Negative plate, preparation method thereof and battery

Abstract

The invention relates to the field of batteries, in particular to a negative plate, a preparation method thereof and a battery. The negative plate comprises a negative current collector, a first negative active layer, a second negative active layer and a third negative active layer which are arranged in sequence; the first negative electrode active layer comprises a modified graphite material, and the modified graphite material comprises graphite and a carboxyl-containing or hydroxyl-containing modified conductive material coating the surface of the graphite; the second negative electrode active layer comprises a modified silicon-based material, and the modified silicon-based material comprises a silicon-based material, a carbon material and a cationic polymer, wherein the surface of the silicon-based material is coated with the carbon material and the cationic polymer; and the third negative electrode active layer modified MXene material comprises an MXene material and a carboxyl-containing or hydroxyl-containing modified conductive material coated on the surface of the MXene material. According to the negative plate designed by the invention, the energy density performance, the long cycle life performance and the rapid charging performance of the lithium ion battery can be improved, high gram volume and dynamic performance are taken into account, and the negative plate has relatively good low-temperature charging capability.

Description

Technical Field

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

[0002] In recent years, as lithium-ion batteries have become more mature, their scope of use and demand have gradually increased. Higher requirements are placed on the performance of lithium-ion batteries. Not only must high energy density be guaranteed, but there must also be a certain demand for fast charging capabilities. Generally, the battery energy density is increased by increasing the thickness of the electrode and increasing the proportion of active materials. However, thick electrode sheets also bring a series of problems. The inner and outer sides of the electrode sheet have large differences in ionic and electronic conductivity due to deviation from the current collector, resulting in significant electrochemical polarization. The electrolyte also lacks good wettability on the inner electrode sheet and does not form a good channel, resulting in poor battery capacity, poor rate performance, large battery temperature rise, and easy lithium plating. Therefore, research and exploration of negative electrode materials with high energy density and long cycle life is an urgent problem to be solved for lithium-ion batteries.

[0003] Thick electrodes can be categorized by number of layers: single, double, triple, or multi-layer. Single-layer coatings fail to address energy density and the significant difference between the outside and inside. Double-layer coatings often utilize a mix of artificial and natural graphite particles for thick electrode designs, but their energy density is lower than that of silicon-carbon or silicon-oxygen systems. While adapting to silicon-carbon systems, they fail to address the low electrical conductivity of silicon-carbon and the large volume expansion during charge and discharge.

[0004] Therefore, it is critical to design the electrode structure by utilizing the characteristics of various negative electrode materials to meet battery performance indicators and ensure compatible interfaces between coatings. Summary of the Invention

[0005] In view of this, the present invention is committed to providing a negative electrode sheet, a preparation method thereof, and a battery to solve the problem in the prior art that the negative electrode sheet cannot take into account both fast charging performance and cycle performance.

[0006] In order to solve the above technical problems, this application is implemented as follows:

[0007] The present invention provides a negative electrode sheet, comprising: a negative electrode current collector, a first negative electrode active layer disposed on at least one surface of the negative electrode current collector in a thickness direction, a second negative electrode active layer disposed on a surface of the first negative electrode active layer away from the negative electrode current collector, and a third negative electrode active layer disposed on a surface of the second negative electrode active layer away from the first negative electrode active layer;

[0008] The first negative electrode active layer includes a first negative electrode active material, the first negative electrode active material includes a modified graphite material; the modified graphite material includes graphite and a first coating layer coated on the surface of the graphite, the first coating layer includes a conductive material modified with a carboxyl group or a hydroxyl group;

[0009] The second negative electrode active layer includes a second negative electrode active material, the second negative electrode active material includes a modified silicon-based material; the modified silicon-based material includes a silicon-based material and a second coating layer coated on the surface of the silicon-based material, the second coating layer includes a carbon material and a cationic polymer;

[0010] The third negative electrode active layer includes a third negative electrode active material, the third negative electrode active material includes a modified MXene material, the modified MXene material includes a MXene material and a third coating layer coated on the surface of the MXene material, and the third coating layer includes a conductive material modified with a carboxyl group or a hydroxyl group.

[0011] Optionally, the surface density ratio of the first negative electrode active layer, the second negative electrode active layer and the third negative electrode active layer is (1-3): (1-3): (1-3); Optionally, the surface density of the first negative electrode active layer is 0.01-0.12 g / cm 2 Optionally, the surface density of the second negative electrode active layer is 0.01 to 0.12 g / cm 2 Optionally, the surface density of the third negative electrode active layer is 0.01 to 0.12 g / cm 2 .

[0012] Optionally, the thickness ratio of the first negative electrode active layer, the second negative electrode active layer and the third negative electrode active layer is (1.25~3.35):(1~2):(1~2); optionally, the thickness of the first negative electrode active layer is 0.044~0.067 mm; optionally, the thickness of the second negative electrode active layer is 0.02~0.040 mm; optionally, the thickness of the third negative electrode active layer is 0.02~0.040 mm.

[0013] Optionally, the mass ratio of the graphite and the conductive material modified with carboxyl or hydroxyl groups is (94-99): (1-6); optionally, the thickness of the first coating layer is 20-80 nm; optionally, the conductive material modified with carboxyl or hydroxyl groups in the modified graphite material includes graphene oxide.

[0014] Optionally, the mass ratio of the silicon-based material, the carbon material and the cationic polymer is (84-97): (2-16): (1-10); Optionally, the thickness of the second coating layer is 10-50 nm; Optionally, the silicon-based material includes at least one of silicon-carbon material, silicon-oxygen material and nano-silicon; Optionally, the silicon-oxygen material includes SiO x , wherein 0.5≤x≤1.5 and / or x=2; optionally, the carbon material includes a one-dimensional carbon material or a two-dimensional carbon material; or, the carbon material includes a zero-dimensional carbon material, and at least one of a one-dimensional carbon material and a two-dimensional carbon material; optionally, the zero-dimensional carbon material includes graphite particles and / or conductive carbon black; optionally, the one-dimensional carbon material includes carbon nanotubes and / or carbon fibers; optionally, the two-dimensional carbon material includes graphene and / or graphene oxide; optionally, the cationic polymer includes polydiallyldimethylammonium chloride.

[0015] Optionally, the mass ratio of the MXene material to the carboxyl- or hydroxyl-modified conductive material is (90-99): (1-10); Optionally, the thickness of the third coating layer is 20 nm to 200 nm; Optionally, the MXene material includes Ti3C2T x ; Optionally, the carboxyl- or hydroxyl-modified conductive material in the modified MXene material includes graphene oxide.

[0016] Optionally, the first negative electrode active layer also includes a first binder, a first dispersant and a first conductive agent; optionally, the mass ratio of the first negative electrode active material, the first binder, the first dispersant and the first conductive agent is (95-99): (0.2-2): (0.7-2): (0.1-1); optionally, the second negative electrode active layer also includes a second binder, a second dispersant and a second conductive agent; optionally, the mass ratio of the second negative electrode active material, the second binder, the second dispersant and the second conductive agent is (95-99): (0.2-2): (0.7-2): (0.1-1); optionally, the third negative electrode active layer also includes a third binder, a third dispersant and a third conductive agent; optionally, the mass ratio of the third negative electrode active material, the third binder, the third dispersant and the third conductive agent is (95-99): (0.2-2): (0.7-2): (0.1-1).

[0017] Optionally, the first binder, the second binder and the third binder each independently include at least one of styrene-butadiene rubber, polyvinylidene fluoride, polyacrylic acid, polyacrylate, polyimide, polyamide, polyvinyl alcohol and polytetrafluoroethylene; optionally, the first dispersant, the second dispersant and the third dispersant each independently include at least one of carboxymethyl cellulose, sodium dodecylbenzene sulfonate and polyvinyl pyrrolidone; optionally, the first conductive agent, the second conductive agent and the third conductive agent each independently include at least one of conductive carbon black, conductive graphite, carbon nanotubes, carbon fiber and graphene.

[0018] A second aspect of the present invention provides a method for preparing a negative electrode sheet, the method comprising the following steps:

[0019] S1, applying a first negative electrode active slurry on at least one side surface of a current collector along a thickness direction to form a first negative electrode active layer on the current collector;

[0020] S2, coating a second negative electrode active slurry on a surface of the first negative electrode active layer away from the current collector to form a second negative electrode active layer on the first negative electrode active layer;

[0021] S3, coating the third negative electrode active slurry on the surface of the second negative electrode active layer away from the first negative electrode active layer to form a third negative electrode active layer on the second negative electrode active layer;

[0022] Wherein, the first negative electrode active slurry includes modified graphite material;

[0023] The second negative electrode active slurry includes a modified silicon-based material;

[0024] The third negative electrode active slurry includes modified MXene material.

[0025] A third aspect of the present invention provides a battery, comprising a negative electrode sheet, wherein the negative electrode sheet comprises the negative electrode sheet described above or a negative electrode sheet prepared according to the above preparation method.

[0026] Through the above technical solution, the beneficial technical effects of the present invention are:

[0027] The negative electrode material of the present invention improves the battery's energy density and fast charging capability through a structured layered design, utilizing the synergistic effects of different materials, and further improving high- and low-temperature performance and interfacial bonding between coatings through surface modification and other methods. The first layer includes a graphite negative electrode, which has the characteristics of good cycle stability and high initial efficiency; the second layer includes a silicon-based negative electrode material, which has a high capacity and can increase the battery's energy density, and the high lithium insertion potential can reduce lithium precipitation; the third layer includes a MXene lithium-ion battery negative electrode material with thermal and electrical conductivity, as well as certain bending strength and tensile strength, which can alleviate the volume expansion of silicon. Silicon can also make up for the relatively low gram capacity of MXene. In addition, MXene itself has excellent electrical conductivity, resulting in good ionic and electronic conductivity on the side away from the current collector.

