Manufacturing method of negative plate, negative plate and lithium battery

Abstract

The invention discloses a manufacturing method of a negative plate, the negative plate and a lithium battery. Belongs to the technical field of lithium batteries, and the manufacturing method of the negative plate comprises the following steps: mixing graphite, a first conductive agent and a first adhesive, coating a negative current collector with the mixture to form a first material layer on the negative current collector, mixing the graphite, a second conductive agent, a second adhesive and lithium powder by a dry method, and tabletting to obtain a second material layer, and hot-pressing the second material layer on the first material layer to obtain the negative plate. According to the manufacturing method of the negative electrode plate, the second material layer of the manufactured negative electrode plate contains the lithium powder, the lithium powder can compensate lithium lost in the charging and discharging process of the lithium battery, the first efficiency of the lithium battery can be improved, the capacity retention ratio of the lithium battery can be improved, and therefore the performance of the lithium battery can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a method for manufacturing a negative electrode sheet, a negative electrode sheet and a lithium battery. Background Art

[0002] Lithium batteries have become the preferred power source for new energy vehicles, smart phones and other electronic products due to their high energy density, long cycle life and light weight. However, during the first charge and discharge process of lithium batteries, the formation of the solid electrolyte interface (SEI) layer and possible side reactions in subsequent charge and discharge cycles lead to irreversible loss of lithium. The capacity of the lithium battery will also decrease, reducing the performance of the lithium battery. Summary of the invention

[0003] The present invention aims to solve at least one of the above technical problems in the prior art to a certain extent. To this end, the first object of the present invention is to provide a method for manufacturing a negative electrode sheet, which is conducive to improving the capacity retention rate of a lithium battery and improving the performance of a lithium battery.

[0004] The second objective of the present invention is to provide a negative electrode sheet.

[0005] The third objective of the present invention is to provide a lithium battery.

[0006] According to the first aspect of the present invention, the method for manufacturing a negative electrode sheet of an embodiment includes: mixing graphite, a first conductive agent and a first adhesive and coating the mixture on a negative electrode current collector to form a first material layer on the negative electrode current collector; mixing graphite, a second conductive agent, a second adhesive and lithium powder by a dry method and pressing the mixture into sheets to obtain a second material layer; hot pressing the second material layer onto the first material layer to obtain the negative electrode sheet.

[0007] According to the manufacturing method of the negative electrode sheet of the embodiment of the present invention, the second material layer of the manufactured negative electrode sheet has lithium powder, which can compensate for the lithium lost during the charging and discharging process of the lithium battery, which is beneficial to improving the initial efficiency of the lithium battery and the capacity retention rate of the lithium battery, thereby helping to improve the performance of the lithium battery.

[0008] According to some embodiments of the present invention, the weight percentage of the lithium powder in the second material layer is 0.1% to 1%.

[0009] According to some embodiments of the present invention, the weight percentage of the first adhesive in the first material layer is 1% to 5%, and the weight percentage of the second adhesive in the second material layer is 1% to 5%.

[0010] According to some embodiments of the present invention, the total weight of the first adhesive and the second adhesive accounts for more than 5% of the total weight of the first material layer and the second material layer.

[0011] According to some embodiments of the present invention, the first adhesive and the second adhesive have the same component.

[0012] According to some embodiments of the present invention, the first adhesive includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, polyvinyl alcohol, and polyacrylic acid.

[0013] According to some embodiments of the present invention, the ambient temperature during the dry mixing is T, and the dew point temperature is Td, which satisfies the relationship: 20°C≤T≤30°C, Td<-40°C.

[0014] According to some embodiments of the present invention, before hot-pressing the second material layer onto the first material layer, the method for manufacturing the negative electrode sheet further includes: roll-pressing the first material layer and the second material layer respectively.

