Adhesive, separator, and lithium-ion battery using this separator

Abstract

The present application relates to the technical field of lithium batteries, and in particular to an adhesive, a separator, and a lithium ion battery using the separator, wherein the adhesive includes a terpolymer formed by copolymerization of a specific first monomer unit, a second monomer unit, and a third monomer unit.

Description

[Technical Field]

[0001] This application relates to the technical field of lithium batteries, and in particular to adhesives, separators and lithium ion batteries using the separators. [Background technology]

[0002] In recent years, as the application range of lithium-ion batteries becomes more and more widespread, lithium-ion batteries are widely used in energy storage power systems such as hydroelectric power plants, thermal power plants, wind power plants and solar power plants, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. With the remarkable development of lithium-ion batteries, the requirements for their energy density, cycle performance and safety performance are becoming increasingly higher.

[0003] Lithium-ion battery separators prevent the passage of electrons, allow the transport of ions, and complete the rapid transport of lithium ions between the positive and negative electrodes during charging and discharging. Lithium-ion battery separators often use adhesives. However, conventional adhesives have problems such as poor compatibility with ceramic particles and poor adhesion to the electrode plates and separator, which can easily cause coating particles to fall off and affect the safety and performance of lithium-ion batteries. Currently, commercially available polyolefin separators and coating films have drawbacks such as relatively poor heat resistance, shrinkage upon heating, and susceptibility to punctures. These drawbacks can lead to lithium dendrite growth, thermal runaway, and direct contact between the positive and negative electrodes, leading to battery short circuits and affecting the safety and lifespan of lithium-ion batteries.

[0004] Therefore, in the conventional technology, there is still a need to provide a separator that is resistant to high temperatures, has high performance, is highly safe, and has excellent overall performance. Summary of the Invention [Problem to be solved by the invention]

[0005] The present application has been made in view of the above-mentioned problems, and its object is to provide an adhesive, a separator, and a lithium ion battery using this separator. [Means for solving the problem]

[0006] In order to achieve the above object, a first aspect of the present application provides an adhesive comprising a terpolymer formed by copolymerization of a first monomer unit, a second monomer unit, and a third monomer unit, wherein the first monomer is a C1-C (meth)acrylic acid. 20 alkyl esters, the second monomer is selected from at least one of acrylonitrile and methacrylonitrile, and the third monomer is selected from at least one optionally substituted (meth)acrylamide, wherein the molar ratio of the first monomer unit to the second monomer unit to the third monomer unit is 50-58:40-44:2-6.

[0007] The acrylate monomer can increase the adhesive's viscosity and swelling resistance, and as a flexible monomer chain segment in the molecular chain segment, it can adjust the adhesive's glass transition temperature, playing a positive role in improving the adhesive's viscosity. The cyano group has strong polarity and can promote ionic conductivity. The amide group's main function is connection, and it undergoes polymerization through a normal addition reaction mechanism, increasing the molecular weight and stabilizing the adhesive. Controlling the molar ratio of these three monomers within a certain range not only ensures the adhesive's viscosity, but also controls the adhesive's molecular weight and glass transition temperature.

[0008] In one embodiment, the terpolymer has a structure of general formula (I): [ka] wherein R1 are the same or different and independently represent H or a methyl group; R2 is C1-C 20 Alkyl groups, C3-C 20Cycloalkyl group or C1-C 20 hydroxyalkyl groups, optionally C1-C 12 Alkyl groups, C3-C 12 Cycloalkyl group or C1-C 12 hydroxyalkyl, and R2 is further optionally methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-octyl, isooctyl, 2-ethylhexyl, dodecyl or isobornyl; R3 is H or a C1-C6 alkyl group monosubstituted by OR4, R4 is H or a C1-C6 alkyl group, and R4 is further optionally H, methyl, ethyl, n-propyl or n-butyl; x, y and z are independently selected from integers from 50 to 2000, and optionally from integers from 100 to 500.

[0009] In one embodiment, the weight-average molecular weight Mw of the terpolymer is 40,000-150,000 g / mol, and optionally 60,000-120,000 g / mol. The weight-average molecular weight of the adhesive within this range ensures that the adhesive has a certain fluidity during the pre-pressing process and ensures the adhesive's adhesive effect during the battery core manufacturing process.

[0010] In any embodiment, the (meth)acrylic acid C1-C 20The alkyl ester is selected from one or more of methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, n-propyl acrylate, cyclohexyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate. In any embodiment, the third monomer is selected from one or more of acrylamide, N-methylolacrylamide, and N-butoxymethacrylamide.

[0011] In any of the embodiments, the glass transition temperature Tg of the terpolymer is from -20°C to 40°C, and optionally from 0°C to 20°C.

[0012] A second aspect of the present application provides a separator including a base layer and an adhesive layer laminated in order, The adhesive layer comprises the adhesive according to any one of claims 1 to 6, heat-expandable microspheres, and ceramic particles.

[0013] The adhesive of this application has relatively high adhesive strength, improving the adhesion between the heat-expandable microspheres and ceramic particles and preventing the separator coating particles from falling off. When the battery experiences thermal runaway, the heat-expandable microspheres expand quickly, filling the gaps between the microspheres in a timely manner and improving the pore-blocking performance of the separator. The ceramic particles ensure the dimensional stability of the separator when temperatures rise, and the three synergistically improve the safety performance of lithium-ion batteries.

[0014] In any embodiment, the heat-expandable microspheres have a glass transition temperature of 40-100° C., optionally 60-90° C. The heat-expandable microspheres have an average particle size Dv50 of 0.1 μm-2 μm, optionally 0.3 μm-1.5 μm.

[0015] In any embodiment, the ceramic particles are at least one of aluminum oxide, boehmite, silicon dioxide, and titanium dioxide, and have an average particle size Dv50 value of 0.5 μm-5 μm, optionally 1 μm-3.5 μm.

