Porous carbon for negative electrode material and composite material for lithium ion secondary battery

Abstract

Porous carbon for a negative electrode material and a preparation method therefor. In a Raman spectrogram of the porous carbon, the ratio (ID / IG) of D peak intensity (ID) to G peak intensity (IG) is 0.10-1.50; and in an X-ray diffraction pattern of the porous carbon, the diffraction angle 2θ of a (002) crystal plane is 24.00-26.53°, and the specific surface area BET of the porous carbon is 600-3000 m2 / g. A composite material comprising the porous carbon, a negative electrode sheet comprising the composite material, and a lithium ion secondary battery. The porous carbon material has desirable properties, such as graphitization degree and pore structure. The composite material can be used as a battery negative electrode material, and can significantly improve the electrical properties of the battery. The methods for preparing the porous carbon and the composite material are simple and easy to operate, and can be applied to batch production.

Description

Porous carbon for negative electrode materials and composite materials for lithium-ion secondary batteries

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims priority to Chinese patent application number 202311835873.X, filed on December 27, 2023, entitled “Porous carbon for negative electrode materials and composite materials for lithium-ion secondary batteries”, and application number 202410652673.9, filed on May 24, 2024, entitled “Porous carbon for negative electrode materials and composite materials for lithium-ion secondary batteries”. The full texts of the above applications are hereby expressly incorporated herein by reference. Technical Field

[0003] The present invention relates to the technical field of batteries, and in particular to a vapor-deposited silicon-carbon negative electrode material for lithium-ion secondary batteries. Background Art

[0004] Lithium-ion batteries are one of the most widely used secondary battery systems. Compared with other rechargeable batteries such as nickel-cadmium batteries and nickel-metal hydride batteries, lithium-ion batteries have the advantages of high energy density, high operating voltage, limited self-discharge, and low maintenance requirements. However, commercial graphite anodes have a capacity of only 372 mAhg -1 The theoretical specific capacity cannot meet the increasing demands of portable electronic devices, electric vehicles and energy storage applications for energy density, operation reliability and system integration.

[0005] Among all potential lithium-ion battery anode materials, silicon is one of the most promising candidates to replace graphite for the following reasons: (1) Silicon has the highest gravimetric capacity (4200 mAh / g) and volumetric capacity (9786 mAh / cm 3 ); (2) The discharge voltage of silicon averages about 0.4 V, which strikes a good balance between maintaining a reasonable open-circuit voltage and avoiding the unfavorable lithium metal; (3) Silicon reserves are abundant (ranking second in the earth's crust) and have the potential advantages of low cost, environmental protection and non-toxicity.

[0006] However, as silicon undergoes lithium insertion and removal, its volume expands and contracts rapidly (volume change >360%) and generates enormous stress, which may lead to the following problems: (1) the integrity of the electrode structure is destroyed during repeated charge and discharge; (2) interfacial stress induces disconnection between the electrode and the current collector; and (3) the solid electrolyte interface (SEI) layer is continuously formed, ruptured, and reformed, resulting in the continuous consumption of lithium ions. These problems may also accelerate electrode collapse and capacity decay in a synergistic manner.

[0007] Silicon nanosizing technology can effectively alleviate the impact of volume expansion on electrodes. Currently, silicon nanosizing can be achieved by depositing silicon within the pores of a porous matrix material (e.g., porous carbon). For example, CN113795945A discloses an electroactive material for a metal ion battery. The electroactive material is a granular material composed of multiple composite particles. The composite particles contain: (a) a porous carbon skeleton including micropores and mesopores and (b) multiple nanometer-sized elemental silicon domains located within the pores of the porous carbon skeleton.

[0008] In order to improve battery performance to better meet market demand, it is necessary to further develop suitable porous carbon materials and nano-silicon-porous carbon composites. Summary of the Invention

[0009] In order to further improve battery performance, the present application provides a porous carbon for negative electrode material and a preparation method thereof, and also provides a composite material containing the porous carbon and an application thereof.

[0010] In one aspect, the present application relates to a porous carbon for a negative electrode material, wherein in a Raman spectrum of the porous carbon, the D peak intensity (I D ) and G peak intensity (I G ) ratio (I D / I G ) is 0.10-1.50; in the X-ray diffraction pattern of the porous carbon, the diffraction angle 2θ of the (002) crystal plane is 24.00°-26.53°; the specific surface area BET of the porous carbon is 600-3000m 2 / g.

[0011] In one embodiment, in the Raman spectrum of the porous carbon, the D peak intensity (I D ) and G peak intensity (I G ) ratio (I D / I G ) is 0.10-1.10, preferably 0.20-0.80, more preferably 0.20-0.70.

[0012] In one embodiment, the porous carbon has a BET surface area of ​​800-2800 m 2 / g, preferably 900-2750m 2 / g.

[0013] In one embodiment, the porous carbon has a pore volume of 0.50 cm 3 / g or more, preferably 0.60cm 3 / g or above.

[0014] In one embodiment, in the X-ray diffraction pattern of the porous carbon, the diffraction angle 2θ of the (002) crystal plane is 24.15°-26.50°.

[0015] On the other hand, the present application relates to a method for preparing porous carbon, which comprises the following steps: providing a porous carbon precursor; and alkali-activating the porous carbon precursor to prepare the porous carbon of the present application.

[0016] In one embodiment, the base used for the base activation of the porous carbon precursor includes: an alkali metal or alkaline earth metal hydroxide, preferably includes: potassium hydroxide, sodium hydroxide or a combination thereof.

[0017] In yet another aspect, the present application relates to a composite material for a lithium-ion secondary battery, comprising: the porous carbon of the present application and nano-silicon dispersed in the porous carbon.

[0018] On the other hand, the present application relates to a method for preparing the composite material of the present application, which comprises the following steps: providing porous carbon; depositing silicon in the porous carbon to form nano-silicon dispersed in the porous carbon; optionally, coating the outer surface of the porous carbon in which the nano-silicon is dispersed to form a shell layer.

[0019] In another aspect, the present application relates to a negative electrode sheet comprising the composite material of the present application.

[0020] In another aspect, the present application relates to a lithium-ion secondary battery, which includes the negative electrode sheet of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1: XRD spectrum of biomass-based porous carbon precursor A.

[0022] Figure 2: XRD spectrum of resin-based porous carbon precursor B.

[0023] Figure 3: XRD spectrum of the coke-like porous carbon precursor C3.

[0024] Figure 4: Raman spectrum of porous carbon A1.

[0025] Figure 5: Raman spectrum of porous carbon B1.

[0026] Figure 6: Raman spectrum of porous carbon C1.

[0027] Figures 7-9: GITT test results of delithiation of half-cells obtained by assembling negative electrode sheets prepared from various samples of the present application.

[0028] Figure 10: Cycling curves of full batteries obtained by assembling negative electrode sheets prepared from various samples of this application.

[0029] Figure 11: Cycling curves of full batteries obtained by assembling negative electrode sheets with different electrode sheet compaction densities.

[0030] Figure 12: Cycling curves of full batteries obtained by assembling negative electrode sheets with different electrode sheet compaction densities.

[0031] Figures 13-15: Cycling curves of full batteries obtained by assembling the negative electrode sheets prepared by various samples of this application under low temperature environment. DETAILED DESCRIPTION

[0032] General Definitions and Terminology

[0033] Unless otherwise indicated, all publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In the event of a conflict, the definitions provided herein will prevail.

[0035] Unless otherwise indicated, all percentages, parts, ratios, etc. are by weight.

[0036] When quantity, concentration or other value or parameter is given as range, preferred range or preferred upper limit and lower limit or specific value, it should be understood that all ranges formed from the paired values ​​of any upper limit range or preferred value and any lower limit range or preferred value are specifically disclosed, regardless of whether the range is disclosed separately. Unless otherwise stated, when numerical range is quoted herein, the range is meant to include its endpoints and integers and fractions within all such ranges. The scope of the present invention is not limited to the specific numerical value quoted when defining the range. For example, "1-8" encompasses 1, 2, 3, 4, 5, 6, 7, 8 and any sub-range consisting of any two values ​​thereof, such as 2-6, 3-5.

[0037] The terms "about" and "approximately" when used in conjunction with a numerical variable generally refer to the value of that variable and all values ​​of that variable are within experimental error (e.g., within a 95% confidence interval for the mean) or within ±10% of the stated value, or wider.

[0038] The terms "comprises," "includes," "has," "contains," or "involves," and other variations thereof herein, are inclusive or open-ended and do not exclude other unrecited elements or method steps. It will be understood by those skilled in the art that the above terms such as "comprising" encompass the meaning of "consisting of." The expression "consisting of" excludes any element, step, or ingredient not specified. The expression "consisting essentially of" means that the scope is limited to the specified elements, steps, or ingredients, plus the optional presence of elements, steps, or ingredients that do not materially affect the basic and novel characteristics of the claimed subject matter. It will be understood that the expression "comprising" encompasses the expressions "consisting essentially of" and "consisting of."

[0039] The term "selected from..." means one or more elements from the group listed thereafter, selected independently, and may include combinations of two or more elements.

[0040] When values ​​or end-points of a range are described herein, it should be understood that the disclosure includes the specific value or end-point recited.

[0041] As used herein, the terms "one or more" or "at least one" refer to one, two, three, four, five, six, seven, eight, nine or more.

[0042] Unless otherwise indicated, the terms "combinations thereof" and "mixtures thereof" refer to multi-component mixtures of the elements described, such as two-, three-, four- and up to the maximum possible multi-component mixtures.

