specific gravity of the resin constituting the resin sheet is preferably close to the specific gravity of the resin constituting the separator. Adjusting the specific gravities of the resin sheet and the separator as described above facilitates the setting of the tension during winding of the separator and the resin sheet, and tends to improve the separator quality during slitting.

[0179] The resins that make up the resin sheet are not limited to those mentioned above, but examples include polyethylene terephthalate (PET), polyethylene terephthalate, cellulose acetate, polystyrene, polyphenylene ether, polyethylene, polypropylene, polyamide, polyetherimide, polysulfone, and polyphenylene sulfide. Of these, at least one selected from the group consisting of PET, polyethylene, and polypropylene is preferred from the viewpoint of having appropriate rigidity and being less prone to wrinkling when manufacturing laminates or wound bodies.

[0180] From the same viewpoint as above, oriented polypropylene (OPP) is preferred as the polypropylene. In particular, OPP has a low specific gravity, which is close to the specific gravity of the resin component in the separator, and a moderately high MD tensile modulus, which makes it easy to set the tension when winding the OPP-containing resin sheet and separator, and tends to result in good separator quality when slit. Resin sheets containing or made of OPP can be manufactured, for example, by biaxial stretching of raw material PP.

[0181] The thickness of the resin sheet is preferably between 5 μm and 50 μm. A thickness of 5 μm or more makes it easier to obtain sufficient flatness. Furthermore, if the thickness of the resin sheet is 50 μm or less, the bulk of the wound material is less likely to become excessively large, and costs can be kept down.

[0182] The basis weight of the resin sheet should be 1.0 g / m² at the lower limit, from the viewpoint of transporting and / or storing separators for energy storage devices that use resin sheets. 2 Preferably, it should be 3.0 g / m 2 It is more preferable that the amount be greater than or equal to 5.0 g / m 2 It is even more preferable that it be greater than or equal to 100.0 g / m², and the upper limit is 100.0 g / m². 2 Preferably, it is 75.0 g / m². 2 Preferably, it is 50.0 g / m 2 The following is preferable:

[0183] From the same perspective as above, the puncture strength of the resin sheet, calculated based on its basis weight, is 50 gf / g / m². 2 Preferably, it is 52 gf / g / m 2 More than 100gf / g / m 2 It is more preferable that the following conditions apply: 60 gf / g / m³ 2 It is even more preferable that the above conditions are met. Also, from a similar viewpoint, it is preferable that the lower limit of the puncture strength of the resin sheet be 100 gf or more, more preferably 150 gf or more, and even more preferably 200 gf or more, and that the upper limit of the puncture strength of the resin sheet be 2000 gf or less, more preferably 1000 gf or less, and even more preferably 800 gf or less.

[0184] Of the surface free energy values ​​of the back and front surfaces of the resin sheet, the highest value is 40 mJ / m². 2 The following is preferable. When the surface free energy of the resin sheet satisfies the above conditions, the ease of unwinding the separator from the winding body, or the ease of peeling the separator or resin sheet from the laminate, tends to improve. From this viewpoint, the higher of the surface free energies of the back surface of the resin sheet is 35 mJ / m 2 The following is more preferable. Here, the back surface refers to one side of the resin sheet (for example, the side that is exposed to the outside in the form of a rolled body) and the other side (for example, the side that is facing inward in the form of a rolled body).

[0185] Of the smoothness values ​​of the back and surface of the resin sheet, the minimum value of the smoothness is 2000. seconds The above is preferable. Although we do not wish to be bound by theory, it is presumed that if the smoothness of the resin sheet satisfies the above conditions, air will escape more easily from the rolled or laminated body of the separator and resin sheet, and wrinkles will be less likely to remain on the separator.

[0186] The haze of the resin sheet is preferably 30% or less when measured according to JIS-K7136. When the haze of the resin sheet is 30% or less, inspection can be performed while transporting the wound body according to the first embodiment or the laminate according to the second embodiment.

[0187] (Method for transporting and / or storing separators for energy storage devices using resin sheets) In a fourth embodiment, a method for transporting and / or storing a separator for an energy storage device using the resin sheet described above is provided.

[0188] In the separator transport and / or storage method according to the fourth embodiment, a resin sheet is used as interleaving paper, and the separator can be transported and / or stored, for example, in the form of a laminate or wound body of the resin sheet and the separator. This makes it possible to suppress or prevent separator blocking over a long period of time, for example, from 1 hour to 1000 days, preferably 365 days or less. In turn, it is possible to maintain the quality of the separator when slitting the separator and to ensure or improve the device characteristics of the energy storage device including the separator. The temperature during storage and transport is preferably 60°C or less, and more preferably 40°C or less. The relative humidity during storage and transport is preferably 95 rh% or less, and more preferably 90 rh% or less.

[0189] <Energy storage devices> The separator described above can be used as a separator or for separating materials in batteries, capacitors, and the like. In particular, when used as a separator for energy storage devices, it is possible to provide excellent adhesion to electrodes and superior battery performance. Below, a suitable embodiment for cases where the energy storage device is a non-aqueous electrolyte secondary battery will be described.

[0190] When manufacturing a non-aqueous electrolyte secondary battery using the separator described above, there are no limitations on the positive electrode, negative electrode, or non-aqueous electrolyte; known types can be used.

