Negative plate, preparation method thereof and battery

Abstract

The embodiment of the invention relates to a negative plate, a preparation method thereof and a battery, the negative plate comprises a current collector, and a first active material layer and a solid electrolyte layer which are arranged on at least one surface of the current collector, and the first active material layer is located between the current collector and the solid electrolyte layer; the first active material layer comprises a silicon-based material; the solid electrolyte layer comprises a three-dimensional network cross-linked product of polyethylene oxide and trimethylaluminum and inorganic lithium salt positioned in pores of the three-dimensional network cross-linked product. Therefore, the volume expansion of the first active material layer can be effectively inhibited through the solid electrolyte layer in the charging and discharging process, the stability of the SEI membrane is improved, the SEI membrane rich in lithium salt can be constructed, the desolvation of active ions is promoted, and the capacity, the cycling stability and the low-temperature performance of the battery can be further improved.

Description

Technical Field

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

[0002] Silicon materials have become one of the potential battery negative electrode materials due to their advantages such as low cost, high theoretical specific capacity (up to about 4200 mAh / g), low lithium intercalation potential, and excellent fast charging performance.

[0003] However, silicon materials have a significant volume expansion problem during the charge and discharge cycles of the battery. The volume expansion rate can reach up to 300%, which leads to a poor contact or even detachment between the negative electrode material and the current collector in the later stage of the battery cycle, resulting in a decline in the cycle stability of the battery. In addition, during the process of significant volume expansion and contraction of the negative electrode containing silicon-based materials, the SEI (Solid Electrolyte Interface) film is prone to rupture, making it difficult to form a stable SEI film at the interface between the negative electrode and the electrolyte. New SEI films are continuously formed by the contact between the negative electrode and the electrolyte, which will cause irreversible consumption of active ions and the electrolyte, resulting in rapid attenuation of the battery capacity and even battery failure. These factors limit the application of negative electrode sheets containing silicon-based materials in batteries. Summary of the Invention

[0004] In view of this, embodiments of the present application provide a negative electrode sheet, a preparation method thereof, and a battery to solve at least one problem in the background art.

[0005] In a first aspect, embodiments of the present application provide a negative electrode sheet, including: a current collector and a first active material layer and a solid electrolyte layer disposed on at least one surface of the current collector, and the first active material layer is located between the current collector and the solid electrolyte layer;

[0006] The first active material layer includes silicon-based materials;

[0007] The solid electrolyte layer includes a three-dimensional network cross-linked product of polyethylene oxide and trimethylaluminum and an inorganic lithium salt located in the pores of the three-dimensional network cross-linked product.

[0008] In combination with the first aspect of the present application, in an optional embodiment, the negative electrode sheet satisfies at least one of the following characteristics:

[0009] (1) The first active material layer further includes a conductive agent and a first binder, and the mass ratio of the silicon-based material, the conductive agent, and the first binder is (92-95):(2-5):(2-3); optionally, the conductive agent includes at least one of conductive carbon black, carbon nanotubes, and graphene; optionally, the first binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyamide, polyvinyl alcohol, and polyimide;

[0010] (2) The inorganic lithium salt includes at least one of Li3PO4, LiF, Li2O, Li2SO3, and Li2CO3;

[0011] (3) The mass ratio of the three-dimensional network cross-linked product to the inorganic lithium salt is 2:(3-3.1);

[0012] (4) The thickness of the first active material layer is 70 μm to 90 μm;

[0013] (5) The thickness of the solid electrolyte layer is 10 μm to 15 μm;

[0014] (6) The thickness of the current collector is 7 μm to 15 μm.

[0015] Combined with the first aspect of the present application, in an optional embodiment, the negative electrode sheet further includes a second active material layer located between the first active material layer and the solid electrolyte layer, and the second active material layer includes carbon fibers.

[0016] Combined with the first aspect of the present application, in an optional embodiment, the second active material layer satisfies at least one of the following characteristics:

[0017] (1) The second active material layer further includes a second binder, and the mass ratio of the carbon fiber and the second binder is (96-98):(2-4); optionally, the second binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyamide, polyvinyl alcohol, and polyimide;

[0018] (2) The thickness of the second active material layer is less than the thickness of the first active material layer;

[0019] (3) The thickness of the second active material layer is 30 μm to 40 μm.

[0020] In a second aspect, an embodiment of the present application provides a method for preparing a negative electrode sheet, and the method includes the following steps:

[0021] Add the silicon-based material, the conductive agent, and the first binder to a first solvent, and after mixing, obtain a first slurry;

[0022] Coat the first slurry on at least one surface of the current collector, and after the first drying treatment, obtain a first active material layer;

[0023] Place polyethylene oxide in the vapor atmosphere of trimethylaluminum to obtain modified polyethylene oxide adsorbed with trimethylaluminum;

[0024] Add the modified polyethylene oxide and inorganic lithium salt to a second solvent. After mixing, add an initiator and carry out a crosslinking reaction to obtain a gel-like substance;

[0025] Coat the gel-like substance on the first active material layer, and after the second drying treatment, obtain a solid electrolyte layer.

[0026] Combined with the second aspect of the present application, in an alternative embodiment, the steps of preparing the first active material layer satisfy at least one of the following characteristics:

[0027] (1) The mass ratio of the silicon-based material, the conductive agent, and the first binder is (92-95):(2-5):(2-3);

[0028] (2) The conductive agent includes at least one of conductive carbon black, carbon nanotubes, and graphene;

[0029] (3) The first binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyamide, polyvinyl alcohol, and polyimide;

[0030] (4) The temperature of the first drying treatment is 80°C to 120°C;

[0031] (5) The thickness of the first active material layer is 70 μm to 90 μm;

[0032] (6) The thickness of the current collector is 7 μm to 15 μm.

[0033] Combined with the second aspect of the present application, in an alternative embodiment, the steps of preparing the solid electrolyte layer satisfy at least one of the following characteristics:

[0034] (1) The vapor atmosphere of trimethylaluminum is a vapor atmosphere formed by heating trimethylaluminum at 97°C to 103°C;

[0035] (2) The inorganic lithium salt includes at least one of Li3PO4, LiF, Li2O, Li2SO3, and Li2CO3;

[0036] (3) The second solvent includes anhydrous acetonitrile and / or anhydrous dimethylformamide;

[0037] (4) The mass ratio of the modified polyethylene oxide, the inorganic lithium salt, and the second solvent is 2:(2.9 - 3.1):(2.9 - 3.1);

[0038] (5) The initiator includes water;

[0039] (6) The molar ratio of the trimethylaluminum to the initiator is 1:(0.9 - 1.1);

[0040] (7) The temperature of the second drying treatment is 60°C - 135°C;

[0041] (8) The thickness of the solid electrolyte layer is 10μm - 15μm.

