Carbon material, silicon-carbon composite material and battery

Abstract

The invention provides a carbon material, application of the carbon material, a silicon-carbon composite material, a negative electrode and a battery, and particularly relates to the technical field of carbon materials and secondary batteries. The carbon material has the characteristics of a porous structure and graphitization at the same time, and has the following characteristics: i) the N2 adsorption pore volume is 0.4-2.0 cm < 3 > / g; ii) the N2 adsorption average pore size is 1.8 to 5.0 nm; and (iii) partial graphitization is carried out, disordered carbon and graphitized carbon are compounded, a diffraction peak P exists between 2theta = 25-30 degrees in an XRD (X-Ray Diffraction) pattern, and the grain size of P calculated according to a Scherrer formula is 2-40 nm. The invention also provides a silicon-carbon composite material, the silicon-carbon composite material comprises a porous carbon material and silicon nanoparticles, the porous carbon material comprises the carbon material provided by the invention, and the silicon nanoparticles are located in pore channels of the porous carbon material. The silicon-carbon composite material provided by the invention has the advantages of high capacity, high first efficiency and high cycle stability when being applied to the lithium ion secondary battery.

Description

Technical Field

[0001] It relates to the technical fields of carbon materials and secondary battery technologies, and in particular to a carbon material, a silicon-carbon composite material and their applications in secondary batteries. Background Art

[0002] Graphite is the negative electrode material in traditional lithium-ion secondary batteries and is still widely used in lithium-ion batteries at present. Its lithium intercalation follows the interlayer lithium intercalation mechanism (Li x C6), and the theoretical capacity is 387 mAh / g. Silicon is a type of alloying lithium intercalation material, and its theoretical lithium intercalation capacity at room temperature is as high as 3579 mAh / g (Li 15 Si4), which has become the preferred active material for new lithium-ion batteries. In order to overcome the problems of poor conductivity and large volume expansion during lithium intercalation of silicon materials themselves, researchers have developed silicon-carbon composite materials. Using porous carbon as a carrier, silicon nanoparticles are in-situ grown in the pores of the porous carbon by chemical vapor deposition of silicon-containing gas. The obtained silicon-carbon composite materials can have a higher capacity, and the volume expansion and cycle stability are much higher than those of granular silicon. However, since the porous carbon in the silicon-carbon composite material is hard carbon and there are many bulk phase defects, the first Coulomb efficiency of the composite material is low and it is difficult to improve by process control means. Therefore, designing and manufacturing porous carbon with fewer defects is expected to fundamentally improve the first efficiency of the silicon-carbon composite material, which is also the key technical problem for this application requirement.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The first object of the present invention is to provide a carbon material, which has the characteristics of both a porous structure and graphitization, and solves the problem of many bulk phase defects in current ordinary porous carbon.

[0005] The second object of the present invention is to provide a preparation method of the carbon material.

[0006] The third object of the present invention is to provide an application of the carbon material.

[0007] The fourth object of the present invention is to provide a silicon-carbon composite material, using partially graphitized porous carbon as a carrier, depositing silicon by chemical vapor deposition to obtain a silicon-carbon composite material, and solving the problem of low first Coulomb efficiency of current silicon-carbon composite materials.

[0008] The fifth object of the present invention is to provide a negative electrode.

[0009] The sixth object of the present invention is to provide a battery.

[0010] To achieve the objects of the present invention, the following technical solutions are adopted: The first aspect of the present invention provides a carbon material, which is a porous carbon material and has the following characteristics: i) the N2 adsorption pore volume is 0.4 - 2.0 cm 3 / g; ii) the average N2 adsorption pore diameter is 1.8 - 5.0 nm; iii) partially graphitized, being a composite of disordered carbon and graphitized carbon, and there is a diffraction peak P in its XRD pattern between 2 θ = 25 - 30°, and the grain size of P calculated according to the Scherrer formula is 2 - 40 nm.

[0011] The second aspect of the present invention provides a preparation method of a carbon material, the carbon material comprising the carbon material described in the first aspect of the present invention, and the preparation method includes the following steps, Step S1, pyrolytic carbonization of a carbon precursor in an inert atmosphere to obtain porous carbon 1; the carbon precursor includes one or more of thermoplastic phenolic resin, thermosetting phenolic resin, ion exchange resin, epoxy resin, biomass, coal, and petroleum coke; the temperature of the pyrolytic carbonization is 500 - 1000 °C; Step S2, crushing the porous carbon 1 obtained in step S1 to obtain porous carbon 1 particles; the particle size of the porous carbon 1 particles d v50 is 4 - 1000 μm; Step S3, treating the porous carbon 1 particles obtained in step S2 in an atmosphere of H2O or CO2 at 700 - 1000 °C to obtain porous carbon 2 particles; Step S4, performing high-temperature heat treatment on the porous carbon 2 particles obtained in step S3 to obtain the carbon material; the temperature of the heat treatment is 1000 - 3000 °C, preferably 1200 - 2000 °C, and the atmosphere of the heat treatment is N2 or Ar; Optionally, before or after the above step S4, the porous carbon particles are crushed and classified, and the particle size of the obtained carbon material d v50 is 4 - 20 μm.

[0012] Or the preparation method includes the following steps: Step S1, pyrolytic carbonization of a carbon precursor in an inert atmosphere to obtain porous carbon 1; the carbon precursor includes one or more of thermoplastic phenolic resin, thermosetting phenolic resin, ion exchange resin, epoxy resin, biomass, coal, and petroleum coke; the temperature of the pyrolytic carbonization is 500 - 1000 °C; Step S2, crushing the porous carbon 1 obtained in step S1 to obtain porous carbon 1 particles; the particle size of the porous carbon 1 particles d v50 is 4 - 1000 μm; Step S3: Mix the porous carbon 1 particles obtained in Step S2 with a strong base, and treat the mixture at 500 - 1000 °C in an inert atmosphere. After pickling, washing with water, and drying the obtained material, porous carbon 2 particles are obtained; the strong base is one or more of KOH, NaOH, K2CO3, and Na2CO3, preferably KOH; Step S4: Perform high-temperature heat treatment on the porous carbon 2 particles obtained in Step S3 to obtain the carbon material; the temperature of the heat treatment is 1000 - 3000 °C, preferably 1200 - 2000 °C, and the atmosphere of the heat treatment is N2 or Ar; Optionally, before or after the above Step S4, the porous carbon particles are crushed and classified, and the particle size of the obtained carbon material d v50 is 4 - 20 μm.

[0013] Or the preparation method includes the following steps: Step S1: Mix the biomass precursor with an aqueous H3PO4 solution to obtain a mixed precursor; the mass ratio of the biomass precursor to H3PO4 is 1:0.5 - 5; Step S2: Dry and cure the mixed precursor obtained in Step S1 to obtain a cured precursor; the temperature of the drying and curing is 120 - 220 °C, and the atmosphere of the drying and curing is one or more of O2, N2, and Ar; Step S3: Sinter the cured precursor obtained in Step S2 to obtain porous carbon 1; the temperature of the sintering is 300 - 700 °C, and the atmosphere of the sintering is one or more of O2, N2, and Ar; Step S4: Wash and dry the porous carbon 1 obtained in Step S3 to obtain porous carbon 2; the content of P element in the porous carbon 2 is less than 500 ppm, preferably less than 200 ppm, and more preferably less than 100 ppm; Step S5: Perform high-temperature heat treatment on the porous carbon 2 obtained in Step S4 to obtain the carbon material; the temperature of the heat treatment is 1000 - 3000 °C, preferably 1200 - 2000 °C, and the atmosphere of the heat treatment is N2 or Ar; Optionally, before or after the above Step S5, the porous carbon particles are crushed and classified, and the particle size of the obtained carbon material d v50 is 4 - 20 μm.

[0014] The third aspect of the present invention provides an application of a carbon material, which comprises the carbon material provided by the first aspect of the present invention or the carbon material obtained by the preparation method according to the second aspect of the present invention. The application of the carbon material includes the use of the carbon material as a catalyst, a porous support, a hard carbon precursor, a graphite precursor, capacitive carbon, an adsorbent, and a drug carrier.

[0015] The fourth aspect of the present invention provides a silicon-carbon composite material, which comprises a porous carbon material and silicon nanoparticles. The porous carbon material comprises the carbon material provided by the first aspect of the present invention or the carbon material obtained by the preparation method according to the second aspect of the present invention. The silicon nanoparticles are located in the pores of the porous carbon material.

[0016] The fifth aspect of the present invention provides a negative electrode, which comprises a negative electrode active material, and the negative electrode active material comprises the silicon-carbon composite material as described in the fourth aspect of the present invention.

