A negative electrode sheet, a method for manufacturing the same, and a battery

Abstract

The application discloses a negative electrode sheet, a preparation method thereof and a battery. The negative electrode sheet comprises at least two layers of graphene layers and silicon-carbon composite layers arranged between adjacent graphene layers, and the material of the silicon-carbon composite layer comprises graphene-coated silicon particles. The silicon-carbon composite layer is prepared by using graphene-coated silicon particles. The coating structure of the material can inhibit the volume expansion of the silicon particles and isolate the direct contact between the electrolyte and the silicon particles. The silicon-carbon composite material and the interlayer structure formed by arranging the silicon-carbon composite layers between adjacent graphene layers can reduce the unevenness of the silicon expansion. The graphene layers can play the roles of bonding and buffering expansion, further reduce the overall expansion rate of the material, and form a stable conductive network. Therefore, the above coating structure and interlayer structure can effectively alleviate the volume expansion of the silicon particles, improve the conductivity of the silicon material, make the negative electrode sheet have excellent conductivity and cycle stability, and improve the cycle stability of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a negative electrode sheet, its preparation method, and a battery. Background Technology

[0002] Lithium-ion batteries are widely used in various portable electronic devices and electric vehicles due to their high operating voltage, long cycle life, and environmental friendliness. Currently, the main anode material used in commercial lithium-ion batteries is graphite, whose actual specific capacity is already very close to the theoretical specific capacity of 372 mAh / g, limiting its development potential. With the improvement of people's living standards, higher demands are being placed on the energy storage capacity, cycle performance, and safety performance of lithium-ion batteries. Graphite materials can no longer meet future development needs, necessitating the search for new anode materials with superior performance. Among various anode materials, silicon has become one of the optimal choices for future high-capacity anode materials due to its extremely high theoretical specific capacity (4200 mAh / g) and its advantages of abundant reserves and readily available raw materials. However, silicon is a semiconductor with poor ionic and electronic conductivity, and it undergoes significant volume changes during charging and discharging, leading to silicon particle pulverization, continuous growth of the surface SEI film, and detachment of the active material from the current collector, severely affecting the battery's electrochemical performance. To address these issues, existing technologies primarily involve nano-sizing, porousifying, or compositing silicon particles to limit volume expansion and improve conductivity, thereby enhancing battery cycle stability. Conventional compositing methods utilize highly conductive carbon materials to completely encapsulate silicon particles, forming a core-shell structure. While this can mitigate silicon volume expansion to some extent, the core-shell structure is damaged during long-term cycling, leading to rapid capacity decay and poor cycle stability. Summary of the Invention

[0003] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes a negative electrode sheet, a method for preparing the same, and a battery.

[0004] In a first aspect, the present invention provides a negative electrode comprising at least two graphene layers and a silicon-carbon composite layer sandwiched between adjacent graphene layers, wherein the silicon-carbon composite layer is made of graphene-coated silicon particles.

[0005] According to embodiments of the present invention, the negative electrode sheet has at least the following beneficial effects: the negative electrode sheet includes at least two graphene layers and a silicon-carbon composite layer sandwiched between adjacent graphene layers. The silicon-carbon composite layer is made of graphene-coated silicon particles. The graphene-coated silicon particle material in the silicon-carbon composite layer, through this coating structure, can suppress the volume expansion of the silicon particles and isolate the electrolyte from direct contact with the silicon particles. By sandwiching the graphene-coated silicon particle material between adjacent graphene layers to form a sandwich structure, this sandwich structure can... To reduce the non-uniformity of silicon expansion, and with the π-π conjugation between the graphene layer and the outer graphene of the silicon-carbon composite layer, there is a stronger interfacial interaction, which fixes the silicon-carbon layer. Thus, the graphene layer can also play a role in bonding and buffering expansion, further reducing the overall expansion rate of the material, thereby forming a stable conductive network and making the overall structure more stable. Through the synergistic effect of the above coating structure and sandwich structure, the volume expansion of silicon particles can be effectively alleviated and the conductivity of silicon materials can be improved, so that the negative electrode sheet has excellent conductivity and cycle stability, thereby improving the cycle stability of the battery.

