Battery monomer and preparation method thereof, secondary battery and power utilization device

Abstract

The embodiment of the invention provides a battery monomer, a preparation method of the battery monomer, a secondary battery and a power utilization device. The battery monomer comprises a shell and an electrode assembly arranged in the shell, the shell comprises a body and an insulating coating arranged on the outer surface of the body; the insulating coating comprises an electrophoretic coating arranged on the outer surface of the body; and the powder coating is arranged on the electrophoresis coating. The insulating coating provided by the invention has good high-voltage-resistant insulating performance, and can meet the high-voltage-resistant insulating requirement of the high-capacity battery monomer.

Description

Technical Field

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

[0002] In recent years, secondary batteries, mainly lithium-ion batteries, have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace. Their safety has become a key focus of attention and improvement.

[0003] The casing of a secondary battery is typically made of aluminum, and it usually has a blue film on the outside to isolate the battery from moisture and dust, preventing short circuits. Currently, the blue film in secondary batteries generally suffers from low adhesive strength and poor high-voltage resistance. Therefore, improving the insulation performance and reliability of the secondary battery casing, thereby enhancing the safety performance of individual battery cells, has become an urgent technical problem to be solved. Summary of the Invention

[0004] This application is made in view of the above-mentioned technical problems, and its purpose is to provide a battery cell, a method for preparing the same, a secondary battery, and an electrical device. The outer shell of the battery cell has an insulating coating, which has good high-voltage insulation properties and can help improve the safety performance of the secondary battery.

[0005] In a first aspect, a battery cell is provided, the battery cell comprising: a housing and an electrode assembly disposed in the housing; the housing comprising a body and an insulating coating disposed on the outer surface of the body; the insulating coating comprising: an electrophoretic coating disposed on the outer surface of the body; and a powder coating disposed on the electrophoretic coating.

[0006] In the embodiments of this application, the electrophoretic coating is directly formed on the outer surface of the main body of the casing, resulting in a strong bond between the insulating coating and the main body. A powder coating is applied over the electrophoretic coating, forming a double-layer insulating coating with excellent insulation and voltage resistance, as well as a smooth appearance. This improves the insulation performance, high-voltage resistance, and aesthetics of the battery cell casing, thereby enhancing the safety performance of the battery cell.

[0007] In one possible implementation, the thickness h1 of the electrophoretic coating satisfies: 60 μm ≤ h1 ≤ 90 μm.

[0008] The thickness of the electrophoretic coating affects both the withstand voltage and the appearance of the insulating coating. In the embodiments of this application, controlling the thickness of the electrophoretic coating within a suitable range helps to improve the withstand voltage of the insulating coating and also enhances its aesthetics.

[0009] In one feasible approach, 70μm≤h1≤80μm.

[0010] In one possible implementation, the thickness h2 of the powder coating satisfies: 70μm≤h2≤120μm.

[0011] The thickness of the powder coating affects both the withstand voltage and the appearance of the insulating coating. In the embodiments of this application, controlling the thickness of the powder coating within a suitable range helps to improve the withstand voltage of the insulating coating and also enhances its aesthetics.

[0012] In one feasible approach, 80μm≤h2≤100μm.

[0013] In one possible implementation, the adhesion strength p between the insulating coating and the body satisfies: 10MPa≤p≤20MPa.

[0014] In the embodiments of this application, the electrophoretic coating of the insulating coating is integrally formed on the outer surface of the shell body by electrophoresis, which can achieve an adhesion strength much higher than that of the blue film.

[0015] In one possible implementation, the DC withstand voltage v of the insulating coating satisfies: 12kV≤v≤21kV.

[0016] In one possible implementation, the insulation resistance R of the insulating coating satisfies: 25 GΩ ≤ R ≤ 40 GΩ.

[0017] In the embodiments of this application, thanks to the double-layer structure, the insulating coating has excellent high-voltage insulation performance.

[0018] In one possible implementation, the raw materials for preparing the electrophoretic coating include a first insulating material, the first insulating material comprising polyphenylene ether, wherein the relative molecular weight Mr of the polyphenylene ether satisfies: 4000≤Mr≤6000.

[0019] In the embodiments of this application, by adding insulating materials to the electrophoretic slurry, the insulation performance, pressure resistance performance, and flame retardant performance of the electrophoretic coating can be improved.

[0020] In one possible implementation, the raw materials for preparing the electrophoretic coating include a first modified epoxy resin, and the raw materials for preparing the first modified epoxy resin include the first epoxy resin and a first chain extender; wherein, the raw materials for preparing the first epoxy resin include at least one of bisphenol A type epoxy resin and phenolic type epoxy resin and a second chain extender; the first chain extender includes an amine chain extender; and the second chain extender includes bisphenol A.

[0021] In one possible implementation, the raw materials for preparing the powder coating include a second insulating material, which includes at least one of alumina, silicon dioxide, and butyl rubber.

[0022] In one possible implementation, the raw material for preparing the powder coating includes a second modified epoxy resin, which includes at least one of polyether epoxy resin, polyester epoxy resin, and polyurethane epoxy resin.

[0023] In one possible implementation, the capacity of the battery cell is greater than or equal to 280 Ah.

[0024] In a second aspect, a secondary battery is provided, the secondary battery comprising the battery cell described in the first aspect.

[0025] Thirdly, an electrical device, which includes the battery cell in the first aspect and / or the secondary battery in the second aspect.

[0026] Fourthly, a method for preparing a battery cell according to the first aspect is provided, comprising: preparing raw materials for electrophoretic coating and raw materials for powder coating respectively; performing electrophoretic coating on the body of the casing of the battery cell using the raw materials for electrophoretic coating to form an electrophoretic coating on the outer surface of the body; performing electrostatic spraying on the body using the raw materials for powder coating to form a powder coating on the electrophoretic coating to obtain a casing with an insulating coating; and placing an electrode assembly in the casing with the insulating coating to obtain the battery cell.

[0027] In one possible implementation, after electrophoretically coating the body using the raw material of the electrophoretic coating, the method includes: rinsing and drying the shell; and baking the shell at 160°C-180°C for 20-30 minutes to form the electrophoretic coating.

[0028] In one possible implementation, after electrostatically spraying the body with a powder coating material, the method includes baking the outer shell at 180°C-280°C for 20-30 minutes to form the powder coating. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of a single battery cell.

[0031] Figure 2 This is a schematic diagram of a battery module.

[0032] Figure 3 This is a schematic diagram of a battery pack.

[0033] Figure 4 This is another schematic diagram of a battery pack.

[0034] Figure 5 This is a schematic flowchart of a transformation method. Detailed Implementation

[0035] The following detailed description of embodiments of the lithium-ion battery and power-consuming device of this application is provided with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0036] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0037] In the description of this application, it should be noted that, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," "outer," etc., indicating orientation or positional relationships are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. Furthermore, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0038] Unless otherwise specified, in this application, the phrase "A and / or B" means "A, B, or both A and B". More specifically, the condition "A and / or B" is satisfied by any of the following conditions: 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).

[0039] Unless otherwise specified, all steps in this 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 it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0040] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0041] Unless otherwise specified, the following terms have the following meanings. Any undefined terms have their technically accepted meanings.

[0042] As mentioned, "epoxy resin" refers to a general term for polymeric or organic compounds with epoxy groups at the end or containing epoxy groups in the side chains. It is generally obtained by the condensation polymerization of polyphenols, polyols, polyacids, and polyamines with excess epichlorohydrin or by the oxidation of olefins. Before curing, epoxy resin is a linear low-molecular-weight polymer or organic compound in a liquid or solid state; after reacting with a curing agent, it can form a thermosetting resin. The main types of epoxy resins include glycidyl ether type epoxy resins (e.g., bisphenol A type epoxy resin), glycidyl ester type epoxy resins, glycidyl amine type epoxy resins, aliphatic epoxides, alicyclic epoxides, and mixed-type epoxy resins.

[0043] If mentioned, "phenolic epoxy resin" refers to linear phenolic resin obtained by the condensation reaction of phenol and formaldehyde in an acidic medium, also known as "F-type epoxy resin", "phenolic epoxy resin", or "linear phenolic polyglycidyl ether".

