Silicon-carbon negative electrode material, preparation method of silicon-carbon negative electrode material and lithium ion battery

Abstract

The application provides a silicon-carbon negative electrode material, a preparation method of the silicon-carbon negative electrode material and a lithium ion battery. The silicon-carbon negative electrode material comprises porous carbon and nano silicon particles in the pores of the porous carbon, and the surface of the porous carbon is coated with inorganic salt. The silicon-carbon negative electrode material provided by the application is deposited in the pores of the porous carbon under the action of the inorganic salt, and will not fall on the surface of the porous carbon material, so that the volume expansion in the lithium storage process of silicon is greatly reduced, and the cycle performance and rate performance of the negative electrode material are improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and relates to a silicon-carbon anode material, a method for preparing the silicon-carbon anode material, and a lithium-ion battery. Background Technology

[0002] Rechargeable lithium-ion batteries (LIBs) are widely used in portable electronic products and show great potential in electric vehicles and stationary energy storage. To meet the growing market demand, the application of high-specific-capacity anode materials has received increasing attention. Among them, silicon is considered the most promising next-generation commercial anode material due to its superior theoretical specific capacity (approximately 4200 mAh / g), low lithium insertion / extraction potential (approximately 0.5V), and extremely high reserves (second largest in the Earth's crust). However, during the charging and discharging process, the formation and decomposition of silicon-lithium alloys in silicon-based anode materials are accompanied by significant volume changes. These drastic volume changes lead to silicon particle breakage and pulverization, detachment of the anode active material from the electrode sheet, and the continuous formation of a solid electrolyte interphase (SEI) film due to pulverization and detachment.

[0003] Currently, the main methods to reduce the expansion of silicon materials include: 1) coating the surface of nano-silicon materials with carbon materials to improve their conductivity and reduce their expansion rate; 2) preparing porous templates and embedding silicon materials into the pores to reduce their expansion rate; or preparing porous silicon materials to reduce their expansion; 3) coating with materials with low expansion rate and high conductivity, such as graphene and carbon nanotubes, to reduce the expansion rate of silicon materials and improve their conductivity. However, although the above methods can improve the expansion of silicon-carbon anode materials to some extent, the effect is not significant. For example, uneven coating and thick coating layers, easy agglomeration of nano-silicon leading to poor uniformity, and poor conductivity of the coating material result in the specific capacity of silicon-carbon composite materials not being fully utilized, as well as poor cycle performance and rate performance, making it difficult to promote in the market.

[0004] Therefore, how to effectively suppress the volume expansion of silicon materials and improve the electrochemical performance of anode materials is an urgent technical problem to be solved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a silicon-carbon anode material, a method for preparing the silicon-carbon anode material, and a lithium-ion battery. The silicon-carbon anode material provided by this invention, under the influence of inorganic salts, allows nano-silicon to deposit within the pores of porous carbon, rather than settling on the surface of the porous carbon material, significantly reducing the volume expansion of silicon during lithium storage; thereby improving the cycle performance and rate performance of the anode material.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a silicon-carbon anode material, the silicon-carbon anode material comprising porous carbon and nano-silicon particles located within the pores of the porous carbon, wherein the surface of the porous carbon is coated with an inorganic salt.

[0008] The inorganic salt in this invention is located on the surface of the porous carbon material and does not cover the pores of the porous carbon material.

[0009] The silicon-carbon anode material provided by this invention allows nano-silicon to be deposited within the pores of porous carbon under the action of inorganic salts, rather than falling onto the surface of the porous carbon material, thus greatly reducing the volume expansion of silicon during lithium storage; thereby improving the cycle performance and rate performance of the anode material.

[0010] Preferably, the porous carbon surface and the interior of the pores are further coated with a carbon layer.

[0011] In this invention, a carbon layer is coated on the surface and inside the pores of porous carbon, which greatly improves the conductivity of silicon-carbon anode material. At the same time, the carbon layer deposited in the pores of porous carbon can further suppress the volume expansion of silicon in the pores. Furthermore, since silicon is not deposited on the surface of porous carbon, the carbon layer coating on the surface of porous carbon is more uniform.

