Silicon-carbon composite negative electrode material, negative electrode plate, preparation method and application

Abstract

The invention discloses a silicon-carbon composite negative electrode material, a negative electrode plate, a preparation method and application. The silicon-carbon composite negative electrode material is of a double-coating structure and sequentially comprises inner core silicon, a lithium phosphate layer and a fluorine-containing carbon layer from inside to outside, and the mass ratio of the lithium phosphate layer to the inner core silicon is (1-5): 100. When the composite material is applied to a lithium ion battery, the core silicon and the specific double coating layers can improve the fast charging performance and the first effect while optimizing an ion transmission path; a specific double-coating structure can be used as a buffer layer, stress generated by volume expansion of silicon can be released, and pulverization of particles is avoided; and moreover, LiF with high ionic conductivity and higher mechanical strength and an SEI film with more stable regulation and control are formed through reaction with an electrolyte, so that the structural integrity of the material is kept, and the cycle performance of the material is improved.

Description

Technical Field

[0001] The present invention relates to a silicon-carbon composite negative electrode material, a negative electrode sheet, a preparation method and applications. Background Art

[0002] With the rapidly increasing demand for energy storage devices such as portable electronic devices and electric vehicles, traditional anode materials such as graphite (~372 mAh / g) exhibit limited specific capacity, necessitating the urgent need for high-energy-density anode materials to drive the development of lithium-ion batteries. Although silicon possesses an extremely high theoretical capacity (~4200 mAh / g) and a relatively low discharge potential (~0.5 V vs. Li / Li+), and is a relatively abundant element on Earth, its commercialization remains limited by the following key issues: Silicon is a semiconductor material with inherently poor conductivity; The significant volume expansion during lithiation (~400%) generates stress that leads to electrode pulverization / detachment, shortening battery life; The significant volume effect during lithiation causes the stable solid electrolyte interphase (SEI) on the silicon surface to continuously break down, leading to an increasingly thick SEI film and ultimately a rapid decrease in capacity and Coulombic efficiency.

[0003] In addition, current commercial negative electrodes require the addition of binders and conductive agents. This operation not only reduces the content of active materials in the electrode and the mass energy density of the battery, but also produces more interface contacts. On the one hand, it is not conducive to the conduction of lithium ions and electrons. At the same time, more side reactions are generated at the interface, affecting the cycle performance. Summary of the Invention

[0004] The present invention addresses the technical problem of overcoming the shortcomings of prior art silicon anodes, such as poor conductivity, large volume expansion, unstable SEI films, and the need to add binders and conductive agents that affect performance. The present invention provides a silicon-carbon composite anode material, anode sheet, preparation method, and application. The anode material comprises a double-coated silicon-carbon composite anode material with a fluorine-containing carbonized outer layer, a lithium phosphate middle layer, and a silicon core. This material suppresses silicon volume expansion, enhances the material's ion and electron transfer capabilities, and improves the material's energy density, cycling performance, and rate capability.

[0005] The present invention solves the above technical problems through the following technical solutions.

[0006] The present invention provides a silicon-carbon composite negative electrode material having a double-coated structure, which comprises, from the inside to the outside, a core silicon layer, a lithium phosphate layer, and a fluorine-containing carbon layer, wherein the mass ratio of the lithium phosphate layer to the core silicon is (1-5):100.

[0007] In some embodiments, the mass ratio of the lithium phosphate layer to the core silicon may be 1:100, 2:100, 3:100, or 5:100, preferably 3:100.

[0008] In some embodiments, the mass ratio of the fluorine-containing carbon layer to the core silicon is preferably (8-12):100, for example, 8:100, 10:100 or 12:100.

[0009] In some embodiments, the particle size D50 of the silicon-carbon composite negative electrode material may be 200-300 μm.

[0010] In some embodiments, the raw material of the fluorine-containing carbon layer is a fluorine-containing resin, which can be a conventional fluorine-containing resin material in the art, such as one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer and fluorine-containing acrylic resin, preferably polyvinylidene fluoride.

[0011] The fluorine content of the fluorine-containing resin is 4-6%.

[0012] In some embodiments, the core silicon is nano-silicon, porous silicon or micro-silicon, preferably nano-silicon.

[0013] In some embodiments, the particle size D50 of the core silicon may be 150-250 nm.

