Isolating membrane, battery monomer, battery and electric device

Abstract

The invention discloses an isolating membrane, a battery monomer, a battery and an electric device. The isolating membrane comprises a base membrane and a coating arranged on at least one side of the base membrane, the coating comprises inorganic particles and polyester, and the glass transition temperature of the polyester is-30 DEG C to-80 DEG C. The coating contains the polyester, so that the performance of the isolating membrane can be improved, the isolating membrane can realize self-repairing in the charging and discharging process of the battery, the stability of the isolating membrane structure is maintained, and the cycle life and the stability of a battery monomer containing the isolating membrane are improved. The invention also provides a battery monomer, a battery and a power utilization device with the above advantages.

Description

Technical Field

[0001] The present application belongs to the technical field of batteries, and particularly relates to a separator, a battery cell, a battery, and an electrical device. Background Art

[0002] With the continuous expansion of the demand for batteries represented by lithium-ion batteries, the separator is an important component of the battery, and the use of the separator is becoming more and more extensive. The separator is an insulating thin film with a porous structure, which can block the positive electrode plate and the negative electrode plate, and prevent the positive electrode plate and the negative electrode plate from short-circuiting inside the battery.

[0003] The battery separator has nano-scale pores inside, allowing active ions including lithium ions to freely pass through during charge and discharge, providing a channel for the rapid transmission of active ions between the positive electrode and the negative electrode. With the widespread use of battery cells and the improvement of the performance requirements for batteries, higher requirements are put forward for the performance of the separator. Summary of the Invention

[0004] The purpose of the present application is to provide a separator, a battery cell, a battery, and an electrical device. The polyester in the separator can enable the separator to achieve self-repair during the charge and discharge process of the battery and maintain the stability of the separator structure; the battery cell containing the separator can obtain improved kinetic performance and cycling performance, and improve the service life of the battery cell; the purpose of the present application is also to provide a battery and an electrical device containing the above battery cell, so as to obtain improved kinetic performance, cycling performance, and service life of the battery cell.

[0005] In a first aspect, an embodiment of the present application provides a separator, including:

[0006] A base film,

[0007] A coating disposed on at least one side of the base film, the coating comprising:

[0008] Inorganic particles and polyester, wherein the glass transition temperature of the polyester is -30°C to -80°C.

[0009] According to the embodiment of the present application, when the glass transition temperature of the polyester is within the above range, the polyester has a certain elasticity or reversible deformation at a suitable temperature; for example, at low temperature or normal temperature, the polyester is in a solid state and has a certain mechanical strength; while under heating conditions, when the temperature is near the glass transition temperature Tg, the chain segments of the polyester undergo a certain free movement, making it have a certain elasticity or reversible deformation, or forming a high elastic state of fluidity. Under the action of the intermolecular force generated by the intermolecular interaction at the interface (which includes non-covalent bonds, intermolecular hydrogen bonds, orientation forces, etc.), the molecular chain segments that can move freely migrate and rearrange at the interface.

[0010] According to the embodiments of the present application, a polyester having a certain elasticity or reversible deformation is applied to the coating in the separator. When the separator is damaged during the charge and discharge of the battery, based on its elasticity or reversible deformation, the interface damage can be repaired, and self-repair of the separator surface can be achieved.

[0011] In addition, the polyester has hydroxyl groups, carboxyl groups, etc. These functional groups also enhance the contact between the polyester and other components of the separator coating, have the effect of enhancing the coating adhesion, and can also promote the interfacial adhesion between the separator containing the polyester and the battery electrode, reducing the risk of electrode wrinkling. The carboxyl group can combine with active ions including lithium ions to provide a migration path for the active ions, greatly improving the ion exchange ability of the separator and improving the charge and discharge efficiency of the battery containing the separator.

[0012] In any embodiment of the present application, based on the total mass of the coating, the coating includes 0.1% to 5% of polyester.

[0013] According to the embodiments of the present application, the polyester contained in the coating can enhance the interfacial adhesion between the separator and the battery electrode, reducing the risk of electrode wrinkling. The carboxyl group can combine with active ions including lithium ions to provide a migration path for the active ions, greatly improving the ion exchange ability of the separator and improving the charge and discharge efficiency of the battery containing the separator.

[0014] According to the embodiments of the present application, the coating includes the polyester with the above mass content. On the one hand, it can enhance the bonding strength between the components in the coating and enhance the cohesion of the coating; when the separator is damaged by the outside world, the polyester in the coating can repair the interface damage of the coating, realizing the self-repair of the separator.

[0015] In any embodiment of the present application, the glass transition temperature of the polyester is -65°C to -80°C.

[0016] According to the embodiments of the present application, the glass transition temperature of the polyester can affect the interfacial stability between the polyester and other components of the separator coating. The glass transition temperature of the polyester is more appropriate, and it is more stable during battery operation, which can make the coating interface stable. At the same time, it can also reduce the damage caused by the volume change of the active material in the battery electrode in contact with the separator, improving the adverse effects on the separator; therefore, the polyester with a suitable glass transition temperature can self-repair the interface damage of the separator, providing more stable cycling performance; it is also beneficial to reduce the risk of thermal runaway of the battery and help extend the cycle life of the battery.

[0017] In some alternative embodiments, the polyester includes structural units shown in formula (1) and formula (2), and at least part of the polyester shown in formula (1) and formula (2);

[0018]

[0019] Among them, R 1 and R 2 each independently represent any one of a single bond, an unsubstituted or substituent-substituted C 1～8 alkyl group, an unsubstituted or substituent-substituted C 1～8 alkoxy group; R a , R b , R c independently include -H, -OH, -COOH, an unsubstituted or substituent-substituted C 1 to 8 alkyl group, an unsubstituted or substituent-substituted C 1 to 8 alkoxy group, and at least one of R 1 , R 2 , R a , R b , R c has a hydroxyl group; at least one of R 1 , R 2 , R a , R b , R c has a carboxyl group; the substituent includes any one of a hydroxyl group, a carboxyl group and a carbonyl group.

[0020] According to the embodiments of the present application, the coating includes the above polyester, which has a certain elasticity or reversible deformation. When the battery is charged and discharged, when the separator is damaged by the outside world, the polyester in the coating can repair the interfacial damage of the coating and realize the self-repair of the separator.

[0021] In any embodiment of the present application, the weight-average molecular weight of the polyester is 50×10 4 to 80×10 4 , and can be optionally 65×10 4 to 75×10 4 .

[0022] According to the embodiments of the present application, when the weight-average molecular weight of the polyester is within the above range, it can have more structural units, can increase reactive functional groups such as hydroxyl groups and carboxyl groups, and improve the bonding performance of the polyester; the polyester with the weight-average molecular weight within the above range can provide more molecular crosslinking points, thereby increasing the bonding strength with other components in the separator coating; and the polyester has appropriate elasticity or reversible deformation, which helps to reduce the restoration of the integrity and flatness of the separator surface after damage, and is beneficial to improving the specific capacity and cycle stability of the battery.

[0023] In any embodiment of the present application, based on the total weight of the polyester, the polyester contains 2×10 -4 to 11×10 -4Carboxyl groups per gram of mole.

[0024] According to the embodiments of the present application, the polyester contains carboxyl groups in the above molar content, so that when the polyester is used for the coating of the separator membrane, the carboxyl groups can combine with lithium ions to provide a migration path for lithium ions, greatly improving the passing rate of active ions through the separator membrane and enhancing the charge and discharge efficiency of the battery.

[0025] In any embodiment of the present application, the polyester includes at least one polyester among formulas (3)-(8):

[0026]

[0027] wherein, n is a positive integer, R 3 and R 4 each independently represents a C 1～6 alkyl group which is unsubstituted or arbitrarily substituted by -OH or -COOH.

[0028] According to the embodiments of the present application, the polyester with the above general structural formula has certain elasticity or reversible deformation. When this polyester is applied to the coating in the separator membrane, when the separator membrane is damaged externally during the charge and discharge of the battery, based on its elasticity or reversible deformation, it can repair the interfacial damage and achieve self-repair on the surface of the separator membrane.

[0029] In any embodiment of the present application, the coating includes a phosphate plasticizer. Optionally, the phosphate plasticizer includes one or more of tricresyl phosphate, tolyldiphenyl phosphate, diphenyl octyl phosphate, tris(2-ethylhexyl) phosphate.

[0030] According to the embodiments of the present application, plasticizers can generally improve the fluidity of materials, reduce the viscosity of materials, and may change and promote the molecular structure of the polyester in the coating at a certain temperature.

[0031] During the charge and discharge process of the battery, the coating contains this phosphate plasticizer and polyester, enabling the separator membrane to be more easily self-repaired at a relatively low temperature, improving the performance of the separator membrane and reducing the risk of short circuit. The binder composition of the present application can achieve a lower self-repair temperature. When the separator membrane uses this binder composition, a lower self-repair temperature can be obtained, realizing the self-repair of the separator membrane and enhancing the stability of the battery.

[0032] In addition, according to the embodiments of the present application, phosphate plasticizers generally have high thermal stability, which can improve the performance of the separator membrane in a high-temperature environment. The coexistence of phosphate plasticizers and binders may enhance the stability of the membrane, making it more durable and more resistant to chemical corrosion.

[0033] Further, the phosphate plasticizer can reduce the melting temperature of the polyester. In the molten state, it has better elasticity and reversible deformation, enabling the polyester to achieve surface self-repair of the separator film at a lower temperature.

[0034] In any embodiment of the present application, based on the total mass of the coating, the coating comprises 0.01% to 2% of a phosphate plasticizer.

[0035] According to the embodiments of the present application, when the mass percentage content of the phosphate plasticizer in the coating is within the above range, the stability of the separator film can be improved, and it can also have better elasticity and reversible deformation at a suitable temperature, enabling the polyester to achieve surface self-repair of the separator film.

[0036] The embodiments of the present application do not impose obvious restrictions on the type of the base film. Commonly used porous base films in the art can all be used. In any embodiment of the present application, the base film comprises one or more of a polyolefin film, a non-woven fabric film, a polyester film, a polyether film, a polyetherimide film, and a fluorinated polyetherimide film.

[0037] The addition of inorganic particles can increase the mechanical strength, wear resistance, and thermal stability of the separator film. The embodiments of the present application do not impose obvious restrictions on the type of the inorganic particles. Commonly used inorganic particles in the art can all be used. In some alternative embodiments, the inorganic particles comprise one or more of ceramic particles, boehmite, and alumina.