[0016] In one embodiment, the mass ratio of the adhesive to the heat-expandable microspheres to the ceramic particles is 25-30:10-20:50-65.

[0017] By controlling the mass ratio of the adhesive, heat-expandable microspheres, and ceramic particles within a specific range, the separator can have significantly improved performance. If the amount of adhesive is too small, the heat-expandable microspheres and ceramic particles cannot be completely coated and bonded, resulting in powder shedding. If the amount of adhesive is too large, the ratio of heat-expandable microspheres to ceramic particles will be affected, reducing the expansion efficiency of the heat-expandable microspheres. If the content of heat-expandable microspheres is too low, the pores of the separator will not be completely blocked after expansion. If the content of ceramic particles is too low, the thermal stability of the separator will be affected, which will further affect the safety performance of lithium-ion batteries.

[0018] A third aspect of the present application provides a lithium ion battery, the lithium ion battery comprising the adhesive of the first aspect of the present application or the separator according to the second aspect of the present application.

[0019] A fourth aspect of the present application provides a battery pack, the battery pack including the lithium-ion battery of the third aspect of the present application.

[0020] A fifth aspect of the present application provides a power consuming device, the power consuming device including the lithium ion battery of the third aspect of the present application or the battery pack of the fourth aspect of the present application. [Brief explanation of the drawings]

[0021] In order to more clearly explain the technical solution of the present application, the following briefly introduces the drawings that need to be used in the embodiments of the present application. It is obvious that the drawings described below are only some embodiments of the present application, and those skilled in the art can obtain other drawings based on the drawings without any creative efforts. [Figure 1] 1 is a schematic diagram of a lithium ion secondary battery according to one embodiment of the present application. [Figure 2] FIG. 2 is an exploded view of the lithium ion secondary battery according to the embodiment of the present application shown in FIG. [Figure 3] 1 is a schematic diagram of a battery pack according to one embodiment of the present application. [Figure 4] FIG. 4 is an exploded view of the battery pack shown in FIG. 3 according to one embodiment of the present application. [Figure 5] 1 is a schematic diagram of an apparatus in which a battery pack is used as a power source in one embodiment of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, with appropriate reference to the drawings, embodiments specifically disclosing the adhesive, separator, and lithium-ion battery using the separator of the present application will be described in detail. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and redundant descriptions of structures that are actually the same may be omitted. This is to avoid unnecessarily lengthening the following description and to facilitate understanding by those skilled in the art. Note that the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0023] The "ranges" disclosed in this application are defined in the form of lower and upper limits. A given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of the particular range. Such defined ranges may be inclusive or exclusive of the end values ​​and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a single range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if 1 and 2 are listed as minimum range values ​​and 3, 4, and 5 are listed as maximum range values, the ranges 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5 are all contemplated. In this application, unless otherwise specified, the numerical range "ab" represents a shorthand notation for any combination of real numbers from a to b, where a and b are both real numbers. For example, the numerical range "0-5" represents that the present specification has already listed all real numbers between "0-5," and "0-5" is merely a shorthand representation of combinations of these numbers. Also, expressing a parameter as an integer ≧2 is equivalent to disclosing that this parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0024] Unless otherwise stated, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0025] Unless otherwise stated, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0026] Unless otherwise stated, all steps in this application may be performed in sequence or randomly, preferably in sequence. For example, a method including steps (a) and (b) means that the method may include steps (a) and (b) performed in sequence, or may include steps (b) and (a) performed in sequence. For example, a method that may further include step (c) means that step (c) may be added to the method in any order, e.g., the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0027] Unless otherwise specified, the terms "comprise" and "include" referred to in this application may be open-ended or closed-ended. For example, "comprise" and "include" may indicate that other components not listed may be further included or included, or that only the listed components may be included or included.

[0028] Unless otherwise stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, "A or B" is satisfied when A is true (or exists) and B is false (or does not exist), when A is false (or does not exist) but B is true (or exists), or when both A and B are true (or exist).

[0029] The term "(meth)acrylic acid" includes the technical versions of acrylic acid and methacrylic acid. Similarly, "(meth)acrylamide" includes the technical versions of acrylamide and methacrylamide.

[0030] Currently, conventional separators for lithium-ion batteries generally suffer from insufficient adhesive strength and poor compatibility between adhesives and ceramic particles, resulting in relatively poor heat resistance, a tendency to shrink when heated, and a tendency to be punctured. In such cases, it is advantageous to improve the adhesive strength of the adhesive and the compatibility of the components in the separator to stabilize the separator in the event of thermal runaway, achieve pore closure, and reduce air permeability. Therefore, there is a need in the art for a new adhesive for separators that can effectively bond the components in the separator and synergistically work with these components to improve the separator's safety and stability under extreme conditions.

[0031] Specifically, a first aspect of the present application provides an adhesive comprising a terpolymer formed by copolymerization of a first monomer unit, a second monomer unit, and a third monomer unit, wherein the first monomer is a C1-C (meth)acrylic acid. 20 alkyl esters, the second monomer is selected from at least one of acrylonitrile and methacrylonitrile, and the third monomer is selected from at least one optionally substituted (meth)acrylamide, wherein the molar ratio of the first monomer unit to the second monomer unit to the third monomer unit is 50-58:40-44:2-6.

[0032] Of the three monomers mentioned above, the acrylate monomer can increase the adhesive's viscosity and swelling resistance, and as a flexible monomer chain segment in the molecular chain segment, it can adjust the adhesive's glass transition temperature, playing a positive role in improving the adhesive's viscosity, the cyano group has strong polarity and can promote ionic conductivity, and the amide group's main function is connection, undergoing polymerization through a normal addition reaction mechanism, increasing the molecular weight and stabilizing the adhesive. Controlling the molar ratio of these three monomers within a certain range not only ensures the adhesive's viscosity, but also controls the adhesive's molecular weight and glass transition temperature.