[0006] In some embodiments of the present invention, the thickness of the graphene layer is 0.5 to 10 μm, for example, it can be 0.5 μm, 0.8 μm, 1 μm, 1.5 μm, 2 μm, 3 μm, 3.5 μm, 4 μm, 5 μm, 6.5 μm, 7 μm, 8 μm, 8.5 μm, 9 μm, or 10 μm.

[0007] In some embodiments of the present invention, the thickness of the silicon-carbon composite layer is 0.1 to 2 μm, for example, it can be 0.1 μm, 0.3 μm, 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.7 μm, or 2 μm.

[0008] In some embodiments of the present invention, the number of silicon-carbon composite layers is M, and the number of graphene layers is M+1, wherein M is an integer greater than or equal to 2, for example, 2, 3, 4, or 5; furthermore, the negative electrode sheet comprises alternating layers of graphene and silicon-carbon composite layers. The thickness of each graphene layer may be equal or unequal, or partially equal; the thickness of each silicon-carbon composite layer may also be equal or unequal, or partially equal. Of course, in some embodiments, M may also be 1.

[0009] A second aspect of the present invention provides a method for preparing any of the negative electrode sheets proposed in the first aspect of the present invention, comprising the following steps:

[0010] S1. Silicon powder and surface modifier are mixed and dispersed in a solvent to obtain a modified silicon dispersion; then the modified silicon dispersion is mixed with graphene oxide dispersion and ionic liquid to obtain a mixed dispersion.

[0011] S2. Prepare a graphene oxide layer on the substrate;

[0012] S3. The mixed dispersion is coated on the surface of the graphene oxide layer and dried to form a graphene oxide-coated silicon material layer; then a graphene oxide layer is prepared on the surface of the graphene oxide-coated silicon material layer to obtain a composite film.

[0013] S4. Under inert gas protection, the composite film is subjected to thermal reduction treatment to obtain a negative electrode sheet;

[0014] The order of steps S1 and S2 is not limited.

[0015] The above method can be used to prepare self-supporting negative electrode sheets without the need for current collectors, additional conductive agents, and binder materials, simplifying raw materials and structure. The prepared negative electrode sheet includes at least two graphene layers and a silicon-carbon composite layer sandwiched between the graphene layers. The silicon-carbon composite layer is made of graphene-coated silicon particles. Based on the graphene-coated silicon particle coating structure in the silicon-carbon composite layer, and the sandwich structure formed by the graphene layer and the silicon-carbon composite layer, the two work together to effectively alleviate the volume expansion of silicon particles and improve the conductivity of silicon materials, so that the negative electrode sheet has excellent conductivity and cycle stability, thereby improving the cycle stability of the battery.

[0016] In some embodiments of the present invention, in step S1, the surface modifier is selected from silane coupling agents, specifically silane coupling agents containing active groups that can react with oxygen-containing functional groups. These active groups can be amino, hydroxyl, carboxyl, etc., and amino-based silane coupling agents can be used. By using the above-mentioned silane coupling agents with active groups that can react with oxygen-containing functional groups to modify the surface of silicon particles, the surface of the silicon particles is coated with active groups that can react with oxygen-containing functional groups. These active groups can then react with the oxygen-containing functional groups on the surface of graphene oxide to form chemical bonds, attaching graphene oxide to the surface of the silicon particles, thus forming graphene oxide-coated silicon particles. The mass ratio of silicon powder to surface modifier can be controlled at 1:(0.1~1), for example, 1:0.1, 1:0.5, 1:0.8, or 1:1.