[0044] If mentioned, "polyether epoxy resin", "polyester epoxy resin", and "polyurethane epoxy resin" refer to composite epoxy resins obtained by polymerization reactions of polyether reactants, polyester reactants, and polyurethane reactants with epoxy resin under the action of a catalyst. They all belong to mixed epoxy resins.

[0045] If mentioned, "chain extender" refers to a substance whose molecular structure contains at least two active functional groups, which can react with epoxy groups to lengthen the molecular chain and increase the molecular weight.

[0046] As mentioned, "toughening agent" refers to a substance containing active groups that can chemically react with resin to change its flexibility. Toughening agents can participate in the curing reaction of resins, increasing their elongation at break.

[0047] If mentioned, "isocyanate" refers to the general term for various esters of isocyanate. Common isocyanates include toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), diphenylmethane diisocyanate (MDI), dicyclohexylmethane diisocyanate (HMDI), hexamethylene diisocyanate (HDI), and lysine diisocyanate (LDI).

[0048] As mentioned, "curing agent" refers to a substance that can react with resin to form a solid material; in other words, it can react with resin to cure it. Common curing agents include amine curing agents and phenolic curing agents. "Amine curing agents" are a class of curing agents that include NH bonds, such as dicyandiamide. "Phenolic curing agents" can be considered as bisphenol A-terminated epoxy resins. From a molecular structure perspective, corresponding phenolic curing agents can be prepared from various types of epoxy resins.

[0049] If mentioned, "flame retardant" refers to a substance that can increase the flame resistance of polymer compounds. It can make polymer compounds flame retardant by physically mixing with polymer compounds or by participating in the polymerization reaction of polymer compounds in the form of monomers.

[0050] If mentioned, "Montmorillonite (MMT)" refers to a type of earthy mineral composed of negatively charged nano-silicate sheets stacked together by electrostatic interactions between the layers, with the theoretical molecular formula being (1 / 2Ca,Na). 0.66 (Al,Mg,Fe)4[(Si,Al)8O 20 ](OH)4·nH2O.

[0051] As mentioned, "pigments and fillers" refers to the general term for pigments and fillers. "Pigments" are a class of colored, finely granular substances, characterized by their color-displaying particles. They are inorganic or organic substances with hiding power and tinting strength, commonly used in the formulation of coatings, inks, and for coloring plastics and rubber; therefore, they are also called colorants. "Fillers" are a class of finely granular substances that primarily function as fillers in a medium. Their dry powder appearance is mostly white or light gray, and generally, their impact on hiding power and tinting strength in a medium is relatively limited. By adding fillers to a medium, the non-color physical and chemical properties of the medium can be effectively altered; therefore, fillers are also called extender pigments. A particular substance may function as both a pigment and a filler. For example, silica powder.

[0052] If mentioned, "benzoin" refers to 2-hydroxy-1,2-diphenyl ethyl ketone, also known as "benzoin," which is an important additive in the powder coating production process.

[0053] The embodiments of this application will be described next.

[0054] In recent years, rechargeable batteries have seen significant development due to their high energy density and long lifespan, finding widespread application in power tools, electronic products, electric vehicles, aerospace, and other fields. Typically, a rechargeable battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of these active ions between the electrodes. The separator, positioned between the positive and negative electrodes, prevents short circuits while allowing active ions to pass through, ensuring the normal electrochemical reaction of the rechargeable battery.

[0055] Besides the need to consider the insulation between the positive and negative electrodes inside the secondary battery, a blue film is typically applied to the outside of the battery casing for electrical insulation during use and transportation. The adhesion strength between the blue film and the casing is usually low (approximately 2 MPa), posing a risk of detachment and insulation failure during battery use. Furthermore, due to limitations in the blue film coating process, creases are unavoidable at the edges, which are prone to wear and insulation failure. Additionally, temperature changes during battery use can cause condensation, forming water droplets on the casing surface. Condensation at the creases can lead to high-voltage breakdown of the blue film, resulting in insulation failure. With the increasing diversity and extreme applications of secondary batteries, the blue film is no longer sufficient to meet the insulation requirements of the battery casing.

[0056] In view of this, embodiments of this application provide a battery cell, a method for preparing the same, a secondary battery, and an electrical device. The battery cell has an insulating coating, and the insulating coating has a high bonding strength with the casing, reaching 10 MPa or higher, without any crease issues. Simultaneously, the insulating coating also possesses excellent insulation and high-voltage resistance properties.

[0057] [Battery cell]

[0058] First, a battery cell is provided, comprising a housing and an electrode assembly disposed within the housing. The housing includes a body and an insulating coating disposed on the outer surface of the body, the insulating coating comprising an electrophoretic coating and a powder coating. The electrophoretic coating is disposed on the outer surface of the battery cell housing, and the powder coating is disposed on the electrophoretic coating.

[0059] In this embodiment, the insulating coating disposed on the outer surface of the battery cell casing has a double-layer structure. The electrophoretic coating is directly formed onto the body of the casing by electrophoresis, and the powder coating is directly formed onto the electrophoretic coating by powder spraying. Compared with the blue film, there is no crease problem, thus solving the problem of insulation failure caused by creases. In addition, compared with the single-layer insulating film, this double-layer insulating coating has superior insulation performance and high-voltage resistance, and has a smooth appearance, which is beneficial to improving the insulation performance, high-voltage resistance, and aesthetics of the battery cell casing, thereby improving the safety performance of the battery cell.

[0060] It should be understood that the outer casing refers to the shell itself, and the outer casing also includes an insulating coating applied to its outer surface. The material of the outer casing can be hard plastic, aluminum, steel, etc.

[0061] In one embodiment, the thickness h1 of the electrophoretic coating satisfies: 60μm≤h1≤90μm; optionally, 70μm≤h1≤80μm.

[0062] Specifically, the thickness h1 of the electrophoretic coating can be 60μm, 61μm, 62μm, 63μm, 64μm, 65μm, 66μm, 67μm, 68μm, 69μm, 70μm, 71μm, 72μm, 73μm, 74μm, 75μm, 76μm, 77μm, 78μm, 79μm, 80μm, 81μm, 82μm, 83μm, 84μm, 85μm, 86μm, 87μm, 88μm, 89μm, 90μm, or a value within the range obtained by any combination of the above two values.

[0063] The thickness h1 of the electrophoretic coating directly affects the insulation and withstand voltage properties of the insulating coating. This application investigated the relationship between the thickness h1 of the electrophoretic coating and the leakage current and DC withstand voltage of the insulating film. Within the above-mentioned range, the larger h1 is, the higher the DC withstand voltage and the better the withstand voltage performance of the insulating coating; the larger h1 is, the smaller the leakage current and the better the insulation performance of the insulating coating. If the thickness h1 exceeds the above range, the larger h1 is, the worse the uniformity of the electrophoretic coating becomes, leading to a decrease in the uniformity of the insulating coating, and consequently, a deterioration in the withstand voltage and insulation performance. A possible reason is that the electrophoretic process involves depositing conductive polymer compounds onto the outer shell by applying voltage. When the thickness h1 of the electrophoretic coating is small, a smaller voltage can be used for deposition, while a larger thickness h1 requires a larger voltage to increase the deposition rate of the polymer compounds. At a lower voltage, the polymer compounds can be deposited more orderly on the outer shell, forming a uniform and smooth film. At higher voltages, polymer compounds tend to deposit irregularly on the outer shell, forming a messy accumulation. This results in poor uniformity of the electrophoretic film layer, causing the insulating coating to appear "orange peel." "Orange peel" refers to an uneven and rough coating that looks like orange peel.

[0064] Therefore, in this embodiment, by controlling the thickness h1 of the electrophoretic coating within a suitable range, the insulation performance and withstand voltage performance of the insulating coating can be improved, and the uniformity of the insulating coating can be improved.

[0065] In one embodiment, the thickness h2 of the powder coating satisfies: 70μm≤h2≤120μm; optionally, 80μm≤h2≤100μm.

[0066] Specifically, the thickness h2 of the powder coating can be 70μm, 72μm, 74μm, 76μm, 78μm, 80μm, 82μm, 84μm, 86μm, 88μm, 90μm, 92μm, 94μm, 96μm, 98μm, 100μm, 102μm, 104μm, 106μm, 108μm, 110μm, 112μm, 114μm, 116μm, 118μm, 120μm, or a value within the range obtained by any combination of the above two values.