[0012] Secondly, the present invention provides a method for preparing a silicon-carbon anode material, the method comprising the following steps:

[0013] (1) The carbon source precursor is mixed with an inorganic salt solution and coated to obtain an inorganic salt-coated carbon source precursor;

[0014] (2) The inorganic salt-coated carbon source precursor described in step (1) is mixed with an etchant and carbonized to obtain an inorganic salt-coated porous carbon material.

[0015] (3) Silane is deposited in the porous carbon material coated with inorganic salt in step (2) by deposition method to obtain silicon-carbon anode material.

[0016] The preparation method provided by this invention first coats the surface of a carbon source precursor with inorganic salts, and the inorganic salts are loosely coated on the surface of the carbon source precursor, that is, they do not completely cover the surface of the carbon source precursor. Then, an etchant is used to etch the carbon source precursor during the carbonization process. The etchant will etch the part of the carbon source precursor surface that is not coated with inorganic salts, thereby forming a porous carbon structure during the carbonization process without destroying the inorganic salt material coated on its surface. The inorganic salt material has extremely high polarity, while silane has the opposite polarity. During the deposition process, the inorganic salt on the surface acts as a silane-free structure, avoiding the deposition of nano-silicon obtained by silane deposition on the surface of the porous carbon. The nano-silicon is deposited in the pores of the porous carbon. The pores of the porous carbon can accommodate the volume expansion during the silicon lithium storage process, thereby eliminating the stress generated during the lithium insertion process and avoiding the situation where the volume expansion during the silicon lithium storage process leads to electrode breakage and pulverization, increased resistance, and a sharp drop in cycle performance.

[0017] In this invention, if the carbon source precursor is not pre-coated with inorganic salts and porous carbon materials are prepared directly, porous carbon materials with silane-like structures cannot be generated, resulting in the deposition of nano-silicon on the porous carbon surface. Furthermore, if inorganic salts are coated after carbonization, both the surface and pores of the porous carbon will be coated with inorganic salts, affecting the deposition of silanes within the porous carbon and causing silicon deposition on the porous carbon surface, leading to a deterioration in the material's electrochemical performance. Additionally, using other non-polar salt materials, such as cobalt naphthenate, dimethyl zinc, and stannous octoate, also fails to solve the problem of nano-silicon deposition on the porous carbon surface.

[0018] Preferably, the carbon source precursor in step (1) includes any one or a combination of at least two of the following: polymer, petrochemical by-products, or biomass.

[0019] Preferably, the carbon source precursor is insoluble in water.

[0020] Preferably, the inorganic salt in step (1) includes any one or a combination of at least two of phosphates, carbonates, sulfates or nitrates.

[0021] Preferably, the cation in the inorganic salt in step (1) is a metal cation, including lithium, sodium, potassium, magnesium, calcium, barium, aluminum, iron, zinc, copper, silver and other ions.

[0022] In this invention, the inorganic salt is a high-temperature resistant polar inorganic salt material. When it is preferably a metallic inorganic salt, the decomposition of the salt can be avoided during the subsequent high-temperature deposition and carbonization process. Once the inorganic salt decomposes, the silane structure on the porous carbon surface will disappear, resulting in the deposition of nano-silicon on the porous carbon surface.

[0023] Preferably, the molar concentration of the inorganic salt solution in step (1) is 0.001 to 1 mol / L, such as 0.001 mol / L, 0.005 mol / L, 0.008 mol / L, 0.01 mol / L, 0.03 mol / L, 0.05 mol / L, 0.08 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, or 1 mol / L, and more preferably 0.01 to 0.05 mol / L.

[0024] In this invention, when the molar concentration of the inorganic salt solution is within a further preferred range, it can better coat the carbon source precursor; however, if the molar concentration is too low, below 0.001 mol / L, the coating time will be long and the coating amount will be small, while if it is too high, above 1 mol / L, the coating will be too thick and dense, resulting in poor etching effect.