[0191] The positive electrode material is not particularly limited, but examples include lithium-containing composite oxides such as LiCoO2, LiNiO2, spinel-type LiMnO4, and olivine-type LiFePO4. As the positive electrode current collector, for example, aluminum foil may be used.

[0192] The negative electrode material is not particularly limited, but examples include carbon materials such as graphite, non-graphitizable carbon, easily graphitizable carbon, and composite carbon bodies; silicon, tin, metallic lithium, and various alloy materials. As the negative electrode current collector, for example, copper foil may be used.

[0193] In the manufacture of a non-aqueous electrolyte secondary battery, it is preferable that at least one of the positive electrode and the negative electrode be selected such that, from the viewpoint of battery characteristics, the adhesive strength with the separator in a dry state is 1.0 N / m or more.

[0194] The non-aqueous electrolyte is not particularly limited, but an electrolyte in which the electrolyte is dissolved in an organic solvent can be used. Examples of organic solvents include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, and examples of electrolytes include lithium salts such as LiClO4, LiBF4, and LiPF6.

[0195] The method for manufacturing an energy storage device is not particularly limited, but in the case of a secondary battery, for example, a separator can be prepared as a vertically elongated separator with a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 200 to 4000 m (preferably 1000 to 4000 m), and the separator can be stacked in the order of positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator, wound into a circular or flat spiral to obtain a wound body, the wound body can be placed in a battery case, and then an electrolyte can be injected to manufacture the device.

[0196] In this case, the laminate described above may be formed by heating and / or pressing the wound body. Alternatively, the laminate described above may be wound in a circular or flat spiral shape as the wound body. Furthermore, the energy storage device may be manufactured by laminating a positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator in a flat plate shape, or by laminating the above laminate with a bag-shaped film, injecting an electrolyte, and optionally performing a heating and / or pressing step. The heating and / or pressing step described above can be performed before and / or after the electrolyte injection step.

[0197] Unless otherwise specified, the measured values ​​of the various parameters mentioned above are those measured in accordance with the measurement methods described in the examples below. [Examples]

[0198] The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited to these examples. The methods for measuring and evaluating various physical properties used in the following manufacturing examples, examples, and comparative examples are as follows. Unless otherwise specified, all measurements and evaluations were performed under conditions of room temperature of 23°C, 1 atmosphere, and relative humidity of 50%.

[0199] [Measurement and evaluation methods] (1) Viscosity-average molecular weight of polyolefins (hereinafter also referred to as "Mv") The intrinsic viscosity [η] (dl / g) at 135°C in decalin solvent was determined in accordance with ASRM-D4020. The Mv of polyethylene was calculated using the following formula. [η] = 6.77 × 10 -4 Mv 0.67 The Mv of polypropylene was calculated using the following formula. [η] = 1.10 × 10 -4 Mv 0.80

[0200] (2) Thickness (μm) 10cm × 10cm samples were cut from the polyolefin porous substrate and porous layer, the separator for energy storage devices, and the resin sheet. Nine locations (3 points × 3 points) were selected in a grid pattern, and the thickness was measured at room temperature (23±2°C) using a microthickness gauge (Toyo Seiki Seisakusho Co., Ltd. Type KBM). The average of the nine measurement values ​​was taken as the film thickness (μm) for the polyolefin porous substrate, the separator for energy storage devices, and the resin sheet. If necessary, the thickness of the thermoplastic polymer layer was calculated by subtracting the thickness of the polyolefin porous substrate and the porous layer from the thickness of the separator for energy storage devices.

[0201] (3) Porosity (%) A 10cm x 10cm square sample is cut from a polyolefin porous substrate or separator, and its volume (cm³) is measured. 3 Calculate the mass (g) and the film density (g), and determine the film density as 0.95 (g / cm³). 3 The calculation was performed using the following formula. Porosity = (1 - mass / volume / 0.95) × 100 The membrane density is 0.95 (g / cm³). 3 ) was calculated as follows.

[0202] (4) Air permeability (sec / 100cm 3 ) In accordance with JIS P-8117, the air permeability of the sample was measured using a Gurley-type air permeability meter, model G-B2 (trademark), manufactured by Toyo Seiki Co., Ltd.

[0203] (5) Pore size (nm): Half dry Following the half-dry method, the average pore size (nm) was measured using a palm porometer (Porous Materials, Inc.: CFP-1500AE). Perfluoropolyester (product name "Galwick," surface tension 15.6 dyn / cm) manufactured by the same company was used as the immersion solution. The applied pressure and air permeability were measured for both the dry and wet curves. The average pore size dHD (nm) was calculated from the pressure PHD (Pa) at which the half-moon curve of the dry curve intersected the wet curve, using the following formula, and was defined as the pore size. dHD = 2860 × γ / PHD

[0204] (6) Piercing strength (gf), Piercing strength converted to area weight (gf / g / m 2 ) Using a Kato Tech KES-G5 (trademark) handy compression tester, a polyolefin porous substrate, porous layer, separator, or resin sheet was fixed as a sample in a sample holder with an opening diameter of 11.3 mm. Next, a puncture test was performed on the center of the fixed sample at a needle tip radius of curvature of 0.5 mm and a puncture speed of 2 mm / sec in a 25°C atmosphere to obtain the raw puncture strength (gf) as the maximum puncture load. Furthermore, the raw puncture strength was converted to the basis weight of the sample to obtain the basis weight equivalent puncture strength (gf / g / m). 2 ) was calculated.