[0017] The sixth aspect of the present invention provides a battery, which comprises a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode comprises the silicon-carbon composite material as described in the fourth aspect of the present invention.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The carbon material provided by the present invention, after being activated under relatively strong conditions and then subjected to high-temperature treatment, is graphitized to a certain extent and can maintain a relatively large pore volume. The pore volume of the carbon material is 0.4 - 2.0 cm 3 / g, the average pore diameter is 1.8 - 5.0 nm, and there is an obvious graphite peak between 2 θ = 25 - 30°. The thickness of its ordered graphite lamellae calculated according to the Scherrer formula is 2 - 40 nm, and there are fewer bulk defects. This special carbon material simultaneously has the large pore volume of porous carbon and the ordered carbon layer structure of graphite material, which is beneficial to better play its role in the fields of catalyst, porous support, hard carbon precursor, graphite precursor, capacitive carbon, adsorbent, and drug carrier.

[0019] The silicon-carbon composite material provided by the present invention is obtained by depositing silicon using the carbon material provided by the present invention as a matrix. Since the carbon material simultaneously exhibits the characteristics of being porous and partially graphitized, and has fewer bulk defects in the carbon material, the obtained silicon-carbon composite material exhibits a relatively high initial Coulomb efficiency. The initial efficiency at 0.8 V can reach more than 88%, approaching that of graphite-based silicon-carbon composite materials, and significantly higher than that of silicon-carbon composite materials obtained from ordinary porous carbon materials.

[0020] The porous carbon material provided by the present invention is used as a matrix. Its rich pore structure can accommodate a large amount of silicon, and the composite material can achieve the same high specific capacity as that of ordinary porous carbon-based silicon-carbon materials. The framework structure of the porous carbon material well restricts the growth of silicon grains. At the same time, for porous carbon materials with larger pore diameters, a precursor containing impurity atoms can be introduced for silicon deposition simultaneously. The impurity-containing precursor further forms a restraint and spacing for the growth of silicon nanoparticles, inhibiting the growth of silicon nanoparticles during the deposition process and the volume effect of the composite material during the electrochemical cycling process. Therefore, the silicon-carbon composite materials of the present invention all exhibit good cycle stability, significantly higher than that of graphite-based silicon-carbon composite materials. BRIEF DESCRIPTION OF THE DRAWINGS <e

[0021] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0022] Figure 1 XRD pattern of the carbon material obtained in Example 1.

[0023] Figure 2 XRD pattern of the carbon material obtained in Example 4.

[0024] Figure 3 XRD pattern of the carbon material obtained in Comparative Example 1.

[0025] Figure 4 Schematic diagram for calculating I / I 1 from the XRD pattern of the carbon material.

[0026] Figure 5 SEM image of the carbon material obtained in Example 7.

[0027] Figure 6 SEM image of the carbon material obtained in Comparative Example 4. [[ID=)34]] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] The following will describe the embodiments of the present invention in detail in combination with the embodiments and examples. However, those skilled in the art will understand that the following embodiments and examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope protected by the present invention.

[0029] The first aspect of the present invention provides a carbon material, which has the following characteristics: The N2 adsorption pore volume is 0.4 - 2.0 cm 3 / g; The average N2 adsorption pore diameter is 1.8 - 5.0 nm; Partially graphitized, a composite of disordered carbon and graphitized carbon, with a diffraction peak P in its XRD pattern between 2 θ = 25 - 30°, and the crystallite size of P calculated according to the Scherrer formula is 2 - 40 nm.

[0030] Carbon materials are classified into hard carbon and soft carbon according to the arrangement of their carbon atom layers. Soft carbon has a smaller interlayer spacing of carbon atom layers and most of them are arranged parallel and orderly. A typical example is graphite, with an interlayer spacing of 0.334 nm, and there is a sharp graphite peak in its XRD pattern at 2 θ = 26.4°; most of its carbon atoms exist in the form of sp hybridization, and the material has good conductivity. In hard carbon, the carbon atom layers are disordered and there is no ordered graphitized structure. Its XRD pattern shows a broadened peak envelope at 2 θ = 18 - 30°, and there is no obvious graphite peak. Hard carbon is usually difficult to graphitize. The porous carbon used in applications such as catalysts, adsorbents, and porous carriers is usually hard carbon.

[0031] The carbon material provided by the present invention has both porous and partially graphitized properties at the same time. Its pore volume is 0.4 - 2.0 cm 3 / g; and the carbon material is not ordinary expanded graphite, but has a porous structure with both micropores and mesopores, and its average pore diameter is 1.8 - 5.0 nm. The pore volume of the carbon material V is obtained according to the maximum adsorption amount in the N2 adsorption test when p / p 0 > 0.99. The specific surface area of the carbon material can be obtained by multi-point BET calculation A , and then the average pore diameter D = 4 V / A *1000 (nm). The pore distribution of the carbon material can be estimated by the average pore diameter. When the average pore diameter D < 2 nm, the proportion of its micropores is usually greater than 80%.

[0032] The graphitization degree of the carbon material can be characterized by XRD and Raman tests. For the long-range ordered graphite sheet structure, a sharp diffraction peak can be observed at 2 θ = 26.4° by X-ray diffraction method (XRD), which reflects the ordered structure of graphite in the c axis (002) direction, and the corresponding interlayer spacing of the carbon hexagonal network plane d 002 = 0.337 nm; the turbostratic graphite structure carbon is long-range disordered and at 2 θ=A broad peak envelope appears in the range of 18~30°, and the peak value is at 2 θ =between 18~25°. The graphitized part in the carbon material will show up as 2 in XRD θ =a crystallization peak near 26.4°. The sharper the graphitized crystallization peak, the higher the degree of graphitization. The sharpness of the XRD peak can be represented by the full width at half maximum and the grain size calculated according to the Scherrer formula. The sharper it is, the smaller the full width at half maximum and the larger the grain size. The carbon material at 2 θ =the grain size of the crystallization peak near 26.4° L c , which reflects the stacking thickness of the carbon hexagonal network plane layers in the graphitized part, and this is an important physical quantity characterizing its degree of graphitization. In the XRD pattern of graphite, the peak at 2 θ =42.2° is the diffraction peak of the (100) crystal plane, and its grain size reflects the in-plane size of the carbon hexagonal network plane layers L a , and can also reflect the degree of graphitization of the carbon material. Since the carbon material of the present invention is partially graphitized carbon, its (100) diffraction peak sometimes cannot be well resolved into peaks. Therefore, the present invention only collects and compares the grain size of the crystallization peak near 2 θ =26.4° L c [[ID=!9]]for expression of the degree of graphitization of the carbon material.

[0033] In the Raman spectrum curve of the carbon material, there are two characteristic peaks. The peak with a peak value between 1310~1360 cm -1 is the disorder peak (D peak); the peak between 1560~1610 cm -1 is the graphite peak (G peak). The degree of disorder or graphitization of the carbon material can be characterized by the intensity ratio of the D peak to the G peak ( I D / I G ). [[ID=!3]] I D / I G The smaller it is, the lower the degree of disorder and the higher the degree of graphitization.

[0034] In the XRD pattern of the carbon material, it shows the characteristics of partial graphitization, which is neither the same as that of graphite materials with only sharp graphite peaks between 18~30° in 2, nor the same as that of ordinary porous hard carbon showing broadened peaks. Instead, there are both broadened diffraction peaks P1 in the low-angle region and 2 in the high-angle region θ =18~30° with only sharp graphite peaks, nor the same as ordinary porous hard carbon showing broadened peaks, but there are both broadened diffraction peaks P1 in the low-angle region and 2 in the high-angle region θGraphite peak P between = 25~30°. The full width at half maximum of the P peak is affected by the degree of graphitization in the carbon material. According to the Scherrer formula, the grain size of the P peak, that is, the thickness of the orderly arranged graphite sheets, can be calculated from the peak position and the full width at half maximum. The grain size corresponding to the P peak of the carbon material provided by the present invention is 2~40 nm.

