Silicon-carbon negative electrode material, preparation method thereof and secondary battery

Abstract

The invention discloses a silicon-carbon negative electrode material, a preparation method thereof and a secondary battery, and relates to the technical field of material preparation. The silicon-carbon negative electrode material comprises a silicon-carbon inner core and a carbon coating layer coating the silicon-carbon inner core, the silicon-carbon inner core comprises porous carbon, a surface modification layer coating the porous carbon and nanometer silicon contained in porous carbon channels, the surface modification layer is a polymer layer, a non-oxide ceramic layer and / or a transition metal oxide layer, and the oxygen content of the porous carbon is 0%-2%. The silicon-carbon negative electrode material provided by the invention can effectively inhibit volume expansion and has good cycle performance.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a silicon-carbon negative electrode material and a preparation method thereof. Background Art

[0002] Silicon anodes have a high theoretical specific capacity (3579 mAh / g) and have become the most promising anode material for lithium-ion batteries. However, silicon expands by >300% during lithium insertion and extraction, causing severe mechanical stress and electrochemical side reactions. This can lead to the formation of a large SEI film on the silicon surface, resulting in capacity loss and shortened cycle life.

[0003] Gas-phase silicon carbon has attracted widespread attention due to its relatively low volume expansion and good recycling effect, and has been applied to digital products. However, when gas-phase silicon carbon is used in power batteries and energy storage batteries, there are higher requirements for its recycling. Therefore, it is necessary to further reduce the volume expansion of the material and improve the recycling performance. Summary of the Invention

[0004] In view of the above problems, the object of the present invention is to provide a silicon-carbon negative electrode material, a preparation method thereof, and a secondary battery. The silicon-carbon negative electrode material of the present invention can effectively inhibit volume expansion and has good cycle performance.

[0005] To achieve the above-mentioned objectives, the first aspect of the present invention provides a silicon-carbon negative electrode material, comprising a silicon-carbon core and a carbon coating layer coating the silicon-carbon core, wherein the silicon-carbon core comprises porous carbon, a surface modification layer coating the porous carbon, and nano-silicon accommodated in the pores of the porous carbon, the surface modification layer is a polymer layer, a non-oxide ceramic layer and / or a transition metal oxide layer, and the oxygen content of the porous carbon is 0%~2%.

[0006] Compared with the prior art, the porous carbon surface of the present invention is coated with a surface modification layer, which is a polymer layer, a non-oxide ceramic layer and / or a transition metal oxide layer. The polymer layer and the non-oxide ceramic layer are relatively stable in a high temperature environment, and the transition metal oxide layer has low activity, which can effectively inhibit the deposition of nano-silicon on the porous carbon surface, inhibit surface floating silicon, thereby inhibiting side reactions, reducing the volume expansion of the silicon-carbon negative electrode material during the cycle, and improving the cycle performance of the secondary battery. At the same time, the oxygen content of the porous carbon is controlled between 0% and 2%, which can effectively avoid the preferential deposition of nano-silicon on the active sites due to excessive oxygen content, blocking the internal pores, making the total deposited silicon amount too low, and thus deteriorating the electrochemical performance of the secondary battery.

[0007] In some embodiments, the volume expansion rate of the silicon-carbon negative electrode material after 100 cycles is ≤32%.

[0008] In some embodiments, the capacity retention rate of the silicon-carbon negative electrode material after 100 cycles is ≥95%.

[0009] In some embodiments, the dQ / dV of the silicon-carbon negative electrode material is ≥1.60, and dQ / dV=0.2V~0.4V delithiation zinc / 0.4V~0.5V delithiation zinc.

[0010] In some embodiments, the reversible specific capacity of the silicon-carbon negative electrode material is 1600 mAh / g to 2500 mAh / g.

[0011] In some embodiments, the first coulombic efficiency of the silicon-carbon negative electrode material is ≥90%.

[0012] In some embodiments, the specific surface area of ​​the silicon-carbon negative electrode material is ≤10 m 2 / g.

[0013] In some embodiments, the particle size D50 of the silicon-carbon negative electrode material is 6 μm to 10 μm.

[0014] In some embodiments, the particle size distribution dispersion of the silicon-carbon negative electrode material is F, 0<F≤1.4, F=(D90-D10) / D50.

[0015] In some embodiments, the true density of the silicon-carbon negative electrode material is ≤1.8 g / cm 3 .

[0016] In some embodiments, the electrical conductivity of the silicon-carbon negative electrode material is 0.1 S / cm to 10.0 S / cm.

[0017] In some embodiments, the tap density of the silicon carbon negative electrode material is 0.7 g / cm 3 ~1.0 g / cm 3 .

[0018] In some embodiments, the silicon grain size of the silicon-carbon anode material is ≤3 nm.

[0019] In some embodiments, the surface silicon content of the silicon-carbon negative electrode material is P, P≤0.5%, P=(nano-silicon content×2.413-ash content)×0.875.

[0020] In some embodiments, the porous carbon has a particle size D50 of 6 μm to 10 μm.

[0021] In some embodiments, the pore volume of the porous carbon is 0.5 g / cm 3 ~1.2 g / cm 3 .

[0022] In some embodiments, the porous carbon has a specific surface area of ​​1500 m 2 / g~2500 m 2 / g.

[0023] In some embodiments, the average pore size of the porous carbon channels is 1.5 nm to 2.0 nm.

[0024] In some embodiments, the microporosity of the porous carbon channels is ≥ 70%.

[0025] In some embodiments, the oxygen content of the silicon-carbon negative electrode material is ≤ 2%.

[0026] In some embodiments, the porous carbon has a nitrogen content of 0% to 0.5%.

[0027] In some embodiments, the ratio of the pore volume of the porous carbon channel with a pore diameter of 0.6 nm to 1.0 nm to the total pore volume is A, and A is ≥40%.

[0028] In some embodiments, the ratio of the pore volume of the porous carbon channel with a pore diameter within the range of 0 nm to 0.6 nm to the total pore volume is B, and B is ≤10%.

[0029] In some embodiments, the porous carbon has an electrical conductivity of ≥ 5 S / cm.

[0030] In some embodiments, the porous carbon has a pH of 6-9.

[0031] In some embodiments, the bulk density of nano-silicon is 1.3 g / cm 3 ~1.5 g / cm 3 .

[0032] In some embodiments, nano-silicon accounts for 40 wt % to 60 wt % of the silicon-carbon negative electrode material.

[0033] In some embodiments, the modified layer is 0.3 wt% to 1.0 wt% of the silicon-carbon negative electrode material.

[0034] In some embodiments, the carbon coating layer is 1 wt% to 4 wt% of the silicon-carbon negative electrode material.

[0035] A second aspect of the present invention provides a method for preparing a silicon-carbon negative electrode material, comprising the steps of: (I) Preparation of porous carbon The carbon source is activated by alkali or water vapor and then crushed and graded to obtain porous carbon; (II) Preparation of surface-modified porous carbon The porous carbon and a surface modification material solution are mixed, dried, and heat-treated to obtain surface-modified porous carbon, wherein the surface modification material is selected from at least one of a polymer material, a non-oxide ceramic material, and a transition metal oxide; (III) Nano-silicon deposition The surface-modified porous carbon and a gaseous silicon source are chemically vapor deposited to obtain a silicon-carbon core. The silicon deposition of the chemical vapor deposition includes an initial stage, an intermediate stage, and an end stage. The flow rates of the gaseous silicon source in the initial stage, the intermediate stage, and the end stage show a decreasing trend. (IV) Primary carbon coating The silicon-carbon core and acetylene are carbon-coated once to obtain an intermediate; (V) Secondary carbon coating The intermediate is subjected to secondary carbon coating with acetylene to obtain a silicon-carbon negative electrode material.

[0036] Compared with the prior art, the present invention first uses a surface modification material to modify the surface of porous carbon and then deposits nano-silicon. The selected surface modification materials, such as polymer materials, non-oxide ceramic materials and transition metal oxides, have good thermal stability and low reactivity with silicon-based species. Therefore, during the nano-silicon deposition process, nano-silicon can be effectively prevented from being deposited on the porous carbon surface, inhibiting surface floating silicon, thereby effectively reducing the occurrence of side reactions. During the silicon deposition process, the gaseous silicon source flow rate is the highest in the initial stage, which allows silicon to be deposited quickly in the initial stage and the internal deposition is not dense, thereby effectively alleviating volume expansion. The gaseous silicon source flow rate in the intermediate stage and the gaseous silicon source flow rate in the terminal stage gradually decrease, allowing silicon to be deposited in the porous carbon pores, avoiding the reduction of the porous carbon pores in the late deposition stage, and the excessive silane flow rate causing silane to be deposited on the surface, reducing the material conductivity and cycle stability.

[0037] In some embodiments, chemical vapor deposition includes placing surface-modified porous carbon in a first fluidized bed, first introducing a protective gas to reduce the oxygen content to 100 ppm or less, then raising the temperature of the first fluidized bed to 400°C~500°C at a heating rate of 1°C / min~10°C / min, and finally introducing a gaseous silicon source and a diluent gas to enter the silicon deposition stage.

[0038] In some embodiments, the carbon source includes at least one of resin, biomass, and petroleum tar.

[0039] In some embodiments, the crushing and classification is performed in a jet mill or a mechanical mill.

[0040] In some embodiments, the surface modification material solution is obtained by dissolving the surface modification material in a solvent, and the solvent is selected from at least one of water, ethanol, acetone, isopropanol, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide and N-methylpyrrolidone.