[0205] (7) Glass transition temperature of thermoplastic polymers A suitable amount of thermoplastic polymer coating solution (non-volatile content = 38-42%, pH = 9.0) was placed in an aluminum dish and dried in a hot air dryer at 130°C for 30 minutes. Approximately 17 mg of the dried film was placed in an aluminum container for measurement, and DSC and DDSC curves under a nitrogen atmosphere were obtained using a DSC analyzer (Shimadzu Corporation, DSC6220). The measurement conditions were as follows. (First stage heating program) The temperature is increased from 70°C at a rate of 15°C per minute. After reaching 110°C, it is maintained for 5 minutes. (Second stage cooling program) The temperature is reduced from 110°C at a rate of 40°C per minute. After reaching -50°C, it is maintained for 5 minutes. (3rd stage heating program) The temperature was increased from -50°C to 130°C at a rate of 15°C per minute. DSC and DDSC data were acquired during this third stage of temperature increase. The glass transition temperature (Tg) was defined as the intersection point of the baseline (a straight line extending the baseline in the obtained DSC curve toward the higher temperature side) and the tangent line at the inflection point (the point where the curve, which is convex upwards, changes to a curve, which is convex downwards).

[0206] (8) Gel fraction of thermoplastic polymers (toluene-insoluble content) A thermoplastic polymer coating solution (non-volatile content = 38-42%, pH = 9.0) was dropped onto a Teflon® plate using a dropper (diameter 5 mm or less) and dried in a hot air dryer at 130°C for 30 minutes. After drying, approximately 0.5 g of the dried film was weighed (a), placed in a 50 mL polyethylene container, and 30 mL of toluene was poured into it. The mixture was then shaken at room temperature for 3 hours. The contents were then filtered through a 325 mesh filter, and the toluene-insoluble residue remaining on the mesh was dried along with the mesh in a hot air dryer at 130°C for 1 hour. The dry weight of the 325 mesh used here was weighed in advance. Then, after the toluene evaporated, the dry weight (b) of the toluene-insoluble portion was obtained by subtracting the pre-measured weight of the 325 mesh from the weight of the dried toluene-insoluble portion and the weight of the 325 mesh. The gel fraction (toluene-insoluble portion) was calculated using the following formula. Gel fraction of thermoplastic polymer (toluene-insoluble content) = (b) / (a) × 100 [%]

[0207] (9) Swelling degree of thermoplastic polymer in relation to electrolyte (times) After standing the thermoplastic polymer or a solution containing a dispersed thermoplastic polymer in an oven at 130°C for 1 hour, the dried thermoplastic polymer was cut to 0.5 g and placed in a 50 mL vial with 10 g of a mixed solvent of ethylene carbonate:ethyl methyl carbonate = 1:2 (volume ratio). After infusion for 3 hours, the sample was removed, washed with the above mixed solvent, and its weight (Wa) was measured. Subsequently, after standing in an oven at 150°C for 1 hour, the weight (Wb) was measured, and the degree of swelling of the thermoplastic polymer in relation to the electrolyte was measured using the following formula. The degree of swelling (times) of a thermoplastic polymer in relation to an electrolyte = (Wa - Wb) ÷ (Wb)

[0208] (10) Average particle size of thermoplastic polymers (nm) The average particle diameter of the thermoplastic polymer was measured using a particle diameter measuring device (Microtrac UPA150, manufactured by Nikkiso Co., Ltd.). The measurement conditions were a loading index of 0.15 to 0.3 and a measurement time of 300 seconds, and the value of the 50% particle diameter in the obtained data was described as the particle diameter.

[0209] (11) Basis weight (11a) Basis weight of the thermoplastic polymer layer (amount supported on the base material of the thermoplastic polymer layer) A 10 cm × 10 cm square sample was cut from the base material (polyolefin porous base material or polyolefin porous base material + inorganic filler porous layer), and the weight was measured using an electronic balance AEL-200 manufactured by Shimadzu Corporation. By multiplying the obtained weight by 100, the basis weight of the base material film per 1 m 2 (g / m 2 ) was calculated. Next, a 10 cm × 10 cm square sample was cut from the separator (thermoplastic polymer layer + base material), and the mass was measured using an electronic balance AEL-200 manufactured by Shimadzu Corporation. By multiplying the obtained mass by 100, the basis weight of the separator per 1 m 2 (g / m 2 ) was calculated. By subtracting the basis weight of the base material per 1 m 2 (g / m 2 ) from the basis weight of the separator per 1 m 2 (g / m 2 ), the basis weight of the thermoplastic polymer layer per 1 m 2 (amount supported on the base material of the thermoplastic polymer layer, g / m 2 ) was calculated.

[0210] (11b) Basis weight of the resin sheet A 10 cm × 10 cm square sample was cut from the resin sheet, and the weight was measured using an electronic balance AEL-200 manufactured by Shimadzu Corporation. By multiplying the obtained weight by 100, the basis weight of the resin sheet per 1 m 2 (g / m 2 ) was calculated, and if necessary, it was converted to the weight per 1 cm 2 .