[0038] In any embodiment of the present application, the average particle size Dv50 of the inorganic particles is from 0.2 μm to 0.5 μm.

[0039] According to the embodiments of the present application, when the average particle size Dv50 of the inorganic particles is within the above range, the uniformity of the coating can be enhanced, facilitating the passage of active ions; and the presence of the inorganic particles improves the reliability of the battery, achieving the "thermal shutdown" effect.

[0040] In any embodiment of the present application, the ratio of the thickness of the base film to the thickness of the coating is 1∶(0.15 - 1).

[0041] According to the embodiments of the present application, the base film and the coating have an appropriate thickness ratio, enabling the separator film to have a suitable total thickness; which helps to reduce the volume and weight of the battery cell and can improve the safety performance of the battery cell containing the separator film.

[0042] In any embodiment of the present application, the thickness of the base film can be from 3 μm to 20 μm. According to the embodiments of the present application, the base film has an appropriate thickness, enabling the separator film to have a suitable total thickness; which helps to reduce the volume and weight of the battery cell and can improve the safety performance of the battery cell containing the separator film.

[0043] In any embodiment of the present application, the thickness of the coating is 0.5 μm to 20 μm. When the thickness of the coating is within the above range, the separator can have an appropriate total thickness, which helps to reduce the volume and weight of the battery cell and can improve the safety performance of the battery cell including the separator.

[0044] In any embodiment of the present application, the porosity of the base film is 30% to 70%.

[0045] According to the embodiments of the present application, when the base film has the above porosity, it has a certain electrolyte wettability, which facilitates the active ions to pass through the separator, improves the transmission rate of the active ions, and improves the kinetic performance of the battery cell including the separator.

[0046] In any embodiment of the present application, the air permeability of the base film is 110 to 310 s / 100 cc respectively.

[0047] According to the embodiments of the present application, controlling the thickness, porosity, and air permeability of the base film within the above ranges can comprehensively control the performance of the separator, which is beneficial to the use of the separator in the battery.

[0048] Fourthly, the embodiments of the present application provide a battery cell, including the separator of the third aspect.

[0049] The fourth aspect of the present application also provides a battery cell, including the battery separator of the third aspect of the present application. Thus, it has at least the same advantages as the separator.

[0050] The fifth aspect of the present application provides an electrical device, including at least one of the binder composition of the first aspect of the present application and the battery cell of the fourth aspect of the present application.

[0051] The electrical device of the present application includes the battery cell provided by the present application. Thus, it has at least the same advantages as the battery cell.

[0052] The details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the specification, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the following described drawings are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained according to the drawings without creative efforts.

[0054] Figure 1 A schematic diagram showing an embodiment of the separator of the present application is shown.

[0055] Figure 2 Shows a schematic diagram of another embodiment of the separator film of the present application.

[0056] Figure 3 Shows a schematic diagram of another embodiment of the separator film of the present application.

[0057] Figure 4 Shows a schematic diagram of an embodiment of the battery cell of the present application.

[0058] Figure 5 Shows Figure 4 An exploded schematic diagram of the battery cell shown.

[0059] Figure 6 Shows a schematic diagram of an embodiment of an electrical device including the battery cell of the present application as a power source.

[0060] In the drawings, the drawings are not necessarily drawn to actual scale. Detailed description of specific embodiments

[0061] Hereinafter, embodiments of the binder composition, separator film, electrode assembly and its preparation method, battery cell, battery module, battery pack and electrical device of the present application specifically disclosed will be described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary details are omitted. For example, there are cases where details of well-known matters are omitted and repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0062] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include or exclude the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, ranges of 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise specified, the numerical range "a-b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are fully listed herein, and "0-5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0063] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0064] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0065] If there is no special instruction, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0066] If there is no special instruction, the "including" and "comprising" mentioned in this application mean open-ended or can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or can also mean that only the listed components are included or comprised.

[0067] Unless otherwise specified, 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, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0068] Unless otherwise specified, in this application, the terms "connected" and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium, and can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0069] Unless otherwise specified, in this application, the term "attached" refers to connection by means such as adhesion or coating.

[0070] Unless otherwise specified, in this application, the terms "first", "second", "third", "fourth", etc. are used to distinguish different objects, rather than to describe a specific order or primary-secondary relationship.

[0071] Unless otherwise specified, in this application, the term "active ion" refers to an ion that can intercalate and deintercalate between the positive and negative electrodes of a battery cell, including but not limited to lithium ions, etc.

[0072] In this application, the terms "a plurality of" and "a variety of" mean two or more than two.

[0073] The term "chain alkyl" encompasses straight-chain and branched-chain alkyls.

[0074] The term "alkyl" refers to a saturated hydrocarbon group, including both straight-chain and branched-chain structures. C 1～18 Alkyl represents an alkyl group having 1 to 18 carbon atoms, and its examples include but are not limited to methyl, ethyl, propyl (such as n-propyl, isopropyl), butyl (such as n-butyl, isobutyl, sec-butyl, tert-butyl), pentyl (such as n-pentyl, isopentyl, neopentyl), etc.

[0075] The term "alkoxy" refers to -OR, where R is an alkyl group. Examples of alkoxy include but are not limited to methoxy (CH 3 O-), ethoxy (C 2 H 5 O-), propoxy (C 3 H 7 O-), etc.

[0076] In various embodiments, C 1 -C 8A chain alkyl group, i.e., a chain alkyl group, may contain 1-8 carbon atoms. Other description methods have similar meanings.

[0077] Throughout this specification, substituents of compounds are disclosed in groups or ranges. It is explicitly contemplated that such descriptions include every individual sub-combination of the members of these groups and ranges. For example, it is explicitly contemplated that the term "C1-C8 alkyl" discloses C1, C2, C3, C4, C5, C6, C7, C8, C1-C8, C1-C7, C1-C6, C1-C5, C1-C4, C1-C3, C1-C2, C2-C8, C2-C7, C2-C6, C2-C5, C2-C4, C2-C3, C3-C8, C3-C7, C3-C6, C3-C5, C3-C4, C4-C8, C4-C7, C4-C6, C4-C5, C5-C8, C5-C7, C5-C6, C6-C8, C6-C7, C7-C8 alkyl individually. As other examples, it is explicitly contemplated that integers in the range of 3-10 disclose 3, 4, 5, 6, 7, 8, 9, and 10 individually. Accordingly, other groups or ranges can be explicitly contemplated.

[0078] In this application, the battery may include a lithium-ion battery, which is not limited in the embodiments of this application. The battery cell may be an aqueous battery or an oil-based battery, which is also not limited in the embodiments of this application. The battery may be in the shape of a flat body, a cuboid, or other shapes, etc., which is also not limited in the embodiments of this application.

[0079] A battery can be called a rechargeable battery or a storage battery, which refers to a battery that can activate the active material through charging after discharging. Usually, a battery cell includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. The positive electrode sheet includes a positive electrode current collector and a positive electrode active material film layer. The positive electrode active material film layer is coated on the surface of the positive electrode current collector, and the positive electrode active material film layer includes a positive electrode active material. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material film layer. The negative electrode active material film layer is coated on the surface of the negative electrode current collector, and the negative electrode active material film layer includes a negative electrode active material. During the charge and discharge process of the battery, active ions shuttle between the positive electrode sheet and the negative electrode sheet (including insertion and extraction, adsorption, etc.). The separator is disposed between the positive electrode sheet and the negative electrode sheet to prevent short circuit between the positive and negative electrodes and at the same time allow active ions to pass through. Therefore, the separator is an important component of a lithium-ion battery, and its performance determines the electrode interface structure, internal resistance, etc. of the battery, and affects the capacity, cycle, and safety performance, etc. of the battery.

[0080] During the charging and discharging process of the battery, the separator film therein contacts the battery electrode plate. The battery electrode plate expands and contracts during the charging and discharging process of the battery, which will generate mechanical stress on the separator film. The mechanical stress may be too large or uneven, and the separator film may be torn or deformed, resulting in surface damage or interface damage, affecting the performance of the battery.

[0081] In view of this, the embodiments of the present application provide a separator film, which has less surface damage or interface damage of the separator film, can achieve a certain degree of self-repair, reduce the adverse effects of the separator film on the cycle performance of the battery during the charging and discharging process, and thus improve the cycle performance of the battery cell containing it.

[0082] Separator film

[0083] In a first aspect, the embodiments of the present application provide a separator film, including:

[0084] A base film,

[0085] A coating provided on at least one side of the base film, the coating includes:

[0086] Inorganic particles and polyester, wherein the glass transition temperature of the polyester is -30°C to -80°C.

[0087] According to the embodiments of the present application, when the glass transition temperature of the polyester is within the above range, the polyester has a certain elasticity or reversible deformation at a suitable temperature; for example, at low temperature or normal temperature, the polyester is in a solid state and has a certain mechanical strength; while under heating conditions, when the temperature is near the glass transition temperature Tg, the chain segments of the polyester undergo a certain degree of free movement, making it have a certain elasticity or reversible deformation, or forming a high elastic state of fluidity. Under the action of the intermolecular forces generated by the intermolecular interaction at the interface (which includes non-covalent bonds, intermolecular hydrogen bonds, orientation forces, etc.), the molecular chain segments that can move freely migrate and rearrange at the interface.

[0088] According to the embodiments of the present application, the polyester with a certain elasticity or reversible deformation is applied to the coating in the separator film. When the separator film is damaged by the outside during the charging and discharging of the battery, based on its elasticity or reversible deformation, it can repair the interface damage and achieve self-repair of the surface of the separator film.

[0089] In addition, the polyester has hydroxyl groups, carboxyl groups, etc. These functional groups also enhance the contact between the polyester and other components of the separator film coating, have the effect of enhancing the coating adhesion, and can also promote the interface adhesion between the separator film containing the polyester and the battery electrode plate, reducing the risk of electrode plate wrinkling. The carboxyl group can combine with active ions including lithium ions to provide a migration path for the active ions, greatly improving the ion exchange ability of the separator film and improving the charging and discharging efficiency of the battery containing the separator film.

[0090] The polyester in the coating can be detected by applying the coating and separating the polyester therein. As an example, a certain amount of the coating is taken, and then the coating is placed in a mixed solution of water and ethanol with a volume ratio of water:ethanol of 1:1 and a mass ratio of the coating to the mixed solution of about 1:10. The mixed solution containing the coating is ultrasonically treated for 20 - 40 min at an ultrasonic frequency of 20 - 40 Hz, which can be 25 Hz, and then washed and filtered to collect the polymer after the coating is peeled off. Then, mass spectrometry is used: by ionizing the polymer molecules and measuring their mass, the molecular weight of the polymer molecules can be determined, or it can be determined whether the polymer molecules contain polyester and the molecular weight of the polyester can be determined.

