Preparation method of negative pole piece, negative pole piece and battery

Abstract

The invention provides a preparation method of a negative pole piece, the negative pole piece and a battery, and the preparation method comprises the following steps: coating two layers of bottom layer slurry and surface layer slurry on the surface of one side of a negative current collector to obtain a bottom layer and a surface layer, and then drying to obtain the negative pole piece, the bottom layer slurry comprises a graphite material and a zero-dimensional conductive agent, and the surface layer slurry comprises a silicon-based material, an acrylic acid binder and a two-dimensional conductive agent; the drying comprises the steps of pre-drying the bottom layer and performing final drying on the surface layer, the pre-drying humidity is greater than the final drying humidity, and the pre-drying humidity is less than 40%, so that the water content of the bottom layer and the water content of the surface layer are changed in a gradient manner. According to the preparation method disclosed by the invention, the bottom layer and the surface layer control different water contents through functional differentiation of the binder on the bottom layer and the surface layer, the surface density fluctuation is reduced, the interlayer binding force is improved, and the contradiction that reduction of silicon-based negative electrode expansion and improvement of fast charging cannot be realized at the same time is solved.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a method for preparing a negative electrode sheet, the negative electrode sheet and the battery. Background Technology

[0002] In lithium-ion batteries, the selection and optimization of anode materials has always been a key research focus. While traditional graphite anode materials possess good cycle stability and high conductivity, their theoretical capacity is only 372 mAh / g, which to some extent limits further improvements in the energy density of lithium-ion batteries. Silicon materials, on the other hand, have a theoretical capacity as high as 4200 mAh / g, more than 11 times that of graphite. Therefore, silicon anodes can achieve significantly higher energy densities compared to graphite anodes.

[0003] However, silicon undergoes significant volume changes during lithium-ion insertion and extraction, with a volume change rate reaching 300%. Therefore, traditional anode sheets only have a single layer of silicon anode material. The expansion of the silicon anode material leads to coating peeling, severely impacting battery cycle life and even posing safety risks. Existing technologies utilize a double-layer coating process to improve the discharge capacity of lithium-ion batteries and reduce silicon material expansion. However, the double-layer coating process suffers from low precision in controlling surface density (±3g / m³). 2 The interlayer bonding force is insufficient (peel strength < 0.2 N / mm), and the problems of adhesive functional differentiation and pore orientation control have not been solved, making it impossible to solve the problem that reducing the expansion of silicon-based anodes and improving fast charging performance are mutually exclusive.

[0004] Based on the above research, there is a need to provide a method for preparing a negative electrode sheet, which can resolve the contradiction between reducing the expansion of silicon-based negative electrodes and improving fast charging. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a negative electrode sheet, a negative electrode sheet and a battery. The preparation method achieves functional differentiation between the bottom layer and the surface layer binder, controls different water contents in the bottom layer and the surface layer, reduces areal density fluctuations, and improves interlayer bonding, thus solving the contradiction between reducing the expansion of silicon-based negative electrodes and improving fast charging.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a negative electrode sheet, the method comprising the following steps:

[0008] A double-layer slurry and a top slurry are applied to one side of the negative electrode current collector to obtain the bottom layer and the top layer, which are then dried to obtain the negative electrode sheet.

[0009] The bottom layer slurry is directly coated on one side surface of the negative electrode current collector. The bottom layer slurry includes graphite material and zero-dimensional conductive agent. The top layer slurry includes silicon-based material, acrylic binder and two-dimensional conductive agent.

[0010] The drying process includes pre-drying the bottom layer and final drying the surface layer. The humidity of the pre-drying layer is greater than that of the final drying layer, and the humidity of the pre-drying layer is less than 40%, so that the moisture content of the bottom layer and the surface layer change in a gradient.