[0211] (12) Peel strength between separator and resin sheet (N / m) For laminates of separators and resin sheets, or laminates of separators and resin sheets unwound from a winding body of separators and resin sheets, the 90° peel strength (N / m) between the separator and the resin sheet was measured at a tensile speed of 50 mm / min using force gauges ZP5N and MX2-500N (product name) manufactured by IMADA Corporation.

[0212] (13) Internal pressure (MPa) in the direction of the roll center in the inner 10% of the wound body For the rolled separator and resin sheet, a pressure-sensitive element (TEKSCAN, model number A201-25) was attached to the upper surface of the 10% inner layer region determined by lateral observation as described above. Subsequently, the resistance value was measured using a resistance measuring instrument (Sanwa Electric Instrument Co., Ltd., model number: Digital Multimeter CD771) in an environment of 23±1℃ and converted into internal pressure in the direction of the roll center. For the conversion from resistance to internal pressure, a calibration curve was created from the resistance values ​​obtained by pressing the pressure-sensitive element at different pressures using a press machine, and the calculation was performed using that calibration curve.

[0213] (14) Tensile modulus of MD and TD (MPa) MD and TD measurements were performed on individually prepared separators or resin sheets, or separators or resin sheets peeled from wound or laminated bodies. For MD and TD measurements, MD samples (MD 120 mm × TD 10 mm) and TD samples (MD 10 mm × TD 120 mm) were cut out. Under ambient temperature of 23 ± 2 °C and humidity of 40 ± 2%, the tensile modulus of the MD and TD of the samples were measured in accordance with JIS K7127 using a Shimadzu Corporation Autograph AG-A (trademark) tensile testing machine. The samples were set with a chuck distance of 50 mm, and stretched at a tensile speed of 200 mm / min until the chuck distance reached 60 mm, i.e., the strain reached 20.0%. The tensile modulus (MPa) was determined from the slope of the resulting stress-strain curve from 1.0% to 4.0% strain. The ratio of the tensile modulus of the separator to the tensile modulus of the resin sheet was also calculated.

[0214] (15) Surface free energy (mJ / m 2 ) Using a contact angle meter or surface free energy analyzer, the contact angles of at least two liquid reagents (e.g., water and diiodomethane) with respect to the front and back surfaces of the resin sheet are measured, and the surface free energy (mJ / m) of the resin sheet is calculated according to the OWRK method or Fowkes method. 2 The following table shows the surface free energy of the higher of the two surfaces of the resin sheet.

[0215] (16) Smoothness (se c) In accordance with ISO 8791-5:2020, the smoothness of polyolefin microporous membranes, resin sheets, and separators for energy storage devices was measured using an EYO-5 air permeability and smoothness meter manufactured by Asahi Seiko Co., Ltd., with a stainless steel nozzle having an inner diameter of 0.15 mm and a length of 50 mm, in an atmosphere of 30°C and 40% humidity.

[0216] Surface smoothness was measured on one surface and the other surface of the resin sheet and the separator for the energy storage device. The table below shows the smoothness of the lower of the two surfaces of the resin sheet and the separator for the energy storage device.

[0217] (17) Adhesion strength between the separator and the electrode in a dry state (N / m) The separator and the positive electrode (manufactured by enertech, positive electrode material: LiCoO2, conductive additive: acetylene black, binder: PVDF, LiCoO2 / acetylene black / PVDF (mass ratio) = 95 / 2 / 3, L / W: 36 mg / cm³ on both sides) 2 , Density: 3.9g / cm 3The Al current collector (thickness: 15 μm, x-width of the pressed positive electrode: 107 μm) and the positive electrode were each cut into rectangular shapes with a width of 15 mm and a length of 50 mm. A laminate was obtained by stacking these pieces so that the thermoplastic polymer layer of the separator and the positive electrode active material faced each other, and then the laminate was pressed under the following conditions. Measurements were performed on one side and the other side of the separator. The table below shows the higher of the two adhesive strengths of the back surface. Press pressure: 1 MPa Temperature: 80℃ Pressing time: 3 minutes

[0218] For the pressed laminate, a 90° peel test was performed at a peeling speed of 50 mm / min using force gauges ZP5N and MX2-500N (product name) manufactured by IMADA Corporation. The electrodes were fixed, and the separator was gripped and pulled to measure the peel strength. The average peel strength of the 40 mm length peel test performed under the above conditions was adopted as the adhesive strength in the dry state.

