A method for preparing hard carbon anode material for sodium-ion batteries

Abstract

This disclosure relates to the field of sodium-ion battery technology, and in particular to a method for preparing a hard carbon anode material for sodium-ion batteries. The preparation method disclosed herein includes: subjecting biomass powder to a series of processes, including bacterial-enzyme co-fermentation, acid washing, treatment with a mixed solution of alkali metal halide and ammonia, treatment with a mixed solution of tin salt and sulfur-containing compounds, low-temperature carbonization, coating with a coating agent, and high-temperature carbonization to finally obtain SnS-loaded material. x The hard carbon anode material for sodium-ion batteries; its internal ordered loose porous structure is SnS x The volume expansion provides space.

Description

Technical Field

[0001] This disclosure relates to the field of sodium-ion battery technology, and in particular to a method for preparing a hard carbon anode material for sodium-ion batteries. Background Technology

[0002] Hard carbon is the preferred anode material for sodium-ion batteries. Hard carbon is carbon that does not graphitize after high-temperature treatment. Its internal crystal arrangement is disordered with large interlayer spacing, allowing it to store more charge in the same volume, thus improving the energy density and battery life of sodium-ion batteries. During discharge, the expansion and contraction of hard carbon anodes are more uniform, increasing their cycle stability, charge-discharge performance, and extending the cycle life of sodium-ion batteries. Common precursors for preparing hard carbon materials include biomass, synthetic polymers, and fossil fuels. Hard carbon materials prepared from different precursors exhibit significant performance differences, and their cost structure also varies significantly due to the different sources of precursor raw materials. Among these, biomass has a wide range of raw material sources, such as straw, bamboo, fruit shells, grapefruit peels, and animal and plant tissues, making it a relatively low-cost and currently the preferred precursor material for hard carbon materials. However, biomass suffers from low carbon production rates, high ash content, low initial efficiency, a controversial sodium storage mechanism, and a complex structure that is difficult to control precisely, hindering its practical application.

[0003] SnS material is considered a promising anode material due to its high theoretical specific capacity (1022 mAh / g). However, its poor conductivity and the significant volume expansion during sodium insertion / extraction cause pulverization and loss of active material, significantly affecting the rate performance and coulombic efficiency of the anode material. Carbon coating of SnS can effectively suppress its volume expansion problem during charge and discharge. Therefore, there is an urgent need for a process that combines biomass materials and SnS materials to prepare hard carbon anode materials for sodium-ion batteries. Summary of the Invention

[0004] This disclosure provides a method for preparing a hard carbon anode material for sodium-ion batteries, thereby addressing the shortcomings of related technologies.

[0005] According to a first aspect of the present disclosure, a method for preparing a hard carbon anode material for a sodium-ion battery is provided, the method comprising the following steps:

[0006] Step 1: Provide biomass raw materials, dry and pulverize the biomass raw materials, and then dry them again to obtain biomass powder;

[0007] Step 2: The biomass powder is subjected to synergistic fermentation with bacteria and enzymes to obtain fermented biomass powder;

[0008] Step 3: Soak the fermented biomass powder in an acidic solution to obtain acid-washed biomass powder;

[0009] Step 4: Immerse the acid-washed biomass powder in the first mixed solution to obtain biomass powder treated with the first mixed solution; wherein the first mixed solution contains at least one alkali metal halide;

[0010] Step 5: Immerse the biomass powder soaked in the first mixed solution in the second mixed solution to obtain biomass powder treated with the second mixed solution; wherein the second mixed solution contains at least one sulfur-containing compound;

[0011] Step 6: The biomass powder treated with the second mixed solution is subjected to a first carbonization to obtain carbon material after the first carbonization;

[0012] Step 7: The carbon material after the first carbonization is mixed with the coating agent and then heated to obtain the coated carbon material;

[0013] Step 8: The coated carbon material is subjected to a second carbonization and post-processing to obtain the sodium-ion battery hard carbon anode material.

[0014] In one aspect of this disclosure, the biomass raw material is selected from one or more of straw, linden wood, pine wood, buckwheat hulls, coconut shells, palm shells, walnut shells, almond shells, hawthorn kernels, and cottonseed kernels.

[0015] In one aspect of this disclosure, the biomass raw material is specifically selected from linden wood.

[0016] In one aspect of the embodiments of this disclosure, in the co-fermentation of bacteria and enzymes in step 2, the enzymes used are selected from one or more of cellulase, hemicellulase, ligninase, polyphenol oxidase and pectinase.

[0017] In one aspect of the embodiments of this disclosure, specifically, in the co-fermentation of bacteria and enzymes in step 2, the enzymes used are cellulase and ligninase, or hemicellulase and ligninase.

[0018] In one aspect of the present disclosure, in the co-fermentation of bacteria and enzymes in step 2, the strains used are selected from Bacillus subtilis, Bacillus licheniformis, cellulose-decomposing bacteria, brown rot fungi, or white rot fungi.

[0019] In one aspect of the embodiments of this disclosure, specifically, in the co-fermentation of bacteria and enzymes in step 2, the strains used are Bacillus licheniformis or Bacillus subtilis.

[0020] In one aspect of the embodiments of this disclosure, specifically, in the co-fermentation of bacteria and enzymes in step 2, the compound bacterial enzymes used include cellulase, ligninase and Bacillus licheniformis; or include cellulase, ligninase and Bacillus subtilis.

[0021] In one aspect of this disclosure, the acidic solution is selected from sodium chlorite and glacial acetic acid and a mixed aqueous solution.

[0022] In one aspect of the embodiments of this disclosure, preferably, the acidic solution is an aqueous solution containing 1.5-3 wt% sodium chlorite and 0.1-0.3 wt% glacial acetic acid.

[0023] In one aspect of this disclosure, specifically, the acidic solution is an aqueous solution containing 2 wt% sodium chlorite and 0.2 wt% glacial acetic acid.

[0024] In one aspect of this disclosure, the first mixed solution is ammonia water containing at least one alkali metal halide, wherein the alkali metal halide is selected from potassium fluoride, lithium chloride, potassium chloride, lithium bromide, sodium bromide, potassium bromide, lithium iodide, sodium iodide, or potassium iodide.

[0025] In one aspect of the embodiments of this disclosure, preferably, the alkali metal halide is selected from potassium fluoride, lithium chloride, potassium chloride, sodium iodide, or potassium iodide.

[0026] In one aspect of this disclosure, specifically, the alkali metal halide is selected from potassium fluoride. More specifically, in the first mixed solution, the mass percentage of potassium fluoride is selected from 10-20 wt%.

[0027] In one aspect of this disclosure, in step 5, the second mixed solution contains at least one tin-containing compound and one sulfur-containing compound; the tin-containing compound is selected from tin oxalate, stannous chloride, stannous chloride, sodium stannate, stannous tartrate, or stannous sulfate; the sulfur-containing compound is selected from thiourea or ammonium sulfide.

[0028] In one aspect of the embodiments of this disclosure, preferably, the tin-containing compound is selected from tin oxalate, stannous chloride, stannous chloride, or sodium stannate; and the sulfur-containing compound is selected from thiourea.

[0029] In one aspect of the embodiments of this disclosure, specifically, the tin-containing compound is selected from tin oxalate or stannous chloride, and the sulfur-containing compound is selected from thiourea.

[0030] In one aspect of this disclosure, in step 6, the temperature of the first carbonization is selected from 450°C to 650°C, and the time of the first carbonization is selected from 2 to 5 hours.

[0031] In one aspect of this disclosure, specifically, in step 6, the temperature of the first carbonization is selected from 550°C, and the time of the first carbonization is selected from 3.5 hours.

[0032] In one aspect of this disclosure, in step 7, the coating agent is selected from polyvinyl alcohol or polyvinylpyrrolidone; the heating temperature is selected from 200°C-300°C; and the heating time is selected from 1-1.5h.

[0033] In one aspect of this disclosure, specifically, in step 7, the heating temperature is selected from 250°C, and the heating time is selected from 1.5 hours.

[0034] In one aspect of this disclosure, in step 8, the temperature of the second carbonization is selected from 850°C to 1450°C, and the time of the second carbonization is selected from 4 to 8 hours.

[0035] In one aspect of the embodiments of this disclosure, specifically, in step 8, the temperature of the second carbonization is selected from 1200°C, and the time of the second carbonization is selected from 6.5h.

[0036] In one aspect of this disclosure, specifically, step 1 includes:

[0037] Step 1-1: Provide biomass raw materials, wherein the biomass raw materials are selected from one or more of the following: straw, linden wood, pine wood, buckwheat hulls, coconut shells, palm shells, walnut shells, almond shells, hawthorn kernels, and cottonseed kernels;

[0038] Steps 1-2: Dry the biomass raw material at 50℃-65℃ for 6-12 hours, and then pulverize it to 1-5mm;

[0039] Steps 1-3: The pulverized biomass raw material is dried at 50℃-65℃ for 6-12 hours to obtain the biomass powder.

