Negative electrode sheet and preparation method thereof, lithium battery

Abstract

The present invention provides a negative electrode sheet and a preparation method thereof, and a lithium battery. The preparation method comprises the following steps: coating a first negative electrode slurry on the outer surface of a current collector to form a first negative electrode layer; sequentially coating a wetting agent and a second negative electrode slurry on the outer surface of the first negative electrode layer away from the current collector to form a second negative electrode layer to obtain a negative electrode sheet; wherein the first negative electrode slurry comprises a first negative electrode material, water and an organic solvent; the second negative electrode slurry comprises a second negative electrode material and water; the first negative electrode material is different from the second negative electrode material. Based on this, the wettability of two completely different negative electrode materials can be greatly improved, further avoiding the incompatibility problem caused by the excessively large contact angle between the materials, so that they are divided into upper and lower layers and completely adhered to the negative electrode current collector, and then the battery can simultaneously take into account a better battery capacity and capacity retention rate at a conventional coating thickness.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a negative electrode plate and a preparation method thereof, and a lithium battery. Background Art

[0002] There are three coating methods in the current lithium-ion battery manufacturing process: blade coating, transfer coating and extrusion coating. The main points to be controlled during the coating process are the thickness of the slurry coating and the surface density after coating; and it is necessary to ensure that the solvent inside the slurry has been removed after the electrode is dried in the oven, so that the slurry can adhere to the current collector evenly and stably.

[0003] In order to seek better performance output of negative electrode materials at the production end, the prior art generally adopts the premise of not changing the thickness of the electrode sheet and the main material of the negative electrode material, rationally changing the ratio of different additives, binders and conductive agents in the slurry configured with the negative electrode material, and then dividing the two slurries with different ratios (containing the same negative electrode material) into two layers and evenly coating them on the copper foil. However, in the above-mentioned double-layer coating process, when the negative electrode main material of the slurry only contains graphite negative electrode material, the battery capacity is slightly worse, and when the negative electrode main material of the slurry only contains silicon-carbon negative electrode material, the volume expansion effect of the silicon-carbon negative electrode material will lead to poor battery capacity retention.

[0004] In summary, the existing double-layer coated negative electrode material has the problem that it is not possible to simultaneously give the battery a better capacity and a better capacity retention rate. Based on this, it is necessary to provide a new negative electrode material that allows the battery to simultaneously give the battery a better capacity and a better capacity retention rate. Summary of the invention

[0005] The main purpose of the present invention is to provide a negative electrode plate and a preparation method thereof, and a lithium battery, so as to solve the problem in the prior art that the negative electrode material cannot make the battery have both better capacity and capacity retention rate.

[0006] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, a method for preparing a negative electrode plate is provided, and the preparation method comprises the following steps: providing a current collector; coating a first negative electrode slurry on the outer surface of the current collector, and forming a first negative electrode layer on the outer surface of the current collector after a first drying; sequentially coating a wetting agent and a second negative electrode slurry on the outer surface of the first negative electrode layer away from the current collector, and forming a second negative electrode layer on the outer surface of the first negative electrode layer away from the current collector after a second drying, to obtain a negative electrode plate; wherein the first negative electrode slurry comprises a first negative electrode material, water and an organic solvent; the second negative electrode slurry comprises a second negative electrode material and water; and the first negative electrode material is different from the second negative electrode material.

[0007] Furthermore, the first negative electrode material and the second negative electrode material are each independently selected from silicon-carbon negative electrode material and / or graphite negative electrode material; preferably, the first negative electrode material is silicon-carbon negative electrode material, and the second negative electrode material is graphite negative electrode material.

[0008] Furthermore, in the first negative electrode slurry, the weight content of the organic solvent is 1-4%; preferably, the solid content of the first negative electrode slurry and the second negative electrode slurry is independently 40-60%.

[0009] Furthermore, the organic solvent and the wetting agent do not chemically react with the first negative electrode material and the second negative electrode material.

[0010] Furthermore, the organic solvent is selected from one or more of N,N-dimethylformamide, N-methylpyrrolidone or 1,3-butanediol.

[0011] Furthermore, the wetting agent is selected from ethanol and / or water.

[0012] Furthermore, the wetting agent is applied by atomization spraying; preferably, during the atomization spraying process, the atomization flow rate of the wetting agent is 120 to 240 mL / min; preferably, the atomization spraying time is 1 to 3 s per square meter of the outer surface to be coated.

