Sodium-ion battery hard carbon negative electrode material preparation method based on oxygen-containing functional group microporous structure control

Abstract

The invention discloses a preparation method of a sodium-ion battery hard carbon negative electrode material based on oxygen-containing functional group microporous structure control, which comprises the following steps: S1, alkalization treatment: soaking a biomass raw material in an alkaline solution for reaction, and then filtering, washing and drying 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 oxidation precursor: performing oxidation in an oxygen atmosphere to obtain the oxidation precursor; s4, low-temperature sintering of the pre-carbonized material: performing low-temperature sintering in a protective atmosphere to obtain the pre-carbonized material; s5, refining treatment of the pre-carbonized material: crushing to obtain a refined pre-carbonized material; s6, purifying the pre-carbonized material: pickling, centrifuging, washing and drying to obtain the pickled and purified pre-carbonized material; and S7, high-temperature sintering: carrying out high-temperature sintering in a protective atmosphere to obtain the sodium-ion battery hard carbon negative electrode material. The method has the characteristics of high capacity, high first efficiency and simple process.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a method for preparing a sodium ion battery hard carbon negative electrode material based on microporous structure control of oxygen-containing functional groups. Background Art

[0002] Sodium-ion batteries have broad application prospects in the field of energy storage due to their abundant resources and low cost. Compared with other types of sodium-ion battery negative electrode 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 pyrolysis of carbon-containing raw materials under an inert atmosphere. At present, 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 the advantages of wide sources, low costs, and sufficient supply, and are a good choice for large-scale production of sodium-ion batteries. However, the 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 growing energy density demand and is not conducive to practical applications.

[0004] Biomass pre-oxidation can introduce oxygen-containing functional groups into the carbon material, forming cross-linked structures such as -COC- and rich microporous structures. However, the biomass structure is relatively dense, and it is difficult for direct oxidation oxidants to penetrate into the biomass, so the improvement of performance is limited. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a sodium ion battery hard carbon negative electrode material based on the control of the microporous structure of oxygen-containing functional groups, which has the characteristics of high capacity, high initial efficiency and simple process.

[0006] The present invention can be implemented by the following technical solutions:

[0007] The present invention discloses a method for preparing a sodium ion battery hard carbon negative electrode material based on microporous structure control of oxygen-containing functional groups, comprising the following steps:

[0008] S1. Alkalinization treatment: soaking the biomass raw material in an alkaline solution for reaction, followed by filtering, washing and drying to obtain a first precursor;

[0009] S2, oxidation treatment: soaking the first precursor obtained in step S1 in an oxidant solution, then filtering and drying to obtain a second precursor;

[0010] S3, preparation of an oxidized precursor: oxidizing the second precursor obtained in step S2 under an oxygen atmosphere to obtain an oxidized precursor;

[0011] S4, low-temperature sintering of the pre-carbonized material: sintering the oxidized precursor obtained in step S3 at low temperature under a protective atmosphere to obtain a pre-carbonized material;

[0012] S5, pre-carbonized material refinement treatment: crushing the pre-carbonized material obtained in step S4 to obtain refined pre-carbonized material;

[0013] S6, pre-carbonized material purification: the refined pre-carbonized material obtained in step S5 is acid-washed, centrifuged, washed with water, and dried to obtain acid-washed and purified pre-carbonized material;

[0014] S7, high temperature sintering: the acid washed, purified and pre-carbonized material obtained in step S6 is subjected to high temperature sintering under a protective atmosphere to obtain a hard carbon negative electrode material for a sodium ion battery.

[0015] During step S1, the ester bonds and phenolic ether bonds on the polymer lignin molecular chain are broken under alkaline conditions, various oxygen-containing functional groups are introduced, the reactivity and solubility of lignin are increased, and a rich pore structure is formed 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 forms smaller monomers or low molecular weight polymers that dissolve in the aqueous solution, resulting in a low yield, which is not conducive to practical application; on the contrary, the amount of chemical bonds on the lignin molecular chain that are broken is small, which is not conducive to the occurrence of subsequent oxidation reactions.

