Negative electrode sheet, method for manufacturing the same, and battery

Abstract

The application relates to the technical field of batteries, in particular to a negative electrode sheet, a preparation method thereof and a battery. The negative electrode sheet comprises a negative electrode current collector and a composite layer; the first negative electrode active material in the composite layer comprises lithium metal particles and a first SEI film coated on the surface of the lithium metal particles, and the first SEI film comprises a first functional layer; the second negative electrode active material in the composite layer comprises nano-silicon particles and a second SEI film coated on the surface of the nano-silicon particles, and the second SEI film comprises a second functional layer; the first functional layer and the second functional layer independently comprise an A substance and a lithium-containing compound, the A substance comprises a weak acid salt containing M and / or an organic salt containing M, wherein M is Zn and / or Mg. The negative electrode sheet can realize the rapid migration of lithium ions between the lithium metal negative electrode and the silicon electrode, and can inhibit the direct reduction of the lithium ions on the interface, thereby inhibiting the nucleation and growth kinetics of lithium dendrites and being beneficial to improving the cycle performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to negative electrode sheets, their preparation methods, and batteries. Background Technology

[0002] In next-generation lithium batteries, lithium metal and silicon anodes are considered key areas of focus for battery development. Lithium metal anodes are particularly advantageous due to their extremely low electrochemical potential (-3.040 V, compared to a standard hydrogen electrode) and extremely high theoretical specific capacity (3860 mAh·g). -1 Lithium has become a key material in lithium metal batteries. However, traditional lithium metal anodes use lithium foil as the active material, which has a small specific surface area, poor reaction kinetics, and disordered deposition of lithium ions on the lithium foil surface, leading to volume changes and making it unsuitable for high-rate charge-discharge cell designs. Silicon anodes, on the other hand, are limited in their further application due to poor conductivity and irreversible capacity decay caused by significant volume expansion during charge-discharge.

[0003] During use, lithium metal and silicon anodes naturally form an SEI film. This naturally formed SEI film exhibits uneven distribution of components in the bulk phase, resulting in an unstable structure and poor flexibility. For lithium metal anodes, lithium ions (Li...) + During migration, lithium ions can deposit unevenly on the surface of the lithium metal anode, leading to the formation of dead lithium and lithium dendrites. Sharp lithium dendrites can pierce the separator, causing a short circuit between the positive and negative electrodes, resulting in serious safety issues. Furthermore, the volume expansion accompanying lithium ion insertion and extraction causes the SEI film to break down, allowing the bulk structure to re-react with the electrolyte and rebuild the SEI film. This process consumes electrolyte while simultaneously thickening the SEI film, increasing R... SEI Increased polarization leads to decreased cycle life. Furthermore, the uneven thickness of the SEI film formed between the lithium metal and the silicon anode results in varying local current densities and inconsistent lithium-ion deposition rates, creating a loose, porous "lithium sponge" on the lithium metal surface. This increases cell thickness and reduces cycle performance. Additionally, naturally formed SEI films exhibit poor electrochemical stability, readily oxidizing at high voltages. The oxidation and decomposition of the SEI film produces gas, and it is prone to detachment during cycling, leaking onto the electrode surface and triggering the growth of new SEI films, leading to the loss of active lithium ions. Summary of the Invention

[0004] In view of this, the present invention provides a negative electrode sheet, its preparation method, and a battery. The negative electrode sheet comprises lithium metal particles and nano-silicon particles, both of which have an artificially synthesized in-situ SEI film on their surfaces. This SEI film possesses excellent ionic conductivity and electronic insulation, enabling rapid migration of lithium ions between the lithium metal negative electrode and the silicon electrode, while simultaneously suppressing direct reduction of lithium ions at the interface, thereby inhibiting lithium dendrite nucleation and growth kinetics. Furthermore, the in-situ SEI film exhibits uniform phase distribution, structural stability, and good flexibility, which is beneficial for improving cycle performance. Lithium metal particles have a larger specific surface area than lithium foil, increasing the reactive surface area of ​​lithium metal and resulting in better reaction kinetics; the close contact between the lithium metal particles and the nano-silicon particles suppresses volume expansion of the silicon negative electrode during charge and discharge, increasing the cycle stability of the silicon negative electrode.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] In a first aspect, the present invention provides a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a composite layer disposed on at least one side surface of the negative electrode current collector;

[0007] The composite layer includes a first negative electrode active material and a second negative electrode active material;

[0008] The first negative electrode active material includes lithium metal particles and a first SEI film coated on the surface of the lithium metal particles. The first SEI film includes a first functional layer.

[0009] The second negative electrode active material includes nano-silicon particles and a second SEI film coated on the surface of the nano-silicon particles. The second SEI film includes a second functional layer.

[0010] The first and second functional layers independently include substance A and lithium-containing compounds. Substance A includes weak acid salts containing M and / or organic salts containing M, wherein M is Zn and / or Mg.

[0011] Preferably, substance A includes at least one of silicate, acetate, citrate, and lactate.

[0012] Preferably, substance A includes at least one of zinc silicate, magnesium silicate, zinc acetate, magnesium acetate, zinc citrate, magnesium citrate, zinc lactate, and magnesium lactate.

[0013] More preferably, substance A is zinc silicate.

[0014] In embodiments of the present invention, the lithium-containing compounds in the first functional layer and the second functional layer include at least one of organic lithium salts, inorganic lithium salts, Li2O, and LiOH.

[0015] As a preferred embodiment, the mass ratio of lithium metal particles, nano-silicon particles, substance A, and lithium-containing compound is (10-40):(5-30):(5-25g):(0.05-1).

[0016] Preferably, the particle size D of the lithium metal particles is... 50 The range is 0.1–100 μm.

[0017] Preferably, the particle size D of the nano-silicon particles is... 50 The wavelength range is 50–500 nm.

[0018] Preferably, the thicknesses of the first functional layer and the second functional layer are independently 1 to 500 nm.

[0019] In another embodiment of the present invention, the first SEI film further includes a mixing layer disposed between the lithium metal particles and the first functional layer, the mixing layer comprising a lithiophilic component, a continuously conducting lithium-ion component, and a lithium-containing compound.

[0020] In embodiments of the present invention, the lithiophilic component includes M metal and Li-M alloy, wherein M is Zn and / or Mg.

[0021] In embodiments of the present invention, the continuous lithium-ion component includes weak acid salts and / or organic salts of lithium, Li2O and LiOH.

[0022] In embodiments of the present invention, the lithium-containing compound in the mixed layer includes at least one of an organic salt of lithium, an inorganic salt of lithium, Li2O, and LiOH.

