Inorganic salt-assisted hard carbon materials, their preparation and application, and negative electrode sheets in sodium-ion batteries.

Abstract

This invention belongs to the field of sodium-ion battery anode material preparation technology, specifically relating to a method for preparing and applying an inorganic salt-assisted hard carbon anode material. This invention uses inexpensive biomass powder as raw material, mixing the biomass powder with inorganic salts in a solid phase, and then performing a two-step heat treatment in a tube furnace under an inert atmosphere to finally obtain the sodium-ion battery hard carbon anode material. The preparation method of the hard carbon anode material provided by this invention is low-cost, simple, and suitable for large-scale production. The obtained hard carbon anode material exhibits good electrochemical performance, excellent cycle stability, and high specific capacity when used in sodium-ion batteries.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to the preparation and application of inorganic salt-assisted hard carbon materials. Background Technology

[0002] Lithium-ion batteries are widely used in industries such as electric vehicles due to their high energy density and high power density. However, with increasing demand for lithium-ion batteries, their further development is constrained by a series of key issues such as lithium resource reserves and cost. Sodium metal is abundant in the Earth's crust, inexpensive, and has similar physical and chemical properties to lithium; moreover, sodium-ion batteries possess natural advantages such as abundant resources, low cost, and high safety, making them a potential alternative to lithium-ion batteries as a new type of energy storage device.

[0003] Although sodium-ion batteries offer significant advantages, sodium ions have a larger radius and volume than lithium ions, and thermodynamically, sodium ions struggle to form stable low-order intercalation compounds with traditional graphite anodes. Therefore, graphite anodes are unsuitable as anode materials for sodium-ion batteries. The insertion and extraction of sodium ions within electrode materials demands higher overall material performance and structural stability. Amorphous hard carbon materials, composed of disordered stacks of small-layer graphite, possess advantages such as numerous defects, abundant pore structure, low cost, high storage capacity, low operating potential, and good safety. They can provide more storage sites for sodium ions, facilitating their diffusion / storage and insertion / extraction within the structure. Therefore, hard carbon shows great promise as anode materials for sodium-ion batteries.

[0004] Carbon materials prepared by directly carbonizing precursor powder at high temperatures exhibit small interlayer spacing and limited pore volume, and the yield is low, which is detrimental to sodium-ion storage and the commercial application of sodium-ion batteries. Existing technologies using inorganic salt-assisted methods can not only increase the yield of carbon materials but also result in carbon materials with a large specific surface area, abundant porosity, and fewer defects. However, these structures severely affect the first-cycle coulombic efficiency and charge-discharge specific capacity of sodium-ion batteries. This invention uses biomass powder as a hard carbon precursor. Low-temperature pre-carbonization and inorganic salt-assisted methods increase the interlayer spacing and defect structure of the carbon material. High-temperature further carbonization increases graphite domains and reduces defect structure. The bonding of heteroatoms in the biomass powder with carbon maintains a large interlayer spacing. When this hard carbon material is used as an anode material for sodium-ion batteries, it exhibits high storage capacity and cycle performance. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a method for preparing hard carbon materials based on inorganic salts. Using biomass powder as a hard carbon precursor and inorganic salts as auxiliary agents, a hard carbon anode material is prepared through a two-step pyrolysis method. Low-temperature heat treatment and the assistance of inorganic salts can prepare a pre-carbonized sample with a large number of pores and defects. Further high-temperature heat treatment can further enhance the graphitization degree of the pre-carbonized sample, giving it a high content of graphite domains and transforming a large number of pores into a closed-pore structure. Furthermore, biomass contains various heteroatoms, which can be introduced in situ into the carbon framework, giving it excellent conductivity and electrochemical performance. Sodium-ion batteries prepared using this as an anode material have high storage capacity and excellent cycle stability.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] The first aspect of this invention provides a method for preparing inorganic salt-assisted hard carbon materials, comprising the following steps:

[0008] (1) After crushing the biomass raw material, it is sieved, acid-washed and dried to obtain biomass powder;

[0009] (2) The biomass powder prepared in step (1) is mixed with inorganic salt by solid-phase ball milling to obtain pretreated biomass precursor powder.

[0010] (3) The pretreated biomass precursor powder prepared in step (2) is placed in a tube furnace protected by an inert atmosphere for pre-carbonization, and the temperature is lowered to obtain the pre-carbonized product.

[0011] (4) After crushing and washing the pre-carbonized product obtained in step (3), it is subjected to high-temperature heat treatment in an inert atmosphere to finally obtain the sodium-ion battery hard carbon anode material.

[0012] Furthermore, in step (1), the biomass raw material is selected from one or more of coconut shells, bamboo, straw, and wood.

[0013] Furthermore, in step (1), the solution used for acid washing of biomass raw materials is a mixed solution of hydrochloric acid, nitric acid and deionized water, wherein the volume ratio of hydrochloric acid, nitric acid and deionized water in the mixed solution is 1-15:1-15:70-100.

[0014] Furthermore, in step (1), the biomass raw material is dried by freeze drying or room temperature drying.

[0015] Further, in step (1), the inorganic salt is one or more of NaCl, KCl, LiCl, ZnCl2, Na2CO3 and / or K2CO3.

[0016] Furthermore, in step (2), the mass ratio of biomass powder to inorganic salt is 1:(1-15).

[0017] Furthermore, in step (3), the inert atmosphere used for the pretreated biomass precursor powder is nitrogen or argon.

[0018] Further, in step (3), the pre-carbonization temperature of the pretreated biomass precursor powder is 500-700℃, the holding time is 1-4h, and the heating rate is 1℃ / min-10℃ / min.

[0019] Furthermore, in step (3), the pre-carbonized product is pulverized and the acid washing solution is a hydrochloric acid solution and / or a nitric acid solution with a concentration of 0.1-5 mol / L.

[0020] Furthermore, in step (4), after the pre-carbonized product is crushed, the high-temperature heat treatment inert atmosphere is nitrogen or argon.

[0021] Furthermore, in step (3), the high-temperature heat treatment temperature of the pre-carbonized product is 1200-1600℃, the holding time is 1-4h, and the heating rate is 1℃ / min-5℃ / min.

[0022] The second aspect of the present invention provides a hard carbon material prepared with the aid of inorganic salts as described in the first aspect.

[0023] Carbon elements and heteroatoms such as nitrogen, sulfur, and phosphorus are present in the hard carbon anode material, forming one or more CN / S / P structures.

[0024] The precursor is pre-carbonized at low temperature using an inorganic salt-assisted method, and the pre-carbonized material is a carbon material with abundant pores and defect structures.

