Method for preparing hard carbon from soft carbonizable precursor and hard carbon

Abstract

The application relates to a method for preparing hard carbon from a soft carbonization precursor and the hard carbon, and the method comprises the following steps: performing first oxidation treatment on the soft carbonization precursor to obtain a primary oxide; performing first ball milling on a first crosslinking agent and the primary oxide to obtain a second mixture; performing second oxidation treatment on the second mixture to obtain a crosslinking and solidification precursor; performing pyrolysis on the crosslinking and solidification precursor in a protective atmosphere to obtain the hard carbon; and the temperature of the second oxidation treatment is at least 20 DEG C higher than that of the first oxidation treatment. The soft carbonization precursor is converted from thermoplasticity to thermosetting through step-by-step temperature rising oxidation, a three-dimensional crosslinking network with stable ester bonds as the core is constructed, the intermolecular pi-pi stacking effect is overcome, the ordered arrangement of aromatic carbon microcrystals in the pyrolysis process is inhibited, the ordered stacking process of carbon layers is destroyed, and thus graphite-like microzones with expanded carbon layer spacing and rich closed pore structures are induced to be generated, so that the performance of the hard carbon is improved.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, and relates to a method for preparing hard carbon from an easily softened carbonization precursor, and the hard carbon itself. Background Technology

[0002] With the increasing depletion of global fossil fuels and the escalating environmental problems, developing efficient and clean renewable energy storage technologies has become a top priority. While lithium-ion batteries are widely used in portable electronic devices and electric vehicles, the low abundance and uneven distribution of lithium resources in the Earth's crust have led to a year-on-year increase in raw material costs, making it difficult to meet the needs of large-scale energy storage power plants. In contrast, sodium resources are abundant, widely distributed, and inexpensive. Furthermore, sodium-ion batteries share a similar "rocking chair" mechanism with lithium-ion batteries; therefore, sodium-ion batteries are considered an ideal choice for next-generation large-scale energy storage systems.

[0003] Among the key materials for sodium-ion batteries, the anode material plays a decisive role in the battery's energy density, cycle life, and safety. Because the radius of sodium ions (1.02 Å) is significantly larger than that of lithium ions (0.76 Å), their intercalation into traditional graphite layers is difficult, thus graphite cannot be directly used as the anode for sodium-ion batteries. Currently, hard carbon (amorphous carbon) is considered the closest to commercialization as a sodium-ion battery anode material due to its excellent sodium storage performance, low cost, and low Na intercalation potential. Its structure mainly consists of randomly stacked, twisted graphene sheets, forming short-range ordered graphite-like microcrystalline regions. However, numerous defects disrupt the orderliness of the graphene sheets, preventing long-range ordered arrangement. The random orientation of the graphene sheets leads to abundant nanopores.

[0004] While biomass materials are widely available as a precursor for hard carbon, they generally suffer from low carbon yield and limited availability of some biomass feedstocks, making stable industrial-scale supply difficult. In contrast, easily softenable carbonizable precursors, such as coal-based pitch, petroleum pitch, heavy oil, residual oil, coal, petroleum coke, and some thermoplastic polymers, offer advantages such as high carbon content, low ash content, high tap density, and low cost, making them ideal raw materials for low-cost, large-scale production of hard carbon anodes. These materials are typical thermoplastic carbon-rich precursors, primarily composed of polycyclic aromatic hydrocarbons or long-chain molecules. During direct high-temperature pyrolysis, these precursors readily soften, melt, and undergo liquid-phase rheology, leading to long-range ordered directional rearrangement of carbon microcrystals, ultimately forming a graphitized structure (soft carbon) with small interlayer spacing. This soft carbon structure not only lacks abundant closed pores but also has insufficient interlayer spacing to accommodate the insertion of larger sodium ions, resulting in a low sodium storage capacity in the final material. Therefore, how to overcome the "soft carbonization" tendency of such precursors through low-cost and easily scalable processes is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing hard carbon from an easily softenable carbonization precursor and the hard carbon itself. This method can at least transform the easily softenable carbonization precursor from thermoplastic to thermosetting through stepwise heating and oxidation, constructing a three-dimensional cross-linked network with stable ester bonds as the core, overcoming the π-π stacking effect between molecules, inhibiting the orderly arrangement of aromatic carbon microcrystals during pyrolysis, and disrupting the orderly stacking process of carbon sheets. This induces the generation of graphite-like microregions with expanded carbon interlayer spacing and abundant closed-pore structure, thereby improving the performance of hard carbon.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing hard carbon from an easily softenable carbonizable precursor, the method comprising:

[0008] S1. The easily carbonized precursor is subjected to a first oxidation treatment to obtain a primary oxide;

[0009] S2. The first ball milling process is used to mix the first crosslinking agent and the primary oxide to obtain a two-component mixture;

[0010] S3. The two mixtures undergo a second oxidation treatment to obtain a cross-linked cured precursor.

[0011] S4. In a protective atmosphere, the cross-linked cured precursor is pyrolyzed to obtain hard carbon;

[0012] The temperature of the second oxidation treatment is at least 20°C higher than the temperature of the first oxidation treatment.

[0013] The method provided by this invention processes easily softenable carbon precursors using a stepwise oxidation process. During the first ball milling mixing, a possible surface oxide hard shell is broken up by mechanical force, and a first crosslinking agent is introduced at this stage. This is followed by a second oxidation process with further increased temperature, promoting a deep condensation reaction between the second crosslinking agent and the previously generated active sites. The sequential first and second oxidation processes transform the easily softenable carbon precursor from thermoplastic to thermosetting, constructing a three-dimensional crosslinked network with stable ester bonds (-C-(O)-O-) as its core. In the subsequent pyrolysis stage, this crosslinked network acts as a rigid framework, creating a steric hindrance effect on the parallel arrangement and orderly growth of aromatic sheets. This effectively overcomes the π-π stacking effect between molecules, inhibits the orderly arrangement of aromatic carbon microcrystals during pyrolysis, and disrupts the orderly stacking process of carbon sheets. This induces the generation of graphite-like microregions with expanded carbon interlayer spacing and abundant closed-pore structures, significantly improving the plateau capacity of hard carbon.

[0014] In some embodiments, before the easily carbonizable precursor undergoes the first oxidation treatment, it is ball-milled and mixed with a second crosslinking agent to obtain a preliminary mixture; then the preliminary mixture undergoes the first oxidation treatment. During the second ball milling, the second crosslinking agent gently opens the framework of the easily carbonizable precursor and introduces initial active sites, preventing the material particles from melting and sticking together.

[0015] In some embodiments, the first crosslinking agent and the second crosslinking agent each independently comprise any one or a combination of at least two of citric acid, maleic acid, humic acid, tannic acid, ascorbic acid, tartaric acid, caffeic acid, glucose, maltose, fructose, sucrose, starch, or cellulose.

