High-performance hard carbon material, preparation method and application thereof

Abstract

The application provides a high-performance hard carbon material and a preparation method and application thereof, wherein the high-performance hard carbon material balances the energy density and kinetic performance of the material by meeting a comprehensive performance parameter K, K = x, and K is between 0.11 and 49. The correlation of the energy density characteristics is related to the powder compaction density P, reversible specific capacity C, first efficiency E and true density T of the material; the correlation of the kinetic characteristics is related to the specific surface area B, median particle size D and high potential platform capacity proportion A of the material. Through accurate limitation and the range of each sub parameter, the hard carbon material obtained by the application has high reversible capacity, high first efficiency and excellent rate performance, and is very suitable for being used as a negative electrode material and applied to a high-performance sodium ion secondary battery.

Description

Technical Field

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

[0002] Hard carbon is produced by carbonizing petrochemical products or biomass materials. Even when heated to 2600℃, hard carbon materials are difficult to graphitize. However, due to its highly disordered structure and numerous micropores, it possesses a layered structure with a larger interlayer spacing than graphite, allowing lithium or sodium ions to be rapidly inserted and extracted. It exhibits excellent rate capability, very little expansion, and high safety performance.

[0003] Hard carbon, as an amorphous carbon material, possesses a microstructure characterized by randomly distributed graphite-like layers, abundant edge and surface defects, and a unique nanoporous structure. When used as an anode material in sodium-ion batteries, hard carbon exhibits a dual-voltage region during charge and discharge: a ramp region (>0.1 V) over a wide voltage range and a plateau region (<0.1 V) at a low voltage range. The ramp region primarily stores sodium via surface defects and interlayer sodium within the graphite-like layers. The sodium ion insertion / extraction rate is high in the ramp region, demonstrating excellent kinetic performance.

[0004] The low-voltage characteristics of the plateau region are beneficial for increasing the operating voltage window and improving the energy density of the full cell. Simultaneously, sodium ions in the closed pores of the low-voltage plateau region mainly exist as quasi-metallic sodium clusters. The closed pores in hard carbon are formed by highly disordered carbon layers, pseudo-graphitized structures, or graphitized-like structures, and these pores play a crucial role in sodium storage in the plateau region. Typically, increasing the closed-pore volume can significantly improve the void-filling capacity, thereby greatly increasing the reversible specific capacity of hard carbon materials and consequently, their energy density. Since the voltage corresponding to the plateau region capacity is close to the deposition potential of sodium metal, the sodium storage characteristics of hard carbon in the low-voltage plateau region make it a major challenge for achieving high-power rapid charge and discharge. In existing technologies, much research focuses on increasing the closed-pore volume to improve capacity; however, the capacity contribution of the plateau region severely limits the kinetic performance of hard carbon materials in secondary batteries. Summary of the Invention

[0005] Based on this, the purpose of this invention is to provide a high-performance hard carbon material, its preparation method, and its application, aiming to solve the problem in the prior art of lacking a high-performance hard carbon material, its preparation method, and its application that can take into account both high kinetics and high energy density.

[0006] According to an embodiment of the present invention, a high-performance hard carbon material is provided, wherein the hard carbon material satisfies the following formula:

[0007] Wherein, D is the median particle size of the hard carbon material, in μm; T is the true density of the hard carbon material, in g / cm³. P is the compacted density of the hard carbon material, in g / cm³. B represents the specific surface area of ​​the hard carbon material, in square meters per g. C represents the reversible specific capacity of a coin cell assembled using the hard carbon material as the negative electrode, expressed in mAh / g. E represents the initial coulombic efficiency of the coin cell, expressed in % (%). A refers to the voltage of the coin cell battery at 0.1V (relative to Na) during the second week of charge and discharge. + The percentage of sodium intercalation capacity above ( / Na) out of the total sodium intercalation capacity, expressed in units of %.

[0008] In one embodiment of this application, the hard carbon material satisfies at least one of the following conditions (i) to (vii): (i) The percentage of sodium-intercalated specific capacity above 0.1V during the second week of charging and discharging meets the following requirement: 20% ≤ A ≤ 38%; (ii) The reversible specific capacity satisfies: 270mAh / g≤C≤360mAh / g; (iii) The initial Coulomb efficiency satisfies: 86% ≤ E ≤ 94%; (iv) The true density satisfies: 1.95 g / cm³ ≤ T ≤ 2.15 g / cm³; (v) The median particle size satisfies: 1.5μm≤D≤10μm; (vi) The compacted density of the powder satisfies: 0.85 g / cm³ ≤ P ≤ 1.2 g / cm³; (vii) The specific surface area satisfies: 2.0 m² / g ≤ B ≤ 10.0 m² / g.

