Metal element-doped nano silicon carbon as well as preparation method and application thereof

Abstract

The invention discloses metal element-doped nano silicon carbon as well as a preparation method and application thereof, and relates to the field of negative electrode materials. The nano silicon carbon takes porous carbon as a carbon skeleton, and the porous carbon is sequentially attached with nano silicon and coated with a carbon material layer through a chemical vapor deposition method; the porous carbon is prepared by carbonizing resin containing metal nitride after alkali activation and pore forming, and the resin containing the metal nitride is prepared by condensation polymerization of a phenolic compound, an aldehyde compound and the metal nitride in the presence of a catalyst. The porous carbon is doped with the metal nitride in the resin polycondensation process, the conductivity of the nano silicon carbon is effectively improved, the powder resistance is reduced, holes in the surface of the porous carbon provide more expansion space for deposited nano silicon, a carbon material layer formed by subsequent deposition and coating provides a protection effect, the reaction between silicon and an electrolyte can be inhibited, and the service life of the nano silicon carbon is prolonged. A stable SEI film is formed, the cycling stability of the material is improved, the volume expansion rate of a pole piece is inhibited, and the cycling life and the stability of the battery are improved.

Description

Technical Field

[0001] The present invention relates to the field of anode materials, and in particular to a doped metal element nano-silicon carbon and its preparation method and application. Background Art

[0002] As an anode material for lithium-ion batteries, nano-silicon has the advantages of high lithium storage capacity, good electron channels, small strain, and an environment that promotes the stable growth of the SEI film. Its theoretical capacity at room temperature is as high as 3580 mAh / g, far exceeding 372 mAh / g of graphite, and it is expected to replace graphite as the anode material for the next generation of high-energy density lithium-ion batteries.

[0003] However, with the continuous improvement of the capacity, it will be difficult to control the silicon particle size and degree of amorphization. As a result, silicon will undergo volume expansion and crystallization transformation during the charge and discharge cycle of the material. This volume expansion may cause the structure of the silicon-carbon anode material to rupture, pulverize, and deactivate, thereby affecting the cycle life and performance stability of the battery. Although the silicon-carbon composite material has a relatively high conductivity, compared with traditional graphite materials, its conductivity is still low. Moreover, as the silicon content increases, the resistivity of silicon-carbon also increases, affecting the conductivity of the material, which may lead to an increase in the internal resistance of the battery and affect the charge and discharge rate and rate performance. Summary of the Invention

[0004] The present invention provides a doped metal element nano-silicon carbon and its preparation method and application. By doping metal nitrides in porous carbon and depositing nano-silicon and carbon coating on the surface, nano-silicon carbon with a spherical morphology and excellent conductivity is obtained. As an anode active material, it has a high capacity and Coulomb efficiency, effectively inhibits the expansion rate of the electrode sheet during the charge and discharge cycle, and improves the cycle life.

[0005] To solve the above technical problems, one of the objectives of the present invention is to provide a doped metal element nano-silicon carbon, wherein the nano-silicon carbon uses porous carbon as a carbon skeleton, and the porous carbon is successively attached with nano-silicon and coated with a carbon material layer by chemical vapor deposition;

[0006] The porous carbon is prepared by carbonizing a resin containing metal nitride after alkali activation to form pores. The mass ratio of the resin containing metal nitride to the alkali is 1:(1 - 5). The resin containing metal nitride is prepared by polycondensation of phenolic compounds, aldehyde compounds, and metal nitride under the condition of a catalyst. The mass ratio of the phenolic compound to the metal nitride is (60 - 300):1.

[0007] In this application, porous carbon is used as the carbon skeleton, and nano-silicon is deposited on the surface and pores by chemical vapor deposition. The nano-silicon serves as the anode material to provide high capacity. The porous structure on the surface of the porous carbon allows for more expansion space for the nano-silicon. Subsequently, a protective carbon material layer is deposited and coated, which can inhibit the reaction between silicon and the electrolyte, form a stable SEI film, enhance the cycling stability of the material, and effectively control the surface morphology of the nano-silicon carbon to form a spherical structure with a relatively large specific surface area and stable structure. In addition, the porous carbon is doped with a specific proportion of metal nitrides during the polycondensation process of phenolic compounds and aldehyde compounds. The metal elements can effectively improve the electrical conductivity of the nano-silicon carbon, reduce the powder resistance. The prepared nano-silicon carbon can be used as the anode active material, and the capacity and Coulomb efficiency are improved during the charge and discharge cycles of the assembled battery, and the volume expansion of the electrode during the cycling process is effectively inhibited, improving the cycle life and stability of the battery.