[0016] In some embodiments, the total mass of the first crosslinking agent and the second crosslinking agent is 5 wt% to 40 wt% of the easily carbonizable precursor.

[0017] In some embodiments, the mass percentage of the second crosslinking agent is 0 wt% to 50 wt%, based on a total mass percentage of 100 wt% for the first crosslinking agent and the second crosslinking agent.

[0018] In some embodiments, the easily softened carbonization precursor includes any one or a combination of at least two of the following: petroleum asphalt, coal-based pitch, mesophase pitch, coal, heavy oil, residual oil, petroleum coke, polyvinyl chloride, polyacrylonitrile, polystyrene, polyvinyl chloride copolymer, phenolic resin, or vegetable tar.

[0019] In some embodiments, the first oxidation treatment and the second oxidation treatment are carried out independently in an oxygen-containing atmosphere; the gas used in the oxygen-containing atmosphere includes oxygen and / or air.

[0020] In some embodiments, the heating rate of the first oxidation treatment is 0.5°C / min to 10°C / min.

[0021] In some embodiments, the temperature of the first oxidation treatment is 100°C to 250°C.

[0022] In some embodiments, the holding time for the first oxidation treatment is 1 hour to 24 hours.

[0023] In some embodiments, the heating rate of the second oxidation treatment is 0.5°C / min to 10°C / min.

[0024] In some embodiments, the temperature of the second oxidation treatment is 250°C to 400°C.

[0025] In some embodiments, the second oxidation treatment lasts for 1 to 24 hours.

[0026] In some embodiments, the protective atmosphere includes any one or a combination of at least two of nitrogen, helium, or argon.

[0027] In some embodiments, the pyrolysis heating rate is 0.5°C / min to 10°C / min.

[0028] In some embodiments, the pyrolysis temperature is 1000°C to 1600°C.

[0029] In some embodiments, the pyrolysis holding time is 0.5h to 24h.

[0030] In some embodiments, the rotational speed of the first ball milling mixture is 150 rpm to 350 rpm.

[0031] In some embodiments, the first ball milling mixing time is 2h to 6h.

[0032] In some embodiments, the rotational speed of the second ball milling is 150 rpm to 350 rpm.

[0033] In some embodiments, the second ball milling mixing time is 3h to 5h.

[0034] In a second aspect, the present invention provides a hard carbon, which is prepared by the method described in any one of the first aspects.

[0035] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) The method provided by the present invention adopts stepwise oxidation treatment, which avoids uneven oxidation and surface sealing effect in a single oxidation. The constructed three-dimensional cross-linked network acts as a steric hindrance, effectively suppressing graphitization in the pyrolysis process and inducing the generation of an ideal hard carbon structure with larger carbon interlayer spacing and abundant closed pores, thereby significantly improving the reversible capacity and rate performance of hard carbon.

[0038] (2) The three-dimensional cross-linked network constructed by the method provided by the present invention, during the shrinkage of the carbon skeleton in high-temperature pyrolysis, some micro-defects inside the material evolve into rich closed-pore structures. The micro-structure dominated by closed pores provides filling sites for the storage of sodium ions, significantly improving the capacity of the plateau region, reducing the irreversible consumption of electrolyte on the carbon surface and the thickening of SEI, thereby improving the first-cycle coulombic efficiency of the hard carbon anode material.

[0039] (3) The first oxidation treatment and the second oxidation treatment carried out in sequence in this invention realize the separation of physical mass transfer (diffusion) and chemical reaction (crosslinking). In the first oxidation treatment stage, the high fluidity of molecular chains brought about by the moderate softening of thermoplastic precursor, combined with the extremely low chemical reaction rate, effectively avoids the premature formation of dense oxide shell on the particle surface, and promotes oxygen molecules and crosslinking agents to deeply penetrate into the bulk phase of the material. In the second oxidation treatment stage, the crosslinking agents and active oxidation sites that are uniformly distributed inside are activated in situ and undergo deep oxidation crosslinking with the aromatic molecules of the material. This mechanism of "deep diffusion first, then bulk phase solidification" enables the material to completely complete the transformation from "thermoplastic" to "thermosetting" before high-temperature and violent melting.

[0040] (4) The method provided by the present invention has the potential to be low cost, readily available raw materials and suitable for large-scale production. The entire process does not require expensive reagents and complex equipment. The crosslinking agents used are all common chemical raw materials, and the reaction conditions are mild and controllable. The combination of ball milling and solid-phase reaction avoids the use of a large amount of solvent, which makes this strategy have significant advantages and application prospects in the large-scale preparation of high-performance, low-cost hard carbon anode materials. Attached Figure Description

[0041] Figure 1 The XRD pattern of the hard carbon obtained in Example 1;

[0042] Figure 2 The N2- adsorption-desorption curve of the hard carbon obtained in Example 1;

[0043] Figure 3 The charge-discharge curves of the hard carbon battery obtained in Example 1 are shown.

[0044] Figure 4 The XRD pattern of the hard carbon obtained in Example 2;

[0045] Figure 5 The N2- adsorption-desorption curve of the hard carbon obtained in Example 2;

[0046] Figure 6 The charge-discharge curves of the hard carbon battery obtained in Example 2 are shown.

[0047] Figure 7 The XRD pattern of the hard carbon obtained in Example 3;

[0048] Figure 8 The N2- adsorption-desorption curve of the hard carbon obtained in Example 3;

[0049] Figure 9 The charge-discharge curves of the hard carbon battery obtained in Example 3 are shown.

[0050] Figure 10 The XRD pattern of the hard carbon obtained in Comparative Example 1 is shown.

[0051] Figure 11 The N2- adsorption-desorption curve of the hard carbon obtained in Comparative Example 1;

[0052] Figure 12 The charge-discharge curves of the hard carbon battery obtained in Comparative Example 1 are shown.

[0053] Figure 13 The XRD pattern of the hard carbon obtained in Comparative Example 2 is shown.

[0054] Figure 14 The N2- adsorption-desorption curve of the hard carbon obtained in Comparative Example 2;

[0055] Figure 15 The image shows the charge-discharge curves of the hard carbon battery obtained in Comparative Example 2. Detailed Implementation

[0056] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0057] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0058] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0059] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0060] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0061] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0062] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0063] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0064] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0065] Hard carbon can store Na through surface adsorption, interlayer insertion, and pore filling. + Ions. However, low-cost, easily soft carbonization precursors exhibit a strong tendency to graphitize during high-temperature carbonization, leading to parallel orientation and orderly stacking of carbon layers, ultimately resulting in soft carbon materials with small interlayer spacing; at the same time, traditional single-stage vigorous pre-oxidation easily forms a dense oxide shell on the surface of material particles, hindering oxygen diffusion into the interior, resulting in impaired mass transfer and uneven cross-linking.

