Negative electrode sheet, method for preparing negative electrode sheet, and battery

Abstract

This application discloses a negative electrode sheet, a method for preparing a negative electrode sheet, and a battery. The negative electrode sheet includes a current collector and an active layer. The active layer is disposed on the current collector. The active layer includes a first active layer, a second active layer, and a third active layer stacked sequentially on the current collector. The first active layer is closer to the current collector than the second active layer, and the third active layer has a groove on a side away from the second active layer. The first and third active layers include a carbon material, the second active layer includes a silicon material, and the mass percentage of the silicon material in the second active layer is greater than 10%. The negative electrode sheet provided in this application can improve the battery's initial coulombic efficiency, battery capacity, and energy density.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a negative electrode sheet, a method for preparing a negative electrode sheet, and a battery. Background Art

[0002] Silicon-based anode materials have high gram capacity, high volumetric capacity, and suitable lithium insertion potential, which can improve the energy density of lithium-ion batteries. Therefore, silicon-based anode materials are very promising lithium-ion battery anode materials. However, during the continuous lithium insertion and removal process, the morphology and structure of silicon will be destroyed, resulting in a low initial coulombic efficiency of the battery. In addition, the mass ratio of silicon-based anode materials in related technologies is low, which limits the application of silicon-based anode materials in lithium-ion batteries. Summary of the Invention

[0003] In order to solve the above technical problems, the present application provides a negative electrode sheet, a method for preparing a negative electrode sheet, and a battery, which can improve the battery's initial coulombic efficiency, battery capacity, and energy density.

[0004] In a first aspect, the present application provides a negative electrode plate, comprising a current collector and an active layer, wherein the active layer is disposed on the current collector, and the active layer comprises a first active layer, a second active layer, and a third active layer sequentially stacked on the current collector, wherein the first active layer is closer to the current collector than the second active layer, and a groove is provided on a side of the third active layer away from the second active layer, wherein the first active layer and the third active layer comprise a carbon material, the second active layer comprises a silicon material, and the mass percentage of the silicon material in the second active layer is greater than 10%.

[0005] The negative electrode sheet provided herein comprises a first active layer, a second active layer, and a third active layer stacked sequentially on the current collector. Because the first active layer, comprising a carbon material, is located closest to the current collector, the second active layer has a greater adhesion to the first active layer than to the current collector. This prevents the second active layer, comprising a silicon material, from detaching from the current collector due to expansion, thereby improving the battery's initial coulombic efficiency, energy density, and battery capacity. Furthermore, because the mass percentage of silicon material in the second active layer is greater than 10%, the active layer has a high silicon content, further improving energy density and battery capacity. Furthermore, the grooves increase the contact area between the active layer and the electrolyte, thereby improving electrolyte wetting, and can also reduce tortuosity, thereby increasing the battery's charge and discharge rate, thereby increasing the battery's charge and discharge rate. Specifically, because the grooves serve as transmission paths for ions, such as lithium ions, lithium ions can reach the interior of the active layer more directly and quickly, thereby reducing tortuosity.

[0006] In a possible implementation, the third active layer further includes a first polymer, which is formed by in-situ polymerization of a first precursor in the first active layer, and the first polymer is mixed with the carbon material and distributed in the third active layer.

[0007] During the groove formation process, after the material, particularly the binder, of the third active layer in the grooved region dissipates, the bonding strength between the remaining material particles weakens. The first precursor polymerizes in the grooved region to form the first polymer, forming a cross-linked network that bonds the remaining material particles of the third active layer in the grooved region. This improves the bonding strength between the material particles of the third active layer at the grooved location, preventing the particles at that location from falling off. This reduces carbon material dissipation, further lowering the Hi-Pot test failure rate. Furthermore, preventing carbon material particle shedding can improve the initial coulombic efficiency and energy density. Furthermore, the first precursor polymerizes at other locations to form the first polymer, strengthening the bonding strength between the material particles of the third active layer at corresponding locations.

[0008] In a possible implementation, the structure of the first precursor includes an aromatic ring and a double bond.

[0009] The structure of the first precursor includes double bonds, enabling polymerization. The structure of the first precursor includes aromatic rings, meaning the first polymer generated by in-situ polymerization also includes aromatic rings. This results in the first polymer having a relatively low polarity. Due to the principle of like attracts like, the relatively low polarity first polymer has a good affinity with the non-polar carbon material in the third active layer. Consequently, the first polymer and the carbon material in the third active layer have good compatibility, strong adhesion between the first polymer and the carbon material, and a relatively stable structure.

[0010] In a possible implementation, the first precursor includes at least one of allylbenzene, allylbenzyl ether, 2-allylphenyl allyl ether, and 2-allylbenzaldehyde.

[0011] The polymerization reaction of these precursors has high reaction efficiency, and the generated first polymer can better bond the materials of the third active layer together. In addition, these precursors have high chemical stability and low cost.

[0012] In a possible implementation, the mass percentage of the first polymer in the third active layer is 3%-5%.

[0013] The mass percentage of the first polymer within this range not only achieves a good bonding effect, thereby reducing the Hi-Pot test failure rate, but also increases the initial coulombic efficiency, battery capacity, and energy density.

[0014] In a possible implementation, the second active layer further includes a second polymer, which is formed by in-situ polymerization of a second precursor in the second active layer, and the second polymer is mixed with the silicon material and distributed in the second active layer.

[0015] During the groove formation process, after the material, particularly the binder, of the second active layer located in the grooved area escapes, the bonding strength between the remaining material particles weakens. However, the second precursor in the grooved area polymerizes to form the second polymer, forming a cross-linked network that bonds the remaining material particles of the second active layer in the grooved area. This improves the bonding strength between the material particles of the second active layer located in the grooved area, thereby reducing silicon material leakage and further lowering the Hi-Pot test failure rate. Furthermore, by preventing silicon material particle shedding, the initial coulombic efficiency and energy density can be improved. Furthermore, the second precursor at other locations polymerizes to form the second polymer, which strengthens the bonding strength between the material particles of the second active layer at the corresponding locations. The second polymer also inhibits the expansion of silicon material particles in the second active layer.

[0016] The structure of the second precursor includes double bonds, enabling polymerization. The structure of the second precursor includes ether oxygen bonds, which have strong polarity and can generate strong interactions with ions, such as lithium ions, such as adsorption and coordination, thereby improving the ion transport performance of the second active layer and, in turn, the battery's kinetic performance.

[0017] In a possible implementation, the second precursor includes at least one of polyethylene glycol diacrylate, polyethylene glycol methyl ether acrylate, and polyethylene glycol methyl ether methacrylate.

[0018] The polymerization reaction of these precursors has high reaction efficiency, and the generated second polymer can better bond the materials of the second active layer together. In addition, these precursors have high chemical stability and low cost.

[0019] In one possible implementation, the weight average molecular weight of the second precursor is 400-20000, which can increase the polymerization efficiency of the second precursor and prevent the second precursor from agglomerating in the slurry.

[0020] In one possible implementation, the mass percentage of the second polymer in the second active layer is 3%-5%. This not only achieves good bonding and a low Hi-Pot test failure rate, but also increases the initial coulombic efficiency, battery capacity, and energy density.

[0021] In one possible implementation, the negative electrode plate also includes a polymer layer, which is arranged between the third active layer and the second active layer. The polymer layer includes a third polymer, and the structure of the third polymer includes a first group and a second group. The first group includes at least one of a carboxyl group, a carboxylate group, an amide group, a hydroxyl group, a cyano group and an ester group, and the second group includes an aromatic group.

[0022] The first group in the third polymer is highly polar and forms hydrogen bonds or dipole-dipole interactions with the surface groups of the silicon material in the second active layer, enhancing the adhesion between the polymer layer and the second active layer. The second group in the third polymer is non-polar and forms π…π interactions with the carbon material in the third active layer, enhancing the adhesion between the polymer layer and the third active layer. Thus, the polymer layer acts as an adhesive. Positioning the polymer layer between the second and third active layers enhances the adhesion between the two layers. When grooves are created in the third active layer, local separation of the second and third active layers due to external energy, such as when grooves are created using a laser, is avoided. This minimizes the shedding of particles from the third and second active layers, further reducing Hi-Pot test failure rates and improving initial coulombic efficiency.

[0023] In one possible implementation, the third polymer has a structure shown in Formula I, Formula I, wherein R1 is the first group, R2 is the second group, R3 and R4 include at least one of carboxyl, hydroxyl, amino and hydrogen, n and m are integers between 10 and 10,000, and the ratio of n to m is 0.1 to 10.

[0024] If n and m are less than 10, the molecular weight of the third polymer will be low, which may cause the polymer layer to have strong fluidity during processing, making it difficult to form a stable coating, and may weaken the adhesion between the polymer layer and the third active layer and the second active layer. If n and m are greater than 10,000, the molecular weight of the third polymer will be high, and the third polymer will easily agglomerate in the slurry, resulting in uneven distribution of the third polymer in the polymer layer, which will affect the electrochemical performance of the battery and increase the difficulty of processing and preparation.

[0025] Since the ratio of n to m is 0.1-10, the number of structural units containing R1 and the number of structural units containing R2 are relatively close, and the length of the chain segments composed of structural units containing R1 and the length of the chain segments composed of structural units containing R2 are also relatively close. Therefore, not only can the structural order of the block copolymer be improved, thereby improving its physical and chemical properties, but also the adhesion force between the polymer layer and the second active layer and the adhesion force between the polymer layer and the third active layer can be more balanced. As a result, when the polymer layer is subjected to external force, the stress distribution within it is more uniform, thereby improving the adhesion performance between the polymer layer and the second active layer and the third active layer.

[0026] In one possible implementation, the thickness of the polymer layer is 0.1 μm to 5 μm. This not only effectively bonds the third active layer to the second active layer, thereby reducing the Hi-Pot test failure rate, but also increases the battery capacity and energy density.

[0027] In a possible implementation, the opening of the groove faces the side of the third active layer away from the second active layer, the bottom of the groove is opposite to the opening, and the bottom of the groove is located in the third active layer or the second active layer.

[0028] By setting the groove 30 not to penetrate into the first active layer 21 , on the one hand, it can prevent the groove 30 from being too deep, which makes the strength of the negative electrode plate 100 weak, and on the other hand, it can prevent the active material content of the negative electrode plate 100 from being low, which affects the electrochemical performance.

[0029] In one possible implementation, the mass percentage of the silicon material in the second active layer is greater than 10% and less than or equal to 70%, which can enable the battery to have a higher battery capacity, energy density, first coulombic efficiency and a lower Hi-Pot test failure rate.

[0030] In one possible implementation, the mass percentage of the silicon material in the active layer 20 is greater than or equal to 5% and less than or equal to 50%, which can enable the battery to have a higher battery capacity, energy density, first coulombic efficiency and a lower Hi-Pot test failure rate.

