A hard carbon material and a method for preparing the same

Abstract

The application provides a hard carbon material and a preparation method thereof, and comprises the following steps: (S1) crushing pitch, and performing heat treatment under an oxidizing atmosphere to obtain a pre-oxidation precursor; (S2) uniformly mixing the pre-oxidation precursor with a crosslinking agent I, and performing primary crosslinking under an inert atmosphere and a heating condition to obtain a crosslinking precursor I; the crosslinking agent I is a high polymer containing a carboxyl group in a side chain; (S3) uniformly mixing the crosslinking precursor I with a crosslinking agent II, and performing secondary crosslinking under an inert atmosphere and a heating condition to obtain a crosslinking precursor II; the crosslinking agent II is a small molecule and an aromatic hydrocarbon compound containing multiple anhydrides and / or carboxyl groups; and (S4) calcining, cooling and grinding the crosslinking precursor II under an inert atmosphere to obtain an amorphous sodium ion battery negative electrode material. The negative electrode material obtained by the preparation method has high capacity and high rate, is low in cost, simple in preparation process, adjustable in disorder degree, high in carbon yield, and suitable for large-scale production of carbon materials.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and in particular to a hard carbon material and its preparation method. Background Technology

[0002] With the increasing global demand for sustainable development, the development and utilization of new energy technologies have become crucial. Secondary battery technology, as the core of energy storage solutions, plays a vital role in promoting efficient energy conversion and stable storage. Its development significantly promotes the integration of renewable energy resources such as wind, solar, and geothermal energy into the power grid, not only optimizing the energy structure but also significantly improving the efficiency of renewable energy use, laying a solid foundation for building a low-carbon society. In recent years, with the continuous growth in demand for clean energy, sodium-ion batteries have become another research hotspot besides lithium batteries due to their abundant resources and low cost. The development of sodium batteries holds promise for solving the problems of lithium resource scarcity, limited distribution, and high cost, attracting the attention of researchers both domestically and internationally. Sodium ions have a similar structure to lithium ions and a similar energy storage process. Based on the research and development experience of lithium battery cathode materials, research on cathode materials has made some progress, meeting the needs of initial applications. However, the larger radius of sodium ions compared to lithium ions means that the graphite anode commonly used in lithium batteries cannot be directly used in sodium batteries, limiting its further development.

[0003] Among the reported sodium-ion battery anode materials, amorphous carbon materials are considered highly promising candidates due to their low sodium storage potential, high capacity, and good cycle stability. Asphalt, a byproduct of coal chemical industry, serves as a raw material for amorphous carbon materials, offering advantages such as low cost, high carbonization rate, and ease of mass production, demonstrating significant market potential. However, carbon materials prepared by directly calcining asphalt exhibit excessive structural order and insufficient porosity, limiting the sodium storage capacity in the plateau region and resulting in lower battery energy density.

[0004] CN118651846A discloses a hard carbon anode material and its preparation method. The hard carbon anode material is prepared by carbonization precursor containing polysulfide compound through two carbonization treatments. The polysulfide compound is obtained by reverse sulfurization reaction of elemental sulfur and polyene compound, and the elemental sulfur and polyene compound achieve self-crosslinking at the molecular level.

[0005] CN118553898A discloses a hard carbon composite anode material, with a core of sodium-phosphorus co-doped hard carbon material and a shell of carbon layer. The preparation method includes the following steps: (1) mixing acid-based resin, organic acid, sodium source, crosslinking agent and organic solvent, and reacting to obtain a hard carbon precursor material; (2) pre-carbonizing the hard carbon precursor material, then performing phosphorus doping, and then carbon coating to obtain the hard carbon composite anode material.

