Low-cost zero-strain high-capacity fast-charging porous silicon carbon negative electrode material as well as preparation method and application thereof

Abstract

The invention discloses a low-cost zero-strain high-capacity fast-charging porous silicon carbon negative electrode material as well as a preparation method and application thereof, and belongs to the field of energy storage. According to the method, a spherical plant-based biomass material is used as a raw material, and is compounded with a high-molecular polymer and a molten salt pore-forming agent to prepare the spherical interconnected hierarchical porous carbon material. In the high-temperature carbonization and pore-forming process of the molten salt, part of metal compounds are subjected to carbothermal reduction to form metal elementary substances, the metal elementary substances serve as active sites for silanization gas, and catalytic reduction growth of superfine silicon nanoparticles is carried out in pores of the interconnected hierarchical porous spherical carbon in a uniformly dispersed manner. The hierarchical interconnected pore structure of the obtained material can relieve volume expansion in the charge-discharge process, optimize electron density distribution and promote charge transfer, so that the conductivity and ion transmission rate of a final product are improved; the dispersed superfine silicon nanoparticles enable the prepared silicon carbon negative electrode to have zero strain, high capacity, fast charging performance and excellent cycling stability, so that the silicon carbon negative electrode becomes a potential ideal material of silicon carbon.

Description

Technical Field

[0001] The present invention relates to the field of energy storage, and in particular to a low-cost, zero-strain, high-capacity, fast-charging porous silicon-carbon negative electrode material and a preparation method and application thereof. Background Art

[0002] Due to the increasing energy demand of electric vehicles and energy storage, the development of advanced lithium-ion batteries with high energy and long cycle life has become an urgent issue to be addressed. Si has a superior theoretical capacity (4200 mAh g -1 ) and a lower delithiation potential (0.4 V vs Li / Li + ), higher reserves and relatively excellent safety performance, it is expected to become the mainstream direction of research and development of the next generation of lithium battery negative electrode materials.

[0003] However, the alloying reaction of Si and Li often causes a huge volume expansion (up to 300%), which inevitably leads to electrode pulverization and a decrease in the overall performance of the battery during the charge and discharge process. In addition, as a semiconductor, silicon has a low electrical conductivity. In this context, it is of great significance to develop an electrode material that has both zero strain performance and high capacity and fast charging. Summary of the invention

[0004] Based on the defects of the prior art, the primary purpose of the present invention is to provide a preparation method and application of a low-cost, zero-strain, high-capacity, fast-charging porous silicon-carbon negative electrode material.

[0005] The present invention uses spherical plant-based biomass materials as raw materials, compounded with high molecular polymers and molten salt pore-forming agents, and after the three raw materials are evenly dispersed to form a gel, a spherical interconnected hierarchical porous carbon material is obtained by calcining, wherein the molten salt has a pore-forming effect as well as a skeleton effect, and the molten salt is carbon-thermally reduced to a metal element during the calcination process, and the metal element is used as an active site to target silane gas, and ultrafine silicon nanoparticles are grown by catalytic reduction in the pores of the interconnected hierarchical porous spherical carbon under a high temperature environment, so as to obtain an interconnected hierarchical porous spherical carbon negative electrode material with ultrafine silicon nanoparticles evenly dispersed in the pores.

[0006] Another object of the present invention is to provide a low-cost, zero-strain, high-capacity, fast-charging porous silicon-carbon negative electrode material prepared by the above preparation method.

[0007] Another object of the present invention is to provide the application of the above-mentioned low-cost, zero-strain, high-capacity, fast-charging porous silicon-carbon negative electrode material in lithium-ion batteries.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is: A method for preparing a porous silicon-carbon negative electrode material comprises the following steps: (1) Fully dissolving the polymer in water, adding a pore-forming agent and a spherical carbon source, and mixing thoroughly to obtain a hydrogel; (2) After freeze-drying the hydrogel, calcining it at 600-1000°C for 1-6h in an oxygen-containing atmosphere, crushing it, acid-washing it, washing it with water, and drying it to obtain spherical interconnected hierarchical porous carbon; (3) Spherical interconnected hierarchical porous carbon is prepared by catalytic reduction at 450-900°C for 10-30 min with metal element as catalyst and 10-50 sccm of electronic grade silane gas under negative pressure to obtain porous silicon-carbon negative electrode material with ultrafine silicon nanoparticles dispersed in the pores.

