Preparation method of sodium ion battery hard carbon negative electrode material based on oxygen-containing functional group micropore structure control

Abstract

The application discloses a preparation method of a sodium ion battery hard carbon negative electrode material based on oxygen-containing functional group micropore structure control, and comprises the following steps: S1, alkalization treatment: biomaterial raw materials are soaked in an alkaline solution for reaction, and then filtered, washed with water and dried to obtain a first precursor; S2, oxidation treatment: soaking in an oxidant solution, and then filtering and drying to obtain a second precursor; S3, preparation of an oxidized precursor: oxidation is carried out in an oxygen atmosphere to obtain the oxidized precursor; S4, low-temperature sintering of a pre-carbonization material: low-temperature sintering is carried out in a protective atmosphere to obtain the pre-carbonization material; S5, refinement treatment of the pre-carbonization material: the pre-carbonization material is crushed to obtain a refined pre-carbonization material; S6, purification of the pre-carbonization material: acid washing, centrifugation, water washing and drying are carried out to obtain an acid-washed and purified pre-carbonization material; and S7, high-temperature sintering: high-temperature sintering is carried out in a protective atmosphere to obtain the sodium ion battery hard carbon negative electrode material. The application has the characteristics of high capacity, high first efficiency and simple process.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to a method for preparing hard carbon anode materials for sodium-ion batteries based on the microporous structure controlled by oxygen-containing functional groups. Background Technology

[0002] Sodium-ion batteries have broad application prospects in the energy storage field due to their abundant resources and low cost. Compared with other types of sodium-ion battery anode materials, hard carbon materials have become the mainstream choice for commercialization due to their abundant resources, low cost, high sodium storage capacity, and low sodium storage potential.

[0003] Hard carbon is generally obtained by pyrolyzing carbon-containing raw materials under an inert atmosphere. Currently, the mainstream hard carbon raw materials include biomass raw materials (coconut shells, walnut shells, apricot shells, bamboo chips, resin glucose, starch, etc.), fossil raw materials (anthracite, lignite, asphalt, etc.), and polymer raw materials (phenolic resin, epoxy resin, etc.). Among them, biomass raw materials have advantages such as wide availability, low cost, and abundant supply, making them a better choice for the large-scale production of sodium-ion batteries. However, hard carbon materials obtained by direct carbonization of biomass raw materials generally have a low micropore content, resulting in fewer sodium storage active sites and low sodium storage capacity, which makes it difficult to meet the ever-increasing energy density requirements and is not conducive to practical applications.

[0004] Biomass pre-oxidation can introduce oxygen-containing functional groups into carbon materials, forming cross-linked structures such as -COC- and abundant microporous structures. However, the relatively dense structure of biomass makes it difficult for direct oxidizing agents to penetrate into the biomass, thus limiting the improvement in performance. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing hard carbon anode materials for sodium-ion batteries based on the microporous structure controlled by oxygen-containing functional groups, which has the characteristics of high capacity, high initial efficiency and simple process.

[0006] This invention can be achieved through the following technical solutions:

[0007] This invention discloses a method for preparing hard carbon anode material for sodium-ion batteries based on the microporous structure controlled by oxygen-containing functional groups, comprising the following steps:

[0008] S1. Alkalinization treatment: The biomass raw material is soaked in an alkaline solution for reaction, followed by filtration, washing with water and drying to obtain the first precursor;

[0009] S2. Oxidation treatment: The first precursor obtained in step S1 is immersed in an oxidizing agent solution, then filtered and dried to obtain the second precursor.

[0010] S3. Preparation of the oxidized precursor: The second precursor obtained in step S2 is oxidized in an oxygen atmosphere to obtain the oxidized precursor.

[0011] S4. Low-temperature sintering of pre-carbonized material: The oxide precursor obtained in step S3 is sintered at low temperature under a protective atmosphere to obtain pre-carbonized material.

[0012] S5. Pre-carbonized material refinement treatment: The pre-carbonized material obtained in step S4 is crushed to obtain refined pre-carbonized material;

[0013] S6. Purification of pre-carbonized material: The refined pre-carbonized material obtained in step S5 is subjected to acid washing, centrifugation, water washing and drying to obtain acid-washed and purified pre-carbonized material.

[0014] S7. High-temperature sintering: The acid-washed and purified pre-carbonized material obtained in step S6 is sintered at high temperature under a protective atmosphere to obtain a hard carbon anode material for sodium-ion batteries.

[0015] In step S1, under alkaline conditions, the ester bonds and phenolic ether bonds on the lignin molecular chain break, introducing various oxygen-containing functional groups, increasing the reactivity and solubility of lignin, and simultaneously forming a rich porous structure in the dense biomass raw material. Specifically, if the amount of alkali added is too high, the reaction temperature is too high, or the reaction time is too long, a large amount of lignin will form smaller monomers or low molecular weight polymers that dissolve in the aqueous solution, resulting in a low yield, which is not conducive to practical applications; conversely, the number of chemical bonds broken on the lignin molecular chain is small, which is not conducive to the occurrence of subsequent oxidation reactions.