[0042] Combined with the second aspect of the present application, in an alternative embodiment, before coating the gel-like substance on the first active material layer, the method further includes:

[0043] Adding carbon fiber and a second binder to a third solvent, and after mixing, obtaining a second slurry;

[0044] Coating the second slurry on the first active material layer, and after the third drying treatment, obtaining a second active material layer.

[0045] Combined with the second aspect of the present application, in an alternative embodiment, the method satisfies at least one of the following features:

[0046] (1) The mass ratio of the carbon fiber to the second binder is (96 - 98):(2 - 4);

[0047] (2) The second binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyamide, polyvinyl alcohol, and polyimide;

[0048] (3) The temperature of the third drying treatment is 80°C - 120°C;

[0049] (4) The thickness of the second active material layer is less than the thickness of the first active material layer;

[0050] (5) The thickness of the second active material layer is 30μm - 40μm.

[0051] In a third aspect, an embodiment of the present application provides a battery, including the negative electrode sheet according to any one of the first aspect or a negative electrode sheet prepared by the preparation method of the negative electrode sheet according to any one of the second aspect.

[0052] Compared with the prior art, the embodiments of the present application have the following beneficial effects:

[0053] The negative electrode sheet, its preparation method and battery provided by the embodiments of the present application, the negative electrode sheet includes: a current collector, and a first active material layer and a solid electrolyte layer disposed on at least one surface of the current collector, the first active material layer is located between the current collector and the solid electrolyte layer; the first active material layer includes a silicon-based material; the solid electrolyte layer includes a three-dimensional network cross-linked product of polyethylene oxide and trimethylaluminum and an inorganic lithium salt located in the pores of the three-dimensional network cross-linked product. In the embodiments of the present application, the first active material layer includes a silicon-based material, which is beneficial to improving the capacity of the negative electrode sheet. The three-dimensional network cross-linked product of polyethylene oxide and trimethylaluminum in the solid electrolyte layer enables the solid electrolyte layer to have high fracture toughness, so that the volume expansion of the first active material layer can be effectively inhibited during the charge and discharge process, ensuring that the SEI film is not easily broken, improving the stability of the SEI film, inhibiting the irreversible consumption of active ions, and further improving the capacity and cycle stability of the battery; in the solid electrolyte layer of the embodiments of the present application, the inorganic lithium salt is located in the pores of the three-dimensional network cross-linked product of polyethylene oxide and trimethylaluminum. Even if it contains a high concentration of inorganic lithium salt, the solid electrolyte layer can still exhibit good elasticity and toughness, making the solid electrolyte layer have high fracture toughness while being beneficial to constructing an SEI film rich in lithium salt, which can further improve the stability of the SEI film, promote the desolvation of active ions, and further improve the low-temperature performance of the battery.

[0054] Additional aspects and advantages of the present application will be given in part in the following description, become apparent in part from the following description, or be understood through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] The drawings described herein are used to provide a further understanding of the present application, and constitute a part of the present application. The schematic embodiments and descriptions thereof of the present application are used to explain the present application, and do not constitute an improper limitation of the present application. In the drawings:

[0056] Figure 1 is a schematic cross-sectional structure diagram of a negative electrode sheet provided by an embodiment of the present application;

[0057] Figure 2 is a schematic cross-sectional structure diagram of another negative electrode sheet provided by an embodiment of the present application;

[0058] Figure 3 is a schematic flow diagram of a method for preparing a negative electrode sheet provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0059] To make the technical solutions and beneficial effects of the present invention more obvious and understandable, the following provides a detailed description by combining the accompanying drawings and listing specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The experimental methods without specific conditions noted in the following embodiments are usually in accordance with conventional experimental conditions. The reagents and raw materials used in the present invention are commercially available unless otherwise specified.

[0060] In the following description, numerous specific details are given to provide a more thorough understanding of the present application. However, it will be apparent to one of ordinary skill in the art that the present application may be practiced without one or more of these details. In other instances, some well-known technical features are not described in order to avoid obscuring the present application; that is, not all features of the actual embodiments are described here, and the well-known functions and steps are not described in detail.

[0061] The purpose of the terms used herein is only to describe specific embodiments and is not a limitation of the present application. As used herein, the singular forms "a", "an" and "the" are also intended to include the plural forms unless the context clearly dictates otherwise. It should also be understood that the terms "comprising" and / or "including", when used in this specification, identify the presence of the stated features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups. As used herein, the term "and / or" includes any and all combinations of the associated listed items.

[0062] To thoroughly understand the present application, detailed steps and structures will be presented in the following description to illustrate the technical solutions of the present application. The preferred embodiments of the present application are described in detail below. However, in addition to these detailed descriptions, the present application may have other embodiments.

[0063] Unless otherwise defined, the technical and scientific terms used in the present application have the same meanings as those in the technical and scientific fields to which the present application pertains.

[0064] For those not noted with specific techniques or conditions in the following embodiments, they are usually in accordance with the conventional techniques or conditions described in the literature in the art, or in accordance with the conditions recommended in the product manuals and by the manufacturers. The numerical ranges in the following embodiments include the endpoint values.

[0065] The embodiments of the present application provide a negative electrode sheet, such as Figure 1As shown in the figure, the negative electrode sheet includes: a current collector 100, and a first active material layer 201 and a solid electrolyte layer 203 disposed on at least one surface of the current collector 100. The first active material layer 201 is located between the current collector 100 and the solid electrolyte layer 203; the first active material layer 201 includes a silicon-based material; the solid electrolyte layer 203 includes a three-dimensional network cross-linked product of polyethylene oxide and trimethylaluminum and an inorganic lithium salt located in the pores of the three-dimensional network cross-linked product.

[0066] In the embodiment of the present application, the first active material layer 201 includes a silicon-based material, which is beneficial to improving the capacity of the negative electrode sheet. The three-dimensional network cross-linked product of polyethylene oxide and trimethylaluminum in the solid electrolyte layer 203 enables the solid electrolyte layer 203 to have high fracture toughness, so as to effectively inhibit the volume expansion of the first active material layer 201 during charge and discharge, ensure that the SEI film is not easily broken, improve the stability of the SEI film, and inhibit the irreversible consumption of active ions (such as lithium ions), thereby improving the capacity and cycle stability of the battery; usually, adding an inorganic lithium salt to a polymer can improve the ionic conductivity, but it is easy to cause a decrease in the mechanical properties of the polymer film. In the solid electrolyte layer 203 of the embodiment of the present application, the inorganic lithium salt is located in the pores of the three-dimensional network cross-linked product of polyethylene oxide and trimethylaluminum (which can be called a polymer salt-inclusion structure). Even if it contains a high concentration of inorganic lithium salt, the solid electrolyte layer 203 can still exhibit good elasticity and toughness, enabling the solid electrolyte layer 203 to have high fracture toughness while being beneficial to constructing an SEI film rich in lithium salt, which can further improve the stability of the SEI film, promote the desolvation of active ions, thereby accelerating the transport of active ions at the electrode-electrolyte interface, and at the same time improving the kinetic performance of active ions at low temperatures, and further improving the low-temperature performance of the battery.