[0009] Preferably, the high molecular weight polymer in step (1) is at least one of acrylamide (PAM), polyvinyl alcohol (PVA), hydroxyethyl cellulose (HEC), polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP).

[0010] Preferably, the pore-forming agent in step (1) is at least one of zinc chloride, sodium chloride, potassium chloride, calcium chloride, magnesium chloride, barium chloride and tin chloride.

[0011] The spherical carbon source in step (1) can be selected from various types of spherical plant-based biomass currently available on the market, and there is no restriction on the molecular weight, oxygen content, group type and other properties of the carbon source itself.

[0012] Preferably, the spherical carbon source in step (1) is at least one of spherical starch, spherical cellulose, spherical lignin, spherical pectin and spherical xylan.

[0013] Preferably, the mass ratio of the high molecular weight polymer, pore former and spherical carbon source in step (1) is (0.5-1.5):(0-4):1, wherein the mass of the pore former is not 0; more preferably, it is 1:3:1.

[0014] Preferably, the mass ratio of the high molecular weight polymer to water in step (1) is (10-30):100.

[0015] Preferably, in step (1), the high molecular weight polymer is fully dissolved in water by stirring at a speed of 750-1000 rpm for 30-60 minutes.

[0016] Preferably, the fully mixing to obtain the hydrogel in step (1) means stirring at 60-80° C. for 6-10 hours to form the hydrogel.

[0017] Preferably, the oxygen-containing atmosphere in step (2) refers to an oxygen-containing atmosphere of 100-2000 ppm.

[0018] Preferably, the crushing in step (2) refers to crushing to a particle size Dv50 of 6-9 μm; the pickling refers to pickling with a mass concentration of 5-10% to an ash content of <0.5%; the water washing refers to water washing to a pH value of 8-9; and the drying refers to drying at 60-100° C. for 9-12 hours.

[0019] The purpose of the pickling and impurity removal in step (2) is to remove inorganic components, expose the carbon surface, and further enrich the pore structure of the carbon material.

[0020] Preferably, the metal element in step (3) is the metal element generated by calcining the pore-forming agent in the hydrogel in step (2).

[0021] Preferably, the negative pressure environment in step (3) refers to vacuuming 10 -6 Up to 10 -7 Torr (1 Torr = 133.322 Pa).

[0022] Preferably, the electronic grade silane in step (3) is at least one of electronic grade monosilane, electronic grade disilane and other electronic grade silicon hydrogen compounds; more preferably, the electronic grade silane is at least one of electronic grade monosilane and electronic grade disilane.

[0023] An interconnected hierarchical porous spherical carbon negative electrode material is prepared by the above preparation method.

[0024] The above-mentioned interconnected hierarchical porous spherical silicon carbon is used in lithium-ion batteries.

[0025] Compared with the prior art, the advantages of the present invention are: (1) The present invention uses spherical plant-based biomass materials as raw materials, and prepares hydrogels by pre-treatment with high molecular polymers and molten salt pore-forming agents. The hydrogels are then optimized and regulated at the molecular level of the material structure by freeze-drying and high-temperature carbonization, thereby achieving homogeneous activation pore formation and preparing defect-rich interconnected hierarchical porous carbon. Finally, ultrafine silicon nanoparticles are uniformly dispersed in the internal pores of the interconnected hierarchical porous spherical carbon under negative pressure.

[0026] (2) The high-strength structure and hierarchical interconnected pore structure of porous carbon can alleviate the volume expansion during the charging and discharging process, optimize the electron density distribution, and promote charge transfer, thereby improving the conductivity and ion transfer rate of the final product; in addition, the carbon layer coating reduces the direct contact between bare silicon and the electrolyte, inhibits the repeated growth of the SEI film (solid electrolyte interface), and thus improves the cycle life and first coulombic efficiency of the lithium battery.