[0016] Furthermore, 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] During step S2, the oxidant penetrates into the pores of the biomass along with the aqueous solution, and then remains inside the biomass raw material after centrifugation and drying the aqueous solution. Specifically, if the degree of biomass alkali treatment is high, the pores inside the biomass are abundant, so the penetration amount of the oxidant is large and the penetration depth is deep, which is conducive to the occurrence of subsequent oxidation reactions. If the degree of biomass alkali treatment is high, it is difficult for the oxidant to penetrate into the interior of the biomass, and a good oxidation effect cannot be achieved subsequently.

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

[0019] During step S3, the biomass raw material forms a rich pore structure during the alkali treatment process of step S1, and the oxidant and oxygen can fully penetrate into the biomass. Under the synergistic effect of the oxidant and oxygen, lignin, cellulose and hemicellulose are further oxidized, and the oxidation breaks some ester bonds and ether bonds to form a pore structure; and oxidation introduces various oxygen-containing functional groups, and in the subsequent carbonization process, the oxygen-containing functional groups cross-link with each other to form cross-linked structures such as -COC, which increases the rigidity of the carbonized material and enables the pore structure to be better maintained during the subsequent high-temperature carbonization process without collapse. At the same time, during the oxidation process, if only oxygen is used as an oxidant, the biomass is prone to combustion reaction with oxygen, resulting in spontaneous combustion of the biomass. The introduction of the chemical oxidant in step S2 can reduce the oxidation temperature, enhance the degree of oxidation reaction, and synergize with oxygen to achieve a better oxidation effect.

[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 the acid used is 10-60wt.% of the amount of the carbonized material used.

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

[0022] Furthermore, in step S7, the protective atmosphere is nitrogen and / or argon, the sintering temperature is 1100-1500°C, and the carbonization time is 0.3-6h. During step S6, the carbon atom arrangement of the low-temperature carbonized material gradually tends to a thermodynamic equilibrium state under the action of high temperature, the carbon atoms shrink inward along the crystal structure direction, and the graphite carbon layer structure gradually forms. Under the alkali treatment of step S1 and the oxidation of step S3, a rich microporous pore structure is formed in the pre-carbonized material, and rich oxygen-containing functional groups are introduced into the carbon material; during the low-temperature sintering process of step S4, the oxygen-containing functional groups are cross-linked to form cross-linked structures such as -COC, which increases the rigidity of the carbonized material and enables the pore structure to be better maintained during the high-temperature carbonization process of step S7 without collapse. Finally, a hard carbon material structure containing rich micropores is formed.

[0023] Furthermore, in step S1, the biomass raw material is one or more of 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 point of view, biomass is mainly composed of lignin, cellulose and hemicellulose, among which cellulose is interwoven into bundles, and lignin forms a dense three-dimensional network structure that is interwoven around cellulose, which plays a role in compressive resistance, water erosion resistance and oxidation resistance for biomass. Therefore, if biomass is directly heat-treated in an oxygen atmosphere, it is difficult for oxygen to evenly penetrate into the dense structure of biomass, resulting in that even if the surface of the biomass is peroxidized (carbon material combustion and ablation), the inside is difficult to oxidize, so the oxidation effect is poor. If the oxidation temperature is too low, the purpose of oxidizing the biomass cannot be achieved. If the treatment temperature is too high, it will burn directly, and the carbon will be ablated to form CO or CO2.

[0025] Furthermore, 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°C, and the reaction time is 0.5-3h.

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

[0027] Further, in step S5, the particle size D50 is 4-12 μm, and the pulverizing method is one or more of a roller mill, a mechanical mill, an air flow mill, a Raymond mill, a ball mill, and a stirred mill.