[0091] The obtained polymer sample to be measured is nitrolyzed to prepare an appropriate solution, and ionization is carried out: under the action of an electric field, the molecules in the sample solution will be ionized into charged ions. Mass analysis: The ionized ions will be sent into a mass spectrometer for mass analysis. In the mass spectrometer, the ions will be focused in a narrow area, and then by measuring the mass and velocity of the ions, the mass of the ions can be calculated. Data processing: The ion mass data measured by the mass spectrometer can be processed and analyzed by a computer. For example, by searching the Mass-to-Charge Ratio vs. Intensity Plot, the mass of various molecules in the sample can be determined. Result analysis: According to the mass spectrometry data, the composition and structure of the sample can be analyzed. For example, it can be determined what types of polyester the polymer in the sample contains, as well as its weight-average molecular weight, relative content, etc. In addition, nuclear magnetic resonance spectroscopy (NMR) can also be used to determine the relative molar content of each structural unit in the polyester, thereby determining the presence of polyester.

[0092] In some alternative embodiments, the glass transition temperature of the polyester is -65 °C to -80 °C.

[0093] According to the embodiments of the present application, the glass transition temperature of the polyester can affect the interfacial stability between the polyester and other components of the separator coating. The glass transition temperature of the polyester is more appropriate. It is more stable during battery operation, which can make the coating interface stable. At the same time, it can also reduce the damage caused by the volume change of the active material in the battery electrode sheet in contact with the separator, and improve the adverse effects on the separator. Therefore, when the polyester has an appropriate glass transition temperature, it can self-repair the interfacial damage of the separator, provide more stable cycling performance, and is also beneficial to reducing the risk of thermal runaway of the battery and helping to extend the cycle life of the battery.

[0094] The glass transition temperature Tg of the polyester has the meaning well-known in the art and can be measured by the instruments and methods well-known in the art. For example, it can be measured by differential scanning calorimetry (DSC) according to the standard ISO 11357-2-2013.

[0095] In some embodiments, the glass transition temperature of the polyester can be any value among -30°C, -31°C, -32°C, -33°C, -34°C, -35°C, -36°C, -37°C, -38°C, -39°C, -40°C, -41°C, -42°C, -43°C, -44°C, -45°C, -46°C, -47°C, -48°C, -49°C, -50°C, -51°C, -52°C, -53°C, -54°C, -55°C, -56°C, -57°C, -58°C, -59°C, -60°C, -61°C, -62°C, -63°C, -64°C, -65°C, -66°C, -67°C, -68°C, -69°C, -70°C, -71°C, -72°C, -73°C, -74°C, -75°C, -76°C, -77°C, -78°C, -79°C, -80°C or the range composed of them. Controlling the glass transition temperature of the polyester within the above range is beneficial to the elasticity or reversible deformation of the polyester. When the battery is charged and discharged and the separator is damaged by the outside world, based on its elasticity or reversible deformation, the interfacial damage can be repaired, realizing self-healing on the surface of the separator.

[0096] The glass transition temperature (Tg) is one of the characteristic temperatures of polymer materials, which refers to the temperature corresponding to the transition of the polymer material from the high elastic state to the glass state or from the glass state to the high elastic state. The glass transition temperature (Tg) of the polyester in this application can be detected by commonly used methods in the art, such as differential scanning calorimetry (DSC), thermomechanical analysis (TMA), dynamic thermomechanical analysis (DMA), etc. in thermal analysis. Taking the DSC method to test Tg as an example, it can be detected in accordance with the standard ISO11357-2-2013. According to the fact that the specific heat of the polymer will change greatly before and after Tg, it is a step in the endothermic direction on the DSC curve. The average value of the temperatures of the two intersection points of the two extrapolated baselines before and after the step with the tangents at the inflection points of the curve is taken as Tg.

[0097] In some alternative embodiments, based on the total mass of the coating, the coating comprises 0.1% to 5% of polyester.

[0098] Optionally, the coating can be any value among 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5% or a range composed of them.

[0099] According to the embodiments of the present application, the polyester contained in the coating can enhance the interfacial adhesion between the separator and the battery electrode sheet, and reduce the risk of electrode sheet wrinkling. The carboxyl group can combine with active ions including lithium ions to provide a migration path for the active ions, greatly improving the ion exchange capacity of the separator and improving the charge and discharge efficiency of the battery including the separator.

[0100] According to the embodiments of the present application, the coating includes the polyester with the above mass content. On the one hand, it can enhance the bonding strength between the components in the coating and enhance the cohesion of the coating; when the separator is damaged externally, the polyester in the coating can repair the interfacial damage of the coating to achieve self-repair of the separator.

[0101] The mass content of the polyester in the coating can be detected by separating the polyester in the coating. As an example, take a certain amount of the coating and weigh it as M1. Then put the coating into a mixed solution of water and ethanol with a volume ratio of water:ethanol of 1:1 and a mass ratio of the coating to the mixed solution of about 1:10. Ultrasonic the mixed solution containing the coating for 20 - 40 min with an ultrasonic frequency of 20 - 40 HZ, which can be 25 HZ. Then clean and filter, collect the mass of the inorganic particles after stripping the polymer, dry it, and weigh the mass of the collected inorganic particles as M2. Then continue to put the collected inorganic particles into the mixed solution of water and ethanol, continue to ultrasonic for 20 - 40 min, then clean and filter to separate, continue to collect the inorganic particles after stripping the polymer, dry it, and weigh the collected inorganic particles as M3. When the mass change between M2 and M3 < 0.1%, it indicates that the polymer of the inorganic particles in the coating is stripped clean. Test to obtain the mass of the polymer in the coating m = M1 - M3. Then, use mass spectrometry: by ionizing the polymer molecules and measuring their mass, the content M4 of the polyester in the separated polymer can be determined. The calculation method of the mass content of the polyester is M4 / M1.

[0102] In some alternative embodiments, the polyester comprises structural units represented by formula (1) and formula (2), and at least a part of the polyester represented by formula (1) and formula (2);

[0103]

[0104]

[0105] wherein, R 1 and R 2 each independently represents any one of a single bond, an unsubstituted or substituted C 1～8 alkyl group, an unsubstituted or substituted C 1～8 alkoxy group; R a , R b , R c independently comprise any one of -H, -OH, -COOH, an unsubstituted or substituted C 1～8 alkyl group, an unsubstituted or substituted C 1～8 alkoxy group, at least one of R 1 , R 2 , R a , R b , R c has a hydroxyl group; at least one of R 1 , R 2 , R a , R b , R c has a carboxyl group; the substituent comprises any one of a hydroxyl group, a carboxyl group and a carbonyl group.

[0106] According to the embodiments of the present application, the coating comprises the above polyester, which has a certain elasticity or reversible deformation. When the battery is charged and discharged, when the separator is damaged by the outside world, the polyester in the coating can repair the interfacial damage of the coating, realizing the self-repair of the separator.

[0107] The structure of the polyester and the content of the structural units contained therein can be determined by methods well known in the art, such as nuclear magnetic resonance spectroscopy. Nuclear magnetic resonance spectroscopy is the study of the absorption of radio frequency radiation by atomic nuclei in a strong magnetic field. It is one of the most powerful tools for qualitative analysis of the composition and structure of various organic and inorganic substances, and can sometimes also be used for quantitative analysis. At the same time, it can also be combined with infrared spectra, for example, it can be tested by a Fourier transform infrared spectrometer FTIR. The interaction between infrared radiation and the vibration or rotation of molecular substances is used for structural analysis by recording the infrared absorption spectrum of the sample. Further, it can also be combined with thermogravimetric analysis and gas chromatography-mass spectrometry for analysis.

[0108] In some alternative embodiments, the weight average molecular weight of the polyester is 50×10 4~80×10 4 and may be optionally 65×10 4 ~75×10 4 .

[0109] Understandably, the weight-average molecular weight of the polyester may include but is not limited to 50×10 4 , 51×10 4 , 53×10 4 , 55×10 4 , 57×10 4 , 59×10 4 , 60×10 4 , 61×10 4 , 63×10 4 , 65×10 4 , 67×10 4 , 69×10 4 , 70×10 4 , 71×10 4 , 73×10 4 , 75×10 4 , 77×10 4 , 79×10 4 , 80×10 4 any value within or the range composed of them.

[0110] According to the embodiments of the present application, when the weight-average molecular weight of the polyester is within the above range, it can have more structural units, can increase reactive functional groups such as hydroxyl and carboxyl groups, and improve the bonding performance of the polyester; the polyester with a weight-average molecular weight within the above range can provide more molecular cross-linking points, thereby increasing the bonding strength with other components in the separator coating; and this polyester has appropriate elasticity or reversible deformation, which helps to reduce the recovery of the integrity and flatness of the separator surface after damage, and is beneficial to improving the specific capacity and cycle stability of the battery.

[0111] The weight-average molecular weight of the polyester has the meaning well-known in the art and can be measured by instruments and methods known in the art. As an example, the weight-average molecular weight of the polymer in this application can be determined with reference to Standard GB / T 21863-2008 Gel Permeation Chromatography. Specifically, in this application, an ultra-high performance polymer chromatograph: ACQUITY APC (detector: ACQUITY refractive index detector) can be used and the following test steps are carried out: (1) Turn on and preheat: Install the chromatographic column and pipeline, turn on the console, test power supply, etc. in sequence, and turn on the test software Empower; (2) Parameter setting, injection volume: 0 μL to 50 μL (determined according to the sample concentration); pump flow rate: 0.2 mL / min; mobile phase: NMP solution of 30 mol / L LiBr; sealing cleaning solution: isopropanol; pre-column: PL gel 10um MiniMIX-B Guard (size: 50 mm × 4.6 mm × 2); analytical column: PL gel 10um MiniMIX-B (size: 250 mm × 4.6 mm); standard: polystyrene set; running time: 30 min; detector: ACQUITY refractive index (RI) detector; column oven temperature: 90 °C; detector temperature: 55 °C; (3) Sample test: a. Preparation of standard sample and test sample: Weigh 0.002 g to 0.004 g of standard sample / test sample respectively and add 2 mL of mobile phase liquid to prepare a mixed standard of 0.1% to 0.5%, and place it in the refrigerator for >8 h; b. Test of standard solution / sample: Edit the group of samples to be tested, select the established sample group method, and click the run queue to start testing the sample after the baseline is stable; (4) Data processing: According to the relationship between retention time and molecular weight, use the chemical workstation to establish a calibration curve, integrate and quantify the sample chromatogram, and the chemical workstation automatically generates the result of the weight-average molecular weight.

