A coating method for reducing negative electrode coating cracking

Abstract

The present invention relates to the field of lithium-ion battery materials, and discloses a coating method for reducing cracking of negative electrode coating, comprising the following steps: (a) device setting: a coating mechanism, a drying mechanism and a blowing mechanism are sequentially arranged along the moving direction of a conveyor belt; (b) preparation of negative electrode slurry; (c) single-sided coating: the negative electrode body is coated with negative electrode slurry and then sent to a drying mechanism, dried at 90-105°C until the weight loss rate of the electrode sheet is 0.8-1.2%, and then blown dry by a blowing mechanism until the weight loss rate of the electrode sheet is 0.4-0.8%; (d) double-sided coating: step (c) is repeated on the other side of the negative electrode sheet, wherein the drying temperature is 95-120°C, and the air pressure of the blowing pipe is 0.315-0.66MPa. The "drying + blowing" method is adopted for drying after coating, and the drying degree of drying and blowing is controlled. During the drying process, the solvent volatilizes stably, and the phenomenon of poor coating of the negative electrode sheet is reduced. The equipment layout is simple, the adjustment is convenient, and the effect is reliable.

Description

Technical Field

[0001] The invention relates to the field of lithium ion battery materials, and in particular to a coating method for reducing negative electrode coating cracking. Background Art

[0002] In the manufacturing process of lithium batteries, negative electrode coating is a key process. Negative electrode coating is to evenly coat the negative electrode slurry on the substrate through extrusion coating, transfer coating, spraying and other coating methods, and dry it in a negative pressure and high temperature environment in an oven to remove the solvent in the negative electrode slurry and obtain a solid powder adhered to the substrate.

[0003] With the development of lithium battery technology and the explosion of the energy storage market, in order to achieve better energy storage investment return technology, people in the industry are pursuing lower and lower battery costs. In the pursuit of low battery costs, new low-cost materials are often introduced. In traditional negative electrode formulas, the binder often uses the more traditional styrene-butadiene rubber, also known as polystyrene butadiene copolymer (SBR for short). SBR is imported from Japan and South Korea, resulting in high costs and uncontrolled supply. In order to reduce the cost of use, lithium power plants introduce polyacrylonitrile multipolymers or polyacrylic acid as substitutes. This type of glue has low cost, but its plasticity is relatively good and its volatilization rate is relatively fast, resulting in the negative electrode often cracking and curling during normal coating. Once the surface of the negative electrode cracks or curls, it will leave marks on the surface of the electrode. This mark will cause lithium precipitation during subsequent cycles.

[0004] At present, there are two main methods in the industry to improve the cracking of the electrode sheet during negative electrode coating. One is to adjust the temperature, air volume, coating speed and other parameters of the oven to dry the negative electrode sheet under reasonable parameters to improve the state of the electrode sheet. However, since the state of the slurry is different each time, the parameters must be adjusted frequently, which brings great unpredictability to production. Another method is to add an organic solvent to the negative electrode slurry to reduce the boiling point of the solvent in the negative electrode slurry and increase the overall volatilization rate of the solvent. For example, Chinese patent publication number "CN114335528A" discloses a negative electrode glue and its preparation method and application, and the negative electrode glue includes: sodium carboxymethyl cellulose, N-methyl pyrrolidone and water. By mixing N-methyl pyrrolidone and sodium carboxymethyl cellulose with water as a negative electrode glue, on the one hand, it can solve the problem of film cracking of graphite negative electrode slurry, and on the other hand, it can effectively reduce the surface tension of graphite negative electrode slurry and improve the problem of graphite and water infiltration, thereby greatly improving the production efficiency of negative electrode coating. However, the problem with this type of method is that conventional organic solvents are N-methylpyrrolidone (NMP) or ethylene carbonate (EC). These two solvents usually cannot be fully volatilized, and the additives remaining inside the electrode will cause a series of side reactions during the subsequent use of the battery, such as loss of battery cell capacity, decomposition of SEI, etc., resulting in unstable quality of the lithium battery. Summary of the invention

