Porous carbon skeleton silicon-based negative electrode material and preparation method and application thereof

Abstract

The invention provides a porous carbon skeleton silicon-based negative electrode material and a preparation method and application thereof, and the preparation method comprises the following steps: (1) modifying nano silicon on the surface of low-softening-point asphalt: stirring and dispersing nano silicon and low-softening-point asphalt into an organic solvent, uniformly mixing, distilling to remove the solvent, drying, and carrying out pre-oxidation treatment to obtain lipophilic nano silicon; (2) fully blending the obtained lipophilic nano silicon, fused salt and high-softening-point mesophase pitch at a high temperature, and performing crushing granulation, primary carbonization, washing and drying to obtain a primary silicon-carbon precursor of which the nano silicon is embedded in a porous carbon matrix; and (3) performing high-temperature solid-phase coating on the primary silicon-carbon precursor by using high-softening-point coating asphalt powder to obtain a secondary silicon-carbon precursor, and performing secondary carbonization to obtain the porous carbon skeleton silicon-based negative electrode material with multi-level buffering, the inner core is a porous carbon skeleton, and the outer layer is a compact carbon coating. The silicon-based negative electrode material with a porous carbon skeleton is ingeniously designed from three kinds of asphalt derived carbon, a silicon volume expansion space, an ion electron channel and expansion stress intensity are provided, the specific capacity, the conductivity and the mechanical stability of the silicon-carbon negative electrode material can be improved, and the silicon-carbon negative electrode material has excellent electrochemical performance when being used for a lithium ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of negative electrode materials for lithium ion batteries, and in particular to a porous carbon skeleton silicon-based negative electrode material and a preparation method and application thereof. Background Art

[0002] With the development of new energy, lithium battery silicon-carbon negative electrode materials have been widely studied due to their high specific capacity. However, although silicon has excellent lithium storage performance, it has poor conductivity and poor cycle stability. Researchers have combined silicon and carbon materials to prepare lithium-ion battery negative electrode materials with high specific capacity and high stability.

[0003] Currently, the packaging structures of silicon-carbon composite materials mainly include core-shell structure, yolk-shell structure and porous structure. (1) The core-shell structure is mainly composed of a carbon shell coating a silicon core. The carbon shell acts as a buffer layer to alleviate the volume expansion of Si. It can effectively prevent the Si core from contacting the electrolyte, reduce side reactions, and form a more stable SEI. The conductive carbon layer coating can improve the overall electronic conductivity of the material. For example, patent CN 118380553 A proposes that nano-silicon particles are uniformly embedded in an asphalt pyrolysis carbon matrix, and a non-conductive polymer coating layer is grown on the surface of the particles by chemical vapor deposition to obtain a silicon-carbon composite material. (2) The yolk-shell structure is mainly composed of a silicon core, a carbon shell and an intermediate gap, which further buffers the volume expansion of the silicon core and forms a more stable SEI layer. For example, patent CN118248828 A proposes to use electrostatic attraction and inorganic chemical reactions to form an adjustable calcium carbonate layer on the surface of the silicon particles as a sacrificial template, and then coat the organic carbon layer. After removing the calcium carbonate layer by acid washing, a porous silicon-carbon negative electrode material with good conductivity and high capacity is prepared. (3) The porous structure is mainly characterized by silicon nanoparticles dispersed in a porous carbon matrix. Patent CN115986085A discloses a three-dimensional carbon skeleton silicon-based negative electrode material, including a carbon frame, a porous carbon skeleton layer covering the surface of the carbon frame, and a silicon layer and a carbon layer. The rich void space alleviates the volume expansion of silicon. However, the carbon composite material still undergoes repeated deformation and fracture during the long-term silicon lithiation / delithiation reaction process.

[0004] In summary, the traditional buffer carbon skeleton has some limitations in practical applications, such as the insufficient mechanical strength of biomass and organic coating layers or porous carbon skeletons, and the structural stability is difficult to offset the expansion stress of silicon. Unlike organic polymers and biomass, asphalt is composed of polycyclic aromatic hydrocarbons with a high carbon content, which has the advantages of cheap raw materials, high carbonization yield and high mechanical strength. Therefore, in order to achieve structural stability and good cycle performance, the need to design and develop asphalt-based multi-level buffer structure silicon-carbon composite materials is still urgently needed. Summary of the invention

[0005] In response to the above technical problems, the present invention proposes a porous carbon skeleton silicon-based negative electrode material and a preparation method and application thereof; the designed porous carbon skeleton silicon-based negative electrode material has a stable multi-level carbon skeleton buffer structure, which is used as a negative electrode material for lithium-ion batteries, effectively buffering the volume expansion of silicon and improving the electrochemical performance.

