A carbon material, its preparation method and application

Abstract

The present application provides a carbon material, a preparation method thereof and an application. The carbon material provided by the present application has a shell layer to form a hollow microsphere structure, the shell layer has a porous structure, and the porous structure includes closed pores. The carbon material provided by the present application has a hollow microsphere structure and closed pores, with stable structure, and can provide relatively many sodium storage sites, which can effectively improve the performance of sodium ion batteries such as the initial Coulomb efficiency and the reversible discharge specific capacity.

Description

Technical Field

[0001] The present invention belongs to the field of sodium-ion batteries, and particularly relates to a carbon material, a preparation method thereof, and an application thereof. Background Art

[0002] With the development of the new energy industry, lithium-ion batteries have been widely used in industries such as electric vehicles, but their further development is restricted by a series of key issues such as lithium resource reserves and the cost of lithium-ion batteries. Sodium-ion batteries have the advantages of low cost, rich sodium reserves, and wide distribution. As the main negative electrode material of sodium-ion batteries, the disordered amorphous structure of hard carbon makes the material itself have more defects and micropores, and these defects and micropores can serve as active sodium storage sites.

[0003] Existing technologies mostly use the template method to regulate the microstructure of materials, which can make the materials form a specific structure. The subsequent removal of the template material requires operations such as pickling and drying, which are relatively cumbersome. Or some etching agents are used to create pores to increase the volume of closed pores in hard carbon. For example, zinc oxide, magnesium oxide, K2CO3, KOH, ZnAc2, etc. are often used as chemical etching reagents. Although these can improve the capacity of the negative electrode material, these etching reagents increase the cost and most of them are corrosive. Removing these reagents requires a complex and time-consuming acid dissolution process, which will inevitably cause environmental pollution, high energy consumption, and the complexity of the production process. In particular, removing the template may lead to a sharp collapse of the structure and internal defects, resulting in a low tap density and first Coulomb efficiency (ICE).

[0004] The content of the background art section is only the technology known to the inventor and does not of course represent the prior art in this field. Summary of the Invention

[0005] The purpose of the present invention is to provide a carbon material and a preparation method thereof, which can avoid using a templating agent or an etching agent, the method is simple, and the carbon material has the advantages of high specific capacity, high first Coulomb efficiency, and high rate performance.

[0006] To achieve the above purpose, in the first aspect of the present application, a carbon material is provided. The carbon material has a shell layer to form a hollow microsphere structure, and the shell layer has a porous structure, and the porous structure includes closed pores.

[0007] The carbon material provided by the present application has a hollow microsphere structure and a porous structure, the structure is stable, and it can provide more sodium storage sites, which can effectively improve the performance of the first Coulomb efficiency, reversible discharge specific capacity, etc. of sodium-ion batteries.

[0008] In some embodiments of the present application, the specific surface area of the shell layer is 2 - 6 cm 2 / g, and the pore volume is 0.6 - 0.8 cm3 / g, with an average pore diameter of 3.0 - 4.5 nm.

[0009] In some embodiments of the present application, the carbon material satisfies at least one of the following conditions:

[0010] a) The carbon material is formed by carbonizing a three-dimensional structure with a double network cross-linked from a biomass carbon source, a resin, and a polymer;

[0011] b) The median particle size D of the carbon material 50 is 5 - 7 μm;

[0012] c) The carbon layer spacing d of the carbon material 002 ≥0.35 nm, preferably 0.38 - 0.39 nm;

[0013] d) The intensity ratio I of the amorphous carbon peak to the graphitized carbon peak of the carbon material D / I G is 1.15 - 1.40;

[0014] e) The sphericity of the carbon material ≥0.8, preferably 0.85 - 0.95.

[0015] The carbon material within the above parameter ranges has few defect sites, a large layer spacing, a high pore volume, a small pore diameter, and many closed pores on its surface, which can provide more sodium storage sites and result in better performance of the sodium-ion battery prepared.

[0016] The second method of the present application provides a method for preparing a carbon material, including the following steps:

[0017] S1: Disperse a biomass carbon source, a resin, and a polymer in an organic solution, and heat and stir to obtain a gel-like precursor;

[0018] S2: Dry the gel-like precursor to obtain a dried precursor;

[0019] S3: Pyrolyze the dried precursor to obtain a hollow carbon material; and

[0020] S4: Carbonize the hollow carbon material to obtain the carbon material;

[0021] wherein the carbon material has a shell layer to form a hollow microsphere structure, and the shell layer has a porous structure, and the porous structure includes closed pores.

[0022] This application uses resin, polymer, and biomass carbon source as raw materials. First, a cross-linking reaction is carried out to generate a three-dimensional structure of a double network. Then, small molecule gases are pyrolyzed and escaped, so that tiny pore structures are generated inside the material. After carbonization, the surfaces of the generated pore structures inside shrink to form closed pores, thereby obtaining a carbon material with a hollow microsphere structure. The preparation method of this application does not require the use of a templating agent or an etching agent, and is safe and simple.

[0023] In some embodiments of this application, in step S1:

[0024] The molecular weight of the biomass carbon source is 1000 - 3000, preferably 1500 - 2000;

[0025] And / or, the biomass carbon source includes lignin and / or cellulose;

[0026] Preferably, the biomass carbon source is derived from one or more of corn, sorghum, or bagasse;

[0027] And / or, the resin includes hydroxyl groups;

[0028] Preferably, the resin includes phenolic resin and / or epoxy resin;

[0029] And / or, the polymer includes enol compounds;

[0030] Preferably, the polymer includes one or more of polyvinyl alcohol, polypropylene alcohol, and polystyrene alcohol;

[0031] And / or, the organic solution is selected from aqueous solutions of alcohols, wherein the volume ratio of alcohol to water is 5:1 - 7:1.

