A hard carbon material, its preparation method and application

Abstract

The present invention provides a hard carbon material, a preparation method thereof and an application thereof. In the Raman spectrum of the hard carbon material, the ratio of the peak intensity at a wavelength of 1345 cm-1 to the peak intensity at a wavelength of 1600 cm-1 is 0.9 to 1.3, and the powder impedance of the hard carbon material under a pressure of 16 to 20 MPa is 0.02 to 0.07 Ω·cm. The present invention helps to improve the reversible specific capacity, the first Coulomb efficiency and the rate performance of the battery.

Description

Technical Field

[0001] The present invention relates to a negative electrode material, and particularly to a hard carbon material, a preparation method thereof, and an application thereof. Background Art

[0002] Sodium ion batteries can be widely used in scenarios such as electric two-wheel vehicles, low-speed electric vehicles, and energy storage systems. Currently, the bottleneck in the industrialization of sodium ion batteries mainly lies in hard carbon negative electrode materials, including problems such as high price of hard carbon, insufficient production capacity, and low industry maturity. Therefore, there is an urgent need to develop high-capacity and low-cost hard carbon negative electrode materials for sodium ion batteries. Biomass-based hard carbon is the first choice for large-scale production of hard carbon negative electrodes due to its abundant raw material production, low cost, and high sodium storage capacity.

[0003] However, currently, biomass-based hard carbon generally has problems of low sodium storage capacity and low initial Coulomb efficiency. Summary of the Invention

[0004] The present invention provides a hard carbon material, a preparation method thereof, and an application thereof. The hard carbon material has a high sodium storage capacity and a high initial Coulomb efficiency.

[0005] The present invention provides a hard carbon material. In the Raman spectrum of the hard carbon material, the ratio of the peak intensity at a wavelength of 1345 cm -1 to the peak intensity at a wavelength of 1600 cm -1 is 0.9 to 1.3, and the powder impedance of the hard carbon material under a pressure of 16 to 20 MPa is 0.02 to 0.07 Ω·cm.

[0006] Optionally, the interlayer spacing d 002 of the (002) crystal plane of the hard carbon material is 0.37 to 0.40 nm; and / or, the hard carbon material includes graphite microcrystals and amorphous carbon, the width La of the graphite microcrystals along the a-axis direction is 1.4 to 2.0 nm, the thickness Lc along the c-axis direction is 0.7 to 1.0 nm; the stacking layer number is 2.9 to 3.5.

[0007] Optionally, the hard carbon material includes a core, a first coating layer on the surface of the core, and a second coating layer on the surface of the first coating layer. The first coating layer includes carbon elements, and the second coating layer includes nitrogen and carbon elements.

[0008] Optionally, the ratio of the atomic number of the nitrogen element to the atomic number in the hard carbon material is 0.1% to 2.0%; and / or, the sum of the thicknesses of the first coating layer and the second coating layer is 5 to 100 nm.

[0009] Optionally, the porosity of the hard carbon material is 1% to 10%; and / or, the specific surface area of the hard carbon material is 0.5 to 20 m 2 / g.

[0010] The present invention provides a method for preparing a hard carbon material as described above, comprising: carbonizing a biomass raw material in a first inert atmosphere to obtain a hard carbon precursor; performing pore-forming treatment on the hard carbon precursor under the action of a pore-forming agent to obtain a porous hard carbon precursor with a specific surface area of 300-900 m 2 / g; mixing the porous hard carbon precursor with a first coating agent and performing a first sintering treatment in a second inert atmosphere to obtain a coated porous hard carbon precursor, wherein the first coating agent includes a carbon source; mixing the coated porous hard carbon precursor with a second coating agent and performing a second sintering treatment in a third inert atmosphere to obtain the hard carbon material, wherein the second coating agent includes a carbon and nitrogen source compound, and the carbon and nitrogen source compound includes an amino group and an alkyl group.

[0011] Optionally, the biomass raw material includes one or more of glucose, sucrose, starch, coconut shell, walnut shell, hazelnut shell, and wood; and / or, in the process of carbonizing the biomass raw material to obtain a hard carbon precursor, the temperature of carbonization is 300-800 °C, the time of carbonization is 1-10 h, and the heating rate is 0.5-3 °C / min; and / or, the process of carbonizing the biomass raw material to obtain a hard carbon precursor further includes: after carbonizing the biomass raw material, performing pulverization and sieving to obtain the hard carbon precursor with a mesh number of 300-500; and / or, the pore-forming agent includes a physical pore-forming agent, and the physical pore-forming agent includes water vapor and / or carbon dioxide, and the temperature of the pore-forming treatment is 650-950 °C; and / or, the pore-forming agent includes a chemical pore-forming agent, and the chemical pore-forming agent includes one or more of potassium hydroxide, sodium hydroxide, zinc chloride, and phosphoric acid, and the temperature of the pore-forming treatment is 500-900 °C.

[0012] Optionally, the carbon source includes pitch and / or resin; and / or, the temperature of the first sintering treatment is 1100-1500 °C, the heat preservation time is 1-8 h, and the heating rate is 0.5-3 °C / min; and / or, the temperature of the second sintering treatment is 700-950 °C; and / or, the carbon and nitrogen source compound further includes a carboxyl group, and the carbon and nitrogen source compound includes one or more of isoleucine, leucine, alanine, glycine, proline, valine, tyrosine, phenylalanine, tryptophan, serine, threonine, cysteine, asparagine, glutamine, aspartic acid, glutamic acid, lysine, and arginine; and / or, in the process of the second sintering treatment, the heating rate is 0.5-3 °C / min, and the heat preservation time is 2-6 h.

[0013] The present invention provides a negative electrode sheet, and the negative electrode sheet includes a negative electrode active material layer, and the negative electrode active material layer includes the hard carbon material as described above or the hard carbon material prepared according to the method for preparing the hard carbon material as described above.

[0014] The present invention provides a battery, and the battery includes the negative electrode sheet as described above.

[0015] The present invention provides a hard carbon material, a preparation method thereof and an application thereof. The hard carbon material has many active ion active sites (such as sodium storage active sites), and the hard carbon material has a relatively low powder impedance, which helps to improve the reversible capacity, the first Coulomb efficiency, the rate performance and the cycle performance. Description of the Drawings

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0017] Figure 1 Scanning electron microscope (SEM) photograph of the hard carbon material prepared in Example 1;

[0018] Figure 2 Scanning electron microscope (SEM) photograph of the hard carbon material prepared in Comparative Example 1;

[0019] Figure 3 X-ray diffraction (XRD) pattern of the hard carbon material prepared in Example 1;

[0020] Figure 4 Raman spectrum (Raman) of the hard carbon material prepared in Example 1;

[0021] Figure 5 Charge-discharge curve of the hard carbon material prepared in Example 1. Detailed Embodiments

[0022] To enable those skilled in the art to better understand the solution of the present invention, the present invention will be further described in detail below. The following specific embodiments listed are only for describing the principles and features of the present invention, and the examples given are only for explaining the present invention and do not limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0023] In the prior art, biomass-based hard carbon generally has problems of low sodium storage capacity and low first Coulomb efficiency.

