Isolating membrane and preparation method thereof, battery and electric device

Abstract

The invention provides an isolating membrane and a preparation method thereof, a battery and a power utilization device, and belongs to the technical field of batteries. The isolating membrane comprises 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, the second polymer is of a body structure and is provided with a branched chain, and the branched chain comprises a phosphate group and / or a phosphite group. The interpenetrating polymer network structure can play a role in enhancing the mechanical property of the isolating membrane, so that the isolating membrane has better mechanical property and thermal stability. And when the internal temperature of the battery is rapidly increased to 80-100 DEG C, the branched chain of the second polymer is broken to generate phosphate free radicals and / or phosphite free radicals, so that hydrogen / hydroxyl free radicals generated by chain decomposition of the electrolyte are neutralized, the time of thermal runaway of the battery is delayed, and the safety of the prepared battery is improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to an isolation membrane and a preparation method thereof, a battery and an electrical device. Background Art

[0002] During the use of lithium-ion batteries, factors such as extreme external high temperatures or internal short circuits may cause the temperature inside the battery to rise rapidly, which can easily lead to the decomposition of the SEI film and the chain decomposition of the electrolyte, which will 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, the present application provides an isolation film and a preparation method thereof, a battery and an electrical device, which can delay the onset of battery thermal runaway and improve the safety of the battery.

[0004] In a first aspect, the present application provides an isolation membrane, which includes a base membrane, the material of the base membrane includes a first polymer and a second polymer, the first polymer and the second polymer form an interpenetrating polymer network structure, wherein the second polymer is a three-dimensional structure, the second polymer has a branch chain, and the branch chain includes a phosphate group and / or a phosphite group.

[0005] In the technical solution of the embodiment of the present application, when the battery is operating normally, the interpenetrating polymer network structure of the isolation membrane of the present application can enhance the mechanical properties of the isolation membrane, so that the isolation membrane has good mechanical properties and thermal stability, and the isolation membrane made of the polymer material with the interpenetrating polymer network structure will not dissolve in the electrolyte, so as not to affect the electrochemical performance of the prepared battery. When the internal temperature of the battery rises rapidly to 80°C to 100°C, the side chain of the second polymer breaks, generating phosphate free radicals and / or phosphite free radicals, which can neutralize the hydrogen / hydroxyl free radicals generated by the chain decomposition of the electrolyte, delay the arrival of thermal runaway of the battery, and improve the safety of the prepared battery.

[0006] In some embodiments, the second polymer includes a flame retardant monomer and a cross-linking monomer obtained by cross-linking, the flame retardant monomer includes at least one phosphate group and / or phosphite group and at least one unsaturated double bond, and the cross-linking monomer includes at least two unsaturated double bonds. The flame retardant monomer and the cross-linking monomer can be polymerized through their respective unsaturated double bonds to form a second polymer with a three-dimensional structure.

[0007] In some embodiments, the molar ratio of the cross-linking monomer to the flame retardant monomer is 0.5 to 3: 1. Optionally, the molar ratio of the cross-linking monomer to the flame retardant monomer is 1 to 2: 1. When the molar ratio of the cross-linking monomer to the flame retardant monomer is 0.5 to 3: 1, it is conducive to forming a second polymer with a body structure, and the network structure of the second polymer is stable, so that the isolation film has good softness.

[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 Alternatively, R1, R2, R3, R4, R5 and R6 are each independently selected from C 1～3 The flame retardant monomer includes at least one phosphate group and / or phosphite group and at least one unsaturated double bond, and can be polymerized with the cross-linking monomer through their respective unsaturated double bonds to form a second polymer with a three-dimensional structure.

[0009] In some embodiments, the crosslinking monomer comprises and / or Wherein, n is 1 to 10, and R7 is selected from H, 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 The cross-linking monomer includes at least two unsaturated double bonds, and can be polymerized with the flame retardant monomer through their respective unsaturated double bonds to form a second polymer with a three-dimensional structure.

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

[0011] In some embodiments, the first polymer includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene terephthalate, polyimide, polyamide, spandex, aramid or cellulose. The linear first polymer can form an interpenetrating polymer network structure with the second polymer of the bulk structure, so that the isolation membrane has good mechanical properties and thermal stability, and the isolation membrane made of the polymer material of the interpenetrating polymer network structure will not dissolve in the electrolyte, so as not to affect the electrochemical performance of the obtained battery.