[0067] It can be understood that Figure 1 in the figure, in the thickness direction of the current collector 100, the first active material layer 201 and the solid electrolyte layer 203 are sequentially stacked on one surface of the current collector 100 is only an example. In some specific embodiments, the first active material layer 201 and the solid electrolyte layer 203 can be sequentially stacked on two opposite surfaces of the current collector 100 along the thickness direction.

[0068] The embodiment of the present application does not particularly limit the silicon-based material in the first active material layer 201, and any silicon-containing material well-known to those skilled in the art that can be used in the negative electrode sheet can be adopted. Exemplarily, the silicon-based material can include at least one of silicon monoxide, silicon carbide, and silicon. In a specific embodiment, the silicon-based material can be silicon.

[0069] In some embodiments, the first active material layer 201 further includes a conductive agent and a first binder, and the mass ratio of the silicon-based material, the conductive agent, and the first binder can be (92 to 95):(2 to 5):(2 to 3). Controlling the mass ratio of the silicon-based material, the conductive agent, and the first binder within the above range can, while better improving the capacity of the negative electrode sheet, take into account the electrical conductivity and mechanical strength of the negative electrode sheet, thereby further improving the capacity and cycle stability of the battery.

[0070] It can be understood that when the first active material layer 201 contains a silicon-based material, a conductive agent, and a first binder, the weight percentage of the silicon-based material in the first active material layer 201 can be 92% to 95%, the weight percentage of the conductive agent in the first active material layer 201 can be 2% to 5%, and the weight percentage of the first binder in the first active material layer 201 can be 2% to 3%.

[0071] Exemplarily, the conductive agent can include at least one of conductive carbon black, carbon nanotubes, and graphene. The first binder can include at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polyamide (PAI), polyvinyl alcohol (PVA), and polyimide (PI).

[0072] In the embodiments of the present application, the inorganic lithium salt can participate in the formation of the SEI film, thereby improving the stability and electrochemical performance of the SEI film, and further improving the comprehensive performance of the battery. Exemplarily, the inorganic lithium salt can include at least one of Li3PO4, LiF, Li2O, Li2SO3, and Li2CO3. Different types of inorganic lithium salts have their own advantages in improving the performance of the SEI film. For example, LiF and Li2O can better optimize the composition of the SEI film and improve the stability of the SEI film, thereby being able to better improve the cycle performance of the battery; Li2SO3 and Li2CO3 can better improve the ion transport performance of the SEI film, and thus be able to better improve the kinetic performance of the battery; Li3PO4 is more conducive to the desolvation of lithium ions from the solvation sheath, so that the SEI film containing Li3PO4 can better accelerate the transport of lithium ions at the electrode-electrolyte interface, and at the same time can also better improve the kinetic performance of lithium ions at low temperatures. Therefore, in practical applications, a combination of multiple inorganic lithium salts can be used to further improve the comprehensive performance of the battery. For example, the inorganic lithium salt can include at least one of LiF and Li2O, at least one of Li2SO3 and Li2CO3, and Li3PO4. In this way, the comprehensive performance of the battery can be further improved.

[0073] In the solid electrolyte layer 203 of the embodiments of the present application, when the mass ratio of the three-dimensional network cross-linked product to the inorganic lithium salt is too low, it is not conducive to improving the toughness and stability of the solid electrolyte layer 203, and thus the inhibitory effect on the volume expansion of the first active material layer 201 is limited; when the mass ratio of the three-dimensional network cross-linked product to the inorganic lithium salt is too high, it is not conducive to optimizing the composition of the SEI film to improve the stability and electrochemical performance of the SEI film. Therefore, in some specific embodiments, the mass ratio of the three-dimensional network cross-linked product to the inorganic lithium salt can be 2:(3-3.1). In this way, while effectively inhibiting the volume expansion of the first active material layer 201, the stability and electrochemical performance of the SEI film can be further improved, the desolvation of active ions can be further promoted, and thus the capacity, cycle stability and low-temperature performance of the battery can be further improved.

[0074] When the thickness of the first active material layer 201 is too thin, the capacity improvement of the negative electrode sheet will be limited; when the thickness of the first active material layer 201 is too thick, it will not only extend the transmission path of active ions, but also easily exacerbate the volume expansion of the negative electrode sheet during charge and discharge; therefore, in some specific embodiments, the thickness of the first active material layer 201 can be 70 μm to 90 μm, for example, it can be 70 μm, 75 μm, 80 μm, 85 μm, 90 μm or any value between any two of the above numerical ranges. This is beneficial to further improving the comprehensive performance of the negative electrode sheet.

[0075] When the thickness of the solid electrolyte layer 203 is too thin, the inhibitory effect on the volume expansion of the first active material layer 201 is limited; when the thickness of the solid electrolyte layer 203 is too thick, it will not only extend the transmission path of active ions, but also be not conducive to the further improvement of the overall capacity of the negative electrode sheet. Therefore, in some specific embodiments, the thickness of the solid electrolyte layer 203 can be 10 μm to 15 μm, for example, it can be 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or any value between any two of the above numerical ranges. This is beneficial to further improving the comprehensive performance of the negative electrode sheet.

[0076] The embodiments of the present application do not particularly limit the type of the current collector 100, and a negative electrode current collector well-known to those skilled in the art can be used. Exemplarily, the current collector 100 can include a copper foil.

[0077] Furthermore, the thickness of the current collector 100 can be 7 μm to 15 μm. In this way, the first active material layer 201 and the solid electrolyte layer 203 can be better loaded through the current collector 100, taking into account the mechanical strength and electrochemical performance of the negative electrode sheet.

[0078] In some embodiments, please refer to Figure 2, the negative electrode sheet may further include a second active material layer 202 located between the first active material layer 201 and the solid electrolyte layer 203, and the second active material layer 202 includes carbon fibers.

[0079] Carbon fibers, especially activated carbon fibers, have high toughness, their surfaces are covered with nano-scale micropores, have a rich pore structure, a large specific surface area, and usually contain oxygen / nitrogen atom doping. Therefore, in the embodiments of the present application, by providing a second active material layer 202 including carbon fibers between the first active material layer 201 and the solid electrolyte layer 203, the second active material layer 202 can not only act as an active material layer to further improve the capacity of the negative electrode sheet, but also enhance the wetting of the negative electrode sheet by the electrolyte and act as a liquid absorption layer to improve the liquid absorption and liquid retention capabilities of the negative electrode sheet; moreover, the high toughness and nano-scale pore structure of the carbon fibers help to provide a space for releasing stress when the first active material layer 201 expands in volume, thereby further improving the mechanical strength of the negative electrode sheet, maintaining the integrity of the negative electrode sheet structure, and further improving the cycle stability of the battery.