[0013] Furthermore, the drying temperature of the first drying is 65-95° C., and the drying time is 20-30 seconds; preferably, the drying temperature of the second drying is 85-105° C., and the drying time is 30-40 seconds.

[0014] In order to achieve the above object, according to one aspect of the present invention, a negative electrode sheet is provided, and the negative electrode sheet is prepared by the above-mentioned method for preparing a negative electrode sheet.

[0015] According to another aspect of the present invention, a lithium-ion battery is provided, and the lithium-ion battery includes the aforementioned negative electrode plate.

[0016] Based on the above-mentioned specific coating steps, on the one hand, the wettability of two completely different negative electrode materials can be greatly improved, further avoiding the incompatibility problem caused by the excessively large contact angle between the materials, so that they are divided into upper and lower layers and completely bonded to the negative electrode current collector, and then the battery can take into account both the better battery capacity and capacity retention rate at the conventional coating thickness; on the other hand, the slurry can have excellent coating uniformity, so that the two completely different negative electrode materials can be evenly dispersed in the product, and their respective performance can be exerted to a greater extent. Furthermore, the above-mentioned preparation method of the present invention does not need to introduce additional binders between layers, so that two completely different negative electrode materials can be divided into upper and lower layers and completely bonded to the negative electrode current collector. The preparation method is simple and easy to operate, the industrial production cost is low, and the application prospect is high. DETAILED DESCRIPTION

[0017] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0018] As described in the background of the present invention, the negative electrode materials in the prior art cannot make the battery have both better capacity and capacity retention rate. In order to solve this problem, the present invention provides a method for preparing a negative electrode plate, which comprises the following steps: providing a current collector; coating a first negative electrode slurry on the outer surface of the current collector, and forming a first negative electrode layer on the outer surface of the current collector after a first drying; sequentially coating a wetting agent and a second negative electrode slurry on the outer surface of the first negative electrode layer away from the current collector, and forming a second negative electrode layer on the outer surface of the first negative electrode layer away from the current collector after a second drying, to obtain a negative electrode plate; wherein the first negative electrode slurry comprises a first negative electrode material, water and an organic solvent; the second negative electrode slurry comprises a second negative electrode material and water; and the first negative electrode material is different from the second negative electrode material.

[0019] The present invention uses two completely different negative electrode materials for double-layer coating, so that the battery can take into account both the better capacity and capacity retention rate. In particular, when using two completely different negative electrode materials for double-layer coating, the technicians of the present invention found that the change of the main material of the double-layer coating will cause coating failure due to the incompatibility between the interfaces, such as the phenomenon of cracks after the top layer is dried, or the phenomenon that the second layer cannot be coated on the first layer due to wettability reasons. Based on this, the present invention further proposes: firstly apply the first negative electrode slurry (first negative electrode material, water and organic solvent) on the outer surface of the current collector, and after the first drying, form the first negative electrode layer on the outer surface of the current collector; then apply the wetting agent and the second negative electrode slurry (including the second negative electrode material and water) on the outer surface of the first negative electrode layer away from the current collector in sequence, and after the second drying, form the second negative electrode layer on the outer surface of the first negative electrode layer away from the current collector to obtain a negative electrode sheet.

[0020] In this way, even if the present application uses two completely different negative electrode materials for double-layer coating, the coating effect is also very excellent. Based on the above-mentioned specific coating steps, on the one hand, the wettability of the two completely different negative electrode materials can be greatly improved, and the incompatibility problem caused by the excessively large contact angle between the materials can be further avoided, so that they are divided into upper and lower layers and completely bonded to the negative electrode current collector, and then at the conventional coating thickness, the battery can simultaneously take into account the better battery capacity and capacity retention rate; on the other hand, the slurry can have excellent coating uniformity, so that the two completely different negative electrode materials can be evenly dispersed in the product, and their respective performances can be exerted to a greater extent. Furthermore, the above-mentioned preparation method of the present invention does not need to introduce additional binders between layers, so that two completely different negative electrode materials can be divided into upper and lower layers and completely bonded to the negative electrode current collector. The preparation method is simple and easy to operate, the industrial production cost is low, and the application prospect is high.

[0021] It should be additionally added here that, in order to further improve the coating effect, those skilled in the art may apply the second negative electrode slurry before the wetting agent is completely dry.

