Battery shell, preparation method thereof and secondary battery

Abstract

The invention relates to the technical field of batteries, in particular to a battery shell, a preparation method thereof and a secondary battery. The battery shell comprises a shell and a heat-conducting insulating coating covering the shell; the heat-conducting insulating coating is prepared from the following raw materials in parts by weight: 40 to 60 parts of waterborne epoxy resin, 10 to 30 parts of curing agent, 5.1 to 20.5 parts of modified filler, 0.2 to 2 parts of flatting agent and 2 to 6 parts of flame retardant; the modified filler comprises a heat-conducting filler and a silane coupling agent loaded on the heat-conducting filler; the mass ratio of the heat-conducting filler to the silane coupling agent is (5-20): (0.1-0.5). The shell is covered with the heat-conducting insulating coating, so that the insulating performance, the heat dissipation performance and the high-temperature protection performance of the battery shell can be effectively improved, the use safety of the battery is improved, and the heat management energy consumption of the battery is reduced.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a battery casing and a preparation method thereof, and a secondary battery. Background Art

[0002] The large-scale use of traditional fossil fuels has led to increasingly serious problems such as resource shortages and environmental pollution. It is of great significance to accelerate the transformation of energy structure and develop clean and renewable new energy. Among them, lithium-ion batteries are widely used in 3C products, energy storage systems and power batteries due to their high energy density, long cycle life, good rate performance and low cost.

[0003] In traditional lithium-ion batteries, the cell shell is mostly made of conductive and easily charged metal aluminum shell. In order to ensure the safety of battery use, it is usually necessary to perform insulation protection treatment on the outer surface of the cell. At present, lithium-ion batteries generally have a layer of blue film on the metal aluminum shell as a protective film to provide insulation protection and wear protection. However, the blue film has defects such as low thermal conductivity, high temperature resistance and flammability, which seriously limits the heat dissipation performance and high temperature protection performance of the battery. Summary of the invention

[0004] Based on this, it is necessary to provide a battery housing and a preparation method thereof and a secondary battery to solve the problem that the thermal conductivity of the blue film is low, which seriously hinders the heat dissipation of the lithium-ion battery.

[0005] The above-mentioned purpose of the present application is achieved through the following technical solutions:

[0006] In a first aspect of the present application, a battery housing is provided, comprising a shell and a thermally conductive insulating coating covering the shell;

[0007] The thermally conductive insulating coating comprises the following raw materials in parts by weight:

[0008] 40~60 parts of waterborne epoxy resin,

[0009] 10~30 parts of curing agent,

[0010] Modified filler 5.1~20.5 parts,

[0011] 0.2~2 parts of leveling agent, and

[0012] 2~6 parts of flame retardant;

[0013] The modified filler includes a thermally conductive filler and a silane coupling agent loaded on the thermally conductive filler;

[0014] The mass ratio of the thermal conductive filler to the silane coupling agent is (5-20): (0.1-0.5).

[0015] In one embodiment, the thermally conductive filler includes one or more of aluminum nitride, boron nitride, silicon nitride, aluminum oxide, magnesium oxide, zinc oxide, beryllium oxide and silicon oxide.

[0016] In one embodiment, the silane coupling agent includes one or more of 3-aminopropyltriethoxysilane, 3-(isomethacryloyloxy)propyltrimethoxysilane, γ-aminopropyltrimethoxysilane and 3-glycidyloxypropyltrimethoxysilane.

[0017] In one embodiment, the water-based epoxy resin includes one or more of bisphenol A epoxy resin, tetrabromobisphenol A epoxy resin, fluorinated epoxy resin, novolac epoxy resin and glycidylamine epoxy resin.

[0018] In one embodiment, the curing agent includes one or more of an amine curing agent, an anhydride curing agent, an imidazole curing agent and a hydrazide curing agent.

[0019] In one embodiment, the leveling agent includes one or more of polyethylene glycol, polyethyleneimine, polydimethylsiloxane, polymethylphenylsiloxane, and polyacrylic acid fluoride ester.

[0020] In one embodiment, the flame retardant includes one or more of silicon dioxide, talc, aluminum hydroxide, ammonium phosphate and tetrabromobisphenol A bis(dibromopropyl) ether.

[0021] In one embodiment, the thermally conductive insulating coating further includes 0.1 to 1 part of a pigment, and the pigment includes one or more of iron oxide red, iron oxide blue, phthalocyanine blue, phthalocyanine green, molybdenum chrome red and chrome yellow.

[0022] In one embodiment, the thickness of the thermally conductive insulating coating is 100 μm to 300 μm;

[0023] A plurality of grooves are provided on a side of the shell facing the thermally conductive insulating coating, wherein the depth of the grooves is less than the thickness of the shell, and the depth of the grooves is less than the thickness of the thermally conductive insulating coating.

[0024] In one embodiment, the depth of the groove is 2% to 30% of the thickness of the shell.

[0025] In a second aspect of the present application, a method for preparing the battery casing as described above is provided, comprising the following steps:

[0026] Provide water-based coatings containing water-based epoxy resin, curing agent, modified filler, leveling agent, flame retardant and pigment;

[0027] Covering the water-based paint on the shell to form a liquid film;

[0028] The liquid film is cured at 80° C. to 160° C. for 2 h to 4 h to form a thermally conductive insulating coating.

[0029] In one embodiment, the preparation method of the water-based coating comprises the following steps:

[0030] The modified filler is uniformly dispersed in the waterborne epoxy resin to obtain a glue solution;

[0031] Mixing the glue, the curing agent, the leveling agent, the flame retardant, the pigment and the water to obtain the water-based paint;

[0032] Wherein, the preparation method of the modified filler comprises the following steps:

[0033] Mixing the thermally conductive filler, the silane coupling agent and the solvent, and performing a modification reaction at 60° C. to 80° C. for 4 h to 6 h, so that the silane coupling agent is loaded on the thermally conductive filler, to obtain a mixture;

[0034] The mixture is subjected to purification, grinding and screening to obtain the modified filler.

[0035] In one embodiment, before the step of covering the shell with the water-based paint, the following steps are also included:

[0036] A plurality of grooves are formed on a side of the housing facing the thermally conductive insulating coating layer by a press forming method.