[0066] Precursors to easily carbonize exhibit significant thermoplastic characteristics. During conventional pre-oxidation processes, the surface molecules of the material heat up rapidly and are highly reactive. Softening and melting often precede cross-linking and solidification, easily forming a dense shell that hinders oxygen from reaching the interior, resulting in low and uneven pre-oxidation efficiency. In the absence of effective rigid framework support or a physical dispersion medium, thermoplastic materials are prone to liquid-phase fusion and severe agglomeration. This agglomeration significantly reduces the specific surface area of ​​the material, making it difficult for oxidizing gases to penetrate into the particle aggregates. Consequently, the internal material fails to achieve sufficient cross-linking and solidification, easily evolving into soft carbon materials with small interlayer spacing and very low sodium storage capacity during subsequent high-temperature carbonization. Moreover, although conventional air pre-oxidation processes can introduce oxygen functional groups to some extent, it is difficult to construct a three-dimensional deep cross-linked network (such as an ester bond network) at the molecular level. This weak cross-linked structure is prone to decomposition or rearrangement during high-temperature carbonization, leading to excessive growth and stacking of graphitized microcrystals.

[0067] Some existing technologies for preparing hard carbon use 1 mol / L to 2 mol / L dilute nitric acid and ammonium persulfate as strong oxidants and crosslinking agents, reacting in a high-temperature liquid-phase environment of 120℃ to 180℃. This not only places high demands on the acid corrosion resistance of the production equipment, but also requires repeated washing with large amounts of deionized water to neutralize the reaction. This process generates difficult-to-treat highly acidic wastewater and polluting nitrogen oxide gases, resulting in high environmental costs and hindering low-cost large-scale industrialization. Furthermore, existing technologies using liquid-phase strong oxidants (such as ammonium persulfate and nitric acid) are prone to violent decomposition upon heating, making precise and gentle control of the oxidation and crosslinking depth difficult, easily leading to over-etching of the carbon skeleton. The violent decomposition of strong oxidants at high temperatures generates gas, resulting in an excessive proportion of open-cell structures, ultimately leading to a larger specific surface area and reduced ICE (internal conductivity). Moreover, if the liquid-phase oxidation is not thoroughly cleaned during the industrial-scale washing step, residual inorganic salt ions or sulfides will permanently remain in the pores of the carbon material after high-temperature carbonization. These impurities can easily trigger side reactions in the electrolyte during subsequent charge and discharge processes. Thermoplastic precursors contain some low molecular weight or easily soluble components, which must undergo repeated washing and filtration with deionized water. This inevitably leads to the dissolution and loss of some effective carbon source components in the material, resulting in a decrease in the final carbon yield.

[0068] An embodiment of the present invention provides a method for preparing hard carbon from an easily softenable carbonization precursor, comprising:

[0069] S1. The easily carbonized precursor is subjected to a first oxidation treatment to obtain a primary oxide;

[0070] S2. The first ball milling process is used to mix the first crosslinking agent and the primary oxide to obtain a two-component mixture;

[0071] S3. The two mixtures undergo a second oxidation treatment to obtain a cross-linked cured precursor.

[0072] S4. In a protective atmosphere, the cross-linked cured precursor is pyrolyzed to obtain hard carbon;

[0073] The temperature of the second oxidation treatment is at least 20°C higher than the temperature of the first oxidation treatment.

[0074] The method provided by this invention processes easily softenable carbon precursors using a stepwise oxidation process. During the first ball milling mixing, a possible surface oxide hard shell is broken up by mechanical force, and a first crosslinking agent is introduced at this stage. This is followed by a second oxidation process with further increased temperature, promoting a deep condensation reaction between the second crosslinking agent and the previously generated active sites. The sequential first and second oxidation processes transform the easily softenable carbon precursor from thermoplastic to thermosetting, constructing a three-dimensional crosslinked network with stable ester bonds (-C-(O)-O-) as its core. In the subsequent pyrolysis stage, this crosslinked network acts as a rigid framework, creating a steric hindrance effect on the parallel arrangement and orderly growth of aromatic sheets. This effectively overcomes the π-π stacking effect between molecules, inhibits the orderly arrangement of aromatic carbon microcrystals during pyrolysis, and disrupts the orderly stacking process of carbon sheets. This induces the generation of graphite-like microregions with expanded carbon interlayer spacing and abundant closed-pore structures, significantly improving the plateau capacity of hard carbon.

[0075] In some embodiments, before the easily carbonizable precursor undergoes the first oxidation treatment, it is ball-milled and mixed with a second crosslinking agent to obtain a preliminary mixture; then the preliminary mixture undergoes the first oxidation treatment. During the second ball milling, the second crosslinking agent gently opens the framework of the easily carbonizable precursor and introduces initial active sites, preventing the material particles from melting and sticking together.

[0076] In some embodiments, the first crosslinking agent and the second crosslinking agent are solid-phase crosslinking agents, which are composed entirely of C, H and O. During the pyrolysis stage, in addition to releasing volatile gases such as H2O and CO2, the skeleton of these crosslinking agents is completely converted into pure carbon, fundamentally eliminating the residue of inorganic impurities such as sulfides or metal salts.

[0077] In some embodiments, the first crosslinking agent and the second crosslinking agent each independently comprise any one or a combination of at least two of citric acid, maleic acid, humic acid, tannic acid, ascorbic acid, tartaric acid, caffeic acid, glucose, maltose, fructose, sucrose, starch, or cellulose.

[0078] In some embodiments, the total mass of the first crosslinking agent and the second crosslinking agent is 5wt% to 40wt% of the easily carbonizable precursor, for example, it can be 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt% or 40wt%, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0079] In some embodiments, with the total mass percentage of the first crosslinking agent and the second crosslinking agent being 100 wt%, the mass percentage of the second crosslinking agent is 0 wt% to 50 wt%, for example, it can be 0 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, or 50 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0080] In some embodiments, the easily softened carbonization precursor includes any one or a combination of at least two of the following: petroleum asphalt, coal-based pitch, mesophase pitch, coal, heavy oil, residual oil, petroleum coke, polyvinyl chloride, polyacrylonitrile, polystyrene, polyvinyl chloride copolymer, phenolic resin, or vegetable tar.

[0081] In some embodiments, the first oxidation treatment and the second oxidation treatment are carried out independently in an oxygen-containing atmosphere; the gas used in the oxygen-containing atmosphere includes oxygen and / or air.

[0082] In some embodiments, the heating rate of the first oxidation treatment is 0.5℃ / min to 10℃ / min, for example, it can be 0.5℃ / min, 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min or 10℃ / min, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0083] In some embodiments, the temperature of the first oxidation treatment is 100°C to 250°C, for example, it can be 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C or 250°C, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0084] In some embodiments, the holding time for the first oxidation treatment is 1h to 24h, for example, it can be 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h or 24h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0085] In some embodiments, the heating rate of the second oxidation treatment is 0.5℃ / min to 10℃ / min, for example, it can be 0.5℃ / min, 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min or 10℃ / min, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0086] In some embodiments, the temperature of the second oxidation treatment is 250°C to 400°C, for example, it can be 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C or 400°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0087] In some embodiments, the second oxidation treatment time is 1h to 24h, for example, it can be 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h or 24h, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0088] In some embodiments, the protective atmosphere includes any one or a combination of at least two of nitrogen, helium, or argon. Typical but non-limiting combinations include combinations of nitrogen and helium, nitrogen and argon, helium and argon, or nitrogen, helium, and argon.