[0006] In order to achieve the above object, the technical solution of the present invention is achieved as follows: The technical solution for realizing the present invention is: A method for preparing a silicon-based negative electrode material having a porous carbon skeleton, the steps are as follows: (1) Nano-silicon modified on the surface of low softening point asphalt: nano-silicon and asphalt are dispersed in an organic solvent by a liquid phase method, the solvent is removed by distillation and then dried, and then pre-oxidized to obtain lipophilic nano-silicon with controllable thickness and good dispersion of asphalt coating; (2) mechanically stirring and fully blending the obtained lipophilic nano-silicon and molten salt under high temperature melting of high softening point mesophase asphalt, crushing and granulating, high temperature primary carbonization, and washing to obtain a primary silicon-carbon precursor in which nano-silicon is embedded in a porous carbon matrix; (3) The primary silicon-carbon precursor is solid-phase coated with high-softening-point asphalt powder to obtain a secondary silicon-carbon precursor. After high-temperature secondary carbonization, a silicon-carbon negative electrode material with a multi-layer buffered carbon skeleton is obtained, with a porous carbon skeleton as the inner core and a dense carbon coating as the outer layer.

[0007] In the step (1), the nano silicon is at least one of elemental silicon, silicon dioxide or silicon monoxide, with a particle size of 50-200nm; the low softening point asphalt includes but is not limited to at least one of the following asphalts: coal tar, petroleum asphalt, coal tar, modified coal tar, and secondary petroleum heavy oil, with a softening point of 40-150°C; the softening point of the low softening point asphalt can be 40-120°C, 40-100°C, 40-80°C, 40-60°C; 60-150°C, 60-120°C, 60-100°C, 60-80°C; 80-150°C, 80-120°C, 80-100°C; 100-150°C, 100-120°C. The mass ratio of the nano silicon to the low softening point asphalt is 100:(1-30), and the asphalt coating is 5-20nm.

[0008] In the step (1), the organic solvent is any one of toluene, xylene, wash oil, kerosene or a combination of at least two thereof, and the mass ratio of asphalt to solvent is (1-5):10; the pre-oxidation treatment temperature is 280-320°C, and the treatment time is 2-4h.

[0009] The mesophase asphalt in step (2) includes but is not limited to the mesophase asphalt obtained by thermal polymerization of the following raw materials: at least one of coal tar, petroleum tar, coal tar, modified coal tar, polycyclic aromatic hydrocarbons or naphthalene, with a softening point of 240-320°C. The molten salt includes but is not limited to any one of metal halides, hydroxides, sulfates, nitrates or carbonates or a combination of at least two of them, wherein the metal ions include Li + 、Na + Mg 2+ 、Al 3+ , K + or Ca 2+ Any one or a combination of at least two of the following.

[0010] The mechanical mixing in step (2) comprises first pre-mixing the dispersed nano-silicon, molten salt and mesophase pitch by ball milling at a mass ratio of (1-30): (50-100): (10-50), and then subjecting the mixture to high-temperature mechanical stirring for melting and mixing at a temperature of 360-420° C. for a stirring time of 2-4 hours, and the protective atmosphere being any one of nitrogen and argon or a combination thereof.

[0011] In step (2), the granulation is followed by carbonization at 3-5°C min -1 The temperature is raised to 600-1000℃ at a rate of 1-4 hours; the carbonization temperature can be 600-800℃; 800-1000℃; the holding time is preferably 2-4 hours; the preferred carbonization treatment protective atmosphere is any one of nitrogen and argon or a combination thereof, and the gas flow rate is 30-100 mL min -1 .

[0012] The washing liquid used in the washing treatment in step (2) is deionized water, the mass ratio of carbonized material to washing liquid is (1-3):10, stirring is 0.5-2h, washing times is 2-4 times, and vacuum drying is 3-12h.

[0013] The coated asphalt in step (3) is coal-based coated asphalt or petroleum-based coated asphalt with a softening point of 220-280°C. The coated asphalt powder has a particle size of 0.5-2µm and is uniformly mixed with the primary silicon-carbon precursor at a mass ratio of 5-15:100. The mixture is melted at 250-650°C for 0.5-2h to obtain a secondary silicon-carbon precursor.

[0014] In step (3), the carbonization treatment temperature is 800-1400°C, the heating rate is 3-10°C / min, and the temperature is kept constant for 0.5-2 h; the carbonization treatment protective atmosphere is any one of nitrogen and argon or a combination thereof, and the gas flow rate is 30-100 mL min -1 .

[0015] The porous carbon skeleton silicon-based negative electrode material has a stable multi-level carbon skeleton buffer structure and is used as a negative electrode material for lithium ion batteries.