[0016] Further, in step S2, the oxidant is one or more of HNO3, H2SO4, H2O2, KMnO4, NaClO, KClO, K2Cr2O7, H2Cr2O7, and HClO4; the concentration of the oxidant solution is 0.1-6 mol / L; and the soaking time is 2-8 h.

[0017] In step S2, the oxidant penetrates into the pores of the biomass along with the aqueous solution. After centrifugation and drying, the aqueous solution remains inside the biomass feedstock. Specifically, if the biomass undergoes a high degree of alkali treatment, the biomass has abundant pores, resulting in a larger amount and deeper penetration of the oxidant, which is beneficial for subsequent oxidation reactions. Conversely, if the biomass undergoes a high degree of alkali treatment, the oxidant struggles to penetrate the biomass, hindering the achievement of a satisfactory oxidation effect.

[0018] Furthermore, in step S3, the oxygen concentration is 2-21%, the oxidation temperature is 120-200℃, and the oxidation time is 0.5-5h.

[0019] In step S3, the biomass raw material forms a rich porous structure during the alkali treatment in step S1, allowing the oxidant and oxygen to fully penetrate the biomass. Under the synergistic effect of the oxidant and oxygen, lignin, cellulose, and hemicellulose are further oxidized. The oxidation process breaks some ester and ether bonds, forming a porous structure. Furthermore, oxidation introduces various oxygen-containing functional groups, which cross-link with each other during subsequent carbonization to form cross-linked structures such as -COC, increasing the rigidity of the carbonized material and ensuring that the porous structure is well maintained and does not collapse during subsequent high-temperature carbonization. Simultaneously, if only oxygen is used as the oxidant during oxidation, the biomass is prone to combustion, leading to spontaneous combustion. The introduction of the chemical oxidant in step S2 lowers the oxidation temperature, enhances the degree of oxidation, and achieves a better oxidation effect through synergistic action with oxygen.

[0020] Furthermore, in step S6, the acid used for pickling and purification is one or more of hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, and oxalic acid, and the amount of acid used is 10-60 wt.% of the amount of carbonized material.

[0021] In step S6, metallic impurities present in the biomass raw material itself and those introduced by the oxidant dissolve in the acid solution under the action of strong acid. These impurities are then removed by centrifugation and washing with water, achieving the purpose of purifying the carbonized material. The type of acid depends on the type and content of metallic impurities in the biomass. Specifically, if the content of metallic impurities in the biomass is high, the amount of acid used is increased; if the content of metallic impurities is low, the amount of acid used can be reduced.

[0022] Further, in step S7, the protective atmosphere is nitrogen and / or argon, the sintering temperature is 1100-1500℃, and the carbonization time is 0.3-6h. During step S6, under high temperature, the carbon atom arrangement in the low-temperature carbonized material gradually approaches thermodynamic equilibrium, and the carbon atoms contract inward along the crystal structure direction, gradually forming a graphite carbon layer structure. Under the alkaline treatment in step S1 and the oxidation in step S3, a rich microporous structure is formed in the pre-carbonized material, while abundant oxygen-containing functional groups are introduced into the carbon material. During the low-temperature sintering in step S4, the oxygen-containing functional groups cross-link to form cross-linked structures such as -COC, increasing the rigidity of the carbonized material and ensuring that the pore structure is well maintained and does not collapse during the high-temperature carbonization in step S7. Finally, a hard carbon material structure containing abundant micropores is formed.

[0023] Furthermore, in step S1, the biomass raw material is one or more of the following: straw, reed, bamboo, coconut shell, walnut shell, nut shell, apricot shell, coffee shell, poplar, eucalyptus, pine, fruit wood, miscellaneous wood, fir, oak, corn cob, and rice husk.

[0024] From a microscopic perspective, biomass is mainly composed of lignin, cellulose, and hemicellulose. Cellulose is interwoven into bundles, while lignin forms a dense three-dimensional network surrounding the cellulose, providing resistance to pressure, water erosion, and oxidation. Therefore, if biomass is directly heat-treated in an oxygen atmosphere, oxygen cannot penetrate evenly into the dense structure of the biomass. This results in poor oxidation even if the surface is peroxidized (carbon materials are burned off), the interior remains difficult to oxidize, leading to a poor oxidation effect. If the oxidation temperature is too low, the purpose of oxidizing the biomass cannot be achieved; if the treatment temperature is too high, it results in direct combustion, with carbon being burned off to form CO or CO2.

[0025] Further, in step S1, the alkaline solution is one or more of NaOH, KOH, Na2CO3, KCO3, NaHCO3, Ca(OH)2, LiOH, and NH3·H2O, the concentration of the alkaline solution is 0.2-5 mol / L, the reaction temperature is 60-150℃, and the reaction time is 0.5-3h.

