An isolation film, a preparation method thereof, a battery and an electric device

Abstract

This application provides a separator membrane and its preparation method, a battery, and an electrical device, belonging to the field of battery technology. The separator membrane includes a base membrane, the material of which comprises a first polymer and a second polymer. The first and second polymers form an interpenetrating polymer network structure, wherein the second polymer has a three-dimensional structure and branched chains, including phosphate ester groups and / or phosphite groups. The interpenetrating polymer network structure enhances the mechanical properties of the separator membrane, giving it better mechanical properties and thermal stability. When the internal temperature of the battery rapidly rises to 80℃~100℃, the branches of the second polymer break, generating phosphate ester free radicals and / or phosphite free radicals, thereby neutralizing the hydrogen / hydroxyl radicals generated by the chain decomposition of the electrolyte, delaying the onset of battery thermal runaway, and improving the safety of the manufactured battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to a separator and its preparation method, a battery, and an electrical device. Background Technology

[0002] During use, extreme external high temperatures or internal short circuits can cause the internal temperature of lithium-ion batteries to rise rapidly, which can easily lead to the decomposition of the SEI film and the chain decomposition of the electrolyte. This can further accumulate heat and cause thermal runaway. After thermal runaway, the battery may catch fire or even explode, seriously threatening the safety of battery use. Summary of the Invention

[0003] In view of the above problems, this application provides a separator and its preparation method, a battery and an electrical device, which can delay the time of battery thermal runaway and improve battery safety.

[0004] In a first aspect, this application provides a separator membrane comprising a base membrane, the base membrane being made of a first polymer and a second polymer, the first polymer and the second polymer forming an interpenetrating polymer network structure, wherein the second polymer is a bulk structure and has branches, the branches including phosphate ester groups and / or phosphite ester groups.

[0005] In the technical solution of this application embodiment, the interpenetrating polymer network structure of the separator enhances the mechanical properties of the separator during normal battery operation, resulting in better mechanical properties and thermal stability. Furthermore, the separator made of polymer materials with an interpenetrating polymer network structure does not dissolve in the electrolyte, thus not affecting the electrochemical performance of the battery. When the internal temperature of the battery rapidly rises to 80°C–100°C, the branches of the second polymer break, generating phosphate ester free radicals and / or phosphite free radicals. These phosphate ester free radicals and / or phosphite free radicals neutralize the hydrogen / hydroxyl radicals generated by the chain decomposition of the electrolyte, delaying the onset of thermal runaway and improving the safety of the battery.

[0006] In some embodiments, the second polymer comprises a flame-retardant monomer and a crosslinking monomer obtained by crosslinking. The flame-retardant monomer comprises at least one phosphate ester group and / or phosphite group and at least one unsaturated double bond, and the crosslinking monomer comprises at least two unsaturated double bonds. The flame-retardant monomer and the crosslinking monomer can polymerize through their respective unsaturated double bonds to form a three-dimensional structure of the second polymer.

[0007] In some embodiments, the molar ratio of crosslinking monomer to flame retardant monomer is 0.5 to 3:1. Optionally, the molar ratio of crosslinking monomer to flame retardant monomer is 1 to 2:1. When the molar ratio of crosslinking monomer to flame retardant monomer is 0.5 to 3:1, it is beneficial to form a two-dimensional structure of the second polymer, and the network structure of the second polymer has good stability, resulting in a membrane with good flexibility.

[0008] In some embodiments, the flame retardant monomer includes or At least one of the following. Wherein R1, R2, R3, R4, R5, and R6 are each independently selected from C. 1～10 Alkyl, C 3～6 Cycloalkyl, aryl, or heteroaryl. Optionally, R1, R2, R3, R4, R5, and R6 are each independently selected from C1. 1～3 Alkyl groups. The flame-retardant monomers described above include at least one phosphate ester group and / or phosphite group and at least one unsaturated double bond, which are capable of polymerizing with crosslinking monomers through their respective unsaturated double bonds to form a second polymer with a three-dimensional structure.

[0009] In some embodiments, the crosslinking monomer includes and / or Where n is 1 to 10, and R7 is selected from H and C. 1～10 Alkyl, C 3～6 Cycloalkyl, aryl, or heteroaryl. Optionally, n is 1 to 3, and R7 is selected from H or C. 1～3 Alkyl groups. The aforementioned crosslinking monomers include at least two unsaturated double bonds, which can polymerize with flame-retardant monomers through their respective unsaturated double bonds to form a second polymer with a three-dimensional structure.

[0010] In some embodiments, the first polymer has a linear structure and a number-average molecular weight of 100,000 to 1,000,000. The linear first polymer can form an interpenetrating polymer network structure with the bulk second polymer. When the number-average molecular weight of the linear first polymer is 100,000 to 1,000,000, the separator membrane has good mechanical properties and thermal stability.

[0011] In some embodiments, the first polymer includes at least one selected from polyethylene, polypropylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene terephthalate, polyimide, polyamide, spandex, aramid, or cellulose. The linear first polymer described above can form an interpenetrating polymer network structure with the three-dimensional second polymer, resulting in a separator with good mechanical properties and thermal stability. Furthermore, the separator made from the polymer material with the interpenetrating polymer network structure will not dissolve in the electrolyte, thus not affecting the electrochemical performance of the resulting battery.

