Asphalt-based hard carbon negative electrode material, preparation method thereof and battery

Abstract

The invention belongs to the technical field of battery materials, and particularly relates to an asphalt-based hard carbon negative electrode material, a preparation method thereof and a battery. According to the preparation method of the asphalt-based hard carbon negative electrode material provided by the invention, firstly, a large number of sulfonic acid groups are selectively grafted on the surface of asphalt molecules through sulfonation to occupy active sites, then the occupied sulfonic acid groups are removed in situ by utilizing CO2 etching, so that a large number of defect sites are generated on the surface of the material, and the defect sites are locked into stable defects after high-temperature carbonization; the interior of the finally prepared hard carbon material is rich in closed pores, meanwhile, the surface of the hard carbon material is also provided with a large number of high-reaction-activity sites beneficial to sodium ion adsorption and combination, the reversible capacity of a slope region (larger than 0.1 V) is mainly reflected in the assembled hard carbon-sodium ion button cell, and the sodium storage capacity is developed due to the corresponding lower diffusion impedance. The influence of polarization on the material under large current density is small, and the material has more excellent rate capability.

Description

[0001] This application claims domestic priority to the patent application filed on September 29, 2025, with application number CN202511404137.8 and title “A pitch-based hard carbon anode material and its preparation method, and a battery”. Technical Field

[0002] This application belongs to the field of battery materials technology, and more specifically, relates to an asphalt-based hard carbon anode material, its preparation method, and a battery. Background Technology

[0003] With the explosive growth of the global energy storage industry, sodium-ion batteries (SIBs), due to their abundant sodium resources and cost advantages, have become an important supplement to lithium-ion battery technology and a crucial solution for large-scale energy storage systems. However, the anode material, a core component of SIBs, is a significant factor limiting the energy density and cycle life of sodium-ion batteries. Currently, hard carbon materials, with their unique structure of graphite-like microcrystalline domains and disordered nanopores, can achieve sodium storage through a dual mechanism of "intercalation + adsorption," making them the only commercially viable anode system for SIBs. However, their performance is still limited by two key issues: the difficulty in artificially controlling the closed-pore structure and the low utilization rate of defect sites.

[0004] Currently, the raw materials for hard carbon mainly include biomass, resins, and fossils such as bitumen and coal. Compared with biomass and resin precursors, bitumen is an ideal hard carbon precursor due to its high carbon content, low impurity content, and superior structural plasticity, used to regulate and modify the closed-cell and defective structures of hard carbon.

[0005] However, how to safely and controllably modify asphalt precursors to achieve closed-cell / defect synergy, and utilize the high reactivity of asphalt molecules to directionally regulate the sodium storage microstructure while avoiding damage to the asphalt structure, in order to realize the production, preparation and application of high-performance sodium-ion battery hard carbon anodes, remains a major research direction for hard carbon materials. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this application is to provide a method for preparing asphalt-based hard carbon anode material, using asphalt as raw material to achieve the production and preparation of high-performance sodium-ion battery hard carbon anodes.

[0007] To achieve the above objectives, in a first aspect, this application provides a method for preparing an asphalt-based hard carbon anode material, comprising:

[0008] Asphalt with a softening point of 180℃~250℃ is mixed with a sulfonating agent and subjected to sulfonation treatment to obtain sulfonated asphalt; wherein, the temperature of the sulfonation reaction is 60~100℃.

[0009] The sulfonated asphalt was etched under a carbon dioxide atmosphere to obtain an asphalt intermediate.

[0010] The asphalt intermediate is carbonized in a protective atmosphere to obtain a hard carbon anode material.

[0011] In some feasible embodiments, the asphalt includes one or more of petroleum asphalt and coal tar pitch; and / or, the softening point of the asphalt is 200°C; and / or, the particle size D50 of the asphalt is 10~100μm; and / or, the ash content of the asphalt is <0.1%.

[0012] In some feasible embodiments, the sulfonating agent includes one or more of concentrated sulfuric acid, fuming sulfuric acid, sulfur trioxide, p-toluenesulfonic acid, benzenesulfonic acid, etc.; and / or,

[0013] The ratio between the mass of the asphalt and the volume of the sulfonating agent is 1 g : (1~8) mL; and / or,

[0014] The sulfonation treatment time is greater than or equal to 2 hours.

[0015] In some feasible embodiments, the sulfonating agent comprises a combination of concentrated sulfuric acid and phosphoric acid; and / or,

[0016] The ratio between the mass of the asphalt and the volume of the sulfonating agent is 1 g : (1~8) mL; and / or,

[0017] The sulfonation treatment time is 4-6 hours.

[0018] In some feasible embodiments, when the sulfonating agent comprises a combination of concentrated sulfuric acid and phosphoric acid, the volume ratio of the concentrated sulfuric acid to the phosphoric acid is 5:1 to 20:1; and / or,

[0019] The concentrated sulfuric acid has a mass percentage of approximately 90%; and / or,

[0020] The mass percentage of the phosphoric acid is greater than or equal to 75%.

[0021] In some feasible embodiments, the sulfonation reaction is followed by solid-liquid separation, and the resulting solid is washed with water until the pH value is neutral, and dried to obtain the sulfonated asphalt.

[0022] In some feasible embodiments, the carbon dioxide atmosphere is a pure carbon dioxide atmosphere, or a mixed atmosphere formed by carbon dioxide and an inert gas; wherein the inert gas includes one or more of nitrogen, helium, neon, argon, and xenon; and / or,

[0023] The etching process is held at a temperature T that satisfies: 700 ≤ T < 900℃; and / or,

[0024] The holding time for the medium-temperature etching process is 1-4 hours; and / or,

[0025] The heating rate to the holding temperature is 2~10℃ / min; and / or,

[0026] The protective atmosphere comprises one or more of nitrogen, helium, neon, argon, and xenon; and / or,

[0027] The carbonization treatment temperature is 1100~1700℃; and / or,

[0028] The carbonization treatment time is 2-8 hours; and / or,

[0029] The median particle size of the hard carbon anode material is 7~20μm.