[0015] According to the negative electrode sheet of the embodiment of the second aspect of the present invention, the negative electrode sheet is prepared by the above-mentioned manufacturing method of the negative electrode sheet, and the negative electrode sheet includes: a first material layer, a second material layer and a negative electrode current collector, the first material layer includes: graphite, a first conductive agent and a first adhesive; the second material layer includes: graphite, a second conductive agent, a second adhesive and lithium powder; the first material layer, the second material layer and the negative electrode current collector are stacked, and the first material layer is located between the second material layer and the negative electrode current collector.

[0016] According to the negative electrode sheet of an embodiment of the present invention, the second material layer includes graphite, a second conductive agent, a second adhesive and lithium powder. The lithium powder can compensate for the lithium lost during the charging and discharging process of the lithium battery, which is beneficial to improving the initial efficiency of the lithium battery and the capacity retention rate of the lithium battery, thereby helping to improve the performance of the lithium battery.

[0017] A lithium battery according to an embodiment of the third aspect of the present invention includes the above-mentioned negative electrode sheet.

[0018] According to the lithium battery of the embodiment of the present invention, the second material layer of the negative electrode sheet includes graphite, a second conductive agent, a second adhesive and lithium powder. The lithium powder can compensate for the lithium lost during the charging and discharging process of the lithium battery, which is beneficial to improving the initial efficiency of the lithium battery and the capacity retention rate of the lithium battery, thereby helping to improve the performance of the lithium battery.

[0019] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a flow chart of a method for manufacturing a negative electrode sheet according to an embodiment of the present invention;

[0021] Figure 2 Schematic diagram of the structure of a negative electrode sheet according to an embodiment of the present invention.

[0022] Reference numerals:

[0023] Negative electrode current collector 1; first material layer 2; second material layer 3; negative electrode sheet 10. DETAILED DESCRIPTION

[0024] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0025] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0026] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or can communicate with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0027] Combine the following Figure 1 and Figure 2 A method for manufacturing a negative electrode sheet, a negative electrode sheet, and a lithium battery according to an embodiment of the present invention are described in detail.

[0028] Reference Figure 1 and Figure 2 As shown, the method for manufacturing a negative electrode sheet according to the first embodiment of the present invention comprises:

[0029] Step S1: Graphite, a first conductive agent and a first adhesive are mixed and coated on the negative electrode current collector to form a first material layer on the negative electrode current collector.

[0030] Among them, graphite, the first conductive agent and the first adhesive can be wet-pulped in a double planetary mixer by a solvent to mix the graphite, the first conductive agent and the first adhesive, the solvent can include at least one of N-methylpyrrolidone (NMP) and water, the graphite can include at least one of artificial graphite, natural graphite, mesophase carbon microbeads and hard carbon, the first conductive agent can include at least one of conductive graphite, acetylene black, carbon black, carbon nanotubes and graphene, the first adhesive can include at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, polyvinyl alcohol and polyacrylic acid, and the negative electrode current collector 1 can be copper foil.

[0031] Step S2: Mix graphite, a second conductive agent, a second adhesive and lithium powder by dry method and press into tablets to obtain a second material layer.

[0032] Among them, dry mixing of graphite, a second conductive agent, a second adhesive and lithium powder can be achieved by a ball mill, the graphite can include at least one of artificial graphite, natural graphite, mesophase carbon microspheres, and hard carbon, the second conductive agent can include at least one of conductive graphite, acetylene black, carbon black, carbon nanotubes, and graphene, and the second adhesive can be at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, polyvinyl alcohol, and polyacrylic acid.

[0033] It is understandable that lithium powder will react violently when in contact with water. Graphite, the second conductive agent, the second adhesive and lithium powder are mixed by a dry method to avoid contact between lithium powder and water, which is beneficial to ensuring the safety and stability of manufacturing the second material layer 3, and can reduce the use of solvents, saving the manufacturing cost of the negative electrode sheet 10. After the graphite, the second conductive agent, the second adhesive and lithium powder are mixed by a dry method, they are pressed into a second material layer 3 with a sheet structure by a press to facilitate the transportation of the second material layer 3 during the subsequent preparation of the negative electrode sheet 10.