[0024] To overcome the defects in the prior art, an embodiment of the present invention provides a hard carbon material (hard carbon negative electrode material). In the Raman spectrum of the hard carbon material, the wavelength is 1345 cm -1The peak intensity at and the wavelength is 1600 cm -1 The ratio of the peak intensity at to that at is 0.9 to 1.3, and the powder impedance of the hard carbon material under a pressure of 16 to 20 MPa is 0.02 to 0.07 Ω·cm.

[0025] According to the research and analysis: In the Raman spectrum of the above hard carbon material, at wavelengths of 1345 cm -1 and 1600 cm -1 characteristic peaks (D peak and G peak respectively) exist, and the peak intensity I -1 at and the peak intensity I D at -1 The ratio (I G / I D / I G ) is 0.9 to 1.3, which improves the structure of the hard carbon material, making the hard carbon material have more active ion active sites for storing (such as sodium storage active sites), and the hard carbon material has a relatively low powder impedance, thereby helping to improve the reversible capacity, initial Coulomb efficiency, rate performance and cycling performance.

[0026] It can be understood that in the Raman spectrum of the above hard carbon material, at wavelengths of 1345 cm -1 and 1600 cm -1 characteristic peaks (D peak and G peak respectively) exist, corresponding to amorphous carbon structure and graphite-like microcrystalline structure respectively, that is, the above hard carbon material includes amorphous carbon and graphite-like microcrystals. By regulating the structures of amorphous carbon and graphite-like microcrystals in the hard carbon material in the embodiments of the present invention, the hard carbon material has excellent reversible specific capacity and high Coulomb efficiency.

[0027] Exemplarily, the ratio of the peak intensity I -1 at and the peak intensity I D at -1 (I G / I D / I G ) can be 0.9, 1.0, 1.1, 1.2, 1.3 or the range composed of any two of them.

[0028] Exemplarily, the powder impedance of the hard carbon material under a pressure of 16 to 20 MPa can be 0.02, 0.03, 0.04, 0.05, 0.06, 0.07 Ω·cm or the range composed of any two of them.

[0029] In some embodiments, the interlayer spacing d 002 of the (002) crystal plane of the above hard carbon material is 0.37 to 0.40 nm.

[0030] In some embodiments, the above-mentioned hard carbon material includes graphite microcrystals and amorphous carbon. The width La(002) of the graphite microcrystals in the a-axis direction is 1.4 - 2.0 nm, and the thickness Lc in the c-axis direction is 0.7 - 1.0 nm; the stacking layer number (N = Lc / d 002 +1) is 2.9 - 3.5. The above-mentioned hard carbon material consists of a hard carbon structure composed of short-range ordered graphite-like microcrystals and amorphous carbon with appropriate average width, stacking thickness, and stacking layer number, having more sodium (or lithium) storage active sites, and the hard carbon material also has a relatively low powder impedance, thus showing good electrochemical performance, which helps to improve the reversible capacity, initial Coulomb efficiency, rate performance, and cycle performance.

[0031] In some embodiments, the above-mentioned hard carbon material includes a core, a first coating layer on the surface of the core, and a second coating layer on the surface of the first coating layer. The first coating layer includes carbon elements, and the second coating layer includes nitrogen and carbon elements.

[0032] Specifically, the ratio of the atomic number of the above-mentioned nitrogen element to the atomic number in the hard carbon material can be 0.1% - 2.0% (that is, the nitrogen doping ratio in the hard carbon material is 0.1 at% - 2.0 at%). A small amount of nitrogen element doping can enhance the defect active sites of the hard carbon material and improve the conductivity, thereby enhancing the reversible capacity, increasing the capacity in the slope region, and improving the rate performance.

[0033] Exemplarily, the ratio of the atomic number of the nitrogen element to the atomic number in the hard carbon material can be 0.1%, 0.5%, 1.0%, 1.5%, 2.0% or the range composed of any two of them.

[0034] The above-mentioned first coating layer can include carbon elements, and the second coating layer can also include carbon elements. That is, when the hard carbon material is coated with nitrogen elements, it also includes a soft carbon coating layer, which can avoid the side effect of increased irreversible capacity caused by nitrogen doping, improve the interface of the hard carbon material, reduce the side reaction between the defect surface generated by doping and the electrolyte, and improve the initial Coulomb efficiency and rate performance of the hard carbon material.

[0035] Furthermore, the sum of the thicknesses of the first coating layer and the second coating layer can be 5 - 100 nm, such as 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100 nm or the range composed of any two of them.

[0036] In some embodiments, the porosity of the above-mentioned hard carbon material is 1% - 10%, such as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or the range composed of any two of them.

[0037] In some embodiments, the specific surface area of the above-mentioned hard carbon material is 0.5 - 20 m2 / g, such as 0.5, 1, 5, 10, 20 m 2 / g or a range composed of any two of them.

[0038] An embodiment of the present invention further provides a method for preparing the above-mentioned hard carbon material, including: carbonizing a biomass raw material in a first inert atmosphere to obtain a hard carbon precursor; performing pore-forming treatment (pore size regulation) on the hard carbon precursor under the action of a pore-forming agent to obtain a porous hard carbon precursor with a specific surface area of 300 - 900 m 2 / g; after mixing the porous hard carbon precursor and a first coating agent, performing a first sintering treatment in a second inert atmosphere to obtain a coated porous hard carbon precursor, the first coating agent including a carbon source; after mixing the coated porous hard carbon precursor and a second coating agent, performing a second sintering treatment in a third inert atmosphere to obtain a hard carbon material, the second coating agent including a carbonitrogen source compound, and the carbonitrogen source compound including an amino group and an alkyl group.

[0039] According to research and analysis: Pore-forming treatment helps to inhibit the graphitization of microcrystals during the carbonization of biomass raw materials, helps to obtain a hard carbon material including graphitic microcrystals and amorphous carbon, and two-layer coating is performed on the hard carbon material, with the second layer being carbonitrogen co - coating. On the one hand, nitrogen doping can enhance the defect active sites and conductivity of the hard carbon material, thereby enhancing the reversible capacity, increasing the capacity in the slope region, and improving the rate performance. On the other hand, carbonitrogen co - coating can avoid the side effect of increased irreversible capacity caused by nitrogen doping, improve the interface of the hard carbon material, reduce the side reaction between the defective surface generated by doping and the electrolyte, and enhance the first Coulombic efficiency and rate performance of the hard carbon material.