[0011] This invention employs a double-layer coating process, consisting of a graphite-based bottom layer and a silicon-based top layer. Firstly, a highly conductive and easily dispersed zero-dimensional conductive agent (such as SP) is incorporated into the bottom layer to improve lateral electron transport efficiency and mitigate current collector edge effects. A two-dimensional conductive agent (such as graphene) is incorporated into the top layer to construct vertical ion channels, enhancing lithium-ion diffusion speed and thus optimizing kinetics and improving fast-charging performance. Secondly, a highly elastic acrylic binder is used on the top layer to absorb the volume expansion of the silicon-based material, preventing coating cracking. Thirdly, the invention employs zoned drying, with the bottom layer pre-drying in a high-humidity environment and the top layer final-drying in a low-humidity environment. This achieves a gradient change in moisture content between the bottom and top layers, preventing slurry interchange and improving interlayer adhesion. Therefore, this invention, through the combination of these three aspects, resolves the contradiction between reducing silicon-based anode expansion and improving fast charging performance.

[0012] The humidity of the pre-drying is greater than that of the final drying, and the humidity of the pre-drying is less than 40%, for example, it can be 38%, 35%, 30% or 25%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably less than 40% and greater than 25%.

[0013] The present invention controls the pre-drying humidity to be <40%. If the pre-drying humidity is >40%, the areal density will fluctuate by >±3.5g / m³. 2 This leads to a decrease in interlayer bonding strength and an increase in the expansion rate of the negative electrode sheet.

[0014] Preferably, the final drying temperature is greater than the pre-drying temperature, the final drying time is greater than the pre-drying time, and the final drying air velocity is greater than the pre-drying air velocity.

[0015] The present invention also controls the temperature, time and wind speed of the final drying to be greater than those of the pre-drying temperature, time and wind speed, thereby achieving humidity zoning through the combination of wind speed and temperature gradient, and further ensuring the gradient change of moisture content between the bottom layer and the surface layer.

[0016] This invention controls the temperature of pre-drying and final drying through a thermostat, the wind speed of pre-drying and final drying through a variable frequency fan, the humidity of pre-drying and final drying through a humidifier and a dehumidifier, and the time of pre-drying and final drying through a conveyor speed control mechanism.

[0017] Preferably, the pre-baking temperature is 75℃-85℃, for example, it can be 75℃, 77.5℃, 80℃, 82.5℃ or 85℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0018] Preferably, the pre-baking time is 55s-65s, for example, 55s, 57.5s, 60s, 62.5s or 65s, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] Preferably, the pre-drying wind speed is 1.5m / s-2.5m / s, for example, it can be 1.5m / s, 1.7m / s, 1.9m / s, 2.1m / s, 2.3m / s or 2.5m / s, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0020] Preferably, the final drying humidity is <10%, for example, it can be 9%, 8%, 7%, 6%, 5%, 4% or 3%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] Preferably, the final drying temperature is 105℃-115℃, for example, it can be 105℃, 107℃, 109℃, 111℃, 113℃ or 115℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0022] Preferably, the final drying time is 85s-95s, for example, it can be 85s, 87s, 89s, 91s, 93s or 95s, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] Preferably, the final drying air velocity is 7.5m / s-8.5m / s, for example, it can be 7.5m / s, 7.7m / s, 7.9m / s, 8.1m / s, 8.3m / s or 8.5m / s, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] Preferably, a first areal density test is performed after the double coating and before drying, and a second areal density test is performed after drying.

[0025] This invention monitors the stability of coating surface density through surface density detection, adjusts surface density through feedback values, and ensures the consistency of coating surface density. When monitoring surface density, one method is to monitor the surface density in the wet state, that is, before drying, and the other method is to monitor the surface density after drying. The purpose of the first surface density detection is mainly: (1) to compensate the surface density of the surface layer in real time before the bottom slurry is cured (before drying), to ensure the accuracy and consistency of surface density; (2) since the slurry is fluid and has leveling properties, it can be adjusted in real time through dynamic surface density control; (3) real-time monitoring can eliminate the problem of uneven coating thickness caused by the shaking of the conveyor current collector, which is also to control the consistency of coating surface density. The second surface density detection is carried out after baking. Through the feedback of the surface density of the dried electrode, the next coating is adjusted in real time to ensure the consistency of the electrode surface density.