[0005] The present invention aims to overcome the problems in the prior art that the volatilization efficiency of the organic solvent in the negative electrode coating is low, resulting in reduced battery capacity, and the negative electrode sheet cracking occurs when no organic solvent is added, and provides a coating method for reducing the cracking of the negative electrode coating.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A coating method for reducing negative electrode coating cracking comprises the following steps:

[0008] (a) Coating device arrangement: The coating device includes a coating mechanism, a drying mechanism and a blowing mechanism sequentially arranged along the moving direction of the conveyor belt, wherein the blowing mechanism includes a plurality of blowing pipes, and regulating valves for adjusting the gas flow rate are respectively arranged on both sides of the blowing pipes, and the distance between the two regulating valves is greater than the width of the conveyor belt. A plurality of blowing holes are arranged on the side of the pipe body close to the conveyor belt between the two regulating valves, and the diameter of the blowing holes is 1 to 2 mm, and the spacing between the blowing holes is 3 to 5 mm;

[0009] (b) Preparation of negative electrode slurry: Mix and stir the raw materials according to the formula, add deionized water to adjust the solid content and viscosity, and sieve to obtain the negative electrode slurry;

[0010] (c) Single-sided coating: the negative electrode body is placed on a conveyor belt, and the negative electrode slurry is sprayed or roller-coated on the upward side of the negative electrode body by a coating mechanism, and then sent to a drying mechanism, dried at 90-105°C until the electrode weight loss rate is 0.8-1.2%, and then sent out of the drying mechanism, blown dry by a blowing mechanism until the electrode weight loss rate is 0.4-0.8%, and the air pressure of the blowing pipe is 0.3-0.6MPa, to obtain a single-sided coated electrode; (d) Double-sided coating: the single-sided coated electrode is turned over and step (c) is repeated to perform double-sided coating, wherein the drying temperature is 95-120°C, the air pressure of the blowing pipe is 0.315-0.66MPa, and the blowing mechanism is blown dry until the electrode weight loss rate is 0.1-0.4%, to obtain a negative electrode.

[0011] In order to reduce the impact of organic solvent residues on the performance of negative electrode sheets, the present invention discards the organic solvent component in the negative electrode sheet coating slurry component. In order to solve the problems of cracking and curling on the electrode sheet surface caused by the good plasticity and fast volatilization rate of the negative electrode binder due to the lack of organic solvent, a "drying + blowing" post-coating drying method is designed, and a drying mechanism and a blowing mechanism arranged after the coating mechanism are used to realize continuous and automated negative electrode sheet coating drying. If the full-process drying method is used for post-coating drying, the binder and solvent on the surface are quickly volatilized. When the drying is carried out in the later stage, the volatilization rate of the internal binder and solvent slows down. At this time, the surface of the negative electrode sheet is prone to cracking, warping, curling and other undesirable phenomena. If the full-process blowing method is used for post-coating drying, the production time will be significantly increased and the production efficiency will be reduced due to the speed limit of the blowing.

[0012] The post-coating drying method of "drying + blowing" adopted by the present invention first dries the negative electrode sheet coated on one side, and uses a high temperature negative pressure environment to volatilize the solvent, so that the electrode sheet is dried to a degree of 80-90%, that is, its weight loss rate is 0.8-1.2%, so that the negative electrode sheet reaches a relatively dry state without adverse conditions, and then transfers it to the blowing mechanism, and uses the blowing mechanism to blow and dry, so that the electrode sheet is dried to a degree of 90-95%, that is, the weight loss rate when blowing is 0.4-0.8% when single-sided coating is applied, thereby reducing the cracking phenomenon on this coated surface. A porous blowing mechanism is used in the blowing process, and the air flow is uniformly covered on the surface of the negative electrode sheet through multiple blowing holes to prevent the negative electrode sheet from cracking due to excessive local drying. The blowing speed can be quickly adjusted by a regulating valve, and the blowing speed is adjusted according to the drying condition of the negative electrode sheet to ensure that the same batch of negative electrode sheets reaches basically the same drying state. At the same time, complete drying is not achieved during single-sided coating. After that, double-sided coating is carried out, and then "drying + blow-drying" is carried out after double-sided coating. At this time, the temperature during drying and the gas flow rate during blow-drying are increased accordingly. In the double-sided coating process, the two coated surfaces are completely dry to prevent the first coated side from warping due to excessive drying.

