Separator, and secondary battery and electric device comprising same

Abstract

The invention provides an isolating membrane, a secondary battery comprising the isolating membrane and an electric device. The isolating membrane comprises a first base membrane and a coating, the coating is located on the surface of the first base membrane, and the coating comprises a thermochromic material.

Description

Separator, secondary battery and electric device containing the same Technical Field

[0001] The present application relates to a separator, a secondary battery comprising the separator, and an electric device. Background Art

[0002] In recent years, secondary batteries have been widely used in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. With the application and promotion of secondary batteries, the requirements for their reliability have become increasingly stringent.

[0003] Summary of the Invention

[0004] The present application provides an isolation film, a secondary battery comprising the same, and an electrical device, aiming to improve the reliability of the secondary battery.

[0005] In a first aspect, the present application provides an isolation film, which includes a first base film and a coating layer. The coating layer is located on the surface of the first base film, and the coating layer includes a thermochromic material.

[0006] Without intending to be bound by any theory or explanation, the separator of the present application includes a coating comprising a thermochromic material whose color changes with changes in the internal temperature of the battery. In other words, as the internal temperature of the battery changes, the color of the separator also changes. When unexpected conditions such as short circuits and overcharges occur, heat is generated and the temperature rises within the battery, causing the color of the separator to change accordingly. By sensing the color change of the separator, thermal runaway conditions can be determined, allowing for timely battery treatment, reducing the risk of explosion and improving battery reliability.

[0007] In any embodiment of the present application, the thermochromic material includes one or more of azobenzene thermochromic materials, stearate thermochromic materials, higher fatty alcohol thermochromic materials, carboxyl-containing hydroxyl compound thermochromic materials, phenolic hydroxyl compound thermochromic materials, metal complex thermochromic materials, polyaromatic ring structure thermochromic materials containing CH=CH, and inorganic metal salt thermochromic materials.

[0008] Optionally, the azobenzene-based thermochromic material includes dimethylaminophenylazobenzene.

[0009] Optionally, the stearate-based thermochromic material includes barium stearate and / or zinc stearate.

[0010] Optionally, the higher fatty alcohol thermochromic material includes cetyl alcohol and / or stearyl alcohol.

[0011] Optionally, the carboxyl-containing hydroxy compound-based thermochromic material includes 6-hydroxyhexanoic acid and / or 2-hydroxyterephthalic acid.

[0012] Optionally, the phenolic hydroxy compound-based thermochromic material includes bisphenol A and / or benzyl parahydroxybenzoate.

[0013] Optionally, the metal complex thermochromic material includes one or more of triphenylmethane metal complex, organic amine metal complex, and ammonium metal complex.

[0014] Optionally, the thermochromic material of the polyaromatic ring structure compound containing CH═CH includes one or more dianthrone compounds.

[0015] Optionally, the inorganic metal salt thermochromic material includes one or more of sulfates, vanadates, and chromates containing a metal element M, and the metal element M includes one or more of Bi, Pb, Ni, Co, and Cd.

[0016] The above-mentioned types of thermochromic materials have a suitable color change temperature range. Therefore, by sensing the color change of the isolation membrane, the thermal runaway risk of the battery can be promptly and accurately prompted when the battery is on the verge of thermal runaway, so that the battery can be processed in time, the risk of battery explosion can be reduced, and the reliability of the battery can be improved.

[0017] In any embodiment of the present application, the thermochromic material includes a reversible thermochromic material.

[0018] Optionally, the reversible thermochromic material includes one or more of higher fatty alcohol thermochromic materials, carboxyl-containing hydroxyl compound thermochromic materials, phenolic hydroxyl compound thermochromic materials, metal complex thermochromic materials, and polyaromatic ring structure thermochromic materials containing CH=CH.

[0019] More optionally, the reversible thermochromic material includes one or more of hexadecanol, octadecanol, 6-hydroxyhexanoic acid, 2-hydroxyterephthalic acid, bisphenol A, benzyl parahydroxybenzoate, triphenylmethane metal complex, organic amine metal complex, ammonium metal complex, and dianthrone compounds.

[0020] Thermochromic materials, including the above-mentioned reversible thermochromic materials, can reduce the risk of permanent discoloration of the separator during normal use of the battery and allow the separator to be used for multiple tests, thereby improving the reliability of the battery.

[0021] In any embodiment of the present application, the thermochromic material includes an inorganic metal salt thermochromic material.

[0022] Optionally, the thermochromic material includes one or more of sulfates, vanadates, and chromates containing a metal element M, and the metal element M includes one or more of Bi, Pb, Ni, Co, and Cd.

[0023] When the coating includes an inorganic metal salt thermochromic material, the heat resistance of the isolation membrane can be improved, further improving the reliability of the battery.

[0024] In any embodiment of the present application, the content of the thermochromic material is 0.5%-7%, optionally 1%-5%, based on the total mass of the coating.

[0025] When the content of thermochromic material in the coating meets the given range, it can improve the accuracy of thermal runaway monitoring, improve the reliability of the battery, and enable the isolation membrane to maintain good air permeability, thereby improving the cycle performance of the battery.

[0026] In any embodiment of the present application, the coating further comprises a binder, and the binder comprises one or more of polyacrylate, polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-trichloroethylene copolymer, polyvinyl pyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, polyacrylonitrile, polyvinyl alcohol, polyethylene, polypropylene, starch, and cyanoethyl pullulan.

[0027] Optionally, the content of the binder is less than or equal to 25%, optionally 5%-25%, based on the total mass of the coating.

[0028] The binder can impart good heat resistance to the separator while ensuring the adhesion strength and uniformity between the first base film and the second base film, thereby improving the reliability of the secondary battery.

[0029] In any embodiment of the present application, the coating further comprises a filler.

[0030] Optionally, the filler includes at least one of inorganic particles, organic particles, and organic-metal framework materials.

[0031] More optionally, the inorganic particles include one or more of inorganic particles having a dielectric constant of 5 or greater, inorganic particles having ion conductivity but not storing ions, and inorganic particles capable of undergoing electrochemical reactions.