[0043] In addition, if the number of parts or components of the present invention is not indicated before, it means that there is no limit to the number of occurrences (or existence) of the parts or components. Therefore, it should be interpreted as including one or at least one, and the singular form of the parts or components also includes the plural form unless the value obviously represents the singular.

[0044] As used herein, the term "optional" or "optionally" means that the subsequently described event or circumstance may or may not occur, and that the description includes both occurring and not occurring.

[0045] "Carbonize," "pyrolyze," "carbonization," and "pyrolysis" all refer to the process of heating a carbonaceous material at a pyrolysis soak temperature under an inert atmosphere (e.g., argon or nitrogen) or in a vacuum so that the target material collected at the end of the process is primarily carbon. "Pyrolyzed" refers to a material or substance (e.g., a carbon material) that has undergone a pyrolysis process.

[0046] "Soak temperature" refers to the temperature of the furnace during the portion of the process that is reserved for maintaining a relatively constant temperature (i.e., not increasing or decreasing the temperature). For example, the pyrolysis soak temperature refers to the relatively constant furnace temperature during the pyrolysis process, and the activation soak temperature refers to the relatively constant furnace temperature during the activation process.

[0047] "Pore structure" refers to the surface layout of the internal pores within a carbon material. The components of pore structure include pore size, pore volume, surface area, density, pore size distribution, and pore length. Typically, the pore structure of porous carbon materials includes micropores, mesopores, and macropores. "Mesopores" refer to pores with a pore diameter of 2-50 nm, "micropores" refer to pores with a pore diameter of less than 2 nm, and "macroporos" refer to pores with a pore diameter greater than 50 nm.

[0048] "Surface area" refers to the total specific surface area of ​​a substance that can be measured by the BET technique. Usually, the surface area is expressed in m 2The BET technique uses an inert gas (such as nitrogen) to measure the amount of gas adsorbed on a material and is commonly used in the art to determine the accessible surface area of ​​a material.

[0049] A "composite material" refers to a composition comprising multiple (2 or more) different chemical species within the same particle, such as a particle comprising a porous carbon material and a silicon material.

[0050] "Soft carbon" is also called "easily graphitizable carbon", which refers to carbon materials that can be graphitized after high-temperature treatment (such as 2200°C, 2500°C, etc.), and their disordered structure can be eliminated.

[0051] “Hard carbon” is also called “difficult to graphitize carbon”, which refers to carbon that is difficult to completely graphitize even after high-temperature treatment (for example, above 2800° C.), and its disordered structure is difficult to eliminate at high temperatures.

[0052] "Coulombic efficiency" refers to the ratio of the discharge capacity to the charge capacity of a lithium-ion energy storage device. Coulombic efficiency is expressed as a percentage or fraction (e.g., 99% = 0.99).

[0053] porous carbon

[0054] In one aspect, the present invention relates to a porous carbon for negative electrode materials. The porous carbon can be used as a porous matrix for depositing silicon, and silicon can be uniformly dispersed in the internal pores of the porous carbon to form nano-silicon.

[0055] Without being bound by theory, porous carbon offers advantages for battery performance based on the following: The porous carbon's pore structure provides suitable void space for silicon volume expansion, thereby reducing overall particle expansion at the electrode level. The porous carbon's pore structure can serve as a template for silicon deposition, resulting in nano-silicon with the desired size, distribution, and morphology.

[0056] The prior art generally teaches that low-graphitization materials are advantageous negative electrode materials, such as Liu Y, Xue, JS, Zheng T, Dahn, JR. Carbon 1996, 34: 193-200; Wu, YP, Fang, SB, Jiang, YY. 1998, 75: 201-206; Buiel E, Dahn JR. Electrochim Acta 1999, 45: 121-130. The disordered nature of the graphene layer allows lithium ions to be embedded on either side of the graphene plane. Therefore, compared with high-graphitization materials, such embedding can theoretically increase the lithium ion content. In addition, the disordered structure of low-graphitization materials allows lithium ions to be embedded isotropically, thereby improving the material's rate capability. The disordered graphene network can provide silicon with increased conductivity, thereby achieving faster charge / discharge rates.

[0057] Different from the teachings in the prior art, the present application has found that a composite material prepared with a porous carbon material having a specific degree of graphitization, especially a higher degree of graphitization and a specific pore structure as a raw material has unexpected advantages for improving the performance of the battery, in particular: the battery obtained by assembling it can have a higher delithiation rate, low-temperature charge and discharge performance and better cycle performance. Such an advantageous effect significantly broadens the application scenarios of the battery. Without being bound by theory, this advantageous effect comes from the synergistic effect of the specific pore structure and the specific degree of graphitization in the porous carbon.

[0058] The degree of graphitization of porous carbon can be studied by methods known in the art, including but not limited to X-ray diffraction (XRD) and Raman spectroscopy. For XRD, the degree of graphitization of the carbon material can be evaluated by monitoring the peak intensity at each 2θ corresponding to each Miller index. The higher the degree of graphitization of the material, the larger the diffraction angle 2θ corresponding to the (002) crystal plane of graphite in the material, and the more prominent the diffraction peak at this position (i.e., a narrow and high morphology). In one embodiment, in the X-ray diffraction pattern of the porous carbon of the present application, the diffraction angle 2θ of the (002) crystal plane is 24.00°-26.53°, preferably 24.15°-26.50°, for example, 24.00°, 24.05°, 24.10°, 24.14°, 24.19°, 24.25°, 24.50°, 24.75°, 25.00°, 25.25°, 24.50°, 24.75°, 25.84°, 26.00°, 24.25°, 26.28°, 26.47°, 26.50°, 26.53°, etc.

[0059] For Raman spectroscopy, the D band (approximately 1300-1400 cm -1 ) and G belt (about 1550-1650cm - 1 ) is used to evaluate the graphitization degree of carbon materials. D ) and G peak intensity (I G ) ratio (I D / I G ), with a higher I D / I G Materials with lower graphitization levels generally have lower I D / I G Typically corresponds to a material with a higher degree of graphitization. In one embodiment, in the Raman spectrum of the porous carbon, the D peak intensity (I D ) and G peak intensity (I G ) ratio (I D / IG ) is 0.10-1.50, preferably 0.10-1.10, more preferably 0.20-0.80, even more preferably 0.20-0.70, for example, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.38, 0.40, 0.45, 0.50, 0.55, 0.56, 0.58, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, 1.10, 1.20, 1.30, etc. In addition, the suitable pore structure of the porous carbon is conducive to providing void space for depositing silicon, reserving space for the expansion of silicon, and can also increase the content of depositable silicon in the composite material, thereby improving battery performance, such as charge specific capacity.

[0060] In one embodiment, the porous carbon has a BET surface area of ​​600-3000 m 2 / g, preferably 800-2800m 2 / g, more preferably 900-2750m 2 / g, for example 600m 2 / g、700m 2 / g、800m 2 / g、900m 2 / g、1000m 2 / g、1100m 2 / g、1200m 2 / g、1300m 2 / g、1400m 2 / g、1500m 2 / g、1600m 2 / g、1700m 2 / g、1800m 2 / g、1900m 2 / g、2000m 2 / g、2100m 2 / g、2200m 2 / g、2300m 2 / g、2400m 2 / g、2500m 2 / g、2600m 2 / g、2700m 2 / g、2800m 2 / g、2900m 2 / g、3000m 2 / g、1844m 2 / g、1286m 2 / g、2703m 2 / g, etc.

[0061] In one embodiment, the porous carbon has a pore volume of 0.50 cm 3 / g or more, preferably 0.60cm 3 / g or more, for example 0.50cm 3 / g, 0.60cm 3 / g, 0.70cm 3 / g, 0.80cm 3 / g, 0.90cm 3 / g, 1.00cm 3 / g, 1.10cm 3 / g, 1.20cm 3 / g, 1.30cm 3 / g, 1.40cm 3 / g, 1.50cm 3 / g, 2.00cm 3 / g, 2.50cm 3 / g, 0.85cm 3 / g, 1.02cm 3 / g, 0.97cm 3 / g, 1.31cm 3 / g, etc.

[0062] In one embodiment, the tap density of the porous carbon is 0.2-1.4 g / cm 3 , for example 0.2 g / cm 3 , 0.3g / cm 3 , 0.4g / cm 3 , 0.5g / cm 3 , 0.6g / cm 3 , 0.7g / cm 3 , 0.8g / cm 3 , 0.9g / cm 3 , 1.0g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 In one embodiment, the minimum particle size Dmin of the porous carbon may be 0.1-1.0 μm, for example, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, etc.

[0063] In one embodiment, the D10 particle size of the porous carbon is 2.0-5.0 μm, for example, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, etc.

[0064] In one embodiment, the porous carbon has a D50 particle size of 5.0-15.0 μm, for example, 2.0 μm, 3.0 μm, 4.0 μm, 5.0 μm, 6.0 μm, 7.0 μm, 8.0 μm, 9.0 μm, 10.0 μm, 11.0 μm, 12.0 μm, 13.0 μm, 14.0 μm, 15.0 μm, etc.

[0065] In one embodiment, the D90 particle size of the porous carbon is 10.0-30.0 μm, for example, 10.0 μm, 15.0 μm, 20.0 μm, 25.0 μm, 30.0 μm, etc.

[0066] In one embodiment, the D100 particle size of the porous carbon is 20.0-50.0 μm, for example, 20.0 μm, 25.0 μm, 30.0 μm, 35.0 μm, 40.0 μm, 45.0 μm, 50.0 μm, etc.

