Hard carbon negative electrode material and preparation method and application thereof

Abstract

The invention discloses a hard carbon negative electrode material and a preparation method and application thereof, the preparation method comprises the following steps: mixing a phenol source, formaldehyde, a solvent and a basic catalyst, and carrying out catalytic reaction on the phenol source and the formaldehyde under an alkaline condition to form phenolic resin to obtain a phenolic resin solution; mixing a metal salt and a phenolic resin solution to obtain a phenolic resin / metal salt precursor solution; curing the phenolic resin / metal salt precursor solution in an air atmosphere, cooling to room temperature to obtain a phenolic resin / metal salt cured material, crushing, grinding and sieving to obtain phenolic resin / metal salt cured material fine powder; and carbonizing the phenolic resin / metal salt cured material fine powder in a nitrogen or inert gas atmosphere, and cooling to room temperature to obtain the hard carbon negative electrode material. The preparation method disclosed by the invention is simple and efficient, the problems of non-uniform distribution of metal particles and weak interface bonding force are avoided, and the buffer effect of hard carbon and the capacity advantage of metal elements are fully exerted.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a hard carbon anode material, its preparation method, and its application. Background Technology

[0002] With the rapid growth of global energy demand and the increasing depletion of fossil fuels, the development and utilization of renewable energy has become a focus of attention in society today. Among these, rechargeable batteries, as efficient energy storage and conversion devices, play a crucial role in electric vehicles, portable electronic devices, and large-scale energy storage systems. Lithium-ion batteries, as the mainstream rechargeable battery technology, have been widely applied in various fields. However, the abundance of lithium resources in the Earth's crust is low (approximately 0.0065%) and their uneven distribution has led to a continuous rise in lithium prices, limiting their further application in large-scale energy storage. In contrast, sodium resources have an abundance of up to 2.74% in the Earth's crust, are widely distributed, and are inexpensive. Therefore, sodium-ion batteries are considered a powerful alternative to lithium-ion batteries and have broad development prospects. The working principle of sodium-ion batteries is similar to that of lithium-ion batteries, mainly composed of positive electrode materials, negative electrode materials, electrolytes, and separators. Among these, the negative electrode material is a key factor affecting the capacity, energy density, cycle stability, and coulombic efficiency of sodium-ion batteries. Currently, sodium-ion battery negative electrode materials mainly include carbon-based materials, alloy materials, conversion materials, and intercalation materials. Hard carbon, as a typical carbon-based material, possesses a disordered carbon layer structure, providing abundant sodium ion intercalation sites. It also exhibits good structural stability and low cost, demonstrating good cycle performance and a low voltage plateau (approximately 0.1 V vs. Na / Na) in sodium-ion batteries. + Hard carbon is one of the ideal choices for anode materials in commercial sodium-ion batteries. However, for hard carbon to achieve commercial application and become a high-performance hard carbon anode, the type of precursor it relies on for preparation is crucial. Hard carbon precursors are categorized into biomass-based hard carbon, fossil fuel-based hard carbon, and resin-based hard carbon. Among these, resin-based hard carbon exhibits a higher practical specific capacity (300-340 mAh g⁻¹). -1 The actual specific capacity of biomass-based hard carbon and fossil fuel-based hard carbon is relatively low (270-310 mAh g⁻¹). -1 However, resin-based hard carbon batteries suffer from problems such as uneven carbon layer stacking and long ion diffusion paths, resulting in battery energy density not yet meeting the ideal requirements for large-scale energy storage.

[0003] To theoretically improve the energy density of sodium-ion batteries based on resin-based hard carbon and enhance the potential of hard carbon anodes in practical applications, it is urgent to regulate the structure and composition of resin-based hard carbon anode materials. High-capacity alloying metals, such as tin (Sn), bismuth (Bi), and antimony (Sb), have theoretical specific capacities far exceeding those of hard carbon (e.g., Sn's theoretical capacity can reach 847 mAh / g, and Bi's is 385 mAh / g). These materials can form alloys with sodium (e.g., Na...). 15 High-capacity sodium storage can be achieved using metal compounds such as Sn4, Na3Bi, and Na3Sb. However, metal compounds exhibit severe volume expansion during charge and discharge, leading to structural collapse, electrode pulverization, and repeated rupture and reconstruction of the SEI layer at the solid electrolyte interface. This results in rapid capacity decay and poor cycle stability.