[0014] The present invention provides a method for preparing a silicon-carbon composite negative electrode material, which comprises the following steps:

[0015] S1: In the presence of a solvent, a lithium source, a phosphate, and a silicon source undergo a hydrothermal reaction, followed by calcination, to prepare a silicon-lithium composite material; wherein the mass ratio of the lithium source, the phosphate, and the silicon source is (0.22-1.09):(0.31-1.55):35;

[0016] S2: calcining the mixture of the silicon-lithium composite material and the fluorine-containing resin to obtain the silicon-carbon composite negative electrode material.

[0017] In S1, the solvent is a commonly used solvent in the art, such as water or anhydrous ethanol, preferably water.

[0018] The water is generally deionized water.

[0019] In S1, the lithium source may be conventional in the art, for example, including one or more of lithium carbonate, lithium oxide and lithium hydroxide, preferably lithium carbonate.

[0020] In S1, the phosphate may be conventional in the art, for example, including ammonium dihydrogen phosphate and / or lithium dihydrogen phosphate, preferably ammonium dihydrogen phosphate.

[0021] In S1, the mass ratio of the lithium source to the phosphate is preferably 0.22:0.31 or 1.09:1.55.

[0022] In S1, the silicon source may be conventional in the art, for example, including one or more of nano-silicon, porous silicon or micro-silicon, preferably nano-silicon.

[0023] In S1, the particle size D50 of the silicon source may be 150-250 nm.

[0024] In S1, the mass ratio of the lithium carbonate, ammonium dihydrogen phosphate and silicon source may be (0.22-1.09): (0.31-1.55): 35; for example, 0.22: 0.31: 35, 0.44: 0.62: 35, 0.66: 0.93: 35 or 1.09: 1.55: 35.

[0025] In S1, the operation and conditions of the hydrothermal reaction may be conventional in the art, and the instrument used may be a hydrothermal reactor.

[0026] The hydrothermal reactor can be conventional in the art, for example, a hydrothermal reactor lined with polytetrafluoroethylene.

[0027] In S1, during the hydrothermal reaction, the heating rate to the hydrothermal reaction temperature may be 3-5°C / min, for example, 5°C / min.

[0028] In S1, the temperature of the hydrothermal reaction may be 160-200°C, preferably 180°C.

[0029] In S1, the hydrothermal reaction time may be 6 to 10 hours, preferably 8 hours.

[0030] In S1, after the hydrothermal reaction and before the calcination, the reaction system is generally subjected to conventional post-treatments such as centrifugation, washing, and drying.

[0031] In S1, the calcination is preferably carried out under the protection of an inert atmosphere or an argon-hydrogen mixed gas.

[0032] The inert atmosphere may be nitrogen or argon, preferably argon atmosphere.

[0033] In S1, during the calcination, the heating rate to the calcination temperature is preferably 3-8°C / min, for example 5°C / min.

[0034] In S1, the calcination temperature may be 500-800°C, preferably 700°C.

[0035] In S1, the calcination time may be 4 to 8 hours, preferably 6 hours.

[0036] In S2, the fluorine-containing resin may be a conventional fluorine-containing resin material in the art, such as one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer and fluorine-containing acrylic resin, preferably polyvinylidene fluoride.

[0037] In S2, the fluorine-containing resin is generally added in the form of a solution.

[0038] When the fluorine-containing resin is added in the form of a solution, the solvent is preferably DMF.

[0039] When the fluorine-containing resin is added in the form of a solution, the mass ratio of the fluorine-containing resin to the solvent may be (10-20):80, preferably 20:80.

[0040] In S2, in the mixture, the mass ratio of the silicon-lithium composite material to the fluorine-containing resin can be 30:(5-15), for example, 6:1, 3:1, or 2:1.

[0041] In S2, the mass ratio of the silicon source to the fluorine-containing resin is 7:(1-3), for example, 7:1, 7:2 or 7:3.

[0042] In S2, the mixture can be prepared by conventional methods in the art, such as ball milling.

[0043] The ball milling is generally carried out using a ball milling jar.

[0044] The rotation speed of the ball mill is preferably 100-400 rpm, for example 200 rpm.

[0045] The ball milling time is preferably 1 to 3 hours, for example 2 hours.

[0046] In the ball milling, the ball-to-material ratio is preferably 25:1 to 35:1, for example 30:1.

[0047] In S2, the calcination is preferably carried out under the protection of an inert atmosphere or an argon-hydrogen mixed gas.