[0067] The thickness h2 of the powder coating directly affects the insulation and withstand voltage performance of the insulating coating. This application also investigated the relationship between the thickness h2 of the powder coating and the leakage current and DC withstand voltage of the insulating film. Within the above range, the larger h2 is, the higher the DC withstand voltage and the better the withstand voltage performance of the insulating coating; the larger h2 is, the smaller the leakage current and the better the insulation performance of the insulating coating. If the thickness h2 exceeds the above range, the larger h2 is, the worse the uniformity of the powder coating becomes, leading to a worse uniformity of the insulating coating, and consequently, a worse withstand voltage and insulation performance. A possible reason is that the powder coating is charged by a high-voltage electrostatic field, and under the action of the electrostatic field and compressed air, it is uniformly adsorbed onto the electrophoretic coating, forming a uniform film after high-temperature self-leveling. During this process, if the thickness h2 of the powder coating is small, subsequent leveling may be hindered, preventing proper spreading and resulting in "orange peel" texture. If the thickness h2 of the powder coating is large, the leveling of the film is poor, also easily leading to "orange peel" texture.

[0068] Therefore, in this embodiment, by controlling the thickness h2 of the powder coating within a suitable range, the insulation performance and withstand voltage performance of the insulating coating can be improved, and the uniformity of the insulating coating can be improved.

[0069] Furthermore, by controlling the thickness h1 of the electrophoretic coating and the thickness h2 of the powder coating to be within the aforementioned ranges, the obtained insulating coating achieves excellent insulation and withstand voltage performance, and possesses a uniform and smooth appearance. Compared to a single electrophoretic coating or a single powder coating of the same thickness, this insulating coating achieves better withstand voltage and insulation performance. Moreover, for the insulating coating, the thickness of both the electrophoretic coating and the powder coating is not excessively thick; within this thickness range, it is easy to form a high-quality coating with high product yield. This coating enables high-quality, high-yield industrial production while achieving good withstand voltage and insulation performance.

[0070] In one embodiment, the bonding strength p between the insulating coating and the casing of the battery cell satisfies: 10MPa≤p≤20MPa.

[0071] Specifically, adhesive strength refers to the shear force required per unit area when the interface between the coating and the casing, or its vicinity, is damaged under external force. The adhesive strength p between the insulating coating and the casing of the battery cell can be 10 MPa, 11 MPa, 12 MPa, 13 MPa, 14 MPa, 15 MPa, 16 MPa, 17 MPa, 18 MPa, 19 MPa, 20 MPa, or a value within the range obtained by any combination of two of the above values.

[0072] In this embodiment, both the electrophoretic coating on the inner side of the insulating coating and the powder coating on the outer side are integrally formed on the outer shell. After the insulating coating is self-leveled at high temperature to form a film, the adhesion strength between it and the outer shell can reach 10MPa-20MPa, which is much higher than the 2MPa of ordinary blue film. Therefore, the insulating coating has good adhesion strength to the battery cell shell, and it is not easy to fall off or break from the shell, thus providing highly reliable electrical insulation for the battery cell.

[0073] In one embodiment, the DC withstand voltage v of the insulating coating satisfies: 12kV≤v≤21kV.

[0074] Specifically, v can be 12kV, 13kV, 14kV, 15kV, 16kV, 17kV, 18kV, 19kV, 20kV, 21kV, or a value within the range obtained by any combination of the above two values.

[0075] In this embodiment, thanks to the double-layer structure of the insulating coating, it can withstand DC voltages of 12kV-21kV. Compared with the withstand voltage performance of ordinary single-layer insulating film (5kV-8.4kV), the withstand voltage performance of the insulating coating is significantly improved, and it can be applied to high-voltage secondary batteries such as energy storage batteries.

[0076] In one embodiment, the insulation resistance R of the insulating coating satisfies: 25GΩ≤R≤40GΩ.

[0077] Specifically, the aforementioned insulation resistance is the insulation resistance of the insulating coating under a 1kV DC voltage for 60 seconds. R can be 25GΩ, 26GΩ, 27GΩ, 28GΩ, 29GΩ, 30GΩ, 31GΩ, 32GΩ, 33GΩ, 34GΩ, 35GΩ, 36GΩ, 37GΩ, 38GΩ, 39GΩ, 40GΩ, or a value within the range obtained by any combination of the above two values.

[0078] In this embodiment, the insulating coating has an insulation resistance of over 25 GΩ, exhibiting excellent insulation performance. Furthermore, thanks to the fabrication process of this insulating coating, there are no creases or interfaces on the housing, reducing the risk of insulation coating failure. It should be understood that the lower the leakage current, the higher the insulation resistance. Insulation resistance can be tested, for example, by a DC bridge method, a DC voltage-current method, or by an insulation resistance tester. Exemplarily, the insulating coating can be prepared on a peelable substrate, and then the substrate can be removed to obtain the insulating coating. The insulation resistance of the insulating coating is measured according to Ohm's law by applying a high voltage (1 kV) to the insulating coating.

[0079] In one embodiment, the raw materials for preparing the electrophoretic coating include a first modified epoxy resin, and the raw materials for preparing the first modified epoxy resin include the first epoxy resin and a first chain extender.

[0080] In one embodiment, the first chain extender comprises an amine chain extender.

[0081] In one embodiment, the amine chain extender includes at least one of N-methylethanolamine and 1,3-propanediamine.

[0082] In this embodiment, amine groups can be introduced into the first epoxy resin by using an amine chain extender to perform a chain extension reaction. Amine groups are polar and ionizable groups; introducing amine groups into the first epoxy resin enables the first epoxy resin to possess electrodeposition capabilities.

[0083] In one embodiment, the mass ratio of the first epoxy resin to the first chain extender in the raw materials for preparing the first modified epoxy resin is (12-15):1. For example, it can be a ratio of 12:1, 13:1, 14:1, 15:1, etc.

[0084] In one embodiment, the number-average molecular weight distribution Mn of the first epoxy resin satisfies: 600≤Mn≤11000.

[0085] In one embodiment, the molecular weight distribution of the first epoxy resin satisfies the following conditions: the amount of first epoxy resin with Mn between 600 and 1500 accounts for 5% to 10% of the total amount of the first epoxy resin; the amount of first epoxy resin with Mn between 1500 and 5000 accounts for 20% to 25% of the total amount of the first epoxy resin; the amount of first epoxy resin with Mn between 5000 and 9000 accounts for 50% to 55% of the total amount of the first epoxy resin; and the amount of first epoxy resin with Mn between 9000 and 11000 accounts for 20% to 25% of the total amount of the first epoxy resin.

[0086] As mentioned earlier, electrophoresis is a process in which a polymer compound is deposited onto the outer shell by applying voltage. The molecular weight of the polymer will affect its deposition rate and deposition pattern during the electrophoresis process. In this embodiment, by controlling the molecular weight distribution of the first epoxy resin within the aforementioned suitable range, it is helpful for the first epoxy resin to be deposited regularly and stably onto the outer surface of the shell body during the electrophoresis process, forming an electrophoretic coating with appropriate thickness and good uniformity.

[0087] In one embodiment, the raw materials for preparing the first epoxy resin include bisphenol A type epoxy resin, phenolic type epoxy resin, a second chain extender, a toughening agent, and a first catalyst.

[0088] In this embodiment, the introduction of phenolic epoxy resin helps to increase the heat resistance and pressure resistance of the electrophoretic film.

[0089] In one embodiment, the second chain extender comprises bisphenol A; the toughening agent comprises bisphenol A polyoxyethylene ether; and the first catalyst comprises at least one of a first amine catalyst and a phosphorus catalyst.

[0090] In one embodiment, the first amine catalyst includes at least one of N,N-dimethylbenzylamine, N,N-dimethylcyclohexylamine, bis(2-dimethylaminoethyl) ether, N,N,N',N'-tetramethylalkylene diamine, and triethylamine.

[0091] In one embodiment, the raw materials for preparing the electrophoretic coating include a first curing agent, which includes a modified isocyanate.

[0092] In one embodiment, the raw materials for preparing the modified isocyanate include a polyhydroxy compound, polypropylene glycol, and isocyanate.

[0093] In this embodiment, the isocyanate curing agent is modified by polyhydroxy compounds and polypropylene glycol, which can increase the hydroxyl groups on the isocyanate backbone, giving the modified isocyanate more crosslinking sites. At the same time, polypropylene glycol also has a certain toughening effect on the resin.