[0040] In one aspect of this disclosure, specifically, step 2 includes:

[0041] Step 2-1: After mixing the biomass powder, corn flour, soybean meal, and compound microbial enzyme evenly, add water and ferment at room temperature for 3-6 days to obtain a fermented mixture; wherein, the compound microbial enzyme contains at least one strain selected from Bacillus subtilis, Bacillus licheniformis, cellulolytic bacteria, brown rot fungi, or white rot fungi, and at least one enzyme selected from cellulase, hemicellulase, ligninase, polyphenol oxidase, or pectinase;

[0042] Step 2-2: Add the fermented mixture to water at 90℃-100℃ to inactivate the enzymes, and obtain the fermented biomass powder.

[0043] In one aspect of this disclosure, specifically, step 3 includes:

[0044] Step 3-1: Prepare the acidic solution, wherein the acidic solution is an aqueous solution containing 1.5-3 wt% sodium chlorite and 0.1-0.3 wt% glacial acetic acid;

[0045] Step 3-2: Add the fermented biomass powder to the prepared acidic solution, then heat at 65℃-75℃ for 2-3 hours, and then wash and dry to obtain the acid-washed biomass powder.

[0046] In one aspect of this disclosure, specifically, step 4 includes:

[0047] Step 4-1: Prepare the first mixed solution, which is an ammonia solution containing 10-20 wt% potassium fluoride, wherein the concentration of the ammonia solution is selected from 10%-25%.

[0048] Step 4-2: Add the acid-washed biomass powder to the prepared first mixed solution, heat at 60℃-80℃ for 3-5 hours, and then wash, filter and dry to obtain the biomass powder treated with the first mixed solution.

[0049] In one aspect of this disclosure, specifically, step 5 includes:

[0050] Step 5-1: Prepare the second mixed solution, which is an aqueous solution containing 3-15 wt% stannous chloride and 5-10 wt% thiourea;

[0051] Step 5-2: Add the biomass powder treated with the first mixed solution to the prepared second mixed solution, soak it for 6-12 hours under a pressure below normal, and then filter and dry it to obtain the biomass powder treated with the second mixed solution.

[0052] In one aspect of this disclosure, specifically, step 6 includes:

[0053] Step 6-1: Place the biomass powder treated with the second mixed solution into a tube furnace and perform the first carbonization under the protection of an inert gas; the temperature of the first carbonization is selected from 450℃-650℃, and the time is selected from 2-5h;

[0054] Step 6-2: The product obtained in step 6-1 is subjected to an ultrafine grinding process to make the powder D50 value 4-6μm, thus obtaining the carbon material after the first carbonization.

[0055] In one aspect of this disclosure, specifically, step 7 includes:

[0056] Step 7-1: Dissolve polyvinyl alcohol and / or polyvinylpyrrolidone in water to obtain a polymer solution;

[0057] Step 7-2: Add the carbon material after the first carbonization to the polymer solution, stir, and then dry it directly at 50℃-65℃ to obtain the product of step 7-2;

[0058] Step 7-3: Place the product from step 7-2 in a tube furnace and heat it at 200℃-300℃ for 1-1.5 hours under the protection of an inert gas to obtain the coated carbon material.

[0059] In one aspect of this disclosure, specifically, step 8 includes:

[0060] Step 8-1: Place the coated carbon material in a tube furnace and perform a second carbonization under the protection of an inert gas; the temperature of the second carbonization is selected from 850℃-1450℃, and the time is selected from 4-8h; to obtain the carbon material after the second carbonization.

[0061] Step 8-2: After the carbon material after the second carbonization is subjected to a second acid washing and ball milling process, the sodium-ion battery hard carbon anode material is obtained.

[0062] In one aspect of the present disclosure, in step 8-2, a second acid wash is performed using 0.2-0.5 mol / L hydrochloric acid.

[0063] In one aspect of the present disclosure, step 8-2 further includes a water washing process after the second pickling.

[0064] In one aspect of the embodiments of this disclosure, in step 8-2, the ball milling process uses grinding balls with diameters of 3 mm, 5 mm, and 10 mm, respectively, in a mass ratio of 1:2:1.

[0065] In one aspect of the embodiments of this disclosure, in step 8-2, the ball milling process includes: placing the proportioned grinding balls and the carbon material after the second carbonization into the ball mill jar of the ball mill at a mass ratio of 3-7:1 for intermittent ball milling, the ball mill speed is 200-300 rpm, each ball milling time is 3-5 minutes, the cooling time after stopping the mill is 5-10 minutes, and the total net ball milling time is 3-7 hours.

[0066] According to a second aspect of the present disclosure, a hard carbon anode material for sodium-ion batteries is provided, which is obtained by the aforementioned preparation method.

[0067] The technical solutions provided by the embodiments of this disclosure may include the following beneficial effects:

[0068] As can be seen from the above embodiments, this disclosure involves sequentially processing biomass powder through a combination of bacterial and enzyme fermentation, acid washing, treatment with a mixed solution of alkali metal halides and ammonia, treatment with a mixed solution of tin salts and sulfur-containing compounds, low-temperature carbonization, coating with a coating agent, and high-temperature carbonization to finally obtain SnS-loaded material. x The hard carbon anode material for sodium-ion batteries; its internal ordered loose porous structure is SnS x The volume expansion provides space, thus endowing it with excellent electrochemical performance.

[0069] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0070] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure.

[0071] Figure 1 This is a SEM image of the hard carbon anode material for sodium-ion batteries shown in Example 1;

[0072] Figure 2 The image is a SEM image of the hard carbon anode material for sodium-ion batteries shown in Comparative Example 1.

[0073] Figure 3 The image is a SEM image of the hard carbon anode material for sodium-ion batteries shown in Comparative Example 2. Detailed Implementation

[0074] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. The embodiments described herein are illustrative in nature and are intended to provide a basic understanding of this invention. The embodiments of this invention should not be construed as limiting the invention.

[0075] For the sake of brevity, this article only discloses a few specific numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0076] In this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0077] In this description, unless otherwise stated, "above" and "below" include the stated number.

[0078] Unless otherwise stated, the terminology used in this invention has the common meanings understood by those skilled in the art. Unless otherwise stated, the values ​​of the parameters mentioned in this invention can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this invention).

[0079] The term "about" is used to describe and indicate small variations. When used in conjunction with an event or situation, the term may refer to examples in which the event or situation occurred precisely or in examples in which the event or situation occurred very approximately. For example, when used in conjunction with numerical values, the term may refer to a range of variation less than or equal to ±10% of the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format herein. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only numerical values ​​explicitly specified as range limits but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0080] The list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another instance, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0081] Sodium-ion battery positive electrode:

[0082] In some embodiments of this disclosure, the sodium-ion battery includes a positive electrode sheet, which includes a current collector and a positive active material layer disposed on the current collector, the positive active material layer including a positive active material, a binder, and a conductive agent.

[0083] The material of the positive electrode current collector disclosed herein is not particularly limited. In some embodiments of this disclosure, the positive electrode current collector may be a conductive carbon sheet, a metal foil, a carbon-coated metal foil, or a porous metal plate. The conductive carbon material of the conductive carbon sheet may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite, graphene, and carbon nanofibers. The metal material of the metal foil, the carbon-coated metal foil, and the porous metal plate may be independently selected from one or more of copper, aluminum, nickel, and stainless steel.

[0084] In some embodiments of this disclosure, the positive current collector may be one or more of copper foil, aluminum foil, nickel foil, stainless steel foil, stainless steel mesh, and carbon-coated aluminum foil, with aluminum foil being preferred.

[0085] In some embodiments of this disclosure, the positive electrode active material layer includes a positive electrode active material, a binder, and a conductive agent.

[0086] In some embodiments of this disclosure, the positive electrode active material may be selected from sodium transition metal oxides; in sodium transition metal oxides, the transition metal may be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Sodium transition metal oxides are, for example, Na. x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, 0 <x≤1。

[0087] In some embodiments of this disclosure, the positive electrode active material layer may further include a conductive agent to improve the conductivity of the positive electrode. This disclosure does not specifically limit the type of conductive agent, which can be selected according to actual needs. As an example, the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphite, graphene, and carbon nanofibers.

[0088] In a preferred embodiment of this disclosure, the conductive agent is selected from one or more of SUPER-P, KS-6, KS-15, VGCF, SFG6, ECP, Ketjen Black, carbon nanotubes, and graphene.