[0026] Furthermore, in step S4, the protective atmosphere is nitrogen and / or argon, the carbonization temperature is 400-800℃, and the carbonization time is 0.3-3h.

[0027] Furthermore, in step S5, the particle size D50 is 4-12μm, and the pulverizing method is one or more of the following: roller mill, mechanical mill, air jet mill, Raymond mill, ball mill, and stirred mill.

[0028] This invention discloses a method for preparing hard carbon anode material for sodium-ion batteries based on the microporous structure controlled by oxygen-containing functional groups, which has the following beneficial effects:

[0029] Under the alkaline treatment in step S1 and the oxidation in step S3, a rich microporous structure is formed in the pre-carbonized material, while abundant oxygen-containing functional groups are introduced into the carbon material. During the low-temperature sintering process in step S4, the oxygen-containing functional groups cross-link to form cross-linked structures such as -COC, increasing the rigidity of the carbonized material and ensuring that the pore structure is well maintained and does not collapse during the high-temperature carbonization process in step S7. Ultimately, a hard carbon material structure with abundant micropores is formed, thereby effectively improving the capacity of the hard carbon material. Alkaline treatment creates a rich porous structure in the originally dense biomass raw material, facilitating the subsequent penetration of oxidants into the biomass and achieving uniform oxidation both internally and externally. This avoids excessive surface area due to external over-oxidation of the biomass, thus giving the hard carbon material a higher first-cycle efficiency. Detailed Implementation

[0030] To enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention will be further described in detail below with reference to embodiments.

[0031] This invention discloses a method for preparing hard carbon anode material for sodium-ion batteries based on the microporous structure controlled by oxygen-containing functional groups, comprising the following steps:

[0032] S1. Alkalinization treatment: The biomass raw material is soaked in an alkaline solution for reaction, followed by filtration, washing with water and drying to obtain the first precursor;

[0033] S2. Oxidation treatment: The first precursor obtained in step S1 is immersed in an oxidizing agent solution, then filtered and dried to obtain the second precursor.

[0034] S3. Preparation of the oxidized precursor: The second precursor obtained in step S2 is oxidized in an oxygen atmosphere to obtain the oxidized precursor.

[0035] S4. Low-temperature sintering of pre-carbonized material: The oxide precursor obtained in step S3 is sintered at low temperature under a protective atmosphere to obtain pre-carbonized material.

[0036] S5. Pre-carbonized material refinement treatment: The pre-carbonized material obtained in step S4 is crushed to obtain refined pre-carbonized material;

[0037] S6. Purification of pre-carbonized material: The refined pre-carbonized material obtained in step S5 is subjected to acid washing, centrifugation, water washing and drying to obtain acid-washed and purified pre-carbonized material.

[0038] S7. High-temperature sintering: The acid-washed and purified pre-carbonized material obtained in step S6 is sintered at high temperature under a protective atmosphere to obtain a hard carbon anode material for sodium-ion batteries.

[0039] Further, in step S2, the oxidant is one or more of HNO3, H2SO4, H2O2, KMnO4, NaClO, KClO, K2Cr2O7, H2Cr2O7, and HClO4; the concentration of the oxidant solution is 0.1-6 mol / L; and the soaking time is 2-8 h.

[0040] Furthermore, in step S3, the oxygen concentration is 2-21%, the oxidation temperature is 120-200℃, and the oxidation time is 0.5-5h.

[0041] Furthermore, in step S6, the acid used for pickling and purification is one or more of hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, and oxalic acid, and the amount of acid used is 10-60 wt.% of the amount of carbonized material.

[0042] Furthermore, in step S7, the protective atmosphere is nitrogen and / or argon, the sintering temperature is 1100-1500℃, and the carbonization time is 0.3-6h.

[0043] Furthermore, in step S1, the biomass raw material is one or more of the following: straw, reed, bamboo, coconut shell, walnut shell, nut shell, apricot shell, coffee shell, poplar, eucalyptus, pine, fruit wood, miscellaneous wood, fir, oak, corn cob, and rice husk.

[0044] Further, in step S1, the alkaline solution is one or more of NaOH, KOH, Na2CO3, KCO3, NaHCO3, Ca(OH)2, LiOH, and NH3·H2O, the concentration of the alkaline solution is 0.2-5 mol / L, the reaction temperature is 60-150℃, and the reaction time is 0.5-3h.

[0045] Furthermore, in step S4, the protective atmosphere is nitrogen and / or argon, the carbonization temperature is 400-800℃, and the carbonization time is 0.3-3h.

[0046] Furthermore, in step S5, the particle size D50 is 4-12μm, and the pulverizing method is one or more of the following: roller mill, mechanical mill, air jet mill, Raymond mill, ball mill, and stirred mill.

