Preparation method of sodium ion battery hard carbon negative electrode material

Abstract

The invention relates to the technical field of sodium-ion batteries, in particular to a preparation method of a sodium-ion battery hard carbon negative electrode material. The preparation method disclosed by the invention comprises the following steps: sequentially carrying out bacterium-enzyme synergistic fermentation, acid pickling, treatment of a mixed solution of alkali metal halide and ammonia water, treatment of a mixed solution of tin salt and a sulfur-containing compound, low-temperature carbonization, coating with a coating agent and high-temperature carbonization on biomass powder to finally obtain the sodium-ion battery hard carbon negative electrode material loaded with SnSx, a space is provided for volume expansion of SnSx by an ordered, loose and porous structure inside the SnSx.

Description

Technical Field

[0001] The present disclosure relates to the technical field of sodium-ion batteries, and particularly to a preparation method of a hard carbon anode material for sodium-ion batteries. Background Art

[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 and the layer spacing is large, which enables the hard carbon anode to store more charges under the same volume, improving the energy density and endurance of sodium-ion batteries. During the discharge process, the expansion and contraction of the hard carbon anode are more uniform, increasing its cycle stability, charge-discharge performance, and extending the cycle service life of sodium-ion batteries. Common precursors for preparing hard carbon materials include biomass, synthetic polymers, and fossil fuels, etc. Hard carbon materials prepared from different precursors have significant performance differences. Due to the different sources of precursor raw materials, the cost composition of hard carbon materials also varies significantly. Among them, biomass has a wide range of raw material sources, such as straw, bamboo, fruit shells, pomelo peels, animal and plant tissues, etc., and the cost is relatively low, becoming the preferred precursor material for preparing hard carbon materials at present. However, biomass has problems such as low carbon production rate, high ash content, low initial efficiency, controversial sodium storage mechanism, and complex structure that is difficult to precisely control, which affects its practical application process.

[0003] The SnS material is considered a promising anode material due to its high theoretical specific capacity (1022 mAh / g), but because of its poor electrical conductivity and large volume expansion during the sodiation and desodiation process, it causes pulverization and loss of active substances, significantly affecting the rate performance and Coulomb efficiency of the anode material. Carbon-coated SnS can effectively inhibit its volume expansion problem during charge and discharge. Therefore, there is an urgent need for a process that combines biomass materials and SnS materials for preparing hard carbon anode materials for sodium-ion batteries. Summary of the Invention

[0004] The present disclosure provides a preparation method of a hard carbon anode material for sodium-ion batteries to solve the deficiencies in the related art.

[0005] According to the first aspect of the embodiments of the present disclosure, a preparation method of a hard carbon anode material for sodium-ion batteries is provided. The preparation method includes the following steps:

[0006] Step 1: Provide a biomass raw material, dry and crush the biomass raw material, and then dry it again to obtain a biomass powder;

[0007] Step 2: Subject the biomass powder to enzyme and bacteria co-fermentation to obtain a fermented biomass powder;

[0008] Step 3: Immerse the fermented biomass powder in an acidic solution to obtain pickled biomass powder;

[0009] Step 4: Immerse the pickled biomass powder in a 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 a 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: Perform first carbonization on the biomass powder treated with the second mixed solution to obtain carbon material after the first carbonization;

[0012] Step 7: Blend the carbon material after the first carbonization with a coating agent and then heat to obtain coated carbon material;

[0013] Step 8: Subject the coated carbon material to second carbonization and post-treatment to obtain the hard carbon negative electrode material for sodium ion battery.

[0014] In one aspect of the embodiments of the present disclosure, the biomass raw material is selected from one or more of straw, basswood, pinewood, buckwheat husk, coconut fruit shell, palm fruit shell, walnut fruit shell, almond fruit shell, hawthorn fruit core, and cottonseed core.

[0015] In one aspect of the embodiments of the present disclosure, specifically, the biomass raw material is selected from basswood.

[0016] In one aspect of the embodiments of the present disclosure, in the enzymatic and microbial co-fermentation 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 the present disclosure, specifically, in the enzymatic and microbial co-fermentation in Step 2, the enzymes used are cellulase and ligninase, or hemicellulase and ligninase.