[0026] Preferably, a beta-ray instrument is used to perform the first areal density detection and the second areal density detection in real time.

[0027] The dynamic areal density control of this invention is achieved through real-time detection using a β-ray instrument, and real-time adjustment of areal density is performed using the following formula: ΔQ=K×ΔDt, K=1.0, where ΔQ represents the pump speed compensation amount, K represents the compensation coefficient, and ΔDt represents the areal density deviation value.

[0028] It is understood that the overall process of the preparation method described in this invention includes the following steps performed in sequence: coating and unwinding → web correction → coating → first surface density detection → drying → web correction → second surface density detection → winding.

[0029] Preferably, the zero-dimensional conductive agent includes SP.

[0030] Preferably, the slurry also includes an underlayer binder, which includes CMC (carboxymethyl cellulose) and SBR (styrene-butadiene rubber).

[0031] The bottom adhesive of this invention uses a highly adhesive adhesive to achieve functional differentiation of the adhesive.

[0032] Preferably, in the bottom slurry, the mass ratio of graphite material, SP, CMC and SBR is (92.5-95.5):(2-3):(1-2):(1.5-2.5), for example, it can be 94:2.5:1.5:2, 92.5:3:2:2.5 or 95.5:2:1:1.5, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Preferably, the two-dimensional conductive agent includes graphene.

[0034] Preferably, in the surface slurry, the mass ratio of silicon-based material, acrylic binder and graphene is (85.7-87.2):(6.3-6.8):(6.5-7.5), for example, it can be 86.5:6.5:7, 85.7:6.8:7.5 or 87.2:6.3:6.5, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] In the preferred embodiment of the present invention, the silicon-based material, acrylic binder and graphene are in a specific mass ratio range, such that the surface layer contains 6.3-6.8 wt% acrylic binder. When the acrylic binder content is too low, the peel strength of the electrode will decrease. For example, when it drops to 5 wt%, the peel strength will decrease by 28%.

[0036] Preferably, the acrylic adhesive includes PAA (polyacrylic acid).

[0037] Preferably, the silicon-based material includes silicon-carbon materials.

[0038] Preferably, the thickness of the bottom layer is 38μm-42μm, for example, it can be 38μm, 39μm, 40μm, 41μm or 42μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] Preferably, the thickness of the surface layer is 25μm-29μm, for example, it can be 25μm, 26μm, 27μm, 28μm or 29μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0040] Preferably, the die gap difference of the double coating is ≥15μm, for example, it can be 15μm, 17.5μm, 20μm, 22.5μm, 25μm, 27.5μm or 30μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0041] When the die gap difference in the double-layer coating of this invention is <15μm, the risk of mixing the slurry increases by more than 40%.

[0042] Preferably, after the preparation method involves double-coating the bottom layer slurry and the top layer slurry, and before drying, double-coating the bottom layer slurry and the top layer slurry on the other side of the negative electrode current collector, so that a bottom layer and a top layer are obtained on both sides of the negative electrode current collector.

[0043] In a second aspect, the present invention provides a negative electrode sheet, which is prepared by the preparation method described in the first aspect.

[0044] Thirdly, the present invention provides a battery comprising a negative electrode as described in the second aspect.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] This invention employs a double-layer coating system consisting of a graphite-based bottom layer and a silicon-based top layer. Firstly, a highly conductive zero-dimensional conductive agent is incorporated into the bottom layer to improve lateral electron transport efficiency and mitigate current collector edge effects. A two-dimensional conductive agent is then incorporated into the top layer to construct vertical ion channels, enhancing lithium-ion diffusion speed and thus optimizing kinetics and improving fast-charging performance. Secondly, a highly elastic acrylic binder is used on the top layer to absorb the volume expansion of the silicon-based material, preventing coating cracking. Thirdly, the invention utilizes a zoned drying process: the bottom layer is pre-dried in a high-humidity environment, while the top layer is final-dried in a low-humidity environment. This achieves a gradient change in moisture content between the bottom and top layers, preventing slurry interchange and improving interlayer adhesion. Therefore, this invention, through the combination of these three aspects, resolves the contradiction between reducing silicon-based anode expansion and improving fast charging performance. Detailed Implementation