[0017] In step S1, the addition of an ionic liquid enhances the dispersibility of graphene oxide-coated silicon particles, ensuring thorough and uniform mixing and dispersion of the particles in the solvent, and preventing agglomeration. In some embodiments of the present invention, the ionic liquid is a silicon-containing ionic liquid, such as at least one of (C2MIM)2SiO3, (C4MIM)2SiO3, (C5MIM)2SiO3, and (C6MIM)2SiO3. In these ionic liquids, the anions are silicate ions, and the cations are relatively large, providing steric hindrance and preventing agglomeration of the graphene oxide-coated silicon particles. Furthermore, these silicon-containing ionic liquids can be decomposed during subsequent thermal reduction treatment, leaving only silicon and carbon elements, thereby providing lithium storage capacity. The amount of ionic liquid added can be controlled at 1‰ to 5% of the total mass of the modified silica dispersion and the graphene oxide dispersion, for example, 1‰, 5‰, 1%, 1.2%, 1.5%, 2%, 2.5%, 3%, 4%, 4.5%, and 5%.

[0018] In some embodiments of the present invention, in step S1, the mass ratio of graphene oxide to silicon powder in the graphene oxide dispersion is (0.1–1.0):1, for example, 0.1:1, 0.3:1, 0.5:1, 0.6:1, 0.8:1, or 1:1. Specifically, silicon powder with a particle size of 0.1–1 μm can be used, the concentration of the graphene oxide dispersion can be controlled at 1–20 g / L, and the sheet size of graphene oxide in the graphene oxide dispersion can be 0.5–20 μm. Water or an organic solvent (such as an alcohol-based organic solvent) can be used as the solvent.

[0019] In step S2, the graphene oxide layer can be prepared on the substrate by methods such as blade coating, spray coating, spin coating, or casting. The substrate can be a smooth material such as glass, ceramic, or release film.

[0020] In step S3, a mixed dispersion can be deposited on the surface of the graphene oxide layer using a spray drying method. After the graphene oxide layer is prepared on the surface of the graphene oxide-coated silicon material layer, step S3 can be repeated as needed to prepare a composite film with the required number of layers and alternating layers of graphene oxide and graphene oxide-coated silicon material. For example, step S3 can be repeated 3 to 9 times.

[0021] In some embodiments of the present invention, in step S4, the temperature of the thermal reduction treatment is 400–800°C. The thermal reduction treatment time can be controlled within 3–8 hours; the inert gas can be nitrogen, helium, or argon; the flow rate of the inert gas can be controlled within 20–100 mL / min.

[0022] In a third aspect, the present invention provides a battery comprising any of the negative electrode sheets proposed in the first aspect of the present invention, or a negative electrode sheet prepared by any of the negative electrode sheet preparation methods proposed in the second aspect of the present invention. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0024] Figure 1 This is a schematic diagram of the structure of the negative electrode sheet prepared in Embodiment 1 of the present invention. Detailed Implementation

[0025] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0026] Example 1

[0027] This embodiment prepares a negative electrode sheet, the preparation method of which includes the following steps:

[0028] S1. Dissolve 3-aminopropyltriethoxysilane in ethanol at a volume ratio of 1:100 to prepare an ethanol solution containing an aminosilane coupling agent. Take the same mass of silicon powder with a diameter of 500 nm as 3-aminopropyltriethoxysilane and add it to the ethanol solution containing the aminosilane coupling agent and disperse it evenly to obtain an aminosilane-modified silicon solution, denoted as solution A.

[0029] S2. Graphene oxide with an average sheet size of 5 μm was dispersed in ethanol and stirred and ultrasonically dispersed to obtain a graphene oxide ethanol dispersion with a concentration of 10 g / L.

[0030] S3. Graphene oxide ethanol dispersion and ionic liquid (a mixture of (C5MIM)2SiO3 and (C6MIM)2SiO3 in equal volume ratio) are added to solution A according to the mass ratio of graphene oxide, ionic liquid and silicon powder of 1:10:5. The mixture is stirred evenly to obtain a mixed dispersion, which is denoted as solution B.