[0009] In one embodiment of this application, the peak intensity ratio ID / IG of the D peak to the G peak in the Raman spectrum of the high-performance hard carbon material is 0.95-1.25.

[0010] Another objective of this invention is to provide a method for preparing a hard carbon material, which is used to prepare the aforementioned high-performance hard carbon material. The preparation method is as follows: The carbon precursor, pore-forming agent and crosslinking agent are mixed in a preset ratio and pre-oxidized under an oxidizing atmosphere to obtain a stabilized precursor. The stabilized precursor was subjected to micron-sized pulverization, with the median particle size D50 controlled between 3 μm and 10 μm.

[0011] The pulverized product was placed in a mixed atmosphere of halogen gas and inert gas and subjected to vapor phase etching at high temperature for a preset time to remove unstable amorphous carbon impurities. The mixture is placed in a high-pressure reactor and subjected to gradient pressure carbonization under an inert atmosphere; the gradient pressure carbonization includes a first heating stage and a second isothermal stage.

[0012] In one embodiment of this application, the steps of the first heating stage include: The temperature is increased from room temperature to 500℃-800℃ at a rate of 0.5℃ / min-5℃ / min, while the pressure inside the vessel is controlled to increase linearly with temperature to 2 MPa-10 MPa.

[0013] In one embodiment of this application, the steps of the second isothermal stage include: The material is kept at 1100℃-1500℃ for 1h-6h, while the pressure inside the reactor is initially maintained at 5MPa-15 MPa for 0.5h-2h, and then depressurized to atmospheric pressure at a rate of 0.1MPa / min-0.5 MPa / min to obtain hard carbon material.

[0014] In one embodiment of this application, the preset ratio is that the carbon precursor, pore-forming agent, and crosslinking agent are mixed at a mass ratio of 100:(5-20):(2-10); the high temperature condition is 600℃-900℃; and the preset time is 10min-60min.

[0015] In one embodiment of this application, the crosslinking agent is one or more of aldehydes, organic acids, epoxy compounds, and metal coordination crosslinking agents. The crosslinking agents include furfural, glutaraldehyde, citric acid, phytic acid, pyromellitic dianhydride, ethylene glycol diglycidyl ether, trimethylolpropane triglycidyl ether, boric acid, lithium metaborate, organoborides, etc.

[0016] In one embodiment of this application, the pore-forming agent may be one or a combination of two or more of the following: divinylbenzene, azodicarbonamide, benzoic acid, polymethyl methacrylate microspheres, polyethylene oxide, polyvinyl butyral, zinc citrate, and zinc acetate.

[0017] Another objective of this invention is to provide the application of the hard carbon material described in the above technical solution or the hard carbon material prepared by the preparation method described in the above technical solution as a negative electrode material for secondary batteries.

[0018] This invention employs a combination of a pore-forming agent and a crosslinking agent, which pre-form a coordination complex in the precursor. During pyrolysis, zinc ions are reduced to metallic zinc and vaporize, while phosphorus is incorporated into the carbon framework to form POC bonds. This mechanism creates a unique ink-bottle-like pore structure—small opening and large internal cavity—ensuring ion transport channels without excessively increasing specific surface area, thus solving the problem of the trade-off between capacity and first-efficiency. During gradient pressure carbonization, the high-density crosslinking network provides the precursor with a sufficiently rigid framework, preventing plastic flow and pore blockage under high pressure, ensuring a synergistic increase in true density and compacted density, thereby achieving the high capacity requirement in the formula. The interconnected channels pre-constructed by the pore-forming agent and crosslinking agent during high-pressure carbonization serve as stress release paths, guiding the uniform dissipation of internal stress under high pressure; the rigid framework maintained by the crosslinking agent ensures the orderly arrangement of microcrystal orientation after pressure release. The combined effect allows for independent control of three key parameters: specific surface area, true density, and low-voltage plateau capacity, ultimately achieving continuously adjustable K-values ​​within the target range—a technical effect that cannot be achieved with single-component pore-forming or conventional crosslinking processes. Therefore, this invention solves the problem in the prior art of lacking a high-performance hard carbon material that can achieve both high kinetics and high energy density, as well as its preparation method and application. Attached Figure Description

[0019] Figure 1 This is a SEM image of hard carbon particles in a hard carbon negative electrode material according to an embodiment of the present invention; Figure 2 This is a first charge-discharge curve of a sodium-ion coin cell made of hard carbon negative electrode material in one embodiment of the present invention. Figure 3 This is a Raman curve of hard carbon particles in a hard carbon anode material according to an embodiment of the present invention.