[0047] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0048] Example 1

[0049] This embodiment provides a method for preparing a negative electrode sheet, the method comprising the following steps:

[0050] After the copper foil is unwound and corrected, a double layer of bottom slurry and a top slurry are applied to one side of the copper foil to obtain a bottom layer with a thickness of 40 μm and a top layer with a thickness of 27 μm. The density of the first surface is detected in real time using a β-ray instrument, and then the foil is dried. After drying, the foil is corrected, and the density of the second surface is detected in real time using a β-ray instrument. After winding, the negative electrode sheet is obtained.

[0051] The bottom layer slurry is directly coated on one side of the copper foil. The bottom layer slurry includes artificial graphite material, SP, CMC and SBR in a mass ratio of 94.0:2.5:1.5:2.0. The top layer slurry includes silicon carbide material, PAA and graphene in a mass ratio of 86.5:6.5:7.

[0052] The drying process includes pre-drying the bottom layer and final drying the top layer. The pre-drying humidity is 30%, the pre-drying temperature is 80°C, the pre-drying time is 60 seconds, and the pre-drying air velocity is 2 m / s. The final drying humidity is 8%, the final drying temperature is 108°C, the final drying time is 90 seconds, and the final drying air velocity is 8 m / s, resulting in a gradient change in the moisture content of the bottom layer and the top layer (the moisture content of the bottom layer is 15%).

[0053] Example 2

[0054] This embodiment provides a method for preparing a negative electrode sheet, the method comprising the following steps:

[0055] After the copper foil is unwound and corrected, a double layer of bottom slurry and a top slurry are applied to one side of the copper foil to obtain a bottom layer with a thickness of 42 μm and a top layer with a thickness of 29 μm. The density of the first surface is detected in real time using a β-ray instrument, and then the foil is dried. After drying, the foil is corrected, and the density of the second surface is detected in real time using a β-ray instrument. After winding, the negative electrode sheet is obtained.

[0056] The bottom layer slurry is directly coated on one side of the copper foil. The bottom layer slurry includes artificial graphite material, SP, CMC and SBR in a mass ratio of 92.5:3:2:2.5. The top layer slurry includes silicon carbide material, PAA and graphene in a mass ratio of 85.7:6.8:7.5.

[0057] The drying process includes pre-drying the bottom layer and final drying the surface layer. The pre-drying humidity is 30%, the pre-drying temperature is 80°C, the pre-drying time is 65 seconds, and the pre-drying air velocity is 2 m / s. The final drying humidity is 3%, the final drying temperature is 115°C, the final drying time is 85 seconds, and the final drying air velocity is 8.5 m / s, thereby creating a gradient change in the moisture content of the bottom layer and the surface layer.

[0058] Example 3

[0059] This embodiment provides a method for preparing a negative electrode sheet, the method comprising the following steps:

[0060] After the copper foil is unwound and corrected, a double layer of bottom slurry and a top slurry are applied to one side of the copper foil to obtain a bottom layer with a thickness of 38 μm and a top layer with a thickness of 25 μm. The density of the first surface is detected in real time using a β-ray instrument, and then the foil is dried. After drying, the foil is corrected, and the density of the second surface is detected in real time using a β-ray instrument. After winding, the negative electrode sheet is obtained.

[0061] The bottom layer slurry is directly coated on one side of the copper foil. The bottom layer slurry includes artificial graphite material, SP, CMC and SBR in a mass ratio of 95.5:2:1:1.5. The top layer slurry includes silicon carbide material, PAA and graphene in a mass ratio of 87.2:6.3:6.5.

[0062] The drying process includes pre-drying the bottom layer and final drying the surface layer. The pre-drying humidity is 30%, the pre-drying temperature is 80°C, the pre-drying time is 55 seconds, and the pre-drying air velocity is 2 m / s. The final drying humidity is 8%, the final drying temperature is 108°C, the final drying time is 90 seconds, and the final drying air velocity is 8 m / s, thereby creating a gradient change in the moisture content of the bottom layer and the surface layer.