[0089] In some embodiments, the heating rate of the pyrolysis is 0.5℃ / min to 10℃ / min, for example, it can be 0.5℃ / min, 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min or 10℃ / min, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0090] In the pyrolysis process provided by this invention, the cross-linked network, acting as a rigid framework, generates a steric hindrance effect, effectively overcoming the π-π stacking between thermoplastic precursor molecules and inhibiting their conversion into soft carbon with smaller interlayer spacing. During the shrinkage of the carbon framework, this deeply cross-linked network induces the formation of graphite-like microregions with expanded carbon interlayer spacing and abundant closed-pore structures. The resulting hard carbon has a moderate specific surface area (20 m²). 2 The specific surface area of ​​the hard carbon material obtained by liquid-phase oxidation is larger (approximately 1 / g).

[0091] In some embodiments, the pyrolysis temperature is 1000℃~1600℃, for example, it can be 1000℃, 1100℃, 1200℃, 1300℃, 1400℃, 1500℃ or 1600℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0092] In some embodiments, the holding time for pyrolysis is 0.5h to 24h, for example, it can be 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h or 24h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0093] In some embodiments, the rotational speed of the first ball mill mixing is 150 rpm to 350 rpm, for example, it can be 150 rpm, 160 rpm, 170 rpm, 180 rpm, 190 rpm, 200 rpm, 210 rpm, 220 rpm, 230 rpm, 240 rpm, 250 rpm, 260 rpm, 270 rpm, 280 rpm, 290 rpm, 300 rpm, 310 rpm, 320 rpm, 330 rpm, 340 rpm or 350 rpm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0094] In some embodiments, the first ball milling mixing time is 2h to 6h, for example, it can be 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h or 6h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0095] In some embodiments, the rotational speed of the second ball mill mixing is 150 rpm to 350 rpm, for example, it can be 150 rpm, 160 rpm, 170 rpm, 180 rpm, 190 rpm, 200 rpm, 210 rpm, 220 rpm, 230 rpm, 240 rpm, 250 rpm, 260 rpm, 270 rpm, 280 rpm, 290 rpm, 300 rpm, 310 rpm, 320 rpm, 330 rpm, 340 rpm or 350 rpm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0096] In some embodiments, the second ball milling mixing time is 3h to 5h, for example, it can be 3h, 3.5h, 4h, 4.5h or 5h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0097] As a preferred technical solution of the method provided by the present invention, the solution includes:

[0098] S1. The easily softened carbonizable precursor and the second crosslinking agent are mixed by ball milling to obtain a preliminary mixture;

[0099] The second ball milling mixing speed is 150 rpm to 350 rpm, and the time is 2 h to 6 h;

[0100] The easily softened carbonization precursor includes any one or a combination of at least two of the following: petroleum asphalt, coal-based asphalt, mesophase asphalt, coal, heavy oil, residual oil, petroleum coke, polyvinyl chloride, polyacrylonitrile, polystyrene, polyvinyl chloride copolymer, phenolic resin, or vegetable tar.

[0101] The second crosslinking agent includes any one or a combination of at least two of the following: citric acid, maleic acid, humic acid, tannic acid, ascorbic acid, tartaric acid, caffeic acid, glucose, maltose, fructose, sucrose, starch, or cellulose.

[0102] S2. The initial mixture undergoes a first oxidation treatment to obtain a primary oxide.

[0103] The first oxidation treatment is carried out in an oxygen-containing atmosphere; the gas used in the oxygen-containing atmosphere includes oxygen and / or air;

[0104] The heating rate of the first oxidation treatment is 0.5℃ / min~10℃ / min, the temperature is 100℃~250℃, and the holding time is 1h~24h;

[0105] S3. The first ball milling process is used to mix the first crosslinking agent and the primary oxide to obtain a two-component mixture;

[0106] The first ball milling mixing speed is 150 rpm to 350 rpm, and the time is 3 h to 5 h;

[0107] The first crosslinking agent includes any one or a combination of at least two of the following: citric acid, maleic acid, humic acid, tannic acid, ascorbic acid, tartaric acid, caffeic acid, glucose, maltose, fructose, sucrose, starch, or cellulose.

[0108] The total mass of the first crosslinking agent and the second crosslinking agent is 5 wt% to 40 wt% of the easily carbonizable precursor; based on a total mass percentage of 100 wt% for the first crosslinking agent and the second crosslinking agent, the mass percentage of the second crosslinking agent is 0 wt% to 50 wt%.

[0109] S4. The two mixtures undergo a second oxidation treatment to obtain a cross-linked cured precursor.

[0110] The second oxidation treatment is carried out in an oxygen-containing atmosphere; the gas used in the oxygen-containing atmosphere includes oxygen and / or air;

[0111] The heating rate of the second oxidation treatment is 0.5℃ / min~10℃ / min, the temperature is 250℃~400℃, and the holding time is 1h~24h;

[0112] S5. In an argon atmosphere, the cross-linked and cured precursor is pyrolyzed to obtain hard carbon;

[0113] The pyrolysis heating rate is 0.5℃ / min to 10℃ / min, the temperature is 1000℃ to 1600℃, and the holding time is 0.5h to 24h.

[0114] One embodiment of the present invention provides a hard carbon, which is prepared by the method described in any embodiment.

[0115] Example 1

[0116] This embodiment provides a method for preparing hard carbon from an easily softenable carbonization precursor, including the following steps:

[0117] S1. The second ball milling process mixes the easily softened carbonizable precursor (coal tar powder, 10g) with the second crosslinking agent (citric acid, 0.45g) to obtain the initial mixture.

[0118] The second ball milling mixing speed was 300 rpm, and the time was 6 hours;

[0119] S2. The initial mixture is placed in a muffle furnace and subjected to a first oxidation treatment in an air atmosphere to obtain a primary oxide.

[0120] The heating rate of the first oxidation treatment is 3℃ / min, the temperature is 150℃, and the holding time is 9h;

[0121] S3. The first ball milling process is used to mix the first crosslinking agent (maleic acid, 1.05 g) with the primary oxide to obtain a second mixture;

[0122] The first ball milling mixing speed was 300 rpm, and the time was 5 hours;

[0123] The total mass of the first crosslinking agent and the second crosslinking agent is 15 wt% of the easily carbonizable precursor; based on a total mass percentage of 100 wt% for the first crosslinking agent and the second crosslinking agent, the mass percentage of the second crosslinking agent is 30 wt%.