[0080] In some embodiments, the second active material layer 202 further includes a second binder, and the mass ratio of the carbon fiber to the second binder may be (96-98):(2-4). In this way, while ensuring the mechanical strength of the second active material layer 202, the capacity and cycle stability of the negative electrode sheet can be further improved through the second active material layer 202.

[0081] It can be understood that when the second active material layer 202 contains carbon fibers and a second binder, the mass fraction of the carbon fiber in the second active material layer 202 may be 96% - 98%, and the mass fraction of the second binder in the second active material layer 202 may be 2% - 4%.

[0082] Exemplarily, the second binder may include at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyamide, polyvinyl alcohol, and polyimide.

[0083] Compared with the first active material layer 201 including a silicon-based material, the second active material layer 202 including carbon fibers can provide limited capacity, and when the second active material layer 202 plays the role of enhancing the liquid absorption and liquid retention capabilities of the negative electrode sheet and providing a space for releasing stress for the volume expansion of the first active material layer 201, the requirement for thickness is not high. Therefore, an overly thick or heavy second active material layer 202 is instead not conducive to improving the volume or mass energy density of the battery. Therefore, in some specific embodiments, the thickness of the second active material layer 202 may be less than the thickness of the first active material layer 201.

[0084] In some specific embodiments, the thickness of the second active material layer 202 may be 30 μm to 40 μm, for example, it may be 30 μm, 35 μm, 40 μm, or any value between any two of the above numerical ranges. In this way, while the liquid absorption and retention capabilities of the negative electrode sheet can be better enhanced through the second active material layer 202 and space can be provided for the volume expansion of the first active material layer 201 to release stress, the capacity of the negative electrode sheet can be better balanced.

[0085] The embodiments of the present application also provide a method for preparing a negative electrode sheet. Please refer to Figure 3 , the method for preparing a negative electrode sheet provided by the embodiments of the present application includes the following steps:

[0086] S1: Add a silicon-based material, a conductive agent, and a first binder to a first solvent, and after mixing, obtain a first slurry;

[0087] S2: Coat the first slurry on at least one surface of the current collector, and after the first drying treatment, obtain a first active material layer;

[0088] S3: Place polyethylene oxide in the vapor atmosphere of trimethylaluminum to obtain modified polyethylene oxide adsorbed with trimethylaluminum;

[0089] S4: Add the modified polyethylene oxide and an inorganic lithium salt to a second solvent, mix them, add an initiator, and carry out a cross-linking reaction to obtain a gel-like substance;

[0090] S5: Coat the gel-like substance on the first active material layer, and after the second drying treatment, obtain a solid electrolyte layer.

[0091] In the embodiments of the present application, first, a first active material layer is formed on at least one surface of the current collector, and then a solid electrolyte layer is formed on the first active material layer; the first active material layer includes a silicon-based material, which is beneficial to improving the capacity of the negative electrode sheet. The three-dimensional network cross-linked product of polyethylene oxide and trimethylaluminum in the solid electrolyte layer makes the solid electrolyte layer have high fracture toughness, so that the volume expansion of the first active material layer can be effectively inhibited during charge and discharge, ensuring that the SEI film is not easily broken, improving the stability of the SEI film, inhibiting the irreversible consumption of active ions, and further improving the capacity and cycle stability of the battery; in the solid electrolyte layer in the embodiments of the present application, the inorganic lithium salt is located in the pores of the three-dimensional network cross-linked product of polyethylene oxide and trimethylaluminum. Even when a high-concentration inorganic lithium salt is added, the solid electrolyte layer can still exhibit good elasticity and toughness, making the solid electrolyte layer have high fracture toughness while being beneficial to constructing an SEI film rich in lithium salt, which can further improve the stability of the SEI film, promote the desolvation of active ions, thereby accelerating the transport of active ions at the electrode-electrolyte interface, and at the same time improving the kinetic performance of active ions at low temperatures, and further improving the low-temperature performance of the battery.

[0092] It should also be understood that although the various steps in the above process flow diagrams are shown in sequence according to the indication of the arrows, these steps are not necessarily executed in the order indicated by the arrows. Moreover, at least a part of the steps in the above process flow diagrams may include multiple steps or multiple stages, and these steps or stages are not necessarily executed and completed at the same moment, nor are they necessarily carried out in sequence.

[0093] In step S1, the mass ratio of the silicon-based material, the conductive agent, and the first binder can be (92 - 95):(2 - 5):(2 - 3). Controlling the mass ratio of the silicon-based material, the conductive agent, and the first binder within the above range can, while better improving the capacity of the finally prepared negative electrode sheet, take into account the conductivity and mechanical strength of the negative electrode sheet, thereby further improving the capacity and cycle stability of the battery.

[0094] In some specific embodiments, based on the total weight of the silicon-based material, the conductive agent, and the first binder being 100%, the weight percentage of the silicon-based material can be 92% - 95%, the weight percentage of the conductive agent can be 2% - 5%, and the weight percentage of the first binder can be 2% - 3%.

[0095] The embodiments of the present application do not particularly limit the types of the silicon-based material, the conductive agent, the first binder, and the first solvent. Any silicon-containing material, conductive agent, binder, and solvent well-known to those skilled in the art that can be used to prepare the negative electrode slurry can be adopted.

[0096] Exemplarily, the silicon-based material can include at least one of silicon monoxide, silicon carbide, and silicon. The conductive agent can include at least one of conductive carbon black, carbon nanotubes, and graphene. The first binder can include at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyamide, polyvinyl alcohol, and polyimide. The first solvent can include water.

[0097] For step S2, in actual processes, for example, a coater can be used to uniformly coat the first slurry on the surface of the current collector. After the first drying treatment, a first active material layer is formed on the surface of the current collector. In a specific embodiment, the temperature of the first drying treatment can be 80°C - 120°C, for example, it can be 80°C, 90°C, 100°C, 110°C, 120°C, or any value between any two of the above numerical ranges. This can fully carry out drying while avoiding affecting the quality of the formed first active material layer.

[0098] In some specific embodiments, after forming the first active material layer on the surface of the current collector, the method for preparing the negative electrode sheet may further include: rolling the first active material layer. By rolling the first active material layer in this way and then coating other slurries, the processing performance of the electrode sheet can be better ensured, which is beneficial to improving the film surface state of other film layers formed on the first active material layer subsequently, and further improving the comprehensive performance of the finally prepared negative electrode sheet.

[0099] In some embodiments, the thickness of the first active material layer prepared in step S2 may be 70 μm to 90 μm. For example, it may be 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, or any value between any two of the above numerical ranges. Controlling the thickness of the first active material layer within the above range can better balance the capacity and cycling performance of the finally prepared negative electrode sheet, which is beneficial to further improving the comprehensive performance of the negative electrode sheet.

[0100] It should be noted that in the case of rolling the first active material layer, the thickness of the above first active material layer refers to the thickness of the first active material layer after rolling treatment.