[0018] In one aspect of the embodiments of the present disclosure, in the enzymatic and microbial co-fermentation in Step 2, the microbial 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 the present disclosure, specifically, in the enzymatic and microbial co-fermentation in Step 2, the microbial strains used are Bacillus licheniformis or Bacillus subtilis.

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

[0021] In one aspect of the embodiments of the present disclosure, the acidic solution is selected from an aqueous solution of sodium chlorite, glacial acetic acid, and a mixture thereof.

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

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

[0024] In one aspect of the embodiments of the present disclosure, the first mixed solution is ammonia water containing at least one alkali metal halide, and 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 the present 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 the embodiments of the present disclosure, specifically, the alkali metal halide is selected from potassium fluoride. Further specifically, in the first mixed solution, the mass percentage content of potassium fluoride is selected from 10 - 20 wt%.

[0027] In one aspect of the embodiments of the present 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 stannous oxalate, stannous chloride, stannic 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 the present disclosure, preferably, the tin-containing compound is selected from stannous oxalate, stannous chloride, stannic chloride, or sodium stannate; the sulfur-containing compound is selected from thiourea.

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

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

[0031] In one aspect of the embodiments of the present 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 h.

[0032] In one aspect of the embodiments of the present 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 - 1.5 h.

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

[0034] In one aspect of the embodiments of the present disclosure, in step 8, the temperature of the second carbonization is selected from 850 °C - 1450 °C, and the time of the second carbonization is selected from 4 - 8 h.

[0035] In one aspect of the embodiments of the present 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 6.5 h.

[0036] In one aspect of the embodiments of the present disclosure, specifically, step 1 includes:

[0037] Step 1-1: Provide a biomass raw material, and the biomass raw material is selected from one or more of straw, basswood, pinewood, buckwheat husk, coconut fruit shell, palm fruit shell, walnut fruit shell, almond fruit shell, hawthorn fruit pit, and cottonseed kernel;

[0038] Step 1-2: Dry the biomass raw material at 50 °C - 65 °C for 6 - 12 h, and then crush it to 1 - 5 mm;

[0039] Step 1-3: Continue to dry the crushed biomass raw material at 50 °C - 65 °C for 6 - 12 h to obtain the biomass powder.

[0040] In one aspect of the embodiments of the present disclosure, specifically, step 2 includes:

[0041] Step 2-1: After uniformly stirring the biomass powder, corn flour, soybean meal, and complex bacterial enzymes, add water and ferment at room temperature for 3 - 6 days to obtain a fermented mixture; wherein, the complex bacterial enzymes include at least one strain selected from Bacillus subtilis, Bacillus licheniformis, cellulose-decomposing 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 °C - 100 °C to inactivate the enzymes to obtain the fermented biomass powder.

[0043] In one aspect of the embodiments of the present disclosure, specifically, step 3 includes:

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

[0045] Step 3-2: Add the fermented biomass powder into the prepared acidic solution, then heat at 65°C - 75°C for 2-3 h, and then obtain the pickled biomass powder after washing and drying.

[0046] In one aspect of the embodiments of the present disclosure, specifically, step 4 includes:

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

[0048] Step 4-2: Add the pickled biomass powder into the prepared first mixed solution, heat at 60°C - 80°C for 3-5 h, and then obtain the biomass powder treated with the first mixed solution after washing, filtering and drying.

[0049] In one aspect of the embodiments of the present disclosure, specifically, step 5 includes:

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

[0051] Step 5-2: Add the biomass powder treated with the first mixed solution into the prepared second mixed solution, soak in an environment below atmospheric pressure for 6-12 h, and then obtain the biomass powder treated with the second mixed solution after filtering and drying.

[0052] In one aspect of the embodiments of the present disclosure, specifically, step 6 includes:

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

[0054] Step 6-2: Subject the product obtained in step 6-1 to an ultrafine pulverization process so that the D50 value of the powder is 4-6 μm, and obtain the carbon material after the first carbonization.