[0041] In some embodiments, the concentration of the surface modification material solution is 1% to 10%.

[0042] In some embodiments, the mass ratio of the porous carbon to the surface modification material is 100:0.3-1.

[0043] In some embodiments, the mixing temperature is 0° C. to 60° C., and the mixing time is 1 h to 4 h. In some embodiments, the drying is spray drying, the spray drying temperature is 130° C. to 200° C., and the solid content of the spray slurry is 10% to 30%.

[0044] In some embodiments, the drying is performed in a drying oven at a temperature of 80° C. to 200° C. for a drying time of 12 h to 36 h.

[0045] In some embodiments, the heat treatment comprises first treating the dried mixture at 150° C. to 180° C. for 1 h to 8 h, then treating it at 200° C. to 250° C. for 1 h to 4 h, and finally treating it at 300° C. to 450° C. for 1 h to 4 h.

[0046] In some embodiments, the heat treatment comprises heating the dried mixture to 700° C. to 1000° C. at a heating rate of 1° C. / min to 5° C. / min and then maintaining the temperature for 1 hour to 4 hours.

[0047] In some embodiments, the polymeric material is selected from at least one of polyimide and polyaniline.

[0048] In some embodiments, the non-oxide ceramic material is selected from at least one of boron nitride, aluminum nitride, and silicon carbide.

[0049] In some embodiments, the transition metal oxide is selected from at least one of yttrium oxide, zirconium oxide, and hafnium oxide.

[0050] In some embodiments, the ratio of the mass of the surface-modified porous carbon to the total volume of the gaseous silicon source is 1:600-1300, kg:L.

[0051] In some embodiments, the flow rate of the gaseous silicon source in the initial stage is 2 L / min·kg to 4 L / min·kg.

[0052] In some embodiments, the flow rate of the gaseous silicon source in the intermediate stage is 1 L / min·kg to 2 L / min·kg.

[0053] In some embodiments, the flow rate of the gaseous silicon source during the termination stage is 0.5 L / min·kg to 1 L / min·kg.

[0054] In some embodiments, the volume of the gaseous silicon source in the initial stage accounts for 5% to 20% of the total volume of the gaseous silicon source.

[0055] In some embodiments, the volume of the gaseous silicon source in the intermediate stage accounts for 60% to 90% of the total volume of the gaseous silicon source.

[0056] In some embodiments, the volume of the gaseous silicon source at the termination stage accounts for 5% to 20% of the total volume of the gaseous silicon source.

[0057] In some embodiments, the protective gas is selected from at least one of nitrogen, argon, and helium.

[0058] In some embodiments, the diluent gas is selected from at least one of nitrogen, argon, and helium.

[0059] In some embodiments, the gaseous silicon source includes at least one of monosilane, disilane, trisilane, monochlorotrihydrogensilane, dichlorodihydrogensilane, and trichlorosilane.

[0060] In some embodiments, the first fluidized bed has a lower temperature zone T1 下 , medium temperature zone T1 中 and upper temperature zone T1 上 , 400℃≤T1 下 <450℃, 450℃≤T1 中 ≤500℃, 450℃≤T1 上 ≤500℃.

[0061] In some embodiments, the volume concentration of the gaseous silicon source is ≤ 30%.

[0062] In some embodiments, the ratio of the mass of the surface-modified porous carbon to the total volume of acetylene in the first carbon coating is 1:100-300, kg:L.

[0063] In some embodiments, the secondary carbon coating includes introducing nitrogen and acetylene at a temperature of 550°C to 620°C, with a nitrogen flow rate of 4 L / min·kg to 10 L / min·kg, and an acetylene flow rate of 0.5 L / min·kg to 2 L / min·kg, and keeping the temperature for 1 hour to 2 hours after the gas introduction is completed.

[0064] In some embodiments, the amount of carbon coated in the secondary carbon coating is 0.5 wt % to 2 wt % of the intermediate.

[0065] In some embodiments, the primary carbon coating comprises first heating to the reaction temperature and then sequentially introducing low-concentration acetylene and high-concentration acetylene for reaction, wherein the volume concentration of the low-concentration acetylene is lower than the volume concentration of the high-concentration acetylene.

[0066] In some embodiments, the primary carbon coating is performed in a second fluidized bed having a lower temperature zone T2. 下 , medium temperature zone T2 中 and upper temperature zone T2 上, T2 下 =T2 中 =T2 上 or T2 下 =T2 中 >T2 上 .

[0067] In some embodiments, the reaction temperature is 550°C to 620°C.

[0068] In some embodiments, the holding time is 0.5 h to 1 h.

[0069] In some embodiments, the volume concentration of the low-concentration acetylene is 5% to 10%.

[0070] In some embodiments, the volume concentration of high concentration acetylene is 15% to 20%.

[0071] In some embodiments, the flow rate of low-concentration acetylene is 0.5 L / min·kg to 1.0 L / min·kg.

[0072] In some embodiments, the low concentration acetylene is introduced for a time period of 10 min to 60 min.

[0073] In some embodiments, the flow rate of high-concentration acetylene is 1.5 L / min·kg to 2.0 L / min·kg.

[0074] In some embodiments, the high concentration acetylene is introduced for a time period of 1 h to 4 h.

[0075] In some embodiments, alkali activation comprises mixing the carbon source and the alkali, heating the mixture to 700°C~900°C at a heating rate of 10°C / min~30°C / min, and heat-treating the mixture for 1 h~4 h; cooling, washing to neutrality, and drying the mixture, and then heating the mixture to 800°C~900°C at a heating rate of 5°C / min~30°C / min, and heat-treating the mixture for 1 h~4 h to obtain a porous carbon activated material.

[0076] In some embodiments, water vapor activation comprises heating the porous carbon and water vapor to 800°C~1000°C at a heating rate of 10°C / min~30°C / min and heat-treating for 1 h~10 h, cooling, washing to neutrality, and drying, and then heating the porous carbon and water vapor to 800°C~900°C at a heating rate of 5°C / min~30°C / min and heat-treating for 1 h~4 h to obtain a porous carbon activated material.

[0077] A third aspect of the present invention provides a secondary battery comprising a positive electrode material and a negative electrode material, wherein the negative electrode material comprises the aforementioned silicon-carbon negative electrode material or the silicon-carbon negative electrode material prepared by the aforementioned method for preparing the silicon-carbon negative electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Figure 1 Schematic diagram of the structure of the silicon-carbon negative electrode material of the present invention; Figure 2 This is an SEM image of the silicon-carbon negative electrode material in Example 1 of the present invention; Figure 3 This is the charge and discharge curve of the silicon-carbon negative electrode material in Example 1 of the present invention; Figure 4 dQ / dV differential capacitance diagram of the silicon-carbon negative electrode material in Example 1 of the present invention; Figure 5 This is the XRD pattern of the silicon-carbon negative electrode material in Example 1 of the present invention; Figure 6 This is an SEM image of the silicon-carbon negative electrode material in Comparative Example 1 of the present invention; Figure 7 This is the charge and discharge curve of the silicon-carbon negative electrode material in Comparative Example 1 of the present invention; Figure 8 dQ / dV differential capacitance diagram of the silicon-carbon negative electrode material in Comparative Example 1 of the present invention; Figure 9 This is the XRD pattern of the silicon-carbon negative electrode material in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0079] The silicon-carbon negative electrode material of the present invention can be used alone or mixed with other negative electrode active materials (such as natural graphite, artificial graphite, soft carbon and / or hard carbon). The silicon-carbon negative electrode material can be used in secondary batteries, which include positive electrode active materials and negative electrode active materials. The positive electrode active material includes at least one of a lithium cobalt oxide positive electrode material, a lithium iron phosphate positive electrode material, a lithium nickel cobalt manganese oxide positive electrode material, and a lithium nickel cobalt aluminum oxide positive electrode material.

[0080] The structure of the silicon-carbon negative electrode material of the present invention can be obtained by Figure 1 An example is given below. Figure 1 As shown, the silicon-carbon negative electrode material 100 includes a silicon-carbon core 10 and a carbon coating layer 20 coating the silicon-carbon core 10. The silicon-carbon core 10 includes porous carbon 11, a surface modification layer 12 coating the porous carbon 11, and nano-silicon 13 accommodated in the pores of the porous carbon. The surface modification layer 12 can be a polymer layer (not shown), a non-oxide ceramic layer (not shown), and / or a transition metal oxide layer (not shown).