[0006] CN118553897A discloses a hard carbon composite material and its preparation method. The preparation method includes the following steps: (a) mixing a metal conductive agent, a sodium ion solid electrolyte, a sodium supplement, a binder, and an organic solvent to obtain a coating liquid; (b) mixing a resin precursor and a crosslinking agent, and performing curing and crosslinking to obtain an intermediate; then mixing the intermediate with asphalt and performing carbonization treatment to obtain an asphalt-based hard carbon material with a secondary particle morphology; (c) mixing the asphalt-based hard carbon material with the coating liquid and performing sintering treatment to obtain the hard carbon composite material. The crosslinking agent includes any one or a combination of at least two of hexanediol diacrylate, triallyl isocyanurate, trimethylolpropane triacrylate, or pentaerythritol triacrylate.

[0007] CN118373409A discloses a hard carbon anode material for sodium-ion batteries based on phenolic resin. The method involves uniformly mixing linear phenolic resin and epoxy resin to obtain a composite resin, adding a curing agent, mixing thoroughly, curing, and then pulverizing and sieving to obtain cured resin powder. Resin carbonization: The cured resin powder is sintered at low temperature under inert gas protection, followed by high-temperature carbonization, cooling, and discharge to obtain the hard carbon anode material for sodium-ion batteries. The curing agent includes hexamethylenetetramine and maleic anhydride; wherein the mass ratio of hexamethylenetetramine to maleic anhydride is 15:(0.8-1.2).

[0008] CN118289738A discloses a biomass hard carbon material and a method for preparing a pre-crosslinked modified biomass hard carbon material, comprising the following steps: mixing biomass raw materials with polycarboxylic acids and placing them in a sealed reactor for a solid-gas two-phase crosslinking reaction to obtain a pre-crosslinked material; and carbonizing the pre-crosslinked material at high temperature to obtain the biomass hard carbon material.

[0009] CN118198309A discloses a method for preparing an asphalt-based hard carbon composite material, comprising the following steps: S1, mixing and reacting asphalt, organic solvent, heteroatom compound, and scandium salt, followed by freeze-drying to obtain a hard carbon precursor material; S2, heating a peroxide crosslinking compound to a preset temperature to obtain a crosslinking gas; subjecting the crosslinking gas and the hard carbon precursor material to a crosslinking curing reaction to obtain an intermediate material; S3, mixing a fast ion conductor, a conductive agent, and the intermediate material, followed by drying and carbonization to obtain the asphalt-based hard carbon composite material.

[0010] CN118026145A discloses a high-carbon-yield nitrogen-doped sodium-ion battery hard carbon anode material, the preparation method of which includes the following steps: (1) physically mixing amino-containing biomass A, hydroxyl-containing biomass B, and a crosslinking agent to obtain a uniformly mixed mixture; (2) transferring the mixture to a homogeneous reactor for crosslinking reaction, the temperature of which is 60-60°C.

[0011] (2) At 150℃, the crosslinking reaction time is 1-10h to obtain a structurally stable crosslinked mixture C; (3) Under an inert atmosphere, the crosslinked mixture C is subjected to low-temperature pretreatment, heated to 200-600℃ at a heating rate of 1-5℃ / min, kept at a constant temperature for 1-6h, and cooled to room temperature to obtain an intermediate product; (4) Under an inert atmosphere, the intermediate product is subjected to high-temperature carbonization, heated to 900-1500℃ at a rate of 1-10℃ / min and held for 0.5-8h, and cooled to room temperature to obtain a high carbon yield nitrogen-doped sodium-ion battery hard carbon anode material.

[0012] CN116404138A discloses a biomass hard carbon anode composite material and its preparation method, including the following steps: S1. Oxidizing a hydrocarbon to obtain an oxide, mixing the oxide with a polyhydroxy organic acid, dehydrating and carbonizing it to obtain a hard carbon intermediate material; S2. Dissolving a metal compound and a phosphate ester dispersant in an organic solvent to prepare a metal solution, and depositing the metal solution onto the surface of the hard carbon intermediate material by gas atomization to obtain a metal-deposited hard carbon precursor material; S3. Transferring the metal-deposited hard carbon precursor material to a tube furnace and introducing a carbon source mixed gas for carbonization to obtain the biomass hard carbon anode composite material.