[0055] In one aspect of the embodiments of the present 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 directly dry at 50°C - 65°C to obtain the product of Step 7-2;

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

[0059] In one aspect of the embodiments of the present 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°C - 1450°C, and the time is selected from 4 - 8 h; obtain the carbon material after the second carbonization;

[0061] Step 8-2: After the carbon material after the second carbonization undergoes a second pickling and ball milling process, obtain the hard carbon negative electrode material for the sodium-ion battery.

[0062] In one aspect of the embodiments of the present disclosure, in Step 8-2, hydrochloric acid with a concentration of 0.2 - 0.5 mol / L is used for the second pickling.

[0063] In one aspect of the embodiments of the present disclosure, in Step 8-2, a water washing process is further included after the second pickling.

[0064] In one aspect of the embodiments of the present disclosure, in Step 8-2, grinding balls with diameters of 3 mm, 5 mm, and 10 mm are used in the ball milling process and are matched according to a mass ratio of 1:2:1.

[0065] In one aspect of the embodiments of the present disclosure, in Step 8-2, the ball milling process includes: putting the prepared grinding balls and the carbon material after the second carbonization into the ball milling tank of the ball mill according to a mass ratio of 3 - 7:1 for intermittent ball milling, the rotation speed of the ball mill is 200 - 300 revolutions per minute, the ball milling time for each 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 the second aspect of the embodiments of the present disclosure, a hard carbon negative electrode material for a sodium-ion battery is provided, and the hard carbon negative electrode material for the sodium-ion battery is obtained by the foregoing preparation method.

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

[0068] As can be seen from the above embodiments, the present disclosure successively subjects biomass powder to combined enzymatic and microbial fermentation, pickling, treatment with a mixed solution of alkali metal halide and ammonia water, treatment with a mixed solution of tin salt and sulfur-containing compound, low-temperature carbonization, coating with a coating agent, and high-temperature carbonization to finally obtain a hard carbon anode material for a sodium-ion battery loaded with SnS x ; the orderly loose and porous structure inside provides space for the volume expansion of SnS x and thus endows excellent electrochemical performance.

[0069] It should be understood that the above general description and the following detailed description are only exemplary and explanatory and should not limit the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] The accompanying drawings herein are incorporated into the specification and form a part of the specification, showing embodiments consistent with the present disclosure and, together with the specification, are used to explain the principles of the present disclosure.

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

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

[0073] Figure 3 is a SEM image of the hard carbon anode material for a sodium-ion battery shown in Comparative Example 2. DETAILED DESCRIPTION OF THE EMBODIMENTS

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

[0075] For the sake of brevity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, each individually disclosed point or single numerical value itself can be used as a lower limit or an upper limit and combined with any other point or single numerical value or combined with other lower limits or upper limits to form a range not explicitly recited.

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

[0077] In the description herein, unless otherwise specified, "above" and "below" include the number itself.

[0078] Unless otherwise specified, the terms used in the present invention have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values of the various parameters mentioned in the present invention can be measured by various common measurement methods in the art (for example, they can be tested according to the methods given in the embodiments of the present invention).

[0079] The term "about" is used to describe and account for small variations. When used in connection with an event or circumstance, the term can refer to instances where the event or circumstance occurs precisely as well as instances where it occurs very nearly. For example, when used in connection with a numerical value, the term can refer to a range of variation of ±10% less than or equal to 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, sometimes quantities, ratios and other numerical values are presented in range format in this document. It should be understood that such range formats are for convenience and brevity and should be understood flexibly to include not only the numerical values expressly specified as range limits but also all individual numerical values or sub-ranges subsumed within the said range as if each numerical value and sub-range were expressly specified.

[0080] A list of items connected by the terms "at least one of", "at least one in", "at least one kind in" 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 example, 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 can include a single component or multiple components. Item B can include a single component or multiple components. Item C can include a single component or multiple components.

[0081] Positive electrode of sodium-ion battery:

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

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

[0084] In some embodiments of the present disclosure, the positive electrode current collector can be selected from one or more of copper foil, aluminum foil, nickel foil, stainless steel foil, stainless steel mesh, and carbon-coated aluminum foil, and aluminum foil is preferably used.