[0028] The present invention provides a method for preparing a sodium ion battery hard carbon negative electrode material based on the control of the microporous structure of oxygen-containing functional groups, which has the following beneficial effects:

[0029] Under the action of alkali treatment in step S1 and oxidation in step S3, a rich microporous pore structure is formed in the pre-carbonized material, and rich oxygen-containing functional groups are introduced into the carbon material; during the low-temperature sintering process in step S4, the oxygen-containing functional groups are cross-linked to form cross-linked structures such as -COC, which increases the rigidity of the carbonized material and enables the pore structure to be well maintained and not collapsed during the high-temperature carbonization process in step S7. Finally, a hard carbon material structure containing rich micropores is formed, thereby effectively improving the capacity of the hard carbon material. The alkali treatment forms a rich pore structure in the originally dense biomass raw material, which facilitates the subsequent oxidant to penetrate into the biomass and achieve the purpose of uniform oxidation inside and outside. The excessive specific surface area of ​​the material caused by overoxidation of the biomass outside is avoided, thereby making the hard carbon material have a higher first-week efficiency. DETAILED DESCRIPTION

[0030] In order to enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention is further described in detail below in conjunction with embodiments.

[0031] The present invention discloses a method for preparing a sodium ion battery hard carbon negative electrode material based on microporous structure control of oxygen-containing functional groups, comprising the following steps:

[0032] S1. Alkalinization treatment: soaking the biomass raw material in an alkaline solution for reaction, followed by filtering, washing and drying to obtain a first precursor;

[0033] S2, oxidation treatment: soaking the first precursor obtained in step S1 in an oxidant solution, then filtering and drying to obtain a second precursor;

[0034] S3, preparation of an oxidized precursor: oxidizing the second precursor obtained in step S2 under an oxygen atmosphere to obtain an oxidized precursor;

[0035] S4, low-temperature sintering of the pre-carbonized material: sintering the oxidized precursor obtained in step S3 at low temperature under a protective atmosphere to obtain a pre-carbonized material;

[0036] S5, pre-carbonized material refinement treatment: crushing the pre-carbonized material obtained in step S4 to obtain refined pre-carbonized material;

[0037] S6, pre-carbonized material purification: the refined pre-carbonized material obtained in step S5 is acid-washed, centrifuged, washed with water, and dried to obtain acid-washed and purified pre-carbonized material;

[0038] S7, high temperature sintering: the acid washed, purified and pre-carbonized material obtained in step S6 is subjected to high temperature sintering under a protective atmosphere to obtain a hard carbon negative electrode material for a sodium ion battery.

[0039] Furthermore, 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] Further, in step S3, the oxygen concentration is 2-21%, the oxidation temperature is 120-200° C., and the oxidation time is 0.5-5 h.

[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 the acid used is 10-60wt.% of the amount of the carbonized material used.

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

[0043] Furthermore, in step S1, the biomass raw material is one or more of 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] Furthermore, 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°C, and the reaction time is 0.5-3h.

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

[0046] Further, in step S5, the particle size D50 is 4-12 μm, and the pulverizing method is one or more of a roller mill, a mechanical mill, an air flow mill, a Raymond mill, a ball mill, and a stirred mill.

[0047] Example 1

[0048] This embodiment relates to a sodium ion battery hard carbon negative electrode material based on the microporous structure control of oxygen-containing functional groups. The preparation method thereof comprises the following steps:

[0049] S1. Alkalinization treatment: soak the biomass raw material in an alkaline solution for reaction, then filter, wash and dry to obtain the first precursor. Specifically, the biomass raw material is straw, reed, bamboo; the alkaline solution is NaOH, KOH, Na2CO3, KCO3, the concentration of the alkaline solution is 5 mol / L, the reaction temperature is 100°C, and the reaction time is 0.5h.

[0050] S2, oxidation treatment: soak the first precursor obtained in step S1 in an oxidant solution, then filter and dry to obtain a second precursor. Specifically, the oxidant is HNO3 or H2SO4, the concentration of the oxidant solution is 6 mol / L, and the soaking time is 5 hours.

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

[0052] 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 a pre-carbonized material. Specifically, the protective atmosphere is nitrogen, the carbonization temperature is 800° C., and the carbonization time is 2 hours.

[0053] S5, refining treatment of pre-carbonized material: crushing the pre-carbonized material obtained in step S4 to obtain refined pre-carbonized material. Specifically, the particle size D50 is 4-12 μm, and the crushing method is a double roller mill or a mechanical mill.