[0032] Biomass carbon source, such as lignin, is itself a three-dimensional compound with a large molecular weight, and lignin contains rich aromatic ring structures, aliphatic and aromatic hydroxyl groups, and active groups such as quinone groups, and is extremely prone to physical and chemical cross-linking.

[0033] The resin has adhesiveness and contains rich hydroxyl groups, and is very easy to cross-link with the biomass carbon source and bond to each other.

[0034] The hydroxyl groups of the polymer are very easy to cross-link with the biomass carbon source. Moreover, the hydroxyl and carboxyl groups of the polymer itself cross-link to form a network structure, and the hydroxyl groups in the resin will also cross-link with it at low temperatures. Phenolic resin, polypropylene alcohol, and lignin first cross-link to form a two-dimensional layered network structure, and then penetrate each other to form a double network three-dimensional structure.

[0035] In some embodiments of this application, in step S1, the mass ratio of the biomass carbon source, the resin, and the polymer is (1 - 2.5):(1 - 2):(1 - 2).

[0036] At these dosages, the molecular weight of the obtained gel-like precursor is relatively large, and the closed pores of the subsequently prepared carbon material can also be sufficient.

[0037] In some embodiments of the present application, in step S1, through the heating and stirring, the biomass carbon source, the resin, and the polymer are caused to undergo a crosslinking reaction;

[0038] And / or, in step S1, the temperature of the heating and stirring is 90 - 120 °C;

[0039] And / or, in step S1, the rotation speed of the heating and stirring is 800 - 2000 rpm;

[0040] And / or, in step S1, the time of the heating and stirring is 0.5 - 2 h.

[0041] By heating and stirring, the biomass carbon source, the resin, and the polymer are caused to undergo a crosslinking reaction. The polymer itself undergoes crosslinking to form a network structure, and moreover, the biomass carbon source, the resin, and the polymer can crosslink, penetrate, and bond together. The obtained gel-like precursor has a three-dimensional structure of a double network, and this double-network three-dimensional structure has a network structure formed by the crosslinking of the polymer itself and the network structure of the biomass carbon source itself, so it is relatively large.

[0042] Under the above parameters, the molecular weight of the obtained gel-like precursor is relatively large, and the closed pores of the subsequently prepared carbon material can also be sufficient.

[0043] In some embodiments of the present application, in step S2, the drying treatment includes one or more of heat drying, freeze drying, room-temperature drying, and CO2 supercritical drying;

[0044] And / or, the temperature of the freeze drying is -50 °C to -70 °C;

[0045] And / or, the time of the freeze drying is 8 - 16 h.

[0046] After the drying treatment, it is more convenient for subsequent pyrolysis and carbonization.

[0047] In some embodiments of the present application, in step S3, the pyrolysis of the dried precursor is carried out in a protective gas;

[0048] And / or, the protective gas is selected from one or more of nitrogen, neon, argon, krypton, xenon, and radon;

[0049] And / or, the flow rate of the protective gas is 1 - 20 L / min;

[0050] And / or, in step S3, the temperature of the pyrolysis is 400~600°C;

[0051] And / or, in step S3, the heating rate of the pyrolysis is 1~5°C / min;

[0052] And / or, in step S3, the time of the pyrolysis is 2~10 h.

[0053] Pyrolysis can vaporize the high molecular polymers in the gel-like precursor into organic gases and escape, thereby generating a pore structure inside the precursor. And after pyrolysis, the structural stability of the material can be improved, the structural order degree of the material can be effectively increased, and the specific surface area of the material can be effectively reduced, etc.

[0054] In some embodiments of the present application, in step S4, the carbonization of the hollow carbon material is carried out in a protective gas;

[0055] And / or, the protective gas is selected from one or more of nitrogen, neon, argon, krypton, xenon, and radon;

[0056] And / or, the flow rate of the protective gas is 1~20 L / min;

[0057] And / or, the temperature of the carbonization is 1100~1400°C;

[0058] And / or, the heating rate of the carbonization is 1~10°C / min;

[0059] And / or, the time of the carbonization is 2~4 h.

[0060] The biomass carbon source and the resin are both carbonized. At high temperature, the surface of the pore structure inside the hollow carbon material will shrink to form closed pores, thereby obtaining a carbon material with a hollow microsphere structure having closed pores.

[0061] The third aspect of the present application provides a negative electrode sheet, which includes the above carbon material or the carbon material prepared by the above preparation method.

[0062] The fourth aspect of the present application provides a sodium ion battery, which includes the above negative electrode sheet.

[0063] The sodium ion battery provided by the present application has good performance such as the first Coulomb efficiency and reversible discharge specific capacity, and good electrical conductivity. The present application comprehensively improves the performance of the finished battery.

[0064] The additional aspects and advantages of the present invention will be partially given in the following description, partially become obvious from the following description, or be understood through the practice of the present invention. Description of the Drawings

[0065] The accompanying drawings, which form a part of this disclosure, are used to provide a further understanding of this disclosure. The illustrative embodiments and descriptions thereof are used to explain this disclosure and do not constitute an improper limitation to this disclosure.

[0066] Figure 1 is a process flow chart for preparing carbon materials provided by an embodiment of this application;

[0067] Figure 2 is an SEM image of the carbon material provided by Embodiment 1 of this application, with a magnification of 5000×; and

[0068] Figure 3 is another SEM image of the carbon material provided by Embodiment 1 of this application, with a magnification of 30000×. Detailed Description of the Invention

[0069] In the following text, only some exemplary embodiments are simply described. As those skilled in the art can recognize, the described embodiments can be modified in various different ways without departing from the spirit or scope of the present invention. Therefore, the drawings and descriptions are considered to be exemplary in nature rather than restrictive.