[0040] Specifically, the biomass raw material can include one or more of glucose, sucrose, starch, coconut shell, walnut shell, hazelnut shell, wood, etc., which have the advantages of rich raw material production, low cost, high sodium (or lithium) storage capacity, etc.

[0041] During the above process of carbonizing the biomass raw material (low - temperature pyrolysis carbonization) to obtain a hard carbon precursor, the carbonization temperature can be 300 - 800 °C, and the carbonization time (holding time) can be 1 - 10 h.

[0042] In addition, the heating rate during the above carbonization process can be 0.5 - 3 °C / min.

[0043] During specific implementation, the above process of carbonizing the biomass raw material to obtain a hard carbon precursor further includes: after carbonizing the biomass raw material to obtain a carbonized material, then pulverizing and sieving (such as pulverizing, classifying, and sieving) the carbonized material. The equipment used in the above pulverization process can include a pneumatic pulverizing classifier, the mesh number of the sieve for sieving can be 300 - 500 meshes, and the specific surface area of the obtained hard carbon precursor is generally less than 300 m2 / g, for example, the specific surface area is about 10 - 250 m 2 / g, and the hard carbon precursor with a particle size of about 4 - 15 µm is beneficial to the uniformity and sufficiency of subsequent sintering, doping coating and other reactions.

[0044] More specifically, for example, a carbide material is obtained by using an air jet milling classifier at the frequencies of 40 Hz for the air crusher and 40 Hz for the classifier, and then sieved through a 325-mesh sieve to obtain a hard carbon precursor with a particle size of about 4 - 6 µm. This particle size is beneficial to the uniformity and sufficiency of subsequent sintering, doping coating and other reactions. For this, no secondary crushing and classification are required subsequently, only sieving is needed; the specific surface area of its hard carbon precursor is generally less than 300 m 2 / g, such as 10 - 250 m 2 / g.

[0045] During the high-temperature carbonization process of biomass raw materials (hard carbon raw materials), volatile gases including water vapor, carbon dioxide, carbon monoxide, etc. are released inside, forming pores in the hard carbon material, resulting in a high porosity and large specific surface area of the hard carbon material, causing problems such as low compaction density of the hard carbon and low initial Coulomb efficiency (first-week Coulomb efficiency). The pore structure of most hard carbons is naturally formed during the high-temperature carbonization process, and it is difficult to regulate the pore size structure, resulting in that hard carbon often has more open pores. Its open pore structure will lead to the consumption of the electrolyte and cause sodium precipitation. Although pore formation will increase the reversible capacity of sodium (or lithium) storage to a certain extent, along with a significant increase in the specific surface area of the hard carbon, the initial Coulomb efficiency will be greatly reduced. At present, there is still a lack of effective methods to regulate the pore structure of hard carbon. At present, the sodium (or lithium) storage capacity of hard carbon materials needs to be further improved, and there are problems with poor cycle performance and rate performance. In addition, generally in the sodium storage carbon material structure, it is almost difficult for the long-range ordered structure (such as graphite microcrystals) to accommodate the insertion of sodium ions. Therefore, the long-range ordered structure carbon will reduce the sodium storage active sites, resulting in the loss of reversible capacity.

[0046] Based on the fact that a rich closed pore structure is the key to improving the reversible storage performance of hard carbon active ions (such as sodium ions or lithium ions), in the embodiments of the present invention, the specific surface area of the porous hard carbon precursor after pore formation treatment is controlled at 300 - 900 m 2 / g. By regulating the graphitization structure of hard carbon through pore engineering, pore formation treatment is carried out on the hard carbon precursor to increase its pores. A large number of pores hinder the formation of graphite microcrystals in the hard carbon, inhibit the tendency of the hard carbon material to over-graphitize microcrystals, increase the interplanar spacing of the carbon layer (002) crystal plane, and increase the sodium (or lithium) storage active sites. After high-temperature carbonization, the reversible capacity of this porous hard carbon precursor can be increased, and the structures of graphite microcrystals and amorphous carbon in the hard carbon material are controlled within a suitable range, thereby helping to obtain I D / I GThe hard carbon material with a value of 0.9 to 1.3 can balance a relatively high reversible capacity, initial Coulombic efficiency, and cycling performance.

[0047] Exemplarily, the specific surface area of the above-mentioned porous hard carbon precursor can be 300, 350, 400, 450, 500, 600, 700, 800, 900 m 2 / g or the range composed of any two of them.

[0048] The above-mentioned pore-forming treatment can include a physical pore-forming treatment method or a chemical pore-forming treatment method. Specific explanations are as follows.

[0049] In the physical pore-forming treatment method, the above-mentioned pore-forming agent includes a physical pore-forming agent, and this physical pore-forming agent can include water vapor and / or carbon dioxide. Correspondingly, the temperature of the pore-forming treatment (i.e., the pyrolysis process of the physical pore-forming agent) can be 650 to 950 °C, for example, it can be 650, 700, 800, 900, 950 °C or the range composed of any two of them.

[0050] More specifically, the above-mentioned physical pore-forming agent can also include nitrogen, that is, a mixed gas of water vapor and / or carbon dioxide and nitrogen is used as the physical pore-forming agent.

[0051] In addition, during specific implementation, the above-mentioned physical pore-forming agent, such as water vapor, carbon dioxide, a mixed gas of water vapor and / or carbon dioxide and nitrogen, can be introduced into the reaction system at a flow rate of 0.15 to 0.25 L / min, for example, 0.15, 0.2, 0.25 L / min or the range composed of any two of them. In the chemical pore-forming treatment method, the above-mentioned pore-forming agent includes a chemical pore-forming agent, and this chemical pore-forming agent can include one or more of potassium hydroxide, sodium hydroxide, zinc chloride (ZnCl2), and phosphoric acid (H3PO4). Correspondingly, the temperature of the pore-forming treatment (i.e., the pyrolysis process of the chemical pore-forming agent) can be 500 to 900 °C, for example, it can be 500, 600, 700, 800, 900 °C or the range composed of any two of them.

