A porous carbon material, a preparation method thereof and application thereof in a silicon-carbon negative electrode material

Abstract

The present application belongs to the technical field of negative electrode materials, and particularly relates to a porous carbon material, a preparation method thereof and application of the porous carbon material in a silicon-carbon negative electrode material. By constructing a multi-level micro-nano structure of "curved graphite layer + layer defect + nano domain + built-in nano twin + interlocking strip-shaped grains" inside the porous carbon framework, the porous carbon significantly improves the yield strength and fracture toughness on the premise of maintaining a high pore volume and specific surface area. Under the action of the large volume expansion and contraction stress generated in the process of lithium intercalation / deintercalation of silicon, the porous carbon framework can "absorb" and buffer the local stress through various mechanisms such as twin slip, grain interlocking bending, and stress redistribution induced by layer defects, effectively inhibiting the cracking of the pore wall and the collapse of the overall framework, and significantly reducing the thickness expansion ratio of the electrode sheet, thereby ensuring the integrity and mechanical stability of the silicon-carbon composite negative electrode under long cycle and high load from the structural level.

Description

Technical Field

[0001] This invention belongs to the field of anode material technology, specifically relating to a porous carbon material, its preparation method, and its application in silicon-carbon anode materials. Background Technology

[0002] Lithium-ion batteries have been widely used in new energy vehicles, new energy aircraft, and smart wearable devices. With the rapid development of emerging applications such as long-range electric vehicles, electric vertical takeoff and landing (eVTOL) aircraft, and flexible / wearable electronics, these systems are placing higher demands on batteries for specific energy, volumetric energy density, and cycle life: the target usable energy density for automotive power batteries has increased from the current approximately 150-250 Wh·kg⁻¹. -1 Increase to 300~350 Wh·kg -1 The system level also requires achieving higher volumetric energy density and fast charging performance while ensuring safety. Traditional graphite anodes have limited capacity (theoretical specific capacity approximately 372 mAh·g). -1 Under the premise that the improvement of cathode materials alone is no longer sufficient to meet the continuous demand for energy density improvement in the above application scenarios, the development of high-capacity anode systems has become one of the key ways to break through the energy density bottleneck of existing lithium-ion batteries.

[0003] Silicon-based anodes have extremely high theoretical specific capacity (in Li). 15 The Si4 mAh / g is approximately 3579 mAh·g. -1 Silicon, with its high energy density (nearly 10 times that of graphite), low lithium intercalation potential, and abundant reserves, is widely considered the most promising next-generation high-energy-density lithium-ion battery anode material. However, silicon undergoes volume expansion and contraction of up to approximately 300% during lithium intercalation / deintercalation, leading to significant mechanical stress and plastic deformation within the particles. This can easily cause particle cracking, pulverization, and loss of connection with the conductive network and current collector, resulting in electrode structural instability and rapid capacity decay. Simultaneously, the repeatedly ruptured / regenerated solid electrolyte interphase (SEI) continuously consumes the electrolyte and reversible lithium source, causing a series of problems such as low initial coulombic efficiency, gas evolution, and severe electrode expansion. These factors significantly limit the engineering application of high-load, high-area-capacity silicon anodes in practical battery systems.

[0004] The silicon-carbon composite negative electrode formed by in-situ deposition of nano-silicon in the pores of porous carbon as a carrier by chemical vapor deposition (CVD) method is a promising technology route that combines the advantages of good electrical conductivity of carbon materials, designable structure and high specific capacity of silicon materials. This kind of material relies on the porous carbon framework to limit the space and mechanically buffer the nano-silicon, which is expected to inhibit the volume effect, relieve the interface side reaction, and improve the electrical continuity and rate performance of the electrode at a high silicon loading. However, the commonly used porous carbon framework (such as hard carbon, activated carbon, etc.) generally has the problems of low mechanical strength and poor fracture toughness: the thin and brittle pore wall is easy to locally yield, crack and even collapse the whole pore under the repeated volume expansion-contraction of silicon, resulting in the instability of the carbon framework structure, irreversible shrinkage of the pore structure and destruction of the conductive network continuity, which further induces the cracking, pulverization and rapid cycle life decay of the electrode. In addition, the high porosity porous carbon also has insufficient compression and bending resistance during rolling, cell assembly and long-term cycling, which also limits its application in high-silicon-content and high-area-capacity actual electrodes. Therefore, it is urgent to construct a porous carbon framework with high strength and high toughness, and deeply couple it with the process of in-situ deposition of nano-silicon, to fundamentally solve the mechanical instability problem of the existing silicon-carbon negative electrode under the action of volume effect from the aspect of structure design. SUMMARY

[0005] To solve the key bottleneck that the porous carbon framework in the existing silicon-carbon negative electrode has low strength and poor toughness, and is easy to crack and collapse under the repeated volume expansion of silicon, resulting in excessive expansion of the whole electrode, instability of the structure and rapid capacity decay, the present application provides a porous carbon material, a preparation method thereof and an application thereof in a silicon-carbon negative electrode material. The porous carbon material prepared by the preparation method provided by the present application can significantly improve the yield strength, fracture strength and fracture toughness of the porous carbon while maintaining the multi-level pores and high specific surface area.