[0047] Example 1

[0048] This embodiment relates to a hard carbon anode material for sodium-ion batteries based on a microporous structure controlled by oxygen-containing functional groups. Its preparation method includes the following steps:

[0049] S1. Alkalinization treatment: The biomass raw material is soaked in an alkaline solution for reaction, followed by filtration, washing with water, and drying to obtain the first precursor. Specifically, the biomass raw material is straw, reed, or bamboo; the alkaline solution is NaOH, KOH, Na2CO3, or KCO3, with a concentration of 5 mol / L, a reaction temperature of 100℃, and a reaction time of 0.5 h.

[0050] S2. Oxidation treatment: The first precursor obtained in step S1 is immersed in an oxidizing agent solution, followed by filtration and drying to obtain the second precursor. Specifically, the oxidizing agents are HNO3 and H2SO4, the concentration of the oxidizing agent solution is 6 mol / L, and the immersion time is 5 h.

[0051] S3. Preparation of the oxidation precursor: The second precursor obtained in step S2 is oxidized in an oxygen atmosphere to obtain the oxidation precursor. Specifically, the oxygen concentration is 21%, the oxidation temperature is 160℃, and the oxidation time is 0.5h.

[0052] S4. Low-temperature sintering of pre-carbonized material: The oxide precursor obtained in step S3 is sintered at low temperature under a protective atmosphere to obtain pre-carbonized material. Specifically, the protective atmosphere is nitrogen, the carbonization temperature is 800℃, and the carbonization time is 2h.

[0053] S5. Refining the pre-carbonized material: The pre-carbonized material obtained in step S4 is pulverized to obtain refined pre-carbonized material. Specifically, the particle size D50 is 4-12μm, and the pulverization method is a roller mill or mechanical mill.

[0054] S6. Purification of Pre-Carbonized Material: The refined pre-carbonized material obtained in step S5 is subjected to acid washing, centrifugation, water washing, and drying to obtain acid-purified pre-carbonized material. Specifically, the acid used for acid washing and purification is hydrochloric acid, and the amount of acid used is 60 wt.% of the amount of carbonized material.

[0055] S7. High-temperature sintering: The acid-washed and purified pre-carbonized material obtained in step S6 is sintered at high temperature under a protective atmosphere to obtain a hard carbon anode material for sodium-ion batteries. Specifically, the protective atmosphere is nitrogen and argon, the sintering temperature is 1500℃, and the carbonization time is 3 hours.

[0056] Example 2

[0057] This embodiment relates to a hard carbon anode material for sodium-ion batteries based on a microporous structure controlled by oxygen-containing functional groups. Its preparation method includes the following steps:

[0058] S1. Alkalinization treatment: The biomass raw material is soaked in an alkaline solution for reaction, followed by filtration, washing with water, and drying to obtain the first precursor. Specifically, the biomass raw material is pine, fruit wood, mixed wood, fir, or oak; the alkaline solution is KCO3, NaHCO3, or Ca(OH)2, with a concentration of 3 mol / L, a reaction temperature of 60℃, and a reaction time of 3 h.

[0059] S2. Oxidation treatment: The first precursor obtained in step S1 is immersed in an oxidizing agent solution, followed by filtration and drying to obtain the second precursor. Specifically, the oxidizing agents are K2Cr2O7, H2Cr2O7, and HClO4, and the concentration of the oxidizing agent solution is 3 mol / L; the immersion time is 2 hours.

[0060] S3. Preparation of the oxidation precursor: The second precursor obtained in step S2 is oxidized in an oxygen atmosphere to obtain the oxidation precursor. Specifically, the oxygen concentration is 11%, the oxidation temperature is 120℃, and the oxidation time is 5h.

[0061] S4. Low-temperature sintering of pre-carbonized material: The oxide precursor obtained in step S3 is sintered at low temperature under a protective atmosphere to obtain pre-carbonized material. Specifically, the protective atmosphere is nitrogen and argon, the carbonization temperature is 600℃, and the carbonization time is 0.5h.

[0062] S5. Refining the pre-carbonized material: The pre-carbonized material obtained in step S4 is pulverized to obtain refined pre-carbonized material. Specifically, the particle size D50 is 4-12μm, and the pulverization method is air-jet grinding.

[0063] S6. Purification of Pre-Carbonized Material: The refined pre-carbonized material obtained in step S5 is subjected to acid washing, centrifugation, water washing, and drying to obtain acid-purified pre-carbonized material. Specifically, sulfuric acid is used for acid washing and purification, and the amount of acid used is 30 wt.% of the amount of carbonized material.

[0064] S7. High-temperature sintering: The acid-washed and purified pre-carbonized material obtained in step S6 is sintered at high temperature under a protective atmosphere to obtain a hard carbon anode material for sodium-ion batteries. Specifically, the protective atmosphere is nitrogen, the sintering temperature is 1300℃, and the carbonization time is 0.3h.