[0101] The embodiments of the present application do not have a special limitation on the type of the current collector, and a negative electrode current collector well-known to those skilled in the art can be used. Exemplarily, the current collector may include a copper foil.

[0102] Furthermore, the thickness of the current collector may be 7 μm to 15 μm. In this way, the formed first active material layer and solid electrolyte layer can be better loaded by the current collector, taking into account the mechanical strength and electrochemical performance of the negative electrode sheet.

[0103] For step S3, in the actual process, trimethylaluminum (TMA) can be heated to form a vapor at 97 °C to 103 °C, and polyethylene oxide (PEO) is placed in the vapor atmosphere of TMA to obtain PEO adsorbed with TMA (i.e., modified polyethylene oxide).

[0104] In step S4, under the action of an initiator, a cross-linking reaction can be initiated to form a viscoelastic gel-like substance, which can form a solid electrolyte layer with high elasticity and high toughness after subsequent drying.

[0105] In a specific embodiment, the initiator may include water, and water can react with the TMA adsorbed in PEO to initiate in-situ cross-linking of Al-O. The Al-O clusters will further cross-link with the PEO chains, thereby forming a gel-like substance. Of course, the embodiments of the present application do not exclude the case of using other types of initiators to initiate cross-linking reactions to form gel-like substances.

[0106] In some embodiments, the molar ratio of trimethylaluminum to the initiator can be 1:(0.9 - 1.1). When the initiator is water, the molar ratio of trimethylaluminum to water can be 1:1, which can better control the degree of crosslinking and further promote the formation of the gel.

[0107] In some embodiments, in step S4, the mass ratio of the modified polyethylene oxide, the inorganic lithium salt, and the second solvent can be 2:(2.9 - 3.1):(2.9 - 3.1). Controlling the mass ratio of the modified polyethylene oxide, the inorganic lithium salt, and the second solvent within the above range is beneficial to promoting the crosslinking reaction, enabling the content of the inorganic lithium salt in the subsequent prepared solid electrolyte layer to be within a suitable range, thereby being beneficial to improving the toughness of the solid electrolyte layer. It can effectively inhibit the volume expansion of the first active material layer while further enhancing the stability and electrochemical performance of the SEI film, further promoting the desolvation of active ions, and thus further improving the capacity, cycle stability, and low-temperature performance of the battery.

[0108] Exemplarily, the inorganic lithium salt can include at least one of Li3PO4, LiF, Li2O, Li2SO3, and Li2CO3. The second solvent can include anhydrous acetonitrile (SN) and / or anhydrous dimethylformamide (DMF).

[0109] For step S5, in the actual preparation process, the gel-like substance can be coated on the first active material layer by means of doctor blade coating, and after the second drying treatment, a solid electrolyte layer is obtained.

[0110] In a specific embodiment, the temperature of the second drying treatment can be 60°C - 135°C.

[0111] Furthermore, the temperature of the second drying treatment can be adjusted according to the type of the second solvent. For example, when the second solvent includes anhydrous acetonitrile, the temperature of the second drying treatment can be 60°C - 80°C, which can better ensure the effect of the drying treatment. When the second solvent includes anhydrous dimethylformamide, the temperature of the second drying treatment can be 125°C - 135°C, which can better ensure the effect of the drying treatment.

[0112] In some embodiments, the thickness of the solid electrolyte layer prepared in step S5 can be 10μm - 15μm, for example, it can be 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, or any value between any two of the above numerical ranges. Controlling the thickness of the solid electrolyte layer within the above range can better inhibit the volume expansion of the first active material layer while taking into account the overall capacity, cycle stability, and low-temperature performance of the negative electrode sheet.

[0113] In some embodiments, before coating the gel-like material on the first active material layer, the method for preparing the negative electrode sheet may further include: adding carbon fiber and a second binder into a third solvent, and after mixing, obtaining a second slurry; coating the second slurry on the first active material layer, and after a third drying treatment, obtaining a second active material layer.

[0114] In the embodiments of the present application, before preparing the solid electrolyte layer, a second active material layer including carbon fiber is first prepared on the first active material layer, that is, a second active material layer is added between the first active material layer and the solid electrolyte layer. Thus, the second active material layer can not only serve as an active material layer to further improve the capacity of the negative electrode sheet, but also enhance the wetting of the negative electrode sheet by the electrolyte and serve as a liquid absorption layer to improve the liquid absorption and liquid retention capabilities of the negative electrode sheet; moreover, the high toughness and nano-scale pore structure of the carbon fiber help to provide a space for releasing stress when the first active material layer expands in volume, thereby further improving the mechanical strength of the negative electrode sheet, maintaining the integrity of the structure of the negative electrode sheet, and further improving the cycle stability of the battery.

[0115] In some embodiments, the mass ratio of the carbon fiber to the second binder may be (96-98):(2-4). Thus, while ensuring the mechanical strength of the obtained second active material layer, the capacity and cycle stability of the negative electrode sheet can be further improved through the second active material layer.

[0116] In some specific embodiments, based on the total weight of the carbon fiber and the second binder being 100%, the weight percentage of the carbon fiber may be 96%-98%, and the weight percentage of the second binder may be 2%-4%. Exemplarily, the carbon fiber may include activated carbon fiber, because the activated carbon fiber not only has high toughness but also is covered with nano-scale micropores on its surface, has a rich pore structure, a large specific surface area, and usually contains oxygen / nitrogen atom doping, which can further improve the performance of the obtained second active material layer. The second binder may include at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyamide, polyvinyl alcohol, and polyimide. The third solvent may include water.

[0117] In some embodiments, the temperature of the third drying treatment may be 80°C-120°C, for example, it may be 80°C, 90°C, 100°C, 110°C, 120°C, or any value between any two of the above numerical ranges. Thus, it can be fully dried while avoiding affecting the quality of the formed second active material layer.

[0118] In some specific embodiments, after forming the second active material layer on the surface of the first active material layer, the method for preparing the negative electrode sheet may further include: performing a rolling process on the first active material layer and the second active material layer. In this way, through the rolling process and then coating other slurries, the processing performance of the electrode sheet can be better ensured, which is beneficial to improving the film surface state of other film layers (such as the solid electrolyte layer) formed on the second active material layer subsequently, and further improving the comprehensive performance of the finally prepared negative electrode sheet.

[0119] Compared with the first active material layer including a silicon-based material, the second active material layer including carbon fiber can provide limited capacity. Moreover, when the second active material layer plays the role of enhancing the liquid absorption and retention capacity of the negative electrode sheet and providing a space for releasing stress caused by the volume expansion of the first active material layer, the requirement for thickness is not high. Therefore, an overly thick or heavy second active material layer is instead not conducive to improving the volume or mass energy density of the battery. Thus, in the actual preparation process, the coating surface density of the second slurry can be less than that of the first slurry. By controlling the coating surface density, the thickness of the second active material layer can be controlled to be less than that of the first active material layer. In this way, the comprehensive performance of the finally prepared negative electrode sheet can be further improved.