[0013] Preferably, the number of the air blowing pipes is 1 to 3. The number of the air blowing pipes can be adjusted according to the drying effect, the number of negative electrode sheets, and the coating production efficiency requirements.

[0014] Preferably, the distance between the two regulating valves is 200-1500 mm.

[0015] Preferably, the diameter of the air blowing tube is 8 to 10 mm.

[0016] Preferably, the blowing holes are evenly distributed along the length of the blowing pipe and evenly distributed along the side. The evenly distributed blowing holes can keep the blown airflow relatively stable, so that the same batch of negative electrode sheets can reach basically the same drying state.

[0017] Preferably, the weight loss rate is determined by keeping the electrode at a constant temperature of 150°C for 5 minutes, and calculating the weight loss rate of the electrode before and after the constant temperature, which is the weight loss rate. The weight loss rate can be used to measure the amount of solvents such as deionized water remaining in the electrode. The inventors found through a large number of experiments and data analysis that the weight loss rate can be used to judge the degree of dryness of the electrode, so it can be used as a judgment indicator for switching the drying method during the drying process of the electrode.

[0018] Preferably, the negative electrode slurry comprises the following components by weight: 92-98 parts of graphite, 1-2 parts of conductive agent, 2-4 parts of binder, and 0.1-1 parts of thickener. No organic solvent is added to the coating slurry to avoid degradation of negative electrode performance caused by residual organic solvent.

[0019] Preferably, the graphite is one of artificial graphite, mesophase graphite, natural graphite, silicon carbon, soft carbon, and hard carbon, or a combination thereof; the conductive agent is one of carbon black, Ketjen black, flaky graphite conductive agent, carbon nanotubes, and graphene, or a combination thereof.

[0020] Preferably, the thickener is sodium carboxymethyl cellulose, and the binder is one or a combination of polyacrylic acid, polyacrylonitrile, and styrene-butadiene rubber.

[0021] Preferably, in the step (2), the raw materials except the binder are first stirred at a stirring speed of 20 to 25 rpm for 30 to 60 min, and then the binder and deionized water are added to make the solid content of the negative electrode slurry 62 to 65%, and after stirring and mixing again, deionized water is added to make the solid content of the negative electrode slurry 52 to 55% and the viscosity 3000 to 8000 mPa·s.

[0022] In the preparation process of the coating slurry, the time and order of adding each component have a direct impact on the quality of the final coating slurry. In the preparation process of the present invention, the graphite, the conductive agent and the thickener are first premixed to ensure that the graphite and the conductive agent are evenly mixed before adding part of the deionized water for mixing, and the solid content is first controlled to ensure that the components other than the binder can be evenly distributed, and then the binder and the remaining deionized water are added, and the solids in the slurry are formed into a whole through the action of the binder.

[0023] Therefore, the present invention has the following beneficial effects: (1) the negative electrode sheet is dried by the method of "drying + blowing", and the degree of drying and blowing is controlled, so that the solvent volatilization is stable during the drying process, and the negative electrode sheet defects such as cracking and warping are reduced; (2) a continuous production device is designed for this method, with a simple equipment layout, a small footprint, easy adjustment, and reliable effect; (3) this method does not require the addition of organic solvents to the negative electrode slurry, which can avoid the performance degradation of the negative electrode sheet caused by the residual organic solvent. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural schematic diagram of the coating device of the present invention.

[0025] Figure 2 It is a structural schematic diagram of the air blowing pipe of the present invention.

[0026] In the figure: 1 conveyor belt, 2 coating mechanism, 3 drying mechanism, 4 blowing mechanism, 41 air blowing pipe, 42 regulating valve, 43 air blowing hole. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with specific embodiments. It should be understood that these embodiments are suitable for illustrating the basic principles, main features and advantages of the present invention, and the present invention is not limited by the scope of the following embodiments; the implementation conditions used in the embodiments can be further adjusted according to specific requirements, and the implementation conditions not specified are usually the conditions used in conventional experiments.