[0032] More optionally, the organic particles include one or more of polycarbonate, polythiophene, polypyridine, polystyrene, polyacrylic wax, polyethylene, polypropylene, cellulose, cellulose modifier, melamine resin, phenolic resin, polyester, silicone resin, polyimide, polyamideimide, polyaramid, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polyaryletherketone, and copolymers of butyl acrylate and ethyl methacrylate.

[0033] More optionally, the organic-metal framework material includes one or more of a nitrogen-containing heterocyclic ligand building structure, an organic carboxylic acid ligand building structure, and a nitrogen-oxygen mixed ligand building structure.

[0034] In any embodiment of the present application, the content of the filler is less than or equal to 90%, and can be optionally 20%-80%, based on the total mass of the coating.

[0035] The filler can further improve the heat resistance and physical properties (such as tensile strength, puncture strength, etc.) of the separator, thereby improving the reliability of the secondary battery.

[0036] In any embodiment of the present application, the coating has a thickness of 0.5 μm to 3 μm. Optionally, the coating has a thickness of 1 μm to 2 μm. This can further improve the accuracy of thermal runaway monitoring, thereby improving battery reliability. Furthermore, a thinner coating can also increase the energy density of the battery.

[0037] In any embodiment of the present application, the isolation film further includes a second base film, and the coating is located between the first and second base films. This, on the one hand, inhibits side reactions between the thermochromic material in the coating and the electrolyte, reducing the risk of thermochromic material failure and improving the accuracy of thermal runaway monitoring. On the other hand, the first and second base films also secure the coating, reducing the risk of the coating falling off due to immersion in the electrolyte.

[0038] In any embodiment of the present application, the thickness of the first base film is 2 μm-10 μm. Optionally, the thickness of the first base film is 3 μm-8 μm.

[0039] In any embodiment of the present application, the thickness of the second base film is 3 μm-9 μm. Optionally, the thickness of the second base film is 3 μm-7 μm.

[0040] When the thickness of the first base film and / or the second base film meets the above conditions, the separator can have a smaller overall thickness, thereby improving the energy density of the secondary battery.

[0041] In any embodiment of the present application, the material of the first base film includes at least one of polyolefins and their derivatives, halogenated polyolefins and their derivatives, polyethers and their derivatives, polyetheretherketones and their derivatives, polyesters and their derivatives, polyimides and their derivatives, polyvinyl alcohols and their derivatives, polytetrafluoroethylenes and their derivatives, polyvinyl fluoride and their derivatives, polyvinylidene fluoride and their derivatives, and polyethylene terephthalate and its derivatives.

[0042] In any embodiment of the present application, the material of the second base film includes at least one of polyolefins and their derivatives, halogenated polyolefins and their derivatives, polyethers and their derivatives, polyetheretherketones and their derivatives, polyesters and their derivatives, polyimides and their derivatives, polyvinyl alcohols and their derivatives, polytetrafluoroethylenes and their derivatives, polyvinyl fluoride and their derivatives, polyvinylidene fluoride and their derivatives, and polyethylene terephthalate and its derivatives.

[0043] In any embodiment of the present application, the transverse heat shrinkage rate of the isolation film at 250° C. for 1 hour is ≤3%, and can be optionally ≤1%.

[0044] In any embodiment of the present application, the longitudinal heat shrinkage rate of the isolation film at 250° C. for 1 hour is ≤3%, and can be optionally ≤1%.

[0045] When the transverse heat shrinkage rate and / or the longitudinal heat shrinkage rate of the separator meets the given range, the separator can have good heat resistance and physical properties, thereby improving the reliability of the secondary battery.

[0046] A second aspect of the present application provides a secondary battery comprising the separator according to the first aspect, thereby enabling the secondary battery to have high reliability.

[0047] A third aspect of the present application provides an electrical device comprising the secondary battery of the second aspect.

[0048] The electric device of the present application includes the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] To more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on the drawings without inventive effort.

[0050] FIG1 is a schematic diagram of an embodiment of a secondary battery provided by the present application.

[0051] FIG2 is an exploded schematic diagram of an embodiment of a secondary battery provided in the present application.

[0052] FIG3 is a schematic diagram of an embodiment of a battery module provided in the present application.

[0053] FIG4 is a schematic diagram of an embodiment of a battery pack provided in the present application.

[0054] FIG. 5 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG. 4 .

[0055] FIG6 is a schematic diagram of an embodiment of an electric device including the secondary battery provided in the present application as a power source.

[0056] In the accompanying drawings, which are not necessarily drawn to scale, the reference numerals are as follows: 1. battery pack; 2. upper housing; 3. lower housing; 4. battery module; 5. secondary battery; 51. housing; 52. electrode assembly; 53. cover plate. DETAILED DESCRIPTION

[0057] Below, with appropriate reference to the accompanying drawings, the embodiments of the separator, secondary battery and electrical device comprising the same are described in detail. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0058] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0059] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0060] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of this application.

[0061] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0062] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0063] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0064] Unless otherwise specified, in this application, the terms "first", "second", etc. are used to distinguish different objects rather than to describe a specific order or a primary-secondary relationship.

[0065] In this application, the terms "plurality", "multiple" and the like refer to two or more.

[0066] Unless otherwise specified, the terms used in this application have the common meanings that are commonly understood by those skilled in the art.

[0067] Unless otherwise stated, the numerical values ​​of the various parameters mentioned in this application can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the examples of this application. Unless otherwise stated, the test temperature of each parameter is 25°C.

[0068] Unless otherwise specified, all ratio parameters involved in this application are compared in the same unit. For example, the thickness ratio of A to B is 1.2:1, and the thickness units of A and B are the same.

[0069] Isolation film

[0070] Typically, a secondary battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. The separator is arranged between the positive electrode sheet and the negative electrode sheet, and mainly serves to prevent the positive and negative electrodes from short-circuiting.

[0071] The isolation film provided in the embodiment of the present application includes a first base film and a coating layer, wherein the coating layer is located on the surface of the first base film and includes a thermochromic material.