[0067] The porous carbon of the present application has a suitable degree of graphitization, pore structure and particle size distribution, which overcomes the disadvantage of poor electrical conductivity of conventional porous carbon materials. The powder resistivity of the porous carbon of the present application is low and has good electrical conductivity. In one embodiment, the powder resistivity of the porous carbon is less than 900mΩ·cm, preferably less than 800mΩ·cm, for example, 900mΩ·cm, 850mΩ·cm, 800mΩ·cm, 750mΩ·cm, 700mΩ·cm, 600mΩ·cm, 500mΩ·cm, 400mΩ·cm, 300mΩ·cm, 200mΩ·cm, 100mΩ·cm, 50mΩ·cm, etc.

[0068] Preparation of porous carbon

[0069] In the present application, a specific porous carbon precursor and preparation process are used to obtain the target porous carbon. Therefore, in another aspect, the present application provides a method for preparing porous carbon, which includes: providing a porous carbon precursor and alkali activating the porous carbon precursor.

[0070] As mentioned above, in order to obtain improved battery performance, porous carbon with suitable properties (such as degree of graphitization, pore structure and particle size distribution) is preferred. To this end, the present application uses a specific porous carbon precursor to prepare porous carbon.

[0071] The appropriate type of porous carbon precursor helps to obtain porous carbon with desired properties. In one embodiment, the porous carbon precursor is a soft carbon material. Preferably, the porous carbon precursor is selected from coke and coal-based materials. The cokes that can be used herein include, but are not limited to, petroleum coke, pitch coke, needle coke, green coke, semi-calcined coke, calcined coke, and the like. More preferably, the porous carbon precursor is petroleum coke. The preferred precursor material can ensure that the porous carbon obtained can obtain the desired degree of graphitization, and further ensure that a porous carbon with a desired pore structure can be obtained through a suitable pore-forming process.

[0072] In one embodiment, in the X-ray diffraction pattern of the porous carbon precursor, the diffraction angle 2θ of the (002) crystal plane is 25.00°-26.50°, preferably 25.25°-26.25°, more preferably 25.40°-26.00°, for example, 25.00°, 25.50°, 25.70°, 25.78°, 25.80°, 25.90°, 25.96°, 26.00°, 26.10°, 26.20°, 26.30°, 26.40°, 26.50°, etc.

[0073] In one embodiment, in the Raman spectrum of the porous carbon precursor, the D peak intensity (I D ) and G peak intensity (I G ) ratio (I D / I G ) is 0.30-0.50, preferably 0.35-0.48, for example, 0.35, 0.36, 0.37, 0.38, 0.39, 0.40, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.50, etc.

[0074] With the appropriate diffraction angle 2θ and D peak intensity (I D ) and G peak intensity (I G ) of the appropriate ratio (I D / I G ) can ensure that the porous carbon has a desired high degree of graphitization while maintaining the porous carbon's pore structure. Porous carbon precursors with too high a degree of graphitization cannot achieve the desired pore structure through the pore-forming process; porous carbon precursors with too low a degree of graphitization can also cause performance degradation in battery products.

[0075] The lower powder resistivity of the porous carbon precursor helps improve the conductive properties of the resulting porous carbon. In one embodiment, the powder resistivity of the porous carbon precursor is 5.0 mΩ·cm or less, for example, about 5.0 mΩ·cm, 4.9 mΩ·cm, 4.5 mΩ·cm, 4.0 mΩ·cm, 3.5 mΩ·cm, 3.1 mΩ·cm, 2.9 mΩ·cm, 2.0 mΩ·cm, 1.5 mΩ·cm, 1.0 mΩ·cm, etc.

[0076] The porous carbon precursor is formed into pores by a suitable pore-forming method to obtain a target pore structure. In the present application, the porous carbon precursor is preferably formed into pores by alkali activation. For coke and coal-based materials, the pore-forming method of alkali activation has excellent pore-forming efficiency and helps to ensure the structural stability of the porous carbon. The alkali activation process can be carried out using an inorganic base, for example, an alkali or alkaline earth metal hydroxide. Suitable bases include, but are not limited to, potassium hydroxide, sodium hydroxide, and the like.

[0077] It should be understood that the preparation process of porous carbon may also include conventional steps for preparing porous carbon in the art, including but not limited to: crushing, washing, etc.

[0078] The pulverization process is used to crush larger-sized materials into materials with desired sizes. Before the porous carbon precursor is subjected to alkali activation and pore-forming treatment, the porous carbon precursor can be subjected to a pulverization process to crush the porous carbon precursor of larger size (such as centimeter level) into porous carbon precursors of smaller size (such as micron level). Porous carbon precursors of such size are convenient for pore formation. After the pore formation process is completed, secondary pulverization can be performed to obtain a porous carbon material with a desired particle size distribution. Compared to single pulverization, the present application adopts a multiple pulverization method, which is beneficial to the pore formation process on the one hand, while also shortening the pulverization time of the porous carbon after pore formation, and reducing the possible adverse effects of the pulverization process on the pore structure.

[0079] The washing process can remove impurities in the material. For example, after pore formation, the impurities (such as alkali) in the material can be removed through a washing process to remove the adverse effects caused by the residual impurities.

[0080] The present application has found that by selecting a specific porous carbon precursor and combining it with a pore-forming and pulverizing process, a desired porous carbon material can be obtained. In particular, by selecting a suitable precursor in the present application, there is no need to perform an additional graphitization step (for example, graphitization by high temperature), thereby avoiding the adverse consequences (such as pore collapse, low pore volume, and low specific surface area) that may be caused by the graphitization process (such as high temperature). Therefore, in one embodiment, the method for preparing porous carbon in the present application does not include a graphitization step, and preferably does not include a high-temperature heating step, for example, does not include a heating step at a temperature above 2500°C, or above 2000°C, or above 1600°C, or above 1200°C.

[0081] Composite materials for secondary lithium-ion batteries

[0082] In one aspect, the present invention relates to a composite material for a lithium ion secondary battery, the composite material comprising: porous carbon and nano-silicon dispersed in the porous carbon.

[0083] In the present application, silicon is uniformly dispersed in the internal pores of the porous carbon to form nano-silicon (ie, nano-silicon particles), while the outer surface of the porous carbon is substantially free of silicon, which is conducive to fully utilizing the advantages of nano-silicon.

[0084] In one embodiment, the nano-silicon dispersed in the porous carbon is hydrogen-containing nano-silicon. In the present application, for the silicon dispersed in the porous carbon, it retains some Si-H bonds, and thus the silicon dispersed in the porous carbon is also referred to as hydrogen-containing silicon. The hydrogen-containing silicon in the present application refers to: all nano-silicon dispersed in the porous carbon. In the hydrogen-containing silicon herein, at least a portion of the nano-silicon particles are nano-silicon particles with Si-H bonds. The presence of Si-H bonds in hydrogen-containing silicon can effectively improve the stability of the composite material during the charge and discharge process and extend the cycle life of the battery. The Si-H bonds in hydrogen-containing silicon can be determined by any means in the art, including but not limited to infrared testing. For example, the infrared spectrum of the composite material can be at 625-640cm -1 The infrared spectrum of the composite material may also have vibration peaks at one or more of the following positions: 845-885cm -1 1990-2010cm -1 .

[0085] In the Raman spectrum of the composite material of the present application, the D peak intensity (I D ) and G peak intensity (I G ) ratio (I D / I G ) is 0.20-1.50, preferably 0.20-1.00, for example, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, 1.05, 1.10, 1.18, 1.32, 1.46, 1.50, etc.

[0086] The appropriate particle size of nano-silicon is beneficial to improving the performance of the composite material. The particle size of nano-silicon can range from 0.1 to 60 nm, preferably from 0.1 to 20 nm, and more preferably from 1 to 5 nm.

[0087] The ratio of silicon dispersed in porous carbon to porous carbon also affects the performance of composite material. The suitable content of silicon dispersed in porous carbon can give the product better electrical properties (such as excellent charge specific capacity), and can also retain some holes in porous carbon, reserve a certain space for the expansion of silicon in the later stage, and avoid that composite material breaks or even crushes due to the volume expansion of silicon. In one embodiment, the weight ratio of nano silicon and porous carbon is 0.3-0.7, preferably 0.5-0.7, for example, about 0.30, 0.40, 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.70 etc.

[0088] The pore structure of porous carbon deposited with nanosilicon can indicate the extent of silicon deposition within the porous carbon. Materials with appropriate porosity exhibit superior performance. Excessively high porosity in porous carbon deposited with nanosilicon leads to insufficient silicon content, resulting in reduced performance. However, excessively low porosity lacks space for silicon expansion.

[0089] In one embodiment, the BET specific surface area of ​​the porous carbon deposited with nano-silicon is 30-300 m 2 / g, for example 30m 2 / g, 50m 2 / g、100m 2 / g, 150m 2 / g, 200m 2 / g, 250m2 / g, 300m2 / g, etc. In one embodiment, the pore volume of the porous carbon deposited with nano-silicon is 0.2cm 3 / g or less.

[0090] In one embodiment, the powder resistivity of the porous carbon deposited with nano-silicon is 1500 Ω·cm or less, for example, 1500 Ω·cm, 1200 Ω·cm, 800 Ω·cm, 300 Ω·cm, 100 Ω·cm, 60 Ω·cm, 20 Ω·cm, etc.

[0091] The outer surface of the porous carbon with deposited nanosilicon can be coated with a shell layer, which serves as the outer layer of the composite material. This shell layer not only prevents the highly active nanosilicon within the porous carbon pores from oxidizing and spontaneously combusting in the air, but also ensures that the porous carbon and the nanosilicon within it do not come into direct contact with the electrolyte during the use of the composite material, which is conducive to the formation of a stable SEI film.

[0092] The shell layer can be formed by subjecting the porous carbon in which nano-silicon is dispersed to a reaction treatment, or by attaching another material to the surface of the porous carbon.