[0035] In some embodiments, in the carbon material, the N2 adsorption pore volume is 0.4~1.5 cm 3 / g, preferably 0.6~1.3 cm 3 / g, specifically for example 0.4~0.5 cm 3 / g, 0.5~0.6 cm 3 / g, 0.6~0.7 cm 3 / g, for example 0.7~0.8 cm 3 / g, for example 0.8~0.9 cm 3 / g, for example 0.9~1.0 cm 3 / g, for example 1.0~1.1 cm 3 / g, for example 1.1~1.2 cm 3 / g, for example 1.2~1.3 cm 3 / g, 1.3~1.4 cm 3 / g, 1.4~1.5 cm 3 / g; In some embodiments, the average N2 adsorption pore diameter is 1.8~4.0 nm, preferably 1.8~3.0 nm, specifically for example 1.8~1.9 nm, 1.8~2.1 nm, 1.8~2.5 nm, 1.8~2.8 nm, 1.8~3.0 nm, 1.8~3.5 nm, 2.0~4.0 nm, 2.0~3.5 nm, 2.0~3.0 nm, 2.0~2.5 nm, 2.5~4.0 nm, 2.5~3.5 nm, 2.5~3.0 nm, 3.0~4.0 nm; In some embodiments, the grain size of the P peak in the XRD pattern is 2~30 nm, preferably 2~20 nm, specifically for example 2~28 nm, 2~25 nm, 2~20 nm, 2~15 nm, 2~10 nm, 2~5 nm, 5~30 nm, 5~25 nm, 5~20 nm, 5~15 nm, 5~10 nm, 10~30 nm, 10~25 nm, 10~20 nm, 10~15 nm, 20~30 nm, 20~25 nm; In some embodiments, there is a diffraction peak P1 in the XRD pattern between 2 θ = 18~25°, and the intensity of the P peak I and the intensity of the P1 peak IThe ratio of 1 is I / I 1, I / I The value of 1 is 0.5 to 20, preferably 0.8 to 10, specifically for example 0.5 to 18, 0.5 to 15, 0.5 to 10, 0.5 to 5, 0.8 to 20, 0.8 to 15, 0.8 to 10, 0.8 to 5, 1 to 20, 1 to 15, 1 to 10, 1 to 5, 2 to 20, 2 to 15, 2 to 10, 2 to 5, 5 to 20, 5 to 15, 5 to 10, 5 to 8, 8 to 20, 8 to 15, 8 to 10, 15 to 20; In some embodiments, in the Raman spectrum I D / I G The value is 0.2 to 2.0, preferably 0.4 to 1.2, specifically for example 0.2 to 1.8, 0.2 to 1.6, 0.2 to 1.4, 0.2 to 1.2, 0.2 to 1.0, 0.2 to 0.8, 0.2 to 0.6, 0.2 to 0.4, 0.4 to 2.0, 0.4 to 1.8, 0.4 to 1.6, 0.4 to 1.4, 0.4 to 1.2, 0.4 to 1.0, 0.4 to 0.8, 0.4 to 0.6, 0.6 to 2.0, 0.6 to 1.8, 0.6 to 1.6, 0.6 to 1.4, 0.6 to 1.2, 0.6 to 1.0, 0.6 to 0.8, 0.8 to 2.0, 0.8 to 1.8, 0.8 to 1.6, 0.8 to 1.4, 0.8 to 1.2, 0.8 to 1.0, 1.0 to 2.0, 1.0 to 1.8, 1.0 to 1.6, 1.0 to 1.4, 1.0 to 1.2, 1.2 to 2.0, 1.2 to 1.8, 1.2 to 1.6, 1.2 to 1.4, 1.4 to 2.0, 1.4 to 1.8, 1.4 to 1.6, 1.6 to 2.0, 1.6 to 1.8, 1.8 to 2.0.

[0036] In some embodiments, the proportion of the pore volume less than 2 nm in the total pore volume of the carbon material is 20 to 90%, the proportion of the pore volume of 2 to 5 nm in the total pore volume is 10 to 50%, and the proportion of the pore volume of 5 to 10 nm in the total pore volume is 0 to 30%; the proportion of the pore volume greater than 10 nm in the total pore volume is 0 to 10%. Excessive large mesopore volume will cause the carbon material structure to be loose, and when the carbon material is used as the carrier of the silicon-carbon composite material, it is easy to cause the silicon nanoparticle size to be too large, resulting in a decrease in the cycle stability of the anode material.

[0037] The second aspect of the present invention provides a method for preparing a carbon material.

[0038] In some embodiments, the preparation method of the carbon material comprises the following steps: obtained by pyrolytic carbonization of a carbon precursor, activation with water or CO2, and high-temperature treatment; in some embodiments, the preparation method of the carbon material comprises the following steps: obtained by pyrolytic carbonization of a carbon precursor, alkali activation, washing, and high-temperature treatment; in some embodiments, the preparation method of the carbon material comprises the following steps: obtained by phosphoric acid activation, washing, and high-temperature treatment of a carbon precursor.

[0039] In some embodiments, the preparation method of the carbon material includes the following steps: Step S1, pyrolytically carbonize the carbon precursor in an inert atmosphere to obtain porous carbon 1; wherein, the carbon precursor comprises one or more of thermoplastic phenolic resin, thermosetting phenolic resin, ion exchange resin, epoxy resin, biomass, coal, and petroleum coke; the temperature of pyrolytic carbonization is 500 - 1000 °C; Step S2, crush the porous carbon 1 obtained in step S1 to obtain porous carbon 1 particles; the particle size of the porous carbon 1 particles d v50 is 4 - 1000 μm; Step S3, treat the porous carbon 1 particles obtained in step S2 at 700 - 1000 °C in an atmosphere of H2O or CO2 to obtain porous carbon 2 particles; Step S4, perform high-temperature heat treatment on the porous carbon 2 particles obtained in step S3 to obtain the carbon material; the temperature of the heat treatment is 1000 - 3000 °C, preferably 1200 - 2000 °C, and the atmosphere of the heat treatment is N2 or Ar; Optionally, before or after step S4, crush and classify the porous carbon particles, and the final particle size of the carbon material d v50 is 4 - 20 μm.

[0040] In some embodiments, the preparation method of the carbon material includes the following steps: Step S1, pyrolytically carbonize the carbon precursor in an inert atmosphere to obtain porous carbon 1; wherein, the carbon precursor comprises one or more of thermoplastic phenolic resin, thermosetting phenolic resin, ion exchange resin, epoxy resin, biomass, coal, and petroleum coke; the temperature of pyrolytic carbonization is 500 - 1000 °C; Step S2, crush the porous carbon 1 obtained in step S1 to obtain porous carbon 1 particles; the particle size of the porous carbon 1 particles d v50 is 4 - 1000 μm; Step S3: Mix the porous carbon 1 particles obtained in Step S2 with a strong base, and treat the mixture at 500 - 1000 °C in an inert atmosphere. After pickling, washing with water, and drying the obtained material, porous carbon 2 particles are obtained; the strong base is one or more of KOH, NaOH, K2CO3, and Na2CO3, preferably KOH; Step S4: Perform high-temperature heat treatment on the porous carbon 2 particles obtained in Step S3 to obtain a carbon material; the heat treatment temperature is 1000 - 3000 °C, preferably 1200 - 2000 °C, and the heat treatment atmosphere is N2 or Ar; Optionally, before or after Step S4, the porous carbon particles are crushed and classified, and the final particle size of the carbon material d v50 is 4 - 20 μm.

[0041] In some embodiments, the preparation method of the carbon material includes the following steps: Step S1: Mix the biomass precursor with an aqueous H3PO4 solution to obtain a mixed precursor; the mass ratio of the biomass precursor to H3PO4 is 1:0.5 - 5, where the biomass precursor includes one or more of sawdust, bamboo powder, straw, fruit shell, coconut shell, palm fiber, lignin, cellulose, and starch; optionally, a first additive can be added to the mixture in Step S1 for blending. The first additive is an oxidant. Preferably, the first additive includes one or more of H2SO4, HNO3, H2O2, KMnO4, K2Cr2O7, KClO3, maleic anhydride, benzenesulfonic acid, and p-toluenesulfonic acid; optionally, a second additive can also be added. The second additive is a hetero-element additive. Preferably, the second additive includes one or more of boric acid, silica sol, silicic acid, tetraethyl orthosilicate, tetraacetic acid titanate, tetraisopropyl titanate, titanium oxysulfate, titanium tetrachloride, alumina, aluminum hydroxide monohydrate, aluminum hydroxide, aluminum phosphate, and lithium aluminum titanium phosphate; preferably, a third additive can also be added. The third additive is potassium humate or potassium fulvate; optionally, the biomass precursor is in powder or particle form. The particle size of the powder is 5 - 150 μm, and the particle size of the particle is 0.15 - 3 mm; Step S2: Dry and cure the mixed precursor obtained in Step S1 to obtain a cured precursor; the drying and curing temperature is 120 - 220 °C, and the drying and curing atmosphere is one or more of O2, N2, and Ar; Step S3: Sinter the cured precursor obtained in Step S2 to obtain porous carbon 1; the sintering temperature is 300 - 700 °C, and the sintering atmosphere is one or more of O2, N2, and Ar; Step S4: Wash and dry the porous carbon 1 obtained in step S3 to obtain porous carbon 2. The content of P element in the porous carbon 2 is less than 500 ppm, preferably less than 200 ppm, and more preferably less than 100 ppm. Step S5: Perform high-temperature heat treatment on the porous carbon 2 obtained in step S4 to obtain a carbon material. The heat treatment temperature is 1000 - 3000 °C, preferably 1200 - 2000 °C, and the heat treatment atmosphere is N2 or Ar. Optionally, before or after step S5, the porous carbon particles are crushed and classified, and the final particle size of the carbon material d v50 is 4 - 20 μm. In some embodiments, there is a crushing and classification step between step S2 and step S3, or between step S3 and step S4, or between step S4 and step S5, or after step S5. The particle size of the classified carbon material powder obtained d v50 is 4 - 20 μm.