[0034] Step S3: hot pressing the second material layer onto the first material layer to obtain a negative electrode sheet.

[0035] The second material layer 3 can be hot-pressed onto the first material layer 2 by a hot-cold press. During the hot-pressing process, the second adhesive is heated and molten, thereby enhancing the adhesion effect of the second adhesive to facilitate connection of the second material layer 3 to the first material layer 2.

[0036] It can be understood that the negative electrode sheet 10 can be used as one of the components of a lithium battery, and the lithium powder in the second material layer 3 can be used as a lithium supplement, which is suitable for compensating for the lithium lost during the charging and discharging process of the lithium battery, which is beneficial to improving the initial efficiency of the lithium battery, and can improve the capacity retention rate of the lithium battery, improve the performance of the lithium battery, and in addition, the lithium powder can also increase the capacity of the lithium battery.

[0037] According to the manufacturing method of the negative electrode sheet 10 of the embodiment of the present invention, the second material layer 3 of the manufactured negative electrode sheet 10 has lithium powder, which can compensate for the lithium lost during the charging and discharging process of the lithium battery, which is beneficial to improving the initial efficiency of the lithium battery and the capacity retention rate of the lithium battery, thereby helping to improve the performance of the lithium battery.

[0038] In some embodiments of the present invention, the weight percentage of lithium powder in the second material layer 3 is 0.1% to 1%, which can effectively improve the capacity and initial efficiency of the lithium battery.

[0039] It is understandable that if the weight percentage of lithium powder in the second material layer 3 is less than 0.1%, the content of lithium powder is small, and the effect of improving the capacity, initial efficiency and capacity retention rate of the battery is not obvious. If the weight percentage of lithium powder in the second material layer 3 is greater than 1%, the content of lithium powder is high. Due to the high activity of lithium powder, more lithium powder increases the safety risk of lithium batteries and is not conducive to the performance of lithium batteries. In this embodiment, it has been verified by experiments that the weight percentage of lithium powder in the second material layer 3 is 0.1% to 1%, and the content of lithium powder is moderate, which can effectively improve the capacity, initial efficiency and capacity retention rate of lithium batteries.

[0040] In some embodiments of the present invention, the weight percentage of the first adhesive in the first material layer 2 is 1% to 5%, and the weight percentage of the second adhesive in the second material layer 3 is 1% to 5%, so as to ensure that the content of the first adhesive in the first material layer 2 is sufficient and the content of the second adhesive in the second material layer 3 is sufficient, which is beneficial to reduce the risk of graphite and the first conductive agent in the first material layer 2 falling off, and reduce the risk of graphite, the second conductive agent and lithium powder in the second material layer 3 falling off, thereby helping to ensure the structural stability of the negative electrode sheet 10.

[0041] In some embodiments of the present invention, the total weight of the first adhesive and the second adhesive accounts for more than 5% of the total weight of the first material layer 2 and the second material layer 3 to ensure that the content of the first adhesive and the second adhesive is sufficient. When the second material layer 3 is hot pressed onto the first material layer 2, it is beneficial for the first adhesive and the second adhesive to reliably bond the first material layer 2 and the second material layer 3 together, thereby improving the connection strength between the first material layer 2 and the second material layer 3, which is beneficial to ensure the structural stability of the negative electrode sheet 10.

[0042] In some embodiments of the present invention, the components of the first adhesive and the second adhesive are the same, and the first adhesive and the second adhesive of the same components have good compatibility, so that the first adhesive and the second adhesive can be better fused, which is beneficial to improve the connection strength between the first material layer 2 and the second material layer 3, and improve the structural stability of the negative electrode sheet 10. In addition, the components of the first adhesive and the second adhesive are the same, which can reduce the types of materials used to manufacture the negative electrode sheet 10, thereby helping to reduce material management costs.