[0012] In some embodiments, the first polymer has a three-dimensional structure and includes at least one of irradiated crosslinked polyethylene, irradiated crosslinked polypropylene, irradiated crosslinked polyvinylidene fluoride, or irradiated crosslinked polyvinylidene fluoride-hexafluoropropylene copolymer. The aforementioned three-dimensional first polymer can form an interpenetrating polymer network structure with a two-dimensional second polymer, resulting in a separator with good mechanical properties and thermal stability. Furthermore, the separator made from the polymer material with the interpenetrating polymer network structure will not dissolve in the electrolyte, thus not affecting the electrochemical performance of the resulting battery.

[0013] In some embodiments, the mass ratio of the first polymer to the second polymer is 1:1 to 30. Optionally, the mass ratio of the first polymer to the second polymer is 1:5 to 25. When the mass ratio of the first polymer to the second polymer is 1:1 to 30, the polymer material has better flame retardant properties, thereby further delaying the onset of battery thermal runaway, and the second polymer can fully swell the first polymer, improving the mechanical properties of the separator.

[0014] In some embodiments, the separator further includes an inorganic coating disposed on at least one side of the base membrane. The base membrane, made of polymer materials, exhibits good mechanical properties and thermal stability, while the inorganic coating can further enhance other properties of the separator.

[0015] In some embodiments, the inorganic coating is made of ceramic materials. Inorganic coatings made of ceramic materials can further improve the mechanical properties and thermal stability of the separator, and enhance its puncture resistance.

[0016] Secondly, this application provides a method for preparing the separator membrane in the above embodiments, comprising: mixing a flame-retardant monomer, a crosslinking monomer, and a first polymer, and performing photo-initiated polymerization to obtain a base membrane. The base membrane is used as a separator membrane, or the base membrane is used as a separator membrane after post-treatment. The base membrane is made of a first polymer and a second polymer, which form an interpenetrating polymer network structure. The second polymer comprises a flame-retardant monomer and a crosslinking monomer obtained by crosslinking. The second polymer has a three-dimensional structure and branches, the branches including phosphate ester groups and / or phosphite ester groups.

[0017] In the technical solution of this application embodiment, the preparation method of the isolation membrane of this application is simple, and the polymerization reaction of the second polymer is carried out in a system including the first polymer. The first polymer provides crosslinking points, and after the second polymer is polymerized and crosslinked, it forms an interpenetrating polymer network structure with the first polymer.

[0018] Thirdly, this application provides a battery that includes the separator membrane described in the above embodiments or the separator membrane prepared according to the preparation method described in the above embodiments.

[0019] Fourthly, this application provides an electrical device that includes the battery described in the above embodiments, the battery being used to provide electrical energy.

[0020] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0021] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0022] Figure 1 This is a schematic diagram of the vehicle structure according to some embodiments of this application;

[0023] Figure 2 This is an exploded structural diagram of a battery according to some embodiments of this application;

[0024] Figure 3 This is an exploded structural diagram of a battery cell according to some embodiments of this application;

[0025] Figure 4 This is a schematic diagram of the body structure of the first polymer in some embodiments of this application.

[0026] The reference numerals in the detailed embodiments are as follows:

[0027] 1000 - Vehicle; 100 - Battery; 200 - Controller; 300 - Motor;

[0028] 10-Box body; 11-First part; 12-Second part;

[0029] 20-Battery cell; 21-End cap; 22-Housing casing; 23-Electrode assembly. Detailed Implementation

[0030] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0032] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0033] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0034] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0035] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0036] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0037] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0038] Currently, judging from market trends, the application of power batteries is becoming increasingly widespread. Power batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of power battery applications, market demand is also constantly increasing.

[0039] During use, extreme external high temperatures or internal short circuits can cause the internal temperature of lithium-ion batteries to rise rapidly, which can easily lead to the decomposition of the SEI film and the chain decomposition of the electrolyte. This can further accumulate heat and cause thermal runaway. After thermal runaway, the battery may catch fire or even explode, seriously threatening the safety of battery use.

[0040] Flame retardants are a common method. While adding flame retardants to the separator can improve its flame retardant effect, it will lead to a deterioration in other properties of the separator. For example, adding flame retardants to the separator will increase its brittleness and weaken its processing performance and compatibility with positive and negative electrode materials.

[0041] Based on the above considerations, to delay the onset of battery thermal runaway and improve battery safety, a separator membrane made of a polymer with an interpenetrating polymer network structure is used. During normal battery operation, the interpenetrating polymer network structure enhances the mechanical properties of the separator membrane, resulting in better mechanical properties and thermal stability. Furthermore, the separator membrane made of polymer materials with an interpenetrating polymer network structure does not dissolve in the electrolyte, thus not affecting the electrochemical performance of the battery. When the internal temperature of the battery rapidly rises to 80℃~100℃, the branches of the second polymer break, generating phosphate ester radicals and / or phosphite radicals. These phosphate ester radicals and / or phosphite radicals can neutralize the hydrogen / hydroxyl radicals generated by the chain decomposition of the electrolyte, delaying the onset of battery thermal runaway and improving the safety of the battery.

[0042] The battery mentioned in the embodiments of this application refers to a single physical module comprising multiple battery cells to provide higher voltage and capacity. A battery generally includes a battery housing for encapsulating the multiple battery cells, which prevents liquids or other foreign matter from affecting the charging or discharging of the battery cells.