[0089] In some embodiments of this disclosure, the positive electrode active material layer may further include a binder to firmly bond the positive electrode active material and, optionally, a conductive agent, to the positive electrode current collector. This disclosure does not specifically limit the type of binder, which can be selected according to actual needs. As an example, the binder may be one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), polyvinyl alcohol (PVA), ethylene-vinyl acetate copolymer (EVA), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), sodium alginate (SA), polymethacrylic acid (PMA), and carboxymethyl chitosan (CMC).

[0090] In a preferred embodiment of this disclosure, the adhesive is selected from one or more of PVDF, PTFE, LA132, LA133, CMC, and SBR.

[0091] Sodium-ion battery negative electrode:

[0092] In some embodiments of this disclosure, the negative electrode of a sodium-ion battery includes a negative electrode sheet, which includes a current collector and a layer of negative electrode active material disposed on the current collector.

[0093] The material of the negative electrode current collector disclosed herein is not particularly limited. In some embodiments of this disclosure, the negative electrode current collector is selected from one or at least two alloys or composite materials of aluminum, copper, iron, tin, zinc, nickel, titanium, manganese, lead, antimony, cadmium, gold, bismuth, and germanium. Among them, the above-mentioned at least two alloys include, but are not limited to, copper-aluminum alloys, copper-iron alloys, copper-tin alloys, nickel-titanium alloys, nickel-manganese alloys, nickel-antimony alloys, gold-bismuth alloys, iron-nickel alloys, lead-manganese alloys, and aluminum-nickel alloys. The above-mentioned at least two composite materials include, but are not limited to, aluminum-copper composite materials, iron-copper composite materials, copper-tin composite materials, nickel-titanium composite materials, nickel-manganese composite materials, nickel-antimony composite materials, gold-bismuth composite materials, iron-nickel composite materials, lead-manganese composite materials, and aluminum-nickel composite materials.

[0094] In other embodiments of this disclosure, the negative current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof.

[0095] In some embodiments of this disclosure, the negative electrode active material layer includes a negative electrode active material, a conductive agent, and a binder.

[0096] In the field of sodium-ion batteries, the negative electrode active material is the key to ensuring that the negative electrode has good charge and discharge performance. The negative electrode active material needs to facilitate the insertion and extraction of sodium ions. Typically, but not limitingly, the negative electrode active material is selected from one or more of the following materials: amorphous carbon materials (hard carbon and soft carbon), metal elements, metal alloys, sulfides, nitrides, oxides, carbides, etc.

[0097] In this disclosure, the negative electrode active material is a hard carbon material prepared by the preparation method of this disclosure.

[0098] In some embodiments of this disclosure, the negative electrode active material is prepared by the following method:

[0099] Step 1-1: Provide linden wood raw materials;

[0100] Steps 1-2: Dry the linden wood raw material at 50℃-65℃ for 6-12 hours, and then crush it to 1-5mm;

[0101] Steps 1-3: Continue drying the pulverized linden wood raw material at 50℃-65℃ for 6-12 hours to obtain linden wood powder;

[0102] Step 2-1: Mix linden wood powder, corn flour, soybean meal, and compound microbial enzymes evenly, add water, and ferment at room temperature for 3-6 days to obtain a fermented mixture; the compound microbial enzymes used include cellulase, ligninase, and Bacillus licheniformis / Bacillus subtilis.

[0103] Step 2-2: Add the fermented mixture to water at 90℃-100℃ to inactivate the enzymes, and obtain fermented linden wood powder;

[0104] Step 3-1: Prepare an acidic solution, which is an aqueous solution containing 1.5-3 wt% sodium chlorite and 0.1-0.3 wt% glacial acetic acid;

[0105] Step 3-2: Add the fermented linden wood powder to the prepared acidic solution, then heat at 65℃-75℃ for 2-3 hours, and then wash and dry to obtain acid-washed linden wood powder;

[0106] Step 4-1: Prepare the first mixed solution, which is ammonia water containing 10-20 wt% potassium fluoride, and the concentration of ammonia water is selected from 10%-25%.

[0107] Step 4-2: Add the acid-washed linden powder to the prepared first mixed solution, heat at 60℃-80℃ for 3-5 hours, and then wash, filter and dry to obtain linden powder treated with the first mixed solution.

[0108] Step 5-1: Prepare a second mixed solution, which is an aqueous solution containing 3-15 wt% stannous chloride and 5-10 wt% thiourea;

[0109] Step 5-2: Add the linden powder treated with the first mixed solution to the prepared second mixed solution, soak it for 6-12 hours under a pressure below normal, and then filter and dry it to obtain the linden powder treated with the second mixed solution.

[0110] Step 6-1: Place the linden wood powder treated with the second mixed solution into a tube furnace and perform the first carbonization under the protection of an inert gas; the temperature of the first carbonization is selected from 450℃-650℃, and the time is selected from 2-5h.

[0111] Step 6-2: The product obtained in Step 6-1 is subjected to an ultrafine grinding process to make the powder D50 value 4-6μm, thus obtaining carbon material after the first carbonization.

[0112] Step 7-1: Dissolve polyvinyl alcohol and / or polyvinylpyrrolidone in water to obtain a polymer solution;

[0113] Step 7-2: Add the carbon material after the first carbonization to the polymer solution, stir and dry it directly at 50℃-65℃ to obtain the product of step 7-2;

[0114] Step 7-3: Place the product from step 7-2 in a tube furnace and heat it at 200℃-300℃ for 1-1.5 hours under the protection of an inert gas to obtain the coated carbon material.

[0115] Step 8-1: Place the coated carbon material in a tube furnace and perform a second carbonization under the protection of an inert gas; the temperature of the second carbonization is selected from 850℃-1450℃, and the time is selected from 4-8h; the carbon material after the second carbonization is obtained.

[0116] Step 8-2: After the carbon material after the second carbonization is subjected to a second acid washing and ball milling process, the hard carbon anode material for sodium-ion batteries is obtained. The ball milling process includes: putting the prepared grinding balls and the carbon material after the second carbonization into the ball mill jar of the ball mill at a mass ratio of 3-7:1 for intermittent ball milling. The ball mill speed is 200-300 rpm, the ball milling time is 3-5 minutes each time, the cooling time after stopping the mill is 5-10 minutes, and the net ball milling time is 3-7 hours.

[0117] The conductive agent in the negative electrode of a sodium-ion battery is used to ensure good charge-discharge performance. Therefore, a certain amount of conductive material is usually added during the fabrication of the negative electrode. This material collects micro-currents between the active materials and between the active materials and the current collector, reducing the contact resistance of the negative electrode and accelerating the electron mobility. It also effectively increases the migration rate of sodium ions in the negative electrode, thereby improving the charge-discharge efficiency. In some embodiments of this disclosure, the conductive agent in the negative electrode can be one or more of, but not limited to, conductive carbon black, conductive carbon spheres, conductive graphite, carbon nanotubes, conductive carbon fibers, graphene, and reduced graphene oxide.

[0118] The binder in the negative electrode ensures a certain bonding strength between the active material particles and between the active particles and the current collector during use, and is beneficial to SEI film formation, thereby improving the cycle performance and service life of the positive electrode. In some embodiments of this disclosure, the binder may be, but is not limited to, at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, carboxymethyl cellulose, styrene-butadiene rubber (SBR), or polyolefins.

[0119] Electrolyte:

[0120] The electrochemical device disclosed herein includes an electrolyte, which comprises an electrolyte and an electrolyte solvent, wherein the electrolyte is a sodium salt and the electrolyte solvent is an organic solvent; the electrolyte is the medium used in the chemical battery, providing ions for the normal operation of the chemical battery and ensuring that the chemical reactions that occur during operation are reversible.

[0121] In some embodiments of this disclosure, the volume concentration of sodium salt is 0.1-10 mol / L. By controlling the volume concentration of sodium salt in the electrolyte, the migration rate of ions in the electrolyte is ensured, thereby guaranteeing the chemical performance of the sodium-ion battery.

[0122] In some embodiments of this disclosure, the sodium salt is selected from one or more of sodium hexafluorophosphate, sodium chloride, sodium fluoride, sodium sulfate, sodium carbonate, sodium phosphate, sodium nitrate, sodium difluorooxalate borate, sodium pyrophosphate, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, trisodium citrate, sodium metaborate, sodium borate, sodium molybdate, sodium tungstate, sodium bromide, sodium nitrite, sodium iodate, sodium iodide, sodium silicate, sodium lignosulfonate, sodium oxalate, sodium aluminate, sodium methanesulfonate, sodium acetate, sodium dichromate, sodium hexafluoroarsenate, sodium tetrafluoroborate, sodium perchlorate, sodium trifluoromethanesulfonylimide, NaCF3SO3, and NaN(SO2CF3)2. In particular, when sodium perchlorate is used as the solute, the migration efficiency of sodium ions is better, and the electrochemical performance of the sodium-ion battery is more excellent.