[0023] Preferably, in the mixed layer, the mass ratio of the lithiophilic component, the continuous lithium-ion conducting component, and the lithium-containing compound is (5-50):(5-50):(0.05-1).

[0024] Preferably, the thickness of the hybrid layer is 5–200 nm.

[0025] Preferably, the thickness ratio of the first functional layer to the hybrid layer is (1-100):(1-200).

[0026] In an embodiment of the present invention, the first negative electrode active material and the second negative electrode active material in the composite layer have a tightly stacked structure.

[0027] Preferably, the composite layer further includes a conductive agent and a binder, and the composite layer satisfies at least one of the following (1) to (3):

[0028] (1) The mass ratio of lithium metal particles, nano-silicon particles, and conductive agent is (10-40):(5-30):(0.5-3g);

[0029] (2) The mass of lithium metal particles is denoted as m1, the mass of nano-silicon particles is denoted as m2, and the mass of conductive agent is denoted as m3. m1, m2, and m3 satisfy the following relationship:

[0030] 1 / 200≤m3 / (m1+m2)≤1 / 20;

[0031] (3) The total mass of the first negative electrode active material, the second negative electrode active material, and the conductive agent is denoted as X1, and the mass of the binder is denoted as X2. X1 and X2 satisfy the following relationship:

[0032] 20≤X1 / X2≤200.

[0033] Secondly, the present invention provides a method for preparing a negative electrode sheet, the method comprising the following steps:

[0034] S1, Mix substance A and electrolyte to obtain a mixed solution; the electrolyte includes lithium salt and organic solvent;

[0035] Substance A includes weak acid salts containing M and / or organic salts containing M, wherein M is Zn and / or Mg;

[0036] S2, lithium metal particles, nano-silicon particles and mixed solution are stirred and mixed, and then negatively charged to obtain reactants; the reactants are filtered and dried to obtain lithium silicon composites with in-situ grown SEI films.

[0037] The lithium-silicon composite with an in-situ grown SEI film includes a first negative electrode active material and a second negative electrode active material.

[0038] The first negative electrode active material includes lithium metal particles and a first SEI film coated on the surface of the lithium metal particles. The first SEI film includes a first functional layer.

[0039] The second negative electrode active material includes nano-silicon particles and a second SEI film coated on the surface of the nano-silicon particles. The second SEI film includes a second functional layer.

[0040] The first and second functional layers independently include substance A and lithium-containing compounds;

[0041] S3, prepare a slurry from a lithium-silicon composite with an in-situ grown SEI film, coat the slurry onto at least one side of the negative electrode current collector, and obtain a negative electrode sheet by hot pressing.

[0042] In embodiments of the present invention, the lithium salt includes at least one of LiFSI, LiPF6, LiClO4, LiTFSI, LiODFB, LiBF4, LiBOB, LiF, LiCl, Li2CO3, and LiOH.

[0043] Preferably, the concentration of lithium salt in the mixed solution is 0.5–2 mol / L.

[0044] Preferably, the concentration of substance A in the mixed solution is 0.01–0.5 mol / L.

[0045] Preferably, the negative current for the negative current treatment is 0.1 to 1 A, and the negative current treatment time is 10 to 90 min.

[0046] Preferably, the hot pressing temperature is 100–180°C, the hot pressing pressure is 1–20 kPa, and the hot pressing time is 5–60 min.

[0047] Thirdly, the present invention provides a battery comprising the above-described negative electrode sheet and / or a negative electrode sheet prepared by the above-described preparation method.

[0048] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0049] (1) The present invention provides a negative electrode sheet with an in-situ grown SEI film, the negative electrode sheet comprising a negative current collector and a composite layer disposed on at least one side surface of the negative current collector; the composite layer comprises a first negative electrode active material and a second negative electrode active material; the first negative electrode active material comprises lithium metal particles and a first SEI film coated on the surface of the lithium metal particles, the first SEI film comprising a first functional layer; the second negative electrode active material comprises nano-silicon particles and a second SEI film coated on the surface of the nano-silicon particles, the second SEI film comprising a second functional layer; the first functional layer and the second functional layer independently comprise a substance A and a lithium-containing compound, the substance A comprising a weak acid salt containing M and / or an organic salt containing M, wherein M is Zn and / or Mg. The first functional layer coated on the surface of lithium metal particles and the second functional layer coated on the surface of nano-silicon particles constitute an artificially synthesized in-situ SEI film. This SEI film has a nano-stacked structure, exhibiting excellent ionic conductivity and electronic insulation. It enables rapid migration of lithium ions between the lithium metal anode and the silicon electrode while suppressing direct reduction of lithium ions at the interface, thereby inhibiting lithium dendrite nucleation and growth kinetics. Furthermore, this in-situ SEI film has a uniform phase distribution, stable structure, and good flexibility, which is beneficial for improving cycle performance.

[0050] (2) In this invention, a mixed layer is further included between the lithium metal particles and the first functional layer. The mixed layer includes a lithiophilic component, a continuously conducting lithium-ion component, and a lithium-containing compound. The first functional layer and the mixed layer together constitute the first SEI film. Substance A reacts in situ with the surface of the lithium metal particles to generate a lithiophilic component including metal M and Li-M alloy (wherein M is Zn and / or Mg), and a continuously conducting lithium-ion component including a weak acid salt and / or organic salt of lithium, Li2O, and LiOH. Among them, the lithiophilic component can induce uniform deposition of lithium ions without generating lithium dendrites; the continuously conducting lithium-ion component can reduce R SEI (The resistance of lithium ions passing through the SEI film) accelerates the redox reaction at the negative electrode interface. Due to the stacking tendency of the low-crystallinity A-material nanoparticle structure, effective in-situ reaction transformation occurs, forming a dense structure of the lithiation product. Simultaneously, the lithiophilic component and the continuously conducting lithium-ion component can reduce surface resistance while promoting uniform lithium-ion deposition.

[0051] (3) In this invention, the volume expansion of nano-silicon particles during the charging and discharging process provides space for lithium ions to transfer within the electrode, forming in-situ pores inside the electrode and promoting the improvement of ion dynamics performance.

[0052] (4) In this invention, lithium metal particles have a larger specific surface area than lithium foil, which can increase the reactive surface area of ​​lithium metal and improve reaction kinetics.

[0053] (5) In step S3 of the preparation method of the present invention, the negative electrode sheet is subjected to hot pressing treatment, and the lithium metal particles are softened by hot melting. Under pressure, the lithium metal particles and nano silicon particles can be in closer contact, which can suppress the volume expansion of the silicon negative electrode during charging and discharging and increase the cycle stability of the silicon negative electrode. Attached Figure Description

[0054] Figure 1-1 A schematic diagram of the structure of a lithium powder anode material that has not undergone in-situ reaction and has no mixing layer.