[0016] The present invention has the following beneficial effects: (1) The silicon-based negative electrode material with a porous carbon skeleton of the present invention is cleverly designed from three types of asphalt-derived carbon. The amorphous carbon formed by low softening point asphalt can improve the interface bonding between nano-silicon and mesophase asphalt, enhance the mechanical strength and conductivity of the material, and at the same time, the low carbonization yield of low softening point amorphous asphalt can derive nanovoids, which have a certain buffering expansion effect; the ordered carbon framework derived from mesophase asphalt and the design of porous void space provide sufficient buffer space, which can adaptively support the stress change of the electrode structure after adapting to the volume expansion, and the ordered carbon has good conductivity and lithium ion diffusion; the asphalt-coated disordered dense carbon coating has good mechanical strength, good compatibility with the electrolyte, and is conducive to the formation of a stable SEI film, improving the first coulomb efficiency and ensuring the cycle stability.

[0017] (2) The macroporous structure in the inner core porous carbon skeleton can be regulated by the composition and proportion of the molten salt. The pore structure exhibits different curvatures and multi-branched channel morphology due to the molten state of the molten salt. The formed porous void structure is conducive to the rapid insertion and extraction of lithium ions and buffers the volume expansion of silicon.

[0018] (3) The silicon-based negative electrode material with a porous carbon skeleton of the present invention provides silicon volume expansion space, ion and electron channels and expansion stress strength, which can improve the specific capacity, conductivity and mechanical stability of the silicon-carbon negative electrode material. It has excellent electrochemical properties when used as a negative electrode material for lithium-ion batteries, and a reversible specific capacity of 600-2200 mA hg -1 , the capacity retention rate after 1000 cycles is 80-95%. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 This is a SEM image of the silicon-based negative electrode material with a porous carbon skeleton in Example 1 of the present invention.

[0021] Figure 2 This is a SEM image of the silicon-based negative electrode material with a porous carbon skeleton in Example 2 of the present invention. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] Example 1 A method for preparing a silicon-based negative electrode material having a porous carbon skeleton, the steps are as follows: (1) Surface modification of low softening point (40°C) coal tar pitch with 50 nm nano-silicon, where nano-silicon is elemental silicon and the mass ratio of nano-silicon to low softening point coal tar pitch is 100:1. Nano-silicon and asphalt are dispersed in an organic solvent, toluene, and the liquid phase is stirred for 12 h. The mass ratio of asphalt to solvent is 1:10. The solvent is removed by distillation and then dried. The asphalt coating is then pre-oxidized at 280°C for 2 h to obtain a well-dispersed lipophilic nano-silicon with a thickness of 5 nm. (2) The obtained lipophilic nano-silicon, lithium hydroxide molten salt and high softening point 240℃ coal-based mesophase pitch were mixed in a mass ratio of 30:100:50, ball milled at a speed of 250 rpm, and processed for 2 h; mechanically stirred and fully blended at a high temperature of 360℃ for 4 h, with a protective atmosphere of nitrogen; the blended mixture was crushed and granulated, and carbonized at high temperature for one time at 5℃ min -1 The temperature was raised to 1000°C at a rate of 1.5 °C and kept at this temperature for 1 h. The protective atmosphere was nitrogen with a gas flow rate of 30-120 mL min -1 The mass ratio of carbonized material to deionized water was 1:10, stirred for 0.5 h, washed twice, and then vacuum dried at 100 ° C for 3 h to obtain a primary silicon-carbon precursor in which nano-silicon was embedded in a porous carbon matrix; The preparation method of the high softening point 240°C coal-based mesophase asphalt is as follows: using coal tar pitch with a softening point of 45°C as a raw material, thermally polymerizing in a high-temperature reactor to prepare the high softening point coal-based mesophase asphalt, the thermal polymerization temperature is 400°C, the polymerization time is 8h, and the softening point of the obtained coal-based mesophase asphalt is 240°C; (3) Using coal-based coated asphalt powder with a high softening point of 220°C and a particle size of 0.5µm, the primary silicon-carbon precursor is subjected to high-temperature solid-phase coating in a high-temperature coating machine, so that the asphalt powder is melted and evenly coated on its surface to form a coating with a mass ratio of 5:100 and a high-temperature melting coating at 250°C for 0.5h to obtain a secondary silicon-carbon precursor; after high-temperature secondary carbonization at a temperature of 1400°C and a heating rate of 10°C min -1 , constant temperature for 0.5 h, protective atmosphere of nitrogen, gas flow rate of 30 mL min -1, a silicon-carbon negative electrode material with a multi-level buffer carbon skeleton is prepared, the inner core is a porous carbon skeleton, and the outer layer is a dense carbon coating; The preparation method of the high softening point 220°C coal-based coated asphalt is to use coal-based asphalt with a softening point of 45°C as raw material, and to prepare the high softening point coal-based coated asphalt by oxidative cross-linking polymerization at a temperature of 300°C for 6 hours. The obtained coal-based coated asphalt has a softening point of 220°C.