[0048] The inert atmosphere may be nitrogen or argon, preferably argon atmosphere.

[0049] In S2, during the calcination, the heating rate to the calcination temperature is preferably 3-8°C / min, for example 5°C / min.

[0050] In S2, the calcination temperature may be 600-1000°C, preferably 700°C.

[0051] In S2, the calcination time may be 4 to 8 hours, preferably 4 hours.

[0052] The present invention provides a silicon-carbon composite negative electrode material prepared by the above-mentioned preparation method.

[0053] The present invention provides a silicon-carbon composite negative electrode sheet, which includes the silicon-carbon composite negative electrode material as described above.

[0054] In the present invention, the silicon-carbon composite negative electrode sheet preferably does not contain a conductive agent and a binder.

[0055] The conductive agent may be conventional in the art, such as one or more of acetylene black, Super-P or Ketjen black.

[0056] The binder may be conventional in the art, such as one or more of carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyvinyl alcohol, sodium alginate, polyacrylonitrile, polyvinyl pyrrolidone or polymethyl methacrylate.

[0057] The present invention provides a method for preparing a silicon-carbon composite negative electrode sheet, which comprises the following steps:

[0058] The mixture of the silicon-lithium composite material obtained above and the fluorine-containing resin is coated on a current collector and calcined to obtain the silicon-carbon composite negative electrode sheet.

[0059] In the present invention, the mixture can be prepared by conventional methods in the art, such as ball milling, wherein the parameters of the ball milling are as described above.

[0060] In the present invention, the current collector is a conventional current collector in the art, such as copper foil.

[0061] In some embodiments, the coating amount may be 1-2 mg / cm 2 , for example 2mg / cm 2 .

[0062] In the present invention, conventional operations such as drying and cutting are generally performed after the coating and before the calcination.

[0063] In some embodiments, the calcination conditions are the same as those described in step S2.

[0064] The present invention also provides an application of the silicon-carbon composite negative electrode material or the silicon-carbon composite negative electrode sheet in the field of lithium-ion batteries.

[0065] The reagents and raw materials used in the present invention are commercially available.

[0066] On the basis of conforming to the common sense in this field, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0067] The positive progress effect of the present invention is:

[0068] The present invention provides a silicon-carbon composite anode material with a double-coated structure, consisting, from the inside out, of a silicon core, a lithium phosphate layer, and a fluorine-containing carbon layer. When used in lithium-ion batteries, the silicon core and the specific double-coating layer optimize the ion transport path while also improving fast-charging performance and initial efficiency. The specific double-coating structure acts as a buffer layer, releasing stress generated by silicon volume expansion and preventing particle pulverization. Furthermore, it reacts with the electrolyte to form LiF with high ionic conductivity and greater mechanical strength, regulating a more stable SEI film, thereby maintaining the structural integrity of the material and improving its cycling performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 Schematic diagram of the structure of the silicon-carbon composite negative electrode sheet.

[0070] Figure 2 Schematic diagram of the structure of silicon-carbon composite negative electrode material. DETAILED DESCRIPTION

[0071] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0072] Example 1

[0073] The structure of silicon-carbon composite negative electrode sheet is as follows Figure 1 The surface is a silicon-carbon composite negative electrode material, and the lower layer is a copper foil.

[0074] The structure of silicon-carbon composite negative electrode material is as follows Figure 2 As shown, the outermost layer is a fluorine-containing carbon layer, the middle layer is a lithium phosphate layer, and the innermost layer is a core silicon (particle size 150~250nm), with a particle size of 200~300μm.

[0075] Preparation method:

[0076] 0.22g lithium carbonate and 0.31g ammonium dihydrogen phosphate were dissolved in deionized water (200g), 35g nano-silicon powder was added, and the mixture was stirred for 2h. The stirred solution was transferred to a hydrothermal reactor lined with polytetrafluoroethylene. After hydrothermal reaction at 180℃ (heating rate of 5℃ / min) for 8h, the mixture was centrifuged, washed, and dried, and then calcined at 700℃ (heating rate of 5℃ / min) for 6h in a tubular furnace under argon atmosphere to obtain 30g Si@Li3PO4 composite material.

[0077] It was then mixed with 50 g of polyvinylidene fluoride solution (20 wt% PVDF dissolved in DMF) and mixed in a ball mill at 200 rpm for 2 h, with a ball-to-material ratio of 30:1.