[0112] In some alternative embodiments, based on the total weight of the polyester, the polyester contains 2×10 -4 ~11×10 -4 moles per gram of carboxyl groups.

[0113] According to the embodiments of the present application, the polyester contains carboxyl groups in the above molar content, so that when the polyester is used for the separator coating, the carboxyl groups can combine with lithium ions to provide a migration path for lithium ions, greatly improving the passing rate of active ions through the separator and enhancing the charge and discharge efficiency of the battery.

[0114] In some alternative embodiments, the polyester includes at least one polyester of Formula (3)-Formula (8):

[0115]

[0116] wherein, n is a positive integer, R 3 and R 4Each independently represents a C which is unsubstituted or optionally substituted by -OH or -COOH 1～6 alkyl group.

[0117] According to the embodiments of the present application, the polyester having the above structural general formula has certain elasticity or reversible deformation. This polyester is applied to the coating in the separator. When the separator is damaged externally during the charging and discharging of the battery, based on its elasticity or reversible deformation, it can repair the interfacial damage and achieve self-repair of the separator surface.

[0118] The mass percentage content of the polyester contained in the coating in the separator has the meaning well-known in the art and can be measured by the instruments and methods well-known in the art. For example, the proportion of the polyester can be measured by the method of pickling and filtration.

[0119] The mass percentage content of the polyester in the coating can be carried out according to the test method of element content. The method includes:

[0120] Immerse the separator sample in an acetone solution and ultrasonically treat it at 40 °C for 3 h to separate the separator and the coating, and collect the acetone mixture containing the coating. Use an inductively coupled plasma optical emission spectrometer (ICP-OES) to test the element content in the mixture. Output the mass percentages of each element. Thus, the functional groups in the polyester and the content of the polyester can be calculated.

[0121] In some alternative embodiments, the polyester is obtained by polycondensation of a polyhydric organic alcohol and a polyhydric organic carboxylic acid. The present application does not make an obvious limitation on the type of alcohol, and any alcohol that can achieve the purpose of the embodiments of the present application, that is, the alcohol for preparing the polyester, can be used. In some alternative embodiments, the polyhydric organic alcohol includes one or more of butanediol and propanediol.

[0122] The present application does not make an obvious limitation on the type of carboxylic acid, and any carboxylic acid that can achieve the purpose of the embodiments of the present application, that is, the carboxylic acid for preparing the polyester, can be used. In some alternative embodiments, the polyhydric organic carboxylic acid includes one or more of sebacic acid, succinic acid, methylene succinic acid, and itaconic acid.

[0123] In some alternative embodiments, the preparation method of the polyester includes:

[0124] Mix an alcohol containing C 2～10 and a carboxylic acid containing C 2～10 and carry out an esterification reaction in a first organic solvent under the action of a first catalyst of phthalate esters. Optionally, under the condition of adding a second catalyst of esters for reducing the melting temperature, the polyester is prepared.

[0125] According to the embodiments of the present application, the alcohol containing C 2～10 can be a polyhydric alcohol, including a dihydric alcohol, a trihydric alcohol, etc. The number of hydroxyl groups therein can be two, three, etc. The alcohol containing C 2～10The carboxylic acid can be a polycarboxylic acid, including dibasic carboxylic acids, tribasic carboxylic acids, etc. The number of carboxyl groups can be two, three, etc.

[0126] According to an embodiment of the present application, the alcohol containing C 2～10 and the carboxylic acid containing C 2～10 undergo an esterification reaction to obtain a polyester that has a certain elasticity or reversible deformation at a suitable temperature (such as the battery temperature of 30 - 55 °C during battery cycling). This polyester is applied to the coating in the separator. When the separator is damaged during battery charging and discharging, based on its elasticity or reversible deformation, it can repair the interfacial damage and achieve self - repair of the separator surface.

[0127] Moreover, under the action of a first phthalate catalyst and a second ester catalyst for reducing the melting temperature, the esterification reaction occurs, causing the polyester obtained from this reaction to react in the direction of the first phthalate catalyst and the second ester catalyst for reducing the melting temperature, that is, in the direction of a lower melting temperature or a lower glass transition temperature. The obtained polyester has a certain elasticity or reversible deformation at a suitable temperature (such as the battery temperature of 30 - 55 °C during battery cycling). This polyester is applied to the coating in the separator. When the separator is damaged during battery charging and discharging, based on its elasticity or reversible deformation, it can repair the interfacial damage and achieve self - repair of the separator surface.

[0128] In some alternative embodiments, the molar ratio of the alcohol containing C 2～10 and the carboxylic acid containing C 2～10 is 1∶(0.5 - 2.0). According to an embodiment of the present application, when the molar ratio of the alcohol containing C 2～10 and the carboxylic acid containing C 2～10 is within the above range, a suitable polyester can be obtained. On the basis of making full use of raw materials such as the alcohol containing C 2～10 and the carboxylic acid containing C 2～10 a polyester with a suitable weight - average molecular weight can be obtained.

[0129] In some alternative embodiments, the first phthalate catalyst includes one or more of tetramethyl phthalate, isopropyl titanate, tetra - isopropyl titanate, n - butyl titanate, and diisopropyl bis(ethyl acetoacetate) titanate.

[0130] According to an embodiment of the present application, the above - mentioned types of first phthalate catalysts exhibit high catalytic activity, promote the ring - opening polymerization reaction between ester monomers, reduce their influence on other functional groups, and also ensure that specific functional groups of the polyester can be formed with high yield and high purity, and can effectively control the molecular weight and molecular weight distribution of the polyester.

[0131] In some alternative embodiments, the second ester catalyst for reducing the melting temperature includes one or more of phosphate ester compounds, benzoate ester compounds, alkyl sulfonate ester compounds, and polyol ester compounds; optionally, the phosphate ester compounds include tricresyl phosphate, tolyldiphenyl phosphate, diphenyl octyl phosphate, and tris(2-ethylhexyl) phosphate. According to the embodiments of the present application, esters of the above types can reduce the melting temperature of the resulting polyester. The melting temperature here refers to the temperature at which the polyester has relatively appropriate elasticity and reversible deformation, such as the temperature near the glass transition temperature.

[0132] In some alternative embodiments, the first organic solvent includes one or more of acetone, chloroform, dichloromethane, and carbon tetrachloride. According to the embodiments of the present application, the above types of first organic solvents can enable the alcohol containing C 2～10 and the carboxylic acid containing C 2～10 to come into sufficient contact, improving the reaction efficiency.

[0133] In some alternative embodiments, the esterification reaction is carried out under an inert atmosphere and with oil bath heating. Optionally, the temperature of the oil bath heating is 170 - 180 °C.

[0134] According to the embodiments of the present application, an inert atmosphere usually uses gases such as nitrogen or argon, and these gases do not react with the compounds in the reaction. Therefore, carrying out the reaction under an inert atmosphere can effectively prevent the reactants and intermediate products from being oxidized by oxygen and can also reduce the generation of by-products. The use of oil bath heating can ensure uniform temperature distribution and can easily adjust and maintain the required temperature conditions. Carrying out oil bath heating at a temperature of 170 - 180 °C can promote the rapid progress of the esterification reaction and increase the reaction rate; in addition, at this temperature, the esterification reaction is usually more selective, producing the desired ester product while reducing the formation of unwanted by-products. This helps to obtain a high yield and high product purity.

[0135] In some alternative embodiments, after the esterification reaction, it further includes removing unreacted monomers and low-molecular-weight oligomers with a second organic solvent; optionally, the second organic solvent includes one or more of chloroform, dichloromethane, and hydroquinone.

[0136] According to the embodiments of the present application, using a second organic solvent to remove unreacted monomers and oligomers can improve the purity of the obtained polyester, which is beneficial to ensuring the stable performance of the polyester.

[0137] In some alternative embodiments, after the esterification reaction, it further includes stabilizing and precipitating the reaction product with a third organic solvent. Optionally, the third organic solvent includes one or more of chloroform, dichloromethane, and hydroquinone.

[0138] According to the embodiments of the present application, after the esterification reaction, the resulting polyester can be stabilized with a solvent, or the obtained polyester can be precipitated to facilitate collection and utilization. Generally, solvents of the above types are used, which is beneficial to quickly stabilize and precipitate the obtained polyester.

[0139] In some alternative embodiments, the method includes: mixing at least one compound shown in formula (A) to formula (C) with at least one compound shown in formula (D) to formula (E) and carrying out an esterification reaction in a first organic solvent under the action of a first phthalate catalyst and a second ester catalyst for reducing the melting temperature to obtain the polyester.

[0140]

[0141] wherein, R 1 and R 2 each independently includes a single bond, C 1 ~ 8 alkyl, C-containing alkyl which is unsubstituted or substituted by a substituent 1～8 or any one of C 1～8 alkoxy, and the substituent includes any one of a hydroxyl group, a carboxyl group, and a carbonyl group.

[0142] According to the embodiments of the present application, the polyester obtained from the above compounds has the above specific structural units, and thus has a certain elasticity or reversible deformation. This polyester is applied to the coating in the separator. When the separator is damaged externally during the charging and discharging of the battery, based on its elasticity or reversible deformation, the interfacial damage can be repaired, realizing the self-repair of the separator surface.

[0143] In some alternative embodiments, the molar ratio of formula (A), formula (B), formula (C), formula (D) and formula (E) is 1∶(25 - 84)∶(25 - 84)∶(119 - 213)∶(25 - 84).

[0144] According to the embodiments of the present application, the specific polyester obtained from the above molar ratio and types of compounds has the above specific structural units, and thus has a certain elasticity or reversible deformation. This polyester is applied to the coating in the separator. When the separator is damaged externally during the charging and discharging of the battery, based on its elasticity or reversible deformation, the interfacial damage can be repaired, realizing the self-repair of the separator surface.

[0145] In some alternative embodiments, the coating includes a phosphate plasticizer. Optionally, the phosphate plasticizer includes one or more of tricresyl phosphate, tolyldiphenyl phosphate, diphenyl octyl phosphate, tris(2-ethylhexyl) phosphate.

[0146] According to the embodiments of the present application, plasticizers can generally improve the fluidity of materials, reduce the viscosity of materials, and may change the molecular structure of polyesters in coatings at a certain temperature.