[0043] In some embodiments of the present invention, the first adhesive includes: at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, polyvinyl alcohol, and polyacrylic acid. That is, the first adhesive can be any one of polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, polyvinyl alcohol, and polyacrylic acid, or a mixture of any two or more thereof. The components of the first adhesive can be adjusted according to specific needs to meet the performance requirements of the lithium battery.

[0044] Similarly, the components of the second adhesive are the same as those of the first adhesive, that is, the second adhesive includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, polyvinyl alcohol, and polyacrylic acid. The components of the second adhesive can be the same as those of the first adhesive according to specific needs.

[0045] In some embodiments of the present invention, the ambient temperature during dry mixing is T, and the dew point temperature is Td, which satisfies the relationship: 20°C ≤ T ≤ 30°C, Td < -40°C, so as to reduce the moisture content in the preparation environment and reduce the risk of reaction between lithium powder and water, thereby facilitating the improvement of the safety during dry mixing and avoiding the failure of lithium powder.

[0046] In some embodiments of the present invention, before hot pressing the second material layer 3 onto the first material layer 2, the method for manufacturing the negative electrode sheet 10 further includes: rolling the first material layer 2 and the second material layer 3 respectively to compact the first material layer 2 and the second material layer 3, so that the surfaces of the first material layer 2 and the second material layer 3 become smooth and flat. In the process of hot pressing the second material layer 3 onto the first material layer 2, it is beneficial for the first material layer 2 and the second material layer 3 to be in close contact. In addition, after the first material layer 2 is rolled, the graphite and the first conductive agent are in closer contact, and after the second material layer 3 is rolled, the graphite, the second conductive agent and the lithium powder are in closer contact, which is beneficial to improving the electronic conductivity, and can reduce the volume of the negative electrode sheet 10, thereby improving the energy density of the lithium battery.

[0047] Reference Figure 1 and Figure 2 As shown, according to the negative electrode sheet 10 of the embodiment of the second aspect of the present invention, the negative electrode sheet 10 is prepared by the manufacturing method of the negative electrode sheet 10 of the above embodiment, and the negative electrode sheet 10 includes: a first material layer 2, a second material layer 3 and a negative electrode current collector 1, the first material layer 2 includes: graphite, a first conductive agent and a first adhesive, the second material layer 3 includes: graphite, a second conductive agent, a second adhesive and lithium powder, the first material layer 2, the second material layer 3 and the negative electrode current collector 1 are stacked, and the first material layer 2 is located between the second material layer 3 and the negative electrode current collector 1, which is beneficial to reduce the manufacturing difficulty of the negative electrode sheet 10.

[0048] It can be understood that the second material layer 3 is made by dry pressing and is difficult to directly adhere to the negative electrode collector 1 through the second adhesive, while the material in the first material layer 2 can be directly coated on the negative electrode collector 1 after wet mixing, and the first adhesive in the first material layer 2 can be used to bond the second material layer 3. When manufacturing the negative electrode sheet 10, by arranging the first material layer 2 between the second material layer 3 and the negative electrode collector 1, the manufacturing difficulty of the negative electrode sheet 10 can be effectively reduced. At the same time, the second material layer 3 containing lithium powder is located on the outside away from the negative electrode collector 1, which can make the lithium powder better play the lithium replenishing effect on the negative electrode sheet 10, which is beneficial to further improve the initial efficiency and capacity retention rate of the lithium battery.

[0049] According to the negative electrode sheet 10 of the embodiment of the present invention, the second material layer 3 includes graphite, a second conductive agent, a second adhesive and lithium powder. The lithium powder can compensate for the lithium lost during the charging and discharging process of the lithium battery, which is beneficial to improving the initial efficiency of the lithium battery and the capacity retention rate of the lithium battery, thereby helping to improve the performance of the lithium battery.

[0050] The lithium battery according to the third embodiment of the present invention includes the negative electrode sheet 10 of the above embodiment.