[0042] The third aspect of the present invention provides the application of the carbon material. The carbon material includes the carbon material as described in the first aspect of the present invention or the carbon material obtained by the preparation method according to the second aspect of the present invention. The application of the carbon material includes the application of the carbon material as a catalyst, a porous carrier, a hard carbon precursor, a graphite precursor, a capacitive carbon, an adsorbent, and a drug carrier.

[0043] The fourth aspect of the present invention provides a silicon-carbon composite material. The silicon-carbon composite material includes a porous carbon material and silicon nanoparticles. The porous carbon material includes the carbon material as described in the first aspect of the present invention or the carbon material obtained by the preparation method according to the second aspect of the present invention. The silicon nanoparticles are located in the pores of the porous carbon material.

[0044] Using the low-defect and partially graphitized porous carbon material provided by the first aspect of the present invention as the porous carbon skeleton can overcome the problem of low initial Coulomb efficiency of the composite material when ordinary porous carbon is used as the skeleton in the prior art, and a high initial efficiency silicon-carbon composite material can be obtained. It is more excellent than the graphite-silicon composite material with graphite as the silicon carrier. The latter has a very low specific surface area of graphite, so it is impossible to obtain a high silicon content, resulting in a lower capacity. Moreover, the relatively large silicon particles on the graphite surface also lead to poor cycle stability of the composite material.

[0045] In some embodiments, the specific surface area of the silicon-carbon composite material is 0.1 - 50 cm 3 / g, preferably 0.1 - 10 cm 3 / g, and more preferably 0.1 - 3 cm 3 / g; In some embodiments, the content of silicon element in the silicon-carbon composite material is 30 - 70 wt.%. In some embodiments, the lithium insertion capacity of the half-cell button battery at 0.8 V is 1000-2500 mAh / g, preferably 1400-2200 mAh / g; In some embodiments, the first efficiency of the half-cell button battery of the silicon-carbon composite material is greater than 87% at 0.8 V.

[0046] In some embodiments, the silicon-carbon composite material is obtained by chemical vapor deposition of a silicon-containing precursor on a porous carbon material at 150-1000 °C; preferably, the silicon-containing precursor is selected from one or more of silane, disilane, trisilane, halogenated silane, polysilane, silole and its derivatives, silafluorene and its derivatives.

[0047] In some embodiments, introducing a heteroatom-containing precursor during the chemical vapor deposition process can play a role in spacing and binding the deposition of silicon nanoparticles, which is particularly important in the silicon-carbon composite material with a large pore diameter porous matrix. Among them, the heteroatom-containing precursor includes at least one of an oxygen-containing precursor, a carbon-containing precursor, a nitrogen-containing precursor, a phosphorus-containing precursor, a sulfur-containing precursor or a boron-containing precursor.

[0048] In some embodiments, the ways in which the silicon-containing precursor and the heteroatom-containing precursor contact the porous matrix include: the silicon-containing precursor and the heteroatom-containing precursor alternately contact the porous matrix; or, the silicon-containing precursor and the heteroatom-containing precursor contact the porous matrix simultaneously; or, the silicon-containing precursor and a mixed gas containing the silicon-containing precursor and the heteroatom-containing precursor alternately contact the porous matrix. Preferably, the silicon-containing precursor continuously contacts the porous matrix, and the heteroatom-containing precursor is intermittently introduced during this process.

[0049] In some embodiments, the silicon-carbon composite material includes a coating layer on the surface of the silicon-carbon composite material; preferably, the material of the coating layer is selected from at least one of a solid electrolyte, a conductive polymer, a carbonaceous material, a metal, an alloy, a metal oxide, a metal hydroxide, a halogen-containing compound, a nitrogen-containing compound, a phosphorus-containing compound, a boron-containing compound, a sulfur-containing compound; more preferably, the material of the coating layer is a carbonaceous material.

[0050] The fifth aspect of the present invention provides a negative electrode, which includes a negative electrode active material, and the negative electrode active material includes the silicon-carbon composite material provided in the fourth aspect of the present invention. Specifically, the silicon-carbon composite material provided in the fourth aspect of the present invention is used as the negative electrode active material, and is stirred and mixed evenly with a conductive agent Super P, a binder polyacrylic acid and a solvent deionized water according to a certain mass ratio, and then evenly coated on the negative electrode current collector. Preferably, the mass ratio is 95:1:4:120, and then dried to obtain the negative electrode.

[0051] The sixth aspect of the present invention provides a battery, which includes a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode includes the silicon-carbon composite material provided by the fourth aspect of the present invention. Specifically, the positive electrode and the negative electrode provided by the fifth aspect of the present invention are separated by a separator to form a battery core, which is then encapsulated into an aluminum-plastic bag or an aluminum-plastic shell. An electrolyte with a corresponding capacity is injected into the aluminum-plastic bag or the aluminum-plastic shell, and the battery is obtained after vacuum sealing. Optionally, the positive electrode can be selected from one of lithium iron phosphate, lithium cobaltate, lithium manganate, and ternary materials, and the separator can be selected from one of polyethylene and polypropylene.

[0052] The present invention will be further illustrated by specific examples and comparative examples below. However, it should be understood that these examples are only for more detailed illustration and should not be construed as limiting the present invention in any form. For the raw materials used in the examples and comparative examples of the present invention, unless otherwise specified, they are carried out under conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0053] 1. Carbon material Example 1

[0054] This example provides a carbon material, and its preparation method is as follows: Step S1, sucrose is pre-oxidized at 220 °C and then pyrolytically carbonized at 800 °C in an inert atmosphere to obtain porous carbon 1; Step S2, the porous carbon 1 obtained in step S1 is crushed and sieved to obtain particles between 10 and 20 mesh to obtain porous carbon 1 particles; Step S3, the porous carbon 1 particles obtained in step S2 are treated in an H2O atmosphere at 930 °C to obtain porous carbon 2 particles; tStep S4, the porous carbon 2 particles obtained in step S3 are subjected to high-temperature heat treatment to obtain a carbon material; the temperature of the heat treatment is 2100 °C and the atmosphere is N2.

[0055] The N2 adsorption pore volume of the carbon material obtained in this example is 0.44 cm 3 / g, the specific surface area is 361 m 2 / g, and the average pore diameter is 4.86 nm. The XRD pattern of the obtained carbon material is as Figure 1 shown, in which there are two peaks, P1 and P, located at 2 θ = 23.7° and 2 θ = 25.9° respectively. By removing the background, peak fitting, and calculating the grain size of the peak at 2 θ = 25.9° according to the Scherrer formula, its grain size can be obtained as 28.5 nm. The intensity of the P peak in the XRD pattern I and the intensity of the P1 peak I 1 ratio isI / I 1, I / I The value of 1 is 6.1; in the Raman spectrum I D / I G The value is 0.58. Example 2

[0056] This example provides a carbon material, and its preparation method is as follows: Step S1: Pyrolyze and carbonize the mixture of epoxy resin and anthracite in an inert atmosphere at 700 °C to obtain porous carbon 1; Step S2: Crush the porous carbon 1 obtained in step S1 and sieve it to obtain particles between 100 and 200 meshes to obtain porous carbon 1 particles; Step S3: Mix the porous carbon 1 particles obtained in step S2 with KOH, where the mass ratio of the porous carbon 1 particles to KOH is 1:3, and treat the mixture at 900 °C in an inert atmosphere. The obtained material is washed with acid, washed with water, and dried to obtain porous carbon 2 particles; Step S4: Perform high-temperature heat treatment on the porous carbon 2 particles obtained in step S3 to obtain a carbon material; the temperature of the heat treatment is 1600 °C, and the atmosphere is N2. Example 3