[0043] Each battery cell is a secondary battery; it can be a lithium-ion battery or a lithium-sulfur battery, but is not limited to these. Battery cells can be cylindrical, flat, cuboid, or other shapes. Battery cells are generally classified into three types according to their packaging method: cylindrical battery cells, prismatic battery cells, and pouch battery cells.

[0044] A battery cell includes an electrode assembly and an electrolyte. The electrode assembly consists of a positive electrode, a negative electrode, and a separator. The battery cell primarily functions by the movement of metal ions between the positive and negative electrodes. The positive electrode includes a positive current collector and a positive active material layer. The positive active material layer is coated on the surface of the positive current collector, and the uncoated positive current collector protrudes beyond the coated one, serving as the positive electrode tab. Taking a lithium-ion battery as an example, the positive current collector can be made of aluminum, and the positive active material can be lithium cobalt oxide, lithium iron phosphate, ternary lithium, or lithium manganese oxide, etc. The negative electrode includes a negative current collector and a negative active material layer. The negative active material layer is coated on the surface of the negative current collector, and the uncoated negative current collector protrudes beyond the coated one, serving as the negative electrode tab. The negative current collector can be made of copper. To ensure that a large current can pass through without melting, multiple positive electrode tabs are stacked together, and multiple negative electrode tabs are stacked together. The separator can be made of polypropylene (PP) or polyethylene (PE), etc. Furthermore, the electrode assembly can be a wound structure or a stacked structure; the embodiments of this application are not limited to these.

[0045] The battery cell also includes a current collector, which is used to electrically connect the tabs and electrode terminals of the battery cell to deliver electrical energy from the electrode assembly to the electrode terminals, and then to the outside of the battery cell via the electrode terminals. Multiple battery cells are electrically connected through a current collector to realize series, parallel or mixed connection of multiple battery cells.

[0046] The battery also includes sampling terminals and a battery management system. The sampling terminals are connected to the busbar and are used to collect information from individual battery cells, such as voltage or temperature. The sampling terminals transmit the collected information from individual battery cells to the battery management system. When the battery management system detects that the information from a battery cell exceeds the normal range, it limits the battery's output power to achieve safety protection.

[0047] It is understood that the power devices applicable to the use of batteries described in the embodiments of this application can take many forms, such as mobile phones, portable devices, laptops, electric vehicles, electric cars, ships, spacecraft, electric toys, and power tools, etc. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers.

[0048] The battery cells and batteries described in the embodiments of this application are not limited to the electrical devices described above, but can also be applied to all electrical devices that use battery cells and batteries. However, for the sake of brevity, the following embodiments are all illustrated using electric vehicles as an example.

[0049] Please see Figure 1 , Figure 1 This is a schematic diagram of the structure of a vehicle provided in some embodiments of this application. The vehicle 1000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid electric vehicle, or a range-extended electric vehicle, etc. A battery 100 is disposed inside the vehicle 1000, and the battery 100 can be located at the bottom, front, or rear of the vehicle 1000. The battery 100 can be used to power the vehicle 1000; for example, the battery 100 can serve as the operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the battery 100 to supply power to the motor 300, for example, to meet the power needs of the vehicle 1000 during startup, navigation, and driving.

[0050] In some embodiments of this application, the battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0051] Please refer to Figure 2 , Figure 2This is an exploded view of a battery provided in some embodiments of this application. The battery 100 includes a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10. The housing 10 provides a space for the battery cell 20 and can have various structures. In some embodiments, the housing 10 may include a first portion 11 and a second portion 12, which overlap each other, jointly defining a space for accommodating the battery cell 20. The second portion 12 may be a hollow structure with one open end, and the first portion 11 may be a plate-like structure, covering the open side of the second portion 12 so that the first portion 11 and the second portion 12 jointly define the space; alternatively, the first portion 11 and the second portion 12 may both be hollow structures with one open side, with the open side of the first portion 11 covering the open side of the second portion 12. Of course, the housing 10 formed by the first portion 11 and the second portion 12 can have various shapes, such as a cylinder, a cuboid, etc.

[0052] In battery 100, there can be multiple battery cells 20, which can be connected in series, parallel, or in a mixed manner. A mixed connection means that multiple battery cells 20 are connected in both series and parallel configurations. Multiple battery cells 20 can be directly connected in series, parallel, or in a mixed manner, and then the entire assembly of the multiple battery cells 20 is housed within the housing 10. Alternatively, battery 100 can also be composed of multiple battery cells 20 first connected in series, parallel, or in a mixed manner to form a battery module, and then multiple battery modules are connected in series, parallel, or in a mixed manner to form a whole, which is also housed within the housing 10. Battery 100 may also include other structures; for example, it may include a busbar component for electrical connection between the multiple battery cells 20.

[0053] Each battery cell 20 is a secondary battery; it can be a lithium-ion battery, or a lithium-sulfur battery, a sodium-ion battery, or a magnesium-ion battery, but is not limited to these. The battery cell 20 can be cylindrical, flat, cuboid, or other shapes.

[0054] Please refer to Figure 3 , Figure 3 This is an exploded structural diagram of a first type of battery cell provided in some embodiments of this application. The battery cell 20 refers to the smallest unit that makes up the battery. Figure 3 The battery cell 20 includes an end cap 21, a housing 22, an electrode assembly 23, and other functional components.