[0123] In some embodiments of this disclosure, the sodium salt used as the electrolyte is not particularly limited, as long as it can dissociate into sodium ions and anions.

[0124] In some embodiments of this disclosure, the organic solvent is selected from one or more of ester solvents, sulfone solvents, ether solvents, and nitrile solvents.

[0125] In preferred embodiments of this disclosure, the organic solvents include, but are not limited to, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl formate (MF), methyl acetate (MA), N,N-dimethylacetamide (DMA), fluoroethylene carbonate (FEC), methyl propionate (MP), ethyl propionate (EP), ethyl acetate (EA), γ-butyrolactone (GBL), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), 1,3-dioxolane (DOL), 4-methyl-1,3-dioxolane (4MeDOL), dimethoxymethane (DMM), 1,2-dimethoxypropane (DMP), triethylene glycol dimethyl ether (DG), dimethyl sulfone (MSM), dimethyl ether (DME), vinyl sulfite (ES), propylene sulfite (PS), and dimethyl sulfite (DM). S), diethyl sulfite (DES), crown ether, 1-ethyl-3-methylimidazolium-hexafluorophosphate, 1-ethyl-3-methylimidazolium-tetrafluoroborate, 1-ethyl-3-methylimidazolium-bis(trifluoromethanesulfonyl)imide, 1-propyl-3-methylimidazolium-hexafluorophosphate, 1-propyl-3-methylimidazolium-tetrafluoroborate, 1-propyl-3-methylimidazolium-bis(trifluoromethanesulfonyl)imide, 1-butyl-1-methylimidazolium-hexafluorophosphate, 1-butyl It is one or more of the following: 1-butyl-1-methylimidazolium-tetrafluoroborate, 1-butyl-1-methylimidazolium-bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidine-bis(trifluoromethanesulfonyl)imide, 1-butyl-1-methylpyrrolidine-bis(trifluoromethanesulfonyl)imide, N-methyl-N-propylpyrrolidine-bis(trifluoromethanesulfonyl)imide, N-methyl,propylpiperidine-bis(trifluoromethanesulfonyl)imide, and N-methyl,butylpiperidine-bis(trifluoromethanesulfonyl)imide.

[0126] In a preferred embodiment of this disclosure, additives may also be added to the electrolyte. Adding additives to the electrolyte improves the cycle stability of the sodium-ion battery; the additives are selected from one or more of esters, sulfones, ethers, nitriles, or olefins.

[0127] In a preferred embodiment of this disclosure, the amount of additive added to the electrolyte is 0.1-20 wt%. By controlling the amount of additive added to the electrolyte, a stable solid electrolyte film can be formed on the surface of the negative electrode current collector, thereby improving the service life of the sodium-ion battery.

[0128] In preferred embodiments of this disclosure, the additive is selected from fluoroethylene carbonate, vinylene carbonate, ethylene ethylene carbonate, 1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, vinyl sulfate, propylene sulfate, ethylene sulfate, vinyl sulfite, propylene sulfite, dimethyl sulfite, diethyl sulfite, ethylene sulfite, methyl chloroformate, dimethyl sulfoxide, anisole, acetamide, diazabenzene, m-diazabenzene, crown ether 12-crown-4, crown ether 18-crown. -6, 4-fluoroanisole, fluorochain ether, difluoromethyl ethylene carbonate, trifluoromethyl ethylene carbonate, chloroethylene carbonate, bromoethylene carbonate, trifluoroethylphosphonic acid, bromobutyrolactone, fluoroacetic acid ethane, phosphate ester, phosphite ester, phosphazene, ethanolamine, dimethyl carbide, cyclobutyl sulfone, 1,3-dioxocyclopentane, acetonitrile, long-chain olefins, aluminum oxide, magnesium oxide, barium oxide, sodium carbonate, calcium carbonate, carbon dioxide, sulfur dioxide, and lithium carbonate, or more thereof.

[0129] Diaphragm:

[0130] The sodium-ion battery disclosed herein has a separator between the positive and negative electrodes to prevent short circuits. The material and shape of the separator used in the sodium-ion battery of this disclosure are not particularly limited, and can be any technology disclosed in the prior art.

[0131] In some embodiments of this disclosure, the diaphragm comprises a polymer or inorganic material formed of a material stable to the electrolyte of this application.

[0132] In some embodiments of this disclosure, the diaphragm is selected from one or more composite films selected from porous polymer films, inorganic porous films, glass fiber paper, or porous ceramic films.

[0133] In a preferred embodiment of this disclosure, the porous polymer film is selected from one of porous polypropylene film, porous polyethylene film, or porous composite polymer film, wherein the porous composite polymer film includes, but is not limited to, porous polyethylene and polypropylene composite film.

[0134] Sodium-ion batteries:

[0135] The sodium-ion battery provided in this disclosure includes, but is not limited to, the above-described positive electrode, negative electrode, separator, and electrolyte.

[0136] In some embodiments of this disclosure, the sodium-ion battery involved in this disclosure is made by stacking the above-mentioned positive and negative electrode sheets.

[0137] In some embodiments of this disclosure, the sodium-ion battery may include an outer packaging, which may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery may also be a soft pack, such as a pouch-type soft pack. The material of the soft pack may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0138] In some embodiments, this disclosure also provides a battery module. This battery module includes the aforementioned sodium-ion battery. The battery module of this disclosure uses the aforementioned sodium-ion battery and therefore has at least the same advantages as the sodium-ion battery. The battery module of this disclosure may contain multiple sodium-ion batteries, the specific number of which can be adjusted according to the application and capacity of the battery module.

[0139] In some embodiments, this disclosure also provides a battery pack that includes the aforementioned battery modules. The number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0140] Device:

[0141] This disclosure also provides an apparatus comprising at least one of the above-described sodium-ion battery, battery module, or battery pack.

[0142] In some embodiments, the device includes, but is not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems. To meet the device's requirements for high power and high energy density of lithium-ion batteries, battery packs or battery modules may be used.

[0143] In other implementations, the device can also be a mobile phone, tablet computer, laptop computer, etc.

[0144] The present disclosure is further illustrated below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the disclosure.

[0145] Examples and comparative examples:

[0146] Example 1:

[0147] Example 1 includes the following steps:

[0148] 1. Preparation of linden wood powder:

[0149] Weigh approximately 50g of linden wood raw material; the linden wood raw material used in this embodiment and comparative example are all small pieces of waste wood after cutting during wood processing; dry the linden wood raw material at 60°C for 8 hours, and then crush it to 1-3mm using an industrial cutting machine; continue to dry the crushed linden wood raw material at 60°C for 12 hours to obtain linden wood powder.

[0150] 2. The solid-state fermentation process:

[0151] Linden wood powder (50g), corn flour (20g), soybean meal (15g), and compound microbial enzymes were mixed evenly, water was added, and fermented at room temperature for 5 days to obtain a fermented mixture. The compound microbial enzymes used contained a mixture of cellulase, ligninase, and Bacillus subtilis; the amount of Bacillus subtilis added was 4 × 10⁻⁶. 13 CFU / kg, cellulase addition amount is 3×10 6 U / kg, the amount of ligninase added is 1.5×10 6 U / kg. After fermentation, the fermented mixture was added to water at 100℃ to inactivate the enzyme (3 min), and then dried to obtain fermented linden wood powder.

[0152] 3. Pre-treatment process:

[0153] 3.1: Prepare an acidic solution, which is a 200 mL aqueous solution containing 2 wt% sodium chlorite and 0.25 wt% glacial acetic acid; add the fermented linden wood powder to the prepared acidic solution, then heat at 70°C for 2.5 h, and then wash and dry to obtain acid-washed linden wood powder.

[0154] 3.2: Prepare the first mixed solution, which is 150 mL of ammonia water containing 12 wt% potassium fluoride and the concentration of ammonia water is 25%. Add the acid-washed linden wood powder to the prepared first mixed solution, heat at 70°C for 4 hours, and then wash, filter and dry to obtain linden wood powder treated with the first mixed solution.

[0155] 3.3: Prepare a second mixed solution, which is 350 mL of an aqueous solution containing 10 wt% stannous chloride and 5 wt% thiourea. Place the second mixed solution in a vacuum filtration flask, add the linden wood powder treated with the first mixed solution, connect the vacuum pump and seal the vacuum filtration flask, maintain the pressure of the system at about 500 Pa, soak at this pressure for 8 h, and then filter and dry to obtain the linden wood powder treated with the second mixed solution.