[0025] Preferably, the solid-liquid ratio of the carbon source precursor to the inorganic salt solution in step (1) is 1-70%, for example, 1%, 3%, 5%, 8%, 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, 40%, 43%, 45%, 48%, 50%, 53%, 55%, 58%, 60%, 63%, 65%, 68%, or 70%, and preferably 5-20%.

[0026] Preferably, the temperature during the mixing and coating process in step (1) is 100-200℃, such as 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 195℃, or 200℃.

[0027] In this invention, if the temperature is too low during the mixing and coating process, the coating time will be too long or the coating effect will be poor. If the temperature is too high, the reaction will be too violent, resulting in side reactions or safety hazards at high temperatures.

[0028] Preferably, the mixing and coating time in step (1) is 1 to 12 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours.

[0029] Preferably, the pressure during the mixing and coating process in step (1) is 0.1 to 1.5 MPa, for example, 0.1 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa, 0.9 MPa, 1 MPa, 1.1 MPa, 1.2 MPa, 1.3 MPa, 1.4 MPa or 1.5 MPa.

[0030] In this invention, the mixing and coating can be carried out in a hydrothermal reactor or a high-pressure reactor. If the pressure is too low during the mixing and coating process, it will not be conducive to the coating reaction. If it is too high, it will increase safety hazards and may also lead to the occurrence of side reactions.

[0031] Preferably, the mixed-coated material described in step (1) is subjected to solid-liquid separation, drying, and depolymerization.

[0032] Preferably, in step (2), the mass ratio of the inorganic salt-coated carbon source precursor to the etchant is 10:(9-12), such as 10:9, 10:10, 10:11 or 10:12.

[0033] Preferably, the etching agent in step (2) includes any one or a combination of at least two of potassium hydroxide, potassium carbonate, or zinc chloride.

[0034] Preferably, the carbonization temperature in step (2) is 750 to 850°C, for example, 750°C, 780°C, 800°C, 830°C or 850°C.

[0035] Preferably, the carbonization time in step (2) is 1 to 3 hours, for example, 1 hour, 2 hours or 3 hours.

[0036] Preferably, the silane in step (3) includes any one or a combination of at least two of the following nonpolar silanes: tris(trimethylsilyl)silane, methylsilane, diethylsilane, tetrafluorosilane, silicon tetrachloride, and hexamethyldisilane.

[0037] Preferably, the deposition method in step (3) includes chemical vapor deposition;

[0038] Preferably, the chemical vapor deposition process in step (3) also includes a carrier gas.

[0039] Preferably, the temperature of chemical vapor deposition in step (3) is 500 to 2000°C, such as 500°C, 800°C, 1000°C, 1300°C, 1500°C, 1800°C or 2000°C.

[0040] Preferably, the chemical vapor deposition time in step (3) is 10 min to 48 h, for example, 10 min, 1 h, 3 h, 5 h, 8 h, 10 h, 15 h, 20 h, 25 h, 30 h, 35 h, 40 h, 45 h or 48 h.

[0041] Preferably, carbon coating is performed after chemical vapor deposition in step (3).

[0042] In this invention, the porous carbon surface has a silane structure, which prevents nano-silicon from depositing on the surface of the porous carbon. This not only facilitates uniform coating of the carbon layer in the subsequent process, but also prevents the expansion of the nano-silicon on the porous carbon surface during lithium storage from damaging the carbon layer, thus avoiding a decrease in the electrochemical performance of the anode material.

[0043] Preferably, the carbon coating includes gaseous carbon coating.

[0044] Preferably, the carbon source for gas-phase carbon coating includes a hydrocarbon carbon source.

[0045] Preferably, the temperature of the gas phase carbon coating is 500 to 2000°C, such as 500°C, 800°C, 1000°C, 1300°C, 1500°C, 1800°C, or 2000°C.

[0046] Preferably, the time for gaseous carbon coating is 10 min to 48 h, such as 10 min, 1 h, 3 h, 5 h, 8 h, 10 h, 15 h, 20 h, 25 h, 30 h, 35 h, 40 h, 45 h, or 48 h.