[0020] The following detailed description, in conjunction with the accompanying drawings, will further illustrate the present invention. Detailed Implementation

[0021] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Several embodiments of the invention are illustrated in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0023] This invention provides a high-performance hard carbon material, which satisfies the following formula:

[0024] Where D is the median particle size of the hard carbon material, in μm; T is the true density of the hard carbon material, in g / cm³; P is the compacted density of the hard carbon powder, in g / cm³; B is the specific surface area of ​​the hard carbon material, in m² / g; C is the reversible specific capacity of the coin cell assembled with the hard carbon material as the negative electrode, in mAh / g; E is the initial coulombic efficiency of the coin cell, in %; and A is the voltage at 0.1V (relative to Na) during the second week of charge-discharge. + The percentage of sodium intercalation capacity above ( / Na) out of the total sodium intercalation capacity, expressed in units of %.

[0025] In this embodiment, the sodium-intercalated specific capacity percentage at 0.1V or higher during the second week of charge-discharge meets the following condition: 20% ≤ A ≤ 38%. For example, the sodium-intercalated specific capacity percentage at 0.1V or higher during the second week of charge-discharge is 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, or 38%, but is not limited to these. Hard carbon, as a secondary battery anode material, has three main sodium storage mechanisms. First, sodium ions are adsorbed from surface defects. As the degree of sodium intercalation increases, it gradually transitions to interlayer sodium storage in a graphite-like structure. When sodium storage reaches a high level, it begins to transition from interlayer sodium storage to pore-filled sodium storage. Within the voltage range with a high degree of sodium intercalation, pore-filled sodium storage dominates. The proportion of sodium intercalation capacity above 0.1V is related to the kinetic performance of the secondary battery. It is generally believed that above 0.1V, sodium ion intercalation in hard carbon materials is mainly due to defect adsorption and interlayer insertion, while below 0.1V, it is mainly due to pore filling in the hard carbon material. A higher proportion of sodium intercalation capacity above 0.1V corresponds to greater defect adsorption and interlayer contribution from the hard carbon, which is beneficial for sodium ion intercalation and deintercalation, resulting in better kinetic performance of the secondary battery. However, a higher proportion also leads to a significant decrease in reversible specific capacity and initial stock efficiency, thus affecting the energy density of the secondary battery.

[0026] In this embodiment, the reversible specific capacity satisfies: 270mAh / g ≤ C ≤ 360mAh / g. Exemplary reversible specific capacities are 270mAh / g, 280mAh / g, 290mAh / g, 300mAh / g, 310mAh / g, 320mAh / g, 330mAh / g, 340mAh / g, 350mAh / g, or 360mAh / g, but are not limited to these.

[0027] In this embodiment, the initial coulombic efficiency satisfies: 86% ≤ E ≤ 94%. For example, the initial coulombic efficiency can be 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, or 94%, but is not limited to these. The reversible specific capacity and initial coulombic efficiency of a material are related to the energy density of a secondary battery. A higher reversible specific capacity allows for the use of less active material to achieve higher volumetric and gravimetric energy densities when applied to secondary batteries. A higher initial efficiency effectively reduces capacity loss in the secondary battery, thereby increasing the gravimetric energy density.