[0027] (3) The interconnected hierarchical porous carbon can provide a large number of active sites due to its well-developed pore structure. During the high-temperature carbonization pore-forming process using the molten salt pore-forming agent, some metal compounds are carbon-thermally reduced to metal elements. The metal elements are used as active sites to in-situ target the silane gas, and the catalytic reduction growth of ultrafine silicon nanoparticles is carried out in a uniformly dispersed manner in the pores of the interconnected hierarchical porous spherical carbon.

[0028] The uniformly dispersed ultrafine silicon nanoparticles make the prepared silicon-carbon negative electrode have zero strain, high capacity, fast charging performance and excellent cycle stability, making it a potential ideal material for silicon-carbon. The silicon doping rate of the product obtained by the present invention is 50%, the gram capacity of the silicon-carbon composite material is 2000 mAh / g, and the first efficiency is 90%. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The first discharge specific capacity and silicon doping rate of the materials obtained in Example 1 and Comparative Examples 1-8 are shown.

[0030] Figure 2 The first discharge specific capacity and first coulombic efficiency diagrams of the materials obtained in Example 1 and Comparative Examples 1-8 are shown.

[0031] Figure 3 It is the cycle capacity retention rate of the materials obtained in Example 1 and Comparative Examples 1-8. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0033] If no specific conditions are specified in the examples of the present invention, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. All raw materials, reagents, etc., whose manufacturers are not specified, are conventional products that can be purchased commercially.

[0034] Example 1 An embodiment of the low-cost zero-strain high-capacity fast-charging porous silicon-carbon negative electrode material and the preparation method thereof of the present invention comprises the following steps: (1) Dissolve 200 g of polyvinyl pyrrolidone (PVP) with a molecular weight of 44,000 in 2 L of water and stir at 900 rpm for 45 min; (2) adding a certain amount of zinc chloride pore-forming agent and spherical starch carbon source, stirring at 70° C. for 8 h to form a hydrogel; the mass of the carbon source is 200 g, and the mass ratio of the pore-forming agent to the carbon source is 3:1; (3) freeze-drying the above materials to obtain aerogel; the obtained aerogel is calcined at 900°C for 2h in an atmosphere containing 500ppm oxygen. During the calcination process, the zinc chloride pore-forming agent is partially carbon-reduced to zinc element while creating pores, thereby obtaining a crude spherical interconnected hierarchical porous carbon product; (4) The crude spherical interconnected hierarchical porous carbon was crushed, and then subjected to acid washing at a mass concentration of 5% to remove impurities, and the inorganic components were removed to an ash content of less than 0.5% and excess zinc on the surface to facilitate the vapor deposition of silane gas inside the pores; after acid washing, the spherical interconnected hierarchical porous carbon was washed with water to a pH value of 8, and dried at 90° C. for 10 h to obtain the spherical interconnected hierarchical porous carbon; (5) The spherical interconnected hierarchical porous carbon is vacuumized to 10 -6 Torr (1 Torr = 133.322 Pa) negative pressure environment, with zinc as a catalyst and 20 sccm of electronic grade monosilane gas catalytic reduction at 600 ° C for 30 minutes to obtain ultrafine silicon nanoparticles, thus obtaining the low-cost zero-strain high-capacity fast-charging porous silicon-carbon negative electrode material.

[0035] Comparative Example 1 (Compared with Example 1, the carbon source is coconut shell block) An embodiment of the low-cost zero-strain high-capacity fast-charging porous silicon-carbon negative electrode material and the preparation method thereof of the present invention comprises the following steps: (1) Dissolve 200 g of polyvinyl pyrrolidone (PVP) with a molecular weight of 44,000 in 2 L of water and stir at 900 rpm for 45 min; (2) adding a certain amount of zinc chloride pore-forming agent and blocky coconut shell carbon source, stirring at 70°C for 8 hours to form a hydrogel; the mass of the carbon source is 200 g, and the mass ratio of the pore-forming agent to the carbon source is 3:1; (3) freeze-drying the above materials to obtain aerogel; the obtained aerogel is calcined at 900°C for 2h in an atmosphere containing 500ppm oxygen. During the calcination process, the zinc chloride pore-forming agent is partially carbon-reduced to zinc element while creating pores, thereby obtaining a crude spherical interconnected hierarchical porous carbon product; (4) The crude spherical interconnected hierarchical porous carbon was crushed and pickled to remove impurities, and the inorganic components were removed to an ash content of less than 0.5% and excess zinc on the surface to facilitate the vapor deposition of silane gas inside the pores; after pickling, it was washed with water to a pH value of 8, and dried at 90° C. for 10 h to obtain spherical interconnected hierarchical porous carbon; (5) The spherical interconnected hierarchical porous carbon is evacuated to a negative pressure environment and catalytically reduced at 600°C for 30 minutes using zinc as a catalyst and assisted by 20 sccm of electronic grade monosilane gas to obtain ultrafine silicon nanoparticles, thereby obtaining the low-cost zero-strain, high-capacity, fast-charging porous silicon-carbon negative electrode material.