[0012] In some embodiments, the first polymer is a bulk structure, and the first polymer 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. The first polymer of the bulk structure can form an interpenetrating polymer network structure with the second polymer of the bulk structure, so that the isolation membrane has good mechanical properties and thermal stability, and the isolation membrane made of the polymer material of the interpenetrating polymer network structure will not dissolve in the electrolyte, so as not to affect the electrochemical performance of the obtained 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 good flame retardant properties, thereby further delaying the time of battery thermal runaway, and the second polymer can fully swell the first polymer to improve the mechanical properties of the isolation membrane.

[0014] In some embodiments, the isolation film further includes an inorganic coating disposed on at least one side of the base film. The base film made of polymer material has good mechanical properties and thermal stability, and the inorganic coating can further improve other properties of the isolation film.

[0015] In some embodiments, the material of the inorganic coating includes a ceramic material. The inorganic coating made of a ceramic material can further improve the mechanical properties and thermal stability of the isolation membrane, and enhance the puncture resistance of the isolation membrane.

[0016] In the second aspect, the present application provides a method for preparing the isolation membrane in the above-mentioned embodiment, which comprises: mixing a flame retardant monomer, a cross-linking monomer and a first polymer, and performing photo-initiated polymerization to obtain a base membrane. The base membrane is used as an isolation membrane, or the base membrane is used as an isolation membrane after post-treatment. The material of the base membrane includes a first polymer and a second polymer, and the first polymer and the second polymer form an interpenetrating polymer network structure, wherein the second polymer includes a flame retardant monomer and a cross-linking monomer obtained by cross-linking, the second polymer is a three-dimensional structure, and the second polymer has a side chain, and the side chain includes a phosphate group and / or a phosphite group.

[0017] In the technical solution of the embodiment of the present application, the preparation method of the isolation membrane of the present 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 cross-linking points, and the second polymer forms an interpenetrating polymer network structure with the first polymer after polymerization and cross-linking.

[0018] In a third aspect, the present application provides a battery, which includes the isolation membrane in the above embodiment or the isolation membrane prepared according to the preparation method in the above embodiment.

[0019] In a fourth aspect, the present application provides an electrical device, which includes the battery in the above embodiment, and the battery is used to provide electrical energy.

[0020] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0022] Figure 1 A schematic diagram of the structure of a vehicle according to some embodiments of the present application;

[0023] Figure 2 A schematic diagram of the exploded structure of a battery according to some embodiments of the present application;

[0024] Figure 3 A schematic diagram of the exploded structure of a battery cell according to some embodiments of the present application;

[0025] Figure 4 Schematic diagram of the first polymer of the body structure in some embodiments of the present application.

[0026] The reference numerals in the specific implementation manner are as follows:

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

[0028] 10-box; 11-first part; 12-second part;

[0029] 20 - battery cell; 21 - end cover; 22 - housing; 23 - electrode assembly. DETAILED DESCRIPTION

[0030] The following embodiments of the technical solution of the present application will be described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0032] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0033] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0034] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0035] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0036] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the embodiments of the present application.

[0037] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like 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 a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0038] At present, from the perspective of market development, the application of power batteries is becoming more and more extensive. Power batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, electric cars, as well as military equipment and aerospace and other fields. With the continuous expansion of the application field of power batteries, the market demand is also constantly expanding.

[0039] During the use of lithium-ion batteries, factors such as extreme external high temperatures or internal short circuits may cause the temperature inside the battery to rise rapidly, which can easily lead to the decomposition of the SEI film and the chain decomposition of the electrolyte, which will 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 commonly used method. Although adding flame retardants to the separator can improve the flame retardant effect of the separator, it will cause other properties of the separator to deteriorate. For example, adding flame retardants to the separator will increase the brittleness of the separator and weaken the processing performance of the separator and its compatibility with positive and negative electrode materials.

[0041] Based on the above considerations, in order to delay the arrival of battery thermal runaway and improve the safety of the battery, a polymer with an interpenetrating polymer network structure is used to make an isolation membrane. When the battery is operating normally, the interpenetrating polymer network structure can enhance the mechanical properties of the isolation membrane, so that the isolation membrane has good mechanical properties and thermal stability, and the isolation membrane made of a polymer material with an interpenetrating polymer network structure will not dissolve in the electrolyte, thereby not affecting the electrochemical properties of the prepared battery. When the internal temperature of the battery rises rapidly to 80°C to 100°C, the side chain of the second polymer breaks, generating phosphate free radicals and / or phosphite free radicals, which can neutralize the hydrogen / hydroxyl free radicals generated by the chain decomposition of the electrolyte, delay the arrival of battery thermal runaway, and improve the safety of the prepared battery.

[0042] The battery mentioned in the embodiments of the present application refers to a single physical module including multiple battery cells to provide higher voltage and capacity. The battery generally includes a battery box for packaging multiple battery cells, and the battery box can prevent liquid 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 thereto. The battery cell can be cylindrical, flat, rectangular or in other shapes. Battery cells are generally divided into three types according to the packaging method: cylindrical battery cells, square battery cells and soft-pack battery cells.