[0070] The following disclosure provides many different embodiments or examples for implementing the present invention. To simplify the disclosure of the present invention, the components and settings of specific examples are described below. Of course, they are only examples and are not intended to limit the present invention. In addition, the present invention may repeat reference numerals and / or reference letters in different examples. This repetition is for the purpose of simplification and clarity and does not itself indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides examples of various specific processes and materials, but those of ordinary skill in the art can be aware of the application of other processes and / or the use of other materials.

[0071] In addition, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. It will also be understood that terms, such as those defined in common dictionaries, should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and the present invention, and will not be interpreted in an idealized or overly formal sense unless explicitly so defined herein.

[0072] Taking into account the measurements discussed and the errors associated with the measurements of specific quantities (i.e., the limitations of the measurement system), as used herein, "about" or "approximately" includes the stated value and means within an acceptable range of deviation from the specific value as determined by those skilled in the art. For example, "about" can mean within one or more standard deviations, or within ±30%, ±20%, ±10%, or ±5% of the stated value.

[0073] The specific embodiments of the present invention will be described in more detail below in conjunction with the accompanying drawings and embodiments, so as to better understand the solution of the present invention and the advantages of its various aspects. However, the specific embodiments and examples described below are for illustrative purposes only and are not limitations on the present invention.

[0074] The carbon material provided in this application is carbonized from a three-dimensional structure of a double network formed by cross-linking a biomass carbon source, a resin, a polymer, etc. This carbon material has a shell layer to form a hollow microsphere structure. The shell layer has a porous structure, and the porous structure includes closed pores and open pores. The open pores include micropores and / or mesopores. Optionally, the sphericity of the hollow microsphere structure is ≥0.8. In some specific embodiments, the sphericity can be 0.80, 0.82, 0.84, 0.86, 0.88, 0.90, 0.92, 0.94, 0.96, etc. Preferably, the sphericity is 0.85 - 0.95, which is relatively close to a sphere. The carbon material provided in this application has a good spherical morphology, which is beneficial to the processing of subsequent materials. Moreover, the material structure is stable, has a rich pore structure, and can provide relatively many sodium storage sites, thereby being beneficial to improving the performance of the sodium-ion battery such as the first Coulombic efficiency and the reversible discharge specific capacity.

[0075] Among them, the specific surface area of the shell layer can be 2 - 6 cm 2 / g. In some specific embodiments, the specific surface area of the shell layer can be 2 cm 2 / g, 2.5 cm 2 / g, 3 cm 2 / g, 3.5 cm 2 / g, 4 cm 2 / g, 4.5 cm 2 / g, 5 cm 2 / g, 5.5 cm 2 / g or 6 cm 2 / g.

[0076] The pore volume of the shell layer can be 0.06 - 0.08 cm 3 / g. In some specific embodiments, the pore volume of the shell layer can be 0.06 cm 3 / g, 0.062 cm 3 / g, 0.064 cm 3 / g, 0.066 cm 3 / g, 0.068 cm 3 / g, 0.07 cm 3 / g, 0.072 cm 3 / g, 0.074 cm 3 / g, 0.076 cm 3 / g, 0.078 cm 3 / g or 0.08 cm 3 / g.

[0077] The average pore diameter of the shell layer can be 3.0 to 4.5 nm. In some specific embodiments, the average pore diameter of the porous structure can be 3 nm, 3.2 nm, 3.5 nm, 3.8 nm, 4 nm, 4.2 nm or 4.5 nm.

[0078] Optionally, the median particle size (D 50 ) of the carbon material is 5 to 7 μm. In some specific embodiments, D 50 can be 5 μm, 5.2 μm, 5.4 μm, 5.6 μm, 5.8 μm, 6.0 μm, 6.2 μm, 6.4 μm, 6.6 μm, 6.8 μm or 7 μm.

[0079] Optionally, the carbon layer spacing d 002 ≥0.35 nm, and d 002 is preferably 0.38 to 0.39 nm. In some specific embodiments, d 002 can be 0.38 nm, 0.382 nm, 0.384 nm, 0.386 nm, 0.388 nm or 0.39 nm.

[0080] Optionally, the intensity ratio I D / I G of the amorphous carbon peak and the graphitized carbon peak of the carbon material is 1.15 to 1.40. In some specific embodiments, I D / I G can be 1.15, 1.17, 1.20, 1.23, 1.25, 1.28, 1.30, 1.32, 1.35, 1.37, 1.39 or 1.40.

[0081] The carbon material within the above parameter ranges has few defect sites, a large layer spacing, a high pore volume, a small pore diameter, and many closed pores on its surface, which can provide more sodium storage sites and result in better performance of the sodium-ion battery prepared.

[0082] Figure 1 FIG. shows a preparation method of the carbon material provided in an embodiment of the present application, including the following steps S1 to S4.

[0083] S1: Disperse the biomass carbon source, resin and polymer in an organic solution, and heat and stir to obtain a gel-like precursor.

[0084] Optionally, the molecular weight of the biomass carbon source is 1000 - 3000, preferably 1500 - 2000. In some specific embodiments, the molecular weight of the biomass carbon source can be 1500, 1550, 1600, 1650, 1700, 1750, 1800, 1850, 1900, 1950 or 2000.

[0085] Optionally, the biomass carbon source includes lignin and / or cellulose. The biomass carbon source can be derived from any plant, such as corn, sorghum, bagasse, etc. The biomass carbon source, such as lignin, is itself a three-dimensional compound with a large molecular weight, and lignin contains rich aromatic ring structures, aliphatic and aromatic hydroxyl groups, quinone groups and other active groups, and is extremely prone to physical and chemical cross-linking.