[0036] Comparative Example 2 (Compared with Example 1, without adding high molecular weight polymer polyvinyl pyrrolidone) An embodiment of the low-cost zero-strain high-capacity fast-charging porous silicon-carbon negative electrode material and the preparation method thereof of the present invention comprises the following steps: (1) Add a certain amount of zinc chloride pore-forming agent and spherical starch carbon source and dissolve them in 2L of water, and stir at 70°C for 8h; the mass of the carbon source is 200g, and the mass ratio of the pore-forming agent to the carbon source is 3:1; (2) After freeze-drying the above materials, they were calcined at 900°C for 2 h in an atmosphere containing 500 ppm oxygen. During the calcination process, the zinc chloride pore-forming agent was partially carbon-reduced to zinc element while creating pores, thereby obtaining a crude spherical interconnected hierarchical porous carbon product. (3) The crude spherical interconnected hierarchical porous carbon was crushed and pickled to remove impurities, and the inorganic components were removed to an ash content of less than 0.5% and excess zinc on the surface to facilitate the vapor deposition of silane gas inside the pores; after pickling, it was washed with water to a pH value of 8, and dried at 90° C. for 10 h to obtain spherical interconnected hierarchical porous carbon; (4) The spherical hierarchical porous carbon is evacuated to a negative pressure environment and catalytically reduced at 600°C for 30 minutes using zinc as a catalyst and assisted by 20 sccm of electronic grade monosilane gas to obtain ultrafine silicon nanoparticles, thereby obtaining the low-cost zero-strain, high-capacity, fast-charging porous silicon-carbon negative electrode material.

[0037] Comparative Example 3 (Compared with Example 1, step 5 was not evacuated to a negative pressure environment) An embodiment of the low-cost zero-strain high-capacity fast-charging porous silicon-carbon negative electrode material and the preparation method thereof of the present invention comprises the following steps: (1) Dissolve 200 g of polyvinyl pyrrolidone (PVP) with a molecular weight of 44,000 in 2 L of water and stir at 900 rpm for 45 min; (2) adding a certain amount of zinc chloride pore-forming agent and spherical starch carbon source, stirring at 70° C. for 8 h to form a hydrogel; the mass of the carbon source is 200 g, and the mass ratio of the pore-forming agent to the carbon source is 3:1; (3) freeze-drying the above materials to obtain aerogel; the obtained aerogel is calcined at 900°C for 2h in an atmosphere containing 500ppm oxygen. During the calcination process, the zinc chloride pore-forming agent is partially carbon-reduced to zinc element while creating pores, thereby obtaining a crude spherical interconnected hierarchical porous carbon product; (4) The crude spherical interconnected hierarchical porous carbon was crushed and pickled to remove impurities, and the inorganic components were removed to an ash content of less than 0.5% and excess zinc on the surface to facilitate the vapor deposition of silane gas inside the pores; after pickling, it was washed with water to a pH value of 8, and dried at 90° C. for 10 h to obtain spherical interconnected hierarchical porous carbon; (5) The spherical interconnected hierarchical porous carbon is catalytically reduced at 600°C for 30 minutes with zinc as a catalyst and 20 sccm of electronic grade monosilane gas to obtain ultrafine silicon nanoparticles, thereby obtaining the low-cost zero-strain high-capacity fast-charging porous silicon-carbon negative electrode material.