[0028] In this embodiment, the true density satisfies: 1.95 g / cm³ ≤ T ≤ 2.15 g / cm³. Exemplary true densities are 1.95 g / cm³, 1.96 g / cm³, 1.97 g / cm³, 1.98 g / cm³, 1.99 g / cm³, 2 g / cm³, 2.01 g / cm³, 2.02 g / cm³, 2.03 g / cm³, 2.04 g / cm³, 2.05 g / cm³, 2.06 g / cm³, 2.07 g / cm³, 2.08 g / cm³, 2.09 g / cm³, 2.1 g / cm³, 2.11 g / cm³, 2.12 g / cm³, 2.13 g / cm³, 2.14 g / cm³, or 2.15 g / cm³, but are not limited to these. The true density of a material is related to the energy density of a secondary battery. Hard carbon, as the negative electrode material of a secondary battery, has a large number of pores. The micropores (<2nm) of the material itself contribute significantly to the capacity. The lower the true density, the more abundant the pores in the hard carbon material. The more micropores there are, the higher the corresponding capacity and energy density. At the same time, the high capacity contribution of hard carbon pore filling results in a low sodium ion insertion / extraction rate in the pores, which affects its kinetic performance, is not conducive to high-rate charge / discharge of the secondary battery, and also affects cycle performance.

[0029] In this embodiment, the median particle size satisfies: 1.5 μm ≤ D ≤ 10 μm. Exemplary median particle sizes are 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, or 10 μm, but are not limited to these. The median particle size of hard carbon materials is related to the kinetics and energy density of secondary batteries. Reducing the median particle size of hard carbon materials can shorten the transport path of sodium ions within the bulk phase of the material, thereby improving the kinetic performance of the secondary battery. However, excessively small particle sizes increase material defects, increase irreversible capacity, and reduce energy density.

[0030] In this embodiment, the powder compaction density satisfies: 0.85 g / cm³ ≤ P ≤ 1.2 g / cm³. Exemplary compaction densities include 0.85 g / cm³, 0.9 g / cm³, 0.95 g / cm³, 1 g / cm³, 1.05 g / cm³, 1.1 g / cm³, 1.15 g / cm³, or 1.2 g / cm³, but are not limited to these. The compaction density of the negative electrode active material is related to the energy density of the secondary battery. The higher the compaction density of the powder, the higher the compaction density of the corresponding electrode, and the higher the volumetric energy density applied to the secondary battery. However, a higher compaction density results in smaller gaps between the active material particles in the secondary battery electrode, leading to lower porosity. This is detrimental to electrolyte wetting, affecting its kinetic performance and hindering high-rate charge / discharge of the secondary battery.

[0031] In this embodiment, the specific surface area satisfies: 2.0 m² / g ≤ B ≤ 10.0 m² / g. Exemplary specific surface areas are 2 m² / g, 2.5 m² / g, 3 m² / g, 3.5 m² / g, 4 m² / g, 4.5 m² / g, 5 m² / g, 5.5 m² / g, 6 m² / g, 6.5 m² / g, 7 m² / g, 7.5 m² / g, 8 m² / g, 8.5 m² / g, 9 m² / g, 9.5 m² / g, or 10 m² / g, but are not limited to these. The specific surface area of ​​the material is related to the kinetic performance of the secondary battery. A larger specific surface area allows for greater adsorption of surface defects in the secondary battery, resulting in higher sodium adsorption and desorption rates, which is beneficial for sodium ion migration and thus improves kinetic performance. However, surface defects significantly increase the occurrence of side reactions in the secondary battery, leading to increased irreversible capacity and severely affecting the energy density of the secondary battery.

[0032] Simply optimizing each of the above parameters individually has significant limitations in achieving batteries with high energy density and high kinetic performance. The negative electrode material design of this invention fully considers various influences and rationally matches the parameters. When 0.11≤K≤49 is satisfied, the secondary battery exhibits both high energy density and good kinetic performance.

[0033] To achieve both high energy density and excellent rate performance, this invention provides a method for preparing high-performance hard carbon materials as described above. The preparation method includes the following steps: The carbon precursor, pore-forming agent and crosslinking agent are mixed in a preset ratio and pre-oxidized under an oxidizing atmosphere to obtain a stabilized precursor. The stabilized precursor was subjected to micron-sized pulverization, with the median particle size D50 controlled between 3 μm and 10 μm.

[0034] The pulverized product was placed in a mixed atmosphere of halogen gas and inert gas and subjected to vapor phase etching at high temperature for a preset time to remove unstable amorphous carbon impurities. It is placed in a high-pressure reactor and subjected to gradient pressure carbonization under an inert atmosphere; the gradient pressure carbonization includes a first heating stage and a second isothermal stage.

[0035] In this embodiment, the steps of the first heating stage include: heating from room temperature to 500℃-800℃ at a rate of 0.5℃ / min-5℃ / min, while controlling the pressure inside the vessel to rise linearly with the temperature to 2MPa-10 MPa.