[0033] In some embodiments, the terpolymer has a structure of general formula (I): [ka] wherein R1 are the same or different and independently represent H or a methyl group; R2 is C1-C 20 Alkyl groups, C3-C 20 Cycloalkyl group or C1-C 20 hydroxyalkyl groups, optionally C1-C 12 Alkyl groups, C3-C 12 Cycloalkyl group or C1-C 12 hydroxyalkyl, and R2 is further optionally methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-octyl, isooctyl, 2-ethylhexyl, dodecyl or isobornyl; R3 is H or a C1-C6 alkyl group monosubstituted by OR4, R4 is H or a C1-C6 alkyl group, and R4 is further optionally H, methyl, ethyl, n-propyl or n-butyl; x, y and z are independently selected from integers from 50 to 2000, and optionally from integers from 100 to 500.

[0034] In the present application, the structure of the above general formula (I) means that the terpolymer of the present application is a (meth)acrylic acid C1-C 20 The formula is not intended to be limited to the form of an alternating block copolymer of alkyl ester, (meth)acrylonitrile, and (meth)acrylamide, but rather indicates the type and relative number of each monomer unit therein. As can be understood, the above structure also includes other possible block and random copolymers of the above monomer units. The adhesive of the present application may also include a mixture of terpolymers having the structure of general formula (I) above. The selection of x, y, and z must be such that the relative proportions of each monomer unit in the final terpolymer satisfy the above-mentioned limited ranges. TIFF0007797636000003.tif11168

[0035] In some embodiments, the weight average molecular weight Mw of the terpolymer is 40,000-150,000 g / mol, and optionally 60,000-120,000 g / mol, and the weight average molecular weight of the adhesive within this range allows the adhesive to have a certain fluidity during the pre-pressing process, ensuring the adhesive's adhesive effect during the battery core manufacturing process.

[0036] In some embodiments, the (meth)acrylic acid C1-C 20 The alkyl ester is selected from one or more of methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, n-propyl acrylate, cyclohexyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate. In some other embodiments, the third monomer is selected from one or more of acrylamide, N-methylolacrylamide, and N-butoxymethacrylamide.

[0037] In some embodiments, the glass transition temperature Tg of the terpolymer is between -20°C and 40°C, and optionally between 0°C and 20°C. Adjusting the Tg of the terpolymer can improve its flowability, making it easier to apply and more compatible with ceramic particles. The Tg can be obtained by the following test method. 1. Sample preparation: The film sample was punched into a small disk with a diameter of 6 mm, weighed out 1-3 mg, placed in an Al crucible, flattened and pressed, and the crucible lid was placed upside down. 1-3 mg of the solid sample was weighed out and the crucible lid was placed on top. 2. Parameter settings: Nitrogen atmosphere, purge gas 50 mL / min, protective gas 100 mL / min. 3. Heating procedure: 10°C / min, 35°C to 200°C, hold at 300°C for 3 minutes, 10°C / min, 200°C to -40°C, hold at -40°C for 3 minutes, 10°C / min, -40°C to 200°C, and then terminated. The instrument used was a Discovery 250 differential scanning calorimeter.

[0038] A second aspect of the present application provides a separator including a base layer and an adhesive layer laminated in order, The adhesive layer comprises the adhesive according to the first aspect of the present application, heat-expandable microspheres, and ceramic particles.

[0039] The adhesive of the present application has relatively high adhesive strength, improving the adhesion between the heat-expandable microspheres and ceramic particles and preventing the separator coating particles from powdering. The heat-expandable microspheres expand rapidly during thermal runaway, filling the gaps between the microspheres in a timely manner and improving the separator's pore-blocking performance. The ceramic particles ensure the separator's dimensional stability at elevated temperatures, and the three synergistically improve the safety performance of lithium-ion batteries. The base layer may be made of materials commonly used in conventional separators, including, but not limited to, polypropylene, polyethylene, polypropylene-polyethylene composites, polyamides, polyimides, and polyester-based materials such as PET film, cellulose film, spandex, and aramid film. Polypropylene, polyethylene, or polypropylene-polyethylene composites are preferred. The base layer may have a thickness of 5-100 μm or 10-50 μm. Micropores may be distributed throughout the base layer to allow efficient conduction of lithium ions through the separator, and the pores may have a diameter of 40-200 nm, for example 60-120 nm.

[0040] The adhesive layer includes the adhesive according to the first embodiment of the present application, heat-expandable microspheres, and ceramic particles. The adhesive primarily functions to provide adhesion, adhere the base layer to the adhesive layer, and bond each component in the adhesive layer. The heat-expandable microspheres have a core-shell structure, with the outer shell being an elastic mesh-like cover layer formed by crosslinking a polymer, and the inner core being an expandable substance or phase-change material. One exemplary core material is a hydrocarbon-based material, which is liquid at room temperature and vaporizes at elevated temperatures, e.g., 65°C, expanding in volume. This increases the volume of the heat-expandable microspheres as a whole, filling the gaps between the microspheres and improving the pore-blocking performance of the separator. The ceramic particles have excellent size stability, ensuring that the separator's overall shape is stable and does not crack, even at high temperatures where thermal runaway occurs. Because ceramic particles are inorganic materials and have poor viscosity and are easily dispersed, an adhesive is required to tightly bond them to each other and to the heat-expandable microspheres. The present inventors have discovered that the use of a combination of the adhesive of the present application, heat-expandable microspheres, and ceramic particles synergistically improves the airtightness of the separator at high temperatures, significantly reducing the air permeability of the separator under thermal runaway conditions, and thereby improving its safety.

[0041] In some embodiments, the heat-expandable microspheres have a glass transition temperature of 40-100°C, optionally 60-90°C. The glass transition temperature of the heat-expandable microspheres refers to the glass transition temperature of the polymer in the core layer, and its measurement method refers to the measurement method for the Tg of the terpolymer described above. The heat-expandable microspheres have an average particle size Dv50 of 0.1 μm-2 μm, optionally 0.3 μm-1.5 μm. If the average particle size is too small, the thermal expansion performance will be insufficient, while if the average particle size is too large, the gaps between particles will be too large, which is not favorable for adhesion.