[0219] (18) Heat shrinkage rate (%) at 120℃ for 1 hour As a sample, a porous membrane was cut to lengths (mm) of 100 mm on the medium diameter (MD) and 100 mm on the top diameter (TD), 50 mm on the MD and 50 mm on the TD, or 30 mm on the MD and 30 mm on the TD before heating, and left standing in a 120°C oven for 1 hour. During this time, the sample was sandwiched between 10 sheets of paper to prevent direct contact with the hot air. After removing the sample from the oven and allowing it to cool, its length was measured to determine the length (mm) after heating, and the thermal shrinkage rate was calculated using the following formula. Measurements were taken separately for the MD and TD, and the larger value was used as the thermal shrinkage rate. Thermal shrinkage rate (%) = {(Length before heating - Length after heating) / Length before heating} × 100

[0220] (19) Long-term storage / transportability Laminates or rolls of separators and resin sheets with a width of 50 mm and the length specified in Table 4 or 5 were stored for 180 days at a temperature of 35°C and a humidity of 90 rh%. Afterward, the presence or absence of blocking between separators and between separators and resin sheets was observed in the inner 10% of the roll or in any portion of the laminate. Specifically, a 1 m length of the separator and resin sheet laminate or roll was cut, and when two adjacent separators and resin sheets were separated, the blocking resistance was evaluated by observing the amount of thermoplastic polymer transferred from the separator surface to the resin sheet relative to the amount of thermoplastic polymer on the separator surface before lamination or winding (transfer ratio). Separation was performed using IMADA force gauges ZP5N and MX2-500N (product name) at a tensile speed of 50 mm / min. A KEYENCE digital microphone rope VHX-8000 was used to observe the surface condition. A (Excellent): Transcription rate between 0% and less than 15% B (Good): Transcription rate between 15% and less than 30% C (Poor): Transfer rate of 30% or more

[0221] (20) Quality when slit The quality of the separators during slitting was evaluated by slitting laminates or windings of separators and resin sheets, slitting separators peeled from the laminates, or slitting separators unwound from the windings. The quality was evaluated comprehensively based on factors such as the degree of foreign matter contamination, runnability, and presence or absence of wrinkles, as follows. A (Excellent); No foreign matter contamination, no problems with running performance, no wrinkles on the separator. B (Good); some foreign matter contamination, issues with drivability, and wrinkles in the separator are present, but it is still deemed acceptable. C (Defective): Foreign matter contamination, poor operability, wrinkles in the separator were observed, resulting in a failing grade.

[0222] (21) Battery characteristics (cycle characteristics) a. Fabrication of the positive electrode The positive electrode active material is nickel, manganese, and cobalt composite oxide (NMC) (Ni:Mn:Co=1:1:1 (elemental ratio), density 4.70 g / cm³).3 ) was 90.4% by mass, graphite powder (KS6) (density 2.26 g / cm 3 , number average particle diameter 6.5 μm) was 1.6% by mass, and acetylene black powder (AB) (density 1.95 g / cm 3 , number average particle diameter 48 nm) was 3.8% by mass. Polyvinylidene fluoride (PVDF) (density 1.75 g / cm 3 ) was mixed at a ratio of 4.2% by mass, and these were dispersed in N-methylpyrrolidone (NMP) to prepare a slurry. This slurry was applied to one side of an aluminum foil with a thickness of 20 μm serving as the positive electrode current collector using a die coater, dried at 130 °C for 3 minutes, and then compression molded using a roll press. The positive electrode active material coating amount at this time was 109 g / m 2 .

[0223] b. Preparation of negative electrode As the negative electrode active material, 87.6% by mass of graphite powder A (density 2.23 g / cm 3 , number average particle diameter 12.7 μm) and 9.7% by mass of graphite powder B (density 2.27 g / cm 3 , number average particle diameter 6.5 μm), 1.4% by mass (in terms of solid content) of ammonium carboxymethyl cellulose (solid content concentration 1.83% by mass aqueous solution) as a binder, and 1.7% by mass (in terms of solid content) of diene rubber latex (solid content concentration 40% by mass aqueous solution) were dispersed in purified water to prepare a slurry. This slurry was applied to one side of a copper foil with a thickness of 12 μm serving as the negative electrode current collector using a die coater, dried at 120 °C for 3 minutes, and then compression molded using a roll press. The negative electrode active material coating amount at this time was 5.2 g / m 2 .

[0224] c. Preparation of non-aqueous electrolyte It was prepared by dissolving LiPF6 as a solute in a mixed solvent of ethylene carbonate:ethyl methyl carbonate = 1:2 (volume ratio) to a concentration of 1.0 mol / L.

[0225] d. Battery assembly The separator unwound from the wound body or the separator peeled off from the laminate was cut into 24 mm diameter circles, and the positive and negative electrodes were cut into 16 mm diameter circles. The negative electrode, separator, and positive electrode were stacked in that order so that the active material surfaces of the positive and negative electrodes faced each other, and placed in a stainless steel container with a lid. The container and the lid were insulated, and the container was in contact with the copper foil of the negative electrode, and the lid was in contact with the aluminum foil of the positive electrode. 0.4 ml of the non-aqueous electrolyte was poured into this container and sealed.

[0226] e. Evaluation of cycle characteristics The simple battery assembled in d. above was subjected to 100 charge-discharge cycles at 25°C under the following cycle conditions: (i) constant current and constant voltage charging at a current of 0.5C and an upper voltage limit of 4.2V for a total of 3 hours, (ii) a 10-minute rest, (iii) constant current discharge at a current of 0.5C and a cutoff voltage of 3.0V, and (iv) a 10-minute rest. All of the above charge-discharge processes were performed in an atmosphere of 25°C. Subsequently, the capacity retention rate (%) was calculated by multiplying the ratio of the discharge capacity after the 100th cycle to the initial battery capacity X (mAh) by 100. The capacity retention rate was evaluated according to the following criteria. Evaluation Criteria for Cycle Characteristics A (Excellent): Volume retention rate of 90% or more B (Good): Volume retention rate is 70% or more but less than 90% C (Defective): Capacity retention rate is 70% or less.