[0031] In one possible implementation, the silicon material includes at least one of elemental silicon, silicon-carbon material, and silicon-oxygen material. Elemental silicon has a high theoretical specific capacity, and its introduction into the second active layer can significantly increase the battery's energy density. Silicon-carbon material combines the advantages of silicon and carbon, with a high specific capacity and good cycle stability, which also helps to increase the battery's energy density. Silicon-oxygen material exhibits minimal volume change during cycling, which helps to improve the battery's cycle life.

[0032] In one possible implementation, the thickness of the first active layer is 5 μm-30 μm, the thickness of the second active layer is 20 μm-100 μm, the thickness of the third active layer is 5 μm-30 μm, and the depth of the groove is 5 μm-40 μm. This can enable the battery to have higher capacity and energy density.

[0033] In one possible implementation, the third active layer has multiple spaced grooves on a side facing away from the second active layer. Each groove has a width of 40 μm to 120 μm, and the spacing between adjacent grooves is 0.5 mm to 3 mm. This can enhance the strength of the negative electrode sheet, and a battery including this negative electrode sheet has a higher energy density and better charge and discharge performance.

[0034] In a possible implementation, an angle is formed between the length direction of the groove and the width direction of the third active layer, and the angle is 0°-10°, so as to prevent the filament from falling during the slicing process.

[0035] In one possible implementation, the first active layer further includes a conductive agent and a binder, and the mass percentage of the carbon material in the first active layer is 90%-95%, the mass percentage of the conductive agent is 1%-5%, and the mass percentage of the binder is 1%-5%; the second active layer further includes a carbon material, a conductive agent, and a binder, and the mass percentage of the carbon material in the second active layer is 20%-80%, the mass percentage of the conductive agent is 1%-5%, and the mass percentage of the binder is 1%-5%; the third active layer further includes a conductive agent and a binder, and the mass percentage of the carbon material in the third active layer is 90%-98%, the mass percentage of the conductive agent is 1%-5%, and the mass percentage of the binder is 1%-5%.

[0036] Among them, the conductive agent can improve the conductivity of the active layer and improve the charge and discharge performance, and the binder can play the role of bonding the granular active materials together.

[0037] A second aspect of the present application provides a method for preparing a negative electrode sheet, the method being used to manufacture the negative electrode sheet described in the first aspect. The method comprises the following steps: providing a current collector, a first slurry, a second slurry, and a third slurry, wherein the first slurry and the third slurry both comprise a carbon material, and the second slurry comprises a silicon material; coating the first slurry on the current collector to form a first active layer; coating the second slurry on a side of the first active layer away from the current collector to form a second active layer, wherein the mass percentage of the silicon material in the second active layer is greater than 10%; coating the third slurry on a side of the second active layer away from the first active layer to form a third active layer; and using a laser to create a groove on a side of the third active layer away from the second active layer.

[0038] In one possible implementation, the third slurry further includes a first precursor, wherein when a laser is used to open the groove on a side of the third active layer away from the second active layer, the first precursor is in-situ polymerized in the third active layer to form a first polymer.

[0039] In one possible implementation, the second slurry further includes a second precursor, wherein when a laser is used to open the groove on a side of the third active layer away from the second active layer, the second precursor is in-situ polymerized in the second active layer to form a second polymer.

[0040] In one possible implementation, before applying the third slurry to a side of the second active layer away from the first active layer to form the third active layer, the method further includes: applying a polymer slurry to a side of the second active layer away from the first active layer to form a polymer layer, wherein the polymer slurry includes a third polymer. Applying the third slurry to a side of the second active layer away from the first active layer to form the third active layer includes applying the third slurry to a side of the polymer layer away from the second active layer to form the third active layer.

[0041] The preparation method provided in the second aspect is used to prepare the negative electrode sheet provided in the first aspect, and thus can achieve the same or corresponding beneficial effects as the solution provided in the first aspect, and will not be described in detail here.

[0042] A third aspect of the present application provides a battery, comprising a positive electrode sheet, a separator, and a negative electrode sheet as described in the first aspect and its various implementations; wherein the separator is located between the positive electrode sheet and the negative electrode sheet.

[0043] The battery provided in the third aspect includes the negative electrode plate provided in the first aspect, and thus can achieve the same or corresponding beneficial effects as the solution provided in the first aspect, which will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings required for use in the implementation. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0045] Figure 1 Schematic diagram of the cross-sectional structure of the negative electrode sheet provided in some embodiments of the present application.

[0046] Figure 2 Schematic diagram of the cross-sectional structure of the negative electrode sheet provided in other embodiments of the present application.

[0047] Figure 3 Schematic diagram of the cross-sectional structure of the negative electrode sheet provided in some further embodiments of the present application.

[0048] Figure 4 Schematic diagram of the cross-sectional structure of the negative electrode sheet provided in some embodiments of the present application.

[0049] Figure 5 Schematic diagram of the planar structure of the negative electrode plate provided in some embodiments of the present application.

[0050] Figure 6 Flowchart of a method for preparing a negative electrode sheet provided in some embodiments of the present application.

[0051] Figure 7 Schematic diagram of the cross-sectional structure obtained after executing step S4.

[0052] Figure 8 Schematic diagram of a battery in some embodiments of the present application.

[0053] Figure 9 This is a structural block diagram of an electronic device in some embodiments of the present application. DETAILED DESCRIPTION

[0054] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0055] In the description of this application, the terms "first," "second," and "third," etc. are used to distinguish different objects, not to describe a specific order, and therefore should not be understood as limiting this application. The terms "upper," "bottom," etc., indicating positions or relationships based on those shown in the accompanying drawings, are intended only to facilitate the description of this application and simplify the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed, or operate in a specific orientation, and therefore should not be understood as limiting this application. In addition, "plurality" refers to two or more than two.

[0056] It should be noted that the illustrations provided in the embodiments of the present application are only schematic illustrations of the basic concept of the present application. The illustrations only show the components related to the present application and are not drawn according to the number, shape and size of the components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed at will, and the component layout may also be more complicated.

[0057] Throughout this application, words such as "exemplarily" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described in this application as "exemplary" or "for example" should not be construed as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplarily" or "for example" is intended to present the relevant concepts in a concrete manner.

[0058] References to "embodiments" in this application mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearance of such phrases in various locations in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described in this application may be combined with other embodiments.

[0059] In the lithium-ion batteries of the related art, the morphology and structure of silicon will be destroyed during the continuous lithium insertion and extraction process, resulting in a low initial coulombic efficiency of the battery. In addition, the mass proportion of silicon-based negative electrode materials in the related art is low, which limits the application of silicon-based negative electrode materials in lithium-ion batteries. In addition, in order to improve battery performance, grooves are cut on the active layer in the related art. However, the applicant of this application found through research that when grooves are cut on the active layer containing silicon material, the escaped silicon dust will fall on the negative electrode sheet. After the negative electrode sheet, diaphragm, and positive electrode sheet are formed into a battery cell through winding or lamination processes, the battery cell needs to be pressurized to make the negative electrode sheet, diaphragm, and positive electrode sheet fit tightly. During the pressurization process, due to the high hardness and large particle size of silicon dust, the silicon dust may be squeezed and directly penetrate the diaphragm and connect the positive and negative electrode sheets, which can easily cause local short circuits under high voltage, resulting in a high Hi-Pot test failure rate and thus a high battery cell failure rate.

[0060] The embodiment of the present application provides a negative electrode plate, which can improve the initial coulombic efficiency, battery capacity and energy density, and can also reduce the Hi-Pot test failure rate.

[0061] The battery involved in the embodiments of the present application is a secondary battery, for example, a lithium-ion battery, a sodium-ion battery, etc.

[0062] The following describes the negative electrode sheet provided in the embodiments of the present application.

[0063] See also Figure 1 , is a schematic diagram of the cross-sectional structure of the negative electrode sheet 100 provided in some embodiments of the present application. Figure 1 As shown, the negative electrode sheet 100 includes a current collector 10 and an active layer 20. The active layer 20 is disposed on the current collector 10 and includes a first active layer 21, a second active layer 22, and a third active layer 23 stacked sequentially on the current collector 10. The first active layer 21 is closer to the current collector 10 than the second active layer 22, and a groove 30 is provided on the side of the third active layer 23 away from the second active layer 22. The first active layer 21 and the third active layer 23 include a carbon material, the second active layer 22 includes a silicon material, and the mass percentage of the silicon material in the second active layer 22 is greater than 10%.

[0064] The negative electrode sheet 100 provided in the embodiment of the present application has the first active layer 21, the second active layer 22, and the third active layer 23 stacked sequentially on the current collector 10. Because the first active layer 21, comprising carbon material, is located closest to the current collector 10, the second active layer 22 has a greater adhesion to the first active layer 21 than to the current collector 10. This prevents the second active layer 22, comprising silicon material, from expanding and falling off the current collector 10, thereby improving the battery's initial coulombic efficiency, energy density, and battery capacity. Furthermore, because the mass percentage of silicon material in the second active layer 22 is greater than 10%, the active layer 20 has a higher silicon content, further improving the energy density and battery capacity. In addition, the groove 30 can increase the contact area between the active layer 20 and the electrolyte, thereby improving the electrolyte infiltration effect, and can also reduce tortuosity, increase the battery charge and discharge rate, and increase the battery charge and discharge rate. Specifically, because the groove 30 can serve as a transmission path for ions, such as lithium ions, the lithium ions can reach the interior of the active layer 20 more directly and quickly, thereby reducing tortuosity. In addition, compared with the related art of grooves on silicon materials, the embodiment of the present application can reduce the cell defect rate by grooves on the third active layer 23 comprising carbon material. Specifically, because carbon materials have lower hardness, smaller particle size, and lower density than silicon materials, the scattered carbon dust is not easy to fall on the negative electrode plate 100. Even if it falls on the negative electrode plate 100, the carbon dust with lower hardness and smaller particle size is not easy to penetrate the diaphragm when pressurized, and thus is not easy to cause local short circuits, thereby reducing the Hi-Pot test defect rate and the cell defect rate.

[0065] The current collector 10 may be in the form of a plate or sheet, and the current collector 10 includes two opposite surfaces in the thickness direction of the current collector 10, wherein the first active layer, the second active layer and the third active layer are sequentially stacked on the current collector, which means that the first active layer, the second active layer and the third active layer are sequentially stacked on one surface of the current collector 10.

[0066] The active layer 20 may be provided on one surface of the current collector 10, or may be provided on both surfaces of the current collector 10. When the active layer 20 is provided on both surfaces of the current collector 10, the active layer 20 provided on each surface may be the same, for example, including a first active layer 21, a second active layer 22, and a third active layer 23 sequentially stacked on the current collector 10, and a surface of the third active layer 23 away from the second active layer 22 is provided with a groove 30, and so on.

[0067] In some embodiments, the third active layer 23 further includes a first polymer, which is formed by in-situ polymerization of a first precursor in the third active layer 23 , and the first polymer is mixed with the carbon material and distributed in the third active layer 23 .