[0025] The inorganic salt used is one or more inorganic salts with a low melting temperature.

[0026] Hard carbon anode materials are prepared by secondary carbonization of pre-carbonized samples using high-temperature carbonization. The pre-carbonized samples exhibit increased graphitization at high temperatures, and a large number of pores gradually evolve into closed-pore structures.

[0027] The third aspect of the present invention provides an application of the inorganic salt-assisted hard carbon material described in the second aspect in the anode material of a sodium-ion battery.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] This invention uses biomass powder as a hard carbon precursor and inorganic salts as auxiliary agents. A pre-carbonized product is obtained through low-temperature pyrolysis, followed by acid washing and high-temperature carbonization to obtain a hard carbon anode material. The hard carbon material prepared from biomass powder rich in aromatic ring structures and heteroatoms has a high content of graphite domains, thus exhibiting good conductivity. It also possesses abundant porous structure, heteroatom doping, and a large graphite interlayer spacing. To address the problem of excessive defects in hard carbon materials affecting the low first-cycle coulombic efficiency and capacity of sodium-ion batteries, this invention employs high-temperature calcination to reduce defects and oxygen-containing functional groups in the hard carbon material, thereby further improving the first-cycle coulombic efficiency and capacity of sodium-ion batteries.

[0030] The method for preparing inorganic salt-assisted hard carbon materials of the present invention is low in cost, simple in process, and can be mass-produced. The hard carbon anode material obtained exhibits good electrochemical performance, good cycle stability and high specific capacity when used in sodium-ion batteries. Attached Figure Description

[0031] Figure 1 The phase diagram of the NaCl-CaCl2 inorganic salt in Example 1;

[0032] Figure 2 The phase diagram of the NaCl-Na2CO3 inorganic salt in Example 2;

[0033] Figure 3 The phase diagram of the ZnCl2-KCl inorganic salt in Example 3;

[0034] Figure 4 The graph shows the electrochemical performance of the hard carbon anode in the sodium-ion battery of Example 8.

[0035] Figure 5 This is an electron microscope image of the hard carbon material in Example 8. Detailed Implementation

[0036] Unless otherwise defined, all techniques and sciences 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 familiarizing oneself with 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.

[0037] As described in the technical background, since sodium ions have a much larger radius and volume than lithium ions, the graphite anode materials currently used in lithium-ion batteries cannot form stable intercalation compounds with sodium ions. Hard carbon materials, on the other hand, have advantages as anode materials for sodium-ion batteries due to their high number of graphite domains, numerous defects, abundant pore structure, and high storage capacity. However, hard carbon materials as anodes for sodium-ion batteries suffer from low first-cycle coulombic efficiency and poor stability.

[0038] To address the aforementioned technical problems, this invention provides a method for preparing inorganic salt-assisted hard carbon materials, comprising the following steps:

[0039] (1) After crushing the biomass raw material, sieve it, acid wash it and dry it to obtain biomass powder.

[0040] (2) The biomass powder prepared in step (1) is mixed with inorganic salt by solid-phase ball milling at a mass ratio of 1:(1-15) to obtain pretreated biomass precursor powder.

[0041] (3) The pretreated biomass precursor powder prepared in step (2) is placed in a tube furnace with an inert atmosphere for pre-carbonization. The pre-carbonization temperature is 500-700℃, the holding time is 1-4h, the heating rate is 1℃ / min-10℃ / min, and the pre-carbonized product is obtained by cooling after pre-carbonization.

[0042] (4) After crushing and washing the pre-carbonized product obtained in step (3), it is subjected to high-temperature heat treatment in an inert atmosphere. The high-temperature heat treatment temperature of the pre-carbonized product is 1200-1600℃, the holding time is 1-4h, and the heating rate is 1℃ / min-5℃ / min. Finally, the sodium-ion battery hard carbon anode material is obtained.

[0043] The following description, in conjunction with this embodiment, provides further details:

[0044] Example 1

[0045] The biomass raw material is crushed and sieved to remove larger particles, obtaining powder that passes through a 60-mesh sieve. The powder is then dispersed in a mixed acid solution (a mixture of 36% hydrochloric acid, 68% nitric acid, and deionized water, with a volume ratio of 5:5:90) for acid washing (powder to mixed acid solution mass ratio 1:20) for 5 hours to remove impurities. The powder is then washed three times with deionized water to remove residual acid and dried in a forced-air oven to obtain biomass powder.

[0046] Biomass powder was weighed with inorganic salts NaCl and CaCl2 (molar ratio of 4.8:5.2) at a mass ratio of 1:5, and ground in a ball mill for 4 hours at a speed of 550 rpm. The sample was collected to obtain pretreated biomass precursor powder.

[0047] The biomass precursor powder was placed in an alumina boat and positioned in the center of an alumina tube. Argon gas was pre-purged for 30 minutes to purge the air from the tube. High-temperature carbonization was then carried out in a tube furnace under an argon atmosphere, starting at room temperature and decreasing at 10°C / min under normal pressure. -1 The temperature was raised to 500℃ and held for 2 hours to prepare a pre-carbonized sample.

[0048] The collected pre-carbonized samples were dispersed in 1 mol / L hydrochloric acid solution and acid-washed to remove inorganic salts. After washing with water until neutral, the pre-carbonized samples were collected by vacuum filtration and dried in a forced-air oven. The dried pre-carbonized samples were placed in the center of a corundum tube, and argon gas was pre-purged for 30 min to purge the air from the tube. High-temperature carbonization was carried out in a tube furnace under an argon atmosphere, starting at room temperature and decreasing at 6°C / min under normal pressure. -1 The temperature was raised to 1200℃ and held for 2 hours to prepare a hard carbon anode for sodium-ion batteries.

[0049] The negative electrode active material, conductive carbon black, and CMC binder were mixed evenly at a mass ratio of 8:1:1, and deionized water was added to prepare the negative electrode slurry. This slurry was then coated onto copper foil and vacuum dried at 80℃ for 12 hours. The slurry was then punched into a 14mm diameter disc to obtain a straight negative electrode sheet. In a glove box filled with an inert Ar atmosphere, the positive electrode shell, positive electrode sheet (sodium sheet), glass fiber diaphragm, electrolyte, negative electrode sheet, gasket, spring sheet, and negative electrode shell were stacked sequentially and sealed using a sealing machine. The electrolyte was prepared with sodium hexafluorophosphate (NaPF6) as the solute and a 1 mol / L mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a 1:1 volume ratio. -1 The solution was used as the electrolyte to complete battery assembly. The battery testing system was a blue battery testing system, with a testing voltage window of 0.01-2.5V. The electrochemical performance of the sodium-ion battery anode material prepared in Example 1 was measured at 50 mAg. -1 At a current density of [value missing], its initial discharge specific capacity can reach 289.53 mAh g. -1 The initial Coulomb efficiency was 78.62%.