[0086] Optionally, the resin includes rich hydroxyl groups. For example, the resin can include phenolic resin and / or epoxy resin. The resin has adhesiveness and contains rich hydroxyl groups, and is very easy to cross-link with the biomass carbon source and bond together with each other.

[0087] Optionally, the high molecular polymer includes enol. For example, the high molecular polymer can include one or more of polyvinyl alcohol, polypropylene alcohol and polystyrene alcohol. The hydroxyl groups of the high molecular polymer are very easy to cross-link with the biomass carbon source. Moreover, the hydroxyl and carboxyl groups of the high molecular polymer itself will cross-link to form a network structure, and the hydroxyl groups in the resin will also cross-link with it at low temperature. Phenolic resin, polypropylene alcohol and lignin first cross-link to form a two-dimensional layered network structure, and then penetrate each other to form a double-network three-dimensional structure.

[0088] Optionally, the organic solution is an aqueous solution of alcohol, such as an aqueous solution of methanol, ethanol, isopropanol, etc. The volume ratio of alcohol to water is, for example, 5:1 - 10:1. In some specific embodiments, the volume ratio of alcohol to water can be 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1, preferably 7:1.

[0089] In this step, by heating and stirring, the biomass carbon source, the resin and the high molecular polymer are made to undergo a cross-linking reaction. In this step, the high molecular polymer itself will cross-link to form a network structure, and moreover, the biomass carbon source, the resin and the high molecular polymer can cross-link, penetrate and bond together, and the obtained gel-like precursor is a double-network three-dimensional structure. This double-network three-dimensional structure has a network structure formed by the self-cross-linking of the high molecular polymer itself and the network structure of the biomass carbon source itself, so it is relatively large.

[0090] Optionally, the temperature of heating and stirring is 90~120°C, and the time is 0.5~2 h. The temperature of heating and stirring should preferably not be too high, so that the molecular weight of the gel-like precursor obtained by the cross-linking reaction is relatively large, and thus the obtained three-dimensional structure will also be larger. In some specific embodiments, the temperature of heating and stirring can be 90°C, 95°C, 100°C, 105°C, 110°C, 115°C or 120°C. In some specific embodiments, the time of heating and stirring can be 0.5 h, 0.75 h, 1 h, 1.25 h, 1.5 h, 1.75 h or 2 h.

[0091] Optionally, the mass ratio of the biomass carbon source, resin, and polymer is (1~2.5):(1~2):(1~2). Under these dosages, the molecular weight of the obtained gel-like precursor is relatively large, and the closed pores of the subsequent prepared carbon material can also be sufficient. In some specific embodiments, the mass ratio of the biomass carbon source, resin, and polymer can be 1:1:1, 1:1:2, 1:2:1, 2:3:3, 1:2:2, 3:2:2, 3:4:4, 2:1:1, 4:3:3, 5:2:2, 5:3:3 or 5:4:4.

[0092] S2: Dry the gel-like precursor to obtain a dried precursor.

[0093] Optionally, the drying treatment includes one or more of heat drying, freeze drying, room temperature drying, and CO2 supercritical drying. Optionally, when freeze drying is used, the temperature of freeze drying is -50°C~-70°C. In some specific embodiments, the temperature of freeze drying can be -50°C, -54°C, -58°C, -60°C, -62°C, -66°C or -70°C.

[0094] The time of freeze drying can be adjusted according to the actual situation. Optionally, the time of freeze drying is 8~16 h. In some specific embodiments, the time of freeze drying can be 8 h, 8.5 h, 9 h, 9.5 h, 10 h, 10.5 h, 11 h, 11.5 h, 12 h, 12.5 h, 13 h, 13.5 h, 14 h, 14.5 h, 15 h, 15.5 h or 16 h.

[0095] After drying the prepared gel-like precursor with a double-network three-dimensional structure in this step, it is more convenient for subsequent pyrolysis and carbonization.

[0096] S3: Pyrolyze the dried precursor to obtain a hollow carbon material.

[0097] Optionally, the pyrolysis of the dried precursor is carried out in a protective gas. Optionally, the protective gas is selected from one or more of nitrogen, neon, argon, krypton, xenon, and radon. Optionally, the flow rate of the protective gas is 1-20 L / min. In some specific embodiments, the flow rate of the protective gas can be 1 L / min, 3 L / min, 5 L / min, 7 L / min, 9 L / min, 10 L / min, 12 L / min, 14 L / min, 16 L / min, 18 L / min, or 20 L / min.

[0098] Optionally, the pyrolysis temperature is 400-600 °C. In some specific embodiments, the pyrolysis temperature can be 400 °C, 440 °C, 480 °C, 500 °C, 520 °C, 560 °C, or 600 °C.

[0099] Optionally, the heating rate of the pyrolysis is 1-5 °C / min. In some specific embodiments, the heating rate of the pyrolysis can be 1 °C / min, 1.5 °C / min, 2 °C / min, 2.5 °C / min, 3 °C / min, 3.5 °C / min, 4 °C / min, 4.5 °C / min, 5 °C / min.

[0100] Optionally, the pyrolysis time is 2-10 h. In some specific embodiments, the pyrolysis time can be 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h.

[0101] In this step, the high molecular polymer in the gel-like precursor can be vaporized into organic gas and escape within this temperature range, thereby generating a pore structure inside the precursor. And after pyrolysis, the structural stability of the material can be improved, the structural order of the material can be effectively improved, and the specific surface area of the material can be effectively reduced, etc.

[0102] S4: Carbonize the hollow carbon material to obtain a carbon material.

