Coating method for the cell casing

Abstract

The present invention belongs to the field of batteries and provides a method for coating the outer shell of an electric core. The method includes: (1) providing a coating solution: providing an impregnating solution for the raw material of the blue film, the impregnating solution containing polyester raw materials, additives and solvents, and the polyester raw materials including polyols and polyacids; performing a first heat treatment on the impregnating solution to enable the polyols and polyacids therein to undergo a first polymerization reaction to obtain a coating solution containing a polyester prepolymer; (2) impregnating the outer shell of the electric core with the coating solution to obtain an outer shell of the electric core with the coating solution on its surface; (3) performing a second heat treatment on the outer shell of the electric core obtained in step (2) to enable the polyester prepolymer in the coating solution to undergo a second polymerization reaction; (4) drying the product obtained in step (3) to form a blue film on the outer shell of the electric core. The method provided by the present invention is simple to operate, has a relatively high production efficiency, and can be used for coating the outer shells of electric cores of various shapes.

Description

Technical Field

[0001] The present invention belongs to the field of batteries, and specifically, relates to a method for coating the outer shell of an electric core. Background Art

[0002] Lithium batteries have the advantages of high energy density, high power density, long cycle life, and environmental friendliness, and are widely used in fields such as new energy vehicles and energy storage devices. In recent years, with the rapid development of the new energy vehicle industry, lithium batteries, as the main power source of new energy vehicles, have become one of the key components of new energy vehicles.

[0003] During the design process of lithium batteries, in order to protect the electric core and reduce the harm caused to the human body and the environment due to the leakage of the electric core, a protective shell is put on the electric core, and a blue film is further wrapped on the protective shell. In the current related technologies, the finished blue film is directly wrapped on the outer shell of the electric core. This process is non - continuous, that is, the preparation and molding of the blue film and the wrapping of the outer shell of the electric core are two separate processes, resulting in a relatively high cost and low production efficiency for the process of wrapping the blue film on the outer shell of the electric core, thus affecting the delivery efficiency of the finished electric core, and there are easily defects such as air holes and wrinkles between the blue film and the outer shell. In addition, for the coating of the outer shell of an electric core with a special - shaped structure, in order to completely wrap the outer shell of the special - shaped electric core, more blue film materials are required, causing waste of blue film materials.

[0004] Therefore, the current method for coating the outer shell of an electric core still needs to be improved. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems in the related technologies to some extent.

[0006] The present invention provides a method for protecting the outer shell of an electric core, including the following steps:

[0007] (1) Provide a coating solution

[0008] Provide a raw material impregnating solution for the blue film, which contains a polyester raw material, an auxiliary agent, and a solvent. Among them, the polyester raw material includes a polyol and a polybasic acid;

[0009] Perform a first heat treatment on the raw material impregnating solution to enable the polyol and polybasic acid therein to undergo a first polymerization reaction, obtaining the coating solution containing a polyester prepolymer;

[0010] (2) Impregnate the outer shell of the electric core with the coating solution to obtain an outer shell of the electric core with the coating solution;

[0011] (3) Perform a second heat treatment on the outer shell of the electric core obtained in step (2) to enable the polyester prepolymer in the coating solution to undergo a second polymerization reaction;

[0012] (4) Dry the product obtained in step (3) to form a blue film on the surface of the battery cell housing.

[0013] The method provided by the present invention can form a blue film with good uniformity on the surface of the battery cell housing. There are no defects such as air holes and wrinkles between the blue film and the battery cell housing. This method can also be used for coating battery cell housings of various shapes, and has the advantages of simple operation, high production efficiency, and low cost, being suitable for popularization and application.

[0014] According to an embodiment of the present invention, before performing step (2), it further includes: performing plasma treatment on the surface of the battery cell housing. Thus, by performing plasma treatment on the surface of the battery cell housing, active groups can be introduced to the surface of the battery cell housing and the surface roughness can be increased.

[0015] According to an embodiment of the present invention, the conditions of the plasma treatment include: a power of 950 W - 1050 W and a time of 30 s - 60 s.

[0016] According to an embodiment of the present invention, in the raw material impregnating solution, the molar ratio of the polybasic acid to the polyhydric alcohol is (1.01 - 1.1)∶1.

[0017] According to an embodiment of the present invention, the polyhydric alcohol includes at least one of ethylene glycol, propylene glycol, and butylene glycol.