[0052] During specific implementation, a solution including a chemical pore-forming agent can be prepared first, for example, a solution including one or more of potassium hydroxide, sodium hydroxide, zinc chloride (ZnCl2), and phosphoric acid (H3PO4), then the hard carbon precursor is impregnated in the above-mentioned solution including the chemical pore-forming agent, then dried, and then pyrolyzed at 500 to 900 °C to obtain a porous hard carbon precursor with a specific surface area of 300 to 900 m 2 / g.

[0053] The dosage of the above-mentioned pore-forming agent and the pore-forming time can both be appropriately adjusted according to the actual situation and the expected specific surface area of the porous hard carbon precursor.

[0054] The conventional coating process generally uses a hard carbon sample after high-temperature sintering. After coating and mixing, secondary high-temperature carbonization is carried out. The above conventional coating process generally leads to an increase in defects and an increase in specific surface area, resulting in a decrease in the initial Coulomb efficiency. In addition, the compacted density of hard carbon prepared from general biomass raw materials is relatively low, and the hard carbon prepared by the pore-forming technology has a lower compacted density due to the generation of a large number of pore structures. However, in the preparation method of the embodiment of the present invention, by coating the porous hard carbon precursor with the first coating agent and the second coating agent, the specific surface area can be effectively reduced, the compacted density of the hard carbon material can be improved, the powder impedance can be reduced, and the initial Coulomb efficiency and rate performance can be improved.

[0055] After mixing the porous hard carbon precursor and the first coating agent (for example, performing VC mixing treatment using a mixing modifier), the process of performing the first sintering treatment (high-temperature carbonization) in a second inert atmosphere to obtain the coated porous hard carbon precursor may include: mixing the porous hard carbon precursor and the first coating agent including (for example, VC mixing treatment), and then performing the first sintering treatment in a second inert atmosphere to obtain the coated porous hard carbon precursor.

[0056] Specifically, in the mixed material obtained by mixing the porous hard carbon precursor and the first coating agent, the mass percentage content (mixing ratio) of the first coating agent is 1wt% to 10wt%, such as 1wt%, 3wt%, 5wt%, 7wt%, 9wt%, 10wt% or any range composed of any two of them.

[0057] In addition, the mixing time of the porous hard carbon precursor and the first coating agent can be 15 to 60 minutes, and the stirring speed can be 1000 to 2000 rpm.

[0058] The above first coating agent (or the carbon source therein) may include pitch and / or resin, including but not limited to one or more of petroleum pitch, coal pitch, β-resin, phenolic resin, and epoxy resin.

[0059] In specific implementation, the temperature of the first sintering treatment (high-temperature carbonization) can be 1100 to 1500 °C, and the holding time can be 1 to 8 hours.

[0060] In addition, during the first sintering treatment (high-temperature carbonization), the heating rate can be 0.5 to 3 °C / min.

[0061] The traditional heteroatom doping process generally leads to an increase in defects and an increase in specific surface area of the carbon material, resulting in a significant decrease in the initial Coulomb efficiency of hard carbon; at the same time, it is difficult to coordinate the coating and doping processes, and the process is complex.

[0062] In the embodiments of the present invention, the above-mentioned second coating agent includes a carbonitrogen source compound, which includes an amino group (-NH2) and an alkyl group (-R). Through one-step modification of nitrogen doping and carbon coating on the hard carbon material, the obtained hard carbon material (hard carbon negative electrode material) has nitrogen element doping and a soft carbon coating layer. A small amount of nitrogen element doping can improve the defect active sites of hard carbon, enhance the conductivity, thereby improving the reversible capacity, increasing the capacity in the slope region, and improving the rate performance. At the same time, the simultaneously constructed soft carbon coating layer can avoid the side effect of increased irreversible capacity caused by nitrogen doping, improve the hard carbon interface, reduce the side reaction between the defect surface generated by doping and the electrolyte, and improve the first Coulomb efficiency and cycle performance of the hard carbon material (hard carbon negative electrode material).

[0063] Specifically, the carbonitrogen source compound may include a carboxyl group, and the carbonitrogen source compound includes one or more of isoleucine, leucine, alanine, glycine, proline, valine, tyrosine, phenylalanine, tryptophan, serine, threonine, cysteine, asparagine, glutamine, aspartic acid, glutamic acid, lysine, arginine, etc.

[0064] Furthermore, the above-mentioned carbonitrogen source compound may further include a carboxyl group (-COOH), which helps to undergo a cross-linking reaction with the oxygen-containing functional groups on the surface of the hard carbon material to form cross-linking structures such as ester groups and anhydrides, hinders the rearrangement of the graphite microcrystalline structure of hard carbon, helps to increase the sodium storage capacity, and helps to improve the reversible capacity, first Coulomb efficiency, rate performance and cycle performance.

[0065] It can be understood that the temperature of the above-mentioned second sintering treatment should be determined in combination with the specific type of the carbonitrogen source compound to achieve a better coating effect.

[0066] In some embodiments, the temperature of the above-mentioned second sintering treatment is 700~950 °C, for example, it can be 700, 800, 900, 950 °C or the range composed of any two of them.

[0067] During specific implementation, during the above-mentioned second sintering treatment, the heating rate can be 0.5~3 °C / min, for example, 0.5, 1, 2, 3 °C / min or the range composed of any two of them, and the holding time can be 2~6 h, for example, 2, 3, 4, 5, 6 h or the range composed of any two of them.

[0068] It can be understood that the inert atmosphere (the first inert atmosphere, the second inert atmosphere, the third inert atmosphere) in the embodiments of the present invention may include one or more of nitrogen, argon, and helium.

[0069] It can be understood that in specific applications, the above-mentioned hard carbon material can be crushed and sieved to facilitate its use in preparing the negative electrode sheet. During the sieving process here, the mesh number of the sieve can be 300~500 meshes.

[0070] The above-mentioned hard carbon material can be used to prepare the negative electrode sheet of a lithium-ion battery or a sodium-ion battery, preferably the negative electrode sheet of a sodium-ion battery, and further used to prepare a lithium-ion battery or a sodium-ion battery, preferably a sodium-ion battery.

[0071] An embodiment of the present invention also provides a negative electrode sheet, which includes a negative electrode active material layer, and the negative electrode active material layer includes the above-mentioned hard carbon material or a hard carbon material prepared according to the preparation method of the above-mentioned hard carbon material. Based on this hard carbon material, the negative electrode sheet has corresponding effects, which will not be elaborated here.

[0072] An embodiment of the present invention also provides a battery, and the above-mentioned battery includes the above-mentioned negative electrode sheet. Based on this negative electrode sheet or hard carbon material, the battery has corresponding effects, which will not be elaborated here.

[0073] In some embodiments, the above-mentioned battery includes a sodium-ion battery.