[0013] The aforementioned patents all employ different techniques to crosslink carbon sources in order to obtain hard carbon anode materials with superior electrochemical performance. However, when using pitch-based carbon materials as raw materials, due to the low softening point of pitch, during high-temperature pyrolysis, the pitch undergoes molten rearrangement, and the conjugated structures in the pitch molecules accumulate under van der Waals forces, easily forming highly ordered graphite structures, which is detrimental to sodium ion storage. This invention proposes a two-stage oxidation process for pitch, sequentially using polymers and small molecules rich in anhydrides or carboxylic acids as crosslinking agents. During pre-carbonization, these agents react with pitch molecules, increasing the molecular weight and crosslinking degree of the pitch, raising the softening point, and inhibiting the molten rearrangement process. More importantly, during pyrolysis, these oxygen-containing functional groups can decompose and release a large number of gaseous small molecules, achieving in-situ etching of the carbon layer and helping to form closed pores. Unlike currently used strategies to increase the crosslinking degree of pitch, this invention's method does not require the introduction of strong acids or strong oxidants, or difficult-to-remove inorganic salts, avoiding complex subsequent impurity removal steps. More importantly, while simplifying the steps, it can also improve the carbonization rate, thereby enhancing the economy and sustainability of the preparation process. Summary of the Invention

[0014] To address the issue that the electrochemical performance of existing asphalt-based hard carbon anode materials cannot meet the requirements of industrial batteries, this invention provides a sodium-ion battery anode material, its preparation method, and its application. The material uses abundant and inexpensive coal chemical byproducts such as coal tar pitch, petroleum pitch, and mesophase pitch as raw materials. Pretreatment in an oxidizing atmosphere introduces oxygen-containing functional groups, increasing the softening point and crosslinking degree, and inhibiting the molten rearrangement of asphaltene.

[0015] To address the aforementioned technical problems, this invention provides a method for preparing hard carbon materials, comprising the following steps:

[0016] (S1) The asphalt is crushed and heat-treated in an oxidizing atmosphere to obtain a pre-oxidized precursor.

[0017] (S2) The pre-oxidized precursor and crosslinking agent I are mixed evenly and crosslinked once under an inert atmosphere and heating conditions to obtain crosslinked precursor I; the crosslinking agent I is a polymer with carboxyl groups in its side chain;

[0018] (S3) Crosslinking precursor I and crosslinking agent II are mixed evenly and subjected to secondary crosslinking under an inert atmosphere and heating conditions to obtain crosslinking precursor II; the crosslinking agent II is a small molecule aromatic compound containing multiple acid anhydrides and / or carboxyl groups.

[0019] (S4) Crosslinked precursor II was calcined, cooled and ground in an inert atmosphere to obtain an amorphous sodium-ion battery anode material.

[0020] Furthermore, the sodium-ion battery anode material obtained by this invention exhibits an irregular morphology with a particle size of 1-20 μm and d 002 The value is between 0.36 and 0.40 nm.

[0021] Further, in step (S1), the asphalt-like substance includes one or more mixtures of coal tar pitch, petroleum pitch, natural pitch, and mesophase pitch; it is crushed to a particle size of less than 5 mm. The crushing method is not particularly limited, and includes, but is not limited to, air jet crushing, high-speed crushing, and grinding. The oxidizing atmosphere includes at least 20% oxygen by volume, such as oxygen, air, a mixture of nitrogen and oxygen, or a mixture of carbon dioxide and oxygen. The oxidizing atmosphere may also contain ozone. The heat treatment involves slowly heating to 250-300°C and holding at that temperature for 5-10 hours; preferably, the slow heating rate is 1-3°C / min.