[0028] Unless otherwise specified in the following examples, all raw materials are commercially available or prepared by conventional methods in the art.

[0029] Example 1

[0030] A coating method for reducing negative electrode coating cracking, characterized in that it comprises the following steps:

[0031] (a) Coating device settings: Figure 1 As shown, the coating device includes a coating mechanism 2, a drying mechanism 3 and a blowing mechanism 4 which are sequentially arranged along the moving direction of the conveyor belt 1, the blowing mechanism includes three blowing pipes 41, and regulating valves 42 for adjusting the gas flow rate are respectively arranged on both sides of the blowing pipes. The width of the conveyor belt is 1200mm, the distance between the two regulating valves is 1500mm, the diameter of the blowing pipe is 9mm, and a blowing hole 43 is arranged on the side of the pipe body close to the conveyor belt between the two regulating valves. The diameter of the blowing hole is 1.5mm, and the blowing holes are evenly distributed along the length direction of the blowing pipe, and the spacing along the length direction of the blowing pipe is 4mm. At the same time, they are evenly distributed along the side, and the spacing along the side direction is 2mm;

[0032] (b) Preparation of negative electrode slurry: The negative electrode slurry includes the following components in parts by weight: 95.5 parts of graphite, 1.2 parts of conductive agent, 2.8 parts of binder, and 0.5 parts of thickener, wherein the graphite is artificial graphite, the conductive agent is carbon black, the binder is polyacrylic acid, and the thickener is sodium carboxymethyl cellulose. First, the raw materials except the binder are stirred at a stirring speed of 23 rpm for 45 min, and then the binder and deionized water are added to make the solid content of the negative electrode slurry 62-65%. After stirring and mixing again, deionized water is added to make the solid content of the negative electrode slurry 52-55% and the viscosity 3000-8000 mPa·s. After mixing, the mixture is sieved to obtain the negative electrode slurry;

[0033] (c) Single-sided coating: The negative electrode body is placed on a conveyor belt, and the negative electrode slurry is sprayed on the upward side of the negative electrode body by a coating mechanism, and then sent to a drying mechanism, dried at 90°C until the electrode weight loss rate is 1.0%, and then sent out of the drying mechanism, and blown dry by a blowing mechanism until the electrode weight loss rate is 0.8%, and the air pressure of the blowing pipe is 0.3MPa, to obtain a single-sided coated electrode;

[0034] (d) Double-sided coating: Flip the single-sided coated electrode sheet and repeat step (c) to perform double-sided coating, wherein the drying temperature is 100° C. and the air pressure of the air blow pipe is 0.33 MPa to obtain a negative electrode sheet. The weight loss rate of the obtained negative electrode sheet is 0.4%.

[0035] Example 2

[0036] A coating method for reducing negative electrode coating cracking, characterized in that it comprises the following steps:

[0037] (a) Coating device arrangement: The coating device comprises a coating mechanism 2, a drying mechanism 3 and a blowing mechanism 4 which are sequentially arranged along the moving direction of the conveyor belt 1. The blowing mechanism comprises three blowing pipes 41. A regulating valve 42 for adjusting the gas flow rate is respectively arranged on both sides of the blowing pipe. The width of the conveyor belt is 1000 mm. The distance between the two regulating valves is 1200 mm. The diameter of the blowing pipe is 8 mm. A blowing hole 43 is arranged on the side of the pipe body close to the conveyor belt between the two regulating valves. The diameter of the blowing hole is 2 mm. The blowing holes are evenly distributed along the length direction of the blowing pipe with a spacing of 5 mm along the length direction of the blowing pipe and are evenly distributed along the side with a spacing of 2 mm along the side direction.