[0030] In some feasible solutions, the holding temperature of the etching process is 700~800℃; or, the holding temperature of the etching process is 750~850℃.

[0031] Secondly, this application provides an asphalt-based hard carbon anode material, which is prepared by the above-mentioned method for preparing asphalt-based hard carbon anode materials.

[0032] Part Four: This application provides a battery comprising the aforementioned pitch-based hard carbon anode material.

[0033] The method for preparing pitch-based hard carbon anode material provided in this application achieves the production of high-performance sodium-ion battery hard carbon anodes through a three-stage linkage of pitch sulfonation modification, CO2 in-situ etching, and high-temperature carbonization. First, an "additive" process is performed, selectively grafting a large number of sulfonic acid groups onto the surface of pitch molecules. These functional groups occupying active sites are then "subtracted" by using CO2 etching to remove the occupying functional groups in situ, resulting in numerous defect sites on the material surface. These defects are then locked into stable defects after high-temperature carbonization. The resulting hard carbon material is rich in closed pores internally and possesses numerous highly reactive active sites on its surface conducive to sodium ion adsorption and binding. In assembled hard carbon-based sodium-ion coin cells, this capacity is mainly characterized by reversible capacity in the ramp region (>0.1V). Furthermore, due to its lower diffusion resistance (higher diffusion coefficient), this sodium storage capacity is less affected by polarization at high current densities, thus exhibiting superior rate performance. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 A schematic flowchart of an embodiment of a method for preparing a hard carbon anode material provided in this application;

[0036] Figure 2 This is a comparison chart of the charge-discharge curves for Examples 1, 2, and 3;

[0037] Figure 3 This is a comparison chart of the rate performance of Examples 1, 2, and 3;

[0038] Figure 4 This is a comparison graph of the charge-discharge curves of Example 4 and Comparative Example 5;

[0039] Figure 5 This is a comparison chart of the rate performance of Example 4 and Comparative Example 5;

[0040] Figure 6 The infrared spectra of Example 4 and Comparative Example 5 are shown in the comparison diagram.

[0041] Figure 7 This is a comparison chart of the charge-discharge curves for Examples 1 and 4;

[0042] Figure 8 This is a comparison chart of the rate performance of Examples 1 and 4;

[0043] Figure 9 This is a comparison chart of charge-discharge curves for Examples 1 and 5 and Comparative Example 4;

[0044] Figure 10 This is a comparison chart of the rate performance of Examples 1 and 5 and Comparative Example 4;

[0045] Figure 11 This is a comparison chart of the charge-discharge curves of Example 1 and Comparative Examples 1, 2, and 3;

[0046] Figure 12 This is a comparison chart of the rate performance of Example 1 and Comparative Examples 1, 2, and 3;

[0047] Figure 13 This is a comparison chart of the charge-discharge curves for Examples 4, 6, and 7;

[0048] Figure 14 The chart shows a comparison of the rate performance of Examples 4, 6, and 7. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0050] In the description of this application, it should be understood that the term "and / or" describes a relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The symbol " / " in this document indicates that the related objects are in an "or" relationship; for example, A / B means A or B.

[0051] In the description of the embodiments in this application, the words "exemplary" or "for example" are used to indicate that they are examples, illustrations, or descriptions. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design options. Specifically, the use of the words "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0052] In the description of the embodiments in this application, unless otherwise stated, "multiple" means two or more.

[0053] In this application, the term "hard carbon" refers to carbon materials that retain a non-graphitized structure after high-temperature treatment above 2000°C, and whose structure is often composed of disordered stacked graphene-like domains and nanopores.

[0054] In this application, the term "graphite-like microcrystals" refers to a structure in which multiple layers of graphite are stacked locally on the structure of hard carbon materials. The interlayer spacing is generally greater than 0.335 nm, the orientation between microcrystal regions is random, and the long-range structure exhibits topological disorder.

[0055] In this application, the term "closed-cell" refers to a nanocavity (typically <2 nm) that is completely surrounded by carbon walls within a hard carbon material and is not connected to the outside. Relevant literature indicates that this structure often corresponds to the contribution of the low-voltage plateau region capacity during sodium storage in hard carbon anodes.

[0056] In this application, the term "defect" refers to a local distortion in the arrangement of six-membered rings of carbon atoms in the structure of hard carbon materials. Examples include topological defects, edge defects, and vacancy defects.

[0057] This application provides a method for preparing an asphalt-based hard carbon material, referencing... Figure 1 , Figure 1 A schematic flowchart of an embodiment of a method for preparing a hard carbon anode material provided in this application includes the following steps:

[0058] Step S11: Mix asphalt with a softening point of 180℃~250℃ with a sulfonating agent and perform sulfonation treatment to obtain sulfonated asphalt;

[0059] Step S12: The sulfonated asphalt is etched under a carbon dioxide atmosphere to obtain an asphalt intermediate;

[0060] Step S13: Carbonize the asphalt intermediate in a protective atmosphere to obtain asphalt-based hard carbon anode material.

[0061] In this embodiment, a three-stage linkage of molecular-level sulfonation modification, CO2 in-situ etching, and high-temperature carbonization is performed on asphalt. First, an "additive" process is used to selectively graft a large number of sulfonic acid groups onto the surface of asphalt molecules. The active sites occupied by these functional groups are then "subtracted" by using CO2 etching to remove the occupying functional groups in situ, resulting in a large number of defect sites on the material surface. After high-temperature carbonization, these defects are locked into stable defects. The hard carbon material prepared in the end is rich in closed pores inside and has a large number of highly reactive active sites on the surface that are conducive to the adsorption and binding of sodium ions. In the assembled hard carbon sodium-ion coin cell, the reversible capacity in the ramp region (>0.1V) is mainly manifested. Moreover, due to its lower diffusion resistance (higher diffusion coefficient), the sodium storage capacity is less affected by polarization at high current densities, thus exhibiting better rate performance.