[0068] Among them, the first polymer is formed by in-situ polymerization of the first precursor, which means that the first polymer is added to the slurry in the form of the first precursor. After the slurry is coated to form the third active layer 23, when grooves are opened on the third active layer 23, the first precursor undergoes a polymerization reaction in the third active layer 23 to generate the first polymer, and the structure of the first polymer has structural units corresponding to the first precursor.

[0069] During the grooving process, after the material, particularly the binder, of the third active layer 23 in the grooving region dissipates, the bonding strength between the remaining material particles weakens. The first precursor in the grooving region polymerizes to form the first polymer, forming a cross-linked network that bonds the remaining material particles of the third active layer 23 in the grooving region. This improves the bonding strength between the material particles of the third active layer 23 at the groove 30, preventing the particles at that location from falling off. This in turn reduces carbon material dissipation, further lowering the Hi-Pot test failure rate. Furthermore, preventing carbon material particle shedding can improve the initial coulombic efficiency and energy density. Furthermore, the first precursor at other locations polymerizes to form the first polymer, which strengthens the bonding strength between the material particles of the third active layer 23 at corresponding locations.

[0070] In some embodiments, the structure of the first precursor includes an aromatic ring and a double bond. The double bond in the structure of the first precursor enables the first precursor to undergo a polymerization reaction. The structure of the first precursor includes an aromatic ring, that is, the first polymer generated by in situ polymerization also includes an aromatic ring, which makes the polarity of the first polymer weaker. Due to the principle of like attracts like, the first polymer with weaker polarity has good affinity with the non-polar carbon material in the third active layer 23. Therefore, the first polymer and the carbon material in the third active layer 23 have good compatibility, the first polymer and the carbon material have a large adhesion force, and a relatively stable structure can be formed.

[0071] In some embodiments, the first precursor includes at least one of allylbenzene, allylbenzyl ether, 2-allylphenyl allyl ether, and 2-allylbenzaldehyde. These precursors have high polymerization efficiency, and the resulting first polymer can effectively bond the materials of the third active layer 23. Furthermore, these precursors have high chemical stability and are relatively low in cost.

[0072] In other embodiments, the structure of the first precursor includes an ether oxygen bond and a double bond. For example, the first precursor includes at least one of polyethylene glycol diacrylate (PEGDA), polyethylene glycol methyl ether acrylate, and polyethylene glycol methyl ether methacrylate.

[0073] In some embodiments, the mass percentage of the first polymer in the third active layer 23 is 3%-5%. The mass percentage of the first polymer within this range not only has a good bonding effect, thereby reducing the Hi-Pot test failure rate, but also has high first coulombic efficiency, battery capacity, and energy density. If the mass percentage of the first polymer is less than 3%, the bonding strength between the material particles of the third active layer 23 at the position of the groove 30 may be reduced, and the material particles may fall off, which may increase the Hi-Pot test failure rate and reduce the first coulombic efficiency, energy density, and battery capacity. If the mass percentage of the first polymer is greater than 5%, the mass proportion of the carbon material in the third active layer 23 will be reduced, thereby affecting the energy density and battery capacity.

[0074] In some embodiments, the second active layer 22 further includes a second polymer, which is formed by in-situ polymerization of a second precursor in the second active layer 22 , and the second polymer is mixed with the silicon material and distributed in the second active layer 22 .

[0075] Among them, the second polymer is formed by in-situ polymerization of the second precursor, which means that the second polymer is added to the slurry in the form of the second precursor. After the slurry is coated to form the second active layer 22, when a groove is opened on the third active layer 23 and penetrates into the second active layer 22, the second precursor undergoes a polymerization reaction in the second active layer 22 to generate the second polymer. The structure of the second polymer has structural units corresponding to the second precursor.

[0076] During the grooving process, after the material, particularly the binder, of the second active layer 22 located in the grooved area dissipates, the bonding strength between the remaining material particles weakens. The second precursor in the grooved area polymerizes to form the second polymer, forming a cross-linked network that bonds the remaining material particles of the second active layer 22 in the grooved area. This improves the bonding strength between the material particles of the second active layer 22 at the groove 30, thereby reducing silicon material dissipation and further lowering the Hi-Pot test failure rate. Furthermore, by preventing silicon material particle shedding, the initial coulombic efficiency and energy density can be improved. Furthermore, the second precursor at other locations polymerizes to form the second polymer, which strengthens the bonding strength between the material particles of the second active layer 22 at corresponding locations. The second polymer also inhibits the expansion of silicon material particles in the second active layer 22.

[0077] In some embodiments, a groove 30 provided on a side of the third active layer 23 away from the second active layer 22 at least penetrates the surface of the third active layer 23 away from the second active layer 22. The opening of the groove 30 faces the side of the third active layer 23 away from the second active layer 22, and the bottom of the groove 30 is located in the third active layer 23 or the second active layer 22. That is, the groove may penetrate part of the third active layer 23, or may penetrate the entire third active layer 23, or may further penetrate part or all of the second active layer 22. When the bottom of the groove 30 is located in the third active layer 23 or the second active layer 22, the second active layer 22 may include the second polymer.

[0078] In some embodiments, the structure of the second precursor includes an ether oxygen bond and a double bond. The double bond in the structure of the second precursor enables the second precursor to undergo a polymerization reaction. The ether oxygen bond in the structure of the second precursor has a strong polarity and can produce strong interactions with ions such as lithium ions, such as adsorption and coordination, thereby improving the ion transport performance of the second active layer 22 and, in turn, the kinetic performance of the battery.

[0079] In some embodiments, the second precursor includes at least one of polyethylene glycol diacrylate, polyethylene glycol methyl ether acrylate, and polyethylene glycol methyl ether methacrylate. These precursors have high polymerization efficiency, and the resulting second polymer can effectively bond the materials of the second active layer 22. Furthermore, these precursors have high chemical stability and are relatively low in cost.

[0080] In some embodiments, the weight average molecular weight of the second precursor is 400-20,000, which can make the polymerization efficiency of the second precursor higher and the second precursor is not easy to agglomerate in the slurry. If the weight average molecular weight of the second precursor is less than 400, the second precursor is easy to volatilize and escape, and the required polymerization time is long, resulting in low polymerization efficiency. If the weight average molecular weight of the second precursor is greater than 20,000, the second precursor is easy to agglomerate in the slurry, and it is difficult to form a uniform and continuous second precursor interface.

[0081] In some other embodiments, the second polymer in the second active layer 22 may include an aromatic ring and a double bond. For example, the second polymer may include at least one of allylbenzene, allylbenzyl ether, 2-allylphenyl allyl ether, and 2-allylbenzaldehyde.

[0082] In some embodiments, the mass percentage of the second polymer in the second active layer 22 is 3%-5%, which not only has a good bonding effect, thereby reducing the Hi-Pot test failure rate, but also has high first coulombic efficiency, battery capacity, and energy density. If the mass percentage of the first polymer is less than 3%, the bonding strength between the material particles in the second active layer 22 may be reduced. For example, when the groove 30 penetrates into the second active layer 22, the bonding strength of the material particles in the second active layer 22 at the position of the groove 30 may be reduced, and the material particles may fall off, which may increase the Hi-Pot test failure rate and reduce the first coulombic efficiency, energy density, and battery capacity. If the mass percentage of the first polymer is greater than 5%, the mass proportion of the silicon material in the second active layer 22 will be reduced, thereby affecting the energy density and battery capacity.

[0083] See also Figure 2 , is a schematic diagram of the cross-sectional structure of the negative electrode sheet 100 provided in some other embodiments of the present application. Figure 2 As shown, in some embodiments, the negative electrode sheet 100 includes not only the aforementioned current collector 10 and active layer 20, but also a polymer layer 40, which is disposed between the third active layer 23 and the second active layer 22. The polymer layer 40 includes a third polymer, and the structure of the third polymer includes a first group and a second group. The first group includes at least one of a carboxyl group (-COOH), a carboxylate (-COOM), an amide group (-CONH2), a hydroxyl group (-OH), a cyano group (-CN), and an ester group (-COOR). In this case, M can be Na, K, or other metal elements, R can be a non-hydrogen group, such as an alkyl group, and the second group includes an aryl group.

[0084] The first group in the third polymer has strong polarity and forms hydrogen bonds or dipole-dipole interactions with the surface groups of the silicon material in the second active layer 22, thereby enhancing the adhesion between the polymer layer 40 and the second active layer 22. The second group in the third polymer is a non-polar group and can form π…π interactions with the carbon material in the third active layer 23, thereby enhancing the adhesion between the polymer layer 40 and the third active layer 23. Therefore, the polymer layer 40 can play a bonding role. Providing the polymer layer 40 between the second active layer 22 and the third active layer 23 can increase the adhesion between the second active layer 22 and the third active layer 23. When grooves are made on the third active layer 23, local separation of the second active layer 22 and the third active layer 23 under the action of external energy can be avoided. For example, when grooves are made on the third active layer 23 using a laser, local separation of the second active layer 22 and the third active layer 23 under the action of light or heat can be avoided. This can minimize the shedding of material particles of the third active layer 23 and the material particles of the second active layer 22, thereby further reducing the Hi-Pot test failure rate and improving the first coulombic efficiency.

[0085] In some embodiments, the third polymer has a structure shown in Formula I, Formula I, wherein R1 is the first group, R2 is the second group, R3 and R4 include at least one of carboxyl, hydroxyl, amino and hydrogen, wherein R3 and R4 may be the same or different.

[0086] In some embodiments, the first group is a carboxyl group, the second group is a phenyl group, and the third polymer is a polyacrylic acid-styrene block copolymer. In other embodiments, the first group is -COOBu, the second group is a phenyl group, and the third polymer is a polybutyl acrylate-styrene block copolymer.

[0087] In some embodiments, n and m are integers between 10 and 10,000. If n and m are less than 10, the molecular weight of the third polymer will be low, which may cause the polymer layer 40 to have strong fluidity during processing, making it difficult to form a stable coating, and may weaken the adhesion between the polymer layer 40 and the third active layer 23 and the second active layer 22. If n and m are greater than 10,000, the molecular weight of the third polymer will be high, and the third polymer will easily agglomerate in the slurry, resulting in uneven distribution of the third polymer in the polymer layer 40, which will affect the electrochemical performance of the battery and increase the difficulty of processing and preparation.

[0088] In some embodiments, the ratio of n to m is 0.1-10, so that the number of structural units containing R1 and the number of structural units containing R2 are relatively close, and the length of the chain segment composed of the structural units containing R1 and the length of the chain segment composed of the structural units containing R2 are also relatively close. Therefore, not only can the structural order of the block copolymer be improved, thereby improving its physical and chemical properties, but also the adhesion force between the polymer layer 40 and the second active layer 22 and the adhesion force with the third active layer 23 can be more balanced. Further, when the polymer layer 40 is subjected to external force, the stress distribution inside it is more uniform, thereby improving the adhesion performance between the polymer layer 40 and the second active layer 22 and the third active layer 23.