[0120] In some specific embodiments, the thickness of the second active material layer can be 30 μm to 40 μm, for example, it can be 30 μm, 35 μm, 40 μm, or any value within any two of the above numerical ranges. In this way, while the second active material layer can better enhance the liquid absorption and retention capacity of the negative electrode sheet and provide a space for releasing stress caused by the volume expansion of the first active material layer, the capacity of the negative electrode sheet can be better balanced.

[0121] It should be noted that in the case of performing the rolling process, the thicknesses of the above-mentioned first active material layer and second active material layer are both the thicknesses after the rolling process.

[0122] The embodiment of the present application also provides a battery, which includes the negative electrode sheet described in any of the above embodiments or a negative electrode sheet prepared by the method for preparing the negative electrode sheet described in any of the above embodiments.

[0123] It should be understood that since the battery in the embodiment of the present application includes the negative electrode sheet described in any of the above embodiments or a negative electrode sheet prepared by the method for preparing the negative electrode sheet described in any of the above embodiments, therefore, the beneficial effects of the negative electrode sheet in the above embodiments are all applicable to this battery. The battery in the embodiment of the present application has both high capacity, high cycle stability, and excellent low-temperature performance.

[0124] In some embodiments, the battery may be a secondary battery, such as a lithium-ion battery. Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charging and discharging process of the battery, active ions are intercalated and deintercalated back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting active ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, mainly to prevent short circuit between the positive and negative electrodes, and at the same time allows active ions to pass through.

[0125] In the actual preparation process of the battery, first, the positive electrode sheet, the separator, the negative electrode sheet, and the separator can be stacked in sequence, and a bare battery cell can be obtained after assembly. The assembly method can be, for example, a stacking or winding method; then, the electrolyte is injected into the dry bare battery cell, and a secondary battery can be obtained after formation and aging. The negative electrode sheet is the negative electrode sheet described in any of the above embodiments or the negative electrode sheet prepared by the preparation method of the negative electrode sheet described in any of the above embodiments.

[0126] The technical solution of the present application will be further described below in conjunction with multiple embodiments and comparative examples.

[0127] Example 1

[0128] The preparation of the negative electrode sheet in this example includes the following steps:

[0129] Step S101: Silicon (silicon-based material), conductive carbon black (conductive agent), and CMC (first binder) are added to water (first solvent) according to a mass ratio of 93:4:3, and mixed and stirred to form a uniform first slurry;

[0130] Step S102: The first slurry prepared in step S101 is coated on a copper foil (current collector) by a coater, and dried in an oven at 100 °C (first drying treatment) to obtain a first active material layer, and the dried electrode sheet is rolled; after the rolling treatment, the thickness of the first active material layer is 85 μm;

[0131] Step S103: At 100 °C, trimethylaluminum (TMA) is heated to form steam, and polyethylene oxide PEO is placed in the steam environment of TMA to obtain PEO adsorbed with TMA (modified polyethylene oxide);

[0132] Step S104: Lithium phosphate (Li3PO4) and the PEO powder adsorbed with TMA prepared in step S103 are added to anhydrous acetonitrile (SN) (second solvent), stirred, and after being dispersed evenly, water (initiator) equimolar to TMA is added to initiate in-situ crosslinking of Al-O, and then a gel-like substance is obtained; wherein, the mass ratio of the PEO powder adsorbed with TMA, SN, and Li3PO4 is 2:3:3;

[0133] Step S105: Coat the gel-like substance prepared in Step S104 on the first active material layer, bake at 70 °C to remove SN, and form a solid electrolyte layer on the first active material layer to obtain a negative electrode sheet, where the thickness of the solid electrolyte layer is 13 μm.

[0134] Example 2

[0135] The preparation of the negative electrode sheet in this example includes the following steps:

[0136] Step S201: Add silicon (silicon-based material), conductive carbon black (conductive agent), and CMC (first binder) to water (first solvent) in a mass ratio of 93:4:3, and perform mixing and stirring to form a uniform first slurry;

[0137] Step S202: Use a coater to coat the first slurry prepared in Step S201 on a copper foil (current collector), and perform drying treatment (first drying treatment) in an oven at 100 °C to obtain a first active material layer, and perform rolling treatment on the dried electrode sheet;

[0138] Step S203: Add activated carbon fiber and CMC (second binder) to water (third solvent) in a mass ratio of 97:3, and perform mixing and stirring to form a uniform second slurry;

[0139] Step S204: Use a coater to coat the second slurry prepared in Step S203 on the first active material layer, and perform drying treatment (third drying treatment) in an oven at 100 °C to obtain a second active material layer, and perform rolling treatment on the dried electrode sheet; after the rolling treatment, the thickness of the first active material layer is 80 μm, and the thickness of the second active material layer is 35 μm;

[0140] Step S205: At 100 °C, heat trimethylaluminum (TMA) to form vapor, and place polyethylene oxide PEO in the vapor environment of TMA to obtain PEO adsorbed with TMA (modified polyethylene oxide);

[0141] Step S206: Add lithium phosphate (Li3PO4) and the PEO powder adsorbed with TMA prepared in Step S205 to anhydrous acetonitrile (SN) (second solvent), stir, and after uniform dispersion, add water (initiator) in an equimolar amount to TMA to initiate in-situ crosslinking of Al-O, and then obtain a gel-like substance; where the mass ratio of the PEO powder adsorbed with TMA, SN, and Li3PO4 is 2:3:3;

[0142] Step S207: Coat the gel-like substance prepared in Step S206 on the second active material layer, bake at 70 °C to remove SN, and form a solid electrolyte layer on the second active material layer to obtain a negative electrode sheet, where the thickness of the solid electrolyte layer is 13 μm.

[0143] Comparative Example 1

[0144] The preparation of the negative electrode sheet in this comparative example includes the following steps:

[0145] Step S301: Add silicon, conductive carbon black, and CMC to water according to a mass ratio of 93:4:3, and perform mixing and stirring to form a uniform negative electrode paste;

[0146] Step S302: Use a coater to coat the negative electrode paste prepared in Step S301 on a copper foil, and perform drying treatment in an oven at 100°C to obtain a negative electrode active material layer, and perform rolling treatment on the dried electrode sheet to obtain a negative electrode sheet; among them, in the obtained negative electrode sheet, the thickness of the negative electrode active material layer is 120 μm.