[0042] In some embodiments, the ceramic particles are at least one of aluminum oxide, boehmite, silicon dioxide, and titanium dioxide, and have an average particle size Dv50 of 0.5 μm-5 μm, optionally 1 μm-3.5 μm. The ceramic particles are flame-retardant, have relatively high hardness, and are resistant to deformation when heated, resulting in excellent size stability. Ceramic materials have low thermal conductivity, which further prevents thermal runaway points in a battery from expanding to form a global thermal runaway, thereby improving battery safety. The distribution of a large amount of lyophilic groups, such as -OH, on the surface of the ceramic particles enhances the permeability and electrolyte retention of the separator, further improving the charge / discharge performance of lithium-ion batteries.

[0043] In some embodiments, the mass ratio of the adhesive to the heat-expandable microspheres to the ceramic particles is 25-30:10-20:50-65. Controlling the mass ratio of the adhesive to the heat-expandable microspheres to the ceramic particles within a specific range can significantly improve the performance of the separator. A low adhesive content can result in incomplete coating and adhesion of the heat-expandable microspheres to the ceramic particles, resulting in powder shedding. A high adhesive content can affect the ratio of the heat-expandable microspheres to the ceramic particles, reducing the expansion efficiency of the heat-expandable microspheres. A low content of the heat-expandable microspheres can result in incomplete sealing of the separator pores after expansion. A low content of the ceramic particles can affect the thermal stability of the separator and further impact the safety performance of lithium-ion batteries. The relative ratios of the adhesive layer can be adjusted by adjusting the amounts of each component. For example, the three components can be mixed in a specific weight ratio using a mechanical stirrer, followed by deionized water, which is then mixed and stirred to form an aqueous slurry. The obtained slurry is coated on the base layer at a certain thickness and dried, and the coating density is 0.1-3 g / m 2 and can be wound up to obtain a separator.

[0044] A third aspect of the present application provides a lithium ion battery, the lithium ion battery comprising the adhesive of the first aspect of the present application or the separator according to the second aspect of the present application.

[0045] A fourth aspect of the present application provides a battery pack, the battery pack including the lithium-ion battery of the third aspect of the present application.

[0046] A fifth aspect of the present application provides a power consuming device, the power consuming device including the lithium ion battery of the third aspect of the present application or the battery pack of the fourth aspect of the present application.

[0047] The materials of each assembly of the lithium-ion battery of the present application can be selected from a wide range. In some embodiments, the battery is specifically a lithium-ion secondary battery. The battery cells of the lithium-ion secondary battery are described in detail below.

[0048] Generally, a lithium-ion secondary battery includes a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. During charging and discharging, active ions are absorbed and released between the positive and negative electrodes. The separator is located between the positive and negative electrodes to provide isolation. The electrolyte conducts ions between the positive and negative electrodes.

[0049] [Electrolyte] The electrolyte serves to conduct ions between the positive and negative electrodes and includes an electrolyte salt and a solvent.

[0050] In the present application, the electrolyte salt may be a common electrolyte salt in lithium ion secondary batteries, for example, the lithium salt includes the lithium salt as the above-mentioned high thermal stability salt, the lithium salt as a low impedance additive, or the lithium salt that suppresses corrosion of aluminum foil. By way of example, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium hexafluoroarsenate (LiAsF), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoro(oxalato)borate (LiDFOB), lithium difluorophosphate (LiPOF), lithium difluorobis(oxalato)phosphate (LiDFOP), lithium fluorosulfonate (LiSOF), difluorobis(oxalato) salt (NDFOP), LiF(SON)SOF, KFSI, CsFSI, Ba(FSI), and LiFSONSOCHCHCF.

[0051] The type of solvent is not particularly limited and can be selected according to actual needs. In some embodiments, the solvent is a non-aqueous solvent. Optionally, the solvent may include one or more of a linear carbonate, a cyclic carbonate, and a carboxylic acid ester. In some embodiments, the solvent may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), tetrahydrofuran, sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE).

[0052] In some embodiments, the electrolyte solution may further optionally contain other additives. For example, the additives may include a negative electrode film-forming additive, a positive electrode film-forming additive, and / or an additive that can improve certain battery performance characteristics, such as an additive that improves the overcharge performance of the battery, an additive that improves the high-temperature performance of the battery, and an additive that improves the low-temperature performance of the battery. For example, the additive may be selected from at least one of an unsaturated bond-containing cyclic carbonate compound, a halogen-substituted cyclic carbonate compound, a sulfate ester compound, a sulfite ester compound, a sultone compound, a disulfonic acid compound, a nitrile compound, an aromatic compound, an isocyanate compound, a phosphazene compound, a cyclic acid anhydride compound, a phosphite ester compound, a phosphate ester compound, a borate ester compound, and a carboxylic acid ester compound.

[0053] [Positive electrode plate] The positive electrode plate includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material and a conductive agent.

[0054] For example, the positive electrode current collector has two surfaces facing each other in the thickness direction thereof, and the positive electrode active material layer is disposed on either one or both of the two facing surfaces of the positive electrode current collector.

[0055] In the lithium-ion secondary battery of the present application, the positive electrode current collector may be a metal foil sheet or a composite current collector. For example, aluminum foil may be used as the metal foil sheet. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. The composite current collector may be formed by forming a metal material (e.g., aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer substrate (e.g., a substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0056] The positive electrode active material layer disposed on the surface of the positive electrode current collector includes a positive electrode active material. The positive electrode active material used in the present application may include any common positive electrode active material used in secondary batteries. In some embodiments, the positive electrode active material may include one or more selected from lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified compounds thereof. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and modified compounds thereof. All of these materials are commercially available. The surface of the positive electrode active material may be coated with carbon.