[0051] According to the lithium battery of the embodiment of the present invention, the second material layer 3 of the negative electrode sheet 10 includes graphite, a second conductive agent, a second adhesive and lithium powder. The lithium powder can compensate for the lithium lost during the charging and discharging process of the lithium battery, which is beneficial to improving the initial efficiency of the lithium battery and the capacity retention rate of the lithium battery, thereby helping to improve the performance of the lithium battery.

[0052] In some embodiments of the present invention, a method for manufacturing a lithium battery includes:

[0053] Step S11: wet-mixing graphite, a first conductive agent, a first adhesive and other materials in a double planetary mixer according to a certain proportion to obtain slurry A.

[0054] Among them, the proportion of graphite is 80% to 98.5%, the proportion of the first conductive agent is 0.5% to 3%, and the proportion of the first adhesive is 1% to 5%. The graphite may include at least one of artificial graphite, natural graphite, mesophase carbon microbeads and hard carbon. The first conductive agent may include at least one of conductive graphite, acetylene black, carbon black, carbon nanotubes and graphene. The first adhesive may include at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, polyvinyl alcohol and polyacrylic acid.

[0055] Step S12: coating the slurry A on the negative electrode current collector using a coating machine at a certain surface density to obtain a pole piece A1.

[0056] Among them, the surface density is 50g / m 2 ~300g / m 2The negative electrode current collector 1 is a copper foil, and the thickness of the copper foil is 3.5 μm to 25 μm.

[0057] Step S13: Roll-press the electrode piece A1 using a roller press according to a certain compaction density to obtain the electrode piece A2.

[0058] Among them, the compacted density is 1.5g / cm 3 ~1.8g / cm 3 .

[0059] Step S14: Use a die-cutting machine to die-cut the pole piece A2 according to a certain size to obtain the pole piece A3.

[0060] Among them, the length is in the range of 5mm to 1000mm, and the width is in the range of 5mm to 1000mm.

[0061] Step S15: Mix graphite, the second conductive agent, the second adhesive, and lithium powder in a certain ratio under a certain environment, put the mixture into a ball mill for ball milling, and obtain material B.

[0062] Among them, the proportion of graphite is 80% to 98.4%, the proportion of the first conductive agent is 0.5% to 3%, the proportion of the first adhesive is 1% to 5%, the proportion of lithium powder is 0.1% to 1%, the ambient temperature is in the range of 20°C to 30°C, the dew point temperature is less than -40°C, the graphite may include at least one of artificial graphite, natural graphite, mesophase carbon microbeads, and hard carbon, the second conductive agent may include at least one of conductive graphite, acetylene black, carbon black, carbon nanotubes, and graphene, and the second adhesive may be at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, polyvinyl alcohol, and polyacrylic acid.

[0063] Step S16: Press material B into a pancake-shaped sheet with a certain thickness through a press to obtain a pole piece B1.

[0064] Among them, the thickness of the pole piece B1 can be in the range of 50μm to 300μm, and the pressure of the press can be in the range of 1 ton to 5 tons. The pressing method is to place a mixed powder consisting of graphite, a second conductive agent, a second adhesive and lithium powder in a mold, and apply a certain pressure through the press to press the mixed powder into a cake-shaped sheet of the required thickness.

[0065] Step S17: Roll-press the electrode piece B1 according to a certain compaction density to obtain the electrode piece B2.

[0066] Among them, the compacted density is 1.5g / cm 3 ~1.8g / cm 3 .

[0067] Step S18: Use a die-cutting machine to die-cut the pole piece B2 according to a certain size to obtain the pole piece B3.

[0068] Among them, the length is in the range of 5mm to 1000mm, and the width is in the range of 5mm to 1000mm.

[0069] Step S19: On a hot and cold press, under a certain temperature and pressure, the second adhesive in the electrode B3 will become molten. The temperature and pressure need to be controlled to hot-press the electrode B3 onto the electrode A3 to obtain the electrode C1.