[0022] In the pre-oxidation step (S1), slow heating and short holding time facilitate sufficient contact between the asphaltene and the molecules in the oxidizing atmosphere, promoting the reaction between them. Sufficient oxidation of the asphaltene minimizes the number of hydrogen atoms, inhibiting subsequent molten rearrangement and promoting the formation of a uniform cross-linked structure. Furthermore, sufficient pre-oxidation of the asphalt forms more oxygen-containing functional groups such as hydroxyl and carboxyl groups, which can react with carboxylic acids / anhydrides in the subsequently added cross-linking agent to form ester groups. This promotes the cross-linking and pyrolysis of asphaltene molecules into short-range, inter-crosslinked graphite domains during subsequent calcination. These graphite domains can be bent to form closed-cell structures that help fill sodium clusters. If the heating rate is too fast during pre-oxidation, rapid cross-linking of the asphalt surface leads to insufficient flow of the asphaltene, causing localized condensation to form highly ordered mesophase carbon microspheres. During subsequent high-temperature carbonization, this results in long-range ordered and tightly stacked graphene layers, hindering the insertion and filling of sodium ions and leading to a decrease in the capacity of the plateau region.

[0023] Further, in step (S2), the crosslinking agent I is selected from at least one of polyacrylic acid, polymethacrylic acid, and alginate; preferably, the number average molecular weight of crosslinking agent I is 4000-20000 g / mol; more preferably, the amount of crosslinking agent I is 5-10 wt% of the pre-oxidized precursor. In a preferred embodiment, the number average molecular weight of polyacrylic acid and polymethacrylic acid is 4000-6000 g / mol, and the molecular weight of alginate is 10000-20000 g / mol.

[0024] Furthermore, in step (S2), the process conditions for the first crosslinking are heat treatment at 300-600℃ for 5-10 hours.

[0025] Further, in step (S3), the crosslinking agent II is selected from at least one of terephthalic acid, phthalic acid, isophthalic acid, gallic acid, perylene dianhydride, pyromellitic acid, and pyromellitic anhydride. The amount of crosslinking agent II is 3-6 wt% of the crosslinking precursor I.

[0026] Furthermore, in step (S3), the process conditions for secondary crosslinking are as follows: first, the temperature is increased to 250-400℃ at a heating rate of 5-10℃ / min and held for 1-2 hours, and then the temperature is increased to 400-600℃ at a slow rate of 5-10℃ / min and held for 3-5 hours.

[0027] This invention uses polymeric crosslinking agent I and small-molecule crosslinking agent II to crosslink asphalt sequentially. During the crosslinking process, acid anhydrides or carboxylic acids can react with the hydroxyl groups in the asphalt to form ester groups, which helps the asphalt to pyrolyze and form amorphous carbon. Polymeric crosslinking agent I, combined with asphalt, can form a three-dimensional network structure. During high-temperature pyrolysis, it forms volatile small molecules, and the oxygen-containing functional groups inherent in this substance can decompose into small gaseous molecules containing carbon dioxide at high temperatures. These molecules can react with the carbon layers inside the asphalt-based carbon material to form closed pores, defects, and heteroatom groups, increasing the interlayer spacing of the graphite domains. This facilitates the adsorption, intercalation, and pore filling of sodium ions on the carbon anode surface, thus forming closed micropores and defects in the crosslinked polymeric asphalt carbon, significantly improving the sodium storage performance of the resulting anode material. However, this also leads to lower initial efficiency and poor rate performance. Small-molecule crosslinking agent II contains aromatic hydrocarbon structures. The introduction of such substances can help improve conductivity, reduce surface defects, and improve rate performance. This strategy balances high capacity and high rate capability, proposes a carbon material that is low-cost, simple to prepare, has high carbon yield, and is easy to scale up, and applies it as a negative electrode material in sodium batteries.

[0028] Furthermore, in steps (S2) and (S3), the method for achieving uniform mixing includes, but is not limited to, ball milling, mechanical pulverization, and high-speed mixer, with ball milling being preferred. The process parameters for ball milling are well known in the art. In one specific embodiment of the present invention, uniform mixing is achieved through ball milling. The ball milling process parameters are: directly placing the acid anhydride or carboxylic acid and pitch in a ball mill jar; a ball-to-material ratio of 10-20:1; a rotational speed of 600-1000 rpm; and a milling time of 5-8 hours.