[0008] As a preferred embodiment, the mass ratio of the phenolic compound to the aldehyde compound is (1 - 3):1.

[0009] As a preferred embodiment, the mass ratio of the catalyst to the phenolic compound is (0.1 - 0.3):1.

[0010] As a preferred embodiment, the mass ratio of the resin containing metal nitride to the base is 1:(1 - 3).

[0011] This application controls the addition ratio of the metal nitride and the base, which can control the effect of activation and pore formation, increase the specific surface area of the nano-silicon carbon, avoid the pore diameter of pore formation being too large and affecting the structural stability of the nano-silicon carbon, and at the same time avoid the pore formation being too small and affecting the subsequent deposition of nano-silicon and reducing the specific surface area.

[0012] As a preferred embodiment, the phenolic compound is at least one of phenol, cresol, resorcinol, nitrophenol, naphthol, and chlorophenol.

[0013] As a preferred embodiment, the aldehyde compound is at least one of formaldehyde, acetaldehyde, and benzaldehyde.

[0014] As a preferred embodiment, the catalyst is concentrated ammonia water.

[0015] As a preferred embodiment, the metal nitride is at least one of lithium nitride, magnesium nitride, aluminum nitride, titanium nitride, and zirconium nitride.

[0016] As a preferred embodiment, the base is at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide, and barium hydroxide.

[0017] To solve the above technical problems, the second object of the present invention provides a method for preparing a nano-silicon carbon doped with metal elements, comprising the following steps:

[0018] (1) Add the resin containing metal nitride and alkali into water, stir and react for activation and pore formation, centrifuge, wash, and dry, then carbonize under inert gas, wash until neutral, and dry to obtain porous carbon;

[0019] (2) Place the porous carbon in a chemical vapor deposition device, heat it to 400 - 700 °C under inert gas, introduce the silicon source gas, continuously react to deposit nanosilicon, cut off the silicon source gas, heat it to 400 - 800 °C, introduce the carbon source gas, continuously react to form a carbon material layer, cut off the carbon source gas, cool it naturally, and screen to obtain the nanosilicon carbon material.

[0020] As a preferred solution, in step (1), the mass ratio of the resin containing metal nitride to water is 1:(15 - 40).

[0021] As a preferred solution, in step (1), the stirring reaction time for activation and pore formation is 1 - 3 h.

[0022] As a preferred solution, in step (1), the carbonization temperature is 400 - 800 °C, and the carbonization time is 30 - 240 min.

[0023] As a preferred solution, in step (1), the carbonization temperature is 500 - 800 °C, and the carbonization time is 60 - 180 min.

[0024] As a preferred solution, in step (1), wash until neutral with hydrochloric acid with a concentration of 0.1 - 1 mol / L.

[0025] As a preferred solution, in step (2), the silicon source gas is at least one of silane, disilane, dichlorosilane, silicon tetrachloride, dichlorosilane dihydride, and trichlorosilane monohydride.

[0026] As a preferred solution, in step (2), the carbon source gas is at least one of acetylene, methane, propane, and cyclohexane.

[0027] As a preferred solution, in step (2), the volume ratio of the silicon source gas to the inert gas is 1:(1 - 10), and the continuous reaction time after introducing the silicon source gas is 60 - 360 min.

[0028] As a preferred solution, in step (2), the volume ratio of the silicon source gas to the inert gas is 1:(3 - 7), and the continuous reaction time after introducing the silicon source gas is 150 - 250 min.

[0029] As a preferred solution, in step (2), the volume ratio of the carbon source gas to the inert gas is 1:(3 - 7), and the continuous reaction time after introducing the carbon source gas is 100 - 150 min.

[0030] As a preferred embodiment, in step (2), the mesh number of the sieve for sieving is 300-500 meshes.

[0031] As a preferred embodiment, the preparation method of the resin containing metal nitride includes the following steps: adding a catalyst and a phenolic compound into an organic solution to disperse them evenly, then adding metal nitride, stirring and reacting, adding a solution containing an aldehyde compound, stirring evenly first, then heating and stirring to react, centrifuging and drying to obtain the resin containing metal nitride.

[0032] As a preferred embodiment, in the preparation method of the resin containing metal nitride, the catalyst is concentrated ammonia water with a concentration of 20wt%-30wt%.

[0033] As a preferred embodiment, in the preparation method of the resin containing metal nitride, the concentration of the aldehyde compound in the solution containing the aldehyde compound is 20wt%-60wt%.

[0034] As a preferred embodiment, in the preparation method of the resin containing metal nitride, the organic solution includes at least one of water, ethanol, methanol, propanol, and n-hexanol.