[0038] (b) Preparation of negative electrode slurry: The negative electrode slurry comprises the following components in parts by weight: 95.5 parts of graphite, 1.2 parts of conductive agent, 2.8 parts of binder, and 0.5 parts of thickener, wherein the graphite is natural graphite, the conductive agent is flake graphite conductive agent, the binder is styrene-butadiene rubber, and the thickener is sodium carboxymethyl cellulose. First, the raw materials except the binder are stirred at a stirring speed of 20 rpm for 60 min, and then the binder and deionized water are added to make the solid content of the negative electrode slurry 62-65%. After stirring and mixing again, deionized water is added to make the solid content of the negative electrode slurry 52-55% and the viscosity 3000-8000 mPa·s. After mixing, the mixture is sieved to obtain the negative electrode slurry;

[0039] (c) Single-sided coating: The negative electrode body is placed on a conveyor belt, and the negative electrode slurry is sprayed on the upward side of the negative electrode body by a coating mechanism, and then sent to a drying mechanism, dried at 95°C until the electrode weight loss rate is 0.8%, and then sent out of the drying mechanism, and blown dry by a blowing mechanism until the electrode weight loss rate is 0.6%, and the air pressure of the blowing pipe is 0.4MPa, to obtain a single-sided coated electrode;

[0040] (d) Double-sided coating: Flip the single-sided coated electrode sheet and repeat step (c) to perform double-sided coating, wherein the drying temperature is 105° C. and the air pressure of the air blow pipe is 0.42 MPa to obtain a negative electrode sheet. The weight loss rate of the obtained negative electrode sheet is 0.4%.

[0041] Example 3

[0042] A coating method for reducing negative electrode coating cracking, characterized in that it comprises the following steps:

[0043] (a) Coating device setting: The coating device includes a coating mechanism 2, a drying mechanism 3 and a blowing mechanism 4 which are sequentially arranged along the moving direction of the conveyor belt 1. The blowing mechanism includes three blowing pipes 41. The blowing pipes are respectively provided with regulating valves 42 on both sides for adjusting the gas flow rate. The width of the conveyor belt is 200 mm. The distance between the two regulating valves is 500 mm. The diameter of the blowing pipe is 10 mm. A blowing hole 43 is provided on the side of the pipe body close to the conveyor belt between the two regulating valves. The diameter of the blowing hole is 1 mm. The blowing holes are evenly distributed along the length direction of the blowing pipe with a spacing of 3 mm along the length direction of the blowing pipe and are evenly distributed along the side with a spacing of 2 mm along the side direction.

[0044] (b) Preparation of negative electrode slurry: The negative electrode slurry includes the following components in parts by weight: 95.5 parts of graphite, 1.2 parts of conductive agent, 2.8 parts of binder, and 0.5 parts of thickener, wherein the graphite is mesophase graphite and silicon carbon in a mass ratio of 1:1, the conductive agent is carbon nanotubes, the binder is polyacrylonitrile, and the thickener is sodium carboxymethyl cellulose. First, the raw materials except the binder are stirred at a stirring speed of 25 rpm for 30 min, and then the binder and deionized water are added to make the solid content of the negative electrode slurry 62-65%, and deionized water is added after stirring and mixing again to make the solid content of the negative electrode slurry 52-55%, and the viscosity is 3000-8000 mPa·s. After mixing, the mixture is sieved to obtain the negative electrode slurry;

[0045] (c) Single-sided coating: The negative electrode body is placed on a conveyor belt, and the negative electrode slurry is sprayed on the upward side of the negative electrode body by a coating mechanism, and then sent to a drying mechanism, dried at 105°C until the electrode weight loss rate is 0.8%, and then sent out of the drying mechanism, and blown dry by a blowing mechanism until the electrode weight loss rate is 0.4%, and the air pressure of the blowing pipe is 0.6MPa, to obtain a single-sided coated electrode;

[0046] (d) Double-sided coating: Flip the single-sided coated electrode sheet and repeat step (c) to perform double-sided coating, wherein the drying temperature is 115° C. and the air pressure of the air blow pipe is 0.63 MPa to obtain a negative electrode sheet. The weight loss rate of the obtained negative electrode sheet is 0.4%.