[0081] The oxygen content of porous carbon is 0% to 2%. As an example, it can be, but not limited to, 0%, 0.1%, 0.2%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.5%, 1.6%, 1.8%, and 2%. Excessive oxygen content causes nano-silicon to preferentially deposit at active sites, blocking internal pores, making the total amount of deposited silicon too low, and thus deteriorating the electrochemical performance of the secondary battery. In addition, high oxygen content causes the product to easily absorb water, requiring long-term heat treatment to remove water during preparation, which is not conducive to improving efficiency, and water content interference is not conducive to batch stability. The volume expansion rate of the silicon-carbon negative electrode material of the present invention after 100 cycles is ≤32%. As an example, it can be, but not limited to, ≤32%, ≤31%, ≤30%, ≤29%, ≤28%, ≤27%, 26%, ≤25%, ≤24%, ≤23%, ≤22%, ≤21%, and ≤20%. The capacity retention rate of the silicon-carbon negative electrode material after 100 cycles is ≥95%. As an example, it can be, but is not limited to, ≥95%, ≥95.5%, ≥96%, ≥96.5%, ≥97%, ≥97.5%, ≥98%, ≥98.5%, or ≥99%. The dQ / dV of the silicon-carbon negative electrode material is ≥1.60, where dQ / dV = 0.2V~0.4V delithiation front / 0.4V~0.5V delithiation front. As an example, it can be, but is not limited to, ≥1.60, ≥1.65, ≥1.70, ≥1.75, ≥1.80, ≥1.85, ≥1.90, ≥1.95, or ≥2.00. The reversible specific capacity of the silicon-carbon negative electrode material is 1600 mAh / g~2500 mAh / g. As an example, it can be, but not limited to, 1600 mAh / g, 1680 mAh / g, 1750 mAh / g, 1820 mAh / g, 1900 mAh / g, 1960 mAh / g, 2140 mAh / g, 2210 mAh / g, 2350 mAh / g, 2460 mAh / g, and 2500 mAh / g. The first coulombic efficiency of the silicon-carbon negative electrode material is ≥90%. As an example, it can be, but not limited to, ≥90%, ≥91%, ≥92%, ≥93%, ≥94%, ≥95%, ≥96%, ≥97%, ≥98%, and ≥99%. The specific surface area of ​​the silicon-carbon negative electrode material is ≤10 m 2 / g, as an example, can be but not limited to ≤10 m 2 / g, ≤9 m 2 / g, ≤8 m 2 / g, ≤7 m 2 / g, ≤6m 2 / g, ≤5 m 2 / g, ≤4 m 2 / g, ≤3 m 2 / g, ≤2 m 2 / g. The particle size D50 of the silicon-carbon negative electrode material is 6 μm~10 μm. As an example, it can be but not limited to 6 μm, 7 μm, 8 μm, 9 μm, and 10 μm. The particle size distribution dispersion of the silicon-carbon negative electrode material is F, 0<F≤1.4, F=(D90-D10) / D50. As an example, it can be but not limited to 0.1, 0.2, 0.3, 0.5, 0.6, 0.8, 1.0, 1.1, 1.2, 1.3, and 1.4. The true density of the silicon-carbon negative electrode material is ≤1.8g / cm 3 As an example, it can be, but not limited to, 1.8 g / cm 3 , 1.79g / cm 3 , 1.78g / cm 3 , 1.77g / cm 3 , 1.76g / cm 3 , 1.75g / cm 3 , 1.74g / cm 3 , 1.73g / cm 3 , 1.72g / cm 3 、1.71g / cm 3 , 1.70g / cm 3 . The true density of existing silicon-carbon negative electrode materials is generally between 1.9 and 2.1, while the true density of the silicon-carbon negative electrode material of the present invention is below 1.8, indicating that the surface carbon coating of the silicon-carbon negative electrode material of the present invention is more dense. The electrical conductivity of the silicon-carbon negative electrode material is 0.1 S / cm~10.0 S / cm. As an example, the electrical conductivity of the silicon-carbon negative electrode material is 0.1 S / cm, 0.2 S / cm, 0.5 S / cm, 0.8 S / cm, 1.0 S / cm, 1.5 S / cm, 2.0 S / cm, 3.0 S / cm, 4.0 S / cm, 5.0 S / cm, 6.0 S / cm, 7.0 S / cm, 8.0 S / cm, 9.0 S / cm, and 10.0 S / cm. The tap density of the silicon-carbon negative electrode material is 0.7 g / cm 3 ~1.0 g / cm 3 , as an example, it can be, but is not limited to, 0.7 g / cm 3 , 0.75 g / cm 3 , 0.8 g / cm 3 , 0.85 g / cm 3 , 0.9 g / cm 3 , 0.95 g / cm 3 , 1.0 g / cm 3The silicon grain size of the silicon-carbon negative electrode material is ≤3 nm. As an example, it can be, but is not limited to, ≤3 nm, ≤2.8 nm, ≤2.5 nm, ≤2.2 nm, ≤2 nm, ≤1.8 nm, ≤1.5 nm, ≤1.2 nm, and ≤1 nm. The surface silicon content of the silicon-carbon negative electrode material is P, where P is ≤0.5%, and P = (nano-silicon content × 2.413 - ash content) × 0.875. As an example, it can be, but is not limited to, ≤0.5%, ≤0.4%, ≤0.3%, ≤0.2%, and ≤0.1%. The oxygen content of the silicon-carbon negative electrode material is ≤2%. As an example, it can be, but is not limited to, ≤2%, ≤1.9%, ≤1.8%, ≤1.6%, ≤1.5%, ≤1.4%, ≤1.3%, ≤1.2%, ≤1.1%, ≤1.0%, ≤0.8%, ≤0.6%, ≤0.4%, and ≤0.2%.

[0082] The particle size D50 of the porous carbon is 6 μm to 10 μm, and as an example, it can be, but is not limited to, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, and 10 μm. The pore volume of the porous carbon is 0.5 g / cm 3 ~1.2 g / cm 3 , as an example, it can be, but is not limited to, 0.5 g / cm 3 , 0.6 g / cm 3 , 0.7 g / cm 3 , 0.8 g / cm 3 , 0.9 g / cm 3 , 1.0 g / cm 3 , 1.1 g / cm 3 , 1.2g / cm 3 The specific surface area of ​​porous carbon is 1500 m 2 / g~2500 m 2 / g, as an example, it can be but not limited to 1500 m 2 / g, 1600 m 2 / g, 1700 m 2 / g, 1800 m 2 / g, 1900 m 2 / g, 2000 m 2 / g, 2100 m 2 / g, 2200 m 2 / g, 2300 m 2 / g, 2400 m 2 / g, 2500 m 2 / g. The average pore diameter of the porous carbon channels is 1.5 nm to 2.0 nm. For example, it can be, but is not limited to, 1.5 nm, 1.6 nm, 1.7 nm, 1.8 nm, 1.9 nm, and 2.0 nm. The microporosity of the porous carbon channels is ≥70%. For example, it can be, but is not limited to, ≥70%, ≥75%, ≥80%, ≥85%, ≥90%, ≥95%, and ≥98%. The nitrogen content of the porous carbon is 0% to 0.5%. For example, it can be, but is not limited to, 0%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5%. The ratio of the pore volume of the porous carbon channels with a pore diameter of 0.6 nm to 1.0 nm to the total pore volume is A, and A is ≥40%. For example, it can be, but is not limited to, ≥40%, ≥45%, ≥50%, ≥55%, ≥60%, ≥70%, ≥80%, ≥90%, and ≥95%. The ratio of the pore volume of the porous carbon channel with a pore diameter of 0 nm to 0.6 nm to the total pore volume is B, where B ≤ 10%. As an example, it can be, but not limited to, ≤ 10%, ≤ 9%, ≤ 8%, ≤ 7%, ≤ 6%, ≤ 5%, ≤ 4%, ≤ 3%, ≤ 2%. The electrical conductivity of the porous carbon is ≥ 5 S / cm. As an example, it can be, but not limited to, ≥ 5 S / cm, ≥ 6 S / cm, ≥ 7 S / cm, ≥ 8 S / cm, ≥ 9 S / cm, ≥ 10 S / cm, ≥ 15 S / cm, ≥ 20 S / cm, ≥ 25 S / cm. The pH of the porous carbon is 6 to 9. As an example, it can be, but not limited to, 6, 6.5, 7, 7.5, 8, 8.5, 9. The bulk density of nano-silicon is 1.3 g / cm 3 ~1.5g / cm 3 , as an example, it can be, but is not limited to, 1.3 g / cm 3 , 1.4 g / cm 3 , 1.5 g / cm 3 . Controlling the packing density of nano-silicon within this range can effectively alleviate the volume expansion of silicon while ensuring the reversible specific capacity and first coulombic efficiency of the silicon-carbon negative electrode material. Nano-silicon is 40wt%~60wt% of the silicon-carbon negative electrode material. As an example, it can be but not limited to 40wt%, 42wt%, 44wt%, 46wt%, 48wt%, 50wt%, 52wt%, 54wt%, 56wt%, 58wt%, and 60wt%. The modified layer is 0.3wt%~1.0wt% of the silicon-carbon negative electrode material. As an example, it can be but not limited to 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, and 1.0wt%. The carbon coating layer is 1wt%~4wt% of the silicon-carbon negative electrode material. As an example, it can be but not limited to 1wt%, 2wt%, 3wt%, and 4wt%.

[0083] The method for preparing the silicon-carbon negative electrode material of the present invention may include the following steps: (I) Preparation of porous carbon The carbon source is activated by alkali or water vapor and then crushed and graded to obtain porous carbon; (II) Preparation of surface-modified porous carbon The porous carbon and the surface modification material solution are mixed, dried, and heat-treated to obtain the surface-modified porous carbon; (III) Nano-silicon deposition Surface-modified porous carbon and a gaseous silicon source are chemically vapor deposited to obtain a silicon-carbon core; (IV) Primary carbon coating The silicon-carbon core and acetylene are carbon-coated once to obtain an intermediate; (V) Secondary carbon coating The intermediate is subjected to secondary carbon coating with acetylene to obtain a silicon-carbon negative electrode material.