[0124] S4. The two mixtures are placed in a muffle furnace and subjected to a second oxidation treatment in an air atmosphere to obtain a cross-linked curing precursor.

[0125] The second oxidation treatment has a heating rate of 5℃ / min, a temperature of 350℃, and a holding time of 10h;

[0126] S5. In an argon atmosphere, the cross-linked and cured precursor is pyrolyzed, and after naturally cooling to room temperature, it is ground and sieved to obtain hard carbon.

[0127] The pyrolysis heating rate is 3℃ / min, the temperature is 1500℃, and the holding time is 5h.

[0128] Example 2

[0129] This embodiment provides a method for preparing hard carbon from an easily softenable carbonization precursor, including the following steps:

[0130] S1. The second ball milling process is used to mix the easily softened carbonizable precursor (anthracite powder, 10g) and the second crosslinking agent (caffeic acid, 0.1g) to obtain the initial mixture.

[0131] The second ball milling process was carried out at a speed of 150 rpm for 2 hours.

[0132] S2. The initial mixture is placed in a muffle furnace and subjected to a first oxidation treatment in an air atmosphere to obtain a primary oxide.

[0133] The heating rate of the first oxidation treatment is 1℃ / min, the temperature is 120℃, and the holding time is 5h;

[0134] S3. The first ball milling process is used to mix the first crosslinking agent (caffeic acid, 0.4 g) with the primary oxide to obtain a second mixture;

[0135] The first ball milling mixing speed was 150 rpm, and the time was 3 hours;

[0136] The total mass of the first crosslinking agent and the second crosslinking agent is 5 wt% of the easily carbonizable precursor; based on a total mass percentage of 100 wt% for the first crosslinking agent and the second crosslinking agent, the mass percentage of the second crosslinking agent is 20 wt%.

[0137] S4. The two mixtures are placed in a muffle furnace and subjected to a second oxidation treatment in an air atmosphere to obtain a cross-linked curing precursor.

[0138] The heating rate of the second oxidation treatment is 1℃ / min, the temperature is 300℃, and the holding time is 12h;

[0139] S5. In an argon atmosphere, the cross-linked and cured precursor is pyrolyzed, and after naturally cooling to room temperature, it is ground and sieved to obtain hard carbon.

[0140] The pyrolysis heating rate is 2℃ / min, the temperature is 1400℃, and the holding time is 12h.

[0141] Example 3

[0142] This embodiment provides a method for preparing hard carbon from an easily softenable carbonization precursor, including the following steps:

[0143] S1. The second ball milling process is used to mix the easily softened carbonizable precursor (petroleum coke powder, 10g) with the second crosslinking agent (tannic acid, 1g) to obtain the initial mixture.

[0144] The second ball milling mixing speed was 350 rpm, and the time was 4 hours;

[0145] S2. The initial mixture is placed in a muffle furnace and subjected to a first oxidation treatment in an air atmosphere to obtain a primary oxide.

[0146] The heating rate of the first oxidation treatment is 10℃ / min, the temperature is 250℃, and the holding time is 12h;

[0147] S3. The first ball milling process is used to mix the first crosslinking agent (tartaric acid, 3g) with the primary oxide to obtain a two-component mixture;

[0148] The first ball milling mixing speed was 350 rpm, and the time was 4 hours;

[0149] The total mass of the first crosslinking agent and the second crosslinking agent is 40 wt% of the easily carbonizable precursor; based on a total mass percentage of 100 wt% for the first crosslinking agent and the second crosslinking agent, the mass percentage of the second crosslinking agent is 25 wt%.

[0150] S4. The two mixtures are placed in a muffle furnace and subjected to a second oxidation treatment in an air atmosphere to obtain a cross-linked curing precursor.

[0151] The second oxidation treatment has a heating rate of 8℃ / min, a temperature of 400℃, and a holding time of 8h;

[0152] S5. In an argon atmosphere, the cross-linked and cured precursor is pyrolyzed, and after naturally cooling to room temperature, it is ground and sieved to obtain hard carbon.

[0153] The pyrolysis heating rate is 5℃ / min, the temperature is 1300℃, and the holding time is 8h.

[0154] Example 4

[0155] This embodiment provides a method for preparing hard carbon from an easily softenable carbonization precursor. Except that the total mass percentage of the first and second crosslinking agents is 100 wt%, and the mass percentage of the second crosslinking agent is 0 wt%, the method is identical to that in Example 1, including the following steps:

[0156] S1. The easily softened carbonization precursor (coal tar pitch powder, 10g) is crushed by ball milling at 300 rpm for 6 hours to obtain primary material; the primary material is placed in a muffle furnace and subjected to a first oxidation treatment in air atmosphere to obtain primary oxide.

[0157] The heating rate of the first oxidation treatment is 3℃ / min, the temperature is 150℃, and the holding time is 9h;

[0158] S2. The first ball milling process is used to mix the first crosslinking agent (maleic acid, 1.5 g) with the primary oxide to obtain a second mixture;

[0159] The first ball milling mixing speed was 300 rpm, and the time was 5 hours;

[0160] The total mass of the first crosslinking agent and the second crosslinking agent is 15 wt% of the easily carbonizable precursor; based on a total mass percentage of 100 wt% for the first crosslinking agent and the second crosslinking agent, the mass percentage of the second crosslinking agent is 0 wt%.

[0161] S4. The two mixtures are placed in a muffle furnace and subjected to a second oxidation treatment in an air atmosphere to obtain a cross-linked curing precursor.

[0162] The second oxidation treatment has a heating rate of 5℃ / min, a temperature of 350℃, and a holding time of 10h;

[0163] S5. In an argon atmosphere, the cross-linked and cured precursor is pyrolyzed, and after naturally cooling to room temperature, it is ground and sieved to obtain hard carbon.

[0164] The pyrolysis heating rate is 3℃ / min, the temperature is 1500℃, and the holding time is 5h.

[0165] Example 5

[0166] This embodiment provides a method for preparing hard carbon from an easily softenable carbonization precursor. Except that the total mass percentage of the first crosslinking agent and the second crosslinking agent is 100 wt%, and the mass percentage of the second crosslinking agent is 50 wt%, the rest is the same as in Example 1, including the following steps:

[0167] S1. The second ball milling process is used to mix the easily softened carbonizable precursor (coal tar pitch powder, 10g) and the second crosslinking agent (citric acid, 0.75g) to obtain the initial mixture.

[0168] The second ball milling mixing speed was 300 rpm, and the time was 6 hours;

[0169] S2. The initial mixture is placed in a muffle furnace and subjected to a first oxidation treatment in an air atmosphere to obtain a primary oxide.