[0035] As a preferred embodiment, in the preparation method of the resin containing metal nitride, the organic solution includes water and ethanol with a mass ratio of 1:(0.1-1).

[0036] As a preferred embodiment, in the preparation method of the resin containing metal nitride, the organic solution includes water and ethanol with a mass ratio of 1:(0.4-0.5).

[0037] As a preferred embodiment, in the preparation method of the resin containing metal nitride, the mass ratio of the organic solution to the phenolic compound is (100-200):1.

[0038] As a preferred embodiment, in the preparation method of the resin containing metal nitride, after adding the metal nitride, the stirring reaction time is 1-10h.

[0039] As a preferred embodiment, in the preparation method of the resin containing metal nitride, after adding the metal nitride, the stirring reaction time is 1-3h.

[0040] As a preferred embodiment, in the preparation method of the resin containing metal nitride, after adding the solution containing the aldehyde compound, stir for 1-25h, then heat and stir to react for 1-30h, and the heating temperature is 40-100°C.

[0041] As a preferred embodiment, in the preparation method of the resin containing metal nitride, after adding the solution containing aldehyde compound, stir for 18 - 22 h, and then heat and stir for reaction for 18 - 22 h, and the heating temperature is 60 - 90 °C.

[0042] As a preferred embodiment, in steps (1), (2) and the preparation method of the resin containing metal nitride, the drying temperature is 40 - 100 °C and the time is 1 - 30 h.

[0043] As a preferred embodiment, in steps (1) and (2), the inert gas is at least one of nitrogen, helium, neon, and argon.

[0044] In order to solve the above technical problems, the third object of the present invention is to provide an application of doped metal element nano - silicon carbon in the preparation of the anode active material of a lithium - ion battery.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] The porous carbon of the present application is doped with metal nitride during the polycondensation process of phenolic compounds and aldehyde compounds, effectively improving the electrical conductivity of nano - silicon carbon, reducing the powder resistance. After activation and pore formation, nano - silicon is deposited on the surface and in the pores by chemical vapor deposition. The nano - silicon improves the capacity of the anode material, and the pores on the surface of the porous carbon provide more expansion space for the nano - silicon. The carbon material layer formed by subsequent deposition and coating provides a protective effect, which can inhibit the reaction between silicon and the electrolyte, form a stable SEI film, improve the cycle stability of the material. The prepared nano - silicon carbon has a large specific surface area and a stable structure, reducing the volume expansion rate of the electrode sheet during the battery assembly cycle, and improving the cycle life and stability of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 : It is a scanning electron microscope image of a doped metal element nano - silicon carbon in Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0049] It should be understood that the terms used in this invention are only for describing particular embodiments and are not intended to limit the invention. Additionally, for the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0050] Unless otherwise indicated, 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 pertains. Although this invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of this invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0051] As used herein, the terms:

[0052] "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variation thereof used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus containing the listed elements need not be limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0053] The connecting phrase "consisting of" excludes any unstated element, step, or component. If used in a claim, this phrase will render the claim closed, excluding materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the claim body rather than immediately following the subject, it only limits the elements described in that clause; other elements are not excluded from the claim as a whole.

[0054] When an equivalent, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values and lower preferred values, it should be understood that all ranges formed by any pairing of any upper range limit or preferred value with any lower range limit or preferred value are specifically invented, regardless of whether the ranges are separately invented. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values and all integers and fractions within the range.

[0055] In these examples, unless otherwise specified, the parts and percentages are by mass.

[0056] "Parts by mass" refers to the basic measurement unit representing the proportional relationship of the masses of multiple components. One part can represent any unit mass. If we say that the mass of component A is a parts by mass and the mass of component B is b parts by mass, it means the mass ratio of component A to component B is a:b. Or, it means the mass of component A is aK and the mass of component B is bK (K is any number representing the multiplication factor). It should not be misunderstood that, different from the number of parts by mass, the sum of the parts by mass of all components is not limited to 100 parts.

[0057] "And / or" is used to indicate that either one or both of the described situations may occur. For example, A and / or B includes (A and B) and (A or B).

[0058] To further illustrate the present invention, the present invention will be described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention. For the raw materials used in the following embodiments and comparative examples of the present application, unless otherwise specified, the raw materials used can be obtained commercially, and the same raw materials are used in parallel experiments.