[0103] Optionally, the carbonization of the hollow carbon material is carried out in a protective gas. Optionally, the protective gas is selected from one or more of nitrogen, neon, argon, krypton, xenon, and radon. Optionally, the flow rate of the protective gas is 1-20 L / min. In some specific embodiments, the flow rate of the protective gas can be 1 L / min, 3 L / min, 5 L / min, 7 L / min, 9 L / min, 10 L / min, 12 L / min, 14 L / min, 16 L / min, 18 L / min, or 20 L / min.

[0104] Optionally, the carbonization temperature is 1100~1400°C. In some specific embodiments, the carbonization temperature can be 1100°C, 1150°C, 1200°C, 1250°C, 1300°C, 1350°C or 1400°C.

[0105] Optionally, the heating rate of carbonization is 1~10°C / min. In some specific embodiments, the heating rate of carbonization can be 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min or 10°C / min.

[0106] Optionally, the carbonization time is 2~4 h. In some specific embodiments, the carbonization time can be 2 h, 2.3 h, 2.6 h, 2.8 h, 3 h, 3.3 h, 3.6 h, 3.8 h or 4 h.

[0107] In this step, both the biomass carbon source and the resin are carbonized. At high temperature, the surface of the pore structure inside the hollow carbon material will shrink to form closed pores, thereby obtaining a carbon material with a hollow microsphere structure having closed pores.

[0108] The specific properties of the obtained carbon material are as described above and will not be elaborated here.

[0109] This application uses resin, polymer and biomass carbon source as raw materials. First, a cross-linking reaction occurs to generate a three-dimensional structure of a double network. Then, small molecule gases are pyrolyzed and escaped, causing pore structures to be generated inside the material. After carbonization, the surface of the generated pore structures inside shrinks to form closed pores, thereby obtaining a carbon material with closed pores and a hollow interior. The preparation method of this application does not require the use of templates or etching agents, and is safe and simple.

[0110] This application further provides a negative electrode sheet, which includes the above carbon material or the carbon material prepared by the above preparation method.

[0111] The negative electrode sheet generally includes a negative electrode current collector and a negative electrode film layer provided on the negative electrode current collector. Among them, the negative electrode film layer can include the above carbon material.

[0112] The current collector can be a metal foil, such as an aluminum foil, a copper foil, etc., preferably a copper foil. The negative electrode film layer can also include a binder, a conductive agent, etc. The binder can be, for example, styrene-butadiene rubber (SBR), polyvinylidene chloride (PVDF), polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC-Na), sodium alginate, etc. The conductive agent can be, for example, graphene, carbon nanotubes, Ketjen black, conductive carbon black (SP), etc. Optionally, the negative electrode film layer can also include other additives, such as a dispersant (such as carboxymethyl cellulose (CMC)), etc.

[0113] The present application also provides a sodium-ion battery, which includes the above-mentioned negative electrode sheet.

[0114] The sodium-ion battery of the present application is a secondary battery, which means a battery that can be activated by charging after discharging and can be used continuously. Usually, a secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. During the charge and discharge process of the battery, active ions are embedded and extracted back and forth between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet to play a role of isolation. The electrolyte plays a role of conducting ions between the positive electrode sheet and the negative electrode sheet.

[0115] The positive electrode sheet may include a current collector and a positive electrode film layer. The current collector can be a metal foil, such as an aluminum foil, a copper foil, etc. The specific type of the active material of the positive electrode film layer is not limited and can be selected according to actual needs. The types of the separator and the electrolyte in the present application are also not limited and can be selected according to actual needs.

[0116] The sodium-ion battery provided by the present application has good performance such as the first Coulomb efficiency and the reversible discharge specific capacity, and good electrical conductivity. The present application comprehensively improves the performance of the finished battery.

[0117] The following describes the present invention with reference to specific embodiments. The numerical values of the process conditions taken in the following embodiments and comparative examples are all exemplary, and their available numerical ranges are as shown in the foregoing invention content. For process parameters not specifically noted, reference can be made to conventional techniques. Unless otherwise specified, the reagents and instruments used in the technical solutions provided by the present invention can be obtained from conventional channels or the market. It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other.

[0118] Example 1

[0119] This example prepares a carbon material, and the specific steps are as follows:

[0120] S1: Take phenolic resin, lignin (molecular weight of 1513.5), and polyvinyl alcohol and disperse them in an ethanol aqueous solution (the mass ratio of ethanol to water is 7:1) in a ratio of 1:2:2, and heat and stir at a temperature of 90 °C for 0.5 h to obtain a gel-like precursor.

[0121] S2: Freeze-dry the gel-like precursor to obtain a dried precursor.

[0122] S3: Pyrolyze the dried precursor at a temperature of 400 °C for 2 h to pyrolyze the polyvinyl alcohol in the cross-linked network into organic gas and escape, forming a hollow carbon material with a pore structure.

[0123] S4: Place the hollow carbon material in a nitrogen atmosphere and carbonize it at 1300 °C for 2 h. The hollow microsphere structure shrinks, and after cooling, a carbon material with a hollow microsphere structure having closed pores in the shell is obtained.

[0124] The carbon material is tested, and its SEM images are shown in Figure 2 and Figure 3 , and the remaining performance parameters are shown in Table 1.

[0125] Among them, the performance characterization methods of the carbon materials prepared in this example, the following examples, and the comparative examples are as follows:

[0126] The BET method is used to conduct adsorption and desorption experiments on the material to obtain the specific surface area, pore volume, and pore diameter of the material; a laser particle size analyzer is used to measure the median particle size (D 50 ) of the sample; XRD is used to calculate the carbon layer spacing (d 002 ), and the incident light wavelength is 1.54056 Å; Raman spectroscopy is used to measure the ratio I D / I G of the intensities of the typical D peak and G peak to calculate the ratio of the amorphous carbon peak and the graphitized carbon peak, and a dynamic particle size and shape analyzer is used to measure the sphericity of the material.