[0057] The positive electrode active material layer may optionally include a conductive agent. However, the type of conductive agent is not specifically limited, and a person skilled in the art may select the conductive agent according to actual needs. For example, the conductive agent for the positive electrode material may be selected from one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0058] The positive electrode active material layer further includes an aqueous adhesive. The aqueous adhesive may be selected from one or more of soluble polysaccharides and their derivatives, and water-soluble or water-dispersible polymers. For example, the aqueous adhesive may be methylcellulose and its salts, xanthan gum and its salts, chitosan and its salts, alginic acid and its salts, polyethyleneimine and its salts, polyacrylamide, acrylic acid copolymers and their derivatives. In particular, the aqueous adhesive may be a composite of xanthan gum and acrylic acid copolymers, with a composite weight ratio of 2:1-0.2:2.8. Optionally, the weight-average molecular weight of the xanthan gum is 300,000-2,000,000 g / mol, and the weight-average molecular weight of the acrylic acid copolymer is 100,000-1,000,000 g / mol.

[0059] In the present application, the positive electrode plate can be manufactured according to a method known in the art. For example, a positive electrode active material to be coated with carbon, a conductive agent, and a water-based adhesive may be dispersed in a solvent (e.g., water) to form a uniform positive electrode slurry, which may then be coated onto a positive electrode current collector, followed by drying, cold pressing, and other processes to obtain a positive electrode plate.

[0060] [Negative electrode plate] The negative electrode plate includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, the negative electrode material layer including a negative electrode active material.

[0061] For example, the negative electrode current collector has two surfaces that face each other in the thickness direction thereof, and the negative electrode material layer is disposed on either one or both of the two facing surfaces of the negative electrode current collector.

[0062] In the lithium-ion secondary battery of the present application, the negative electrode current collector may be a metal foil sheet or a composite current collector. For example, a copper foil may be used as the metal foil sheet. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (e.g., copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer substrate (e.g., a substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0063] In the lithium-ion secondary battery of the present application, the negative electrode material layer generally includes a negative electrode active material, an optional adhesive, an optional conductive agent, and other optional auxiliary agents, and is generally obtained by coating and drying a negative electrode slurry. The negative electrode slurry is generally formed by dispersing the negative electrode active material, the optional conductive agent, and the adhesive in a solvent and stirring the resulting mixture uniformly. The solvent may be N-methylpyrrolidone (NMP) or deionized water.

[0064] The specific type of the negative electrode active material is not limited, and any active material known in the art that can be used for the negative electrode of a lithium ion secondary battery may be used, and those skilled in the art may select one according to actual needs. For example, the negative electrode active material may be selected from one or more of graphite, soft carbon, hard carbon, mesocarbon microspheres, carbon fibers, carbon nanotubes, silicon monomers, silicon compounds, silicon carbon composites, and lithium titanate.

[0065] By way of example, the conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0066] By way of example, the adhesive may be selected from one or more of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0067] Other optional auxiliaries include, for example, thickeners (eg, sodium carboxymethylcellulose (CMC-Na)).

[0068] [Separator] A lithium-ion secondary battery employing an electrolyte includes a separator. The separator is disposed between a positive electrode plate and a negative electrode plate to separate them. The separator of the present application is described above, but the lithium-ion battery of the present application may further include a conventional separator. The type of conventional separator is not particularly limited, and any known porous separator with good chemical and mechanical stability may be selected. In some embodiments, the material of the conventional separator may be selected from one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without any particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without any particular limitation.

[0069] In some embodiments, the positive and negative electrodes and the separator can be fabricated into an electrode assembly by a winding or lamination process.

[0070] In some embodiments, the secondary battery may include an exterior body, which may be used to package the electrode assembly and the electrolyte.

[0071] In some embodiments, the exterior of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The exterior of the secondary battery may be a pouch, such as a bag-shaped pouch. The pouch may be made of plastic, such as polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0072] The present application does not particularly limit the shape of the secondary battery, which may be cylindrical, rectangular, or any other shape. For example, Figure 1 shows an example of a lithium ion secondary battery 5 with a rectangular structure.

[0073] In some embodiments, referring to FIG. 2 , the exterior body may include a case 51 and a cover plate 53. Here, the case 51 may include a bottom plate and side plates connected to the bottom plate, which together form a surrounding accommodating cavity. The case 51 has an opening communicating with the accommodating cavity, and the cover plate 53 may be installed over the opening to seal the accommodating cavity. The positive electrode plate, the negative electrode plate, and the separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is packaged within the accommodating cavity. An electrolyte is impregnated into the electrode assembly 52. ​​The number of electrode assemblies 52 included in the lithium ion secondary battery 5 may be one or more, and this can be selected by those skilled in the art according to actual needs.

[0074] In some embodiments, the lithium ion secondary batteries may be assembled into a battery module 4. The number of lithium ion secondary batteries included in the battery module 4 may be one or more, and the specific number may be selected by those skilled in the art depending on the application and capacity of the battery module 4. In the battery module 4, the plurality of lithium ion secondary batteries 5 may be arranged in sequence along the length of the battery module. Of course, they may also be arranged in any other manner. Furthermore, the plurality of lithium ion secondary batteries 5 may be fixed using fasteners. Optionally, the battery module 4 may further include a housing having an accommodating space, and the plurality of lithium ion secondary batteries 5 are accommodated in the accommodating space.

[0075] In some embodiments, the lithium ion secondary batteries 5 or battery modules 4 may be assembled into a battery pack 1, and the number of lithium ion secondary batteries 5 or battery modules 4 included in the battery pack 1 may be selected by those skilled in the art according to the application and capacity of the battery pack 1.

[0076] 3 and 4 show an example of a battery pack 1. Referring to Fig. 3 and Fig. 4, the battery pack 1 may include a battery box and a plurality of battery cells installed in the battery box. The battery box includes an upper housing 2 and a lower housing 3, and the upper housing 2 is attached to the lower housing 3 as a lid to form a sealed space for accommodating the battery cells.