[0063] Example 4

[0064] This embodiment provides a method for preparing a negative electrode sheet. The preparation method is the same as in Embodiment 1, except that the humidity of the pre-drying is 25% (achieved by setting the pre-drying temperature to 84°C and the wind speed to 2m / s).

[0065] Example 5

[0066] This embodiment provides a method for preparing a negative electrode sheet. The preparation method is the same as in Embodiment 1, except that the humidity of the pre-drying is 38% (achieved by setting the pre-drying temperature to 78°C and the wind speed to 2m / s, resulting in a humidity of 35%).

[0067] Example 6

[0068] This embodiment provides a method for preparing a negative electrode sheet. The preparation method is the same as in Example 1, except that the mass ratio of silicon carbide, PAA and graphene in the surface slurry is 87.5:5.5:7.

[0069] Comparative Example 1

[0070] This comparative example provides a method for preparing a negative electrode sheet. The preparation method is the same as in Example 1, except that the PAA and other components in the surface slurry are replaced with SBR.

[0071] Comparative Example 2

[0072] This comparative example provides a method for preparing a negative electrode sheet. The preparation method is the same as in Example 1, except that the humidity of the pre-drying is 40% (achieved by setting the pre-drying temperature to 76°C and the wind speed to 2m / s).

[0073] Comparative Example 3

[0074] This comparative example provides a method for preparing a negative electrode sheet. The preparation method is the same as in Example 1, except that the humidity of the pre-drying is 45% (achieved by setting the pre-drying temperature to 45°C and the wind speed to 2m / s).

[0075] Comparative Example 4

[0076] This comparative example provides a method for preparing a negative electrode sheet. The preparation method is the same as in Example 1, except that the pre-drying conditions and the final drying conditions are the same: humidity is 8%, temperature is 108℃, time is 90s, and wind speed is 8m / s.

[0077] The negative electrode sheets obtained in the above embodiments and comparative examples were assembled into batteries with lithium nickel cobalt manganese oxide positive electrodes, polypropylene separators, and lithium hexafluorophosphate electrolyte. The batteries were then subjected to expansion rate and fast-charging performance tests. The expansion rate test involved cutting the coated negative electrode sheet to a specified size, measuring its initial thickness H0, assembling the electrode sheet into a battery, and performing charge-discharge cycles. After 500 cycles, the battery was disassembled, the electrode sheet was removed, cleaned, dried, and its thickness was measured and recorded as H1. The expansion rate of the electrode sheet after 500 cycles was calculated as [(H1-H0) / H0]×100%. The expansion rate test conditions were: ambient temperature... Temperature: 25±2°C; Cycling regime: Charging: Charge at 3C constant current to the upper limit voltage (e.g., 4.2V), then charge at constant voltage until the current drops to 0.05C; Discharging: Discharge at 3C constant current to the cutoff voltage (e.g., 3.0V), this is one cycle; Number of cycles: 500 cycles; Disassembly environment: After cycling, the battery is fully charged (at which point the negative electrode has the most lithium intercalation and the largest expansion), disassembled in an argon-protected glove box, remove the electrode sheets and gently rinse with DMC solvent to remove electrolyte residue, dry and then measure the thickness; Measuring tool: Micrometer, take at least 5 points at the same position on the electrode sheet to measure the thickness.

[0078] The fast charging performance test method and conditions are as follows: (1) Discharge the battery at 1C constant current to the cutoff voltage (e.g., 3.0V); (2) Let it stand for 5 minutes; (3) Charge the battery at different high rates (e.g., 2C, 3C) at constant current to the upper limit voltage (e.g., 4.2V) and record the charging time; (4) Discharge the battery at 1C constant current to the cutoff voltage and record the discharged capacity C0 fast charging; (5) Compare the discharged capacity C1 after 1C constant current charging; 1C fast charging capacity retention rate = (C0 fast charging / C1) × 100%; The test steps for 3C fast charging capacity retention rate are the same as above, and the test environment is within 25℃±2°C.