[0127] Example 2

[0128] In this example, a carbon material is prepared, and the specific steps are as follows:

[0129] S1: Take phenolic resin, lignin (molecular weight of 1513.5), and polyvinyl alcohol and disperse them in an ethanol aqueous solution (mass ratio of ethanol to water is 7:1) at a ratio of 1:2:1, and heat and stir at 70 °C for 0.5 h to obtain a gel-like precursor.

[0130] S2: Freeze-dry the gel-like precursor to obtain a dry precursor.

[0131] S3: Pyrolyze the dry precursor at 400 °C for 2 h to cause the polyvinyl alcohol in the cross-linked network to pyrolyze into organic gas and escape, forming a hollow carbon material with a pore structure.

[0132] S4: Place the hollow carbon material in a nitrogen atmosphere and carbonize it at 1300 °C for 2 h. The hollow microsphere structure shrinks, and after cooling, a carbon material with a hollow microsphere structure having closed pores in the shell is obtained.

[0133] The carbon material is tested, and the performance parameters are shown in Table 1.

[0134] Example 3

[0135] In this example, a carbon material is prepared, and the specific steps are as follows:

[0136] S1: Take phenolic resin, lignin (molecular weight is 1513.5), and polyvinyl alcohol and disperse them in an ethanol aqueous solution (the mass ratio of ethanol to water is 7:1) in a ratio of 1:1:2. Heat and stir at a temperature of 110 °C for 0.5 h to obtain a gel-like precursor.

[0137] S2: Freeze-dry the gel-like precursor to obtain a dry precursor.

[0138] S3: Pyrolyze the dry precursor at a temperature of 400 °C for 2 h to pyrolyze the polyvinyl alcohol in the crosslinked network into organic gas and escape, forming a hollow carbon material with a pore structure.

[0139] S4: Place the hollow carbon material in a nitrogen atmosphere and carbonize it at a temperature of 1300 °C for 2 h. The hollow microsphere structure shrinks, and after cooling, a carbon material with a hollow microsphere structure having closed pores in the shell is obtained.

[0140] Detect the carbon material, and the performance parameters are shown in Table 1.

[0141] Example 4

[0142] This example prepares a carbon material, and the specific steps are as follows:

[0143] S1: Take epoxy resin, lignin (molecular weight is 1513.5), and polyvinyl alcohol and disperse them in an ethanol aqueous solution (the mass ratio of ethanol to water is 7:1) in a ratio of 1:2:2. Heat and stir at a temperature of 90 °C for 0.5 h to obtain a gel-like precursor.

[0144] S2: Freeze-dry the gel-like precursor to obtain a dry precursor.

[0145] S3: Pyrolyze the dry precursor at a temperature of 400 °C for 2 h to pyrolyze the polyvinyl alcohol in the crosslinked network into organic gas and escape, forming a hollow carbon material with a pore structure.

[0146] S4: Place the hollow carbon material in a nitrogen atmosphere and carbonize it at a temperature of 1300 °C for 2 h. The hollow microsphere structure shrinks, and after cooling, a carbon material with a hollow microsphere structure having closed pores in the shell is obtained.

[0147] Detect the carbon material, and the performance parameters are shown in Table 1.

[0148] Example 5

[0149] This example prepares a carbon material, and the specific steps are as follows:

[0150] S1: Take phenolic resin, lignin (molecular weight of 1513.5), and polyvinyl alcohol and disperse them in an ethanol aqueous solution (mass ratio of ethanol to water is 7:1) at a ratio of 1:2:2, and heat and stir at 90 °C for 0.5 h to obtain a gel-like precursor.

[0151] S2: Freeze-dry the gel-like precursor to obtain a dried precursor.

[0152] S3: Pyrolyze the dried precursor at 600 °C for 2 h to pyrolyze the polyvinyl alcohol in the crosslinked network into organic gas and escape, forming a hollow carbon material with a pore structure.

[0153] S4: Place the hollow carbon material in a nitrogen atmosphere and carbonize it at 1300 °C for 2 h. The hollow microsphere structure shrinks, and after cooling, a carbon material with a hollow microsphere structure having closed pores on the shell is obtained.

[0154] Detect the carbon material, and the performance parameters are shown in Table 1.

[0155] Example 6

[0156] This example prepares a carbon material, and the specific steps are as follows:

[0157] S1: Take phenolic resin, lignin (molecular weight of 1513.5), and polyvinyl alcohol and disperse them in an ethanol aqueous solution (mass ratio of ethanol to water is 7:1) at a ratio of 1:2:2, and heat and stir at 90 °C for 0.5 h to obtain a gel-like precursor.

[0158] S2: Freeze-dry the gel-like precursor to obtain a dried precursor.

[0159] S3: Pyrolyze the dried precursor at 400 °C for 2 h to pyrolyze the polyvinyl alcohol in the crosslinked network into organic gas and escape, forming a hollow carbon material with a pore structure.

[0160] S4: Place the hollow carbon material in a nitrogen atmosphere and carbonize it at 1100 °C for 2 h. The hollow microsphere structure shrinks, and after cooling, a carbon material with a hollow microsphere structure having closed pores on the shell is obtained.

[0161] Detect the carbon material, and the performance parameters are shown in Table 1.

[0162] Comparative Example 1

[0163] This comparative example prepares a carbon material, and the specific steps are as follows:

[0164] S1': Take phenolic resin, lignin (molecular weight of 1513.5) and disperse them in an ethanol aqueous solution (mass ratio of ethanol to water is 7:1) at a ratio of 1:2, and heat and stir at 90 °C for 0.5 h to obtain a gel-like precursor.

[0165] S2: Freeze-dry the gel-like precursor to obtain a dried precursor.