[0050] Example 2

[0051] The biomass raw material is crushed and sieved to remove larger particles, obtaining powder that passes through a 60-mesh sieve. The powder is then dispersed in a mixed acid solution (a mixture of 36% hydrochloric acid, 68% nitric acid, and deionized water, with a volume ratio of 5:5:90) for acid washing (powder to mixed acid solution mass ratio 1:40) for 15 hours to remove impurities. The powder is then washed several times with deionized water to remove residual acid and dried in a forced-air oven to obtain biomass powder.

[0052] Biomass powder was weighed with inorganic salts NaCl and Na2CO3 (molar ratio of 5.8:4.2) at a mass ratio of 1:10, and ground in a ball mill for 4 hours at a speed of 550 rpm. The sample was collected to obtain pretreated biomass precursor powder.

[0053] The biomass precursor powder was placed in an alumina boat and positioned in the center of an alumina tube. Argon gas was pre-purged for 30 minutes to purge the air from the tube. High-temperature carbonization was then carried out in a tube furnace under an argon atmosphere, starting at room temperature and decreasing at 5°C / min under normal pressure. -1 The temperature was raised to 600℃ and held for 2 hours to prepare a pre-carbonized sample.

[0054] The collected pre-carbonized samples were dispersed in 1 mol / L hydrochloric acid solution and acid-washed to remove inorganic salts. After washing with water until neutral, the pre-carbonized samples were collected by vacuum filtration and dried in a forced-air oven. The dried pre-carbonized samples were placed in the center of a corundum tube, and argon gas was pre-purged for 30 min to purge the air from the tube. High-temperature carbonization was carried out in a tube furnace under an argon atmosphere, starting at room temperature and decreasing at 2°C / min under normal pressure. -1 The temperature was raised to 1200℃ and held for 2 hours to prepare a hard carbon anode for sodium-ion batteries.

[0055] The negative electrode active material, conductive carbon black, and CMC binder were mixed evenly at a mass ratio of 8:1:1, and deionized water was added to prepare the negative electrode slurry. This slurry was then coated onto copper foil and vacuum dried at 80°C for 12 hours to obtain the negative electrode sheet. In a glove box filled with an inert Ar atmosphere, the positive electrode shell, positive electrode sheet (sodium sheet), glass fiber diaphragm, electrolyte, negative electrode sheet, gasket, spring sheet, and negative electrode shell were stacked sequentially and sealed using a sealing machine. The electrolyte was prepared with sodium hexafluorophosphate (NaPF6) as the solute and a 1 mol / L mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a 1:1 volume ratio. -1 The solution was used as the electrolyte to complete battery assembly. The battery testing system was a blue battery testing system, with a testing voltage window of 0.01-2.5V. The electrochemical performance of the sodium-ion battery anode material prepared in Example 2 was measured at 50 mAg. -1 At a current density of [value missing], its initial discharge specific capacity can reach 305.18 mAh g. -1 The initial Coulomb efficiency was 80.25%.

[0056] Example 3

[0057] The biomass raw material is crushed and sieved to remove larger particles, obtaining powder that passes through a 60-mesh sieve. The powder is then dispersed in a mixed acid solution (a mixture of 36% hydrochloric acid, 68% nitric acid, and deionized water, with a volume ratio of 5:5:90) for acid washing (powder to mixed acid solution mass ratio 1:40) for 5 hours to remove impurities. The powder is then washed several times with deionized water to remove residual acid and dried in a forced-air oven to obtain biomass powder.

[0058] Biomass powder was weighed with inorganic salts ZnCl2 and KCl (molar ratio 1:1) at a mass ratio of 1:15, and ground in a ball mill for 4 hours at a speed of 550 rpm. The sample was collected to obtain pretreated biomass precursor powder.

[0059] The biomass precursor powder was placed in an alumina boat and positioned in the center of an alumina tube. Argon gas was pre-purged for 30 minutes to purge the air from the tube. High-temperature carbonization was then carried out in a tube furnace under an argon atmosphere, starting at room temperature and decreasing at 10°C / min under normal pressure. -1 The temperature was raised to 700℃ and held for 2 hours to prepare a pre-carbonized sample.

[0060] The collected pre-carbonized samples were dispersed in 1 mol / L hydrochloric acid solution and acid-washed to remove inorganic salts. After washing with water until neutral, the pre-carbonized samples were collected by vacuum filtration and dried in a forced-air oven. The dried pre-carbonized samples were placed in the center of a corundum tube, and argon gas was pre-purged for 30 min to purge the air from the tube. High-temperature carbonization was carried out in a tube furnace under an argon atmosphere, starting at room temperature and decreasing at 5°C / min under normal pressure. -1 The temperature was raised to 1200℃ and held for 2 hours to prepare a hard carbon anode for sodium-ion batteries.

[0061] The negative electrode active material, conductive carbon black, and CMC binder were mixed evenly at a mass ratio of 8:1:1, and deionized water was added to prepare the negative electrode slurry. This slurry was then coated onto copper foil and vacuum dried at 80°C for 12 hours to obtain the negative electrode sheet. In a glove box filled with an inert Ar atmosphere, the positive electrode shell, positive electrode sheet (sodium sheet), glass fiber diaphragm, electrolyte, negative electrode sheet, gasket, spring sheet, and negative electrode shell were stacked sequentially and sealed using a sealing machine. The electrolyte was prepared with sodium hexafluorophosphate (NaPF6) as the solute and a 1 mol / L mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a 1:1 volume ratio. -1 The solution was used as the electrolyte to complete battery assembly. The battery testing system was a blue battery testing system, with a testing voltage window of 0.01-2.5V. The electrochemical performance of the sodium-ion battery anode material prepared in Example 3 was measured at 50 mAg. -1 At a current density of [value missing], its initial discharge specific capacity can reach 311.09 mAh g. -1 The initial Coulomb efficiency was 81.46%.

[0062] Example 4

[0063] The biomass raw material is crushed and sieved to remove larger particles, obtaining powder that passes through a 60-mesh sieve. The powder is then dispersed in a mixed acid solution (a mixture of 36% hydrochloric acid, 68% nitric acid, and deionized water, with a volume ratio of 5:5:90) for acid washing (powder to mixed acid solution mass ratio 1:20) for 15 hours to remove impurities. The powder is then washed several times with deionized water to remove residual acid and dried in a forced-air oven to obtain biomass powder.