[0055] End cap 21 refers to a component that covers the opening of housing 22 to isolate the internal environment of battery cell 20 from the external environment. The shape of end cap 21 can be adapted to the shape of housing 22 to fit it. Optionally, end cap 21 can be made of a material with certain hardness and strength (such as aluminum alloy), so that end cap 21 is not easily deformed under pressure and impact, giving battery cell 20 higher structural strength and improved safety performance. Functional components such as electrode terminals can be provided on end cap 21. Electrode terminals can be used for electrical connection with electrode assembly 23 for outputting or inputting electrical energy into battery cell 20. In some embodiments, end cap 21 can also be provided with a pressure relief mechanism for releasing internal pressure when the internal pressure or temperature of battery cell 20 reaches a threshold. The material of end cap 21 can also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and this application embodiment does not impose special limitations on this. In some embodiments, an insulating element may be provided on the inner side of the end cap 21. The insulating element can be used to isolate the electrical connection components within the housing 22 from the end cap 21 to reduce the risk of short circuits. For example, the insulating element may be made of plastic, rubber, etc.

[0056] The housing 22 is a component used to cooperate with the end cap 21 to form the internal environment of the battery cell 20. This internal environment can accommodate the electrode assembly 23, electrolyte, and other components. The housing 22 and the end cap 21 can be independent components. An opening can be provided on the housing 22, and the end cap 21 can be used to close the opening to form the internal environment of the battery cell 20. Alternatively, the end cap 21 and the housing 22 can be integrated. Specifically, the end cap 21 and the housing 22 can form a common connecting surface before other components are inserted into the housing. When it is necessary to encapsulate the interior of the housing 22, the end cap 21 closes the housing 22. The housing 22 can be of various shapes and sizes, such as cuboid, cylindrical, hexagonal prism, etc. Specifically, the shape of the housing 22 can be determined according to the specific shape and size of the electrode assembly 23. The material of the housing 22 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc. This application embodiment does not impose any special limitations on this.

[0057] Electrode assembly 23 is the component in the battery cell 20 where electrochemical reactions occur. The casing 22 may contain one or more electrode assemblies 23. The electrode assembly 23 is mainly formed by winding or stacking positive and negative electrode sheets, and typically a separator is provided between the positive and negative electrode sheets. The portions of the positive and negative electrode sheets containing active material constitute the main body of the electrode assembly, while the portions without active material each constitute a tab. The positive and negative tabs may be located together at one end of the main body or separately at both ends of the main body. During the charging and discharging process of the battery, the positive and negative active materials react with the electrolyte, and the tabs connect to the electrode terminals to form a current loop.

[0058] According to some embodiments of this application, this application provides a separating membrane, which includes a base membrane. The base membrane is made of a first polymer and a second polymer. The first polymer and the second polymer form an interpenetrating polymer network structure, wherein the second polymer has a three-dimensional structure and has branches, the branches including phosphate ester groups and / or phosphite ester groups.

[0059] Interpenetrating polymer network structures are network structures formed by blends of two or more polymers, with the molecular chains interpenetrating each other and at least one polymer molecular chain cross-linked by chemical bonds.

[0060] Phosphate ester groups and / or phosphite ester groups are groups that can improve the flame retardancy of the second polymer, serving purposes including but not limited to preventing the second polymer from being ignited and inhibiting the spread of combustion.

[0061] During normal battery operation, the interpenetrating polymer network structure of the separator in this application enhances its mechanical properties, resulting in better mechanical performance and thermal stability. Furthermore, the separator made from polymer materials with an interpenetrating polymer network structure does not dissolve in the electrolyte, thus not affecting the electrochemical performance of the battery. When the internal temperature of the battery rapidly rises to 80℃~100℃, the branches of the second polymer break, generating phosphate ester radicals and / or phosphite radicals. These phosphate ester radicals and / or phosphite radicals neutralize the hydrogen / hydroxyl radicals generated by the chain decomposition of the electrolyte, delaying the onset of thermal runaway and improving the safety of the battery.

[0062] According to some embodiments of this application, optionally, the second polymer is obtained by crosslinking a flame retardant monomer and a crosslinking monomer, wherein the flame retardant monomer includes at least one phosphate ester group and / or phosphite ester group and at least one unsaturated double bond, and the crosslinking monomer includes at least two unsaturated double bonds.

[0063] As an example, a flame-retardant monomer may include one phosphate ester group and / or one phosphite group and one unsaturated double bond, or may include two phosphate ester groups and / or one phosphite group and one unsaturated double bond, or may include three phosphate ester groups and / or one phosphite group and one unsaturated double bond, or may include one phosphate ester group and / or one phosphite group and two unsaturated double bonds, or may include one phosphate ester group and / or one phosphite group and three unsaturated double bonds, or may include two phosphate ester groups and / or one phosphite group and two unsaturated double bonds.

[0064] Crosslinked monomers may include two or three unsaturated double bonds.

[0065] Flame retardant monomers and crosslinking monomers can polymerize through their respective unsaturated double bonds to form a second polymer with a three-dimensional structure.

[0066] According to some embodiments of this application, optionally, the molar ratio of crosslinking monomer to flame retardant monomer is 0.5 to 3:1.

[0067] As an example, the molar ratio of crosslinking monomer to flame retardant monomer can be 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, or 3:1.