[0047] As a preferred technical solution, the preparation method includes the following steps:

[0048] (1) The carbon source precursor is mixed with a metal inorganic salt solution with a molar concentration of 0.01-0.05 mol / L at a solid-liquid ratio of 5-20% under the conditions of 100-200℃ and 0.1-1.5 MPa for 1-12 h. The solid and liquid are separated, dried, and depolymerized to obtain the inorganic salt-coated carbon source precursor.

[0049] (2) The inorganic salt-coated carbon source precursor described in step (1) is mixed with an etchant at a mass ratio of 10:(9-12), and carbonized at 750-850°C for 1-3 hours to obtain an inorganic salt-coated porous carbon material.

[0050] (3) Silane is deposited in the porous carbon material coated with inorganic salt in step (2) at a temperature of 500 to 2000°C for 10 min to 48 h by chemical vapor deposition to obtain a core material of nano-silicon deposited in the pores of porous carbon. The core material is then coated with carbon to obtain a silicon-carbon anode material.

[0051] Furthermore, the preparation method provided in the second aspect of the present invention is used to prepare the silicon-carbon anode material described in the first aspect.

[0052] Thirdly, the present invention also provides a lithium-ion battery, the lithium-ion battery comprising a silicon-carbon anode material as described in the first aspect or a silicon-carbon anode material prepared by the method described in the second aspect.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] (1) The silicon-carbon anode material provided by the present invention allows nano-silicon to be deposited in the pores of porous carbon under the action of inorganic salts, rather than falling on the surface of the porous carbon material, which greatly reduces the volume expansion during the silicon lithium storage process; and because nano-silicon does not deposit on the surface of porous carbon, the carbon coating layer is more uniform, thereby improving the cycle performance and rate performance of the anode material.

[0055] (2) The preparation method provided by this invention involves a loose coating of inorganic salts on the surface of the carbon source precursor, meaning that the inorganic salts do not completely cover the surface of the carbon source precursor. Then, an etchant is used to etch the carbon source precursor during the carbonization process. The etchant etches the part of the carbon source precursor surface that is not coated with inorganic salts, thereby forming a porous carbon structure during the carbonization process without destroying the inorganic salt material coating its surface. Utilizing the opposite polarity between the inorganic salt material and silane, a silane-free structure is formed on the surface of the porous carbon material, avoiding the deposition of nano-silicon obtained from silane deposition onto the porous carbon. The porous carbon surface allows the nano-silicon to ultimately deposit within the pores of the porous carbon. The pores of the porous carbon can accommodate the volume expansion during the lithium storage process, thereby eliminating the stress generated during lithium insertion and preventing the electrode from breaking, pulverizing, increasing resistance, and drastically reducing cycle performance due to volume expansion during lithium storage. Furthermore, the nano-silicon does not deposit on the surface of the porous carbon, which is beneficial for the uniform coating of subsequent carbon layers. It also prevents the carbon layer from being destroyed by the expansion of nano-silicon during lithium storage if it were coated on the surface of the porous carbon, thus avoiding a decline in the electrochemical performance of the anode material. Detailed Implementation

[0056] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments are merely illustrative of the present invention and should not be construed as limiting the invention.

[0057] Example 1

[0058] This embodiment provides a silicon-carbon anode material, which includes a core and a carbon coating layer on the surface of the core. The core includes porous carbon and nano-silicon particles located in the pores of the porous carbon. The surface of the porous carbon is coated with lithium phosphate.

[0059] The preparation method of the silicon-carbon anode material is as follows:

[0060] (1) Under an argon atmosphere, polyfurfuryl alcohol and lithium phosphate solution (molar concentration of 0.01 mol / L) were mixed at a solid-liquid ratio of 25% and added to a high-pressure reactor for mixing and coating. The temperature during the coating process was set at 150℃, the pressure at 0.5 MPa, and the time at 8 h. After mixing and coating, solid-liquid separation (vacuum filtration), drying, and depolymerization were carried out in sequence to obtain polyfurfuryl alcohol coated with lithium phosphate.

[0061] (2) After mixing lithium phosphate-coated polyfurfuryl alcohol and potassium hydroxide at a mass ratio of 10:10, the mixture was ground thoroughly and carbonized at 800℃ for 2 hours. Then, it was cooled, filtered, washed and dried to obtain phosphate-coated porous carbon (lithium phosphate coated on the surface of porous carbon).