[0064] Biomass powder was weighed with inorganic salts ZnCl2 and KCl (molar ratio 1:1) at a mass ratio of 1:5, and ground in a ball mill for 4 hours at a speed of 550 rpm. The sample was collected to obtain pretreated biomass precursor powder.

[0065] The biomass precursor powder was placed in an alumina boat and positioned in the center of an alumina tube. Argon gas was pre-purged for 30 minutes to purge the air from the tube. High-temperature carbonization was then carried out in a tube furnace under an argon atmosphere, starting at room temperature and decreasing at 5°C / min under normal pressure. -1 The temperature was raised to 500℃ and held for 2 hours to prepare a pre-carbonized sample.

[0066] The collected pre-carbonized samples were dispersed in 1 mol / L hydrochloric acid solution and acid-washed to remove inorganic salts. After washing with water until neutral, the pre-carbonized samples were collected by vacuum filtration and dried in a forced-air oven. The dried pre-carbonized samples were placed in the center of a corundum tube, and argon gas was pre-purged for 30 min to purge the air from the tube. High-temperature carbonization was carried out in a tube furnace under an argon atmosphere, starting at room temperature and decreasing at 2°C / min under normal pressure. -1 The temperature was raised to 1400℃ and held for 2 hours to prepare a hard carbon anode for sodium-ion batteries.

[0067] The negative electrode active material, conductive carbon black, and CMC binder were mixed evenly at a mass ratio of 8:1:1, and deionized water was added to prepare the negative electrode slurry. This slurry was then coated onto copper foil and vacuum dried at 80°C for 12 hours to obtain the negative electrode sheet. In a glove box filled with an inert Ar atmosphere, the positive electrode shell, positive electrode sheet (sodium sheet), glass fiber diaphragm, electrolyte, negative electrode sheet, gasket, spring sheet, and negative electrode shell were stacked sequentially and sealed using a sealing machine. The electrolyte was prepared with sodium hexafluorophosphate (NaPF6) as the solute and a 1 mol / L mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a 1:1 volume ratio. -1 The solution was used as the electrolyte to complete battery assembly. The battery testing system was a blue battery testing system, with a testing voltage window of 0.01-2.5V. The electrochemical performance of the sodium-ion battery anode material prepared in Example 5 was measured at 50 mAg. -1 At a current density of [value missing], its initial discharge specific capacity can reach 352.49 mAh g. -1The initial Coulomb efficiency was 83.17%.

[0068] Example 5

[0069] The biomass raw material is crushed and sieved to remove larger particles, obtaining powder that passes through a 60-mesh sieve. The powder is then dispersed in a mixed acid solution (a mixture of 36% hydrochloric acid, 68% nitric acid, and deionized water, with a volume ratio of 5:5:90) for acid washing (powder to mixed acid solution mass ratio 1:20) for 10 hours to remove impurities. The powder is then washed several times with deionized water to remove residual acid and dried in a forced-air oven to obtain biomass powder.

[0070] Biomass powder was weighed with inorganic salts NaCl and Na2CO3 (molar ratio of 5.8:4.2) at a mass ratio of 1:5, and ground in a ball mill for 4 hours at a speed of 550 rpm. The sample was collected to obtain pretreated biomass precursor powder.

[0071] The biomass precursor powder was placed in an alumina boat and positioned in the center of an alumina tube. Argon gas was pre-purged for 30 minutes to purge the air from the tube. High-temperature carbonization was then carried out in a tube furnace under an argon atmosphere, starting at room temperature and decreasing at 5°C / min under normal pressure. -1 The temperature was raised to 500℃ and held for 2 hours to prepare a pre-carbonized sample.

[0072] The collected pre-carbonized samples were dispersed in 1 mol / L hydrochloric acid solution and acid-washed to remove inorganic salts. After washing with water until neutral, the pre-carbonized samples were collected by vacuum filtration and dried in a forced-air oven. The dried pre-carbonized samples were placed in the center of a corundum tube, and argon gas was pre-purged for 30 min to purge the air from the tube. High-temperature carbonization was carried out in a tube furnace under an argon atmosphere, starting at room temperature and decreasing at 2°C / min under normal pressure. -1 The temperature was raised to 1600℃ and held for 2 hours to prepare a hard carbon anode for sodium-ion batteries.

[0073] The negative electrode active material, conductive carbon black, and CMC binder were mixed evenly at a mass ratio of 8:1:1, and deionized water was added to prepare the negative electrode slurry. This slurry was then coated onto copper foil and vacuum dried at 80°C for 12 hours to obtain the negative electrode sheet. In a glove box filled with an inert Ar atmosphere, the positive electrode shell, positive electrode sheet (sodium sheet), glass fiber diaphragm, electrolyte, negative electrode sheet, gasket, spring sheet, and negative electrode shell were stacked sequentially and sealed using a sealing machine. The electrolyte was prepared with sodium hexafluorophosphate (NaPF6) as the solute and a 1 mol / L mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a 1:1 volume ratio. -1The solution was used as the electrolyte to complete battery assembly. The battery testing system was a blue battery testing system, with a testing voltage window of 0.01-2.5V. The electrochemical performance of the sodium-ion battery anode material prepared in Example 5 was measured at 50 mAg. -1 At a current density of [value missing], its initial discharge specific capacity can reach 332.74 mAh g. -1 The initial Coulomb efficiency was 85.93%.

[0074] Example 6

[0075] The biomass raw material is crushed and sieved to remove larger particles, obtaining powder that passes through a 60-mesh sieve. The powder is then dispersed in a mixed acid solution (a mixture of 36% hydrochloric acid, 68% nitric acid, and deionized water, with a volume ratio of 5:5:90) for acid washing (powder to mixed acid solution mass ratio 1:40) for 10 hours to remove impurities. The powder is then washed several times with deionized water to remove residual acid and dried in a forced-air oven to obtain biomass powder.

[0076] Biomass powder was weighed with inorganic salts NaCl and CaCl2 (molar ratio of 4.8:5.2) at a mass ratio of 1:10, and ground in a ball mill for 4 hours at a speed of 550 rpm. The sample was collected to obtain pretreated biomass precursor powder.

[0077] The biomass precursor powder was placed in an alumina boat and positioned in the center of an alumina tube. Argon gas was pre-purged for 30 minutes to purge the air from the tube. High-temperature carbonization was then carried out in a tube furnace under an argon atmosphere, starting at room temperature and decreasing at 5°C / min under normal pressure. -1 The temperature was raised to 500℃ and held for 2 hours to prepare a pre-carbonized sample.