[0166] S3: Pyrolyze the dried precursor at a temperature of 400 °C for 2 h to pyrolyze the polyvinyl alcohol in the cross-linked network into organic gas and escape, forming a hollow carbon material with a pore structure.

[0167] S4: Place the hollow carbon material in a nitrogen atmosphere and carbonize it at a temperature of 1300 °C for 2 h. The hollow microsphere structure shrinks, and a carbon material is obtained after cooling.

[0168] Detect the carbon material, and the performance parameters are shown in Table 1.

[0169] Comparative Example 2

[0170] A carbon material is prepared in this comparative example, and the specific steps are as follows:

[0171] S1'': Disperse phenolic resin and polyvinyl alcohol in an ethanol aqueous solution (the mass ratio of ethanol to water is 7:1) according to a ratio of 1:2, and heat and stir at a temperature of 90 °C for 0.5 h to obtain a gel-like precursor.

[0172] S2: Freeze-dry the gel-like precursor to obtain a dried precursor.

[0173] S3: Pyrolyze the dried precursor at a temperature of 400 °C for 2 h to pyrolyze the polyvinyl alcohol in the cross-linked network into organic gas and escape, forming a hollow carbon material with a pore structure.

[0174] S4: Place the hollow carbon material in a nitrogen atmosphere and carbonize it at a temperature of 1300 °C for 2 h. The hollow structure shrinks, and a carbon material is obtained after cooling.

[0175] Detect the carbon material, and the performance parameters are shown in Table 1.

[0176] Comparative Example 3

[0177] A carbon material is prepared in this comparative example, and the specific steps are as follows:

[0178] S1''': Disperse phenolic resin in an ethanol aqueous solution (the mass ratio of ethanol to water is 7:1), and heat and stir at a temperature of 90 °C for 0.5 h to obtain a gel-like precursor.

[0179] S2: Freeze-dry the gel-like precursor to obtain a dried precursor.

[0180] S3: Pyrolyze the dried precursor at a temperature of 400 °C for 2 h to pyrolyze the polyvinyl alcohol in the cross-linked network into organic gas and escape, forming a hollow carbon material with a pore structure.

[0181] S4: Place the hollow carbon material in a nitrogen atmosphere and carbonize it at a temperature of 1300 °C for 2 h. The hollow structure shrinks, and a carbon material is obtained after cooling.

[0182] Detect the carbon material, and the performance parameters are shown in Table 1.

[0183] Comparative Example 4

[0184] In this comparative example, a carbon material is prepared, and the specific steps are as follows:

[0185] S1: Take phenolic resin, lignin (molecular weight is 1513.5), and polyvinyl alcohol and disperse them in an ethanol aqueous solution (the mass ratio of ethanol to water is 7:1) according to the ratio of 1:2:2. Heat and stir at a temperature of 90 °C for 0.5 h to obtain a gel-like precursor.

[0186] S2: Freeze-dry the gel-like precursor to obtain a dry precursor.

[0187] S3’: Place the dry precursor in a nitrogen atmosphere and carbonize it at a temperature of 1300 °C for 2 h. The hollow structure shrinks, and a carbon material is obtained after cooling.

[0188] Detect the carbon material, and the performance parameters are shown in Table 1.

[0189] Experimental Example

[0190] Assemble the carbon materials prepared in Examples 1-6 and Comparative Examples 1-4 into batteries respectively. The specific steps are as follows:

[0191] According to the mass ratio of active material:SP:CMC:SBR = 92:2:2:4, weigh the carbon material, SP, CMC, and SBR respectively and uniformly mix them in deionized water to prepare a slurry; coat the uniformly mixed slurry on an aluminum foil current collector and bake it in an oven at 80 °C for 1 h, and then cool it to room temperature.

[0192] Adjust the roller pressing distance to perform pole piece rolling. Cut the rolled pole piece to make small round pieces with a diameter of 14 mm and weigh them as m1. Similarly, cut the aluminum foil current collector to make aluminum foil round pieces with a diameter of 14 mm and weigh them as m2. Among them, (m1 - m2) × 0.94 is the mass of the active material, denoted as m3. The weighed small round pieces are then placed in an oven at 80 °C and vacuum baked for 12 h.

[0193] Transfer the vacuum-baked small round pieces to a glove box. Using a sodium sheet as the counter electrode and auxiliary electrode, with an electrolyte of 1 M NaPF6 / EC:DMC:DEC = 2:2:1 and a glass fiber separator as the separator, assemble a sodium-ion button battery in a glove box with the oxygen and water content both less than 0.01 ppm.

[0194] Let the assembled button-type sodium-ion battery stand still for 12 h. Test the electrochemical performance of the stationary button-type sodium-ion battery on a Wuhan Blue Electric battery testing system under constant current. The specific parameters are shown in Table 2.

[0195] Table 1

[0196]

[0197] Table 2

[0198]

[0199] As can be seen from Table 1 and Table 2, the specific surface area of the carbon material prepared in the examples of the present application is about 2-6 cm 2 / g, the pore volume is about 0.06-0.08 cm 3 / g, the pore diameter is about 3.0-4.5 nm, D 50 is about 5-7 μm, d(002) is about 0.38-0.39 nm, I D / I G is about 1.15-1.40, and the sphericity is about 0.85-0.95. Therefore, after cross-linking with resin, biomass carbon source and polymer, the present application can effectively reduce the defect sites on the surface of the carbon material and increase the layer spacing, which is beneficial to improving the electrochemical performance of the material. After high-temperature pyrolysis, the specific surface area of the obtained carbon material can be effectively reduced. Moreover, the obtained carbon material has a high pore volume, a small pore diameter, and many closed pore structures on its surface, which can provide more sodium storage sites.