[0074] It can be understood that the above-mentioned battery further includes a positive electrode sheet, a separator and an electrolyte.

[0075] The above-mentioned positive electrode sheet specifically includes a positive electrode current collector and a positive electrode active layer provided on at least one functional surface of the positive electrode current collector, and the positive electrode active layer includes a positive electrode active material.

[0076] When specifically preparing the positive electrode sheet, for example, the positive electrode active material, a conductive agent and a binder can be dispersed in an appropriate amount of N-methylpyrrolidone (NMP) solvent, and fully stirred and mixed to form a uniform positive electrode slurry; the positive electrode slurry is uniformly coated on the positive electrode current collector, and after drying, rolling and slitting, the positive electrode sheet is obtained.

[0077] Among them, the material of the positive electrode current collector can be at least one of aluminum foil and nickel foil; the conductive agent can be selected from at least one of carbon black, acetylene black, graphene, Ketjen black, carbon fiber, carbon nanotube, conductive graphite; the binder can be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane.

[0078] The above-mentioned positive electrode active material can include one or more of layered oxides, polyanionic compounds, Prussian blue compounds, sodium peroxide and sodium superoxide.

[0079] The embodiments of the present invention do not strictly limit the selection of the electrolyte, which may include one or more of the solvents commonly used in current sodium-ion battery electrolytes, as well as the electrolyte sodium salts commonly used in current sodium-ion electrolytes. For example, the solvent can be ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, ethyl methyl carbonate (EMC), ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, sulfolane, γ-butyrolactone, etc.; electrolytes such as sodium hexafluorophosphate, sodium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium fluorotrifluoromethanesulfonylimide can be selected, one or more of them.

[0080] The embodiments of the present invention do not strictly limit the material selection of the separator, which can be the separator materials commonly used in current sodium-ion batteries, such as polypropylene separator (PP), polyethylene separator (PE), polypropylene / polyethylene double-layer composite film (PP / PE), polyimide electrospun separator (PI), polypropylene / polyethylene / polypropylene three-layer composite film (PP / PE / PP), cellulose non-woven separator, separator with a ceramic coating, etc.

[0081] When preparing a sodium-ion battery, the positive electrode sheet, the separator, and the negative electrode sheet are wound or laminated to obtain a bare battery cell, and the bare battery cell is encapsulated into a pre-stamped aluminum-plastic film bag. After the encapsulated battery is dried at 85 °C to remove moisture, the electrolyte is injected into the dried battery, and the battery is completed after standing, formation, and secondary sealing to prepare the sodium-ion battery.

[0082] The present invention will be further described below through specific examples and comparative examples. Unless otherwise specified, the reagents, materials, and instruments used below are all conventional reagents, conventional materials, and conventional instruments, which can be obtained commercially, and the reagents and materials involved can also be synthesized by conventional synthesis methods.

[0083] Example 1

[0084] This example provides a preparation method for a hard carbon material (hard carbon negative electrode material) of a sodium-ion battery, including:

[0085] 1) Carbonize coconut shell in nitrogen, the carbonization temperature is 300 °C, the heating rate is 2 °C / min, the carbonization time is 4 h, and then it is crushed and sieved. The mesh number of the sieve used for sieving is 325 mesh, and a hard carbon precursor with a particle size of 6 µm is obtained. After detection, the specific surface area of this hard carbon precursor is about 250 m 2 / g;

[0086] 2) Carbon dioxide gas is introduced into the hard carbon precursor for pore formation treatment. The temperature of the pore formation treatment is 800 °C, the time is 1 h, the heating rate is 3 °C / min, and the flow rate of the carbon dioxide gas is 0.2 L / min, obtaining a porous hard carbon precursor with a specific surface area of 650 m 2 / g;

[0087] 3) The porous hard carbon precursor with a specific surface area of 650 m 2 / g and pitch are mixed at a stirring speed of 1500 rpm. In the mixed material obtained by mixing the porous hard carbon precursor and pitch, the mass percentage content (mixing ratio) of pitch is 5 wt%, and the mixing time is 30 min; then, a first sintering treatment is carried out in nitrogen to obtain a coated porous hard carbon precursor. Among them, the temperature of the first sintering treatment is 1300 °C, the heat preservation time is 4 h, and the heating rate can be 3 °C / min;

[0088] 4) After mixing the coated porous hard carbon precursor and glutamic acid, a second sintering treatment is carried out in nitrogen. The temperature of the second sintering treatment is 900 °C, the heating rate is 2 °C / min, and the heat preservation time is 4 h; then, it is pulverized and sieved. The mesh number of the sieve for sieving is 325 mesh, obtaining a hard carbon material (hard carbon negative electrode material), and the thickness of its carbon coating layer (coating layer) is 10 nm.

[0089] Example 2

[0090] This example is basically the same as Example 1, except that:

[0091] 1) Walnut shells are used to replace coconut shells, and the carbonization temperature is adjusted to 400 °C;

[0092] 2) β-resin is used to replace pitch;

[0093] 3) Glycine is used to replace glutamic acid, and the nitrogen doping ratio (at%) is 2.0 at%;

[0094] 4) The amount of the coating agent is adjusted so that the thickness of the carbon coating layer (coating layer) is 5 nm;

[0095] Other conditions remain unchanged.

[0096] Example 3

[0097] This example is basically the same as Example 1, except that:

[0098] 1) The carbonization temperature is adjusted to 800 °C;

[0099] 2) Step 2) is adjusted to mix the hard carbon precursor and potassium hydroxide in a mass ratio of 1:1, and then perform pore-forming treatment (pyrolysis) at 800 °C with a heating rate of 3 °C / min and a reaction time of 2 h to obtain a porous hard carbon precursor;

[0100] 3) Adjust the dosage of the coating agent so that the thickness of the carbon coating layer (coating layer) is 100 nm;

[0101] Other conditions remain unchanged.

[0102] Example 4

[0103] This example is basically the same as Example 1, with the differences being: <{

[0104] In step 1), glucose is used to replace the coconut shell, the carbonization time is adjusted to 10 h, the heating rate is adjusted to 0.5 °C / min, and the mesh number of the sieve used for sieving is 300 mesh; other conditions remain unchanged.

[0105] Example 5

[0106] This example is basically the same as Example 1, with the differences being:

[0107] In step 1), starch is used to replace the coconut shell, the carbonization time is adjusted to 1 h, the heating rate is adjusted to 3 °C / min, and the mesh number of the sieve used for sieving is 500 mesh; other conditions remain unchanged.