[0036] In this embodiment, the steps of the second isothermal stage include: maintaining the temperature at 1100℃-1500℃ for 1h-6h, while controlling the pressure inside the reactor to be maintained at 5MPa-15 MPa for 0.5h-2h, and then depressurizing to atmospheric pressure at a rate of 0.1MPa / min-0.5 MPa / min to obtain hard carbon material.

[0037] In this embodiment, the preset ratio is that the carbon precursor, pore-forming agent, and crosslinking agent are mixed at a mass ratio of 100:(5-20):(2-10); the high temperature condition is 600℃-900℃; and the preset time is 10min-60min.

[0038] In this embodiment, the crosslinking agent is one or more of the following: aldehydes, organic acids, epoxy compounds, and metal coordination crosslinking agents. The crosslinking agents include furfural, glutaraldehyde, citric acid, phytic acid, pyromellitic dianhydride, ethylene glycol diglycidyl ether, trimethylolpropane triglycidyl ether, boric acid, lithium metaborate, organoborides, etc.

[0039] In this embodiment, the pore-forming agent may be one or a combination of two or more of the following: divinylbenzene, azodicarbonamide, benzoic acid, polymethyl methacrylate microspheres, polyethylene oxide, polyvinyl butyral, zinc citrate, and zinc acetate.

[0040] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0041] Example 1 500g of camellia husks were coarsely crushed to a particle size of 0.5~2.0cm using a coarse crusher, then placed in a ceramic boat and put into a tube furnace. Under nitrogen atmosphere protection, the oxygen content in the furnace was kept <100ppm. The temperature was increased to 600℃ at 3℃ / min for low-temperature heat treatment, held at a constant temperature for 1 hour, and then cooled naturally to obtain low-temperature heat-treated char. The low-temperature heat-treated carbon was pulverized using a pulverizer to a median particle size of 4.0~7.0μm. Then, the pulverized material and ammonium chloride deashing additive were added to a mixer at a mass ratio of 85:15 and stirred at 30Hz for 30 minutes. The resulting mixture was placed in a crucible and placed in a specially modified high-temperature atmosphere furnace. Nitrogen gas was introduced to make the oxygen content <100ppm. The temperature was increased from room temperature to 1300℃ at a heating rate of 3℃ / min for high-temperature deashing and carbonization treatment. The temperature was kept constant for 2 hours. After natural cooling, the material was sieved through a 325-mesh sieve to obtain deashed hard carbon material.

[0042] The process parameters for preparing deashed hard carbon materials in Examples 2-11 and Comparative Examples 1-6 are shown in Table 1. The rest of the parameters are the same as those in Example 1.

[0043] Table 1. Process parameters for preparing deashed hard carbon materials in Examples 1-7 and Comparative Examples 1-6.

[0044] Performance testing: (1) The morphology of the hard carbon anode material obtained in Example 1 was analyzed using a JSM-7160 scanning electron microscope from Nippon Electronics Corporation. The results are as follows: Figure 1 As shown.

[0045] Depend on Figure 1 It can be seen that the hard carbon particles prepared by the present invention are uniformly distributed.

[0046] (2) The ash content, median particle size (D50), specific surface area and powder compaction density of the deashed hard carbon materials obtained in Examples 1-7 and Comparative Examples 1-6 were tested, and the results are shown in Table 2.

[0047] Ash content was determined according to GB / T1429-2009 using a muffle furnace; median particle size (D50) was determined according to Appendix A of GB / T24533-2019 using a Malvern Mastersizer 3000 laser particle size analyzer; specific surface area was determined according to GB / T19587 using a nitrogen adsorption-desorption apparatus; and powder compaction density was determined according to GB / T24533-2019 using a powder compaction density meter.

[0048] Table 2. Physical properties of the deashed hard carbon materials obtained in Examples 1-7 and Comparative Examples 1-6

[0049] As shown in Table 2, the ash content of the deashed hard carbon material prepared by this invention is 0.13~0.42%, the median particle size is 6.2~6.8µm, the specific surface area is 4.3~8.9m2 / g, and the powder compaction density at 5T is 0.93~0.96g / cm3.

[0050] (3) The carbon interlayer spacing d002, trace elements, and fixed carbon content of the deashed hard carbon materials obtained in Examples 1-7 and Comparative Examples 1-6 were tested, and the results are shown in Table 3.