[0018] According to an embodiment of the present invention, the polybasic acid includes at least one of terephthalic acid and adipic acid.

[0019] According to an embodiment of the present invention, the auxiliary agent includes at least one of a plasticizer, a heat stabilizer, a light shielding agent, a flame retardant, and an inorganic filler.

[0020] According to an embodiment of the present invention, the solvent includes cyclohexanone.

[0021] According to an embodiment of the present invention, the plasticizer includes diphenyl isooctyl phosphate.

[0022] According to an embodiment of the present invention, the heat stabilizer includes tribasic lead sulfate and / or dibasic lead phosphite.

[0023] According to an embodiment of the present invention, the flame retardant includes tris(isopropylphenyl) phosphate and / or tris(2-chloroethyl) phosphate.

[0024] According to an embodiment of the present invention, the inorganic filler includes ultramarine blue.

[0025] According to an embodiment of the present invention, the light shielding agent includes carbon black.

[0026] According to an embodiment of the present invention, the antioxidant includes antioxidant 1010 and / or antioxidant 264.

[0027] According to an embodiment of the present invention, the lubricant includes at least one of stearic acid, calcium stearate, stearate ester, and aluminum stearate.

[0028] According to an embodiment of the present invention, in the raw material impregnation solution, the mass ratio of the polyester raw material, the auxiliary agent, and the solvent is 1∶(0.3 - 0.45)∶(0.5 - 1).

[0029] According to an embodiment of the present invention, by mass, the auxiliary agent includes: 10 - 50 parts of a plasticizer, 3 - 10 parts of a heat stabilizer, 0 - 5 parts of an antioxidant, 0 - 5 parts of a light shielding agent, 10 - 50 parts of a flame retardant, 20 - 50 parts of an inorganic filler, 0 - 5 parts of a lubricant, and the total amount of the auxiliary agent is 100 parts.

[0030] According to an embodiment of the present invention, the temperature of the first heat treatment is 150°C - 200°C.

[0031] According to an embodiment of the present invention, the time of the first heat treatment is 5 min - 30 min.

[0032] According to an embodiment of the present invention, the temperature of the impregnation is 260°C - 280°C.

[0033] According to an embodiment of the present invention, the time of the impregnation is 20 s - 60 s.

[0034] According to an embodiment of the present invention, the second heat treatment is carried out under a vacuum degree of 0.001 Pa - 100 Pa.

[0035] According to an embodiment of the present invention, the temperature of the second heat treatment is 200°C - 280°C.

[0036] According to an embodiment of the present invention, the time of the second heat treatment is 10 min - 20 min.

[0037] According to an embodiment of the present invention, the drying treatment is vacuum drying.

[0038] According to an embodiment of the present invention, the temperature of the drying treatment is 25°C - 40°C.

[0039] According to an embodiment of the present invention, the time of the drying treatment is 6 h - 24 h.

[0040] According to an embodiment of the present invention, it further includes repeating steps (2) to (4) until the coating thickness of the cell housing is 0.1 mm - 0.15 mm. Description of the Drawings

[0041] The above and / or additional aspects and advantages of the present invention will become apparent and be readily understood from the following description of embodiments in conjunction with the accompanying drawings, where:

[0042] Figure 1 is a flowchart of a method for coating the outer shell of an electric cell according to some embodiments of the present invention;

[0043] Figure 2 is a schematic diagram of a process operation of a method for coating the outer shell of an electric cell according to some embodiments of the present invention.

[0044] Description of reference numerals:

[0045] 1: Stirring paddle; 2: Temperature panel; 3: Square aluminum shell; 4: Special-shaped aluminum shell; 5: Melting pool; 6: Coating solution; 7: Square aluminum shell with coating solution; 8: Special-shaped aluminum shell with coating solution; 9: Air inlet; 10: Air outlet; 11: Carrying platform; 12: Vacuum heating box. Detailed description of the embodiments

[0046] Embodiments of the present invention will be described in detail below. Among them, the embodiments described with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as a limitation to the present invention.