[0004] In summary, existing technologies still have many shortcomings in improving the performance of sodium-ion batteries prepared from hard carbon anodes, and cannot achieve a sodium-ion battery that balances high capacity and cycle stability. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a hard carbon anode material.

[0006] Another object of the present invention is to provide a method for preparing the above-mentioned hard carbon anode material.

[0007] Another object of the present invention is to provide the application of the above-mentioned hard carbon anode material in sodium-ion batteries.

[0008] The objective of this invention is achieved through the following technical solution.

[0009] A method for preparing a hard carbon anode material includes the following steps:

[0010] S1, phenol source, formaldehyde, solvent and alkaline catalyst are mixed to catalyze the reaction of phenol source and formaldehyde under alkaline conditions (pH=8~11) to form phenolic resin, and a phenolic resin solution is obtained. The ratio of phenol source, formaldehyde and alkaline catalyst by mass is 10:20:(0.87~1).

[0011] In S1, the phenolic resin content in the phenolic resin solution is 10 wt%.

[0012] In S1, the phenol source is one or a mixture of several of phenol, resorcinol, and phloroglucinol.

[0013] In S1, the alkaline catalyst is one or a mixture of several of sodium carbonate (powder), ammonia, and sodium hydroxide (granules).

[0014] In S1, the solvent is anhydrous ethanol.

[0015] In S1, the ratio of phenol source to solvent by mass is 1:15.

[0016] In S1, the catalytic reaction is carried out at room temperature for 1 to 12 hours.

[0017] S2, mix the metal salt and phenolic resin solution until homogeneous to obtain a phenolic resin / metal salt precursor solution. The ratio of phenolic resin to metal salt in the phenolic resin solution is (5~10):1 by molar amount. The metal salt is at least one of zinc chloride, bismuth chloride, tin tetrachloride and antimony trichloride.

[0018] In S2, the metal salt (particles) and phenolic resin solution are mixed at room temperature and stirred until homogeneous. The stirring time is 1~12h.

[0019] S3. In an air atmosphere, the phenolic resin / metal salt precursor solution is cured at 150~250℃ for 2~24h (so that the phenolic resin is cured and the metal salt is cured in situ in the phenolic resin at the same time). After cooling to room temperature, the phenolic resin / metal salt cured material is obtained. The phenolic resin / metal salt cured material is crushed, ground and sieved to obtain fine powder of phenolic resin / metal salt cured material.

[0020] In S3, ball milling is used for grinding, and the ball-to-material ratio is (5~20):1.

[0021] In S3, the particle size of the fine powder of phenolic resin / metal salt curing agent is 2~10 μm.

[0022] In S3, the heating rate to 150~250℃ is 5~15℃ / min.

[0023] S4. Under a nitrogen or inert gas atmosphere, the fine powder of the phenolic resin / metal salt curing agent is carbonized at 1350~1450℃ for 1~8 h and then cooled to room temperature to obtain a hard carbon anode material.

[0024] In S4, the heating rate to 1350~1450℃ is 1~5℃ / min.

[0025] In S4, cooling to room temperature includes: first reducing the temperature to 500-700°C at a rate of 3-5°C / min, and then cooling it to room temperature along with the furnace.

[0026] The hard carbon anode material obtained by the above preparation method.

[0027] A sodium-ion battery, comprising: the hard carbon anode material.

[0028] Among the above technical solutions, the sodium-ion battery has the highest first-charge specific capacity of 392.92 mAh / g and a first-charge coulombic efficiency of more than 91.0%.

[0029] Application of hard carbon anode materials in improving the ramp capacity of sodium-ion batteries.

[0030] Among the above technical solutions, the sodium-ion battery has the highest ramp capacity of 134.18 mAh / g.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) This invention uses phenolic resin as a hard carbon precursor, introduces metal salts into a system containing phenolic resin, and successively cures them in situ in air and carbonizes them at high temperature in a nitrogen or inert gas atmosphere to achieve highly uniform dispersion of the metal salts in the hard carbon anode material. Compared with the physical mixing or mechanical alloying methods of the prior art, the preparation method of this invention is simple and efficient, avoids the problems of uneven metal particle distribution and weak interfacial bonding, enhances the synergistic effect between hard carbon and metal, and fully utilizes the buffering effect of hard carbon and the capacity advantage of metal elements.