[0156] 4. Carbonization and coating:

[0157] 4.1: The linden wood powder treated with the second mixed solution was placed in a tube furnace and carbonized for the first time under nitrogen atmosphere. The temperature of the first carbonization was selected as 550℃, the heating rate was 5℃ / min, the carbonization time was 4h, and then it was naturally cooled to room temperature. The carbonized powder was then ultra-finely pulverized to a D50 of 5μm to obtain the first carbonized powder.

[0158] 4.2: Polyvinyl alcohol (PVA1788, 2.5g) was dissolved in 50mL of water. After it was fully dissolved, the first carbonized powder was added to it and stirred thoroughly. The mixture was then dried directly in an oven at 60℃. The dried product was then placed in a tube furnace and heated at 250℃ for 1.5h under nitrogen atmosphere to obtain the coated carbon material. The temperature was then increased at a rate of 8℃ / min until it reached 1250℃, and the carbonization time was 6.5h to obtain the second carbonized powder.

[0159] 5. Post-processing:

[0160] The second carbonized powder was subjected to acid washing (0.5 mol / L dilute hydrochloric acid solution), water washing, and alcohol washing, followed by ball milling. The ball milling process included: placing pre-mixed grinding balls (made of agate, with diameters of 3 mm, 5 mm, and 10 mm, in a mass ratio of 1:2:1) and carbonized powder in the ball mill jar at a mass ratio of 4:1 for intermittent ball milling. The ball mill speed was 250 rpm, each milling session lasted 3 minutes, with a 5-minute cooling period after each milling stop, for a total net milling time of 4 hours. This yielded hard carbon material. The SEM image of the hard carbon anode material in Example 1 is shown below. Figure 1 As shown.

[0161] 6. Assembly of sodium-ion battery button cells:

[0162] The hard carbon material prepared above was used as the active material, SP as the conductive agent, and PVDF as the binder, weighed in a mass ratio of 94:3:3. A uniformly mixed slurry was prepared using NMP as the solvent and a planetary disperser. This slurry was then uniformly coated onto a composite copper current collector to obtain the negative electrode. A CR2025 coin-type sodium-ion half-cell was assembled using sodium hexafluorophosphate / EC+DEC as the electrolyte, a sodium sheet as the counter electrode, and glass fiber (GF / F) as the separator. Electrochemical performance tests were conducted in an argon-filled glove box with both water and oxygen content below 1 ppm.

[0163] Example 2:

[0164] Example 2 includes the following steps:

[0165] 1. Preparation of linden wood powder:

[0166] Weigh approximately 50g of linden wood raw material; dry the linden wood raw material at 60℃ for 8 hours, and then pulverize it to 1-3mm using an industrial cutting machine; continue to dry the pulverized linden wood raw material at 60℃ for 12 hours to obtain linden wood powder.

[0167] 2. The solid-state fermentation process:

[0168] Linden wood powder (50g), corn flour (20g), soybean meal (15g), and compound microbial enzymes were mixed evenly, water was added, and fermented at room temperature for 5 days to obtain a fermented mixture. The compound microbial enzymes used contained a mixture of cellulase, ligninase, and Bacillus subtilis; the amount of Bacillus subtilis added was 4 × 10⁻⁶. 13 CFU / kg, cellulase addition amount is 3×10 6 U / kg, the amount of ligninase added is 1.5×10 6 U / kg. After fermentation, the fermented mixture was added to water at 100℃ to inactivate the enzyme (3 min), and then dried to obtain fermented linden wood powder.

[0169] 3. Pre-treatment process:

[0170] 3.1: Prepare an acidic solution, which is a 200 mL aqueous solution containing 2 wt% sodium chlorite and 0.25 wt% glacial acetic acid; add the fermented linden wood powder to the prepared acidic solution, then heat at 70°C for 2.5 h, and then wash and dry to obtain acid-washed linden wood powder.

[0171] 3.2: Prepare the first mixed solution, which is 150 mL of ammonia water containing 12 wt% potassium chloride and the concentration of ammonia water is 25%. Add the acid-washed linden wood powder to the prepared first mixed solution, heat at 70°C for 4 hours, and then wash, filter and dry to obtain linden wood powder treated with the first mixed solution.

[0172] 3.3: Prepare a second mixed solution, which is 350 mL of an aqueous solution containing 10 wt% stannous chloride and 5 wt% thiourea. Place the second mixed solution in a vacuum filtration flask, add the linden wood powder treated with the first mixed solution, connect the vacuum pump and seal the vacuum filtration flask, maintain the pressure of the system at about 500 Pa, soak at this pressure for 8 h, and then filter and dry to obtain the linden wood powder treated with the second mixed solution.

[0173] 4. Carbonization and coating:

[0174] 4.1: The linden wood powder treated with the second mixed solution was placed in a tube furnace and carbonized for the first time under nitrogen atmosphere. The temperature of the first carbonization was selected as 550℃, the heating rate was 5℃ / min, the carbonization time was 4h, and then it was naturally cooled to room temperature. The carbonized powder was then ultrafinely pulverized to a D50 of 5μm to obtain the first carbonized powder.

[0175] 4.2: Polyvinyl alcohol (PVA1788, 2.5g) was dissolved in 50mL of water. After it was fully dissolved, the first carbonized powder was added to it and stirred thoroughly. The mixture was then dried directly in an oven at 60℃. The dried product was then placed in a tube furnace and heated at 250℃ for 1.5h under nitrogen atmosphere to obtain the coated carbon material. The temperature was then increased at a rate of 8℃ / min until it reached 1250℃, and the carbonization time was 6.5h to obtain the second carbonized powder.

[0176] 5. Post-processing:

[0177] The second carbonized powder was subjected to acid washing (0.5 mol / L dilute hydrochloric acid solution), water washing, and alcohol washing, followed by ball milling. The ball milling process included: placing the prepared grinding balls (made of agate balls with diameters of 3 mm, 5 mm, and 10 mm, mixed in a mass ratio of 1:2:1) and the carbonized powder in the ball mill jar at a mass ratio of 4:1 for intermittent ball milling. The ball mill speed was 250 rpm, each ball milling time was 3 minutes, the cooling time after milling was stopped was 5 minutes, and the total net ball milling time was 4 hours; thus, hard carbon material was obtained.

[0178] 6. Assembly of sodium-ion battery button cells:

[0179] The hard carbon material prepared above was used as the active material, SP as the conductive agent, and PVDF as the binder, weighed in a mass ratio of 94:3:3. A uniformly mixed slurry was prepared using NMP as the solvent and a planetary disperser. This slurry was then uniformly coated onto a composite copper current collector to obtain the negative electrode. A CR2025 coin-type sodium-ion half-cell was assembled using sodium hexafluorophosphate / EC+DEC as the electrolyte, a sodium sheet as the counter electrode, and glass fiber (GF / F) as the separator. Electrochemical performance tests were conducted in an argon-filled glove box with both water and oxygen content below 1 ppm.

[0180] The main difference between Example 1 and Example 2 is that the alkali metal halides contained in the first mixed solution are different. Example 1 used potassium fluoride, while Example 2 used potassium chloride.

[0181] Example 3:

[0182] Example 3 includes the following steps:

[0183] 1. Preparation of linden wood powder:

[0184] Weigh approximately 50g of linden wood raw material; dry the linden wood raw material at 60℃ for 8 hours, and then pulverize it to 1-3mm using an industrial cutting machine; continue to dry the pulverized linden wood raw material at 60℃ for 12 hours to obtain linden wood powder.

[0185] 2. The solid-state fermentation process:

[0186] Linden wood powder (50g), corn flour (20g), soybean meal (15g), and compound microbial enzymes were mixed evenly, water was added, and fermented at room temperature for 5 days to obtain a fermented mixture. The compound microbial enzymes used contained a mixture of cellulase, ligninase, and Bacillus subtilis; the amount of Bacillus subtilis added was 4 × 10⁻⁶. 13 CFU / kg, cellulase addition amount is 3×10 6 U / kg, the amount of ligninase added is 1.5×10 6 U / kg. After fermentation, the fermented mixture was added to water at 100℃ to inactivate the enzyme (3 min), and then dried to obtain fermented linden wood powder.

[0187] 3. Pre-treatment process:

[0188] 3.1: Prepare an acidic solution, which is a 200 mL aqueous solution containing 2 wt% sodium chlorite and 0.25 wt% glacial acetic acid; add the fermented linden wood powder to the prepared acidic solution, then heat at 70°C for 2.5 h, and then wash and dry to obtain acid-washed linden wood powder.