[0070] The temperature of the hot and cold press is in the range of 100° C. to 300° C., the pressure of the hot and cold press is in the range of 10 tons to 100 tons, and the thickness of the electrode C1 is in the range of 70 μm to 500 μm.

[0071] Step S20: die-cut the pole piece C1 into a certain size by a die-cutting machine to obtain the pole piece C2.

[0072] Among them, the length is in the range of 5mm to 1000mm, and the width is in the range of 5mm to 1000mm.

[0073] Step S21: Use the electrode C2 to prepare a soft-pack full battery by laminating the electrodes and test the performance of the battery cell.

[0074] The stacked pole pieces C2 can form a lithium battery cell, and the cell capacity is in the range of 5Ah to 200Ah.

[0075] The present invention is further described in detail below in conjunction with specific embodiments and comparative examples:

[0076] Embodiment 1:

[0077] The present embodiment provides a method for manufacturing a lithium battery, the manufacturing method comprising wet slurrying graphite, acetylene black, and polyvinylidene fluoride in a weight ratio of 97.5%:0.5%:2% in a double planetary mixer, and coating the mixture with a coating machine at a surface density of 100 g / m 2 For coating, use a roller press to compact the density at 1.65 g / cm 3 Rolling is performed and a die-cutting machine is used to prepare the pole piece A3. Under the required environment and humidity, graphite, carbon black, polyvinylidene fluoride, and lithium powder are mixed in a ball mill according to a weight ratio of 93.9%:1%:5%:0.1%, and the mixture is pressed into a cake of about 200 μm on a press. The compaction density is 1.65 g / cm 3Rolling is performed, and a die-cutting machine is used to prepare the electrode piece B3. Then, a hot and cold press is used at a hot pressing temperature of about 180°C to thermally composite and bond the electrode pieces A3 and B3 together to obtain the required electrode piece. The electrode piece is die-cut again using a die-cutting machine, matched with a certain lithium iron phosphate positive electrode piece, to prepare a 30Ah full battery, and the performance of the battery cell is tested.

[0078] Embodiment 2:

[0079] The present embodiment provides a method for manufacturing a lithium battery, the manufacturing method comprising wet slurrying graphite, carbon black, and polyvinylidene fluoride in a weight ratio of 95%:2%:3% in a double planetary mixer, and coating the mixture with a coating machine at a surface density of 150 g / m 2 For coating, use a roller press to compact the density at 1.7 g / cm 3 Rolling is performed and a die-cutting machine is used to prepare the pole piece A3. Under the required environment and humidity control, graphite, carbon black, polyvinylidene fluoride, and lithium powder are mixed in a ball mill according to a weight ratio of 95%:1%:3:%:1%, and the mixture is pressed into a cake of about 300 μm on a press. The compaction density is 1.6 g / cm 3 Rolling is performed, and a die-cutting machine is used to prepare the electrode piece B3. Then, a hot and cold press is used at a hot pressing temperature of about 180°C to thermally composite and bond the electrode pieces A3 and B3 together to obtain the required electrode piece. The electrode piece is die-cut again using a die-cutting machine, matched with a certain lithium iron phosphate positive electrode piece, to prepare a 30Ah full battery, and the performance of the battery cell is tested.

[0080] Embodiment three:

[0081] The present embodiment provides a method for manufacturing a lithium battery, the manufacturing method comprising wet slurrying graphite, carbon black, and polyvinylidene fluoride in a weight ratio of 94.5%:0.5%:5% in a double planetary mixer, and coating the mixture with a coating machine at a surface density of 200 g / m 2 For coating, use a roller press to compact the density at 1.7 g / cm 3 Rolling is performed and a die-cutting machine is used to prepare the pole piece A3. Under the required environment and humidity control, graphite, carbon black, polyvinylidene fluoride, and lithium powder are mixed in a ball mill according to a weight ratio of 93.5%:1%:5%:0.5%, and the mixture is pressed into a cake of about 300 μm on a press. The compaction density is 1.6 g / cm 3 Rolling is performed, and a die-cutting machine is used to prepare the electrode piece B3. Then, a hot and cold press is used at a hot pressing temperature of about 180°C to thermally composite and bond the electrode pieces A3 and B3 together to obtain the required electrode piece. The electrode piece is die-cut again using a die-cutting machine, matched with a certain lithium iron phosphate positive electrode piece, to prepare a 30Ah full battery, and the performance of the battery cell is tested.