[0033] (2) The sodium-ion battery prepared by the present invention has a first-cycle charge specific capacity of up to 392.92 mAh / g, which is much higher than the existing resin-based hard carbon of 300-340 mAh / g and biomass-based hard carbon / fossil fuel-based hard carbon of 270-310 mAh / g; and the first-cycle coulombic efficiency is greater than 91.0%, which reduces the irreversible capacity loss during the first charge and discharge process.

[0034] (3) As a flexible and porous carbon material, hard carbon anode material can effectively alleviate the volume expansion problem of metal compounds and inhibit repeated cracking of the SEI layer. This invention highly disperses metal salts in the hard carbon anode material, with the hard carbon acting as a buffer layer to absorb stress changes in metal particles during alloying / dealloying, maintaining the structural integrity of the hard carbon anode material and inhibiting the aggregation and shedding of metal particles. This enhances the sodium storage performance of the hard carbon anode material, thereby improving the cycle performance and coulombic efficiency of sodium-ion batteries. This provides a new approach for the development of high-energy-density sodium-ion batteries. Attached Figure Description

[0035] Figure 1 The XRD patterns of the hard carbon anode materials prepared in Example 4 and Comparative Example 3 are shown.

[0036] Figure 2 SEM image of the hard carbon anode material prepared in Comparative Example 3;

[0037] Figure 3 SEM image of the hard carbon anode material prepared in Example 4;

[0038] Figure 4The image shows the first charge-discharge test of a sodium-ion battery (CR2032 coin cell) prepared based on the hard carbon anode material of Example 1.

[0039] Figure 5 The image shows the first charge-discharge test results of a sodium-ion battery (CR2032 coin cell) prepared based on the hard carbon anode material of Example 2.

[0040] Figure 6 The image shows the first charge-discharge test results of a sodium-ion battery (CR2032 coin cell) prepared based on the hard carbon anode material of Example 3.

[0041] Figure 7 The image shows the first charge-discharge test of the sodium-ion battery (CR2032 coin cell) prepared based on the hard carbon anode material of Example 4.

[0042] Figure 8 The image shows the first charge-discharge test results of a sodium-ion battery (CR2032 coin cell) prepared based on the hard carbon anode material of Comparative Example 1.

[0043] Figure 9 The image shows the first charge-discharge test results of a sodium-ion battery (CR2032 coin cell) prepared based on the hard carbon anode material of Comparative Example 2.

[0044] Figure 10 The image shows the first charge-discharge test results of a sodium-ion battery (CR2032 coin cell) prepared based on the hard carbon anode material of Comparative Example 3.

[0045] Figure 11 The image shows the first charge-discharge test results of a sodium-ion battery (CR2032 coin cell) prepared based on the hard carbon anode material of Comparative Example 4.

[0046] Figure 12 The image shows the first charge-discharge test results of a sodium-ion battery (CR2032 coin cell) prepared based on the hard carbon anode material of Comparative Example 5.

[0047] Figure 13 The image shows the first charge-discharge test results of a sodium-ion battery (CR2032 coin cell) prepared based on the hard carbon anode material of Comparative Example 6.

[0048] Figure 14 The graph shows the rate performance test results of sodium-ion batteries (CR2032 coin cells) prepared based on the hard carbon anode materials of Example 4 and Comparative Example 3. Detailed Implementation

[0049] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0050] The raw material information involved in the following examples and comparative examples is as follows:

[0051]

[0052] Unless otherwise specified, the reagents, materials and instruments used in this invention are all conventional reagents, materials and instruments, and can be obtained commercially.

[0053] In the following embodiments, the sodium-ion battery (CR2032 coin cell) is assembled as follows: a hard carbon negative electrode is used as the working electrode, a sodium metal sheet is used as the counter electrode, a Whatman glass fiber membrane is used as the separator, and the electrolyte is NaPF6-DIGLYME electrolyte (NaPF6-DIGLYME). 6- The DIGLYME electrolyte consists of sodium hexafluorophosphate (electrolyte, NaPF6) and diethylene glycol dimethyl ether (solvent, DIGLYME), with a NaPF6 concentration of 1 mol / L (purchased from Suzhou Duoduo Chemical Technology Co., Ltd.). The electrolyte is then encapsulated in a glove box (where O2 and H2O content are both below 0.01 ppm) to obtain a CR2032 coin cell.