[0084] In step (I), the carbon source comprises at least one of resin, biomass, and tar. For example, the resin may be, but is not limited to, phenolic resin, and the biomass may be, but is not limited to, coconut shell. Crushing and classification may be performed in a jet mill or a mechanical mill.

[0085] The alkali activation comprises mixing a carbon source with an alkali, heating the mixture to 700-900°C at a heating rate of 10-30°C / min, and then maintaining the temperature for 1-4 hours. After cooling, washing to neutrality, and drying, the mixture is then heated to 800-900°C at a heating rate of 5-30°C / min, and then maintained for 1-4 hours to obtain a porous carbon activated material. A porous carbon material can be obtained by heating the carbon source with an alkali at a heating rate of 10-30°C / min to 700-900°C, and then maintaining the temperature for 1-4 hours. As an example, the heating rate can be, but is not limited to, 10°C / min, 15°C / min, 20°C / min, 25°C / min, and 30°C / min, and the holding temperature can be, but is not limited to, 700°C, 720°C, 740°C, 750°C, 760°C, 780°C, 800°C, 820°C, 840°C, 850°C, 860°C, 880°C, and 900°C. The porous carbon material is cooled, washed, and dried, and then heated to 800°C~900°C at a heating rate of 5°C / min~30°C / min and held for 1 h~4 h to activate the porous carbon material. Activation treatment under these conditions can effectively reduce the oxygen content in the porous carbon material, effectively avoiding the influence of the presence of oxygen on the subsequent nano-silicon deposition. By way of example, the heating rate may be, but is not limited to, 5°C / min, 10°C / min, 15°C / min, 20°C / min, 25°C / min, or 30°C / min. The holding temperature may be, but is not limited to, 800°C, 810°C, 820°C, 830°C, 840°C, 850°C, 860°C, 870°C, 880°C, 890°C, or 900°C. Specifically, the base may be selected from at least one of sodium hydroxide and potassium hydroxide. The mass ratio of the base to the carbon source may be between 1 and 4:1, and by way of example, may be, but is not limited to, 1:1, 2:1, 3:1, or 4:1. The washing solvent may be deionized water. The drying temperature may be between 60°C and 100°C. The drying time may be between 8 and 24 hours.

[0086] The water vapor activation process involves heating the porous carbon and water vapor at a heating rate of 10°C / min to 30°C / min to 800°C to 1000°C for 1 to 10 hours. The process is followed by cooling, washing to neutrality, and drying, followed by heating the porous carbon and water vapor at a heating rate of 5°C / min to 30°C / min to 800°C to 900°C for 1 to 4 hours to obtain an activated porous carbon material. Specifically, the washing solvent may be deionized water. The drying temperature is 60°C to 100°C, and the drying time is 8 to 24 hours.

[0087] In step (II), the surface modification material is selected from at least one of a polymer material, a non-oxide ceramic material, and a transition metal oxide. Specifically, the polymer material is selected from at least one of polyimide and polyaniline; the non-oxide ceramic material is selected from at least one of boron nitride, aluminum nitride, and silicon carbide; and the transition metal oxide is selected from at least one of yttrium oxide, zirconium oxide, and hafnium oxide. A surface modification material solution is prepared by dissolving the surface modification material in a solvent selected from at least one of water, ethanol, acetone, isopropanol, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone. The concentration of the surface modification material solution is 1% to 10%, and by way of example, can be, but is not limited to, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%. The mass ratio of the porous carbon to the surface modification material is 100:0.3 to 1, and by way of example, can be, but is not limited to, 100:0.3, 100:0.5, 100:0.8, or 100:1. The mixing temperature is 0°C to 60°C, and the mixing time is 1 hour to 4 hours. Drying can be performed by spray drying, with the spray drying temperature being 130°C to 200°C and the solids content of the spray slurry being 10%-30%. Drying can also be performed in a drying oven, with the temperature being 80°C to 200°C, and the drying time being 12 hours to 36 hours. Heat treatment can include treating the dried mixture at 150°C to 180°C for 1 hour to 8 hours, then at 200°C to 250°C for 1 hour to 4 hours, and finally at 300°C to 450°C for 1 hour to 4 hours. Heat treatment can also include heating the dried mixture at a rate of 1°C / min to 5°C / min to 700°C to 1000°C and maintaining the temperature for 1 hour to 4 hours.

[0088] In step (III), chemical vapor deposition involves placing the surface-modified porous carbon in a first fluidized bed, first introducing a protective gas to reduce the oxygen content to 100 ppm or less, then increasing the temperature of the first fluidized bed to 400°C to 500°C at a heating rate of 1°C / min to 10°C / min, and finally introducing a gaseous silicon source and a diluent gas to enter the silicon deposition stage. The silicon deposition stage includes an initial stage, an intermediate stage, and a final stage, with the gaseous silicon source flow rates in the initial stage, the intermediate stage, and the final stage decreasing in sequence. The flow rate of the gaseous silicon source in the initial stage is 2 L / min·kg~4 L / min·kg. As an example, it can be but is not limited to 2 L / min·kg, 2.2 L / min·kg, 2.4 L / min·kg, 2.5 L / min·kg, 2.6 L / min·kg, 2.8 L / min·kg, 3.0 L / min·kg, 3.2 L / min·kg, 3.4 L / min·kg, 3.6 L / min·kg, 3.8 L / min·kg, and 4.0 L / min·kg. The flow rate of the gaseous silicon source in the intermediate stage is 1 L / min·kg to 2 L / min·kg. As an example, it can be, but is not limited to, 1 L / min·kg, 1.1 L / min·kg, 1.2 L / min·kg, 1.3 L / min·kg, 1.4 L / min·kg, 1.5 L / min·kg, 1.6 L / min·kg, 1.7 L / min·kg, 1.8 L / min·kg, 1.9 L / min·kg, and 2 L / min·kg. The flow rate of the gaseous silicon source in the termination stage is 0.5 L / min·kg to 1 L / min·kg. As an example, it can be, but is not limited to, 0.5 L / min·kg, 0.6 L / min·kg, 0.7 L / min·kg, 0.8 L / min·kg, 0.9 L / min·kg, and 1 L / min·kg. The volume of the gaseous silicon source in the initial stage accounts for 5% to 20% of the total volume of the gaseous silicon source. For example, it can be, but is not limited to, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 14%, 16%, 18%, and 20%. The volume of the gaseous silicon source in the intermediate stage accounts for 60% to 90% of the total volume of the gaseous silicon source. For example, it can be, but is not limited to, 60%, 65%, 70%, 75%, 80%, 85%, and 90%. The volume of the gaseous silicon source in the final stage accounts for 5% to 20% of the total volume of the gaseous silicon source. For example, it can be, but is not limited to, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 14%, 16%, 18%, and 20%.

[0089] The ratio of the mass of the surface-modified porous carbon to the total volume of the gaseous silicon source is 1:600~1300, kg:L. As an example, it can be, but is not limited to, 1:600, 1:700, 1:800, 1:900, 1:1000, 1:1100, 1:1200, and 1:1300. The protective gas is selected from at least one of nitrogen, argon, and helium. The diluent is selected from at least one of nitrogen, argon, and helium. The protective gas and the diluent may be the same or different. The gaseous silicon source includes at least one of monosilane, disilane, trisilane, monochlorotrihydrogen silicon, dichlorodihydrogen silicon, and trichlorosilane. The first fluidized bed has a lower temperature zone T1 下 , medium temperature zone T1 中 and upper temperature zone T1 上 , 400℃≤T1 下 <450℃, 450℃≤T1 中 ≤500℃, 450℃≤T1 上 ≤500℃. Controlling the temperature of the lower temperature zone within this range can increase the adsorption rate, control the reaction rate, and avoid floating silicon. The temperatures of the middle and upper temperature zones are higher than that of the lower temperature zone to ensure sufficient cracking of silane. The volume concentration of the gaseous silicon source is ≤30%. As an example, it can be but not limited to ≤30%, ≤28%, ≤26%, ≤25%, ≤24%, ≤22%, ≤20%, ≤18%, ≤16%, ≤14%, ≤12%, and ≤10%.

[0090] In step (IV), the ratio of the mass of the surface-modified porous carbon to the total volume of acetylene in the first carbon coating is 1:100 to 300, kg:L. As an example, it can be, but not limited to, 1:100, 1:150, 1:200, 1:250, and 1:300. The primary carbon coating includes first heating to the reaction temperature and then sequentially introducing low-concentration acetylene and high-concentration acetylene for reaction, wherein the volume concentration of the low-concentration acetylene is lower than the volume concentration of the high-concentration acetylene. The primary carbon coating is carried out in a second fluidized bed having a lower temperature zone T2. 下 , medium temperature zone T2 中 and upper temperature zone T2 上 , T2 下 =T2 中 =T2 上 or T2 下 =T2 中 >T2 上. The first fluidized bed and the second fluidized bed may be the same or different. The reaction temperature is 550°C~620°C. As an example, it can be but not limited to 550°C, 560°C, 570°C, 580°C, 590°C, 620°C, 610°C, and 620°C. The insulation time is 0.5 h~1 h. As an example, it can be but not limited to 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, and 1 h. The volume concentration of low-concentration acetylene is 5%~10%. The volume concentration of high-concentration acetylene is 15%~20%. The flow rate of low-concentration acetylene is 0.5 L / min·kg~1.0 L / min·kg. As an example, it can be but not limited to 0.5 L / min·kg, 0.6 L / min·kg, 0.7 L / min·kg, 0.8 L / min·kg, 0.9 L / min·kg, and 1.0 L / min·kg. The low-concentration acetylene introduction time is 10 min to 60 min, and as an example, it can be, but is not limited to, 10 min, 20 min, 30 min, 40 min, 50 min, and 60 min. The high-concentration acetylene flow rate is 1.5 L / min·kg to 2.0 L / min·kg, and as an example, it can be, but is not limited to, 1.5 L / min·kg, 1.6 L / min·kg, 1.7 L / min·kg, 1.8 L / min·kg, 1.9 L / min·kg, and 2.0 L / min·kg. The high-concentration acetylene introduction time is 1 h to 4 h, and as an example, it can be, but is not limited to, 1 h, 2 h, 3 h, and 4 h.