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

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

[0087] In some embodiments of the present disclosure, the positive electrode active material layer can further include a conductive agent to improve the conductivity of the positive electrode. The type of the conductive agent is not specifically limited in the present disclosure and can be selected according to actual needs. As an example, the conductive agent can 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 the present 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 the present disclosure, the positive electrode active material layer may further include a binder to firmly bond the positive electrode active material and the optional conductive agent to the positive electrode current collector. The present disclosure does not specifically limit the type of binder and can be selected according to actual needs. As an example, the binder can 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 the present disclosure, the binder 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 the present disclosure, a negative electrode for a sodium ion battery includes a negative electrode sheet, which includes a current collector and a negative electrode active material layer disposed on the current collector.

[0093] The material of the negative electrode current collector of the present disclosure is not particularly limited. In some embodiments of the present disclosure, the negative electrode current collector is selected from one of aluminum, copper, iron, tin, zinc, nickel, titanium, manganese, lead, antimony, cadmium, gold, bismuth, and germanium, an alloy of at least two of them, or a composite material of at least two of them; wherein the at least two alloys include but are not limited to copper-aluminum alloy, copper-iron alloy, copper-tin alloy, nickel-titanium alloy, nickel-manganese alloy, nickel-antimony alloy, gold-bismuth alloy, iron-nickel alloy, lead-manganese alloy and aluminum-nickel alloy; the 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 the present disclosure, the negative electrode current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0095] In some embodiments of the present 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 be conducive to the deintercalation and intercalation of sodium ions. Typically, but not restrictively, the negative electrode active material is selected from one or more of amorphous carbon materials (hard carbon and soft carbon), metal elements, metal alloys, sulfides, nitrides, oxides, carbides and other materials.

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

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

[0099] Step 1-1: Provide basswood raw materials;

[0100] Step 1-2: Dry the basswood raw materials at 50°C - 65°C for 6 - 12 h, and then crush them to 1 - 5 mm;

[0101] Step 1-3: Continue to dry the crushed basswood raw materials at 50°C - 65°C for 6 - 12 h to obtain basswood powder;

[0102] Step 2-1: After uniformly stirring the basswood powder, corn flour, soybean meal, and composite fungal enzymes, add water and ferment at room temperature for 3 - 6 days to obtain a fermented mixture; wherein, the composite fungal enzymes used include cellulase, ligninase, and Bacillus licheniformis / Bacillus subtilis;

[0103] Step 2-2: Add the fermented mixture to water at 90°C - 100°C to inactivate the enzymes and obtain fermented basswood powder;

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

[0105] Step 3-2: Add the fermented basswood powder to the prepared acidic solution, then heat at 65°C - 75°C for 2 - 3 h, and then wash and dry to obtain pickled basswood powder;

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

[0107] Step 4-2: Add the pickled basswood powder to the prepared first mixed solution, heat at 60°C - 80°C for 3 - 5 h, and then wash, filter, and dry to obtain the basswood 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% of stannous chloride and 5 - 10 wt% of thiourea;

[0109] Step 5-2: Add the basswood powder treated with the first mixed solution into the prepared second mixed solution, soak it in an environment below atmospheric pressure for 6-12 h, and then filter and dry it to obtain the basswood powder treated with the second mixed solution;

[0110] Step 6-1: Place the basswood powder treated with the second mixed solution in a tubular furnace and carry out the first carbonization under the protection of an inert gas; the temperature of the first carbonization is selected from 450°C - 650°C, and the time is selected from 2-5 h;

[0111] Step 6-2: Subject the product obtained in Step 6-1 to an ultrafine grinding process so that the D50 value of the powder is 4-6 μm to obtain the 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 into the polymer solution, stir it, and directly dry it at 50°C - 65°C to obtain the product of Step 7-2;

[0114] Step 7-3: Place the product of Step 7-2 in a tubular furnace and heat it at 200°C - 300°C for 1-1.5 h under the protection of an inert gas to obtain the coated carbon material;