[0078] The collected pre-carbonized samples were dispersed in 1 mol / L hydrochloric acid solution and acid-washed to remove inorganic salts. After washing with water until neutral, the pre-carbonized samples were collected by vacuum filtration and dried in a forced-air oven. The dried pre-carbonized samples were placed in the center of a corundum tube, and argon gas was pre-purged for 30 min to purge the air from the tube. High-temperature carbonization was carried out in a tube furnace under an argon atmosphere, starting at room temperature and decreasing at 2°C / min under normal pressure. -1 The temperature was raised to 1400℃ and held for 2 hours to prepare a hard carbon anode for sodium-ion batteries.

[0079] The negative electrode active material, conductive carbon black, and CMC binder were mixed evenly at a mass ratio of 8:1:1, and deionized water was added to prepare the negative electrode slurry. This slurry was then coated onto copper foil and vacuum dried at 80°C for 12 hours to obtain the negative electrode sheet. In a glove box filled with an inert Ar atmosphere, the positive electrode shell, positive electrode sheet (sodium sheet), glass fiber diaphragm, electrolyte, negative electrode sheet, gasket, spring sheet, and negative electrode shell were stacked sequentially and sealed using a sealing machine. The electrolyte was prepared with sodium hexafluorophosphate (NaPF6) as the solute and a 1 mol / L mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a 1:1 volume ratio. -1 The solution was used as the electrolyte to complete battery assembly. The battery testing system was a blue battery testing system, with a testing voltage window of 0.01-2.5V. The electrochemical performance of the sodium-ion battery anode material prepared in Example 6 was measured at 50 mAg. -1 At a current density of [value missing], its initial discharge specific capacity can reach 326.43 mAh g. -1 The initial Coulomb efficiency was 82.36%.

[0080] Example 7

[0081] The biomass raw material was pulverized and sieved to remove larger particles, obtaining powder that passed through a 60-mesh sieve. This powder was then dispersed in a mixed acid solution (a mixture of 36% hydrochloric acid, 68% nitric acid, and deionized water, with a volume ratio of 5:5:90) and acid-washed (powder to mixed acid solution mass ratio 1:30) for 15 hours to remove impurities. The powder was then washed several times with deionized water to remove residual acid and dried in a forced-air oven to obtain biomass powder. The biomass powder was then weighed with inorganic salts NaCl and CaCl2 (molar ratio 4.8:5.2) at a mass ratio of 1:15 and ground in a ball mill for 4 hours at 550 rpm. The sample was collected to obtain pretreated biomass precursor powder.

[0082] The biomass precursor powder was placed in an alumina boat and positioned in the center of an alumina tube. Argon gas was pre-purged for 30 minutes to purge the air from the tube. High-temperature carbonization was then carried out in a tube furnace under an argon atmosphere, starting at room temperature and decreasing at 5°C / min under normal pressure. -1 The temperature was raised to 500℃ and held for 2 hours to prepare a pre-carbonized sample.

[0083] The collected pre-carbonized samples were dispersed in 1 mol / L hydrochloric acid solution and acid-washed to remove inorganic salts. After washing with water until neutral, the pre-carbonized samples were collected by vacuum filtration and dried in a forced-air oven. The dried pre-carbonized samples were placed in the center of a corundum tube, and argon gas was pre-purged for 30 min to purge the air from the tube. High-temperature carbonization was carried out in a tube furnace under an argon atmosphere, starting at room temperature and decreasing at 2°C / min under normal pressure. -1The temperature was raised to 1600℃ and held for 2 hours to prepare a hard carbon anode for sodium-ion batteries.

[0084] The negative electrode active material, conductive carbon black, and CMC binder were mixed evenly at a mass ratio of 8:1:1, and deionized water was added to prepare the negative electrode slurry. This slurry was then coated onto copper foil and vacuum dried at 80°C for 12 hours to obtain the negative electrode sheet. In a glove box filled with an inert Ar atmosphere, the positive electrode shell, positive electrode sheet (sodium sheet), glass fiber diaphragm, electrolyte, negative electrode sheet, gasket, spring sheet, and negative electrode shell were stacked sequentially and sealed using a sealing machine. The electrolyte was prepared with sodium hexafluorophosphate (NaPF6) as the solute and a 1 mol / L mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a 1:1 volume ratio. -1 The solution was used as the electrolyte to complete battery assembly. The battery testing system was a blue battery testing system, with a testing voltage window of 0.01-2.5V. The electrochemical performance of the sodium-ion battery anode material prepared in Example 7 was measured at 50 mAg. -1 At a current density of [value missing], its initial discharge specific capacity can reach 347.16 mAh g. -1 The initial Coulomb efficiency was 85.31%.

[0085] Example 8

[0086] The biomass raw material was pulverized and sieved to remove larger particles, obtaining powder that passed through a 60-mesh sieve. This powder was then dispersed in a mixed acid solution (a mixture of 36% hydrochloric acid, 68% nitric acid, and deionized water, with a volume ratio of 5:5:90) for 10 hours to remove impurities. The powder was then washed several times with deionized water to remove residual acid and dried in a forced-air oven to obtain biomass powder. The biomass powder was then weighed with inorganic salts ZnCl2 and KCl (molar ratio 1:1) at a mass ratio of 1:10 and ground in a ball mill for 4 hours at 550 rpm. The sample was collected to obtain pretreated biomass precursor powder.

[0087] The biomass precursor powder was placed in an alumina boat and positioned in the center of an alumina tube. Argon gas was pre-purged for 30 minutes to purge the air from the tube. High-temperature carbonization was then carried out in a tube furnace under an argon atmosphere, starting at room temperature and decreasing at 5°C / min under normal pressure. -1 The temperature was raised to 500℃ and held for 2 hours to prepare a pre-carbonized sample.

[0088] The collected pre-carbonized samples were dispersed in 1 mol / L hydrochloric acid solution and acid-washed to remove inorganic salts. After washing with water until neutral, the pre-carbonized samples were collected by vacuum filtration and dried in a forced-air oven. The dried pre-carbonized samples were placed in the center of a corundum tube, and argon gas was pre-purged for 30 min to purge the air from the tube. High-temperature carbonization was carried out in a tube furnace under an argon atmosphere, starting at room temperature and decreasing at 2°C / min under normal pressure. -1 The temperature was raised to 1600℃ and held for 2 hours to prepare a hard carbon anode for sodium-ion batteries.