[0024] Figure 1 This is a SEM image of the silicon-based negative electrode material with a porous carbon skeleton in this embodiment; it can be seen from the image that the pore structure of the porous carbon skeleton is evenly distributed and the surface is evenly covered with a carbon coating.

[0025] Lithium battery assembly and performance Appropriate amounts of porous carbon skeleton silicon-based negative electrode materials, polyvinylidene fluoride and acetylene black, and appropriate amounts of N-methylpyrrolidone were weighed in a mass ratio of 8:1:1, and evenly coated on copper foil after ball milling at a rate of 150 rpm for 2 h. The battery pole piece was obtained after vacuum drying at 80 °C for 12 h. The obtained battery pole piece was used as the working electrode and the lithium sheet as the counter electrode to assemble the lithium-ion button cell in the glove box. At a current density of 100 mA g -1 The first reversible specific capacity is 2226 mA h g -1 The first coulombic efficiency is 89.5%, the capacity retention rate after 1000 cycles is 80.6%, and it has excellent cycle and rate characteristics.

[0026] Example 2 A method for preparing a silicon-based negative electrode material having a porous carbon skeleton, the steps are as follows: (1) Surface modification of low softening point 150℃ petroleum asphalt with 200nm nano-silicon, where nano-silicon is elemental silicon and the mass ratio of nano-silicon to low softening point petroleum asphalt is 100:30. Nano-silicon and asphalt are dispersed in organic solvent washing oil, stirred for 12h, the mass ratio of asphalt to solvent is 5:10, the solvent is removed by distillation and then dried, and then pre-oxidized at 320℃ for 4h to obtain asphalt coating with 20nm thickness and well-dispersed lipophilic nano-silicon. (2) The obtained lipophilic nano-silicon, calcium hydroxide molten salt and high softening point 320℃ coal-based mesophase pitch were mixed in a mass ratio of 1:50:10, ball milled at a speed of 250 rpm, and processed for 2 h; mechanically stirred and fully blended at a high temperature of 420℃ for 2 h, with a protective atmosphere of nitrogen; the blended mixture was crushed and granulated, and carbonized at high temperature for one time at 5℃ min -1 The temperature was raised to 600 °C at a rate of 1.5 °C and kept at this temperature for 4 h. The protective atmosphere was nitrogen with a gas flow rate of 100 mL min -1The mass ratio of carbonized material to deionized water was 3:10, stirred for 2 hours, washed 4 times, and then vacuum dried at 100°C for 12 hours to obtain a primary silicon-carbon precursor in which nano-silicon was embedded in a porous carbon matrix; In step (2), the method for preparing the high softening point 320°C coal-based mesophase asphalt is as follows: using coal tar pitch with a softening point of 40°C as a raw material, thermally polymerizing in a high-temperature reactor to prepare the high softening point coal-based mesophase asphalt, the thermal polymerization temperature is 420°C, the polymerization time is 10h, and the obtained coal-based mesophase asphalt has a softening point of 320°C; (3) Using a high softening point 280℃ petroleum-based coated asphalt powder with a particle size of 2µm, the primary silicon-carbon precursor is subjected to high-temperature solid phase coating in a high-temperature coating machine, so that the asphalt powder is melted and evenly coated on its surface to form a coating with a mass ratio of 15:100 and a high-temperature melting coating at 650℃ for 2h to obtain a secondary silicon-carbon precursor; after high-temperature secondary carbonization at 800℃ and a heating rate of 3℃ min -1 , constant temperature for 2h, protective atmosphere is nitrogen, gas flow rate is 100mL min -1 , a silicon-carbon negative electrode material with a multi-level buffer carbon skeleton is prepared, the inner core is a porous carbon skeleton, and the outer layer is a dense carbon coating; In step (3), the method for preparing the petroleum-based coated asphalt with a high softening point of 280°C is to use petroleum asphalt as a raw material, and to prepare the high softening point petroleum-based coated asphalt by oxidative cross-linking polymerization at a temperature of 390°C for 8 hours, and the obtained coal-based coated asphalt has a softening point of 280°C; Figure 2 This is a SEM image of the silicon-based negative electrode material with a porous carbon skeleton in this embodiment; it can be seen from the image that the pore structure of the porous carbon skeleton is evenly distributed and the surface is evenly covered with a carbon coating.

[0027] Lithium battery assembly and performance The porous carbon skeleton silicon-based negative electrode material prepared in this embodiment is used to assemble battery pole pieces and lithium batteries; the remaining steps are consistent with the assembly process of the battery pole pieces and lithium batteries in Example 1.

[0028] At a current density of 100 mA g -1 The first reversible specific capacity is 614 mA hg -1 The first coulombic efficiency is 90.3%, the capacity retention rate after 1000 cycles is 95.3%, and it has excellent cycle and rate characteristics.