[0091] In step (V), the secondary carbon coating includes introducing nitrogen and acetylene at a temperature of 550°C to 620°C, with a nitrogen flow rate of 4 L / min·kg to 10 L / min·kg, and an acetylene flow rate of 0.5 L / min·kg to 2 L / min·kg. After the gas is introduced, the mixture is kept warm for 1h to 2h; the amount of carbon coated in the secondary carbon coating is 0.5wt% to 2wt% of the intermediate. As an example, it can be but not limited to 0.5wt%, 0.6wt%, 0.8wt%, 1wt%, 1.2wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.8wt%, and 2wt%.

[0092] In order to better illustrate the purpose, technical solutions and beneficial effects of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that the following implementation method is a further explanation of the present invention and should not be used as a limitation of the present invention.

[0093] Example 1 This embodiment is a method for preparing a silicon-carbon negative electrode material, comprising the steps of: (I) Preparation of porous carbon The phenolic resin carbonized material and potassium hydroxide were mixed in a mass ratio of 1:2 and placed in a box furnace. The temperature was raised to 800 ° C at a rate of 30 ° C / min and kept for 2 hours. After cooling, the mixture was filtered and washed with water until neutral. It was dried at 80 ° C for 24 hours and then raised to 850 ° C at a rate of 5 ° C / min and kept for 3 hours to obtain a porous carbon activation material. The activated material was crushed and graded to obtain porous carbon. The prepared porous carbon had a particle size D50 = 8.5 μm and a DFT pore volume of 0.74 g / cm 3 , than 1823 m 2 / g, the average pore diameter is 1.74nm, and the microporosity is 97%.

[0094] (II) Preparation of surface-modified porous carbon Porous carbon and 1% polyimide solution (obtained by polymerization of 1.02 mol PMDA and 1.0 mol ODA) were mixed at a porous carbon: polyimide mass ratio of 100:0.5, and then spray-dried at 180°C. After drying, the mixture was placed in a box furnace, first treated at 150°C for 2h, then heated to 200°C for 2h, and then heated to 300°C for 2h to obtain polyimide surface-modified porous carbon.

[0095] (III) Nano-silicon deposition 1 kg of surface-modified porous carbon was placed in a fluidized bed, and nitrogen was continuously introduced (flow rate of 8 L / min). After the oxygen content was reduced to below 100PPm, heating was started and the temperature was raised to 410°C in the lower temperature zone of the fluidized bed and 460°C in the middle and upper temperature zones at a heating rate of 3°C / min. Monosilane and nitrogen were introduced for silicon deposition. The volume concentration of monosilane was 20%. The gaseous silicon source flow rate in the initial stage of silicon deposition was 3 L / min, and the time was 40 min. The gaseous silicon source flow rate in the middle stage was 2 L / min, and the time was 310 min. The gaseous silicon source flow rate in the terminal stage was 0.8 L / min, and the time was 75 min, to obtain a silicon-carbon core.

[0096] (IV) Primary carbon coating The temperature of the fluidized bed is raised to 560 °C (the upper temperature zone T2 of the fluidized bed). 下 , medium temperature zone T2 中 and lower temperature zone T2 上 The mixture was heated for 1 h, and low-concentration acetylene of 8% was introduced at a flow rate of 0.8 L / min for 60 min. Then high-concentration acetylene of 16% was introduced at a flow rate of 1.6 L / min for 120 min. After the introduction, the mixture was heated for 2 h to obtain the intermediate.

[0097] (V) Secondary carbon coating 2.0 kg of the intermediate was placed in a fluidized bed and heated to 560 °C. Nitrogen and acetylene were introduced at a nitrogen flow rate of 5 L / min and an acetylene flow rate of 1.2 L / min. The ventilation time was 150 min. After the ventilation was completed, the intermediate was kept warm for 2 h to obtain a silicon-carbon negative electrode material with a carbon coating amount of 1.4 wt%.

[0098] Figure 2 This is the SEM image of the silicon-carbon negative electrode material of this comparative example. It can be seen from the figure that the morphology is normal and there are no obvious floating silicon particles. Figure 3 This is the charge and discharge curve of the silicon-carbon negative electrode material of this comparative example. It can be seen from the figure that the initial efficiency is relatively high and no floating silicon occurs. Figure 4 This is the dQ / dV differential capacitance diagram of the silicon-carbon negative electrode material of this comparative example. It can be seen from the figure that the 1dQ / dV value is relatively high, the silicon is highly amorphous, and is conducive to cycling. Figure 5 This is the XRD diagram of the silicon-carbon negative electrode material of Comparative Example 1. It can be seen from the figure that the silicon peak is relatively flat and the grain size is relatively small.

[0099] Example 2 This embodiment is a method for preparing a silicon-carbon negative electrode material, comprising the steps of: (I) Preparation of porous carbon Same as step (I) of Example 1.

[0100] (II) Preparation of surface-modified porous carbon The porous carbon and the boron nitride precursor solution (the boron nitride precursor solution is an ethanol solution of urea and boric acid, and the molar ratio of urea to boric acid is 1:1) are mixed at a porous carbon:boron nitride mass ratio of 100:1. The ethanol is removed by an evaporator, and the mixture is dried at 80°C and placed in a box furnace. The temperature is increased to 800°C at a heating rate of 2°C / min and the mixture is kept warm for 4 h. The mixture is washed with 80°C hot water for 2 h and dried to obtain the boron nitride surface-modified porous carbon.

[0101] (III) Nano-silicon deposition Same as step (III) of Example 1.

[0102] (IV) Primary carbon coating Same as step (IV) of Example 1.

[0103] (V) Secondary carbon coating Same as step (V) of Example 1.

[0104] Example 3 This embodiment is a method for preparing a silicon-carbon negative electrode material, comprising the steps of: (I) Preparation of porous carbon Same as step (I) of Example 1.

[0105] (II) Preparation of surface-modified porous carbon Porous carbon and 10% yttrium oxide sol were mixed in a mass ratio of 100:2, dried at 80°C, and placed in a box furnace. The temperature was raised to 600°C at a heating rate of 3°C / min and kept for 3 h to obtain yttrium oxide surface-modified porous carbon.

[0106] (III) Nano-silicon deposition Same as step (III) of Example 1.

[0107] (IV) Primary carbon coating Same as step (IV) of Example 1.

[0108] (V) Secondary carbon coating Same as step (V) of Example 1.

[0109] Example 4 This embodiment is a method for preparing a silicon-carbon negative electrode material, comprising the steps of: (I) Preparation of porous carbon The carbonized phenolic resin material and potassium hydroxide were mixed in a mass ratio of 1:3 and placed in a rotary kiln. The temperature was raised to 800°C at a heating rate of 30°C / min and kept for 2 hours. After cooling, the mixture was filtered and washed with water until neutral. The mixture was dried at 80°C for 24 hours and then raised to 850°C at a heating rate of 5°C / min and kept for 2 hours to obtain the activated material. The activated material was crushed and graded to obtain porous carbon. The prepared porous carbon had a particle size D50 = 8.5 μm and a DFT pore volume of 0.86 g / cm 3 , compared to 2023 m 2 / g, the average pore diameter is 1.84nm, and the microporosity is 84%.

[0110] (II) Preparation of surface-modified porous carbon Same as step (II) of Example 1.

[0111] (III) Nano-silicon deposition 1 kg of surface-modified porous carbon was placed in a fluidized bed, and nitrogen was continuously introduced (flow rate of 8 L / min) to reduce the oxygen content to below 100 PPm. Heating was started and the temperature was raised to 410 ℃ in the lower temperature zone and 460 ℃ in the middle and upper temperature zones at a rate of 3 ℃ / min. Monosilane and nitrogen were introduced for silicon deposition. The volume concentration of monosilane was 20%. The gaseous silicon source flow rate in the initial stage of silicon deposition was 3 L / min, and the time was 40 min. The gaseous silicon source flow rate in the middle stage was 2 L / min, and the time was 390 min. The gaseous silicon source flow rate in the terminal stage was 0.8 L / min, and the time was 75 min to obtain a silicon-carbon core.

[0112] (IV) Primary carbon coating Same as step (IV) of Example 1.

[0113] (V) Secondary carbon coating Same as step (V) of Example 1.

[0114] Example 5 This embodiment is a method for preparing a silicon-carbon negative electrode material, comprising the steps of: (I) Preparation of porous carbon The coconut shell carbonized material was heated to 900°C in a steam environment at a rate of 30°C / min and kept at this temperature for 3 hours. After cooling, it was filtered and washed with water until neutral. It was dried at 80°C for 24 hours and then heated to 900°C at a rate of 5°C / min and kept at this temperature for 2 hours to obtain an activated material. The activated material was crushed and graded to produce porous carbon. The prepared porous carbon had a particle size D50 = 8.3 μm and a DFT pore volume of 0.93 g / cm 3 , than 2123 m 2 / g, the average pore diameter is 1.89nm, and the microporosity is 80%.