[0028] The present invention performs surface modification on the surface of each layer of material to improve interface problems and overall kinetic problems. The ion diffusion capacity of each level of material is maximized; by designing a stacked structure of negative electrode materials with different physical and electrochemical properties, the overall performance of the negative electrode material in terms of composite negative electrode adhesion, internal structure, diffusion channel, and safety can be improved. The three-layer coating structure of the negative electrode of the lithium-ion battery material of the present invention improves the energy density performance, long cycle life performance and fast charging performance of the lithium-ion battery through the synergistic effect of different negative electrode active materials, achieving a balance between high gram capacity and kinetic performance, and having better low-temperature charging capability, which is beneficial to increasing the capacity of the lithium-ion battery and achieving fast charging of the lithium-ion battery.

[0029] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention, but do not constitute a limitation of the present invention.

[0031] Figure 1 Shown is a schematic structural diagram of the negative electrode sheet of the present invention;

[0032] Figure 2 Shown is a schematic diagram of the interface between the first negative electrode active layer and the second negative electrode active layer in the negative electrode sheet of the present invention.

[0033] Description of reference numerals:

[0034] 10- negative electrode current collector;

[0035] 20-first negative electrode active layer;

[0036] 30- second negative electrode active layer;

[0037] 40-third negative electrode active layer;

[0038] 50-conductive material modified with carboxyl or hydroxyl groups;

[0039] 60-cationic polymer;

[0040] 70-silicon-based materials;

[0041] 80-Carbon material. DETAILED DESCRIPTION

[0042] The present invention discloses a negative electrode sheet, a method for preparing the same, and a battery. Those skilled in the art may refer to the contents herein and appropriately modify the process parameters to achieve the desired results. It is particularly important to note that all similar substitutions and modifications apparent to those skilled in the art are considered encompassed by the present invention. The methods and applications of the present invention have been described through preferred embodiments. It is apparent that those skilled in the art can modify or appropriately alter and combine the methods and applications described herein to implement and apply the technology of the present invention without departing from the content, spirit, and scope of the present invention.

[0043] In the description of the present invention, a list of items connected by the term "at least one of" or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A can include a single element or multiple elements. Item B can include a single element or multiple elements. Item C can include a single element or multiple elements.

[0044] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range or the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0045] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0046] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0047] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0048] In order to solve the problem that the negative electrode sheet in the prior art cannot take into account both fast charging performance and cycle performance, the present invention adopts the following technical solutions:

[0049] refer to Figure 1 As shown, the present invention provides a negative electrode sheet, which includes: a negative electrode current collector 10, a first negative electrode active layer 20 provided on at least one side surface of the negative electrode current collector along the thickness direction, a second negative electrode active layer 30 provided on a side surface of the first negative electrode active layer away from the negative electrode current collector, and a third negative electrode active layer 40 provided on a side surface of the second negative electrode active layer away from the first negative electrode active layer;

[0050] The first negative electrode active layer 20 includes a first negative electrode active material, which includes a modified graphite material; the modified graphite material includes graphite and a first coating layer coated on the surface of the graphite, and the first coating layer includes a conductive material modified with a carboxyl group or a hydroxyl group;

[0051] The second negative electrode active layer 30 includes a second negative electrode active material, which includes a modified silicon-based material; the modified silicon-based material includes a silicon-based material and a second coating layer coated on the surface of the silicon-based material, and the second coating layer includes a carbon material and a cationic polymer;

[0052] The third negative electrode active layer 40 includes a third negative electrode active material, which includes a modified MXene material. The modified MXene material includes a MXene material and a third coating layer coated on the surface of the MXene material. The third coating layer includes a conductive material modified with a carboxyl group or a hydroxyl group.

[0053] In the present application, the negative electrode sheet provided includes a negative electrode current collector 10 designed to be stacked in sequence, a first negative electrode active layer 20 with a modified graphite material coated with a carbon material as an active material, a second negative electrode active layer 30 with a modified silicon-based material as an active material, and a third negative electrode active layer 40 with a modified MXene material as an active material, that is, by combining negative electrode materials with different characteristics, utilizing the synergistic effect of different materials, and further surface modification of graphite, silicon-based materials and MXene materials to improve the energy density and fast charging capability of the negative electrode sheet, improve high and low temperature performance and interface bonding between coatings, and other issues.

[0054] In the present invention, the first layer includes a graphite material with a small volume change and a long cycle life, which meets the requirements of the good use of the battery under large current charge and discharge, and the graphite material is coated with a conductive material modified with carboxyl or hydroxyl groups. The conductive material modified with carboxyl or hydroxyl groups has excellent conductivity and can improve the kinetic performance of the first layer material; the second layer includes a silicon-based material coated with a carbon material and a cationic polymer. The silicon-based material is in the middle layer, which can improve the lithium insertion potential of the overall negative electrode material on the one hand, and can ensure that the lithium precipitation phenomenon is reduced compared to a single graphite layer, and has high safety performance; and the silicon-based material has a high capacity, so that lithium insertion is sufficient, which helps to exert the specific capacity; The silicon-based material expands greatly during charge and discharge, and is placed in the middle layer. Due to the restrictions of the upper and lower layers, the expansion is suppressed; the high elastic strength of the carbon material can effectively connect the material particles when the silicon-based material expands, reduce the shedding of active substances, improve the structural stability of the negative electrode material, and make up for the poor conductivity of the silicon-carbon material; at the same time, the cationic polymer will cause the negatively charged surface materials of the first and third layers to combine with the positively charged surface materials of the second layer due to electrostatic attraction, thereby improving the compatibility and tightness of the interface. Among them, the interface diagram between the first negative electrode active layer and the second negative electrode active layer is shown as follows Figure 2 As shown, the third layer comprises MXene. While MXene has a lower capacity, the silicon-based material in the middle layer compensates for this disadvantage. MXene has high tensile and flexural strength, absorbing the expansion of the silicon in the middle layer. The introduction of a conductive material modified with carboxyl or hydroxyl groups also addresses the inherent self-stacking problem of MXene, increasing the interlayer spacing. Its excellent lithium-ion diffusion pathways enhance the battery's high-current charge-discharge and low-temperature performance, meeting power performance requirements. Furthermore, the high stability of hard carbon in the electrolyte effectively reduces electrolyte side reactions. MXene's excellent conductivity also improves the kinetics of the outer layer. Overall, the structured and layered design of the anode materials improves the compaction density of the hierarchical composite anode, avoids structural damage to the anode materials, and maximizes the ion diffusion capacity of each layer. By stacking anode materials with different physical and electrochemical properties, the composite anode can achieve effective improvements in adhesion, internal structure, and diffusion pathways, enhancing the overall performance of the anode materials and promoting the balanced energy density and power characteristics of lithium-ion batteries.

[0055] The negative electrode sheet of the present invention has a three-layer coating structure. Through the synergistic effect of different negative electrode active materials, the energy density performance, long cycle life performance and fast charging performance of the lithium-ion battery are improved, achieving a balance between high gram capacity and kinetic performance, and has better low-temperature charging capability. It is a three-layer coating structure of lithium-ion batteries with potential to achieve high capacity and fast charging; through reasonable layer matching and regulation, the problem of poor interface compatibility between layers is improved while ensuring high energy density and fast charging capability.

[0056] According to the present invention, the surface density ratio of the first negative electrode active layer, the second negative electrode active layer and the third negative electrode active layer can be (1 to 3): (1 to 3): (1 to 3). In the present invention, a suitable surface density ratio of the first negative electrode active layer, the second negative electrode active layer and the third negative electrode active layer helps to balance performance such as capacity, interface and kinetics. As an example, the surface density ratio of the first negative electrode active layer, the second negative electrode active layer and the third negative electrode active layer can be any value among 1:1:1, 1:1:2, 1:1:3, 1:2:1, 1:2:2, 1:2:3, 2:1:3, 2:2:3, 3:1:1 and 3:2:1, or any value within the range of any two of the above values. In the present invention, if the surface density ratio of the first negative electrode active layer, the second negative electrode active layer and the third negative electrode active layer is too large, it will lead to insufficient power performance and poor interface stability, thereby affecting the fast charging capability; if the surface density ratio of the first negative electrode active layer, the second negative electrode active layer and the third negative electrode active layer is too small, it will lead to lower gram capacity.

[0057] According to the present invention, the surface density of the first negative electrode active layer can be 0.01 to 0.12 g / cm 2 In the present invention, the appropriate surface density of the first negative electrode active layer helps to ensure a certain fast charging capability. As an example, the surface density of the first negative electrode active layer can be 0.01 g / cm 2 , 0.02g / cm 2 , 0.04g / cm 2 , 0.05g / cm 2 , 0.06g / cm 2 , 0.08g / cm 2 , 0.1g / cm 2 and 0.12g / cm 2 In the present invention, if the surface density of the first negative electrode active layer is too large, the capacity of the composite electrode will be insufficient; if the surface density of the first negative electrode active layer is too small, the kinetic performance will be poor.

[0058] According to the present invention, the surface density of the second negative electrode active layer can be 0.01 to 0.12 g / cm2 In the present invention, a suitable surface density of the second negative electrode active layer helps to improve the overall capacity. As an example, the surface density of the second negative electrode active layer can be 0.01 g / cm 2 , 0.02g / cm 2 , 0.04g / cm 2 , 0.05g / cm 2 , 0.06g / cm 2 , 0.08g / cm 2 , 0.1g / cm 2 and 0.12g / cm 2 In the present invention, if the surface density of the second negative electrode active layer is too large, the expansion coefficient will be large and the interface stability will be poor; if the surface density of the second negative electrode active layer is too small, the capacity will be insufficient.