[0089] The negative electrode active material, conductive carbon black, and CMC binder were mixed evenly at a mass ratio of 8:1:1, and deionized water was added to prepare the negative electrode slurry. This slurry was then coated onto copper foil and vacuum dried at 80°C for 12 hours to obtain the negative electrode sheet. In a glove box filled with an inert Ar atmosphere, the positive electrode shell, positive electrode sheet (sodium sheet), glass fiber diaphragm, electrolyte, negative electrode sheet, gasket, spring sheet, and negative electrode shell were stacked sequentially and sealed using a sealing machine. The electrolyte was prepared with sodium hexafluorophosphate (NaPF6) as the solute and a 1 mol / L mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a 1:1 volume ratio. -1 The solution was used as the electrolyte to complete battery assembly. The battery testing system was a blue battery testing system, with a testing voltage window of 0.01-2.5V. The electrochemical performance of the sodium-ion battery anode material prepared in Example 8 was measured at 50 mAg. -1 At a current density of [value missing], its initial discharge specific capacity can reach 372.04 mAh g. -1 The initial Coulomb efficiency was 89.42%.

[0090] Example 9

[0091] The biomass raw material is crushed and sieved to remove larger particles, obtaining powder that passes through a 60-mesh sieve. The powder is then dispersed in a mixed acid solution (a mixture of 36% hydrochloric acid, 68% nitric acid, and deionized water, with a volume ratio of 5:5:90) for acid washing (powder to mixed acid solution mass ratio 1:30) for 5 hours to remove impurities. The powder is then washed several times with deionized water to remove residual acid and dried in a forced-air oven to obtain biomass powder.

[0092] Biomass powder was weighed with inorganic salts NaCl and Na2CO3 (molar ratio of 5.8:4.2) at a mass ratio of 1:15, and ground in a ball mill for 4 hours at a speed of 550 rpm. The sample was collected to obtain pretreated biomass precursor powder.

[0093] The biomass precursor powder was placed in an alumina boat and positioned in the center of an alumina tube. Argon gas was pre-purged for 30 minutes to purge the air from the tube. High-temperature carbonization was then carried out in a tube furnace under an argon atmosphere, starting at room temperature and decreasing at 5°C / min under normal pressure. -1 The temperature was raised to 500℃ and held for 2 hours to prepare a pre-carbonized sample.

[0094] The collected pre-carbonized samples were dispersed in 1 mol / L hydrochloric acid solution and acid-washed to remove inorganic salts. After washing with water until neutral, the pre-carbonized samples were collected by vacuum filtration and dried in a forced-air oven. The dried pre-carbonized samples were placed in the center of a corundum tube, and argon gas was pre-purged for 30 min to purge the air from the tube. High-temperature carbonization was carried out in a tube furnace under an argon atmosphere, starting at room temperature and decreasing at 2°C / min under normal pressure. -1 The temperature was raised to 1400℃ and held for 2 hours to prepare a hard carbon anode for sodium-ion batteries.

[0095] The negative electrode active material, conductive carbon black, and CMC binder were mixed evenly at a mass ratio of 8:1:1, and deionized water was added to prepare the negative electrode slurry. This slurry was then coated onto copper foil and vacuum dried at 80°C for 12 hours to obtain the negative electrode sheet. In a glove box filled with an inert Ar atmosphere, the positive electrode shell, positive electrode sheet (sodium sheet), glass fiber diaphragm, electrolyte, negative electrode sheet, gasket, spring sheet, and negative electrode shell were stacked sequentially and sealed using a sealing machine. The electrolyte was prepared with sodium hexafluorophosphate (NaPF6) as the solute and a 1 mol / L mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a 1:1 volume ratio. -1 The solution was used as the electrolyte to complete battery assembly. The battery testing system was a blue battery testing system, with a testing voltage window of 0.01-2.5V. The electrochemical performance of the sodium-ion battery anode material prepared in Example 9 was measured at 50 mAg. -1 At a current density of [value missing], its initial discharge specific capacity can reach 318.75 mAh g. -1 The initial Coulomb efficiency was 82.09%.

[0096] This comparative example relates to the preparation of an inorganic salt-assisted hard carbon material. The main difference from the above embodiments is that a single inorganic salt is used as the auxiliary agent, and no pre-carbonization heat treatment is performed. Specific operation details are provided in Comparative Example 1.

[0097] The biomass raw material was pulverized and sieved to remove larger particles, obtaining powder that passed through a 60-mesh sieve. This powder was then dispersed in a mixed acid solution (a mixture of 36% hydrochloric acid, 68% nitric acid, and deionized water, with a volume ratio of 5:5:90) for acid washing (powder to mixed acid solution mass ratio 1:30) for 10 hours to remove impurities. The powder was then washed several times with deionized water to remove residual acid and dried in a forced-air oven to obtain biomass powder. The biomass powder was then weighed with inorganic salt NaCl at a mass ratio of 1:10 and ground in a ball mill for 4 hours at 550 rpm. The sample was collected to obtain pretreated biomass precursor powder.

[0098] The biomass precursor powder was placed in a corundum boat and positioned in the center of a corundum tube. Argon gas was pre-purged for 30 minutes to purge the air from the tube. High-temperature carbonization was then carried out in a tube furnace under an argon atmosphere, starting at room temperature and proceeding at 2°C / min under normal pressure. -1 The temperature was raised to 1600℃ and held for 2 hours. The inorganic salts were removed by washing several times with 1 mol / L hydrochloric acid solution and deionized water to prepare a hard carbon anode for sodium-ion batteries.

[0099] The negative electrode active material, conductive carbon black, and CMC binder were mixed evenly at a mass ratio of 8:1:1, and deionized water was added to prepare the negative electrode slurry. This slurry was then coated onto copper foil and vacuum dried at 80°C for 12 hours to obtain the negative electrode sheet. In a glove box filled with an inert Ar atmosphere, the positive electrode shell, positive electrode sheet (sodium sheet), glass fiber diaphragm, electrolyte, negative electrode sheet, gasket, spring sheet, and negative electrode shell were stacked sequentially and sealed using a sealing machine. The electrolyte was prepared with sodium hexafluorophosphate (NaPF6) as the solute and a 1 mol / L mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a 1:1 volume ratio. -1 The solution was used as the electrolyte to complete battery assembly. The battery testing system was a blue battery testing system, with a testing voltage window of 0.01-2.5V. The electrochemical performance of the sodium-ion battery anode material prepared in Comparative Example 1 was measured at 50 mAg. -1 At a current density of [value missing], its initial discharge specific capacity can reach 253.03 mAh g. -1 The initial Coulomb efficiency was 75.12%.