[0047] The present invention provides a method for coating the outer shell of an electric cell, including the following steps:

[0048] (1) Provide a coating solution

[0049] Provide a raw material impregnating solution for a blue film, which includes a polyester raw material, an auxiliary agent, and a solvent. Among them, the polyester raw material includes a polyol and a polybasic acid;

[0050] Perform a first heating treatment on the raw material impregnating solution to enable a first polymerization reaction of the polyol and the polybasic acid therein, and obtain a coating solution containing a polyester prepolymer;

[0051] (2) Immerse the outer shell of the electric cell with the coating solution to obtain an outer shell of the electric cell with the coating solution;

[0052] (3) Perform a second heating treatment on the outer shell of the electric cell obtained in step (2) to enable a second polymerization reaction of the polyester prepolymer in the coating solution;

[0053] (4) Perform a drying treatment on the product obtained in step (3) to form a blue film on the surface of the outer shell of the electric cell.

[0054] The method of the present invention can form a blue film with good uniformity on the surface of the battery cell casing, and there are no defects such as air holes and wrinkles between the blue film and the casing, thereby improving the corrosion resistance of the battery cell casing. In addition, this method has high production efficiency, can improve the delivery capacity of the finished battery cell, and forms a coating solution on the battery cell casing through an impregnation process. Compared with the traditional process of directly wrapping a blue film with the same thickness on the battery cell casing, it can reduce the material cost. In addition, this method can also be applied to battery cell casings of various shapes and is suitable for popularization and application.

[0055] Furthermore, the method of the present invention forms a coating solution by performing a first heat treatment (prepolymerization) on the raw material impregnation solution, then immerses the battery cell casing in the coating solution, and then performs a second heat treatment (final polymerization) on the battery cell casing with the coating solution to form a blue film on the surface of the battery cell casing. This process combining prepolymerization → impregnation → final polymerization can directly coat the coating solution on the surface of the battery cell casing, which can reduce or even eliminate bubbles and wrinkles in the blue film, making the blue film firmly adhered to the battery cell casing without breakpoints. Moreover, the process route of this method is simple, has strong operability, and is suitable for popularization and use.

[0056] According to the present invention, preferably, before performing step (2), it further includes: performing plasma treatment on the surface of the battery cell casing. Thus, by performing plasma treatment on the surface of the battery cell casing, active groups are introduced to the surface of the battery cell casing and the surface roughness is increased, which is beneficial for the coating solution to adhere to the surface of the battery cell casing when the coating solution impregnates the battery cell casing subsequently.

[0057] Furthermore, the conditions for plasma treatment include: the power is 950W - 1050W, and the time is 30s - 60s, for example, the time is 30s, 40s, 50s, 60s.

[0058] The method of the present invention is suitable for coating various battery casings, and the battery casing can be various battery cell casings in existing secondary batteries. In some embodiments, the battery cell casing includes a square casing, a cylindrical casing, or a special-shaped casing. Optionally, the cross-section of the special-shaped casing includes one or more of a circle, a polygon, and an ellipse. Among them, the polygon is, for example, a pentagon, a hexagon, a heptagon, etc. As an example, the special-shaped casing has the same cross-sectional shape along its height direction, and the cross-section is, for example, a pentagon, a hexagon, or a heptagon. As another example, the special-shaped casing has different cross-sectional shapes along its height direction. For example, it has the same first cross-sectional shape at the bottom and the top, and a second cross-sectional shape different from the first cross-sectional shape in the region between the two. The method of the present invention is not only suitable for coating battery cell casings with regular shapes, but also particularly suitable for coating special-shaped casings with diverse shapes.

[0059] According to the present invention, the material of the battery cell housing can be a metal material and / or a non-metal material with heat conduction and conductivity. In some embodiments, the material of the battery cell housing includes steel or aluminum alloy.

[0060] According to the present invention, in step (1), in the raw material impregnating solution of the blue film, the polyester raw materials include polyols and polyacids. In some embodiments, the molar ratio of polyacid to polyol is (1.01 - 1.1)∶1, so that the free hydrogen ions play a catalytic role and improve the reaction degree and control the molecular weight.

[0061] According to the present invention, the polyol can be an alcohol compound having two or more hydroxyl groups. In some embodiments, the polyol includes at least one of ethylene glycol, propylene glycol, and butanediol.

[0062] According to the present invention, the polyacid can be a carboxylic acid compound having two or more carboxyl groups. In some embodiments, the polyacid includes at least one of terephthalic acid and adipic acid.