[0170] The heating rate of the first oxidation treatment is 3℃ / min, the temperature is 150℃, and the holding time is 9h;

[0171] S3. The first ball milling process is used to mix the first crosslinking agent (maleic acid, 0.75 g) with the primary oxide to obtain a second mixture;

[0172] The first ball milling mixing speed was 300 rpm, and the time was 5 hours;

[0173] The total mass of the first crosslinking agent and the second crosslinking agent is 15 wt% of the easily carbonizable precursor; based on a total mass percentage of 100 wt% for the first crosslinking agent and the second crosslinking agent, the mass percentage of the second crosslinking agent is 50 wt%.

[0174] S4. The two mixtures are placed in a muffle furnace and subjected to a second oxidation treatment in an air atmosphere to obtain a cross-linked curing precursor.

[0175] The second oxidation treatment has a heating rate of 5℃ / min, a temperature of 350℃, and a holding time of 10h;

[0176] S5. In an argon atmosphere, the cross-linked and cured precursor is pyrolyzed, and after naturally cooling to room temperature, it is ground and sieved to obtain hard carbon.

[0177] The pyrolysis heating rate is 3℃ / min, the temperature is 1500℃, and the holding time is 5h.

[0178] Example 6

[0179] This embodiment provides a method for preparing hard carbon from an easily softenable carbonization precursor, including the following steps:

[0180] S1. The second ball milling process mixes the easily softened carbonizable precursor (coal tar powder, 10g) with the second crosslinking agent (citric acid, 0.45g) to obtain the initial mixture.

[0181] The second ball milling mixing speed was 300 rpm, and the time was 6 hours;

[0182] S2. The initial mixture is placed in a muffle furnace and subjected to a first oxidation treatment in an air atmosphere to obtain a primary oxide.

[0183] The heating rate of the first oxidation treatment is 0.5℃ / min, the temperature is 100℃, and the holding time is 24h;

[0184] S3. The first ball milling process is used to mix the first crosslinking agent (maleic acid, 1.05 g) with the primary oxide to obtain a second mixture;

[0185] The first ball milling mixing speed was 300 rpm, and the time was 5 hours;

[0186] The total mass of the first crosslinking agent and the second crosslinking agent is 15 wt% of the easily carbonizable precursor; based on a total mass percentage of 100 wt% for the first crosslinking agent and the second crosslinking agent, the mass percentage of the second crosslinking agent is 30 wt%.

[0187] S4. The two mixtures are placed in a muffle furnace and subjected to a second oxidation treatment in an air atmosphere to obtain a cross-linked curing precursor.

[0188] The heating rate of the second oxidation treatment is 0.5℃ / min, the temperature is 250℃, and the holding time is 24h;

[0189] S5. In an argon atmosphere, the cross-linked and cured precursor is pyrolyzed, and after naturally cooling to room temperature, it is ground and sieved to obtain hard carbon.

[0190] The pyrolysis heating rate is 0.5℃ / min, the temperature is 1000℃, and the holding time is 24h.

[0191] Example 7

[0192] This embodiment provides a method for preparing hard carbon from an easily softenable carbonization precursor, including the following steps:

[0193] S1. The second ball milling process mixes the easily softened carbonizable precursor (coal tar powder, 10g) with the second crosslinking agent (citric acid, 0.45g) to obtain the initial mixture.

[0194] The second ball milling mixing speed was 300 rpm, and the time was 6 hours;

[0195] S2. The initial mixture is placed in a muffle furnace and subjected to a first oxidation treatment in an air atmosphere to obtain a primary oxide.

[0196] The heating rate of the first oxidation treatment is 10℃ / min, the temperature is 250℃, and the holding time is 1h;

[0197] S3. The first ball milling process is used to mix the first crosslinking agent (maleic acid, 1.05 g) with the primary oxide to obtain a second mixture;

[0198] The first ball milling mixing speed was 300 rpm, and the time was 5 hours;

[0199] The total mass of the first crosslinking agent and the second crosslinking agent is 15 wt% of the easily carbonizable precursor; based on a total mass percentage of 100 wt% for the first crosslinking agent and the second crosslinking agent, the mass percentage of the second crosslinking agent is 30 wt%.

[0200] S4. The two mixtures are placed in a muffle furnace and subjected to a second oxidation treatment in an air atmosphere to obtain a cross-linked curing precursor.

[0201] The heating rate of the second oxidation treatment is 10℃ / min, the temperature is 400℃, and the holding time is 1h;

[0202] S5. In an argon atmosphere, the cross-linked and cured precursor is pyrolyzed, and after naturally cooling to room temperature, it is ground and sieved to obtain hard carbon.

[0203] The pyrolysis heating rate is 10℃ / min, the temperature is 1600℃, and the holding time is 0.5h.

[0204] Comparative Example 1

[0205] This comparative example provides a method for preparing hard carbon, comprising the following steps:

[0206] S1. The second ball milled easily softened carbonized precursor (coal tar pitch powder, 10g) was used to obtain the initial grinding material;

[0207] The second ball mill operates at a speed of 300 rpm for 6 hours.

[0208] S2. The initial abrasive is placed in a muffle furnace and subjected to a first oxidation treatment in an air atmosphere to obtain a primary oxide.

[0209] The heating rate of the first oxidation treatment is 3℃ / min, the temperature is 150℃, and the holding time is 9h;

[0210] S3. The primary oxide is ball-milled in the first process to obtain a second abrasive.

[0211] The first ball mill rotates at 300 rpm for 5 hours;

[0212] S4. The two abrasives are placed in a muffle furnace and subjected to a second oxidation treatment in an air atmosphere to obtain a cross-linked and cured precursor.

[0213] The second oxidation treatment has a heating rate of 5℃ / min, a temperature of 350℃, and a holding time of 10h;

[0214] S5. In an argon atmosphere, the cross-linked and cured precursor is pyrolyzed, and after naturally cooling to room temperature, it is ground and sieved to obtain hard carbon.

[0215] The pyrolysis heating rate is 3℃ / min, the temperature is 1500℃, and the holding time is 5h.

[0216] Comparative Example 2

[0217] This comparative example provides a method for preparing hard carbon, comprising the following steps:

[0218] S1. Ball milling and mixing the easily softened carbonizable precursor (coal tar pitch powder, 10g), the second crosslinking agent (citric acid, 0.45g) and the first crosslinking agent (maleic acid, 1.05g) to obtain a mixed powder;

[0219] The ball milling mixing speed is 300 rpm and the time is 6 hours;

[0220] S2. The mixed powder is placed in a muffle furnace and oxidized in an air atmosphere to obtain an oxide.

[0221] The oxidation treatment has a heating rate of 5℃ / min, a temperature of 400℃, and a holding time of 24h.

[0222] S3. In an argon atmosphere, the oxide is pyrolyzed, and after naturally cooling to room temperature, it is ground and sieved to obtain hard carbon.

[0223] The pyrolysis heating rate is 3℃ / min, the temperature is 1500℃, and the holding time is 5h.