[0031] S4. The graphene oxide ethanol dispersion is coated onto a glass substrate and dried to obtain a graphene oxide layer. The thickness of the scraper is 0.5 mm and the coating speed is 10 mm / s.

[0032] S5. Solution B is deposited on the surface of the graphene oxide layer using a spray drying method, and dried to form a graphene oxide-coated silicon material layer; then a layer of graphene oxide is coated on the surface of the graphene oxide-coated silicon material layer by scraping, wherein the thickness of the scraper is 0.5 mm and the scraping speed is 10 mm / s; then the above operation is repeated to prepare a composite film with alternating layers of graphene oxide and graphene oxide-coated silicon material, wherein there are 3 layers of graphene oxide and 2 layers of graphene oxide-coated silicon material.

[0033] S6. The composite membrane was placed in a tube furnace at 600℃ for thermal reduction for 4 hours, with argon gas provided for protection at a flow rate of 60 mL / min, to obtain the negative electrode sheet, the structural schematic of which is shown in the figure. Figure 1 As shown, it includes three graphene layers 11 and two silicon-carbon composite layers 12. The graphene layers 11 and silicon-carbon composite layers 12 are stacked alternately. Specifically, the silicon-carbon composite layers 12 are sandwiched between adjacent graphene layers 11. The thickness of each graphene layer 11 is 3 μm, and the thickness of each silicon-carbon composite layer 12 is 1 μm. The material of the silicon-carbon composite layer 12 is graphene-coated silicon particles.

[0034] Example 2

[0035] This embodiment prepares a negative electrode sheet. The difference between this embodiment and embodiment 1 is that in step S3 of this embodiment, graphene oxide ethanol dispersion and ionic liquid (a mixture of (C5MIM)2SiO3 and (C6MIM)2SiO3 in equal volume ratio) are added to solution A according to the mass ratio of graphene oxide, ionic liquid and silicon powder of 1:10:10, and stirred evenly to obtain a mixed dispersion, which is denoted as solution B; other operations are the same as in embodiment 1.

[0036] Example 3

[0037] This embodiment prepares a negative electrode sheet. The difference between this embodiment and Embodiment 1 is that the thickness of the scraper used to prepare the graphene oxide layer in steps S4 and S5 of this embodiment is adjusted from 0.5 mm in Embodiment 1 to 1 mm. Other operations are the same as in Embodiment 1. The negative electrode sheet prepared in this embodiment includes 3 graphene layers and 2 silicon-carbon composite layers. The graphene layers and silicon-carbon composite layers are alternately stacked. Specifically, the silicon-carbon composite layers are sandwiched between adjacent graphene layers. The thickness of each graphene layer is 6 μm, and the thickness of each silicon-carbon composite layer is 1 μm. The material of the silicon-carbon composite layer is graphene-coated silicon particles.

[0038] Comparative Example 1

[0039] This comparative example prepared a negative electrode material, and the preparation method includes the following steps:

[0040] S1. Dissolve 3-aminopropyltriethoxysilane in ethanol at a volume ratio of 1:100 to prepare an ethanol solution containing an aminosilane coupling agent. Take the same mass of silicon powder with a diameter of 500 nm as 3-aminopropyltriethoxysilane and add it to the ethanol solution containing the aminosilane coupling agent and disperse it evenly to obtain an aminosilane-modified silicon solution, denoted as solution A.

[0041] S2. Graphene oxide with an average sheet size of 5 μm was dispersed in ethanol and stirred and ultrasonically dispersed to obtain a graphene oxide ethanol dispersion with a concentration of 10 g / L.