[0100] Comparative Example 2

[0101] The biomass raw material was pulverized and sieved to remove larger particles, obtaining powder that passed through a 60-mesh sieve. This powder was then dispersed in a mixed acid solution (a mixture of 36% hydrochloric acid, 68% nitric acid, and deionized water, with a volume ratio of 5:5:90) for acid washing (powder to mixed acid solution mass ratio 1:30) for 10 hours to remove impurities. The powder was then washed several times with deionized water to remove residual acid and dried in a forced-air oven to obtain biomass powder. The biomass powder was then weighed with inorganic salt KCl at a mass ratio of 1:10 and ground in a ball mill for 4 hours at 550 rpm. The sample was collected to obtain pretreated biomass precursor powder.

[0102] The biomass precursor powder was placed in an alumina boat and positioned in the center of an alumina tube. Argon gas was pre-purged for 30 minutes to purge the air from the tube. High-temperature carbonization was then carried out in a tube furnace under an argon atmosphere, starting at room temperature and decreasing at 5°C / min under normal pressure. -1 The temperature was raised to 1600℃ and held for 2 hours. The inorganic salts were removed by washing several times with 1 mol / L hydrochloric acid solution and deionized water to prepare a hard carbon anode for sodium-ion batteries.

[0103] The negative electrode active material, conductive carbon black, and CMC binder were mixed evenly at a mass ratio of 8:1:1, and deionized water was added to prepare the negative electrode slurry. This slurry was then coated onto copper foil and vacuum dried at 80°C for 12 hours to obtain the negative electrode sheet. In a glove box filled with an inert Ar atmosphere, the positive electrode shell, positive electrode sheet (sodium sheet), glass fiber diaphragm, electrolyte, negative electrode sheet, gasket, spring sheet, and negative electrode shell were stacked sequentially and sealed using a sealing machine. The electrolyte was prepared with sodium hexafluorophosphate (NaPF6) as the solute and a 1 mol / L mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a 1:1 volume ratio. -1 The solution was used as the electrolyte to complete battery assembly. The battery testing system was a blue battery testing system, with a testing voltage window of 0.01-2.5V. The electrochemical performance of the sodium-ion battery anode material prepared in Comparative Example 1 was measured at 50 mAg. -1 At a current density of [value missing], its initial discharge specific capacity can reach 268.16 mAh g. -1 The initial Coulomb efficiency was 77.29%.

[0104] Comparative Example 3

[0105] The biomass raw material is crushed and sieved to remove larger particles, obtaining powder that passes through a 60-mesh sieve. The powder is then dispersed in a mixed acid solution (a mixture of 36% hydrochloric acid, 68% nitric acid, and deionized water, with a volume ratio of 5:5:90) for acid washing (powder to mixed acid solution mass ratio 1:30) for 10 hours to remove impurities. The powder is then washed several times with deionized water to remove residual acid and dried in a forced-air oven to obtain biomass powder.

[0106] Biomass powder and inorganic salt Na2CO3 were weighed at a mass ratio of 1:10, placed in a ball mill and ground for 4 hours at a speed of 550 rpm. The sample was collected to obtain pretreated biomass precursor powder.

[0107] The biomass precursor powder was placed in a corundum boat and positioned in the center of a corundum tube. Argon gas was pre-purged for 30 minutes to purge the air from the tube. High-temperature carbonization was then carried out in a tube furnace under an argon atmosphere, starting at room temperature and proceeding at 2°C / min under normal pressure. -1 The temperature was raised to 1600℃ and kept at that temperature for 2 hours. The sample was collected and washed several times with 1 mol / L hydrochloric acid solution and deionized water to remove inorganic salts, thus preparing a hard carbon anode for sodium-ion batteries.

[0108] The negative electrode active material, conductive carbon black, and CMC binder were mixed evenly at a mass ratio of 8:1:1, and deionized water was added to prepare the negative electrode slurry. This slurry was then coated onto copper foil and vacuum dried at 80°C for 12 hours to obtain the negative electrode sheet. In a glove box filled with an inert Ar atmosphere, the positive electrode shell, positive electrode sheet (sodium sheet), glass fiber diaphragm, electrolyte, negative electrode sheet, gasket, spring sheet, and negative electrode shell were stacked sequentially and sealed using a sealing machine. The electrolyte was prepared with sodium hexafluorophosphate (NaPF6) as the solute and a 1 mol / L mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a 1:1 volume ratio. -1 The solution was used as the electrolyte to complete battery assembly. The battery testing system was a blue battery testing system, with a testing voltage window of 0.01-2.5V. The electrochemical performance of the sodium-ion battery anode material prepared in Example 1 was measured at 50 mAg. -1 At a current density of [value missing], its initial discharge specific capacity can reach 282.24 mAh g. -1 The initial Coulomb efficiency was 78.11%.

[0109] Comparative Example 4

[0110] The biomass raw material was pulverized and sieved to remove larger particles, obtaining powder that passed through a 60-mesh sieve. This powder was then dispersed in a mixed acid solution (a mixture of 36% hydrochloric acid, 68% nitric acid, and deionized water, with a volume ratio of 5:5:90) for acid washing (powder to mixed acid solution mass ratio 1:30) for 10 hours to remove impurities. The powder was then washed several times with deionized water to remove residual acid and dried in a forced-air oven to obtain biomass powder. The biomass powder was then weighed with inorganic salts ZnCl2 and KCl (molar ratio 1:1) at a mass ratio of 1:10 and ground in a ball mill for 4 hours at 550 rpm. The sample was collected to obtain pretreated biomass precursor powder.

[0111] The biomass precursor powder was placed in a corundum boat and positioned in the center of a corundum tube. Argon gas was pre-purged for 30 minutes to purge the air from the tube. High-temperature carbonization was then carried out in a tube furnace under an argon atmosphere, starting at room temperature and proceeding at 2°C / min under normal pressure. -1 The temperature was raised to 1600℃ and kept at that temperature for 2 hours. The sample was collected and washed several times with 1 mol / L hydrochloric acid solution and deionized water to remove inorganic salts, thus preparing a hard carbon anode for sodium-ion batteries.