[0051] The carbon interlayer spacing d002 was determined according to the provisions of Appendix E of GB / T24533-2019 standard. The phase analysis of the material was performed using an XRD diffractometer (X'Pert3 Powder), and the carbon interlayer spacing d002 was calculated. The trace elements were determined according to the provisions of Appendix H of GB / T24533-2019 standard, and were tested using an inductively coupled plasma atomic emission spectrometer. The fixed carbon content was determined according to the provisions of GB / T3521 standard, and was tested using a muffle furnace.

[0052] Table 3. Physical properties of the deashed hard carbon materials obtained in Examples 1-11 and Comparative Examples 1-6

[0053] As shown in Table 3, the fixed carbon content of the deashed hard carbon material prepared by the present invention is 99.3-99.7%, the carbon interlayer spacing d002 is 0.38-0.39 nm, and the trace elements are Ca 8-16 ppm, Mg 7-18 ppm, Al 3-8 ppm, Si 5-16 ppm, and Na 4-8 ppm.

[0054] (4) The hard carbon negative electrode material obtained in Example 1 was used to fabricate a sodium-ion coin cell. The first charge-discharge curve of the sodium-ion coin cell was obtained by the sodium-ion coin cell test method. The results are shown in […]. Figure 2 .

[0055] Depend on Figure 2 It can be seen that, under the condition of charge and discharge cutoff voltage of 2.0~0V, the first reversible capacity of hard carbon anode material is above 330mAh / g and the first efficiency is above 92.5%.

[0056] (5) The hard carbon anode material obtained in Example 1 was subjected to Raman spectroscopy testing using a high-resolution confocal microlaser Raman spectroscopy instrument. The laser wavelength was 532 nm, the laser energy was 0.5 mW, the grating was 300 g / mm, the objective lens was Olympus 20x / 0.25, the integration time was 35 s, and the number of integrations was 6. The results are shown in […]. Figure 3 .

[0057] Depend on Figure 3 As shown in the Raman characterization spectrum, two relatively obvious characteristic peaks can be observed: the D peak (1338 cm⁻¹) and the G peak (1580 cm⁻¹). The intensity of the D peak reflects the degree of disorder in the disordered carbon within the hard carbon material, while the G peak represents the vibration of ordered carbon. Therefore, the ratio of the intensities of the D peak to the G peak (ID / IG) can, to some extent, reflect the degree of disorder in the hard carbon material. Figure 3 As shown, ID / IG=1.13, indicating high disorder.

[0058] (6) The hard carbon anode materials obtained in Examples 1-11 and Comparative Examples 1-7 were used to make sodium-electric / lithium-electric button cells and then tested. The results are shown in Table 4.

[0059] Sodium / lithium coin cell batteries consist of a commercially available negative electrode shell, positive electrode shell, separator, lithium sheet, nickel foam, electrode sheet, and electrolyte. The conductive agent is acetylene black, the binder is CMC or SBR, and the solvent is deionized water. The electrolyte consists of three parts: sodium / lithium salt, solvent, and additives. The lithium salt is sodium hexafluorophosphate / lithium, the solvent is ethylene carbonate (EC), and the additive is dimethyl carbonate (DMC). The separator thickness is 30 μm, and the current collector is copper foil (12 μm thick).

[0060] A method for preparing sodium-ion / lithium-ion coin cells includes the following steps: Hard carbon anode material, acetylene black and binder are mixed in deionized water at a mass ratio of 96:1:3, homogenized, and the solid content is controlled at 50%. The mixture is coated on copper foil current collector, and then vacuum baked at 100~110℃ for 4~8h. After pressing and forming, the anode sheet is obtained by stamping. A button half-cell was assembled in an argon-filled glove box. The counter electrode was a sodium metal sheet, the separator was PE, and the electrolyte was 1 mol / L NaPF6 EC / DMC (Vol 1:1). The counter electrode was a lithium metal sheet, and the electrolyte was 1 mol / L LiPF6 EC / DMC (Vol 1:1).

[0061] The obtained coin cells were subjected to charge-discharge tests (the testing equipment for the coin cells was the LAND battery testing system of Wuhan Landian Electronics Co., Ltd.). The counter electrode was a sodium metal sheet. The test procedure was 0.1C DC to 0V, 0V CV 10uA, Rest 10min, 0.1C CC to 2V to obtain the first reversible capacity and efficiency of the hard carbon anode material.