[0094] In one embodiment, the polyhydroxy compound includes at least one of ethylene glycol, glycerol, pentaerythritol, and dipentaerythritol; the isocyanate includes at least one of toluene diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate.

[0095] In one embodiment, the mass ratio of the hydroxyl compound and polypropylene glycol to the isocyanate in the raw materials for preparing the modified isocyanate is 1:(3-5). For example, it can be a ratio of 1:3, 1:4, 1:5, etc.

[0096] In one embodiment, the raw materials for preparing the electrophoretic coating include a first insulating material, which includes polyphenylene ether.

[0097] In the case of preparing a single electrophoretic coating on the outer shell, some powdered inorganic fillers may be added to the electrophoretic slurry to impart color, hiding power, and corrosion resistance to the coating. Inorganic fillers have some insulation properties, but cannot simultaneously provide insulation while withstanding high voltage. Furthermore, if these inorganic fillers are not demagnetized, they are prone to agglomeration during electrophoresis, creating more conductive defects in the electrophoretic coating. Polyphenylene ether (PPE) is a material with outstanding insulating properties, as well as excellent pressure resistance and flame retardancy. In this embodiment, by introducing PPE into the slurry, the insulation properties of the electrophoretic coating can be effectively improved, thereby enhancing the insulation performance of the insulating coating, especially its pressure resistance insulation.

[0098] In one embodiment, the relative molecular weight Mr of polyphenylene ether satisfies: 4000≤Mr≤6000.

[0099] Specifically, Mr can be 4000, 4200, 4400, 4600, 4800, 5000, 5200, 5400, 5600, 5800, 6000, or a value within the range obtained by any combination of two of the above values. It should be understood that relative molecular weight refers to the ratio of the average mass of polyphenylene ether to 1 / 12 of the atomic mass of 12C.

[0100] In one embodiment, the raw material for preparing the powder coating includes a second modified epoxy resin, which includes at least one of polyether epoxy resin, polyester epoxy resin, and polyurethane epoxy resin.

[0101] In one embodiment, the raw material for preparing the powder coating includes a second insulating material, which includes at least one of alumina, silicon oxide, and butyl rubber.

[0102] In this embodiment, the powder coating component incorporates a second insulating material compared to common powder coating formulations. This enhances the insulation performance of the powder coating, thereby further improving the insulation performance of the insulating coating. By covering the electrophoretic coating with a powder coating, the insulating coating can achieve high-voltage insulation performance that a single coating cannot achieve.

[0103] In one embodiment, the raw materials for preparing the powder coating include flame retardants, which include at least one of inorganic flame retardants and organic flame retardants.

[0104] In one embodiment, the inorganic flame retardant includes at least one of aluminum hydroxide, magnesium hydroxide, magnesium oxide, montmorillonite, and graphene; the organic flame retardant includes at least one of silicone resin and polysiloxane.

[0105] In one embodiment, the mixture includes a second curing agent, which includes a phenolic curing agent.

[0106] In one embodiment, the phenolic curing agent includes at least one of epoxyacetylacetonol, catechol, m-cresol, o-cresol, nonylphenol, bisphenol A, phenol, mixed cresols, octylphenol, p-tert-butylphenol, resorcinol, catechol, and hydroquinone.

[0107] In one embodiment, the raw material for preparing the powder coating includes a second catalyst, which includes a second amine catalyst.

[0108] In one embodiment, the second amine catalyst includes at least one of benzyltriethylammonium chloride and hexadecyltrimethylammonium bromide.

[0109] In one embodiment, the raw materials for preparing the powder coating include pigments and fillers, which include at least one of phthalocyanine blue, titanium dioxide, silica powder, and kaolin.

[0110] In one embodiment, the raw materials for preparing the powder coating include additives, including benzoin. Benzoin is also known as "benzoin".

[0111] Typically, a single battery cell also includes an electrode assembly, which comprises a positive electrode, a negative electrode, an electrolyte, and a separator. The following section uses a lithium-ion battery as a specific example to provide a detailed description of the positive electrode, negative electrode, separator, and electrolyte in a secondary battery. It should be understood that the lithium-ion battery is merely an example, and the solution provided in this application can also be applied to other types of secondary batteries, such as sodium-ion batteries, magnesium-ion batteries, and lithium-sulfur batteries.

[0112] [Negative electrode plate]

[0113] A negative electrode typically includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. The negative electrode film layer includes a negative electrode active material.

[0114] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0115] In one embodiment, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymeric material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0116] In one embodiment, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0117] In one embodiment, the negative electrode film layer further includes an adhesive. The adhesive may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0118] In one embodiment, the negative electrode film layer further includes a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0119] In one embodiment, the negative electrode film layer also includes other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0120] In one embodiment, the negative electrode sheet can be prepared by forming a negative electrode slurry using the components described above. For example, the negative electrode active material, conductive agent, binder, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form the negative electrode slurry. The negative electrode slurry is then coated onto a negative electrode current collector, and after drying, cold pressing, and other processes, the negative electrode sheet is obtained.

[0121] [Positive electrode plate]

[0122] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0123] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0124] In one embodiment, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0125] In one embodiment, the positive electrode active material may be a known positive electrode active material for batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium-containing phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites. During the charging and discharging process, Li undergoes insertion / extraction and consumption, resulting in different molar contents of Li in the positive electrode active material when the battery is discharged to different states. In the examples of positive electrode active materials in this application, the molar content of Li refers to the initial state of the material, i.e., the state before feeding. After charge-discharge cycles, the molar content of Li changes when the positive electrode active material is applied to the battery system. In the examples of positive electrode active materials in this application, the molar content of O is only an ideal value; lattice oxygen release causes changes in the molar content of O, and the actual molar content of O will fluctuate.

[0126] In one embodiment, the positive electrode film layer further includes a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0127] In one embodiment, the positive electrode film layer further includes a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0128] In one embodiment, the positive electrode sheet can be prepared by forming a positive electrode slurry from the components described above. For example, a first positive electrode active material and / or a second positive electrode active material, a conductive agent, a binder, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry. The positive electrode slurry is then coated onto a positive electrode current collector, and after drying, cold pressing, and other processes, the positive electrode sheet is obtained.

[0129] Electrolyte

[0130] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0131] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0132] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0133] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0134] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0135] [Isolation Component]

[0136] This application does not impose any particular restrictions on the type of separator. For example, any known porous membrane with good chemical and mechanical stability can be selected.

[0137] In one embodiment, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0138] In one embodiment, the negative electrode, positive electrode, and separator can be fabricated into an electrode assembly using a winding process or a stacking process.

[0139] This application provides a housing for a battery cell, the outer surface of which is provided with an insulating coating as described in any embodiment of this application, and the housing is used to encapsulate the aforementioned electrode assembly and electrolyte.

[0140] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured battery cell 100.

[0141] In one embodiment, the capacity of the battery cell 100 is greater than or equal to 280Ah.

[0142] Specifically, the insulating coating provided in this application can be applied to battery cells 100 with a capacity of 280Ah and above. In other words, it can be applied to high-capacity energy storage batteries to provide them with good voltage resistance and insulation performance.

[0143] Figure 2 This is a battery module 200 as an example. (See reference...) Figure 2 In the battery module 200, multiple battery cells 100 can be arranged sequentially along the length of the battery module 200. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 100 can be fixed in place using fasteners. The multiple battery cells 100 can be battery cells 100 with the same chemical system or battery cells 100 with different chemical systems.

[0144] Alternatively, in one embodiment, the battery module 200 may further include a housing with a receiving space in which a plurality of battery cells 100 are received.

[0145] Optionally, in one embodiment, the battery module 200 can also be directly assembled into a battery. The number of battery modules 200 contained in the battery can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery.

[0146] Figure 3 and Figure 4 This is a sample battery pack 300. (See reference...) Figure 3 and Figure 4 The battery pack 300 may include a battery box and multiple battery modules 200 disposed within the battery box. The battery box includes an upper box 301 and a lower box 302, with the upper box 301 covering the lower box 302 to form a closed space for accommodating the battery modules 200. The multiple battery modules 200 may be arranged in any manner within the battery box.