[0006] The present application provides a preparation method of a porous carbon material, comprising the following steps:

[0007] The phenolic resin is pre-carbonized under a protective atmosphere to obtain a phenolic-based carbon material;

[0008] The phenolic-based carbon material, KOH and a solvent are mixed and then dried to obtain a KOH-loaded carbon powder;

[0009] The KOH-loaded carbon powder is activated under a protective atmosphere to obtain a porous carbon precursor;

[0010] The porous carbon precursor is sequentially subjected to high-temperature thermal shock treatment and cooling under a protective atmosphere to obtain a metastable porous carbon powder;

[0011] The metastable porous carbon powder is sequentially subjected to molding and hot-press sintering to obtain a porous carbon material.

[0012] Preferably, the temperature of the pre-carbonization is 600-900 DEG C; the temperature rising rate for rising to the temperature of the pre-carbonization is 1-5 DEG C / min; and the holding time of the pre-carbonization is 1-4 h.

[0013] Preferably, the mass ratio of the phenolic-based carbon material to KOH is 1:1-1:4; the temperature of the activation is 650-900 DEG C; the temperature rising rate for rising to the temperature of the activation is 2-10 DEG C / min; and the holding time of the activation is 0.5-3 h.

[0014] Preferably, the gas pressure of the protective atmosphere during the high-temperature thermal shock treatment is 10-50 kPa; and the temperature of the high-temperature thermal shock treatment is 2000-2300 DEG C.

[0015] Preferably, the temperature rising rate for rising to the temperature of the high-temperature thermal shock treatment is not less than 50 DEG C / min; the holding time of the high-temperature thermal shock treatment is 0.5-30 min; and the average cooling rate for cooling from the temperature of the high-temperature thermal shock treatment to 1000 DEG C is not less than 50 DEG C / min.

[0016] Preferably, the pressure of the hot-press sintering is 2-10 GPa; the temperature of the hot-press sintering is 1600-2000 DEG C; the temperature rising rate for rising to the temperature of the hot-press sintering is 50-200 DEG C / min; and the time of the hot-press sintering is 5-120 min.

[0017] The application further provides the porous carbon material prepared by the preparation method.

[0018] The application further provides the porous carbon material prepared by the preparation method or the porous carbon material in the application of the porous carbon-nano silicon composite negative electrode material.

[0019] The application further provides a porous carbon-nano silicon composite negative electrode material, which comprises the porous carbon material prepared by the preparation method, nano silicon deposited in the pore channel of the porous carbon material, and a carbon coating layer deposited on the surface of the porous carbon material and the nano silicon.

[0020] The application further provides a preparation method of the porous carbon-nano silicon composite negative electrode material, which comprises the following steps:

[0021] After the nano silicon is deposited in the pore channel of the porous carbon material by using SiH4 as the reaction gas through the chemical vapor deposition method, C2H2 is used as the reaction gas to continue depositing the carbon coating layer, so that the porous carbon-nano silicon composite negative electrode material is obtained.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] Firstly, the present application significantly improves the yield strength and fracture toughness of the porous carbon by constructing a multi-level micro-nano structure of "curved graphite layer + layer defect + nano domain + built-in nano twin + interlocking strip-shaped grain" inside the porous carbon framework, while maintaining a high pore volume and specific surface area. Under the action of the large volume expansion and contraction stress generated during the lithium insertion / extraction of silicon, the porous carbon framework can "absorb" and buffer local stress through various mechanisms such as twin slip, grain interlocking bending, and stress redistribution induced by layer defects, effectively inhibiting the cracking of the pore wall and the collapse of the overall framework, significantly reducing the thickness expansion ratio of the electrode, and ensuring the integrity and mechanical stability of the silicon-carbon composite anode under long-term cycling and high load from a structural perspective.