[0224] Performance Characterization

[0225] The specific surface area and electrochemical performance of the hard carbon obtained in the above examples and comparative examples were tested, and the results are shown in Table 1.

[0226] The specific surface area was determined according to GB / T19587-2017 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method": 0.2 g of the hard carbon sample to be tested was accurately weighed and placed in a sample tube. The sample tube was then connected to a vacuum degassing device and continuously degassed for 8 hours at 250℃ and a vacuum degree ≤10 Pa to thoroughly remove adsorbed moisture, residual gas, and volatile impurities from the sample surface. After degassing, the sample tube was allowed to cool naturally to room temperature under vacuum. The pretreated sample tube was then connected to an analyzer, and adsorption isotherms were measured in a liquid nitrogen isothermal environment (77 K) within the range of nitrogen relative pressure P / P0 from 0.05 to 0.99. Adsorption data were collected at five uniformly distributed pressure points. A multi-point BET model was used to linearly fit the obtained adsorption data to calculate the specific surface area of ​​the hard carbon sample, in m². 2 / g.

[0227] Methods for testing electrochemical performance include:

[0228] Hard carbon, conductive agent Super P, and binder polyacrylic acid (PAA) were precisely weighed at a mass ratio of 80:10:10. Using deionized water as the dispersion solvent, the mixture was stirred to obtain a negative electrode slurry with a solid content of 45 wt%. A doctor blade coater was used to uniformly coat the negative electrode slurry onto one side of a 10 μm thick electrolytic copper foil current collector, controlling the dry coating surface density to be 10 mg / cm². After coating, the electrode was pre-dried in a 60℃ forced-air drying oven for 2 hours, then transferred to a 100℃ vacuum drying oven and dried under a vacuum of ≤-0.09 MPa for 12 hours to completely remove moisture. The dried electrode was then removed and rolled using a roller press to a compaction density of 1.2 g / cm². 3 The negative electrode sheet is obtained by punching the electrode sheet into a circular shape with a diameter of 14mm using a precision punching machine.

[0229] A 1.0 mol / L sodium-ion battery electrolyte was prepared by using battery-grade sodium hexafluorophosphate (NaPF6) as the solute, a mixture of battery-grade ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1 as the base solvent, and adding 5% by volume of battery-grade fluoroethylene carbonate (FEC) as a film-forming additive.

[0230] Using a sodium metal sheet as the positive electrode and a polypropylene microporous membrane as the separator, the above-obtained negative electrode sheet and sodium-ion battery electrolyte are assembled into a CR2032 coin-type sodium-ion half-cell. The cell is placed in a constant temperature environment of 25±2℃ and left to stand for 12 hours to allow the electrolyte to fully wet the electrode sheet and the separator before charge-discharge testing.

[0231] The charge-discharge cycle was performed at a constant current rate of 0.1C (sodium insertion) until the cutoff voltage reached 0.005V, then switched to constant voltage discharge until the current dropped to 0.05C, and allowed to stand for 10 minutes. Next, the charge-discharge cycle was performed at a constant current rate of 0.1C (sodium removal) until the cutoff voltage reached 2.0V, and allowed to stand for 10 minutes. This constitutes one complete first charge-discharge cycle. The total specific capacity during the constant current charging (sodium removal) phase in the first charge-discharge cycle is expressed in mAh / g.

[0232] First-week coulomb efficiency = (first-week charge specific capacity / first-week discharge specific capacity) × 100%.

[0233] The XRD pattern of the hard carbon obtained in Example 1 is shown below. Figure 1 As shown, the N2- adsorption-desorption curves are as follows: Figure 2 As shown, the corresponding charge and discharge curves of the battery are as follows: Figure 3 As shown. Figure 1 The XRD pattern shows two broad and weak diffraction peaks (002 and 100 crystal planes), indicating that the material has a typical amorphous hard carbon structure and no obvious graphitization peaks. Figure 2 The BET test results show that the specific surface area of ​​this material is 20m². 2 / g. Combined with the adsorption curve characteristics, it is demonstrated that the method of this invention forms a highly cross-linked three-dimensional network structure within the material, inhibiting the orderly growth of the graphite layer. Figure 3 The charge-discharge curves show an extremely long low-voltage plateau. Test data show that its reversible specific capacity is as high as 321 mAh / g, and the first-week coulombic efficiency (ICE) reaches 77%. This confirms the moderate specific surface area (20 m² / g). 2 / g) creates an excellent balance: it effectively limits electrolyte side reactions caused by excessively open pores, while providing good ion diffusion channels and abundant closed-pore sodium storage sites.

[0234] The XRD pattern of the hard carbon obtained in Example 2 is shown below. Figure 4 As shown, the N2- adsorption-desorption curves are as follows: Figure 5 As shown, the corresponding charge and discharge curves of the battery are as follows: Figure 6 As shown; the XRD pattern of the hard carbon obtained in Example 3 is shown below. Figure 7 As shown, the N2- adsorption-desorption curves are as follows: Figure 8 As shown, the corresponding charge and discharge curves of the battery are as follows: Figure 9 As shown. By Figures 4-9 It is evident that the microstructure of the material changes as the crosslinking agent ratio or processing temperature shifts towards the process boundary value. Due to the use of the lower limit for crosslinking agent addition and a relatively low oxidation temperature, the overall oxidative crosslinking reaction is relatively mild. The weaker reaction level results in fewer microscopic defects and pores derived from the carbon skeleton during pyrolysis, thus leading to a lower specific surface area (12m²). 2 / g). Meanwhile, due to the underdeveloped cross-linking network, the number of induced sodium-storing closed pores was also insufficient, resulting in a lower reversible capacity (310 mAh / g) than in Example 1. In Example 3, due to the parameters reaching their upper limit, the gas release during the pyrolysis stage was more intense, causing some pores to fail to close, increasing the proportion of open-pore structures, and raising the specific surface area to 41 m². 2 / g. The increase in open surface area consumed some of the effective closed pores, resulting in a decrease in capacity to 274mAh / g, while the first-efficiency ratio remained at 76%.

[0235] The XRD pattern of the hard carbon obtained in Comparative Example 1 is shown below. Figure 10 As shown, the N2- adsorption-desorption curves are as follows: Figure 11 As shown, the corresponding charge and discharge curves of the battery are as follows: Figure 12 As shown, Figure 11 BET testing showed that the specific surface area of ​​this material was only 4 m². 2 / g. Combined with XRD analysis, it can be seen that, since no crosslinking agent was added throughout the process, air oxidation alone could not build a three-dimensional network crosslinking framework in the precursor bulk phase, resulting in the orderly accumulation of graphite layers and the formation of a soft carbon structure. Figure 12 Electrochemical data show that its reversible specific capacity is only 191 mAh / g.