[0078] Apply the slurry evenly on the copper foil (coating amount is 2mg / cm -2 ), dried in a vacuum drying oven at 80°C for 12 hours to remove the solvent, cut into pieces with a diameter of 16 mm, and then calcined at 700°C (heating rate of 3~8°C / min) for 4 hours in an argon atmosphere in a tubular furnace to obtain a Si@1%Li3PO4@C silicon-carbon composite negative electrode sheet.

[0079] In the silicon-carbon composite negative electrode material, the mass ratio of the lithium phosphate layer to the core silicon is 1:100, and the mass ratio of the fluorine-containing carbon layer to the core silicon is 10:100.

[0080] Example 2

[0081] The difference between this embodiment and embodiment 1 is that the amount of lithium source and phosphate source used is 0.44g lithium carbonate and 0.62g ammonium dihydrogen phosphate, and the other preparation methods and parameters are consistent with those of embodiment 1.

[0082] In the silicon-carbon composite negative electrode material, the mass ratio of the lithium phosphate layer to the core silicon is 2:100, and the mass ratio of the fluorine-containing carbon layer to the core silicon is 10:100.

[0083] Example 3

[0084] The difference between this embodiment and embodiment 1 lies in the amount of lithium source and phosphate source used, 0.66 g of lithium carbonate and 0.93 g of ammonium dihydrogen phosphate. The rest of the preparation method and parameters remain the same as in embodiment 1.

[0085] In the silicon-carbon composite negative electrode material, the mass ratio of the lithium phosphate layer to the core silicon is 3:100, and the mass ratio of the fluorine-containing carbon layer to the core silicon is 10:100.

[0086] Example 4

[0087] The difference between this embodiment and embodiment 1 lies in the amount of lithium source and phosphate source used, 1.09 g of lithium carbonate and 1.55 g of ammonium dihydrogen phosphate. The rest of the preparation method and parameters remain the same as in embodiment 1.

[0088] In the silicon-carbon composite negative electrode material, the mass ratio of the lithium phosphate layer to the core silicon is 5:100, and the mass ratio of the fluorinated carbon layer to the core silicon is 10:100.

[0089] Example 5

[0090] The difference between this embodiment and embodiment 3 is that the amount of resin used is different. 25g of polyvinylidene fluoride solution (20.wt% PVDF dissolved in DMF) is used.

[0091] In the silicon-carbon composite negative electrode material, the mass ratio of the lithium phosphate layer to the core silicon is 3:100, and the mass ratio of the fluorine-containing carbon layer to the core silicon is 8:100.

[0092] Example 6

[0093] The difference between this embodiment and embodiment 3 is that the amount of resin used is different. 75g of polyvinylidene fluoride solution (20.wt% PVDF dissolved in DMF) is used.

[0094] In the silicon-carbon composite negative electrode material, the mass ratio of the lithium phosphate layer to the core silicon is 3:100, and the mass ratio of the fluorine-containing carbon layer to the core silicon is 12:100.

[0095] Comparative Example 1

[0096] 30g of nano-silicon powder was mixed with 50g of polyvinylidene fluoride solution (20.wt% PVDF dissolved in DMF) and mixed in a ball mill at 200 rpm for 2h, with a ball-to-material ratio of 30:1. A uniform slurry was applied (coating amount of 2mg / cm -2 ) on copper foil and dried in a vacuum drying oven at 80°C for 12 hours to remove the solvent, cut into pieces with a diameter of 16 mm, and then calcined at 700°C for 4 hours in an argon atmosphere in a tubular furnace to obtain a Si@C integrated negative electrode sheet.

[0097] Comparative Example 2

[0098] Mix nano-silicon, PAA (4.wt%) and Super P in a ratio of 80:10:10 and apply homogenously (coating amount is 2mg / cm -2 ) On the surface of the copper foil, after drying, use a punching machine to punch the above-mentioned electrode into a negative electrode sheet with a diameter of 16 mm.

[0099] Comparative Example 3

[0100] The difference between this embodiment and embodiment 3 is that the resin is different. The resin is mixed with 50 g of polyacrylonitrile solution (20.wt% PAN dissolved in DMF). The rest of the preparation methods and parameters are consistent with those of embodiment 3.