[0063] According to the present invention, in the raw material impregnating solution of the blue film, the auxiliary agent can include functional additives well-known in the art for forming blue film materials, and the functional additives can, for example, improve one or several of the optical properties, insulation properties, flame retardancy, mechanical properties, and antioxidant properties of the blue film. In some embodiments, the auxiliary agent includes at least one of a plasticizer, a heat stabilizer, a light shielding agent, a flame retardant, an inorganic filler, an antioxidant, and a lubricant.

[0064] According to the present invention, the plasticizer can be selected from various insulating plasticizers. Optionally, the plasticizer includes diphenyl isooctyl phosphate (DPOP).

[0065] Optionally, the heat stabilizer includes tribasic lead sulfate and / or dibasic lead phosphite.

[0066] According to the present invention, the flame retardant can be selected from various phosphate flame retardants. Optionally, the flame retardant includes tris(isopropylbenzene) phosphate and / or tris(2-chloroethyl) phosphate.

[0067] Optionally, the inorganic filler includes ultramarine blue.

[0068] Optionally, the light shielding agent includes carbon black.

[0069] According to the present invention, the antioxidant can be selected from various phenolic antioxidants. Optionally, the antioxidant includes antioxidant 1010 and / or antioxidant 264.

[0070] According to the present invention, the lubricant can be selected from various stearic acid soaps. Optionally, the lubricant includes at least one of stearic acid, calcium stearate, stearate ester, and aluminum stearate.

[0071] According to the present invention, in the raw material impregnating solution of the blue film, the solvent can be selected from various solvents suitable for the polymerization of polyols and polyacids. Optionally, the solvent includes cyclohexanone.

[0072] In some embodiments, in the raw material impregnating solution of the blue film, the mass ratio of the polyester raw material, the auxiliary agent and the solvent is 1∶(0.3 - 0.45)∶(0.5 - 1). By controlling the weight portions of the polyester raw material, the auxiliary agent and the solvent within the above range conditions, the obtained blue film has better mechanical strength, better color development performance and better corrosion resistance, and the bonding force between the blue film and the battery cell housing is better.

[0073] Further, by mass portions, the auxiliary agent includes: 10 - 50 parts of a plasticizer, for example, the plasticizer is 10 parts, 20 parts, 30 parts, 40 parts, 50 parts; 3 - 10 parts of a heat stabilizer, for example, the heat stabilizer is 3 parts, 5 parts, 8 parts, 10 parts; 0 - 5 parts of an antioxidant; 0 - 5 parts of a light shielding agent; 10 - 50 parts of a flame retardant, for example, the flame retardant is 10 parts, 15 parts, 25 parts, 40 parts, 50 parts; 20 - 50 parts of an inorganic filler, for example, the inorganic filler is 20 parts, 30 parts, 40 parts, 50 parts; 0 - 5 parts of a lubricant, and the total amount of the auxiliary agent is 100 parts. By controlling the plasticizer, the heat stabilizer, the light shielding agent, the flame retardant, the antioxidant, the lubricant and the inorganic filler within the above range conditions, the blue film has better comprehensive performance. Specifically, the plasticizer can increase the fluidity of the coating solution, which is beneficial to the subsequent impregnation process; the heat stabilizer can delay the thermal aging of the blue film and extend the service life of the blue film; the flame retardant can form a glassy or foamy covering layer at high temperatures, isolate oxygen, and prevent the escape of combustible gases, so that the blue film has flame retardant properties; the inorganic filler can improve the mechanical strength of the blue film, reduce costs, and color the blue film; the light shielding agent can inhibit the ultraviolet radiation of the blue film.

[0074] In some embodiments, in step (1), the temperature of the first heat treatment is 150°C - 200°C, such as 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, etc.; the time of the first heat treatment is 5 min - 30 min, such as 5 min, 8 min, 10 min, 15 min, 20 min, 25 min, 30 min, etc. By controlling the temperature of the first heat treatment and the time of the first heat treatment, the polyacid and the polyol are subjected to the first polymerization reaction to obtain a coating solution of a polyester prepolymer with a low degree of polymerization.

[0075] In some specific embodiments, the polyol is ethylene glycol and the polyacid is terephthalic acid. Through the first heat treatment, ethylene glycol and terephthalic acid are subjected to the first polymerization reaction to form a PET prepolymer.