[0112] The negative electrode active material, conductive carbon black, and CMC binder were mixed evenly at a mass ratio of 8:1:1, and deionized water was added to prepare the negative electrode slurry. This slurry was then coated onto copper foil and vacuum dried at 80°C for 12 hours to obtain the negative electrode sheet. In a glove box filled with an inert Ar atmosphere, the positive electrode shell, positive electrode sheet (sodium sheet), glass fiber diaphragm, electrolyte, negative electrode sheet, gasket, spring sheet, and negative electrode shell were stacked sequentially and sealed using a sealing machine. The electrolyte was prepared with sodium hexafluorophosphate (NaPF6) as the solute and a 1 mol / L mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a 1:1 volume ratio. -1 The solution was used as the electrolyte to complete battery assembly. The battery testing system was a blue battery testing system, with a testing voltage window of 0.01-2.5V. The electrochemical performance of the sodium-ion battery anode material prepared in Comparative Example 4 was compared at 50 mAg. -1 At a current density of [value missing], its initial discharge specific capacity can reach 212.24 mAh g. -1 The initial Coulomb efficiency was 70.52%.

[0113] The sodium-ion battery anode carbon materials prepared in Examples 1-9 have higher initial discharge specific capacity and initial coulombic efficiency than those in Comparative Examples 1-4, indicating that the use of ZnCl and KCl inorganic salts to assist in the preparation of anode materials for ion batteries is effective, and the optimal amount of inorganic salts is 10g.

[0114] The sodium-ion battery anode carbon materials prepared in Examples 3, 4 and 8 have higher initial discharge specific capacity and initial coulombic efficiency than those in Comparative Example 4, indicating that the two-step heat treatment method assisted by ZnCl2 and KCl inorganic salts is effective in preparing sodium-ion battery anode materials. Moreover, the optimal pre-carbonization temperature is 500℃ and the high-temperature pyrolysis temperature is 1600℃.

[0115] Battery performance tests show that the sodium-ion battery hard carbon anode material provided by this invention has superior electrochemical performance. The inorganic salts play a role in regulating the pore structure of the biomass carbon material and catalyzing biomass dehydration during carbonization, facilitating the subsequent recombination of carbon molecules to form closed pore structures. During pre-carbonization at 500℃, biomass undergoes dehydration and deoxygenation, and with the assistance of inorganic salts, a large number of microporous structures are formed. During further high-temperature carbonization, these pore structures gradually close, providing space for the formation of sodium clusters during sodium storage and improving the material's sodium storage capacity. In contrast, NaCl, KCl, and ZnCl2 in Comparative Examples 1-3 are difficult to modify biomass due to their difficulty in decomposition and volatilization. In summary, the sodium-ion battery hard carbon anode material of Example 8 has the advantages of high specific capacity, good cycle stability, and good rate performance.

[0116] Compared to techniques requiring single or multiple salts for modifying biomass materials using the melting point of inorganic salts, this invention offers greater precision and accuracy in controlling material properties. A comparison with patents CN117486198A and CN117902575A reveals that the proposed solution requires only two steps of high-temperature carbonization, eliminating the need for impregnation, hydrothermal treatments, and other complex processes. This simplifies operation, ensures good repeatability, and facilitates large-scale production. Furthermore, the precursors used in the material preparation are widely available, resulting in relatively low overall production costs and further reducing the cost of sodium-ion battery production, thus maximizing its advantages. The entire preparation process is conducted under normal pressure, providing relatively mild conditions and enhancing safety during production.

[0117] Due to the difference in ionic radii between lithium ions and sodium ions, the requirements for materials in energy storage are not the same. The same material can exhibit excellent performance when used as a negative electrode material for lithium-ion batteries, but its performance often decreases in sodium-ion batteries. However, in sodium-ion battery applications, through a comprehensive comparison of performance and preparation methods, this invention is still competitive.

[0118] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, and substitutions and selections of auxiliary components, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing hard carbon materials based on inorganic salts, characterized in that, Includes the following steps: (1) After crushing the biomass raw material, it is sieved, acid-washed and dried to obtain biomass powder; (2) The above biomass powder and inorganic salt are mixed by solid-phase ball milling to obtain pretreated biomass precursor powder. (3) The pretreated biomass precursor powder was placed in an inert atmosphere for precarbonization to obtain the precarbonized product. (4) After the pre-carbonized product is acid-washed and water-washed, it is subjected to high-temperature heat treatment in an inert atmosphere to finally obtain inorganic salt-assisted hard carbon material.

2. The preparation method according to claim 1, characterized in that, The biomass raw materials are selected from one or more of coconut shells, bamboo, straw, and wood; after crushing, the powder that passes through a 1-60 mesh sieve is collected. The mass ratio of powder to mixed acid solution is 1:(10-50), preferably 1:(20-40), more preferably 1:30; the pickling treatment is 1-24h, preferably 5-15h, more preferably 10h; The solution used for acid washing of the biomass raw materials is a mixed solution of 36% hydrochloric acid, 68% nitric acid and deionized water, wherein the volume ratio of hydrochloric acid, nitric acid and deionized water in the mixed solution is 1-15:1-15:70-100, preferably 5-15:5-15:70-90, and more preferably 5:5:

90.

3. The preparation method according to claim 1, characterized in that, The inorganic salt is one or more of NaCl, KCl, LiCl, ZnCl2, AlCl3, CaCl2, NaOH, Na2CO3 and / or KHCO3; The mass ratio of biomass powder to inorganic salt is 1:(1-30), preferably 1:(5-15), and more preferably 1:

10.

4. The preparation method according to claim 1, characterized in that, The pre-carbonization temperature of the pretreated biomass precursor powder is 500-700℃, and the holding time is 1-4h. The high-temperature heat treatment temperature of the pre-carbonized product is 1200-1600℃, and the holding time is 1-4h.

5. The preparation method according to claim 1 or 4, characterized in that, The pre-carbonization heating rate of the pretreated biomass precursor powder is 1℃ / min-10℃ / min; The high-temperature heat treatment rate of the pre-carbonized product is 1℃ / min-5℃ / min.

6. The preparation method according to claim 1, characterized in that, The pre-carbonized product pickling solution is a hydrochloric acid solution and / or a nitric acid solution with a concentration of 0.1-5 mol / L; In steps (3) and (4), the inert atmosphere is nitrogen and / or argon.

7. A hard carbon anode material prepared by any one of the preparation methods described in claims 1-6.

8. The application of a hard carbon anode material prepared by the preparation method of claim 7 in sodium-ion battery anode materials.

9. A negative electrode sheet, characterized in that, It includes a negative electrode current collector and a negative electrode active material layer, wherein the negative electrode active material layer comprises a hard carbon negative electrode material prepared by any of the preparation methods described in claims 1-6, or a hard carbon composite material as described in claim 7.

10. A sodium-ion battery, characterized in that, Includes the negative electrode sheet as described in claim 9.

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