[0054] S6, pre-carbonized material purification: the refined pre-carbonized material obtained in step S5 is acid-washed, centrifuged, washed with water, and dried to obtain acid-washed purified pre-carbonized material. Specifically, the acid used for acid washing and purification is hydrochloric acid, and the amount of acid used is 60wt.% of the amount of carbonized material used.

[0055] S7, high temperature sintering: the acid washed, purified and pre-carbonized material obtained in step S6 is subjected to high temperature sintering under a protective atmosphere to obtain a hard carbon negative electrode material for a sodium ion battery. Specifically, the protective atmosphere is nitrogen and argon, the sintering temperature is 1500° C., and the carbonization time is 3 hours.

[0056] Example 2

[0057] This embodiment relates to a sodium ion battery hard carbon negative electrode material based on the microporous structure control of oxygen-containing functional groups. The preparation method thereof comprises the following steps:

[0058] S1. Alkalinization treatment: soak the biomass raw material in an alkaline solution for reaction, then filter, wash and dry to obtain the first precursor. Specifically, the biomass raw material is pine, fruit wood, miscellaneous wood, fir, and oak; the alkaline solution is KCO3, NaHCO3, and Ca(OH)2, the concentration of the alkaline solution is 3 mol / L, the reaction temperature is 60°C, and the reaction time is 3 hours.

[0059] S2, oxidation treatment: soak the first precursor obtained in step S1 in an oxidant solution, then filter and dry to obtain a second precursor. Specifically, the oxidant is K2Cr2O7, H2Cr2O7, HClO4, the concentration of the oxidant solution is 3 mol / L, and the soaking time is 2 hours.

[0060] S3, preparation of oxidation precursor: oxidize the second precursor obtained in step S2 in an oxygen atmosphere to obtain an oxidation precursor. Specifically, the oxygen concentration is 11%, the oxidation temperature is 120° C., and the oxidation time is 5 hours.

[0061] 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 a pre-carbonized material. Specifically, the protective atmosphere is nitrogen and argon, the carbonization temperature is 600° C., and the carbonization time is 0.5 h.

[0062] S5, pre-carbonized material refinement treatment: the pre-carbonized material obtained in step S4 is crushed to obtain refined pre-carbonized material. Specifically, the particle size D50 is 4-12 μm, and the crushing method is air flow pulverization.

[0063] S6, pre-carbonized material purification: the refined pre-carbonized material obtained in step S5 is acid-washed, centrifuged, washed with water, and dried to obtain acid-washed purified pre-carbonized material. Specifically, the acid used for acid-washing purification is sulfuric acid, and the amount of acid used is 30wt.% of the amount of carbonized material used.

[0064] S7, high temperature sintering: the acid-washed, purified and pre-carbonized material obtained in step S6 is subjected to high temperature sintering under a protective atmosphere to obtain a hard carbon negative electrode material for a sodium ion battery. Specifically, the protective atmosphere is nitrogen, the sintering temperature is 1300° C., and the carbonization time is 0.3 h.

[0065] Example 3

[0066] This embodiment relates to a sodium ion battery hard carbon negative electrode material based on the microporous structure control of oxygen-containing functional groups. The preparation method thereof comprises the following steps:

[0067] S1. Alkalinization treatment: soak the biomass raw material in an alkaline solution for reaction, then filter, wash and dry to obtain the first precursor. Specifically, the biomass raw material is miscellaneous wood, fir, oak, corn cob, rice husk; the alkaline solution is NaOH, KOH, NH3·H2O, the concentration of the alkaline solution is 0.2 mol / L, the reaction temperature is 150°C, and the reaction time is 2h.

[0068] S2, oxidation treatment: soak the first precursor obtained in step S1 in an oxidant solution, then filter and dry to obtain a second precursor. Specifically, the oxidant is HNO3, H2SO4, H2Cr2O7, HClO4, the concentration of the oxidant solution is 0.1 mol / L, and the soaking time is 8 hours.

[0069] S3, preparation of oxidation precursor: oxidize the second precursor obtained in step S2 in an oxygen atmosphere to obtain an oxidation precursor. Specifically, the oxygen concentration is 41%, the oxidation temperature is 200° C., and the oxidation time is 3 hours.