[0076] In some embodiments, in step (2), the impregnation temperature is 260°C - 280°C, such as 260°C, 265°C, 280°C, etc. By controlling the impregnation temperature, the viscosity of the coating solution is made appropriate, which is beneficial to the impregnation process and enables the coating solution to effectively adhere to the surface of the battery cell housing.

[0077] In some embodiments, the viscosity of the coating solution at a temperature of 260°C - 280°C is 0.4 mPa·s - 0.7 mPa·s.

[0078] In some embodiments, in step (2), the impregnation time is 20 s - 60 s, such as 20 s, 30 s, 40 s, 50 s, 60 s, etc.

[0079] In some embodiments, in step (3), the second heat treatment is carried out under a vacuum degree of 0.001 Pa - 100 Pa, such as 0.001 Pa, 0.01 Pa, 1 Pa, 10 Pa, 20 Pa, 50 Pa, 60 Pa, 80 Pa, 100 Pa, etc. By controlling the second heat treatment to be carried out under vacuum conditions, it is beneficial to the polymerization reaction and can eliminate the bubbles in the coating solution wrapped on the surface of the battery cell housing.

[0080] Optionally, the temperature of the second heat treatment is 200°C - 280°C, such as 200°C, 210°C, 230°C, 250°C, 270°C, 280°C, etc.

[0081] Optionally, the time of the second heat treatment is 10 min - 20 min, such as 10 min, 13 min, 15 min, 18 min, 20 min.

[0082] In some embodiments, in step (3), the second heat treatment is carried out in a vacuum heating chamber.

[0083] In some embodiments, in step (4), the drying treatment is carried out under vacuum conditions. Optionally, the vacuum degree is 80 Pa - 100 Pa.

[0084] Optionally, the temperature of the drying treatment is 25°C - 40°C, such as 25°C, 30°C, 35°C, 40°C, etc.

[0085] Optionally, the time of the drying treatment is 6 h - 24 h, such as 6 h, 8 h, 10 h, 15 h, 20 h, 24 h, etc.

[0086] Through the drying treatment in step (4), the residual stress between the battery cell housing and the polyester end polymer can be relieved to form a blue film on the battery cell housing. The drying treatment can be carried out in a vacuum chamber.

[0087] According to the present invention, the method may further include or not include repeating steps (2) to (4), and the number of repetitions may be selected according to the thickness of the blue film to be prepared.

[0088] In some embodiments, it further includes repeating steps (2) to (4) until the coating thickness of the battery cell housing is 0.1 mm - 0.15 mm.

[0089] In some specific embodiments, in combination Figure 1 , the method includes the following steps:

[0090] S1: Provide a coating solution and a battery cell housing respectively

[0091] S1a: Provide a coating solution

[0092] Add polyol, polyacid, and an auxiliary agent to a solvent and stir evenly to obtain a raw material impregnation solution for the blue film; then perform a first heat treatment on the raw material impregnation solution to form a coating solution containing a polyester prepolymer;

[0093] S1b: Perform plasma treatment on the battery housing.

[0094] S2: Impregnation treatment

[0095] Immerse the plasma-treated battery cell housing in the coating solution.

[0096] S3: Second heat treatment

[0097] Under vacuum conditions, perform a second heat treatment on the impregnated battery cell housing to further polymerize the polyester prepolymer in the coating solution to form a polyester end polymer.

[0098] S4: Drying treatment

[0099] Under vacuum conditions, perform vacuum drying on the battery cell housing after the second heat treatment to obtain a battery cell housing with a blue film wrapped on its surface.

[0100] S5: Repeat S2 - S4

[0101] Repeat S2 - S4 to make the thickness of the blue film wrapped on the battery cell housing meet the requirements.