[0059] According to the present invention, the surface density of the third negative electrode active layer can be 0.01 to 0.12 g / cm 2 In the present invention, a suitable surface density of the third negative electrode active layer helps to form a good conductive network, thereby improving the overall dynamics. As an example, the surface density of the third negative electrode active layer can be 0.01g / cm 2 , 0.02g / cm 2 , 0.04g / cm 2 , 0.05g / cm 2 , 0.06g / cm 2 , 0.08g / cm 2 , 0.1g / cm 2 and 0.12g / cm 2 Any value in or any value within the range formed by any two of the above values. In the present invention, if the surface density of the third negative electrode active layer is too large, the structure of the conductive network formed will be uneven, affecting the fast charging capability; if the surface density of the third negative electrode active layer is too small, it will affect the capacity and kinetics.

[0060] According to the present invention, the compaction density of the first negative electrode active layer can be 1.2 to 1.8 g / cc. In the present invention, the appropriate compaction density of the first negative electrode active layer helps to balance the overall capacity and ensure a certain void structure. As an example, the compaction density of the first negative electrode active layer can be any value among 1.2 g / cc, 1.3 g / cc, 1.4 g / cc, 1.5 g / cc, 1.6 g / cc, 1.7 g / cc and 1.8 g / cc or any value within the range of values ​​consisting of any two of the above values. In the present invention, if the compaction density of the first negative electrode active layer is too large, the ion transmission distance will be hindered; if the compaction density of the first negative electrode active layer is too small, the overall capacity will be low.

[0061] According to the present invention, the compaction density of the second negative electrode active layer can be 1.2 to 1.8 g / cc. In the present invention, the appropriate compaction density of the second negative electrode active layer helps to improve the overall energy density and ensure a certain crystal structure. As an example, the compaction density of the second negative electrode active layer can be any value among 1.2 g / cc, 1.3 g / cc, 1.4 g / cc, 1.5 g / cc, 1.6 g / cc, 1.7 g / cc and 1.8 g / cc or any value within the range of values ​​consisting of any two of the above values. In the present invention, if the compaction density of the second negative electrode active layer is too large, it may cause particle breakage and crystal structure failure; if the compaction density of the second negative electrode active layer is too small, it will lead to a large expansion coefficient, thereby affecting the cycle performance.

[0062] According to the present invention, the compaction density of the third negative electrode active layer may be 1.2 to 1.8 g / cc. In the present invention, a suitable compaction density of the third negative electrode active layer helps to improve the conductive network structure. As an example, the compaction density of the third negative electrode active layer may be any one of 1.2 g / cc, 1.3 g / cc, 1.4 g / cc, 1.5 g / cc, 1.6 g / cc, 1.7 g / cc and 1.8 g / cc or any value within the range of any two of the above values. In the present invention, if the compaction density of the third negative electrode active layer is too large, it will affect the fast charging capability; if the compaction density of the third negative electrode active layer is too small, it will lead to an increase in the rebound rate after the cycle and lead to insufficient capacity.

[0063] According to the present invention, the thickness ratio of the first negative electrode active layer, the second negative electrode active layer and the third negative electrode active layer can be (1.25-3.35): (1-2): (1-2). In the present invention, the appropriate thickness ratio of the first negative electrode active layer, the second negative electrode active layer and the third negative electrode active layer helps to ensure fast charging capability, capacity utilization and the construction of a conductive network. As an example, the thickness ratio of the first negative electrode active layer, the second negative electrode active layer and the third negative electrode active layer can be any value among 1.25:1:1, 1.25:1:2, 1.5:2:2, 2:1:1, 2:2:1, 2.5:1:1, 2.5:2:1, 3:1:1, 3:2:1, 3.35:1:2 and 3.35:2:1 or any value within the range of any two of the above values. In the present invention, if the thickness ratio of the first negative electrode active layer, the second negative electrode active layer and the third negative electrode active layer is too large, the fast charging capability will be insufficient; if the thickness ratio of the first negative electrode active layer, the second negative electrode active layer and the third negative electrode active layer is too small, the capacity will be insufficient.

[0064] According to the present invention, the thickness of the first negative electrode active layer may be 0.044 to 0.067 mm. In the present invention, a suitable thickness of the first negative electrode active layer helps to balance the fast charging capability and capacity. As an example, the thickness of the first negative electrode active layer may be any value among 0.044 mm, 0.045 mm, 0.05 mm, 0.055 mm, 0.06 mm, 0.065 mm and 0.067 mm or any value within the range of values ​​consisting of any two of the above values. In the present invention, if the thickness of the first negative electrode active layer is too thick, it will lead to an increase in the ion transport path and affect the kinetic performance; if the thickness of the first negative electrode active layer is too thin, it will lead to the inability to suppress the changes in the silicon-based rebound, thereby causing interface failure.

[0065] According to the present invention, the thickness of the second negative electrode active layer can be 0.02 to 0.040 mm. In the present invention, an appropriate thickness of the second negative electrode active layer helps to improve capacity. As an example, the thickness of the second negative electrode active layer can be any value among 0.02 mm, 0.025 mm, 0.03 mm, 0.035 mm and 0.04 mm, or any value within the range of any two of the above values. In the present invention, if the thickness of the second negative electrode active layer is too thick, it will lead to a large cycle rebound rate of the electrode sheet and capacity demolding; if the thickness of the second negative electrode active layer is too thin, it will lead to an insignificant capacity improvement.

[0066] According to the present invention, the thickness of the third negative electrode active layer may be 0.02 to 0.040 mm. In the present invention, a suitable thickness of the third negative electrode active layer helps to suppress the expansion change of the second layer and construct a suitable conductive network. As an example, the thickness of the third negative electrode active layer may be any value among 0.02 mm, 0.025 mm, 0.03 mm, 0.035 mm and 0.04 mm or any value within the range of values ​​consisting of any two of the above values. In the present invention, if the thickness of the third negative electrode active layer is too thick, it will affect the effect of electrolyte infiltration and affect the fast charging capability; if the thickness of the third negative electrode active layer is too thin, it will cause the interface between the second layer and the third layer to be unstable and make the kinetic network formation uneven.

[0067] According to the present invention, the mass ratio of the graphite and the conductive material modified with carboxyl or hydroxyl groups can be (94-99): (1-6). In the present invention, a suitable mass ratio of graphite and the conductive material modified with carboxyl or hydroxyl groups helps to form a uniform coating layer. As an example, the mass ratio of graphite and the conductive material modified with carboxyl or hydroxyl groups can be any of 94:6, 95:5, 96:4, 97:3, 98:2, 99:1, 99:2, 99:3 and 99:6 or any value within the range of any two of the above values. In the present invention, if the mass ratio of graphite and the conductive material modified with carboxyl or hydroxyl groups is too large, it will lead to insufficient dynamic performance or uneven coating; if the mass ratio of graphite and the conductive material modified with carboxyl or hydroxyl groups is too small, it will lead to reduced capacity and first effect.

[0068] According to the present invention, the thickness of the first coating layer can be 20 to 80 nm. In the present invention, the appropriate thickness of the first coating layer helps to not only improve the fast charging performance of the first layer itself, but also compound other interfaces and form a good conductive network for the new car. As an example, the thickness of the first coating layer can be any value among 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm and 80 nm or any value within the range of values ​​composed of any two of the above values. In the present invention, if the thickness of the first coating layer is too thick, it will result in a large capacity loss; if the thickness of the first coating layer is too thin, it will cause breakage after a short cycle, and a complete and uniform coating layer cannot be formed.

[0069] Optionally, the conductive material modified with carboxyl or hydroxyl groups in the modified graphite material includes graphene oxide. The graphite material coated with graphene oxide is flaky and has excellent conductivity, which can improve the dynamic performance of the first layer material.

[0070] According to the present invention, the mass ratio of the silicon-based material, the carbon material and the cationic polymer can be (84-97): (2-16): (1-10). In the present invention, a suitable mass ratio of the silicon-based material, the carbon material and the cationic polymer helps to suppress volume expansion. As an example, the mass ratio of the silicon-based material, the carbon material and the cationic polymer can be any of 84:2:1, 85:3:3, 86:5:5, 88:6:8, 90:8:9, 95:10:10 and 97:15:10 or any value within the range of any two of the above values. In the present invention, if the mass ratio of the silicon-based material, the carbon material and the cationic polymer is too large, it will affect the silicon-based capacity; if the mass ratio of the silicon-based material, the carbon material and the cationic polymer is too small, it will lead to loose interface bonding and demolding of the electrode after cycling.

[0071] According to the present invention, the thickness of the second coating layer is 10 to 50 nm. In the present invention, the appropriate thickness of the second coating layer helps to improve the interface stability. As an example, the thickness of the second coating layer can be any value among 10 nm, 20 nm, 30 nm, 40 nm and 50 nm, or any value within the range of any two of the above values. In the present invention, if the thickness of the second coating layer is too thick, it will affect the capacity; if the thickness of the second coating layer is too thin, it will lead to a loose composite effect with other interfaces.

[0072] Optionally, the silicon-based material includes at least one of silicon-carbon material, silicon-oxygen material and nano-silicon.

[0073] Optionally, the silicon-oxygen material includes SiO x , where 0.5≤x≤1.5 and / or x=2.

[0074] Optionally, the carbon material includes a one-dimensional carbon material or a two-dimensional carbon material; or, the carbon material includes a zero-dimensional carbon material, and at least one of a one-dimensional carbon material and a two-dimensional carbon material.

[0075] Optionally, the zero-dimensional carbon material includes graphite particles and / or conductive carbon black.

[0076] Optionally, the one-dimensional carbon material includes carbon nanotubes and / or carbon fibers.