[0227] [Manufacturing Example 1-1A] (Manufacturing of Polyolefin Microporous Membrane 1A) 45 parts by mass of high-density polyethylene, a homopolymer with a viscosity-average molecular weight (Mv) of 700,000, 45 parts by mass of high-density polyethylene, a homopolymer with an Mv of 300,000, and 5 parts by mass of polypropylene, a homopolymer with a viscosity-average molecular weight of 400,000, were dry-blended using a tumbler blender. 1 part by mass of tetrakis-[methylene-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane was added to the resulting polyolefin mixture (99 parts by mass) as an antioxidant, and the mixture was dry-blended again using a tumbler blender to obtain a mixture. The resulting mixture was fed to a twin-screw extruder via a feeder under a nitrogen atmosphere. Furthermore, liquid paraffin (kinematic viscosity at 37.78°C: 7.59 × 10⁻⁶) was used. -5 m 2 The mixture ( / s) was injected into the extruder cylinder using a plunger pump. The operating conditions of the feeder and pump were adjusted so that the proportion of liquid paraffin in the total mixture extruded was 65 parts by mass, i.e., the polymer concentration was 35 parts by mass.

[0228] Next, these materials were melt-kneaded in a twin-screw extruder while being heated to 200°C. The resulting molten mixture was extruded through a T-die onto a cooling roll with a surface temperature controlled to 80°C. The extruded material was then brought into contact with the cooling roll for molding (casting) and cooled and solidified to obtain a sheet-like molded product with a thickness of 500 μm. This sheet was stretched in a simultaneous twin-screw stretcher at a magnification of 7 × 6.4 times and a temperature of 118°C. After that, it was immersed in methylene chloride to extract and remove the liquid paraffin, dried, and then stretched twice in the transverse direction at a temperature of 130°C in a tenter stretcher. Subsequently, this stretched sheet was relaxed by approximately 10% in the width direction and heat-treated to obtain the polyolefin microporous membrane 1A shown in Table 1.

[0229] The physical properties of the obtained polyolefin microporous film 1A were measured using the method described above. The results are shown in Table 1.

[0230] [Manufacturing Example 1-2A] (Manufacturing of Polyolefin Microporous Membrane 2A) In Production Example 1-1A, a sheet-like molded material with a thickness of 900 μm was obtained, stretched at 120°C, and then processed at 128°C in a tenter stretcher. Except for these differences, the polyolefin microporous membrane 2A shown in Table 1 was obtained using the same method as in Production Example 1-1A and evaluated using the same method as in Production Example 1-1A. The results are shown in Table 1.

[0231] [Manufacturing Example 1-3A] (Manufacturing of Polyolefin Microporous Membrane 3A) In Production Example 1-1A, a sheet-like molded material with a thickness of 1300 μm was obtained, stretched at 115°C, and then treated at 125°C in a tenter stretcher. Except for these differences, the polyolefin microporous membrane 3A shown in Table 1 was obtained using the same method as in Production Example 1-1A and evaluated using the same method as in Production Example 1-1A. The results are shown in Table 1.

[0232] [Manufacturing Example 1-4A] (Manufacturing of polyolefin microporous membrane and porous layer 4A) A coating solution was prepared by uniformly dispersing 96.0 parts by mass of aluminum hydroxide oxide (average particle size 1.0 μm), 4.0 parts by mass of acrylic latex (solid content concentration 40%, average particle size 145 nm, minimum film formation temperature 0°C or lower), and 1.0 part by mass of aqueous solution of ammonium polycarboxylate (Sunopco SN Dispersant 5468) in 100 parts by mass of water. The obtained coating solution was applied to the surface of a polyolefin resin porous film 3A using a microgravure coater. The water was removed by drying at 60°C, and a porous layer with a thickness of 1 μm was formed to obtain a microporous film 4A. The obtained polyolefin microporous film and porous layer 4A were evaluated using the same method as in Production Example 1-1A. The results are shown in Table 1.

[0233] [Manufacturing Example 1-5A] (Manufacturing of polyolefin microporous membrane and porous layer 5A) In Production Example 1-4A, the polyolefin microporous membrane and porous layer 5A shown in Table 1 were obtained using the same method as in Production Example 1-4A, except that a porous layer with a thickness of 3 μm was formed on the surface of the polyolefin resin porous membrane 2A. These were evaluated using the same method as in Production Example 1-1A. The results obtained are shown in Table 1.

[0234] [Manufacturing Example 1-6A] (Manufacturing of polyolefin microporous membrane and porous layer 6A) In Production Example 1-4A, the polyolefin microporous membrane and porous layer 6A shown in Table 1 were obtained using the same method as in Production Example 1-4A, except that a porous layer with a thickness of 5 μm was formed on the surface of the polyolefin resin porous membrane 1A. These were evaluated using the same method as in Production Example 1-1A. The results obtained are shown in Table 1.