[0062] Specifically, in the early stage, the large-volume sulfonic acid groups introduced through electrophilic substitution reaction utilize their steric hindrance effect to suppress the longitudinal dense stacking and lateral ordered extension of the carbon layer during sp² hybridization and recombination in the asphalt during carbonization, inducing it to transform into a hard carbon material with short-range order and long-range disorder. In the middle stage, the carbon dangling bonds generated by CO2 etching are also reconstructed into stable five / seven-membered ring topological defects through structural relaxation. At the same time, the high-temperature environment promotes local melting and reconnection at the carbon layer edges, transforming the mesopores and open pores formed by CO2 etching into closed pores. The trace sulfur / oxygen impurities remaining in the system are also further removed in the form of SO2 / CO at high temperature. Finally, an asphalt-based hard carbon anode material that facilitates sodium ion insertion and extraction is formed.

[0063] In step S11:

[0064] In some embodiments, the asphalt may include one or more of petroleum asphalt and coal tar pitch.

[0065] In some embodiments, the softening point of the asphalt can be 100℃~350℃, specifically 100℃~150℃, 150℃~200℃, 200℃~250℃, 250℃~300℃, 300℃~350℃, etc. Asphalt itself is a complex mixture composed of hydrocarbons of different molecular weights and their non-metallic derivatives; asphalt with different softening points has different degrees of aromatization.

[0066] In some specific embodiments, the softening point of the asphalt can be 180℃~250℃, specifically 180℃~200℃, 200℃~220℃, 220℃~250℃, etc. Asphalt within the above softening point range contains a suitable amount of aromatic core components, which can provide sufficient carbon chains to condense during pyrolysis to form a stable carbon skeleton support structure and avoid excessive defects, while retaining an appropriate amount of unsaturated aromatic components and active sites for sulfonation and subsequent etching and pore-forming.

[0067] In some embodiments, the ash content of the bitumen is <0.1%, and raw materials with less ash content are beneficial for controlling the ash content in the resulting hard carbon to be within a lower range.

[0068] The asphalt can be asphalt particles or asphalt powder, which allows for more complete contact between the asphalt and concentrated sulfuric acid, increasing the solid-liquid reaction contact area and thus achieving more complete electrophilic substitution and sulfonation modification. Specifically, the particle size D50 of the asphalt can be 10~100μm.

[0069] In some embodiments, the sulfonating agent includes one or more of concentrated sulfuric acid, fuming sulfuric acid, sulfur trioxide (SO3), p-toluenesulfonic acid, benzenesulfonic acid, etc. Sulfonating agents such as concentrated sulfuric acid can selectively graft a large number of sulfonic acid groups onto the surface of asphalt molecules. By having the sulfonic acid groups occupy some active sites on the asphalt surface, a large number of defect sites can be generated on the surface of the asphalt by removing the occupying functional groups in subsequent processes.

[0070] In some specific embodiments, the sulfonating agent includes concentrated sulfuric acid and phosphoric acid. Further, the volume ratio of the concentrated sulfuric acid to phosphoric acid is 5:1 to 20:1, specifically 5:1 to 16:1, 8:1 to 16:1, 8:1 to 10:1, etc.

[0071] In this embodiment, the addition of phosphoric acid, a non-oxidizing strong protic acid component, serves as a highly efficient catalyst and reaction medium regulator. Synergistically, it works with concentrated sulfuric acid to significantly promote the sulfonation reaction and influence the structure of the final hard carbon material. Specifically, on the one hand, phosphoric acid can provide a high concentration of protons during the high-temperature sulfonation reaction to catalyze the electrophilic substitution reaction, accelerating the sulfonation process. On the other hand, phosphoric acid also acts as a dehydrating agent, promoting dehydration condensation crosslinking between asphalt molecules, thereby promoting the crosslinking of asphalt molecules into a more stable three-dimensional network structure. Furthermore, concentrated sulfuric acid is oxidizing; prolonged reaction at high temperatures may lead to side reactions such as oxidation of the asphalt skeleton, chain breakage, or the formation of quinone structures. The addition of phosphoric acid shares the role of providing protons, reducing the oxidizing properties of the reaction system to a certain extent, thus protecting the asphalt molecular skeleton from excessive oxidative degradation and allowing the reaction to more readily proceed towards sulfonation and condensation crosslinking.

[0072] It is particularly noteworthy that this application chose phosphoric acid as a co-catalyst, which has irreplaceable advantages over other strong protic acids (such as nitric acid). Nitric acid is also a strong protic acid, but it has strong oxidizing properties. In the high-temperature reaction environment coexisting with concentrated sulfuric acid, it significantly exacerbates the oxidative corrosion and chain breakage risk of the pitch molecular skeleton, leading to the destruction of the carbon source structure and hindering the final formation of a complete and stable carbon skeleton. Phosphoric acid, as a non-oxidizing moderately strong acid, can effectively avoid the aforementioned excessive oxidation problem while providing sufficient catalytic protons, ensuring that the reaction selectivity proceeds in the expected direction of sulfonation and condensation crosslinking. In addition, phosphoric acid is stable and non-volatile at 80°C, and can serve as a stable reaction medium to assist in the sulfonation of sulfuric acid. Conversely, some volatile strong acids (such as hydrochloric acid) or easily decomposed organic acids are difficult to exist stably and function in this high-temperature system.

[0073] Understandably, the concentrated sulfuric acid has a mass percentage of approximately 90%, specifically between 90% and 98%, for example, 98%. High-concentration sulfuric acid can decompose at relatively high temperatures into electrophilic sulfonic acid groups (-SO3H) that attack the aromatic rings in asphalt molecules, followed by deprotonation, thus achieving sulfonation modification. At lower sulfuric acid concentrations, the electrophilic substitution reaction is less likely to occur, and the oxidizing properties of sulfuric acid become more prominent. In this case, at relatively higher temperatures, the oxidation of the highly reactive aliphatic side chains of asphalt is more likely to occur, generating oxygen-containing functional groups such as carbonyl or carboxyl groups. Phosphoric acid can be reagent-grade phosphoric acid (75%-85% (w / w)) or commercially available concentrated phosphoric acid at 85% (w / w), meaning the mass percentage of phosphoric acid can be greater than or equal to 75%.