[0189] 3.2: Prepare the first mixed solution, which is 150 mL of ammonia water containing 12 wt% sodium bromide and the concentration of ammonia water is 25%. Add the acid-washed linden wood powder to the prepared first mixed solution, heat at 70°C for 4 h, and then wash, filter and dry to obtain linden wood powder treated with the first mixed solution.

[0190] 3.3: Prepare a second mixed solution, which is 350 mL of an aqueous solution containing 10 wt% stannous chloride and 5 wt% thiourea. Place the second mixed solution in a vacuum filtration flask, add the linden wood powder treated with the first mixed solution, connect the vacuum pump and seal the vacuum filtration flask, maintain the pressure of the system at about 500 Pa, soak at this pressure for 8 h, and then filter and dry to obtain the linden wood powder treated with the second mixed solution.

[0191] 4. Carbonization and coating:

[0192] 4.1: The linden wood powder treated with the second mixed solution was placed in a tube furnace and carbonized for the first time under nitrogen atmosphere. The temperature of the first carbonization was selected as 550℃, the heating rate was 5℃ / min, the carbonization time was 4h, and then it was naturally cooled to room temperature. The carbonized powder was then ultrafinely pulverized to a D50 of 5μm to obtain the first carbonized powder.

[0193] 4.2: Polyvinyl alcohol (PVA1788, 2.5g) was dissolved in 50mL of water. After it was fully dissolved, the first carbonized powder was added to it and stirred thoroughly. The mixture was then dried directly in an oven at 60℃. The dried product was then placed in a tube furnace and heated at 250℃ for 1.5h under nitrogen atmosphere to obtain the coated carbon material. The temperature was then increased at a rate of 8℃ / min until it reached 1250℃, and the carbonization time was 6.5h to obtain the second carbonized powder.

[0194] 5. Post-processing:

[0195] The second carbonized powder was subjected to acid washing (0.5 mol / L dilute hydrochloric acid solution), water washing, and alcohol washing, followed by ball milling. The ball milling process included: placing the prepared grinding balls (made of agate balls with diameters of 3 mm, 5 mm, and 10 mm, mixed in a mass ratio of 1:2:1) and the carbonized powder in the ball mill jar at a mass ratio of 4:1 for intermittent ball milling. The ball mill speed was 250 rpm, each ball milling time was 3 minutes, the cooling time after milling was stopped was 5 minutes, and the total net ball milling time was 4 hours; thus, hard carbon material was obtained.

[0196] 6. Assembly of sodium-ion battery button cells:

[0197] The hard carbon material prepared above was used as the active material, SP as the conductive agent, and PVDF as the binder, weighed in a mass ratio of 94:3:3. A uniformly mixed slurry was prepared using NMP as the solvent and a planetary disperser. This slurry was then uniformly coated onto a composite copper current collector to obtain the negative electrode. A CR2025 coin-type sodium-ion half-cell was assembled using sodium hexafluorophosphate / EC+DEC as the electrolyte, a sodium sheet as the counter electrode, and glass fiber (GF / F) as the separator. Electrochemical performance tests were conducted in an argon-filled glove box with both water and oxygen content below 1 ppm.

[0198] The main difference between Example 1 and Example 3 is that the alkali metal halides contained in the first mixed solution are different. Example 1 used potassium fluoride, while Example 2 used lithium bromide.

[0199] Comparative Example 1:

[0200] Comparative Example 1 includes the following steps:

[0201] 1. Preparation of linden wood powder:

[0202] Weigh approximately 50g of linden wood raw material; dry the linden wood raw material at 60℃ for 8 hours, and then pulverize it to 1-3mm using an industrial cutting machine; continue to dry the pulverized linden wood raw material at 60℃ for 12 hours to obtain linden wood powder.

[0203] 2. Pretreatment process:

[0204] 3.1: Prepare an acidic solution, which is a 200 mL aqueous solution containing 2 wt% sodium chlorite and 0.25 wt% glacial acetic acid; add linden wood powder to the prepared acidic solution, then heat at 70°C for 2.5 h, and then wash and dry to obtain acid-washed linden wood powder.

[0205] 3.2: Prepare the first mixed solution, which is 150 mL of ammonia water containing 12 wt% sodium bromide and the concentration of ammonia water is 25%. Add the acid-washed linden wood powder to the prepared first mixed solution, heat at 70°C for 4 h, and then wash, filter and dry to obtain linden wood powder treated with the first mixed solution.

[0206] 3.3: Prepare a second mixed solution, which is 350 mL of an aqueous solution containing 10 wt% stannous chloride and 5 wt% thiourea. Place the second mixed solution in a vacuum filtration flask, add the linden wood powder treated with the first mixed solution, connect the vacuum pump and seal the vacuum filtration flask, maintain the pressure of the system at about 500 Pa, soak at this pressure for 8 h, and then filter and dry to obtain the linden wood powder treated with the second mixed solution.

[0207] 4. Carbonization and coating:

[0208] 4.1: The linden wood powder treated with the second mixed solution was placed in a tube furnace and carbonized for the first time under nitrogen atmosphere. The temperature of the first carbonization was selected as 550℃, the heating rate was 5℃ / min, the carbonization time was 4h, and then it was naturally cooled to room temperature. The carbonized powder was then ultra-finely pulverized to a D50 of 5μm to obtain the first carbonized powder.

[0209] 4.2: Polyvinyl alcohol (PVA1788, 2.5g) was dissolved in 50mL of water. After it was fully dissolved, the first carbonized powder was added to it and stirred thoroughly. The mixture was then dried directly in an oven at 60℃. The dried product was then placed in a tube furnace and heated at 250℃ for 1.5h under nitrogen atmosphere to obtain the coated carbon material. The temperature was then increased at a rate of 8℃ / min until it reached 1250℃, and the carbonization time was 6.5h to obtain the second carbonized powder.

[0210] 5. Post-processing:

[0211] The second carbonized powder was subjected to acid washing (0.5 mol / L dilute hydrochloric acid solution), water washing, and alcohol washing, followed by ball milling. The ball milling process included: placing pre-mixed grinding balls (made of agate, with diameters of 3 mm, 5 mm, and 10 mm, in a mass ratio of 1:2:1) and carbonized powder in the ball mill jar at a mass ratio of 4:1 for intermittent ball milling. The ball mill speed was 250 rpm, each milling session lasted 3 minutes, with a 5-minute cooling period after each milling stop, for a total net milling time of 4 hours; resulting in hard carbon material. The SEM image of the hard carbon anode material of Comparative Example 1 is shown below. Figure 2 As shown.

[0212] 6. Assembly of sodium-ion battery button cells:

[0213] The hard carbon material prepared above was used as the active material, SP as the conductive agent, and PVDF as the binder, weighed in a mass ratio of 94:3:3. A uniformly mixed slurry was prepared using NMP as the solvent and a planetary disperser. This slurry was then uniformly coated onto a composite copper current collector to obtain the negative electrode. A CR2025 coin-type sodium-ion half-cell was assembled using sodium hexafluorophosphate / EC+DEC as the electrolyte, a sodium sheet as the counter electrode, and glass fiber (GF / F) as the separator. Electrochemical performance tests were conducted in an argon-filled glove box with both water and oxygen content below 1 ppm.

[0214] The main difference between Example 1 and Comparative Example 1 is that Example 1 includes a solid-state fermentation process, while Comparative Example 1 does not.

[0215] Comparative Example 2:

[0216] Comparative Example 2 includes the following steps:

[0217] 1. Preparation of linden wood powder:

[0218] Weigh approximately 50g of linden wood raw material; dry the linden wood raw material at 60℃ for 8 hours, and then pulverize it to 1-3mm using an industrial cutting machine; continue to dry the pulverized linden wood raw material at 60℃ for 12 hours to obtain linden wood powder.

[0219] 2. The solid-state fermentation process:

[0220] Linden wood powder (50g), corn flour (20g), soybean meal (15g), and compound microbial enzymes were mixed evenly, water was added, and fermented at room temperature for 5 days to obtain a fermented mixture. The compound microbial enzymes used contained a mixture of cellulase, ligninase, and Bacillus subtilis; the amount of Bacillus subtilis added was 4 × 10⁻⁶. 13 CFU / kg, cellulase addition amount is 3×10 6U / kg, the amount of ligninase added is 1.5×10 6 U / kg. After fermentation, the fermented mixture was added to water at 100℃ to inactivate the enzyme (3 min), and then dried to obtain fermented linden wood powder.

[0221] 3. Pre-treatment process:

[0222] 3.1: Prepare an acidic solution, which is a 200 mL aqueous solution containing 2 wt% sodium chlorite and 0.25 wt% glacial acetic acid; add the fermented linden wood powder to the prepared acidic solution, then heat at 70°C for 2.5 h, and then wash and dry to obtain acid-washed linden wood powder.