[0089] In some embodiments, m may be greater than n. Since silicon material particles are prone to expansion during the charging and discharging process, by setting m greater than n, that is, the number of the first groups is greater than the number of the second groups, the interaction between more of the first groups and the silicon material in the second active layer 22 can be utilized to alleviate the volume change of the silicon material.

[0090] In some embodiments, the molecular weight of the third polymer is 5000-1000000. If the molecular weight of the third polymer is less than 5000, the polymer chain segments are short, making it difficult to form a stable coating and possibly weakening the adhesion between the polymer layer 40 and the third active layer 23 and the second active layer 22. If the molecular weight of the third polymer is greater than 1000000, the third polymer may easily agglomerate in the slurry, resulting in uneven distribution of the third polymer in the polymer layer 40 and increased difficulty in processing and preparation.

[0091] In some embodiments, the thickness of the polymer layer 40 is 0.1 μm-5 μm, which not only can better bond the third active layer 23 and the second active layer 22 together, thereby reducing the Hi-Pot test failure rate, but also has higher battery capacity and energy density. If the thickness of the polymer layer 40 is less than 0.1 μm, the bonding strength between the third active layer 23 and the second active layer 22 is weak, which may increase the Hi-Pot test failure rate. If the thickness of the polymer layer 40 is greater than 5 μm, the mass proportion of the active material in the negative electrode plate 100 will be reduced, and it may affect the transmission performance of ions such as lithium ions, thereby affecting the battery capacity and energy density. The thickness of the polymer layer 40 is the size of the polymer layer 40 in the stacking direction of the active layer 20 and the current collector 10.

[0092] See also Figures 1 to 4 , Figure 3Schematic diagram of the cross-sectional structure of the negative electrode sheet 100 provided in some embodiments of the present application, Figure 4 Schematic diagram of the cross-sectional structure of the negative electrode sheet 100 provided in some embodiments of the present application. Figures 1 to 4 As shown, the opening 31 of the groove 30 faces the side of the third active layer 23 away from the second active layer 22 , and the bottom 32 of the groove 30 is opposite to the opening 31 .

[0093] In some embodiments, as Figure 1 and Figure 2 As shown, the bottom 32 of the groove 30 is located in the third active layer 23, that is, the groove 30 extends into the third active layer 23, wherein the groove 30 may penetrate the third active layer 23 along the stacking direction of the active layer 20 and the current collector 10, or may not penetrate the third active layer 23.

[0094] When the negative electrode plate 100 includes the polymer layer 40 , the bottom 32 of the groove 30 may be located in the polymer layer 40 , that is, the groove 30 extends deep into the polymer layer 40 . The groove 30 may penetrate the polymer layer 40 along the stacking direction of the active layer 20 and the current collector 10 , or may not penetrate the polymer layer 40 .

[0095] In other embodiments, Figure 3 and Figure 4 As shown, the bottom 32 of the groove 30 is located in the second active layer 22, that is, the groove 30 extends deep into the second active layer 22, wherein the groove 30 may penetrate the second active layer 22 along the stacking direction of the active layer 20 and the current collector 10, or may not penetrate the second active layer 22.

[0096] By setting the groove 30 not to penetrate into the first active layer 21 , on the one hand, it can prevent the groove 30 from being too deep, which makes the strength of the negative electrode plate 100 weak, and on the other hand, it can prevent the active material content of the negative electrode plate 100 from being low, which affects the electrochemical performance.

[0097] Preferably, in some embodiments, the bottom 32 of the groove 30 is located in the second active layer 22 and does not penetrate the second active layer 22. By providing the groove 30 deep into the second active layer 22, the contact area between the second active layer 22 and the electrolyte can be increased, improving the electrolyte infiltration effect of the second active layer 22. In addition, the tortuosity of the second active layer 22 can be reduced, which helps ions, such as lithium ions, reach the interior of the second active layer 22 more directly and quickly, thereby facilitating improved lithium ion transmission efficiency in the second active layer 22.

[0098] In some embodiments, the mass percentage of the silicon material in the second active layer 22 is greater than 10% and less than or equal to 70%, which can enable the battery to have a higher battery capacity, energy density, first coulombic efficiency, and a lower Hi-Pot test failure rate. If the mass percentage of the silicon material is less than 10%, the battery capacity and energy density will be reduced. If the mass percentage of the silicon material is greater than 70%, due to the high content of the silicon material, the silicon material particles may expand and crack, thereby causing a decrease in the first coulombic efficiency. Moreover, if the groove is deep into the second active layer 22, the high content of the silicon material may cause the Hi-Pot test failure rate to increase.

[0099] Preferably, in some embodiments, the mass percentage of the silicon material in the second active layer 22 is greater than 10% and less than or equal to 40%, which can reduce the failure rate of the battery in Hi-Pot testing.

[0100] In some embodiments, the mass percentage of the silicon material in the active layer 20 is greater than or equal to 5% and less than or equal to 50%, which can enable the battery to have a higher battery capacity, energy density, first coulombic efficiency and a lower Hi-Pot test failure rate. If the mass percentage of the silicon material in the active layer 20 is less than 5%, the silicon content of the negative electrode plate 100 is low, and the contribution of the silicon material to the capacity is limited, which limits the improvement of the battery energy density. If the mass percentage of the silicon material in the active layer 20 is greater than 50%, the volume expansion of the silicon material during the charge and discharge process may destroy the structure of the active layer 20, resulting in a decrease in the first coulombic efficiency and battery capacity, and an increase in the Hi-Pot test failure rate.

[0101] In some embodiments, the mass percentage of the silicon material in the active layer 20 is greater than or equal to 10% and less than or equal to 40%, which can enable the battery to have a higher battery capacity and better cycle performance.

[0102] In some embodiments, the silicon material in the second active layer 22 includes at least one of elemental silicon, silicon-carbon material, and silicon-oxygen material. Elemental silicon has a high theoretical specific capacity, and its introduction into the second active layer can significantly increase the battery's energy density. Silicon-carbon material combines the advantages of silicon and carbon, with high specific capacity and good cycle stability, which also helps to increase the battery's energy density. Silicon-oxygen material exhibits minimal volume change during cycling, which helps to improve the battery's cycle life.

[0103] In some other embodiments, the silicon material is other types of silicon materials.

[0104] In some embodiments, the carbon material in the first active layer 21 and the third active layer 23 includes at least one of graphite, hard carbon, and soft carbon. The carbon materials in the first active layer 21 and the third active layer 23 can be the same or different. In other embodiments, the carbon material can be another type of carbon material.

[0105] In some embodiments, the thickness of the first active layer 21 is 5 μm-30 μm, the thickness of the second active layer 22 is 20 μm-100 μm, the thickness of the third active layer 23 is 5 μm-30 μm, and the depth of the groove 30 is 5 μm-40 μm. The thickness of the first active layer 21, the thickness of the second active layer 22, the thickness of the third active layer 23, and the depth of the groove 30 are all dimensions along the stacking direction of the active layer 20 and the current collector 10.

[0106] If the thickness of the first active layer 21, the second active layer 22, and the third active layer 23 is below the lower limit of the corresponding thickness range, the battery capacity may be low. If the thickness of the first active layer 21, the second active layer 22, and the third active layer 23 is above the upper limit of the corresponding thickness range, the negative electrode sheet 100 is thicker, reducing the effective utilization area of the active material, which may lead to a decrease in capacity and energy density. The diffusion distance of ions in the electrode is increased, which may increase the resistance during the charge and discharge process and reduce the charge and discharge efficiency. In addition, the thicker negative electrode sheet 100 is more likely to undergo volume changes during the charge and discharge process, causing powdering and shedding, shortening the cycle life.

[0107] If the depth of the groove 30 is less than 5 μm, it will have limited effect on improving electrolyte wetting and reducing tortuosity. If the depth of the groove 30 is greater than 40 μm, the groove 30 is too deep, which may weaken the strength of the negative electrode sheet 100 and cause a large loss of active material in the active layer 20, thereby affecting the battery capacity.

[0108] In some embodiments, a plurality of grooves 30 are provided on a side of the third active layer 23 away from the second active layer 22. The width of each groove 30 is 40 μm to 120 μm, and the spacing between two adjacent grooves 30 is 0.5 mm to 3 mm. This not only significantly improves the electrolyte infiltration effect and reduces tortuosity, but also provides the negative electrode plate 100 with a higher structural strength. The widths of the plurality of grooves 30 may be the same or different, and the spacing between two adjacent grooves 30 may be the same or different. The width of the groove 30 is the dimension perpendicular to the length of the groove 30.

[0109] If the width of the groove 30 is less than 40 μm, the effect of improving electrolyte wetting and reducing tortuosity may be limited due to the small width of the groove 30. If the width of the groove 30 is greater than 120 μm, the strength of the negative electrode sheet 100 may be reduced due to the large width of the groove 30.

[0110] If the distance between two adjacent grooves 30 is less than 0.5 mm, that is, the distance between two adjacent grooves 30 is small, the multiple grooves 30 are densely distributed, which may reduce the strength of the negative electrode sheet 100. If the distance between two adjacent grooves 30 is greater than 3 mm, that is, the distance between two adjacent grooves 30 is large, the multiple grooves 30 are sparsely distributed, which may have limited effect on improving electrolyte infiltration and reducing tortuosity.

[0111] In some embodiments, an angle is formed between the length direction of the groove 30 and the width direction of the third active layer 23, and the angle is greater than or equal to 0° and less than or equal to 10°. The width direction of the third active layer 23 is perpendicular to the extension direction of the third active layer 23, i.e., the length direction.

[0112] For example, see Figure 5 , is a schematic diagram of the planar structure of the negative electrode sheet 100 provided in some embodiments of the present application. Figure 5 As shown, the angle between the length direction of the groove 30 and the width direction of the negative electrode plate 100 , that is, the width direction (Y direction) of the third active layer 23 is 0°.

[0113] In order to adapt to the battery design requirements, the negative electrode sheet 100 is usually cut along the width direction of the negative electrode sheet 100 to obtain slices with the required size. When the angle is 0°, that is, the length direction of the groove 30 is parallel to the width direction of the negative electrode sheet 100, since the cutting direction is parallel to the width direction of the negative electrode sheet 100, by setting the cutting position of the blade between two adjacent grooves 30, the blade will not cut into the groove 30, thereby preventing the material wire from falling.