[0062] (3) The phosphate-coated porous carbon is placed in a chemical vapor deposition furnace, and then gaseous silane (silicon source) is deposited at 1000°C for 15 hours using a carrier gas (argon) to obtain nano-silicon particles inside the pores of the phosphate-coated porous carbon material; then, ethylene is used as the gaseous carbon source, and gaseous carbon coating is carried out at 800°C for 10 hours to obtain the silicon-carbon anode material.

[0063] Example 2

[0064] This embodiment provides a silicon-carbon anode material, which includes a core and a carbon coating layer on the surface of the core. The core includes porous carbon and nano-silicon particles located in the pores of the porous carbon. The surface of the porous carbon is coated with sodium sulfate.

[0065] The preparation method of the silicon-carbon anode material is as follows:

[0066] (1) Under an argon atmosphere, phenolic resin and sodium sulfate solution (molar concentration of 0.03 mol / L) were mixed at a solid-liquid ratio of 20% and added to a high-pressure reactor for mixing and coating. The temperature during the coating process was set to 100℃, the pressure to 0.1 MPa, and the time to 12 h. After mixing and coating, solid-liquid separation (vacuum filtration), drying and depolymerization were carried out in sequence to obtain sodium sulfate coated phenolic resin.

[0067] (2) After the sodium sulfate-coated phenolic resin and zinc chloride are mixed evenly at a mass ratio of 10:9, the mixture is ground thoroughly, carbonized at 850℃ for 1 hour, then cooled, filtered, washed and dried to obtain sodium sulfate-coated porous carbon (sodium sulfate is coated on the surface of porous carbon).

[0068] (3) Sodium sulfate-coated porous carbon is placed in a chemical vapor deposition furnace, and then gaseous silane (silicon source) is deposited at 800°C for 20 hours using a carrier gas (nitrogen) to obtain nano-silicon particles inside the pores of sodium sulfate-coated porous carbon; then acetylene is used as a gaseous carbon source, and gaseous carbon coating is carried out at 1000°C for 8 hours to obtain the silicon-carbon anode material.

[0069] Example 3

[0070] This embodiment provides a silicon-carbon anode material, which includes a core and a carbon coating layer on the surface of the core. The core includes porous carbon and nano-silicon particles located in the pores of the porous carbon. The surface of the porous carbon is coated with aluminum nitrate.

[0071] The preparation method of the silicon-carbon anode material is as follows:

[0072] (1) Under an argon atmosphere, coal tar and aluminum nitrate solution (molar concentration of 0.05 mol / L) were mixed at a solid-liquid ratio of 50% and added to a hydrothermal reactor for mixing and coating. The heat preservation temperature during the coating process was set at 200℃, the pressure at 1 MPa, and the time at 2 h. After mixing and coating, solid-liquid separation (vacuum filtration), drying, and depolymerization were carried out in sequence to obtain coal tar coated with aluminum nitrate.

[0073] (2) After mixing the aluminum nitrate-coated coal tar with potassium carbonate at a mass ratio of 10:12, grind thoroughly, carbonize at 750℃ for 3 hours, then cool, filter, wash and dry to obtain aluminum nitrate-coated porous carbon (aluminum nitrate is coated on the surface of porous carbon).

[0074] (3) The porous carbon coated with aluminum nitrate was placed in a chemical vapor deposition furnace, and then gaseous hexamethyldisilane (silicon source) was deposited at 1500°C for 5 hours using a carrier gas (argon) to obtain nano-silicon particles inside the pores of the porous carbon material coated with aluminum nitrate; then, ethylene was used as the gaseous carbon source, and gaseous carbon coating was carried out at 800°C for 10 hours to obtain the silicon-carbon anode material.

[0075] Example 4

[0076] The difference between this embodiment and Embodiment 1 is that the molar concentration of lithium phosphate in this embodiment is 1 mol / L.

[0077] The remaining preparation methods and parameters are consistent with those in Example 1.