[0115] Step 8-1: Place the coated carbon material in a tubular furnace and carry out the second carbonization under the protection of an inert gas; the temperature of the second carbonization is selected from 850°C - 1450°C, and the time is selected from 4-8 h; obtain the carbon material after the second carbonization;

[0116] Step 8-2: After subjecting the carbon material after the second carbonization to a second pickling and ball milling process, obtain the hard carbon negative electrode material for a sodium-ion battery; the ball milling process includes: putting the prepared grinding balls and the carbon material after the second carbonization into the ball milling tank of a ball mill at a mass ratio of 3-7:1 for intermittent ball milling, the rotation speed of the ball mill is 200-300 revolutions per minute, the ball milling time each 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.

[0117] The conductive agent in the negative electrode of the sodium-ion battery is to ensure good charge-discharge performance of the negative electrode. Therefore, a certain amount of conductive substance is usually added during the production of the negative electrode to collect microcurrents between the negative electrode active materials and between the negative electrode active material and the negative electrode current collector, so as to reduce the contact resistance of the negative electrode and accelerate the electron movement rate. At the same time, it can also effectively improve the migration rate of sodium ions in the negative electrode, thereby improving the charge-discharge efficiency of the negative electrode. In some embodiments of the present disclosure, the conductive agent in the negative electrode can be, but is not limited to, one or several of 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 can ensure a certain bonding strength between the active substance particles and between the active particles and the current collector during the use of the negative electrode, and is conducive to the formation of the SEI film, which can improve the cycle performance and service life of the positive electrode. In some embodiments of the present disclosure, the binder can 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 of the present disclosure includes an electrolyte, which includes an electrolyte and an electrolyte solvent. The electrolyte is a sodium salt, and the electrolyte solvent is an organic solvent; the electrolyte is the medium used in a chemical battery, provides ions for the normal operation of the chemical battery, and ensures that the chemical reactions occurring during operation are reversible.

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

[0122] In some embodiments of the present disclosure, the sodium salt is selected from one or several of sodium hexafluorophosphate, sodium chloride, sodium fluoride, sodium sulfate, sodium carbonate, sodium phosphate, sodium nitrate, sodium difluorooxalate borate, sodium pyrophosphate, sodium dodecylbenzenesulfonate, 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 methyl sulfonate, sodium acetate, sodium dichromate, sodium hexafluoroarsenate, sodium tetrafluoroborate, sodium perchlorate, sodium trifluoromethanesulfonimide, NaCF3SO3, NaN(SO2CF3)2. In particular, when sodium perchlorate is selected as the solute, the migration efficiency of its sodium ions is better, and the electrochemical performance of the prepared sodium-ion battery is more excellent.

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

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

[0125] In a preferred embodiment of the present disclosure, the organic solvent includes, but is 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), ethylene sulfite (ES), propylene sulfite (PS), dimethyl sulfite (DMS), diethyl sulfite (DES), crown ether, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-propyl-3-methylimidazolium hexafluorophosphate, 1-propyl-3-methylimidazolium tetrafluoroborate, 1-propyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-1-methylimidazolium hexafluorophosphate, 1-butyl-1-methylimidazolium tetrafluoroborate, 1-butyl-1-methylimidazolium bis(trifluoromethylsulfonyl)imide, N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, N-methyl-N-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide, N-methylpropylpiperidinium bis(trifluoromethylsulfonyl)imide, N-methylbutylpiperidinium bis(trifluoromethylsulfonyl)imide, or one or more of them.

[0126] In a preferred embodiment of the present disclosure, an additive can also be added to the electrolyte. By adding an additive to the electrolyte, the cycle stability of the sodium-ion battery can be improved; the additive is selected from one or more of esters, sulfones, ethers, nitriles, or olefins.

[0127] In a preferred embodiment of the present disclosure, the addition amount of the additive in the electrolyte is 0.1-20 wt%; by controlling the addition amount of the additive in the electrolyte, it is convenient to form a stable solid electrolyte film on the surface of the negative electrode current collector, thereby improving the service life of the sodium-ion battery.