[0024] Secondly, the present application uses the above high-toughness porous carbon framework to spatially confine and three-dimensionally support the nano-silicon, so that the volume change of the silicon is mainly "absorbed" inside the pore cavity, greatly reducing the exposure of the silicon particles to the electrolyte side and the generation of repeated fresh interfaces, thereby facilitating the formation of a uniform, dense and relatively stable SEI film on the silicon / carbon composite interface. The stable SEI film can not only reduce lithium loss and electrolyte consumption caused by continuous side reactions, but also inhibit crack-induced SEI rupture and regeneration, significantly improve the first-week coulomb efficiency and the integrity of the SEI during long-term cycling, effectively slow down the capacity decay and the increase of internal resistance, and enable the silicon-carbon negative electrode to maintain good capacity retention rate and electrode size stability under high surface capacity conditions.

[0025] Thirdly, thanks to the high strength and toughness of the porous carbon framework and the through multi-level pore structure, the silicon-carbon composite negative electrode prepared by the present application still maintains a good electronic conduction network and lithium ion transport channel while ensuring mechanical reliability: the continuous porous carbon framework provides a fast electron transport path, the uniform deposition of nano-silicon on the pore wall shortens the lithium ion diffusion distance, and the pore structure provides a low-resistance channel for electrolyte infiltration and ion migration. As a result, the composite negative electrode exhibits smaller polarization and excellent rate performance under high-rate charging and discharging, and can maintain relatively stable capacity output and interface impedance in low-temperature and high-temperature environments, significantly expanding the application range of lithium-ion batteries in wide temperature and fast charging conditions, and improving the overall energy density, power characteristics and service life of the battery. DETAILED DESCRIPTION

[0026] The present application provides a method for preparing a porous carbon material, comprising the following steps:

[0027] The phenolic resin is pre-carbonized under a protective atmosphere to obtain a phenolic-based carbon material;

[0028] The phenolic-based carbon material, KOH and solvent are mixed and then dried to obtain a KOH-loaded carbon powder;

[0029] The KOH-loaded carbon powder is activated under a protective atmosphere to obtain a porous carbon precursor;

[0030] The porous carbon precursor is sequentially subjected to high-temperature thermal shock treatment and cooling under a protective atmosphere to obtain a metastable porous carbon powder;

[0031] The metastable porous carbon powder is sequentially subjected to molding and hot-press sintering to obtain a porous carbon material.

[0032] The phenolic resin is pre-carbonized under a protective atmosphere to obtain a phenolic-based carbon material.

[0033] As an embodiment of the present application, the pre-carbonization temperature can be 600-900℃, specifically 600℃, 700℃, 800℃ or 900℃; the temperature rising rate to the pre-carbonization temperature can be 1-5℃ / min, specifically 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min or 5℃ / min; the holding time of the pre-carbonization can be 1-4h, specifically 1h, 2h, 3h or 4h.

[0034] As an embodiment of the present application, after obtaining the phenolic-based carbon material, it is preferably further included that the phenolic-based carbon material is crushed and ground to an average particle size of 1-50μm; the mass ratio of the phenolic-based carbon material to KOH can be 1:1-1:4, specifically 1:2-1:3; the solvent can be deionized water and / or ethanol;

[0035] The phenolic-based carbon material, KOH and solvent are mixed, and then dried to obtain a KOH-loaded carbon powder.

[0036] As an embodiment of the present application, the mixing method can be stirring, and the stirring time can be 0.5-4h; the drying temperature can be 80-120℃, and the time can be 6-24h.

[0037] The KOH-loaded carbon powder is activated under a protective atmosphere to obtain a porous carbon precursor.

[0038] As an embodiment of the present application, the activation temperature can be 650-900℃, specifically 700-800℃; the temperature rising rate to the activation temperature can be 2-10℃ / min, specifically 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min or 10℃ / min; the holding time of the activation can be 0.5-3h, specifically 0.5h, 1h, 2h or 3h.

[0039] As an embodiment of the present application, the activation preferably further comprises natural cooling and impurity removal in sequence. As an embodiment of the present application, the natural cooling can cool to room temperature; the step of impurity removal is to immerse the cooled product in a hydrochloric acid or nitric acid solution, then wash with deionized water, and then dry; the concentration of the hydrochloric acid or nitric acid solution can independently be 0.5-2.0 mol / L; the immersion time can be 2-12 h; the immersion can dissolve residual K and inorganic salts; the washing is preferably washed until the filtrate pH is close to 7; the drying temperature can be 80-120℃, and the time can be 8-24 h; the specific surface area of the porous carbon precursor can be 800-2500 m 2 / g, the total pore volume can be 0.3-1.5 cm 3 / g, and the Raman ID / IG ratio can be 0.8-1.5.

[0040] The present application obtains metastable porous carbon powder by sequentially performing high-temperature thermal shock treatment and cooling of the porous carbon precursor under a protective atmosphere.