[0082] Embodiment 4:

[0083] This embodiment provides a method for manufacturing a lithium battery, which differs from the manufacturing method of the third embodiment in that the first adhesive in the pole piece A3 and the second adhesive in the pole piece B3 are changed from polyvinylidene fluoride to polyvinylidene fluoride, a 30Ah battery cell is prepared, and the performance of the battery cell is tested.

[0084] Embodiment five:

[0085] This embodiment provides a method for manufacturing a lithium battery, which differs from the manufacturing method of Example 3 in that the first adhesive in the formula of electrode A3 is changed from 3% polyvinylidene fluoride to 2% polyvinylidene fluoride, and the second adhesive in the formula of electrode B3 is changed from 2% polyvinylidene fluoride to 3% polyvinylidene fluoride, a 30Ah battery cell is prepared, and the performance of the battery cell is tested.

[0086] Comparative Example 1:

[0087] Graphite, carbon black and polyvinylidene fluoride were wet-mixed in a planetary mixer using NMP in a weight ratio of 97%:1%:2%. The slurry was then coated on copper foil, followed by rolling and die-cutting to prepare the negative electrode sheet. A certain amount of lithium iron phosphate positive electrode sheet was then matched to prepare a 30Ah full battery, and the performance of the battery cell was tested.

[0088] Comparative Example 2:

[0089] Graphite, carbon black, carbon nanotubes and polyvinylidene fluoride were wet-mixed in a planetary mixer using NMP in a weight ratio of 96%:0.5%:1.5%:2%. The slurry was then coated on copper foil, and then rolled and die-cut to prepare the negative electrode sheet. A certain amount of lithium iron phosphate positive electrode sheet was then matched to prepare a 30Ah full battery, and the performance of the battery cell was tested.

[0090] Comparative Example 3:

[0091] The second adhesive in the electrode B3 formula in Example 3 was changed from polyvinylidene fluoride to polyvinylidene fluoride, and a 30Ah full battery was prepared to test the performance of the battery cell.

[0092] The 30Ah full batteries in the above-mentioned Embodiment 1, Embodiment 2, Embodiment 3, Embodiment 4, Embodiment 5, Comparative Example 1, Comparative Example 2 and Comparative Example 3 are soft-pack batteries, and the size of the negative electrode sheets in the batteries of each embodiment and comparative example is the same. The test results of each embodiment and comparative example are shown in the following table:

[0093] serial number Battery capacity First efficiency 100-week cycle retention rate 500-week cycle retention rate Embodiment 1 31.128 91.6％ 98.33％ 95.54％ Embodiment 2 31.638 92.5％ 98.74％ 95.84％ Embodiment 3 31.294 92.0％ 98.76％ 96.59％ Embodiment 4 31.382 91.8％ 98.83％ 96.54％ Embodiment 5 31.386 91.9％ 98.79％ 96.25％ Comparative Example 1 30.432 90.1％ 97.98％ 95.42％ Comparative Example 2 30.987 90.5％ 98.21％ 95.38％ Comparative Example 3 31.382 92.1％ 98.63％ 66.54％

[0094] It can be seen from the above table that the first efficiency of the full battery prepared using the negative electrode sheet 10 manufactured by the manufacturing method of the negative electrode sheet 10 of the embodiment of the present invention is significantly improved, among which the first efficiency of Example 2 is the highest, which is about 2.4% higher than the first efficiency of Comparative Example 1 and about 2% higher than the first efficiency of Comparative Example 2.