[0062] The counter electrode is a lithium metal sheet. The test procedure is 0.2C DC to 0V, 0.05C DC to 0V, 0V CV 50uA, 0.01C DC to 0V, 0V CV 20uA, Rest for 10min, 0.2C CC to 2V, to obtain the first reversible capacity and efficiency of the hard carbon anode material.

[0063] Table 4. Electrochemical performance of the deashed hard carbon materials obtained in Examples 1-11 and Comparative Example 17

[0064] As shown in Table 4, the reversible specific capacity of sodium-ion coin cells made from the deashed hard carbon material prepared in this invention is 314~350mAh / g, and the initial efficiency is 92~93.9%. The reversible specific capacity of lithium-ion coin cells is 385mAh / g, and the initial efficiency is 86.6%.

[0065] As can be seen from Examples 1 to 3 in Tables 2 to 4, under the same experimental conditions, Comparative Example 1 did not add any deashing additives, and the ash content of the finished product was very high. The content of elements such as Ca, Mg, Al, Si, and Na in the finished product was very high, while the fixed carbon content was very low. This ash content provided mass but could not provide capacity. Therefore, the reversible specific capacity of the finished product in Comparative Example 1 was very low and could not be used commercially.

[0066] As can be seen from Examples 4-7 in Tables 2-4, under the same experimental conditions, the amount of deashing additive added in Comparative Examples 2 and 3 was either too little or too much. Adding too much deashing additive resulted in the generation of more NH3 and strongly acidic gases, leading to a more significant improvement in deashing and reversible specific capacity. However, excessive additive production, accompanied by excessive NH3 generation, resulted in a less pronounced effect on pore size distribution control and a greater impact on surface area, significantly reducing the initial efficiency. Furthermore, the excessive acidic gases generated caused greater corrosion to the equipment, placed higher demands on the equipment, and drastically increased costs. Conversely, adding too little deashing additive resulted in less NH3 and acidic gases generated during the high-temperature deashing process, indicating a significantly higher ash content, poorer deashing effect, and a weaker effect on pore size control of the carbon material, thus substantially reducing the reversible specific capacity.

[0067] As can be seen from Examples 1 in Tables 2-4, under the same experimental conditions, the median particle size of Comparative Examples 4 and 5 has a significant impact on the finished product. A median particle size that is too small leads to increased surface defects, significantly increasing the specific surface area of ​​the finished product, reducing the coulombic efficiency of the material, and also reducing the stability of the prepared slurry, which is detrimental to the slurry processing of secondary batteries. A median particle size that is too large will cause particle scratches during the coating and rolling processes of the secondary battery cells, affecting the processing performance of the electrode sheets. Simultaneously, a particle size that is too large will increase the charge transfer resistance of lithium ions or sodium ions on the negative electrode surface and increase the diffusion path within the bulk phase of the material during the charging and discharging process of the prepared lithium / sodium secondary battery, reducing the solid-phase transport rate and thus significantly reducing the rate performance.

[0068] As can be seen from Examples 1 in Tables 2-4, under the same experimental conditions, the high-temperature deashing and carbonization temperatures in Comparative Examples 6 and 7 have a significant impact on the final product. Lower temperatures result in less effective deashing and capacity improvement, more surface defects, and a larger specific surface area in the prepared carbon material. This leads to the formation of a large amount of SEI film on the material surface during the first cycle, causing irreversible capacity loss and a decrease in initial efficiency. Excessively high temperatures promote over-graphitization of the hard carbon material, negatively impacting specific capacity and lithium / sodium ion diffusion barriers. Therefore, excessively high temperatures can lead to a decrease in initial efficiency and specific capacity, and a significant reduction in rate performance. Furthermore, they increase energy consumption and cost. To obtain ideal high-performance hard carbon anode materials, carbonization conditions should be controlled within a reasonable range.

[0069] The hard carbon anode material provided by this invention can significantly improve the reversible specific capacity of hard carbon while deashing or purifying it.