[0108] Example 6

[0109] This example is basically the same as Example 1, with the differences being:

[0110] In step 2), water vapor is used to replace carbon dioxide, the temperature of the pore-forming treatment is adjusted to 650 °C, and a porous hard carbon precursor with a specific surface area of 300 m 2 / g is obtained after the pore-forming treatment; other conditions remain unchanged.

[0111] Example 7

[0112] This example is basically the same as Example 1, with the differences being:

[0113] In step 2), a mixed gas of carbon dioxide and nitrogen (volume ratio of 1:3) is used to replace carbon dioxide, the temperature of the pore-forming treatment is adjusted to 950 °C, and a porous hard carbon precursor with a specific surface area of 900 m 2 / g is obtained after the pore-forming treatment; other conditions remain unchanged. "

[0114] Example 8

[0115] This example is basically the same as Example 3, with the differences being:

[0116] In step 2), potassium hydroxide is replaced by zinc chloride, and the temperature for pore-forming treatment is 500 °C; other conditions remain unchanged.

[0117] Example 9

[0118] This example is basically the same as Example 3, except that:

[0119] In step 2), potassium hydroxide is replaced by phosphoric acid, and the temperature for pore-forming treatment is 900 °C; other conditions remain unchanged.

[0120] Example 10

[0121] This example is basically the same as Example 1, except that:

[0122] In step 3), the temperature of the first sintering treatment is 1100 °C, the heat preservation time is 8 h, and the heating rate is 0.5 °C / min;

[0123] In step 4), glutamic acid is replaced by phenylalanine, the temperature of the second sintering treatment is 950 °C, the heating rate is 0.5 °C / min, and the heat preservation time is 6 h.

[0124] Example 11

[0125] This example is basically the same as Example 1, except that:

[0126] In step 3), the temperature of the first sintering treatment is 1500 °C, the heat preservation time is 1 h, and the heating rate is 3 °C / min;

[0127] In step 4), glutamic acid is replaced by proline, the temperature of the second sintering treatment is 700 °C, the heating rate is 3 °C / min, and the heat preservation time is 2 h.

[0128] Comparative Example 1

[0129] This comparative example is basically the same as Example 1, except that:

[0130] Pore-forming treatment and coating treatment are not carried out; other conditions remain unchanged.

[0131] This comparative example provides a preparation method of a hard carbon material (hard carbon negative electrode material) for a sodium ion battery, including:

[0132] 1) Carbonize coconut shell in nitrogen, the carbonization temperature is 300 °C, the heating rate is 2 °C / min, the carbonization time is 4 h, then carry out crushing and sieving, the mesh number of the sieve used for sieving is 325 mesh, and a hard carbon precursor with a particle size of 6 µm is obtained. After detection, the specific surface area of this hard carbon precursor is about 250 m 2 / g;

[0133] 2) Then, a first sintering treatment is carried out in nitrogen, followed by pulverization and sieving. The mesh number of the sieve used for sieving is 325 mesh, to obtain a hard carbon material (hard carbon negative electrode material). Among them, the temperature of the first sintering treatment is 1300 °C, the heat preservation time is 4 h, and the heating rate can be 3 °C / min.

[0134] Comparative Example 2

[0135] This comparative example is basically the same as Example 1, except that:

[0136] Coating treatment is not carried out; other conditions remain unchanged.

[0137] This comparative example provides a method for preparing a hard carbon material (hard carbon negative electrode material) for a sodium-ion battery, including:

[0138] 1) Carbonize coconut shell in nitrogen. The carbonization temperature is 300 °C, the heating rate is 2 °C / min, and the carbonization time is 4 h. Then, pulverize and sieve. The mesh number of the sieve used for sieving is 325 mesh, to obtain a hard carbon precursor with a particle size of 6 µm. After detection, the specific surface area of this hard carbon precursor is about 250 m 2 / g;

[0139] 2) Pass carbon dioxide gas into this hard carbon precursor for pore-forming treatment. The temperature of the pore-forming treatment is 800 °C, the time is 1 h, the heating rate is 3 °C / min, and the flow rate of the carbon dioxide gas is 0.2 L / min, to obtain a porous hard carbon precursor with a specific surface area of 650 m 2 / g;

[0140] 3) Then, a first sintering treatment is carried out in nitrogen, followed by pulverization and sieving. The mesh number of the sieve used for sieving is 325 mesh, to obtain a hard carbon material (hard carbon negative electrode material). Among them, the temperature of the first sintering treatment is 1300 °C, the heat preservation time is 4 h, and the heating rate can be 3 °C / min.

[0141] Comparative Example 3

[0142] This comparative example is basically the same as Example 1, except that:

[0143] Pore-forming treatment is not carried out; other conditions remain unchanged.

[0144] This comparative example provides a method for preparing a hard carbon material (hard carbon negative electrode material) for a sodium-ion battery, including:

[0145] 1) Carbonize coconut shell in nitrogen. The carbonization temperature is 300 °C, the heating rate is 2 °C / min, and the carbonization time is 4 h. Then, pulverize and sieve. The mesh number of the sieve used for sieving is 325 mesh, to obtain a hard carbon precursor with a particle size of 6 µm. After detection, the specific surface area of this hard carbon precursor is about 250 m2 / g;

[0146] 2) Mix the hard carbon precursor and pitch at a stirring speed of 1500 rpm. In the mixed material obtained after mixing the hard carbon precursor and pitch, the mass percentage content (mixing ratio) of pitch is 5 wt%, and the mixing time is 30 min. Then, perform the first sintering treatment in nitrogen to obtain the coated porous hard carbon precursor. Among them, the temperature of the first sintering treatment is 1300 °C, the heat preservation time is 4 h, and the heating rate can be 3 °C / min;

[0147] 3) After mixing the coated porous hard carbon precursor and glutamic acid, perform the second sintering treatment in nitrogen. The temperature of the second sintering treatment is 900 °C, the heating rate is 2 °C / min, the heat preservation time is 4 h, and the nitrogen doping ratio (at%) is 0.5%. Then, perform crushing and sieving. The mesh number of the sieve for sieving is 325 meshes to obtain the hard carbon material (hard carbon negative electrode material).

[0148] Comparative Example 4

[0149] This comparative example is basically the same as Example 1, except that:

[0150] Do not perform the nitrogen-carbon co - coating treatment; other conditions remain unchanged.