[0095] The cycle retention rates of Example 3, Example 4 and Example 5 are all relatively good. The content of the same type of adhesive in the formula of the negative electrode sheet 10 is relatively reasonable. The bonding effect between the electrode sheet B3 (second material layer 3) and the electrode sheet A3 (first material layer 2) is tighter, which helps to reduce the interface impedance between the electrode sheet B3 and the electrode sheet A3. In addition, it is related to the design of the electrode, which shows that the material has a better effect at this surface density and compaction level.

[0096] In comparative example 3, the types of adhesives in electrode B3 and electrode A3 are inconsistent. There is no abnormality in the initial cycle. When the number of cycles increases, the battery cell cycle drops. After disassembly, it is found that the negative electrode sheet has fallen off.

[0097] According to the lithium battery of the embodiment of the present invention, the negative electrode sheet 10 can give full play to the high capacity and high initial efficiency characteristics of the negative electrode material through the negative electrode pre-lithiation multilayer electrode design. Combined with the multilayer electrode design, the purpose of taking both fast charging and energy density into consideration can be achieved. The negative electrode sheet 10 has two layers of electrodes, wherein the first layer of electrode (first material layer 2) close to the negative electrode current collector 1 is a wet electrode, and the second layer of electrode (second material layer 3) is a dry electrode. The lithium powder contained in the dry electrode can compensate for the lithium lost during the charging and discharging process of the lithium battery, which is beneficial to improving the initial efficiency of the lithium battery, and can improve the capacity retention rate of the lithium battery, thereby helping to improve the performance of the lithium battery.

[0098] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example" or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification.

[0099] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for manufacturing a negative electrode sheet, characterized in that: include: Mixing graphite, a first conductive agent and a first adhesive and coating the mixture on the negative electrode current collector to form a first material layer on the negative electrode current collector; The graphite, the second conductive agent, the second adhesive and the lithium powder are mixed by a dry method and then tabletted to obtain a second material layer; The second material layer is hot pressed onto the first material layer to obtain the negative electrode sheet.

2. The method for manufacturing a negative electrode sheet according to claim 1, characterized in that: The weight percentage of the lithium powder in the second material layer is 0.1% to 1%.

3. The method for manufacturing a negative electrode sheet according to claim 1, characterized in that: The weight percentage of the first adhesive in the first material layer is 1% to 5%, and the weight percentage of the second adhesive in the second material layer is 1% to 5%.

4. The method for manufacturing a negative electrode sheet according to claim 3, characterized in that: The total weight of the first adhesive and the second adhesive accounts for more than 5% of the total weight of the first material layer and the second material layer.

5. The method for manufacturing a negative electrode sheet according to claim 4, characterized in that: The first adhesive and the second adhesive have the same component.

6. The method for manufacturing a negative electrode sheet according to claim 5, characterized in that: The first adhesive includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, polyvinyl alcohol, and polyacrylic acid.

7. The method for manufacturing a negative electrode sheet according to claim 1, characterized in that: The ambient temperature during the dry mixing is T, and the dew point temperature is Td, which satisfies the relationship: 20°C≤T≤30°C, Td<-40°C.

8. The method for manufacturing a negative electrode sheet according to any one of claims 1 to 7, characterized in that: Before hot pressing the second material layer onto the first material layer, the method for manufacturing the negative electrode sheet further includes: The first material layer and the second material layer are respectively rolled.

9. A negative electrode sheet, characterized in that: The negative electrode sheet is prepared by the method for manufacturing a negative electrode sheet according to any one of claims 1 to 8, and the negative electrode sheet comprises: A first material layer, wherein the first material layer comprises: graphite, a first conductive agent and a first adhesive; A second material layer, wherein the second material layer comprises: graphite, a second conductive agent, a second adhesive and lithium powder; A negative electrode current collector, wherein the first material layer, the second material layer and the negative electrode current collector are stacked, and the first material layer is located between the second material layer and the negative electrode current collector.

10. A lithium battery, characterized in that: The invention comprises the negative electrode sheet according to claim 9.

Images