[0038] Comparative Example 4 (Compared with Example 1, no pore-forming agent was added) An embodiment of the low-cost zero-strain high-capacity fast-charging porous silicon-carbon negative electrode material and the preparation method thereof of the present invention comprises the following steps: (1) Dissolve 200 g of polyvinyl pyrrolidone (PVP) with a molecular weight of 44,000 in 2 L of water and stir at 900 rpm for 45 min; (2) adding spherical starch carbon source and stirring at 70° C. for 8 h to form a hydrogel; the mass of the carbon source is 200 g; (3) freeze-drying the above materials to obtain aerogel; calcining the obtained aerogel at 900° C. for 2 h in an atmosphere containing 500 ppm oxygen to obtain a crude spherical interconnected hierarchical porous carbon; (4) The crude spherical interconnected hierarchical porous carbon is crushed, acid-washed and impurized to remove inorganic components to an ash content of less than 0.5% to facilitate the vapor deposition of silane gas inside the pores; after acid washing, it is washed with water to a pH value of 8, and dried at 90° C. for 10 h to obtain a spherical interconnected hierarchical porous carbon; (5) The spherical interconnected hierarchical porous carbon is catalytically reduced at 600°C for 30 minutes in a vacuum environment with the aid of 20 sccm of electronic grade monosilane gas to obtain ultrafine silicon nanoparticles, thereby obtaining the low-cost zero-strain, high-capacity, fast-charging porous silicon-carbon negative electrode material.

[0039] Comparative Example 5 (Compared with Example 1, step 4 does not include pickling and water washing treatment) An embodiment of the low-cost zero-strain high-capacity fast-charging porous silicon-carbon negative electrode material and the preparation method thereof of the present invention comprises the following steps: (1) Dissolve 200 g of polyvinyl pyrrolidone (PVP) with a molecular weight of 44,000 in 2 L of water and stir at 900 rpm for 45 min; (2) adding a certain amount of zinc chloride pore-forming agent and spherical starch carbon source, stirring at 70° C. for 8 h to form a hydrogel; the mass of the carbon source is 200 g, and the mass ratio of the pore-forming agent to the carbon source is 3:1; (3) freeze-drying the above materials to obtain aerogel; the obtained aerogel is calcined at 900°C for 2h in an atmosphere containing 500ppm oxygen. During the calcination process, the zinc chloride pore-forming agent is partially carbon-reduced to zinc element while creating pores, thereby obtaining a crude spherical interconnected hierarchical porous carbon product; (4) crushing the crude spherical interconnected hierarchical porous carbon to obtain spherical interconnected hierarchical porous carbon; (5) The spherical interconnected hierarchical porous carbon is evacuated to a negative pressure environment and catalytically reduced at 600°C for 30 minutes using zinc as a catalyst and assisted by 20 sccm of electronic grade monosilane gas to obtain ultrafine silicon nanoparticles, thereby obtaining the low-cost zero-strain, high-capacity, fast-charging porous silicon-carbon negative electrode material.

[0040] Comparative Example 6 A low-cost, zero-strain, high-capacity, fast-charging porous silicon-carbon negative electrode material and a preparation method thereof, wherein the preparation method is different from that of Example 1 only in that the mass ratio of the pore-forming agent to the carbon source is 1:1.

[0041] Comparative Example 7 A low-cost zero-strain, high-capacity, fast-charging porous silicon-carbon negative electrode material and a preparation method thereof, wherein the preparation method is different from that in Example 1 only in that the rotation speed in step (1) is 300 rpm for stirring for 45 min.

[0042] Comparative Example 8 A low-cost zero-strain, high-capacity, fast-charging porous silicon-carbon negative electrode material and a preparation method thereof, wherein the preparation method is different from that in Example 1 only in that the aerogel precursor is calcined at 1250° C. for 2 h in a 500 ppm oxygen-containing atmosphere.