[0065] Example 3

[0066] This embodiment relates to a hard carbon anode material for sodium-ion batteries based on a microporous structure controlled by oxygen-containing functional groups. Its preparation method includes the following steps:

[0067] S1. Alkalinization treatment: The biomass raw material is soaked in an alkaline solution for reaction, followed by filtration, washing with water, and drying to obtain the first precursor. Specifically, the biomass raw material is mixed hardwood, fir, oak, corn cob, and rice husk; the alkaline solution is NaOH, KOH, or NH3·H2O, with a concentration of 0.2 mol / L, a reaction temperature of 150℃, and a reaction time of 2 hours.

[0068] S2. Oxidation treatment: The first precursor obtained in step S1 is immersed in an oxidizing agent solution, followed by filtration and drying to obtain the second precursor. Specifically, the oxidizing agents are HNO3, H2SO4, H2Cr2O7, and HClO4, and the concentration of the oxidizing agent solution is 0.1 mol / L; the immersion time is 8 h.

[0069] S3. Preparation of the oxidation precursor: The second precursor obtained in step S2 is oxidized in an oxygen atmosphere to obtain the oxidation precursor. Specifically, the oxygen concentration is 41%, the oxidation temperature is 200℃, and the oxidation time is 3h.

[0070] S4. Low-temperature sintering of pre-carbonized material: The oxide precursor obtained in step S3 is sintered at low temperature under a protective atmosphere to obtain pre-carbonized material. Specifically, the protective atmosphere is argon, the carbonization temperature is 400℃, and the carbonization time is 3h.

[0071] S5. Refining the pre-carbonized material: The pre-carbonized material obtained in step S4 is pulverized to obtain refined pre-carbonized material. Specifically, the particle size D50 is 4-12μm, and the pulverization method is ball milling or stirred milling.

[0072] S6. Purification of Pre-Carbonized Material: The refined pre-carbonized material obtained in step S5 is subjected to acid washing, centrifugation, water washing, and drying to obtain acid-purified pre-carbonized material. Specifically, the acids used for acid washing and purification are hydrochloric acid and oxalic acid, and the amount of acid used is 10 wt.% of the amount of carbonized material.

[0073] S7. High-temperature sintering: The acid-washed and purified pre-carbonized material obtained in step S6 is sintered at high temperature under a protective atmosphere to obtain a hard carbon anode material for sodium-ion batteries. Specifically, the protective atmosphere is nitrogen and argon, the sintering temperature is 1100℃, and the carbonization time is 6 hours.

[0074] Example 4

[0075] This embodiment relates to a hard carbon anode material for sodium-ion batteries based on a microporous structure controlled by oxygen-containing functional groups. Its preparation method includes the following steps:

[0076] S1. Alkalinization treatment: The biomass raw materials are soaked in an alkaline solution for reaction, followed by filtration, washing with water, and drying to obtain the first precursor. Specifically, the biomass raw materials are straw, reeds, bamboo, corn cobs, and rice husks; the alkaline solution is NaOH, KOH, or NH3·H2O, with a concentration of 2 mol / L, a reaction temperature of 80℃, and a reaction time of 1 h.

[0077] S2. Oxidation treatment: The first precursor obtained in step S1 is immersed in an oxidizing agent solution, followed by filtration and drying to obtain the second precursor. Specifically, the oxidizing agents are HNO3, H2SO4, and H2O2, and the concentration of the oxidizing agent solution is 2 mol / L; the immersion time is 3 h.

[0078] S3. Preparation of the oxidation precursor: The second precursor obtained in step S2 is oxidized in an oxygen atmosphere to obtain the oxidation precursor. Specifically, the oxygen concentration is 8%, the oxidation temperature is 140℃, and the oxidation time is 2 hours.

[0079] S4. Low-temperature sintering of pre-carbonized material: The oxide precursor obtained in step S3 is sintered at low temperature under a protective atmosphere to obtain pre-carbonized material. Specifically, the protective atmosphere is nitrogen and argon, the carbonization temperature is 700℃, and the carbonization time is 1 hour.

[0080] S5. Refining the pre-carbonized material: The pre-carbonized material obtained in step S4 is pulverized to obtain refined pre-carbonized material. Specifically, the particle size D50 is 4-12μm, and the pulverization method is Raymond milling or ball milling.

[0081] S6. Purification of Pre-Carbonized Material: The refined pre-carbonized material obtained in step S5 is subjected to acid washing, centrifugation, water washing, and drying to obtain acid-purified pre-carbonized material. Specifically, the acids used for acid washing and purification are hydrochloric acid and nitric acid, and the amount of acid used is 20 wt.% of the amount of carbonized material.

[0082] S7. High-temperature sintering: The acid-washed and purified pre-carbonized material obtained in step S6 is sintered at high temperature under a protective atmosphere to obtain a hard carbon anode material for sodium-ion batteries. Specifically, the protective atmosphere is nitrogen and argon, the sintering temperature is 1400℃, and the carbonization time is 5 hours.