[0047] Example 4

[0048] The only difference between this embodiment and embodiment 1 is that in step (c), the electrode is sent out of the drying mechanism after being dried to a weight loss rate of 1.2%, and then blown dry by the blowing mechanism to a weight loss rate of 0.8%.

[0049] Comparative Example 1

[0050] The difference between this comparative example and Example 1 is that no drying mechanism is used for drying, and in step (c), the electrode is dried by a drying mechanism until the electrode weight loss rate is 0.4%.

[0051] Comparative Example 2

[0052] The difference between this comparative example and Example 1 is that no drying mechanism is used for drying, and in step (c), the electrode is dried by a drying mechanism until the electrode weight loss rate is 0.8%.

[0053] Comparative Example 3

[0054] The difference between this comparative example and Example 1 is that 2% by mass of ethylene carbonate is added to the negative electrode slurry, and no drying mechanism is used for drying. In step (c), the electrode slurry is dried by a drying mechanism until the electrode weight loss rate is 0.4%.

[0055] Comparative Example 4

[0056] The difference between this comparative example and Example 1 is that 2% by mass of N-methylpyrrolidone is added to the negative electrode slurry, and no drying mechanism is used for drying. In step (c), the negative electrode slurry is dried by a drying mechanism until the electrode weight loss rate is 0.4%.

[0057] Comparative Example 5

[0058] The difference between this comparative example and Example 1 is that 1% by mass of N-methylpyrrolidone is added to the negative electrode slurry, and no drying mechanism is used for drying. In step (c), the electrode is dried by a drying mechanism until the electrode weight loss rate is 0.6%.

[0059] For Examples 1-4 of the present invention and Comparative Examples 1-5, abnormalities of the electrode pieces during the coating process and the coating pass rate, including curling and cracking, were counted, the electrode pieces were prepared into battery cells, and the performance of the battery cells was measured. The test results are shown in Table 1.

[0060] Table 1 Negative electrode coating results and performance measurement

[0061] Group Curling Cracking Coating pass rate (%) First efficiency (%) Cycle times (times) Example 1 No curling No cracking 95.5 89.6 2040 Example 2 No curling No cracking 95.3 89.4 2050 Example 3 No curling No cracking 95.6 89.3 2030 Example 4 No curling No cracking 95.4 89.5 2035 Comparative Example 1 crimping Cracking 90.2 88.2 1500 Comparative Example 2 crimping No cracking 94.4 86.5 1300 Comparative Example 3 No curling No cracking 95.2 87.1 1800 Comparative Example 4 No curling No cracking 95.3 87.2 1750 Comparative Example 5 No curling No cracking 95.6 86.5 1700

[0062] It can be seen from Examples 1-4 in the above table that coating the negative electrode sheet according to the method described in the present invention can prevent abnormal phenomena in the electrode sheet during the drying process, improve the coating pass rate, and the quality of the prepared negative electrode sheet is better without curling, cracking and other undesirable phenomena.

[0063] Comparative Examples 1-5 are set up based on Example 1, which has the best comprehensive performance among the above four embodiments. Comparative Example 1 is dried throughout the preparation process. During the drying process, the pole piece is prone to abnormal phenomena such as curling and cracking, which not only has a significant impact on the production efficiency of the coating, but also the obtained negative pole piece is prone to lithium precipitation during the subsequent use, which greatly affects the subsequent use of the negative pole piece. In the preparation process of Comparative Example 2, after the negative pole piece is coated on one side, it is dried by a drying mechanism until the pole piece weight loss rate is 0.8%. If it is not dried to a suitable degree after the single-sided coating, it will cause the roller to stick during the subsequent double-sided coating process, and normal production cannot be achieved. At the same time, it will also lead to a decrease in the coating qualification rate. Comparative Examples 3-5 use organic solvents in the negative electrode slurry. Although the abnormal coating of the pole piece can be improved without using a blowing mechanism to dry, the prepared negative pole piece will cause the quality of the battery cell to decrease during the preparation of the battery cell application, including the first efficiency of the battery cell and the number of cycles. This may be due to the residual organic solvent inside the pole piece during the coating process.