[0147] Comparative Example 2

[0148] The preparation of the negative electrode sheet in this comparative example includes the following steps:

[0149] Step S401: Add silicon, conductive carbon black, and CMC to water according to a mass ratio of 93:4:3, and perform mixing and stirring to form a uniform first negative electrode paste;

[0150] Step S402: Use a coater to coat the first negative electrode paste prepared in Step S401 on a copper foil, and perform drying treatment in an oven at 100°C to obtain a first negative electrode active material layer, and perform rolling treatment on the dried electrode sheet;

[0151] Step S403: Add activated carbon fiber and CMC to water according to a mass ratio of 97:3, and perform mixing and stirring to form a uniform second negative electrode paste;

[0152] Step S404: Use a coater to coat the second negative electrode paste prepared in Step S403 on the first negative electrode active material layer, and perform drying treatment in an oven at 100°C to obtain a second negative electrode active material layer, and perform rolling treatment on the dried electrode sheet to obtain a negative electrode sheet; among them, in the obtained negative electrode sheet, the thickness of the first negative electrode active material layer is 85 μm, and the thickness of the second negative electrode active material layer is 35 μm.

[0153] Prepare the negative electrode sheets obtained in the above examples and comparative examples into batteries to test the electrochemical performance of the batteries.

[0154] The preparation steps of the battery are as follows: Add the cathode active material NCM811, conductive carbon black, and PVDF to N-methylpyrrolidone (NMP) in a mass ratio of 86:7:7, stir evenly to obtain the cathode slurry. Use a coater to evenly coat the cathode slurry on aluminum foil, dry it at 80 °C, and then roll it to obtain the cathode sheet; the anode sheet is the anode sheet prepared in the above examples and comparative examples; the separator is a polypropylene film; the electrolyte is a solution of 1 mol / L LiTFSI in a mixture of 1,3-dioxolane (DOL) and dimethyl carbonate (DMC) with a volume ratio of 1:1. Cut the above-mentioned cathode sheet and anode sheet into circular pieces with a diameter of 1.2 cm, put them into a glove box, and then assemble a button battery in the glove box under argon protection. Among them, the order of assembling the battery is negative electrode shell - anode sheet - separator - cathode sheet - gasket - spring piece - positive electrode shell. After the battery assembly is completed, let it stand for 12 h.

[0155] Test the performance of the assembled battery. The specific tests are as follows:

[0156] (1) Room temperature discharge capacity and room temperature capacity retention rate test: First, let the battery stand at 25 °C for 1 h. Next, discharge it at a constant current of 0.33C to 2.5V, stand for 30 min, then charge it at a constant current of 0.33C to 4.3V, and then charge it at a constant voltage of 4.3V until the current is less than or equal to 0.05C, and then stand for 30 min. Next, discharge it at a constant current of 0.33C to 2.5V, and then discharge it at a constant voltage of 2.5V until the current is less than or equal to 0.05C. Record the discharge capacity at this time as the room temperature discharge capacity, that is, the discharge capacity of the first cycle. Next, stand for 30 min, continue the cycle, and record the discharge capacity of the battery when it reaches the 500th cycle, that is, the discharge capacity of the 500th cycle. The room temperature capacity retention rate of the 500th cycle = (discharge capacity of the 500th cycle / discharge capacity of the first cycle) × 100%.

[0157] (2) Low-temperature discharge capacity and low-temperature capacity retention rate test: The test steps are basically the same as those of the above room temperature discharge capacity and room temperature capacity retention rate test, except that: First, let the battery stand at -20 °C for 1 h, and then conduct the test to obtain the low-temperature discharge capacity and the low-temperature capacity retention rate of the 500th cycle.

[0158] The test results of the above tests are shown in Table 1.

[0159] Table 1

[0160]

[0161] As can be seen from the data in Table 1, compared with Comparative Example 1 and Comparative Example 2, for the batteries containing the negative electrode sheets prepared in Example 1 and Example 2, the capacity retention rates at room temperature and low temperature after the 500th cycle are significantly improved, that is, the cycle stability of the batteries is significantly improved. At the same time, the discharge capacities at room temperature and low temperature are also at a relatively high level. This shows that in the present application, first, a first active material layer is formed on at least one surface of the current collector, and then a solid electrolyte layer is formed on the first active material layer; the first active material layer includes a silicon-based material, which is beneficial to improving the capacity of the negative electrode sheet. The three-dimensional network cross-linked product of polyethylene oxide and trimethylaluminum in the solid electrolyte layer endows the solid electrolyte layer with high fracture toughness, so that the volume expansion of the first active material layer can be effectively inhibited during charge and discharge, ensuring that the SEI film is not easily broken, improving the stability of the SEI film, inhibiting the irreversible consumption of active ions, and further improving the capacity and cycle stability of the battery. In addition, in the solid electrolyte layer, the inorganic lithium salt is located in the pores of the three-dimensional network cross-linked product of polyethylene oxide and trimethylaluminum. Even when a high-concentration inorganic lithium salt is added, the solid electrolyte layer can still exhibit good elasticity and toughness, endowing the solid electrolyte layer with high fracture toughness and being beneficial to constructing an SEI film rich in lithium salt, which can further improve the stability of the SEI film, promote the desolvation of active ions, thereby accelerating the transport of active ions at the electrode-electrolyte interface and improving the kinetic performance of active ions at low temperature, and further improving the low-temperature performance of the battery.

[0162] The negative electrode sheet in Comparative Example 1 includes a single-layer silicon-containing active material layer. As can be seen from the data in Table 1, although the use of silicon material is beneficial to improving the capacity of the negative electrode sheet, resulting in a relatively high room-temperature discharge capacity of the corresponding battery, due to the large volume expansion of the silicon material during the cycle, it is difficult to form a stable SEI film at the interface between the negative electrode and the electrolyte, resulting in poor cycle stability of the negative electrode sheet in Comparative Example 1, and relatively low low-temperature discharge capacity, room-temperature and low-temperature capacity retention rates after the 500th cycle of the corresponding battery, and poor comprehensive performance of the battery.

[0163] The negative electrode sheet in Comparative Example 2 includes a silicon-containing active material layer and an activated carbon fiber layer stacked in sequence on the current collector. As can be seen from the data in Table 1, since the activated carbon fiber layer enhances the liquid absorption and retention capacity of the electrode sheet, and the activated carbon fiber layer has good toughness and can provide a certain stress relief space for the volume expansion of the silicon-containing active material layer, the cycle stability of the battery containing the negative electrode sheet prepared in Comparative Example 2 is slightly improved compared with Comparative Example 1. However, compared with Example 1 and Example 2, the comprehensive performance of the battery corresponding to Comparative Example 2 is still poor.

[0164] Compared with Example 1, in Example 2, a second active material layer containing activated carbon fibers is added between the first active material layer and the solid electrolyte layer. The second active material layer can not only act as an active material layer to further improve the capacity of the negative electrode sheet, but also enhance the wetting of the negative electrode sheet by the electrolyte and act as a liquid absorption layer to improve the liquid absorption and liquid retention capabilities of the negative electrode sheet. Moreover, the high toughness and nano-scale pore structure of carbon fibers help to provide a space for releasing stress when the first active material layer expands in volume, thereby further improving the mechanical strength of the negative electrode sheet, maintaining the integrity of the negative electrode sheet structure, and further improving the cycle stability of the battery. This is consistent with the test results in Table 1. This shows that in the negative electrode sheet of the present application, by sequentially laminating the first active material layer, the second active material layer, and the solid electrolyte layer on the current collector, the three layers can cooperate to better improve the comprehensive performance of the battery, which is a relatively preferred solution.