[0077] Optionally, the two-dimensional carbon material includes graphene and / or graphene oxide.

[0078] Optionally, the cationic polymer comprises polydiallyldimethylammonium chloride.

[0079] According to the present invention, the mass ratio of the MXene material and the conductive material modified with a carboxyl group or a hydroxyl group can be (90-99): (1-10). In the present invention, a suitable mass ratio of the MXene material and the conductive material modified with a carboxyl group or a hydroxyl group contributes to a uniform conductive network and the effect of suppressing cyclic volume expansion. As an example, the mass ratio of the MXene material and the conductive material modified with a carboxyl group or a hydroxyl group can be any of 90:10, 91:9, 92:8, 93:7, 94:6, 95:5, 96:4, 97:3, 98:2 and 99:1 or any value within the range of any two of the above values. In the present invention, if the mass ratio of the MXene material and the conductive material modified with a carboxyl group or a hydroxyl group is too large, it will result in; if the mass ratio of the MXene material and the conductive material modified with a carboxyl group or a hydroxyl group is too small, it will result in an uneven coating layer and insufficient conductive performance. Secondly, it will not be able to suppress volume expansion and stabilize the interface.

[0080] According to the present invention, the thickness of the third coating layer is 20nm to 200nm. In the present invention, the appropriate thickness of the third coating layer helps to balance the conductive network structure and the interface structure. As an example, the thickness of the third coating layer can be any value among 20nm, 30nm, 40nm, 50nm, 80nm, 100nm, 120nm, 150nm, 180nm and 200nm or any value within the range of values ​​composed of any two of the above values. In the present invention, if the thickness of the third coating layer is too thick, it will lead to poor interface effect and affect the performance of gram capacity; if the thickness of the third coating layer is too thin, it will lead to insufficient conductive performance.

[0081] Optionally, M n+1 X n T x In the material, M is a transition metal element, X is carbon and / or nitrogen, and T x is a surface group, wherein the surface group includes at least one of -O, -OH and -F, and n is an integer of 1 to 3.

[0082] Optionally, the MXene material comprises Ti3C2T x .

[0083] Optionally, the carboxyl- or hydroxyl-modified conductive material in the modified MXene material includes graphene oxide.

[0084] According to the present invention, the first negative electrode active layer may further include a first binder, a first dispersant, and a first conductive agent.

[0085] According to the present invention, the mass ratio of the first negative electrode active material, the first binder, the first dispersant, and the first conductive agent may be (95-99): (0.2-2): (0.7-2): (0.1-1). As an example, the mass ratio of the first negative electrode active material, the first binder, the first dispersant, and the first conductive agent may be any of 95:2:2:1, 96:1:2:1, 97:1:1:1, 98:0.5:1:0.5, and 99:0.2:0.7:0.3, or any value within a range consisting of any two of the above values.

[0086] According to the present invention, the second negative electrode active layer may further include a second binder, a second dispersant, and a second conductive agent.

[0087] According to the present invention, the mass ratio of the second negative electrode active material, the second binder, the second dispersant, and the second conductive agent may be (95-99): (0.2-2): (0.7-2): (0.1-1). As an example, the mass ratio of the second negative electrode active material, the second binder, the second dispersant, and the second conductive agent may be any value among 95:2:2:1, 96:1:2:1, 97:1:1:1, 98:0.5:1:0.5, and 99:0.2:0.7:0.3, or any value within a range consisting of any two of the above values.

[0088] According to the present invention, the third negative electrode active layer may further include a third binder, a third dispersant and a third conductive agent.

[0089] According to the present invention, the mass ratio of the third negative electrode active material, the third binder, the third dispersant, and the third conductive agent may be (95-99):(0.2-2):(0.7-2):(0.1-1). As an example, the mass ratio of the third negative electrode active material, the third binder, the third dispersant, and the third conductive agent may be any of 95:2:2:1, 96:1:2:1, 97:1:1:1, 98:0.5:1:0.5, and 99:0.2:0.7:0.3, or any value within a range consisting of any two of the above values.

[0090] Optionally, the first binder, the second binder and the third binder each independently include at least one of styrene-butadiene rubber, polyvinylidene fluoride, polyacrylic acid, polyacrylate, polyimide, polyamide, polyvinyl alcohol and polytetrafluoroethylene.

[0091] Optionally, the first dispersant, the second dispersant and the third dispersant each independently include at least one of carboxymethyl cellulose, sodium dodecylbenzene sulfonate and polyvinyl pyrrolidone.

[0092] Optionally, the first conductive agent, the second conductive agent and the third conductive agent each independently include at least one of conductive carbon black, conductive graphite, carbon nanotubes, carbon fibers and graphene.

[0093] A second aspect of the present invention provides a method for preparing a negative electrode sheet, the method comprising the following steps:

[0094] S1, applying a first negative electrode active slurry on at least one side surface of a current collector along a thickness direction to form a first negative electrode active layer on the current collector;

[0095] S2, coating a second negative electrode active slurry on a surface of the first negative electrode active layer away from the current collector to form a second negative electrode active layer on the first negative electrode active layer;

[0096] S3, coating the third negative electrode active slurry on the surface of the second negative electrode active layer away from the first negative electrode active layer to form a third negative electrode active layer on the second negative electrode active layer;

[0097] Wherein, the first negative electrode active slurry includes modified graphite material;

[0098] The second negative electrode active slurry includes a modified silicon-based material;

[0099] The third negative electrode active slurry includes modified MXene material.

[0100] According to the present invention, in step S1, after coating, a first drying and a first rolling may be further included; in step S2, after coating, a second drying and a second rolling may be further included; in step S3, after coating, a third drying and a third rolling may be further included; or, after coating is completed in steps S1, S2, and S3, drying and rolling may be performed.

[0101] According to the present invention, the preparation step of the modified graphite material includes: mixing a graphite solution and a conductive material solution modified with a carboxyl group or a hydroxyl group, and then performing a fourth drying process and a first ball milling process.

[0102] According to the present invention, the mass ratio of graphite in the graphite solution to the carboxyl- or hydroxyl-modified conductive material in the carboxyl- or hydroxyl-modified conductive material solution can be (500-1000):(5-30). As an example, the mass ratio of graphite in the graphite solution to the carboxyl- or hydroxyl-modified conductive material in the carboxyl- or hydroxyl-modified conductive material solution can be any of 500:5, 600:10, 700:15, 800:20, 900:25, 1000:30, 1000:20, 1000:10, and 1000:5, or any value within a range consisting of any two of the above values.

[0103] According to the present invention, the solution of the conductive material modified with a carboxyl group or a hydroxyl group may further include a dispersant.

[0104] According to the present invention, the mass ratio of the dispersant to the carboxyl- or hydroxyl-modified conductive material in the carboxyl- or hydroxyl-modified conductive material solution can be 25:(5-30). As an example, the mass ratio of the dispersant to the carboxyl- or hydroxyl-modified conductive material in the carboxyl- or hydroxyl-modified conductive material solution can be any of 25:5, 25:10, 25:15, 25:20, 25:25, and 25:30, or any value within a range consisting of any two of the above values.

[0105] Optionally, the dispersant includes at least one of polyvinyl alcohol, sodium lauryl sulfate and sodium dodecylbenzene sulfonate.

[0106] In the present invention, the dispersant forms entanglement and coverage of molecular chains in water through steric hindrance, thereby forming a steric hindrance effect to prevent the reaggregation of the conductive material modified with carboxyl or hydroxyl groups, among which polyvinyl alcohol has a better dispersing effect.

[0107] In the present invention, the first ball milling process may be dry ball milling; the dry ball milling is performed under an inert atmosphere, which may include argon; and the dry ball milling conditions include: a rotation speed of 300 to 500 rpm and a time of 6 to 12 hours. As an example, the rotation speed of the dry ball milling may be any one of 300 rpm, 350 rpm, 400 rpm, 450 rpm, and 500 rpm, or any value within a range consisting of any two of the above values, and the dry ball milling time may be any one of 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, and 12 hours, or any value within a range consisting of any two of the above values.

[0108] In the present invention, the uniformity of the coating layer in the modified graphite material and the bonding strength of the matrix are ensured through the fourth drying process and the first ball milling process.

[0109] According to the present invention, the solvent in the graphite solution may include an alcohol; optionally, the alcohol includes n-hexanol; optionally, the amount ratio of graphite to solvent in the graphite solution is (500-100) g:102 mL.

[0110] According to the present invention, the solvent of the solution of the conductive material modified with a carboxyl group or a hydroxyl group may include water.

[0111] According to the present invention, the preparation step of the modified silicon-based material may include:

[0112] S21, mixing, dispersing, and performing a first separation on a silicon-based material and a carbon material solution to obtain a first precipitate; and carbonizing the first precipitate to obtain an intermediate;

[0113] S22, mixing and dispersing the solution containing the intermediate and the cationic polymer suspension and performing a second separation to obtain a second precipitate;

[0114] S23, performing a fifth drying process and an annealing process on the second precipitate in sequence.

[0115] According to the present invention, in step S21, the mass ratio of the silicon-based material to the carbon material in the carbon material solution may be 50:(1-8). As an example, the mass ratio of the silicon-based material to the carbon material in the carbon material solution is any one of 50:1, 50:2, 50:3, 50:4, 50:5, 50:6, 50:7, and 50:8, or any value within a range consisting of any two of the above values.

[0116] According to the present invention, in step S21, the solvent in the carbon material solution may include an alcohol solvent. Optionally, the alcohol solvent includes ethanol.

[0117] According to the present invention, in step S22, the volume ratio of the solution containing the intermediate to the cationic polymer suspension can be 2:1 to 10:1. As an example, the volume ratio of the solution containing the intermediate to the cationic polymer suspension can be any value among 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 and 10:1, or any value within a range consisting of any two of the above values.