[0022] In a preferred embodiment, the first negative electrode material and the second negative electrode material are each independently selected from silicon-carbon negative electrode materials and / or graphite negative electrode materials. For example, the first negative electrode material is a silicon-carbon negative electrode material, and the second negative electrode material is a graphite negative electrode material; or, the first negative electrode material is a graphite negative electrode material, and the second negative electrode material is a silicon-carbon negative electrode material; or, the first negative electrode material is a silicon-carbon negative electrode material, and the second negative electrode material is a silicon-carbon negative electrode material and a graphite negative electrode material mixed in a certain proportion; or, the first negative electrode material is a silicon-carbon negative electrode material and a graphite negative electrode material mixed in a certain proportion, and the second negative electrode material is a silicon-carbon negative electrode material; or, the first negative electrode material is a silicon-carbon negative electrode material and a graphite negative electrode material mixed in a certain proportion, and the second negative electrode material is a silicon-carbon negative electrode material; or, the first negative electrode material is a silicon-carbon negative electrode material and a graphite negative electrode material mixed in a certain proportion, and the second negative electrode material is a silicon-carbon negative electrode material and a graphite negative electrode material mixed in a different proportion from the first negative electrode material.

[0023] More preferably, the first negative electrode material is a silicon-carbon negative electrode material, and the second negative electrode material is a graphite negative electrode material. Based on this, the silicon-carbon negative electrode material as the first negative electrode material can greatly increase the capacity of the battery, and it is arranged as an intermediate layer between the graphite layer and the current collector, which can effectively alleviate the volume expansion effect of the silicon-carbon negative electrode material, so that the battery can also take into account a better capacity retention rate at the same time. In addition, when the first negative electrode material is a silicon-carbon negative electrode material, the first negative electrode slurry may also include a binder commonly used in the art, such as polyacrylic acid, to better bond the silicon-carbon negative electrode material. Preferably, the amount of the binder is 3 to 5% of the weight of the silicon-carbon negative electrode material.

[0024] In order to further improve the coating effect, the weight content of the organic solvent in the first negative electrode slurry is preferably 1-4%, for example, 1%, 2%, 3% or 4%. The addition of 1-4% organic solvent can reduce the surface tension of the slurry in a solidified state after drying, so as to facilitate the attachment of the second negative electrode to the first negative electrode. Preferably, the solid content of the first negative electrode slurry and the second negative electrode slurry is independently 40-60%. Based on this, on the one hand, the wettability of the two completely different negative electrode materials can be further improved, so that they are divided into upper and lower layers and completely adhered to the negative electrode current collector, and then the battery can take into account the better battery capacity and capacity retention rate at the conventional coating thickness; on the other hand, the slurry can have excellent coating uniformity, so that the two completely different negative electrode materials can be evenly dispersed in the product, and their respective performance can be exerted to a greater extent.

[0025] Considering that the battery also needs to meet better electrochemical performance, it is further preferred that the organic solvent and the wetting agent do not chemically react with the first negative electrode material and the second negative electrode material. The organic solvent and the wetting agent do not react with the negative electrode material itself in the slurry, so as not to have an adverse effect on the battery performance, so that the battery can simultaneously take into account better capacity, capacity retention rate and electrochemical performance.

[0026] In order to further improve the capacity and capacity retention rate of the battery, the organic solvent is preferably selected from one or more of N,N-dimethylformamide, N-methylpyrrolidone or 1,3-butanediol. More preferably, the organic solvent is selected from 1,3-butanediol.

[0027] In order to further improve the capacity and capacity retention rate of the battery, the wetting agent is preferably selected from ethanol and / or water. In a preferred embodiment, the wetting agent is applied by atomization spraying, and during the atomization spraying process, the atomization flow rate of the wetting agent is 120 to 240 mL / min. Further preferably, the atomization spraying time is 1 to 3 s per square meter of the outer surface to be coated.

[0028] In a preferred embodiment, the coating thickness of the first negative electrode slurry is 70-100 μm; the coating thickness of the second negative electrode slurry is 100-150 μm. Based on this, the double-layer coating effect is better, and the battery can simultaneously take into account better capacity, capacity retention rate and electrochemical performance.