[0147] During the charging and discharging process of the battery, the coating contains the phosphate plasticizer and polyester, enabling the separator to be more easily self-repaired at a relatively low temperature, improving the performance of the separator, and reducing the risk of short circuit. The binder composition of the present application can achieve a lower self-repair temperature. When the separator uses this binder composition, a lower self-repair temperature can be obtained, realizing the self-repair of the separator and improving the stability of the battery.

[0148] In addition, according to the embodiments of the present application, phosphate plasticizers generally have high thermal stability, which can improve the performance of the separator in a high-temperature environment. The coexistence of phosphate plasticizers and binders may enhance the stability of the film, making it more durable and more resistant to chemical corrosion.

[0149] Furthermore, the phosphate plasticizer can reduce the melting temperature of the polyester. In the molten state, it has better elasticity and reversible deformation, enabling the polyester to achieve surface self-repair of the separator at a lower temperature.

[0150] In some alternative embodiments, based on the total mass of the coating, the coating includes 0.01% to 2% of the phosphate plasticizer.

[0151] According to the embodiments of the present application, when the mass percentage content of the phosphate plasticizer in the coating is within the above range, it can improve the stability of the separator, and can also make it have better elasticity and reversible deformation at a suitable temperature, enabling the polyester to achieve surface self-repair of the separator.

[0152] The embodiments of the present application do not impose obvious restrictions on the type of the base film. Commonly used porous base films in the art can be used. In some alternative embodiments, the base film includes one or more of a polyolefin film, a non-woven fabric film, a polyester film, a polyether film, a polyetherimide film, and a fluorinated polyetherimide film.

[0153] The addition of inorganic particles can increase the mechanical strength, wear resistance, and thermal stability of the separator. The embodiments of the present application do not impose obvious restrictions on the type of inorganic particles. Commonly used inorganic particles in the art can be used. In some alternative embodiments, the inorganic particles include one or more of ceramic particles, boehmite, and alumina.

[0154] In some alternative embodiments, the average particle size Dv50 of the inorganic particles is 0.2 μm to 0.5 μm.

[0155] According to the embodiments of the present application, when the average particle size Dv50 of the inorganic particles is within the above range, the uniformity of the coating can be enhanced, facilitating the penetration of active ions; and the presence of the inorganic particles improves the reliability of the battery, achieving the "thermal shut-off" effect.

[0156] The average particle size Dv50 of the inorganic particles has the meaning well-known in the art, which represents the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 50%, and can be measured by the instruments and methods well-known in the art. For example, it can be conveniently measured with a laser particle size analyzer by referring to GB / T19077-2016 Laser diffraction method for particle size distribution, such as the Mastersizer 2000E type laser particle size analyzer of Malvern Instruments Limited, UK.

[0157] In some embodiments, the coating includes a binder and ceramic particles. The coating including ceramic particles and a binder endows the separator with good mechanical strength and has a "thermal shut-off" function, improving the safety performance of the battery cell including the separator.

[0158] In some embodiments, the average particle size Dv50 of the ceramic particles is from 0.2 μm to 6 μm. When the average particle size of the ceramic particles is within the above range, the uniformity of the coating surface in the separator can be improved, the stability of the coating structure can be maintained, and the safety performance of the battery cell including the separator is enhanced.

[0159] In some embodiments, the mass content of the ceramic particles in the coating is from 20% to 60%. When the mass content of the ceramic particles is within the above range, the stability of the coating structure can be maintained, and the safety performance of the battery cell including the separator is enhanced.

[0160] In some embodiments, the ceramic particles can have a microstructure similar to a "fluffy" structure. It has a certain flexibility and elasticity, which can enhance the liquid absorption capacity of the separator.

[0161] In some alternative embodiments, the ratio of the thickness of the base film to that of the coating is 1:(0.15 - 1).

[0162] According to the embodiments of the present application, the base film and the coating have an appropriate thickness ratio, enabling the separator to have a suitable total thickness; which helps to reduce the volume and weight of the battery cell and can improve the safety performance of the battery cell including the separator.

[0163] In some embodiments, the thickness of the base film can be from 3 μm to 20 μm. The thicknesses of the first base film and the second base film can be any value among 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm or a range composed of them. According to the embodiments of the present application, the base film has an appropriate thickness, so that the separator film has a suitable total thickness; it helps to reduce the volume and weight of the battery cell, and can improve the safety performance of the battery cell including the separator film.

[0164] In some alternative embodiments, the thickness of the coating is from 0.5 μm to 20 μm.

[0165] The thickness of the coating can be any value among 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.S μm, 1.9 μm, 2.0 μm, 5.0 μm, 6.0 μm, 7.0 μm, 8.0 μm, 9.0 μm, 10.0 μm, 12.0 μm, 15.0 μm, 18.0 μm, 19.0 μm, 20.0 μm or a range composed of any values. When the thickness of the coating is within the above range, the separator film can have a suitable total thickness, which helps to reduce the volume and weight of the battery cell, and can improve the safety performance of the battery cell including the separator film.

[0166] The thicknesses of the base film, the separator film and the coating have the meanings well-known in the art, and can be measured by the instruments and methods known in the art. An exemplary test method for the thickness of the separator film is as follows: Take a sample with a length of 500 mm × a width of 100 mm; Uniformly take 5 points on the sample (for example, take a point every 100 mm along the length direction of the sample), and use a ten-thousandth thickness gauge to measure the thickness of the separator film at these 5 different positions, and take the average value as the thickness of the separator film. The length direction of the sample is parallel to the TD direction of the separator film. The thicknesses of the first base film and the second base film can be measured with reference to the above method. One side of the separator film is provided with a coating. Subtracting the thickness of the base film from the thickness of the separator film gives the thickness of the coating. If the two opposite sides of the separator film are respectively provided with the coating to be measured and the coating on the opposite side of the coating to be measured, subtracting the sum of the thicknesses of the base film and the coating on the opposite side from the thickness of the separator film gives the thickness of the coating to be measured.

[0167] In some alternative embodiments, the porosity of the base film is from 30% to 70%.

[0168] According to the embodiments of the present application, the base film has the above-mentioned porosity and certain electrolyte wettability, which facilitates the passage of active ions through the separator membrane, improves the transport rate of active ions, and improves the kinetic performance of the battery cell including the separator membrane.

[0169] In some embodiments, the porosity of the separator membrane is 25% to 65%.

[0170] When the porosity of the separator membrane is within an appropriate range, it helps the separator membrane to have an appropriate electrolyte retention amount, thereby improving the kinetic performance of the battery cell including the separator membrane.

[0171] The porosities of the base film and the separator membrane have the meanings well-known in the art and can be measured by the instruments and methods known in the art. An exemplary test method is as follows:

[0172] Use a Micromeritics AUTOPORE V 9620 mercury intrusion porosimeter to measure the porosity of the separator membrane. Under compressed conditions, a certain amount of mercury liquid is filled into the separator membrane, and then the ratio of the volume occupied by the mercury liquid to the material volume is measured to obtain the porosity of the separator membrane.

[0173] In some embodiments, under the condition of testing at 130 °C for 1 h, the thermal shrinkage of the separator membrane in the longitudinal direction (MD) is ≤5.0%, and the thermal shrinkage in the width direction (TD) is ≤5.0%. The test of the thermal shrinkage rate in the longitudinal (Machine Direction, abbreviated as MD) direction and the transverse (Transverse Direction, abbreviated as TD) direction can refer to the national standard GB / T36363-2018. The separator membrane according to the embodiments of the present application has a multi-layer composite structure, which can enable the separator membrane to have a relatively small thermal shrinkage rate in the MD or TD direction. Therefore, even when the separator membrane is damaged, the pore expansion rate at the damaged part under heated conditions is relatively low. Therefore, even when the battery cell including the separator membrane is mechanically damaged such as by nail penetration, the separator membrane can still maintain a good isolation effect, thereby reducing the risk of thermal runaway of the battery cell and improving the safety performance.

[0174] As an example, the test method includes: The separator membrane can be cut into a specimen with a length l M0 of 100 mm in the MD direction and a length l T0 of 100 mm in the TD direction. The MD direction of the specimen is parallel to the MD direction of the separator membrane, and the TD direction of the specimen is parallel to the TD direction of the separator membrane; the specimen is placed in an oven at 130 °C and heated for 1 h; the length l M in the MD direction or the length l T in the TD direction of the specimen after heating is measured, and the thermal shrinkage rate in the MD or TD direction is calculated. The test can refer to the national standard GB / T 36363-2018.

[0175] In some alternative embodiments, the air permeability of the base film is 110 to 310 s / 100 cc respectively.

[0176] According to the embodiments of the present application, controlling the thickness, porosity, and air permeability of the base film within the above ranges can comprehensively control the performance of the separator film, which is beneficial to the use of the separator film in the battery.

[0177] In some embodiments, the air permeability of the separator film is 300 s / 100 cc to 500 s / 100 cc; when the air permeability of the separator film is within an appropriate range, it is convenient for ions to pass through the separator film, which helps the battery cell to have high capacity performance and cycling performance.

[0178] The air permeability of the separator film refers to the degree to which an object or medium allows gas to pass through. Under a stable pressure, the time required for a certain volume of gas (25 cubic centimeters (abbreviated as cc) to 300 cc) to flow through a specific area of the specimen is measured.

[0179] The air permeability of the base film and the separator film can be detected by commonly used detection methods in the art. For example, a Gurley 4110N air permeability tester produced in the United States is used to test the air permeability of the separator film. Detection method: Measure the time required for 100 cc of air to pass through a separator film with a circular area of 3 inches in diameter under a pressure of 4.88 inches of water column, and the unit is seconds (s).

[0180] In some embodiments, the transverse (TD) tensile strength of the separator film is 1000 to 2000 kg / cm 2 ; when the tensile strength of the separator film in the transverse (TD) direction is within an appropriate range, it can have high toughness and strength in this direction. Even when the battery cell with this separator film is mechanically damaged such as by nail penetration, since the separator film can still play a good isolation role, the risk of secondary thermal runaway can be reduced and the safety performance can be improved.

[0181] In some embodiments, the longitudinal (MD) tensile strength of the separator film is 1200 to 1800 kg / cm 2 . When the tensile strength of the separator film in the longitudinal (MD) direction is within an appropriate range, it can have high toughness and strength in this direction. Even when the battery cell with this separator film is mechanically damaged such as by nail penetration, since the separator film can still play a good isolation role, the risk of secondary thermal runaway can be reduced and the safety performance can be improved.