[0200] As can be seen from Table 2, the reversible charge and discharge and the first efficiency of the untreated resin are poor. Adding a single substance for cross-linking cannot effectively improve the electrochemical performance of the material. By adding a polymer compound and lignin for reaction cross-linking to form a network structure, and then mutually penetrating to form a gel-like precursor with a three-dimensional structure of a double network. During the high-temperature pyrolysis process of the formed three-dimensional network structure, the high-molecular organic matter in the cross-linking network pyrolyzes into organic gases and escapes, forming an internal hollow structure. Under the action of high temperature, the material structure is stabilized. More closed pore structures can be formed during the subsequent carbonization process, which can provide more sodium storage sites. The results show that its reversible discharge specific capacity and first Coulomb efficiency have been significantly improved.

[0201] From Figure 2 and Figure 3 it can be seen that the carbon material prepared in the present application has a uniform hollow microsphere structure with a particle size of about 5-7 μm and a sphericity of about 0.85-0.95, and its shell layer has abundant closed pores.

[0202] Obviously, the above embodiments are merely examples given to clearly illustrate the present invention and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for preparing a carbon material, characterized in that, It includes the following steps: S1: Dispersing a biomass carbon source, a resin, and a polymer in an organic solution, and heating and stirring to obtain a gel-like precursor; S2: Subjecting the gel-like precursor to a drying treatment to obtain a dried precursor; S3: Pyrolyzing the dried precursor to obtain a hollow carbon material; and S4: Carbonizing the hollow carbon material to obtain the carbon material; wherein, the carbon material has a shell layer to form a hollow microsphere structure, the shell layer has a porous structure, and the porous structure includes closed pores; wherein, the resin contains hydroxyl groups, the polymer includes enol compounds, and the mass ratio of the biomass carbon source, the resin, and the polymer is (1 - 2.5):(1 - 2):(1 - 2).

2. The preparation method according to claim 1, characterized in that, Step S1 satisfies at least one of the following conditions: The molecular weight of the biomass carbon source is 1000 - 3000; The biomass carbon source includes lignin and / or cellulose; The organic solution is selected from aqueous solutions of alcohols, wherein the volume ratio of alcohol to water is 5:1 - 7:

1.

3. The preparation method according to claim 2, wherein Step S1 also satisfies at least one of the following conditions: The molecular weight of the biomass carbon source is 1500 - 2000; The biomass carbon source is derived from one or more of corn, sorghum, or bagasse; The resin includes phenolic resin and / or epoxy resin; The polymer includes one or more of polyvinyl alcohol, polypropylene alcohol, and polystyrene alcohol.

4. The preparation method according to claim 1, wherein, In step S1, through the heating and stirring, the biomass carbon source, the resin, and the polymer undergo a crosslinking reaction.

5. The preparation method according to claim 4, wherein Step S1 also satisfies at least one of the following conditions: The temperature of the heating and stirring is 90 - 120°C; The rotation speed of the heating and stirring is 800 - 2000 rpm; The time of the heating and stirring is 0.5 - 2 h.

6. The preparation method according to claim 1, wherein In step S2, the drying treatment includes one or more of heat drying, freeze drying, normal temperature drying, and CO2 supercritical drying.

7. The preparation method according to claim 6, characterized in that, The temperature of the freeze drying is -50°C to -70°C; and / or The time of the freeze drying is 8 - 16 h.

8. The preparation method according to claim 1, wherein In step S3, pyrolyzing the dried precursor is carried out in a protective gas.

9. The preparation method according to claim 8, characterized in that, Step S3 also satisfies at least one of the following conditions: The protective gas is selected from one or more of nitrogen, neon, argon, krypton, xenon, and radon; The flow rate of the protective gas is 1 - 20 L / min; The temperature of the pyrolysis is 400 - 600°C; The heating rate of the pyrolysis is 1 - 5°C / min; The time of the pyrolysis is 2 - 10 h.

10. The preparation method according to claim 1, characterized in that, In step S4, carbonizing the hollow carbon material is carried out in a protective gas.

11. The preparation method according to claim 10, characterized in that, Step S4 also satisfies at least one of the following conditions: The protective gas is selected from one or more of nitrogen, neon, argon, krypton, xenon, and radon; The flow rate of the protective gas is 1 - 20 L / min; The temperature of the carbonization is 1100 - 1400°C; The heating rate of the carbonization is 1 - 10°C / min; The time of the carbonization is 2 - 4 h.

12. A carbon material, characterized in that, Obtained by the preparation method according to any one of claims 1 - 11.

13. The carbon material according to claim 12, characterized in that, The specific surface area of the shell layer is 2 to 6 cm 2 / g, the pore volume is 0.6 to 0.8 cm 3 / g, and the average pore diameter is 3.0 to 4.5 nm.

14. The carbon material according to claim 12, wherein The carbon material satisfies at least one of the following conditions: a) The carbon material is formed by carbonizing a double-network three-dimensional structure crosslinked from a biomass carbon source, a resin, and a high molecular polymer; b) The median particle size D of the carbon material 50 is 5 to 7 μm; c) The carbon layer spacing d of the carbon material 002 ≥0.35 nm; d) The intensity ratio I of the amorphous carbon peak to the graphitized carbon peak of the carbon material D / I G is 1.15 to 1.40; e) The sphericity of the carbon material is ≥ 0.

8.

15. The carbon material according to claim 14, characterized in that, The carbon layer spacing d of the carbon material 002 is 0.38 to 0.39 nm; and / or The sphericity of the carbon material is 0.85 to 0.

95.

16. A negative electrode sheet, characterized in that, It includes the carbon material described in any one of claims 12 to 15.

17. A sodium-ion battery, characterized in that, It includes the negative electrode sheet described in claim 16.

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