[0093] The components of the shell layer may include, but are not limited to, amorphous carbon, graphene, carbon nanotubes, conductive polymers, titanium carbide, aluminum oxide, aluminum nitride, silicon carbide, silicon nitride, silicon oxide (such as silicon dioxide), silicon oxynitride, or combinations thereof. In certain embodiments, the shell layer of the composite material of the present invention is a carbon shell.

[0094] The shell layer can be a single layer or multiple layers. Any layer in the shell layer is not limited to the above-mentioned one component, and can be a combination of several substances.

[0095] The appropriate thickness of the shell helps to fully exert the effect of the shell. The thickness of the shell can be 1-1000 nm. In some embodiments, the shell thickness of the composite material is 1-10 nm. In certain embodiments, the shell thickness of the composite material is 10-50 nm. In certain embodiments, the shell thickness of the composite material is 50-100 nm. In certain embodiments, the shell thickness of the composite material is 100-500 nm. In certain embodiments, the shell thickness of the composite material is 500-1000 nm.

[0096] It should be understood that the term "shell layer coated on the outer surface of the porous carbon" herein does not mean that the shell layer material is located only on the outer surface of the porous carbon. For example, the shell layer material may be incorporated into the pores of the porous carbon near the outer surface. For another example, the shell layer may be formed by reacting the outer portion of the porous carbon in which nano-silicon is dispersed.

[0097] It should also be understood that there may be a distinct interface between the shell layer and the porous carbon described herein. There may also be no distinct interface between the shell layer and the porous carbon described herein, for example, there may be a boundary region with a certain thickness between the shell layer and the porous carbon.

[0098] It should also be understood that the shell layer described herein may have a uniform thickness at various locations or may have variations in thickness.

[0099] In one embodiment, the tap density of the porous carbon coated with the shell and deposited with nano-silicon can be 0.5-2 g / cm 3 , for example 0.5 g / cm 3 , 0.6g / cm 3 , 0.8g / cm 3 , 1.0g / cm 3 , 1.2g / cm 3 , 1.4g / cm 3 , 1.6g / cm 3 , 1.8g / cm 3 , 2.0g / cm 3 wait.

[0100] In one embodiment, the specific surface area of ​​the porous carbon coated with the shell layer and deposited with nano-silicon is 10 m 2 / g or less, for example, 10m 2 / g or less, 9m 2 / g or less, 8m 2 / g or less, 7m 2 / g or less, 6m 2 / g or less, 5m 2 / g and below.

[0101] In one embodiment, the pore volume of the shell-coated porous carbon deposited with nano-silicon is 0.1 cm 3 / g or less, for example, 0.1cm 3 / g or less, 0.1cm 3 / g or less, 0.08cm 3 / g or less, 0.06cm 3 / g or less, 0.05cm 3 / g or less.

[0102] In one embodiment, the powder resistivity of the shell-coated porous carbon deposited with nano-silicon is less than 100 Ω·cm, for example, 100 Ω·cm, 60 Ω·cm, 30 Ω·cm, 10 Ω·cm, 2 Ω·cm, etc.

[0103] Based on the total weight of the porous carbon coated with a shell and deposited with nano-silicon, the carbon content can be 30-70wt%, preferably 30-50wt%, for example 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt% and the like.

[0104] Based on the total weight of the porous carbon coated with a shell and deposited with nano-silicon, the hydrogen content can be 0-10wt%, preferably 0.3-5wt%, for example 0.1wt%, 0.3wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt% and the like.

[0105] Based on the total weight of the porous carbon coated with the shell layer and deposited with nano-silicon, the oxygen content may be 0-3 wt%, 0.1 wt%, 0.3 wt%, 1 wt%, 2 wt%, 3 wt%, etc.

[0106] The nanosilicon may be in the form of crystalline silicon or amorphous silicon. In certain embodiments, the nanosilicon comprises crystalline nanosilicon. In certain embodiments, the nanosilicon comprises polycrystalline nanosilicon. In certain other embodiments, the nanosilicon comprises amorphous nanosilicon. In certain other embodiments, the nanosilicon comprises crystalline nanosilicon and amorphous nanosilicon.

[0107] The degree of crystallinity of silicon in nano-silicon can be measured by any method in the art, such as by electrochemical curve measurement. For the test sample obtained from the composite material, the platform of its charging curve at 0.4-0.5V and the characteristic peak of the corresponding DQ / DV curve at 0.4-0.5V are related to the degree of crystallinity of the nano-silicon. In the nano-silicon, the higher the proportion of crystalline silicon, the more obvious the platform of the charging curve at 0.4-0.5V, and the stronger the characteristic peak intensity of its DQ / DV curve at 0.4-0.5V.

[0108] In some embodiments, in a lithium ion half-cell test prepared from the composite material of a secondary lithium ion battery of the present invention, the electrochemical charging curve thereof has a platform at 0.4-0.5 V. In some embodiments, in a lithium ion half-cell test prepared from the composite material of a secondary lithium ion battery of the present invention, the electrochemical charging curve thereof has a characteristic peak at 0.4-0.5 V.

[0109] On the other hand, the present application relates to a method for the above-mentioned composite material, which comprises the following steps: providing porous carbon; depositing silicon in the porous carbon to form nano-silicon dispersed in the porous carbon; optionally, coating the outer surface of the porous carbon in which the nano-silicon is dispersed to form a shell layer.

[0110] The silicon dispersion process can be achieved by any method known in the art, including but not limited to CVD deposition and liquid impregnation. Appropriate parameters during the dispersion process help to obtain the desired composite material.

[0111] There is no particular limitation on the coating method herein, and the outer surface of the porous carbon can be coated by reactive coating, adhesive coating, or a combination of reactive coating and adhesive coating, or by other methods capable of forming a shell on the surface of a porous substrate dispersed with nano-silicon. Reactive coating refers to forming a shell by reaction treatment to achieve coating. For example, a shell can be formed by reaction treatment of porous carbon dispersed with nano-silicon. Specifically, coating can be achieved by reaction treatment of partial oxidation, nitridation, or carbonization of nano-silicon. Adhesive coating refers to attaching a material to the surface of the porous carbon to form a shell. The outer surface of the porous carbon can be coated by a combination of reactive coating and adhesive coating.

[0112] The present application found that the composite material prepared with porous carbon material of a specific degree of graphitization as raw material, and the assembled battery showed better performance in terms of delithiation rate, discharge capacity retention rate, and low-temperature discharge capacity percentage, which are usually difficult to improve through current conventional means in this field (for example, adjusting the silicon content in the composite material, etc.).

[0113] In one embodiment, a half-cell assembled with a negative electrode sheet made of the composite material of the present application can be tested at room temperature 0.1C / 0.1C, and the delithiation GITT can be calculated according to the following formula:

[0114] Where, D is the diffusion coefficient; τ is the relaxation time; R s ——Active particle radius; ΔE s ——voltage change caused by the pulse; ΔE t ——Voltage change of constant current charge (discharge). Peak value of delithiation GITT test curve of half-cell assembled with composite materials of this application It is 1.30 or more, preferably 1.40 or more, and more preferably 1.45 or more.

[0115] In one embodiment, the discharge capacity percentage of a full battery assembled from the composite material of the present application is measured under the following conditions: 1C charge at room temperature (25°C), 0.2C discharge at low temperature (-20°C); voltage range: 2.8-4.25V. The discharge capacity percentage of a full battery assembled from a negative electrode sheet made from the composite material of the present application is greater than 70%.

[0116] In one embodiment, the discharge capacity retention rate of a full battery assembled from the composite material of the present application is measured under the following conditions: 1C charge at room temperature (25°C), 0.2C discharge to 2.5V, measure the discharge capacity, repeat three times and take the average value, which is recorded as the room temperature discharge capacity. Charge at room temperature at 1C, place at low temperature (-20°C) for 6-12 hours, discharge at 0.2C to 2.5V, measure the discharge capacity, and the ratio of this value to the room temperature discharge capacity is the discharge capacity retention rate. The discharge capacity retention rate of a full battery assembled from the negative electrode sheet made from the composite material of the present application is 70% or more, preferably 73% or more.

[0117] The present invention also includes the following embodiments:

[0118] Embodiment 1: A porous carbon for negative electrode material, characterized in that, in the Raman spectrum of the porous carbon, the ratio (ID / IG) of the D peak intensity (ID) to the G peak intensity (IG) is 0.10-1.10; in the X-ray diffraction pattern of the porous carbon, the diffraction angle 2θ of the (002) crystal plane is 24.00°-26.53°; and the specific surface area BET of the porous carbon is 600-3000m2 / g.

[0119] Embodiment 2: The porous carbon according to Embodiment 1 is characterized in that, in the Raman spectrum of the porous carbon, the ratio (ID / IG) of the D peak intensity (ID) to the G peak intensity (IG) is 0.20-0.80, preferably 0.25-0.70.

[0120] Embodiment 3: The porous carbon according to Embodiment 1 is characterized in that the porous carbon has a BET specific surface area of ​​800-2800 m2 / g, preferably 900-2750 m2 / g.

[0121] Embodiment 4: The porous carbon according to Embodiment 1 is characterized in that the pore volume of the porous carbon is greater than 0.50 cm3 / g, preferably greater than 0.60 cm3 / g.

[0122] Embodiment 5: The porous carbon according to Embodiment 1 is characterized in that, in the X-ray diffraction pattern of the porous carbon, the diffraction angle 2θ of the (002) crystal plane is 24.15°-26.50°.