[0055] Figure 1-2 A schematic diagram of the structure of a lithium powder anode material that undergoes in-situ reaction and has a mixed layer.

[0056] Figure 2 A schematic diagram of the structure of nano-silicon anode materials.

[0057] Figure 3-1 Schematic diagram of the Li@Si composite electrode.

[0058] Figure 3-2 A schematic diagram of the composite material in the Li@Si composite electrode composite layer.

[0059] Figure 4SEM image of Li@Si composite electrode. Detailed Implementation

[0060] This invention discloses a negative electrode sheet, its preparation method, and a battery. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired result. It is particularly important to note that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments. Those skilled in the art can clearly modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0061] In the description of this invention, it should be noted that the terms "first," "second," etc., are used for descriptive purposes only and are not intended to indicate or imply relative importance.

[0062] In the description of this invention, the list of items connected by the term "at least one of" or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then 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, then 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 may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0063] The endpoints and any values ​​of the ranges 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 endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0064] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0065] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0066] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0067] Specifically, the present invention adopts the following technical solution:

[0068] In a first aspect, the present invention provides a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a composite layer disposed on at least one side surface of the negative electrode current collector;

[0069] The composite layer includes a first negative electrode active material and a second negative electrode active material;

[0070] The first negative electrode active material includes lithium metal particles and a first SEI film coated on the surface of the lithium metal particles. The first SEI film includes a first functional layer.

[0071] The second negative electrode active material includes nano-silicon particles and a second SEI film coated on the surface of the nano-silicon particles. The second SEI film includes a second functional layer.

[0072] The first and second functional layers independently include substance A and lithium-containing compounds. Substance A includes weak acid salts containing M and / or organic salts containing M, wherein M is Zn (zinc) and / or Mg (magnesium).

[0073] In this invention, the first functional layer coated on the surface of lithium metal particles and the second functional layer coated on the surface of nano-silicon particles are artificially synthesized in-situ SEI films. These SEI films possess a nano-stacked structure, exhibiting excellent ionic conductivity and electronic insulation. This allows for rapid migration of lithium ions between the lithium metal anode and the silicon electrode, while simultaneously suppressing direct reduction of lithium ions at the interface, thereby inhibiting lithium dendrite nucleation and growth kinetics. Furthermore, the in-situ SEI film exhibits uniform phase distribution, structural stability, and good flexibility, which is beneficial for improving cycle performance. Simultaneously, the anode sheet of this invention utilizes the volume expansion of the nano-silicon particles during charge and discharge to provide space for ion transport within the electrode, forming in-situ pores within the electrode and promoting improved ion kinetics. The lithium metal particles have a larger specific surface area than lithium foil, increasing the reactive surface area of ​​the lithium metal and resulting in better reaction kinetics.

[0074] Preferably, substance A includes at least one of silicate, acetate, citrate, and lactate.

[0075] Preferably, substance A includes at least one of zinc silicate, magnesium silicate, zinc acetate, magnesium acetate, zinc citrate, magnesium citrate, zinc lactate, and magnesium lactate.

[0076] More preferably, substance A is zinc silicate. Compared to other types of substance A, zinc silicate has a suitable redox potential and metallic activity for lithium metal battery systems, making it easier for zinc silicate to undergo in-situ reactions with the surface of lithium metal particles, generating substances including Zn metal and Li. x Zn yThe lithium-loving component of the alloy and Li x SiO y The continuous lithium-ion-conducting components are Li₂O and LiOH. The zinc silicate nanoparticles with low crystallinity exhibit a tendency to stack, enabling efficient in-situ reaction transformation and forming a dense structure of the lithiation product.

[0077] In this invention, the first and second functional layers, in addition to substance A, also include lithium-containing compounds, which are conventional SEI film components. The lithium-containing compounds effectively prevent further decomposition of the electrolyte, protecting the electrode materials; regulate ion transport rates, improving battery energy density and cycle life; reduce side reactions, and improve battery safety and cycle stability. In embodiments of this invention, the lithium-containing compounds in the first and second functional layers include at least one of organic lithium salts, inorganic lithium salts, Li₂O, and LiOH. During the preparation of the negative electrode, different lithium salts and organic solvents will affect the specific composition of the lithium-containing compounds.

[0078] In embodiments of the present invention, among the specific types of lithium-containing compounds, the organic salt of lithium includes at least one of ROCO2Li, ROLi, and (ROCO2Li)2. Wherein, R is an alkyl group, such as methyl (-CH3), ethyl (-CH2CH3), etc.

[0079] In embodiments of the present invention, among the specific types of lithium-containing compounds, inorganic lithium salts include at least one of Li2CO3 and LiF.

[0080] Preferably, the mass ratio of lithium metal particles, nano-silicon particles, substance A, and lithium-containing compound is (10–40):(5–30):(5–25 g):(0.05–1). For example, the mass ratio of lithium metal particles, nano-silicon particles, substance A, and lithium-containing compound is any value from 30:10:11:0.5, 30:10:22:1, 30:10:5.6:0.25, 30:20:11:0.5, 30:5:11:0.5, 10:30:5:1, 40:5:25:0.05, or any value within the range of any two of the above ratios. Within this range, the thickness of the first and second functional layers is moderate, and the in-situ formed SEI film has good ionic conductivity and electronic insulation, enabling rapid migration of lithium ions between the lithium metal anode and the silicon electrode, while suppressing direct reduction of lithium ions at the interface, thereby inhibiting dendrite nucleation and growth kinetics.

[0081] Preferably, the particle size D of the lithium metal particles is... 50 The diameter ranges from 0.1 to 100 μm. For example, the particle size D of lithium metal particles... 50The particle size is any value from 0.1μm, 1μm, 10μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, and 100μm, or any value within the range of any two of the above values. Within this particle size range, lithium metal particles have a large specific surface area, which can increase the reactive surface area of ​​lithium metal and result in good reaction kinetics.

[0082] Preferably, the particle size D of the nano-silicon particles is... 50 The particle size is 50–500 nm. For example, the particle size D of the nano-silicon particles... 50 The value is any one of the following: 50nm, 100nm, 200nm, 300nm, 400nm, 500nm, or any value within the range of any two of the above values. Within this particle size range, it is beneficial to improve the performance of lithium-silicon composite materials.