[0074] In some embodiments, the ratio between the mass of the asphalt and the volume of the sulfonating agent is 1g:(1~8)mL, specifically 1g:(1~6)mL, 1g:(2~6)mL, 1g:(2~4)mL, etc.

[0075] In some embodiments, the sulfonation reaction temperature is 60~100℃, specifically 60℃, 70℃, 80℃, 90℃, 100℃, etc. It is understood that the temperature control of the sulfonation reaction can employ conventional temperature control methods in the art, such as water bath or oil bath methods, and is not limited here. In this embodiment, a relatively high temperature is used to promote the decomposition of high-concentration sulfuric acid into electrophilic sulfonic acid groups -SO3H at a relatively high temperature, which attack the aromatic rings in the asphalt molecules, followed by deprotonation, thereby achieving sulfonation modification. The sulfonation reaction time is greater than or equal to 2 hours to promote the grafting of a large number of -SO3H groups. Further, the sulfonation reaction time is 2~6 hours, specifically 4~6 hours, etc. Within the above range, the sulfonation reaction is close to complete; a longer reaction time may not result in more -SO3H group grafting.

[0076] Understandably, the asphalt and sulfonating agent can be mixed using methods known in the art, such as one or more of the following: stirring, ultrasonication, etc.

[0077] In some embodiments, after the sulfonation reaction, the process further includes solid-liquid separation, followed by drying of the obtained solid to obtain the sulfonated asphalt. The drying temperature can be 80-120°C, such as 80°C, 100°C, or 120°C; the drying time can be 12-48 hours, such as 12 hours, 24 hours, 36 hours, 40 hours, or 48 hours. The drying method can be a commonly used method in the art, such as forced-air drying or vacuum drying, and is not limited here.

[0078] Furthermore, after solid-liquid separation, the mixture can be washed with water until the pH value is neutral. Specifically, deionized water can be used for washing. After solid-liquid separation, the solid can be crushed and washed more thoroughly to remove unreacted reagents and impurities, thus obtaining sulfonated asphalt powder.

[0079] In step S12:

[0080] In some embodiments, the carbon dioxide atmosphere can be a pure carbon dioxide atmosphere or a mixed atmosphere formed by carbon dioxide and an inert gas, wherein the inert gas may include one or more of nitrogen, helium, neon, argon, and xenon. In some specific embodiments, the volume percentage of carbon dioxide in the carbon dioxide atmosphere is greater than or equal to 65%, specifically 65%~80%, 80%~90%, 90%~100%, etc.

[0081] In some embodiments, the holding temperature T of the etching process satisfies: 700 ≤ T < 900℃. Specifically, the holding temperature of the etching process can be 700~850℃, such as 700℃~800℃, 750℃~850℃, 750℃~800℃, etc. This temperature range is beneficial for achieving deep and uniform bulk etching of sulfonated asphalt by CO2, forming a high-density porous network; on the other hand, it also ensures the full removal of sulfonic acid groups, allowing carbon dangling bonds to be reconstructed into defects that can be adsorbed by sodium ions.

[0082] In some specific embodiments, the heating rate to the holding temperature can be 2~10℃ / min, such as 2~3℃ / min, 3~5℃ / min, etc.

[0083] In some embodiments, the holding time for the medium-temperature etching process can be 1 to 4 hours, specifically 1 to 2 hours, 2 to 3 hours, 3 to 4 hours, etc.

[0084] In some embodiments, during the etching process of the sulfonated asphalt in a carbon dioxide atmosphere, a carbon dioxide gas is also introduced to continuously supply carbon dioxide for etching and to carry away other substances produced in the reaction through the gas flow. Specifically, the flow rate of the carbon dioxide gas can be 10~40 ml / min, specifically 10~30 ml / min, 15~30 ml / min, 15~20 ml / min, etc. In some specific embodiments, the carbon dioxide gas can be pure carbon dioxide gas or a mixture of carbon dioxide and an inert gas. Specifically, the volume percentage of carbon dioxide in the carbon dioxide gas is greater than or equal to 65%, specifically 65%~80%, 80%~90%, 90%~100%, etc. The inert gas can include one or more of nitrogen, helium, neon, argon, and xenon.

[0085] In some embodiments, after the etching process is completed and kept at room temperature, the material is cooled down and crushed or pulverized to obtain asphalt intermediate powder. In some specific embodiments, the particle size D50 of the asphalt intermediate is 7~20μm, specifically 7~10μm, 10~25μm, 15~20μm, etc.

[0086] In step S13:

[0087] In some embodiments, the protective atmosphere is formed by one or more of nitrogen, helium, neon, argon, and xenon.

[0088] The carbonization temperature can be 1100~1700℃, specifically 1100~1200℃, 1200~1300℃, 1300~1500℃, 1500~1700℃, etc.; the time can be 2~8h, specifically 2~4h, 4~6h, 6~8h, etc.

[0089] In some embodiments, the heating rate to the carbonization process can be 1~10℃ / min, such as 1~3℃ / min, 3~5℃ / min, etc.

[0090] This application provides an asphalt-based hard carbon material, prepared by the above-described preparation method. Specifically, the median particle size of the hard carbon anode material is 7~20 μm, and can be 7~10 μm, 10~25 μm, 15~20 μm, etc.

[0091] In some embodiments, the hard carbon anode material prepared in this application can be used in sodium-ion batteries as an active anode material for sodium-ion batteries.

[0092] This application also provides a battery anode material comprising the above-mentioned hard carbon anode material.

[0093] This application also provides a sodium-ion battery, including a negative electrode, which comprises an active material, a conductive agent, and a binder, wherein the active material includes the hard carbon negative electrode material. Further, the active material is the hard carbon negative electrode material. The conductive agent may include conductive carbon black, Super P, acetylene black, Ketjen black, etc. The binder may include one or more of sodium alginate, sodium carboxymethyl cellulose, polyacrylic acid, and polyvinylidene fluoride, etc., in combination.

[0094] Furthermore, the sodium-ion battery also includes a positive electrode, a separator, an electrolyte, and a current collector.