[0037] In a third aspect of the present application, a secondary battery is provided, comprising the battery casing as described above, or comprising a battery casing manufactured by the method for manufacturing the battery casing as described above.

[0038] This application has at least the following beneficial effects:

[0039] The present application adopts water-based epoxy resin with high resistivity, low dielectric loss, excellent mechanical properties, good chemical stability and high temperature resistance as the matrix, so that the thermally conductive insulating coating has good insulation, mechanical strength and high temperature resistance; adopts thermally conductive fillers with high insulation and high thermal conductivity, and loads silane coupling agents on its surface, so that it can be evenly dispersed in the thermally conductive insulating coating, and constructs a stable and perfect thermal conductive network and insulation network, so that the thermally conductive insulating coating has excellent insulation high voltage resistance and thermal conductivity; curing agent is used to cure the washed epoxy resin, flame retardant is used to improve the flame retardant effect, and leveling agent is used to form a flat and uniform coating without bubbles. The raw materials such as water-based epoxy resin, curing agent, modified filler and the like in a specific ratio are made into a thermally conductive insulating coating, and the thermally conductive insulating coating is covered on the shell, which can effectively improve the insulation performance, heat dissipation performance and high temperature protection performance of the battery shell, thereby improving the safety of the battery and reducing the thermal management energy consumption of the battery. In addition, the production process of the battery shell provided by the present application is simple, environmentally pollution-free, and low in preparation cost, which is very suitable for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present application and to more completely understand the present application and its beneficial effects, the following is a brief introduction to the drawings required for the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can obtain other drawings based on these drawings without creative work.

[0041] Figure 1 is a schematic structural diagram of a battery housing in one embodiment;

[0042] Figure 2 is a schematic cross-sectional view of a housing in one embodiment;

[0043] Figure 3 Schematic diagram of the structure of a shell in one embodiment.

[0044] Figure 4 The figure is a schematic flow chart of a method for preparing a battery casing in one embodiment.

[0045] Reference numerals: housing 10, thermally conductive insulating coating 20, groove 11, thickness d of the housing 10 , the thickness d of the thermally conductive insulating coating 20 20 , the depth of the groove d 11 . DETAILED DESCRIPTION

[0046] In order to facilitate the understanding of the present application, the present application is further described in detail below in conjunction with specific embodiments. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0048] In the present application, the meaning of "and / or" includes any and all combinations of one or more related listed items. "At least one" means more than one, such as one, two and more than two. "Multiple" or "several" means at least two, such as two, three, etc., and "multi-layer" means at least two layers, such as two layers, three layers, etc., unless otherwise clearly and specifically defined. In the description of the present application, "several" means at least one, such as one, two, etc., unless otherwise clearly and specifically defined.

[0049] When a numerical range is disclosed in this application, the above range is considered to be continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed in this application should be understood to include any and all subranges included therein.

[0050] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0051] In this application, "above" or "below" includes the number itself. For example, "1 below" includes 1.

[0052] The temperature parameters in this application, unless otherwise specified, are allowed to be either constant temperature treatment or to vary within a certain temperature range. It should be understood that the constant temperature treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument. Fluctuations within the range of ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are allowed.

[0053] In the present application, room temperature refers to indoor temperature, normal temperature or general temperature. Generally speaking, the range of room temperature can be any one of the following temperature intervals: 23°C ± 2°C, 25°C ± 5°C or 20°C ± 5°C.

[0054] In traditional lithium-ion batteries, the cell shells are mostly made of conductive and easily charged metal aluminum shells. In order to ensure the safety of battery use, the outer surface of the cell usually needs to be insulated and protected. At present, lithium-ion batteries generally have a layer of blue film on the metal aluminum shell as a protective film to provide insulation and wear protection. Blue film is a single-sided tape made of a pressure-sensitive adhesive (PSA) on the back of a polyethylene terephthalate (PET) substrate. This type of product is mostly dark blue, so it is usually referred to as "blue film". The blue film has good insulation and tensile strength, and can achieve insulation protection for the battery shell.

[0055] In a battery pack, thermal management design for the battery is crucial. Good heat dissipation performance of the battery can effectively guarantee the lifespan while improving safety. However, the blue film made of PET material has defects such as low thermal conductivity and high temperature resistance. On the one hand, the existence of the blue film with low thermal conductivity hinders the heat dissipation of the battery. On the other hand, the blue film is not resistant to high temperatures and is flammable, which makes the battery unable to be effectively protected at high temperatures. At the same time, the process of coating the battery cell with blue film involves problems such as folding and easy generation of bubbles, which further reduces the heat dissipation performance of the battery cell.

[0056] In order to simplify the production process of battery cells and reduce costs, some reports have proposed to achieve insulation protection by spraying insulating paint on the outer surface of the battery shell. However, traditional insulating paints often use high molecular polymers with low thermal conductivity as the matrix, which significantly hinders the heat dissipation performance of the battery.

[0057] Based on this, in the first aspect of the present application, a battery housing is provided to solve the problem that the thermal conductivity of the blue film is low, which seriously hinders the heat dissipation of the lithium-ion battery.

[0058] See also Figure 1 , which is a schematic diagram of the structure of a battery housing in one embodiment. Figure 1 As shown, the battery housing includes a shell 10 and a thermally conductive insulating coating 20 covering the shell 10;

[0059] The thermally conductive insulating coating 20 includes the following raw materials in parts by weight:

[0060] 40~60 parts of waterborne epoxy resin,

[0061] 10~30 parts of curing agent,

[0062] Modified filler 5.1~20.5 parts,

[0063] 0.2~2 parts of leveling agent, and

[0064] 2~6 parts of flame retardant;

[0065] The modified filler includes a thermally conductive filler and a silane coupling agent loaded on the thermally conductive filler;

[0066] The mass ratio of thermal conductive filler to silane coupling agent is (5~20): (0.1~0.5).