[0041] As an embodiment of the present application, during the high-temperature thermal shock treatment, the gas pressure of the protective atmosphere can be 10-50 kPa; the temperature of the high-temperature thermal shock treatment can be 2000-2300℃, and can specifically be 2000℃, 2100℃, 2200℃, or 2300℃; the temperature rising rate for rising to the temperature of the high-temperature thermal shock treatment is not less than 50℃ / min, and can specifically be 100-300℃ / min; and the holding time of the high-temperature thermal shock treatment can be 0.5-30 min, and can specifically be 1-10 min.

[0042] In the present application, the high-temperature thermal shock treatment can induce rearrangement, bending, and refinement of the internal graphite crystallites.

[0043] As an embodiment of the present application, after completing the high-temperature thermal shock treatment, rapid cooling is performed, and specifically, the average cooling rate for cooling from the temperature of the high-temperature thermal shock treatment to the 1000℃ range is not less than 50℃ / min, and can specifically be 100-300℃ / min; this can be achieved by cutting off the power supply and maintaining high-flow (250-300 mL / min) inert gas cooling.

[0044] After the thermal shock and cooling process, the interior of the porous carbon is transformed from the original disordered carbon and small size graphite-like microcrystalline into a sheet structure mainly composed of curved graphite layers, accompanied by a large number of stacking faults and changes in stacking sequence, and graphite nanocrystalline domains with a size of 2-20 nm, thereby forming a metastable porous carbon structure between non-complete graphitization and amorphous carbon, which significantly improves the local interlayer internal stress and defect density while retaining the macroscopic pore structure, and provides a favorable structural basis for subsequent high-pressure induced twinning and grain interlocking.

[0045] The present application sequentially performs molding and hot-pressing sintering on the metastable porous carbon powder to obtain a porous carbon material.

[0046] As an embodiment of the present application, the molding can be cold pressing molding, which can be that the metastable porous carbon powder is sieved to a particle size of 1-50 μm, then loaded into a mold (steel mold or carbon mold), and then pressed to form a molding; the unidirectional pressure during the pressing can be 50-500 MPa; the pressing is performed at room temperature; and the pressed block after the pressing molding is preferably a pressed block with a diameter of 1-3 mm and a height of 0.5-3 mm.

[0047] As an embodiment of the present application, the pressure of the hot-pressing sintering can be 2-10 GPa, and specifically can be 3-8 GPa; the temperature of the hot-pressing sintering can be 1600-2000℃, and specifically can be 1700-1900℃; the heating rate for heating to the temperature of the hot-pressing sintering can be 50-200℃ / min; and the time of the hot-pressing sintering can be 5-120 min, and specifically can be 10-60 min.

[0048] As an embodiment of the present application, after the hot-pressing sintering, the sample is further cooled to below 800℃ under the condition of maintaining high pressure (0.5-10 GPa), and then gradually released to normal pressure at a rate of 0.1-1 GPa / min.

[0049] In the present application, the specific operation after the cold pressing molding is as follows:

[0050] (1) The obtained porous carbon pressed block is loaded into a micro crucible made of boron nitride (BN), magnesium oxide (MgO) or high-purity graphite, the crucible is placed in the central hole of a high-pressure medium octahedron (for example, an MgO or spinel / MgO composite octahedron with a side length of 8-18 mm), and a resistance furnace body (such as graphite or Re heating element) and an insulation layer are arranged around the periphery to form a standard high-pressure assembly suitable for a multi-anvil high-pressure device;

[0051] (2) The above components are loaded into a large-volume high-pressure device with multiple anvils, and the octahedron is subjected to approximately uniform pressure in each direction by driving the primary anvil and the secondary anvil by an external hydraulic machine, so that the pressure in the sample cavity gradually increases to 2-10 GPa; at the target pressure, the electric resistance furnace is powered to heat, and the temperature is increased to 1600-2000 DEG C at a rate of 50-200 DEG C / min, and the temperature is maintained for 5-120 min. After the holding period ends, the pressure is naturally cooled to room temperature while maintaining the pressure, and then the pressure is gradually released to atmospheric pressure at a rate of 0.1-1 GPa / min, the high-pressure assembly is disassembled, the porous carbon block after hot-pressing sintering is taken out, and according to the needs, it is broken and sieved to a particle size range suitable for gas phase deposition, and used as a super-strong and high-toughness porous carbon skeleton for subsequent CVD deposition of nano-silicon.

[0052] The application further provides the porous carbon material prepared by the preparation method.

[0053] The application further provides the application of the porous carbon material prepared by the preparation method or the porous carbon material in a porous carbon-nano-silicon composite negative electrode material.