[0114] In some cases, due to deviations in the cutting position during the actual cutting process, after multiple cuts, the cutting position of the blade may get closer and closer to the groove 30. When the deviations are superimposed until the blade just cuts the groove 30, the blade will cut the groove 30 along the length of the groove 30, and the material will fall off. However, by setting the angle greater than 0°, that is, the groove 30 is tilted relative to the third active layer 23, even if the cutting position has deviations, the blade will not cut the groove 30 along the length of the groove 30 when cutting the groove 30, thereby minimizing the drop of material. Furthermore, by setting the angle less than or equal to 10°, that is, the groove 30 is slightly tilted relative to the third active layer 23, the length difference of the multiple grooves 30 in the slices obtained after cutting can be small, that is, the lengths of the multiple grooves 30 are relatively uniform, which is beneficial to improving the electrolyte infiltration effect and the balance of ion transmission performance.

[0115] In some other embodiments, the angle may be greater than 10°, such as 20°, 45°, 90°, etc.

[0116] In some embodiments, the shape of the groove 30 may be as follows: Figure 5 The straight line shown may be a curved line or any other shape as required.

[0117] In some embodiments, the third active layer 23 further includes a conductive agent and a binder, the mass percentage of the carbon material in the third active layer 23 is 90%-95%, the mass percentage of the conductive agent in the third active layer 23 is 1%-5%, and the mass percentage of the binder in the third active layer 23 is 1%-5%.

[0118] The conductive agent in the third active layer 23 can enhance the conductivity of the third active layer 23, reduce the resistance of the third active layer 23, accelerate the mobility of electrons, and thus improve the charge and discharge performance of the battery. The first polymer generated by the in-situ polymerization of the first precursor and the binder both serve to connect the granular carbon material and the conductive agent together, thereby ensuring the structural integrity and stability of the third active layer 23.

[0119] In some embodiments, the second active layer 22 further includes a carbon material, a conductive agent, and a binder. The mass percentage of the carbon material in the second active layer 22 is 20%-80%, the mass percentage of the conductive agent in the second active layer 22 is 1%-5%, and the mass percentage of the binder in the second active layer 22 is 1%-5%.

[0120] The conductive agent in the second active layer 22 can enhance the conductivity of the second active layer 22, reduce the resistance of the second active layer 22, accelerate the mobility of electrons, and thus improve the charge and discharge performance of the battery. The second polymer generated by the in-situ polymerization of the aforementioned second precursor and the binder both serve to connect the granular silicon material, carbon material, and conductive agent together to ensure the structural integrity and stability of the second active layer 22. By adding carbon material and silicon material in combination to the second active layer 22, the expansion of the silicon material can be alleviated to a certain extent, improving the cycling stability of the battery.

[0121] In some embodiments, the first active layer 21 further includes a conductive agent and a binder, the mass percentage of the carbon material in the first active layer 21 is 90%-98%, the mass percentage of the conductive agent in the first active layer 21 is 1%-5%, and the mass percentage of the binder in the first active layer 21 is 1%-5%.

[0122] The conductive agent in the first active layer 21 can enhance the conductivity of the first active layer 21, reduce the resistance of the first active layer 21, and accelerate the mobility of electrons, thereby improving the charge and discharge performance of the battery. The binder in the first active layer 21 can connect the granular carbon material and the conductive agent together, ensuring the structural integrity and stability of the first active layer 21.

[0123] The following describes the method for preparing the negative electrode sheet provided in the embodiments of the present application.

[0124] See also Figure 6 , is a flow chart of a method for preparing a negative electrode sheet provided in some embodiments of the present application. The preparation method is used to manufacture the negative electrode sheet 100 described in any of the aforementioned embodiments. Figure 6 As shown, the preparation method comprises the following steps:

[0125] S1: providing a current collector 10, a first slurry, a second slurry, and a third slurry, wherein the first slurry and the third slurry both include carbon materials, and the second slurry includes silicon materials.

[0126] S2 : coating the first slurry on the current collector 10 to form a first active layer 21 .

[0127] S3: coating the second slurry on a side of the first active layer 21 away from the current collector 10 to form a second active layer 22 , wherein the mass percentage of the silicon material in the second active layer 22 is greater than 10%.

[0128] S4: Coating the third slurry on the side of the second active layer 22 away from the first active layer 21 to form a third active layer 23. The structure after forming the third active layer 23 is as follows: Figure 7 shown.

[0129] S5: Using laser to open a groove 30 on the side of the third active layer 23 away from the second active layer 22. The structure after opening the groove is as follows: Figure 1 shown.

[0130] When using laser grooving, a laser beam can be used to irradiate the side of the third active layer 23 away from the second active layer 22. The material in the third active layer 23 absorbs the laser energy and converts it into heat energy, causing the material in the irradiated area to melt, decompose, and evaporate, thereby achieving the removal of the material in the irradiated area. Alternatively, the material in the second active layer 22 is heated to melt, decompose, and evaporate to form the groove 30.

[0131] The depth of the groove 30 can be controlled by controlling the energy of the laser beam, the irradiation time, etc., so as to control the bottom 32 of the groove 30 to be located in the third active layer 23 or the second active layer 22 .

[0132] In some embodiments, when laser grooving, the power of the laser equipment is 100W-2000W, and the laser beam quality M 2 The factor is less than 1.5, so that the emitted laser can not only etch away a portion of the third active layer 23, or further etch away a portion of the second active layer 22 to form the groove 30, but also the energy of the laser is sufficient to induce the first precursor in the third active layer 23 to undergo an in-situ polymerization reaction to generate the first polymer, or further induce the second precursor in the second active layer 22 to undergo an in-situ polymerization reaction to generate the second polymer.

[0133] In some embodiments, the first slurry may further include the aforementioned conductive agent, the aforementioned binder, and a solvent. The second slurry may further include a carbon material, the aforementioned conductive agent, the aforementioned binder, and a solvent. The third slurry may further include the aforementioned conductive agent, the aforementioned binder, and a solvent. The solvent may be deionized water or an organic solvent.

[0134] In some embodiments, the third slurry further includes a first precursor and a first initiator, wherein the first precursor, the first initiator, and the carbon material are uniformly mixed in the third slurry. During step S5, i.e., when the laser is used to form the groove 30 on the side of the third active layer 23 away from the second active layer 22, the first initiator, under the action of the laser, triggers a polymerization reaction of the first precursor, causing the first precursor to polymerize in situ in the third active layer 23 to form the aforementioned first polymer.

[0135] In some embodiments, the first initiator may include a photoinitiator. When the laser irradiates the third active layer 23, the photoinitiator in the third active layer 23 absorbs the laser energy and undergoes a decomposition reaction to generate free radicals. The generated free radicals combine with the first precursor molecules to generate first precursor free radicals. The generated first precursor free radicals combine with other first precursor molecules to form polymer chains, thereby generating the first polymer.

[0136] The photoinitiator may include at least one of 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexylphenyl ketone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and ethyl 2,4,6-trimethylbenzoylphenylphosphonate. The first precursor may include at least one of the aforementioned allylbenzene, allyl benzyl ether, 2-allylphenyl allyl ether, and 2-allylbenzaldehyde. The first precursor may undergo a polymerization reaction under the action of the photoinitiator.

[0137] In other embodiments, the first initiator may include a thermal initiator. When the laser irradiates the third active layer 23, the material in the third active layer 23 absorbs the laser energy and converts it into thermal energy, causing the temperature to rise. Then, the thermal initiator in the third active layer 23 decomposes under the heat to generate free radicals. The generated free radicals combine with the first precursor molecules to generate first precursor free radicals. The generated first precursor free radicals combine with other first precursor molecules to form polymer chains, thereby generating the first polymer.

[0138] The thermal initiator may include at least one of azobisisoheptanonitrile, azobismethoxyisoheptanonitrile, dilauroyl peroxide, dicyclohexyl peroxydicarbonate, benzoyl peroxide, azobisisobutyronitrile, and potassium persulfate. The first precursor may include at least one of the aforementioned polyethylene glycol diacrylate, polyethylene glycol methyl ether acrylate, and polyethylene glycol methyl ether methacrylate. The first precursor may undergo a polymerization reaction under the action of the thermal initiator.

[0139] The first initiator may be at least one of the above-mentioned photoinitiator and thermal initiator.

[0140] In some embodiments, the second slurry further includes a second precursor and a second initiator, wherein the second precursor, the second initiator, and the silicon material are uniformly mixed in the second slurry. During step S5, when the laser is used to form the groove 30 on the side of the third active layer 23 away from the second active layer 22, the second initiator triggers a polymerization reaction of the second precursor, causing the second precursor to polymerize in situ in the second active layer 22 to form the aforementioned second polymer.

[0141] In some embodiments, the second initiator may include a thermal initiator. When the laser irradiates the third active layer 23, the third active layer 23 absorbs the laser energy and converts it into thermal energy. The converted thermal energy will be conducted to the second active layer 22. In addition, the second active layer 22 may also absorb the laser energy and convert it into thermal energy. The thermal energy causes the temperature of the second active layer 22 to increase, and then the thermal initiator in the second active layer 22 decomposes under the heat to generate free radicals. The generated free radicals combine with the second precursor molecules to generate second precursor free radicals. The generated second precursor free radicals combine with other second precursor molecules to form polymer chains, thereby generating the second polymer.

[0142] The thermal initiator may include at least one of azobisisoheptanonitrile, azobismethoxyisoheptanonitrile, dilauroyl peroxide, dicyclohexyl peroxydicarbonate, benzoyl peroxide, azobisisobutyronitrile, and potassium persulfate. The first precursor may include at least one of the aforementioned polyethylene glycol diacrylate, polyethylene glycol methyl ether acrylate, and polyethylene glycol methyl ether methacrylate. The second precursor may undergo a polymerization reaction under the action of the thermal initiator.

[0143] In other embodiments, the second initiator may include a photoinitiator. When irradiated by laser, the photoinitiator in the second active layer 22 absorbs laser energy and undergoes a decomposition reaction to generate free radicals. The generated free radicals combine with the second precursor molecules to generate second precursor free radicals. The generated second precursor free radicals combine with other second precursor molecules to form polymer chains, thereby generating the second polymer.

[0144] The photoinitiator may include at least one of 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexylphenyl ketone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and ethyl 2,4,6-trimethylbenzoylphenylphosphonate. The first precursor may include at least one of the aforementioned allylbenzene, allyl benzyl ether, 2-allylphenyl allyl ether, and 2-allylbenzaldehyde. The second precursor may undergo a polymerization reaction under the action of the photoinitiator.

[0145] The second initiator may be at least one of the above-mentioned photoinitiator and thermal initiator.

[0146] Preferably, in some embodiments, the first initiator in the third active layer 23 may be a photoinitiator, and the second initiator in the second active layer 22 may be a thermal initiator, and the decomposition temperature of the thermal initiator is lower than 70° C. and the half-life is 7 hours to 13 hours, for example, 10 hours. The first initiator may include at least one of 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexylphenyl ketone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and ethyl 2,4,6-trimethylbenzoylphenylphosphonate, and the second initiator may include at least one of azobisisoheptanenitrile, azobismethoxyisoheptanenitrile, dilauroyl peroxide, and dicyclohexyl peroxydicarbonate.