[0123] Embodiment 6: The porous carbon according to Embodiment 1 is characterized in that the powder resistivity of the porous carbon is 900 mΩ·cm or less, preferably 800 mΩ·cm or less.

[0124] Embodiment 7: The porous carbon according to Embodiment 1 is characterized in that the porous carbon has one or more of the following characteristics: (a) the tap density of the porous carbon is 0.2-1.4 g / cm 3 ; (b) the minimum particle size Dmin of the porous carbon is 0.1-1.0 μm; (c) the D10 particle size of the porous carbon is 2.0-5.0 μm; (d) the D50 particle size of the porous carbon is 5.0-15.0 μm; (e) the D90 particle size of the porous carbon is 10.0-30.0 μm; (f) the D100 particle size of the porous carbon is 20.0-50.0 μm.

[0125] Embodiment 8: The porous carbon according to Embodiment 1 is characterized in that the porous carbon is prepared by alkali activation of a porous carbon precursor; preferably, the alkali includes: hydroxides of alkali metals or alkaline earth metals; more preferably, the alkali includes: potassium hydroxide: sodium hydroxide or a combination thereof.

[0126] Embodiment 9: The porous carbon according to Embodiment 8 is characterized in that the porous carbon precursor is a soft carbon material, preferably a coke or coal-based material, and more preferably petroleum coke.

[0127] Embodiment 10: The porous carbon according to Embodiment 8 is characterized in that, in the X-ray diffraction pattern of the porous carbon precursor, the diffraction angle 2θ of the (002) crystal plane is 25.00°-26.50°, preferably 25.25°-26.25°, and more preferably 25.40°-26.00°.

[0128] Embodiment 11: The porous carbon according to embodiment 8 is characterized in that, in the Raman spectrum of the porous carbon precursor, the D peak intensity (ID ) and G peak intensity (I G ) ratio (I D / I G ) is 0.35-0.48, preferably 0.41-0.47.

[0129] Embodiment 12: The porous carbon according to Embodiment 8 is characterized in that the powder resistivity of the porous carbon precursor is less than 5.0 mΩ·cm.

[0130] Embodiment 13: A method for preparing the porous carbon described in any one of Embodiments 1-12, comprising the following steps: providing a porous carbon precursor; and alkali-activating the porous carbon precursor to prepare the porous carbon.

[0131] Embodiment 14: A composite material for lithium-ion secondary batteries, characterized in that the composite material comprises: the porous carbon described in any one of Embodiments 1-12, and nanosilicon dispersed in the porous carbon; preferably, the nanosilicon dispersed in the porous carbon is hydrogen-containing nanosilicon.

[0132] Embodiment 15: The composite material according to embodiment 14, characterized in that in the Raman spectrum of the composite material, the D peak intensity (I D ) and G peak intensity (I G ) ratio (I D / I G ) is 0.35-1.10, preferably 0.40-1.00.

[0133] Embodiment 16: The composite material according to Embodiment 14 is characterized in that the composite material has one or more of the following characteristics: (a) the particle size range of the nano-silicon is 0.1-60 nm, preferably 0.1-20 nm, more preferably 1-5 nm; (b) the weight ratio of the nano-silicon to the composite material is 0.3-0.7, preferably 0.5-0.7; (c) the powder resistivity of the composite material is less than 1500 Ω·cm; (d) the BET specific surface area of ​​the composite material is 30-300 m 2 / g; (e) the pore volume of the composite material is 0.2cm 3 / g or less.

[0134] Embodiment 17: The composite material according to Embodiment 14 is characterized in that the composite material further comprises: a shell layer coated on the outer surface of the porous carbon; preferably, the components of the shell layer include: amorphous carbon, graphene, carbon nanotubes, conductive polymers, titanium carbide, aluminum oxide, aluminum nitride, silicon carbide, silicon nitride, silicon oxide, silicon oxynitride or a combination thereof.

[0135] Embodiment 18: The composite material according to Embodiment 17 is characterized in that, based on the total weight of the composite material, its carbon content is 30-70wt%, preferably 30-50wt%; based on the total weight of the composite material, its hydrogen content is 0-10wt%, preferably 0.3-5wt%; based on the total weight of the composite material, its oxygen content is 0-3wt%.

[0136] Embodiment 19: The composite material according to Embodiment 17, characterized in that the tap density of the composite material is 0.5-2 g / cm 3 The powder resistivity of the composite material is less than 100Ω·cm; the specific surface area of ​​the composite material is 10m 2 / g or less; the pore volume of the composite material is 0.1cm 3 / g or less.

[0137] Embodiment 20: The composite material according to Embodiment 17 is characterized in that the electrochemical charging curve of the half-cell prepared from the composite material has a platform at 0.4-0.5V; and / or the DQ / DV curve of the half-cell prepared from the composite material has a characteristic peak at 0.4-0.5V.

[0138] Embodiment 21: A method for preparing a composite material according to any one of Embodiments 14 to 20, comprising the following steps: providing porous carbon; depositing silicon in the porous carbon to form nano-silicon dispersed in the porous carbon; and optionally, coating the outer surface of the porous carbon in which the nano-silicon is dispersed to form a shell layer.

[0139] Embodiment 22: A negative electrode plate, characterized in that the negative electrode plate includes the composite material described in any one of Embodiments 14-20.

[0140] Embodiment 23: A lithium-ion secondary battery, characterized in that the lithium-ion battery includes the negative electrode sheet described in Embodiment 22. Beneficial effects

[0141] In the present application, a specific porous carbon precursor is used in combination with a pore-forming and pulverizing process to obtain a porous carbon material with desired properties (such as high graphitization degree and rich pore structure), which can realize the desired silicon deposition process. The composite material of the present application can be used as a negative electrode material for a battery and significantly improves the electrical performance of the battery. In the preparation method of the present application, by selecting a suitable precursor, there is no need to perform an additional graphitization step (such as graphitization by high temperature), thereby avoiding the adverse consequences (such as pore collapse, low pore volume, and low specific surface area) that may be caused by the graphitization process (such as high temperature). And the preparation method of the present application is simple and easy to operate and can be applied to mass production.

[0142] Example

[0143] The solution of the present invention is further described in detail below with reference to specific embodiments.

[0144] It should be noted that the following examples are merely examples for clearly illustrating the technical solutions of the present invention and are not intended to limit the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all embodiments here, and the obvious variations or modifications derived therefrom are still within the scope of protection of the present invention. Unless otherwise specified, the instruments, equipment, and reagents used herein are all commercially available.

[0145] Test Method

[0146] 1. Powder resistivity test

[0147] The test was performed using an automated powder resistivity tester (ST2742B model), and the test standard was in accordance with Appendix G of GB / T 30835-2014.

[0148] (1) Weighing: Weigh the sample to be tested on weighing paper using a balance. For porous carbon samples, weigh 0.25-0.3 g (accurate to 0.01 g); for porous carbon samples with deposited silicon and porous carbon samples with deposited silicon coated with a shell, weigh 0.5-0.6 g (accurate to 0.01 g);

[0149] (2) Setting parameters: Open the test software of the ST2742B powder resistivity tester, click "Connect instrument" on the measurement interface, the software switches to the instrument setting interface, set the lower limit of the test pressure to 8 MPa, the upper limit to 10 MPa, the pressure holding time to 10 s, enter the sample mass, and click "Set" to save the data;

[0150] (3) Test: Pour the sample into the sampler, hold the sampler in your hand, and gently tap the table to vibrate and compact the material in the cup. Place the sampler on the lifting platform, switch the software to the measurement control interface, and fill in the "measurement identification" and "tester" information in the lower right area of ​​the software. Under the "automatic" and "ascending" conditions, click the "start" button in the software to start the automatic measurement. After the test is completed, the test results will be displayed on the measurement interface. After the measurement is completed, remove the sampler, clean the sampler, and then shut down the machine or proceed to the next sample test.

[0151] 2. Raman spectroscopy test

[0152] The test was performed using a Raman spectrometer (HORIBA XploRA PLUS).

[0153] (1) Sample preparation: Take an appropriate amount of powder sample and place it in the middle of a slide. Cover it with another slide and use a tablet press to maintain a pressure of 10 MPa for 30 seconds to evenly compact the sample on the slide.

[0154] (2) Test: Set the test wavelength range to 0~3000cm -1 The grating is 1200gr / mm, the slit width is 0.1mm at the wavelength of 532nm, the integration time is 25s, and three positions are selected for testing on each sample.

[0155] 3. XRD test

[0156] The test was performed using an X-ray diffractometer (SmartLab SE).

[0157] The sample powder was placed in an XRD diffractometer at 10-65°, 5° / min, using a copper target for X-rays with a wavelength of 0.154 nm for testing.

[0158] preparation

[0159] Preparation of porous carbon

[0160] Porous carbon was prepared from the porous carbon precursor shown in Table 1. The precursor was subjected to the steps of crushing, pore formation, secondary crushing, and washing to prepare a porous carbon sample. Biomass precursor materials were pore-formed by water vapor or carbon dioxide activation. Resin precursor materials were pore-formed by water vapor or carbon dioxide. Coke materials were pore-formed by alkali activation. Graphite materials could not be pore-formed by any conventional pore-formation method. The parameters of the obtained porous carbon samples are shown in Tables 2 and 3.

[0161] Preparation of sample A1-SC and sample A1-SC-BF

[0162] 12 kg of porous carbon (numbered porous carbon A1) was added to the fluidized bed as a deposition substrate (the parameters of the porous carbon used are shown in Tables 2 and 3), and nitrogen was introduced to replace the air in the fluidized bed at a nitrogen flow rate of 21 L / min.