[0059] Example 1

[0060] A method for preparing doped metal element nano silicon carbide, comprising the following steps:

[0061] (1) Measure 600 mL of pure water and 250 mL of absolute ethanol and pour them into a beaker, stir evenly, add 3 mL of concentrated ammonia water with a concentration of 30 wt%, stir for 1.5 h, add 6 g of resorcinol, continue to stir at 30 °C for 1.5 h, add 0.05 g of lithium nitride, stir at 30 °C for 1 h, add 10 mL of formaldehyde aqueous solution with a concentration of 40 wt%, stir and react for 20 h, heat up to 75 °C and stir at a constant temperature for 20 h, centrifuge and then put it into a constant temperature drying oven, dry at 60 °C for 20 h to obtain lithium nitride resorcinol formaldehyde resin;

[0062] (2) Dissolve 1 g of KOH in 20 mL of pure water, add 1 g of the product of step (1), stir for 1 h for activation and pore formation, centrifuge the mixture and then add 20 ml of absolute ethanol for washing, centrifuge and then put it into a vacuum oven and dry at 60 °C for 20 h. Put the dried sample into a crucible and place it in a tube furnace, carbonize it in an inert gas environment, control the heating rate to rise to 220 °C at 5 °C / min, hold for 40 min, then rise to 700 °C at 5 °C / min and hold for 2 h. Take out the carbonized sample and wash it with diluted hydrochloric acid until neutral, put it into a vacuum oven and dry at 60 °C for 20 h to obtain porous carbon;

[0063] (3) Place 700 g of porous carbon in a fluidized bed, purge with nitrogen at a flow rate of 12 L / min to remove air, then heat it to 530 °C at a heating rate of 8 °C / min. Then, continuously introduce silane gas at a rate of 2.5 L / min for 200 min to attach nano-silicon. Then, cut off the silane gas, heat it to 620 °C at a rate of 8 °C / min, and then continuously introduce acetylene gas at a rate of 2.5 L / min for 120 min to coat the carbon material layer. Cut off the acetylene gas, let it cool naturally to room temperature, take out the material, sieve it through a 400-mesh sieve, and then demagnetize it with a demagnetizer to obtain a nano-silicon carbon material.

[0064] Example 2

[0065] A preparation method of a metal element-doped nano-silicon carbon, the reagents, equipment, and process parameters used in each step are the same as those in Example 1. The difference is that in step (1), measure 600 mL of pure water and 250 mL of absolute ethanol and pour them into a beaker, stir evenly, add 3 mL of concentrated ammonia water with a concentration of 30 wt%, stir for 1.5 h, add 6 g of resorcinol, continue to stir at 30 °C for 1.5 h, add 0.05 g of magnesium nitride, stir at 30 °C for 1 h, add 10 mL of formaldehyde aqueous solution with a concentration of 40 wt%, stir and react for 20 h, heat up to 75 °C and stir constantly for 20 h, centrifuge and then put it into a constant temperature drying oven, dry at 60 °C for 20 h to obtain magnesium nitride resorcinol formaldehyde resin.

[0066] Example 3

[0067] A preparation method of a metal element-doped nano-silicon carbon, the reagents, equipment, and process parameters used in each step are the same as those in Example 1. The difference is that in step (1), measure 600 mL of pure water and 250 mL of absolute ethanol and pour them into a beaker, stir evenly, add 3 mL of concentrated ammonia water with a concentration of 30 wt%, stir for 1.5 h, add 6 g of resorcinol, continue to stir at 30 °C for 1.5 h, add 0.05 g of aluminum nitride, stir at 30 °C for 1 h, add 10 mL of formaldehyde aqueous solution with a concentration of 40 wt%, stir and react for 20 h, heat up to 75 °C and stir constantly for 20 h, centrifuge and then put it into a constant temperature drying oven, dry at 60 °C for 20 h to obtain aluminum nitride resorcinol formaldehyde resin.

[0068] Example 4

[0069] A preparation method of metal element-doped nano silicon carbide, where the reagents, equipment, and process parameters used in each step are the same as those in Example 1. The difference is that in step (1), 600 mL of pure water and 250 mL of absolute ethanol are measured and poured into a beaker, stirred evenly, 3 mL of concentrated ammonia water with a concentration of 30 wt% is added, stirred for 1.5 h, 6 g of resorcinol is added, continuously stirred at 30 °C for 1.5 h, 0.05 g of titanium nitride is added, stirred at 30 °C for 1 h, 10 mL of formaldehyde aqueous solution with a concentration of 40 wt% is added, stirred and reacted for 20 h, heated to 75 °C and stirred at a constant temperature for 20 h, centrifuged and then placed in a constant temperature drying oven, dried at 60 °C for 20 h to obtain titanium nitride resorcinol formaldehyde resin.