[0078] Example 5

[0079] The difference between this embodiment and Embodiment 1 is that in this embodiment, lithium phosphate is replaced with ammonium dihydrogen phosphate.

[0080] The remaining preparation methods and parameters are consistent with those in Example 1.

[0081] Example 6

[0082] The difference between this embodiment and embodiment 1 is that the heat preservation temperature (mixed coating) in step (1) of this embodiment is 80°C.

[0083] The remaining preparation methods and parameters are consistent with those in Example 1.

[0084] Example 7

[0085] The difference between this embodiment and embodiment 1 is that the insulation temperature (mixed coating) in step (1) of this embodiment is 230℃.

[0086] The remaining preparation methods and parameters are consistent with those in Example 1.

[0087] Comparative Example 1

[0088] The difference between this comparative example and Example 1 is that in the silicon-carbon anode material provided in this comparative example, nano-silicon is located inside the pores of the porous material and on the surface of the porous carbon material, and the surface of the porous carbon material is not coated with lithium phosphate. In the preparation method, step (1) is not performed, and the carbon source precursor polyfurfuryl alcohol is directly subjected to steps (2) and (3).

[0089] The remaining preparation methods and parameters are consistent with those in Example 1.

[0090] Comparative Example 2

[0091] The difference between this comparative example and Example 1 is that lithium phosphate is replaced with cobalt naphthenate in this comparative example.

[0092] The remaining preparation methods and parameters are consistent with those in Example 1.

[0093] Comparative Example 3

[0094] The difference between this comparative example and Example 1 is that this comparative example performs step (2) first, and then performs step (1).

[0095] The remaining preparation methods and parameters are consistent with those in Example 1.

[0096] Anode sheets were prepared using the silicon-carbon anode materials provided in Examples 1-7 and Comparative Examples 1-3, and then batteries were fabricated using lithium sheets as counter electrodes. A 7% (w / w) polyvinylidene fluoride (PVDF) solution was prepared using N-methylpyrrolidone as a solvent. The anode materials provided in Examples 1-7 and Comparative Examples 1-3, PVDF, and conductive carbon black were mixed uniformly at a mass ratio of 80:10:10 and coated onto copper foil. The coated electrode sheets were then vacuum-dried in a vacuum drying oven at 90°C for 4 hours and rolled to a surface density of 4-7 mg / cm³. 2 For backup, a lithium metal sheet is used as the counter electrode, and a 1 mol / L LiPF6 three-component mixed solvent is used as the electrolyte in a mixture of EC:DMC:EMC = 1:1:1 (volume ratio). The mixture is then assembled into a 2032 type coin cell in an argon-filled glove box.

[0097] The batteries provided in Examples 1-7 and Comparative Examples 1-3 were tested under the following conditions: the charge / discharge voltage range was 5mV to 2.0V. The fast charging performance at 1C and the capacitance retention rate after 100 cycles were tested. The test results are shown in Table 1.

[0098] Table 1

[0099]

[0100]

[0101] The data from Examples 1 and 4 show that if the molar concentration of the inorganic salt solution is too high, the coating will be too thick and dense, resulting in poor etching effect and insufficient suppression of silicon volume expansion.

[0102] The data results from Examples 1 and 5 show that when the inorganic salt is a non-metallic inorganic salt that is easily decomposed at high temperatures, it will cause the silane structure on the porous carbon surface to fail, and silicon will be deposited on the porous carbon surface.

[0103] The data results from Examples 1, 6 and 7 show that during the mixing and coating process in step (1), if the temperature is too low, the amount of inorganic salt coating will be too small, and the silane structure after etching will not be dense enough. If the temperature is too high, the inorganic salt coating layer before etching will be too dense, affecting the etching effect.

[0104] The data from Example 1 and Comparative Example 1 show that without coating the carbon source with inorganic salts, silicon will be partially deposited on the porous carbon surface.

[0105] The data results from Example 1 and Comparative Example 2 show that if the carbon source surface is coated with a non-polar salt, it cannot solve the problem of silicon deposition on the porous carbon surface.