[0115] (II) Preparation of surface-modified porous carbon Same as step (II) of Example 1.

[0116] (III) Nano-silicon deposition 1 kg of surface-modified porous carbon was placed in a fluidized bed, and nitrogen was continuously introduced (flow rate of 8 L / min) to reduce the oxygen content to below 100 PPm. Heating was started and the temperature was raised to 410 ℃ in the lower temperature zone and 460 ℃ in the middle and upper temperature zones at a heating rate of 3 ℃ / min. Monosilane and nitrogen were introduced for silicon deposition. The volume concentration of monosilane was 25%. The gaseous silicon source flow rate in the initial stage of silicon deposition was 3 L / min, and the time was 40 min. The gaseous silicon source flow rate in the middle stage was 2 L / min, and the time was 450 min. The gaseous silicon source flow rate in the terminal stage was 0.8 L / min, and the time was 75 min to obtain a silicon-carbon core.

[0117] (IV) Primary carbon coating Same as step (IV) of Example 1.

[0118] (V) Secondary carbon coating Same as step (V) of Example 1.

[0119] Example 6 This embodiment is a method for preparing a silicon-carbon negative electrode material, comprising the steps of: (I) Preparation of porous carbon Same as step (I) of Example 1.

[0120] (II) Preparation of surface-modified porous carbon Same as step (II) of Example 1.

[0121] (III) Nano-silicon deposition 1 kg of surface-modified porous carbon was placed in a fluidized bed, and nitrogen was continuously introduced (flow rate of 8 L / min) to reduce the oxygen content to below 100 PPm. Heating was started and the temperature was raised to 430 ℃ in the lower temperature zone of the fluidized bed and 470 ℃ in the middle and upper temperature zones at a heating rate of 3 ℃ / min. Monosilane and nitrogen were introduced for silicon deposition. The volume concentration of monosilane was 15%. The gaseous silicon source flow rate in the initial stage of silicon deposition was 3 L / min, and the time was 40 min. The gaseous silicon source flow rate in the middle stage was 2 L / min, and the time was 310 min. The gaseous silicon source flow rate in the terminal stage was 0.8 L / min, and the time was 75 min to obtain a silicon-carbon core.

[0122] (IV) Primary carbon coating Same as step (IV) of Example 1.

[0123] (V) Secondary carbon coating Same as step (V) of Example 1.

[0124] Example 7 This embodiment is a method for preparing a silicon-carbon negative electrode material, comprising the steps of: (I) Preparation of porous carbon Same as step (I) of Example 1.

[0125] (II) Preparation of surface-modified porous carbon Same as step (II) of Example 1.

[0126] (III) Nano-silicon deposition 1 kg of surface-modified porous carbon was placed in a fluidized bed, and nitrogen was continuously introduced (flow rate of 8 L / min) to reduce the oxygen content to below 100 PPm. Heating was started and the temperature was raised to 410 ℃ in the lower temperature zone of the fluidized bed and 460 ℃ in the middle and upper temperature zones at a heating rate of 3 ℃ / min. Monosilane and nitrogen were introduced for silicon deposition. The volume concentration of monosilane was 25%. The gaseous silicon source flow rate in the initial stage of silicon deposition was 3.5 L / min, and the time was 40 min. The gaseous silicon source flow rate in the middle stage was 2 L / min, and the time was 290 min. The gaseous silicon source flow rate in the terminal stage was 0.5 L / min, and the time was 100 min, to obtain a silicon-carbon core.

[0127] (IV) Primary carbon coating Same as step (IV) of Example 1.

[0128] (V) Secondary carbon coating Same as step (V) of Example 1.

[0129] Example 8 This embodiment is a method for preparing a silicon-carbon negative electrode material, comprising the steps of: (I) Preparation of porous carbon Same as step (I) of Example 1.

[0130] (II) Preparation of surface-modified porous carbon Same as step (II) of Example 1.

[0131] (III) Nano-silicon deposition Same as step (III) of Example 1.

[0132] (IV) Primary carbon coating The temperature of the fluidized bed is raised to 600 °C (the upper temperature zone T2 of the fluidized bed). 下 , medium temperature zone T2 中 and lower temperature zone T2 上 The mixture was stirred for 1 h, and then 6.7% low-concentration acetylene was introduced at a flow rate of 0.8 L / min for 60 min. Then 15% high-concentration acetylene was introduced at a flow rate of 1.8 L / min for 120 min. After the introduction, the mixture was kept warm for 2 h to obtain the intermediate.

[0133] (V) Secondary carbon coating Same as step (V) of Example 1.

[0134] Example 9 This embodiment is a method for preparing a silicon-carbon negative electrode material, comprising the steps of: (I) Preparation of porous carbon Same as step (I) of Example 1.

[0135] (II) Preparation of surface-modified porous carbon Same as step (II) of Example 1.

[0136] (III) Nano-silicon deposition Same as step (III) of Example 1.

[0137] (IV) Primary carbon coating Same as step (IV) of Example 1.

[0138] (V) Secondary carbon coating 2.0 kg of the intermediate was placed in a fluidized bed and heated to 590 °C. Nitrogen and acetylene were introduced at a nitrogen flow rate of 8 L / min and an acetylene flow rate of 1.5 L / min. The ventilation time was 120 min. After the ventilation was completed, the intermediate was kept warm for 2 h to obtain a silicon-carbon negative electrode material with a carbon coating amount of 1.4 wt%.

[0139] Comparative Example 1 The difference from Example 1 is that step (II) is not performed, and the rest is the same as Example 1.

[0140] Figure 6 This is the SEM image of the silicon-carbon negative electrode material of this comparative example, from which it can be seen that there are floating silicon particles. Figure 7 This is the charge and discharge curve of the silicon-carbon negative electrode material in this comparative example. It can be seen from the figure that the initial efficiency is low and there are obvious side reactions. Figure 8 This is the dQ / dV differential capacitance diagram of the silicon-carbon negative electrode material of this comparative example. It can be seen from the figure that the dQ / dV value is relatively low, the degree of silicon amorphism is low, and it is not conducive to cycling. Figure 9 This is the XRD diagram of the silicon-carbon negative electrode material of Comparative Example 1. It can be seen from the figure that the silicon peak is relatively sharp and the grain size is relatively large.

[0141] Comparative Example 2 The difference between this comparative example and Example 1 is that: (III) nano-silicon deposition 1 kg of surface-modified porous carbon was placed in a fluidized bed, and nitrogen was continuously introduced (flow rate of 8 L / min) to reduce the oxygen content to below 100 PPm. Heating was started and the temperature was increased at a rate of 3 ℃ / min to 460 ℃ in the lower temperature zone, 460 ℃ in the middle temperature zone and 460 ℃ in the upper temperature zone. Monosilane and nitrogen were introduced for silicon deposition. The volume concentration of monosilane was 20%, the flow rate of the gaseous silicon source was 2 L / min, and the time was 400 min to obtain a silicon-carbon core.

[0142] The remaining steps are the same as those in Example 1.

[0143] Comparative Example 3 The difference between this comparative example and Example 1 is that: (III) nano-silicon deposition 1 kg of surface-modified porous carbon was placed in a fluidized bed, and nitrogen was continuously introduced (flow rate of 8 L / min) to reduce the oxygen content to below 100 PPm. Heating was started and the temperature was raised to 550 ℃ in the lower temperature zone and 550 ℃ in the middle and upper temperature zones at a heating rate of 3 ℃ / min. Monosilane and nitrogen were introduced for silicon deposition. The volume concentration of monosilane was 20%, the flow rate of the gaseous silicon source was 2 L / min, and the time was 385 min to obtain a silicon-carbon core.

[0144] The remaining steps are the same as those in Example 1.

[0145] Comparative Example 4 This comparative example is a method for preparing a silicon-carbon negative electrode material, comprising the steps of: (I) Preparation of porous carbon Same as step (I) of Example 1.

[0146] (II) Nano-silicon deposition 1 kg of porous carbon was placed in a fluidized bed, and nitrogen was continuously introduced (flow rate of 8 L / min) to reduce the oxygen content to below 100PPm. Heating was started and the temperature was raised to 460°C in the lower temperature zone and 460°C in the middle and upper temperature zones at a heating rate of 3°C / min. Monosilane and nitrogen were introduced for silicon deposition. The volume concentration of monosilane was 20%. The gaseous silicon source flow rate in the initial stage of silicon deposition was 1 L / min, and the time was 80 min. The gaseous silicon source flow rate in the middle stage was 2 L / min, and the time was 310 min. The gaseous silicon source flow rate in the terminal stage was 1 L / min, and the time was 100 min, to obtain a silicon-carbon core.

[0147] (III) Primary carbon coating Same as step (IV) of Example 1.

[0148] (IV) Secondary carbon coating Same as step (V) of Example 1.