[0128] In a preferred embodiment of the present disclosure, the additive is selected from one or more of fluoroethylene carbonate, vinylene carbonate, ethylene ethylene carbonate, 1,3 - propanesultone, 1,4 - butanesultone, ethylene sulfate, propylene sulfate, ethylene sulfite, vinyl sulfite, propylene sulfite, dimethyl sulfite, diethyl sulfite, ethylene sulfite, methyl chloroformate, dimethyl sulfoxide, anisole, acetamide, pyridine, m - pyridine, crown ether 12 - crown - 4, crown ether 18 - crown - 6, 4 - fluoroanisole, fluorinated chain ether, difluoromethyl ethylene carbonate, trifluoromethyl ethylene carbonate, chloroethylene carbonate, bromoethylene carbonate, trifluoroethyl phosphonic acid, bromobutyrolactone, fluoroacetylethane, phosphate ester, phosphite ester, phosphazene, ethanolamine, dimethylcarbamide, cyclobutyl sulfone, 1,3 - dioxolane, acetonitrile, long - chain olefin, aluminum oxide, magnesium oxide, barium oxide, sodium carbonate, calcium carbonate, carbon dioxide, sulfur dioxide, and lithium carbonate.

[0129] Separator:

[0130] The sodium - ion battery of the present disclosure is provided with a separator between the positive electrode and the negative electrode to prevent short - circuit. There are no particular limitations on the material and shape of the separator used in the sodium - ion battery of the present disclosure, and it can be any technology disclosed in the prior art.

[0131] In some embodiments of the present disclosure, the separator includes a polymer or an inorganic substance formed of a material stable to the electrolyte of the present application.

[0132] In some embodiments of the present disclosure, the separator is selected from a porous polymer film, an inorganic porous film, a glass fiber paper, or a composite film of one or more of the above porous ceramic films.

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

[0134] Sodium - ion battery:

[0135] The sodium - ion battery provided by the present disclosure includes the above - mentioned positive electrode, negative electrode, separator, and electrolyte, but is not limited thereto.

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

[0137] In some embodiments of the present disclosure, the sodium-ion battery involved in the present disclosure may include an outer package, and the outer package may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery may also be a soft package, such as a pouch soft package. The material of the soft package may be plastic, such as one or several of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0138] In some embodiments, the present disclosure also provides a battery module. The battery module includes the above-mentioned sodium-ion battery. Since the battery module of the present disclosure adopts the above-mentioned sodium-ion battery, it has at least the same advantages as the sodium-ion battery. The number of sodium-ion batteries included in the battery module of the present disclosure can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0139] In some embodiments, the present disclosure also provides a battery pack, which includes the above-mentioned battery module. 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] The present disclosure also provides a device, which includes at least one of the above-mentioned 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, energy storage systems, etc. In order to meet the high power and high energy density requirements of the device for lithium-ion batteries, a battery pack or a battery module can be adopted.

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

[0144] The following further elaborates the present disclosure in conjunction with embodiments. It should be understood that these embodiments are only used to illustrate the present disclosure and not to limit the scope of the present disclosure.

[0145] Examples and comparative examples:

[0146] Example 1:

[0147] Example 1 includes the following steps:

[0148] 1. Preparation of basswood powder material:

[0149] Weigh about 50 g of basswood raw material; the basswood raw materials used in the embodiments and comparative examples of the present disclosure are all small pieces of waste wood cut during wood processing; dry the basswood raw material at 60 °C for 8 h, and then use an industrial cutting machine to crush it to 1-3 mm; continue to dry the crushed basswood raw material at 60 °C for 12 h to obtain basswood powder material.

[0150] 2. Process of solid-state fermentation:

[0151] After evenly mixing basswood powder (50 g), corn flour (20 g), soybean meal (15 g), and complex fungal enzyme, add water and ferment at room temperature for 5 days to obtain a fermented mixture; among them, the complex fungal enzyme used contains a mixture of cellulase, ligninase, and Bacillus subtilis; among them, the addition amount of Bacillus subtilis is 4×10 13 CFU / kg, the addition amount of cellulase is 3×10 6 U / kg, and the addition amount of ligninase is 1.5×10 6 U / kg. After the fermentation ends, add the fermented mixture to water at 100 °C to inactivate the enzyme (3 min), and then dry to obtain the fermented basswood powder material.