[0054] The preparation method of the hard carbon anode sheet includes: mixing hard carbon anode material, sodium carboxymethyl cellulose (CMCNa) aqueous solution, carbon nanotubes, and styrene-butadiene rubber (SBR) solution, stirring for 6 h until homogeneous to obtain a slurry. The ratio of CMCNa in the hard carbon anode material, sodium carboxymethyl cellulose (CMCNa) aqueous solution, carbon nanotubes, and SBR in the SBR solution is 92.5:1.5:3:3 by mass, wherein the concentration of CMCNa in the CMCNa aqueous solution is 1 wt%, and the concentration of SBR in the SBR solution is 40 wt%. The slurry is uniformly coated onto copper foil using a scraper, dried in a 120°C drying oven for 6 h, rolled and punched into a disc with a diameter of 12 mm to obtain the hard carbon anode sheet. The hard carbon anode material is one of the hard carbon anode materials prepared in Examples 1-4 and Comparative Examples 1-6, and a corresponding sodium-ion battery is obtained based on each hard carbon anode material.

[0055] In the following examples, the electrochemical performance of CR2032 coin cells was tested using a Blue Battery Tester, with a voltage window of 0.005~2 V (vs. Na / Na). + The test temperature was room temperature. In this invention, 1C is defined as 300 mA / g.

[0056] Examples 1-4

[0057] A method for preparing a hard carbon anode material (resin-based hard carbon anode material) includes the following steps:

[0058] S1, phenol source, formaldehyde, solvent and alkaline catalyst are mixed, and phenol source and formaldehyde are catalytically reacted at room temperature and alkaline conditions (pH=9) for 2 hours to form phenolic resin (catalytic reaction is carried out under stirring conditions, stirring speed is 500 r / min), to obtain phenolic resin solution (the content of phenolic resin in phenolic resin solution is 10 wt%), the ratio of phenol source, formaldehyde and alkaline catalyst by mass is 10:20:1, the ratio of phenol source and solvent by mass is 1:15, the phenol source is resorcinol, the alkaline catalyst is sodium hydroxide (granules), and the solvent is anhydrous ethanol;

[0059] S2, mix the metal salt and phenolic resin solution, stir at 500 r / min for 2 h at room temperature until homogeneous, and obtain phenolic resin / metal salt precursor solution. The ratio of phenolic resin to metal salt in the phenolic resin solution is 5:1 by molar amount, and the metal salt is X (X is shown in Table 1).

[0060] S3. Under an air atmosphere, the phenolic resin / metal salt precursor solution is placed in an oven and heated to 180°C at a rate of 10°C / min and cured at 180°C for 12 hours (so that the metal salt is cured in situ in the phenolic resin). After cooling to room temperature, the phenolic resin / metal salt cured material is obtained. The phenolic resin / metal salt cured material is crushed and ground (dry ball milling is used, the ball-to-material ratio of dry ball milling is 20:1, and the ball milling speed is 1200 r / min for 30 minutes). After sieving, fine powder of phenolic resin / metal salt cured material with a particle size of 2~10 μm is obtained.

[0061] S4. Under an argon atmosphere, fine powder of phenolic resin / metal salt curing agent is placed in a tube furnace, heated to 1400°C at a rate of 2°C / min, and carbonized at 1400°C for 4 hours. After cooling to room temperature, a hard carbon anode material is obtained. The cooling to room temperature includes: first reducing the temperature to 600°C at a rate of 4°C / min, and then cooling to room temperature with the furnace.

[0062] Table 1

[0063]

[0064] Comparative Example 1

[0065] A method for preparing a hard carbon anode material is basically the same as in Example 4, except that "heating to 1400°C at a rate of 2°C / min and carbonizing at 1400°C for 4 hours" is replaced with "heating to 1300°C at a rate of 2°C / min and carbonizing at 1300°C for 4 hours".

[0066] Comparative Example 2

[0067] A method for preparing a hard carbon anode material is basically the same as in Example 4, except that "heating to 1400°C at a rate of 2°C / min and carbonizing at 1400°C for 4 hours" is replaced with "heating to 1500°C at a rate of 2°C / min and carbonizing at 1500°C for 4 hours".