[0235] [Manufacturing Example 1-7A] (Manufacturing of polyolefin microporous membrane and porous layer 7A) In Production Example 1-4A, a porous layer with a thickness of 1 μm was formed on the surface of the polyolefin resin porous membrane 2A, and then a porous layer of 1 μm was formed on the other surface of the polyolefin microporous membrane using the same method (forming a total porous layer with a thickness of 2 μm on both sides). Except for these differences, the polyolefin microporous membrane and porous layer 7A shown in Table 1 were obtained using the same method as in Production Example 1-4A and were evaluated using the same method as in Production Example 1-1A. The results obtained are shown in Table 1.

[0236] [Manufacturing Example 1-8A] (Manufacturing of polyolefin microporous membrane and porous layer 8A) In Production Example 1-4A, a porous layer with a thickness of 3 μm was formed on the surface of the polyolefin resin porous membrane 1A, and then a porous layer of 3 μm was formed on the other surface of the polyolefin microporous membrane using the same method (forming a total porous layer with a thickness of 6 μm on both sides). Except for these differences, the polyolefin microporous membrane and porous layer 8A shown in Table 1 were obtained using the same method as in Production Example 1-4A and were evaluated using the same method as in Production Example 1-1A. The results obtained are shown in Table 1.

[0237] [Table 1]

[0238] [Manufacturing Examples 2-1B~3B] (Manufacturing of Acrylic Emulsion Coating Solution) In a reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer, 70.4 parts of deionized water, 0.34 parts of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and 0.34 parts of "Adekaria Soap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation) were added. The internal temperature of the reaction vessel was raised to 80°C, and while maintaining the temperature at 80°C, 7.5 parts of ammonium persulfate (2% aqueous solution) were added to obtain the initial mixture.

[0239] Five minutes after adding aqueous ammonium persulfate (APS), 71.5 parts methyl methacrylate (MMA), 18.9 parts n-butyl acrylate (BA), 2 parts 2-ethylhexyl acrylate (EHA), 0.1 parts methacrylic acid (MAA), 0.1 parts acrylic acid (AA), 2 parts 2-hydroxyethyl methacrylate (HEMA), 5 parts acrylamide (AM), 0.4 parts glycidyl methacrylate (GMA), and 0.4 parts trimethylolpropane triacrylate (A-TMPT, manufactured by Shin-Nakamura Chemical Industry Co., Ltd.) were added. A mixture of 1 part "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), 3 parts "Adekaria Soap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation), 0.05 parts p-sodium styrene sulfonate (NaSS), 7.5 parts ammonium persulfate (2% aqueous solution), 0.3 parts γ-methacryloxypropyltrimethoxysilane, and 52 parts ion-exchanged water was mixed in a homomixer for 5 minutes to prepare an emulsion, which was then added dropwise from the dropping tank to the reaction vessel over 150 minutes.

[0240] After the emulsion was added dropwise, the reaction vessel was kept at 80°C for 90 minutes, and then cooled to room temperature. The resulting emulsion was adjusted to pH=9.0 with an aqueous solution of ammonium hydroxide (25% aqueous solution) to obtain thermoplastic polymer-containing coating solution 1B. The obtained solution 1B was evaluated using the method described above. The results are shown in Table 2.

[0241] [Table 2]

[0242] The Tg values ​​for raw material polymers 1B to 2B listed in Table 2 are all approximate values ​​calculated using the FOX formula. The abbreviations in Table 2 refer to the following materials, respectively. MMA: Methyl methacrylate BA: n-butyl acrylate EHA: 2-ethylhexyl acrylate MAA: Methacrylic acid AA: Acrylic acid HEMA: 2-hydroxyethyl methacrylate AM: Acrylamide GMA: Glycidyl methacrylate NaSS: Sodium p-styrene sulfonate A-TMPT: Trimethylolpropane triacrylate (manufactured by Shin-Nakamura Chemical Industry Co., Ltd.) KH1025: Aqualon KH1025 (Registered trademark, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) SR1025: Adekaria Soap SR1025 (Registered Trademark, Manufactured by ADEKA Corporation) APS: Ammonium persulfate

[0243] [Resin Sheet 3-1C] Based on the evaluation using the above method, the thickness was 16.5 μm and the basis weight was 14.1 m². 2 , Piercing strength 889gf, Piercing strength converted to area weight 63gf / g / m 2 MD tensile modulus: 4453 kgf / cm² 2 Surface free energy 31 mJ / m 2 Smoothness 15590 seconds A certain OPP sheet was prepared. The results obtained are shown in Table 3.

[0244] [Resin Sheet 3-2C~5C] A resin sheet having the same constituent resin and physical properties as resin sheet 3-1C was prepared as shown in Table 3.

[0245] [Table 3]

[0246] [Examples 1-9, Comparative Examples 1-8] As shown in Table 4 or Table 5, the raw material polymers from Table 2 or a vinylidene fluoride-hexafluoropropylene copolymer (indicated as PVdF in the table) with a weight-average molecular weight of 300,000 and a vinylidene fluoride / hexafluoropropylene molar ratio of 93 / 7 were applied to one side of the polyolefin microporous membrane shown in Table 1 using a gravure coater, and the water in the coating solution was removed by drying at 60°C. If necessary, the other side was also coated with the same coating solution and dried again to produce a separator having a thermoplastic polymer on both sides of the polyolefin microporous membrane.