[0029] Further, in steps (S2), (S3), and (S4), the inert atmosphere is at least one of argon and nitrogen.

[0030] Further, in step (S4), the hydrocarbon is at least one of methane, ethane, propane, butane, ethylene, acetylene, and toluene; the calcination is carried out by heating to 1000-1500℃ at a heating rate of 5-10℃ / min and calcining for 3-8 hours.

[0031] The sodium-ion battery anode material prepared by this invention has an irregular blocky morphology. After reacting with crosslinking agent II, a graphite layer forms on the surface of the carbon material, improving initial efficiency and cycle stability. This invention uses asphalt-like substances as raw materials, which are inexpensive and readily available. After pre-oxidation, the asphalt is mixed with acid anhydrides or carboxylic acids, followed by pre-carbonization to achieve isotropic crosslinking and inhibit the formation of mesophase carbon microspheres. Utilizing the difference between the oxygen-containing functional groups in the crosslinking agent and the pyrolysis behavior of asphalt, small gas molecules are formed, helping the carbon material to form closed pores in situ, resulting in a sodium-ion battery carbon anode material with high capacity and high rate performance.

[0032] The present invention also provides a hard carbon anode material for ion batteries, which is prepared by the above-described preparation method.

[0033] The present invention also provides a sodium battery carbon anode sheet, comprising: a current collector, a binder, a conductive agent, and a sodium-ion battery anode material prepared by the above preparation method.

[0034] The present invention also provides a sodium-ion secondary battery, wherein the negative electrode comprises the sodium-ion battery negative electrode material prepared by the above preparation method.

[0035] This invention provides a sodium-ion battery anode material based on coal chemical byproducts, its preparation method, and its application. It utilizes widely available and inexpensive asphalt-like substances as raw materials, and performs a two-step crosslinking process using a polymeric crosslinking agent I and a small-molecule crosslinking agent II. This approach balances high capacity and high rate performance, developing a low-cost, simple-process, controllable structural disorder, and high residual carbon material for use as an anode material in sodium-ion secondary batteries. Sodium-ion secondary batteries made using this anode material exhibit high operating voltage and good rate performance, making them suitable not only for energy supply in mobile devices and electric vehicles but also for energy storage needs in renewable energy generation and storage, smart grid peak shaving, distributed power stations, backup power supplies, and communication base stations. Attached Figure Description

[0036] Figure 1 These are the charge-discharge curves of carbon anodes prepared from coal tar pitch (XLC), Comparative Example 1 (OXLC), and Example 1 (POXLC).

[0037] Figure 2 High-resolution transmission electron microscope images of Example 1 and Comparative Example 1.

[0038] Figure 3 The images show the XRD patterns of the carbon anodes prepared in Comparative Example 1 (OXLC) and Example 1 (POXLC).

[0039] Figure 4 This is a constant current charge-discharge curve of Example 1 (POXLC) at different current densities. Detailed Implementation

[0040] The amorphous carbon anode material for pitch-based sodium-ion batteries described in this invention will be further described below with reference to specific embodiments and accompanying drawings. However, it should be understood that the scope of protection of this invention is not limited to the following embodiments.

[0041] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0042] Example 1

[0043] (S1) Weigh 100 parts by mass of lumpy coal tar pitch, crush it and then sieve it (200 mesh). Place the obtained pitch powder on aluminum foil and heat it to 300℃ at a rate of 3℃ / min under air conditions and keep it at the temperature for 10h to obtain the pre-oxidized precursor.

[0044] (S2) The pre-oxidized precursor and polyacrylic acid (number average molecular weight about 4000 g / mol) were ball-milled at a mass ratio of 100:4, with a ball-to-material ratio of 10:1, a rotation speed of 600 r, and a ball-milling time of 5 h. The mixture obtained after ball milling was made into tablets, heated to 600 °C at a heating rate of 10 °C / min under an argon atmosphere, held at that temperature for 5 h, and then cooled to obtain crosslinking precursor I.