[0163] After the fluidized bed was heated to 500°C at a heating rate of 2°C / min, monosilane SiH4 was introduced into the fluidized bed and vapor-deposited on the porous carbon. The monosilane gas flow rate was 35 L / min and the deposition time was 6 hours to obtain a porous carbon sample with deposited silicon (No. A1-SC).

[0164] After the silicon deposition is completed, acetylene as a carbon source gas is introduced to carbon-coat the porous carbon sample with deposited silicon (No. A1-SC) by vapor deposition to obtain a porous carbon sample with deposited silicon coated with a shell layer (No. A1-SC-=BF).

[0165] Preparation of sample A2-SC and sample A2-SC-BF

[0166] 12 kg of porous carbon (numbered porous carbon A2) was added to the fluidized bed as a deposition substrate (the parameters of the porous carbon used are shown in Tables 2 and 3), and nitrogen was introduced to replace the air in the fluidized bed at a nitrogen flow rate of 24 L / min.

[0167] After the fluidized bed was heated to 400°C at a heating rate of 1°C / min, monosilane SiH4 was introduced into the fluidized bed and vapor-deposited on the porous carbon. The silane gas flow rate was 40 L / min and the deposition time was 5 hours to obtain a porous carbon sample with deposited silicon (No. A2-SC).

[0168] After the silicon deposition is completed, propane gaseous carbon source is introduced to perform carbon coating on the deposited silicon porous carbon sample (No. A2-SC) by vapor deposition to obtain a shell-coated deposited silicon porous carbon sample (No. A2-SC-BF).

[0169] Preparation of sample A3-SC and sample A3-SC-BF

[0170] 12 kg of porous carbon (numbered porous carbon A3) was added to the fluidized bed as a deposition substrate (the parameters of the porous carbon used are shown in Tables 2 and 3), and nitrogen was introduced to replace the air in the fluidized bed at a nitrogen flow rate of 23 L / min.

[0171] After the fluidized bed was heated to 480°C at a heating rate of 5°C / min, monosilane SiH4 was introduced into the fluidized bed and vapor-deposited on the porous carbon. The silane gas flow rate was 35 L / min and the deposition time was 6 hours to obtain a porous carbon sample with deposited silicon (No. A3-SC).

[0172] After the silicon deposition is completed, acetylene as a carbon source gas is introduced to perform carbon coating on the deposited silicon porous carbon sample (No. A3-SC) by vapor deposition to obtain the shell-coated deposited silicon porous carbon sample (No. A3-SC-BF) of Example 3.

[0173] Preparation of sample A4-SC and sample A4-SC-BF

[0174] 12 kg of porous carbon (numbered porous carbon A4) was added to the fluidized bed as a deposition substrate (the parameters of the porous carbon used are shown in Tables 2 and 3), and nitrogen was introduced to replace the air in the fluidized bed at a nitrogen flow rate of 24 L / min.

[0175] After the fluidized bed was heated to 600°C at a heating rate of 5°C / min, monosilane SiH4 was introduced into the fluidized bed and vapor-deposited on the porous carbon. The silane gas flow rate was 35 L / min and the deposition time was 6 hours to obtain a porous carbon sample with deposited silicon (No. A4-SC).

[0176] After the silicon deposition is completed, propane gas as a carbon source is introduced to perform carbon coating on the porous carbon sample with deposited silicon (No. A4-SC) by vapor deposition to obtain a porous carbon sample with deposited silicon coated with a shell layer (No. A4-SC-BF).

[0177] Preparation of sample B1-SC and sample B1-SC-BF

[0178] 12 kg of porous carbon (numbered porous carbon B1) was added to the fluidized bed as a deposition substrate (the parameters of the porous carbon used are shown in Tables 2 and 3), and nitrogen was introduced to replace the air in the fluidized bed at a nitrogen flow rate of 25 L / min.

[0179] After the fluidized bed was heated to 425°C at a heating rate of 4°C / min, monosilane SiH4 was introduced into the fluidized bed and vapor-deposited on the porous carbon. The silane gas flow rate was 30 L / min and the deposition time was 8 hours to obtain a porous carbon sample with deposited silicon (No. B1-SC).

[0180] After the silicon deposition is completed, propane gaseous carbon source is introduced to perform carbon coating on the deposited silicon porous carbon sample (No. B1-SC) by vapor deposition method to obtain a shell-coated deposited silicon porous carbon sample (No. B1-SC-BF).

[0181] Preparation of sample B2-SC and sample B2-SC-BF

[0182] 12 kg of porous carbon (numbered porous carbon B2) was added to the fluidized bed as a deposition substrate (the parameters of the porous carbon used are shown in Tables 2 and 3), and nitrogen was introduced to replace the air in the fluidized bed at a nitrogen flow rate of 27 L / min.

[0183] After the fluidized bed was heated to 450°C at a heating rate of 5°C / min, monosilane SiH4 was introduced into the fluidized bed and vapor-deposited on the porous carbon. The silane gas flow rate was 50 L / min and the deposition time was 4 hours to obtain a porous carbon sample with deposited silicon (No. B2-SC).

[0184] After the silicon deposition is completed, acetylene as a carbon source gas is introduced to perform carbon coating on the deposited silicon porous carbon sample (No. B2-SC) by vapor deposition to obtain a shell-coated deposited silicon porous carbon sample (No. B2-SC-BF).

[0185] Preparation of samples C1-SC and C1-SC-BF

[0186] 12 kg of porous carbon (numbered porous carbon C1) was added to the fluidized bed as a deposition substrate (the parameters of the porous carbon used are shown in Tables 2 and 3), and nitrogen was introduced to replace the air in the fluidized bed at a nitrogen flow rate of 23 L / min.

[0187] After the fluidized bed was heated to 525°C at a heating rate of 5°C / min, monosilane SiH4 was introduced into the fluidized bed and vapor-deposited on the porous carbon. The silane gas flow rate was 35 L / min and the deposition time was 6 hours to obtain a porous carbon sample with deposited silicon (No. C1-SC).

[0188] After the silicon deposition is completed, the gaseous carbon source propylene is introduced to perform carbon coating on the deposited silicon porous carbon sample (No. C1-SC) by vapor deposition method to obtain the deposited silicon porous carbon sample (No. C1-SC-BF) coated with a shell layer.

[0189] Preparation of samples C2-SC and C2-SC-BF

[0190] 12 kg of porous carbon (numbered porous carbon C2) was added to the fluidized bed as a deposition substrate (the parameters of the porous carbon used are shown in Tables 2 and 3), and nitrogen was introduced to replace the air in the fluidized bed at a nitrogen flow rate of 25 L / min.

[0191] After the fluidized bed was heated to 475°C at a heating rate of 6°C / min, monosilane SiH4 was introduced into the fluidized bed and vapor-deposited on the porous carbon. The silane gas flow rate was 30 L / min and the deposition time was 6 hours to obtain a porous carbon sample with deposited silicon (No. C2-SC).

[0192] After the silicon deposition is completed, acetylene as a carbon source gas is introduced to perform carbon coating on the deposited silicon porous carbon sample (number C2-SC) by vapor deposition to obtain a shell-coated deposited silicon porous carbon sample (number C2-SC-BF).

[0193] Preparation of samples C3-SC and C3-SC-BF

[0194] 12 kg of porous carbon (numbered porous carbon C3) was added to the fluidized bed as a deposition substrate (the parameters of the porous carbon used are shown in Tables 2 and 3), and nitrogen was introduced to replace the air in the fluidized bed at a nitrogen flow rate of 25 L / min.

[0195] After the fluidized bed was heated to 525°C at a heating rate of 5°C / min, monosilane SiH4 was introduced into the fluidized bed and vapor-deposited on the porous carbon. The silane gas flow rate was 30 L / min and the deposition time was 8 hours to obtain a porous carbon sample with deposited silicon (No. C3-SC).

[0196] After the silicon deposition is completed, the gaseous carbon source propylene is introduced to perform carbon coating on the deposited silicon porous carbon sample (No. C3-SC) by vapor deposition to obtain a shell-coated deposited silicon porous carbon sample (No. C3-SC-BF).

[0197] Preparation of sample B1-SC and sample B1-SC-BF

[0198] 12 kg of porous carbon (numbered porous carbon C4) was added to the fluidized bed as a deposition substrate (the parameters of the porous carbon used are shown in Tables 2 and 3), and nitrogen was introduced to replace the air in the fluidized bed at a nitrogen flow rate of 23 L / min.

[0199] After the fluidized bed was heated to 450°C at a heating rate of 6°C / min, monosilane SiH4 was introduced into the fluidized bed and vapor-deposited on the porous carbon. The silane gas flow rate was 35 L / min and the deposition time was 10 hours to obtain a porous carbon sample with deposited silicon (numbered C4-SC).

[0200] After the silicon deposition is completed, acetylene as a carbon source gas is introduced to perform carbon coating on the deposited silicon porous carbon sample (number C4-SC) by vapor deposition to obtain a deposited silicon porous carbon sample coated with a shell layer (number C4-SC-BF).

[0201] Preparation of sample B1-SC and sample B1-SC-BF

[0202] 12 kg of porous carbon (numbered porous carbon C5) was added to the fluidized bed as a deposition substrate (the parameters of the porous carbon used are shown in Tables 2 and 3), and nitrogen was introduced to replace the air in the fluidized bed at a nitrogen flow rate of 27 L / min.

[0203] After the fluidized bed was heated to 450°C at a heating rate of 5°C / min, monosilane SiH4 was introduced into the fluidized bed and vapor-deposited on the porous carbon. The silane gas flow rate was 36 L / min and the deposition time was 5 hours to obtain a porous carbon sample with deposited silicon (numbered C5-SC).