[0152] 3. Pretreatment 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 basswood powder to the prepared acidic solution, then heat at 70 °C for 2.5 h, and then wash and dry to obtain the pickled basswood powder material.

[0154] 3.2: Prepare a 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 pickled basswood powder material to the prepared first mixed solution, heat at 70 °C for 4 h, and then wash, filter, and dry to obtain the basswood powder material 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 basswood powder material treated with the first mixed solution, then connect a 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 basswood powder material treated with the second mixed solution.

[0156] 4. Carbonization and coating:

[0157] 4.1: Place the basswood powder material treated with the second mixed solution in a tubular furnace and conduct the first carbonization in a nitrogen environment; the temperature of the first carbonization is selected from 550 °C, the heating rate is 5 °C / min, the carbonization time is 4 h, then naturally cool to room temperature, and then ultrafinely crush the carbonized powder to D50 of 5 μm to obtain the first carbonized powder.

[0158] 4.2: Dissolve polyvinyl alcohol (PVA1788, 2.5 g) in 50 mL of water. After complete dissolution, add the first carbonized powder and stir well. Then, directly dry it in an oven at 60 °C. After that, place the dried product in a tubular furnace and heat it at 250 °C for 1.5 h in a nitrogen environment to obtain the coated carbon material. Then, continue to heat and carbonize it at a heating rate of 8 °C / min until the temperature reaches 1250 °C, and the carbonization time is 6.5 h to obtain the second carbonized powder.

[0159] 5. Post-treatment:

[0160] After pickling the second carbonized powder with dilute hydrochloric acid solution (0.5 mol / L), washing with water and alcohol washing, perform the ball milling process. The ball milling process includes: putting 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 into the ball milling tank of the ball mill at a mass ratio of 4:1 for intermittent ball milling. The rotational speed of the ball mill is 250 revolutions per minute, the ball milling time each time is 3 minutes, the cooling time after stopping the mill is 5 minutes, and the total net ball milling time is 4 hours to obtain the hard carbon material. The SEM image of the hard carbon negative electrode material of Example 1 is as Figure 1 shown.

[0161] 6. Assembly of sodium-ion battery button-type half-cell:

[0162] Take the hard carbon material prepared above as the active material, SP as the conductive agent, and PVDF as the binder, and weigh them according to the mass ratio of hard carbon material:SP:PVDF = 94:3:3. Using NMP as the solvent, prepare a uniformly mixed slurry through a planetary disperser, and then uniformly coat the slurry on the composite copper current collector to obtain the negative electrode sheet. Using sodium hexafluorophosphate / EC + DEC as the electrolyte, sodium sheet as the counter electrode, and glass fiber (GF / F) as the separator, assemble a CR2025 type button-type sodium-ion half-cell and conduct electrochemical performance tests. The tests are carried out in a glove box filled with argon with the water content and oxygen content both lower than 1 ppm.

[0163] Example 2:

[0164] Example 2 includes the following steps:

[0165] 1. Preparation of basswood powder material:

[0166] Weigh about 50 g of basswood raw material; dry the basswood raw material in an oven at 60 °C for 8 h, and then use an industrial cutting machine to crush it to 1 - 3 mm; continue to dry the crushed basswood raw material in an oven at 60 °C for 12 h to obtain the basswood powder material.

[0167] 2. Process of solid-state fermentation:

[0168] After mixing basswood powder (50 g), corn flour (20 g), soybean meal (15 g), and complex fungal enzymes evenly, water is added and fermentation is carried out at room temperature for 5 days to obtain a fermented mixture; among them, the complex fungal enzymes used include a mixture of cellulase, ligninase, and Bacillus subtilis; among them, the addition amount of Bacillus subtilis is 4×10 13 CFU / kg, the addition amount of cellulase is 3×10 6 U / kg, and the addition amount of ligninase is 1.5×10 6 U / kg. After the fermentation is completed, the fermented mixture is added to water at 100°C to inactivate the enzymes (3 min), and then dried to obtain the fermented basswood powder material.