[0102] The method provided by the present invention can be carried out by a continuous process. According to some embodiments, as Figure 2 shown, the process includes the following flow:

[0103] (1) Place the blue film raw material in a temperature-controllable melting pool 5 and stir it with a stirring paddle 1 to fully mix the blue film raw material to obtain a raw material impregnation solution;

[0104] (2) Control the temperature at 150°C - 200°C through the temperature panel 2 on the molten pool 5, and maintain the heating time at 5 min - 30 min to obtain the coating solution 6 containing the polyester prepolymer;

[0105] (3) Treat the surface of the cell housing with plasma;

[0106] (4) Immerse the cell housing treated in step (3) in the coating solution 6;

[0107] (5) Place the cell housing immersed in step (4) on the carrier table 11 in the vacuum heating chamber 12, which has an air inlet 9 and an air outlet 10, to achieve vacuum pumping;

[0108] (6) Control the temperature of the vacuum heating chamber 12 between 200°C and 280°C, and conduct vacuum pumping to maintain the vacuum degree at 0.001 Pa - 100 Pa, with a reaction time of 10 min - 20 min;

[0109] (7) Place the cell housing that has completed step (6) in a vacuum chamber for drying, and conduct vacuum pumping on the vacuum chamber. Control the drying temperature between 25°C and 40°C, and the drying time at 6 h - 24 h;

[0110] (8) Repeat steps (4) to (7) until the thickness of the formed blue film reaches 0.1 mm - 0.15 mm.

[0111] The method provided by the present invention is simple to operate, can form a blue film with good uniformity on the surface of the cell housing, and this method is applicable to housings of various shapes, and is particularly suitable for popularization and application.

[0112] The following illustrates the solution of the present invention through specific embodiments. It should be noted that the following embodiments are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those not specified in the embodiments in terms of specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in this field or according to the product instructions. For reagents or instruments not specified in terms of the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0113] In the following examples and comparative examples, by weight, in the raw material impregnation solution of the blue film, by mass, the additive formulation is shown in Table 1:

[0114] Table 1

[0115]

[0116] Example 1

[0117] This example is combined with Figure 2 to illustrate the coating method of the present invention.

[0118] (1) Impregnation solution for the blue film

[0119] Add polyester raw materials (ethylene glycol and terephthalic acid, molar ratio 1:1.01), solvent (cyclohexanone), and additives to the melting pool 5 in a mass ratio of 1:0.3:0.5, and stir evenly to obtain the impregnation solution.

[0120] (2) Coating solution

[0121] Under stirring conditions, turn on the heating system of the melting pool 5, and by controlling the temperature panel 2 on the melting pool 5, raise the temperature of the melting pool 5 to 180 °C and keep it warm for 20 min to obtain the coating solution 6 containing polyester prepolymer.

[0122] (3) Plasma treatment

[0123] Use plasma to treat the surface of the square aluminum shell 3. The conditions of the plasma are: time is 30 s, and power is 1000 W.

[0124] (4) Impregnation

[0125] Immerse the plasma-treated square aluminum shell 3 in the melting pool 5 containing the coating solution 6, control the temperature on the melting pool 5 at 265 °C for 60 s to obtain the square aluminum shell 8 with the coating solution.

[0126] (5) Second heat treatment

[0127] Place the square aluminum shell 3 with the coating solution on the stage 11 of the vacuum heating box 12, control the vacuum degree of the vacuum heating box at 50 Pa, the temperature at 250 °C, and the time at 15 min to obtain the battery cell housing wrapped with polyester end polymer.

[0128] (6) Drying treatment

[0129] Place the battery cell housing with polyester end polymer in a vacuum box, evacuate the vacuum box, and control the temperature at 25 °C for 15 h to form the battery cell housing wrapped with the blue film.

[0130] (7) Repeat impregnation, second heat treatment, and drying treatment until the thickness of the blue film wrapped on the battery cell housing is 0.15 mm.

[0131] Example 2

[0132] The same as Example 1, except that the battery cell housing used is the special-shaped aluminum shell 4. The cross-section of the special-shaped aluminum shell in the horizontal direction is hexagonal, and after being impregnated with the coating solution 6, the special-shaped aluminum shell 8 with the coating solution on the surface is formed.

[0133] Test example

[0134] The following tests were performed on the outer casings of the encapsulated battery cells obtained in the above Examples 1-2, and the results are shown in Table 2.

[0135] Peeling force test

[0136] Referring to GB / T2792-2014 "Test Method for Peel Strength of Adhesive Tape", the peeling force of the outer casing of the battery cell wrapped with blue film on the surface was tested, and three parallel tests were performed on each group of samples.

[0137] Table 2

[0138] Example Peeling force (N / m) Bond strength requirement Example 1 350-420 300 N / m - 500 N / m Example 2 350-420 300 N / m - 500 N / m

[0139] As can be seen from the above table, the outer casing of the encapsulated battery cell prepared by the method of the present invention meets the requirements for bonding strength.