[0043] Effect Example 1 In order to verify the performance of the low-cost zero-strain high-capacity fast-charging porous silicon-carbon negative electrode material of the present invention, the products of each embodiment and comparative example were prepared into a slurry according to the mass ratio of silicon-carbon material: sodium carboxymethyl cellulose (CMC): conductive carbon black (BP) = 80:10:10 and a lithium-ion battery negative electrode was prepared. The metal lithium sheet was used as the battery, and the electrolyte was 1 mol / L LiPF 6 Button cells were assembled in a ternary mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) in a volume ratio of 1:1:1, and then the button half-cell was charged and discharged using a CT2001A blue electricity test system with a test voltage range of 0.005 to 3.0 V at a rate of 0.1C. The first discharge specific capacity and first coulomb efficiency of the product were recorded, and then the cycle was repeated 100 times, and the capacity retention rate of the discharge specific capacity was recorded. The results are shown in Table 1. Energy dispersive spectroscopy (EDS) was used for element content identification.

[0044] Table 1 It can be clearly seen from Table 1 that the low-cost zero-strain, high-capacity, fast-charging porous silicon-carbon negative electrode material prepared by the preparation method of the present invention has a first discharge specific capacity of up to 2000.6 mAh / g, a first coulombic efficiency of 90.08%, a silicon doping rate of 50.8%, and a capacity retention rate of 93.52% after 100 cycles, with excellent comprehensive performance.

[0045] In the process of preparing porous carbon materials, if the carbon source is not spherical in shape, as shown in Comparative Example 1, the morphology is irregular and the homogeneous pore formation is partially differentiated, resulting in a decrease in active sites.

[0046] The use of high molecular polymers is crucial in the preparation process, otherwise, as shown in Comparative Example 2, hydrogels cannot be formed and the pore structure of the product is not interconnected; the pore distribution on the surface of the spherical hierarchical porous carbon without high molecular polymers is uneven, and no obvious interconnected hierarchical porous structure is observed. This may be because the activator is not easy to diffuse into the spherical carbon source, resulting in uneven activation.

[0047] If the vacuum is not applied during the preparation of vapor-deposited silicon, the silicon nanoparticles are mainly reduced on the porous carbon surface and cannot be evenly diffused into the porous carbon pores to anchor and reduce the silicon nanoparticles in situ in the pores. Moreover, due to the large size of the silicon particles on the surface and the lack of protection, the efficiency is low and the cycle performance is poor. The results show that the presence of activator metal elements between the carbon lattices is a necessary condition for the large-scale generation of Si, and due to the spatial confinement effect, the confinement of the metal catalyst in the porous carbon nanopores is crucial for the in-situ formation of Si nanodots.

[0048] As shown in Comparative Examples 4 and 6, if the concentration of the pore former is low, more microporous structures and defects cannot be formed, which reduces the electrochemical performance of the material. During the preparation process, in the absence of an activator, the material itself does not have an obvious porous structure. With the increase in the amount of zinc chloride used, the development of the pore structure is significantly improved, and dense pores appear. It shows that during the synthesis process, as the mass ratio of the activator to the carbon source increases, the active sites gradually increase. In addition, the activator inserted into the carbon layer distorts the carbon lattice, which is beneficial to the expansion of the interlayer distance. The interconnected hierarchical pore structure effectively alleviates the transport resistance and promotes the rapid transfer of ions. In addition, the activator metal element between the carbon lattices provides more sites, optimizes the electron density distribution of the carbon material, and thus improves the doping rate and uniform dispersion of silicon carbon.

[0049] In comparative example 7, the rotation speed is low during the preparation of the hydrogel, which causes uneven dispersion of the pore former in the carbonization and high molecular polymer, resulting in a decrease in the pore volume and specific surface area of ​​the porous carbon.

[0050] During the carbonization process, if the carbonization temperature is high, a large number of micropores formed will be closed at high temperature, reducing the pore volume and specific surface area, as shown in Comparative Example 8.

[0051] The low-cost zero-strain high-capacity fast-charging porous silicon-carbon negative electrode material prepared by the present invention has excellent electrochemical properties, including significant cycle stability and fast-charging high-capacity performance. The main reasons are: (1) The fast-charging performance is attributed to its excellent conductivity and porous structure. The micro-mesoporous structure and hierarchically interconnected nanopore structure are conducive to more efficient charge transport of electrons and Li ions, thereby reducing the diffusion resistance of ions; (2) The high capacity performance is attributed to the high specific surface performance and high silicon loading of the porous carbon. The metal element is in-situ gas-phase reduced ultrafine nano-silicon material and is uniformly dispersed in the hierarchically interconnected pore structure of the porous carbon, giving the material a high lithium storage capacity; (3) The long cycle performance is attributed to the high structural stability of the spherical interconnected hierarchical porous carbon, which can effectively alleviate the volume expansion problem of silicon and solve its large volume change during the charging and discharging process.