[0070] 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 a pre-carbonized material. Specifically, the protective atmosphere is argon, the carbonization temperature is 400° C., and the carbonization time is 3 hours.

[0071] S5, refining treatment of pre-carbonized material: crushing the pre-carbonized material obtained in step S4 to obtain refined pre-carbonized material. Specifically, the particle size D50 is 4-12 μm, and the crushing method is ball milling or stirring milling.

[0072] S6, pre-carbonized material purification: the refined pre-carbonized material obtained in step S5 is acid-washed, centrifuged, washed with water, and dried to obtain acid-washed purified pre-carbonized material. Specifically, the acid used for acid washing and purification is hydrochloric acid and oxalic acid, and the amount of acid used is 10wt.% of the amount of carbonized material used.

[0073] S7, high temperature sintering: the acid washed, purified and pre-carbonized material obtained in step S6 is subjected to high temperature sintering under a protective atmosphere to obtain a hard carbon negative electrode material for a sodium ion battery. Specifically, the protective atmosphere is nitrogen and argon, the sintering temperature is 1100° C., and the carbonization time is 6 hours.

[0074] Example 4

[0075] This embodiment relates to a sodium ion battery hard carbon negative electrode material based on the microporous structure control of oxygen-containing functional groups. The preparation method thereof comprises the following steps:

[0076] S1. Alkalinization treatment: soak the biomass raw material in an alkaline solution for reaction, then filter, wash and dry to obtain the first precursor. Specifically, the biomass raw material is straw, reed, bamboo, corn cob, rice husk; the alkaline solution is NaOH, KOH, NH3·H2O, the concentration of the alkaline solution is 2 mol / L, the reaction temperature is 80°C, and the reaction time is 1 hour.

[0077] S2, oxidation treatment: soak the first precursor obtained in step S1 in an oxidant solution, then filter and dry to obtain a second precursor. Specifically, the oxidant is HNO3, H2SO4, H2O2, the concentration of the oxidant solution is 2 mol / L, and the soaking time is 3 hours.

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

[0079] 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 a pre-carbonized material. Specifically, the protective atmosphere is nitrogen and argon, the carbonization temperature is 700° C., and the carbonization time is 1 hour.

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

[0081] S6, pre-carbonized material purification: the refined pre-carbonized material obtained in step S5 is acid-washed, centrifuged, washed with water, and dried to obtain acid-washed and purified pre-carbonized material. Specifically, the acid used for acid washing and purification is hydrochloric acid or nitric acid, and the amount of acid used is 20wt.% of the amount of carbonized material used.

[0082] S7, high temperature sintering: the acid-washed, purified and pre-carbonized material obtained in step S6 is subjected to high temperature sintering under a protective atmosphere to obtain a hard carbon negative electrode material for a sodium ion battery. Specifically, the protective atmosphere is nitrogen and argon, the sintering temperature is 1400° C., and the carbonization time is 5 hours.

[0083] Example 5

[0084] This embodiment relates to a sodium ion battery hard carbon negative electrode material based on the microporous structure control of oxygen-containing functional groups. The preparation method thereof comprises the following steps:

[0085] S1. Alkalinization treatment: soak the biomass raw material in an alkaline solution for reaction, then filter, wash and dry to obtain the first precursor. Specifically, the biomass raw material is straw, reed, bamboo, coconut shell, walnut shell, nut shell, apricot shell; the alkaline solution is NaOH, KOH, Na2CO3, the concentration of the alkaline solution is 4 mol / L, the reaction temperature is 130°C, and the reaction time is 2h.

[0086] S2, oxidation treatment: soak the first precursor obtained in step S1 in an oxidant solution, then filter and dry to obtain a second precursor. Specifically, the oxidant is NaClO, KClO, K2Cr2O7, the concentration of the oxidant solution is 4 mol / L, and the soaking time is 6 hours.

[0087] S3, preparation of oxidation precursor: oxidize the second precursor obtained in step S2 in an oxygen atmosphere to obtain an oxidation precursor. Specifically, the oxygen concentration is 13%, the oxidation temperature is 180° C., and the oxidation time is 4 hours.