[0044] The battery cell includes an electrode assembly and an electrolyte. The electrode assembly is composed of a positive electrode sheet, a negative electrode sheet and a separator. The battery cell mainly relies on the movement of metal ions between the positive electrode sheet and the negative electrode sheet to work. The positive electrode sheet includes a positive electrode collector and a positive electrode active material layer. The positive electrode active material layer is coated on the surface of the positive electrode collector. The positive electrode collector not coated with the positive electrode active material layer protrudes from the positive electrode collector coated with the positive electrode active material layer. The positive electrode collector not coated with the positive electrode active material layer serves as the positive electrode tab. Taking lithium-ion batteries as an example, the material of the positive electrode collector can be aluminum, and the positive electrode active material can be lithium cobalt oxide, lithium iron phosphate, ternary lithium or lithium manganese oxide. The negative electrode sheet includes a negative electrode collector and a negative electrode active material layer. The negative electrode active material layer is coated on the surface of the negative electrode collector. The negative electrode collector not coated with the negative electrode active material layer protrudes from the negative electrode collector coated with the negative electrode active material layer. The negative electrode collector not coated with the negative electrode active material layer serves as the negative electrode tab. The material of the negative electrode collector can be copper. In order to ensure that a large current does not melt, the number of positive electrode tabs is multiple and stacked together, and the number of negative electrode tabs is multiple and stacked together. The material of the isolation film can be polypropylene (PP) or polyethylene (PE). In addition, the electrode assembly can be a winding structure or a laminated structure, and the embodiments of the present application are not limited thereto.

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

[0046] The battery also includes a sampling terminal and a battery management system. The sampling terminal is connected to the busbar to collect information about the battery cells, such as voltage or temperature, etc. The sampling terminal transmits the collected information about the battery cells to the battery management system. When the battery management system detects that the information about the battery cells exceeds the normal range, it will limit the output power of the battery to achieve safety protection.

[0047] It can be understood that the electrical devices used by the batteries described in the embodiments of the present application can be in various forms, for example, mobile phones, portable devices, laptops, battery vehicles, electric cars, ships, spacecraft, electric toys and electric tools, etc. For example, spacecraft include airplanes, rockets, space shuttles and spacecraft, etc. Electric toys include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys and electric airplane toys, etc. Electric tools include metal cutting electric tools, grinding electric tools, assembly electric tools and railway electric 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 the present application are not limited to the electrical devices described above, but can also be applied to all electrical devices using battery cells and batteries. However, for the sake of simplicity, the following embodiments are described using electric vehicles as examples.

[0049] See also Figure 1 , Figure 1 A schematic diagram of the structure of a vehicle provided for some embodiments of the present application. Vehicle 1000 may be a fuel vehicle, a gas vehicle or a new energy vehicle, and the new energy vehicle may be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A battery 100 is provided inside the vehicle 1000, and the battery 100 may be provided at the bottom, head or tail of the vehicle 1000. The battery 100 may be used to power the vehicle 1000, for example, the battery 100 may be used as an operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300, and the controller 200 is used to control the battery 100 to power the motor 300, for example, for starting, navigating and driving the vehicle 1000.

[0050] In some embodiments of the present application, the battery 100 can not only serve as an operating power source for the vehicle 1000, but also serve as a 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 2An exploded diagram of a battery provided for some embodiments of the present application. The battery 100 includes a housing 10 and a battery cell 20, and the battery cell 20 is contained in the housing 10. Among them, the housing 10 is used to provide a storage space for the battery cell 20, and the housing 10 can adopt a variety of structures. In some embodiments, the housing 10 may include a first part 11 and a second part 12, and the first part 11 and the second part 12 cover each other, and the first part 11 and the second part 12 jointly define a storage space for accommodating the battery cell 20. The second part 12 may be a hollow structure with one end open, and the first part 11 may be a plate-like structure, and the first part 11 covers the open side of the second part 12, so that the first part 11 and the second part 12 jointly define a storage space; the first part 11 and the second part 12 may also be hollow structures with one side open, and the open side of the first part 11 covers the open side of the second part 12. Of course, the housing 10 formed by the first part 11 and the second part 12 may be in a variety of shapes, such as a cylinder, a cuboid, etc.