[0072] The isolation membrane currently used in commercial secondary batteries is usually a polyolefin porous membrane, which has poor heat resistance. When the temperature inside the battery is too high, a significant thermal shrinkage effect will occur, causing the positive and negative electrodes inside the battery to directly contact, resulting in an internal short circuit and increasing the safety risk of the secondary battery.

[0073] Without intending to be bound by any theory or explanation, the separator of the present application includes a coating comprising a thermochromic material whose color changes with changes in the internal temperature of the battery. In other words, as the internal temperature of the battery changes, the color of the separator also changes. When unexpected conditions such as short circuits and overcharges occur, heat is generated and the temperature rises within the battery, causing the color of the separator to change accordingly. By sensing the color change of the separator, thermal runaway conditions can be determined, allowing for timely battery treatment, reducing the risk of explosion and improving battery reliability.

[0074] In some embodiments, the thermochromic material may include one or more of azobenzene thermochromic materials, stearate thermochromic materials, higher fatty alcohol thermochromic materials, carboxyl-containing hydroxyl compound thermochromic materials, phenolic hydroxyl compound thermochromic materials, metal complex thermochromic materials, polyaromatic ring structure thermochromic materials containing CH=CH, and inorganic metal salt thermochromic materials.

[0075] Alternatively, in some embodiments, the azobenzene-based thermochromic material may include dimethylaminophenylazobenzene.

[0076] Alternatively, in some embodiments, the stearate-based thermochromic material may include barium stearate and / or zinc stearate.

[0077] Alternatively, in some embodiments, the higher fatty alcohol-based thermochromic material may include cetyl alcohol and / or stearyl alcohol.

[0078] Alternatively, in some embodiments, the carboxyl-containing hydroxy compound-based thermochromic material may include 6-hydroxyhexanoic acid and / or 2-hydroxyterephthalic acid.

[0079] Alternatively, in some embodiments, the phenolic hydroxy compound-based thermochromic material may include bisphenol A and / or benzyl parahydroxybenzoate.

[0080] Alternatively, in some embodiments, the metal complex thermochromic material may include one or more of a triphenylmethane metal complex, an organic amine metal complex, and an ammonium metal complex. More preferably, in some embodiments, the metal in the metal complex thermochromic material may include at least one of Ni, Co, and Al.

[0081] Optionally, in some embodiments, the thermochromic material containing a polyaromatic ring structure of CH═CH may include one or more dianthrone compounds.

[0082] Alternatively, in some embodiments, the inorganic metal salt thermochromic material may include one or more of sulfates, vanadates, and chromates containing a metal element M, wherein the metal element M includes one or more of Bi, Pb, Ni, Co, and Cd. For example, the inorganic metal salt thermochromic material may include one or more of BiVO4, BiSO4, BiCrO4, PbVO4, PbSO4, PbCrO4, NiVO4, NiSO4, NiCrO4, CoVO4, CoSO4, CoCrO4, CdVO4, CdSO4, and CdCrO4.

[0083] Without intending to be bound by any theory or explanation, these types of thermochromic materials have a suitable color change temperature range, allowing them to undergo a corresponding color change when a battery is about to experience thermal runaway. Therefore, by sensing the color change of the separator, a timely and accurate warning of the battery's impending thermal runaway risk can be provided, allowing for timely battery treatment, reducing the risk of explosion and improving battery reliability.

[0084] In some embodiments, the thermochromic material may include a reversible thermochromic material.

[0085] In some embodiments, the reversible thermochromic material may include one or more of higher fatty alcohol thermochromic materials, carboxyl-containing hydroxyl compound thermochromic materials, phenolic hydroxyl compound thermochromic materials, metal complex thermochromic materials, and polyaromatic ring structure thermochromic materials containing CH=CH.

[0086] Optionally, in some embodiments, the reversible thermochromic material may include one or more of hexadecanol, octadecanol, 6-hydroxyhexanoic acid, 2-hydroxyterephthalic acid, bisphenol A, benzyl parahydroxybenzoate, triphenylmethane metal complex, organic amine metal complex, ammonium metal complex, and dianthrone compounds.

[0087] Reversible thermochromic materials change color when the temperature rises within a certain range and return to their original color when the temperature is lowered. During normal battery use, the internal temperature fluctuates, for example, when the external temperature changes or when the battery is charging. The use of reversible thermochromic materials can reduce the risk of permanent discoloration of the separator during normal battery use, improve the accuracy of thermal runaway monitoring, and enhance battery reliability.

[0088] Furthermore, by sensing the color change of the separator when a battery is about to experience thermal runaway, timely treatment can be performed to reduce the battery temperature. If the separator's color change is irreversible, it would be unusable for subsequent testing during battery use. By employing a reversible thermochromic material, the present embodiment allows the separator to be used for multiple tests, improving battery reliability.

[0089] In some embodiments, the thermochromic material may include an inorganic metal salt-based thermochromic material.

[0090] Alternatively, in some embodiments, the thermochromic material may include one or more of sulfates, vanadates, and chromates containing a metal element M, wherein the metal element M includes one or more of Bi, Pb, Ni, Co, and Cd. For example, the thermochromic material may include one or more of BiVO4, BiSO4, BiCrO4, PbVO4, PbSO4, PbCrO4, NiVO4, NiSO4, NiCrO4, CoVO4, CoSO4, CoCrO4, CdVO4, CdSO4, and CdCrO4.

[0091] Inorganic metal salt-based thermochromic materials have excellent heat resistance. When included in a coating, they can improve the heat resistance of the separator and reduce its shrinkage when heated, thereby reducing the probability of short circuits between the positive and negative electrodes and further improving battery reliability.

[0092] In some embodiments, the content of the thermochromic material can be 0.5%-7% based on the total mass of the coating, for example, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, or a range consisting of any two of the above values.

[0093] Optionally, in some embodiments, based on the total mass of the coating, the content of the thermochromic material can also be 1%-5%, for example, it can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range consisting of any two of the above values.

[0094] Without intending to be limited by any theory or explanation, when the content of the thermochromic material in the coating satisfies the given range, on the one hand, when there is a risk of thermal runaway in the battery, a more obvious color change can occur in a timely manner, thereby improving the accuracy of thermal runaway monitoring and improving the reliability of the battery; on the other hand, it can also enable the isolation membrane to maintain good air permeability, thereby improving the cycle performance of the battery.