[0083] Preferably, the thicknesses of the first and second functional layers are independently between 1 and 500 nm. For example, the thicknesses of the first and second functional layers are independently any value from 1 nm, 10 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, and 500 nm, or any value within a range formed by any two of these values. Within this thickness range, the in-situ formed SEI film exhibits good ionic conductivity and electronic insulation, enabling rapid migration of lithium ions between the lithium metal anode and the silicon electrode, while suppressing direct reduction of lithium ions at the interface, thereby inhibiting dendrite nucleation and growth kinetics. If the first and second functional layers are too thick, the energy density of the battery will be reduced, decreasing lithium-ion transport efficiency; if the first and second functional layers are too thin, they will fail to protect the anode material.

[0084] In another embodiment of the present invention, the first SEI film further includes a mixing layer disposed between the lithium metal particles and the first functional layer, the mixing layer comprising a lithiophilic component, a continuously conducting lithium-ion component, and a lithium-containing compound.

[0085] In this invention, the lithiophilic component in the mixed layer can induce uniform lithium ion deposition without the formation of lithium dendrites; the continuous lithium-ion-conducting component can reduce R SEI (The impedance of lithium ions passing through the SEI film) accelerates the redox reaction at the negative electrode interface. Due to the stacking tendency of the low-crystallinity A-material nanoparticle structure, effective in-situ reaction transformation occurs, forming a dense structure of the lithiation product. Simultaneously, the lithiophilic component and the continuously conducting lithium-ion component can reduce surface resistivity while promoting uniform lithium-ion deposition.

[0086] The lithium-containing compound in the hybrid layer is a common component of the SEI film. This lithium-containing compound effectively prevents further decomposition of the electrolyte, protecting the electrode materials; it regulates ion transport rates, improving the battery's energy density and cycle life; and it reduces side reactions, enhancing battery safety and cycle stability.

[0087] In this invention, the formation mechanism of the lithiophilic component and the continuously conducting lithium-ion component in the mixed layer is as follows: Because lithium is more reactive than metal M, a redox reaction can spontaneously occur when substance A adheres to the surface of lithium metal particles. Substance A reacts with lithium metal to generate the lithiophilic component and the continuously conducting lithium-ion component. The lithiophilic component can induce uniform lithium-ion deposition without the formation of lithium dendrites; the continuously conducting lithium-ion component can reduce R... SEI (The impedance of lithium ions passing through the SEI film) accelerates the redox reaction at the negative electrode interface. Due to the stacking tendency of the low-crystallinity A-material nanoparticle structure, an effective in-situ reaction transformation occurs, forming a dense structure of the lithiation product, including a product layer with a porosity of <5% for the first functional layer and the mixed layer. Simultaneously, the first SEI film of this invention exhibits good electrochemical compatibility with the lithium metal particles, is not easily reduced, and remains stable during long-term cycling.

[0088] In this invention, the formation mechanism of the lithium-containing compounds in the first functional layer, the second functional layer, and the mixed layer is as follows:

[0089] (1) Electrolyte decomposition: During the preparation of the negative electrode, the solute in the electrolyte will undergo reduction decomposition on the surface of the lithium metal particles after negative charge treatment, forming new chemical products, which will then precipitate on the surface of the lithium metal particles.

[0090] (2) Reduction reaction: including the reduction reaction of electrolyte solvent, lithium salt, additives and trace air impurities.

[0091] (3) Specific chemical reactions: Components in the electrolyte, such as EC, DMC, and LiPF6, will react to generate substances such as (CH2OCO2Li)2, LiOH, and Li2CO3. These substances are deposited on the surface of lithium metal particles to form a conventional SEI film.

[0092] In this embodiment of the invention, the lithium compound in the mixed layer can effectively prevent further decomposition of the electrolyte, protect the electrode material, regulate the ion transport rate, improve the energy density and cycle life of the battery, reduce side reactions, and improve the safety and cycle stability of the battery.

[0093] In embodiments of the present invention, the lithiophilic component includes M metal and Li-M alloy, wherein M is Zn and / or Mg.

[0094] In embodiments of the present invention, the M metal in the lithiophilic component includes Zn metal and / or Mg metal.

[0095] In embodiments of the present invention, the Li-M alloy in the lithiophilic component includes Li-Zn alloy and / or Li-Mg alloy.

[0096] In this invention, the "continuously conducting lithium-ion component" is equivalent to an SEI film, possessing the characteristics of a solid electrolyte, and is an electronic insulator and Li... + Li is an excellent conductor. + It can freely insert and extract through this layer. In embodiments of the present invention, the continuously conducting lithium-ion component includes weak acid salts and / or organic salts of lithium, Li₂O, and LiOH.

[0097] In embodiments of the present invention, the weak acid salt or organic salt of lithium in the continuous-conducting lithium-ion component includes lithium silicate (Li₂O₃). x SiO y Where 2≤x≤8, 3≤y≤6, for example, at least one of Li8SiO6, Li4SiO4, Li2SiO3, etc., lithium acetate, lithium citrate, and lithium lactate.

[0098] In embodiments of the present invention, the lithium-containing compound in the mixed layer includes at least one of an organic salt of lithium, an inorganic salt of lithium, Li2O, and LiOH.

[0099] Preferably, in the mixed layer, the mass ratio of the lithiophilic component, the continuously conducting lithium-ion component, and the lithium-containing compound is (5–50):(5–50):(0.05–1). For example, the mass ratio of the lithiophilic component, the continuously conducting lithium-ion component, and the lithium-containing compound is any value from 10:10:0.5, 20:30:0.8, 5:50:0.05, 50:5:1, or any value within the range formed by any pair of the above values.

[0100] Preferably, the thickness of the hybrid layer is 5–200 nm. For example, the thickness of the hybrid layer can be any value from 5 nm, 10 nm, 50 nm, 100 nm, 150 nm, and 200 nm, or any value within a range formed by any two of these values. If the hybrid layer is too thick, the energy density of the battery will be reduced, and the lithium-ion transport efficiency will decrease; if the hybrid layer is too thin, it will fail to protect the negative electrode material.

[0101] Preferably, the thickness ratio of the first functional layer to the hybrid layer is (1-100):(1-200). For example, the thickness ratio of the first functional layer to the hybrid layer is any value from 3:5, 1:10, 1:100, 1:200, 1:1, 10:1, 100:1, or any value within the range of any two of the above values. Controlling the thickness ratio of the first functional layer to the hybrid layer within this range allows for a balance between the combined effects of the first functional layer and the hybrid layer. On one hand, the first functional layer is an artificially synthesized in-situ SEI film with a nano-stacked structure, exhibiting good ionic conductivity and electronic insulation. This allows for rapid migration of lithium ions between the lithium metal anode and the silicon electrode, while simultaneously suppressing direct reduction of lithium ions at the interface, thereby inhibiting lithium dendrite nucleation and growth kinetics. Furthermore, this in-situ SEI film has a uniform phase distribution, stable structure, and good flexibility, which is beneficial for improving cycle performance. On the other hand, the lithiophilic component in the hybrid layer can induce uniform lithium ion deposition without generating lithium dendrites; the continuously conducting lithium ion component can reduce R... SEI (The resistance of lithium ions passing through the SEI film) accelerates the redox reaction at the negative electrode interface.