[0042] S3. According to the mass ratio of graphene oxide, ionic liquid and silicon powder 1:10:5, add the graphene oxide ethanol dispersion and the ionic liquid (a mixture of (C5MIM)2SiO3 and (C6MIM)2SiO3 in equal volume ratio) to solution A, stir evenly, and obtain a mixed dispersion, which is denoted as solution B.

[0043] S4. Spray dry solution B to obtain graphene oxide-coated silicon particle composite material;

[0044] S5. The graphene oxide-coated silicon particle composite material was placed in a tube furnace at 600℃ for thermal reduction for 4 hours, with argon gas protection at a flow rate of 60 mL / min, to obtain the negative electrode material.

[0045] Comparative Example 2

[0046] This comparative example prepared a negative electrode sheet, the preparation method of which includes the following steps:

[0047] S1. Dissolve 3-aminopropyltriethoxysilane in ethanol at a volume ratio of 1:100 to prepare an ethanol solution containing an aminosilane coupling agent. Take the same mass of silicon powder with a diameter of 500 nm as 3-aminopropyltriethoxysilane and add it to the ethanol solution containing the aminosilane coupling agent and disperse it evenly to obtain an aminosilane-modified silicon solution, denoted as solution A.

[0048] S2. Graphene oxide with an average sheet size of 5 μm was dispersed in ethanol and stirred and ultrasonically dispersed to obtain a graphene oxide ethanol dispersion with a concentration of 10 g / L.

[0049] S3. The graphene oxide ethanol dispersion is coated onto a glass substrate and dried to obtain a graphene oxide layer. The thickness of the scraper is 0.5 mm and the coating speed is 10 mm / s.

[0050] S4. Solution A is sprayed onto the surface of the graphene oxide layer using a spray drying method, and dried to form an aminosilane-modified silicon material layer; then a layer of graphene oxide is coated onto the surface of the aminosilane-modified silicon material layer by scraping, wherein the thickness of the scraper is 0.5 mm and the scraping speed is 10 mm / s; then the above operation is repeated to prepare a composite film with alternating layers of graphene oxide and aminosilane-modified silicon material, wherein there are 3 layers of graphene oxide and 2 layers of aminosilane-modified silicon material.

[0051] S6. The composite membrane is placed in a tube furnace at 600℃ for thermal reduction for 4 hours, with argon gas protection at a flow rate of 60mL / min, to obtain the negative electrode sheet.

[0052] Comparative Example 3

[0053] This comparative example prepared a negative electrode sheet, the preparation method of which includes the following steps:

[0054] S1. Dissolve 3-aminopropyltriethoxysilane in ethanol at a volume ratio of 1:100 to prepare an ethanol solution containing an aminosilane coupling agent. Take the same mass of silicon powder with a diameter of 500 nm as 3-aminopropyltriethoxysilane and add it to the ethanol solution containing the aminosilane coupling agent and disperse it evenly to obtain an aminosilane-modified silicon solution, denoted as solution A.

[0055] S2. Graphene oxide with an average sheet size of 5 μm was dispersed in ethanol and stirred and ultrasonically dispersed to obtain a graphene oxide ethanol dispersion with a concentration of 10 g / L.

[0056] S3. Add the graphene oxide ethanol dispersion to solution A at a mass ratio of 1:5 for graphene oxide to silicon powder, stir evenly, and obtain a graphene oxide-silicon mixed solution, denoted as solution B.

[0057] S4. The graphene oxide ethanol dispersion is coated onto a glass substrate and dried to obtain a graphene oxide layer. The thickness of the scraper is 0.5 mm and the coating speed is 10 mm / s.

[0058] S5. Solution B is deposited on the surface of the graphene oxide layer using a spray drying method, and dried to form a graphene oxide-silicon composite material layer; then a layer of graphene oxide is coated on the surface of the graphene oxide-silicon composite material layer by scraping, wherein the thickness of the scraper is 0.5 mm and the scraping speed is 10 mm / s; then the above operation is repeated to prepare a composite film with alternating layers of graphene oxide and graphene oxide-silicon composite material, wherein there are 3 layers of graphene oxide and 2 layers of graphene oxide-silicon composite material.