[0067] The present application adopts water-based epoxy resin with high resistivity, low dielectric loss, excellent mechanical properties, good chemical stability and high temperature resistance as the matrix, so that the thermally conductive insulating coating 20 has good insulation, mechanical strength and high temperature resistance; adopts a thermally conductive filler with high insulation and thermal conductivity, and loads a silane coupling agent on its surface, so that it can be evenly dispersed in the thermally conductive insulating coating 20, and constructs a stable and perfect thermal conductive network and insulation network, so that the thermally conductive insulating coating 20 has excellent insulation high voltage resistance and thermal conductivity; the curing agent is used to cure the washed epoxy resin, the flame retardant is used to improve the flame retardant effect, and the leveling agent is used to form a flat and uniform coating without bubbles. The raw materials such as water-based epoxy resin, curing agent, modified filler and the like in a specific ratio are made into a thermally conductive insulating coating 20, and the thermally conductive insulating coating 20 is covered on the housing 10, which can effectively improve the insulation performance, heat dissipation performance and high temperature protection performance of the battery shell, thereby improving the safety of the battery and reducing the thermal management energy consumption of the battery. In addition, the production process of the battery shell provided by the present application is simple, environmentally pollution-free, and low in preparation cost, which is very suitable for mass production.

[0068] As an example, in the thermally conductive insulating coating 20, the weight proportions of the water-based epoxy resin include but are not limited to 40 parts, 42 parts, 44 parts, 46 parts, 48 ​​parts, 50 parts, 52 parts, 54 parts, 56 parts, 58 parts or 60 parts, and can be further selected as 40 parts to 50 parts; the weight proportions of the curing agent include but are not limited to 10 parts, 12 parts, 14 parts, 16 parts, 18 parts, 20 parts, 22 parts, 24 parts, 26 parts, 28 parts or 30 parts, and can be further selected as 10 parts to 15 parts; the weight proportions of the modified filler include but are not limited to 5.1 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts, 16 parts, 17 parts, 18 parts, 19 parts, 20 parts or 20.5 parts, and can be further selected from 6 parts to 16 parts; the weight proportions of leveling agent include but are not limited to 0.2 parts, 0.4 parts, 0.6 parts, 0.8 parts, 1 part, 1.2 parts, 1.4 parts, 1.6 parts, 1.8 parts or 2 parts, and can be further selected from 1 part to 2 parts; the weight proportions of flame retardant include but are not limited to 2 parts, 2.2 parts, 2.5 parts, 2.8 parts, 3 parts, 3.2 parts, 3.5 parts, 3.8 parts, 4 parts, 4.2 parts, 4.5 parts, 4.8 parts, 5 parts, 5.2 parts, 5.5 parts, 5.8 parts or 6 parts, and can be further selected from 2 parts to 4 parts.

[0069] As an example, in the modified coating, the mass ratio of the thermally conductive filler to the silane coupling agent includes but is not limited to 5:0.1, 10:0.1, 15:0.1, 20:0.1, 5:0.2, 10:0.2, 15:0.2, 20:0.2, 5:0.3, 10:0.3, 15:0.3, 20:0.3, 5:0.4, 10:0.4, 15:0.4, 20:0.4, 5:0.5, 10:0.5, 15:0.5 or 20:0.5, and can be further selected as (6~15):(0.2~0.5), and further selected as (12~15):(0.4~0.5).

[0070] Optionally, the modified filler includes the following raw materials in parts by weight: 5 to 20 parts of thermal conductive filler and 0.1 to 0.5 parts of silane coupling agent.

[0071] As an example, the weight proportion of thermally conductive filler includes but is not limited to 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts, 16 parts, 17 parts, 18 parts, 19 parts or 20 parts, and can be further selected as 6 parts to 15 parts, and further can be selected as 12 parts to 15 parts; the weight proportion of silane coupling agent includes but is not limited to 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts or 0.5 parts, and can be further selected as 0.2 parts to 0.5 parts, and further can be selected as 0.4 parts to 0.5 parts.

[0072] Optionally, the thermally conductive filler includes one or more of aluminum nitride, boron nitride, silicon nitride, aluminum oxide, magnesium oxide, zinc oxide, beryllium oxide and silicon oxide.

[0073] Optionally, the silane coupling agent includes one or more of 3-aminopropyltriethoxysilane, 3-(methacryloyloxy)propyltrimethoxysilane, γ-aminopropyltrimethoxysilane and 3-glycidoxypropyltrimethoxysilane.

[0074] In this embodiment, the silane coupling agent can not only be loaded on the surface of the thermally conductive filler, so that the modified filler has good dispersion uniformity in the epoxy resin matrix, thereby constructing a complete and stable thermally conductive insulation network, but also can significantly improve the bonding strength between the thermally conductive insulation coating 20 and the shell 10, thereby preventing the thermally conductive insulation coating 20 from falling off.

[0075] Optionally, the waterborne epoxy resin includes one or more of bisphenol A epoxy resin, tetrabromobisphenol A epoxy resin, fluorinated epoxy resin, novolac epoxy resin and glycidylamine epoxy resin.

[0076] Optionally, the curing agent includes one or more of an amine curing agent, an acid anhydride curing agent, an imidazole curing agent and a hydrazide curing agent.

[0077] Optionally, the amine curing agent includes one or more of aliphatic polyamine curing agents, aromatic amine curing agents and dicyandiamide curing agents. As an example, aliphatic polyamine curing agents include but are not limited to ethylenediamine (EDA), diethylenetriamine (DETA) and triethylenetetramine (TETA); aromatic amine curing agents include but are not limited to metaphenylenediamine (MPD), diaminodiphenylmethane (DDM) and diaminodiphenyl sulfone; dicyandiamide curing agents include but are not limited to dicyandiamide, dicyandiamide-aliphatic polyamine adducts, dicyandiamide-epoxy resin adducts, dicyandiamide-carboxylic acid compound adducts and dicyandiamide-imidazoline compound adducts.

[0078] Optionally, the anhydride curing agent includes one or more of phthalic anhydride (PA), methyltetrahydrophthalic anhydride (MeTHPA) and pyromellitic dianhydride (PMDA).

[0079] Optionally, the imidazole curing agent includes one or more of 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole and 2-phenyl-4-methylimidazole.