[0070] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A high-performance hard carbon material, characterized in that: The hard carbon material satisfies the following formula: Wherein, D is the median particle size of the hard carbon material, in μm; T is the true density of the hard carbon material, in g / cm³. P is the compacted density of the hard carbon material, in g / cm³. B represents the specific surface area of ​​the hard carbon material, in square meters per g. C represents the reversible specific capacity of a coin cell assembled using the hard carbon material as the negative electrode, expressed in mAh / g. E represents the initial coulombic efficiency of the coin cell, expressed in % (%). A refers to the voltage of the coin cell battery at 0.1V (relative to Na) during the second week of charge and discharge. + The percentage of sodium intercalation capacity above (Na) out of the total sodium intercalation capacity, expressed in units of %.

2. The high-performance hard carbon material according to claim 1, characterized in that, The hard carbon material satisfies at least one of the following conditions (i) to (vii): (i) The percentage of sodium intercalation specific capacity above 0.1V during the second week of charging and discharging meets the following requirement: 20% ≤ A ≤ 38%; (ii) The reversible specific capacity satisfies: 270mAh / g≤C≤360mAh / g; (iii) The initial Coulomb efficiency satisfies: 86% ≤ E ≤ 94%; (iv) The true density satisfies: 1.95 g / cm³ ≤ T ≤ 2.15 g / cm³; (v) The median particle size satisfies: 1.5 μm ≤ D ≤ 10 μm; (vi) The compacted density of the powder satisfies: 0.85 g / cm³ ≤ P ≤ 1.2 g / cm³; (vii) The specific surface area satisfies: 2.0 m² / g ≤ B ≤ 10.0 m² / g.

3. The high-performance hard carbon material according to claim 1, characterized in that, In the Raman spectrum of the high-performance hard carbon material, the peak intensity ratio ID / IG of the D peak to the G peak is 0.95-1.

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4. A method for preparing hard carbon material, characterized in that, The preparation method for the high-performance hard carbon material according to any one of claims 1 to 3 is as follows: The carbon precursor, pore-forming agent and crosslinking agent are mixed in a preset ratio and pre-oxidized under an oxidizing atmosphere to obtain a stabilized precursor. The stabilized precursor was subjected to micron-sized pulverization, with the median particle size D50 controlled between 3 μm and 10 μm. The pulverized product was placed in a mixed atmosphere of halogen gas and inert gas and subjected to vapor phase etching at high temperature for a preset time to remove unstable amorphous carbon impurities. The mixture is placed in a high-pressure reactor and subjected to gradient pressure carbonization under an inert atmosphere; the gradient pressure carbonization includes a first heating stage and a second isothermal stage.

5. The method for preparing hard carbon material according to claim 4, characterized in that, The steps of the first heating stage include: The temperature is increased from room temperature to 500℃-800℃ at a rate of 0.5℃ / min-5℃ / min, while the pressure inside the vessel is controlled to increase linearly with temperature to 2MPa-10 MPa.

6. The method for preparing hard carbon material according to claim 4, characterized in that, The steps of the second isothermal stage include: The material is kept at 1100℃-1500℃ for 1h-6h, while the pressure inside the reactor is initially maintained at 5MPa-15 MPa for 0.5h-2h, and then depressurized to atmospheric pressure at a rate of 0.1MPa / min-0.5 MPa / min to obtain hard carbon material.

7. The method for preparing hard carbon material according to claim 4, characterized in that, The preset ratio is that the carbon precursor, pore-forming agent, and crosslinking agent are mixed at a mass ratio of 100:(5-20):(2-10); the high temperature condition is 600℃-900℃; and the preset time is 10min-60min.

8. The method for preparing hard carbon material according to claim 4, characterized in that, The crosslinking agent is one or more of the following: aldehydes, organic acids, epoxy compounds, and metal coordination crosslinking agents. Crosslinking agents include furfural, glutaraldehyde, citric acid, phytic acid, pyromellitic dianhydride, ethylene glycol diglycidyl ether, trimethylolpropane triglycidyl ether, boric acid, lithium metaborate, organoborides, etc.

9. The method for preparing hard carbon material according to claim 4, characterized in that, The pore-forming agent can be one or a combination of two or more of the following: divinylbenzene, azodicarbonamide, benzoic acid, polymethyl methacrylate microspheres, polyethylene oxide, polyvinyl butyral, zinc citrate, and zinc acetate.

10. The application of the high-performance hard carbon material according to any one of claims 1 to 3 or the high-performance hard carbon material prepared by the preparation method according to any one of claims 4 to 9 as a negative electrode material for secondary batteries.

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