[0059] S6. The composite membrane is placed in a tube furnace at 600℃ for thermal reduction for 4 hours, with argon gas protection at a flow rate of 60 mL / min, to obtain the negative electrode sheet. This negative electrode sheet consists of 3 graphene layers and 2 silicon-carbon composite layers, which are alternately stacked. The silicon-carbon composite layers are specifically sandwiched between adjacent graphene layers, and the material of the silicon-carbon composite layers is a graphene-silicon composite material.

[0060] Comparative Example 4

[0061] This comparative example prepared a negative electrode sheet, the preparation method of which includes the following steps:

[0062] S1. Dissolve asphalt and silica powder in toluene at a mass ratio of 1:5:100, and denote the solution as A.

[0063] S2. Graphene oxide with an average sheet size of 5 μm was dispersed in ethanol and stirred and ultrasonically dispersed to obtain a graphene oxide ethanol dispersion with a concentration of 10 g / L.

[0064] S3. The graphene oxide ethanol dispersion is coated onto a glass substrate and dried to obtain a graphene oxide layer. The thickness of the scraper is 0.5 mm and the coating speed is 10 mm / s.

[0065] S4. Solution A is deposited on the surface of the graphene oxide layer using a spray drying method and dried to form a pitch-coated silicon composite material layer; then a layer of graphene oxide is coated on the surface of the pitch-coated silicon composite material layer, wherein the thickness of the scraper is 0.5 mm and the scraping speed is 10 mm / s; then the above operation is repeated to prepare a composite film with alternating layers of graphene oxide and pitch-coated silicon composite material, wherein there are 3 layers of graphene oxide and 2 layers of pitch-coated silicon composite material.

[0066] S5. The composite membrane is placed in a tube furnace at 600℃ for thermal reduction for 4 hours, with argon gas protection at a flow rate of 60 mL / min, to obtain the negative electrode sheet. The negative electrode sheet consists of 3 graphene layers and 2 silicon-carbon composite layers, which are alternately stacked. The silicon-carbon composite layers are specifically sandwiched between adjacent graphene layers, and the material of the silicon-carbon composite layers is pitch-derived carbon-coated silicon composite material.

[0067] Performance testing

[0068] The negative electrode sheets prepared in Examples 1-3 and Comparative Examples 2-4 were used directly as self-supporting negative electrode sheets. A lithium metal sheet was used as the counter electrode, a Celgard 2400 microporous polypropylene membrane was used as the separator, and 1M lithium hexafluorophosphate was used as the electrolyte (the solvent was ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1). They were assembled into a button cell with the model number 2032.

[0069] In addition, the negative electrode material prepared in Comparative Example 1 was mixed with conductive agent SP and binder LA136 in a mass ratio of 8:1:1 to prepare a negative electrode active slurry, which was then coated on the negative electrode current collector copper foil with a coating thickness of 12μm to prepare a negative electrode sheet. Then, a lithium metal sheet was used as the counter electrode and a Celgard 2400 microporous polypropylene membrane was used as the separator to assemble a button battery with model number 2032.

[0070] The button batteries prepared using the negative electrode sheets or materials of Examples 1-3 and Comparative Examples 1-4 are respectively designated as Samples 1-7. The electrochemical performance of each button battery was tested and analyzed, specifically within the voltage range of 0.01-1.5V, using 0.1A g. -1 Constant current charging and discharging were performed at a current density, and the test results are shown in Table 1.