[0054] The application further provides a porous carbon-nano-silicon composite negative electrode material, which comprises the porous carbon material prepared by the preparation method, nano-silicon deposited in the pore channel of the porous carbon material, and a carbon coating layer deposited on the surface of the porous carbon material and the nano-silicon.

[0055] The application further provides a preparation method of a porous carbon-nano-silicon composite negative electrode material, which comprises the following steps:

[0056] After the nano-silicon is deposited in the pore channel of the porous carbon material by chemical vapor deposition using SiH4 as the reaction gas, a carbon coating layer is further deposited using C2H2 as the reaction gas, and the porous carbon-nano-silicon composite negative electrode material is obtained.

[0057] As an embodiment of the application, when the nano-silicon is deposited by chemical vapor deposition, the carrier gas can be argon, the volume percentage of SiH4 in the mixed gas of SiH4 and argon can be 5-45%, and can be specifically 8-12%; the volume percentage of C2H2 in the mixed gas of C2H2 and argon can be 1-10%, and can be specifically 2-4%.

[0058] As an embodiment of the present application, the specific operation of the chemical vapor deposition is as follows: the porous carbon is placed in a quartz tube furnace, inert gas is purged, and the temperature is raised to 450-550℃; silane / carrier gas is introduced (under low pressure or normal pressure conditions) for 20-60 min to obtain 5-30wt% of nanosilicon; after the deposition is completed, inert gas is purged, the temperature is raised to 700-800℃, and C2H2 / carrier gas is introduced for 10-30 min to form a dense outer layer of carbon; the nanocrystals can be amorphous or fine nanocrystals, which ensure preferential entry and coverage of the inner pore wall rather than complete blockage of the pore channel.

[0059] The present application first designs the chemical composition and pore structure in the porous carbon precursor stage to precisely control the internal defect distribution and crystallite size, and then applies a rapid thermal shock treatment to induce the bending, misorientation rearrangement and size refinement of the graphite layers under the conditions of high temperature and rapid cooling in a short time, thereby constructing a high-energy metastable porous carbon skeleton composed of bent graphite layers, layer fault structures and nanocrystalline domains; on this basis, the metastable porous carbon is further densified and restructured under high temperature and high pressure conditions, so that a composite microstructure of high-density built-in twin crystals and interlocked strip-shaped grains is formed in situ in the interior, thereby significantly improving the yield strength, fracture strength and fracture toughness of the porous carbon while maintaining the multi-level pore channels and high specific surface area, and providing a three-dimensional bearing skeleton with "super strength and high toughness" characteristics for subsequent uniform deposition of nanosilicon in the pore channels by chemical vapor deposition method, so as to fundamentally improve the structural stability and cycle life during the volume expansion of silicon.

[0060] In order to further illustrate the present application, the technical solutions provided by the present application are described in detail below in conjunction with examples, but they should not be understood as limiting the scope of protection of the present application.

[0061] Example 1

[0062] (1) Commercial phenolic resin was cured in a mold at 80℃ for 4h to obtain a cured resin block;

[0063] (2) The resin block was ball milled to an average particle size of about 10μm, and pre-carbonization was completed by heating to 800℃ at a heating rate of 3℃ / min and holding for 2h under a nitrogen atmosphere to obtain pre-carbonized carbon powder.

[0064] (3) The pre-carbonized carbon powder was mixed with KOH solid at a mass ratio of 1:3, a small amount of deionized water was added to make a slurry, and the slurry was mechanically stirred for 2h and then dried at 80℃ for 12h to obtain KOH-loaded carbon powder.

[0065] (4) The KOH loaded carbon powder was placed in a quartz boat and put into a tube furnace, and then heated to 750 °C at a rate of 5 °C / min under a nitrogen flow of 200 mL / min, and kept for 1 h to complete the chemical activation; after activation, the solid product was naturally cooled to room temperature, and then soaked in a 1 mol / L hydrochloric acid solution for 6 h to dissolve K and residual inorganic salts, and then washed with deionized water until the pH of the filtrate was about 7, and finally dried at 100 °C for 12 h to obtain a porous carbon precursor with a specific surface area of 1800 m 2 / g, a total pore volume of 0.9 cm 3 / g, and a Raman ID / IG of 1.1.

[0066] (5) The obtained porous carbon was loaded into a graphite crucible and placed in a graphite resistance furnace under an argon atmosphere, and then heated to 2200 °C at a rate of 200 °C / min and kept for 5 min, after which the power was immediately turned off and the argon flow was maintained at 300 mL / min to cool, so that the average cooling rate of the sample was 150 °C / min during the process of decreasing from 2200 °C to 1000 °C, and a metastable porous carbon with a bent internal graphite layer accompanied by a large number of stacking faults and nanocrystalline domains was obtained.