[0182] In some embodiments, the method for detecting the longitudinal (MD) tensile strength of the separator membrane includes: taking 5 specimens with a length of 100 mm and a width of 15 mm along the MD direction of the base film, wherein the length direction of the specimens is parallel to the MD direction of the base film; clamping each specimen in two opposite clamps of a tensile testing machine, setting the gauge length of the specimen to 40 mm (i.e., the distance between the clamps), and performing a tensile test at a constant speed of 50 mm / min. Read the force value F and the tensile displacement ΔL when the specimen breaks. Calculate the tensile per unit thickness of each specimen according to the formula for calculating the tensile energy per unit thickness.

[0183] In some embodiments, the peel strength between the coating and the base film is ≥50 N / m, and can be optionally 50 - 1500 N / m. Optionally, it can be any one of 50 N / m to 1200 N / m, 150 N / m to 1000 N / m, 200 N / m to 800 N / m, 400 N / m to 700 N / m, 500 N / m to 600 N / m. If the peel strength between the coating and the base film is relatively high, the interlayer adhesion of the separator membrane is better. Therefore, the performance of the separator membrane is further improved. It can be tested using instruments and methods known in the art. An exemplary test method is as follows: bond the green glue to the surface of the coating of the separator membrane; then cut it into a width w of 15 mm; peel the coating and the base film at 180° at a speed of 50 mm / min; according to the data graph of the tensile force and displacement, read the maximum tensile force x (N), and calculate the peel strength F' (N / m) between the coating and the base film according to F' = x / w. The tensile testing equipment can use a tensile testing machine from Gaotie Testing Instruments Company, such as the AI-3000-S model.

[0184] Reference Figure 1 Describe an embodiment of the separator membrane according to the first aspect of the present application. As Figure 1 shown, the separator membrane 1 includes: a base film 10, and a coating 30 provided on one side of the base film 10, and the coating contains the polyester of the first aspect of the present application or the polyester prepared by the preparation method of the second aspect of the present application or the binder composition of the third aspect.

[0185] Figure 2 Shows another embodiment of the separator membrane according to the first aspect of the present application. As Figure 2 shown, the separator membrane 1 includes: a base film 10, and a first coating 30a and a second coating 30b provided on one side of the base film 10.

[0186] Figure 3 Shows yet another embodiment of the separator membrane according to the first aspect of the present application. The separator membrane 1 includes a first base film 10, a second base film 20, a first coating 30 provided between the first base film 10 and the second base film 20, and also includes a first coating 30a provided on the surface of the first base film 10 and a second coating 30b provided on the surface of the second base film 20.

[0187] The description of any embodiment of the base film 10 above is independently applicable to the first base film 10 and the second base film 20 in this embodiment, and will not be repeated here. The description of any embodiment of the coating above is independently applicable to the coating 30, the first coating 30a and the second coating 30b in this embodiment, and will not be repeated here. This will not be repeated here.

[0188] The description of any embodiment of polyester above is independently applicable to the polyester contained in the coating 30, the first coating 30a and the second coating 30b in this embodiment, and will not be repeated here.

[0189] Battery cell

[0190] In a fourth aspect, an embodiment of the present application provides a battery cell, including the separator of the third aspect.

[0191] In some embodiments, the battery cell includes a positive electrode plate and a negative electrode plate

[0192] [Negative electrode plate]

[0193] The specific composition and structure of the negative electrode plate can be selected according to the type of the battery cell, and the embodiments of the present application do not limit this.

[0194] For example, when the battery cell is a lithium-ion battery cell, the negative electrode plate includes a negative electrode current collector and a negative electrode active material film layer provided on at least one surface of the negative electrode current collector and including a negative electrode active material. For example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode active material film layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector.

[0195] The negative electrode active material is a material capable of deintercalating and intercalating active ions (such as lithium ions, etc.). The negative electrode active material can adopt materials well known in the art. As an example, the negative electrode active material includes, but is not limited to, one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based materials can include one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloy materials. The tin-based materials can include one or more of elemental tin, tin oxides, and tin alloy materials. The present application is not limited to these materials, and other conventionally well-known materials that can be used as the negative electrode active material can also be used.

[0196] In some embodiments, the negative electrode active material film layer may optionally further include a negative electrode conductive agent. The present application does not particularly limit the type of the negative electrode conductive agent. As an example, the negative electrode conductive agent can include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0197] In some embodiments, the negative electrode active material film layer may optionally further include a negative electrode binder. There is no particular limitation on the type of the negative electrode binder in the present application. As an example, the negative electrode binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (for example, polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0198] In some embodiments, the negative electrode active material film layer may optionally further include other additives. As an example, the other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, and the like.

[0199] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of the metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0200] The negative electrode active material film layer is generally formed by coating a negative electrode slurry on a negative electrode current collector and then drying and cold pressing. The negative electrode slurry is generally formed by dispersing a negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring evenly. The solvent may be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

[0201] The negative electrode sheet does not exclude other additional functional layers other than the negative electrode active material film layer. For example, in some embodiments, the negative electrode sheet of the present application may further include a conductive bottom coating (for example, composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode active material film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode sheet of the present application may further include a protective layer covering the surface of the negative electrode active material film layer.

[0202] When the battery cell is a lithium metal battery cell, the negative electrode sheet may not include a negative electrode active material capable of extracting and inserting active ions. For example, in some embodiments, the negative electrode sheet may include a lithium sheet or a lithium alloy sheet; in other embodiments, the negative electrode sheet includes a reticular or foamed three-dimensional skeleton layer, such as foamed copper (or copper alloy), foamed nickel (or nickel alloy), copper (or copper alloy) mesh, nickel (or nickel alloy) mesh, and the like.

[0203] [Positive electrode tab]

[0204] In some embodiments, the positive electrode tab includes a positive electrode current collector and a positive electrode active material film layer provided on at least one surface of the positive electrode current collector and including a positive electrode active material. For example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode active material film layer is provided on either or both of the two opposite surfaces of the positive electrode current collector.

[0205] The positive electrode active material film layer includes a positive electrode active material, and the positive electrode active material can be a positive electrode active material for battery cells known in the art.

[0206] For example, when the battery cell is a lithium-ion battery cell or a lithium metal battery cell, the positive electrode active material can include one or more of lithium transition metal oxides, lithium-containing phosphates with olivine structure, and their respective modified compounds. Examples of lithium transition metal oxides can include 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 their respective modified compounds. Examples of lithium-containing phosphates with olivine structure can include one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and their respective modified compounds. The present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials can also be used.

[0207] In some embodiments, in order to further improve the energy density of the battery cell, the positive electrode active material can include a lithium transition metal oxide having the general formula Li a Ni b Co c M d O e A f and one or more of its modified compounds. 0.8 ≤ a ≤ 1.2, 0.5 ≤ b < 1, 0 < c < 1, 0 < d < 1, 1 ≤ e ≤ 2, 0 ≤ f ≤ 1, M includes one or more selected from Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A includes one or more selected from N, F, S, and Cl.

[0208] As an example, the positive electrode active material can include LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), LiNi 0.80 Co 0.15 Al 0.05 O 2 , LiFePO 4 and LiMnPO 4 one or more of the following.

[0209] The modified compounds of the above-mentioned cathode active materials may be doping modification and / or surface coating modification of the cathode active materials.

[0210] In some embodiments, the cathode active material film layer may further optionally include a cathode conductive agent. The present application does not particularly limit the type of the cathode conductive agent. As an example, the cathode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0211] In some embodiments, the cathode active material film layer may further optionally include a cathode binder. The present application does not particularly limit the type of the cathode binder. As an example, the cathode binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0212] In some embodiments, the cathode current collector may be a metal foil or a composite current collector. As an example of the metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0213] The positive electrode active material film layer is usually formed by coating a positive electrode paste on a positive electrode current collector and then drying and cold pressing. The positive electrode paste is usually formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0214] [Preparation method]

[0215] The preparation method of the battery of the present application is well-known. In some embodiments, a positive electrode plate, a separator, a negative electrode plate, and an electrolyte can be assembled to form a battery cell. As an example, the positive electrode plate, the separator, and the negative electrode plate can be formed into an electrode assembly through a winding process and / or a stacking process, the electrode assembly is placed in an outer package, dried and then injected with an electrolyte, and after processes such as encapsulation, standing, formation, and shaping, a battery cell is obtained. Multiple battery cells can further be combined in series or in parallel or in a hybrid connection to form a battery module. Multiple battery modules can also be formed into a battery pack through series or parallel or hybrid connection. In some embodiments, multiple battery cells can also directly form a battery pack.

[0216] [Electrolyte]

[0217] In some embodiments, the battery cell includes an electrolyte. The electrolyte plays a role in conducting active ions between the positive electrode plate and the negative electrode plate. The present application does not specifically limit the type of electrolyte, and it can be selected according to requirements. For example, the electrolyte can be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolytic solution).

[0218] In some embodiments, the electrolyte uses an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0219] The type of the electrolyte salt is not specifically limited and can be selected according to actual requirements. For example, the electrolyte salt includes a lithium salt used for a lithium-ion battery. As an example, the lithium salt includes a selection from lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluoro(oxalato)phosphate (LiDFOP), lithium tetrafluoro(oxalato)phosphate (LiTFOP), etc. As an example, the sodium salt includes a selection from NaPF 6 , NaClO 4, NaBCl 4 , NaSO 3 CF 3 , Na(CH 3 )C 6 H 4 SO 3 or one or more of the above.

[0220] The type of the solvent is not particularly limited and can be selected according to actual needs. In some embodiments, by way of example, the solvent may include one or more selected from 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), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE).

[0221] In some embodiments, the electrolyte may optionally further include additives. For example, the additives may include negative electrode film-forming additives, or may include positive electrode film-forming additives, or may also include additives that can improve certain battery performance, such as additives for improving battery overcharge performance, additives for improving battery high-temperature performance, additives for improving battery low-temperature power performance, etc.

[0222] In addition, the battery cell may have various outer packages and forms of existence.

[0223] In some embodiments, the battery cell may include an outer package. The outer package can be used to encapsulate the above electrode assembly including the positive electrode sheet, the negative electrode sheet, and the separator, and the electrolyte.

[0224] In some embodiments, the outer package of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the battery cell can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0225] This application does not particularly limit the shape of the battery cell, and it can be a flat body, a cuboid, or other shapes. As Figure 4 is a battery cell 5 with a cuboid structure as an example.