[0088] 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 a pre-carbonized material. Specifically, the protective atmosphere is nitrogen and argon, the carbonization temperature is 700° C., and the carbonization time is 2 hours.

[0089] S5, refining treatment of pre-carbonized material: crushing the pre-carbonized material obtained in step S4 to obtain refined pre-carbonized material. Specifically, the particle size D50 is 4-12 μm, and the crushing method is ball milling or stirring milling.

[0090] S6, pre-carbonized material purification: the refined pre-carbonized material obtained in step S5 is acid-washed, centrifuged, washed with water, and dried to obtain acid-washed purified pre-carbonized material. Specifically, the acid used for acid washing and purification is hydrochloric acid or nitric acid, and the amount of acid used is 30wt.% of the amount of carbonized material used.

[0091] S7, high temperature sintering: the acid washed, purified and pre-carbonized material obtained in step S6 is subjected to high temperature sintering under a protective atmosphere to obtain a hard carbon negative electrode material for a sodium ion battery. Specifically, the protective atmosphere is nitrogen and argon, the sintering temperature is 1200° C., and the carbonization time is 3 hours.

[0092] Application Example 1

[0093] This embodiment relates to a sodium ion battery hard carbon negative electrode material based on the control of the microporous structure of oxygen-containing functional groups, and the preparation method thereof comprises the following steps:

[0094] S1. Alkalinization treatment: soak the walnut shell raw material in 0.8 mol / L NaOH solution, react in a reactor at 90° C. for 2 h, then filter, wash with water, and dry to obtain a first precursor;

[0095] S2, oxidation treatment: soak the first precursor obtained in step S1 in 1 mol / L HNO3 aqueous solution for 4 h, then filter and dry to obtain a second precursor;

[0096] S3, preparation of an oxidative precursor: reacting the second precursor obtained in step S2 at 150° C. for 3 h in an atmosphere with an oxygen content of 15% to obtain an oxidative precursor;

[0097] S4, low-temperature sintering of the pre-carbonized material: the oxidized precursor obtained in step S3 is subjected to low-temperature sintering in a nitrogen atmosphere at a sintering temperature of 600° C. for a sintering time of 2 h to obtain a pre-carbonized material;

[0098] S5, refining treatment of the pre-carbonized material: using a roller mill and air flow powder to crush the pre-carbonized material obtained in step S4 in turn, crushing it to a D50 of 7 μm to obtain a refined crushed material;

[0099] S6, purification treatment of the pre-carbonized material: using 20wt.% HNO3 to acid-wash, centrifuge, wash with water, and dry the finely crushed material obtained in step S5 to obtain an acid-washed and purified pre-carbonized material;

[0100] S7, high temperature sintering: the acid washed, purified and pre-carbonized material obtained in step S6 is subjected to high temperature sintering in a nitrogen atmosphere at a sintering temperature of 1300° C. for 4 hours to obtain a high capacity hard carbon negative electrode material.

[0101] The electrochemical performance of the obtained material was tested according to the following method: hard carbon material, Super P, CMC, SBR were mixed into a slurry in a mass ratio of 94:1.5:2:2.5, and the black slurry was coated on the copper foil using a 120um four-sided preparation device, and then the film was dried in a vacuum drying oven at 100°C for 2 hours. The electrode film was punched into a disc with a radius of 0.6mm using a punching machine, with metallic sodium as the counter electrode, 1mol / LNaClO4 EC+DEC (1:1vol%) as the electrolyte, and the diaphragm was a PP / PE / PP three-layer diaphragm, and assembled into a CR2016 button cell in a glove box. The above button cell was subjected to constant current charge and discharge tests, with 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 negative electrode material for a sodium ion battery. Compared with Application Example 1, the main difference is that no oxidant is used for oxidation treatment. The preparation method thereof includes the following steps:

[0104] S1. Alkalinization treatment: soak the walnut shell raw material in 0.8 mol / L NaOH solution, react in a reactor at 90° C. for 2 h, then filter, wash with water, and dry to obtain a first precursor;