[0147] It should be understood that battery cells 100 can be first assembled into battery modules 200, and battery pack 300 is composed of battery modules 200. Alternatively, battery cells 100 can be directly assembled into battery pack 300, omitting the intermediate form of battery modules 200. The secondary battery mentioned in this application may include only one of battery cells 100, battery modules 200, and battery pack 300, or it may include two or more of battery cells 100, battery modules 200, and battery pack 300 simultaneously.

[0148] In addition, this application also provides an electrical device that includes the lithium-ion battery described in the foregoing embodiments.

[0149] In another embodiment, the electrical device includes at least one of the battery cell 100, battery module 200, or battery pack 300 provided in this application. The battery cell 100, battery module 200, or battery pack 300 can be the power source of the electrical device or the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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.

[0150] As an electrical device, the number of battery cells 100, battery modules 200, or battery packs 300 can be selected according to its usage requirements.

[0151] This is an example of an electrical device. The device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0152] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0153] [Methods for preparing battery cells]

[0154] This application also provides a method for preparing the battery cells described in the foregoing embodiments. Figure 5 This is a schematic flowchart illustrating a method for preparing a battery cell according to this application. Figure 5 As shown, method 500 includes:

[0155] S501, prepare the raw materials for electrophoretic coating and powder coating respectively.

[0156] S502, using the raw material for electrophoretic coating, electrophores the body of the battery cell casing to form an electrophoretic coating on the outer surface of the body.

[0157] S503, using powder coating raw materials to electrostatically spray the body to form a powder coating on the electrophoretic coating, thereby obtaining a shell with an insulating coating.

[0158] S504, placing the electrode assembly in a housing with an insulating coating to obtain a battery cell.

[0159] Specifically, Method 500 mainly involves two steps to prepare an insulating coating with a double-layer structure. First, an electrophoretic coating is formed on the outer surface of the shell body, so that the insulating coating and the shell have good adhesion strength. Then, a powder coating is prepared on the electrophoretic coating by electrostatic spraying, so that the insulating coating has good adhesion strength and also has beneficial pressure resistance insulation.

[0160] Optionally, after step S502, method 500 includes:

[0161] Rinse and air dry the shell; bake the shell at 160℃-180℃ for 20-30 minutes to form an electrophoretic coating.

[0162] Specifically, the baking temperature can be selected from 160℃, 165℃, 170℃, 175℃, 180℃, or a value within the range obtained by any combination of two of the above values. The baking time can be selected from 20min, 22min, 24min, 26min, 28min, 30min, or a value within the range obtained by any combination of two of the above values.

[0163] In this process, the moist electrophoretic coating formed on the body of the shell during electrophoresis is cured after being baked at high temperature. During the baking process, the electrophoretic coating self-levels at high temperature, which helps to ensure the uniformity of the electrophoretic coating.

[0164] Optionally, after step S503, method 500 includes:

[0165] The shell is baked at 180℃-280℃ for 20-30 minutes to form a powder coating.

[0166] Specifically, the baking temperature can be selected from 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, or a value within the range obtained by any combination of two of the above values. The baking time can be selected from 20min, 22min, 24min, 26min, 28min, 30min, or a value within the range obtained by any combination of two of the above values.

[0167] In this process, the powder coating formed during electrostatic spraying is further cured after high-temperature baking. During baking, both the electrophoretic coating and the electrostatic coating self-level at high temperatures, and together they form a uniform and stable insulating coating. Therefore, the insulating coating prepared by this application through two-step high-temperature curing has good uniformity and stability.

[0168] Optionally, in S501, the raw materials for preparing the electrophoretic coating include:

[0169] Prepare the first modified epoxy resin, the first curing agent, and the first insulating material respectively.

[0170] The first modified epoxy resin, the first curing agent, and the first insulating material are mixed evenly to obtain a first intermediate product; a wetting agent and a cosolvent are added to the first intermediate product and mixed evenly to obtain a second intermediate product; a neutralizing agent is added to the second intermediate product and then water is added for emulsification to obtain a slurry for electrophoresis.

[0171] The specific processes and procedures for preparing the above-mentioned raw materials can be implemented by referring to existing processes and will not be elaborated in this application.

[0172] Optionally, in the first intermediate product, the mass ratio of the first modified epoxy resin, the first curing agent, and the first insulating material is 20:16:1; in the second intermediate product, the wetting agent accounts for 0.5% to 1% of the mass of the second intermediate product, and the cosolvent accounts for 0.5% to 0.1% of the mass of the second intermediate product.

[0173] Specifically, the wetting agent may constitute 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1.0% of the second intermediate product by mass, or a value within the range obtained by any combination of the above two values. The cosolvent may constitute 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1.0% of the second intermediate product by mass, or a value within the range obtained by any combination of the above two values.

[0174] Optionally, the first curing agent includes a modified isocyanate; the first insulating material includes polyphenylene ether; the wetting aid includes at least one of polyether-modified dimethylsiloxane, acetylenol bis-surfactant, and polyether-modified siloxane; the co-solvent includes at least one of ethylene glycol hexyl ether, ethylene glycol isooctyl ether, propylene glycol phenyl ether, and propylene glycol methyl ether; and the neutralizing agent includes at least one of formic acid, acetic acid, and lactic acid.

[0175] Optionally, preparing the first modified epoxy resin includes: preparing a first epoxy resin; and subjecting the first epoxy resin and a first chain extender to a chain extension reaction at 60°C-100°C to obtain the first modified epoxy resin.

[0176] Specifically, the temperature of the chain extension reaction can be 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, or a ratio thereof within the range obtained by any combination of the above two ratios.

[0177] Optionally, the first chain extender includes an amine chain extender; the amine chain extender includes at least one of N-methylethanolamine and 1,3-propanediamine.

[0178] In this embodiment, the first epoxy resin is extended by an amine chain extender, which introduces amine groups into the first epoxy resin. The amine groups are polar groups and ionizable groups. Through this step, the first modified epoxy resin can be made to have the function of electrodeposition.

[0179] Optionally, the mass ratio of the first epoxy resin to the first chain extender is (12-15):1.

[0180] Specifically, the mass ratio of the first epoxy resin to the first chain extender can be 12:1, 13:1, 14:1, 15:1, or a ratio within the range obtained by any combination of the above two ratios.

[0181] Optionally, preparing the first epoxy resin includes: carrying out a chain extension reaction of bisphenol A type epoxy resin, phenolic type epoxy resin, a second chain extender, a toughening agent, and a first catalyst at 140℃-150℃ to obtain the first epoxy resin.

[0182] Bisphenol A type epoxy resin is the most commonly used and readily available epoxy resin, while phenolic epoxy resin has excellent heat resistance and insulation properties. The chain extension reaction temperature can be 140℃, 142℃, 144℃, 146℃, 148℃, or 150℃, or a ratio thereof within the range obtained by any combination of two of the above ratios. In this embodiment, phenolic epoxy resin is introduced into the electrophoretic slurry, thereby improving the insulation performance of the electrophoretic coating.

[0183] Optionally, the second chain extender includes bisphenol A; the toughening agent includes bisphenol A polyoxyethylene ether; and the first catalyst includes at least one of a first amine catalyst and a phosphorus catalyst.

[0184] Optionally, the first amine catalyst includes at least one of N,N-dimethylbenzylamine, N,N-dimethylcyclohexylamine, bis(2-dimethylaminoethyl) ether, N,N,N',N'-tetramethylalkylene diamine, and triethylamine.

[0185] Optionally, the number-average molecular weight distribution Mn of the first epoxy resin satisfies: 600≤Mn≤11000.

[0186] Optionally, the amount of the first epoxy resin with Mn in the range of 600 to 1500 accounts for 5% to 10% of the total amount of the first epoxy resin; the amount of the first epoxy resin with Mn in the range of 1500 to 5000 accounts for 20% to 25% of the total amount of the first epoxy resin; the amount of the first epoxy resin with Mn in the range of 5000 to 9000 accounts for 50% to 55% of the total amount of the first epoxy resin; and the amount of the first epoxy resin with Mn in the range of 9000 to 11000 accounts for 20% to 25% of the total amount of the first epoxy resin.