[0223] 3.2: Prepare a mixed solution, which is 350 mL of an aqueous solution containing 10 wt% stannous chloride and 5 wt% thiourea; place the mixed solution in a vacuum filtration flask, add the acid-washed linden wood powder, then connect the vacuum pump and seal the vacuum filtration flask, maintain the pressure of the system at about 500 Pa, soak under this pressure for 8 h, and then filter and dry to obtain the linden wood powder treated with the mixed solution.

[0224] 4. Carbonization and coating:

[0225] 4.1: The linden wood powder treated with the mixed solution was placed in a tube furnace and carbonized for the first time under nitrogen atmosphere. The temperature of the first carbonization was selected as 550℃, the heating rate was 5℃ / min, the carbonization time was 4h, and then it was naturally cooled to room temperature. The carbonized powder was then ultra-finely pulverized to a D50 of 5μm to obtain the first carbonized powder.

[0226] 4.2: Polyvinyl alcohol (PVA1788, 2.5g) was dissolved in 50mL of water. After it was fully dissolved, the first carbonized powder was added to it and stirred thoroughly. The mixture was then dried directly in an oven at 60℃. The dried product was then placed in a tube furnace and heated at 250℃ for 1.5h under nitrogen atmosphere to obtain the coated carbon material. The temperature was then increased at a rate of 8℃ / min until it reached 1250℃, and the carbonization time was 6.5h to obtain the second carbonized powder.

[0227] 5. Post-processing:

[0228] The second carbonized powder was subjected to acid washing (0.5 mol / L dilute hydrochloric acid solution), water washing, and alcohol washing, followed by ball milling. The ball milling process included: placing pre-mixed grinding balls (made of agate, with diameters of 3 mm, 5 mm, and 10 mm, in a mass ratio of 1:2:1) and carbonized powder in the ball mill jar at a mass ratio of 4:1 for intermittent ball milling. The ball mill speed was 250 rpm, each milling session lasted 3 minutes, with a 5-minute cooling period after each milling stop, for a total net milling time of 4 hours; resulting in hard carbon material. The SEM image of the hard carbon anode material of Comparative Example 2 is shown below. Figure 3 As shown.

[0229] 6. Assembly of sodium-ion battery button cells:

[0230] The hard carbon material prepared above was used as the active material, SP as the conductive agent, and PVDF as the binder, weighed in a mass ratio of 94:3:3. A uniformly mixed slurry was prepared using NMP as the solvent and a planetary disperser. This slurry was then uniformly coated onto a composite copper current collector to obtain the negative electrode. A CR2025 coin-type sodium-ion half-cell was assembled using sodium hexafluorophosphate / EC+DEC as the electrolyte, a sodium sheet as the counter electrode, and glass fiber (GF / F) as the separator. Electrochemical performance tests were conducted in an argon-filled glove box with both water and oxygen content below 1 ppm.

[0231] The main difference between Example 1 and Comparative Example 2 is that Comparative Example 2 does not use the first mixed solution (alkali metal halide salt + ammonia water) for pretreatment.

[0232] Comparative Example 3:

[0233] Comparative Example 3 includes the following steps:

[0234] 1. Preparation of linden wood powder:

[0235] Weigh approximately 50g of linden wood raw material; dry the linden wood raw material at 60℃ for 8 hours, and then pulverize it to 1-3mm using an industrial cutting machine; continue to dry the pulverized linden wood raw material at 60℃ for 12 hours to obtain linden wood powder.

[0236] 2. The solid-state fermentation process:

[0237] Linden wood powder (50g), corn flour (20g), soybean meal (15g), and compound microbial enzymes were mixed evenly, water was added, and fermented at room temperature for 5 days to obtain a fermented mixture. The compound microbial enzymes used contained a mixture of cellulase, ligninase, and Bacillus subtilis; the amount of Bacillus subtilis added was 4 × 10⁻⁶. 13 CFU / kg, cellulase addition amount is 3×10 6U / kg, the amount of ligninase added is 1.5×10 6 U / kg. After fermentation, the fermented mixture was added to water at 100℃ to inactivate the enzyme (3 min), and then dried to obtain fermented linden wood powder.

[0238] 3. Pre-treatment process:

[0239] 3.1: Prepare an acidic solution, which is a 200 mL aqueous solution containing 2 wt% sodium chlorite and 0.25 wt% glacial acetic acid; add the fermented linden wood powder to the prepared acidic solution, then heat at 70°C for 2.5 h, and then wash and dry to obtain acid-washed linden wood powder.

[0240] 3.2: Prepare the first mixed solution, which is 150 mL of ammonia water containing 12 wt% potassium chloride and the concentration of ammonia water is 25%. Add the acid-washed linden wood powder to the prepared first mixed solution, heat at 70°C for 4 hours, and then wash, filter and dry to obtain linden wood powder treated with the first mixed solution.

[0241] 4. Carbonization and coating:

[0242] 4.1: The linden wood powder treated with the first mixed solution was placed in a tube furnace and carbonized for the first time under nitrogen atmosphere. The temperature of the first carbonization was selected as 550℃, the heating rate was 5℃ / min, the carbonization time was 4h, and then it was naturally cooled to room temperature. The carbonized powder was then ultra-finely pulverized to a D50 of 5μm to obtain the first carbonized powder.

[0243] 4.2: Polyvinyl alcohol (PVA1788, 2.5g) was dissolved in 50mL of water. After it was fully dissolved, the first carbonized powder was added to it and stirred thoroughly. The mixture was then dried directly in an oven at 60℃. The dried product was then placed in a tube furnace and heated at 250℃ for 1.5h under nitrogen atmosphere to obtain the coated carbon material. The temperature was then increased at a rate of 8℃ / min until it reached 1250℃, and the carbonization time was 6.5h to obtain the second carbonized powder.

[0244] 5. Post-processing:

[0245] The second carbonized powder was subjected to acid washing (0.5 mol / L dilute hydrochloric acid solution), water washing, and alcohol washing, followed by ball milling. The ball milling process included: placing the prepared grinding balls (made of agate balls with diameters of 3 mm, 5 mm, and 10 mm, mixed in a mass ratio of 1:2:1) and the carbonized powder in the ball mill jar at a mass ratio of 4:1 for intermittent ball milling. The ball mill speed was 250 rpm, each ball milling time was 3 minutes, the cooling time after milling was stopped was 5 minutes, and the total net ball milling time was 4 hours; thus, hard carbon material was obtained.

[0246] 6. Assembly of sodium-ion battery button cells:

[0247] The hard carbon material prepared above was used as the active material, SP as the conductive agent, and PVDF as the binder, weighed in a mass ratio of 94:3:3. A uniformly mixed slurry was prepared using NMP as the solvent and a planetary disperser. This slurry was then uniformly coated onto a composite copper current collector to obtain the negative electrode. A CR2025 coin-type sodium-ion half-cell was assembled using sodium hexafluorophosphate / EC+DEC as the electrolyte, a sodium sheet as the counter electrode, and glass fiber (GF / F) as the separator. Electrochemical performance tests were conducted in an argon-filled glove box with both water and oxygen content below 1 ppm.

[0248] The main difference between Example 1 and Comparative Example 3 is that Comparative Example 3 does not introduce SnS. x .

[0249] Example 4:

[0250] The steps in Example 4 are the same as those in Example 1, except that the same molar amount of tin oxalate is used in Example 4 instead of stannous chloride used in Example 1.

[0251] Example 5:

[0252] The steps in Example 5 are the same as those in Example 1, except that the same molar amount of stannous sulfate is used in Example 5 instead of the stannous chloride used in Example 1.

[0253] Example 6:

[0254] The steps in Example 6 are the same as those in Example 1, except that the same molar amount of sodium stannate is used in Example 6 to replace the stannous chloride used in Example 1.

[0255] Example 7:

[0256] The steps in Example 7 are the same as those in Example 1, except that stannous chloride is not used in Example 7 (the second mixed solution contains only thiourea).

[0257] Electrochemical performance testing of half-cells:

[0258] The products of Examples 1-7 and Comparative Examples 1-3 were discharged in a voltage range of 0-2V. During discharge, the current density was first constant current of 0.1C to 0.01V, then constant current of 0.2C to 0.01V. After standing for 20 minutes, they were charged at a constant current of 0.1C to 2V. Their electrochemical performance was tested. The specific values ​​are shown in Table 1 below.