[0071] Table 1

[0072]

[0073] As shown in Table 1 above, compared to the graphene-coated silicon material used in Comparative Example 1 and the sandwich structure formed by alternating layers of graphene and aminosilane-modified silicon in Comparative Example 2, the use of graphene-coated silicon in Examples 1-3, combined with the sandwich structure formed by alternating layers of graphene and silicon-carbon composite (made from graphene-coated silicon material), significantly improves the cycle stability of the battery. However, compared to Example 1, in Comparative Example 3, the lack of ionic liquid in the silicon-carbon composite layer preparation slurry resulted in uneven dispersion and even agglomeration of the graphene-coated silicon particles. Consequently, the graphene and silicon particles in the resulting silicon-carbon composite layer could not form a good coating structure, leading to lower initial coulombic efficiency and cycle stability. In Comparative Example 4, the silicon-carbon composite layer was pitch-derived carbon-coated silicon. The pitch-derived carbon on the outer silicon layer had poorer deformation ability than the graphene layer, causing the carbon shell to be damaged during long-term cycling, resulting in decreased cycle stability.

[0074] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a negative electrode, characterized in that, Includes the following steps: S1. Silicon powder and a surface modifier are mixed and dispersed in a solvent to obtain a modified silicon dispersion. The surface modifier is a silane coupling agent containing active groups that can react with oxygen-containing functional groups. The modified silicon particles in the modified silicon dispersion have the active groups on their surface. Then, the modified silicon dispersion is mixed with a graphene oxide dispersion and an ionic liquid. The active groups on the surface of the modified silicon particles react with the oxygen-containing functional groups on the surface of the graphene oxide to form chemical bonds, thus attaching the graphene oxide to the surface of the silicon particles and forming graphene oxide-coated silicon particles, thus obtaining a mixed dispersion. The ionic liquid is a silicon-containing ionic liquid. S2. Prepare a graphene oxide layer on the substrate; S3. The mixed dispersion is coated on the surface of the graphene oxide layer and dried to form a graphene oxide-coated silicon material layer; A graphene oxide layer is then prepared on the surface of the graphene oxide-coated silicon material layer to obtain a composite film; S4. Under the protection of inert gas, the composite membrane is subjected to thermal reduction treatment. At the same time, the silicon-containing ionic liquid is decomposed during the thermal reduction treatment, leaving silicon and carbon elements as residues, to obtain a negative electrode sheet. The order of steps S1 and S2 is not limited.

2. The method for preparing the negative electrode sheet according to claim 1, characterized in that, In step S1, the mass ratio of graphene oxide to silicon powder in the graphene oxide dispersion is (0.1~1.0):

1.

3. The method for preparing the negative electrode sheet according to claim 1, characterized in that, In step S4, the temperature of the thermal reduction treatment is 400~800℃.

4. A negative electrode sheet, characterized in that, The negative electrode sheet is prepared by the method for preparing a negative electrode sheet according to any one of claims 1 to 3; the negative electrode sheet comprises at least two graphene layers and a silicon-carbon composite layer sandwiched between adjacent graphene layers, the silicon-carbon composite layer being made of graphene-coated silicon particles, wherein the graphene in the graphene-coated silicon particles is attached to the surface of the silicon particles and is connected to the silicon particles by chemical bonds; there is a π-retention relationship between the graphene layers and the outer graphene of the silicon-carbon composite layer. π conjugation.

5. The negative electrode sheet according to claim 4, characterized in that, The thickness of the graphene layer is 0.5~10μm.

6. The negative electrode sheet according to claim 5, characterized in that, The thickness of the silicon-carbon composite layer is 0.1~2μm.

7. The negative electrode sheet according to claim 4, characterized in that, The number of layers in the silicon-carbon composite layer is M, and the number of layers in the graphene layer is M+1, where M is an integer greater than or equal to 2. During the preparation of the negative electrode, after a graphene oxide layer is prepared on the surface of the graphene oxide-coated silicon material layer, the operation of step S3 is repeated M-1 times to prepare a composite film in which the graphene oxide layer and the graphene oxide-coated silicon material layer are alternately stacked.

8. A battery, characterized in that, The negative electrode sheet includes any one of claims 4 to 7.

Images