[0187] Epoxy resins have a wide molecular weight distribution. In electrophoretic slurries, molecules of different molecular weights have different interaction forces, causing them to become entangled, form aggregates, and increase the viscosity of the slurry. Generally, the higher the molecular weight, the higher the viscosity of the slurry. Low molecular weight resins have simpler structures, are more flexible in electrophoretic slurries, and have faster film deposition rates during the electrophoresis process. Because resin molecules carry surface charges during electrophoresis, resins with excessively large or small molecular weights will cause electric field disturbances, leading to molecular contact and flocculent formation.

[0188] Therefore, the molecular weight distribution of the first epoxy resin, as the "precursor" of the first modified epoxy resin, directly affects the electrophoresis effect and the quality of the electrophoretic film. In this embodiment, controlling the molecular weight distribution of the first epoxy resin within a suitable range helps to regulate the viscosity of the slurry, reduce the risk of flocculation in the electrophoretic slurry, and thus improve the quality of electrophoresis.

[0189] Optionally, in S501, preparing the first curing agent includes:

[0190] The polyhydroxy compound, polypropylene glycol and isocyanate are mixed evenly to obtain the first curing agent.

[0191] It should be understood that in the above steps, the polyhydroxy compound, polypropylene glycol, and isocyanate are physically mixed. During the reaction of the obtained first curing agent with the first modified epoxy resin, the polyhydroxy compound, polypropylene glycol, and isocyanate react to achieve the modification of the isocyanate.

[0192] In the modification of isocyanates, the use of polyhydroxy compounds and polypropylene glycol can increase the hydroxyl groups on the isocyanate backbone, thereby increasing the curing and crosslinking sites of the isocyanate and enabling it to react more efficiently with the first modified epoxy resin. Simultaneously, the introduction of polypropylene glycol into the first curing agent allows it to react with a portion of the first modified epoxy resin during the reaction between the first curing agent and the first modified epoxy resin, thereby increasing the toughness of the first modified epoxy resin and ultimately improving the toughness of the electrophoretic film.

[0193] Optionally, the polyhydroxy compound includes at least one of ethylene glycol, glycerol, pentaerythritol, and dipentaerythritol; the isocyanate includes at least one of toluene diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate.

[0194] Optionally, the mass ratio of the polyhydroxy compound and polypropylene glycol to isocyanate is 1:(3-5).

[0195] Specifically, the mass ratio of the polyhydroxy compound and polypropylene glycol to the isocyanate can be 1:3, 1:4, 1:5, or a ratio within any combination of the above ratios. The mass ratio of dipentaerythritol to polypropylene glycol in the polyhydroxy compound can be 1:3.

[0196] Optionally, in S501, the raw materials for preparing the powder coating include:

[0197] First, the second modified epoxy resin, the second curing agent, the second catalyst, pigments and fillers, the flame retardant, the second insulating material, and the additives are placed in a mixer and mixed to obtain the third intermediate product.

[0198] The mixing in this step is physical mixing. By physically mixing the above substances evenly, the subsequent melt extrusion will produce an extrudate with a uniformly distributed composition.

[0199] Then, the third intermediate product is placed in an extruder for melt blending and extrusion.

[0200] For example, in this step, a twin-screw extruder can be used to melt-blend the third intermediate product. The purpose of this step is to further homogenize the physically homogeneous mixture.

[0201] Then, the extrudate is compressed into tablets, cooled, and sliced ​​to obtain the fourth intermediate product.

[0202] In this step, the molten blend can be extruded using a twin-screw extruder, and then the extrudate can be pressed into tablets. After cooling, it can be sliced ​​in a slicer to obtain the fourth intermediate product, which is the semi-finished product of the final powder.

[0203] Subsequently, the fourth intermediate product was placed in a pulverizer and pulverized and ground to obtain the fifth intermediate product.

[0204] In this step, the fourth intermediate product is physically pulverized into powder particles of varying sizes. These powder particles can be classified using a cyclone separator, and the larger particles can be further pulverized in a pulverizer until they meet the required particle size; the smaller particles are the fifth intermediate product. Alternatively, other known methods can be used to screen the smaller particles to obtain the fifth intermediate product, which will not be elaborated upon here.

[0205] The fifth intermediate product was sieved to obtain the aforementioned powder for spraying.

[0206] In this step, the fifth intermediate product is further screened, and particles that meet the size requirements are used as powder for electrostatic spraying and will be coated onto the electrophoretic coating.

[0207] Optionally, in the above physical mixing step, the mass ratio of the second modified epoxy resin, the second curing agent, the second catalyst, pigments and fillers, the flame retardant, the second insulating material, and the additives is 55:6:0.5:30:5:3:0.5.

[0208] Optionally, the second modified epoxy resin includes at least one of polyether-type epoxy resin, polyester-type epoxy resin, and polyurethane-type epoxy resin; the second curing agent includes a phenolic curing agent; the second catalyst includes a second amine catalyst; the pigments and fillers include at least one of phthalocyanine blue, titanium dioxide, silica powder, and kaolin; the flame retardant includes at least one of inorganic flame retardants and organic flame retardants; the second insulating material includes at least one of alumina, silica, and butyl rubber; and the additives include benzoin.

[0209] Optionally, the phenolic curing agent includes at least one of epoxyacetylacetonol, catechol, m-cresol, o-cresol, nonylphenol, bisphenol A, phenol, mixed cresols, octylphenol, p-tert-butylphenol, resorcinol, catechol, and hydroquinone; the second amine catalyst includes at least one of benzyltriethylammonium chloride and hexadecyltrimethylammonium bromide; the inorganic flame retardant includes at least one of aluminum hydroxide, magnesium hydroxide, magnesium oxide, montmorillonite, and graphene; and the organic flame retardant includes at least one of silicone resin and polysiloxane.

[0210] Therefore, the insulating coating described in the foregoing embodiments of this application can be prepared on the casing of the battery cell using method 500. This insulating coating is smooth, uniform, and has excellent insulation and high-voltage resistance. An insulating coating with a thickness of 130μm-210μm exhibits an insulation resistance R greater than 25GΩ at 1kV DC for 60s, a leakage current less than 0.1mA at 7.2kV DC for 60s, and a DC withstand voltage v reaching 20kV. Furthermore, this insulating coating also possesses excellent high-temperature resistance and heat dissipation performance, withstanding temperatures up to 350℃ for over 1 hour, and a thermal conductivity greater than 0.2W / (m×K). Furthermore, this insulating coating possesses high hardness, strength, and good toughness, with a hardness reaching 2H level (approximately 200MPa-300 MPa). Its adhesion to the aluminum shell is also excellent; in the cross-cut adhesion test (refer to ASTM D3359, ISO-2409, and GB9286-98 standards), it achieves a 2mm cross-cut test with grade 0 and no peeling. Grade 0 indicates completely smooth cut edges with no paint film peeling in any section. This fully meets the voltage withstand insulation requirements of secondary batteries, especially high-energy storage secondary batteries.

[0211] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0212] [Examples and Comparative Examples]

[0213] Example 1

[0214] (1) Preparation of electrophoretic coating

[0215] 1-1) A mixture of bisphenol A type epoxy resin (E51 type, E44 type), bisphenol A, bisphenol A polyoxyethylene ether (BPE-06), and phenolic epoxy resin (EPN) in a mass ratio of 12.8:3.6:2.5:1.2 was subjected to a chain extension reaction at 140℃-150℃ under an amine catalyst (N,N-dimethylbenzylamine) to obtain the first epoxy resin.

[0216] 1-2) The first epoxy resin and N-methylethanolamine were subjected to a chain extension reaction at a mass ratio of 13:1 at 60℃-100℃ to obtain the first modified epoxy resin.

[0217] 1-3) Dipentaerythritol and polypropylene glycol are mixed with isocyanate at a mass ratio of 1:4 to obtain the first curing agent. The mass ratio of dipentaerythritol to polypropylene glycol is 1:3.

[0218] 1-4) The first modified epoxy resin, the first curing agent, and the insulating material PPO (relative molecular weight 4000-6000) are mixed evenly at a mass ratio of 20:16:1 to obtain a first intermediate product; the co-solvent ethylene glycol isooctyl ether and the wetting agent polyether-modified siloxane are added to the first intermediate product and mixed evenly to obtain a second intermediate product; then, formic acid is added as a neutralizing agent to the second intermediate product, and after emulsification with water, a slurry for preparing an electrophoretic coating is obtained. The co-solvent ethylene glycol isooctyl ether accounts for 1.0% of the mass fraction of the second intermediate product, and the wetting agent polyether-modified siloxane accounts for 0.5% of the mass fraction of the second intermediate product.