[0140] Unless otherwise specified, all scientific and technical terms used in the present invention have the same meaning as commonly understood by those skilled in the art to which the present invention belongs. All patents and published publications referred to in the present invention are incorporated herein by reference in their entirety. The term "comprising" or "including" is an open-ended expression, that is, it includes the content specified in the present invention, but does not exclude other aspects.

[0141] In the description of this specification, the description referring to terms such as "some embodiments" means that the specific features, structures, materials or characteristics described in connection with the embodiment are included in at least one embodiment of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples. Additionally, it should be noted that in this specification, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features.

[0142] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for coating the outer shell of an electric core, characterized in that, it comprises the following steps: (1) Provide a coating solution Provide a raw material impregnating solution for a blue film, which raw material impregnating solution contains polyester raw materials, additives and solvents. Among them, the polyester raw materials include polyols and polyacids; the polyols include at least one of ethylene glycol, propylene glycol and butanediol; and the polyacids include at least one of terephthalic acid and adipic acid; Perform a first heat treatment on the raw material impregnating solution so that the polyols and polyacids therein undergo a first polymerization reaction to obtain the coating solution containing a polyester prepolymer; The temperature of the first heat treatment is 150°C - 200°C; the time of the first heat treatment is 5 min - 30 min; (2) Immerse the outer shell of the electric core with the coating solution to obtain an outer shell of the electric core with the coating solution; (3) Perform a second heat treatment on the outer shell of the electric core obtained in step (2) to cause the polyester prepolymer in the coating solution to undergo a second polymerization reaction; the temperature of the second heat treatment is 200°C - 280°C; the time of the second heat treatment is 10 min - 20 min (4) Perform a drying treatment on the product obtained in step (3) to form a blue film on the surface of the outer shell of the electric core.

2. The coating method according to claim 1, characterized in that, before performing step (2), it further includes: performing plasma treatment on the surface of the outer shell of the electric core.

3. The coating method according to claim 2, characterized in that, the conditions of the plasma treatment include: the power is 950 W - 1050 W, and the time is 30 s - 60 s.

4. The coating method according to claim 1, characterized in that, in the raw material impregnating solution, the molar ratio of the polyacid to the polyol is (1.01 - 1.1)∶1.

5. The coating method according to claim 1, characterized in that, the additives include at least one of a plasticizer, a heat stabilizer, a light shielding agent, a flame retardant, an antioxidant, an inorganic filler and a lubricant; the plasticizer includes diphenyl isooctyl phosphate; the heat stabilizer includes tribasic lead sulfate and / or dibasic lead phosphite; the flame retardant includes tris(isopropylphenyl) phosphate and / or tris(2-chloroethyl) phosphate; the inorganic filler includes ultramarine blue; the light shielding agent includes carbon black; the antioxidant includes antioxidant 1010 and / or antioxidant 264; the lubricant includes at least one of stearic acid, calcium stearate, stearate ester and aluminum stearate; the solvent includes cyclohexanone.

6. The coating method according to claim 1 or 5, characterized in that, in the raw material impregnating solution, the mass ratio of the polyester raw materials, additives and solvents is 1∶(0.3 - 0.45)∶(0.5 - 1).

7. The coating method according to claim 1 or 5, characterized in that, calculated by mass parts, the additives include: 10 - 50 parts of plasticizer, 3 - 10 parts of heat stabilizer, 0 - 5 parts of antioxidant, 0 - 5 parts of light shielding agent, 10 - 50 parts of flame retardant, 20 - 50 parts of inorganic filler, 0 - 5 parts of lubricant, and the total amount of the additives is 100 parts.

8. The coating method according to claim 1, It is characterized in that the temperature of the impregnation is 260°C - 280°C; and / or, the time of the impregnation is 20s - 60s.

9. The coating method according to claim 1, it is characterized in that the second heat treatment is carried out under the condition that the vacuum degree is 0.001Pa - 100Pa.

10. The coating method according to claim 1, it is characterized in that the drying treatment is vacuum drying, the drying temperature is 25°C - 40°C; and / or, the time is 6h - 24h.

11. The coating method according to claim 1, it is characterized in that it further includes: repeating step (2) to step (4) until the thickness of the blue film formed on the surface of the battery cell housing is 0.1mm - 0.15mm.

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