[0052] In the battery 100, there may be multiple battery cells 20, and the multiple battery cells 20 may be connected in series, in parallel, or in a mixed connection. A mixed connection means that the multiple battery cells 20 are both connected in series and in parallel. The multiple battery cells 20 may be directly connected in series, in parallel, or in a mixed connection, and then the whole formed by the multiple battery cells 20 is accommodated in the box 10; of course, the battery 100 may also be a battery module formed by connecting multiple battery cells 20 in series, in parallel, or in a mixed connection, and then the multiple battery modules are connected in series, in parallel, or in a mixed connection to form a whole, and accommodated in the box 10. The battery 100 may also include other structures, for example, the battery 100 may also include a busbar component for realizing electrical connection between the multiple battery cells 20.

[0053] Each battery cell 20 is a secondary battery, which may be a lithium-ion battery, a lithium-sulfur battery, a sodium-ion battery or a magnesium-ion battery, but is not limited thereto. The battery cell 20 may be cylindrical, flat, rectangular or in other shapes.

[0054] Please refer to Figure 3 , Figure 3 The first battery cell 20 is a schematic diagram of the decomposed structure of some embodiments of the present application. The battery cell 20 refers to the smallest unit that constitutes the battery. Figure 3 The battery cell 20 includes an end cover 21, a shell 22, an electrode assembly 23 and other functional components.

[0055] The end cap 21 refers to a component that covers the opening of the shell 22 to isolate the internal environment of the battery cell 20 from the external environment. Without limitation, the shape of the end cap 21 can be adapted to the shape of the shell 22 to match the shell 22. Optionally, the end cap 21 can be made of a material with a certain hardness and strength (such as aluminum alloy), so that the end cap 21 is not easily deformed when squeezed and collided, so that the battery cell 20 can have a higher structural strength and the safety performance can also be improved. Functional components such as electrode terminals can be provided on the end cap 21. The electrode terminal can be used to electrically connect to the electrode assembly 23 for outputting or inputting electrical energy of the battery cell 20. In some embodiments, the end cap 21 can also be provided with a pressure relief mechanism for releasing the internal pressure when the internal pressure or temperature of the battery cell 20 reaches a threshold. The material of the end cap 21 can also be a variety of materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiments of the present application do not impose special restrictions on this. In some embodiments, an insulating member may be provided inside the end cap 21, and the insulating member may be used to isolate the electrical connection components in the housing 22 from the end cap 21 to reduce the risk of short circuit. For example, the insulating member may be plastic, rubber, or the like.

[0056] The shell 22 is a component used to cooperate with the end cap 21 to form the internal environment of the battery cell 20, wherein the formed internal environment can be used to accommodate the electrode assembly 23, the electrolyte and other components. The shell 22 and the end cap 21 can be independent components, and an opening can be set on the shell 22, and the internal environment of the battery cell 20 is formed by covering the opening with the end cap 21 at the opening. Without limitation, the end cap 21 and the shell 22 can also be integrated. Specifically, the end cap 21 and the shell 22 can form a common connection surface before other components are put into the shell, and when the interior of the shell 22 needs to be encapsulated, the end cap 21 covers the shell 22. The shell 22 can be of various shapes and sizes, such as a rectangular parallelepiped, a cylindrical shape, a hexagonal prism, etc. Specifically, the shape of the shell 22 can be determined according to the specific shape and size of the electrode assembly 23. The material of the shell 22 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiment of the present application does not impose any special restrictions on this.

[0057] The electrode assembly 23 is a component in the battery cell 20 where electrochemical reactions occur. One or more electrode assemblies 23 may be included in the housing 22. The electrode assembly 23 is mainly formed by winding or stacking positive and negative electrode sheets, and a separator is usually provided between the positive and negative electrode sheets. The parts of the positive and negative electrode sheets with active materials constitute the main body of the electrode assembly, and the parts of the positive and negative electrode sheets without active materials each constitute a tab. The positive tab and the negative tab may be located together at one end of the main body or at both ends of the main body, respectively. During the charge and discharge process of the battery, the positive active material and the negative active material react with the electrolyte, and the tabs connect the electrode terminals to form a current loop.

[0058] According to some embodiments of the present application, the present application provides an isolation membrane, which includes a base membrane, the material of the base membrane includes a first polymer and a second polymer, the first polymer and the second polymer form an interpenetrating polymer network structure, wherein the second polymer is a body structure, the second polymer has a branch chain, and the branch chain includes a phosphate group and / or a phosphite group.

[0059] The interpenetrating polymer network structure is a network structure formed by two or more blended polymers, in which the molecular chains penetrate each other and at least one polymer molecular chain is cross-linked in the form of chemical bonds.

[0060] The phosphate group and / or phosphite group is a group that can improve the flame retardancy of the second polymer, and serves the purpose of, but not limited to, preventing the second polymer from being ignited and inhibiting the spread of combustion.