[0083] Example 5

[0084] This embodiment relates to a hard carbon anode material for sodium-ion batteries based on a microporous structure controlled by oxygen-containing functional groups. Its preparation method includes the following steps:

[0085] S1. Alkalinization treatment: The biomass raw materials are soaked in an alkaline solution for reaction, followed by filtration, washing with water, and drying to obtain the first precursor. Specifically, the biomass raw materials are straw, reeds, bamboo, coconut shells, walnut shells, nut shells, and apricot shells; the alkaline solution is NaOH, KOH, or Na2CO3, with a concentration of 4 mol / L, a reaction temperature of 130℃, and a reaction time of 2 hours.

[0086] S2. Oxidation treatment: The first precursor obtained in step S1 is immersed in an oxidizing agent solution, followed by filtration and drying to obtain the second precursor. Specifically, the oxidizing agents are NaClO, KClO, and K2Cr2O7, and the concentration of the oxidizing agent solution is 4 mol / L; the immersion time is 6 h.

[0087] S3. Preparation of the oxidation precursor: The second precursor obtained in step S2 is oxidized in an oxygen atmosphere to obtain the oxidation precursor. Specifically, the oxygen concentration is 13%, the oxidation temperature is 180℃, and the oxidation time is 4h.

[0088] S4. Low-temperature sintering of pre-carbonized material: The oxide precursor obtained in step S3 is sintered at low temperature under a protective atmosphere to obtain pre-carbonized material. Specifically, the protective atmosphere is nitrogen and argon, the carbonization temperature is 700℃, and the carbonization time is 2h.

[0089] S5. Refining the pre-carbonized material: The pre-carbonized material obtained in step S4 is pulverized to obtain refined pre-carbonized material. Specifically, the particle size D50 is 4-12μm, and the pulverization method is ball milling or stirred milling.

[0090] S6. Purification of Pre-Carbonized Material: The refined pre-carbonized material obtained in step S5 is subjected to acid washing, centrifugation, water washing, and drying to obtain acid-purified pre-carbonized material. Specifically, the acids used for acid washing and purification are hydrochloric acid and nitric acid, and the amount of acid used is 30 wt.% of the amount of carbonized material.

[0091] S7. High-temperature sintering: The acid-washed and purified pre-carbonized material obtained in step S6 is sintered at high temperature under a protective atmosphere to obtain a hard carbon anode material for sodium-ion batteries. Specifically, the protective atmosphere is nitrogen and argon, the sintering temperature is 1200℃, and the carbonization time is 3 hours.

[0092] Application Example 1

[0093] This embodiment relates to a hard carbon anode material for sodium-ion batteries based on a microporous structure controlled by oxygen-containing functional groups. Its preparation method includes the following steps:

[0094] S1. Alkalization treatment: The walnut shell raw material is soaked in 0.8 mol / L NaOH solution and reacted in a reactor at 90°C for 2 hours. Then it is filtered, washed with water and dried to obtain the first precursor.

[0095] S2. Oxidation treatment: The first precursor obtained in step S1 is soaked in a 1 mol / L HNO3 aqueous solution for 4 hours, then filtered and dried to obtain the second precursor.

[0096] S3. Preparation of the oxidation precursor: The second precursor obtained in step S2 is reacted at 150°C for 3 hours under an atmosphere with 15% oxygen content to obtain the oxidation precursor.

[0097] S4. Low-temperature sintering of pre-carbonized material: The oxidized precursor obtained in step S3 is sintered at a low temperature of 600℃ and for 2 hours under a nitrogen atmosphere to obtain pre-carbonized material.

[0098] S5. Refining treatment of pre-carbonized material: The pre-carbonized material obtained in step S4 is pulverized by a roller mill and an air-flow powder mill in sequence until D50 is 7μm, and refined pulverized material is obtained.

[0099] S6. Purification treatment of pre-carbonized material: The finely pulverized material obtained in step S5 is acid-washed, centrifuged, washed with water and dried using 20wt.% HNO3 to obtain acid-washed and purified pre-carbonized material.

[0100] S7. High-temperature sintering: The acid-washed and purified pre-carbonized material obtained in step S6 is sintered at high temperature in a nitrogen atmosphere. The sintering temperature is 1300℃ and the sintering time is 4h to obtain a high-capacity hard carbon anode material.

[0101] The electrochemical performance of the obtained materials was tested as follows: Hard carbon material, Super P, CMC, and SBR were mixed in a mass ratio of 94:1.5:2:2.5 to form a slurry. A 120µm four-sided coating tool was used to coat the black slurry onto copper foil, and the membrane was then dried in a vacuum oven at 100°C for 2 hours. The electrode membrane was punched into a 0.6mm radius disc using a die-cutting machine. Using metallic sodium as the counter electrode, 1mol / L NaClO4 EC+DEC (1:1 vol%) as the electrolyte, and a PP / PE / PP three-layer separator, a CR2016 type button cell was assembled in a glove box. The above button cell was subjected to constant current charge-discharge testing at a current density of 0.1C (1C = 300mAh / g) and a voltage range of 1-0.005V.