[0080] Optionally, the hydrazide curing agent includes one or more of adipic acid dihydrazide, sebacic acid dihydrazide and isophthalic acid dihydrazide.

[0081] Optionally, the leveling agent includes one or more of polyethylene glycol, polyethyleneimine, polydimethylsiloxane, polymethylphenylsiloxane and polyacrylic fluoride ester.

[0082] Optionally, the flame retardant includes one or more of silicon dioxide, talc, aluminum hydroxide, ammonium phosphate and tetrabromobisphenol A bis(dibromopropyl) ether.

[0083] Optionally, the thermally conductive insulating coating 20 further includes 0.1 to 1 part of a pigment, and the pigment includes one or more of iron oxide red, iron oxide blue, phthalocyanine blue, phthalocyanine green, molybdenum chrome red and chrome yellow.

[0084] As an example, in the thermally conductive insulating coating 20, the weight proportion of the pigment includes but is not limited to 0.1 part, 0.2 part, 0.3 part, 0.4 part, 0.5 part, 0.6 part, 0.7 part, 0.8 part, 0.9 part or 1 part, and can be further optionally 0.5 part to 0.8 part.

[0085] like Figure 1 As shown, the thickness of the housing 10 is denoted as d 10 The thickness of the thermal conductive insulating coating 20 is denoted as d 20 .

[0086] Optionally, the thickness d of the thermally conductive insulating coating 20 is 20 It is 100μm~300μm.

[0087] As an example, the thickness d of the thermally conductive insulating coating 20 is 20 Including but not limited to 100μm, 120μm, 140μm, 160μm, 180μm, 200μm, 220μm, 240μm, 260μm, 280μm or 300μm.

[0088] Optionally, the thickness d of the housing 10 10 It is 0.2mm~1.2mm.

[0089] As an example, the thickness d of the housing 10 is 10 Including but not limited to 0.2mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1mm, 1.1mm or 1.2mm.

[0090] Optionally, the shell 10 includes one or more of an aluminum shell, a steel shell and an aluminum alloy shell, and can further be an aluminum shell.

[0091] See also Figure 2 and Figure 3 , Figure 2 is a schematic cross-sectional view of a housing in an embodiment, Figure 3 FIG. 1 is a schematic diagram of the structure of a housing in an embodiment. Figure 2 As shown, the depth of the groove 11 is denoted as d 11 .

[0092] Optionally, a plurality of grooves 11 are provided on one side of the housing 10 facing the heat-conducting insulating coating 20, and the depth d of the grooves 11 is 11 Less than the thickness d of the housing 10 10 , the depth d of the groove 11 11 Less than the thickness d of the thermally conductive insulating coating 20 20 .

[0093] It can be understood that when a plurality of grooves 11 are provided on the side of the housing 10 facing the heat-conducting insulating coating 20, the thickness d of the heat-conducting insulating coating 20 is 20 The depth d of the groove 11 is the maximum thickness of the heat-conducting insulating coating 20, that is, the vertical distance from the bottom wall of the groove 11 to the surface of the heat-conducting insulating coating 20 away from the housing 10. 11 Less than the thickness d of the thermally conductive insulating coating 20 20 Therefore, the thermally conductive insulating coating 20 can completely fill the inside of the groove 11 and cover the groove 11, and the thermally conductive insulating coating 20 completely covers all surfaces of the shell 10 facing the side of the thermally conductive insulating coating 20 and forms a continuous thermally conductive insulating sleeve.

[0094] The shell 10 will be slightly deformed during the charging and discharging process of the battery. The smooth and flat shell surface is prone to cause the thermal conductive insulating coating 20 to fall off after deformation, thereby causing insulation protection failure. In view of the above findings, in this embodiment, a plurality of grooves 11 are provided on the side of the shell 10 facing the thermal conductive insulating coating 20, which can increase the contact area between the thermal conductive insulating coating 20 and the surface of the shell 10, improve the adhesion of the thermal conductive insulating coating 20, and effectively prevent the thermal conductive insulating coating 20 from falling off and cracking.

[0095] Optionally, the shape of the groove 11 includes one or more of a bar, a square, a diamond, a circle, an ellipse and an irregular shape.

[0096] Optionally, the grooves 11 may be regularly distributed or irregularly distributed. In some specific examples, the grooves 11 are regularly distributed and form a mesh structure. The regular mesh structure can further prevent the thermally conductive insulating coating 20 from cracking.

[0097] Optionally, the depth d of the groove 11 11 It is 2% to 30% of the thickness of the shell 10.

[0098] As an example, the depth d of the groove 11 is 11It may be 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28% or 30% of the thickness of the shell 10 .

[0099] Optionally, the depth d of the groove 11 11 20μm~300μm.

[0100] As an example, the depth d of the groove 11 is 11 Including but not limited to 20μm, 40μm, 60μm, 80μm, 100μm, 120μm, 140μm, 160μm, 180μm, 200μm, 220μm, 240μm, 260μm, 280μm or 300μm.

[0101] In a second aspect of the present application, a method for preparing a battery casing is provided, for preparing the battery casing as described above.

[0102] See also Figure 4 , which is a schematic diagram of a process for preparing a battery shell in one embodiment. Figure 4 As shown, the method for preparing a battery casing comprises the following steps:

[0103] S100: Provides water-based coatings containing water-based epoxy resin, curing agent, modified filler, leveling agent, flame retardant and pigment;

[0104] S200: Covering the shell with water-based paint to form a liquid film;

[0105] S300: Curing treatment at 80℃~160℃ for 2h~4h to solidify the liquid film to form a thermally conductive insulating coating.

[0106] Optionally, the preparation method of the modified filler comprises the following steps:

[0107] S111: mixing a thermal conductive filler, a silane coupling agent and a solvent, and performing a modification reaction at 60° C. to 80° C. for 4 h to 6 h, so that the silane coupling agent is loaded on the thermal conductive filler, to obtain a mixture;

[0108] S112: Purifying, grinding and screening the mixture to obtain a modified filler.

[0109] Optionally, in step S111, the mass ratio of the thermal conductive filler to the solvent is (5-20):100, and the solvent includes ethanol and water in a mass ratio of (85-95):(5-15).