[0095] The positive electrode material may include one or more of transition metal oxides, Prussian blue and its analogues, and polyanionic compounds. The transition metal oxides include layered metal oxides (such as sodium nickel iron manganese oxide) and tunnel-structured compounds. The polyanionic compounds include phosphates (such as sodium iron phosphate), pyrophosphates (such as sodium iron pyrophosphate), sulfate-type compounds (such as sodium iron sulfate), and complex polyanionic compounds (such as sodium iron phosphate sulfate, sodium iron phosphate, etc.). Furthermore, the polyanionic compounds may also include cation-doped or anion-doped compounds.

[0096] The diaphragm may include polyolefin diaphragms such as polyethylene and polypropylene.

[0097] The electrolyte may include sodium salts such as sodium hexafluorophosphate (NaPF6), organic solvents such as carbonates or ethers, etc.

[0098] The current collector can be made of aluminum foil or copper foil, etc. In one specific embodiment, the current collector is made of aluminum foil, which is relatively low in cost.

[0099] The technical solutions and effects of this application will be described in detail below through specific embodiments, comparative examples and experimental examples. The following embodiments are only some embodiments of this application and are not intended to limit this application.

[0100] It should be understood that materials of the same or similar type, model, quality, properties, or function as the reagents and instruments used in the following embodiments can be used to implement this application. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods. Unless otherwise specified, the materials and reagents used in the following embodiments are commercially available.

[0101] Example 1

[0102] The hard carbon anode material and its preparation method provided in this embodiment include the following steps:

[0103] Step 1: Slowly add 80 mL of 98% concentrated sulfuric acid and 5 mL of 85% phosphoric acid to a three-necked flask containing 20 g of asphalt powder. After stirring and mixing, maintain the reaction temperature at 80°C for 4 hours, then stop the reaction and cool. The asphalt powder is petroleum fractionated asphalt with a softening point of 200°C and an ash content of <0.1%.

[0104] Step 2: Filter the reaction mixture and continuously wash the material with deionized water to remove the remaining sulfuric acid. Adjust the pH value to neutral and then put the sulfonated asphalt into a vacuum oven to dry at 80°C for 24 hours. Then, take out the dried sulfonated asphalt and crush it to obtain sulfonated asphalt powder.

[0105] Step 3: Place the sulfonated asphalt powder into a tube furnace with a carbon dioxide atmosphere for medium-temperature etching. The heating rate is set to 2~3℃ / min, the heating temperature is set to 800℃, the holding time is set to 2h, and the gas flow rate is controlled to 15~20mL / min. After the holding time is completed, the material is cooled down with the furnace and crushed to obtain the etched sulfonated asphalt powder.

[0106] Step 4: The etched sulfonated asphalt powder is placed in a tube furnace under a high-purity argon atmosphere for high-temperature carbonization. The heating rate is set to 3℃ / min, the gas flow rate in the tube furnace is set to 20mL / min, the heating temperature is set to 1300℃, and the holding time is set to 2h to obtain the asphalt-based hard carbon anode material after high-temperature carbonization.

[0107] Example 2

[0108] Similar to Example 1, the difference is that the heating temperature of the sulfonation reaction in step 1 is 60°C.

[0109] Example 3

[0110] Similar to Example 1, the difference is that the heating temperature of the sulfonation reaction in step 1 is 100°C.

[0111] Example 4

[0112] Similar to Example 1, the difference is that only concentrated sulfuric acid is added in step 1, and phosphoric acid is not added.

[0113] Example 5

[0114] Similar to Example 4, the difference is that the temperature for carbon dioxide medium-temperature etching in step 3 is 700°C.

[0115] Example 6

[0116] Similar to Example 4, the difference is that in step 1, the asphalt with a softening point of 180°C replaced the original asphalt with a softening point of 200°C.

[0117] Example 7

[0118] Similar to Example 4, the difference is that in step 1, the asphalt with a softening point of 250°C was used instead of the original asphalt with a softening point of 200°C.

[0119] Comparative Example 1

[0120] Similar to Example 1, the difference is that steps 1-3 are omitted, and the petroleum fractionated pitch with a softening point of 200°C and an ash content of <0.1% is directly carbonized in step 4.

[0121] Comparative Example 2

[0122] Similar to Example 1, the difference is that the medium-temperature etching treatment with carbon dioxide in step 3 is not performed, and the sulfonated asphalt powder obtained in step 2 is directly carbonized in step 4.

[0123] Comparative Example 3

[0124] Similar to Example 1, the difference is that steps 1 and 2 are not performed, that is, the asphalt is not sulfonated and washed with water, and the original asphalt powder with a softening point of 200°C is directly subjected to the medium-temperature etching treatment in step 3 and the carbonization in step 4.

[0125] Comparative Example 4

[0126] Similar to Example 4, the difference is that the temperature for carbon dioxide medium-temperature etching in step 3 is 900°C.

[0127] Comparative Example 5

[0128] Similar to Example 4, except that the sulfonation reaction in step 1 is carried out at room temperature.

[0129] [Sulfonation Time Exploration Experiment]

[0130] The reaction was carried out under constant temperature stirring at 80°C according to step 1 in Example 1. During the 0-2h stage, the reaction system was a flowable liquid, and the asphalt was uniformly dispersed in the strong acid system. During the 2-4h stage, the reaction system was a viscous colloid. During this stage, concentrated sulfuric acid continuously attacked the aromatic ring of the asphalt at high temperature, grafting a large number of -SO3H groups through electrophilic substitution reaction. The strong polar effect of these -SO3H groups caused electrostatic repulsion between the asphalt molecular chains, forcing the asphalt molecular chains to extend and expose more reaction sites, further accelerating cross-linking, and the viscosity of the reaction system continued to increase. When the reaction reached 4h, the reaction system was a solid gel. It would also remain a solid gel for 4h and above (such as 6h). This is because the -SO3H grafted on the asphalt activated the adjacent carbon sites due to the electron-withdrawing effect, which promoted the dehydration condensation cross-linking between asphalt molecules and formed a three-dimensional network structure.