[0070] Example 5

[0071] A preparation method of metal element-doped nano silicon carbide, where the reagents, equipment, and process parameters used in each step are the same as those in Example 1. The difference is that in step (1), 600 mL of pure water and 250 mL of absolute ethanol are measured and poured into a beaker, stirred evenly, 3 mL of concentrated ammonia water with a concentration of 30 wt% is added, stirred for 1.5 h, 6 g of resorcinol is added, continuously stirred at 30 °C for 1.5 h, 0.05 g of zirconium nitride is added, stirred at 30 °C for 1 h, 10 mL of formaldehyde aqueous solution with a concentration of 40 wt% is added, stirred and reacted for 20 h, heated to 75 °C and stirred at a constant temperature for 20 h, centrifuged and then placed in a constant temperature drying oven, dried at 60 °C for 20 h to obtain zirconium nitride resorcinol formaldehyde resin.

[0072] Example 6

[0073] A preparation method of metal element-doped nano silicon carbide, where the reagents, equipment, and process parameters used in each step are the same as those in Example 1. The difference is that in step (1), 600 mL of pure water and 250 mL of absolute ethanol are measured and poured into a beaker, stirred evenly, 3 mL of concentrated ammonia water with a concentration of 30 wt% is added, stirred for 1.5 h, 6 g of resorcinol is added, continuously stirred at 30 °C for 1.5 h, 0.1 g of lithium nitride is added, stirred at 30 °C for 1 h, 10 mL of formaldehyde aqueous solution with a concentration of 40 wt% is added, stirred and reacted for 20 h, heated to 75 °C and stirred at a constant temperature for 20 h, centrifuged and then placed in a constant temperature drying oven, dried at 60 °C for 20 h to obtain lithium nitride resorcinol formaldehyde resin.

[0074] Example 7

[0075] A preparation method of metal element-doped nano silicon carbide, the reagents, equipment, and process parameters used in each step are the same as those in Example 1. The difference lies in that in step (1), 600 mL of pure water and 250 mL of absolute ethanol are measured and poured into a beaker, stirred evenly, 3 mL of concentrated ammonia water with a concentration of 30 wt% is added, stirred for 1.5 h, 6 g of resorcinol is added, and stirring is continued at 30 °C for 1.5 h. 0.03 g of lithium nitride is added, stirred at 30 °C for 1 h, 10 mL of formaldehyde aqueous solution with a concentration of 40 wt% is added, and the reaction is stirred for 20 h. The temperature is raised to 75 °C and stirred at a constant temperature for 20 h. After centrifugation, it is placed in a constant temperature drying oven and dried at 60 °C for 20 h to obtain lithium nitride resorcinol formaldehyde resin.

[0076] Example 8

[0077] A preparation method of metal element-doped nano silicon carbide, the reagents, equipment, and process parameters used in each step are the same as those in Example 1. The difference lies in that in step (2), 3 g of KOH is dissolved in 20 mL of pure water, 1 g of the product of step (1) is added, and stirred for 1 h. After centrifuging the mixture, it is added with 20 ml of absolute ethanol for washing, and after centrifugation, it is placed in a vacuum oven and dried at 60 °C for 20 h. The dried sample is placed in a crucible and put into a tube furnace, and carbonized in an inert gas environment. The heating rate is controlled at 5 °C / min and heated to 220 °C, maintained for 40 min, and then heated to 700 °C at 5 °C / min and maintained for 2 h. The carbonized sample is taken out and washed with diluted hydrochloric acid until neutral, and then placed in a vacuum oven and dried at 60 °C for 20 h to obtain porous carbon.

[0078] Comparative Example 1

[0079] A preparation method of metal element-doped nano silicon carbide, the reagents, equipment, and process parameters used in each step are the same as those in Example 1. The difference lies in that in step (1), 600 mL of pure water and 250 mL of absolute ethanol are measured and poured into a beaker, stirred evenly, 3 mL of concentrated ammonia water with a concentration of 30 wt% is added, stirred for 1.5 h, 6 g of resorcinol is added, and stirring is continued at 30 °C for 1.5 h. 10 mL of formaldehyde aqueous solution with a concentration of 40 wt% is added, and the reaction is stirred for 20 h. The temperature is raised to 75 °C and stirred at a constant temperature for 20 h. After centrifugation, it is placed in a constant temperature drying oven and dried at 60 °C for 20 h to obtain resorcinol formaldehyde resin.