[0029] Example 3 A method for preparing a silicon-based negative electrode material having a porous carbon skeleton, the steps are as follows: (1) 150nm nano-silicon was modified on the surface of coal tar with a low softening point of 40℃. Nano-silicon was a mixture of elemental silicon and silicon dioxide. The mass ratio of nano-silicon to low softening point coal tar was 100:20. Nano-silicon and asphalt were dispersed in a mixture of organic solvents toluene and kerosene, and the liquid phase was stirred for 12h. The mass ratio of asphalt to solvent was 3:10. The solvent was removed by distillation and then dried. The asphalt coating was pre-oxidized at a temperature of 310℃ for 3h to obtain a well-dispersed lipophilic nano-silicon with a thickness of 16nm. (2) The obtained lipophilic nano-silicon, potassium hydroxide molten salt and high softening point 300℃ petroleum-based mesophase asphalt were mixed in a mass ratio of 20:80:50, ball milled at a speed of 250 rpm, and processed for 2 h; the mixture was fully blended by mechanical stirring at a high temperature of 400℃ for 3 h, and the protective atmosphere was argon; the mixture was crushed and granulated, and carbonized at high temperature for one time at 3℃ min -1 The temperature was raised to 900 °C at a rate of 1.5 °C and kept at this temperature for 3 h. The protective atmosphere was nitrogen with a gas flow rate of 50 mL min -1 The mass ratio of carbonized material to deionized water was 2:10, stirred for 1 hour, washed 3 times, and then vacuum dried at 100°C for 10 hours to obtain a primary silicon-carbon precursor in which nano-silicon was embedded in a porous carbon matrix; In step (2), the preparation method of the petroleum-based mesophase asphalt with a high softening point of 300°C is as follows: using petroleum asphalt with a softening point of 45°C as a raw material, thermally polymerizing in a high-temperature reactor to prepare the high-softening-point petroleum-based mesophase asphalt, the thermal polymerization temperature is 440°C, the polymerization time is 6 hours, and the obtained petroleum-based mesophase asphalt has a softening point of 300°C; (3) Using coal-based coated asphalt powder with a high softening point of 260°C and a particle size of 1µm, the primary silicon-carbon precursor is subjected to high-temperature solid-phase coating in a high-temperature coating machine, so that the asphalt powder is melted and evenly coated on its surface to form a coating with a mass ratio of 10:100 and high-temperature melting coating at 500°C for 1h to obtain a secondary silicon-carbon precursor; after high-temperature secondary carbonization at a temperature of 1400°C and a heating rate of 10°C min -1 , constant temperature for 0.5 h, protective atmosphere of nitrogen, gas flow rate of 30 mL min -1 , a silicon-carbon negative electrode material with a multi-layer buffer carbon skeleton was obtained, the inner core of which was a porous carbon skeleton and the outer layer was a dense carbon coating.

[0030] In step (3), the method for preparing the high softening point 260°C coal-based coated asphalt is to use coal tar as raw material, and to prepare the high softening point coal-based coated asphalt by oxidative crosslinking polymerization, wherein the oxidative crosslinking temperature is 320°C and the time is 6 hours; the obtained coal-based coated asphalt has a softening point of 260°C; Lithium battery assembly and performance The porous carbon skeleton silicon-based negative electrode material prepared in this embodiment is used to assemble battery pole pieces and lithium batteries; the remaining steps are consistent with the assembly process of the battery pole pieces and lithium batteries in Example 1.

[0031] At a current density of 100 mA g -1 The first reversible specific capacity is 1523 mA h g -1 The first coulombic efficiency is 84.1%, the capacity retention rate after 1000 cycles is 82.6%, and it has excellent cycle and rate characteristics.