[0102] Comparative Example 1

[0103] This embodiment relates to a hard carbon anode material for sodium-ion batteries. Compared with application embodiment 1, the main difference is that it does not use an oxidizing agent for oxidation treatment. The preparation method includes the following steps:

[0104] S1. Alkalization treatment: The walnut shell raw material is soaked in 0.8 mol / L NaOH solution and reacted in a reactor at 90°C for 2 hours. Then it is filtered, washed with water and dried to obtain the first precursor.

[0105] S2. Preparation of oxidation precursor: The first precursor obtained in step S1 is reacted at 150°C for 3 hours under an atmosphere with 15% oxygen content to obtain the oxidation precursor.

[0106] S3. Low-temperature sintering of pre-carbonized material: The oxidized precursor obtained in step S2 is sintered at a low temperature in a nitrogen atmosphere at a temperature of 600℃ for 2 hours to obtain pre-carbonized material.

[0107] S4. Refining treatment of pre-carbonized material: The pre-carbonized material obtained in step S3 is pulverized by a roller mill and an air-flow powder mill in sequence until the D50 is 7μm, and refined pulverized material is obtained.

[0108] S5. Purification treatment of pre-carbonized material: The finely pulverized material obtained in step S4 is acid-washed, centrifuged, washed with water and dried using 20wt.% HNO3 to obtain acid-washed and purified pre-carbonized material.

[0109] S6. High-temperature sintering: The acid-washed and purified pre-carbonized material obtained in step S5 is sintered at high temperature in a nitrogen atmosphere. The sintering temperature is 1300℃ and the sintering time is 4h to obtain a high-capacity hard carbon anode material.

[0110] The electrochemical performance of the obtained materials was tested as follows: Hard carbon material, Super P, CMC, and SBR were mixed in a mass ratio of 94:1.5:2:2.5 to form a slurry. A 120µm four-sided coating tool was used to coat the black slurry onto copper foil, and the membrane was then dried in a vacuum oven at 100°C for 2 hours. The electrode membrane was punched into a 0.6mm radius disc using a die-cutting machine. Using metallic sodium as the counter electrode, 1mol / L NaClO4 EC+DEC (1:1 vol%) as the electrolyte, and a PP / PE / PP three-layer separator, a CR2016 type button cell was assembled in a glove box. The above button cell was subjected to constant current charge-discharge testing at a current density of 0.1C (1C = 300mAh / g) and a voltage range of 1-0.005V.

[0111] Comparative Example 2

[0112] This embodiment relates to a hard carbon anode material for sodium-ion batteries. Compared with application embodiment 1, the main difference is that it does not use alkaline solution for alkalization treatment. The preparation method includes the following steps:

[0113] S1. Oxidation treatment: The walnut shell raw material was soaked in a 1 mol / L HNO3 aqueous solution for 4 hours, then filtered and dried to obtain the first precursor;

[0114] S2. Preparation of oxidation precursor: The first precursor obtained in step S1 is reacted at 150°C for 3 hours under an atmosphere with 15% oxygen content to obtain the oxidation precursor.

[0115] S3. Low-temperature sintering of pre-carbonized material: The oxidized precursor obtained in step S2 is sintered at a low temperature in a nitrogen atmosphere at a temperature of 600℃ for 2 hours to obtain pre-carbonized material.

[0116] S4. Refining treatment of pre-carbonized material: The pre-carbonized material obtained in step S3 is pulverized by a roller mill and an air-flow powder mill in sequence until the D50 is 7μm, and refined pulverized material is obtained.

[0117] S5. Purification treatment of pre-carbonized material: The finely pulverized material obtained in step S4 is acid-washed, centrifuged, washed with water and dried using 20wt.% HNO3 to obtain acid-washed and purified pre-carbonized material.

[0118] S6. High-temperature sintering: The acid-washed and purified pre-carbonized material obtained in step S5 is sintered at high temperature in a nitrogen atmosphere. The sintering temperature is 1300℃ and the sintering time is 4h to obtain a high-capacity hard carbon anode material.

[0119] The electrochemical performance of the obtained materials was tested as follows: Hard carbon material, Super P, CMC, and SBR were mixed in a mass ratio of 94:1.5:2:2.5 to form a slurry. A 120µm four-sided coating tool was used to coat the black slurry onto copper foil, and the membrane was then dried in a vacuum oven at 100°C for 2 hours. The electrode membrane was punched into a 0.6mm radius disc using a die-cutting machine. Using metallic sodium as the counter electrode, 1mol / L NaClO4 EC+DEC (1:1 vol%) as the electrolyte, and a PP / PE / PP three-layer separator, a CR2016 type button cell was assembled in a glove box. The above button cell was subjected to constant current charge-discharge testing at a current density of 0.1C (1C = 300mAh / g) and a voltage range of 1-0.005V.