[0204] After the silicon deposition is completed, acetylene as a carbon source gas is introduced to perform carbon coating on the deposited silicon porous carbon sample (number C5-SC) by vapor deposition to obtain a deposited silicon porous carbon sample coated with a shell layer (number C5-SC-BF).

[0205] Preparation of samples C6-SC and C6-SC-BF

[0206] 12 kg of porous carbon (numbered porous carbon C6) was added to the fluidized bed as a deposition substrate (the parameters of the porous carbon used are shown in Tables 2 and 3), and nitrogen was introduced to replace the air in the fluidized bed at a nitrogen flow rate of 23 L / min.

[0207] After the fluidized bed was heated to 550°C at a heating rate of 5°C / min, monosilane SiH4 was introduced into the fluidized bed and vapor-deposited on the porous carbon. The silane gas flow rate was 35 L / min and the deposition time was 6 hours to obtain a porous carbon sample with deposited silicon (numbered C6-SC).

[0208] After the silicon deposition is completed, acetylene as a carbon source gas is introduced to perform carbon coating on the deposited silicon porous carbon sample (number C6-SC) by vapor deposition to obtain a shell-coated deposited silicon porous carbon sample (number C6-SC-BF).

[0209] Preparation of sample C7-SC and sample C7-SC-BF

[0210] 12 kg of porous carbon (numbered porous carbon C7) was added to the fluidized bed as a deposition substrate (the parameters of the porous carbon used are shown in Tables 2 and 3), and nitrogen was introduced to replace the air in the fluidized bed at a nitrogen flow rate of 23 L / min.

[0211] After the fluidized bed was heated to 420°C at a heating rate of 5°C / min, monosilane SiH4 was introduced into the fluidized bed and vapor-deposited on the porous carbon. The silane gas flow rate was 35 L / min and the deposition time was 6 hours to obtain a porous carbon sample with deposited silicon (No. C7-SC).

[0212] After the silicon deposition is completed, acetylene gas as a carbon source is introduced to perform carbon coating on the deposited silicon porous carbon sample (No. C7-SC) by vapor deposition to obtain a shell-coated deposited silicon porous carbon sample (No. C7-SC-BF).

[0213] Preparation of samples C8-SC and C8-SC-BF

[0214] 12 kg of porous carbon (numbered porous carbon C8) was added to the fluidized bed as a deposition substrate (the parameters of the porous carbon used are shown in Tables 2 and 3), and nitrogen was introduced to replace the air in the fluidized bed at a nitrogen flow rate of 23 L / min.

[0215] After the fluidized bed was heated to 405°C at a heating rate of 5°C / min, monosilane SiH4 was introduced into the fluidized bed and vapor-deposited on the porous carbon. The silane gas flow rate was 35 L / min and the deposition time was 6 hours to obtain a porous carbon sample with deposited silicon (No. C8-SC).

[0216] After the silicon deposition is completed, acetylene as a carbon source gas is introduced to perform carbon coating on the deposited silicon porous carbon sample (No. C8-SC) by vapor deposition to obtain a deposited silicon porous carbon sample coated with a shell layer (No. C8-SC-BF).

[0217] Preparation of sample C9-SC and sample C9-SC-BF

[0218] 12 kg of porous carbon (numbered porous carbon C9) was added to the fluidized bed as a deposition substrate (the parameters of the porous carbon used are shown in Tables 2 and 3), and nitrogen was introduced to replace the air in the fluidized bed at a nitrogen flow rate of 23 L / min.

[0219] After the fluidized bed was heated to 500°C at a heating rate of 5°C / min, monosilane SiH4 was introduced into the fluidized bed and vapor-deposited on the porous carbon. The silane gas flow rate was 35 L / min and the deposition time was 6 hours to obtain a porous carbon sample with deposited silicon (No. C9-SC).

[0220] After the silicon deposition is completed, acetylene gas as a carbon source is introduced to carbon-coat the porous carbon sample with deposited silicon (No. C9-SC) by vapor deposition to obtain a porous carbon sample with deposited silicon coated with a shell layer (No. C9-SC-BF).

[0221] Preparation of sample C10-SC and sample C10-SC-BF

[0222] 12 kg of porous carbon (numbered porous carbon C10) was added to the fluidized bed as a deposition substrate (the parameters of the porous carbon used are shown in Tables 2 and 3), and nitrogen was introduced to replace the air in the fluidized bed at a nitrogen flow rate of 27 L / min.

[0223] After the fluidized bed was heated to 450°C at a heating rate of 5°C / min, monosilane SiH4 was introduced into the fluidized bed and vapor-deposited on the porous carbon. The silane gas flow rate was 35 L / min and the deposition time was 6 hours to obtain a porous carbon sample with deposited silicon (No. C10-SC).

[0224] After the silicon deposition is completed, acetylene as a carbon source gas is introduced to perform carbon coating on the deposited silicon porous carbon sample (No. C10-SC) by vapor deposition to obtain a shell-coated deposited silicon porous carbon sample (No. C10-SC-BF).

[0225] Table 1

[0226] Table 2

[0227] Table 3

[0228] Performance Testing

[0229] Half-cell test

[0230] The porous carbon sample of deposited silicon or the porous carbon sample of deposited silicon coated with a shell prepared in the examples of the present application was used to prepare a negative electrode sheet to assemble a button half-cell, and the test was carried out as follows:

[0231] Preparation of the negative electrode: The prepared porous carbon sample of deposited silicon or the porous carbon sample of deposited silicon coated with a shell, carbon black as a conductive additive, and a binder (sodium carboxymethyl cellulose and styrene-butadiene rubber in a 1:1 mass ratio) were weighed in a 95:2:3 mass ratio and slurried in a beater at room temperature. The prepared slurry was evenly coated on copper foil and dried in a forced air drying oven at 50°C for 2 hours. The slurry was then cut into 8mm diameter electrodes and dried in a vacuum drying oven at 100°C for 10 hours. The dried electrodes were then transferred to a glove box for later use in battery assembly.

[0232] Battery Assembly: The simulated battery was assembled in a glove box containing a high-purity Ar atmosphere. Metallic lithium was used as the counter electrode, and a solution of 1 mol LiPF6 in ethylene carbonate (EC) / dimethyl carbonate (DMC) (volume ratio v:v = 1:1) was used as the electrolyte.

[0233] Half-cell test conditions: A charge and discharge instrument was used to perform constant current charge and discharge mode tests. The discharge cut-off voltage was 0.005 V, and the charge cut-off voltage was 1.5 V. The charge and discharge tests were performed at a current density of C / 10. The relevant test data (charge specific capacity, first coulombic efficiency) obtained are detailed in Tables 4 and 5.

[0234] Half-cell test conditions: room temperature, 0.1°C / 0.1°C. The delithiation GITT was calculated using the following formula. Figures 7-9 show the comparative delithiation GITT results for half-cells assembled with negative electrode sheets from relevant samples. The peak values ​​for each test curve are shown in Table 5.

[0235] Where, D is the diffusion coefficient; τ is the relaxation time; R s ——Active particle radius; ΔE s ——voltage change caused by the pulse; ΔE t ——Voltage change during constant current charging (discharging).

[0236] Full battery test

[0237] The porous carbon sample of deposited silicon or the porous carbon sample of deposited silicon coated with a shell prepared in the examples of the present application was used to prepare a negative electrode sheet to assemble a battery, and the test was carried out as follows:

[0238] Preparation of positive electrode: Formula parameters: 96.2wt% LiNi 0.6 Co 0.2 Mn 0.2 O2 (622 cathode material) + 1.1wt% PVDF (binder) + 2.7wt% Super P (conductive agent); Ingredient parameters: dry mixing, high-speed dispersion (solid content 72%), adjust the viscosity to about 5000cP before coating; Coating parameters: single-sided density 21mg / cm 2 After being cut into 15 cm wide strips, the positive electrode sheets with a size of 73 mm × 44 mm were obtained by die cutting.

[0239] Preparation of negative electrode sheet: Formula parameters: 95.0wt% negative electrode material (prepared porous carbon sample of deposited silicon or porous carbon sample of deposited silicon coated with shell) + 3.5wt% binder (sodium carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of 1:1) + 1.5wt% conductive agent carbon black; Ingredient parameters: dry mixing and kneading (solid content 65%), high-speed dispersion (solid content 45%), adjust the viscosity to about 5000 for coating; Coating parameters: single-side density 9mg / cm 2 After being cut into 15 cm wide strips, negative electrode sheets with a size of 75 mm × 46 mm were obtained by die cutting.

[0240] Assemble the battery: proceed as follows: stacking: 9 negative electrode sheets and 8 positive electrode sheets are stacked in a Z shape; welding the tabs: the positive and negative electrodes are welded with tabs (positive electrode: aluminum; negative electrode: nickel); hot pressing and cold pressing: hot pressing at 80°C for 1 minute and cold pressing at room temperature for 1 minute; aluminum mold punching: the punching depth is 3mm; top sealing and side sealing: the heat sealing temperature is 190°C and the heat sealing time is 6 seconds; baking: keep warm at 95°C for 3 days, during which nitrogen replacement is performed to ensure that the sample is in an inert atmosphere; water content test: take About 1g of each positive electrode and negative electrode are heated at 120℃ to remove water to reduce the moisture content to less than 200ppm; liquid injection: a solution of 1 mol of LiPF6 in ethylene carbonate (EC) / dimethyl carbonate (DMC) (volume ratio v:v=1:1) is injected as the electrolyte between the positive electrode and the negative electrode, and the liquid injection coefficient calculated according to the first charge is 3.5; sealing: heat sealing temperature 190℃, heat sealing time 3 seconds, vacuum degree -90; soak at 45℃ for 2 days to obtain the assembled battery sample.