[0077] The present application also provides a device, the device including a battery pack according to the present application. The battery pack may be used as a power source for the device or as an energy storage unit for the device. The device may be, but is not limited to, a mobile device (e.g., a mobile phone, a laptop, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc. The device may select a battery pack according to its usage needs.

[0078] An example device, such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, is shown in Figure 5. To meet the device's demand for high power and high energy density from lithium-ion secondary batteries, a battery pack or battery module can be employed. [Example]

[0079] Example The following examples of the present application are described. The examples described below are illustrative and are intended only to interpret the present application and should not be understood as limitations on the present application. If specific techniques or conditions are not specified in the examples, they are carried out according to techniques or conditions described in documents in the art or according to product specifications. The reagents or equipment used are not specified by manufacturer and are all ordinary products that are commercially available.

[0080] Adhesive manufacturing Manufacturing Example 1 At room temperature, 60.92g of methyl acrylate, 33.04g of acrylonitrile, and 6.04g of acrylamide were weighed out in a molar ratio of 50:44:6, totaling 100g of mixed monomers. The mixture was added to a 500mL four-neck flask equipped with a mechanical stirrer, thermometer, and condenser. 3g of sodium lauryl sulfate emulsifier, 1g of ammonium persulfate initiator, and 120g of deionized water were then added. The mixture was emulsified by stirring at 1600rpm for 30min, and then heated to 75℃ under nitrogen atmosphere and reacted for 4h. The pH was adjusted to 6-8, and the mixture was immediately cooled to below 40℃ and discharged to obtain the product.

[0081] Manufacturing Examples 2 to 5 The molar ratio of the monomers was changed to 51:43:6, 52:42:6, 53:41:6, and 54:40:6 in order, and the mass of the corresponding monomers was calculated. The total mass of the three monomers was 100 g. The other steps of Preparations 2 to 5 were the same as those of Preparation 1.

[0082] Manufacturing Example 6 At room temperature, 69.71g of n-butyl acrylate, 24.90g of acrylonitrile, and 5.39g of N-methylolacrylamide were weighed out, totaling 100g of mixed monomers, in a molar ratio of 51:44:5. The mixture was added to a 500mL four-neck flask equipped with a mechanical stirrer, thermometer, and condenser. 3g of sodium lauryl sulfate emulsifier, 1g of ammonium persulfate initiator, and 120g of deionized water were then added. The mixture was emulsified by stirring at 1600 rpm for 30 minutes, and then heated to 75°C under nitrogen atmosphere and reacted for 4 hours. The pH was adjusted to 6-8, and the mixture was immediately cooled to below 40°C and discharged to obtain the product.

[0083] Manufacturing Examples 7-10 The molar ratio of the monomers was changed to 52:43:5, 53:42:5, 54:41:5, and 55:40:5 in order, and the mass of the corresponding monomers was calculated. The total mass of the three monomers was 100 g. The other steps of Preparations 7 to 10 were the same as those of Preparation 6.

[0084] Manufacturing Example 11 At room temperature, 68.42g of ethyl methacrylate, 26.91g of acrylonitrile, and 4.66g of N-methylolacrylamide were weighed out, totaling 100g of mixed monomers, in a molar ratio of 52:44:4. The mixture was added to a 500mL four-neck flask equipped with a mechanical stirrer, thermometer, and condenser. 3g of sodium lauryl sulfate emulsifier, 1g of ammonium persulfate initiator, and 120g of deionized water were then added. The mixture was emulsified by stirring at 1600 rpm for 30 minutes, and then heated to 75°C under nitrogen atmosphere and reacted for 4 hours. The pH was adjusted to 6-8, and the mixture was immediately cooled to below 40°C and discharged to obtain the product.

[0085] Manufacturing Examples 12-15 Except for changing the molar ratio of the monomers in order to 53:43:4, 54:42:4, 55:41:4, and 56:40:4, the mass of the corresponding monomers was calculated, and the total mass of the three monomers was 100 g. The other steps of Preparations 12 to 15 were the same as those of Preparation 11.

[0086] Manufacturing Example 16 At room temperature, 67.94g of 2-hydroxyethyl methacrylate, 29.08g of methacrylonitrile, and 2.99g of N-butoxymethacrylamide were weighed out in a molar ratio of 53:44:3, totaling 100g of mixed monomers, and added to a 500mL four-neck flask equipped with a mechanical stirrer, thermometer, and condenser. 3g of sodium lauryl sulfate emulsifier, 1g of ammonium persulfate initiator, and 120g of deionized water were then added, and emulsified by stirring at 1600rpm for 30min. The mixture was then heated to 75℃ under nitrogen atmosphere and reacted for 4h, the pH was adjusted to 6-8, and the mixture was immediately cooled to below 40℃ and discharged to obtain the product.

[0087] Manufacturing Examples 17-20 Except for changing the molar ratio of the monomers in order to 54:43:3, 55:42:3, 56:41:3, and 57:40:3, the mass of the corresponding monomers was calculated, and the total mass of the three monomers was 100 g. The other steps of Preparations 17 to 20 were the same as those of Preparation 16.

[0088] Manufacturing Example 21 At room temperature, 70.44g of 2-hydroxypropyl methacrylate, 26.71g of methacrylonitrile, and 2.85g of N-butoxymethacrylamide were weighed out in a molar ratio of 54:44:2, totaling 100g of mixed monomers, and added to a 500mL four-neck flask equipped with a mechanical stirrer, thermometer, and condenser. 3g of sodium lauryl sulfate emulsifier, 1g of ammonium persulfate initiator, and 120g of deionized water were then added, and the mixture was emulsified by stirring at 1600rpm for 30min. The mixture was then heated to 75℃ under nitrogen atmosphere and reacted for 4h, the pH was adjusted to 6-8, and the mixture was immediately cooled to below 40℃ and discharged to obtain the product.