[0219] 1-5) The casing (aluminum casing) of the battery cell is placed in the aforementioned slurry and electrophoresed in a closed circuit with a DC power supply and an anode to obtain a casing with an electrophoretic coating. At this time, the electrophoretic coating is a wet film.

[0220] 1-6) Rinse the shell prepared in 1-5) with ultrapure water and dry it. Place it in an oven and bake at 180°C for 20 minutes to obtain a shell with an electrophoretic coating.

[0221] (2) Preparation of powder coating

[0222] 2-1) E12 epoxy resin (a bisphenol A type solid epoxy resin product), Amanda969 (a hydroxyl-terminated linear phenolic curing agent), benzyltriethylammonium chloride (an amine catalyst), pigments and fillers, aluminum hydroxide (a flame retardant), alumina (an insulating material), and benzoin were mixed in a mixer at a mass ratio of 55:6:0.5:30:5:3:0.5 to obtain the third intermediate product.

[0223] 2-2) The third intermediate product, i.e. the blend in 2-1), is placed in a twin-screw extruder for melt blending and then extruded.

[0224] 2-3) The extrudate from 2-2) is compressed into tablets, cooled, and then sliced ​​using a slicer to obtain the fourth intermediate product.

[0225] 2-4) The fourth intermediate product is placed in a pulverizer and pulverized into powder particles. Then the powder particles are sent to a cyclone separator for classification. Large particles are sent to the pulverizer for further grinding and pulverization, while small particles are sent to the next step.

[0226] 2-5) Sieve the small particles from 2-4) and select powder particles of the required size to obtain powder for electrostatic spraying.

[0227] 2-6) The powder from 2-5) is electrostatically sprayed onto the shell from 1-6), and then the shell is placed in an oven and baked at 200°C for 15 minutes to obtain a shell with an insulating coating.

[0228] In the shell of Example 1, the thickness of the electrophoretic coating is h1 = 80 μm, the thickness of the powder coating is h2 = 100 μm, and the thickness of the insulating coating is h = h1 + h2 = 180 μm.

[0229] Examples 2-5

[0230] The difference between Example 1 and Example 2 is that the thickness h2 of the powder coating is different.

[0231] Examples 6-9

[0232] The difference between Example 1 and Example 2 is that the thickness h1 of the electrophoretic coating is different.

[0233] Examples 10-12

[0234] Compared with Embodiment 1, the difference is that the thickness of the powder coating is h2 = 110 μm, and the thickness of the electrophoretic coating is h1 = 70 μm, 80 μm, and 90 μm, respectively.

[0235] Comparative Examples 1-4

[0236] Compared with Example 1, the shells in Comparative Examples 1-4 were only provided with an electrophoretic coating with thicknesses of 60 μm, 80 μm, 90 μm, and 180 μm, respectively.

[0237] Comparative Examples 5-8

[0238] Compared with Example 1, the shells in Comparative Examples 5-8 were only provided with powder coatings with thicknesses of 70 μm, 100 μm, 120 μm, and 180 μm, respectively.

[0239] Product parameters and performance parameters of Examples 1-12 and Comparative Examples 1-8.

[0240] Table 1: Product parameters and performance parameters of Examples 1-12 and Comparative Examples 1-8

[0241] In Table 1, "h1" represents the thickness of the electrophoretic coating, "h2" represents the thickness of the powder coating, "h" represents the thickness of the insulating coating, "v" represents the DC withstand voltage of the coating on the shell, "insulation resistance" represents the insulation resistance of the insulating coating on the shell, "leakage current" represents the leakage current test of the coating under DC 7.2kV for 60s. If the leakage current is less than 0.1mA, it is considered a pass; if it is greater than or equal to 0.1mA, it is considered a fail. "Adhesive strength" represents the adhesive strength between the insulating coating on the shell and the shell body.

[0242] Comparative analysis of the embodiments and comparative examples shows that the DC withstand voltage capability of embodiments 1-12 is significantly higher than that of comparative examples 1-8; in the leakage current test, the leakage current of the embodiments is less than 0.1mA, while the comparative examples fail the leakage current test; the insulation resistance of the embodiments is higher than that of the comparative examples. Therefore, it is demonstrated that the embodiments exhibit superior withstand voltage insulation performance compared to the comparative examples. Furthermore, the insulating film layer of the embodiments has good adhesive strength, and by setting different coating thicknesses, it can achieve uniform spacing and a peel-like appearance. When applied to secondary battery casings, it enables high-capacity, high-voltage secondary battery casings to have reliable high-voltage insulation.

[0243] Comparative analysis of Examples 1-5 shows that the DC withstand voltage and insulation resistance of Examples 1-3 all increase with the increase of the powder coating thickness h2. This indicates that within the range of h2 (70μm-120μm), a larger h2 results in a higher DC withstand voltage and better withstand voltage performance of the insulating coating; a larger h2 also results in a smaller leakage current and better insulation performance of the insulating coating. In Example 4, the powder coating thickness is relatively small (60μm), and its DC withstand voltage and insulation resistance decrease significantly compared to Example 2. In Example 5, although the powder coating thickness is relatively large (130μm), its DC withstand voltage only increases by 0.1kV compared to Example 3, and its insulation resistance only decreases by 0.2GΩ. This indicates that when h2 is below the above range, the withstand voltage and insulation performance are relatively poor; when h2 is above the above range, further increasing h2 does not significantly improve the withstand voltage and insulation performance of the insulating coating. Furthermore, in Example 3, when h2 was 120 μm, the insulating coating already exhibited a slight orange peel appearance; in Example 5, where h2 was further increased to 130 μm, the insulating coating exhibited an orange peel appearance. Moreover, the adhesive strength in Examples 3 and 5 showed a significant decrease. This indicates that further increasing h2 beyond the aforementioned range leads to more severe orange peel, which affects the uniformity of the insulating coating, consequently preventing further improvement or even reducing the voltage withstand and insulation properties of the insulating coating. Furthermore, an excessively thick powder coating is also detrimental to the adhesive strength between the insulating coating and the shell.

[0244] In summary, the embodiments of this application, by controlling the thickness h2 of the powder coating within a suitable range, can improve the insulation performance and withstand voltage performance of the insulating coating, while also enabling the insulating coating to obtain a uniform, orange-peel-free appearance.

[0245] Comparative analysis of Examples 1 and 6-9 shows that the DC withstand voltage and insulation performance of Examples 1 and 5-7 both increase with the increase of the electrophoretic coating thickness h1. This indicates that within the range of h1 (60μm-90μm), the larger h1 is, the higher the DC withstand voltage and the better the withstand voltage performance of the insulating coating; the larger h1 is, the smaller the leakage current and the better the insulation performance of the insulating coating. In Example 8, the electrophoretic coating thickness is relatively small (50μm), and its DC withstand voltage is lower than that of Example 2, while the insulation impedance is significantly reduced. In Example 9, although the electrophoretic coating thickness is large (100μm), the DC withstand voltage and insulation performance of the insulating coating are both inferior to those of Example 7. This indicates that when h1 is below the above range, the insulation performance of the insulating coating is relatively poor; when h1 is above the above range, the DC withstand voltage and insulation performance of the insulating coating decrease. Furthermore, in Example 9, when h1 is 100μm, the insulating coating is already non-uniform. This proves that when the thickness h1 of the electrophoretic coating exceeds the above range, the uniformity of the electrophoretic coating deteriorates, which in turn leads to a deterioration in the uniformity of the insulating coating, resulting in a decrease in the voltage withstand performance and insulation performance of the insulating coating.

[0246] In summary, the embodiments of this application, by controlling the thickness h1 of the electrophoretic coating within a suitable range, can improve the insulation performance and withstand voltage performance of the insulating coating, while also enabling the insulating coating to obtain a uniform, orange-peel-free appearance.

[0247] Analysis of examples 10-12 shows that when the overall insulating coating is thick, a slight orange peel effect is likely to appear, and if it is too thick, unevenness in the insulating coating is likely to occur. Therefore, h1 and h2 can be adjusted within appropriate ranges as needed to obtain the best withstand voltage insulation performance and appearance.