[0110] As an example, the mass ratio of the thermally conductive filler and the solvent includes but is not limited to 5:100, 6:100, 7:100, 8:100, 9:100, 10:100, 11:100, 12:100, 13:100, 14:100, 15:100, 16:100, 17:100, 18:100, 19:100 or 20:100; the mass ratio of ethanol and water includes but is not limited to 85:5, 85:10, 85:15, 90:5, 90:10, 90:15, 95:5, 95:10 or 95:15.

[0111] As an example, in step S111, the reaction temperature of the modification reaction includes but is not limited to 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C or 80°C; the reaction time of the modification reaction includes but is not limited to 4h, 4.2h, 4.5h, 4.8h, 5h, 5.2h, 5.5h, 5.8h or 6h.

[0112] Optionally, in step S112, the purification treatment of the mixture includes one or more of filtration treatment, suction filtration treatment, filter press treatment, centrifugation treatment, washing treatment and drying treatment. In some specific examples, the purification treatment of the mixture includes the following steps: subjecting the mixture to suction filtration treatment and washing treatment, and drying at 60°C to 80°C for 12h to 24h; wherein the drying temperature of the drying treatment includes but is not limited to 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C or 80°C; the drying time of the drying treatment includes but is not limited to 12h, 14h, 16h, 18h, 20h, 22h or 24h.

[0113] Optionally, in step S112, the grinding process includes one or more of ball milling and sand milling, and the mesh size of the sieve used in the screening process is 100-400 mesh, wherein the particle size of the modified filler corresponding to the 100-mesh sieve is ≤150 μm, and the particle size of the modified filler corresponding to the 400-mesh sieve is ≤37.5 μm.

[0114] Optionally, the preparation method of the water-based coating comprises the following steps:

[0115] S121: uniformly dispersing the modified filler in the waterborne epoxy resin to obtain a glue solution;

[0116] S122: Mixing glue, curing agent, leveling agent, flame retardant, pigment and water to obtain water-based paint.

[0117] Optionally, in step S121, the modified filler is uniformly dispersed in the waterborne epoxy resin, comprising the following steps: adding the modified filler to the waterborne epoxy resin, stirring at 60°C to 80°C for 4h to 8h, and ultrasonically treating for 30min to 60min. The stirring temperature of the stirring treatment includes but is not limited to 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C or 80°C; the stirring time of the stirring treatment includes but is not limited to 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h or 8h; the ultrasonic time of the ultrasonic treatment includes but is not limited to 30min, 35min, 40min, 45min, 50min, 55min or 60min.

[0118] Optionally, the water-based coating includes 30 to 60 parts of water, including but not limited to 30 parts, 32 parts, 35 parts, 38 parts, 40 parts, 42 parts, 45 parts, 48 ​​parts, 50 parts, 52 parts, 55 parts, 58 parts or 60 parts.

[0119] Optionally, before step S200, that is, before the step of covering the shell with the water-based paint, the following step is also included: forming a plurality of grooves on the side of the shell facing the thermal conductive insulating coating by a press molding method.

[0120] Optionally, the press forming method includes one or more of a stamping method and a roll forming method.

[0121] Optionally, after forming the groove, the method further comprises the following steps: plasma cleaning the side of the shell having the groove. The plasma cleaning can improve the surface roughness and surface activity of the shell, thereby enhancing the adhesion between the shell and the thermally conductive insulating coating.

[0122] Optionally, in step S200, the method of covering the shell with the water-based paint includes one or more of a spraying method, a dipping method, a screen printing method and an inkjet printing method.

[0123] As an example, in step S300, the curing temperature of the curing treatment includes but is not limited to 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, 155°C or 160°C, and the curing temperature of the curing treatment includes but is not limited to 2h, 2.5h, 3h, 3.5h or 4h.

[0124] In a third aspect of the present application, a secondary battery is provided, comprising the battery casing as described above, or comprising a battery casing manufactured by the method for manufacturing the battery casing as described above.

[0125] Optionally, the secondary battery includes a positive electrode, a negative electrode, a separator and an electrolyte. During the charge and discharge process of the secondary battery, active ions (such as Li + 、Na + ) is inserted and removed back and forth between the positive and negative electrodes. The separator is set between the positive and negative electrodes, mainly to prevent the positive and negative electrodes from short-circuiting, and to allow active ions to pass through. The electrolyte is between the positive and negative electrodes, mainly to conduct active ions.

[0126] Optionally, the positive electrode sheet, the negative electrode sheet and the separator are made into an electrode assembly through a winding process or a lamination process.

[0127] Optionally, the secondary battery includes a battery housing as described above, which is used to encapsulate the electrode assembly and the electrolyte. The outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0128] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. In some specific examples, the shape of the secondary battery is square.

[0129] The following is further described in conjunction with specific embodiments and comparative examples. The raw materials involved in the following specific embodiments and comparative examples, unless otherwise specified, can all be commercially available, the instruments used, unless otherwise specified, can all be commercially available, and the processes involved, unless otherwise specified, are all routinely selected by those skilled in the art.

[0130] Example 1

[0131] Referring to Table 1, this embodiment provides a battery casing for packaging a square lithium-ion battery, and the preparation method thereof is as follows:

[0132] (1) Preparation of modified fillers:

[0133] 90 parts of anhydrous ethanol and 10 parts of deionized water were evenly mixed, and 0.3 parts of silane coupling agent (3-glycidyloxypropyltrimethoxysilane) and 9 parts of thermal conductive filler (aluminum nitride powder) were added respectively, and the reaction was carried out at 60°C for 6 hours to obtain a mixture; the mixture was filtered and washed, and then dried at 60°C for 24 hours; the dried product was crushed and ground, and then sieved with a 200-mesh sieve to obtain a modified filler.

[0134] (2) Preparation of water-based coatings:

[0135] 9.3 parts of modified filler were added to 60 parts of bisphenol A-based epoxy resin, stirred and dispersed at 60°C for 4 hours, and then ultrasonically treated for 30 minutes to obtain a glue solution; 20 parts of amine curing agent (ethylenediamine), 1 part of leveling agent (polydimethylsiloxane), 5 parts of flame retardant (silicon dioxide powder), 1 part of pigment (red iron oxide) and 40 parts of water were added to the glue solution, and stirring was continued at 60°C for 30 minutes to obtain a water-based coating.