[0029] In order to further remove the solvent in the product, the first drying temperature is preferably 65-95°C and the drying time is 20-30s. The second drying temperature is 85-105°C and the drying time is 30-40s. Based on this, solvents such as wetting agents, water, and organic solvents can be dried to remove the product without negatively affecting the performance of the product itself.

[0030] The present invention also provides a negative electrode sheet, which is prepared by the above-mentioned method for preparing the negative electrode material. Based on the above reasons, the battery can simultaneously take into account better capacity, capacity retention rate and electrochemical performance.

[0031] The present invention also provides a lithium ion battery, which includes the above-mentioned negative electrode plate. Based on the above reasons, the battery can simultaneously take into account better capacity, capacity retention rate and electrochemical performance.

[0032] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0033] Example 1

[0034] Negative electrode sheet preparation:

[0035] providing a fluid collector;

[0036] The first negative electrode slurry is coated on the outer surface of the current collector and dried to form a first negative electrode layer on the outer surface of the current collector.

[0037] A wetting agent is sprayed on the outer surface of the first negative electrode layer away from the current collector, and a second negative electrode slurry is applied before the wetting agent is completely dried. After the second drying, a second negative electrode layer is formed on the outer surface of the first negative electrode layer away from the current collector to obtain a negative electrode sheet. Wherein:

[0038] The current collector is copper foil (thickness 6 μm).

[0039] The first negative electrode slurry includes a silicon-carbon negative electrode material (Shenzhen B&T S1000), water, an organic solvent (N,N-dimethylformamide) and polyacrylic acid; the solid content of the first negative electrode slurry is 54%; the weight content of N,N-dimethylformamide is 3%.

[0040] The second negative electrode slurry includes a graphite negative electrode material (FSN-1 produced by Shanshan Technology) and water; the solid content of the second negative electrode slurry is 54%.

[0041] The wetting agent is ethanol, and the wetting agent is sprayed in an atomization manner at a flow rate of 150 mL / min. The atomization spraying time is 2 s per square meter of the outer surface to be coated.

[0042] The first drying was carried out at a drying temperature of 75° C. and a drying time of 30 seconds, and the second drying was carried out at a drying temperature of 100° C. and a drying time of 30 seconds.

[0043] The thickness of the first negative electrode layer was 70 μm, and the thickness of the second negative electrode layer was 150 μm.

[0044] Example 2

[0045] The difference from Example 1 is that the wetting agent is water.

[0046] Example 3

[0047] The difference from Example 1 is that the organic solvent is selected from N-methylpyrrolidone.

[0048] Example 4

[0049] The difference from Example 1 is that the organic solvent is selected from 1,3-butanediol.

[0050] Example 5

[0051] The difference from Example 1 is that the wetting agent is selected from hydrogen peroxide.

[0052] Example 6

[0053] The difference from Example 1 is that the organic solvent is selected from butanone.

[0054] Example 7

[0055] The difference from Example 1 is that the wetting agent is sprayed in an atomization manner at a flow rate of 120 mL / min.

[0056] Example 8

[0057] The difference from Example 1 is that the wetting agent is sprayed in an atomization manner at a flow rate of 240 mL / min.

[0058] Example 9

[0059] The difference from Example 1 is that the drying temperature of the first drying is 105° C. and the drying time is 1 min.

[0060] Comparative Example 1

[0061] Negative electrode sheet preparation:

[0062] providing a fluid collector;

[0063] The first negative electrode slurry is coated on the outer surface of the current collector and dried to form a first negative electrode layer on the outer surface of the current collector.

[0064] The second negative electrode slurry is coated on the outer surface of the first negative electrode layer away from the current collector, and after the second drying, a second negative electrode layer is formed on the outer surface of the first negative electrode layer away from the current collector to obtain a negative electrode sheet.

[0065] The current collector is copper foil (thickness 6 μm). The first negative electrode slurry includes silicon-carbon negative electrode material (Shenzhen B&T S1000), water and polyacrylic acid; the solid content of the first negative electrode slurry is 54%. The second negative electrode slurry includes graphite negative electrode material (Shanshan Technology FSN-1) and water; the solid content of the second negative electrode slurry is 54%.

[0066] The first drying was carried out at a drying temperature of 75° C. and a drying time of 30 seconds, and the second drying was carried out at a drying temperature of 100° C. and a drying time of 30 seconds.