[0057] This example provides a carbon material, and its preparation method is as follows: Step S1: Mix 100-200 mesh pine sawdust with an aqueous H3PO4 solution to obtain a mixed precursor; the mass ratio of the pine sawdust to H3PO4 is 1:2.5, and the concentration of the phosphoric acid aqueous solution is 72 wt.%; Step S2: Dry and cure the mixed precursor obtained in step S1 in a forced-air drying oven to obtain a cured precursor; the temperature of the drying and curing is 150 °C; Step S3: Sinter the cured precursor obtained in step S2 in an air atmosphere to obtain porous carbon 1; the sintering temperature is 400 °C; Step S4: Wash and dry the porous carbon 1 obtained in step S3 to obtain porous carbon 2; the content of P element in the porous carbon 2 is less than 100 ppm; Step S5: Perform high-temperature heat treatment on the porous carbon 2 obtained in step S4 to obtain a carbon material; the temperature of the heat treatment is 1400 °C and the atmosphere is N2. Example 4

[0058] This example provides a carbon material, and its preparation method is as follows: Step S1: Sucrose is pre-oxidized at 220 °C and then pyrolytically carbonized at 600 °C in an inert atmosphere to obtain porous carbon 1; Step S2: The porous carbon 1 obtained in Step S1 is crushed and sieved to obtain particles between 10 and 20 mesh, resulting in porous carbon 1 particles; Step S3: The porous carbon 1 particles obtained in Step S2 are treated at 930 °C in an H2O atmosphere to obtain porous carbon 2 particles; Step S4: The porous carbon 2 particles obtained in Step S3 are subjected to high-temperature heat treatment to obtain a carbon material; the heat treatment temperature is 1600 °C and the atmosphere is N2. Example 5

[0059] This example provides a carbon material, and its preparation method is as follows: Step S1: Sucrose is pre-oxidized at 220 °C and then pyrolytically carbonized at 600 °C in an inert atmosphere to obtain porous carbon 1; Step S2: The porous carbon 1 obtained in Step S1 is crushed and sieved to obtain particles between 100 and 200 mesh, resulting in porous carbon 1 particles; Step S3: The porous carbon 1 particles obtained in Step S2 are mixed with KOH, where the mass ratio of the porous carbon 1 particles to KOH is 1:3, and the mixture is treated at 900 °C in an inert atmosphere. The obtained material is washed with acid, washed with water, and dried to obtain porous carbon 2 particles; Step S4: The porous carbon 2 particles obtained in Step S3 are subjected to high-temperature heat treatment to obtain a carbon material; the heat treatment temperature is 3000 °C and the atmosphere is N2. Example 6

[0060] This example provides a carbon material, and its preparation method is as follows: Step S1: Sucrose is pre-oxidized at 220 °C and then pyrolytically carbonized at 600 °C in an inert atmosphere to obtain porous carbon 1; Step S2: The porous carbon 1 obtained in Step S1 is crushed and sieved to obtain particles between 100 and 200 mesh, resulting in porous carbon 1 particles; Step S3: The porous carbon 1 particles obtained in Step S2 are mixed with KOH, where the mass ratio of the porous carbon 1 particles to KOH is 1:3, and the mixture is treated at 900 °C in an inert atmosphere. The obtained material is washed with acid, washed with water, and dried to obtain porous carbon 2 particles; Step S4: The porous carbon 2 particles obtained in Step S3 are subjected to high-temperature heat treatment to obtain a carbon material; the heat treatment temperature is 1200 °C and the atmosphere is N2. Comparative Example 1

[0061] This comparative example provides a carbon material, and its preparation method is as follows: Step S1: Sucrose is pre-oxidized at 200 °C and then pyrolytically carbonized at 800 °C in an inert atmosphere to obtain porous carbon 1. Step S2: The porous carbon 1 obtained in Step S1 is crushed and sieved to obtain particles between 10 and 20 mesh, resulting in porous carbon 1 particles. Step S3: The porous carbon 1 particles obtained in Step S2 are treated in an H2O atmosphere at 820 °C to obtain porous carbon 2 particles. Comparative Example 2

[0062] This comparative example provides a carbon material, which is commercially available flake graphite (Qingdao Tianheda Graphite Co., Ltd., 80 mesh).

[0063] 2. Silicon-carbon composite Example 7

[0064] This example provides a silicon-carbon composite, and its preparation method is as follows: Step S1: Provide a porous carbon material, which is the carbon material obtained in Example 1. Step S2: Crush and classify the porous carbon in Step S1 to obtain d v50 Porous carbon powder with a particle size of 8 μm. Step S3: Place the porous carbon powder obtained in Step S2 in a tubular furnace, heat it from room temperature to 550 °C at a rate of 2 °C / min in an N2 atmosphere; then change to a 20% SiH4 - 0.05% O2 - N2 mixed gas, and keep it at 550 °C for 10 h in the 20% SiH4 - 0.05% O2 - N2 mixed atmosphere; change to a 10% C2H2 - N2 mixed gas and keep it at 600 °C for 30 min; then naturally cool down in an N2 atmosphere to obtain the silicon-carbon composite. Example 8

[0065] This example provides a silicon-carbon composite, and its preparation method is as follows: Step S1: Provide a porous carbon material, which is the carbon material obtained in Example 2. Step S2: Crush and classify the porous carbon in Step S1 to obtain d v50 Porous carbon powder with a particle size of 8 μm. Step S3: Place the porous carbon powder obtained in Step S2 in a tubular furnace, heat it from room temperature to 550 °C at a rate of 2 °C / min in an N2 atmosphere; then change to a 20% SiH4 - N2 mixed gas, and keep it at 550 °C for 50 h in the 20% SiH4 - N2 mixed atmosphere; change to a 10% C2H2 - N2 mixed gas and keep it at 600 °C for 2 h; then naturally cool down in an N2 atmosphere to obtain the silicon-carbon composite. Example 9

[0066] This embodiment provides a silicon-carbon composite material, and its preparation method is as follows: Step S1: Provide a porous carbon material, which is the carbon material obtained in Example 3; Step S2: Crush and classify the porous carbon in Step S1 to obtain d v50 porous carbon powder with a particle size of 8 μm; Step S3: Place the porous carbon powder obtained in Step S2 in a tubular furnace, heat it from room temperature to 550 °C at a rate of 2 °C / min in an N2 atmosphere; then change to a 20% SiH4 - 0.01% O2 - N2 mixed gas, and keep it at 550 °C for 30 h in the 20% SiH4 - 0.01% O2 - N2 mixed atmosphere; change to introduce a 10% C2H2 - N2 mixed gas and keep it at 600 °C for 1 h; naturally cool it in an N2 atmosphere to obtain the silicon-carbon composite material. Example 10

[0067] This embodiment provides a silicon-carbon composite material, and its preparation method is as follows: Step S1: Provide a porous carbon material, which is the carbon material obtained in Example 4; Step S2: Crush and classify the porous carbon in Step S1 to obtain d v50 porous carbon powder with a particle size of 8 μm; Step S3: Place the porous carbon powder obtained in Step S2 in a tubular furnace, heat it from room temperature to 550 °C at a rate of 2 °C / min in an N2 atmosphere; then change to a 20% SiH4 - N2 mixed gas, and keep it at 550 °C for 30 h in the 20% SiH4 - N2 mixed atmosphere; change to introduce a 10% C2H2 - N2 mixed gas and keep it at 600 °C for 2 h; naturally cool it in an N2 atmosphere to obtain the silicon-carbon composite material. Example 11

[0068] This embodiment provides a silicon-carbon composite material, and its preparation method is as follows: Step S1: Provide a porous carbon material, which is the carbon material obtained in Example 5; Steps S2 and S3 are the same as Steps S2 and S3 in Example 7. Example 12

[0069] This embodiment provides a silicon-carbon composite material, and its preparation method is as follows: Step S1: Provide a porous carbon material, which is the carbon material obtained in Example 6; Step S2: Crush and classify the porous carbon in Step S1 to obtain d v50Porous carbon powder with a size of 8 μm; Step S3: Place the porous carbon powder obtained in Step S2 into a tube furnace. Heat it from room temperature to 550 °C at a rate of 2 °C / min in an N2 atmosphere. Then change to a 20% SiH4 - 0.05% O2 - N2 mixed gas, and keep it at 550 °C for 70 h in the 20% SiH4 - 0.05% O2 - N2 mixed atmosphere. Then change to a 10% C2H2 - N2 mixed gas and keep it at 600 °C for 2 h. Naturally cool it in an N2 atmosphere to obtain a silicon-carbon composite material. Comparative Example 3

[0070] This comparative example provides a silicon-carbon composite material, and its preparation method is as follows: Step S1: Provide a porous carbon material, and the porous carbon material is the carbon material obtained in Comparative Example 1; Step S2: Crush and classify the porous carbon in Step S1 to obtain d v50 Porous carbon powder with a size of 8 μm; Step S3: Place the porous carbon powder obtained in Step S2 into a tube furnace. Heat it from room temperature to 550 °C at a rate of 2 °C / min in an N2 atmosphere. Then change to a 20% SiH4 - N2 mixed gas, and keep it at 550 °C for 30 h in the 20% SiH4 - N2 mixed atmosphere. Then change to a 10% C2H2 - N2 mixed gas and keep it at 600 °C for 1 h. Naturally cool it in an N2 atmosphere to obtain a silicon-carbon composite material. Comparative Example 4

[0071] This comparative example provides a silicon-carbon composite material, and its preparation method is as follows: Step S1: Provide a porous carbon material, and the porous carbon material is the graphite particles provided in Comparative Example 2; Step S2: Crush and classify the graphite particles in Step S1 to obtain d v50 Graphite powder with a size of 8 μm; Step S3: Place the graphite powder in Step S2 into a tube furnace. Heat it from room temperature to 550 °C at a rate of 2 °C / min in an N2 atmosphere. Then change to a 20% SiH4 - N2 mixed gas, and keep it at 550 °C for 3 h in the 20% SiH4 - N2 mixed atmosphere. Then change to a 10% C2H2 - N2 mixed gas and keep it at 600 °C for 10 min. Naturally cool it in an N2 atmosphere to obtain a silicon-carbon composite material.