[0102] In this embodiment of the invention, there is no reaction between substance A in the second functional layer and the nano-silicon particles, so there is no mixed layer between the nano-silicon particles and the second functional layer.

[0103] In this embodiment of the invention, the first negative electrode active material and the second negative electrode active material in the composite layer have a tight stacked structure, which can reduce the resistance of lithium ions entering and leaving the layer and enhance the ionic conductivity.

[0104] Preferably, the composite layer also includes a conductive agent and a binder. Since substance A has the property of conducting ions but not conducting electrons, after substance A is coated on the surface of lithium metal particles and nano-silicon particles, the composite layer conducts ions but does not conduct electrons. Therefore, it is necessary to add a conductive agent to conduct electricity and realize the function of conducting electrons.

[0105] Preferably, the composite layer satisfies at least one of the following conditions (1) to (3):

[0106] (1) The mass ratio of lithium metal particles, nano-silicon particles, and conductive agent is (10-40):(5-30):(0.5-3g);

[0107] (2) The mass of lithium metal particles is denoted as m1, the mass of nano-silicon particles is denoted as m2, and the mass of conductive agent is denoted as m3. m1, m2, and m3 satisfy the following relationship:

[0108] 1 / 200≤m3 / (m1+m2)≤1 / 20;

[0109] (3) The total mass of the first negative electrode active material, the second negative electrode active material, and the conductive agent is denoted as X1, and the mass of the binder is denoted as X2. X1 and X2 satisfy the following relationship:

[0110] 20≤X1 / X2≤200.

[0111] For example, the mass ratio of lithium metal particles, nano-silicon particles, and conductive agent is any one of the following values: 30:10:1, 30:20:0.5, 30:5:1.5, 10:30:0.5, 40:5:3, or any value within the range of any two of the above values.

[0112] For example, the ratio of m3 / (m1+m2) is any value among 1 / 200, 1 / 150, 1 / 100, 1 / 50, 1 / 40, and 1 / 20, or any value within the range of any pair of the above values.

[0113] For example, the ratio of X1 / X2 is any value among 20, 25, 40, 60, 80, 100, 120, 140, 160, 180, 200, or any value within the range of any pair of the above values.

[0114] For the composite layer to meet the conditions (1) to (2), if the proportion of conductive agent is too high, the energy density of the negative electrode composite layer system will decrease due to the low density of conductive agent, resulting in battery capacity decay; if the proportion of conductive agent is too low, the conductivity will be poor, which will affect the overall performance of the battery.

[0115] For the composite layer to meet condition (3), too much binder will reduce the proportion of active material and make the electrode more brittle; too little binder will result in low electrode peel strength, or even powder loss during die cutting, increased side reactions, and increased battery short circuit rate.

[0116] In embodiments of the present invention, the distribution state of the conductive agent includes at least one of the following:

[0117] (a) A conductive agent is disposed on the surface of the first functional layer and / or the second functional layer;

[0118] (b) A conductive agent is disposed on the surface of lithium metal particles and / or nano-silicon particles.

[0119] In an embodiment of the present invention, the conductive agent has a spherical chain structure.

[0120] Secondly, the present invention provides a method for preparing a negative electrode sheet, the method comprising the following steps:

[0121] S1, Mix substance A and electrolyte to obtain a mixed solution; the electrolyte includes lithium salt and organic solvent;

[0122] Substance A includes weak acid salts containing M and / or organic salts containing M, wherein M is Zn and / or Mg;

[0123] S2, lithium metal particles, nano-silicon particles and mixed solution are stirred and mixed, and then negatively charged to obtain reactants; the reactants are filtered and dried to obtain lithium silicon composites with in-situ grown SEI films.

[0124] The lithium-silicon composite with an in-situ grown SEI film includes a first negative electrode active material and a second negative electrode active material.

[0125] The first negative electrode active material includes lithium metal particles and a first SEI film coated on the surface of the lithium metal particles. The first SEI film includes a first functional layer.

[0126] The second negative electrode active material includes nano-silicon particles and a second SEI film coated on the surface of the nano-silicon particles. The second SEI film includes a second functional layer.

[0127] The first and second functional layers independently include substance A and lithium-containing compounds;

[0128] S3, prepare a slurry from a lithium-silicon composite with an in-situ grown SEI film, coat the slurry onto at least one side of the negative electrode current collector, and obtain a negative electrode sheet by hot pressing.

[0129] In embodiments of the present invention, the lithium salt includes at least one selected from LiFSI, LiPF6, LiClO4, LiTFSI, LiODFB, LiBF4, LiBOB, LiF, LiCl, Li2CO3, and LiOH. The lithium salt can participate in the chemical reaction to form an artificial SEI film during negative charge treatment. After negative charge treatment, a lithium-containing compound can be generated, which further combines with substance A to form an artificial SEI film.

[0130] In a specific embodiment of the present invention, the lithium salt includes LiFSI and LiPF6. The two can be combined in any ratio, with a preferred mass ratio of LiFSI to LiPF6 of 1:4 to 4:1.

[0131] Preferably, the concentration of the lithium salt in the mixed solution is 0.5–2 mol / L. For example, the concentration of the lithium salt in the mixed solution is any value from 0.5 mol / L, 0.7 mol / L, 0.9 mol / L, 1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.5 mol / L, 1.7 mol / L, 1.9 mol / L, 2 mol / L, or any value within the range formed by any pair of the above values.

[0132] Preferably, the concentration of lithium salt in the mixed solution is 0.9–1.3 mol / L.

[0133] Preferably, the concentration of substance A in the mixed solution is 0.01–0.5 mol / L. For example, the concentration of substance A in the mixed solution is any one of 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, or 0.5 mol / L, or any value within the range formed by any pair of the above values.

[0134] Preferably, the concentration of substance A in the mixed solution is 0.05–0.2 mol / L.

[0135] In specific embodiments of the present invention, the organic solvents include dimethyl ethylene glycol (DME), ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), vinylene carbonate (VC), and fluoroethylene carbonate (FEC). However, the types of organic solvents are not limited to these; any type of organic solvent recognized by those skilled in the art is within the scope of protection of the present invention. In the mixed solvent composed of the above-mentioned organic solvents, the volume ratio of each organic solvent is a conventional ratio, for example, the volume ratio of DME, EC, EMC, DMC, VC, and FEC is (10-20):(35-45):(15-20):(15-20):(1-10):(1-10).