[0147] That is, the polymerization system in the third active layer 23 is a photoinitiated polymerization system, while the polymerization system in the second active layer 22 is a thermally initiated polymerization system. Because the laser directly irradiates the third active layer 23, the first initiator can directly absorb the laser energy and initiate polymerization, thereby improving polymerization efficiency. Because the second active layer 22 is located on the side of the third active layer 23 away from the laser, and the second initiator is a thermal initiator with a low decomposition temperature and short half-life, when the second active layer 22 receives thermal energy from the third active layer 23, the second initiator can rapidly decompose at a relatively low temperature to generate free radicals, which in turn initiate polymerization, thereby improving polymerization efficiency.

[0148] When the first initiator is a photoinitiator, the mass ratio of the photoinitiator to the first precursor is 0.1:100 to 5:100. When the second initiator is a photoinitiator, the mass ratio of the photoinitiator to the second precursor is 0.1:100 to 5:100. Thus, the photoinitiator can generate sufficient free radicals to initiate the polymerization reaction of the precursor and reduce the generation of byproducts.

[0149] When the first initiator is a thermal initiator, the mass ratio of the thermal initiator to the first precursor is 1:100 to 10:100. When the second initiator is a thermal initiator, the mass ratio of the thermal initiator to the second precursor is 1:100 to 10:100. Thus, the thermal initiator can generate sufficient free radicals to initiate the polymerization reaction of the precursor and reduce the formation of byproducts.

[0150] In some embodiments, the solid content of the first slurry may be 30%-56%, for example, 43%. The solid content of the second slurry may be 35%-65%, for example, 50%. The solid content of the third slurry may be 34%-63%, for example, 48%. This allows for uniform coating of the slurries.

[0151] In some embodiments, before step S4 of "coating the third slurry on the side of the second active layer 22 away from the first active layer 21 to form the third active layer 23", the method for preparing the negative electrode sheet further includes the step of coating a polymer slurry on the side of the second active layer 22 away from the first active layer 21 to form a polymer layer 40, wherein the polymer slurry includes a third polymer and a solvent, and the solid content of the polymer slurry can be 7%-13%, for example, 10%. The solvent can be deionized water or an organic solvent.

[0152] Step S4 “coating the third slurry on the side of the second active layer 22 away from the first active layer 21 to form the third active layer 23 ” includes: coating the third slurry on the side of the polymer layer 40 away from the second active layer 22 to form the third active layer 23 .

[0153] See also Figure 8 , is a schematic diagram of a battery 200 in some embodiments of the present application. Figure 8 As shown, an embodiment of the present application further provides a battery 200 , which includes a positive electrode plate 210 , a separator 220 , and the negative electrode plate 100 described in any of the aforementioned embodiments, wherein the separator 220 is located between the positive electrode plate 210 and the negative electrode plate 100 .

[0154] See also Figure 9 , is a structural block diagram of an electronic device 300 in some embodiments of the present application. Figure 9 As shown, an embodiment of the present application further provides an electronic device 300 , and the electronic device 300 includes the battery 200 .

[0155] Among them, the electronic device can be a mobile phone, tablet computer, laptop computer, large-screen device (for example: smart TV, smart screen), computer, wearable electronic device, vehicle-mounted device, virtual reality device, electric car, home appliance, drone, etc.

[0156] The electronic device may further include other components, such as a display screen, a memory, etc., which are irrelevant to the improvement of the present invention and are therefore not described in detail here.

[0157] The present application is described in detail below using implementation examples 1-23 and comparative examples 1-2. The following implementation examples are only used to illustrate and explain the present application, and the scope of protection of the present application is not limited by the following implementation examples.

[0158] Implementation Example 1

[0159] (1) Preparation of the first slurry: Graphite, a conductive agent, and a binder in a mass ratio of 92:4:4 were mixed with deionized water to obtain a first slurry with a solid content of 43%. Preparation of the second slurry: Precipitated silicon carbon, graphite, a conductive agent, a binder, polyvinyl alcohol diacrylate, and dilauroyl peroxide in a mass ratio of 40:54:2:1:3:0.03 were mixed with deionized water to obtain a second slurry with a solid content of 50%, wherein the weight-average molecular weight of polyvinyl alcohol diacrylate was 20,000. Preparation of the third slurry: Graphite, a conductive agent, a binder, allyl benzyl ether, and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide in a mass ratio of 94:2:1:3:0.03 were mixed with deionized water to obtain a third slurry with a solid content of 48%. Preparation of polymer slurry: Polyacrylic acid-styrene block copolymer was mixed with deionized water to obtain a polymer slurry with a solid content of 10%.

[0160] (2) Slurry coating: The first slurry, the second slurry, the polymer slurry and the third slurry are sequentially coated on opposite sides of the copper foil and dried to obtain a first active layer 21, a second active layer 22, a polymer layer 40 and a third active layer 23. The thickness of the first active layer 21 is 10 μm, the thickness of the second active layer 22 is 40 μm, the thickness of the polymer layer 40 is 1 μm, and the thickness of the third active layer 23 is 10 μm.

[0161] (3) Laser grooving: A laser is used to etch the side of the third active layer 23 away from the copper foil to form a plurality of grooves 30. The depth of the grooves 30 is 20 μm, the width of the grooves is 60 μm, and the distance between two adjacent grooves 30 is 1 mm, thereby obtaining the negative electrode 100. The power of the laser equipment is 500 W, and the beam quality is M 2 The factor is less than 1.5. The mass percentage of deposited silicon carbon in the second active layer 22 of the negative electrode plate 100 is 40%, the mass percentage of deposited silicon carbon in the active layer 20 is 30%, the mass percentage of the first polymer in the third active layer 23 is 3%, and the mass percentage of the second polymer in the second active layer 22 is 3%.

[0162] (4) Battery assembly: The negative electrode sheet 100 obtained after laser grooving is stacked with the separator and the positive electrode sheet to obtain a battery cell, and the battery cell is made into a soft-pack battery.

[0163] Implementation Example 2

[0164] Implementation Example 2 differs from Implementation Example 1 in that the mass ratio of deposited silicon carbon, graphite, conductive agent, binder, polyvinyl alcohol diacrylate and dilauroyl peroxide in the second slurry is 7.4:54:2:1:3:0.03, the mass percentage of deposited silicon carbon in the second active layer 22 of the negative electrode sheet 100 is 11%, and the mass percentage of deposited silicon carbon in the active layer 20 is 5%.

[0165] Implementation Example 3

[0166] Implementation Example 3 is different from Implementation Example 1 in that the mass ratio of deposited silicon carbon, graphite, conductive agent, binder, polyvinyl alcohol diacrylate and dilauroyl peroxide in the second slurry is 140:54:2:1:3:0.03, the mass percentage of deposited silicon carbon in the second active layer 22 of the negative electrode sheet 100 is 70%, and the mass percentage of deposited silicon carbon in the active layer 20 is 50%.

[0167] Implementation Example 4

[0168] Implementation Example 4 is different from Implementation Example 1 in that the mass ratio of deposited silicon carbon, graphite, conductive agent, binder, polyvinyl alcohol diacrylate and dilauroyl peroxide in the second slurry is 5:54:2:1:3:0.03, the mass percentage of deposited silicon carbon in the second active layer 22 of the negative electrode sheet 100 is 8%, and the mass percentage of deposited silicon carbon in the active layer 20 is 4%.

[0169] Implementation Example 5

[0170] Implementation Example 5 is different from Implementation Example 1 in that the mass ratio of deposited silicon carbon, graphite, conductive agent, binder, polyvinyl alcohol diacrylate and dilauroyl peroxide in the second slurry is 180:54:2:1:3:0.03, the mass percentage of deposited silicon carbon in the second active layer 22 of the negative electrode sheet 100 is 75%, and the mass percentage of deposited silicon carbon in the active layer 20 is 52%.

[0171] Implementation Example 6

[0172] Implementation Example 6 differs from Implementation Example 1 in that the mass ratio of graphite, conductive agent, binder, allyl benzyl ether and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide in the third slurry is 94:2:1:5:0.03, and the mass percentage of the first polymer in the third active layer 23 of the negative electrode sheet 100 is 5%.

[0173] Implementation Example 7

[0174] Implementation Example 7 is different from Implementation Example 1 in that the mass ratio of graphite, conductive agent, binder, allyl benzyl ether and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide in the third slurry is 94:2:1:2:0.03, and the mass percentage of the first polymer in the third active layer 23 of the negative electrode sheet 100 is 2%.

[0175] Implementation Example 8

[0176] Implementation Example 8 is different from Implementation Example 1 in that the mass ratio of graphite, conductive agent, binder, allyl benzyl ether and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide in the third slurry is 94:2:1:6:0.03, and the mass percentage of the first polymer in the third active layer 23 of the negative electrode plate 100 is 6%.

[0177] Implementation Example 9

[0178] Implementation Example 9 differs from Implementation Example 1 in that the mass ratio of deposited silicon carbon, graphite, conductive agent, binder, polyvinyl alcohol diacrylate and dilauroyl peroxide in the second slurry is 40:54:2:1:5:0.03, and the mass percentage of the second polymer in the second active layer 22 of the negative electrode sheet 100 is 5%.

[0179] Implementation Example 10

[0180] Implementation Example 10 differs from Implementation Example 1 in that the mass ratio of deposited silicon carbon, graphite, conductive agent, binder, polyvinyl alcohol diacrylate and dilauroyl peroxide in the second slurry is 40:54:2:1:2:0.03, and the mass percentage of the second polymer in the second active layer 22 of the negative electrode sheet 100 is 2%.

[0181] Implementation Example 11

[0182] Implementation Example 11 differs from Implementation Example 1 in that the mass ratio of deposited silicon carbon, graphite, conductive agent, binder, polyvinyl alcohol diacrylate and dilauroyl peroxide in the second slurry is 40:54:2:1:6:0.03, and the mass percentage of the second polymer in the second active layer 22 of the negative electrode plate 100 is 6%.

[0183] Implementation Example 12

[0184] Implementation Example 12 differs from Implementation Example 1 in that: the first precursor and the first initiator are not added to the third slurry, that is, there is no first polymer in the third active layer 23; and the second precursor and the second initiator are not added to the second slurry, that is, there is no second polymer in the second active layer 22.

[0185] Implementation Example 13

[0186] The difference between Example 1 and Example 1 is that the thickness of the polymer layer 40 is 0.1 μm.

[0187] Implementation Example 14

[0188] The difference between Example 14 and Example 1 is that the thickness of the polymer layer 40 is 5 μm.

[0189] Implementation Example 15

[0190] The difference between Example 1 and Example 1 is that the thickness of the polymer layer 40 is 0.05 μm.

[0191] Implementation Example 16

[0192] The difference between Example 16 and Example 1 is that the thickness of the polymer layer 40 is 6 μm.

[0193] Implementation Example 17

[0194] Compared with Example 1, Example 17 differs in that no polymer slurry is coated, that is, there is no polymer layer 40 in the negative electrode sheet 100 .