[0068] Optionally, the molar ratio of crosslinking monomer to flame retardant monomer is 1 to 2:1.

[0069] When the molar ratio of crosslinking monomer to flame retardant monomer is 0.5 to 3:1, it is beneficial to form a two-dimensional structure of the second polymer, and the network structure of the second polymer has good stability, which makes the separator membrane have good flexibility.

[0070] According to some embodiments of this application, optionally, the flame-retardant monomer includes or At least one of them. Wherein, R1, R2, R3, R4, R5, and R6 are each independently selected from C. 1～10 Alkyl, C 3～6 Cycloalkyl, aryl, or heteroaryl.

[0071] Optionally, R1, R2, R3, R4, R5, and R6 are each independently selected from C. 1～3 alkyl.

[0072] As an example, flame-retardant monomers may include only or include or include or include or include

[0073] The aforementioned flame-retardant monomer includes at least one phosphate ester group and / or phosphite ester group and at least one unsaturated double bond, which can polymerize with crosslinking monomers through their respective unsaturated double bonds to form a second polymer with a three-dimensional structure.

[0074] According to some embodiments of this application, optionally, the crosslinking monomer includes and / or Where n is 1 to 10, and R7 is selected from H and C. 1～10 Alkyl, C 3～6 Cycloalkyl, aryl, or heteroaryl.

[0075] Optionally, n is 1 to 3, and R7 is selected from H or C. 1～3 alkyl.

[0076] As an example, crosslinking monomers may include only or include

[0077]

[0078] The aforementioned crosslinking monomer includes at least two unsaturated double bonds, which can polymerize with flame retardant monomers through their respective unsaturated double bonds to form a second polymer with a three-dimensional structure.

[0079] According to some embodiments of this application, optionally, the first polymer has a linear structure and the number-average molecular weight of the first polymer is 100,000 to 1,000,000.

[0080] As an example, the number-average molecular weight of the first polymer can be 100,000, 200,000, 300,000, 400,000, 500,000, 600,000, 700,000, 800,000, 900,000, or 1,000,000.

[0081] Optionally, the number-average molecular weight of the first polymer is 100,000 to 400,000.

[0082] The first polymer with a linear structure can form an interpenetrating polymer network structure with the second polymer with a three-dimensional structure. When the number-average molecular weight of the first polymer with a linear structure is 100,000 to 1,000,000, the separator has good mechanical properties and thermal stability.

[0083] According to some embodiments of this application, optionally, the first polymer includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene terephthalate, polyimide, polyamide, spandex, aramid, or cellulose.

[0084] The first polymer with the linear structure can form an interpenetrating polymer network structure with the second polymer with the bulk structure, which gives the separator good mechanical properties and thermal stability. Furthermore, the separator made of polymer material with interpenetrating polymer network structure will not dissolve in the electrolyte, thus not affecting the electrochemical performance of the battery.

[0085] Optionally, the first polymer includes polyethylene, polypropylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene terephthalate, polyimide, polyamide, spandex, aramid, or cellulose.

[0086] According to some embodiments of this application, optionally, please refer to... Figure 4 , Figure 4 This is a schematic diagram of a first polymer with a three-dimensional structure in some embodiments of this application. The first polymer has a three-dimensional structure and includes at least one of irradiated cross-linked polyethylene, irradiated cross-linked polypropylene, irradiated cross-linked polyvinylidene fluoride, or irradiated cross-linked polyvinylidene fluoride-hexafluoropropylene copolymer.

[0087] Irradiated crosslinked polyethylene is a polymer with a three-dimensional structure obtained by crosslinking polyethylene through radiation crosslinking technology.

[0088] Irradiation crosslinked polypropylene is a three-dimensional polymer obtained by crosslinking polypropylene through radiation crosslinking technology.

[0089] Irradiation-crosslinked polyvinylidene fluoride (PVDF) is a three-dimensional polymer obtained by crosslinking PVDF through radiation crosslinking technology.

[0090] Irradiation-crosslinked polyvinylidene fluoride-hexafluoropropylene copolymer is a three-dimensional polymer obtained by crosslinking polyvinylidene fluoride-hexafluoropropylene copolymer through radiation crosslinking technology.

[0091] The first polymer with the aforementioned three-dimensional structure can form an interpenetrating polymer network structure with the second polymer with the same three-dimensional structure, which gives the separator good mechanical properties and thermal stability. Furthermore, the separator made of polymer material with an interpenetrating polymer network structure will not dissolve in the electrolyte, thus not affecting the electrochemical performance of the battery.

[0092] Optionally, the first polymer includes irradiated crosslinked polyethylene, irradiated crosslinked polypropylene, irradiated crosslinked polyvinylidene fluoride, or irradiated crosslinked polyvinylidene fluoride-hexafluoropropylene copolymer.

[0093] According to some embodiments of this application, optionally, the mass ratio of the first polymer and the second polymer is 1:1 to 30.

[0094] The mass of the second polymer can be the sum of the masses of the flame-retardant monomer and the crosslinking monomer.

[0095] As an example, the mass ratio of the first polymer to the second polymer can be 1:1, 1:5, 1:10, 1:15, 1:20, 1:25 or 1:30.

[0096] Optionally, the mass ratio of the first polymer to the second polymer is 1:5 to 25.