[0032] Example 4 A method for preparing a silicon-based negative electrode material having a porous carbon skeleton, the steps are as follows: (1) 50 nm nano-silicon was modified on the surface of coal tar with a low softening point of 100 °C. Nano-silicon was a mixture of elemental silicon and silicon monoxide. The mass ratio of nano-silicon to low softening point coal tar was 100:10. Nano-silicon and asphalt were dispersed in an organic solvent xylene, stirred for 12 h, and the mass ratio of asphalt to solvent was 2:10. The solvent was removed by distillation and dried. The asphalt was then pre-oxidized at 280 °C for 4 h to obtain an asphalt coating with a thickness of 10 nm and well-dispersed lipophilic nano-silicon. (2) The obtained lipophilic nano-silicon, aluminum chloride molten salt and naphthyl mesophase pitch with a high softening point of 283°C were mixed in a mass ratio of 25:100:50, ball milled at a speed of 250 rpm, and processed for 2 h; the mixture was fully mixed by mechanical stirring at a high temperature of 380°C for 3 h, and the protective atmosphere was nitrogen; the mixture was crushed and granulated, and carbonized at high temperature for one time at 5°C min -1 The temperature was raised to 1000 °C at a rate of 1.5 °C and kept at this temperature for 1 h. The protective atmosphere was argon with a gas flow rate of 60 mL min -1 The mass ratio of carbonized material to deionized water was 1:10, stirred for 1 hour, washed 3 times, and then vacuum dried at 100°C for 8 hours to obtain a primary silicon-carbon precursor in which nano-silicon was embedded in a porous carbon matrix; In step (2), the method for preparing the naphthyl mesophase asphalt with a high softening point of 283°C is as follows: using naphthalene as a raw material, thermally polymerizing in a high-temperature reactor to prepare the naphthyl mesophase asphalt with a high softening point, the thermal polymerization temperature is 450°C, the polymerization time is 6 hours, and the obtained naphthyl mesophase asphalt has a softening point of 283°C; (3) Using high softening point 275℃ coated asphalt powder with a particle size of 2µm, the primary silicon-carbon precursor is subjected to high-temperature solid phase coating in a high-temperature coating machine, so that the asphalt powder is melted and evenly coated on its surface to form a coating with a mass ratio of 10:100 and high-temperature melting coating at 450℃ for 1h to obtain a secondary silicon-carbon precursor; after high-temperature secondary carbonization at a temperature of 1200℃ and a heating rate of 5℃ min -1 , constant temperature for 1 h, protective atmosphere of nitrogen, gas flow rate of 30 mL min-1 , a silicon-carbon negative electrode material with a multi-level buffer carbon skeleton is prepared, the inner core is a porous carbon skeleton, and the outer layer is a dense carbon coating; In step (3), the method for preparing the high softening point 275°C coated asphalt is to use petroleum asphalt as a raw material, and to prepare the high softening point petroleum-based coated asphalt by oxidative crosslinking polymerization, wherein the oxidative crosslinking temperature is 400°C and the time is 6 hours; the obtained petroleum-based coated asphalt has a softening point of 275°C; Lithium battery assembly and performance The porous carbon skeleton silicon-based negative electrode material prepared in this embodiment is used to assemble battery pole pieces and lithium batteries; the remaining steps are consistent with the assembly process of the battery pole pieces and lithium batteries in Example 1.

[0033] At a current density of 100 mA g -1 The first reversible specific capacity is 1803 mA h g -1 The first coulombic efficiency is 88.2%, the capacity retention rate after 1000 cycles is 90.3%, and it has excellent cycle and rate characteristics.

[0034] Example 5 A method for preparing a silicon-based negative electrode material having a porous carbon skeleton, the steps are as follows: (1) Surface modification of low softening point 120℃ petroleum asphalt with 80nm nano-silicon: Nano-silicon is elemental silicon, and the mass ratio of nano-silicon to low softening point petroleum asphalt is 100:15. Nano-silicon and asphalt are dispersed in an organic solvent toluene, stirred for 12h, the mass ratio of asphalt to solvent is 2:10, the solvent is removed by distillation and then dried, and then pre-oxidized at 290℃ for 3h to obtain an asphalt coating with a thickness of 12nm and well-dispersed lipophilic nano-silicon; (2) The obtained lipophilic nano-silicon, magnesium nitrate molten salt and high softening point 255°C coal-based mesophase pitch were mixed in a mass ratio of 5:100:20, ball milled at a speed of 250 rpm, and processed for 2 h; the mixture was fully blended by mechanical stirring at a high temperature of 410°C for 2 h, with an argon protective atmosphere; the mixture was crushed and granulated, and carbonized at high temperature for one time at 5°C min -1 The temperature was raised to 1000 °C at a rate of 1.5 °C and kept at this temperature for 1 h. The protective atmosphere was nitrogen with a gas flow rate of 50 mL min -1 The mass ratio of carbonized material to deionized water was 3:10, stirred for 0.5 h, washed twice, and then vacuum dried at 100 ° C for 6 h to obtain a primary silicon-carbon precursor in which nano-silicon was embedded in a porous carbon matrix; In step (2), the method for preparing the high softening point 255°C coal-based mesophase pitch is to use coal tar pitch with a softening point of 100°C as a raw material, and to prepare the high softening point coal-based mesophase pitch by thermal polymerization in a high-temperature reactor, the thermal polymerization temperature is 400°C, the polymerization time is 10h, and the obtained coal-based mesophase pitch has a softening point of 255°C; (3) Using a high softening point 246℃ petroleum-based coated asphalt powder with a particle size of 1.5µm, the primary silicon-carbon precursor was subjected to high-temperature solid-phase coating in a high-temperature coating machine, so that the asphalt powder was melted and evenly coated on its surface to form a coating with a mass ratio of 12:100 and a high-temperature melting coating at 320℃ for 0.5h to obtain a secondary silicon-carbon precursor; after high-temperature secondary carbonization at a temperature of 1100℃ and a heating rate of 5℃ min -1 , constant temperature for 2 h, protective atmosphere is argon, gas flow rate is 30 mL min -1 , a silicon-carbon negative electrode material with a multi-level buffer carbon skeleton is prepared, the inner core is a porous carbon skeleton, and the outer layer is a dense carbon coating; In step (3), the method for preparing the petroleum-based coated asphalt with a high softening point of 246°C is as follows: using petroleum asphalt as a raw material, oxidative cross-linking polymerization is used to prepare the high softening point petroleum-based coated asphalt, the oxidative cross-linking temperature is 380°C, and the time is 7 hours; the obtained petroleum-based coated asphalt has a softening point of 246°C.