[0095] In some embodiments, the coating layer may further include a filler. The filler can further improve the heat resistance and physical properties (such as tensile strength, puncture strength, etc.) of the separator, thereby improving the reliability of the secondary battery.

[0096] In some embodiments, the filler may include at least one of inorganic particles, organic particles, and organic-metal framework materials.

[0097] Alternatively, the inorganic particles may include one or more of inorganic particles having a dielectric constant of 5 or greater, inorganic particles having ion conductivity but not storing ions, and inorganic particles capable of undergoing electrochemical reactions.

[0098] Alternatively, the organic particles may include one or more of polycarbonate, polythiophene, polypyridine, polystyrene, polyacrylic wax, polyethylene, polypropylene, cellulose, a cellulose modifier (e.g., carboxymethyl cellulose), a melamine resin, a phenolic resin, a polyester (e.g., polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate), a silicone resin, a polyimide, a polyamideimide, a polyaramid, polyphenylene sulfide, a polysulfone, a polyethersulfone, a polyetheretherketone, a polyaryletherketone, a copolymer of butyl acrylate and ethyl methacrylate (e.g., a cross-linked polymer of butyl acrylate and ethyl methacrylate).

[0099] Optionally, the organic-metal framework material may include one or more of a nitrogen-containing heterocyclic ligand building structure, an organic carboxylic acid ligand building structure, and a nitrogen-oxygen mixed ligand building structure.

[0100] In some embodiments, the thickness of the coating can be 0.5μm-3μm, for example, 0.5μm, 0.8μm, 1μm, 1.2μm, 1.5μm, 1.8μm, 2μm, 2.2μm, 2.5μm, 2.8μm, 3μm, or a range consisting of any two of the above values.

[0101] Optionally, in some embodiments, the thickness of the coating can also be 1 μm-2 μm, for example, it can be 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, or a range consisting of any two of the above values.

[0102] When the coating is thin, it absorbs less heat and heats up quickly. When the internal temperature of the battery rises, the temperature of the coating can also rise rapidly. Therefore, the thermochromic material in the coating can change color promptly when the battery is at risk of thermal runaway. This can further improve the accuracy of thermal runaway monitoring, thereby enhancing battery reliability. Furthermore, a thin coating can also increase the energy density of the battery.

[0103] The thickness of the coating has a meaning well known in the art and can be tested using equipment and methods known in the art. In some embodiments, a scanning electron microscope (e.g., a ZEISS Sigma 300) can be used to obtain a cross-sectional scanning electron microscope (SEM) image of the isolation membrane, with reference to JY / T 0584-2020. As an example, the following method can be used to test: randomly select multiple areas on the cross section of the isolation membrane, measure the coating thickness at least five times at a certain magnification, and calculate the measured values ​​of different areas, and take the average value as the coating thickness.

[0104] In some embodiments, the isolation film may further include a second base film, and the coating layer is located between the first base film and the second base film.

[0105] The coating is located between the first and second base films, reducing the risk of the coating shedding during processing or use. Furthermore, the first and second base films protect the coating from both sides, effectively isolating the coating from the electrolyte, reducing the area of ​​direct contact between the coating and the electrolyte, and mitigating the swelling of the gel caused by immersion in the electrolyte. This, on the one hand, inhibits side reactions between the thermochromic material in the coating and the electrolyte, reducing the risk of thermochromic material failure and improving the accuracy of thermal runaway monitoring. On the other hand, the first and second base films also stabilize the coating, reducing the risk of the coating shedding due to immersion in the electrolyte.

[0106] In some embodiments, the bonding strength between the coating and the first base film can be greater than or equal to 3 N / m, for example, it can be 3 N / m, 5 N / m, 7 N / m, 9 N / m, 12 N / m, 15 N / m, 20 N / m, 25 N / m, or a range consisting of any two of the above values.

[0107] Optionally, in some embodiments, the bonding strength between the coating and the first base film can also be 5N / m-20N / m, for example, it can be 5N / m-20N / m, 5N / m-18N / m, 5N / m-15N / m, 5N / m-10N / m, 8N / m-20N / m, 8N / m-16N / m, 8N / m-12N / m, 10N / m-20N / m, 10N / m-15N / m, 15N / m-20N / m.

[0108] The bonding strength between the coating and the first base film satisfies the given range, which can improve the structural stability of the isolation membrane and help reduce the risk of the coating falling off due to immersion in the electrolyte, thereby improving the cycle performance of the battery.

[0109] In some embodiments, the bonding strength between the coating and the second base film can be greater than or equal to 3 N / m, for example, it can be 3 N / m, 5 N / m, 7 N / m, 9 N / m, 12 N / m, 15 N / m, 20 N / m, 25 N / m, or a range consisting of any two of the above values.

[0110] Optionally, in some embodiments, the bonding strength between the coating and the second base film can also be 5N / m-20N / m, for example, it can be 5N / m-20N / m, 5N / m-18N / m, 5N / m-15N / m, 5N / m-10N / m, 8N / m-20N / m, 8N / m-16N / m, 8N / m-12N / m, 10N / m-20N / m, 10N / m-15N / m, 15N / m-20N / m.

[0111] The bonding strength between the coating and the second base film satisfies the given range, which can improve the structural stability of the isolation membrane and help reduce the risk of the coating falling off due to immersion in the electrolyte, thereby improving the cycle performance of the battery.

[0112] The bond strength between the coating and the base film has a well-known meaning in the art and can be measured using equipment and methods known in the art, for example, according to GB / T 2790-1995.

[0113] In some embodiments, the thickness of the first base film may be 2 μm-10 μm, for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or a range consisting of any two of the above values.

[0114] Optionally, in some embodiments, the thickness of the first base film can also be 3μm-8μm, for example, it can be 3μm-8μm, 3μm-7μm, 3μm-6μm, 3μm-5μm, 3μm-4μm, 4μm-8μm, 4μm-7μm, 4μm-6μm, 4μm-5μm, 5μm-8μm, 5μm-7μm, 5μm-6μm.