[0080] Comparative Example 2

[0081] A preparation method of metal element-doped nano-silicon carbide, where the reagents, equipment, and process parameters used in each step are the same as those in Example 1. The difference lies in that in step (2), 1 g of KOH is dissolved in 20 mL of pure water, 1 g of commercial phenolic resin is added, and stirred for 1 h. After centrifuging the mixture, 20 ml of absolute ethanol is added for washing, and after centrifuging, it is placed in a vacuum oven and dried at 60 °C for 20 h. The dried sample is placed in a crucible and then put into a tube furnace for carbonization in an inert gas environment. The heating rate is controlled at 5 °C / min to rise to 220 °C and maintained for 40 min. Subsequently, it is heated to 700 °C at 5 °C / min and maintained for 2 h. The carbonized sample is taken out and washed with diluted hydrochloric acid until neutral, and then placed in a vacuum oven and dried at 60 °C for 20 h to obtain porous carbon.

[0082] Comparative Example 3

[0083] A preparation method of metal element-doped nano-silicon carbide, where the reagents, equipment, and process parameters used in each step are the same as those in Example 1. The difference lies in that in step (1), 600 mL of pure water and 250 mL of absolute ethanol are measured and poured into a beaker, stirred evenly, 3 mL of concentrated ammonia water with a concentration of 30 wt% is added, and stirred for 1.5 h. 6 g of resorcinol is added, and stirring continues at 30 °C for 1.5 h. 0.05 g of melamine is added, and stirred at 30 °C for 1 h. 10 mL of formaldehyde aqueous solution with a concentration of 40 wt% is added, and stirred and reacted for 20 h. The temperature is raised to 75 °C and stirred at a constant temperature for 20 h. After centrifuging, it is placed in a constant temperature drying oven and dried at 60 °C for 20 h to obtain melamine-resorcinol-formaldehyde resin.

[0084] Comparative Example 4

[0085] A preparation method of metal element-doped nano-silicon carbide, where the reagents, equipment, and process parameters used in each step are the same as those in Example 1. The difference lies in that in step (1), 600 mL of pure water and 250 mL of absolute ethanol are measured and poured into a beaker, stirred evenly, 3 mL of concentrated ammonia water with a concentration of 30 wt% is added, and stirred for 1.5 h. 6 g of resorcinol is added, and stirring continues at 30 °C for 1.5 h. 0.01 g of lithium nitride is added, and stirred at 30 °C for 1 h. 10 mL of formaldehyde aqueous solution with a concentration of 40 wt% is added, and stirred and reacted for 20 h. The temperature is raised to 75 °C and stirred at a constant temperature for 20 h. After centrifuging, it is placed in a constant temperature drying oven and dried at 60 °C for 20 h to obtain lithium nitride-resorcinol-formaldehyde resin.

[0086] Comparative Example 5

[0087] A preparation method of metal element-doped nano silicon carbide, wherein the reagents, equipment, and process parameters used in each step are the same as those in Example 1. The difference lies in that in step (1), 600 mL of pure water and 250 mL of absolute ethanol are measured and poured into a beaker, stirred evenly, 3 mL of concentrated ammonia water with a concentration of 30 wt% is added, stirred for 1.5 h, 6 g of resorcinol is added, and stirring is continued at 30 °C for 1.5 h. Then 0.5 g of lithium nitride is added, stirred at 30 °C for 1 h, 10 mL of formaldehyde aqueous solution with a concentration of 40 wt% is added, and the reaction is stirred for 20 h. The temperature is raised to 75 °C and stirred at a constant temperature for 20 h. After centrifugation, it is placed in a constant temperature drying oven and dried at 60 °C for 20 h to obtain lithium nitride resorcinol formaldehyde resin.

[0088] Comparative Example 6

[0089] A preparation method of metal element-doped nano silicon carbide, wherein the reagents, equipment, and process parameters used in each step are the same as those in Example 1. The difference lies in that in step (2), 0.5 g of KOH is dissolved in 20 mL of pure water, 1 g of the product of step (1) is added, and stirred for 1 h. After centrifugation of the mixture, it is added with 20 ml of absolute ethanol for washing, centrifuged and then placed in a vacuum oven and dried at 60 °C for 20 h. The dried sample is placed in a crucible and then placed in a tube furnace and carbonized in an inert gas environment. The heating rate is controlled at 5 °C / min and heated to 220 °C, maintained for 40 min, and then heated to 700 °C at 5 °C / min and maintained for 2 h. The carbonized sample is taken out and washed with diluted hydrochloric acid until neutral, and then placed in a vacuum oven and dried at 60 °C for 20 h to obtain porous carbon.