[0035] Lithium battery assembly and performance The porous carbon skeleton silicon-based negative electrode material prepared in this embodiment is used to assemble battery pole pieces and lithium batteries; the remaining steps are consistent with the assembly process of the battery pole pieces and lithium batteries in Example 1.

[0036] At a current density of 100 mA g -1 The first reversible specific capacity is 1058 mA h g -1 The first coulombic efficiency is 83.6%, the capacity retention rate after 1000 cycles is 92.1%, and it has excellent cycle and rate characteristics.

[0037] Example 6 A method for preparing a silicon-based negative electrode material having a porous carbon skeleton, the steps are as follows: (1) 50 nm nano-silicon was used to modify the surface of coal tar with a low softening point of 128 °C. The nano-silicon was silicon monoxide. The mass ratio of nano-silicon to low softening point coal tar was 100:20. The nano-silicon and tar were dispersed in an organic solvent, toluene, and the liquid phase was stirred for 12 h. The mass ratio of tar to solvent was 1:10. The solvent was removed by distillation and then dried. The pre-oxidation treatment was then performed at a temperature of 300 °C for a treatment time of 2 h. The asphalt coating was 16 nm thick and well-dispersed lipophilic nano-silicon was obtained. (2) The obtained lipophilic nano-silicon, sodium carbonate molten salt and high softening point 291°C coal-based mesophase asphalt were mixed in a mass ratio of 15:60:40, ball milled at a speed of 250 rpm, and processed for 2 h; mechanically stirred and fully blended at a high temperature of 390°C for 3 h, with a protective atmosphere of nitrogen; the blended mixture was crushed and granulated, and carbonized at high temperature for one time at 5°C min -1 The temperature was raised to 1000 °C at a rate of 1.5 °C and kept at this temperature for 1 h. The protective atmosphere was nitrogen with a gas flow rate of 30 mL min -1 The mass ratio of carbonized material to deionized water was 1:10, stirred for 2 hours, washed twice, and then vacuum dried at 100°C for 10 hours to obtain a primary silicon-carbon precursor in which nano-silicon was embedded in a porous carbon matrix; In step (2), the method for preparing the high softening point 291°C coal-based mesophase asphalt is as follows: using reformed coal tar pitch with a softening point of 80°C as a raw material, thermally polymerizing in a high-temperature reactor to prepare the high softening point coal-based mesophase asphalt, the thermal polymerization temperature is 410°C, the polymerization time is 10h, and the obtained coal-based mesophase asphalt has a softening point of 291°C; (3) Using coal-based coated asphalt powder with a high softening point of 267°C and a particle size of 0.5 µm, the primary silicon-carbon precursor was subjected to high-temperature solid-phase coating in a high-temperature coating machine, so that the asphalt powder was melted and evenly coated on its surface to form a coating with a mass ratio of 6:100 and high-temperature melting coating at 300°C for 1.5h to obtain a secondary silicon-carbon precursor; after high-temperature secondary carbonization at a temperature of 1400°C and a heating rate of 10°C min -1 , constant temperature for 0.5 h, protective atmosphere is argon, gas flow rate is 30 mL min -1 , a silicon-carbon negative electrode material with a multi-level buffer carbon skeleton is prepared, the inner core is a porous carbon skeleton, and the outer layer is a dense carbon coating; In step (3), the method for preparing the high softening point 267°C coal-based coated asphalt is as follows: using coal tar as raw material, oxidative cross-linking polymerization is used to prepare the high softening point coal-based coated asphalt, the oxidative cross-linking temperature is 310°C, and the time is 7h; the obtained coal-based coated asphalt has a softening point of 267°C.

[0038] Lithium battery assembly and performance The porous carbon skeleton silicon-based negative electrode material prepared in this embodiment is used to assemble battery pole pieces and lithium batteries; the remaining steps are consistent with the assembly process of the battery pole pieces and lithium batteries in Example 1.