[0115] In some embodiments, the thickness of the second base film may be 3 μm-9 μm, for example, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or a range consisting of any two of the above values.

[0116] Optionally, in some embodiments, the thickness of the second base film can also be 3μm-7μm, for example, it can be 3μm-7μm, 3μm-6μm, 3μm-5μm, 3μm-4μm, 4μm-7μm, 4μm-6μm, 4μm-5μm, 5μm-7μm, 5μm-6μm, 6μm-7μm.

[0117] Without intending to be bound by any theory or explanation, when the thickness of the first base film and / or the second base film meets the above conditions, the separator can have a smaller overall thickness, thereby improving the energy density of the secondary battery.

[0118] The thickness of the base film has a well-known meaning in the art and can be measured using equipment and methods known in the art. For example, six sets of parallel samples can be taken and the thickness of each set of samples can be measured at different locations using a micrometer thickness gauge. At least 20 locations are measured for each set of samples, and the average thickness of the six sets of samples is taken as the sample thickness.

[0119] In some embodiments, the material of the first base film may include at least one of polyolefins and their derivatives, halogenated polyolefins and their derivatives, polyethers and their derivatives, polyetheretherketones and their derivatives, polyesters and their derivatives, polyimides and their derivatives, polyvinyl alcohols and their derivatives, polytetrafluoroethylenes and their derivatives, polyvinyl fluoride and its derivatives, polyvinylidene fluoride and its derivatives, and polyethylene terephthalate and its derivatives.

[0120] In some embodiments, the material of the second base film may include at least one of polyolefins and their derivatives, halogenated polyolefins and their derivatives, polyethers and their derivatives, polyetheretherketones and their derivatives, polyesters and their derivatives, polyimides and their derivatives, polyvinyl alcohols and their derivatives, polytetrafluoroethylenes and their derivatives, polyvinyl fluoride and its derivatives, polyvinylidene fluoride and its derivatives, and polyethylene terephthalate and its derivatives.

[0121] Derivatives usually refer to products derived from polymers in which hydrogen atoms or atomic groups are replaced by other atoms or atomic groups.

[0122] In some embodiments, the coating layer may further include a binder. The binder can ensure the adhesion strength and uniformity between the first base film and the second base film while imparting good heat resistance to the separator, thereby improving the reliability of the secondary battery.

[0123] In some embodiments, the binder may include one or more of polyacrylate, polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-trichloroethylene copolymer, polyvinyl pyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, polyacrylonitrile, polyvinyl alcohol, polyethylene, polypropylene, starch, and cyanoethyl pullulan.

[0124] In some embodiments, based on the total mass of the coating, the content of the filler may be less than or equal to 90%, and optionally 20%-80%.

[0125] In some embodiments, based on the total mass of the coating, the content of the binder may be less than or equal to 25%, and may be optionally 5%-25%.

[0126] In some embodiments, the coating may further include a dispersant, such as carboxymethyl cellulose, to adjust the viscosity of the coating slurry and improve the quality and uniformity of the film layer.

[0127] In some embodiments, the transverse heat shrinkage rate of the isolation film at 250° C. for 1 hour may be less than or equal to 3%, and optionally less than or equal to 1%.

[0128] In some embodiments, the longitudinal heat shrinkage rate of the isolation film at 250° C. for 1 hour may be less than or equal to 3%, and optionally less than or equal to 1%.

[0129] When the transverse heat shrinkage rate and / or the longitudinal heat shrinkage rate of the separator meets the given range, the separator can have good heat resistance and physical properties, thereby improving the reliability of the secondary battery.

[0130] The transverse and longitudinal thermal shrinkage rates of the separator may have meanings well known in the art and may be measured using equipment and methods known in the art. For example, both may be tested in accordance with GB / T 36363-2018.

[0131] In some embodiments, the isolation film of the present application can be prepared by the following steps: providing a first base film; providing a coating slurry, the coating slurry including a thermochromic material; coating the coating slurry on the surface of the first base film and drying it to obtain the isolation film.

[0132] Optionally, in some embodiments, the isolation film of the present application can also be prepared by the following steps: providing a first base film and a second base film; providing a coating slurry, the coating slurry including a thermochromic material; applying the coating slurry on one of the first base film and the second base film and drying it to form a coating, and then compounding it with the other of the first base film and the second base film so that the coating is located between the first base film and the second base film to obtain an isolation film.

[0133] In some embodiments, the coating slurry may further include a binder. Optionally, the coating slurry may further include a filler.

[0134] In some embodiments, the coating slurry may be applied by transfer coating, spin coating, dip coating, etc., which is not limited in the embodiments of the present application.

[0135] Unless otherwise specified, all raw materials used in the method for preparing the isolation film (eg, the first base film, the second base film, the thermochromic material, the adhesive, the filler, etc.) can be purchased commercially.

[0136] secondary batteries

[0137] An embodiment of the present application also provides a secondary battery.

[0138] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged after discharge to reactivate the active materials and continue to be used. Typically, a secondary battery consists of an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. The separator is placed between the positive and negative electrodes to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through.

[0139] The present application has no particular limitation on the type of secondary battery. For example, the secondary battery may be a lithium ion battery, a sodium ion battery, a lithium metal battery, a sodium metal battery, etc. In particular, the secondary battery may be a lithium ion battery.

[0140] The secondary battery provided in the embodiment of the present application includes the isolation membrane as described above in the present application. By sensing the color change of the isolation membrane, the thermal runaway state of the battery can be judged, so that the battery can be processed in time, the risk of battery explosion can be reduced, and the reliability of the battery can be improved.

[0141] [Positive electrode]

[0142] In some embodiments, the positive electrode sheet may include a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector and comprising a positive electrode active material. For example, the positive electrode current collector may have two opposing surfaces in its thickness direction, and the positive electrode film layer may be disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0143] When the secondary battery is a lithium-ion battery, the positive electrode active material may include, but is not limited to, at least one of a lithium transition metal oxide, a lithium-containing phosphate, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Examples of lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and their respective modified compounds.