[0136] In embodiments of the present invention, the conductive agent includes at least one of conductive carbon black (Super P), vapor-generated carbon fiber (VGCF), graphene, and carbon nanotubes (CNTs).

[0137] In this embodiment of the invention, in step S2, adding a conductive agent during the negative charge treatment can make the conductive agent uniformly distributed on the surface of lithium metal particles and / or nano-silicon particles, resulting in a more uniform and stable SEI film.

[0138] In embodiments of the present invention, the binder includes at least one of the following: vinylidene fluoride (PVDF), polyethylene terephthalate (PET), polyimide (PI), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), polyvinyl alcohol (PVA), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), carbonized polyvinylidene fluoride (C-PVDF), poly(acrylamide-co-diallyldimethylammonium chloride) (PAMAC), methyl cellulose (MC), ethyl cellulose (EC), hydroxyethyl cellulose (HEC), aqueous copolymer of polyacrylic acid-sodium carboxymethyl cellulose (c-PAA-CMC), and conductive binder for silicon electrodes (Conductive Binder-CB).

[0139] Preferably, the negative current for the negative current treatment is 0.1 to 1 A, and the negative current treatment time is 10 to 90 minutes. For example, the negative current for the negative current treatment is any value from 0.1 A, 0.2 A, 0.3 A, 0.4 A, 0.5 A, 0.6 A, 0.7 A, 0.8 A, 0.9 A, 1 A, or any value within the range of any two of the above values, and the negative current treatment time is any value from 10 minutes, 15 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, 60 minutes, 70 minutes, 80 minutes, 90 minutes, or any value within the range of any two of the above values.

[0140] Preferably, the hot-pressing temperature is 100–180°C, the hot-pressing pressure is 1–20 kPa, and the hot-pressing time is 5–60 min. For example, the hot-pressing temperature is any value from 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, and 180°C, or any value within the range of any two of the above values; the hot-pressing pressure is any value from 1 kPa, 2 kPa, 4 kPa, 5 kPa, 6 kPa, 8 kPa, 10 kPa, 12 kPa, 14 kPa, 16 kPa, 18 kPa, and 20 kPa, or any value within the range of any two of the above values; and the hot-pressing time is any value from 5 min, 10 min, 20 min, 30 min, 40 min, 50 min, and 60 min, or any value within the range of any two of the above values. In this invention, the negative electrode sheet undergoes hot pressing treatment, which softens the lithium metal particles through thermal melting. Under pressure, the lithium metal particles and nano-silicon particles can be brought into closer contact, which can suppress the volume expansion of the silicon negative electrode during charging and discharging and increase the cycle stability of the silicon negative electrode.

[0141] In this embodiment of the invention, step S2 further includes adding a conductive agent, specifically: stirring and mixing lithium metal particles, nano-silicon particles, a conductive agent, and a mixed solution, followed by negative charge treatment to obtain a reactant; filtering and drying the reactant to obtain a lithium-silicon composite with an in-situ grown SEI film; the lithium-silicon composite with an in-situ grown SEI film includes a first negative electrode active material, a second negative electrode active material, and a conductive agent. Adding the conductive agent in step S2, followed by negative charge treatment, allows the conductive agent to uniformly adhere to the surfaces of the lithium metal particles and nano-silicon particles, making the first SEI film more uniform and stable.

[0142] In an embodiment of the present invention, step S3 further includes the step of adding a binder, specifically: preparing a slurry from a lithium-silicon composite having an in-situ grown SEI film and a binder, coating the slurry onto at least one side of the negative electrode current collector, and obtaining a negative electrode sheet by hot pressing.

[0143] In this embodiment of the invention, step S3 is performed in an oxygen-free environment.

[0144] In an embodiment of the present invention, the preparation method of substance A includes: mixing a first salt containing M, ammonium chloride, a second salt containing weak acid anions and / or organic acid anions, and a second organic solvent, followed by ball milling, washing, and vacuum drying to obtain substance A; wherein M is Zn and / or Mg.

[0145] In embodiments of the present invention, the weak acid anion includes at least one of silicate and acetate.

[0146] In embodiments of the present invention, the organic acid radical includes at least one of citrate and lactate.

[0147] In one embodiment of the present invention, the second organic solvent is a mixed solution of water and N-methyl-2-pyrrolidone (NMP) in any proportion, for example, water and NMP are mixed in a volume ratio of 1:1.

[0148] In another embodiment of the present invention, the second organic solvent may be water.

[0149] In this embodiment of the invention, the ball milling speed is 100-1000 rpm and the ball milling time is 10-20 h.

[0150] In this embodiment of the invention, the temperature of the vacuum drying process is 50℃~120℃, and the time is 1~24h.

[0151] Thirdly, the present invention provides a battery comprising the above-described negative electrode sheet and / or a negative electrode sheet prepared by the above-described preparation method.

[0152] In embodiments of the present invention, the battery structure includes, but is not limited to, button cells, pouch cells, cylindrical cells, etc.

[0153] This application does not impose any particular restrictions on the positive electrode, separator, and electrolyte in the battery. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0154] The reagents, instruments, and materials used in this invention can all be obtained through commercial channels.

[0155] The present invention will be further illustrated below with reference to the embodiments:

[0156] Example 1

[0157] The preparation of the negative electrode in this embodiment includes the following steps:

[0158] (1) Preparation method of zinc silicate

[0159] ZnCl2 (204.0 mg), NH4Cl (1069.8 mg), and Na2SiO3·9H2O (719.6 mg) were dissolved in 10 mL of a mixed solution of deionized water (DIW) and N-methylpyrrolidone (NMP). DIW :V NMP The solution was prepared by mixing a 1:1 ratio of zinc silicate with ethanol, and then transferred to a ball mill. The solution was milled at 500 rpm for 12 hours to synthesize zinc silicate nanoparticles. The product was washed with deionized water in a centrifuge until the supernatant was neutral, washed three times with ethanol, and dried in a vacuum oven at 60°C for at least 12 hours. The product was then ready for use.

[0160] (2) Construction of artificial SEI in lithium metal composite anode

[0161] A mixed solution was prepared by dissolving LiFSI, LiPF6, and zinc silicate in a mixed solvent with a volume ratio of DME:EC:EMC:DMC:VC:FEC = 10:45:15:20:5:5. The molar ratio of LiFSI to LiPF6 was 2:1, with a total concentration of 1.2 mol / L for both LiFSI and LiPF6, and 0.1 mol / L for zinc silicate.