[0195] Implementation Example 18

[0196] (1) Preparation of the first slurry: Graphite, a conductive agent, and a binder in a mass ratio of 92:4:4 were mixed evenly with deionized water to obtain a first slurry with a solid content of 43%. Preparation of the second slurry: Precipitated silicon carbon, graphite, a conductive agent, and a binder in a mass ratio of 40:57:2:1 were mixed evenly with deionized water to obtain a second slurry with a solid content of 50%. Preparation of the third slurry: Graphite, a conductive agent, a binder, polyvinyl alcohol diacrylate, and potassium persulfate in a mass ratio of 94:2:1:3:0.03 were mixed evenly with deionized water to obtain a third slurry with a solid content of 48%, wherein the weight average molecular weight of the polyvinyl alcohol diacrylate was 20,000.

[0197] (2) Slurry coating: The first slurry, the second slurry, and the third slurry are sequentially coated on opposite sides of the copper foil and dried to obtain a first active layer 21, a second active layer 22, and a third active layer 23. The thickness of the first active layer 21 is 10 μm, the thickness of the second active layer 22 is 40 μm, and the thickness of the third active layer 23 is 10 μm.

[0198] (3) Laser grooving: A laser is used to etch the side of the third active layer 23 away from the copper foil to form a plurality of grooves 30. The depth of the grooves 30 is 20 μm, the width of the grooves is 60 μm, and the distance between two adjacent grooves 30 is 1 mm, thereby obtaining the negative electrode 100. The power of the laser equipment is 500 W, and the beam quality is M2 The factor is less than 1.5. The mass percentage of deposited silicon carbon in the second active layer 22 of the negative electrode 100 is 40%, the mass percentage of deposited silicon carbon in the active layer 20 is 30%, and the mass percentage of the first polymer in the third active layer 23 is 3%.

[0199] (4) Battery assembly: The negative electrode sheet 100 obtained after laser grooving is stacked with the separator and the positive electrode sheet to obtain a battery cell, and the battery cell is made into a soft-pack battery.

[0200] Implementation Example 19

[0201] The difference between Example 19 and Example 18 is that the depth of the groove 30 is 10 μm.

[0202] Implementation Example 20

[0203] The difference between Example 20 and Example 18 is that the depth of the groove 30 is 30 μm.

[0204] Implementation Example 21

[0205] Compared with Example 18, Example 21 differs in that the thickness of the first active layer 21 is 5 μm, and the thickness of the second active layer 22 is 45 μm.

[0206] Implementation Example 22

[0207] Compared with Example 18, Example 22 differs in that the thickness of the second active layer 22 is 45 μm, and the thickness of the third active layer 23 is 5 μm.

[0208] Implementation Example 23

[0209] The difference between Example 23 and Example 18 is that polyvinyl alcohol diacrylate and potassium persulfate are not added to the first slurry, and the third active layer 23 does not contain the first polymer.

[0210] Comparative Example 1

[0211] (1) Slurry preparation: Graphite, conductive agent, and binder in a mass ratio of 92:4:4 were mixed evenly with deionized water to obtain a slurry with a solid content of 43%.

[0212] (2) Slurry coating: Slurry is sequentially coated on opposite sides of the copper foil and dried to obtain a negative electrode sheet, wherein the negative electrode sheet has an active layer with a thickness of 60 μm.

[0213] (3) Battery assembly: The negative electrode sheet, the separator, and the positive electrode sheet are stacked to obtain a battery cell, and the battery cell is made into a soft-pack battery.

[0214] Comparative Example 2

[0215] (1) Slurry preparation: Graphite, deposited silicon carbon, conductive agent, and binder in a mass ratio of 62:30:4:4 were mixed evenly with deionized water to obtain a slurry with a solid content of 43%.

[0216] (2) Slurry coating: Slurry is sequentially coated on opposite sides of the copper foil and dried to obtain an active layer, wherein the thickness of the active layer is 60 μm.

[0217] (3) Laser grooving: Use laser to etch the side of the active layer away from the copper foil to form several grooves with a depth of 20 μm, a width of 60 μm, and a spacing of 1 mm between two adjacent grooves to obtain the negative electrode. The power of the laser equipment is 500 W and the beam quality is M 2 The factor is less than 1.5.

[0218] (4) Battery assembly: The negative electrode sheets obtained after laser grooving are stacked with the separator and the positive electrode sheets to obtain battery cells, and the battery cells are made into soft-pack batteries.

[0219] The thicknesses of the first active layer 21, second active layer 22, third active layer 23, and polymer layer 40 in Examples 1-23, as well as the thickness of the active layer in Comparative Examples 1-2, can all be measured using a micrometer or a scanning electron microscope (SEM). The depth, width, and spacing of the grooves 30 in Examples 1-23, as well as the depth, width, and spacing of the grooves in Comparative Example 2, can all be measured using an SEM.

[0220] The relevant parameters of Implementation Examples 1-23 can be found in Table 1, and the relevant parameters of Comparative Examples 1-2 can be found in Table 2.

[0221] Table 1

[0222]

[0223] Table 1

[0224]

[0225] Table 1

[0226]

[0227] In Table 1, A represents allyl benzyl ether and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, B represents PEGDA and K2O8S2, C represents polyacrylic acid-styrene block copolymer, and D represents PEGDA and dilauroyl peroxide.

[0228] Table 2

[0229]

[0230] The battery cells prepared in Example 1-23 and Comparative Example 1-2 were subjected to a Hi-Pot test under the following test conditions: voltage 100 V, test time 2±1 s, pressure 0.16±0.02 MPa, and the passing standard was internal resistance ≥ 4 MΩ.

[0231] The assembled pouch cells from Examples 1-23 and Comparative Examples 1-2 were subjected to a 0.2C discharge capacity test to determine the 0.2C discharge capacity, initial coulombic efficiency, and energy density. The 0.2C discharge capacity test conditions were as follows: the pouch cells were charged at a 0.2C constant current to 4.55V, then charged at a constant voltage until the current was less than 0.02C or the charge time was greater than or equal to 180 minutes, and then discharged at a 0.2C constant current to 2.75V.

[0232] Among them, during the calculation of energy density, the thickness of the soft-pack battery is measured by a PPG (Panel Pressure Gap) thickness gauge.

[0233] The test results of the above Hi-Pot test, the 0.2C discharge capacity, the first coulombic efficiency and the energy density obtained from the test are shown in Table 3.

[0234] Table 3

[0235]

[0236] It can be seen from the energy densities corresponding to Examples 1-23 and Comparative Example 1 in Table 3 that the negative electrode plate 100 includes silicon material, which can significantly improve the energy density of the battery.

[0237] From the 0.2C discharge capacity, first coulomb efficiency, energy density and Hi-Pot defective rate corresponding to Example 23 and Comparative Example 2 in Table 3, it can be seen that compared with directly grooving the active layer comprising silicon material, the present application provides a third active layer 23 comprising carbon material on the second active layer 22 comprising silicon material, and grooves are made on the third active layer 23, which can significantly reduce the Hi-Pot defective rate. Among them, since the silicon material has a higher hardness, larger particle size and irregular morphology than the carbon material, it is easy to cause local micro-short circuits, which can easily cause Hi-Pot test failures. In the present application, by grooving the third active layer 23 comprising carbon material, the Hi-Pot defective rate can be significantly reduced. In addition, the present application also provides the first active layer 21 between the second active layer 22 and the current collector 10. The multi-layer active layer structure of the negative electrode sheet 100 of the present application improves the 0.2C discharge capacity, first coulomb efficiency and energy density of the battery.

[0238] As shown in Table 3 for the 0.2C discharge capacity and energy density corresponding to Examples 1-4, the discharge capacity and energy density when the silicon material content in the second active layer 22 is greater than 10% are both higher than those when the silicon material content is less than 10%. As shown in Table 3 for the first coulombic efficiency and Hi-Pot failure rate corresponding to Examples 1-3 and 5, the first coulombic efficiency and Hi-Pot failure rate when the silicon material content in the second active layer 22 is less than or equal to 70% are higher and lower, respectively, than those when the silicon material content is greater than 70%. While increasing the silicon material content can increase the discharge capacity and energy density, excessively high silicon material content can easily lead to Hi-Pot test failures, affecting the machinability of the negative electrode 100. To balance energy density and machinability, an appropriate silicon material content is necessary. Therefore, considering the 0.2C discharge capacity, first coulombic efficiency, energy density, and Hi-Pot failure rate, selecting a silicon material content in the second active layer 22 greater than 10% and less than or equal to 70% for battery fabrication results in superior battery performance. Furthermore, the test results of Examples 1-3 show that the Hi-Pot defective rate is 0 when the silicon content in the second active layer 22 is greater than 10% and less than or equal to 40%. However, the Hi-Pot defective rate is 6.95% when the silicon content is greater than 40% and less than or equal to 70%. This indicates that the Hi-Pot test performance is better when the silicon content is greater than 10% and less than or equal to 40%. Therefore, it is further preferred that the silicon content in the second active layer 22 is greater than 10% and less than or equal to 40%.

[0239] From the 0.2C discharge capacity, first coulombic efficiency, energy density, and Hi-Pot defect rate corresponding to Examples 1, 6, and 7 in Table 3, it can be seen that when the mass percentage of the first polymer in the third active layer 23 is 3%-5%, the 0.2C discharge capacity, first coulombic efficiency, and energy density are all higher than the corresponding values when the mass percentage of the first polymer is 2%, and the Hi-Pot defect rate is lower than the Hi-Pot defect rate when the mass percentage of the first polymer is 2%. From the 0.2C discharge capacity, first coulombic efficiency, and energy density corresponding to Examples 1, 6, and 8 in Table 3, it can be seen that when the mass percentage of the first polymer in the third active layer 23 is 3%-5%, the 0.2C discharge capacity, first coulombic efficiency, and energy density are all higher than the corresponding values when the mass percentage of the first polymer is 6%. If the first polymer content is too low, it may affect the binding of dust generated by laser grooving, increase the Hi-Pot defect rate, and thus affect processing performance. If the first polymer content is too high, it may hinder carrier transport, which is not conducive to rate performance and reduces battery capacity and energy density. Therefore, considering the 0.2C discharge capacity, first coulombic efficiency, energy density and Hi-Pot defect rate, the battery performance is better when the mass percentage of the first polymer in the third active layer 23 is within the range of 3%-5%.