[0144] In some embodiments, in order to further improve the energy density of the secondary battery, the positive electrode active material for the lithium ion battery may include a general formula of Li a Ni b Co c M d O e A f At least one of lithium transition metal oxides and modified compounds thereof. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M is selected from at least one of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A is selected from at least one of N, F, S and Cl.

[0145] As an example, the positive active material for lithium ion batteries may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333),LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523),LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622),LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 Co 0.15 Al 0.05 At least one of O2, LiFePO4, and LiMnPO4.

[0146] When the secondary battery is a sodium ion battery, the positive electrode active material may include but is not limited to at least one of sodium-containing transition metal oxides, polyanion materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue materials.

[0147] As an example, the positive active material for sodium ion batteries may include NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, NaNi 1 / 2 Ti 1 / 2 O2、NaNi 1 / 2 Mn 1 / 2 O2、Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2、NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, NaFePO4, NaMnPO4, NaCoPO4, Prussian blue materials, general formula X p M' q (PO4) r O x Y 3-x At least one of the materials. p M' q (PO4) r O x Y 3-x , 0<p≤4, 0<q≤2, 1≤r≤3, 0≤x≤2, X is selected from H + 、Li + 、Na + , K + and NH4 + At least one of , M' is a transition metal cation, optionally at least one of V, Ti, Mn, Fe, Co, Ni, Cu and Zn, and Y is a halogen anion, optionally at least one of F, Cl and Br.

[0148] The modified compounds of the above-mentioned positive electrode active materials may be used to perform doping modification and / or surface coating modification on the positive electrode active materials.

[0149] In some embodiments, the positive electrode film layer may further include a positive electrode conductive agent. The present application does not particularly limit the type of the positive electrode conductive agent. For example, the positive electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0150] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. This application does not particularly limit the type of positive electrode binder. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin.

[0151] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include at least one of aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0152] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying it, and cold pressing it. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP).

[0153] [Negative electrode]

[0154] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and comprising a negative electrode active material. For example, the negative electrode current collector may have two opposing surfaces in its thickness direction, and the negative electrode film layer may be disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0155] The negative electrode active material may be any negative electrode active material known in the art for use in secondary batteries. For example, the negative electrode active material may include, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may include at least one of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include at least one of elemental tin, tin oxide, and tin alloys.

[0156] In some embodiments, the negative electrode film layer may further optionally include a negative electrode conductive agent. The present application does not particularly limit the type of the negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0157] In some embodiments, the negative electrode film layer may further optionally include a negative electrode binder. The present application does not particularly limit the type of the negative electrode binder. As examples, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0158] In some embodiments, the negative electrode film layer may further include other additives, such as thickeners, sodium carboxymethyl cellulose (CMC), PTC thermistor materials, and the like.

[0159] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include at least one of copper, a copper alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0160] The negative electrode film layer is typically formed by coating the negative electrode slurry onto the negative electrode current collector, drying it, and cold pressing it. The negative electrode slurry is typically formed by dispersing the negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0161] The negative electrode plate does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode plate also includes a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In some embodiments, the negative electrode plate of the present application also includes a protective layer covering the surface of the negative electrode film layer.

[0162] [Electrolyte]

[0163] During the charge and discharge process of a secondary battery, active ions are embedded and released back and forth between the positive and negative electrodes, and the electrolyte conducts the active ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte, and the electrolyte can be selected according to actual needs.

[0164] The electrolyte solution includes an electrolyte salt and a solvent. The types of the electrolyte salt and the solvent are not particularly limited and can be selected according to actual needs.

[0165] When the secondary battery is a lithium ion battery, as an example, the electrolyte salt may include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0166] When the secondary battery is a sodium ion battery, as an example, the electrolyte salt may include but is not limited to at least one of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium bisfluorosulfonyl imide (NaFSI), sodium bistrifluoromethanesulfonyl imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalatoborate (NaDFOB), sodium dioxalatoborate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorobisoxalatophosphate (NaDFOP) and sodium tetrafluorooxalatophosphate (NaTFOP).

[0167] As an example, the solvent may include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE).

[0168] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0169] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly by a winding process and / or a lamination process. It is understood that in some embodiments, the separator of the present application includes both a first base film and a second base film, and the first base film or the second base film can optionally face the positive electrode sheet or the negative electrode sheet. For example, the first base film faces the positive electrode sheet, and the second base film faces the negative electrode sheet; or the first base film faces the negative electrode sheet, and the second base film faces the positive electrode sheet.

[0170] In some embodiments, the secondary battery may include an outer packaging. The outer packaging may be used to enclose the electrode assembly and electrolyte. In some embodiments, the outer packaging may also contain a detection device for sensing color changes of the separator. For example, the outer packaging may contain a color sensor that can be aligned with the separator to detect the separator's color.

[0171] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0172] The present application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square, or any other shape. FIG1 shows a secondary battery 5 with a square structure as an example.

[0173] In some embodiments, as shown in FIG2 , the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation film can be formed into an electrode assembly 52 through a winding process and / or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, which can be adjusted according to demand.

[0174] Methods for preparing secondary batteries are well known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte can be assembled to form a secondary battery. For example, the positive electrode sheet, separator, and negative electrode sheet can be wound and / or laminated to form an electrode assembly. The electrode assembly is then placed in an outer package, dried, and then injected with electrolyte. The secondary battery is then vacuum packaged, allowed to stand, formed, and shaped.

[0175] In some embodiments, the secondary batteries according to the present application can be assembled into a battery module. The battery module can contain multiple secondary batteries, and the specific number can be adjusted according to the application and capacity of the battery module.

[0176] Figure 3 is a schematic diagram of an exemplary battery module 4. As shown in Figure 3 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured using fasteners.

[0177] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0178] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0179] Figures 4 and 5 are schematic diagrams of an exemplary battery pack 1. As shown in Figures 4 and 5, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 covers the lower case 3 and forms an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0180] Electrical devices

[0181] The embodiments of the present application also provide an electrical device, which includes at least one of the secondary batteries, battery modules, or battery packs provided in the embodiments of the present application. The secondary batteries, battery modules, or battery packs can be used as power sources for the electrical device, or as energy storage units for the electrical device. The electrical device can be, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0182] The electrical device can select a secondary battery, a battery module or a battery pack according to its usage requirements.