[0097] When the mass ratio of the first polymer to the second polymer is 1:1 to 30, the polymer material has good flame retardant properties, thereby further delaying the time of battery thermal runaway. In addition, the second polymer can fully swell the first polymer, improving the mechanical properties of the separator.

[0098] According to some embodiments of this application, optionally, the separator membrane further includes an inorganic coating disposed on at least one side of the base membrane.

[0099] The base membrane made of polymer materials has good mechanical properties and thermal stability, and the inorganic coating can further improve other properties of the separator.

[0100] According to some embodiments of this application, the inorganic coating may optionally be made of ceramic materials.

[0101] Inorganic coatings made of ceramic materials can further improve the mechanical properties and thermal stability of the separator, as well as enhance its puncture resistance.

[0102] Alternatively, the ceramic material may include alumina and / or boehmite.

[0103] Optionally, the mass ratio of the inorganic coating to the base film is 0.1 to 2:1.

[0104] Optionally, the mass ratio of the inorganic coating to the base film is 0.5 to 1:1.

[0105] Optionally, according to some embodiments of this application, this application also provides a method for preparing the separator membrane in the above embodiments, which includes: mixing a flame-retardant monomer, a crosslinking monomer, and a first polymer, and performing photo-initiated polymerization to obtain a base membrane. The base membrane is used as a separator membrane, or the base membrane is used as a separator membrane after post-treatment. The base membrane is made of a first polymer and a second polymer, which form an interpenetrating polymer network structure. The second polymer is obtained by crosslinking a flame-retardant monomer and a crosslinking monomer. The second polymer has a three-dimensional structure and branches, the branches including phosphate ester groups and / or phosphite ester groups.

[0106] The embodiments of this application do not limit the source of the first polymer; it can be obtained by direct purchase or synthesized by oneself.

[0107] Photoinitiated polymerization is carried out under the protection of an inert gas, and a photoinitiator needs to be added to the system when photoinitiated polymerization is carried out.

[0108] Optionally, the photo-initiated polymerization reaction can be carried out for 12 to 24 hours.

[0109] Optionally, the mass ratio of the photoinitiator to the flame retardant monomer is 0.01 to 5:100.

[0110] Alternatively, the photoinitiator includes phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide.

[0111] After the photo-initiated polymerization reaction was completed, the product was washed with dimethyl carbonate and dried under vacuum to obtain the polymer material.

[0112] The method for preparing the separator membrane of this application is simple, and the polymerization reaction of the second polymer is carried out in a system including the first polymer. The first polymer provides crosslinking points, and after the second polymer is polymerized and crosslinked, it forms an interpenetrating polymer network structure with the first polymer.

[0113] The following describes in further detail an isolation membrane and its preparation method according to the present application, with reference to the embodiments.

[0114] The parameters of the separators in Examples 1-20 and Comparative Examples 1-4 of this application are shown in Table 1.

[0115] Table 1. Parameters of the separators in Examples 1-20 and Comparative Examples 1-4

[0116]

[0117]

[0118]

[0119] In Examples 1-20 and Comparative Examples 1-4, the mass ratio of the inorganic coating to the base film was 0.5:1. The structural formula of A1 is... The structural formula of A2 is: The structural formula of B1 is: The structural formula of B2 is:

[0120]

[0121] The separators in Examples 1-20 were synthesized by the following method:

[0122] In a mold, a mixture of the first polymer, flame-retardant monomer, and crosslinking monomer was prepared by dispersing them in dimethyl sulfoxide. Phenylenol bis(2,4,6-trimethylbenzoyl)oxide was then added to the mixture at a mass ratio of 2:100 to the flame-retardant monomer. Photoinitiated polymerization was carried out under light irradiation and inert gas (Ar) protection for 24 hours. After the reaction, the product was washed with dimethyl carbonate and vacuum dried to obtain a base film with a thickness of 45 μm.

[0123] Boehmite slurry was uniformly coated on both surfaces of the base film and dried to form an inorganic coating with a thickness of 2 μm, thus obtaining a separator with a thickness of 49 μm.

[0124] The inorganic coating comprises 95 wt% boehmite, 1 wt% ammonium polycarboxylate and 4 wt% polyvinyl alcohol, with N-methylpyrrolidone as the solvent for the boehmite slurry.

[0125] Experimental Example 1

[0126] The polymer materials prepared in Examples 1-20 and Comparative Examples 1-4 were subjected to heating and swelling experiments, and their glass transition temperature (Tg) and tensile modulus were measured. The results are shown in Table 2.

[0127] Heating swelling experiment:

[0128] Equipment: Oven, temperature setting: 65℃; Sample: 15mm×20mm strip.

[0129] Test procedure: Immerse the test sample in a petri dish containing N,N-dimethylacetamide, place it in an oven at 65°C for 24 hours, and observe whether the test sample dissolves or only swells.

[0130] Glass transition temperature (Tg):

[0131] Equipment: Dynamic Thermomechanical Analyzer (DMA), TA850; Sample size: 20mm × 3mm; Temperature: 25℃.

[0132] Test procedure: First, lower the temperature to -50℃, then raise it to 100℃ at a heating rate of 1K / min. Test the composite modulus at five frequencies (1Hz, 10Hz, 100Hz, 300Hz, 1000Hz). Determine the glass transition temperature from the loss angle.

[0133] Tensile modulus:

[0134] Equipment: Tensile testing machine: Instron 3343, single-arm tensile testing machine; Sample size: 20mm × 3mm; Temperature: 25℃.