[0248] The comparative analysis of Examples 1-4 shows that while a single electrophoretic coating can increase its pressure resistance and insulation performance to some extent with increasing thickness, its pressure resistance and insulation performance are far inferior to those of the embodiments. Referring to Example 1 and Comparative Example 4, even if the thickness of the single electrophoretic coating is set to be the same as the thickness of the insulating coating, the single electrophoretic coating cannot achieve the same pressure resistance and insulation performance as the insulating coating.

[0249] The comparative analysis of Examples 5-8 shows that while a single powder coating can increase its pressure resistance and insulation performance to some extent with increasing thickness, its pressure resistance and insulation performance are far inferior to those of the examples. Referring to Example 1 and Comparative Example 8, even if the thickness of the single powder coating is set to be the same as the thickness of the insulating coating, the single powder coating cannot achieve the same pressure resistance and insulation performance as the insulating coating.

[0250] In summary, the insulating coating provided in this application has a double-layer structure, which can achieve excellent high-voltage insulation performance, while also having a uniform, orange-peel-free appearance, thereby improving the insulation performance, high-voltage resistance, and aesthetics of the battery cell casing.

[0251] The following is a brief description of the testing methods for the physicochemical and performance parameters involved in the embodiments of this application. It should be understood that the following testing methods are only examples, and other testing methods known in the art can also be used for testing.

[0252] 1. Test method for coating thickness

[0253] The measurement method can be found in GB / T 13452.2-2008.

[0254] For example, coating thickness can be measured mechanically. Specifically, a micrometer or dial indicator can be used. There are two main testing methods in practice.

[0255] One method is a destructive approach, which involves first measuring the total thickness of a specified area, then removing the coating from the measured area and measuring the thickness of the substrate in that area again. The difference between the two measurements is the coating thickness.

[0256] Another method is a non-destructive method, which involves first measuring the thickness of the substrate in a specified area, and then measuring the total thickness of that area after the coating is prepared. The difference between the two is the thickness of the coating.

[0257] 2. DC withstand voltage test method

[0258] The measurement method can be found in GB / T 1408.2-2016.

[0259] A short-time (rapid) DC test can be performed using electrodes with diameters of 25mm / 25mm. A uniformly thick sample (insulating coating) is clamped between the two electrodes using a fixture. The control valve's voltage ramp rate is set to 2KV / s. Upon opening the control valve, the equipment will alarm upon completion of the test, and the voltage displayed on the meter will be the DC withstand voltage. The insulating coating can be obtained by preparing an insulating coating on a peelable substrate and then removing the peelable substrate.

[0260] 3. Leakage current test method

[0261] Using a conformal gauge, apply a force of ≥1.5 kgf to the large surface of the casing, ensuring the voltage rises from zero to the specified voltage in <1 second. Apply the specified (DC) voltage to the test sample with uniform thickness and maintain the voltage for 60 seconds. The edge of the conformal gauge should be 5 ± 0.5 mm from the coating edge, ensuring the breakdown point is not located at the edge. If no dielectric electrical breakdown or flashover occurs within the specified leakage current range, the test is considered passed; otherwise, it is considered failed.

[0262] 4. Test methods for bond strength

[0263] An insulating coating was prepared on a sample with an aluminum shell. The sample size was 100 mm × 25 mm × 1.6–2.5 mm. Following GB / T 7124, the sample with the insulating coating was fixed to a tensile testing machine using a fixture. The test was conducted at a speed of 5 mm / min, and data were collected. The adhesive strength (MPa) was calculated as: maximum force / adhesive area. This maximum force is the maximum stress applied by the testing machine when the insulating coating fails.

[0264] 5. Test methods for coating appearance

[0265] An orange peel analyzer can be used to test the surface of the coating. The orange peel condition is determined based on the measured DOI value. Specifically, if the long wave (LW) and short wave (SW) values ​​are ≤10 and the DOI value is ≥90, it is evaluated as no orange peel; if 10 ≤ long wave (LW) and short wave (SW) values ​​are ≤30 and 80 ≤ DOI value is ≤90, it is evaluated as slight orange peel; if long wave (LW) and short wave (SW) values ​​are ≥30 and the DOI value is ≤80, it is judged as orange peel.

[0266] Uniformity can be judged by visual observation and color difference. Specifically, if there are obvious spots on the surface of the coating, the uniformity is poor and it is not uniform; if there are no obvious spots on the surface, the color difference ΔE ≥ 3.0, the uniformity is relatively poor and it is not uniform; if there are no obvious spots on the surface, the color difference 1.0 ≤ ΔE ≤ 3.0, the uniformity is good and it is uniform; if there are no obvious spots on the surface, the color difference ΔE ≤ 1.0, the uniformity is excellent and it is uniform.

[0267] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A battery cell, characterized in that, The battery cell includes: Housing and electrode assembly disposed within the housing; The outer shell includes a body and an insulating coating disposed on the outer surface of the body; The insulating coating includes: An electrophoretic coating is disposed on the outer surface of the body; A powder coating is disposed on the electrophoretic coating.

2. The battery cell according to claim 1, characterized in that, The thickness h1 of the electrophoretic coating satisfies: 60μm≤h1≤90μm; and / or, The thickness h2 of the powder coating satisfies: 70μm≤h2≤120μm.

3. The battery cell according to claim 2, characterized in that, 70μm≤h1≤80μm; and / or, 80μm≤h2≤100μm.

4. The battery cell according to any one of claims 1-3, characterized in that, The bonding strength p between the insulating coating and the body satisfies: 10MPa≤p≤20MPa.

5. The battery cell according to any one of claims 1-4, characterized in that, The DC withstand voltage v of the insulating coating satisfies: 12kV≤v≤21kV.

6. The battery cell according to any one of claims 1-5, characterized in that, The insulation resistance R of the insulating coating satisfies: 25GΩ≤R≤40GΩ.

7. The battery cell according to any one of claims 1-6, characterized in that, The raw materials for preparing the electrophoretic coating include a first insulating material, which includes polyphenylene ether, and the relative molecular weight Mr of the polyphenylene ether satisfies: 4000≤Mr≤6000.

8. The battery cell according to any one of claims 1-7, characterized in that, The raw materials for preparing the electrophoretic coating include a first modified epoxy resin, and the raw materials for preparing the first modified epoxy resin include the first epoxy resin and a first chain extender; wherein, The raw materials for preparing the first epoxy resin include at least one of bisphenol A type epoxy resin and phenolic type epoxy resin and a second chain extender; The first chain extender includes an amine chain extender, and the second chain extender includes bisphenol A.

9. The battery cell according to any one of claims 1-8, characterized in that, The raw materials for preparing the powder coating include a second insulating material, which includes at least one of alumina, silicon dioxide, and butyl rubber.

10. The battery cell according to any one of claims 1-9, characterized in that, The raw materials for preparing the powder coating include a second modified epoxy resin, which includes at least one of polyether epoxy resin, polyester epoxy resin, and polyurethane epoxy resin.

11. The battery cell according to any one of claims 1-10, characterized in that, The capacity of the battery cell is greater than or equal to 280Ah.

12. A secondary battery, characterized in that, The secondary battery includes a battery cell as described in any one of claims 1-11.

13. An electrical appliance, characterized in that, The electrical device includes a battery cell as described in any one of claims 1-11, and / or a secondary battery as described in claim 12.

14. A method for preparing a battery cell according to any one of claims 1-11, characterized in that, include: Prepare the raw materials for electrophoretic coating and powder coating respectively; The raw materials for the electrophoretic coating are used to electrophoretically coat the body of the battery cell casing to form an electrophoretic coating on the outer surface of the body. The body is electrostatically sprayed with the raw material of the powder coating to form a powder coating on the electrophoretic coating, thereby obtaining a shell with an insulating coating. The electrode assembly is placed in the housing with the insulating coating to obtain the battery cell.

15. The method according to claim 14, characterized in that, After electrophoretically coating the bulk material using the raw material of the electrophoretic coating, the method includes: Rinse and air dry the outer casing; The outer shell is baked at 160℃-180℃ for 20min-30min to form the electrophoretic coating.

16. The method according to claim 14 or 15, characterized in that, After electrostatically spraying the body using the raw material of the powder coating, the method includes: The outer shell is baked at 180℃-280℃ for 20min-30min to form the powder coating.

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