[0120] The specific surface areas of Application Example 1, Comparative Example 1, and Comparative Example 2, as measured by gas adsorption-desorption tests, were 5.3, 6.6, and 13.1 m² / g, respectively, indicating that alkali treatment can effectively ensure that biomass raw materials are uniformly oxidized, and that their specific surface areas are too large.

[0121] The true densities of Application Example 1, Comparative Example 1, and Comparative Example 2, measured by helium gas true density testing, were 1.85, 1.98, and 2.03 g / cm3, respectively, indicating that alkali treatment and oxidation treatment can effectively increase the internal pore volume of hard carbon materials.

[0122] The first-week charge specific capacity of Application Example 1, Example 2, and Comparative Example 1, measured by constant current charge-discharge testing, was 348, 283, and 302 mAh / g, respectively, indicating that alkaline treatment and oxidation treatment can effectively improve their sodium storage capacity. The first-week efficiencies of Application Example 1, Example 2, and Comparative Example 1, measured by constant current charge-discharge testing, were 92.3%, 90.6%, and 86.5%, respectively. The higher first-week efficiency of Application Example 1 is attributed to the fact that alkaline treatment effectively ensures uniform oxidation of the biomass feedstock, resulting in a smaller specific surface area and thus less irreversible capacity loss due to contact with the electrolyte.

[0123] The above embodiments are merely specific examples of the present invention, and their descriptions are quite specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these obvious substitutions all fall within the protection scope of the present invention.

Claims

1. A method for preparing hard carbon anode material for sodium-ion batteries based on microporous structure controlled by oxygen-containing functional groups, characterized in that... Includes the following steps: S1. Alkalinization treatment: The biomass raw material is soaked in an alkaline solution for reaction, followed by filtration, washing with water, and drying to obtain the first precursor; the alkaline solution is one or more of NaOH, KOH, Na2CO3, K2CO3, NaHCO3, Ca(OH)2, LiOH, and NH3·H2O, the concentration of the alkaline solution is 0.2-5 mol / L, the reaction temperature is 60-150℃, and the reaction time is 0.5-3h; S2. Oxidation treatment: The first precursor obtained in step S1 is immersed in an oxidizing agent solution, followed by filtration and drying to obtain the second precursor; the oxidizing agent is one or more of HNO3, H2SO4, H2O2, KMnO4, NaClO, KClO, K2Cr2O7, H2Cr2O7, and HClO4; the concentration of the oxidizing agent solution is 0.1-6 mol / L; the immersion time is 2-8 h; S3. Preparation of the oxidation precursor: The second precursor obtained in step S2 is oxidized in an oxygen atmosphere to obtain the oxidation precursor; the oxygen concentration is 2-21%, the oxidation temperature is 120-200℃, and the oxidation time is 0.5-5h. S4. Low-temperature sintering of pre-carbonized material: The oxidized precursor obtained in step S3 is sintered at low temperature under a protective atmosphere to obtain pre-carbonized material; the protective atmosphere is nitrogen and / or argon, the carbonization temperature is 400-800℃, and the carbonization time is 0.3-3h. S5. Pre-carbonized material refinement treatment: The pre-carbonized material obtained in step S4 is crushed to obtain refined pre-carbonized material; S6. Purification of pre-carbonized material: The refined pre-carbonized material obtained in step S5 is subjected to acid washing, centrifugation, water washing, and drying to obtain acid-purified pre-carbonized material; the acid used for acid washing and purification is one or more of hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, and oxalic acid, and the amount of acid used is 10-60 wt.% of the amount of carbonized material. S7. High-temperature sintering: The acid-washed and purified pre-carbonized material obtained in step S6 is sintered at high temperature under a protective atmosphere at a temperature of 1100-1500℃ to obtain a hard carbon anode material for sodium-ion batteries.

2. The method for preparing hard carbon anode material for sodium-ion batteries based on oxygen-containing functional group microporous structure control according to claim 1, characterized in that: In step S7, the protective atmosphere is nitrogen and / or argon, and the sintering time is 0.3-6h.

3. The method for preparing hard carbon anode material for sodium-ion batteries based on oxygen-containing functional group microporous structure control according to claim 1, characterized in that: In step S1, the biomass raw materials are one or more of the following: straw, reeds, bamboo, coconut shells, walnut shells, nut shells, apricot shells, coffee shells, poplar, eucalyptus, pine, fruit wood, fir, oak, corn cobs, and rice husks.

4. The method for preparing hard carbon anode material for sodium-ion batteries based on oxygen-containing functional group microporous structure control according to claim 1, characterized in that: In step S5, the particle size D50 is 4-12μm, and the pulverization method is one or more of the following: roller mill, mechanical mill, air jet mill, Raymond mill, ball mill, and stirred mill.