[0136] (3) Pretreatment of the shell:

[0137] An aluminum shell with a thickness of 0.4 mm is used as the shell. A plurality of grooves are formed on one side of the shell by a stamping method. The depth of the grooves is 50 μm. The grooves are formed in a diamond shape and are distributed in a regular mesh. The side of the shell with the grooves is plasma cleaned to improve its surface roughness and surface activity.

[0138] (4) Formation of thermally conductive insulating coating:

[0139] The side of the shell with the groove is completely immersed in the water-based coating, taken out after dipping for 1 minute, and placed in an oven at 140°C for high-temperature curing for 2 hours to form a thermally conductive insulating coating with a thickness of 100 μm on the side of the shell with the groove, thereby obtaining a battery shell for encapsulating square lithium-ion batteries.

[0140] Example 2

[0141] Referring to Table 1, this embodiment provides a battery casing for packaging a square lithium-ion battery, and the preparation method thereof is as follows:

[0142] (1) Preparation of modified fillers:

[0143] 95 parts of anhydrous ethanol and 5 parts of deionized water were evenly mixed, and 0.5 parts of silane coupling agent (3-aminopropyltriethoxysilane) and 15 parts of thermal conductive filler (composed of aluminum oxide powder and magnesium oxide powder in a mass ratio of 1:1) were added respectively, and the reaction was carried out at 80°C for 4 hours to obtain a mixture; the mixture was filtered and washed, and then dried at 80°C for 12 hours; the dried product was crushed and ground, and then sieved with a 300-mesh sieve to obtain a modified filler.

[0144] (2) Preparation of water-based coatings:

[0145] 15.5 parts of modified filler were added to 50 parts of phenolic epoxy resin, stirred and dispersed at 80°C for 2 hours, and then ultrasonically treated for 60 minutes to obtain a glue solution; 15 parts of aromatic amine curing agent (meta-phenylenediamine), 0.5 parts of leveling agent (polymethylphenylsiloxane), 2 parts of flame retardant (tetrabromobisphenol A bis(dibromopropyl) ether), 0.5 parts of pigment (phthalocyanine blue) and 60 parts of water were added to the glue solution, and stirring was continued at 70°C for 20 minutes to obtain a water-based coating.

[0146] (3) Pretreatment of the shell:

[0147] An aluminum shell with a thickness of 0.6 mm is used as the shell. A plurality of grooves are formed on one side of the shell by a stamping method. The depth of the grooves is 100 μm. The grooves are formed in a diamond shape and are distributed in a regular mesh. The side of the shell with the grooves is plasma cleaned to improve its surface roughness and surface activity.

[0148] (4) Formation of thermally conductive insulating coating:

[0149] The water-based coating is sprayed evenly and slowly on the side of the shell with the groove to ensure that the outer surface is completely covered with a uniform liquid film on one side. After spraying, it is placed in a forced air drying oven at 80°C for constant temperature curing for 4 hours to form a thermally conductive insulating coating with a thickness of 140 μm on the side of the shell with the groove, thereby obtaining a battery shell for encapsulating square lithium-ion batteries.

[0150] Example 3

[0151] Referring to Table 1, this embodiment provides a battery casing for packaging a square lithium-ion battery, and the preparation method thereof is as follows:

[0152] (1) Preparation of modified fillers:

[0153] 95 parts of anhydrous ethanol and 5 parts of deionized water were evenly mixed, and 0.4 parts of silane coupling agent (γ-aminopropyltrimethoxysilane) and 12 parts of thermal conductive filler (composed of boron nitride powder and aluminum oxide powder in a mass ratio of 3:1) were added respectively, and the modified reaction was carried out at 70°C for 5 hours to obtain a mixture; the mixture was filtered and washed, and then dried at 70°C for 14 hours; the dried product was crushed and ground, and then sieved with a 150-mesh sieve to obtain a modified filler.

[0154] (2) Preparation of water-based coatings:

[0155] 12.4 parts of modified filler were added to 40 parts of fluorinated epoxy resin, stirred and dispersed at 70°C for 2 hours, and then ultrasonically treated for 45 minutes to obtain a glue solution; 10 parts of anhydride curing agent (hexahydrophthalic anhydride), 2 parts of leveling agent (polyethylene glycol), 3 parts of flame retardant (talc), 0.8 parts of pigment (molybdate chrome red) and 30 parts of water were added to the glue solution, and stirring was continued at 70°C for 45 minutes to obtain a water-based coating.

[0156] (3) Pretreatment of the shell:

[0157] An aluminum shell with a thickness of 0.8 mm is used as the shell. A plurality of grooves are formed on one side of the shell by a stamping method. The depth of the grooves is 150 μm. The grooves are formed in a diamond shape and are distributed in a regular mesh. The side of the shell with the grooves is plasma cleaned to improve its surface roughness and surface activity.

[0158] (4) Formation of thermally conductive insulating coating:

[0159] The side of the shell with the groove is completely immersed in the water-based coating, taken out after dipping for 0.5 minutes, and placed in an oven at 120°C for high-temperature curing for 2 hours to form a thermally conductive insulating coating with a thickness of 180 μm on the side of the shell with the groove, thereby obtaining a battery shell for encapsulating square lithium-ion batteries.

[0160] Example 4

[0161] Referring to Table 1, this embodiment provides a battery casing for packaging a square lithium-ion battery, and the preparation method thereof is as follows:

[0162] (1) Preparation of modified fillers:

[0163] 85 parts of anhydrous ethanol and 15 parts of deionized water were evenly mixed, and 0.2 parts of a silane coupling agent (3-(isobutyleneoxy)propyltrimethoxysilane) and 6 parts of a thermal conductive filler (composed of alumina powder and aluminum nitride powder in a mass ratio of 1:2) were added respectively, and the mixture was modified and reacted at 60°C for 6 hours to obtain a mixture; the mixture was filtered and washed, and then dried at 80°C for 20 hours; the dried product was crushed and ground, and then sieved with a 400-mesh sieve to obtain a modified filler.