[0162] Take 500 mL of the mixed solution and place it in an electrically powered stirring device, then add lithium powder (D 50 30g of nano-silicon (D) with a wavelength of 1000nm 50 10g of 100nm silicon powder anode material and 1g of conductive carbon black were mixed and stirred for 90 min. Then, a negative current of 0.5A was applied to the stirring paddle and mixing vessel for 15 min to complete the construction of the artificial SEI film. The sample was then filtered and dried to obtain a composite material containing both lithium powder anode material and nano-silicon anode material with an artificial SEI film. A schematic diagram of the lithium powder anode material is shown below. Figure 1-1 (i.e., lithium powder anode materials that do not undergo in-situ reactions and have no mixed layer) and Figure 1-2 (That is, lithium powder anode materials that undergo in-situ reactions and have a mixed layer, with the first functional layer thickness approximately 30 nm and the mixed layer thickness approximately 50 nm.) A schematic diagram of the nano-silicon anode material is shown below. Figure 2 (Its second functional layer is about 30nm thick.)

[0163] (3) Preparation method of lithium-silicon composite electrode

[0164] 5g of lithium powder anode material and nano-silicon anode material after the artificial SEI film was constructed, 0.2g of PVDF binder, and 5.2g of NMP solvent were mixed evenly and then coated onto both sides of the copper current collector. After drying, the electrode was hot-pressed at 100℃ and 5MPa for 5 minutes using a heating plate. All the above operations were completed in an oxygen-free and anhydrous glove box to prepare a Li@Si composite electrode (anode sheet) with dimensions of 100mm×55mm. A schematic diagram of the Li@Si composite electrode structure is shown below. Figure 3-1 The structural schematic diagram of the composite material in the Li@Si composite electrode composite layer is shown below. Figure 3-2 SEM images of the Li@Si composite electrode are shown below. Figure 4 In this embodiment, both lithium powder and nano-silicon are artificially coated with SEI films and stacked in an alternating manner. The surface of the Li@Si composite electrode is compact, and the shaped lithium powder can effectively bind the nano-silicon.

[0165] Example 2

[0166] The only difference between this embodiment and Embodiment 1 is:

[0167] In step (2), LiFSI, LiPF6, and zinc silicate are dissolved in a mixed solvent with a volume ratio of DME:EC:EMC:DMC:VC:FEC = 15:40:20:15:5:5 to prepare a mixed solution. The ratio of LiFSI / LiPF6 is 4:1, with a total concentration of 1.3 mol / L for both LiFSI and LiPF6, and 0.2 mol / L for zinc silicate.

[0168] Example 3

[0169] The only difference between this embodiment and Embodiment 1 is:

[0170] In step (2), LiFSI, LiPF6, and zinc silicate are dissolved in a mixed solvent with a volume ratio of DME:EC:EMC:DMC:VC:FEC = 20:35:20:15:5:5 to prepare a mixed solution. The ratio of LiFSI / LiPF6 is 1:2, with a total concentration of 0.9 mol / L for both LiFSI and LiPF6, and 0.05 mol / L for zinc silicate.

[0171] Example 4

[0172] The only difference between this embodiment and Embodiment 1 is:

[0173] In step (2), the amount of nano-silicon added is 20g, and the amount of conductive carbon black added is 0.5g.

[0174] Example 5

[0175] The only difference between this embodiment and Embodiment 1 is:

[0176] In step (2), the amount of nano-silicon added is 5g, and the amount of conductive carbon black added is 1.5g.

[0177] Example 6

[0178] The only difference between this embodiment and Embodiment 1 is:

[0179] In step (2), zinc silicate is replaced with zinc lactate.

[0180] Comparative Example 1

[0181] The only difference between this embodiment and Embodiment 1 is:

[0182] In step (2), no lithium powder is added.

[0183] Comparative Example 2

[0184] The only difference between this embodiment and Embodiment 1 is:

[0185] In step (2), no nano-silicon is added.

[0186] Comparative Example 3

[0187] The only difference between this embodiment and Embodiment 1 is:

[0188] In step (2), no conductive carbon black is added.

[0189] Comparative Example 4

[0190] The only difference between this embodiment and Embodiment 1 is:

[0191] In step (2), zinc silicate is not added.

[0192] Comparative Example 5

[0193] The only difference between this embodiment and Embodiment 1 is:

[0194] In step (3), the composite material was not hot-pressed.

[0195] Battery fabrication and performance testing:

[0196] 1. Battery manufacturing:

[0197] (1) Preparation of positive electrode sheet: NCM811 is used as positive electrode material. The positive electrode material, conductive carbon black (SP), lithium titanium aluminum phosphate (LTAP) solid electrolyte, polyvinylidene fluoride (PVDF) and other materials are coated on aluminum foil in a mass ratio of 96:2:1:1. The positive electrode sheet is made by drying, pressing and other processes. The size of the positive electrode sheet is 96mm×51mm.

[0198] (2) Preparation of diaphragm: PP diaphragm is used as diaphragm.

[0199] (3) Battery assembly:

[0200] The assembly process uses a soft-pack stacking method. Stacking: The positive electrode, separator, and negative electrode are stacked in sequence to obtain the battery cell. Assembly: After heat pressing, the stacked battery cell is placed in an aluminum-plastic film and sealed from top to side. The charge / discharge cutoff voltage is set to 1.0-4.2V, the charge / discharge current is 1A / g, and the test ends after 2000 cycles.

[0201] 2. Battery performance testing:

[0202] (1) First-time efficiency (first-effect) test method:

[0203] After the battery is manufactured, it is first charged at a constant current rate of 0.1C to 3.75V to obtain the formation capacity C0. Then, the battery is divided into equal parts and charged at a constant current rate of 0.33C to 4.2V, and then charged at a constant voltage of 4.2V until I≤0.05C, to obtain the divided battery capacity C1. After standing for 5 minutes, the battery is discharged at a constant current rate of 1C to 1.0V to obtain the discharge capacity C2, then discharged at a constant current rate of 0.1C to 1.0V to obtain the discharge capacity C3, and finally discharged at a constant current rate of 0.01C to 1.0V to obtain the discharge capacity C4. The initial coulombic efficiency (first efficiency) is calculated as (C2+C3+C4) / (C0+C1)×100%.

[0204] (2) 2000-cycle capacity retention test method:

[0205] 1) After the capacity test is completed, the battery is first charged at a constant current rate of 1C to 4.2V, and then charged at a constant voltage of 4.2V until I≤0.05C;

[0206] 2) After standing for 5 minutes, discharge the battery at a constant current rate of 1C to 1.0V to obtain the discharge capacity C1;

[0207] 3) Let stand for 30 minutes.