[0052] In summary, defect-rich spherical interconnected hierarchical porous carbon was successfully constructed through the homogeneous activation strategy. The optimized material has a good pore structure, a large specific surface area, fast ion diffusion and strong charge transfer kinetics. When the nano-silicon particles are reduced in situ by gas phase, the composite material exhibits long cyclability, high capacity and excellent rate capability.

[0053] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing a low-cost, zero-strain, high-capacity, fast-charging porous silicon-carbon negative electrode material, characterized in that: The following steps are involved: (1) Fully dissolving the polymer in water, adding a pore-forming agent and a spherical carbon source, and mixing thoroughly to obtain a hydrogel; (2) After freeze-drying the hydrogel, calcining, crushing, acid washing, water washing, and drying, spherical interconnected hierarchical porous carbon is obtained; (3) Ultrafine silicon nanoparticles are prepared by catalytic reduction of spherical interconnected hierarchical porous carbon under negative pressure with metal elements as catalysts and assisted by electronic grade silane gas, thereby obtaining a porous silicon-carbon negative electrode material with ultrafine silicon nanoparticles dispersed in the pores.

2. The method for preparing a porous silicon-carbon negative electrode material according to claim 1, characterized in that: The temperature of the catalytic reduction in step (3) is 450-900°C and the time is 10-30 minutes; The amount of electronic grade silane gas used in step (3) is 10-50 sccm; The electronic grade silane in step (3) is at least one of electronic grade monosilane, electronic grade disilane and other electronic grade silicon hydrogen compounds.

3. The method for preparing a porous silicon-carbon negative electrode material according to claim 1, characterized in that: The mass ratio of the high molecular weight polymer, pore former and spherical carbon source in step (1) is (0.5-1.5):(0-4):1, wherein the mass of the pore former is not 0; The mass ratio of the high molecular weight polymer to water in step (1) is (10-30):100; The spherical carbon source in step (1) is at least one of spherical starch, spherical cellulose, spherical lignin, spherical pectin and spherical xylan; The pore-forming agent in step (1) is at least one of zinc chloride, sodium chloride, potassium chloride, calcium chloride, magnesium chloride, barium chloride and tin chloride; The high molecular weight polymer in step (1) is at least one of acrylamide, polyvinyl alcohol, hydroxyethyl cellulose, polyethylene glycol and polyvinyl pyrrolidone.

4. The method for preparing a porous silicon-carbon negative electrode material according to claim 1, characterized in that: The calcination in step (2) is performed at 600-1000° C. for 1-6 hours in an atmosphere containing 100-2000 ppm oxygen.

5. The method for preparing a porous silicon-carbon negative electrode material according to claim 1, characterized in that: The negative pressure environment in step (3) refers to vacuuming 10 -6 Up to 10 -7 Torr; The electronic grade silane in step (3) is at least one of electronic grade monosilane and electronic grade disilane.

6. The method for preparing a porous silicon-carbon negative electrode material according to claim 1, characterized in that: The metal element in step (3) is the metal element generated after the pore-forming agent in the hydrogel is calcined in step (2).

7. The method for preparing a porous silicon-carbon negative electrode material according to claim 1, characterized in that: The high molecular weight polymer in step (1) is fully dissolved in water by stirring at a speed of 750-1000 rpm for 30-60 minutes; The step (1) of fully mixing to obtain a hydrogel means stirring at 60-80° C. for 6-10 hours to form a hydrogel.

8. The method for preparing a porous silicon-carbon negative electrode material according to claim 1, characterized in that: The crushing in step (2) refers to crushing to a particle size Dv50 of 6-9 μm; the pickling refers to pickling with acid to an ash content of <0.5%; the water washing refers to water washing to a pH value of 8-9; and the drying refers to drying at 60-100° C. for 9-12 hours.

9. A porous silicon-carbon negative electrode material obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the porous silicon-carbon negative electrode material according to claim 9 in lithium-ion batteries.

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