[0089] Manufacturing Examples 22-25 Except for changing the molar ratio of the monomers to 55:43:2, 56:42:2, 57:41:2, and 58:40:2 in order, the mass of the corresponding monomers was calculated, and the total mass of the three monomers was 100 g. The other steps of Preparations 22 to 25 were the same as those of Preparation 21.

[0090] Comparative Manufacturing Example 1 At room temperature, 69.50g of methyl acrylate, 22.85g of acrylonitrile, and 7.65g of acrylamide were weighed out, totaling 100g of mixed monomers, in a molar ratio of 60:32:8. The mixture was added to a 500mL four-neck flask equipped with a mechanical stirrer, a thermometer, and a condenser. 3g of sodium lauryl sulfate emulsifier, 1g of ammonium persulfate initiator, and 120g of deionized water were then added. The mixture was emulsified by stirring at 1600 rpm for 30 minutes, and then heated to 75°C under nitrogen atmosphere and reacted for 4 hours. The pH was adjusted to 6-8, and the mixture was immediately cooled to below 40°C and discharged to obtain the product.

[0091] Comparative Manufacturing Example 2 At room temperature, 74.42g of 2-hydroxyethyl methacrylate and 25.58g of methacrylonitrile were weighed out, totaling 100g of mixed monomers, according to a molar ratio of 60:40, and added to a 500mL four-necked flask equipped with a mechanical stirrer, a thermometer and a condenser pipe. Then, 3g of sodium lauryl sulfate emulsifier, 1g of ammonium persulfate initiator and 120g of deionized water were added, and the mixture was emulsified by stirring at 1600rpm for 30min. The mixture was then heated to 75℃ under nitrogen atmosphere and reacted for 4h, the pH was adjusted to 6-8, and the mixture was immediately cooled to below 40℃ and discharged to obtain the product.

[0092] Comparative Manufacturing Example 3 At room temperature, 44.70g of methyl acrylate, 52.56g of 2-hydroxypropyl methacrylate, and 2.73g of acrylamide were weighed out in a molar ratio of 54:42:4, totaling 100g of mixed monomers, and added to a 500mL four-neck flask equipped with a mechanical stirrer, thermometer, and condenser. 3g of sodium lauryl sulfate emulsifier, 1g of ammonium persulfate initiator, and 120g of deionized water were then added. The mixture was emulsified by stirring at 1600 rpm for 30 minutes, and then heated to 75°C under nitrogen atmosphere and reacted for 4 hours. The pH was adjusted to 6-8, and the mixture was immediately cooled to below 40°C and discharged to obtain the product.

[0093] The weight average molecular weight (g / mol) of the adhesives of Preparation Example 1-25 and Comparative Preparation Example 1-3 was measured using gel permeation chromatography, and the results are shown in Table 1.

[0094] [Table 1] TIFF0007797636000005.tif180168

[0095] Lithium-ion battery manufacturing Example 1 Separator manufacturing A commercially available PP-PE copolymer microporous film (Model No. 20, manufactured by Zhuoga Electronics Technology Co., Ltd.) with a thickness of 20 μm and an average pore size of 80 nm was used as the substrate. The adhesive from Preparation Example 2, heat-expandable microspheres, and aluminum oxide were mixed uniformly in deionized water in a mass ratio of 28:15:57 with stirring to obtain a slurry. The heat-expandable microspheres had a glass transition temperature of 65°C and an average particle size of 0.8 μm, and the ceramic particles were silicon dioxide particles with an average particle size of 0.8 μm. The slurry was applied to the substrate and dried to remove the water, and the coating density of the slurry on the substrate was 0.5 g / m. 2 and then wound up to finally obtain a separator.

[0096] Positive electrode plate manufacturing Polyvinylidene fluoride (PVDF), lithium iron phosphate (LFP), conductive carbon black, and N-methylpyrrolidone (NMP) were uniformly stirred and mixed in a weight ratio of 1.2:58.38:0.42:40 to obtain a positive electrode slurry. After sufficient uniform stirring and mixing, the positive electrode slurry was manufactured into a positive electrode slurry. The positive electrode slurry was uniformly coated on a positive electrode current collector aluminum foil, which was then dried, cold pressed, and slit to obtain a positive electrode plate.

[0097] Negative electrode plate manufacturing The negative electrode active material artificial graphite, the conductive agent acetylene black, the adhesive styrene butadiene rubber (SBR), and the thickener carboxymethyl cellulose sodium (CMC-Na) were dissolved in deionized water as a solvent in a mass ratio of 96.2:1.0:1.6:1.2, and after thoroughly stirring and mixing to a uniform degree, a negative electrode slurry was produced. The negative electrode slurry was coated onto a negative electrode current collector copper foil, which was then dried, cold pressed, and slit to obtain a negative electrode plate.

[0098] Electrolyte production Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and LiPF6 was uniformly dissolved in the solution to obtain an electrolyte solution with a LiPF6 concentration of 1 mol / L.

[0099] Lithium-ion battery manufacturing The positive electrode plate, separator, and negative electrode plate were stacked in this order and wound to obtain an electrode assembly. The electrode assembly was then placed in an outer casing, and the prepared electrolyte solution was added. After going through processes such as packaging, standing, chemical formation, and aging, a lithium ion battery was obtained.

[0100] Examples 2 to 4 The other steps in Examples 2 to 4 were the same as in Example 1, except that the vitrification transition temperatures of the heat-expandable microspheres were changed to 78°C, 89°C, and 106°C, respectively.

[0101] Examples 5 to 8 The adhesive used was Preparation Example 8, the glass transition temperature of the heat-expandable microspheres was changed to 89°C, the average particle diameters were changed to 0.2 μm, 1 μm, 1.7 μm, and 2.2 μm, respectively, and the ceramic particles were changed to aluminum oxide. Other steps in Examples 5 to 8 were the same as those in Example 1.

[0102] Examples 9 to 12 The other steps of Examples 9 to 12 are the same as those of Example 3, except that the adhesive used is Preparation Example 13, the ceramic particles are changed to boehmite, and the average particle sizes are changed to 1.0 μm, 2.1 μm, 3.9 μm, and 5.5 μm, respectively.