[0164] (2) Preparation of water-based coatings:

[0165] 6.2 parts of modified filler were added to 45 parts of fluorinated epoxy resin, stirred and dispersed at 60°C for 4 hours, and then ultrasonically treated for 30 minutes to obtain a glue solution; 10 parts of aliphatic polyamine curing agent (diethylenetriamine), 0.4 parts of leveling agent (polymethylphenylsiloxane), 4 parts of flame retardant (composed of silica powder and ammonium phosphate powder in a mass ratio of 1:1), 0.2 parts of pigment (red iron oxide) and 55 parts of water were added to the glue solution, and stirring was continued at 70°C for 40 minutes to obtain a water-based coating.

[0166] (3) Pretreatment of the shell:

[0167] An aluminum shell with a thickness of 0.4 mm is used as the shell. A plurality of grooves are formed on one side of the shell by a stamping method. The depth of the grooves is 100 μm. The grooves are formed in a diamond shape and are distributed in a regular mesh. The side of the shell with the grooves is plasma cleaned to improve its surface roughness and surface activity.

[0168] (4) Formation of thermally conductive insulating coating:

[0169] By spraying, the water-based paint is evenly and slowly sprayed on the side of the shell with the groove to ensure that the outer surface is completely covered with a uniform liquid film on one side. After spraying, it is placed in a 100°C forced air drying oven for constant temperature curing for 2 hours to form a thermally conductive insulating coating with a thickness of 150μm on the side of the shell with the groove, thereby obtaining a battery shell for encapsulating square lithium-ion batteries.

[0170] Example 5

[0171] This embodiment is basically the same as the embodiment 1, except that in step (3), no groove is formed on one side of the shell, and only plasma cleaning is performed.

[0172] Comparative Example 1

[0173] Please refer to Table 1. This comparative example is basically the same as Example 1, except that the water-based coating includes 41.2 parts of modified filler and 5 parts of pigment (red iron oxide), and the modified filler is made of 40 parts of thermal conductive filler (aluminum nitride powder) and 1.2 parts of silane coupling agent (3-glycidyloxypropyltrimethoxysilane).

[0174] Comparative Example 2

[0175] Please refer to Table 1. This comparative example is basically the same as Example 1, except that the water-based coating includes 5 parts of thermal conductive filler (magnesium oxide powder) and 1 part of pigment (phthalocyanine blue).

[0176] Comparative Example 3

[0177] Please refer to Table 1. This comparative example is basically the same as Example 1, except that: no thermal conductive filler is added to the water-based coating, and in step (2), 0.3 parts of silane coupling agent (3-glycidyloxypropyltrimethoxysilane) is directly added to 60 parts of bisphenol A-based epoxy resin.

[0178] Comparative Example 4

[0179] Please refer to Table 1. This comparative example is basically the same as Example 1, except that: no leveling agent and flame retardant are added to the water-based filler.

[0180] Comparative Example 5

[0181] This comparative example is basically the same as Example 1, except that: the silane coupling agent and the thermal conductive filler are not subjected to a modification reaction to prepare the modified filler, and in step (2), 0.3 parts of a silane coupling agent (3-glycidyloxypropyltrimethoxysilane) and 9 parts of a thermal conductive filler (aluminum nitride powder) are directly added to 60 parts of a bisphenol A-based epoxy resin.

[0182] Test Case

[0183] Please refer to Table 2, the battery housings of each embodiment and each comparative example were tested as follows:

[0184] (1) Thickness of thermally conductive insulating coating and depth of groove: The battery shell was sliced ​​and the groove depth was measured by metallographic analysis. The coating thickness of the battery shell was measured using a paint film thickness gauge. The average value was taken after 6 consecutive measurements at different positions.

[0185] (2) Thermal conductivity of thermally conductive insulating coating: The thermal conductivity of thermally conductive insulating coating is measured by heat flow meter method. The aluminum sheet sample with thermally conductive insulating coating is inserted between two plates and a certain temperature gradient is set. The heat flow through the sample is measured by a calibrated heat flow sensor. The sensor is in contact with the sample between the plate and the sample. The thermal conductivity of the sample can be calculated by measuring the thickness of the sample, the temperature gradient between the upper and lower plates, and the heat flow through the sample.

[0186] (3) High voltage resistance: Take a battery case with a thermally conductive insulating coating and conduct a breakdown test at different positions of the battery case. The test conditions are: temperature 20℃~45℃, frequency 50Hz, steady voltage increase, electrode is copper or brass, diameter is 10mm. Then take the arithmetic mean of the test results as the average breakdown voltage (kV).

[0187] (4) Weather resistance: High and low temperature shock cycles at -55℃~130℃ for 30 minutes each, for 6 consecutive times.

[0188] (5) Flame retardancy: The vertical burning test method is used to hang the battery case with a thermally conductive insulating coating in a vertical position, ignite its lower part, and measure the flame extension speed and time to evaluate its flame retardancy.

[0189] The thermal conductivity of the traditional PET blue film is 0.15W / (m·K)~0.24W / (m·K), which has low thermal conductivity and poor heat dissipation performance, hindering the heat dissipation of the battery cells in the battery pack. As can be seen from Table 2, the thermal conductivity of the thermally conductive insulating coating of Examples 1~5 reaches 2.4W / (m·K)~3.8W / (m·K), which is an order of magnitude higher than that of the PET blue film, and has excellent heat dissipation performance. The breakdown voltage of Examples 1~5 reaches 2000V, and the flame retardant grade is V-0, with excellent insulation protection effect and high temperature protection effect. At the same time, compared with Example 5 in which no groove is set on the surface of the shell, the thermally conductive insulating coating of Examples 1~4 has good weather resistance, and there is no cracking or falling off after multiple high and low temperature impact cycles, which proves that setting a groove on the side of the shell facing the coating can effectively enhance the adhesion of the coating, thereby inhibiting the shedding and cracking of the coating.