[0067] Failure to use the organic solvent and wetting agent of the present invention will result in the second negative electrode being peeled off from the first negative electrode during winding, thereby failing to achieve double-layer coating.

[0068] Performance characterization:

[0069] The negative electrode sheet, lithium sheet, and electrolyte 1M LiF6PO4 in the embodiment and comparative example were dissolved in a solvent of EC:DMC (volume ratio 1:1) to assemble into 2032 button cells, and the capacity change of the cells was tested for 100 cycles of 0.1C constant current charge and discharge cycles. The battery performance characteristics in the embodiment and comparative example are shown in Table 1:

[0070] Table 1

[0071] capacity Capacity retention rate Example 1 421.2mAh 93.2％ Example 2 418.8mAh 93.7％ Example 3 432.7mAh 94.1％ Example 4 441.9mAh 95.5％ Example 5 402.8mAh 91.9％ Example 6 391.6mAh 90.3％ Example 7 418.6mAh 93.6％ Example 8 423.5mAh 92.8％ Example 9 389.1mAh 89.4％ Comparative Example 1 336.7mAh 81.7％

[0072] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a negative electrode sheet of a lithium ion battery, characterized in that: The preparation method comprises the following steps: providing a fluid collector; Applying a first negative electrode slurry on the outer surface of the current collector, and first drying to form a first negative electrode layer on the outer surface of the current collector; Sequentially coating the outer surface of the first negative electrode layer away from the current collector with a wetting agent and coating the second negative electrode slurry, and after the second drying, forming the second negative electrode layer on the outer surface of the first negative electrode layer away from the current collector to obtain the negative electrode sheet of the lithium ion battery; the wetting agent is selected from ethanol and / or water; The first negative electrode slurry includes a first negative electrode material, water and an organic solvent; the second negative electrode slurry includes a second negative electrode material and water; the first negative electrode material is different from the second negative electrode material; and in the first negative electrode slurry, the weight content of the organic solvent is 1-4%.

2. The method for preparing a negative electrode sheet for a lithium ion battery according to claim 1, characterized in that: The first negative electrode material and the second negative electrode material are each independently selected from silicon-carbon negative electrode materials and / or graphite negative electrode materials.

3. The method for preparing a negative electrode sheet for a lithium ion battery according to claim 2, characterized in that: The first negative electrode material is a silicon-carbon negative electrode material, and the second negative electrode material is a graphite negative electrode material.

4. The method for preparing a negative electrode sheet for a lithium ion battery according to any one of claims 1 to 3, characterized in that: The solid content of the first negative electrode slurry and the second negative electrode slurry is independently 40-60%.

5. The method for preparing a negative electrode sheet for a lithium ion battery according to any one of claims 1 to 3, characterized in that: The organic solvent and the wetting agent do not chemically react with the first negative electrode material and the second negative electrode material.

6. The method for preparing a negative electrode sheet for a lithium ion battery according to any one of claims 1 to 3, characterized in that: The organic solvent is selected from one or more of N,N-dimethylformamide, N-methylpyrrolidone or 1,3-butanediol.

7. The method for preparing a negative electrode sheet for a lithium ion battery according to any one of claims 1 to 3, characterized in that: The wetting agent is applied in the form of atomized spraying.

8. The method for preparing a negative electrode sheet for a lithium ion battery according to claim 7, characterized in that: During the atomization spraying process, the atomization flow rate of the wetting agent is 120-240 mL / min.

9. The method for preparing a negative electrode sheet for a lithium-ion battery according to claim 7, characterized in that: The atomization spraying time is 1 to 3 seconds per square meter of the outer surface to be coated.

10. The method for preparing a negative electrode sheet for a lithium ion battery according to any one of claims 1 to 3, characterized in that: The first drying process has a drying temperature of 65-95° C. and a drying time of 20-30 seconds.

11. The method for preparing a negative electrode sheet for a lithium ion battery according to claim 10, characterized in that: The second drying process has a drying temperature of 85-105° C. and a drying time of 30-40 seconds.

12. A negative electrode plate for a lithium ion battery, characterized in that: The negative electrode sheet of the lithium-ion battery is prepared by the method for preparing the negative electrode sheet of the lithium-ion battery according to any one of claims 1 to 11.

13. A lithium ion battery, characterized in that: The lithium-ion battery comprises the lithium-ion battery negative electrode sheet according to claim 12.