[0067] (6) The metastable porous carbon powder was sieved through a 100-mesh sieve and loaded into a steel mold with a diameter of 2 mm, and then pressed into a small cylindrical compact with a diameter of 2 mm and a height of 1.5 mm by applying a unidirectional pressure of 200 MPa at room temperature; the compact was loaded into a boron nitride crucible with an inner diameter of 3 mm and sealed, and the crucible was placed in the center hole of an MgO octahedron with a side length of 10 mm, and a graphite resistance furnace wire was wound around the periphery and filled with an MgO insulation layer to assemble a high-pressure assembly suitable for a Kawai-type multi-anvil device of 6-8. The assembly was installed in the multi-anvil high-pressure device, and the sample pressure was increased to 5 GPa by an external hydraulic machine, and then heated to 1800 °C at a rate of 100 °C / min and kept for 30 min, after which it was naturally cooled to room temperature while maintaining the pressure, and then released to atmospheric pressure at a rate of 0.5 GPa / min, and the assembly was disassembled to obtain the porous carbon block, which was slightly ground and sieved to obtain an ultra-strong and high-toughness porous carbon skeleton with an average particle size of about 8 μm.

[0068] Subsequently, the porous carbon skeleton was placed in a quartz tube furnace and heated to 450 °C under an argon atmosphere, and a mixed gas of 10% SiH4 / Ar by volume fraction was introduced at a total flow rate of 100 sccm, and deposited for 30 min at 450 °C to obtain a porous carbon-nano silicon composite material with a silicon mass fraction of about 30 wt%; after stopping the introduction of SiH4, pure argon was continued to be introduced and heated to 750 °C, and a mixed gas of 3% C2H2 / Ar by volume fraction was introduced at a flow rate of 100 sccm, and kept for 10 min to form an outer carbon coating with an average thickness of about 3 nm, thereby obtaining an ultra-strong and high-toughness porous carbon-nano silicon composite negative electrode material.

[0069] Example 2

[0070] (1) The phenolic resin was cured at 90°C for 3h to obtain a cured resin block;

[0071] (2) The resin block was ball-milled to an average particle size of about 8μm, and pre-carbonization was performed by heating to 750°C at a heating rate of 2°C / min under an argon atmosphere and maintaining for 3h to obtain a pre-carbonized carbon powder;

[0072] (3) The pre-carbonized carbon powder was mixed with KOH solid at a mass ratio of 1:2, a small amount of ethanol was added to make a pulp, and magnetic stirring was performed for 3h, and then drying was performed at 100°C for 10h to obtain a KOH-loaded carbon powder.

[0073] (4) The KOH-loaded carbon powder was placed in a tube furnace and activated by heating to 700°C at a heating rate of 4°C / min under a nitrogen flow of 150mL / min and maintaining for 2h, and then soaked in 0.5mol / L hydrochloric acid for 8h after cooling, and then washed with deionized water until neutral, and then dried at 90°C for 16h to obtain a porous carbon precursor with a specific surface area of about 1500m 2 / g and a total pore volume of about 0.7cm 3 / g.

[0074] (5) The obtained porous carbon was loaded into a high-purity carbon crucible, and then placed in an induction heating furnace under an argon atmosphere, and heated to 2200°C at a heating rate of 150°C / min and maintained for 3min, and then the power was turned off and the argon flow was maintained at 250mL / min to cool, and the sample was rapidly cooled in the high-temperature section to form a metastable porous carbon coexisting with a large number of stacking faults and curved graphite layers.

[0075] (6) The obtained metastable porous carbon powder was sieved through a 120-mesh sieve and loaded into a steel mold with a diameter of 3mm, and then uniaxial pressure of 250MPa was applied at room temperature to press into a cylindrical compact with a diameter of 3mm and a height of 1mm; the compact was loaded into a MgO crucible with an inner diameter of 4mm and sealed, and the crucible was placed in the center hole of a spinel / MgO composite octahedron with a side length of 12mm, and the periphery was embedded with Re resistance furnace wire and MgO insulation layer to assemble a multi-anvil assembly. The assembly was loaded into a Kawai-type multi-anvil device, the pressure of the sample was increased to 3GPa, and then heated to 1700°C at a rate of 80°C / min and maintained for 45min, and then naturally cooled to room temperature under the condition of maintaining the pressure, and then unloaded at a rate of 0.4GPa / min to obtain a bulk porous carbon, which was ground and sieved to obtain a high-strength and high-toughness porous carbon skeleton with an average particle size of about 10μm.