Claims

1. A coating method for reducing cracking of negative electrode coating, characterized in that: The following steps are involved: (a) Coating device arrangement: The coating device comprises a coating mechanism (2), a drying mechanism (3) and a blowing mechanism (4) which are arranged in sequence along the moving direction of the conveyor belt (1), the blowing mechanism comprising a plurality of blowing pipes (41), both sides of which are provided with regulating valves (42) for regulating the gas flow rate, the distance between the two regulating valves being greater than the width of the conveyor belt, and a plurality of blowing holes (43) being provided on the side of the pipe body between the two regulating valves close to the conveyor belt, the diameter of the blowing holes being 1 to 2 mm, and the spacing between the blowing holes being 3 to 5 mm; (b) Preparation of negative electrode slurry: Mix and stir the raw materials according to the formula, add deionized water to adjust the solid content and viscosity, and sieve to obtain the negative electrode slurry; (c) Single-sided coating: The negative electrode body is placed on a conveyor belt, and the negative electrode slurry is sprayed or rolled on the upward side of the negative electrode body by a coating mechanism, and then sent to a drying mechanism, dried at 90-105°C until the electrode weight loss rate is 0.8-1.2%, and then sent out of the drying mechanism, and blown dry by a blowing mechanism until the electrode weight loss rate is 0.4-0.8%, and the air pressure of the blowing pipe is 0.3-0.6MPa, to obtain a single-sided coated electrode; (d) Double-sided coating: Flip the single-sided coated electrode and repeat step (c) to perform double-sided coating, wherein the drying temperature is 95-120°C, the air pressure of the air blower is 0.315-0.66MPa, and the air blowing mechanism is used to dry the electrode until the weight loss rate of the electrode is 0.1-0.4%, thereby obtaining a negative electrode.

2. A coating method for reducing negative electrode coating cracking according to claim 1, characterized in that: The number of the air blowing pipes is 1 to 3.

3. A coating method for reducing negative electrode coating cracking according to claim 1, characterized in that: The distance between the two regulating valves is 200-1500 mm.

4. A coating method for reducing negative electrode coating cracking according to claim 1, characterized in that: The diameter of the air blowing tube is 8-10 mm.

5. A coating method for reducing negative electrode coating cracking according to claim 1, characterized in that: The blowing holes are evenly distributed along the length direction of the blowing pipe, and the blowing holes are evenly distributed along the side.

6. A coating method for reducing negative electrode coating cracking according to claim 1, characterized in that: The weight loss rate is determined by keeping the pole piece at a constant temperature of 150° C. for 5 minutes, and calculating the weight loss rate of the pole piece before and after the constant temperature, which is the weight loss rate.

7. A coating method for reducing negative electrode coating cracking according to claim 1, characterized in that: The negative electrode slurry comprises the following components in parts by weight: 92-98 parts of graphite, 1-2 parts of a conductive agent, 2-4 parts of a binder, and 0.1-1 parts of a thickener.

8. A coating method for reducing negative electrode coating cracking according to claim 7, characterized in that: The graphite is one of artificial graphite, mesophase graphite, natural graphite, silicon carbon, soft carbon, and hard carbon, or a combination thereof; the conductive agent is one of carbon black, Ketjen black, flaky graphite conductive agent, carbon nanotubes, and graphene, or a combination thereof.

9. A coating method for reducing negative electrode coating cracking according to claim 7, characterized in that: The thickener is sodium carboxymethyl cellulose, and the binder is one of polyacrylic acid, polyacrylonitrile, styrene-butadiene rubber or a combination thereof.

10. A coating method for reducing negative electrode coating cracking according to claim 7, characterized in that: In the step (b), the raw materials except the binder are first stirred at a stirring speed of 20-25 rpm for 30-60 min, and then the binder and deionized water are added to make the solid content of the negative electrode slurry 62-65%, and after stirring and mixing again, deionized water is added to make the solid content of the negative electrode slurry 52-55% and the viscosity 3000-8000 mPa·s.

Images