[0118] According to the present invention, in step S22, the concentration of the intermediate in the solution containing the intermediate may be 1 to 10 mg / mL. As an example, the concentration of the intermediate may be any value among 1 mg / mL, 2 mg / mL, 3 mg / mL, 4 mg / mL, 5 mg / mL, 6 mg / mL, 7 mg / mL, 8 mg / mL, 9 mg / mL, and 10 mg / mL, or any value within a range consisting of any two of the above values.

[0119] According to the present invention, in step S22, the solvent in the solution containing the intermediate may include water.

[0120] According to the present invention, in step S22, the concentration of the cationic polymer in the cationic polymer suspension may be 0.1 to 1 mg / mL. As an example, the concentration of the cationic polymer may be any value selected from 0.1 mg / mL, 0.2 mg / mL, 0.3 mg / mL, 0.4 mg / mL, 0.5 mg / mL, 0.6 mg / mL, 0.7 mg / mL, 0.8 mg / mL, 0.9 mg / mL, and 1 mg / mL, or any value within a range consisting of any two of the above values.

[0121] According to the present invention, in step S22, the solvent in the cationic polymer suspension may include water.

[0122] According to the present invention, in step S21, the first separation can be vacuum filtration; optionally, the carbonization treatment is carried out under an inert atmosphere, and the inert atmosphere includes nitrogen; the conditions of the carbonization treatment include: a temperature of 300 to 500°C and a time of 1 to 4 hours. As an example, the temperature of the carbonization treatment can be any value among 300°C, 350°C, 400°C, 450°C and 500°C, or any value within the range of any two of the above values, and the time of the carbonization treatment can be any value among 1 hour, 2 hours, 3 hours and 4 hours, or any value within the range of any two of the above values.

[0123] According to the present invention, in step S23, the fifth drying process may be a first freeze-drying process, and the conditions for the first freeze-drying process may include: a temperature of -40 to -80°C and a time of 12 to 36 hours. As an example, the temperature for the first freeze-drying process may be any one of -40°C, -50°C, -60°C, -70°C, and -80°C, or any value within a range consisting of any two of the above values, and the time for the first freeze-drying process may be any one of 12 hours, 15 hours, 20 hours, 24 hours, 25 hours, 30 hours, 35 hours, and 36 hours, or any value within a range consisting of any two of the above values.

[0124] According to the present invention, in step S23, the annealing conditions may include: a temperature of 400° C. and a time of 5 to 12 hours. As an example, the annealing time may be any value among 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, and 12 hours, or any value within a range consisting of any two of the above values.

[0125] According to the present invention, the preparation step of the modified MXene material may include: mixing a carboxyl- or hydroxyl-modified conductive material dispersion and a MXene dispersion, and then sequentially performing a second ball milling treatment, a standing treatment, and a sixth drying treatment.

[0126] According to the present invention, the volume ratio of the carboxyl- or hydroxyl-modified conductive material dispersion to the MXene dispersion can be 1:2 to 1:10. As an example, the volume ratio of the carboxyl- or hydroxyl-modified conductive material dispersion to the MXene dispersion can be any value among 1:2, 5, 1:6, 1:7, 1:8, 1:9, and 1:10, or any value within a range consisting of any two of the above values.

[0127] According to the present invention, the concentration of the carboxyl- or hydroxyl-modified conductive material in the carboxyl- or hydroxyl-modified conductive material dispersion may be 0.1 to 0.4 mg / mL. For example, the concentration of the carboxyl- or hydroxyl-modified conductive material may be any value among 0.1 mg / mL, 0.2 mg / mL, 0.3 mg / mL, and 0.4 mg / mL, or any value within a range consisting of any two of these values.

[0128] According to the present invention, the solvent in the dispersion of the conductive material modified with a carboxyl group or a hydroxyl group may include water.

[0129] According to the present invention, the concentration of MXene in the MXene dispersion may be 1 to 4 mg / mL. As an example, the concentration of MXene may be any value among 1 mg / mL, 2 mg / mL, 3 mg / mL, and 4 mg / mL, or any value within a range consisting of any two of the above values.

[0130] According to the present invention, the solvent in the MXene dispersion may include water.

[0131] According to the present invention, the second ball milling process may be wet ball milling, and the conditions of the wet ball milling may include: a rotation speed of 400 to 600 rpm and a time of 20 to 60 minutes. As an example, the rotation speed of the wet ball milling process may be any value among 400 rpm, 450 rpm, 500 rpm, 550 rpm, and 600 rpm, or any value within a range consisting of any two of the above values, and the time of the wet ball milling process may be any value among 20 minutes, 30 minutes, 40 minutes, 50 minutes, and 60 minutes, or any value within a range consisting of any two of the above values.

[0132] According to the present invention, the conditions for the static treatment may include: a temperature of 15 to 35°C and a time of 1.5 to 2.5 hours. As an example, the static temperature may be any one of 15°C, 20°C, 25°C, 30°C, and 35°C, or any value within a range consisting of any two of the above values, and the static time may be any one of 1.5 hours, 2 hours, and 2.5 hours, or any value within a range consisting of any two of the above values.

[0133] According to the present invention, the sixth drying process may be a second freeze-drying process, and the conditions for the second freeze-drying process may include: a temperature of -40 to -80°C and a time of 18 to 30 hours. As an example, the temperature of the second freeze-drying process may be any value among -40°C, -50°C, -60°C, -70°C, and -80°C, or any value within a range consisting of any two of the above values, and the time of the second freeze-drying process may be any value among 18 hours, 20 hours, 24 hours, 25 hours, and 30 hours, or any value within a range consisting of any two of the above values.

[0134] A third aspect of the present invention provides a battery, comprising a negative electrode sheet, wherein the negative electrode sheet comprises the negative electrode sheet described above or a negative electrode sheet prepared according to the above preparation method.

[0135] The present invention is further described in detail below by way of examples. The raw materials used in the examples can all be obtained through commercial sources.

[0136] Preparation Example 1

[0137] The preparation of modified graphite material comprises the following steps:

[0138] (1) Add 500 g of artificial graphite powder to 102 mL of n-hexanol and stir at a rate of 300 r / min for 10 h to obtain a graphite solution;

[0139] (2) dissolving 5 g of graphene oxide and 25 g of polyvinyl alcohol in deionized water and stirring to obtain a graphene oxide solution;

[0140] (3) The graphite solution and the graphene oxide solution were mixed and stirred at room temperature for 8 h to obtain a suspension; the suspension was dried in an oven at 85° C., the dried product was sieved, and then dry-milled at a speed of 400 rpm under an Ar protective atmosphere for 8 h to obtain a modified graphite material.

[0141] Preparation Example 2

[0142] The preparation of the modified silicon-based material comprises the following steps:

[0143] (1) Weigh 50 g of carbon nanotubes and place them in a 1000 mL beaker. Add 300 mL of ethanol to the beaker and disperse the carbon nanotubes in the ethanol by magnetic stirring to obtain a carbon nanotube solution. Add 1 g of silicon dioxide to the carbon nanotube solution, dilute with 100 mL of ethanol, perform ultrasonication, stir and mix for 30 minutes, and then perform vacuum filtration step by step. After the filtration, the obtained product is dried at 80°C, and then the dried product is carbonized at 400°C under a nitrogen atmosphere for 2 hours to obtain an intermediate.

[0144] (2) 100 mL of a 0.5 mg / mL polydiallyldimethylammonium chloride (PDDA) suspension and 200 mL of a 1 mg / mL intermediate solution were mixed, stirred, dispersed, and separated to obtain a precipitate;

[0145] (3) The precipitate was freeze-dried at -40°C for 12 h. After freeze-drying, the obtained product was annealed at 400°C for 10 h to obtain a modified silicon-based material.

[0146] Preparation Example 3

[0147] The preparation of modified MXene materials includes the following steps:

[0148] (1) 1 g of lithium fluoride (LiF) was mixed with 9 mol / L hydrochloric acid (HCl) and stirred for 20 min, then placed in a 30 °C water bath, and 1 g of titanium aluminum carbide (Ti3AlC2, MAX phase) was added in batches and magnetic stirring etching was performed for 36 h. After the water bath reaction, the product was centrifuged and washed to pH ≈ 6, then ultrasonicated in an ice bath under argon atmosphere for 1 h, centrifuged for 0.5 h, and freeze-dried for 36 h to obtain Ti3C2T x ;

[0149] (2) 20 mL of 0.2 mg / mL graphene oxide aqueous dispersion and 40 mL of 2 mg / mL Ti3C2T x The aqueous dispersion was ultrasonicated for 40 min and then the two were mixed. The wet ball milling was performed at room temperature and a rotation speed of 400 rpm / min for 3 h. After the wet ball milling, the mixture was allowed to stand for 2 h and finally freeze-dried at -40 °C for 24 h to obtain the modified MXene material.