[0061] When the isolation membrane of the present application is in normal operation of the battery, the interpenetrating polymer network structure can enhance the mechanical properties of the isolation membrane, so that the isolation membrane has good mechanical properties and thermal stability, and the isolation membrane made of polymer materials with an interpenetrating polymer network structure will not dissolve in the electrolyte, thereby not affecting the electrochemical properties of the manufactured battery. When the internal temperature of the battery rises rapidly to 80°C to 100°C, the side chains of the second polymer break to generate phosphate free radicals and / or phosphite free radicals, which can neutralize the hydrogen / hydroxyl free radicals generated by the chain decomposition of the electrolyte, delay the arrival of thermal runaway of the battery, and improve the safety of the manufactured battery.

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

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

[0064] The crosslinking monomer may include two unsaturated double bonds or three unsaturated double bonds.

[0065] The flame retardant monomer and the cross-linking monomer can be polymerized through their respective unsaturated double bonds to form a second polymer with a three-dimensional structure.

[0066] According to some embodiments of the present application, optionally, the molar ratio of the cross-linking monomer to the flame retardant monomer is 0.5 to 3:1.

[0067] As an example, the molar ratio of the crosslinking monomer to the 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 the cross-linking monomer to the flame retardant monomer is 1 to 2:1.

[0069] When the molar ratio of the cross-linking monomer to the flame-retardant monomer is 0.5 to 3:1, it is conducive to forming a second polymer with a three-dimensional structure, and the network structure of the second polymer has good stability, so that the isolation film has good softness.

[0070] According to some embodiments of the present application, optionally, the flame retardant monomer includes or At least one of. 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, the flame retardant monomer may include only or include or include or include or include

[0073] The flame retardant monomer includes at least one phosphate group and / or phosphite group and at least one unsaturated double bond, and can be polymerized with the cross-linking monomer through their respective unsaturated double bonds to form a second polymer with a three-dimensional structure.

[0074] According to some embodiments of the present application, optionally, the cross-linking monomer includes and / or Wherein, n is 1 to 10, and R7 is selected from H, 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, the crosslinking monomer may include only or include

[0077]

[0078] The cross-linking monomer includes at least two unsaturated double bonds, and can be polymerized with the flame-retardant monomer through their respective unsaturated double bonds to form a second polymer with a three-dimensional structure.

[0079] According to some embodiments of the present application, optionally, the first polymer is 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 stereotyped structure. When the number average molecular weight of the first polymer with a linear structure is 100,000 to 1,000,000, the isolation film has good mechanical properties and thermal stability.

[0083] According to some embodiments of the present 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 linear first polymer can form an interpenetrating polymer network structure with the stereotyped second polymer, so that the isolation membrane has good mechanical properties and thermal stability. The isolation membrane made of the polymer material with the interpenetrating polymer network structure will not dissolve in the electrolyte, and thus will not affect the electrochemical properties of the manufactured 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 the present application, optionally, refer to Figure 4 , Figure 4 Schematic diagram of a first polymer of a body structure in some embodiments of the present application. The first polymer is a body structure, and the first polymer includes at least one of radiation cross-linked polyethylene, radiation cross-linked polypropylene, radiation cross-linked polyvinylidene fluoride, or radiation cross-linked polyvinylidene fluoride-hexafluoropropylene copolymer.

[0087] Radiation cross-linked polyethylene is a polymer with a three-dimensional structure obtained by cross-linking polyethylene through radiation cross-linking technology.

[0088] Radiation cross-linked polypropylene is a polymer with a three-dimensional structure obtained by cross-linking polypropylene through radiation cross-linking technology.

[0089] Radiation-crosslinked polyvinylidene fluoride is a polymer with a three-dimensional structure obtained by cross-linking polyvinylidene fluoride through radiation cross-linking technology.

[0090] The radiation cross-linked polyvinylidene fluoride-hexafluoropropylene copolymer is a polymer with a three-dimensional structure obtained by cross-linking the polyvinylidene fluoride-hexafluoropropylene copolymer through the radiation cross-linking technology.

[0091] The first polymer with the above-mentioned body structure can form an interpenetrating polymer network structure with the second polymer with the body structure, so that the isolation membrane has good mechanical properties and thermal stability, and the isolation membrane made of the polymer material with the interpenetrating polymer network structure will not dissolve in the electrolyte, thereby not affecting the electrochemical properties of the manufactured battery.

[0092] Optionally, the first polymer includes radiation cross-linked polyethylene, radiation cross-linked polypropylene, radiation cross-linked polyvinylidene fluoride or radiation cross-linked polyvinylidene fluoride-hexafluoropropylene copolymer.

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

[0094] The mass of the second polymer may be the sum of the mass of the flame retardant monomer and the mass of the cross-linking monomer.