[0183] Figure 6 is a schematic diagram of an exemplary electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of this device, a battery pack or battery module may be used.

[0184] As another example, the electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a secondary battery as a power source.

[0185] Example

[0186] The following examples describe the present disclosure in more detail. These examples are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing. The instruments used in the examples are commercially available.

[0187] Example 1

[0188] Preparation of isolation membrane

[0189] A first base film is provided, wherein the material includes polypropylene (PP) and the thickness is 9 μm.

[0190] A second base film is provided, wherein the material includes polyethylene (PE) and the thickness is 7 μm.

[0191] Preparation of coating slurry: The thermochromic material dimethylaminophenylazobenzene, filler boehmite, binder polyacrylate, and dispersant carboxymethyl cellulose are mixed uniformly in an appropriate amount of solvent deionized water at a mass ratio of 3%:77%:10%:10% to prepare a coating slurry.

[0192] The coating slurry is applied to a PE base film to form a coating, and the PP base film and the PE base film are compounded so that the coating is between the PP base film and the PE base film, and then dried to prepare an isolation film with a coating thickness of 2 μm.

[0193] Preparation of positive electrode

[0194] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive agent carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are mixed evenly in an appropriate amount of solvent N-methylpyrrolidone (NMP) in a mass ratio of 96.2%:2.7%:1.1% to obtain a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector aluminum foil, and the positive electrode sheet is obtained through processes such as drying, cold pressing, slitting, and cutting.

[0195] Preparation of negative electrode sheet

[0196] The negative electrode active material artificial graphite, the conductive agent carbon black (Super P), the binder styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) are mixed uniformly in a proper amount of solvent deionized water in a mass ratio of 96.4%:0.7%:1.8%:1.1% to obtain a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector copper foil, and the negative electrode sheet is obtained through the processes of drying, cold pressing, slitting and cutting.

[0197] Preparation of electrolyte

[0198] Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 30:30:40 to obtain an organic solvent, and fully dried LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0199] Preparation of secondary batteries

[0200] The positive electrode sheet, the separator prepared above, and the negative electrode sheet are stacked and wound in sequence to obtain an electrode assembly, wherein the first base film in the separator faces the negative electrode; the electrode assembly is placed in an outer package, and after drying, the electrolyte is injected, and after vacuum packaging, standing, formation, shaping and other processes, a secondary battery is obtained.

[0201] The secondary batteries of Examples 2-20 and Comparative Examples 1-2 are similar to Example 1, except that different base films are used or coating parameters are adjusted, as detailed in Table 1. The isolation membranes of Example 20 and Comparative Example 2 only include a first base film and a coating composited on the surface of the first base film.

[0202] Test section

[0203] The following tests were performed on the separators and secondary batteries of Examples 1-20 and Comparative Examples 1-2. The test results are shown in Table 2.

[0204] (1) Thermal shrinkage test of isolation film

[0205] Sample preparation: The isolation film prepared above was punched out into samples with a width of 50 mm and a length of 100 mm using a punching machine. Five parallel samples were placed on a glass plate and fixed.

[0206] Sample test: The temperature of the forced air oven is set to 250°C. After the temperature reaches the set temperature and stabilizes for 30 minutes, the glass plate is placed in the forced air oven and the time is set for 1 hour. After the time is up, the width of the isolation film is measured. The width value is marked as a in mm.

[0207] Calculation of thermal shrinkage: Transverse direction (TD) thermal shrinkage = [(50-a) / 50] × 100%, and the average value of 5 parallel samples is taken as the test result.

[0208] (2) Color change temperature test of isolation film

[0209] Sample Preparation: Use a punch to punch the separator film prepared above into samples with a width of 50 mm and a length of 100 mm. Prepare four samples simultaneously, one of which serves as a standard sample and is stored at room temperature.

[0210] Sample testing: Place the sample in a controlled constant temperature chamber and gradually heat it. Compare it to a standard sample. When the sample changes color, record the color change temperature and remove it. Repeat the measurement three times and calculate the average temperature, which will be used as the color change temperature of the barrier film.

[0211] (3) Battery cycle performance test

[0212] At 25°C, the batteries of the above examples and comparative examples were charged at a constant current of 1C to a voltage of 4.2V. They were then charged at a constant voltage of 4.2V to a current of ≤0.05C. The batteries were then discharged at a constant current of 1C to a voltage of 2.8V. This constituted one charge-discharge cycle, and the discharge capacity at this point was recorded as the discharge capacity of the battery's first cycle. This charge and discharge cycle was repeated, and the number of cycles corresponding to the capacity reduction to 85% was recorded.

[0213] Table 1

[0214] Table 2

[0215] From the test results in Table 1 and Table 2, it can be seen that the isolation films of Examples 1-20 can change color between 120°C and 138°C. Therefore, the thermal runaway state of the battery can be judged by sensing the color change of the isolation film, so that the battery can be processed in time to improve the reliability of the battery.

[0216] The test results of Examples 1-16 show that, compared to other thermochromic materials, inorganic metal salt thermochromic materials, such as BiVO4, can improve the heat resistance of the isolation membrane. The test results of Examples 17-19 show that, under the same conditions, the heat resistance of the isolation membrane improves with increasing coating thickness. The results of Examples 8 and 20 show that, compared to isolation membranes with a base film laminated on one side of the coating, isolation membranes with a base film laminated on both sides of the coating exhibit higher heat resistance.

[0217] In contrast, the coatings of Comparative Examples 1 and 2 do not contain thermochromic materials, and the thermal runaway state of the battery cannot be determined by sensing the color change of the isolation membrane. Therefore, batteries with thermal runaway risks cannot be handled in a timely manner.

[0218] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present application, embodiments having substantially the same structure as the technical idea and exerting the same effects are all included in the technical scope of the present application. In addition, within the scope of the subject matter of the present application, various modifications that can be conceived by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A separation film, comprising: First basement membrane; as well as The coating is located on the surface of the first base film, and the coating includes a thermochromic material.