[0135] Test procedure: Stretch the specimen at a rate of 5% / second at its initial length until it breaks.

[0136] Table 2. Parameters of the polymer materials obtained in Examples 1-20 and Comparative Examples 1-4

[0137]

[0138] When the first polymer has a linear structure, as shown in Examples 1-10, the base films of Examples 1-10 only swell but do not dissolve, indicating that the first and second polymers in the base films of Examples 1-10 form an interpenetrating polymer network structure. Furthermore, the base films of Examples 1-10 have only one glass transition temperature, indicating that the base films have a homogeneous structure and good compatibility. Comparative Example 1 only contains polyvinylidene fluoride with a linear structure, which dissolves upon heating. Comparative Example 2 is a mixture of the first and second polymers from Example 1, synthesized separately and then mixed. Upon heating, it partially dissolves, i.e., the linear polyvinylidene fluoride dissolves. The first and second polymers do not form an interpenetrating polymer network structure, and it has two glass transition temperatures.

[0139] When the first polymer has a three-dimensional structure, a comparison between Example 11 and Comparative Example 4 shows that Comparative Example 4 only involves the individual synthesis and mixing of the first and second polymers from Example 11. The first and second polymers do not form an interpenetrating polymer network structure. The tensile modulus of Comparative Example 4 is 41 MPa, while the tensile modulus of Example 11 is higher than that of Comparative Example 4, at 46 MPa. This indicates that the first and second polymers in the base film of Example 11 formed an interpenetrating polymer network structure. The preparation methods of Examples 11-20 are the same as those of Example 11, meaning that the first and second polymers in the base films of Examples 11-20 also formed an interpenetrating polymer network structure. Furthermore, the base films of Examples 11-20 have only one glass transition temperature, indicating that the base films have a homogeneous structure and good compatibility. Comparative Example 4 has two glass transition temperatures.

[0140] Experimental Example 2

[0141] The shrinkage rate of the separators of Examples 1-20 and Comparative Examples 1-4 at 120°C was measured. The separators of Examples 1-20 and Comparative Examples 1-4 were used to make batteries. The time from the start of heating to the occurrence of thermal runaway and the peak temperature in the thermal runaway test were measured. The results are shown in Table 3.

[0142] The steps for fabricating batteries using the separators from Examples 1-20 and Comparative Examples 1-4 are as follows:

[0143] (1) Preparation of positive electrode sheet

[0144] 96 wt% of lithium iron phosphate, 1.0 wt% of conductive agent (conductive carbon black), 2.5 wt% of binder (polyvinylidene fluoride), and 0.5 wt% of dispersant (isopropanolamine) were mixed, and then N-methylpyrrolidone was added and stirred to disperse the mixture, thus preparing a positive electrode slurry. The positive electrode slurry was then coated on both sides of aluminum foil, dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0145] (2) Preparation of negative electrode sheet

[0146] A mixture of 95 wt% negative electrode active material (artificial graphite), 1.0 wt% conductive agent (conductive carbon black), 2.0 wt% binder (styrene-butadiene rubber (SBR)), and 2.0 wt% thickener (sodium carboxymethyl cellulose (CMC)) was prepared by mixing with deionized water and stirring. The mixture was then coated onto a Cu foil. After coating both sides, the foil was dried, cold-pressed, slit, and sheeted to obtain the negative electrode sheet.

[0147] (3) Battery fabrication

[0148] The positive electrode, composite separator, and negative electrode are stacked in sequence, with the composite separator positioned between the anode and cathode to provide isolation. The bare cell is placed in the outer packaging (aluminum-plastic film), and the prepared electrolyte is injected. The process includes sealing, electrolyte injection, formation, and venting to obtain a lithium-ion battery (soft-pack battery) with a theoretical capacity of 2.7Ah.

[0149] The electrolyte contains lithium hexafluorophosphate at a molar concentration of 1 mol / L, and the mass ratio of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate is 2:3:5.

[0150] Shrinkage test:

[0151] Equipment Model: SYSTESTER FST-3102 Thin Film Heat Shrinkage Performance Tester.

[0152] Sample preparation: Cut the sample into strips of 15mm × 120mm. When taking samples, a better area should be cut to ensure that the characteristics of the sample can characterize the material being tested.

[0153] Test conditions: 23℃±2℃, 50%RH±2%RH.

[0154] Test procedure: Clamp the pre-treated sample at the test station, set the test temperature to 120℃ and the heat shrinkage time to 2h. When the test temperature is reached, click the test button, and the heating cover will descend. The sample is in a high-temperature environment, and the material shrinkage will generate shrinkage force. The shrinkage force is applied to the sensor. By analyzing and calculating the electrical signal of the sensor, the heat shrinkage rate of the sample can be obtained.

[0155] Thermal runaway test:

[0156] Test Procedure: The battery was charged to 3.65V and then held at 3.65V for 30 minutes to achieve a fully charged state. An accelerating calorimeter (ARC) was then used to precisely track the internal temperature changes of the fully charged battery in an adiabatic environment. The time from the start of heating to the occurrence of thermal runaway (a rapid temperature rise with an acceleration of temperature rise (dT / dt) greater than or equal to 1°C / s) was recorded, along with the peak temperature during thermal runaway.