[0068] Comparative Example 3

[0069] A method for preparing a hard carbon anode material includes the following steps:

[0070] S1, phenol source, formaldehyde, solvent and alkaline catalyst are mixed, and phenol source and formaldehyde are catalytically reacted at room temperature and alkaline conditions (pH=9) for 2 hours to form phenolic resin (catalytic reaction is carried out under stirring conditions, stirring speed is 500 r / min), to obtain phenolic resin solution (the content of phenolic resin in phenolic resin solution is 10 wt%), the ratio of phenol source, formaldehyde and alkaline catalyst by mass is 10:20:1, the ratio of phenol source and solvent by mass is 1:15, the phenol source is resorcinol, the alkaline catalyst is sodium hydroxide (granules), and the solvent is anhydrous ethanol;

[0071] S2, In an air atmosphere, the phenolic resin solution is placed in an oven, heated to 180°C at a rate of 10°C / min, and cured at 180°C for 12 hours. After cooling to room temperature, phenolic resin cured material is obtained. The phenolic resin cured material is crushed, ground (dry ball milling is used, the ball-to-material ratio is 20:1, and the ball milling speed is 1200 r / min for 30 minutes), and sieved to obtain fine powder of phenolic resin cured material with a particle size of 2~10 μm.

[0072] S3. Under an argon atmosphere, fine powder of phenolic resin curing material is placed in a tube furnace, heated to 1400°C at a rate of 2°C / min, and carbonized at 1400°C for 4 hours. After cooling to room temperature, a hard carbon anode material is obtained. The cooling to room temperature includes: first reducing the temperature to 600°C at a rate of 4°C / min, and then cooling to room temperature with the furnace.

[0073] Comparative Example 4

[0074] A method for preparing a hard carbon anode material is basically the same as that of Comparative Example 3, except that "heating to 1400℃ at a rate of 2℃ / min and carbonizing at 1400℃ for 4h" is replaced with "heating to 1300℃ at a rate of 2℃ / min and carbonizing at 1300℃ for 4h".

[0075] Comparative Example 5

[0076] A method for preparing a hard carbon anode material is basically the same as that of Comparative Example 3, except that "heating to 1400℃ at a rate of 2℃ / min and carbonizing at 1400℃ for 4h" is replaced with "heating to 1500℃ at a rate of 2℃ / min and carbonizing at 1500℃ for 4h".

[0077] Comparative Example 6

[0078] A method for preparing a hard carbon anode material is basically the same as that in Example 4, except for step S3. Step S3 in Comparative Example 6 is as follows: Under an argon atmosphere, a phenolic resin / metal salt precursor solution is placed in an oven and heated to 180°C at a rate of 10°C / min and cured at 180°C for 12 hours (so that the metal salt is cured in situ in the phenolic resin). After cooling to room temperature, a phenolic resin / metal salt cured material is obtained. The phenolic resin / metal salt cured material is crushed, ground (dry ball milling is used, the ball-to-material ratio is 20:1, and the ball milling speed is 1200 r / min for 30 minutes), and sieved to obtain fine powder of phenolic resin / metal salt cured material with a particle size of 2~10 μm.

[0079] Figure 1 The images show the XRD patterns of the hard carbon anode materials prepared in Example 4 and Comparative Example 3. Figure 1 It can be seen that the characteristic peaks shown in Example 4 can be matched with the standard card PDF#86-2264 of Sn, confirming that Sn was successfully introduced into the hard carbon anode material prepared in Example 4.

[0080] Figure 2 This is a SEM image of the hard carbon anode material prepared in Comparative Example 3. Figure 3 The image shows a SEM image of the hard carbon anode material prepared in Example 4. Figure 2 and Figure 3 It can be seen that the hard carbon anode materials prepared in Example 4 and Comparative Example 3 are all in bulk form, and the introduction of Sn did not affect the morphology of the hard carbon anode materials.

[0081] At 0.1C, charge-discharge tests were conducted on sodium-ion batteries (CR2032 coin cells) prepared based on the hard carbon anode materials of Examples 1-4 and Comparative Examples 1-6. The first charge-discharge test diagrams obtained are shown below. Figures 4-13 As shown in Table 2. (in Figures 4-13 In this context, "first efficiency" refers to the efficiency of the first round of Coulombs.