[0106] The data results from Example 1 and Comparative Example 3 show that if the carbon source is etched first and then coated, the porous carbon pores will also be coated with inorganic salts, which will affect the deposition of silicon in the porous carbon pores and also cause some silicon to be deposited on the surface of the porous carbon.

[0107] In summary, this invention loosely coats the surface of a carbon source with inorganic salts, meaning it does not completely cover the surface. The uncoated portions of the carbon source surface are etched using an etchant, forming a porous carbon structure without damaging the inorganic salt coating. Utilizing the opposite polarity between the inorganic salt and silane, a silane-free structure is formed on the surface of the porous carbon material. This prevents the deposition of nano-silicon obtained from silane deposition on the surface of the porous carbon, ensuring that the nano-silicon is ultimately deposited within the pores of the porous carbon. The pores of the porous carbon can accommodate silicon-lithium storage processes. The volume expansion during the process eliminates the stress generated during lithium insertion, avoiding the situation where volume expansion during silicon lithium storage leads to electrode breakage and pulverization, increased resistance, and a sharp drop in cycle performance. Furthermore, the nano-silicon does not deposit on the surface of porous carbon, which is beneficial for the uniform coating of subsequent carbon. It also prevents the carbon layer from being destroyed by the expansion during lithium storage once the nano-silicon coats the porous carbon surface, thus avoiding the decline in the electrochemical performance of the anode material. As a result, the cycle performance and rate performance of the silicon-carbon anode material provided by this invention are improved.

[0108] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A silicon-carbon anode material, characterized in that, The silicon-carbon anode material includes porous carbon and nano-silicon particles located in the pores of the porous carbon, and the surface of the porous carbon is coated with inorganic salt. The preparation method of the silicon-carbon anode material includes the following steps: (1) The carbon source precursor is mixed with an inorganic salt solution and coated to obtain an inorganic salt-coated carbon source precursor; (2) The inorganic salt-coated carbon source precursor described in step (1) is mixed with an etchant and carbonized to obtain an inorganic salt-coated porous carbon material. (3) Silane is deposited in the porous carbon material coated with inorganic salt in step (2) to obtain silicon-carbon anode material.

2. The silicon-carbon anode material according to claim 1, characterized in that, The porous carbon surface and the interior of the pores are also coated with a carbon layer.

3. A method for preparing the silicon-carbon anode material as described in claim 1 or 2, characterized in that, The preparation method includes the following steps: (1) The carbon source precursor is mixed with an inorganic salt solution and coated to obtain an inorganic salt-coated carbon source precursor; (2) The inorganic salt-coated carbon source precursor described in step (1) is mixed with an etchant and carbonized to obtain an inorganic salt-coated porous carbon material. (3) Silane is deposited in the porous carbon material coated with inorganic salt in step (2) to obtain silicon-carbon anode material.

4. The method for preparing the silicon-carbon anode material according to claim 3, characterized in that, The carbon source precursor in step (1) includes any one or a combination of at least two of the following: high molecular polymers, petroleum chemical by-products, or biomass.

5. The method for preparing the silicon-carbon anode material according to claim 3, characterized in that, The carbon source precursor is insoluble in water.

6. The method for preparing the silicon-carbon anode material according to claim 3, characterized in that, The inorganic salt in step (1) includes any one or a combination of at least two of phosphates, carbonates, sulfates or nitrates.

7. The method for preparing the silicon-carbon anode material according to claim 3, characterized in that, The cation in the inorganic salt in step (1) is a metal cation.

8. The method for preparing the silicon-carbon anode material according to claim 3, characterized in that, The molar concentration of the inorganic salt solution in step (1) is 0.001~1 mol / L.

9. The method for preparing the silicon-carbon anode material according to claim 3, characterized in that, The molar concentration of the inorganic salt solution in step (1) is 0.01~0.05 mol / L.

10. The method for preparing the silicon-carbon anode material according to claim 3, characterized in that, The solid-liquid ratio of the carbon source precursor to the inorganic salt solution in step (1) is 1~70%.

11. The method for preparing the silicon-carbon anode material according to claim 3, characterized in that, The solid-liquid ratio of the carbon source precursor to the inorganic salt solution in step (1) is 5-20%.