[0247] In Example 9, a coating solution was prepared by uniformly dispersing 100.0 parts by mass of aluminum hydroxide oxide (average particle size 0.5 μm), 7.0 parts by mass of a raw material polymer with the same composition as 1B in Table 2 but a particle size (50% particle size) of 4200 μm, 4.0 parts by mass of acrylic latex (solid content concentration 40%, average particle size 145 nm, minimum film formation temperature 0°C or lower), and 1.0 part by mass of an aqueous solution of ammonium polycarboxylate (Sunopco SN Dispersant 5468) in 100 parts by mass of water. The obtained coating solution was applied to the surface of a polyolefin resin porous film 2A using a microgravure coater, dried at 60°C to remove water, and a porous layer with a thickness of 4 μm was formed.

[0248] Furthermore, as shown in Table 4 or Table 5, a laminate was obtained by laminating the separator and the resin sheet shown in Table 3, and a wound body was obtained by winding the laminate around an ABS core with an outer diameter of 8 inches and an inner diameter of 3 inches, and having 8 spokes connecting the outer and inner circumferences. The separator, resin sheet, laminate, and wound body were measured and evaluated using the method described above. The results are shown in Table 4 or Table 5.

[0249] [Table 4]

[0250] [Table 5]

Claims

1. A winding body comprising a separator for an energy storage device and a resin sheet, The separator for the energy storage device comprises a polyolefin porous substrate and a thermoplastic polymer layer containing a thermoplastic polymer on at least a portion of at least one side of the polyolefin porous substrate. The aforementioned polyolefin porous substrate is a microporous membrane mainly composed of polyethylene. The main component of the thermoplastic polymer layer is acrylic resin. The resin constituting the aforementioned resin sheet is polyethylene or polypropylene. The MD tensile modulus of the aforementioned resin sheet is 1000 kgf / cm². ２ More than 15000kgf / cm ２ The following: The ratio of the MD tensile modulus of the separator for the energy storage device to the MD tensile modulus of the resin sheet is 0.35 or more and 10.0 or less, and A wound body wherein the minimum value of the smoothness of the back surface of the separator for the energy storage device is 49,460 seconds or more.

2. The winding body according to claim 1, wherein the peel strength between the separator for the energy storage device and the resin sheet is 0.1 N / m or more and 10.0 N / m or less, and the adhesive strength between the separator and the electrode in a dry state is 1.0 N / m or more.

3. The aforementioned resin sheet has a basis weight equivalent puncture strength of 50 gf / g / m². ２ The above is the winding body according to claim 1 or 2.

4. The winding body according to any one of claims 1 to 3, wherein the internal pressure in the direction of the roll center in the inner 10% of the inner layer is 5 MPa or less.

5. Of the surface free energies of the back surface of the aforementioned resin sheet, the highest value of the surface free energy is 40 mJ / m ２ The following is the winding body according to any one of claims 1 to 4.

6. The wound body according to any one of claims 1 to 5, wherein the minimum value of the smoothness of the back surface of the resin sheet is 2000 seconds or more.

7. The wound body according to any one of claims 1 to 6, wherein the ratio of the puncture strength of the separator for the energy storage device to the puncture strength of the resin sheet is 0.12 or more and 2.0 or less.

8. The air permeability of the separator for the aforementioned energy storage device is 200 seconds / 100 cm. ３ The following is the winding body according to any one of claims 1 to 7.

9. A resin sheet used when transporting separators for energy storage devices, The separator for the energy storage device comprises a polyolefin porous substrate and a thermoplastic polymer layer containing a thermoplastic polymer on at least a portion of at least one side of the polyolefin porous substrate. The aforementioned polyolefin porous substrate is a microporous membrane mainly composed of polyethylene. The main component of the thermoplastic polymer layer is acrylic resin. The resin constituting the aforementioned resin sheet is polyethylene or polypropylene. The MD tensile modulus of the aforementioned resin sheet is 1000 kgf / cm². ２ More than 15000kgf / cm ２ The following: The ratio of the MD tensile modulus of the separator to the MD tensile modulus of the resin sheet is 0.35 or more and 10.0 or less, and A resin sheet having a minimum smoothness value of 49,460 seconds or more on the back surface of the separator for the energy storage device.

10. The resin sheet according to claim 9, wherein the peel strength between the separator for the energy storage device and the resin sheet is 0.1 N / m or more and 10.0 N / m or less.

11. A laminate comprising a separator for energy storage devices and a resin sheet, The separator for the energy storage device comprises a polyolefin porous substrate and a thermoplastic polymer layer containing a thermoplastic polymer on at least a portion of at least one side of the polyolefin porous substrate. The aforementioned polyolefin porous substrate is a microporous membrane mainly composed of polyethylene. The main component of the thermoplastic polymer layer is acrylic resin. The resin constituting the aforementioned resin sheet is polyethylene or polypropylene. The MD tensile elastic modulus of the resin sheet is 1000 kgf / cm ２ or more and 15000 kgf / cm ２ or less, and The ratio of the MD tensile modulus of the separator for the energy storage device to the MD tensile modulus of the resin sheet is 0.35 or more and 10.0 or less, and A laminate in which the minimum value of the smoothness of the back surface of the separator for the energy storage device is 49,460 seconds or more.

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