[0082] Table 2

[0083]

[0084] Examples 1-4 and Comparative Examples 3-5 were compared to verify the effect of introducing metal salts on the performance of sodium-ion batteries. A comparison between Example 4 and Comparative Example 3 showed that the sodium-ion battery prepared from the hard carbon anode material of Example 4 had a first-cycle charge specific capacity of 392.92 mAh g⁻¹. -1 The discharge specific capacity is 430.36 mAh g. -1 The sodium-ion battery prepared from the hard carbon anode material of Comparative Example 3 had a first-cycle charge specific capacity of 331.59 mAh g⁻¹. -1 The discharge specific capacity is 361.60 mAhg. -1 This directly verifies the mechanism by which the metal salt (tin tetrachloride) contributes high specific capacity by forming a Na-Sn alloy phase, while the hard carbon anode material buffers the volume expansion and ensures the stability of the structure.

[0085] Examples 1, 2, 3, and 4 were compared to verify the effect of different metal salts on the performance of sodium-ion batteries. Table 2 shows that the sodium-ion battery prepared with the hard carbon anode material in Example 4 not only had the highest charge and discharge specific capacities but also a high ramp capacity. A high ramp capacity typically represents high rate performance. The high ramp capacity in Example 4 may be due to the more uniform dispersion of Sn nanoparticles in the hard carbon during carbonization, which improves the ramp capacity of the sodium-ion battery. While the introduction of other metal salts also improved the performance of the sodium-ion battery, the improvement in ramp capacity was relatively small (the ramp capacity of the sodium-ion battery prepared with the hard carbon anode material in Example 1 was 111.53 mAh g). -1 The sodium-ion battery prepared from the hard carbon anode material of Example 2 has a ramp capacity of 109.25 mAh g. -1 The sodium-ion battery prepared from the hard carbon anode material of Example 3 has a ramp capacity of 119.77 mAh g. -1 This indicates that the alloying behavior of Sn more effectively improves the first-cycle charge specific capacity under low-voltage conditions. In terms of coulombic efficiency, the sodium-ion battery prepared with the hard carbon anode material of Example 2 exhibits a slightly higher coulombic efficiency than those of Examples 1, 3, and 4. This may be attributed to the advantage of the metal salt (antimony trichloride) in terms of interfacial stability through the formed Na3Sb alloy phase, which reduces SEI layer rupture. Overall, the sodium-ion battery prepared with the hard carbon anode material of Example 4 demonstrates the best performance.

[0086] Comparative Examples 1, 2, and 4 were compared to verify the effect of carbonization temperature on the performance of sodium-ion batteries. Table 2 shows that the carbonization temperature for the hard carbon anode material in Comparative Example 1 was 1300°C, and the first-cycle specific capacity of the sodium-ion battery prepared from this material was only 369.26 mAh g⁻¹. -1This indicates that lower temperatures may lead to incomplete carbonization and insufficient metal dispersion. The carbonization temperature for the hard carbon anode material in Comparative Example 2 was 1500°C, and the first-cycle specific capacity of the sodium-ion battery prepared from the hard carbon anode material in Comparative Example 2 was only 355.85 mAh g⁻¹. -1 This indicates that excessively high temperatures may induce metal particle agglomeration or excessive graphitization of the hard carbon structure, weakening the buffering effect and sodium storage sites. Similarly, in Comparative Examples 3-5, the carbonization temperature for preparing the hard carbon anode material in Comparative Example 3 was 1400°C, resulting in sodium-ion batteries prepared from the hard carbon anode material of Comparative Example 3 exhibiting superior performance compared to Comparative Examples 4 and 5. This clearly demonstrates the influence of carbonization temperature on hard carbon anode materials.