[0226] In some embodiments, such as Figure 5As shown, the outer package may include a housing 51 and a cover plate 53. Among them, the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The electrode assembly 52 of the first aspect of the embodiment of the present application or the electrode assembly 52 prepared by the method of the second aspect of the embodiment of the present application is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 included in the battery cell 5 may be one or several, which can be adjusted according to requirements.

[0227] The preparation method of the battery cell of the present application is well-known. In some embodiments, the electrode assembly can be placed in the outer package, dried and then injected with electrolyte, and after processes such as vacuum packaging, standing, forming, and shaping, the battery cell is obtained.

[0228] In some embodiments, the battery cells can be assembled into any one or several of a battery cell, a battery module, or a battery pack.

[0229] In some embodiments of the present application, the battery cells according to the present application can be assembled into a battery module, and the number of battery cells included in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0230] Optionally, the battery module may further include a housing having a receiving space, and a plurality of battery cells are received in the receiving space.

[0231] In some embodiments, the above battery module can be further assembled into a battery pack, and the number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0232] In a fifth aspect, an embodiment of the present application provides a battery including the battery cell of the fourth aspect. The battery cells can be assembled into a battery.

[0233] Power-consuming device

[0234] In a sixth aspect, an embodiment of the present application provides a power-consuming device including the battery of the fifth aspect.

[0235] An embodiment of the present application provides a power-consuming device, which may include at least one of the above-mentioned battery cells, battery modules, and battery packs

[0236] By controlling the content of the self-healing binder in the separator binder coating, the present application can increase the porosity of the separator, reduce the ionic resistance, and enhance the kinetic performance and cycling performance of the battery cell. Under the comprehensive influence of many properties such as the thermal shrinkage and air permeability of the separator, the thermal stability and safety of the battery core, the lithium-ion battery cell and power-consuming device including the separator of the present application can obtain excellent performance.

[0237] The battery cell can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer, etc.), an electric vehicle (such as 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.

[0238] Figure 6 It is a schematic diagram of an electrical device as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the requirements of the electrical device for high power and high energy density, a battery pack or a battery module can be adopted.

[0239] Another example of an electrical device can be a mobile phone, a tablet computer, a laptop computer, etc. This electrical device usually requires being thin and light, and a battery cell can be used as the power source.

[0240] Embodiment

[0241] The following embodiments more specifically describe the content disclosed in the present application. These embodiments are only for illustrative purposes, because various modifications and changes within the scope of the content disclosed in the present application are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the embodiments are all commercially available.

[0242] Embodiment 1

[0243] Preparation method of the separator:

[0244] Preparation of polyester: The raw materials POD, BOD, IA, SuA, and SeA are added to a three-necked flask in a molar ratio of 1:1:1:1:1 for co-esterification reaction, and then the solvent chloroform, the catalyst tetramethyl phthalate, and the stabilizer hydroquinone are added. N is blown in 2 and heated in an oil bath to 180 °C and maintained for 2 h. The product is dissolved in chloroform to remove unreacted monomers and oligomers, and then excess cold methanol is added to precipitate the product. The product is filtered, washed, and dried to obtain the target polyester. Among them, the meanings of the following English abbreviations involved: POD represents 1,3-propanediol, CAS number is 504-63-2; BOD represents 1,4-butanediol, CAS number is 110-63-4; IA represents methylene succinic acid, CAS number is 97-65-4; SuA represents succinic acid, CAS number is 110-15-6; SeA represents sebacic acid, CAS number is 111-20-6.

[0245] Tris(2-ethylhexyl) phosphate was added to the target polyester, and the mixture was slowly heated to 220 °C and vacuum reacted for 4 h and then cooled to room temperature to obtain the binder composition.

[0246] The mass ratio of the target polyester to the plasticizer tris(2-ethylhexyl) phosphate in the above binder composition was 98:2.

[0247] A commercial 5-μm PE-based film purchased from Ningde Zhuogao New Material Technology Co., Ltd. was used, and its porosity was 30%.

[0248] The inorganic particles alumina and the prepared binder composition containing polyester were mixed uniformly in a solvent (deionized water) according to a mass ratio of 8.5:1.5 to form an aqueous slurry with a solid content of 25 wt% and a viscosity of 100 mPa·s, and the coating slurry was obtained. The slurry was coated onto both surfaces of a 5-μm polyethylene PE-based film by a coater, as Figure 2 shown, to form a wet coating with a thickness of about 14 μm, which was transferred to an oven and dried at 60 °C for 2 minutes, and then reversed over the roller, and the base film was pressed on the wet coating with a pressure of 1000 Mpa to obtain a composite separator membrane. It was detected that the porosity of the composite separator membrane prepared in Example 1 was 32%, the thermal shrinkage in the longitudinal direction (MD) was 4.45.0%, the thermal shrinkage in the width direction (TD) was 3.27%, and the tensile strength in the transverse direction (TD) was 1503 kg / cm 2 .

[0249] Preparation of Lithium-Ion Batteries

[0250] Preparation of the positive electrode plate: A 60-Ah LFP square hard-shell battery cell from CATL was used, and the positive LFP electrode plate after 3000 full charge-discharge cycles contained lithium iron phosphate positive active material, and its structural formula was LiFePO 4 .

[0251] Preparation of the negative electrode plate: 97.5 parts by weight of negative active material artificial graphite, 1.5 parts by weight of binder SBR, and 1 part by weight of thickener CMC-Na were added to deionized water, stirred and mixed evenly, and then coated on the surface of the Cu foil, and after drying, cold pressing, and slitting, the negative electrode plate was obtained.

[0252] Separator membrane: The above-prepared separator membrane.

[0253] Preparation of the electrolyte: In a glove box under an argon atmosphere with a water content <10 ppm, 11.9 parts by weight of lithium hexafluorophosphate was added to a solution of 88.1 parts by weight of EC and DEC (mass ratio 1:1), and after stirring and dissolving evenly, the electrolyte was obtained.

[0254] Assembly: Assemble the obtained positive electrode sheet, separator, and negative electrode sheet into a stacked bare battery cell, place it in an aluminum-plastic film, bake it in a vacuum at 80 °C for 8 h, then inject the above electrolyte for infiltration and formation to complete the preparation of the lithium-ion battery monomer.

[0255] Examples 2 to 12

[0256] The preparation methods of Preparation Examples 2 to 12 are similar to that of Preparation Example 1. The differences are as follows: In Examples 2 to 7, the molar ratios of POD, BOD, IA, SuA, and SeA in the raw materials are 1:2:2:1:1, 1:2:1:2:2, 2:1:2:1:1, 2:1:1:2:1, 0.5:1:0.5:1:1, and 2:2:1:2:2 in sequence. In Examples 8 to 10, the mass ratios of the polyester and tris(2-ethylhexyl) phosphate plasticizer obtained in the binder composition are 96.5:3.5, 99:1, and 95:5 in sequence. In Examples 11 to 12, the types of plasticizers are different, and the specific parameters are shown in Table 1 below.

[0257] Example 13

[0258] The preparation method of this example is similar to that of Preparation Example 1. The difference is that all the above raw materials are replaced with POD, BOD, IA, and SuA, and their molar ratio is 1:1:1:1.

[0259] Example 14

[0260] The preparation method of this example is similar to that of Preparation Example 1. The difference is that the raw materials are replaced with BOD, IA, and SuA, and their molar ratio is 2:1:1.

[0261] Example 15

[0262] The preparation method of this example is similar to that of Preparation Example 1. The differences are as follows: Do not add the raw material POD. Do not add tris(2-ethylhexyl) phosphate to the target polyester. Use the obtained polyester to replace the binder composition in Example 1 and add it to the slurry.

[0263] Example 16

[0264] The preparation method of this example is similar to that of Preparation Example 1. The differences are as follows: Do not add the raw material IA. Do not add tris(2-ethylhexyl) phosphate to the target polyester. Use the obtained polyester to replace the binder composition in Example 1 and add it to the slurry.

[0265] Examples 17 to 19

[0266] The battery cells of Examples 17 to 19 are prepared in a similar manner to the battery cell of Example 1, and the binder composition prepared in Example 1 is used in all of them. The difference lies in that: the mass percentage content of polyester in the coating of the binder composition is adjusted, and the reduced content of polyester relative to Example 1 is replaced by the binder polyvinylidene fluoride (PVDF) to make up the mass content of the binder composition in the coating. See Table 2 for details.

[0267] Example 20

[0268] The preparation method of this example is similar to that of Preparation Example 1. The difference lies in that: the preparation method of the separator is different. A commercial 5μm PE-based film and a 6μm PP-based film purchased from Ningde Zhuogao New Materials Technology Co., Ltd. are slit on one side to make a first base film and a second base film, and their porosity is 30%. Alumina and the binder composition prepared in Preparation Example 1 are mixed evenly in a solvent (deionized water) according to a mass ratio of 8.5:1.5 to form an aqueous slurry with a solid content of 25 wt% and a viscosity of 100 mPa·s, and the coating slurry is obtained. The slurry is coated onto the 5μm polyethylene (PE) base film by a coater, and the other unwind roll is a 6μm polypropylene (PP) base film. The slurry is applied to the surface of the PE base film by extrusion to form a wet coating with a thickness of about 12μm. The coating has two layers and is transferred to an oven and baked at a temperature of 60°C for 2 minutes. Then, it is reversed over the roll, and the PP base film is pressed onto the wet coating. The slurry is coated on the side of the PP base film facing away from the PE base film to form an 8μm wet coating under a pressure of 1000 Mpa, and the composite separator as shown in Figure 3 is obtained.

[0269] Example 21

[0270] The preparation method of this example is similar to that of Preparation Example 1. The difference lies in that: the preparation method of the separator is different. A commercial 5μm PE-based film purchased from Ningde Zhuogao New Materials Technology Co., Ltd. is slit to make a base film, and its porosity is 30%.

[0271] Alumina and the binder composition containing polyester prepared in Preparation Example are mixed evenly in a solvent (deionized water) according to a mass ratio of 8.5:1.5 to form an aqueous slurry with a solid content of 25 wt% and a viscosity of 100 mPa·s, and the coating slurry is obtained. The slurry is coated onto the 5μm polyethylene (PE) base film by a coater. The slurry is applied to one surface of the PE base film by extrusion to form a wet coating with a thickness of about 8μm and is transferred to an oven and baked at a temperature of 60°C for 2 minutes. Then, it is reversed over the roll, and the PP base film is pressed onto the wet coating under a pressure of 1000 Mpa, and the composite separator is obtained, as shown in Figure 1 is shown.