[0095] As an example, the mass ratio of the first polymer to the second polymer may 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 1:5-25.

[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 arrival of thermal runaway of the battery, and the second polymer can fully swell the first polymer to improve the mechanical properties of the isolation membrane.

[0098] According to some embodiments of the present application, optionally, the isolation film further includes an inorganic coating layer disposed on at least one side of the base film.

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

[0100] According to some embodiments of the present application, optionally, the material of the inorganic coating includes a ceramic material.

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

[0102] Optionally, the ceramic material comprises alumina and / or boehmite.

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

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

[0105] According to some embodiments of the present application, optionally, the present application also provides a method for preparing the isolation membrane in the above-mentioned embodiment, which comprises: mixing a flame retardant monomer, a cross-linking monomer and a first polymer, and performing photo-initiated polymerization to obtain a base membrane. The base membrane is used as an isolation membrane, or the base membrane is used as an isolation membrane after post-treatment. The material of the base membrane comprises a first polymer and a second polymer, and the first polymer and the second polymer form an interpenetrating polymer network structure, wherein the second polymer comprises a flame retardant monomer and a cross-linking monomer obtained by cross-linking, the second polymer is a body structure, and the second polymer has a side chain, and the side chain comprises a phosphate group and / or a phosphite group.

[0106] The embodiment of the present application does not limit the source of the first polymer, which can be directly purchased or synthesized by itself.

[0107] The photopolymerization reaction is carried out under the protection of an inert gas, and a photoinitiator needs to be added to the system during the photopolymerization reaction.

[0108] Optionally, the photo-initiated polymerization reaction time is 12 hours to 24 hours.

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

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

[0111] After the photopolymerization reaction is completed, the product is washed with dimethyl carbonate and vacuum dried to obtain a polymer material.

[0112] The preparation method of the isolation membrane of the present 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 cross-linking points, and the second polymer forms an interpenetrating polymer network structure with the first polymer after polymerization and cross-linking.

[0113] The following is a further detailed description of an isolation membrane and a preparation method thereof of the present application in conjunction with embodiments.

[0114] The parameters of the isolation films of Examples 1 to 20 and Comparative Examples 1 to 4 of the present application are shown in Table 1.

[0115] Table 1 Parameters of the isolation films of Examples 1 to 20 and Comparative Examples 1 to 4

[0116]

[0117]

[0118]

[0119] The mass ratio of the inorganic coating layer to the base film in Examples 1 to 20 and Comparative Examples 1 to 4 is 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 isolation membranes of Examples 1 to 20 were synthesized by the following method:

[0122] In the mold, the first polymer, the flame retardant monomer and the cross-linking monomer are mixed and dispersed in dimethyl sulfoxide to prepare a mixture, and phenyl bis (2,4,6-trimethylbenzoyl) phosphine oxide is added to the mixture. The mass ratio of phenyl bis (2,4,6-trimethylbenzoyl) phosphine oxide and the flame retardant monomer is 2:100, and a photo-initiated polymerization reaction is carried out under light conditions and inert gas (Ar) protection. The reaction time is 24 hours. After the reaction is completed, the product is washed with dimethyl carbonate and vacuum dried to obtain a base film with a thickness of 45 μm.

[0123] The boehmite slurry was evenly coated on both surfaces of the base film and dried to form an inorganic coating with a thickness of 2 μm, thereby obtaining a separation film with a thickness of 49 μm.

[0124] The inorganic coating comprises 95 wt % of boehmite, 1 wt % of polycarboxylic acid ammonium salts and 4 wt % of polyvinyl alcohol, and the solvent of the boehmite slurry is N-methylpyrrolidone.

[0125] Test Example 1

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

[0127] Heating swelling experiment:

[0128] Equipment: oven, set temperature: 65°C; sample: 15mm×20mm strip.

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

[0130] Glass transition temperature (Tg):

[0131] Equipment: dynamic mechanical analyzer (DMA), TA850; sample: 20mm×3mm; temperature: 25℃.

[0132] Test steps: first lower the temperature to -50°C, then heat it up to 100°C at a heating rate of 1K / min, and test the composite modulus at 5 frequencies (1Hz, 10Hz, 100Hz, 300Hz, 1000Hz). Determine the glass transition temperature from the loss angle.

[0133] Tensile modulus:

[0134] Equipment: tensile tester: Instron 3343, single-arm tensile machine; specimen: 20 mm × 3 mm; temperature: 25 °C.

[0135] Test procedure: At the initial length of the sample, stretch the sample at a rate of 5% / s until it breaks.