[0076] (7) The skeleton was placed in a quartz tube furnace, heated to 430℃ under argon atmosphere, introduced 8% SiH4 / Ar mixed gas with a flow rate of 120 sccm, and deposited for 40 min at 430℃ to obtain a porous carbon-nanosilicon composite material with a silicon mass fraction of about 25wt%; then stop SiH4 and continue to heat to 730℃ in argon, introduce 2% C2H2 / Ar mixed gas with a flow rate of 120 sccm, and heat for 15 min to form a 5nm outer carbon coating layer to obtain a super-strong and high-toughness porous carbon-nanosilicon composite negative electrode material.

[0077] Example 3

[0078] (1) The phenolic resin was solidified at 85℃ for 5h and then ball-milled to an average particle size of about 12μm, and pre-carbonized at 820℃ for 1.5h under a nitrogen atmosphere with a heating rate of 4℃ / min to obtain pre-carbonized carbon powder;

[0079] (2) The pre-carbonized carbon powder was mixed with KOH solid at a mass ratio of 1:4, added with appropriate amount of deionized water to make a slurry, and planetary ball-milled for 2h to intensify the mixing, and then dried at 90℃ for 14h to obtain KOH-loaded carbon powder.

[0080] (3) The KOH-loaded carbon powder was placed in a tube furnace, activated at 800℃ for 45min under a nitrogen flow of 250mL / min, and then cooled, soaked in 1.5mol / L hydrochloric acid solution for 4h, washed with deionized water until the pH approached 7, and dried at 110℃ for 10h to obtain a porous carbon precursor with a specific surface area of about 2100m 2 / g and a total pore volume of about 1.1cm 3 / g.

[0081] (4) The porous carbon was loaded into a graphite crucible, placed in a graphite resistance furnace under a helium atmosphere, heated to 2100℃ at a rate of 250℃ / min and kept for 8min, then the power was cut off and the helium flow was maintained at 300mL / min to cool, so that the internal graphite crystallites were obviously bent and refined in size, forming a metastable structure rich in stacking faults and nanocrystalline domains.

[0082] (5) The obtained metastable porous carbon powder was sieved through an 80-mesh screen and loaded into a steel mold with a diameter of 2.5 mm, and a uniaxial pressure of 300 MPa was applied at room temperature to press the powder into small cylindrical briquettes with a diameter of 2.5 mm and a height of 1.2 mm; the briquettes were loaded into a boron nitride crucible with an inner diameter of 3.5 mm, the crucible was placed at the center of an MgO octahedron with a side length of 14 mm, and graphite resistance furnace wires and MgO insulation layers were arranged around the crucible to assemble a multi-anvil high-pressure assembly. The assembly was loaded into a 6-8 type multi-anvil device, the pressure of the sample was increased to 7 GPa, and the sample was heated to 1900°C at a rate of 120°C / min and held for 20 min at 7 GPa, and then naturally cooled to room temperature while maintaining the pressure, and then the pressure was released at a rate of 0.6 GPa / min to obtain a dense bulk porous carbon, which was ground and sieved to obtain an ultra-strong and high-toughness porous carbon skeleton with an average particle size of about 9 μm.

[0083] (6) The porous carbon skeleton was placed in a quartz tube furnace, heated to 460°C under an argon atmosphere, and a 12% SiH4 / Ar mixed gas was introduced at a total flow rate of 110 sccm, and the deposition was carried out at 460°C for 20 min to obtain a porous carbon-nano silicon composite material with a silicon mass fraction of about 35 wt%; then the SiH4 was stopped and the temperature was increased to 780°C in argon, a 4% C2H2 / Ar mixed gas was introduced at a flow rate of 110 sccm, and a 4 nm outer carbon coating layer was formed after 8 min of heat preservation to obtain an ultra-strong and high-toughness porous carbon-nano silicon composite negative electrode material.