[0131] The asphalt-based hard carbon anode materials prepared in the above examples and comparative examples were used to prepare anode sheets. 80 mg of asphalt-based hard carbon material, 10 mg of conductive carbon black (Super P), and 500 μL of sodium alginate solution with a concentration of 20 mg / mL were weighed at a mass ratio of 8:1:1. The mixture was stirred evenly for 10 min until a black slurry was formed. This slurry was then evenly coated onto carbon-coated aluminum foil using a 200 μm scraper. The coated aluminum foil was first dried in an 80°C oven for 1 h to remove water from the sodium alginate binder. Then, it was dried in a 105°C vacuum oven for 6 h. The dried electrode sheets were then cut into circular pieces using a slicing machine. A sodium foil sheet was used as the counter electrode, and a commercially available 1.0 M NaPF6 in DIGLYME = 100 Vol% electrolyte was used to assemble a coin cell.

[0132] The charge and discharge performance of the button batteries in the above embodiments and comparative examples was tested. The battery testing method adopted constant current and constant voltage discharge and constant current charging. The charge and discharge test was carried out at a current density of 0.1C. The discharge cutoff voltage was 0V, the charging cutoff voltage was 2.5V, and the nominal specific capacity was 200mAh / g.

[0133] The rate performance of the button cells in the above embodiments and comparative examples was tested. The battery test was conducted using the Xinwei Battery Test System, and the test method was constant current charge and discharge. Charge and discharge tests were carried out sequentially at current densities of 0.1C, 0.5C, 1C, 2.5C, 5C, 10C, 20C, and 0.1C. The discharge cutoff voltage was 0V, and the charging cutoff voltage was 2.5V.

[0134] The test results are shown in Table 1 and Figures 2 to 14 .

[0135] Table 1:

[0136]

[0137] As can be seen from Table 1, compared with direct carbonization of asphalt in Comparative Example 1, carbonization after sulfonation in Comparative Example 2, and direct etching and carbonization without sulfonation in Comparative Example 3, the asphalt-based hard carbon in Examples 1-6 of this application, after three-step treatment of sulfonation-carbon dioxide etching-carbonization, has high reversible capacity, low voltage plateau capacity, and excellent rate performance at high current density.

[0138] Figure 2 This is a comparison chart of the charge-discharge curves for Examples 1, 2, and 3. Figure 3 This is a comparison chart of the rate capability of Examples 1, 2, and 3. Combined with... Figure 2 and Figure 3As shown in Table 1, the charging capacity and rate performance of the three embodiments are all at the same level (the reversible charging capacity of the first cycle at a current density of 0.1C is all >320mAh / g). This indicates that within the sulfonation reaction temperature range of 60℃ to 100℃, the grafting degree of sulfonic acid groups on the pitch molecules has approached saturation, thus its effect on the microstructure regulation of the final hard carbon material has reached a relatively stable state. In other words, this temperature range is sufficient to ensure that the electrophilic substitution reaction proceeds fully, allowing the subsequent CO2 etching and high-temperature carbonization to generate a sufficient number and stable number of topological defects and closed-pore structures. Therefore, the hard carbon materials prepared within this sulfonation temperature window do not show significant differences in their ramp capacity (mainly from surface defects and the adsorption of sodium ions by functional groups) and rate performance (thanks to low diffusion resistance and high ion diffusion coefficient), and all exhibit excellent levels among pitch-based hard carbon anode materials.

[0139] Figure 4 This is a comparison graph of the charge-discharge curves of Example 4 and Comparative Example 5. Figure 5 This is a comparison chart of the rate capability of Example 4 and Comparative Example 5. (Combined with...) Figure 4 and Figure 5 As shown in Table 1, the first-cycle reversible capacity of Example 4 (80°C high-temperature sulfonation) (305.39 mAh / g) is significantly better than that of Comparative Example 5 (room temperature sulfonation) (158.18 mAh / g), representing a nearly 100% performance improvement. More importantly, in the low-voltage plateau region (<0.1V, mainly corresponding to the filling of sodium ions between graphitized microcrystal layers and the storage in nanopores), which is crucial for the sodium storage capacity of hard carbon materials, Example 4 achieves a capacity as high as 196 mAh / g, while Comparative Example 5 only achieves 72 mAh / g. This demonstrates that high-temperature sulfonation (as in Examples 1-4) is essential for the formation of an effective nanoporous structure in the final material. Because the electrophilic substitution reaction rate is strongly temperature-dependent, the sulfonation reaction kinetics are slow at room temperature. The sulfuric acid sulfonating agent struggles to effectively break down the aromatic lamellar structure of asphalt molecules, resulting in a limited and uneven distribution of sulfonic acid groups (-SO3H) grafted onto the asphalt molecules. However, at the preferred temperature of 60–100°C, molecular thermal motion intensifies, significantly increasing reactivity and enabling a large number of sulfonic acid groups to successfully graft onto the asphalt skeleton. These large-volume sulfonic acid groups introduced in the early stages are a prerequisite for subsequent CO2 etching to create pores and generate defects.

[0140] To further verify the decisive role of temperature in the degree of sulfonation, we performed Fourier transform infrared spectroscopy (FT-IR) analysis on the sulfonated asphalt products obtained after step 2 in Example 4 (sulfonation at 80°C) and Comparative Example 5 (sulfonation at room temperature). The results are as follows: Figure 6 As shown, Figure 6 The image shows a comparison of the infrared spectra of Example 4 and Comparative Example 5. Figure 6 It can be seen that in the spectrum of Example 4, at 1180 cm⁻¹... -1 and 1040 cm -1 A pair of sharp, strong, and distinct characteristic absorption peaks appeared nearby, which are attributed to the asymmetric (as S=O) and symmetric (s S=O) stretching vibrations of the sulfonic acid group (-SO3H), respectively. The appearance of these strong peaks proves the successful grafting of sulfonic acid groups onto the asphalt molecules. In contrast, the absorption peak at the same position in the spectrum of Comparative Example 5 is very weak and broad, indicating that under room temperature reaction conditions, only a small amount of sulfonic acid groups were introduced into the asphalt skeleton, and the sulfonation reaction was incomplete; furthermore, the absorption peak at 700-900 cm⁻¹... -1 In the infrared absorption range (often attributed to the out-of-plane bending vibration absorption peaks of the CH bonds in the aromatic ring of pitch molecules), the absorption peak intensity of Example 4 is significantly weaker than that of Comparative Example 5. This is because the sulfonation reaction replaces hydrogen atoms on the aromatic ring, generating CS bonds, thereby reducing the number of CH bonds on the aromatic ring and resulting in a weakening of the corresponding infrared absorption. This also confirms that the sulfonation reaction occurred to a greater extent in Example 4.