[0087] Furthermore, the curing atmosphere also has a significant impact on the hard carbon anode material. Example 4 and Comparative Example 6 used the same carbonization temperature, but S3 in Example 4 was cured in an air atmosphere, while S3 in Comparative Example 6 was cured in an argon atmosphere. Comparing the test data of sodium-ion batteries prepared from the hard carbon anode materials of Example 4 and Comparative Example 6, it can be seen that the first-cycle charge specific capacity of the sodium-ion battery prepared from the hard carbon anode material of Example 4 is 392.92 mAh g. -1 This is significantly higher than the 317.87 mAh g⁻¹ of the sodium-ion battery prepared using the hard carbon anode material of Comparative Example 6. -1 This indicates that curing in an air atmosphere may introduce oxygen-containing functional groups into the phenolic resin precursor. These oxygen-containing functional groups contribute to the formation of richer pore structures or defect sites during subsequent high-temperature carbonization, thereby providing more sodium ion insertion sites and improving the reversible specific capacity of the material. This demonstrates the importance of air-atmosphere curing in S3 of this invention for preparing high-capacity hard carbon matrices.

[0088] At current densities of 0.1 C, 0.2 C, 0.3 C, 0.5 C, 1 C, 2 C, 3 C, 5 C, and 10 C, the sodium-ion batteries prepared from the hard carbon anode materials of Example 4 and Comparative Example 3 were subjected to charge specific capacity tests (5 cycles at each current density). The rate performance graphs are shown below. Figure 14 As shown, by Figure 14 It can be seen that at current densities of 0.1 C, 0.2 C, 0.3 C, 0.5 C, 1 C, 2 C, 3 C, 5 C, and 10 C, the specific capacity of the sodium-ion battery prepared from the hard carbon anode material of Example 4 is much higher than that of Comparative Example 3, proving that the high ramp capacity brings good rate performance. Furthermore, although the specific capacity decreases with increasing current density at current densities of 0.1 C, 0.2 C, 0.3 C, 0.5 C, 1 C, 2 C, 3 C, 5 C, and 10 C, it can still reach the initial capacity when returning to 0.1 C.

[0089] In general, introducing metal salts during the preparation of hard carbon anode materials and curing them in air to allow the metal salts to be in situ solidified in phenolic resin can effectively improve the charge-discharge specific capacity of sodium-ion batteries, providing a basis for the design of high-energy-density sodium-ion battery anodes.

[0090] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing a hard carbon anode material, characterized in that, Includes the following steps: S1, phenol source, formaldehyde, solvent and alkaline catalyst are mixed, phenol source and formaldehyde react under alkaline conditions to form phenolic resin, and phenolic resin solution is obtained. By mass parts, the ratio of phenol source, formaldehyde and alkaline catalyst is 10:20:(0.87~1). S2, mix the metal salt and phenolic resin solution until homogeneous to obtain a phenolic resin / metal salt precursor solution. The ratio of phenolic resin to metal salt in the phenolic resin solution is (5~10):1 by molar amount. The metal salt is at least one of zinc chloride, bismuth chloride, tin tetrachloride and antimony trichloride. S3. In an air atmosphere, the phenolic resin / metal salt precursor solution is cured at 150~250℃ for 2~24h, cooled to room temperature to obtain phenolic resin / metal salt cured material. The phenolic resin / metal salt cured material is crushed, ground, and sieved to obtain fine powder of phenolic resin / metal salt cured material. S4. Under a nitrogen or inert gas atmosphere, the fine powder of the phenolic resin / metal salt curing agent is carbonized at 1350~1450℃ for 1~8 h and then cooled to room temperature to obtain a hard carbon anode material.

2. The preparation method according to claim 1, characterized in that, In S1, the phenol source is one or a mixture of several of phenol, resorcinol, and phloroglucinol.

3. The preparation method according to claim 1, characterized in that, In S1, the alkaline catalyst is one or a mixture of sodium carbonate, ammonia, and sodium hydroxide.

4. The preparation method according to claim 1, characterized in that, In S1, the catalytic reaction is carried out at room temperature for 1 to 12 hours.

5. The preparation method according to claim 1, characterized in that, In S1, the solvent is anhydrous ethanol.

6. The hard carbon anode material obtained by the preparation method according to any one of claims 1 to 5.

7. A sodium-ion battery, characterized in that, include: The hard carbon anode material according to claim 6.

8. The sodium-ion battery according to claim 7, characterized in that, The sodium-ion battery has a maximum first-charge specific capacity of 392.92 mAh / g and a first-charge coulombic efficiency of over 91.0%.

9. The application of the hard carbon anode material as described in claim 6 in improving the ramp capacity of sodium-ion batteries.

10. The application according to claim 9, characterized in that, The highest ramp capacity of sodium-ion batteries is 134.18 mAh / g.

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