2. The isolation film according to claim 1, wherein: The thermochromic material includes one or more of azobenzene thermochromic materials, stearate thermochromic materials, higher fatty alcohol thermochromic materials, carboxyl-containing hydroxyl compound thermochromic materials, phenolic hydroxyl compound thermochromic materials, metal complex thermochromic materials, polyaromatic ring structure thermochromic materials containing CH=CH, and inorganic metal salt thermochromic materials; Optionally, the azobenzene thermochromic material includes dimethylaminophenylazobenzene; Optionally, the stearate-based thermochromic material includes barium stearate and / or zinc stearate; Optionally, the higher fatty alcohol thermochromic material includes hexadecanol and / or stearyl alcohol; Optionally, the carboxyl-containing hydroxy compound-based thermochromic material includes 6-hydroxycaproic acid and / or 2-hydroxyterephthalic acid; Optionally, the phenolic hydroxy compound thermochromic material includes bisphenol A and / or benzyl p-hydroxybenzoate; Optionally, the metal complex thermochromic material includes one or more of triphenylmethane metal complex, organic amine metal complex, and ammonium metal complex; Optionally, the thermochromic material of the polyaromatic ring structure compound containing CH=CH includes one or more of dianthrone compounds; Optionally, the inorganic metal salt thermochromic material includes one or more of sulfates, vanadates, and chromates containing a metal element M, and the metal element M includes one or more of Bi, Pb, Ni, Co, and Cd.

3. The isolation film according to claim 1 or 2, wherein: The thermochromic material includes a reversible thermochromic material; Optionally, the reversible thermochromic material includes one or more of a higher fatty alcohol thermochromic material, a carboxyl-containing hydroxy compound thermochromic material, a phenolic hydroxy compound thermochromic material, a metal complex thermochromic material, and a polyaromatic ring structure thermochromic material containing CH=CH; More optionally, the reversible thermochromic material includes one or more of hexadecanol, octadecyl alcohol, 6-hydroxyhexanoic acid, 2-hydroxyterephthalic acid, bisphenol A, benzyl p-hydroxybenzoate, triphenylmethane metal complex, organic amine metal complex, ammonium metal complex, and dianthrone compounds.

4. The isolation film according to claim 1 or 2, wherein: The thermochromic material includes an inorganic metal salt thermochromic material; Optionally, the thermochromic material includes one or more of sulfates, vanadates, and chromates containing a metal element M, and the metal element M includes one or more of Bi, Pb, Ni, Co, and Cd.

5. The isolation film according to any one of claims 1 to 4, wherein: The content of the thermochromic material is 0.5%-7%, optionally 1%-5%, based on the total mass of the coating.

6. The isolation film according to any one of claims 1 to 5, wherein: The coating further comprises a binder, and the binder comprises one or more of polyacrylate, polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-trichloroethylene copolymer, polyvinyl pyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, polyacrylonitrile, polyvinyl alcohol, polyethylene, polypropylene, starch, and cyanoethyl pullulan; Optionally, the content of the binder is less than or equal to 25%, and optionally 5%-25%, based on the total mass of the coating.

7. The isolation film according to any one of claims 1 to 6, wherein: The coating further comprises a filler; Optionally, the filler includes at least one of inorganic particles, organic particles, and organic-metal framework materials; More optionally, the inorganic particles include one or more of inorganic particles having a dielectric constant of 5 or more, inorganic particles having ion conductivity but not storing ions, and inorganic particles capable of electrochemical reaction; More optionally, the organic particles include one or more of polycarbonate, polythiophene, polypyridine, polystyrene, polyacrylic wax, polyethylene, polypropylene, cellulose, cellulose modifier, melamine resin, phenolic resin, polyester, silicone resin, polyimide, polyamideimide, polyaramid, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polyaryletherketone, copolymer of butyl acrylate and ethyl methacrylate; More optionally, the organic-metal framework material includes one or more of a nitrogen-containing heterocyclic ligand building structure, an organic carboxylic acid ligand building structure, and a nitrogen-oxygen mixed ligand building structure.

8. The isolation film according to claim 7, wherein: The content of the filler is less than or equal to 90%, and can be optionally 20%-80%, based on the total mass of the coating.

9. The isolation film according to any one of claims 1 to 8, wherein: The thickness of the coating is 0.5 μm-3 μm, and can be 1 μm-2 μm.

10. The isolation film according to any one of claims 1 to 9, wherein: The isolation film further includes a second base film, and the coating layer is located between the first base film and the second base film.

11. The isolation film according to any one of claims 1 to 10, wherein: The thickness of the first base film is 2 μm-10 μm, and can be 3 μm-8 μm; and / or, The thickness of the second base film is 3 μm-9 μm, and can be optionally 3 μm-7 μm.

12. The isolation film according to any one of claims 1 to 11, wherein: The material of the first base film includes polyolefin and its derivatives, halogenated polyolefin and its derivatives, polyether and its derivatives, polyetheretherketone and its derivatives, polyester and its derivatives, polyimide and its derivatives, polyvinyl alcohol and its derivatives At least one of biological materials, polytetrafluoroethylene and its derivatives, polyvinyl fluoride and its derivatives, polyvinylidene fluoride and its derivatives, polyethylene terephthalate and its derivatives; and / or, The material of the second base film includes at least one of polyolefins and their derivatives, halogenated polyolefins and their derivatives, polyethers and their derivatives, polyetheretherketones and their derivatives, polyesters and their derivatives, polyimides and their derivatives, polyvinyl alcohols and their derivatives, polytetrafluoroethylene and their derivatives, polyvinyl fluoride and their derivatives, polyvinylidene fluoride and their derivatives, and polyethylene terephthalate and its derivatives.

13. The isolation film according to any one of claims 1 to 12, wherein: The transverse heat shrinkage rate of the isolation film at 250° C. for 1 hour is ≤3%, and can be optionally ≤1%; and / or, The longitudinal heat shrinkage rate of the isolation film at 250° C. for 1 hour is ≤3%, and can be optionally ≤1%.

14. A secondary battery comprising the separator according to any one of claims 1 to 13.

15. An electric device comprising the secondary battery according to claim 14.

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