[0241] Full battery test conditions: Cycling conditions: room temperature (25°C), 1C / 1C; voltage range: 2.8-4.25V. Figure 10 shows the cycling curves of the soft-pack full battery assembled with the negative electrode sheet prepared from the sample. Figure 11 shows the cycling curves of the soft-pack full battery assembled with the negative electrode sheet with different electrode sheet compaction densities prepared from C1-SC-BF. Figure 12 shows the cycling curves of the soft-pack full battery assembled with the negative electrode sheet with different electrode sheet compaction densities prepared from sample A1-SC-BF.

[0242] Full-cell test conditions: 1C charge at room temperature (25°C), 0.2C discharge at low temperature (-20°C); voltage range: 2.8-4.25V. Figures 13-15 show the discharge capacity percentages of full-cells assembled with negative electrode sheets from relevant samples at -20°C.

[0243] Full-cell test conditions: Charge at room temperature (25°C) at 1C, discharge at 0.2C to 2.5V, measure the discharge capacity, repeat three times, and take the average value, which is recorded as the room-temperature discharge capacity. Charge at room temperature at 1C, store at low temperature (-20°C) for 6-12 hours, then discharge at 0.2C to 2.5V, measure the discharge capacity, and the ratio of this value to the room-temperature discharge capacity is the discharge capacity retention rate. The discharge capacity retention rates of full cells assembled with negative electrode sheets prepared from relevant samples are detailed in Table 5.

[0244] Table 4

[0245] Table 5

[0246] It can be seen from Tables 4-5 that the battery samples prepared from the composite material samples obtained by preparing the porous carbon material from the coke precursor all have excellent charge capacity, first coulombic efficiency and delithiation rate, and have good discharge capacity retention rate under low temperature environment.

[0247] According to the delithiation GITT results in Figures 7-9, it can be seen that compared with the porous carbon materials obtained from biomass or resin precursors, the composite material samples obtained by the porous carbon materials obtained by the coke precursors in this application have a higher delithiation rate for the battery samples prepared.

[0248] The composite material sample obtained by the porous carbon material obtained from the coke precursor in this application has excellent cycle performance of the battery sample prepared therefrom. As can be seen from the cycle curve shown in Figure 10, the battery sample prepared by the composite material sample in this application has a better capacity retention rate.

[0249] As can be seen from the cycle curves of soft-pack full batteries at different pole piece compaction densities shown in Figures 11-12, the battery samples prepared from the composite material samples obtained by the porous carbon material obtained from the coke precursor in this application have basically no degradation in capacity retention as the pole piece compaction density increases, and can maintain excellent cycle performance. However, for the composite material samples obtained from the biomass precursor, the cycle performance of the battery samples deteriorates as the pole piece compaction density increases.

[0250] Figures 13-15 show the discharge capacity percentages of different test samples under low-temperature conditions. As can be seen from the results in Figures 13-15, compared to porous carbon materials obtained from biomass or resin precursors, the battery samples prepared from the composite material samples obtained from the porous carbon material obtained from the coke precursor in this application have a higher discharge capacity percentage at low temperatures. In other words, the battery samples prepared from the composite material in this application have better tolerance to low-temperature environments.

[0251] It will be apparent to those skilled in the art that many modifications and variations of the present invention may be made without departing from its spirit and scope. The specific embodiments described herein are provided by way of example only and are not intended to be limiting in any way. The true scope and spirit of the present invention are shown by the appended claims, and the description and examples are merely exemplary.

Claims

1. A porous carbon for a negative electrode material, characterized in that, In the Raman spectrum of the porous carbon, the D peak intensity (I D ) and G peak intensity (I G ) ratio (I D / I G ) is 0.10-1.50; in the X-ray diffraction pattern of the porous carbon, the diffraction angle 2θ of the (002) crystal plane is 24.00° - 26.53°; The BET specific surface area of the porous carbon is 600 - 3000 m 2 / g.

2. The porous carbon according to claim 1, characterized in that, In the Raman spectrum of the porous carbon, the ratio (I D ) of the intensity of the D peak (I G ) to the intensity of the G peak (I D / I G ) is 0.10 - 1.10, preferably 0.20 - 0.80, more preferably 0.20 - 0.

70.

3. The porous carbon according to claim 1, characterized in that, The BET specific surface area of the porous carbon is 800 - 2800 m 2 / g, preferably 900 - 2750 m 2 / g.

4. The porous carbon according to claim 1, characterized in that, The pore volume of the porous carbon is 0.50 cm 3 / g or more, preferably 0.60 cm 3 / g or more.

5. The porous carbon according to claim 1, characterized in that, in the X-ray diffraction pattern of the porous carbon, the diffraction angle 2θ of the (002) crystal plane is 24.15° - 26.50°.

6. The porous carbon according to claim 1, characterized in that, the powder resistivity of the porous carbon is 900 mΩ·cm or less, preferably 800 mΩ·cm or less.

7. The porous carbon according to claim 1, characterized in that, The porous carbon has one or more of the following characteristics: The tapped density of the porous carbon is 0.2 - 1.4 g / cm 3 ; the minimum particle size Dmin of the porous carbon is 0.1 - 1.0 μm; the D10 particle size of the porous carbon is 2.0 - 5.0 μm; the D50 particle size of the porous carbon is 5.0 - 15.0 μm; the D90 particle size of the porous carbon is 10.0 - 30.0 μm; the D100 particle size of the porous carbon is 20.0 - 50.0 μm.

8. The porous carbon according to claim 1, characterized in that, the porous carbon is prepared by alkali activation of a porous carbon precursor; preferably, the alkali includes: hydroxides of alkali metals or alkaline earth metals; more preferably, the alkali includes: potassium hydroxide, sodium hydroxide or a combination thereof.

9. The porous carbon according to claim 8, characterized in that, the porous carbon precursor is a soft carbon material, preferably a coke-like or coal-based material, more preferably petroleum coke.

10. The porous carbon according to claim 8, characterized in that, in the X-ray diffraction pattern of the porous carbon precursor, the diffraction angle 2θ of the (002) crystal plane is 25.00° - 26.50°, preferably 25.25° - 26.25°, more preferably 25.40° - 26.00°.

11. The porous carbon according to claim 8, characterized in that, In the Raman spectrum of the porous carbon precursor, the D peak intensity (I D ) and G peak intensity (I G ) ratio (I D / I G ) is 0.30-0.50, preferably 0.35-0.

48.

12. The porous carbon according to claim 8, characterized in that, the powder resistivity of the porous carbon precursor is 5.0 mΩ·cm or less.

13. A method for preparing the porous carbon according to any one of claims 1 - 12, which comprises the following steps: providing a porous carbon precursor; performing alkali activation on the porous carbon precursor to prepare the porous carbon.

14. A composite material for a lithium-ion secondary battery, characterized in that, the composite material includes: the porous carbon according to any one of claims 1 - 12, and, nano-silicon dispersed in the porous carbon; preferably, the nano-silicon dispersed in the porous carbon is hydrogen-containing nano-silicon.

15. The composite material according to claim 14, characterized in that, In the Raman spectrum of the composite material, the D peak intensity (I D ) and G peak intensity (I G ) ratio (I D / I G ) is 0.20-1.50, preferably 0.20-1.

00.

16. The composite material according to claim 14, characterized in that, the composite material has one or more of the following characteristics: the particle size range of the nano-silicon is 0.1 - 60 nm, preferably 0.1 - 20 nm, more preferably 1 - 5 nm; the weight ratio of the nano-silicon to the composite material is 0.3 - 0.7, preferably 0.5 - 0.7; The powder resistivity of the composite material is 1500 Ω·cm or less; The BET specific surface area of the composite material is 30 - 300 m 2 / g; The pore volume of the composite material is 0.2 cm 3 / g or less.

17. The composite material according to claim 14, wherein the composite material further comprises: a shell layer coated on the outer surface of the porous carbon; Preferably, the components of the shell layer include: amorphous carbon, graphene, carbon nanotubes, conductive polymers, titanium carbide, aluminum oxide, aluminum nitride, silicon carbide, silicon nitride, silicon oxide, silicon oxynitride, or a combination thereof.

18. The composite material according to claim 17, wherein based on the total weight of the composite material, its carbon content is 30-70 wt%, preferably 30-50 wt%; based on the total weight of the composite material, its hydrogen content is 0-10 wt%, preferably 0.3-5 wt%; based on the total weight of the composite material, its oxygen content is 0-3 wt%.

19. The composite material according to claim 17, wherein, The composite material has one or more of the following characteristics: The tapped density of the composite material is 0.5 - 2 g / cm 3 ; the powder resistivity of the composite material is 100 Ω·cm or less; The BET specific surface area of the composite material is 10 m 2 / g or less; The pore volume of the composite material is 0.1 cm 3 / g or less.

20. The composite material according to claim 17, wherein in the electrochemical charging curve of the half-cell prepared from the composite material, there is a plateau at 0.4-0.5 V; and / or in the DQ / DV curve of the half-cell prepared from the composite material, there is a characteristic peak at 0.4-0.5 V.

21. A method for preparing the composite material according to any one of claims 14-20, comprising the following steps: providing porous carbon; performing silicon deposition in the porous carbon to form nano-silicon dispersed in the porous carbon; optionally, coating the outer surface of the porous carbon in which nano-silicon is dispersed to form a shell layer.

22. A negative electrode sheet, wherein the negative electrode sheet comprises the composite material according to any one of claims 14-20.

23. A lithium-ion secondary battery, wherein the lithium-ion secondary battery comprises the negative electrode sheet according to claim 22.

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