[0079] The test results are shown in Table 1 below:

[0080] Table 1

[0081]

[0082] As can be seen from Table 1 above:

[0083] As can be seen from Examples 1-5 and Comparative Example 1, the surface adhesive of the present invention uses a highly elastic acrylic adhesive, which absorbs the volume expansion of the silicon-based material, thereby reducing electrode expansion. As can be seen from Examples 1-5 and Comparative Examples 2-3, when the humidity of the pre-baking is <40% and greater than the humidity of the final baking, it can prevent the mixing of the bottom slurry and the surface slurry, improve the interlayer bonding force, and reduce electrode expansion. As can be seen from Examples 1-5 and Comparative Example 4, when the pre-baking conditions are the same as the final baking conditions, the interlayer bonding force decreases and the electrode expansion rate increases. As can be seen from Examples 1 and 6, when the content of the surface adhesive of the present invention is too low, it will affect the electrode expansion rate, preferably within a specific range.

[0084] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a negative electrode sheet, characterized in that, The preparation method includes the following steps: A double-layer slurry and a top slurry are applied to one side of the negative electrode current collector to obtain the bottom layer and the top layer, which are then dried to obtain the negative electrode sheet. The bottom layer slurry is directly coated on one side surface of the negative electrode current collector. The bottom layer slurry includes graphite material and zero-dimensional conductive agent. The top layer slurry includes silicon-based material, acrylic binder and two-dimensional conductive agent. The drying process includes pre-drying the bottom layer and final drying the surface layer. The humidity of the pre-drying layer is greater than that of the final drying layer, and the humidity of the pre-drying layer is less than 40%, so that the moisture content of the bottom layer and the surface layer change in a gradient.

2. The preparation method according to claim 1, characterized in that, The final drying temperature is greater than the pre-drying temperature, the final drying time is greater than the pre-drying time, and the final drying air velocity is greater than the pre-drying air velocity.

3. The preparation method according to claim 1 or 2, characterized in that, The humidity of the pre-drying process is <40% and ≥25%; And / or, the pre-baking temperature is 75℃-85℃; And / or, the pre-baking time is 55s-65s; And / or, the pre-drying air velocity is 1.5m / s-2.5m / s.

4. The preparation method according to claim 3, characterized in that, The final drying humidity is <10%; And / or, the final drying temperature is 105℃-115℃; And / or, the final drying time is 85s-95s; And / or, the final drying air velocity is 7.5 m / s-8.5 m / s.

5. The preparation method according to claim 1 or 2, characterized in that, After the double coating is applied and before drying, a first surface density test is performed, and after drying, a second surface density test is performed. The first areal density and the second areal density were detected in real time using a beta-ray instrument.

6. The preparation method according to claim 1 or 2, characterized in that, The zero-dimensional conductive agent includes SP; And / or, the underlying slurry further includes an underlying binder, the underlying binder including CMC and SBR; in the underlying slurry, the mass ratio of graphite material, SP, CMC and SBR is (92.5-95.5):(2-3):(1-2):(1.5-2.5).

7. The preparation method according to claim 1 or 2, characterized in that, The two-dimensional conductive agent includes graphene; in the surface slurry, the mass ratio of silicon-based material, acrylic binder and graphene is (85.7-87.2):(6.3-6.8):(6.5-7.5); the acrylic binder includes PAA.

8. The preparation method according to claim 1 or 2, characterized in that, The thickness of the bottom layer is 38μm-42μm; And / or, the thickness of the surface layer is 25μm-29μm; And / or, the die gap difference of the double coating is ≥15μm; And / or, after the preparation method involves double-coating the bottom layer slurry and the top layer slurry, and before drying, double-coating the bottom layer slurry and the top layer slurry on the other side of the negative electrode current collector, thus obtaining the bottom layer and the top layer on both sides of the negative electrode current collector.

9. A negative electrode sheet, characterized in that, The negative electrode sheet is prepared by the preparation method according to any one of claims 1-8.

10. A battery, characterized in that, The battery includes the negative electrode as described in claim 9.

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