[0236] The XRD pattern of the hard carbon obtained in Comparative Example 2 is shown below. Figure 13 As shown, the N2- adsorption-desorption curves are as follows: Figure 14 As shown, the corresponding charge and discharge curves of the battery are as follows: Figure 15 As shown. Figure 14 The BET results show that the specific surface area of ​​this material reaches 42m². 2 / g. This is because it uses a single-stage isothermal oxidation process at 400℃, without undergoing a low-temperature kinetic buffer. Under these conditions, the dehydration and decarboxylation reaction rate of the precursor and crosslinking agent is too fast, and gaseous byproducts are released in a concentrated manner within a short period of time, resulting in a significant increase in local gas pressure inside the material, transforming it into open mesopores or macropores. Figure 15 Electrochemical tests showed that its reversible specific capacity dropped to 253 mAh / g.

[0237] Table 1

[0238]

[0239] The “-” in Table 1 indicates that no measurement was performed.

[0240] As can be seen from Examples 1 to 7 in Table 1, the stepwise oxidative crosslinking method for preparing hard carbon provided by the present invention can transform easily soft carbonized precursors into hard carbon anode materials with high reversible capacity and high first-cycle coulombic efficiency, and can obtain optimal electrochemical performance under appropriate process parameter combinations.

[0241] As can be seen from the comparison between Comparative Example 1 and Example 1, air oxidation alone cannot build a stable three-dimensional cross-linked framework in the precursor bulk phase. During pyrolysis, aromatic carbon microcrystals will form a soft carbon structure, reducing sodium storage sites and resulting in a decrease in reversible specific capacity and first-cycle coulombic efficiency.

[0242] As can be seen from the comparison between Comparative Example 2 and Example 1, the process of using a single mixing of crosslinking agents and a single high-temperature oxidation cannot obtain the ideal hard carbon performance.

[0243] In summary, the method provided by this invention employs a stepwise solid-phase mixing of crosslinking agents and a stepwise oxidation process, avoiding the unevenness and surface sealing effect of single oxidation. The constructed three-dimensional crosslinked network acts as a steric hindrance, effectively suppressing graphitization during pyrolysis and inducing the formation of an ideal hard carbon structure with larger carbon interlayer spacing and abundant closed pores, thereby significantly improving the reversible capacity and rate performance of hard carbon. During the high-temperature pyrolysis carbon skeleton shrinkage process, some micro-defects within the material evolve into abundant closed-pore structures in the three-dimensional crosslinked network constructed by the method provided by this invention. These closed-pore-dominated microstructures provide filling sites for sodium ion storage, significantly improving the plateau region capacity, reducing irreversible electrolyte consumption on the carbon surface and SEI thickening, thereby improving the first-cycle coulombic efficiency of the hard carbon anode material. The sequential first and second oxidation processes of this invention achieve the separation of physical mass transfer (diffusion) and chemical reaction (crosslinking). In the first stage, the high fluidity of molecular chains resulting from the moderate softening of thermoplastic precursors, combined with an extremely low chemical reaction rate, effectively avoids the premature formation of a dense oxide shell on the particle surface, allowing oxygen molecules and crosslinking agents to deeply penetrate into the bulk phase of the material. In the second oxidation treatment stage, the crosslinking agents and active oxidation sites that are already uniformly distributed inside are activated in situ, undergoing deep oxidative crosslinking with the aromatic molecules of the material. This mechanism of "deep diffusion first, followed by bulk solidification" ensures that the material completely transforms from "thermoplastic" to "thermosetting" before undergoing high-temperature and intense melting. The method provided by this invention has the potential to be low-cost, use readily available raw materials, and be suitable for large-scale production. The entire process does not require expensive reagents or complex equipment, and the crosslinking agents used are all common chemical raw materials. Moreover, the reaction conditions are mild and controllable. The combination of ball milling and solid-phase reaction avoids the use of large amounts of solvents, making this strategy have significant advantages and application prospects in the large-scale preparation of high-performance, low-cost hard carbon anode materials.

[0244] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for producing hard carbon from a soft carbonizable precursor, characterized by, The method includes: S1. The easily carbonized precursor is subjected to a first oxidation treatment to obtain a primary oxide; S2. The first ball milling process is used to mix the first crosslinking agent and the primary oxide to obtain a two-component mixture; S3. The two mixtures undergo a second oxidation treatment to obtain a cross-linked cured precursor. S4. In a protective atmosphere, the cross-linked cured precursor is pyrolyzed to obtain hard carbon; The temperature of the second oxidation treatment is at least 20°C higher than the temperature of the first oxidation treatment.

2. The method of claim 1, wherein, Before undergoing the first oxidation treatment, the easily carbonizable precursor is mixed with a second crosslinking agent by a second ball mill to obtain a preliminary mixture; then the preliminary mixture is subjected to the first oxidation treatment.

3. The method of claim 2, wherein, The first crosslinking agent and the second crosslinking agent each independently comprise any one or a combination of at least two of the following: citric acid, maleic acid, humic acid, tannic acid, ascorbic acid, tartaric acid, caffeic acid, glucose, maltose, fructose, sucrose, starch, or cellulose. And / or, the total mass of the first crosslinking agent and the second crosslinking agent is 5wt% to 40wt% of the easily carbonizable precursor; And / or, based on a total mass percentage of 100 wt% for the first crosslinking agent and the second crosslinking agent, the mass percentage of the second crosslinking agent is 0 wt% to 50 wt%.

4. The method according to claim 1 or 2, characterized in that, The easily softened carbonization precursor includes any one or a combination of at least two of the following: petroleum asphalt, coal-based asphalt, mesophase asphalt, coal, heavy oil, residual oil, petroleum coke, polyvinyl chloride, polyacrylonitrile, polystyrene, polyvinyl chloride copolymer, phenolic resin, or vegetable tar.

5. The method according to claim 1 or 2, characterized in that, The first oxidation treatment and the second oxidation treatment are carried out independently in an oxygen-containing atmosphere; The gases used in the oxygen-containing atmosphere include oxygen and / or air.

6. The method according to claim 5, characterized in that, The heating rate of the first oxidation treatment is 0.5℃ / min to 10℃ / min; And / or, the temperature of the first oxidation treatment is 100℃~250℃; And / or, the holding time for the first oxidation treatment is 1h to 24h.

7. The method according to claim 5, characterized in that, The heating rate for the second oxidation treatment is 0.5℃ / min to 10℃ / min; And / or, the temperature of the second oxidation treatment is 250°C to 400°C; And / or, the second oxidation treatment lasts for 1 to 24 hours.

8. The method according to claim 1 or 2, characterized in that, The protective atmosphere includes any one or a combination of at least two of nitrogen, helium, or argon.

9. The method according to claim 8, characterized in that, The heating rate of the pyrolysis is 0.5℃ / min to 10℃ / min; And / or, the pyrolysis temperature is 1000℃~1600℃; And / or, the holding time for the pyrolysis is 0.5h to 24h.

10. A type of hard carbon, characterized in that, The hard carbon is prepared by the method described in any one of claims 1 to 9.

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