[0039] At a current density of 100 mA g -1 The first reversible specific capacity is 1436 mA h g -1 The first coulombic efficiency is 86.8%, the capacity retention rate after 1000 cycles is 93.7%, and it has excellent cycle and rate characteristics.

[0040] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a porous carbon skeleton silicon-based negative electrode material, characterized in that: Here are the steps: (1) Nano-silicon modified on the surface of low softening point asphalt: Nano-silicon and low softening point asphalt are dispersed in an organic solvent and stirred to mix evenly, the solvent is removed by distillation and then dried, and then pre-oxidized to obtain lipophilic nano-silicon; (2) fully blending the obtained lipophilic nano-silicon, molten salt and high softening point mesophase pitch, and after crushing and granulation, primary carbonization, washing and drying, obtaining a primary silicon-carbon precursor in which nano-silicon is embedded in a porous carbon matrix; (3) The primary silicon-carbon precursor is solid-phase coated with high-softening-point asphalt powder at high temperature to obtain a secondary silicon-carbon precursor, which is then carbonized for the second time to obtain a porous carbon skeleton silicon-based negative electrode material with multi-level buffering.

2. The method for preparing the porous carbon skeleton silicon-based negative electrode material according to claim 1, characterized in that: In the step (1), the nano silicon is at least one of elemental silicon, silicon dioxide and silicon monoxide, and the particle size of the nano silicon is 50-200nm; the low softening point asphalt is low softening point coal asphalt and / or low softening point petroleum asphalt, and the softening point of the low softening point asphalt is 40-150°C; the mass ratio of the nano silicon to the low softening point asphalt is 100:(1-30).

3. The method for preparing the porous carbon skeleton silicon-based negative electrode material according to claim 1, characterized in that: The organic solvent in step (1) is at least one of toluene, xylene, wash oil and kerosene, and the mass ratio of low softening point asphalt to organic solvent is (1-5):10; the pre-oxidation treatment temperature is 280-320°C, and the treatment time is 2-4h.

4. The method for preparing the porous carbon skeleton silicon-based negative electrode material according to claim 1, characterized in that: The high softening point mesophase pitch in step (2) is a mesophase pitch obtained by thermal polymerization of a heavy aromatic hydrocarbon feedstock; the heavy aromatic hydrocarbon feedstock is at least one of coal tar, petroleum tar, coal tar, modified coal tar and naphthalene aromatics; the softening point of the high softening point mesophase pitch is 240-320°C; the molten salt is at least one of a metal halide, a metal hydroxide, a metal sulfate, a metal nitrate or a metal carbonate; the metal is Li + 、Na + Mg 2+ 、Al 3+ , K + or Ca 2+ Any of .

5. The method for preparing a porous carbon skeleton silicon-based negative electrode material according to claim 1, characterized in that: In the step (2), the mass ratio of oleophilic nano-silicon, molten salt and high softening point mesophase asphalt is (1-30): (50-100): (10-50), and the blending process is: firstly pre-mixing by ball milling; then high-temperature melting mechanical stirring and mixing, the high-temperature melting temperature is 360-420°C, and the stirring time is 2-4 hours; the protective atmosphere is nitrogen and / or argon.

6. The method for preparing the porous carbon skeleton silicon-based negative electrode material according to claim 1, characterized in that: The carbonization process in step (2) is as follows: 3-5°C min -1 The temperature was raised to 600-1000℃ at a rate of 1000℃ and kept at this temperature for 1-4 h. The protective atmosphere for carbonization treatment was nitrogen and / or argon with a gas flow rate of 30-100 mL min -1 The washing liquid used in the washing treatment is deionized water, and the drying condition is vacuum drying for 3-12 h.

7. The method for preparing the porous carbon skeleton silicon-based negative electrode material according to claim 1, characterized in that: In the step (3), the high softening point coated asphalt is a coal-based coated asphalt or a petroleum-based coated asphalt, and the softening point is 220-280°C; the particle size of the high softening point coated asphalt powder is 0.5-2µm, the mass ratio of the high softening point coated asphalt to the primary silicon-carbon precursor is 5-15:100, the temperature of the high-temperature solid phase coating is 250-650°C, and the time is 0.5-2h.

8. The method for preparing the porous carbon skeleton silicon-based negative electrode material according to claim 1, characterized in that: In step (3), the secondary carbonization treatment temperature is 800-1400°C, the heating rate is 3-10°C / min, and the temperature is kept constant for 0.5-2 h; the carbonization treatment protective atmosphere is nitrogen and / or argon, and the gas flow rate is 30-100 mL min -1 .

9. The porous carbon skeleton silicon-based negative electrode material prepared by the method according to any one of claims 1 to 8, characterized in that: The porous carbon skeleton silicon-based negative electrode material has a core of a porous carbon skeleton and an outer layer of a dense carbon coating, and has a stable multi-level carbon skeleton buffer structure.

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

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