[0045] (S3) Crosslinking precursor I and perylene dianhydride were ball-milled at a mass ratio of 100:10, with a ball-to-material ratio of 10:1, a rotation speed of 600 r, and a ball-milling time of 5 h. After ball milling, the mixture was prepared into tablets. After the tablets were prepared, they were heated to 300 °C at a heating rate of 5 °C / min under an argon atmosphere and held at that temperature for 2 h. Then, they were heated to 400 °C at a heating rate of 5 °C / min and held at that temperature for 4 h. After cooling, crosslinking precursor II was obtained.

[0046] (S4) The crosslinking precursor II is placed in a high-temperature tube furnace and heated to 1300°C at 5°C / min under an argon atmosphere. The temperature is held for 4 hours and then cooled to room temperature to obtain the amorphous carbon anode material.

[0047] (S5) The obtained amorphous carbon negative electrode material, conductive additive SP, and binder CMC / SBR are mixed in a weight ratio of 94:2:4, dissolved in water, and stirred to obtain a uniform slurry. The slurry is then uniformly coated on carbon-coated aluminum foil using a 50μm scraper, dried, and sliced ​​to obtain the negative electrode sheet.

[0048] Comparative Example 1

[0049] Other conditions are the same as in Example 1, except that steps (S2) and (S3) are omitted, and the pre-oxidized precursor obtained in step (S1) is directly subjected to high-temperature calcination in an argon atmosphere in step (S4).

[0050] Comparative Example 2

[0051] The other conditions are the same as in Example 1, except that step (S2) is omitted. The pre-oxidized precursor obtained in step (S1) is directly used in step (S3), that is, the pre-oxidized precursor and perylene tetracarboxylic dianhydride are ball-milled and mixed at a mass ratio of 100:10, and the subsequent steps are the same as in Example 1.

[0052] Comparative Example 3

[0053] The other conditions are the same as in Example 1, except that step (S3) is omitted, that is, the crosslinked precursor I obtained in step (S2) is directly subjected to step (S4).

[0054] Comparative Example 4

[0055] Other conditions are the same as in Example 1, except that step (S2) is changed to: pre-oxidized precursor, polyacrylic acid (number average molecular weight of about 5000 g / mol) and perylene dianhydride are ball-milled at a mass ratio of 100:4:10, ball-to-material ratio of 10:1, rotation speed of 600 r, ball milling time of 5 h, the mixture obtained after ball milling is prepared into tablets, heated to 600 °C at a heating rate of 10 °C / min under argon atmosphere, and held at that temperature for 5 h to obtain crosslinking precursor I; then proceed to step (S4). That is, steps (S2) and (S3) are combined, and the pre-oxidized precursor and crosslinking agent I and crosslinking agent II are mixed together for crosslinking modification.

[0056] Figure 1 The constant current charge-discharge curves of the electrode sheets made from coal tar pitch (XLC), Comparative Example 1 (OXLC), and Example 1 (POXLC) after being assembled into batteries show that, compared with materials made from coal tar pitch by direct high-temperature carbonization, the carbon anode material prepared in Example 1 has a higher capacity and an improved plateau capacity.

[0057] Figure 2 High-resolution transmission electron microscopy (HRTEM) images of the hard carbon materials obtained in Comparative Example 1 and Example 1 show that the materials after two-step crosslinking modification possess bent and closed local graphite domains, and simultaneously form a large number of closed-pore structures. This is closely related to the improvement in the low-pressure plateau capacity. The formation of closed pores provides favorable conditions for the precipitation of sodium metal clusters inside the hard carbon, without affecting the diffusion of sodium ions in the negative electrode material. Furthermore, high-temperature calcination reduces the formation of oxygen-containing functional groups and defects on the surface by the activator, eliminating its influence on the coulombic efficiency of the material. This structure is completely different from the carbon material obtained by direct calcination of pitch. Meanwhile, the hard carbon sample of Example 1, obtained by a pore-forming agent composed of various oxygen-containing organic compounds, has richer pores, which will lead to a higher plateau capacity.