[0150] Example 1

[0151] The preparation of the negative electrode sheet includes the following steps:

[0152] (1) A modified graphite material, a binder styrene butadiene rubber (SBR), a dispersant sodium carboxymethyl cellulose (CMC), a conductive agent carbon black and water are mixed to obtain a first slurry with a solid content of 50 wt%; wherein the mass ratio of the modified graphite material, the binder styrene butadiene rubber, the dispersant sodium carboxymethyl cellulose and the conductive agent carbon black in the first slurry is 96.5:1:1.5:1; the first slurry is coated on both sides of a current collector copper foil 10 with a thickness of 8 μm along the thickness direction, and then dried at 80°C and rolled, and the compaction density after rolling is 0.2 g / cc, so as to form a 0.05 mm thick and 0.08 g / cm2 surface density on the current collector copper foil 10. 2 a first coating layer 20;

[0153] (2) The modified silicon-based material, the binder styrene-butadiene rubber (SBR), the dispersant sodium carboxymethyl cellulose (CMC), the conductive agent carbon black and water are mixed to obtain a second slurry with a solid content of 50 wt%; wherein the mass ratio of the modified silicon-based material, the binder styrene-butadiene rubber, the dispersant sodium carboxymethyl cellulose and the conductive agent carbon black in the second slurry is 96.5:1:1.5:1; the second slurry is coated on the first coating 20, and then dried at 80°C, and then rolled, and the compaction density after rolling is 0.2 g / cc, so as to form a 0.025 mm thick and 0.04 g / cm 2 a second coating layer 30;

[0154] (3) The modified MXene material, the binder styrene butadiene rubber (SBR), the dispersant sodium carboxymethyl cellulose (CMC), the conductive agent carbon black and water are mixed to obtain a third slurry with a solid content of 50 wt%; wherein the mass ratio of the modified MXene material, the binder styrene butadiene rubber, the dispersant sodium carboxymethyl cellulose and the conductive agent carbon black in the third slurry is 96.5:1:1.5:1; the third slurry is coated on the second coating 20, and then dried at 80°C, and then rolled, and the compaction density after rolling is 0.2 g / cc, so as to form a 0.025 mm thick and 0.04 g / cm 2 The third coating layer 40 is formed to obtain a negative electrode sheet.

[0155] Example 2

[0156] The preparation of the negative electrode sheet includes the following steps:

[0157] (1) A modified graphite material, a binder styrene butadiene rubber (SBR), a dispersant sodium carboxymethyl cellulose (CMC), a conductive agent carbon black and water are mixed to obtain a first slurry with a solid content of 50 wt%; wherein the mass ratio of the modified graphite material, the binder styrene butadiene rubber, the dispersant sodium carboxymethyl cellulose and the conductive agent carbon black in the first slurry is 96.5:1:1.5:1; the first slurry is coated on both sides of a current collector copper foil 10 with a thickness of 8 μm along the thickness direction, and then dried at 80°C and rolled, and the compaction density after rolling is 0.2 g / cc, so as to form a 0.05 mm thick and 0.04 g / cm2 surface density on the current collector copper foil 10. 2 a first coating layer 20;

[0158] (2) The modified silicon-based material, the binder styrene-butadiene rubber (SBR), the dispersant sodium carboxymethyl cellulose (CMC), the conductive agent carbon black and water are mixed to obtain a second slurry with a solid content of 50 wt%; wherein the mass ratio of the modified silicon-based material, the binder styrene-butadiene rubber, the dispersant sodium carboxymethyl cellulose and the conductive agent carbon black in the second slurry is 96.5:1:1.5:1; the second slurry is coated on the first coating 20, and then dried at 80°C, and then rolled, and the compaction density after rolling is 0.2 g / cc, so as to form a 0.025 mm thick and 0.08 g / cm 2 a second coating layer 30;

[0159] (3) The modified MXene material, the binder styrene butadiene rubber (SBR), the dispersant sodium carboxymethyl cellulose (CMC), the conductive agent carbon black and water are mixed to obtain a third slurry with a solid content of 50 wt%; wherein the mass ratio of the modified MXene material, the binder styrene butadiene rubber, the dispersant sodium carboxymethyl cellulose and the conductive agent carbon black in the third slurry is 96.5:1:1.5:1; the third slurry is coated on the second coating 20, and then dried at 80°C, and then rolled, and the compaction density after rolling is 0.2 g / cc, so as to form a 0.025 mm thick and 0.04 g / cm 2 The third coating layer 40 is formed to obtain a negative electrode sheet.

[0160] Example 3

[0161] The preparation of the negative electrode sheet includes the following steps:

[0162] (1) A modified graphite material, a binder styrene butadiene rubber (SBR), a dispersant sodium carboxymethyl cellulose (CMC), a conductive agent carbon black and water are mixed to obtain a first slurry with a solid content of 50 wt%; wherein the mass ratio of the modified graphite material, the binder styrene butadiene rubber, the dispersant sodium carboxymethyl cellulose and the conductive agent carbon black in the first slurry is 96.5:1:1.5:1; the first slurry is coated on both sides of a current collector copper foil 10 with a thickness of 8 μm along the thickness direction, and then dried at 80°C and rolled, and the compaction density after rolling is 0.2 g / cc, so as to form a 0.05 mm thick and 0.04 g / cm2 surface density on the current collector copper foil 10. 2 a first coating layer 20;

[0163] (2) The modified silicon-based material, the binder styrene-butadiene rubber (SBR), the dispersant sodium carboxymethyl cellulose (CMC), the conductive agent carbon black and water are mixed to obtain a second slurry with a solid content of 50 wt%; wherein the mass ratio of the modified silicon-based material, the binder styrene-butadiene rubber, the dispersant sodium carboxymethyl cellulose and the conductive agent carbon black in the second slurry is 96.5:1:1.5:1; the second slurry is coated on the first coating 20, and then dried at 80°C, and then rolled, and the compaction density after rolling is 0.2 g / cc, so as to form a 0.025 mm thick and 0.04 g / cm 2 a second coating layer 30;

[0164] (3) The modified MXene material, the binder styrene butadiene rubber (SBR), the dispersant sodium carboxymethyl cellulose (CMC), the conductive agent carbon black and water are mixed to obtain a third slurry with a solid content of 50 wt%; wherein the mass ratio of the modified MXene material, the binder styrene butadiene rubber, the dispersant sodium carboxymethyl cellulose and the conductive agent carbon black in the third slurry is 96.5:1:1.5:1; the third slurry is coated on the second coating 20, and then dried at 80°C, and then rolled, and the compaction density after rolling is 0.2 g / cc, so as to form a 0.025 mm thick and 0.08 g / cm 2 The third coating layer 40 is formed to obtain a negative electrode sheet.

[0165] Comparative Example 1

[0166] The preparation of the negative electrode sheet includes the following steps:

[0167] (1) A modified graphite material, a binder styrene butadiene rubber (SBR), a dispersant sodium carboxymethyl cellulose (CMC), a conductive agent carbon black and water are mixed to obtain a first slurry with a solid content of 50 wt%; wherein the mass ratio of the modified graphite material, the binder styrene butadiene rubber, the dispersant sodium carboxymethyl cellulose and the conductive agent carbon black in the first slurry is 96.5:1:1.5:1; the first slurry is coated on both sides of a current collector copper foil 10 with a thickness of 8 μm along the thickness direction, and then dried at 80°C and rolled, and the compaction density after rolling is 0.2 g / cc, so as to form a 0.05 mm thick and 0.08 g / cm2 surface density on the current collector copper foil 10. 2 a first coating layer 20;

[0168] (2) The modified silicon-based material, the binder styrene-butadiene rubber (SBR), the dispersant sodium carboxymethyl cellulose (CMC), the conductive agent carbon black and water are mixed to obtain a second slurry with a solid content of 50 wt%; wherein the mass ratio of the modified silicon-based material, the binder styrene-butadiene rubber, the dispersant sodium carboxymethyl cellulose and the conductive agent carbon black in the second slurry is 96.5:1:1.5:1; the second slurry is coated on the first coating 20, and then dried at 80°C, and then rolled, and the compaction density after rolling is 0.2 g / cc, so as to form a 0.025 mm thick and 0.04 g / cm 2 The second coating layer 30 is formed to obtain a negative electrode sheet.

[0169] Comparative Example 2

[0170] The preparation of the negative electrode sheet includes the following steps:

[0171] (1) artificial graphite material, binder styrene butadiene rubber (SBR), dispersant sodium carboxymethyl cellulose (CMC), conductive agent carbon black and water are mixed to obtain a first slurry with a solid content of 50 wt%; wherein the mass ratio of artificial graphite material, binder styrene butadiene rubber, dispersant sodium carboxymethyl cellulose and conductive agent carbon black in the first slurry is 96.5:1:1.5:1; the first slurry is coated on both sides of the current collector copper foil 10 with a thickness of 8 μm along the thickness direction, and then dried at 80°C and rolled, and the compaction density after rolling is 0.2 g / cc, so as to form a 0.05 mm thick and 0.08 g / cm2 surface density on the current collector copper foil 10. 2 a first coating layer 20;

[0172] (2) Silicon-based material silica, binder styrene butadiene rubber (SBR), dispersant sodium carboxymethyl cellulose (CMC), conductive agent carbon black and water are mixed to obtain a second slurry with a solid content of 50 wt%; wherein the mass ratio of silicon-based material silica, binder styrene butadiene rubber, dispersant sodium carboxymethyl cellulose and conductive agent carbon black in the second slurry is 96.5:1:1.5:1; the second slurry is coated on the first coating 20, and then dried at 80°C, and then rolled, and the compaction density after rolling is 0.2 g / cc, so as to form a 0.025 mm thick and 0.04 g / cm2 surface density coating. 2 a second coating layer 30;

[0173] (3) MXene material Ti3C2T x , binder styrene-butadiene rubber (SBR), dispersant sodium carboxymethyl cellulose (CMC), conductive agent carbon black and water are mixed to obtain a third slurry with a solid content of 50 wt%; wherein the MXene material Ti3C2T xThe mass ratio of the binder styrene-butadiene rubber, the dispersant sodium carboxymethyl cellulose and the conductive agent carbon black is 96.5:1:1.5:1; the third slurry is coated on the second coating 20, and then dried at 80°C, and then rolled. The compaction density after rolling is 0.2g / cc to form a film with a thickness of 0.025mm and a surface density of 0.04g / cm 2 The third coating layer 40 is formed to obtain a negative electrode sheet.