[0141] Combination Figures 4 to 6 Analysis shows that the asphalt modified by room-temperature sulfonation in Comparative Example 5 is insufficient to effectively prevent the orderly rearrangement and graphitization of asphalt molecules during carbonization, resulting in a final carbon material that is closer to a graphitized soft carbon structure with small interlayer spacing and a small number of closed pores, thus exhibiting extremely low plateau capacity. In contrast, the asphalt modified by high-temperature sulfonation in Example 4 can more effectively introduce sulfonic acid groups, creating conditions for subsequent etching and the formation of stable defects. This comparison strongly demonstrates that the "molecular-level sulfonation modification" step of this invention must be carried out under appropriate heating conditions and introduce sufficient occupying functional groups to produce a synergistic effect with the subsequent "CO2 in-situ etching" and "high-temperature carbonization" steps, ultimately successfully constructing a high-performance hard carbon anode material with both a high-capacity ramp region (rich surface defects) and a high-capacity plateau region (rich nanopores).

[0142] In summary, the asphalt with higher softening points (180℃, 200℃, 250℃) used in this application requires relatively high temperatures to achieve sulfonation modification. At room temperature (25℃±5℃), it may tend to oxidize and acid wash to remove impurities rather than fully sulfonate, and thus cannot achieve the effect of molecular modification.

[0143] Figure 7 This is a comparison chart of the charge-discharge curves for Examples 1 and 4. Figure 8 This is a comparison chart of the rate capability of Examples 1 and 4. Combined with... Figure 7 and Figure 8As shown in Table 1, compared to Example 4 without phosphoric acid, the composite sulfonating agent using concentrated sulfuric acid and phosphoric acid in Example 1 exhibits a more significant advantage in capacity and rate performance: its first-cycle charge specific capacity (0.1C) increased from 305.39 mAh / g to 332.23 mAh / g, and at a high rate of 10C, the capacity jumped significantly from 51.19 mAh / g to 130.09 mAh / g. This is due to the multiple synergistic effects of phosphoric acid: firstly, as a strong protic acid and a highly efficient dehydrating agent, phosphoric acid significantly catalyzes the sulfonation reaction, promoting a denser and more uniform grafting of sulfonic acid groups, effectively strengthening the cross-linking network of asphalt molecules, creating a better "template" for subsequent CO2 etching, thereby generating more defects and closed pores conducive to sodium storage; secondly, phosphoric acid effectively reduces the oxidizing properties of the reaction system, protecting the structural stability of the asphalt carbon layer. Ultimately, these microstructural optimizations translate into more abundant sodium ion active sites, a more robust hard carbon framework, and more efficient ion / electron transport channels, enabling the phosphoric acid-assisted sulfonated pitch-based hard carbon in the embodiments to exhibit higher capacity and stability at higher current densities.

[0144] Figure 9 This is a comparison graph of the charge-discharge curves of Examples 1 and 5 and Comparative Example 4. Figure 10 This is a comparison chart of the rate capability of Examples 1 and 5 and Comparative Example 4. Combined with... Figure 9 and Figure 10 As shown in Table 1, the hard carbon prepared at etching temperatures of 700℃ and 800℃ exhibits better sodium storage performance, with an initial charge capacity of over 290 mAh / g at 0.1C and a charge specific capacity greater than 190 mAh / g in the low-voltage plateau region (<0.1V). However, when the etching temperature is increased to 900℃, the sodium storage performance decreases significantly. This indicates that the higher etching temperature leads to over-etching of the asphalt material, which damages the carbon skeleton structure and causes the internal pores of the material to collapse (the plateau region capacity is only 20 mAh / g).

[0145] Furthermore, compared to etching at 700℃, the hard carbon prepared at 800℃ exhibits a significant improvement in charge specific capacity at 5C and 10C. This is likely because at the optimized etching temperature of 800℃, the reactivity of CO2 with carbon and the migration ability of carbon atoms achieve a good balance. At this temperature, the etching reaction is more complete and uniform, effectively removing sulfonic acid groups to generate a large number of stable topological defects and initial pores of suitable size. It also creates ideal conditions for the rearrangement of the carbon framework during subsequent high-temperature carbonization, resulting in a richer and more stable closed-pore structure and a more continuous, more conductive three-dimensional carbon network. In contrast, etching at 700℃, being relatively low-temperature etching, may not be sufficient, resulting in some sulfonic acid groups not being completely removed. The resulting defect and pore structures are not as perfect as those at 800℃, limiting the migration ability of carbon atoms and making it difficult to achieve effective structural relaxation and pore healing. Consequently, the sodium ion diffusion path inside the carbon material etched at 700℃ is not smooth, and the electronic conductivity of the material is relatively low. During high-rate charge and discharge, the polarization impedance of ion diffusion and electron transport increases sharply, leading to rapid capacity decay. However, etching at 800℃ creates a more optimized channel structure and a more developed conductive network, significantly improving the diffusion rate of sodium ions and the migration efficiency of electrons, allowing it to maintain excellent capacity even under high-current impact. Therefore, an etching temperature range of 750-850℃ is considered suitable.