[0058] Figure 3 The XRD patterns of the carbon materials obtained in Example 1 (POXLC) and Comparative Example 1 (OXLC) show that the amorphous carbon anode obtained by cross-linking activation of sodium ions has increased amorphousness compared to the carbon material obtained by direct calcination after pre-oxidation. The modified carbon material has a larger interlayer spacing and lower crystallinity, indicating that the average packing degree of graphite domains has decreased. The short-range ordered graphite domains are more conducive to forming a closed microporous structure when they cross-link with each other, thereby effectively storing sodium ion clusters in the low-pressure plateau region.

[0059] Figure 4The constant current charge-discharge curves of Example 1 (POXLC) at different current densities show that it can still exhibit high specific capacity at high current densities, indicating that the cross-linked structure can maintain stability and retain high specific capacity under high current.

[0060] It can be seen that, compared with the asphalt material without crosslinking, the asphalt-based hard carbon material obtained by the two-step crosslinking in Example 1 has a higher specific capacity. The newly formed pores are conducive to the adsorption and deposition of sodium ions and sodium clusters on its inner surface, and the electrochemical performance is significantly improved.

[0061] Example 2

[0062] The other conditions are the same as in Example 1, except that in step (S2), polyacrylic acid is replaced with polymethyl methacrylate with a number average molecular weight of 5000, and the mass ratio of the pre-oxidized precursor to polymethyl methacrylate is 100:6.

[0063] Example 3

[0064] The other conditions are the same as in Example 1, except that in step (S3), perylene dianhydride is replaced with terephthalic acid, and the mass ratio of crosslinking precursor I to terephthalic acid is 100:5.

[0065] Example 4

[0066] The other conditions are the same as in Example 1, except that in step (S3), perylenetetracarboxylic dianhydride is replaced with 1,3,5-benzenetricarboxylic acid, and the mass ratio of crosslinking precursor I to 1,3,5-benzenetricarboxylic acid is 100:10.

[0067] Example 5

[0068] Other conditions are the same as in Example 1, except that step (S3) is changed to: crosslinking precursor I and perylene tetracarboxylic dianhydride are ball-milled at a mass ratio of 100:10, ball-to-material ratio is 10:1, rotation speed is 600 r, ball milling time is 5 h, after ball milling the mixture is made into tablets, and after the tablets are made, they are heated to 400°C at a heating rate of 5°C / min under argon atmosphere, held at the temperature for 6 h, and after cooling, crosslinking precursor II is obtained.

[0069] Example 6

[0070] The other conditions are the same as in Example 1, except that in step (S1), the heating rate is changed from 3°C / min to 10°C / min.

[0071] Application examples Electrochemical performance testing

[0072] The dried negative electrode sheet was assembled into a coin cell with a sodium metal negative electrode, a carboxylic acid cellulose membrane, and EC / DEC / 1M NaPF6 electrolyte. The cell was then tested on the Newwell testing platform, yielding the first cycle curve shown in Table 1. Within the voltage range of 0.001–2V, the cell was first activated for 5 cycles at a current density of 20 mA / g, followed by charge-discharge cycles.

[0073] The electrochemical performance of the negative electrode materials obtained in the above embodiments and comparative examples is listed in Table 1 below:

[0074] Table 1 Electrochemical performance data of anode materials

[0075]

[0076]

[0077] The test results of the half-cells in Table 1 for each embodiment show that the sodium storage capacity and rate performance of the amorphous carbon anode in the sodium-ion battery are significantly improved after cross-linking and activation of fossil mineral precursors such as pitch. (50 mA g) -1 The specific capacity during the first charge cycle at the current density is 300mA g. -1 Above, 200mA g -1 The specific capacity during the first charge cycle is 230mAh g at the given current density. -1 The above results show that the unmodified Comparative Example 1 has a specific capacity of 290 mAh / g. It is worth noting that the crosslinking activation conditions need to be properly controlled; by controlling the activation conditions, the optimal carbon layer structure and the maximum specific capacity can be obtained.