[0240] From the first coulombic efficiency, energy density and Hi-Pot defective rate corresponding to Implementation Examples 1, 9-10 in Table 3, it can be seen that the first coulombic efficiency and energy density when the mass percentage of the second polymer in the second active layer 22 is 3%-5% are higher than the corresponding values when the mass percentage of the second polymer is 2%, and the Hi-Pot defective rate is lower than the Hi-Pot defective rate when the mass percentage of the second polymer is 2%. From the first coulombic efficiency and energy density corresponding to Implementation Examples 1, 9 and 11 in Table 3, it can be seen that the first coulombic efficiency and energy density when the mass percentage of the second polymer in the second active layer 22 is 3%-5% are higher than the corresponding values when the mass percentage of the second polymer is 6%. Among them, if the content of the second polymer is too low, it will affect the binding of dust generated by laser grooving, increase the Hi-Pot defective rate, and thus affect the processing performance; if the content of the second polymer is too high, it will hinder carrier transmission, which is not conducive to rate performance and reduces battery capacity and energy density. Therefore, considering the first coulombic efficiency, energy density and Hi-Pot defect rate, the battery performance is better when the mass percentage of the second polymer in the second active layer 22 is within the range of 3%-5%.

[0241] From the first coulombic efficiency, energy density, and Hi-Pot defective rate corresponding to Implementation Examples 1 and 12 in Table 3, it can be seen that if the third active layer 23 does not include the first polymer and the second active layer 22 does not include the second polymer, the first coulombic efficiency is significantly reduced, the Hi-Pot defective rate is significantly improved, and the energy density is also reduced, indicating that setting the third active layer 23 to include the first polymer and the second active layer 22 to include the second polymer can significantly improve battery performance.

[0242] From the first coulombic efficiency and Hi-Pot defective rate corresponding to Implementation Examples 1, 13-15, and 17 in Table 3, it can be seen that the first coulombic efficiency and Hi-Pot defective rate when the thickness of the polymer layer 40 is 0.1μm-5μm are higher and lower than the corresponding values when the thickness is 0.05μm, respectively. From the first coulombic efficiency and energy density corresponding to Implementation Examples 1, 13-14, and 16 in Table 3, it can be seen that the first coulombic efficiency and energy density when the thickness of the polymer layer 40 is 0.1μm-5μm are higher than the corresponding values when the thickness is 6μm. Among them, if the thickness of the polymer layer 40 is too low, it will affect the adhesion of the third active layer 23 and the second active layer 22, and increase the Hi-Pot defective rate; if the thickness of the polymer layer 40 is too high, it will hinder carrier transmission, which is not conducive to rate performance and reduces battery capacity and energy density. Therefore, considering the initial coulombic efficiency, energy density and Hi-Pot defect rate, the battery performance is better when the thickness of the polymer layer 40 is 0.1 μm-5 μm.

[0243] From the first coulombic efficiency, energy density, and Hi-Pot defect rate corresponding to Examples 18-19 in Table 3, it can be seen that when the thickness of the third active layer 23 is 10 μm and the depth of the groove 30 is 20 μm, that is, when the groove 30 penetrates into the second active layer 22, the first coulombic efficiency and energy density are higher than the corresponding values when the depth of the groove 30 is 10 μm, and the Hi-Pot defect rate is lower, indicating that the battery performance is better when the groove 30 penetrates into the second active layer 22. Among them, the groove 30 penetrates into the second active layer 22, which is conducive to the contact between the electrolyte and the second active layer 22 and reduces the tortuosity of the second active layer 22, thereby helping ions such as lithium ions to reach the interior of the second active layer 22 more directly and quickly, thereby helping to improve the transmission efficiency of lithium ions in the second active layer 22, thereby helping to improve the energy density and the first coulombic efficiency. From the first coulombic efficiency, energy density and Hi-Pot defect rate corresponding to Examples 18 and 20 in Table 3, it can be seen that the depth of the groove 30 is greater than 20 μm, which will increase the Hi-Pot defect rate.

[0244] From the 0.2C discharge capacity, first coulombic efficiency, energy density, and Hi-Pot defective rate corresponding to Examples 18 and 21 in Table 3, it can be seen that reducing the thickness of the third active layer 23 and increasing the thickness of the second active layer 22 will reduce the battery capacity, first coulombic efficiency, energy density, and increase the Hi-Pot defective rate.

[0245] From the 0.2C discharge capacity, first coulombic efficiency, energy density, and Hi-Pot defective rate corresponding to Implementation Examples 18 and 22 in Table 3, it can be seen that compared with Implementation Example 18, reducing the thickness of the first active layer 21 and increasing the thickness of the second active layer 22 will reduce the battery capacity, first coulombic efficiency, energy density, and increase the Hi-Pot defective rate.

[0246] The above is an implementation method of the embodiment of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the embodiment of the present application. These improvements and modifications are also considered to be within the scope of protection of the present application.

Claims

1. A negative electrode plate, characterized in that: The negative electrode plate comprises: current collector; an active layer disposed on the current collector, the active layer comprising a first active layer, a second active layer, and a third active layer sequentially stacked on the current collector, the first active layer being closer to the current collector than the second active layer, and a groove being provided on a side of the third active layer away from the second active layer, wherein the first active layer and the third active layer comprise a carbon material, the second active layer comprises a silicon material, and the mass percentage of the silicon material in the second active layer is greater than 10%; The third active layer further includes a first polymer, which is mixed with the carbon material and distributed in the third active layer. The first polymer is formed by an in-situ polymerization reaction of a first precursor in the third active layer induced by a first initiator in the third active layer under the action of a laser when the groove is formed on a side of the third active layer away from the second active layer using a laser. The structure of the first precursor includes an aromatic ring and a double bond. The second active layer further includes a second polymer, which is formed by in-situ polymerization of a second precursor in the second active layer. The second polymer is mixed with the silicon material and distributed in the second active layer, wherein the structure of the second precursor includes an ether oxygen bond and a double bond.

2. The negative electrode sheet according to claim 1, characterized in that: The first precursor includes at least one of allylbenzene, allylbenzyl ether, 2-allylphenyl allyl ether and 2-allylbenzaldehyde.

3. The negative electrode sheet according to claim 1, characterized in that: The mass percentage of the first polymer in the third active layer is 3%-5%.

4. The negative electrode sheet according to claim 1, characterized in that: The second precursor includes at least one of polyethylene glycol diacrylate, polyethylene glycol methyl ether acrylate, and polyethylene glycol methyl ether methacrylate.

5. The negative electrode sheet according to claim 1, characterized in that: The weight average molecular weight of the second precursor is 400-20,000.

6. The negative electrode sheet according to claim 1, characterized in that: The mass percentage of the second polymer in the second active layer is 3%-5%.

7. The negative electrode sheet according to claim 1, characterized in that: The negative electrode plate also includes a polymer layer, which is arranged between the third active layer and the second active layer. The polymer layer includes a third polymer. The structure of the third polymer includes a first group and a second group. The first group includes at least one of a carboxyl group, a carboxylate group, an amide group, a hydroxyl group, a cyano group and an ester group, and the second group includes an aromatic group.

8. The negative electrode sheet according to claim 7, characterized in that: The third polymer has a structure shown in Formula I, Formula I, wherein R1 is the first group, R2 is the second group, R3 and R4 include at least one of carboxyl, hydroxyl, amino and hydrogen, n and m are integers between 10 and 10,000, and the ratio of n to m is 0.1 to 10.

9. The negative electrode sheet according to claim 7, characterized in that: The thickness of the polymer layer is 0.1 μm-5 μm.

10. The negative electrode sheet according to claim 1, characterized in that: The opening of the groove faces the side of the third active layer away from the second active layer, the bottom of the groove is opposite to the opening, and the bottom of the groove is located in the third active layer or the second active layer.

11. The negative electrode sheet according to claim 1, characterized in that: The mass percentage of the silicon material in the second active layer is greater than 10% and less than or equal to 70%.

12. The negative electrode sheet according to claim 1, characterized in that: The mass percentage of the silicon material in the active layer is greater than or equal to 5% and less than or equal to 50%.

13. The negative electrode sheet according to claim 1, characterized in that: The silicon material includes at least one of elemental silicon, silicon-carbon material and silicon-oxygen material.

14. The negative electrode sheet according to claim 1, characterized in that: The thickness of the first active layer is 5 μm-30 μm, the thickness of the second active layer is 20 μm-100 μm, the thickness of the third active layer is 5 μm-30 μm, and the depth of the groove is 5 μm-40 μm.

15. The negative electrode sheet according to claim 1, characterized in that: A plurality of grooves are provided at intervals on a side of the third active layer away from the second active layer. The width of each groove is 40 μm-120 μm, and the distance between two adjacent grooves is 0.5 mm-3 mm.

16. The negative electrode sheet according to claim 1, characterized in that: An angle is formed between the length direction of the groove and the width direction of the third active layer, and the angle is 0°-10°.

17. The negative electrode sheet according to claim 1, characterized in that: The first active layer also includes a conductive agent and a binder. The mass percentage of the carbon material in the first active layer is 90%-95%, the mass percentage of the conductive agent is 1%-5%, and the mass percentage of the binder is 1%-5%; the second active layer also includes a carbon material, a conductive agent and a binder. The mass percentage of the carbon material in the second active layer is 20%-80%, the mass percentage of the conductive agent is 1%-5%, and the mass percentage of the binder is 1%-5%; the third active layer also includes a conductive agent and a binder. The mass percentage of the carbon material in the third active layer is 90%-98%, the mass percentage of the conductive agent is 1%-5%, and the mass percentage of the binder is 1%-5%.

18. A method for preparing a negative electrode sheet, characterized in that: The preparation method is used to manufacture the negative electrode sheet according to any one of claims 1 to 17, and the preparation method comprises: Providing a current collector, a first slurry, a second slurry, and a third slurry, wherein the first slurry and the third slurry both include a carbon material, the second slurry includes a silicon material, the third slurry further includes a first precursor and a first initiator, and the second slurry further includes a second precursor, wherein the structure of the first precursor includes an aromatic ring and a double bond, and the structure of the second precursor includes an ether oxygen bond and a double bond; coating the first slurry on the current collector to form a first active layer; coating the second slurry on a side of the first active layer away from the current collector to form a second active layer, wherein the mass percentage of the silicon material in the second active layer is greater than 10%; coating the third slurry on a side of the second active layer away from the first active layer to form a third active layer; A laser is used to open a groove on a side of the third active layer away from the second active layer, wherein when the laser is used to open the groove, the first initiator triggers the first precursor to undergo an in-situ polymerization reaction in the third active layer under the action of the laser to form a first polymer, and the second precursor is in-situ polymerized in the second active layer to form a second polymer.

19. The method for preparing a negative electrode sheet according to claim 18, wherein: Before coating the third slurry on a side of the second active layer away from the first active layer to form the third active layer, the method further includes: coating a polymer slurry on a side of the second active layer away from the first active layer to form a polymer layer, wherein the polymer slurry includes a third polymer; The step of coating the third slurry on a side of the second active layer away from the first active layer to form a third active layer comprises: The third slurry is coated on a side of the polymer layer away from the second active layer to form the third active layer.

20. A battery, characterized in that: The battery comprises a positive electrode sheet, a separator, and a negative electrode sheet according to any one of claims 1 to 17; wherein the separator is located between the positive electrode sheet and the negative electrode sheet.

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