[0151] This comparative example provides a preparation method of a hard carbon material (hard carbon negative electrode material) for a sodium - ion battery, including:

[0152] 1) Carbonize the coconut shell in nitrogen. The carbonization temperature is 300 °C, the heating rate is 2 °C / min, and the carbonization time is 4 h. Then, perform crushing and sieving. The mesh number of the sieve used for sieving is 325 meshes to obtain a hard carbon precursor with a particle size of 6 µm. After detection, the specific surface area of this hard carbon precursor is about 250 m 2 / g;

[0153] 2) Pass carbon dioxide gas into the hard carbon precursor for pore - forming treatment. The temperature of the pore - forming treatment is 800 °C, the time is 1 h, the heating rate is 3 °C / min, and the flow rate of carbon dioxide gas is 0.2 L / min to obtain a porous hard carbon precursor with a specific surface area of 650 m 2 / g;

[0154] 3) At a stirring speed of 1500 rpm, the specific surface area is 650 m 2Mix the porous hard carbon precursor at a rate of / g with pitch. In the mixed material obtained after mixing the porous hard carbon precursor and pitch, the mass percentage of pitch (mixing ratio) is 5 wt%, and the mixing time is 30 min. Then, perform the first sintering treatment in nitrogen to obtain the coated porous hard carbon precursor. Among them, the temperature of the first sintering treatment is 1300 °C, the heat preservation time is 4 h, and the heating rate can be 3 °C / min.

[0155] 4) Then, perform crushing and sieving. The mesh number of the sieve for sieving is 325 mesh to obtain the hard carbon material (hard carbon negative electrode material).

[0156] Comparative Example 5

[0157] This comparative example is basically the same as Example 1, except that:

[0158] During the pore-forming treatment in step 2), adjust parameters such as the time of the pore-forming treatment and the dosage of the pore-forming agent to obtain a porous hard carbon precursor with a specific surface area of 250 m 2 / g; other conditions remain unchanged.

[0159] Comparative Example 6

[0160] This comparative example is basically the same as Example 1, except that:

[0161] During the pore-forming treatment in step 2), adjust parameters such as the time of the pore-forming treatment and the dosage of the pore-forming agent to obtain a porous hard carbon precursor with a specific surface area of 950 m 2 / g; other conditions remain unchanged.

[0162] Comparative Example 7

[0163] This comparative example is basically the same as Example 1, except that:

[0164] In step 4), the temperature of the second sintering treatment is adjusted to 650 °C; other conditions remain unchanged.

[0165] Comparative Example 8

[0166] This comparative example is basically the same as Example 1, except that:

[0167] In step 4), the temperature of the second sintering treatment is adjusted to 1000 °C; other conditions remain unchanged.

[0168] Test Example

[0169] 1. Detect the following parameters of the hard carbon materials of each example and comparative example:

[0170] 1) Scanning electron microscope (SEM) test: SEM photos were obtained by testing with Hitachi Regulus 8100 / SU 8010 scanning electron microscope;

[0171] 2) X-ray diffraction (XRD): XRD was obtained by testing with an X-ray powder diffractometer, and the interplanar spacing d of the (002) crystal plane was calculated 002 , the average width La of the graphite microcrystal along the a-axis direction, the stacking thickness Lc along the c-axis direction, and the stacking layer number N, where d 002 = λ / (2sinθ); La = 1.84λ / (βcosθ); Lc = 0.9λ / (βcosθ); N = Lc / d 002 + 1, where λ is the X-ray wavelength, β is the full width at half maximum of the (002) crystal plane, and θ is the diffraction angle of the (002) crystal plane;

[0172] 3) Raman test: Raman spectra were obtained by testing with a laser confocal Raman spectrometer, and the value of ID / IG was calculated according to the intensity ratio of the D peak and the G peak in the Raman spectrum; D / I G value;

[0173] 4) X-ray photoelectron spectroscopy (XPS): The nitrogen element doping ratio was obtained by testing with an X-ray photoelectron spectrometer;

[0174] 5) The thickness of the carbon coating layer was tested by transmission electron microscope (TEM), and the thickness of the carbon coating layer was measured from the high-resolution transmission electron microscope photos;

[0175] 6) Sectional porosity: The sectional porosity was obtained by taking SEM photos of the material section and then analyzing the porosity with software from OLYMPUS;

[0176] 7) Specific surface area (BET): BET was obtained by using BELSORP 3H-2000BET-A and testing according to the national standard GB / T 19587-2017;

[0177] 8) Impedance (powder impedance): It was obtained by the four-probe method and tested according to the national standard GB / T 30835-2014.

[0178] 2. The above hard carbon materials were respectively used to fabricate the negative electrode sheets and assembled into CR2032 coin cells. Among them, the method for assembling the CR2032 cell is as follows: The hard carbon material (hard carbon negative electrode material), conductive carbon black, and sodium carboxymethyl cellulose were placed in a slurry mixer according to a mass ratio of 80:10:10, and then N-methylpyrrolidone solvent was added and mixed evenly to obtain a slurry. The slurry was evenly coated on the surface of carbon-coated aluminum foil and dried in a vacuum drying oven at 100 °C for 12 h. At the same time, a CR2032 cell was assembled with metallic sodium as the counter electrode, glass fiber as the separator, and a mixed solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio 1:1) containing 1 mol / L sodium hexafluorophosphate (NaPF6) as the electrolyte.

[0179] The above coin cells were subjected to constant current charge-discharge tests on a Neware multi-channel test system at 25 °C, with a voltage range of 0 - 2.0 V and a rate of 0.1 C, where 1 C = 300 mA / g.

[0180] Reversible capacity: The discharge capacity obtained by discharging at a constant current of 0.1 C to 0 V is the first discharge capacity, and then the charge capacity obtained by charging at a constant current of 0.1 C to 2 V is the first charge capacity. The first charge capacity is the reversible capacity.

[0181] Initial Coulombic efficiency: The percentage obtained by dividing the first charge capacity by the first discharge capacity.

[0182] Capacity retention rate after 50 cycles at 1 C: The percentage obtained by dividing the charge capacity of the 50th cycle by the charge capacity of the first cycle at a rate of 1 C.

[0183] Capacity retention rate at 2 C: The percentage obtained by dividing the charge capacity obtained at a rate of 2 C by the reversible capacity.

[0184] Test results:

[0185] Table 1

[0186]

[0187] Data analysis: As can be seen from the above table, through pore-forming treatment (pore size regulation) and coordinated nitrogen-carbon co-deposition in each example, it is helpful to obtain a hard carbon material with a ratio (I -1 / I D ) of the peak intensity I -1 at a wavelength of 1345 cm G and the peak intensity I D at a wavelength of 1600 cm G in the Raman spectrum of 0.9 - 1.3 and a low powder impedance.