[0078] This invention provides an application of fossil mineral-based pyrolytic amorphous carbon material in sodium-ion batteries. Its contribution to the prior art lies in utilizing acid anhydrides or carboxylic acids as crosslinking agents to increase the crosslinking degree of the precursor. Simultaneously, the release of gas molecules during pyrolysis increases the porosity within the carbon material, inhibiting the molten rearrangement of asphaltenes. During high-temperature carbonization, local graphite domains can close to form closed pores, significantly improving the electrochemical performance of the sodium-ion battery. It is understood that while the various embodiments of this invention have described the invention in detail with specific electrolytes, separators, current collectors, active materials, binders, conductive additives, etc., these descriptions are merely for fulfilling legal requirements and illustrating the composition of sodium-ion batteries. This invention is not limited to the given embodiments. Any modifications, equivalent substitutions, and improvements made using this specification within the spirit and principles of this invention, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this invention.

Claims

1. A method for preparing a hard carbon material, characterized in that, Includes the following steps: (S1) The asphalt is crushed and heat-treated in an oxidizing atmosphere to obtain a pre-oxidized precursor; the heat treatment is to slowly heat up to 250-300℃ and hold for 5-10 hours, and the heating rate of the slow heating is 1-3℃ / min. (S2) The pre-oxidized precursor and crosslinking agent I are mixed evenly and crosslinked once under an inert atmosphere and heating conditions to obtain crosslinked precursor I; the crosslinking agent I is a polymer with carboxyl groups in the side chain; the amount of crosslinking agent I is 5-10 wt% of the pre-oxidized precursor; the process conditions for the first crosslinking are heat treatment at 300-600 ℃ for 5-10 h. (S3) Crosslinking precursor I and crosslinking agent II are mixed evenly and subjected to secondary crosslinking under an inert atmosphere and heating conditions to obtain crosslinking precursor II; the crosslinking agent II is a small molecule aromatic compound containing multiple acid anhydrides and / or carboxyl groups; the amount of crosslinking agent II is 3-6 wt% of crosslinking precursor I; the process conditions for secondary crosslinking are to first heat to 250-400 ℃ at a heating rate of 5-10 ℃ / min and hold for 1-2 h, and then heat to 400-600 ℃ at a slow rate of 5-10 ℃ / min and hold for 3-5 h; (S4) Crosslinked precursor II was calcined, cooled and ground in an inert atmosphere to obtain an amorphous sodium-ion battery anode material.

2. The preparation method according to claim 1, characterized in that, The asphalt-like substances include one or more mixtures of coal tar pitch, petroleum asphalt, natural asphalt, and mesophase asphalt; crushed to a particle size of less than 5 mm; and / or The oxidizing atmosphere comprises at least 20% by volume oxygen or is an atmosphere containing ozone.

3. The preparation method according to claim 1, characterized in that, In step (S2), the crosslinking agent I is selected from at least one of polyacrylic acid, polymethacrylic acid, and alginate.

4. The preparation method according to claim 3, characterized in that, In step (S2), the number average molecular weight of crosslinking agent I is 4000-20000 g / mol.

5. The preparation method according to claim 3, characterized in that, The number-average molecular weights of the polyacrylic acid and polymethacrylic acid are 4000-6000 g / mol; the molecular weight of the alginate is 10000-20000 g / mol.

6. The preparation method according to claim 1, characterized in that, In step (S3), the crosslinking agent II is selected from at least one of terephthalic acid, phthalic acid, isophthalic acid, gallic acid, perylene dianhydride, pyromellitic acid, and pyromellitic anhydride.

7. The preparation method according to claim 1, characterized in that, In step (S4), the calcination is carried out by heating the temperature to 1000-1500℃ at a heating rate of 5-10℃ / min and calcining for 3-8 hours.

8. A hard carbon material for sodium-ion batteries, prepared by the preparation method described in any one of claims 1-7.

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