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

[0137]

[0138] When the first polymer is a linear structure, it can be seen from Examples 1 to 10 that the base films of Examples 1 to 10 only swell but do not dissolve, indicating that the first polymer and the second polymer in the base films of Examples 1 to 10 form an interpenetrating polymer network structure, and the base films of Examples 1 to 10 have only one glass transition temperature, indicating that the base film is a homogeneous structure with good compatibility. Comparative Example 1 has only linear polyvinylidene fluoride, which dissolves upon heating. Comparative Example 2 is the first polymer and the second polymer in Example 1 that are synthesized separately and mixed, and partially dissolved upon heating, that is, the linear polyvinylidene fluoride dissolves, the first polymer and the second polymer do not form an interpenetrating polymer network structure, and have two glass transition temperatures.

[0139] When the first polymer is a body structure, it can be seen from the comparison between Example 11 and Comparative Example 4 that Comparative Example 4 is only the first polymer and the second polymer in Example 11 synthesized separately and mixed, and the first polymer and the second polymer do not form an interpenetrating polymer network structure. The tensile modulus of Comparative Example 4 is 41MPa, while the tensile modulus of Example 11 is higher than that of Comparative Example 4, which is 46MPa, indicating that the first polymer and the second polymer in the base film of Example 11 form an interpenetrating polymer network structure. The preparation method of Examples 11 to 20 is the same as that of Example 11, that is, the first polymer and the second polymer in the base film of Examples 11 to 20 also form an interpenetrating polymer network structure, and the base film of Examples 11 to 20 has only one glass transition temperature, indicating that the base film is a homogeneous structure with good compatibility, and Comparative Example 4 has two glass transition temperatures.

[0140] Test Example 2

[0141] The shrinkage rates of the isolation films of Examples 1 to 20 and Comparative Examples 1 to 4 at 120°C were measured, and the isolation films of Examples 1 to 20 and Comparative Examples 1 to 4 were made into batteries. The time from the start of heating to the occurrence of thermal runaway in the thermal runaway test and the peak temperature in the thermal runaway test were measured. The results are shown in Table 3.

[0142] The steps of making the separators of Examples 1 to 20 and Comparative Examples 1 to 4 into batteries are as follows:

[0143] (1) Preparation of positive electrode sheet

[0144] 96wt% of positive electrode active material lithium iron phosphate, 1.0wt% of conductive agent (conductive carbon black), 2.5wt% of binder (polyvinylidene fluoride), and 0.5wt% of dispersant (isopropanolamine) are mixed, and then N-methylpyrrolidone is added, stirred, and dispersed to prepare positive electrode slurry; then the positive electrode slurry is coated on both sides of aluminum foil, dried, cold pressed, and cut to prepare positive electrode sheets.

[0145] (2) Preparation of negative electrode sheet

[0146] 95wt% of negative electrode active material (artificial graphite), 1.0wt% of conductive agent (conductive carbon black), 2.0wt% of binder (styrene-butadiene rubber (SBR)) and 2.0wt% of thickener (sodium carboxymethyl cellulose (CMC)) were mixed, added with deionized water, stirred, and dispersed to form negative electrode slurry. Then, the negative electrode slurry was coated on Cu foil, and after both sides were completed, it was dried, cold pressed, cut, and sliced ​​to prepare the negative electrode sheet.

[0147] (3) Preparation of batteries

[0148] The positive electrode sheet, composite isolation membrane, and negative electrode sheet are stacked in order, so that the composite isolation membrane is located between the positive and negative electrodes to play an isolating role. The bare battery cell is placed in an outer package (aluminum-plastic film), injected with the prepared electrolyte, and packaged, injected, formed, and vented to obtain a lithium-ion battery (soft-pack battery) with a theoretical capacity of 2.7Ah.

[0149] The molar concentration of lithium hexafluorophosphate in the electrolyte is 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 film heat shrink performance tester.

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

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

[0154] Test steps: Clamp the pre-processed sample to 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, the heating cover moves downward, the sample is in a high temperature environment, the material shrinks and generates a shrinkage force, which is applied to the sensor. The thermal shrinkage rate of the sample is obtained by analyzing and calculating the sensor's electrical signal.

[0155] Thermal runaway testing:

[0156] Test steps: Charge the battery to 3.65V, then keep it at 3.65V for 30 minutes to reach a fully charged state, and then use an accelerating calorimeter (ARC) measurement to accurately track the temperature changes inside the fully charged battery in an adiabatic environment. Record the time from the start of heating to the occurrence of thermal runaway (the battery has a rapid temperature rise, and the temperature rise acceleration (dT / dt) is greater than or equal to 1℃ / s), as well as the peak temperature during the thermal runaway process.