[0101] A half-cell was prepared using the negative electrode sheets from each example and comparative example, including the following steps: The cells were assembled in an argon-filled Braun glove box in Germany. The battery model was 2032, and the electrolyte consisted of 1M LiPF6:EC:DEC:DMC in a 1:1:1 volume ratio. A lithium metal sheet served as the counter electrode (positive electrode). The prepared half-cells were tested for discharge capacity and initial discharge efficiency using a Land test system battery tester. Rate charge and discharge capacity was tested at 0.1C and 3C over a charge and discharge voltage range of 0.005V to 1.5V. Capacity retention was also tested at 0.5C for 100 cycles.

[0102] The test results are shown in Table 1.

[0103] Table 1 Electrochemical performance test results of the battery

[0104]

[0105] Test result analysis:

[0106] Example 3 exhibits good capacity and first efficiency, the best capacity retention at 3C, and excellent cycle performance.

[0107] 1) Compared with Comparative Example 1, the Si@Li3PO4@C silicon-carbon composite negative electrode sheet of the present invention significantly improves initial charge and discharge efficiency. The lithium phosphate coating replenishes the irreversible consumption of lithium ion capacity, achieving a pre-lithiation effect. At a 0.1C rate, the capacity of the silicon-carbon composite negative electrode sheet decreases with increasing lithium phosphate content, primarily due to the lack of capacity provided by the addition of lithium phosphate. At a 3C rate, the capacity retention rate of the silicon-carbon composite negative electrode sheet of Example 3 is even higher, indicating that the carbon-coated lithium phosphate coating of the silicon substrate facilitates lithium ion transfer and improves the material's rate performance.

[0108] 2) Compared with Examples 5, 6, and Comparative Example 3, the presence of the fluorine-containing carbon layer can regulate the SEI composition, forming a more stable SEI film, reducing the irreversible lithium ion consumption, and improving the cycle performance. In addition, the first effect also increases with the increase of the resin coating content.

[0109] 3) Compared with the comparative example, the capacity retention rate of the Si@Li3PO4@C silicon-carbon composite negative electrode sheet of the present invention after 100 cycles is higher, indicating that the coating of lithium phosphate and fluorine-containing carbon layer as a buffer layer can release the stress caused by the volume expansion of silicon and maintain the integrity of the material structure.

Claims

1. A silicon-carbon composite negative electrode material, characterized in that: It is a double-coated structure, which comprises a core silicon, a lithium phosphate layer and a fluorine-containing carbon layer from the inside to the outside. The mass ratio of the lithium phosphate layer to the core silicon is (1-5):

100.

2. The silicon-carbon composite negative electrode material according to claim 1, wherein It meets one or more of the following conditions: (1) The mass ratio of the lithium phosphate layer to the core silicon is 1:100, 2:100, 3:100, or 5:100, preferably 3:100; (2) The mass ratio of the fluorine-containing carbon layer to the core silicon is (8-12):100, for example, 8:100, 10:100 or 12:100; (3) The particle size D50 of the silicon-carbon composite negative electrode material is 200-300 μm; (4) The raw material of the fluorine-containing carbon layer is a fluorine-containing resin, and the fluorine-containing resin is one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer and fluorine-containing acrylic resin, preferably polyvinylidene fluoride; preferably, the fluorine content of the fluorine-containing resin is 4-6%; and, (5) The core silicon is nano-silicon, porous silicon or micro-silicon, preferably nano-silicon; The particle size D50 of the core silicon is preferably 150-250 nm.

3. A method for preparing the silicon-carbon composite negative electrode material according to claim 1 or 2, characterized in that it comprises the following steps: S1: In the presence of a solvent, a lithium source, a phosphate, and a silicon source undergo a hydrothermal reaction, followed by calcination, to prepare a silicon-lithium composite material; wherein the mass ratio of the lithium source, the phosphate, and the silicon source is (0.22-1.09):(0.31-1.55):35; S2: calcining the mixture of the silicon-lithium composite material and the fluorine-containing resin to obtain the silicon-carbon composite negative electrode material.