[0272] Examples 22 to 25

[0273] The preparation method of this example is similar to that of Preparation Example 1. The difference lies in: the preparation method of the negative electrode sheet is different. Preparation of the negative electrode sheet: 97.5 parts by weight of silicon-containing negative electrode active material, 1.5 parts by weight of binder SBR, and 1 part by weight of thickener CMC-Na are added to deionized water. Among them, in Examples 322 to 25, the mass content of silicon element in the silicon-containing negative electrode active material is controlled to be 4%, 4.5%, 5.0%, and 6.0% in sequence. After stirring and mixing evenly, it is coated on the surface of the Cu foil, and after drying, cold pressing, and slitting, the negative electrode sheet is obtained.

[0274] Comparative Example 1

[0275] The preparation method of this comparative example is similar to that of Preparation Example 1. The difference lies in: polyvinylidene fluoride PVDF is used to replace the binder composition prepared in Example 1.

[0276] Comparative Example 2

[0277] The preparation method of this comparative example is similar to that of Preparation Example 1. The difference lies in: polyvinylidene fluoride PVDF is used to replace the binder composition prepared in Example 1. The preparation method of the negative electrode sheet is different. Preparation of the negative electrode sheet: 97.5 parts by weight of silicon-containing negative electrode active material, 1.5 parts by weight of binder SBR, and 1 part by weight of thickener CMC-Na are added to deionized water. Among them, the mass content of silicon element in the silicon-containing negative electrode active material is controlled to be 4%, and after stirring and mixing evenly, it is coated on the surface of the Cu foil, and after drying, cold pressing, and slitting, the negative electrode sheet is obtained.

[0278] Test section

[0279] 1) Test method for the thickness of the separator and the coating: Use a thickness gauge to test, and measure according to the determination method of the thickness of films and sheets in GB / T6672-2001; first, the thickness of the base film of the separator is measured and defined as W1, and the thickness of the coated film is measured after coating and defined as W1. The coating thickness W3 = W1 - W2. If it is a double-sided coating, the thickness of each layer of the coating is W4 = (W1 - W2) / 2.

[0280] 2) Test method for the cycling performance of the battery cell: Place the battery in the test channel of the Chenhua electrochemical workstation, charge it at a constant current rate of 1C until the charging cut-off voltage of 3.65V, stand for 5 minutes, and then discharge it at a constant current rate of 1C until the discharge cut-off voltage of 2.25V, record the discharge capacity, and then stand for 5 minutes. Cycle in this way, and the cycle capacity retention rate = capacity after cycling / capacity of the first cycle × 100%. Generally, it is the ratio of the capacity after 800 cycles to the capacity of the first cycle.

[0281] Another group of simultaneously prepared batteries was placed in the test channel of a Chenhua electrochemical workstation and charged at a constant current of 0.5C to a charging cut-off voltage of 3.65V. After standing for 5 minutes, it was discharged at a constant current of 0.5C to a discharging cut-off voltage of 2.25V, and the discharge capacity was recorded. Then it was left standing for another 5 minutes. Such cycles were repeated, and the cycle capacity retention rate = (capacity after cycling) / (capacity of the first cycle) × 100%. Generally, it is the ratio of the capacity after 800 cycles to the capacity of the first cycle.

[0282] Another group of simultaneously prepared batteries was placed in the test channel of a Chenhua electrochemical workstation and charged at a constant current of 2C to a charging cut-off voltage of 3.65V. After standing for 5 minutes, it was discharged at a constant current of 2C to a discharging cut-off voltage of 2.25V, and the discharge capacity was recorded. Then it was left standing for another 5 minutes. Such cycles were repeated, and the cycle capacity retention rate = (capacity after cycling) / (capacity of the first cycle) × 100%. Generally, it is the ratio of the capacity after 800 cycles to the capacity of the first cycle.

[0283] 3) Swelling test of the negative electrode plate

[0284] The test equipment can use an electrochemistry reaction visualization confocal display system ECCS (such as Lasertec 1320).

[0285] During the test, the battery can be made in a special visual mold and tested according to the following charge-discharge process. At 25°C, the prepared battery was left standing for 30 minutes, charged at a constant current of 0.05C to 3.65V, left standing for 10 minutes, then discharged at a constant current of 0.33C to 2.5V, and then discharged at a constant current of 0.05C to 2.5V; then the battery was charged at a constant current of 0.1C to 3.65V, and then charged at a constant voltage until the current was 0.05C.

[0286] Before the test started, the distance from the separator to the negative current collector was denoted as H1; after the test ended, the distance from the separator to the negative current collector was denoted as H2. H2 - H1 is the increased thickness of the negative electrode plate swelling at 100% SOC as shown in Table 2.

[0287] 4) Cycle performance test of the battery

[0288] At 25°C, the prepared battery was left standing for 30 minutes, charged at a constant current of 0.05C to 3.65V, left standing for 10 minutes, then discharged at a constant current of 0.33C to 2.5V, and then discharged at a constant current of 0.05C to 2.5V. Then the following cycle performance test was started.

[0289] The battery was charged at a constant current of 0.1C to 3.65V, left standing for 10 minutes, then discharged at a constant current of 0.1C to 2.5V, and left standing for 10 minutes; the above operations were repeated until the capacity of the battery decayed to 80% of the initial capacity, and the number of cycles was recorded. The results are shown in Table 2.

[0290] The test results are shown in Table 1 and Table 2.

[0291] The value of the weight-average molecular weight of the polyester in Table 1 represents that the weight-average molecular weight of the obtained polyester product is around this value. The thickness 5 + 6 of the base film in Table 1 and Table 2 represents that there are two layers of base film. The coating thicknesses 4 + 4 and 4 + 2 + 4 respectively represent the thickness of each coating from one side of the separator film to the other side.

[0292] According to the data in Table 1, it can be seen from the examples and Comparative Example 1 that by controlling the raw materials of the polyester, the glass transition temperature and / or the weight-average molecular weight of the polyester are controlled, and the advantages of the elasticity or reversible deformation of the polyester in the separator film coating are fully utilized, so that the separator film has good self-healing properties. When the battery is charged and discharged, the separator film can achieve self-healing, improving the stability of the battery, which is characterized by the cycle capacity retention rate of the battery at different rates.

[0293] According to the data in Table 2, it can be known that when the separator film of the embodiment of the present application is applied to the anode electrode sheet containing silicon element with a large expansion, due to its different silicon element contents, the anode electrode sheet itself has a specific expansion thickness with specific properties. When this kind of anode electrode sheet is used in combination with the separator film of the embodiment of the present application, it can be seen from the examples and Comparative Example 2 that among the anode electrode sheets with different expansion thicknesses, the self-healing ability of the separator film is different. The battery using the separator film in Comparative Example 2 has a lower number of battery cycles, and the battery with a smaller expansion thickness in the examples has a higher number of battery cycles, indicating that using separator films with different self-healing abilities can improve the service life of the battery and the stability of the battery.

[0294] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments with the same structure and the same function as the technical idea within the technical solution scope of the present application are all included in the technical scope of the present application. In addition, within the scope not departing from the gist of the present application, various modifications that can be thought of by those skilled in the art are applied to the embodiments, and other ways constructed by combining some constituent elements of the embodiments are also included in the scope of the present application.

[0295]

[0296]

[0297]

[0298]

Claims

1. A separator membrane, characterized in that, it comprises: a base film, a coating provided on at least one side of the base film, the coating comprising: inorganic particles and polyester, wherein the glass transition temperature of the polyester is -30°C to -80°C.

2. The separator membrane according to claim 1, characterized in that, based on the total mass of the coating, the coating comprises 0.1% to 15% of polyester.

3. The separator membrane according to claim 1 or 2, characterized in that, the polyester has the structure shown in formula (1) and / or formula (2); Among them, R 1 and R 2 each independently represents any one of a single bond, an unsubstituted or substituent-substituted C 1～8 alkyl group, an unsubstituted or substituent-substituted C 1～8 alkoxy group; R a , R b , R c independently include -H, -OH, -COOH, an unsubstituted or substituent-substituted C 1～8 alkyl group, an unsubstituted or substituent-substituted C 1～8 alkoxy group, and at least one of R 1 , R 2 , R a , R b , R c has a hydroxyl group; at least one of R 1 , R 2 , R a , R b , R c has a carboxyl group; the substituent includes any one of a hydroxyl group, a carboxyl group, and a carbonyl group; Optionally, the weight-average molecular weight of the polyester is 50×10 4 ~80×10 4 , and can be optionally 65×10 4 ~75×10 4 .

4. The separator membrane according to any one of claims 1-3, characterized in that, the polyester satisfies at least one of the following conditions: 1) The glass transition temperature of the polyester is -65°C to -80°C; 2) Based on the total weight of the polyester, the polyester contains 2×10 -4 to 11×10 -4 moles per gram of carboxyl groups.

5. The separator membrane according to any one of claims 1-4, characterized in that, the polyester comprises at least one of formula (3)-formula (8): wherein, n is a positive integer, R 3 and R 4 each independently represents an unsubstituted or -OH-, -COOH-optionally substituted C 1～6 alkyl group.

6. The separator membrane according to any one of claims 1-5, characterized in that, the ratio of the thickness of the base film to the thickness of the coating is 1:(0.15-1); Optionally, the thickness of the coating is 0.5 μm to 20 μm; Optionally, the thickness of the base film is 3 μm to 20 μm.

7. The separator membrane according to any one of claims 1-6, characterized in that, the coating comprises a phosphate plasticizer, optionally, the phosphate plasticizer comprises one or more of tricresyl phosphate, tolyldiphenyl phosphate, diphenyl octyl phosphate, tris(2-ethylhexyl) phosphate.

8. The separator membrane according to any one of claims 1-7, characterized in that, based on the total mass of the coating, the coating comprises 0.01% to 2% of a phosphate plasticizer.

9. The separator membrane according to any one of claims 1-8, characterized in that, the separator membrane satisfies at least one of the following conditions: 1) The base film comprises one or several of a polyolefin film, a non-woven fabric film, a polyester film, a polyether film, a polyetherimide film, a fluorinated polyetherimide film; 2) The porosity of the base film is 30% to 70%; 3) The air permeability of the base film is 110 to 310 s / 100 cc; 4) The inorganic particles comprise one or several of ceramic particles, boehmite, alumina; 5) The average particle size Dv50 of the inorganic particles is 0.2 μm to 0.5 μm.

10. A battery cell, characterized in that, it comprises the separator membrane according to any one of claims 1-9.

11. A battery, characterized in that, it comprises the battery cell according to claim 10.

12. An electrical device, characterized in that, it comprises the battery according to claim 11.

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