[0105] S2, preparation of an oxidative precursor: reacting the first precursor obtained in step S1 at 150° C. for 3 h in an atmosphere with an oxygen content of 15% to obtain an oxidative precursor;

[0106] S3, low-temperature sintering of the pre-carbonized material: the oxidized precursor obtained in step S2 is subjected to low-temperature sintering in a nitrogen atmosphere at a sintering temperature of 600° C. for a sintering time of 2 h to obtain a pre-carbonized material;

[0107] S4, refining treatment of the pre-carbonized material: using a roller mill and air flow powder to crush the pre-carbonized material obtained in step S3, and crushing it to a D50 of 7 μm to obtain a refined crushed material;

[0108] S5, purification treatment of the pre-carbonized material: using 20wt.% HNO3 to acid-wash, centrifuge, wash with water, and dry the finely crushed material obtained in step S4 to obtain an acid-washed and purified pre-carbonized material;

[0109] S6. High-temperature sintering: The acid-washed, purified and pre-carbonized material obtained in step S5 is subjected to high-temperature sintering in a nitrogen atmosphere at a sintering temperature of 1300° C. for 4 hours to obtain a high-capacity hard carbon negative electrode material.

[0110] The electrochemical performance of the obtained material was tested according to the following method: hard carbon material, Super P, CMC, SBR were mixed into a slurry in a mass ratio of 94:1.5:2:2.5, and the black slurry was coated on copper foil using a 120um four-sided preparation device, and then the film was dried in a vacuum drying oven at 100°C for 2 hours. The electrode film was punched into a disc with a radius of 0.6mm using a punching machine, with metallic sodium as the counter electrode, 1mol / L NaClO4 EC+DEC (1:1vol%) as the electrolyte, and the diaphragm was a PP / PE / PP three-layer diaphragm, assembled into a CR2016 button cell in a glove box. The above button cell was subjected to constant current charge and discharge tests, with 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 negative electrode material for a sodium ion battery. Compared with Application Example 1, the main difference is that no alkali solution is used for alkalization treatment. The preparation method thereof includes the following steps:

[0113] S1, oxidation treatment: soak the walnut shell raw material in 1 mol / L HNO3 aqueous solution for 4 hours, then filter and dry to obtain the first precursor;

[0114] S2, preparation of an oxidative precursor: reacting the first precursor obtained in step S1 at 150° C. for 3 h in an atmosphere with an oxygen content of 15% to obtain an oxidative precursor;

[0115] S3, low-temperature sintering of the pre-carbonized material: the oxidized precursor obtained in step S2 is subjected to low-temperature sintering in a nitrogen atmosphere at a sintering temperature of 600° C. for a sintering time of 2 h to obtain a pre-carbonized material;

[0116] S4, refining treatment of the pre-carbonized material: using a roller mill and air flow powder to crush the pre-carbonized material obtained in step S3, and crushing it to a D50 of 7 μm to obtain a refined crushed material;

[0117] S5, purification treatment of the pre-carbonized material: using 20wt.% HNO3 to acid-wash, centrifuge, wash with water, and dry the finely crushed material obtained in step S4 to obtain an acid-washed and purified pre-carbonized material;

[0118] S6. High-temperature sintering: The acid-washed, purified and pre-carbonized material obtained in step S5 is subjected to high-temperature sintering in a nitrogen atmosphere at a sintering temperature of 1300° C. for 4 hours to obtain a high-capacity hard carbon negative electrode material.

[0119] The electrochemical performance of the obtained material was tested according to the following method: hard carbon material, Super P, CMC, SBR were mixed into a slurry in a mass ratio of 94:1.5:2:2.5, and the black slurry was coated on copper foil using a 120um four-sided preparation device, and then the film was dried in a vacuum drying oven at 100°C for 2 hours. The electrode film was punched into a disc with a radius of 0.6mm using a punching machine, with metallic sodium as the counter electrode, 1mol / L NaClO4 EC+DEC (1:1vol%) as the electrolyte, and the diaphragm was a PP / PE / PP three-layer diaphragm, assembled into a CR2016 button cell in a glove box. The above button cell was subjected to constant current charge and discharge tests, with a current density of 0.1C (1C=300mAh / g) and a voltage range of 1-0.005V.