[0157] Table 3 shows the parameters of the separators in Examples 1-20 and Comparative Examples 1-4, as well as the parameters for the batteries manufactured from them.

[0158]

[0159]

[0160] Examples 1-10 all exhibited a shrinkage rate of 0 at 120°C. In the thermal runaway test, the time from the start of heating to the occurrence of thermal runaway was ≥12 hours, and the peak temperature in the thermal runaway test was ≤385°C. Comparative Examples 1-2 showed shrinkage rates of 3% and 10% at 120°C, respectively. In the thermal runaway test, the time from the start of heating to the occurrence of thermal runaway was only 9.5 hours and 10.5 hours, respectively, and the peak temperatures in the thermal runaway test were 389°C and 395°C, respectively. A comparison between Examples 1-10 and Comparative Examples 1-2 shows that the separators of Examples 1-10 have better thermal stability and can delay the onset of battery thermal runaway, thus improving the safety of the manufactured batteries.

[0161] Examples 11-20 all exhibited a shrinkage rate of 0 at 120°C. In the thermal runaway test, the time from the start of heating to the occurrence of thermal runaway was ≥13 hours, and the peak temperature in the thermal runaway test was ≤381°C. Comparative Examples 3-4 showed shrinkage rates of 6% and 1% at 120°C. In the thermal runaway test, the time from the start of heating to the occurrence of thermal runaway was only 10 hours and 10.7 hours, respectively, and the peak temperatures in the thermal runaway test were 390°C and 387°C, respectively. A comparison between Examples 11-20 and Comparative Examples 3-4 shows that the separators of Examples 11-20 have better thermal stability and can delay the onset of battery thermal runaway, thus improving the safety of the manufactured batteries.

[0162] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A separating membrane, characterized in that, The separator includes a base membrane, the base membrane being made of a first polymer and a second polymer, the first polymer and the second polymer forming an interpenetrating polymer network structure, wherein the second polymer is a three-dimensional structure and has branches, the branches including phosphate ester groups and / or phosphite ester groups; The second polymer is obtained by crosslinking a flame retardant monomer and a crosslinking monomer. The flame retardant monomer includes at least one phosphate ester group and / or phosphite ester group and at least one unsaturated double bond. The crosslinking monomer includes at least two unsaturated double bonds.

2. The separator membrane according to claim 1, characterized in that, The molar ratio of the crosslinking monomer to the flame retardant monomer is 0.5 to 3:

1.

3. The separator membrane according to claim 2, characterized in that, The molar ratio of the crosslinking monomer to the flame retardant monomer is 1~2:

1.

4. The separator according to claim 1, characterized in that, The flame-retardant monomer includes , or At least one of them; Among them, R1, R2, R3, R4, R5, and R6 are each independently selected from C. 1~10 Alkyl, C 3~6 Cycloalkyl, aryl, or heteroaryl.

5. The separator according to claim 4, characterized in that, R1, R2, R3, R4, R5, and R6 are each independently selected from C. 1~3 alkyl.

6. The separator according to claim 1, characterized in that, The crosslinking monomer includes and / or ; Where n is 1 to 10, and R7 is selected from H and C. 1~10 Alkyl, C 3~6 Cycloalkyl, aryl, or heteroaryl.

7. The separator membrane according to claim 6, characterized in that, n is 1 to 3, and R7 is selected from H or C. 1~3 alkyl.

8. The separator according to any one of claims 1 to 7, characterized in that, The first polymer has a linear structure and a number-average molecular weight of 100,000 to 1,000,000.

9. The separator according to claim 8, characterized in that, The first polymer includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene terephthalate, polyimide, polyamide, spandex, aramid, or cellulose.

10. The separator according to any one of claims 1 to 7, characterized in that, The first polymer has a three-dimensional structure and includes at least one of irradiated cross-linked polyethylene, irradiated cross-linked polypropylene, irradiated cross-linked polyvinylidene fluoride, or irradiated cross-linked polyvinylidene fluoride-hexafluoropropylene copolymer.

11. The separator according to any one of claims 1 to 7, characterized in that, The mass ratio of the first polymer to the second polymer is 1:1 to 30.

12. The separator membrane according to claim 11, characterized in that, The mass ratio of the first polymer to the second polymer is 1:5~25.

13. The separator according to any one of claims 1 to 7, characterized in that, The isolation membrane also includes an inorganic coating disposed on at least one side of the base membrane.

14. The separator according to claim 13, characterized in that, The inorganic coating is made of ceramic materials.

15. A method for preparing a separating membrane, characterized in that, The preparation method includes: mixing flame-retardant monomers, crosslinking monomers and a first polymer, and performing photo-initiated polymerization to obtain a base film; Wherein, the base film is used as a separator, or the base film is used as a separator after post-processing; The base film is made of a first polymer and a second polymer, which form an interpenetrating polymer network structure. The second polymer is obtained by crosslinking the flame retardant monomer and the crosslinking monomer. The second polymer has a three-dimensional structure and branches, which include phosphate groups and / or phosphite groups. The flame retardant monomer includes at least one unsaturated double bond, and the crosslinking monomer includes at least two unsaturated double bonds.

16. A battery, characterized in that, The battery includes the separator as described in any one of claims 1 to 14 or the separator prepared by the method described in claim 15.

17. An electrical device, characterized in that, The electrical device includes the battery of claim 16, the battery being used to provide electrical energy.

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