[0090] Performance detection test

[0091] 1. Using nitrogen as the adsorbent, the specific surface area of the nano silicon carbide in the examples and comparative examples was measured using TriStarⅡplus 3030 in accordance with the national standard GB / T19587-2017; the Dv50 pore diameter of the nano silicon carbide was measured in accordance with the national standard GB / T21650.2-2008; the powder resistivity of the nano silicon carbide was measured using a powder resistivity & compacted density instrument (PRCN-3100) in accordance with the GB / T 12476.9 standard. The test results are shown in Table 1 below.

[0092] 2. The nano-silicon carbide prepared in the examples and comparative examples was used as the negative electrode active material to prepare the negative electrode material of the lithium-ion battery. Lithium cobaltate, carbon black, and polyvinylidene fluoride with a mass ratio of 8:1:1 were used as the positive electrode material. An alumina separator was used, and then a CR2032 type button lithium-ion battery was assembled. The raw materials used for assembling the lithium-ion battery were the same. Among them, the positive electrode was a lithium sheet, and the negative electrode current collector was a copper foil. Test method for the expansion rate of the silicon-based negative electrode material: Use a blue battery testing system to perform charge and discharge tests on the battery, 0.1C cycle test, the charging cut-off voltage is 2V, and the discharging cut-off voltage is 0.005V. The first charge capacity and the first cycle efficiency were measured. After 100 weeks of cycling and full charge, the button battery was disassembled in a glove box, and the thickness of the electrode sheet was measured. The expansion rate = [(the thickness of the electrode sheet after cycling - the thickness of the electrode sheet before cycling) / the thickness of the electrode sheet before cycling] × 100%. The test results are shown in Table 1 below.

[0093] Table 1 - Performance test results of the nano-silicon carbide prepared in the examples and comparative examples

[0094]

[0095] As shown in Table 1, in Example 1 of the present application, lithium nitride was doped during the polycondensation of resorcinol formaldehyde resin in the porous carbon. Lithium element has high conductivity, which can reduce the powder resistance of nano-silicon carbide and simultaneously inhibit the volume expansion rate of the electrode sheet. In Comparative Examples 1-2, since lithium nitride was not doped during the polycondensation of resorcinol formaldehyde resin or phenolic resin, although the specific surface area of the nano-silicon carbide prepared was slightly increased, the powder resistance was large, the conductivity was extremely poor, and both the first charge capacity and the first cycle efficiency decreased. The volume expansion rate of the prepared negative electrode sheet increased during the cycling process.

[0096] As shown in Table 1, compared with Example 1, in Comparative Example 3, melamine was doped during the polycondensation of resorcinol formaldehyde resin, and no metal element was doped. The conductivity was low, the powder resistance of the prepared nano-silicon carbide decreased, and the first cycle efficiency decreased. The volume expansion rate of the prepared negative electrode sheet increased during the cycling process.

[0097] As shown in Table 1, compared with Example 1, the doping amount of lithium nitride in the resorcinol formaldehyde resin of Example 6 increased. It can be found that the powder resistivity further decreased, and the volume expansion rate of the electrode sheet was effectively inhibited. In Comparative Example 5, too much lithium nitride was doped in the resorcinol formaldehyde resin. Although the powder resistivity was significantly lower, both the first charge capacity and the first cycle efficiency of the battery decreased to a large extent, and the kinetic performance of the battery was poor.

[0098] As shown in Table 1, in Example 1, the addition ratio of the base is moderate, which can control the effect of activation and pore formation, increase the specific surface area of nano-silicon carbide, avoid the pore diameter of pore formation being too large and affecting the structural stability of nano-silicon carbide, and at the same time avoid the pore formation being too small and affecting the subsequent deposition of nano-silicon and reducing the specific surface area. In Comparative Example 6, the addition amount of the base is too low, resulting in too small pore formation and less precipitant of nano-silicon, resulting in a significant decrease in the first charge capacity and efficiency of the battery, and a relatively high volume expansion rate of the electrode sheet.

[0099] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. In particular, for those skilled in the art, any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A nano-silicon carbide doped with a metal element, characterized in that, The nano-silicon carbide uses porous carbon as the carbon skeleton, and the porous carbon is successively attached with nano-silicon and coated with a carbon material layer by chemical vapor deposition; The porous carbon is prepared by carbonizing a resin containing metal nitride after alkali activation to form pores. The mass ratio of the resin containing metal nitride to the alkali is 1:(1 - 5). The resin containing metal nitride is prepared by polycondensation reaction of a phenolic compound, an aldehyde compound and a metal nitride under the condition of a catalyst. The mass ratio of the phenolic compound to the metal nitride is (60 - 300):

1.

2. The doped metal element-containing nano-silicon carbide according to claim 1, wherein The mass ratio of the phenolic compound to the aldehyde compound is (1 - 3):1; And / or, the mass ratio of the catalyst to the phenolic compound is (0.1 - 0.3):

1.