[0072] 3. Testing method

[0073] N2 adsorption test, XRD, Raman, and SEM are all well-known material characterization means for those skilled in the art, and their specific test conditions will not be elaborated here.

[0074] 3-1. N2 Adsorption Test: Specific Surface Area of Carbon Material A Obtained by multi-point BET calculation, and the settlement result satisfies the intercept C value > 0 and the correlation coefficient R2 ≥ 0.9999. Pore volume V According to the N2 adsorption test p / p The maximum adsorption amount when 0>0.99 is obtained, and the average pore diameter D =4 V / A *1000 (nm). The pore distribution of the carbon material can be estimated by the average pore diameter. When the average pore diameter D < 2 nm, the micropore proportion is usually greater than 80%.

[0075] 3-2. Calculation of Grain Size in XRD Test: The grain size of the crystallization peak of the carbon material near 2 θ = 26.4° L c , which reflects the stacking thickness of the carbon hexagonal network plane layer of the graphitized part, is an important physical quantity characterizing its graphitization degree. The grain size of the XRD peak can be calculated using the full width at half maximum and according to the Scherrer formula.

[0076]

[0077] D is the grain size, that is, the average thickness of the grain perpendicular to the crystal plane direction, with the unit Å; K is the Scherrer constant. If B is the full width at half maximum of the diffraction peak, then K = 0.89; if B is the integrated width of the diffraction peak, then K = 1; γ is the X-ray wavelength. For Cu k α it is generally 1.54056 Å; B is the full width at half maximum of the diffraction peak of the measured sample (double-line correction and instrument factor correction must be carried out), and during the calculation, it needs to be converted to radians (rad); θ is the Bragg diffraction angle, with the unit in degrees.

[0078] 3-3. I / I1 in XRD Test: The carbon material provided by the present invention has the characteristics of partial graphitization, which is a composite of disordered carbon and graphitized carbon. Its XRD pattern at 2 θThere is a diffraction peak P between = 25° and 30°; in some embodiments, there is a diffraction peak P1 between = 18° and 25°, and the intensity of peak P θ and the intensity of peak P1 I The ratio of I is I / I 1.

[0079] First, it is necessary to perform background subtraction on the XRD pattern. Due to the influence of different operators' habits in taking points for background subtraction, the unified method in the present invention is: connect the data point B1 at 2 θ = 15 with the data point B2 at 2 θ = 35, and B1B2 is used as the background line. As shown in the appendix Figure 4 .

[0080] As shown in the appendix Figure 4 , draw a straight line perpendicular to the x-axis from the vertex C1 of peak P, which intersects B1B2 at point C2; draw a straight line perpendicular to the x-axis from the vertex D1 of peak P1, which intersects B1B2 at point D2; then I is the intensity difference between C1 and C2, I 1 is the intensity difference between D1 and D2, and then I / I 1 is obtained.

[0081] 3 - 4. Raman test: Raman characterizes the degree of disorder and graphitization of carbon materials. The disorder peak (D peak) is located between 1310~1360 cm -1 ; the graphite peak (G peak) is located between 1560~1610 cm -1 . The degree of disorder or graphitization of carbon materials is characterized by the intensity ratio of the D peak to the G peak ( I D / I G ). The smaller I D / I G , the lower the degree of disorder and the higher the degree of graphitization.

[0082] 3 - 5. Si content test: Place 3.0 g of the silicon-carbon composite material in an oven at 150 °C and dry it to a constant weight, and record the mass m1; place the dried composite material in a muffle furnace, heat it to 1100 °C and keep it for 2 h, cool it down and weigh it, and record the mass m2. The Si content calculation formula: 3 - 6. Half-cell test: The silicon-carbon composite materials obtained in Examples 7-12 and Comparative Examples 3 and 4 were tested for their electrochemical properties, and the results are shown in Table 2. Using the silicon-carbon composite materials obtained in Examples 7-12 and Comparative Examples 3 and 4 as the negative electrode active materials, negative electrode sheets were respectively prepared. The negative electrode sheets were used to prepare CR2032-type button cells by conventional methods, and the electrical properties of the cells were tested. A LAND battery test system was used to perform charge-discharge tests on the cells.

[0083] Half-cell assembly: CR2032-type button cells were assembled in a glove box, with a lithium metal sheet as the counter electrode, a polypropylene microporous membrane as the separator, and an electrolyte of LiPF6 dissolved in a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio EC:DEC = 1:1), where the concentration of LiPF6 was 1 mol / L.

[0084] Cyclic specific capacity and first efficiency test: After the CR2032-type button cell was left standing for 6 h, it was discharged to 0.005 V at 0.05 C and then discharged to 0.005 V at 0.01 C; after standing for 5 min, it was charged at a constant current of 0.05 C to 1.5 V; the first lithium deintercalation specific capacity at 0.8 V was the 0.8 V specific capacity (or mass specific capacity) of the electrode material, and the ratio of the first lithium deintercalation capacity at 0.8 V to the first lithium intercalation capacity at 1.5 V was the 0.8 V first Coulombic efficiency of the cell.

[0085] 3-7. Full-cell test Using the silicon-carbon composite materials obtained in Examples 7-12 and Comparative Examples 3 and 4 as the negative electrode active materials, the electrode sheets containing the negative electrode active materials were used to prepare soft-pack batteries by conventional methods and their electrical properties were tested. The soft-pack batteries were prepared in a dehumidifying chamber with a dew point of -45°C. A LANBTS battery test system was used to perform charge-discharge cycle tests on the batteries, and the results are shown in Table 2. The specific test method was as follows: (1) Fabrication of the positive electrode sheet: The positive electrode active material LiCoO2, the conductive agent Super P, the binder PVDF, and the solvent NMP were stirred and mixed evenly in a mass ratio of 92:3:5:150, and then evenly coated on the positive electrode current collector, and then dried at 80 °C to obtain the positive electrode sheet.

[0086] (2) Fabrication of the negative electrode sheet: The negative electrode active material, the conductive agent Super P, the binder polyacrylic acid, and the solvent deionized water were stirred and mixed evenly in a mass ratio of 95:1:4:120, and then evenly coated on the negative electrode current collector, and then dried at 100 °C to obtain the negative electrode sheet.

[0087] (3) The positive electrode sheet and the negative electrode sheet are stacked in a square shape and separated by a polypropylene separator to form a battery core, which is then encapsulated in an aluminum-plastic bag. An electrolyte with a corresponding capacity is injected into the aluminum-plastic bag, and after vacuum sealing, a soft-pack battery is obtained. The electrolyte is a mixed solution of EC and DEC with LiPF6, where the concentration of LiPF6 is 1 mol / L, and the volume ratio of EC to DEC is 1:1.

[0088] (4) Formation and grading: The battery after injection and sealing starts to be formed. It is left standing in an incubator at 25 °C for 12 h, then charged at a constant current of 0.02C to 3.3 V, left standing for 30 min, charged at a constant current of 0.025 C to 3.8 V, left standing for 10 min, and charged at a constant current of 0.33 C to 4.2 V. After formation, the battery is evacuated and the air bag is cut, and then graded. It is charged at a constant current of 0.33 C to 4.45 V, left standing for 10 min, discharged at a constant current of 1 C to 3 V, left standing for 10 min, and discharged at a constant current of 0.33 C to 3 V. The grading is completed. The ratio of the discharge capacity to the charge capacity during the formation and grading of the soft-pack battery is the first efficiency of the battery.