12. The method for preparing the silicon-carbon anode material according to claim 3, characterized in that, The temperature during the mixing and coating process in step (1) is 100~200℃.

13. The method for preparing the silicon-carbon anode material according to claim 3, characterized in that, The mixing and coating time in step (1) is 1~12h.

14. The method for preparing the silicon-carbon anode material according to claim 3, characterized in that, The pressure during the mixing and coating process in step (1) is 0.1~1.5MPa.

15. The method for preparing the silicon-carbon anode material according to claim 3, characterized in that, The mixed and coated material described in step (1) is subjected to solid-liquid separation, drying and depolymerization.

16. The method for preparing the silicon-carbon anode material according to claim 3, characterized in that, In step (2), the mass ratio of the inorganic salt-coated carbon source precursor to the etchant is 10: (9~12).

17. The method for preparing the silicon-carbon anode material according to claim 3, characterized in that, The etching agent in step (2) includes any one or a combination of at least two of potassium hydroxide, potassium carbonate, or zinc chloride.

18. The method for preparing the silicon-carbon anode material according to claim 3, characterized in that, The carbonization temperature in step (2) is 750~850℃.

19. The method for preparing the silicon-carbon anode material according to claim 3, characterized in that, The carbonization time in step (2) is 1 to 3 hours.

20. The method for preparing the silicon-carbon anode material according to claim 3, characterized in that, The silane in step (3) includes any one or a combination of at least two of tris(trimethylsilyl)silane, methylsilane, diethylsilane, tetrafluorosilane, tetrachlorosilane, and hexamethyldisilane.

21. The method for preparing the silicon-carbon anode material according to claim 3, characterized in that, The deposition method described in step (3) includes chemical vapor deposition.

22. The method for preparing the silicon-carbon anode material according to claim 21, characterized in that, The chemical vapor deposition process in step (3) also includes a carrier gas.

23. The method for preparing the silicon-carbon anode material according to claim 21, characterized in that, The temperature for chemical vapor deposition in step (3) is 500~2000℃.

24. The method for preparing the silicon-carbon anode material according to claim 21, characterized in that, The chemical vapor deposition time in step (3) is 10 min to 48 h.

25. The method for preparing the silicon-carbon anode material according to claim 21, characterized in that, In step (3), carbon coating is performed after chemical vapor deposition.

26. The method for preparing the silicon-carbon anode material according to claim 25, characterized in that, The carbon coating includes gas-phase carbon coating.

27. The method for preparing the silicon-carbon anode material according to claim 26, characterized in that, The carbon source for gas-phase carbon coating includes hydrocarbon carbon sources.

28. The method for preparing the silicon-carbon anode material according to claim 26, characterized in that, The temperature of the gas phase carbon coating is 500~2000℃.

29. The method for preparing the silicon-carbon anode material according to claim 26, characterized in that, The time for gaseous carbon coating is 10 min to 48 h.

30. The method for preparing the silicon-carbon anode material according to claim 3, characterized in that, The preparation method includes the following steps: (1) The carbon source precursor is mixed with a metal inorganic salt solution with a molar concentration of 0.01~0.5mol / L at a solid-liquid ratio of 5~20% at 100~200℃ and 0.1~1.5MPa for 1~12h, then the solid and liquid are separated, dried, and depolymerized to obtain the inorganic salt-coated carbon source precursor. (2) The inorganic salt-coated carbon source precursor described in step (1) is mixed with an etchant at a mass ratio of 10: (9~12), and carbonized at 750~850℃ for 1~3h to obtain an inorganic salt-coated porous carbon material. (3) Silane is deposited in the porous carbon material coated with inorganic salt in step (2) at a temperature of 500~2000℃ for 10min~48h by chemical vapor deposition to obtain the core material of nano-silicon deposited in the pores of porous carbon. The core material is then coated with carbon to obtain silicon-carbon anode material.

31. A lithium-ion battery, characterized in that, The lithium-ion battery includes a silicon-carbon anode material prepared by the method described in claim 1 or 2, or the method described in any one of claims 3-30.

Images