[0259] Table 1

[0260]

[0261]

[0262] Compare the values ​​in Table 1 and Figure 1 and Figure 2 As can be seen, Comparative Example 1, which does not include the solid-state fermentation process, lacks through-pores and interconnected structures in its structure compared to Example 1, which uses the solid-state fermentation process. Its electrochemical performance is also significantly weaker than that of the example. In this disclosure, the co-fermentation of bacteria and enzymes decomposes some lignin in the linden wood structure, thereby forming numerous through-pores and interconnected structures, which are SnS... x The load and expansion provided sufficient space. Compare the values ​​in Table 1 with... Figure 1 and Figure 3 As can be seen, Comparative Example 2, which does not include pretreatment with the first mixed solution (alkali metal halide salt + ammonia), forms a larger SnS group compared to Example 1, which uses the first mixed solution for pretreatment. x The electrochemical performance of the particles also decreased; in this disclosure, the combined use of lithium metal halide and ammonia is to remove lignin from the surface of the pores in the wood structure, maintain the unobstructed flow of wood fiber channels, and thus facilitate the processing of SnS. x The deposition provided better sites, therefore, unlike Comparative Example 2, which was pretreated with the first mixed solution, its wood fiber channel surface formed larger SnS deposits after sintering. x The particles undergo uneven expansion during charging and discharging, affecting their electrochemical performance. Furthermore, it is noteworthy that the electrochemical performance of Example 1 is further improved compared to Examples 2 and 3. This is because the alkali metal halide salt used in Example 1 contains fluorine, thus introducing fluorine while removing lignin from the pores of the wood structure, thereby doping fluorine atoms into the final hard carbon material and further enhancing its electrochemical performance.

[0263] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein.

Claims

1. A method for preparing a hard carbon anode material for sodium-ion batteries, characterized in that, The preparation method includes the following steps: Step 1: Provide biomass raw materials, dry and pulverize the biomass raw materials, and then dry them again to obtain biomass powder; Step 2: The biomass powder is subjected to synergistic fermentation with bacteria and enzymes to obtain fermented biomass powder; Step 3: Soak the fermented biomass powder in an acidic solution to obtain acid-washed biomass powder; Step 4: Immerse the acid-washed biomass powder in the first mixed solution to obtain biomass powder treated with the first mixed solution; wherein the first mixed solution contains at least one alkali metal halide; Step 5: Immerse the biomass powder soaked in the first mixed solution in the second mixed solution to obtain biomass powder treated with the second mixed solution; wherein the second mixed solution contains at least one sulfur-containing compound; Step 6: The biomass powder treated with the second mixed solution is subjected to a first carbonization to obtain carbon material after the first carbonization; Step 7: The carbon material after the first carbonization is mixed with the coating agent and then heated to obtain the coated carbon material; Step 8: The coated carbon material is subjected to a second carbonization and post-processing to obtain the sodium-ion battery hard carbon anode material; In step 4, the first mixed solution is ammonia water containing at least one alkali metal halide; In step 5, the second mixed solution contains at least one tin-containing compound and one sulfur-containing compound; the tin-containing compound is selected from tin oxalate, stannous chloride, stannous chloride, sodium stannate, stannous tartrate, and stannous sulfate; the sulfur-containing compound is selected from thiourea or ammonium sulfide.

2. The preparation method according to claim 1, characterized in that, The preparation method satisfies at least one of the following conditions: The biomass raw materials are selected from one or more of the following: straw, linden wood, pine wood, buckwheat hulls, coconut shells, palm shells, walnut shells, almond shells, hawthorn kernels, and cottonseed kernels; In the co-fermentation of bacteria and enzymes in step 2, the enzymes used are selected from one or more of cellulase, hemicellulase, ligninase, polyphenol oxidase and pectinase. In the co-fermentation of bacteria and enzymes in step 2, the strains used are selected from Bacillus subtilis, Bacillus licheniformis, cellulose-decomposing bacteria, brown rot fungi, or white rot fungi. In step 3, the acidic solution is selected from sodium chlorite and glacial acetic acid and a mixed aqueous solution; The alkali metal halide is selected from potassium fluoride, lithium chloride, potassium chloride, lithium bromide, sodium bromide, potassium bromide, lithium iodide, sodium iodide, or potassium iodide. In step 6, the temperature of the first carbonization is selected from 450℃-650℃, and the time of the first carbonization is selected from 2-5h; In step 7, the coating agent is selected from polyvinyl alcohol or polyvinylpyrrolidone; the heating temperature is selected from 200℃-300℃; and the heating time is selected from 1-1.5h. In step 8, the temperature of the second carbonization is selected from 850℃-1450℃, and the time of the second carbonization is selected from 4-8h.

3. The preparation method according to claim 1 or 2, characterized in that, Step 1 includes: Step 1-1: Provide biomass raw materials, wherein the biomass raw materials are selected from one or more of the following: straw, linden wood, pine wood, buckwheat hulls, coconut shells, palm shells, walnut shells, almond shells, hawthorn kernels, and cottonseed kernels; Steps 1-2: Dry the biomass raw material at 50℃-65℃ for 6-12 hours, and then pulverize it to 1-5mm; Steps 1-3: The pulverized biomass raw material is dried at 50℃-65℃ for 6-12 hours to obtain the biomass powder.

4. The preparation method according to claim 1 or 2, characterized in that, Step 2 includes: Step 2-1: After mixing the biomass powder, corn flour, soybean meal, and compound microbial enzyme evenly, add water and ferment at room temperature for 3-6 days to obtain a fermented mixture; wherein, the compound microbial enzyme contains at least one strain selected from Bacillus subtilis, Bacillus licheniformis, cellulolytic bacteria, brown rot fungi, or white rot fungi, and at least one enzyme selected from cellulase, hemicellulase, ligninase, polyphenol oxidase, or pectinase; Step 2-2: Add the fermented mixture to water at 90℃-100℃ to inactivate the enzymes, and obtain the fermented biomass powder.

5. The preparation method according to claim 1 or 2, characterized in that, Step 3 includes: Step 3-1: Prepare the acidic solution, wherein the acidic solution is an aqueous solution containing 1.5-3 wt% sodium chlorite and 0.1-0.3 wt% glacial acetic acid; Step 3-2: Add the fermented biomass powder to the prepared acidic solution, then heat at 65℃-75℃ for 2-3 hours, and then wash and dry to obtain the acid-washed biomass powder.

6. The preparation method according to claim 1 or 2, characterized in that, Step 4 includes: Step 4-1: Prepare the first mixed solution, which is an ammonia solution containing 10-20 wt% potassium fluoride, wherein the concentration of the ammonia solution is selected from 10%-25%; Step 4-2: Add the acid-washed biomass powder to the prepared first mixed solution, heat at 60℃-80℃ for 3-5 hours, and then wash, filter and dry to obtain the biomass powder treated with the first mixed solution.

7. The preparation method according to claim 1 or 2, characterized in that, Step 5 includes: Step 5-1: Prepare the second mixed solution, which is an aqueous solution containing 3-15 wt% stannous chloride and 5-10 wt% thiourea; Step 5-2: Add the biomass powder treated with the first mixed solution to the prepared second mixed solution, soak it for 6-12 hours under a pressure below normal, and then filter and dry it to obtain the biomass powder treated with the second mixed solution.

8. The preparation method according to claim 1 or 2, characterized in that, Step 6 includes: Step 6-1: Place the biomass powder treated with the second mixed solution into a tube furnace and perform the first carbonization under the protection of an inert gas; the temperature of the first carbonization is selected from 450℃-650℃, and the time is selected from 2-5h; Step 6-2: The product obtained in step 6-1 is pulverized and then subjected to an ultrafine pulverization process to make the powder D50 value 4-6μm, thus obtaining the carbon material after the first carbonization.

9. The preparation method according to claim 1 or 2, characterized in that, Step 7 includes: Step 7-1: Dissolve polyvinyl alcohol and / or polyvinylpyrrolidone in water to obtain a polymer solution; Step 7-2: Add the carbon material after the first carbonization to the polymer solution, stir, and then dry it directly at 50℃-65℃ to obtain the product of step 7-2; Step 7-3: Place the product from step 7-2 in a tube furnace and heat it at 200℃-300℃ for 1-1.5 hours under the protection of an inert gas to obtain the coated carbon material.

10. The preparation method according to claim 1 or 2, characterized in that, Step 8 includes: Step 8-1: Place the coated carbon material in a tube furnace and perform a second carbonization under the protection of an inert gas; the temperature of the second carbonization is selected from 850℃-1450℃, and the time is selected from 4-8h; to obtain the carbon material after the second carbonization. Step 8-2: After the carbon material after the second carbonization is subjected to a second acid washing and ball milling process, the sodium-ion battery hard carbon anode material is obtained.

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