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

[0121] The helium true density test shows that the true densities of Application Example 1, Comparative Example 1 and Comparative Example 2 are 1.85, 1.98 and 2.03 g / cm3 respectively, indicating that the alkali treatment and oxidation treatment can effectively increase the internal pore volume of the hard carbon material.

[0122] The constant current charge and discharge test measured that the first week charging specific capacity of application example 1, example 2 and comparative example 1 was 348, 283 and 302 mAh / g, respectively, indicating that the alkali treatment and oxidation treatment can effectively improve their sodium storage capacity. The constant current charge and discharge test measured that the first week efficiency of application example 1, example 2 and comparative example 1 was 92.3%, 90.6% and 86.5%, respectively. The higher first week efficiency of application example 1 is attributed to the fact that the alkali treatment effectively ensures that the biomass raw materials are uniformly oxidized, the specific surface area is small, and the irreversible capacity loss caused by contact with the electrolyte is small.

[0123] The above embodiments are only specific embodiments of the present invention, and their descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, and these obvious replacement forms all belong to the protection scope of the present invention.

Claims

1. A method for preparing a sodium ion battery hard carbon negative electrode material based on microporous structure control of oxygen-containing functional groups, characterized in that The following steps are involved: S1. Alkalinization treatment: soaking the biomass raw material in an alkaline solution for reaction, followed by filtering, washing and drying to obtain a first precursor; S2, oxidation treatment: soaking the first precursor obtained in step S1 in an oxidant solution, then filtering and drying to obtain a second precursor; S3, preparation of an oxidized precursor: oxidizing the second precursor obtained in step S2 under an oxygen atmosphere to obtain an oxidized precursor; S4, low-temperature sintering of the pre-carbonized material: sintering the oxidized precursor obtained in step S3 at a low temperature under a protective atmosphere to obtain a pre-carbonized material; S5, pre-carbonized material refinement treatment: crushing the pre-carbonized material obtained in step S4 to obtain refined pre-carbonized material; S6, pre-carbonized material purification: the refined pre-carbonized material obtained in step S5 is acid-washed, centrifuged, washed with water, and dried to obtain acid-washed and purified pre-carbonized material; S7, high temperature sintering: the acid washed, purified and pre-carbonized material obtained in step S6 is subjected to high temperature sintering under a protective atmosphere to obtain a hard carbon negative electrode material for a sodium ion battery.

2. The method for preparing a sodium ion battery hard carbon negative electrode material based on microporous structure control of oxygen-containing functional groups according to claim 1, characterized in that: 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.

3. The method for preparing a sodium ion battery hard carbon negative electrode material based on microporous structure control of oxygen-containing functional groups according to claim 1, characterized in that: In step S3, the oxygen concentration is 2-21%, the oxidation temperature is 120-200° C., and the oxidation time is 0.5-5 h.

4. The method for preparing a sodium ion battery hard carbon negative electrode material based on microporous structure control of oxygen-containing functional groups according to claim 1, characterized in that: 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 the acid used is 10-60wt.% of the amount of the carbonized material used.

5. The method for preparing a sodium ion battery hard carbon negative electrode material based on microporous structure control of oxygen-containing functional groups according to claim 1, characterized in that: In step S7, the protective atmosphere is nitrogen and / or argon, the sintering temperature is 1100-1500°C, and the carbonization time is 0.3-6h.

6. The method for preparing a sodium ion battery hard carbon negative electrode material based on microporous structure control of oxygen-containing functional groups according to claim 1, characterized in that: In step S1, the biomass raw material is one or more of 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.

7. The method for preparing a sodium ion battery hard carbon negative electrode material based on microporous structure control of oxygen-containing functional groups according to claim 1, characterized in that: 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°C, and the reaction time is 0.5-3h.

8. The method for preparing a sodium ion battery hard carbon negative electrode material based on microporous structure control of oxygen-containing functional groups according to claim 1, characterized in that: In step S4, the protective atmosphere is nitrogen and / or argon, the carbonization temperature is 400-800° C., and the carbonization time is 0.3-3 h.

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