[0084] The ultra-strong and high-toughness porous carbon-nano silicon composite materials obtained in Examples 1-3 were respectively prepared into electrode slurries, and the slurry ratio was active material: binder: conductive agent = 80:10:10, wherein the binder was polyacrylic acid (PAA) and the conductive agent was conductive carbon black (Super P); the active material, binder and conductive agent were added to a suitable amount of deionized water, and stirred in a planetary mixer for 2 h to obtain a uniform electrode slurry. The slurry was uniformly coated on a treated copper foil current collector by a doctor blade coating method, and the wet film thickness was controlled to make the dry film surface capacity 2 mAh / cm 2After coating, the sample was dried in a vacuum oven at 80℃ for 12h to remove the solvent, and then rolled on a roller press with appropriate pressure to improve the compactness, and punched into circular electrode sheets with a diameter of 12mm for use. In a glove box, the above circular electrode sheets were used as the working electrode, and a piece of lithium metal as the counter electrode, to assemble a CR2032 button cell with a microporous polypropylene separator. The electrolyte was selected as 1mol / L LiPF6dissolved in a mixed solvent of EC / DEC with a volume ratio of 1:1, and 5wt% of fluoroethylene carbonate (FEC) was added as a film-forming additive. The battery was tested for constant current charge and discharge at 25℃: first, 2 formation cycles were performed at a current of 0.1C to test the initial charge and discharge capacity and the initial coulombic efficiency; then, long cycle tests were performed at a current of 0.2C in the voltage range of 0.01~1.5V, and the capacity retention rate after 1250 cycles was recorded to evaluate the cycle stability; at the same time, the rate performance test was performed at a rate of 4.25C, and the ratio of the capacity at a rate of 4.25C to that at a rate of 0.2C was compared to represent the rapid charge and discharge capacity; the cycle test at a rate of 0.2C was repeated at-17.5℃ and 55℃, and the capacity ratio at-17.5℃, 55℃ and 25℃ was used to evaluate the low-temperature and high-temperature performance of the material. The test results are shown in Table 1. By comparing the electrochemical performance of the materials obtained in Examples 1~3 under the above conditions, the comprehensive beneficial effects of the ultra-strong and high-toughness porous carbon skeleton in the present application in buffering the volume expansion of silicon, stabilizing the SEI film, and improving the cycle life and rate performance can be systematically verified.

[0085] Table 1 Test results of Examples

[0086]

[0087] Although the above examples have made a detailed description of the present application, it is only a part of the embodiments of the present application, but not all the embodiments, and other embodiments can be obtained according to the present embodiments without creativity, which are all within the protection scope of the present application.

Claims

1. A method for preparing porous carbon materials, characterized in that, Includes the following steps: Phenolic resin is pre-carbonized under a protective atmosphere to obtain phenolic carbon materials; Phenolic carbon material, KOH and solvent are mixed and dried to obtain KOH-loaded carbon powder; KOH-supported carbon powder was activated under a protective atmosphere to obtain a porous carbon precursor. The porous carbon precursor was subjected to high-temperature thermal shock treatment and cooling under a protective atmosphere to obtain metastable porous carbon powder. Metastable porous carbon powder was sequentially molded and hot-pressed to obtain porous carbon materials. During the high-temperature thermal shock treatment, the pressure of the protective atmosphere is 10~50 kPa; the temperature of the high-temperature thermal shock treatment is 2000~2300℃. The heating rate to the temperature of the high-temperature thermal shock treatment is not less than 50°C / min, and the holding time of the high-temperature thermal shock treatment is 0.5~30 min; the average cooling rate from the temperature of the high-temperature thermal shock treatment to the 1000°C range is not less than 50°C / min. The pressure of the hot pressing sintering is 2~10 GPa; the temperature of the hot pressing sintering is 1600~2000℃; the heating rate to the hot pressing sintering temperature is 50~200℃ / min; and the hot pressing sintering time is 5~120 min.

2. The preparation method according to claim 1, characterized in that, The pre-carbonization temperature is 600~900℃; the heating rate to the pre-carbonization temperature is 1~5℃ / min; and the pre-carbonization holding time is 1~4 h.

3. The preparation method according to claim 1, characterized in that, The mass ratio of the phenolic carbon material to KOH is 1:1 to 1:4; the activation temperature is 650 to 900°C; the heating rate to the activation temperature is 2 to 10°C / min; and the activation holding time is 0.5 to 3 h.

4. The porous carbon material prepared by the preparation method according to any one of claims 1 to 3.

5. The application of the porous carbon material prepared by the preparation method according to any one of claims 1 to 3 or the porous carbon material according to claim 4 in porous carbon-nano silicon composite anode materials.

6. A porous carbon-nano silicon composite anode material, characterized in that, It includes a porous carbon material prepared by the preparation method according to any one of claims 1 to 3, nano-silicon deposited inside the pores of the porous carbon material, and a carbon coating layer deposited on the surface of the porous carbon material and the nano-silicon.

7. The method for preparing the porous carbon-nano silicon composite anode material according to claim 6, characterized in that, Includes the following steps: Using SiH4 as the reactant gas, a chemical vapor deposition method is employed to deposit nano-silicon in the pores of a porous carbon material. After this process, a carbon coating layer is deposited using C2H2 as the reactant gas, thus obtaining the porous carbon-nano-silicon composite anode material.

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