[0089] (5) 25 °C cycle test: The battery is placed in an incubator at 25 °C, charged at a constant current of 1 C to 4.45 V, and then charged at a constant voltage of 4.45 V until the current is 0.1 C. After standing for 10 min, it is discharged at a constant current of 1 C to 3.0 V, left standing for 10 min, and the above charging and discharging steps are repeated until the discharge capacity is lower than 80% of the discharge capacity in the first cycle and then stopped. At this time, the number of cycles obtained is the cycle life of the soft-pack battery; record the capacity retention rate after 100 cycles.

[0090] 4. Results and analysis of the examples The test results of the basic physical and chemical properties of the carbon materials in Examples 1-6 and Comparative Examples 1 and 2 are shown in Table 1. The physical and chemical properties of the silicon-carbon composite materials obtained in Examples 7-12 and Comparative Examples 3 and 4 are shown in Table 2.

[0091] Table 1 Physical and chemical properties of the carbon materials obtained in Examples 1-6 and Comparative Examples 1 and 2 <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Pore volume (cm 3 / g)]]> Average pore diameter (nm) <![CDATA L c (nm)]]> <![CDATA I / I 1]]> <![CDATA I D / I G > Example 1 362.1 0.44 4.86 28.5 6.1 0.58 Example 2 2288.2 1.31 2.29 17.3 3.5 0.82 Example 3 1205.9 0.82 2.72 2.0 1.0 1.08 Example 4 1798.9 0.85 1.89 9.0 1.6 0.95 Example 5 400.0 0.42 4.2 39.0 9.8 0.20 Example 6 2459.6 1.98 3.22 2.0 0.8 1.20 Comparative Example 1 1720.2 0.83 1.93 0.0 0.0 3.50 Comparative Example 2 1.5 / / 42 Infinity 0.15 Table 2 Physical and chemical properties of the silicon-carbon composite materials obtained in Examples 7-12 and Comparative Examples 3 and 4 Silicon content (wt.%) <![CDATA[Specific surface area (m 2 / g)]]> 0.8 V specific capacity (mAh / g) 0.8 V initial efficiency (%) Capacity retention rate at 25°C after 100 cycles (%) Example 7 35.6 1.2 1436 92.1 99.2 Example 8 59.4 3.5 1989 90.3 98.1 Example 9 50.2 2.1 1721 88.5 98.7 Example 10 51.5 2.3 1763 89.8 98.5 Example 11 33.5 0.9 1415 92.3 99.5 Example 12 62.1 3.9 2098 89.2 98 Comparative Example 3 46.8 2.6 1598 82.4 98.5 Comparative Example 4 10.2 3.7 602 91.9 <80 (Invalid) In Examples 7-12 and Comparative Examples 3 and 4, the carbon materials in Examples 1-6 and Comparative Examples 1 and 2 were used as the matrix for silicon deposition to obtain silicon-carbon composite materials. As can be seen from Table 1, the carbon materials provided in Examples 1-6, after being activated under strong conditions and then subjected to high-temperature treatment, are graphitized to a certain extent and can maintain a relatively large pore volume. Figure 1 、 2XRD patterns of Examples 1, 4 and Comparative Example 1 are shown in Figures 3 and 5 respectively. It can be seen that obvious graphite peaks exist between 2 θ = 25~30° for Examples 1 and 4, while a broadened peak envelope is shown between 2 θ = 18~30° for Comparative Example 1.

[0092] Compared with the carbon materials of Comparative Example 1, the bulk phase defects of Examples 1~6 are less. The silicon-carbon composite materials of Examples 7~12 prepared from the carbon materials of Examples 1~6 show higher initial Coulomb efficiency. As can be seen from Table 2, the initial Coulomb efficiency at 0.8 V of the silicon-carbon composite materials of Examples 7~12 is above 88.5%, close to that of the graphite-based silicon-carbon composite materials, and significantly higher than that of the silicon-carbon composite material of Comparative Example 3 obtained from Comparative Example 1. Comparative Example 4 uses high initial efficiency graphite as the carrier of silicon, and the initial efficiency of its silicon-carbon composite material reaches 91.9%. However, due to the extremely small specific surface area and pore volume of graphite, the amount of silicon that can be accommodated is extremely limited, so its capacity is only 602 mAh / g. Examples 7~12 use the porous carbon materials provided by the present invention as the matrix. Their rich pore structures can accommodate a large amount of silicon, and the 0.8 V specific capacity of the composite materials reaches above 1400 mAh / g; among them, Examples 8 and 12 use porous carbon materials with large pore volumes as the carriers, and the silicon content in the composite materials can reach 59.4% and 62.1% respectively, and the 0.8 V specific capacities reach 1955 and 2098 mAh / g respectively.

[0093] Since the framework structure of the porous carbon material well restricts the growth of silicon grains; at the same time, for porous carbon materials with larger pore diameters, such as Examples 1, 3, 5, and 6, in the preparation of silicon-carbon composite materials (Examples 7, 9, 11, and 12), in the present invention, a precursor containing impurity atoms is introduced for silicon deposition at the same time, and the impurity-containing precursor further forms a restraint and spacing for the growth of silicon nanoparticles, inhibiting the growth of silicon nanoparticles during the deposition process and the volume effect of the composite material during the electrochemical cycling process; therefore, Examples 7~12 all show good cycle stability, and their 100-cycle capacity retention rates are above 98%. There is no accumulation of silicon particles on the surface of the silicon-carbon composite materials of Examples 7~12. The SEM backscattered image of Example 7 is shown in Figure 5 . The contrast of the backscattered image reflects element information, Figure 4 and the particles show uniform light gray, indicating the uniform distribution of silicon and carbon in the composite material particles of Example 7 and no obvious local silicon enrichment on the surface.

[0094] Comparative Example 4 uses graphite as the matrix for silicon deposition. Due to the extremely small specific surface area of graphite, silicon deposition can only occur on the surface of graphite. Therefore, silicon wire and silicon island structures cover the surface of graphite. The SEM backscattered image is shown in Figure 6, in the figure, the white areas are all silicon, and the dark gray parts are carbon. The results of graphite as the silicon deposition matrix are reflected in two aspects. On the one hand, the silicon content in the composite material is very low, resulting in a decrease in the specific capacity. The specific capacity of 0.8 V in Comparative Example 4 is only 602 mAh / g. On the other hand, the surface silicon has a large size, and the volume expansion during the charge and discharge cycle is uncontrolled, resulting in poor cycle stability. The capacity retention rate has dropped below 80% after 100 cycles, and the battery fails.

[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A carbon material, characterized in that, The carbon material is a porous carbon material and has the following characteristics: i) The N2 adsorption pore volume is 0.4 - 2.0 cm 3 / g; ii) The average pore diameter of N2 adsorption is 1.8 - 5.0 nm; iii) Partial graphitization, which is a composite of disordered carbon and graphitized carbon, and its XRD pattern has a diffraction peak P between 2 θ = 25~30°, and the grain size of P calculated according to the Scherrer formula is 2~40 nm.

2. The carbon material according to claim 1, characterized in that The N2 adsorption pore volume of the carbon material is 0.4 to 1.5 cm 3 / g, preferably 0.6 to 1.3 cm 3 / g.

3. The carbon material according to claim 1, wherein The average pore diameter of N2 adsorption of the carbon material is 1.8 - 4.0 nm, preferably 1.8 - 3.0 nm.

4. The carbon material according to claim 1, wherein The grain size of the P peak in the XRD pattern of the carbon material is 2 - 30 nm, preferably 2 - 20 nm.

5. The carbon material according to claim 1, characterized in that, The XRD pattern of the carbon material has diffraction peaks P1 between 2 θ = 18~25°, and the intensity of the P peak I and the intensity of the P1 peak I The ratio of 1 is I / I 1, I / I The value of 1 is 0.5~20, preferably 0.8~10.

6. The carbon material according to claim 1, characterized in that, In the Raman spectrum of the carbon material I D / I G The value is 0.2 to 2.0, preferably 0.4 to 1.

2.

7. The carbon material according to claim 1, characterized in that The proportion of the pore volume less than 2 nm in the total pore volume of the carbon material is 20 - 90%, the proportion of the pore volume of 2 - 5 nm in the total pore volume is 10 - 50%, the proportion of the pore volume of 5 - 10 nm in the total pore volume is 0 - 30%; the proportion of the pore volume greater than 10 nm in the total pore volume is 0 - 10%.