[0190] In Comparative Example 1, the amount of modified filler used was too much. Although the thermal conductivity was greatly improved, the weather resistance of the coating was poor, and cracking occurred in the high and low temperature impact test. In Comparative Example 2, 5 parts of thermal conductive filler were added, but no silane coupling agent was used for modification. The thermal conductive filler was easy to agglomerate and could not form a complete thermal conductive network, so the thermal conductivity dropped significantly; in Comparative Example 3, no thermal conductive filler was added, and the thermal conductivity was very low; in Comparative Example 4, no leveling agent and flame retardant were added, and the prepared thermal conductive insulation coating had bubbles, which affected its thermal conductivity, so the thermal conductivity was greatly reduced, and the flame retardant performance was significantly deteriorated; in Comparative Example 5, silane coupling agent and thermal conductive filler were not made into modified fillers, and the thermal conductive filler had poor dispersibility and also had the defect of easy agglomeration, which significantly reduced the thermal conductivity of the coating and had poor heat dissipation performance.

[0191] In summary, the battery shell provided by the present application is suitable for encapsulating various square lithium-ion batteries. The thermally conductive insulating coating has a thermally conductive insulating network formed by modified fillers, which can achieve high thermal conductivity while ensuring high insulation, so that the battery shell has excellent insulation performance, heat dissipation performance and high temperature protection performance, effectively improving the heat dissipation effect of the battery cells in the battery pack, reducing the overall thermal management energy consumption of the battery pack, and having high safety in use. In addition, the present application uses water-based paint to form a thermally conductive insulating coating on one side of the shell, which can simplify the production process of the battery shell (omitting the coating process), has no environmental pollution, has low preparation cost, does not have problems such as bubbles and folding, and the coating is uniform and stable with good coating effect, which is very suitable for mass production.

[0192] Table 1. Water-based coating formulation (unit: weight parts)

[0193]

[0194] Table 2. Battery housing properties

[0195]

[0196] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0197] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of protection of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the scope of protection of the present application. Therefore, the scope of protection of the present application shall be subject to the attached claims.

Claims

1. A battery casing, characterized in that: It comprises a shell and a heat-conducting insulating coating covering the shell; The thermally conductive insulating coating comprises the following raw materials in parts by weight: 40~60 parts of waterborne epoxy resin, 10~30 parts of curing agent, Modified filler 5.1~20.5 parts, 0.2~2 parts of leveling agent, and 2~6 parts of flame retardant; The modified filler includes a thermally conductive filler and a silane coupling agent loaded on the thermally conductive filler; The mass ratio of the thermal conductive filler to the silane coupling agent is (5-20): (0.1-0.5).

2. The battery housing according to claim 1, wherein: The thermal conductive filler includes one or more of aluminum nitride, boron nitride, silicon nitride, aluminum oxide, magnesium oxide, zinc oxide, beryllium oxide and silicon oxide.

3. The battery housing according to claim 1, characterized in that: The silane coupling agent includes one or more of 3-aminopropyltriethoxysilane, 3-(isomethacryloyloxy)propyltrimethoxysilane, γ-aminopropyltrimethoxysilane and 3-glycidyloxypropyltrimethoxysilane.

4. The battery case according to any one of claims 1 to 3, characterized in that One or more of the following conditions are met: (1) The water-based epoxy resin includes one or more of bisphenol A epoxy resin, tetrabromobisphenol A epoxy resin, fluorinated epoxy resin, phenolic epoxy resin and glycidylamine epoxy resin; (2) The curing agent includes one or more of an amine curing agent, an anhydride curing agent, an imidazole curing agent and a hydrazide curing agent; (3) The leveling agent includes one or more of polyethylene glycol, polyethylene imine, polydimethylsiloxane, polymethylphenylsiloxane, and polyacrylic acid fluoride ester; (4) The flame retardant includes one or more of silicon dioxide, talc, aluminum hydroxide, ammonium phosphate and tetrabromobisphenol A bis(dibromopropyl) ether; (5) The thermally conductive insulating coating further comprises 0.1 to 1 part of a pigment, wherein the pigment comprises one or more of iron oxide red, iron oxide blue, phthalocyanine blue, phthalocyanine green, molybdenum chrome red and chrome yellow.

5. The battery housing according to claim 4, characterized in that: The thickness of the thermally conductive insulating coating is 100 μm to 300 μm; A plurality of grooves are provided on a side of the shell facing the thermally conductive insulating coating, wherein the depth of the grooves is less than the thickness of the shell, and the depth of the grooves is less than the thickness of the thermally conductive insulating coating.

6. The battery housing according to claim 5, characterized in that: The depth of the groove is 2% to 30% of the thickness of the shell.

7. A method for preparing a battery casing according to any one of claims 1 to 6, characterized in that: The following steps are involved: Provide water-based coatings containing water-based epoxy resin, curing agent, modified filler, leveling agent, flame retardant and pigment; Covering the water-based paint on the shell to form a liquid film; Curing the liquid film at 80° C. to 160° C. for 2 h to 4 h to form a thermally conductive insulating coating; Wherein, the preparation method of the water-based coating comprises the following steps: The modified filler is uniformly dispersed in the waterborne epoxy resin to obtain a glue solution; The glue, the curing agent, the leveling agent, the flame retardant, the pigment and the water are mixed to obtain the water-based paint.

8. The method for preparing a battery casing according to claim 7, characterized in that: The preparation method of the modified filler comprises the following steps: The thermally conductive filler, the silane coupling agent and the solvent are mixed, and modified and reacted at 60° C. to 80° C. for 4 h to 6 h, so that the silane coupling agent is loaded on the thermally conductive filler to obtain a mixture; The mixture is subjected to purification, grinding and screening to obtain the modified filler.

9. The method for preparing a battery casing according to claim 7, characterized in that: Before the step of covering the shell with the water-based paint, the method further includes the following steps: A plurality of grooves are formed on a side of the housing facing the thermally conductive insulating coating layer by a press forming method.

10. A secondary battery, characterized in that: The invention comprises a battery shell as claimed in any one of claims 1 to 6, or a battery shell prepared by the method for preparing a battery shell as claimed in any one of claims 7 to 9.

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