[0146] Figure 11 This is a comparison graph of the charge-discharge curves of Example 1 and Comparative Examples 1, 2, and 3. Figure 12 This is a comparison chart of the rate capability of Example 1 with Comparative Examples 1, 2, and 3. Combined with... Figure 11 and Figure 12 As shown in Table 1, compared to direct carbonization of asphalt in Comparative Example 1, carbonization after sulfonation in Comparative Example 2, and direct etching and carbonization without sulfonation in Comparative Example 3, the sodium storage performance of the hard carbon prepared by sulfonation, etching, and carbonization of asphalt in Example 1 of this application is greatly improved. The initial charge-discharge specific capacity and the charging specific capacity in the low-voltage plateau region (<0.1V) of the corresponding sodium coin cell are much higher than those of Comparative Examples 1-3. The dual treatment process of sulfonation modification and CO2 etching works synergistically, and the asphalt-based hard carbon anode material prepared by the combination of the two has abundant closed pores and defect sites, effectively realizing the synergy of pore-confined adsorption (plateau region) and defect adsorption (slope region).

[0147] Figure 13 This is a comparison chart of the charge-discharge curves for Examples 4, 6, and 7. Figure 14 This is a comparison chart of the rate performance of Examples 4, 6, and 7. Combined with... Figure 13 and Figure 14As shown in Table 1, the softening point of the asphalt raw material has a certain impact on the charging performance and plateau capacity of the final hard carbon material. Specifically, Example 4, using asphalt with a softening point of 200℃, significantly outperformed Example 6 (199.34 mAh / g, 90 mAh / g) and Example 7 (228.38 mAh / g, 133 mAh / g) in both the first-cycle charging capacity (305.39 mAh / g) and plateau capacity (196 mAh / g) with a softening point of 180℃. This indicates that there is an optimal range of softening points: when the softening point is too low (180℃), the thermal stability of the asphalt molecular skeleton is poor, making it difficult to form a stable three-dimensional cross-linked network during sulfonation and carbonization, leading to the collapse of the closed-cell structure; when the softening point is too high (250℃), the molecules are too dense, hindering the full sulfonation reaction and limiting effective etching and pore formation. The asphalt softening point selected in Example 4 is moderate, which can better balance reactivity and structural stability, thus successfully constructing a rich array of nanopores through a three-stage linkage process.

[0148] In addition, from Figure 14 It can be seen that although the absolute capacity of the three at low rates is significantly different, their decay trends are similar. The absolute capacity difference at high current densities is not significant. This may be because the solid-phase diffusion of sodium ions becomes a common bottleneck at high currents. Ions can only use surface sites for rapid reactions, which prevents the capacity advantage of closed pores inside the material from being fully utilized, thus showing the relative convergence of the performance differences of Examples 4, 6, and 7.

[0149] The foregoing has provided a detailed description of the asphalt-based hard carbon anode material and its preparation method, as well as the sodium-ion battery provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for preparing pitch-based hard carbon negative electrode material, characterized in that, The preparation method comprises the following steps: mixing bitumen with a softening point of 180-250 DEG C and a sulfonating agent to perform sulfonation treatment, to obtain sulfonated bitumen; wherein, the sulfonation reaction temperature is 60-100 DEG C; performing etching treatment on the sulfonated bitumen in a carbon dioxide atmosphere, to obtain bitumen intermediate; performing carbonization treatment on the bitumen intermediate in a protective atmosphere, to obtain bitumen-based hard carbon negative electrode material.

2. The preparation method according to claim 1, wherein the bitumen comprises one or more of petroleum pitch and coal tar pitch; and / or the softening point of the bitumen is 200 DEG C; and / or the particle size D50 of the bitumen is 10-100 microns; and / or the ash content of the bitumen is less than 0.1%.

3. The preparation method according to claim 1 or 2, wherein the sulfonating agent comprises one or more of concentrated sulfuric acid, fuming sulfuric acid, sulfur trioxide, p-toluene sulfonic acid and benzene sulfonic acid; and / or the ratio between the mass of the bitumen and the volume of the sulfonating agent is 1g:(1-8)mL; and / or the sulfonation treatment time is greater than or equal to 2h.

4. The preparation method according to claim 1 or 2, wherein the sulfonating agent comprises a composite of concentrated sulfuric acid and phosphoric acid; and / or the sulfonation treatment time is 4-6h.

5. The preparation method according to claim 4, wherein when the sulfonating agent comprises a composite of concentrated sulfuric acid and phosphoric acid, the volume ratio of the concentrated sulfuric acid to the phosphoric acid is 5:1-20:1; and / or the mass percentage of the concentrated sulfuric acid is approximately equal to 90%; and / or the mass percentage of the phosphoric acid is greater than or equal to 75%. After the sulfonation reaction, the method further comprises solid-liquid separation, water washing of the obtained solid to a neutral pH value, drying, to obtain the sulfonated bitumen.

7. The preparation method according to claim 1 or 2, wherein the carbon dioxide atmosphere is a pure carbon dioxide atmosphere or a mixed atmosphere formed by carbon dioxide and inert gas; wherein the inert gas comprises a mixture of one or more of nitrogen, helium, neon, argon and xenon; and / or the etching treatment holding temperature T satisfies 700≤T<900 DEG C; and / or the holding time of the medium-temperature etching treatment is 1-4h; and / or the heating rate for heating to the holding temperature is 2-10 DEG C / min; and / or the protective atmosphere is formed by mixing one or more of nitrogen, helium, neon, argon and xenon; and / or the carbonization treatment temperature is 1100-1700 DEG C; and / or the carbonization treatment time is 2-8h; and / or the median particle size of the hard carbon negative electrode material is 7-20 microns. The holding temperature of the etching treatment is 700-800 DEG C; or the holding temperature of the etching treatment is 750-850 DEG C. The bitumen-based hard carbon negative electrode material is prepared by the preparation method of any one of claims 1-8. The battery comprises the bitumen-based hard carbon negative electrode material of claim 9. ​ ​ ​ ​ ​ ​ ​ 6. The production method according to claim 1 or 2, characterized by, ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 8. The production method according to claim 7, characterized by, ​ 9. A pitch-based hard carbon negative electrode material, characterized in that, ​ 10. A battery, characterized by ​

Images