[0174] Comparative Example 3

[0175] The preparation of the negative electrode sheet includes the following steps:

[0176] (1) A modified graphite material, a binder styrene butadiene rubber (SBR), a dispersant sodium carboxymethyl cellulose (CMC), a conductive agent carbon black and water are mixed to obtain a first slurry with a solid content of 50 wt%; wherein the mass ratio of the modified graphite material, the binder styrene butadiene rubber, the dispersant sodium carboxymethyl cellulose and the conductive agent carbon black in the first slurry is 96.5:1:1.5:1; the first slurry is coated on both sides of a current collector copper foil 10 with a thickness of 8 μm along the thickness direction, and then dried at 80°C and rolled, and the compaction density after rolling is 0.2 g / cc, so as to form a 0.05 mm thick and 0.08 g / cm2 surface density on the current collector copper foil 10. 2 a first coating layer 20;

[0177] (2) The modified silicon-based material, the binder styrene-butadiene rubber (SBR), the dispersant sodium carboxymethyl cellulose (CMC), the conductive agent carbon black and water are mixed to obtain a second slurry with a solid content of 50 wt%; wherein the mass ratio of the modified silicon-based material, the binder styrene-butadiene rubber, the dispersant sodium carboxymethyl cellulose and the conductive agent carbon black in the second slurry is 96.5:1:1.5:1; the second slurry is coated on the first coating 20, and then dried at 80°C, and then rolled, and the compaction density after rolling is 0.2 g / cc, so as to form a 0.025 mm thick and 0.04 g / cm 2 a second coating layer 30;

[0178] The method for preparing the modified silicon-based material comprises the following steps:

[0179] A 0.5 mg / mL polydiallyldimethylammonium chloride (PDDA) solution and a 1 mg / mL silicon-based material silica solution were stirred, dispersed, and separated in a volume ratio of 1:2 to obtain a precipitate.

[0180] The precipitate was freeze-dried at -40°C for 12 hours, and after freeze-drying, the obtained product was annealed at 400°C for 10 hours to obtain a modified silicon-based material;

[0181] (3) The modified MXene material, the binder styrene butadiene rubber (SBR), the dispersant sodium carboxymethyl cellulose (CMC), the conductive agent carbon black and water are mixed to obtain a third slurry with a solid content of 50 wt%; wherein the mass ratio of the modified MXene material, the binder styrene butadiene rubber, the dispersant sodium carboxymethyl cellulose and the conductive agent carbon black in the third slurry is 96.5:1:1.5:1; the third slurry is coated on the second coating 20, and then dried at 80°C, and then rolled, and the compaction density after rolling is 0.2 g / cc, so as to form a 0.025 mm thick and 0.04 g / cm 2 The third coating layer 40 is formed to obtain a negative electrode sheet.

[0182] Comparative Example 4

[0183] The preparation of the negative electrode sheet includes the following steps:

[0184] (1) A modified graphite material, a binder styrene butadiene rubber (SBR), a dispersant sodium carboxymethyl cellulose (CMC), a conductive agent carbon black and water are mixed to obtain a first slurry with a solid content of 50 wt%; wherein the mass ratio of the modified graphite material, the binder styrene butadiene rubber, the dispersant sodium carboxymethyl cellulose and the conductive agent carbon black in the first slurry is 96.5:1:1.5:1; the first slurry is coated on both sides of a current collector copper foil 10 with a thickness of 8 μm along the thickness direction, and then dried at 80°C and rolled, and the compaction density after rolling is 0.2 g / cc, so as to form a 0.05 mm thick and 0.08 g / cm2 surface density on the current collector copper foil 10. 2 a first coating layer 20;

[0185] (2) The modified silicon-based material, the binder styrene-butadiene rubber (SBR), the dispersant sodium carboxymethyl cellulose (CMC), the conductive agent carbon black and water are mixed to obtain a second slurry with a solid content of 50 wt%; wherein the mass ratio of the modified silicon-based material, the binder styrene-butadiene rubber, the dispersant sodium carboxymethyl cellulose and the conductive agent carbon black in the second slurry is 96.5:1:1.5:1; the second slurry is coated on the first coating 20, and then dried at 80°C, and then rolled, and the compaction density after rolling is 0.2 g / cc, so as to form a 0.025 mm thick and 0.04 g / cm 2 a second coating layer 30;

[0186] The method for preparing the modified silicon-based material comprises the following steps:

[0187] 500 g of carbon nanotubes were weighed and placed in a 1000 mL beaker, 300 mL of ethanol was added to the beaker, and the carbon nanotubes were dispersed in the ethanol by magnetic stirring to obtain a carbon nanotube solution; the carbon nanotube aqueous solution was added to the beaker using a pipette according to the ratio of silicon oxide material silicon dioxide: carbon nanotubes = 50:1, 100 mL of ethanol was added to dilute it, and ultrasonication was performed, and then the solution was added to the silicon-carbon-ethanol system. After stirring and mixing for 30 minutes, vacuum filtration was performed step by step. After the filtration, the obtained product was dried at 80° C., and then the dried product was carbonized at 400° C. under a nitrogen atmosphere for 2 hours to obtain a modified silicon-based material;

[0188] (3) The modified MXene material, the binder styrene butadiene rubber (SBR), the dispersant sodium carboxymethyl cellulose (CMC), the conductive agent carbon black and water are mixed to obtain a third slurry with a solid content of 50 wt%; wherein the mass ratio of the modified MXene material, the binder styrene butadiene rubber, the dispersant sodium carboxymethyl cellulose and the conductive agent carbon black in the third slurry is 96.5:1:1.5:1; the third slurry is coated on the second coating 20, and then dried at 80°C, and then rolled, and the compaction density after rolling is 0.2 g / cc, so as to form a 0.025 mm thick and 0.04 g / cm 2 The third coating layer 40 is formed to obtain a negative electrode sheet.

[0189] Performance Testing

[0190] 1. Preparation of batteries

[0191] (1) Preparation of positive electrode sheet: The positive electrode active material lithium iron phosphate (LFP), the binder polyvinylidene fluoride (PVDF), and the conductive agent conductive carbon black are mixed in a mass ratio of 97:1.5:1.5, and the mixture is dispersed. Then, the solvent N-methylpyrrolidone (NMP) is added to obtain a positive electrode slurry with a solid content of 75 wt%; the positive electrode slurry is coated on an aluminum foil with a thickness of 10 μm, dried, cold pressed, and then die-cut to obtain a positive electrode sheet.

[0192] (2) Assembling the battery: The positive electrode sheet, the negative electrode sheet in the embodiment and the comparative example are dried and cold pressed, and the treated positive electrode sheet and the separator (polypropylene separator) are stacked in order with the treated negative electrode sheet in the embodiment and the comparative example, and a bare cell is obtained by winding. The aluminum tabs and the copper-plated nickel tabs are connected respectively, and the bare cell is placed in a high temperature vacuum bake at 85°C for 24 hours and encapsulated with an aluminum-plastic film. The electrolyte uses a 1M lithium hexafluorophosphate electrolyte and the solvent is a mixed solvent of ethylene carbonate / dimethyl carbonate / 1,2-propylene glycol carbonate in a ratio of 1:1:1 (volume ratio). After encapsulation, a sufficient amount of electrolyte is injected, and then the battery is subjected to formation and aging to obtain a lithium-ion battery.

[0193] 2. Performance Testing

[0194] This experiment uses a soft-pack battery system to perform various electrochemical performance tests. The Wuhan Blue Electric CT200A battery test system is used to perform constant current charge and discharge cycle performance, rate performance, and charge and discharge curves. The voltage scan range is 2 to 3.65V.

[0195] (1) Negative electrode design gram capacity: refers to the design of the negative electrode material, that is, the amount of charge (usually in milliampere hours, mAh) that can be stored per unit mass (usually in grams) of the negative electrode material in the battery.

[0196] (2) The method for testing the maximum continuous charging rate is as follows: ① Let the battery stand at room temperature (25°C) for 4 hours; ③ Charge at nC constant current and constant voltage to 3.65V, with a cutoff of 0.05C, with n=1, 1.5, 2, 2.5, 3, 3.5, 4…; ④ Let the battery stand at room temperature for 2 hours; Repeat the above steps to complete charging at all different rates. After charging at the rate, perform an electrical disassembly to confirm the lithium deposition. If lithium deposition is observed on the electrode of the battery group after full charge, it indicates that lithium deposition occurs at this rate. If no lithium deposition occurs on the electrode interface at the previous test rate, the maximum continuous charging rate is this rate.

[0197] (3) The method for testing the 0-100% SOC fast charge time is as follows: ① At 25°C, first charge the battery to 3.65V at a rate of 4C, then charge it to 3.65V at 3.6C, and so on, charging at different rates (4C, 3.6C, 3.2C, 2.8C, 2.6C, 2.2C, 1.8C, 1.6C, 1.2C, 0.8C, 0.33C), until the final charge is 100% SOC at 0.33C, record the time it takes to charge to 3.65V at each rate, and the accumulated time is the 0-100% fast charge time;

[0198] (4) The method for testing low-temperature charging capability is as follows: ① Voltage range is 2.5V~3.65V, temperature: -20℃; ② Stand for 120min; ③ Constant current charging: charge with IC constant current to the upper limit voltage, until the voltage setting charging cut-off voltage of 3.65V is reached; ④ Stand for 30min; ⑤ 0.3C discharge to the lower limit voltage; ⑥ Repeat steps ②~⑤ 10 times; ⑦ Stand for 30min; Change the current, where I=0.1C, 0.15C, 0.2C, 0.25C, 0.3C, 0.4C, 0.5C…. Repeat steps ①-⑦, record the lithium plating at the negative electrode interface of each battery at different rates. If lithium plating occurs at the negative electrode interface after 10 cycles at this rate, and no lithium plating occurs at the interface at the previous rate test, then the previous rate is the maximum acceptable charging current at a low temperature of -20℃;

[0199] (5) 500-cycle full charge thickness test of the negative electrode: First, record the original negative electrode thickness, denoted as L1, and place the battery in a room temperature environment (25°C ± 2). Then, charge the battery at a constant current of 1C to 3.65V, let it rest for 30 minutes, and discharge it at a constant current to 2.5V. This step is considered one cycle. After recording 500 cycles, fully charge the battery and disassemble it. Use a micrometer to measure the fully charged negative electrode thickness, denoted as L2. The rate of change = (L2 - L1) / (L1 - foil thickness).