[0165] In the negative electrode sheet structure proposed by the present invention, a solid electrolyte layer rich in inorganic lithium salts with high fracture toughness (which can also be called an artificial solid electrolyte membrane or an artificial SEI layer) is constructed on the first active material layer containing a silicon-based material, which can better inhibit the volume expansion of the first active material layer, maintain the integrity of the electrode sheet structure, form a stable SEI film at the electrode and electrolyte interface, and thus, while ensuring the battery has a high capacity, take into account high cycle stability and excellent low-temperature performance.

[0166] It should be noted that the negative electrode sheet embodiments, the preparation method embodiments of the negative electrode sheet, and the battery embodiments provided in the present application belong to the same concept; among the technical features in the technical solutions recorded in each embodiment, they can be arbitrarily combined without conflict.

[0167] It should be understood that the above embodiments are all exemplary and do not cover all possible implementation manners of the present application. Without departing from the scope of the present disclosure, various deformations and changes can also be made on the basis of the above embodiments. Similarly, the technical features of the above embodiments can also be arbitrarily combined to form other embodiments of the present invention that may not be clearly described. Therefore, the above embodiments only represent several implementation manners of the present invention and do not limit the protection scope of the present invention patent.

Claims

1. A negative electrode sheet, characterized in that, Comprising: A current collector and a first active material layer and a solid electrolyte layer disposed on at least one surface of the current collector, the first active material layer being located between the current collector and the solid electrolyte layer; The first active material layer includes a silicon-based material; The solid electrolyte layer includes a three-dimensional network cross-linked product of polyethylene oxide and trimethylaluminum and an inorganic lithium salt located in the pores of the three-dimensional network cross-linked product.

2. The negative electrode sheet according to claim 1, characterized in that, The negative electrode sheet satisfies at least one of the following characteristics: (1) The first active material layer further includes a conductive agent and a first binder, and the mass ratio of the silicon-based material, the conductive agent, and the first binder is (92-95):(2-5):(2-3); Optionally, the conductive agent includes at least one of conductive carbon black, carbon nanotubes, and graphene; Optionally, the first binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyamide, polyvinyl alcohol, and polyimide; (2) The inorganic lithium salt includes at least one of Li3PO4, LiF, Li2O, Li2SO3, and Li2CO3; (3) The mass ratio of the three-dimensional network cross-linked product to the inorganic lithium salt is 2:(3-3.1); (4) The thickness of the first active material layer is 70 μm to 90 μm; (5) The thickness of the solid electrolyte layer is 10 μm to 15 μm; (6) The thickness of the current collector is 7 μm to 15 μm.

3. The negative electrode sheet according to claim 1 or 2, characterized in that The negative electrode sheet further includes a second active material layer located between the first active material layer and the solid electrolyte layer, and the second active material layer includes carbon fibers.

4. The negative electrode sheet according to claim 3, wherein The second active material layer satisfies at least one of the following characteristics: (1) The second active material layer further includes a second binder, and the mass ratio of the carbon fibers and the second binder is (96-98):(2-4); Optionally, the second binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyamide, polyvinyl alcohol, and polyimide; (2) The thickness of the second active material layer is less than the thickness of the first active material layer; (3) The thickness of the second active material layer is 30 μm to 40 μm.

5. A method for preparing a negative electrode sheet, characterized in that, The method includes the following steps: Adding a silicon-based material, a conductive agent, and a first binder to a first solvent, and after mixing, obtaining a first slurry; Coating the first slurry on at least one surface of the current collector, and after a first drying treatment, obtaining a first active material layer; Placing polyethylene oxide in a vapor atmosphere of trimethylaluminum to obtain a modified polyethylene oxide adsorbed with trimethylaluminum; Adding the modified polyethylene oxide and an inorganic lithium salt to a second solvent, mixing, and adding an initiator to carry out a cross-linking reaction to obtain a gel-like substance; Coating the gel-like substance on the first active material layer, and after a second drying treatment, obtaining a solid electrolyte layer.

6. The method for preparing a negative electrode sheet according to claim 5, wherein The step of preparing the first active material layer satisfies at least one of the following characteristics: (1) The mass ratio of the silicon-based material, the conductive agent, and the first binder is (92-95):(2-5):(2-3); (2) The conductive agent includes at least one of conductive carbon black, carbon nanotubes, and graphene; (3) The first binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyamide, polyvinyl alcohol, and polyimide; (4) The temperature of the first drying treatment is 80°C to 120°C; (5) The thickness of the first active material layer is 70 μm to 90 μm; (6) The thickness of the current collector is 7 μm to 15 μm.

7. The method for preparing a negative electrode sheet according to claim 5, characterized in that, The steps for preparing the solid electrolyte layer satisfy at least one of the following characteristics: (1) The vapor atmosphere of trimethylaluminum is the vapor atmosphere formed by heating trimethylaluminum at 97°C to 103°C; (2) The inorganic lithium salt includes at least one of Li3PO4, LiF, Li2O, Li2SO3, and Li2CO3; (3) The second solvent includes anhydrous acetonitrile and / or anhydrous dimethylformamide; (4) The mass ratio of the modified poly(ethylene oxide), the inorganic lithium salt, and the second solvent is 2:(2.9 - 3.1):(2.9 - 3.1); (5) The initiator includes water; (6) The molar ratio of trimethylaluminum to the initiator is 1:(0.9 - 1.1); (7) The temperature of the second drying treatment is 60°C to 135°C; (8) The thickness of the solid electrolyte layer is 10 μm to 15 μm.

8. The method for preparing the negative electrode sheet according to any one of claims 5 to 7, characterized in that, Before coating the gel-like material on the first active material layer, the method further includes: Adding carbon fiber and a second binder to a third solvent, and after mixing, obtaining a second slurry; Coating the second slurry on the first active material layer, and after a third drying treatment, obtaining a second active material layer.

9. The method for preparing a negative electrode sheet according to claim 8, wherein The method satisfies at least one of the following characteristics: (1) The mass ratio of the carbon fiber and the second binder is (96 - 98):(2 - 4); (2) The second binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyamide, polyvinyl alcohol, and polyimide; (3) The temperature of the third drying treatment is 80°C to 120°C; (4) The thickness of the second active material layer is less than the thickness of the first active material layer; (5) The thickness of the second active material layer is 30 μm to 40 μm.

10. A battery, characterized in that, A negative electrode sheet prepared by the method for preparing a negative electrode sheet according to any one of claims 1 to 4 or a negative electrode sheet prepared by the method for preparing a negative electrode sheet according to any one of claims 5 to 9.

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