8. A method for preparing a carbon material, characterized in that, The obtained carbon material contains the carbon material described in any one of claims 1 - 7; the preparation method includes the following steps: Step S1, pyrolyzing and carbonizing the carbon precursor in an inert atmosphere to obtain porous carbon 1; the carbon precursor contains one or more of thermoplastic phenolic resin, thermosetting phenolic resin, ion exchange resin, epoxy resin, biomass, coal, petroleum coke; the temperature of the pyrolysis carbonization is 500 - 1000 °C; Step S2: Crush the porous carbon 1 obtained in Step S1 to obtain porous carbon 1 particles; the particle size of the porous carbon 1 particles d v50 is 4 to 1000 μm; Step S3, treating the porous carbon 1 particles obtained in step S2 at 700 - 1000 °C in an atmosphere of H2O or CO2 to obtain porous carbon 2 particles; Step S4, performing high-temperature heat treatment on the porous carbon 2 particles obtained in step S3 to obtain the carbon material; the temperature of the heat treatment is 1000 - 3000 °C, preferably 1200 - 2000 °C, and the atmosphere of the heat treatment is N2 or Ar; Optionally, before or after the above step S4, the porous carbon particles are crushed and classified, and the particle size of the obtained carbon material d v50 is 4 to 20 μm.

9. A method for preparing a carbon material, characterized in that, The obtained carbon material contains the carbon material described in any one of claims 1 - 7; the preparation method includes the following steps: Step S1, pyrolyzing and carbonizing the carbon precursor in an inert atmosphere to obtain porous carbon 1; the carbon precursor contains one or more of thermoplastic phenolic resin, thermosetting phenolic resin, ion exchange resin, epoxy resin, biomass, coal, petroleum coke; the temperature of the pyrolysis carbonization is 500 - 1000 °C; Step S2: Crush the porous carbon 1 obtained in step S1 to obtain porous carbon 1 particles; the particle size of the porous carbon 1 particles d v50 is 4 to 1000 μm; Step S3, mixing the porous carbon 1 particles obtained in step S2 with a strong base, and treating the mixture at 500 - 1000 °C in an inert atmosphere, and the obtained material is pickled, washed with water, and dried to obtain porous carbon 2 particles; the strong base is one or more of KOH, NaOH, K2CO3, Na2CO3, preferably KOH; Step S4, performing high-temperature heat treatment on the porous carbon 2 particles obtained in step S3 to obtain the carbon material; the temperature of the heat treatment is 1000 - 3000 °C, preferably 1200 - 2000 °C, and the atmosphere of the heat treatment is N2 or Ar; Optionally, before or after the above step S4, the porous carbon particles are crushed and classified, and the particle size of the obtained carbon material d v50 is 4 to 20 μm.

10. A method for preparing a carbon material, characterized in that, The obtained carbon material contains the carbon material described in any one of claims 1 - 7; the preparation method includes the following steps: Step S1, mixing the biomass precursor with an aqueous H3PO4 solution to obtain a mixed precursor; the mass ratio of the biomass precursor to H3PO4 is 1:0.5 - 5; Step S2: Dry and cure the mixed precursor obtained in Step S1 to obtain a cured precursor; the temperature for drying and curing is 120 - 220 °C, and the atmosphere for drying and curing is one or more of O2, N2, and Ar; Step S3: Sinter the cured precursor obtained in Step S2 to obtain porous carbon 1; the temperature for sintering is 300 - 700 °C, and the atmosphere for sintering is one or more of O2, N2, and Ar; Step S4: Wash and dry the porous carbon 1 obtained in Step S3 to obtain porous carbon 2; the content of P element in the porous carbon 2 is less than 500 ppm, preferably less than 200 ppm, and more preferably less than 100 ppm; Step S5: Perform high-temperature heat treatment on the porous carbon 2 obtained in Step S4 to obtain the carbon material; the temperature for heat treatment is 1000 - 3000 °C, preferably 1200 - 2000 °C, and the atmosphere for heat treatment is N2 or Ar; Optionally, before or after the above step S5, the porous carbon particles are crushed and classified, and the particle size of the obtained carbon material d v50 is 4 - 20 μm.

11. The method for preparing the carbon material according to claim 10, wherein, the biomass precursor in Step S1 comprises one or more of wood chips, bamboo powder, straw, fruit shells, coconut shells, palm fibers, lignin, cellulose, and starch; and / or, a first additive is further added in Step S1 for blending, and the first additive is an oxidant. Preferably, the first additive comprises one or more of H2SO4, HNO3, H2O2, KMnO4, K2Cr2O7, KClO3, maleic anhydride, benzenesulfonic acid, and p-toluenesulfonic acid; and / or, a second additive is further added in Step S1, and the second additive is a hetero-element additive. Preferably, the second additive comprises one or more of boric acid, silica sol, silicic acid, tetraethyl orthosilicate, tetraacetic acid titanate, tetra-isopropyl titanate, titanium oxysulfate, titanium tetrachloride, alumina, aluminum hydroxide monohydrate, aluminum hydroxide, aluminum phosphate, and lithium aluminum titanium phosphate; and / or, a third additive is further added in Step S1, and the third additive is potassium humate or potassium fulvate; and / or, the biomass precursor in Step S1 is in powder or granular form, the particle size of the powder is 5 - 150 μm, and the particle size of the granule is 0.15 - 3 mm.

12. The preparation method of the carbon material according to claim 10, characterized in that, Between the step S2 and the step S3, or between the step S3 and the step S4, or between the step S4 and the step S5, or after the step S5, there is a crushing and classification step, and the particle size of the classified carbon material powder obtained d v50 is 4 to 20 μm.

13. Application of carbon materials, characterized in that, The carbon material comprises the carbon material according to any one of claims 1 - 7 or the carbon material obtained by the preparation method according to any one of claims 8 - 12, and the applications of the carbon material include the applications of the carbon material as a catalyst, a porous carrier, a hard carbon precursor, a graphite precursor, a capacitive carbon, an adsorbent, and a drug carrier.

14. Silicon-carbon composite material, characterized in that, The silicon-carbon composite material comprises a porous carbon material and silicon nanoparticles, the porous carbon material comprises the carbon material according to any one of claims 1 - 7 or the carbon material obtained by the preparation method according to any one of claims 8 - 12, and the silicon nanoparticles are located in the pores of the porous carbon material.

15. The silicon-carbon composite material according to claim 14, wherein The silicon-carbon composite material has any one or more of the following characteristics: i) The specific surface area is 0.1 to 50 cm 3 / g, preferably 0.1 to 10 cm 3 / g, more preferably 0.1 to 3 cm 3 / g; ii) The content of silicon element is 30 - 70 wt.%; iii) The lithium intercalation capacity of the half-cell button battery at 0.8 V is 1000-2500 mAh / g, preferably 1400-2200 mAh / g; iv) The first Coulombic efficiency of the half-cell button battery at 0.8 V is greater than 87%.

16. The silicon-carbon composite material according to claim 14, characterized in that, The silicon-carbon composite material is obtained by chemical vapor deposition of a silicon-containing precursor on the porous carbon material at 150-1000 °C; preferably, the silicon-containing precursor is selected from one or more of silane, disilane, trisilane, halogenated silane, polysilane, silole and its derivatives, silafluorene and its derivatives.

17. The silicon-carbon composite material according to claim 16, wherein A heteroatom-containing precursor is introduced during the chemical vapor deposition process; the heteroatom-containing precursor includes at least one of an oxygen-containing precursor, a carbon-containing precursor, a nitrogen-containing precursor, a phosphorus-containing precursor, a sulfur-containing precursor or a boron-containing precursor; preferably, the contact mode of the silicon-containing precursor and the heteroatom-containing precursor with the porous matrix includes: the silicon-containing precursor and the heteroatom-containing precursor alternately contact the porous matrix; or, the silicon-containing precursor and the heteroatom-containing precursor contact the porous matrix simultaneously; or, the silicon-containing precursor and a mixed gas containing the silicon-containing precursor and the heteroatom-containing precursor alternately contact the porous matrix, preferably, the silicon-containing precursor continuously contacts the porous matrix, and the heteroatom-containing precursor is intermittently introduced during this process.

18. The silicon-carbon composite material according to claim 14, wherein The silicon-carbon composite material includes a coating layer on the surface of the silicon-carbon composite material; preferably, the material of the coating layer is selected from at least one of a solid electrolyte, a conductive polymer, a carbonaceous material, a metal, an alloy, a metal oxide, a metal hydroxide, a halogen-containing compound, a nitrogen-containing compound, a phosphorus-containing compound, a boron-containing compound, a sulfur-containing compound; more preferably, the material of the coating layer is a carbonaceous material.

19. Negative electrode, characterized in that, The negative electrode includes a negative electrode active material, and the negative electrode active material includes the silicon-carbon composite material according to any one of claims 14 to 18.

20. The battery is characterized in that, The battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, and the negative electrode includes the silicon-carbon composite material according to any one of claims 14 to 18.

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