[0149] Comparative Example 5 The difference between this comparative example and Example 1 is that: (III) nano-silicon deposition 1 kg of surface-modified porous carbon was placed in a fluidized bed, and nitrogen was continuously introduced (flow rate of 8 L / min). After the oxygen content was reduced to below 100PPm, heating was started and the temperature was increased at a rate of 3°C / min to 410°C in the lower temperature zone of the fluidized bed, and 460°C in the middle and upper temperature zones. Monosilane and nitrogen were introduced for silicon deposition. The volume concentration of monosilane was 20%. The gaseous silicon source flow rate in the initial stage of silicon deposition was 1 L / min, and the time was 80 min. The gaseous silicon source flow rate in the middle stage was 2 L / min, and the time was 310 min. The gaseous silicon source flow rate in the terminal stage was 1 L / min, and the time was 100 min, to obtain a silicon-carbon core.

[0150] The remaining steps are the same as those in Example 1.

[0151] Comparative Example 6 The difference between this comparative example and Example 1 is that: (III) nano-silicon deposition 1 kg of surface-modified porous carbon was placed in a fluidized bed, and nitrogen was continuously introduced (flow rate of 8 L / min). After the oxygen content was reduced to below 100 ppm, heating was started and the temperature was increased at a rate of 3 ℃ / min to 410 ℃ in the lower temperature zone of the fluidized bed, 460 ℃ in the middle and upper temperature zones. Monosilane and nitrogen were introduced for silicon deposition. The volume concentration of monosilane was 20%, the flow rate of the gaseous silicon source was 2 L / min, and the time was 400 min to obtain a silicon-carbon core.

[0152] The remaining steps are the same as those in Example 1.

[0153] Comparative Example 7 The difference between this comparative example and Example 1 is that: (I) Preparation of porous carbon The carbonized phenolic resin and potassium hydroxide were mixed in a 1:2 mass ratio and placed in a box furnace. The temperature was raised to 800°C at a rate of 30°C / min and held for 2 hours. After cooling, the mixture was filtered, washed with water until neutral, and dried at 80°C for 24 hours. The dried material was crushed and graded to produce porous carbon. The prepared porous carbon had a particle size D50 of 8.5 μm, a DFT pore volume of 0.76 g / cm3, a specific surface area of ​​1897 m2 / g, an average pore diameter of 1.75 nm, a microporosity of 97%, and an oxygen content of 4.6%.

[0154] The remaining steps are the same as those in Example 1.

[0155] The porous carbons prepared in Examples 1 to 9 and Comparative Examples 1 to 7 were subjected to relevant tests, and the results are shown in Table 1. The silicon-carbon negative electrode materials prepared in Examples 1 to 9 and Comparative Examples 1 to 7 were subjected to various performance tests, and the test results are shown in Table 2 and Table 3. The relevant test conditions are as follows.

[0156] (1) Aperture test The pore size analysis was performed using an ASAP2460 multi-station fully automatic specific surface area and pore size analyzer. The test mode was Micropore Analysis, the degassing temperature was 300°C, the degassing time was 6 hours, the pressure value point was 69, and the low-pressure air intake volume was 10CC.

[0157] (2) Density test The true density was measured using a 1200e true density tester with a gas pressure of 0.14 MPa to 0.15 MPa and a weighing volume of 80% of the sample cell. The RSD of the five test data was ≤ 0.02%.

[0158] The tap density was measured using a BT-312 tap density tester with a sample height of 21 mL to 25 mL in the measuring cylinder, a vibration frequency of 250 times / min, and 5000 vibrations.

[0159] (2) Use a specific surface area analyzer to detect the specific surface area.

[0160] (3) Use a carbon-sulfur analyzer to test the carbon content of the silicon-carbon negative electrode material.

[0161] (4) An oxygen and nitrogen analyzer was used to test the oxygen and nitrogen content of the silicon-carbon negative electrode material, and XRF was used to test the silicon and metal element content.

[0162] (5) Use a muffle furnace and analytical balance to calculate the ash content of the silicon-carbon negative electrode.

[0163] (6) The particle size of porous carbon and silicon-carbon negative electrode materials was tested using Malvern particle size analyzer MS3000.

[0164] (7) Crystal structure characterization: XRD analysis of the prepared silicon-carbon anode material was performed using a PANalytical Xpert3 Powder powder diffractometer. The test voltage was 40 kV, the test current was 40 mA, the scanning range was 10° to 90°, the scanning step was 0.008°, and the scanning time per step was 12 s. The average size of the Si grains was calculated using the Scherrer formula.

[0165] (8) The pH value of the porous carbon was obtained by using a pH meter.

[0166] (9) The electrical conductivity of porous carbon and silicon-carbon negative electrode materials was tested using a powder resistivity test system.

[0167] (10) Electrochemical testing The prepared silicon-carbon anode material, used as the active material, was mixed with an aqueous dispersion of acrylonitrile multipolymer (LA132, 15% solids content) as a binder and a conductive agent (SuperP) in a mass ratio of 92:6:2. An appropriate amount of water was added as a solvent to create a slurry with a solids content of 55%. The slurry was then coated onto copper foil, vacuum-dried, and roller-pressed to form a negative electrode sheet. A metallic lithium sheet was used as the counter electrode, and the electrolyte was formed using 1 mol / L LiPF6 and a three-component solvent mixture with an EC:DMC:EMC ratio of 1:1:1 (v / v / v). A polypropylene microporous membrane was used as the separator. CR2032 button cells were assembled in an inert gas glove box. Charge and discharge tests of the button cells were conducted on a LANHE battery testing system.

[0168] First charge and discharge performance test: Under room temperature conditions, discharge at a constant current of 0.1C to a voltage of 0.01V, then discharge at a constant current of 0.02C to a voltage of 0.005V, and charge at a constant current of 0.1C to a voltage of 1.5V to obtain the first reversible specific capacity and the first coulombic efficiency.

[0169] Cycling performance test: Under normal temperature conditions, 1C constant current charge and discharge to 0.01V, then 0.05C constant current discharge to 0.005V, and finally 1C constant current charge to 1.5V to obtain the lithium-free specific capacity. This cycle is repeated 100 times, and the capacity retention rate and expansion rate after 100 cycles are calculated. At the same time, the initial thickness H1 of the electrode and the lithium-inserted thickness H2 after 100 cycles are tested. The volume expansion rate after 100 cycles = (H2-H1) / H1 Table 1 Physical property test results of porous carbon of Examples 1 to 9 and Comparative Examples 1 to 7

[0170] It can be seen from the test results in Table 1 that when no activation treatment is performed, the oxygen content of the porous carbon is relatively high.

[0171] Table 2 Physical properties and chemical compositions of silicon-carbon negative electrode materials prepared in Examples 1 to 9 and Comparative Examples 1 to 7

[0172] Table 3 Electrochemical properties of silicon-carbon negative electrode materials prepared in Examples 1 to 9 and Comparative Examples 1 to 7

[0173] The test results in Tables 2 and 3 show that the silicon-carbon negative electrode materials prepared in Examples 1 to 9 of the present invention exhibit superior physical and electrochemical properties compared to Comparative Examples 1 to 7. Failure to perform surface modification leads to an increase in floating silicon and a decrease in conductivity. Increasing the temperature in the lower temperature zone of the fluidized bed also leads to an increase in floating silicon and a decrease in conductivity. High-temperature deposited silicon and porous carbon without activation treatment both result in significant floating silicon. Failure to follow a sequentially decreasing silane flow rate can also increase floating silicon. Furthermore, post-cycle volume expansion is significant, resulting in a low cycle retention rate.

[0174] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the scope of protection of the present invention. Although the present invention is described in detail with reference to the preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. Silicon-carbon negative electrode material, characterized in that: The invention comprises a silicon-carbon core and a carbon coating layer covering the silicon-carbon core, wherein the silicon-carbon core comprises porous carbon, a surface modification layer covering the porous carbon, and nano-silicon accommodated in the pores of the porous carbon, the surface modification layer is a polymer layer, a non-oxide ceramic layer and / or a transition metal oxide layer, and the oxygen content of the porous carbon is 0% to 2%.

2. The silicon-carbon negative electrode material according to claim 1, wherein At least one of the following features (1) to (28): (1) The volume expansion rate of the silicon-carbon negative electrode material after 100 cycles is ≤32%; (2) The capacity retention rate of the silicon-carbon negative electrode material after 100 cycles is ≥95%; (3) The dQ / dV of the silicon-carbon negative electrode material is ≥1.60, dQ / dV=0.2V~0.4V delithiation front / 0.4V~0.5V delithiation front; (4) The reversible specific capacity of the silicon-carbon negative electrode material is 1600 mAh / g to 2500 mAh / g; (5) The initial coulombic efficiency of the silicon-carbon negative electrode material is ≥90%; (6) The specific surface area of ​​the silicon-carbon negative electrode material is ≤10 m 2 / g; (7) The particle size D50 of the silicon-carbon negative electrode material is 6 μm to 10 μm; (8) The particle size distribution dispersion of the silicon-carbon negative electrode material is F, 0<F≤1.4, F=(D90-D10) / D50; (9) The true density of the silicon-carbon negative electrode material is ≤1.8 g / cm 3 ; (10) The electrical conductivity of the silicon-carbon negative electrode material is 0.1 S / cm to 10.0 S / cm; (11) The tap density of the silicon-carbon negative electrode material is 0.7 g / cm 3 ~1.0 g / cm 3 ; (12) The silicon grain size of the silicon-carbon negative electrode material is ≤3 nm; (13) The surface silicon content of the silicon-carbon negative electrode material is P, P≤0.5%, P=(nano-silicon content×2.413-ash content)×0.875; (14) The particle size D50 of the porous carbon is 6 μm to 10 μm; (15) The pore volume of the porous carbon is 0.5 g / cm 3 ~1.2 g / cm 3 ; (16) The specific surface area of ​​the porous carbon is 1500 m 2 / g~2500 m 2 / g; (17) The average pore size of the porous carbon channel is 1.5 nm to 2.0 nm; (18) The microporosity of the porous carbon channel is ≥70%; (19) The oxygen content of the silicon-carbon negative electrode material is ≤ 2%; (20) The nitrogen content of the porous carbon is 0% to 0.5%; (21) The ratio of the pore volume of the porous carbon channel with a pore diameter of 0.6 nm to 1.0 nm to the total pore volume is A, and A is ≥ 40%; (22) The ratio of the pore volume of the porous carbon channel with a pore diameter of 0 nm to 0.6 nm to the total pore volume is B, and B≤10%; (23) The electrical conductivity of the porous carbon is ≥5 S / cm; (24) The pH of the porous carbon is 6 to 9; (25) The bulk density of the nano-silicon is 1.3 g / cm 3 ~1.5 g / cm 3 ; (26) The nano-silicon is 40 wt% to 60 wt% of the silicon-carbon negative electrode material; (27) The modified layer is 0.3 wt% to 1.0 wt% of the silicon-carbon negative electrode material; (28) The carbon coating layer is 1 wt% to 4 wt% of the silicon-carbon negative electrode material.