[0188] Table 2

[0189]

[0190] Data analysis: It can be seen from Table 1 and Table 2 that, compared with the comparative example, the hard carbon in the embodiment of the present invention contains a composite carbon structure of amorphous carbon and graphite-like microcrystals and has a suitable Raman spectrum peak intensity ratio I D / I G (0.9-1.3), resulting in a large number of sodium storage active sites, giving the hard carbon material an excellent reversible specific capacity and high Coulombic efficiency. Furthermore, by regulating the pore size of the precursor and then nitrogen doping and co-coating the carbon layer, a hard carbon material with a suitable Raman spectral peak intensity ratio (0.9-1.3), a large interlayer spacing (0.37-0.40 nm), and a low powder impedance (0.02-0.07 Ω·cm) was obtained in the embodiment, which further helps to improve the reversible capacity, first Coulombic efficiency, rate capability, and cycling performance of the hard carbon material.

[0191] Figure 1 and Figure 2 The scanning electron microscope images of the hard carbon materials prepared in Example 1 and Comparative Example 1 are shown in Figure 2. By comparison, it can be seen that both of them have blocky morphology, while Figure 1 The particle size is slightly larger and there is a wrinkled coating layer on the surface, which proves that the hard carbon material prepared in Example 1 has a surface coating modification effect compared with Comparative Example 1;

[0192] from Figure 3 The X-ray diffraction pattern of the hard carbon material prepared in Example 1 shows two characteristic bulge peaks of typical hard carbon materials, corresponding to the (002) and (100) crystal planes, respectively. The (002) crystal plane spacing d is calculated to be 002 The average width La of graphite crystals along the a-axis and the thickness Lc of graphite crystals along the c-axis are 1.48 nm and 0.72 nm respectively, and the number of stacking layers N is 2.9.

[0193] according to Figure 4 The Raman spectrum of the hard carbon material prepared in Example 1 can be calculated to have a wavelength of 1345 cm -1 The D peak intensity I D and a wavelength of 1600 cm -1 G peak intensity I G The ratio of (I D / I G ) is 1.1;

[0194] from Figure 5 The charge and discharge curves of the hard carbon material prepared in Example 1 show that the material exhibits excellent sodium storage performance, with a reversible specific capacity of 337 mAh / g and a first coulombic efficiency of 92%.

[0195] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A hard carbon material, characterized in that The invention comprises a hard carbon core, a first coating layer located on the surface of the core, and a second coating layer located on the surface of the first coating layer, wherein the first coating layer is a carbon coating layer, and the second coating layer is a nitrogen-doped synergistic carbon coating layer; The ratio of the number of atoms of the nitrogen element to the number of atoms in the hard carbon material is 0.1% to 2.0%; In the Raman spectrum of the hard carbon material, the wavelength is 1345 cm -1 The peak intensity and wavelength at 1600 cm -1 The ratio of the peak intensities at 0.9 to 1.3 is 0.9 to 1.3, and the powder impedance of the hard carbon material under a pressure of 16 to 20 MPa is 0.02 to 0.07 Ω·cm.

2. The hard carbon material according to claim 1, wherein The interlayer spacing d of the (002) crystal plane of the hard carbon material 002 0.37~0.40nm; And / or, the hard carbon material includes graphite crystals and amorphous carbon, the width La of the graphite crystals along the a-axis direction is 1.4-2.0 nm, the thickness Lc along the c-axis direction is 0.7-1.0 nm, and the number of stacked layers is 2.9-3.

5.

3. The hard carbon material according to claim 1, wherein The sum of the thicknesses of the first cladding layer and the second cladding layer is 5-100 nm.

4. The hard carbon material according to claim 1 or 2, characterized in that The porosity of the hard carbon material is 1% to 10%; And / or, the specific surface area of the hard carbon material is 0.5 to 20 m 2 / g.

5. A method for preparing the hard carbon material according to any one of claims 1 to 4, characterized in that: include: Carbonizing the biomass raw material in a first inert atmosphere to obtain a hard carbon precursor; The hard carbon precursor is subjected to pore forming treatment under the action of a pore forming agent to obtain a specific surface area of 300-900 m 2 / g porous hard carbon precursor; After mixing the porous hard carbon precursor and a first coating agent, performing a first sintering treatment in a second inert atmosphere to obtain a coated porous hard carbon precursor, wherein the first coating agent includes a carbon source; The coated porous hard carbon precursor and a second coating agent are mixed and then subjected to a second sintering treatment in a third inert atmosphere to obtain the hard carbon material, wherein the second coating agent includes a carbon and nitrogen source compound, and the carbon and nitrogen source compound includes an amino group and an alkyl group.

6. The method for preparing a hard carbon material according to claim 5, wherein: The biomass raw materials include one or more of glucose, sucrose, starch, coconut shells, walnut shells, hazelnut shells, and wood; And / or, in the process of carbonizing the biomass raw material to obtain the hard carbon precursor, the carbonization temperature is 300-800° C., the carbonization time is 1-10 hours, and the heating rate is 0.5-3° C. / min; And / or, the process of carbonizing the biomass raw material to obtain the hard carbon precursor further comprises: crushing and sieving the biomass raw material after carbonizing to obtain the hard carbon precursor with a mesh size of 300-500 mesh; And / or, the pore-forming agent includes a physical pore-forming agent, the physical pore-forming agent includes water vapor and / or carbon dioxide, and the temperature of the pore-forming treatment is 650-950° C.; And / or, the pore-forming agent includes a chemical pore-forming agent, the chemical pore-forming agent includes one or more of potassium hydroxide, sodium hydroxide, zinc chloride, and phosphoric acid, and the temperature of the pore-forming treatment is 500-900°C.

7. The method for preparing a hard carbon material according to claim 5 or 6, characterized in that: The carbon source includes pitch and / or resin; And / or, the temperature of the first sintering treatment is 1100-1500° C., the holding time is 1-8 hours, and the heating rate is 0.5-3° C. / min; And / or, the temperature of the second sintering treatment is 700-950° C.; And / or, the carbon and nitrogen source compound further includes a carboxyl group, and the carbon and nitrogen source compound includes one or more of isoleucine, leucine, alanine, glycine, proline, valine, tyrosine, phenylalanine, tryptophan, serine, threonine, cysteine, asparagine, glutamine, aspartic acid, glutamic acid, lysine, and arginine; And / or, during the second sintering process, the heating rate is 0.5-3°C / min and the holding time is 2-6h.

8. A negative electrode sheet, characterized in that: The negative electrode sheet comprises a negative electrode active material layer, and the negative electrode active material layer comprises the hard carbon material according to any one of claims 1 to 4 or the hard carbon material prepared according to the method for preparing the hard carbon material according to any one of claims 5 to 7.

9. A battery, characterized in that: The battery comprises the negative electrode sheet according to claim 8.

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