[0200]

[0201] As can be seen from Table 1, the negative electrode capacity design: Since the silicon-oxygen ratio is higher in Example 2, and silicon-oxygen itself has a higher capacity, the capacity design is relatively high. Example 3 is mainly due to the high content of MXene material, which leads to a significant decrease in capacity. The comparative example has a slightly higher capacity than Example 1 due to the lack of the third layer of MXene coating. The other comparative examples are basically consistent with Example 1.

[0202] Sustained maximum rate / fast charging time: Combining Examples 1-3, it is found that Example 1 is the best. Since Example 3 has more MXene materials than Example 2, the graphene oxide-coated MXene solves the self-stacking and widens the interlayer spacing, which enhances the fast charging capability. Compared with Comparative Example 1, there is no MXene and the fast charging capability decreases. Comparative Example 2 is the worst due to poor dynamics and all coating materials have not been surface modified.

[0203] Low-temperature charging performance: At low temperatures, Examples 1-3 and Comparative Example 4 exhibit relatively rapid temperature rise due to the construction of a three-dimensional conductive network. The graphene, carbon nanotubes, and the third layer of MXene material all possess excellent electrical and thermal conductivity, resulting in improved charging performance at low temperatures. Comparative Example 2, while coated with three layers, lacks a highly conductive surface coating, resulting in poor charging performance at low temperatures. Comparative Examples 1 and 3, while exhibiting some conductivity, lack a three-dimensional conductive network.

[0204] Negative electrode full discharge thickness change rate: Comparing Examples 1-3, it is found that the optimal Example 1 has the smallest negative electrode thickness change rate. This is due to the reasonable ratio and the strong bending strength and large interlayer spacing of the MXene coated with graphene oxide, which can accommodate the volume expansion of the second layer of silicon and oxygen during the charge and discharge process, and the downward stress expansion is released by the first layer. Compared with Comparative Example 1, it is found that the thickness change of MXene without a third layer of tensile and bending strength reaches 22.1%. Therefore, placing the silicon layer in the second layer can not only increase the capacity and the lithium insertion potential, but also suppress the expansion and protect the electrode structure. In addition, in Example 1 and Comparative Example 3, the bonding force between PDDA and the surface of graphene oxide improves the stability of the interface and plays a key role.

[0205] The above is only a preferred embodiment of the present invention. 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 present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A negative electrode sheet, characterized in that: The negative electrode sheet includes: a negative electrode current collector, a first negative electrode active layer provided on at least one side of the negative electrode current collector in the thickness direction, a second negative electrode active layer provided on a side of the first negative electrode active layer away from the negative electrode current collector, and a third negative electrode active layer provided on a side of the second negative electrode active layer away from the first negative electrode active layer; The first negative electrode active layer includes a first negative electrode active material, the first negative electrode active material includes a modified graphite material; the modified graphite material includes graphite and a first coating layer coated on the surface of the graphite, the first coating layer includes a conductive material modified with a carboxyl group or a hydroxyl group; The second negative electrode active layer includes a second negative electrode active material, the second negative electrode active material includes a modified silicon-based material; the modified silicon-based material includes a silicon-based material and a second coating layer coated on the surface of the silicon-based material, the second coating layer includes a carbon material and a cationic polymer; The third negative electrode active layer includes a third negative electrode active material, the third negative electrode active material includes a modified MXene material, the modified MXene material includes a MXene material and a third coating layer coated on the surface of the MXene material, and the third coating layer includes a conductive material modified with a carboxyl group or a hydroxyl group.

2. The negative electrode sheet according to claim 1, characterized in that: The negative electrode sheet includes one or more of the following features (1) to (4): (1) the surface density ratio of the first negative electrode active layer, the second negative electrode active layer and the third negative electrode active layer is (1-3): (1-3): (1-3); (2) The surface density of the first negative electrode active layer is 0.01 to 0.12 g / cm 2 ; (3) The surface density of the second negative electrode active layer is 0.01 to 0.12 g / cm 2 ; (4) The surface density of the third negative electrode active layer is 0.01 to 0.12 g / cm 2 .

3. The negative electrode sheet according to claim 1, characterized in that: The negative electrode sheet includes one or more of the following features (1) to (4): (1) The thickness ratio of the first negative electrode active layer, the second negative electrode active layer, and the third negative electrode active layer is (1.25-3.35): (1-2): (1-2); (2) The thickness of the first negative electrode active layer is 0.044 to 0.067 mm; (3) The thickness of the second negative electrode active layer is 0.02 to 0.040 mm; (4) The thickness of the third negative electrode active layer is 0.02 to 0.040 mm.

4. The negative electrode sheet according to claim 1, characterized in that: The modified graphite material includes one or more of the following features (1) to (3): (1) The mass ratio of the graphite to the conductive material modified with a carboxyl group or a hydroxyl group is (94-99): (1-6); (2) The thickness of the first coating layer is 20 to 80 nm; (3) The conductive material modified with carboxyl or hydroxyl in the modified graphite material includes graphene oxide.

5. The negative electrode sheet according to claim 1, characterized in that: The modified silicon-based material includes one or more of the following features (1) to (5): (1) The mass ratio of the silicon-based material, the carbon material and the cationic polymer is (84-97): (2-16): (1-10); (2) The thickness of the second coating layer is 10 to 50 nm; (3) The silicon-based material includes at least one of silicon-carbon material, silicon-oxygen material and nano-silicon; optionally, the silicon-oxygen material includes SiO x , where 0.5≤x≤1.5 and / or x=2; (4) The carbon material comprises a one-dimensional carbon material or a two-dimensional carbon material; or, the carbon material comprises a zero-dimensional carbon material, and at least one of a one-dimensional carbon material and a two-dimensional carbon material; optionally, the zero-dimensional carbon material comprises graphite particles and / or conductive carbon black; optionally, the one-dimensional carbon material comprises carbon nanotubes and / or carbon fibers; optionally, the two-dimensional carbon material comprises graphene and / or graphene oxide; (5) The cationic polymer includes polydiallyldimethylammonium chloride.

6. The negative electrode sheet according to claim 1, characterized in that: The modified MXene material includes one or more of the following characteristics (1) to (4): (1) The mass ratio of the MXene material to the carboxyl- or hydroxyl-modified conductive material is (90-99): (1-10); (2) The thickness of the third coating layer is 20 nm to 200 nm; (3) The MXene material includes Ti3C2T x ; (4) The conductive material modified with carboxyl or hydroxyl in the modified MXene material includes graphene oxide.

7. The negative electrode sheet according to claim 1, characterized in that: The negative electrode sheet includes one or more of the following features (1) to (3): (1) The first negative electrode active layer further includes a first binder, a first dispersant, and a first conductive agent; optionally, the mass ratio of the first negative electrode active material, the first binder, the first dispersant, and the first conductive agent is (95-99): (0.2-2): (0.7-2): (0.1-1); (2) The second negative electrode active layer further includes a second binder, a second dispersant, and a second conductive agent; optionally, the mass ratio of the second negative electrode active material, the second binder, the second dispersant, and the second conductive agent is (95-99): (0.2-2): (0.7-2): (0.1-1); (3) The third negative electrode active layer further includes a third binder, a third dispersant and a third conductive agent; optionally, the mass ratio of the third negative electrode active material, the third binder, the third dispersant and the third conductive agent is (95-99): (0.2-2): (0.7-2): (0.1-1).

8. The negative electrode sheet according to claim 7, characterized in that: The negative electrode sheet includes one or more of the following features (1) to (3): (1) The first binder, the second binder, and the third binder each independently comprise at least one of styrene-butadiene rubber, polyvinylidene fluoride, polyacrylic acid, polyacrylate, polyimide, polyamide, polyvinyl alcohol, and polytetrafluoroethylene; (2) the first dispersant, the second dispersant, and the third dispersant each independently comprise at least one of carboxymethyl cellulose, sodium dodecylbenzenesulfonate, and polyvinyl pyrrolidone; (3) The first conductive agent, the second conductive agent, and the third conductive agent each independently include at least one of conductive carbon black, conductive graphite, carbon nanotubes, carbon fibers, and graphene.

9. A method for preparing the negative electrode sheet according to any one of claims 1 to 8, characterized in that: The preparation method comprises the following steps: S1, applying a first negative electrode active slurry on at least one side surface of a current collector along a thickness direction to form a first negative electrode active layer on the current collector; S2, coating a second negative electrode active slurry on a surface of the first negative electrode active layer away from the current collector to form a second negative electrode active layer on the first negative electrode active layer; S3, coating the third negative electrode active slurry on the surface of the second negative electrode active layer away from the first negative electrode active layer to form a third negative electrode active layer on the second negative electrode active layer; Wherein, the first negative electrode active slurry includes modified graphite material; The second negative electrode active slurry includes a modified silicon-based material; The third negative electrode active slurry includes modified MXene material.

10. A battery, characterized in that: The battery includes a negative electrode sheet, wherein the negative electrode sheet includes the negative electrode sheet according to any one of claims 1 to 8 or the negative electrode sheet prepared by the preparation method according to claim 9.

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