3. The doped metal element-containing nano-silicon carbide according to claim 1, wherein, The phenolic compound is at least one of phenol, cresol, resorcinol, nitrophenol, naphthol, chlorophenol; And / or, the aldehyde compound is at least one of formaldehyde, acetaldehyde, benzaldehyde; And / or, the catalyst is concentrated ammonia water; And / or, the metal nitride is at least one of lithium nitride, magnesium nitride, aluminum nitride, titanium nitride, zirconium nitride; And / or, the alkali is at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide.

4. A method for preparing doped metal element-containing nano silicon carbide as described in any one of claims 1-3, characterized in that, It includes the following steps: (1) Add the resin containing metal nitride and the alkali into water, stir and react to activate and form pores, centrifuge, wash, and dry, then carbonize under an inert gas, wash until neutral, and dry to obtain porous carbon; (2) Place the porous carbon in a chemical vapor deposition device, heat to 400 - 700 °C under an inert gas, introduce a silicon source gas, continuously react to attach nano-silicon, cut off the silicon source gas, heat to 400 - 800 °C, introduce a carbon source gas, continuously react to form a carbon material layer, cut off the carbon source gas, naturally cool down, and sieve to obtain the nano-silicon carbide material.

5. The preparation method of the doped metal element nano silicon carbide according to claim 4, characterized in that, In step (1), the mass ratio of the resin containing metal nitride to water is 1:(15 - 40); And / or, in step (1), the stirring reaction time for activating and forming pores is 1 - 3 h; And / or, in step (1), the carbonization temperature is 400 - 800 °C, and the carbonization time is 30 - 240 min; And / or, in step (1), it is washed until neutral with hydrochloric acid having a concentration of 0.1 - 1 mol / L.

6. The preparation method of the doped metal element nano silicon carbide according to claim 4, characterized in that In step (2), the silicon source gas is at least one of silane, disilane, dichlorosilane, silicon tetrachloride, dichlorodihydrogen silane, trichlorosilane; And / or, in step (2), the carbon source gas is at least one of acetylene, methane, propane, cyclohexane; And / or, in step (2), the volume ratio of the silicon source gas to the inert gas is 1:(1 - 10), and the continuous reaction time after introducing the silicon source gas is 60 - 360 min; And / or, in step (2), the volume ratio of the carbon source gas to the inert gas is 1:(1 - 10), and the continuous reaction time after introducing the carbon source gas is 60 - 360 min; And / or, in step (2), the mesh number of the sieve for sieving is 300 - 500 meshes.

7. The preparation method of the metal element-doped nano silicon carbide according to claim 4, characterized in that, The preparation method of the resin containing metal nitride comprises the following steps: adding a catalyst and a phenolic compound into an organic solution to disperse them evenly, then adding the metal nitride, stirring for reaction, adding a solution containing an aldehyde compound, stirring evenly first, then heating and stirring for reaction, centrifuging and drying to obtain the resin containing metal nitride.

8. The preparation method of the metal element-doped nano-silicon carbide according to claim 7, characterized in that, In the preparation method of the resin containing metal nitride, the catalyst is concentrated ammonia water with a concentration of 20wt%-30wt%; And / or, in the preparation method of the resin containing metal nitride, the concentration of the aldehyde compound in the solution containing the aldehyde compound is 20wt%-60wt%; And / or, in the preparation method of the resin containing metal nitride, the organic solution includes at least one of water, ethanol, methanol, propanol, and n-hexanol; And / or, in the preparation method of the resin containing metal nitride, the organic solution includes water and ethanol with a mass ratio of 1:(0.1-1); And / or, in the preparation method of the resin containing metal nitride, the mass ratio of the organic solution to the phenolic compound is (100-200):1; And / or, in the preparation method of the resin containing metal nitride, after adding the metal nitride, the stirring reaction time is 1-10h; And / or, in the preparation method of the resin containing metal nitride, after adding the solution containing the aldehyde compound, stir for 1-25h, then heat and stir for reaction for 1-30h, and the heating temperature is 40-100°C.

9. The preparation method of the doped metal element nano silicon carbide according to claim 7, characterized in that, In steps (1), (2) and the preparation method of the resin containing metal nitride, the drying temperature is 40-100°C and the time is 1-30h; And / or, in steps (1) and (2), the inert gas is at least one of nitrogen, helium, neon, and argon.

10. Use of the doped metal element nano silicon carbon as described in any one of claims 1-3 in the preparation of the anode active material of a lithium ion battery.

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