3. A method for preparing a silicon-carbon negative electrode material, characterized in that: Including steps: (I) Preparation of porous carbon The carbon source is activated by alkali or water vapor and then crushed and graded to obtain porous carbon; (II) Preparation of surface-modified porous carbon The porous carbon and a surface modification material solution are mixed, dried, and heat-treated to obtain surface-modified porous carbon, wherein the surface modification material is selected from at least one of a polymer material, a non-oxide ceramic material, and a transition metal oxide; (III) Nano-silicon deposition The surface-modified porous carbon and a gaseous silicon source are subjected to chemical vapor deposition to obtain a silicon-carbon core, wherein the silicon deposition stage of the chemical vapor deposition includes an initial stage, an intermediate stage, and an end stage, and the flow rate of the gaseous silicon source in the initial stage, the flow rate of the gaseous silicon source in the intermediate stage, and the flow rate of the gaseous silicon source in the end stage show a decreasing trend in sequence; (IV) Primary carbon coating Carrying out a carbon coating of the silicon-carbon core and acetylene to obtain an intermediate; (V) Secondary carbon coating The intermediate is subjected to secondary carbon coating with acetylene to obtain a silicon-carbon negative electrode material.

4. The method for preparing the silicon-carbon negative electrode material according to claim 3, wherein: The chemical vapor deposition process includes placing the surface-modified porous carbon in a first fluidized bed, first introducing a protective gas to reduce the oxygen content to 100 ppm or below, then raising the temperature of the first fluidized bed to 400°C to 500°C at a heating rate of 1°C / min to 10°C / min, and finally introducing a gaseous silicon source and a diluent gas to enter the silicon deposition stage.

5. The method for preparing the silicon-carbon negative electrode material according to claim 4, wherein: Includes at least one of the following features (1) to (28): (1) the carbon source comprises at least one of resin, biomass and tar; (2) The crushing and classification is carried out in a jet mill or a mechanical mill; (3) the surface modification material solution is obtained by dissolving the surface modification material in a solvent, wherein the solvent is selected from at least one of water, ethanol, acetone, isopropanol, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide and N-methylpyrrolidone; (4) the concentration of the surface modification material solution is 1% to 10%; (5) the mass ratio of the porous carbon to the surface modification material is 100:0.3-1; (6) the mixing temperature is 0°C to 60°C, and the mixing time is 1 hour to 4 hours; (7) The drying is spray drying, the spray drying temperature is 130°C to 200°C, and the solid content of the spray slurry is 10% to 30%; (8) The drying is carried out in a drying oven at a temperature of 80°C to 200°C and a drying time of 12 hours to 36 hours; (9) The heat treatment comprises first treating the dried mixture at 150°C to 180°C for 1 hour to 8 hours, then treating it at 200°C to 250°C for 1 hour to 4 hours, and finally treating it at 300°C to 450°C for 1 hour to 4 hours; (10) The heat treatment comprises heating the dried mixture to 700°C to 1000°C at a heating rate of 1°C / min to 5°C / min and maintaining the temperature for 1 hour to 4 hours; (11) The polymer material is selected from at least one of polyimide and polyaniline; (12) The non-oxide ceramic material is selected from at least one of boron nitride, aluminum nitride, and silicon carbide; (13) The transition metal oxide is at least one selected from yttrium oxide, zirconium oxide, and hafnium oxide; (14) The ratio of the mass of the surface-modified porous carbon to the total volume of the gaseous silicon source is 1:600 ​​to 1300, kg:L; (15) The flow rate of the gaseous silicon source in the initial stage is 2 L / min·kg to 4 L / min·kg; (16) The flow rate of the gaseous silicon source in the intermediate stage is 1 L / min·kg to 2 L / min·kg; (17) The flow rate of the gaseous silicon source during the termination stage is 0.5 L / min·kg to 1 L / min·kg; (18) The volume of the gaseous silicon source in the initial stage accounts for 5% to 20% of the total volume of the gaseous silicon source; (19) The volume of the gaseous silicon source in the intermediate stage accounts for 60% to 90% of the total volume of the gaseous silicon source; (20) The volume of the gaseous silicon source at the termination stage accounts for 5% to 20% of the total volume of the gaseous silicon source; (21) The protective gas is selected from at least one of nitrogen, argon, and helium; (22) The diluent gas is selected from at least one of nitrogen, argon, and helium; (23) The gaseous silicon source includes at least one of monosilane, disilane, trisilane, monochlorotrihydrogen silicon, dichlorodihydrogen silicon and trichlorosilane; (24) The volume concentration of the gaseous silicon source is ≤30%; (25) The first fluidized bed has a lower temperature zone T1 下 , medium temperature zone T1 中 and upper temperature zone T1 上 , 400 ℃≤T1 下 <450℃, 450℃≤T1 中 ≤500℃, 450℃≤T1 上 ≤500 ℃; (26) The ratio of the mass of the surface-modified porous carbon to the total volume of the acetylene in the first carbon coating is 1:100 to 300, kg:L; (XXVII) The secondary carbon coating comprises introducing nitrogen and acetylene at a temperature of 550°C to 620°C, wherein the flow rate of the nitrogen is 4 L / min·kg to 10 L / min·kg, and the flow rate of the acetylene is 0.5 L / min·kg to 2 L / min·kg, and the temperature is kept at 1 h to 2 h after the gas introduction is completed; (28) The amount of carbon coated in the secondary carbon coating is 0.5wt%~2wt% of the intermediate.

6. The method for preparing the silicon-carbon negative electrode material according to claim 3, wherein: The primary carbon coating includes heating to the reaction temperature and then sequentially introducing low-concentration acetylene and high-concentration acetylene for reaction, wherein the volume concentration of the low-concentration acetylene is lower than the volume concentration of the high-concentration acetylene.

7. The method for preparing the silicon-carbon negative electrode material according to claim 6, wherein: comprising at least one of the following features (i) to (ix): (i) The primary carbon coating is carried out in a second fluidized bed having a lower temperature zone T2 下 , medium temperature zone T2 中 and upper temperature zone T2 上 , T2 下 =T2 中 =T2 上 or T2 下 =T2 中 >T2 上 ; (ii) the reaction temperature is 550° C. to 620° C.; (iii) the insulation time is 0.5 h to 1 h; (iv) the volume concentration of the low-concentration acetylene is 5% to 10%; (v) the volume concentration of the high concentration acetylene is 15% to 20%; (vi) the flow rate of the low-concentration acetylene is 0.5 L / min·kg to 1.0 L / min·kg; (vii) the low concentration acetylene is introduced for a time period of 10 min to 60 min; (viii) the flow rate of the high concentration acetylene is 1.5 L / min·kg to 2.0 L / min·kg; (ix) The high concentration acetylene is introduced for a time period of 1 h to 4 h.

8. The method for preparing the silicon-carbon negative electrode material according to claim 3, wherein: The alkali activation comprises mixing the carbon source with an alkali, heating the mixture to 700°C to 900°C at a heating rate of 10°C / min to 30°C / min, and heat-treating the mixture for 1 hour to 4 hours; cooling, washing to neutrality, and drying the mixture, and then heating the mixture to 800°C to 900°C at a heating rate of 5°C / min to 30°C / min, and heat-treating the mixture for 1 hour to 4 hours to obtain a porous carbon activation material.

9. The method for preparing the silicon-carbon negative electrode material according to claim 3, wherein: The water vapor activation comprises heating the porous carbon and water vapor to 800°C~1000°C at a heating rate of 10°C / min~30°C / min, maintaining the temperature for 1 hour~10 hours, cooling, washing to neutrality, and drying, and then heating the porous carbon and water vapor to 800°C~900°C at a heating rate of 5°C / min~30°C / min, maintaining the temperature for 1 hour~4 hours to obtain a porous carbon activation material.

10. A secondary battery comprising a positive electrode material and a negative electrode material, characterized in that: The negative electrode material includes the silicon-carbon negative electrode material according to any one of claims 1 to 2 or the silicon-carbon negative electrode material prepared by the preparation method of the silicon-carbon negative electrode material according to any one of claims 6 to 9.

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