[0157] Table 3 Parameters of the separators of Examples 1 to 20 and Comparative Examples 1 to 4 and parameters of the manufactured batteries

[0158]

[0159]

[0160] The shrinkage rates of Examples 1 to 10 at 120°C are all 0, and in the thermal runaway test, the time from the start of heating to the occurrence of thermal runaway is ≥12h, and the peak temperature in the thermal runaway test is ≤385°C; the shrinkage rates of Comparative Examples 1 to 2 at 120°C are 3% and 10%, and in the thermal runaway test, the time from the start of heating to the occurrence of thermal runaway is only 9.5h and 10.5h, and the peak temperature in the thermal runaway test is 389°C and 395°C. By comparing Examples 1 to 10 with Comparative Examples 1 to 2, it can be seen that the isolation films of Examples 1 to 10 have good thermal stability, and can delay the arrival of battery thermal runaway, thereby improving the safety of the obtained battery.

[0161] The shrinkage rates of Examples 11 to 20 at 120°C are all 0, and in the thermal runaway test, the time from the start of heating to the occurrence of thermal runaway is ≥13h, and the peak temperature in the thermal runaway test is ≤381°C; the shrinkage rates of Comparative Examples 3 to 4 at 120°C are 6% and 1%, and in the thermal runaway test, the time from the start of heating to the occurrence of thermal runaway is only 10h and 10.7h, and the peak temperature in the thermal runaway test is 390°C and 387°C. By comparing Examples 11 to 20 with Comparative Examples 3 to 4, it can be seen that the isolation films of Examples 11 to 20 have good thermal stability, and can delay the arrival of battery thermal runaway, thereby improving the safety of the manufactured battery.

[0162] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A separation film, characterized in that: The isolation membrane includes a base membrane, the material of the base membrane includes a first polymer and a second polymer, the first polymer and the second polymer form an interpenetrating polymer network structure, wherein the second polymer is a body structure, the second polymer has a branch chain, and the branch chain includes a phosphate group and / or a phosphite group.

2. The isolation film according to claim 1, characterized in that: The second polymer is obtained by cross-linking a flame retardant monomer and a cross-linking monomer, wherein the flame retardant monomer includes at least one phosphate group and / or phosphite group and at least one unsaturated double bond, and the cross-linking monomer includes at least two unsaturated double bonds.

3. The isolation film according to claim 2, characterized in that: The molar ratio of the cross-linking monomer to the flame retardant monomer is 0.5 to 3:1; Optionally, the molar ratio of the cross-linking monomer to the flame retardant monomer is 1 to 2:

1.

4. The isolation membrane according to claim 2 or 3, characterized in that: The flame retardant monomer includes or At least one of; 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 C 1～3 alkyl.

5. The isolation film according to any one of claims 2 to 4, characterized in that: The cross-linking monomer includes and / or Wherein, n is 1 to 10, and R7 is selected from H, 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.

6. The isolation film according to any one of claims 1 to 5, characterized in that: The first polymer has a linear structure, and the number average molecular weight of the first polymer is 100,000 to 1,000,000.

7. The isolation film according to claim 6, 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.

8. The isolation film according to any one of claims 1 to 5, characterized in that: The first polymer is a body-type structure, and the first polymer includes at least one of radiation cross-linked polyethylene, radiation cross-linked polypropylene, radiation cross-linked polyvinylidene fluoride, or radiation cross-linked polyvinylidene fluoride-hexafluoropropylene copolymer.

9. The isolation film according to any one of claims 1 to 8, characterized in that: 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 1:5-25.

10. The isolation film according to any one of claims 1 to 9, characterized in that: The isolation film further includes an inorganic coating layer disposed on at least one side of the base film.

11. The isolation film according to claim 10, characterized in that: The material of the inorganic coating includes ceramic material.

12. A method for preparing an isolation film, characterized in that: The preparation method comprises: mixing a flame retardant monomer, a cross-linking monomer and a first polymer, and performing photo-initiated polymerization to obtain a base film; Wherein, the base film is used as an isolation film, or the base film is used as an isolation film after post-treatment; The material of the base film includes a first polymer and a second polymer, and the first polymer and the second polymer form an interpenetrating polymer network structure, wherein the second polymer includes the flame retardant monomer and the cross-linking monomer obtained by cross-linking, and the second polymer is a three-dimensional structure. The second polymer has a side chain, and the side chain includes a phosphate group and / or a phosphite group.

13. A battery, characterized in that: The battery comprises the isolation membrane according to any one of claims 1 to 11 or the isolation membrane prepared by the preparation method according to claim 12.

14. An electrical device, characterized in that: The electrical device comprises the battery according to claim 13, and the battery is used for providing electrical energy.

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