4. The method for preparing a silicon-carbon composite negative electrode material according to claim 3, wherein: It meets one or more of the following conditions: (1) In S1, the solvent is water or anhydrous ethanol, preferably water; (2) In S1, the lithium source includes one or more of lithium carbonate, lithium oxide and lithium hydroxide, preferably lithium carbonate; (3) In S1, the phosphate includes ammonium dihydrogen phosphate and / or lithium dihydrogen phosphate, preferably ammonium dihydrogen phosphate; (4) In S1, the mass ratio of the lithium source to the phosphate is 0.22:0.31 or 1.09:1.55; (5) In S1, the silicon source includes one or more of nano-silicon, porous silicon or micro-silicon, preferably nano-silicon; In S1, the particle size D50 of the silicon source is preferably 150-250 nm; (6) In S1, during the hydrothermal reaction, the heating rate to the hydrothermal reaction temperature is 3-5°C / min, for example, 5°C / min; (7) In S1, the temperature of the hydrothermal reaction is 160-200°C, preferably 180°C; (8) In S1, the hydrothermal reaction time is 6 to 10 hours, preferably 8 hours; (9) In S1, the calcination is carried out under the protection of an inert atmosphere or an argon-hydrogen mixed gas; (10) In S1, during the calcination, the heating rate to the calcination temperature is 3-8°C / min, for example, 5°C / min; (11) In S1, the calcination temperature is 500-800°C, preferably 700°C; (12) In S1, the calcination time is 4 to 8 hours, preferably 6 hours; (13) In S2, the fluorine-containing resin is one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer and fluorine-containing acrylic resin, preferably polyvinylidene fluoride; (14) In S2, the fluorine-containing resin is added in the form of a solution; (15) In S2, in the mixture, the mass ratio of the silicon-lithium composite material to the fluorine-containing resin is 30:(5-15), for example, 6:1, 3:1, 2:1; In S2, the mass ratio of the silicon source to the fluorine-containing resin is preferably 7:(1-3), such as 7:1, 7:2 or 7:3; (16) In S2, the mixture is prepared by ball milling; (17) In S2, the calcination is carried out under the protection of an inert atmosphere or an argon-hydrogen mixed gas; (18) In S2, during the calcination, the heating rate to the calcination temperature is 3-8°C / min, for example, 5°C / min; (19) In S2, the calcination temperature is 600-1000°C, preferably 700°C; And, in (20) S2, the calcination time is 4 to 8 hours, preferably 4 hours.

5. The method for preparing the silicon-carbon composite negative electrode material according to claim 4, wherein: It meets one or more of the following conditions: (1) In S1, the mass ratio of lithium carbonate, diammonium dihydrogen phosphate and silicon source is (0.22-1.09):(0.31-1.55):35; for example, 0.22:0.31:35, 0.44:0.62:35, 0.66:0.93:35 or 1.09:1.55:35; (2) In S1, the inert atmosphere is nitrogen or argon; preferably argon atmosphere; (3) In S2, when the fluorine-containing resin is added in the form of a solution, the solvent is DMF; (4) In S2, when the fluorine-containing resin is added in the form of a solution, the mass ratio of the fluorine-containing resin to the solvent is (10-20):80, preferably 20:80; (5) In S2, the rotation speed of the ball mill is 100-400 rpm, for example, 200 rpm; (6) In S2, the ball milling time is 1 to 3 hours, for example, 2 hours; (7) In S2, in the ball milling, the ball-to-material ratio is 25:1 to 35:1, for example 30:1; and (8) In S2, the inert atmosphere is nitrogen or argon, preferably argon atmosphere.

6. A silicon-carbon composite negative electrode material prepared by the preparation method according to any one of claims 3 to 5.

7. A silicon-carbon composite negative electrode sheet, characterized in that: It includes the silicon-carbon composite negative electrode material according to any one of claims 1 to 2 and 6; The silicon-carbon composite negative electrode sheet preferably does not contain a conductive agent and / or a binder.

8. A method for preparing a silicon-carbon composite negative electrode sheet according to claim 7, characterized in that: The method comprises the following steps: coating the mixture according to any one of claims 3 to 5 on a current collector, and calcining the mixture to obtain the silicon-carbon composite negative electrode sheet.

9. The method for preparing a silicon-carbon composite negative electrode sheet according to claim 8, wherein: It meets one or more of the following conditions: (1) The current collector is copper foil; (2) The coating amount is 1~2 mg / cm 2 , for example 2mg / cm 2 ;and, (3) The calcination conditions are the same as the calcination conditions described in step S2 in any one of claims 3 to 5.

10. Use of the silicon-carbon composite negative electrode material according to any one of claims 1 to 2 and 6 or the silicon-carbon composite negative electrode sheet according to claim 7 in the field of lithium-ion batteries.

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