[0208] 4) Repeat steps 1)-3) 1999 times to obtain the discharge capacity C2000; the capacity retention rate after 2000 cycles is calculated as (C2000) / (C1)×100%.

[0209] Table 1 Cyclic Performance Test

[0210]

[0211]

[0212] Note: Since no conductive carbon black was added in Comparative Example 3, electronic conduction was not possible, so the first-efficiency and 2000-cycle capacity retention data could not be tested.

[0213] The cycling results show that, compared with Comparative Examples 1-5, the lithium powder and nano-silicon anodes in Examples 1-6 with in-situ SEI film coating have the best cycling performance, indicating that the lithium powder in-situ SEI plus nano-silicon strategy has a significant effect on enhancing electrode kinetic behavior and suppressing the volume expansion of nano-silicon.

[0214] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered 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 and a composite layer disposed on at least one side surface of the negative electrode current collector; The composite layer includes a first negative electrode active material and a second negative electrode active material; The first negative electrode active material includes lithium metal particles and a first SEI film coated on the surface of the lithium metal particles, the first SEI film including a first functional layer. The second negative electrode active material includes nano-silicon particles and a second SEI film coated on the surface of the nano-silicon particles, the second SEI film including a second functional layer; The first functional layer and the second functional layer independently include substance A and a lithium-containing compound, wherein substance A includes a weak acid salt containing M and / or an organic salt containing M, wherein M is Zn and / or Mg; Substance A includes at least one of silicate, acetate, citrate, and lactate; The lithium-containing compounds in the first functional layer and the second functional layer include at least one of organic lithium salts, inorganic lithium salts, Li2O, and LiOH; The first SEI film further includes a mixing layer disposed between the lithium metal particles and the first functional layer, the mixing layer comprising a lithiophilic component, a continuously lithium-ion-conducting component, and a lithium-containing compound; Substance A reacts with lithium metal to generate a lithiophilic component and a continuously lithium-ion-conducting component. The lithiophilic component comprises M metal and Li-M alloy, wherein M is Zn and / or Mg; The continuous lithium-ion-conducting component includes weak acid salts and / or organic salts of lithium, Li2O and LiOH; The lithium-containing compound in the mixed layer includes at least one of organic lithium salts, inorganic lithium salts, Li₂O, and LiOH. The composite layer is obtained by coating a slurry containing a first negative electrode active material and a second negative electrode active material onto a current collector and then hot-pressing it.

2. The negative electrode sheet according to claim 1, characterized in that, Substance A includes at least one of zinc silicate, magnesium silicate, zinc acetate, magnesium acetate, zinc citrate, magnesium citrate, zinc lactate, and magnesium lactate.

3. The negative electrode sheet according to claim 2, characterized in that, Substance A is zinc silicate.

4. The negative electrode sheet according to claim 1, characterized in that, The mass ratio of the lithium metal particles, the nano-silicon particles, the substance A, and the lithium-containing compound is (10-40):(5-30):(5-25):(0.05-1).

5. The negative electrode sheet according to claim 1, characterized in that, The particle size D of the lithium metal particles 50 The range is 0.1–100 μm; And / or, the particle size D of the nano-silicon particles 50 The wavelength is 50–500 nm. And / or, the thicknesses of the first functional layer and the second functional layer are independently 1 to 500 nm.

6. The negative electrode sheet according to claim 1, characterized in that, The thickness of the hybrid layer is 5–200 nm; And / or, the thickness ratio of the first functional layer to the hybrid layer is (1-100):(1-200).

7. The negative electrode sheet according to claim 1, characterized in that, The first negative electrode active material and the second negative electrode active material in the composite layer have a tightly stacked structure; And / or, the composite layer further includes a conductive agent and a binder, and the composite layer satisfies at least one of the following (1) to (3): (1) The mass ratio of the lithium metal particles, the nano-silicon particles, and the conductive agent is (10-40):(5-30):(0.5-3); (2) The mass of the lithium metal particles is denoted as m1, the mass of the nano-silicon particles is denoted as m2, and the mass of the conductive agent is denoted as m3. m1, m2, and m3 satisfy the following relationship: 1 / 200≤m3 / (m1+m2)≤1 / 20; (3) The total mass of the first negative electrode active material, the second negative electrode active material, and the conductive agent is denoted as X1, and the mass of the binder is denoted as X2. X1 and X2 satisfy the following relationship: 20≤X1 / X2≤200.

8. The method for preparing the negative electrode sheet according to any one of claims 1 to 7, characterized in that, The preparation method includes the following steps: S1, Mix substance A and electrolyte to obtain a mixed solution; the electrolyte includes lithium salt and organic solvent; The substance A includes a weak acid salt containing M and / or an organic salt containing M, wherein M is Zn and / or Mg; S2, lithium metal particles, nano-silicon particles, conductive carbon black and the mixed solution are stirred and mixed, and then subjected to negative charge treatment to obtain a reactant; the reactant is filtered and dried to obtain a lithium silicon composite with an in-situ grown SEI film. The lithium-silicon composite with an in-situ grown SEI film includes a first negative electrode active material and a second negative electrode active material. The first negative electrode active material includes lithium metal particles and a first SEI film coated on the surface of the lithium metal particles, the first SEI film including a first functional layer. The second negative electrode active material includes nano-silicon particles and a second SEI film coated on the surface of the nano-silicon particles, the second SEI film including a second functional layer; The first functional layer and the second functional layer independently include substance A and a lithium-containing compound; S3, the lithium-silicon composite with the in-situ grown SEI film is prepared into a slurry, the slurry is coated on at least one side of the negative electrode current collector, and the negative electrode sheet is obtained by hot pressing.

9. The preparation method according to claim 8, characterized in that, The lithium salt includes at least one of LiFSI, LiPF6, LiClO4, LiTFSI, LiODFB, LiBF4, LiBOB, LiF, LiCl, and Li2CO3; And / or, the concentration of the lithium salt in the mixed solution is 0.5–2 mol / L; And / or, the concentration of substance A in the mixed solution is 0.01 to 0.5 mol / L.

10. The preparation method according to claim 9, characterized in that, The current for the negative current treatment is 0.1 to 1 A, and the duration of the negative current treatment is 10 to 90 min. And / or, the temperature of the hot pressing treatment is 100-180°C, the pressure of the hot pressing treatment is 1-20 kPa, and the time of the hot pressing treatment is 5-60 min.

11. A battery, characterized in that, The battery includes a negative electrode sheet according to any one of claims 1 to 7, and / or a negative electrode sheet prepared by the preparation method according to any one of claims 8 to 10.

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