[0103] Examples 13 to 16 The other steps of Examples 13 to 16 were the same as those of Example 3, except that Preparation Example 22 was selected as the adhesive, the ceramic particles were changed to titanium dioxide, and the mass ratios of adhesive:thermoexpandable microspheres:ceramic particles were changed to 20:20:60, 24:18:58, 28:16:56, and 32:14:54, respectively.

[0104] Comparative Examples 1 to 3 The other steps of Comparative Examples 1 to 3 are the same as those of Example 3, except that Comparative Production Example 1, Comparative Production Example 2, and Comparative Production Example 3 are selected as adhesives.

[0105] The separators produced in Examples 1-16 and Comparative Examples 1-3 were measured for air permeability at room temperature and after heating at 100° C., and the results are summarized in Table 2 below.

[0106] Measurement method for air permeability: Cut the separator into a 5cm square, apply a pressure of 1.21kPa using an air permeability meter, and measure the air permeability of 100ml of gas at 6.45cm. 2 The time required for the gas to permeate the separator was tested and the gas permeability value (s / 100 ml) was obtained.

[0107] [Table 2]

[0108] As can be seen from a comparison between Example 3 and Comparative Examples 1-3, when the terpolymer of the present application is used as an adhesive in a separator and other conditions are the same, the permeability of a lithium ion battery including this separator can be significantly reduced, specifically as shown by a significantly increased air permeability value after heating at 100°C. The significantly increased air permeability value indicates that the time required for the same volume of gas to permeate is significantly longer, reflecting the lithium ion battery of Example 3 having stronger shielding performance at high temperatures and being less susceptible to short circuits and thermal runaway.

[0109] Furthermore, when the same adhesive is used, if the glass transition temperature of the heat-expandable microspheres is higher than 100°C, the air permeability value decreases, thereby deteriorating the shielding performance of the separator (see Example 4). Similarly, if the average particle size Dv50 of the heat-expandable microspheres is higher than 2.0 μm, the air permeability value of the resulting separator also decreases significantly (see Example 8). The average particle size of the ceramic particles also affects the air permeability performance of the separator. If the average particle size of the ceramic particles is higher than 5 μm, the air permeability value of the resulting separator also decreases significantly (see Example 12).

[0110] The weight ratio of the adhesive, heat-expandable microspheres, and ceramic particles in the adhesive layer of the separator also affects the gas permeability of the separator. As can be seen from the comparison of Examples 13 to 16, by selecting a specific ratio range of these three components, a separator with a higher gas permeability value at 100°C can be obtained.

[0111] Although the present application has been described with reference to the above embodiments, various modifications can be made thereto and equivalents can be substituted for the components therein without departing from the scope of the present application. In particular, unless there is a structural contradiction, the technical features recited in each embodiment can be combined in any manner. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions included within the scope of the claims. [Explanation of symbols]

[0112] 1 battery pack 2 Upper housing 3 Lower housing 4 battery modules 5 Lithium-ion secondary battery 51 cases 52 electrode assembly 53 cover plate

Claims

1. An adhesive for lithium ion batteries, comprising a terpolymer formed by copolymerizing a first monomer unit, a second monomer unit, and a third monomer unit, wherein the first monomer is (meth)acrylic acid C １ -C ２０ the first monomer is selected from alkyl esters, the second monomer is selected from at least one of acrylonitrile and methacrylonitrile, and the third monomer is selected from at least one optionally substituted (meth)acrylamide, wherein the molar ratio of the first monomer unit to the second monomer unit to the third monomer unit is 50-58:40-44:2-6.

2. The terpolymer has a structure of the following general formula (I): 【Chemistry 1】 Here, R １ are the same or different and independently represent H or a methyl group, R ２ is C １ -C ２０ Alkyl group, C ３ -C ２０ Cycloalkyl group or C １ -C ２０ is a hydroxyalkyl group, R ３ is H or OR ４ C monosubstituted by １ -C ６ is an alkyl group, and R ４ is H or C １ -C ６ is an alkyl group, 2. The adhesive of claim 1, wherein x, y, and z are independently selected from integers from 50 to 2000.

3. 3. The adhesive according to claim 1, wherein the weight average molecular weight Mw of the terpolymer is 40,000 to 150,000 g / mol.

4. The (meth)acrylic acid C １ -C ２０ 3. The adhesive of claim 1 or 2, wherein the alkyl ester is selected from one or more of methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, n-propyl acrylate, cyclohexyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate.

5. The adhesive of claim 1 or 2, wherein the third monomer is selected from one or more of acrylamide, N-methylolacrylamide, and N-butoxymethacrylamide.

6. 3. The adhesive according to claim 1, wherein the glass transition temperature Tg of the terpolymer is −20° C. to 40° C.

7. A separator including a base layer and an adhesive layer laminated in order, A separator, wherein the adhesive layer comprises the adhesive of claim 1 , heat-expandable microspheres, and ceramic particles.

8. 8. The separator according to claim 7, wherein the heat-expandable microspheres have a vitrification transition temperature of 40 to 100°C.

9. 9. The separator according to claim 8, wherein the heat-expandable microspheres have an average particle size Dv50 of 0.1 μm to 2 μm.

10. 8. The separator according to claim 7, wherein the ceramic particles are at least one of aluminum oxide, boehmite, silicon dioxide, and titanium dioxide, and have an average particle size Dv50 value of 0.5 μm to 5 μm.

11. 8. The separator according to claim 7, wherein a mass ratio of the adhesive to the heat-expandable microspheres to the ceramic particles is 25-30:10-20:50-65.

12. A lithium ion battery comprising the adhesive of claim 1 or the separator of claim 7.

13. A battery pack comprising the lithium ion battery of claim 12.

14. 13. A power consuming device comprising the lithium ion battery of claim 12.

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