[0169] 3. Pretreatment 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 basswood powder to the prepared acidic solution, then heat at 70°C for 2.5 h, and then after washing and drying, obtain the pickled basswood powder material.

[0171] 3.2: Prepare a 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 pickled basswood powder material to the prepared first mixed solution, heat at 70°C for 4 h, and then after washing, filtering, and drying, obtain the basswood powder material 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 basswood powder material treated with the first mixed solution, then connect a 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 after filtering and drying, obtain the basswood powder material treated with the second mixed solution.

[0173] 4. Carbonization and coating:

[0174] 4.1: Place the basswood powder material treated with the second mixed solution in a tube furnace and carry out the first carbonization in a nitrogen environment; the temperature of the first carbonization is selected from 550°C, the heating rate is 5°C / min, the carbonization time is 4 h, and then it is naturally cooled to room temperature, and then the carbonized powder is ultrafinely pulverized to D50 of 5 μm to obtain the first carbonized powder.

[0175] 4.2: Dissolve polyvinyl alcohol (PVA1788, 2.5 g) in 50 mL of water. After complete dissolution, add the first carbonized powder and stir well. Then, directly dry it in an oven at 60 °C, and place the dried product in a tubular furnace. Heat it at 250 °C for 1.5 h under a nitrogen atmosphere to obtain the coated carbon material. Then continue to heat and carbonize it at a heating rate of 8 °C / min until the temperature reaches 1250 °C, and the carbonization time is 6.5 h to obtain the second carbonized powder.

[0176] 5. Post-treatment:

[0177] After pickling (0.5 mol / L dilute hydrochloric acid solution), washing with water, and washing with alcohol of the second carbonized powder, perform the ball milling process. The ball milling process includes: putting 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 into the ball milling tank of the ball mill at a mass ratio of 4:1 for intermittent ball milling. The rotational speed of the ball mill is 250 revolutions per minute, the ball milling time for each time is 3 minutes, the cooling time after stopping the mill is 5 minutes, and the total net ball milling time is 4 hours to obtain the hard carbon material.

[0178] 6. Assembly of sodium-ion battery button-type half-cell:

[0179] Use the above-prepared hard carbon material as the active material, SP as the conductive agent, and PVDF as the binder, and weigh them according to the mass ratio of hard carbon material, SP, and PVDF of 94:3:3. Use NMP as the solvent, and prepare a uniformly mixed slurry through a planetary disperser. Then evenly coat the slurry on the composite copper current collector to obtain the negative electrode sheet. Use sodium hexafluorophosphate / EC+DEC as the electrolyte, a sodium sheet as the counter electrode, and glass fiber (GF / F) as the separator to assemble a CR2025-type button-type sodium-ion half-cell, and perform electrochemical performance tests in a glove box filled with argon with a water content and an oxygen content both lower than 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. Potassium fluoride is used in Example 1, while potassium chloride is used in Example 2.

[0181] Example 3:

[0182] Example 3 includes the following steps:

[0183] 1. Preparation of basswood powder material:

[0184] Weigh about 50 g of basswood raw material; dry the basswood raw material at 60 °C for 8 h, and then use an industrial cutting machine to crush it to 1-3 mm; continue to dry the crushed basswood raw material at 60 °C for 12 h to obtain the basswood powder material.

[0185] 2. Process of solid-state fermentation:

[0186] After mixing the basswood powder (50 g), corn flour (20 g), soybean meal (15 g) and complex fungal enzyme evenly, add water and ferment at room temperature for 5 days to obtain a fermented mixture. Among them, the complex fungal enzyme used contains a mixture of cellulase, ligninase and Bacillus subtilis. Among them, the addition amount of Bacillus subtilis is 4×10 13 CFU / kg, the addition amount of cellulase is 3×10 6 U / kg, and the addition amount of ligninase is 1.5×10 6 U / kg. After the fermentation ends, add the fermented mixture to water at 100°C to inactivate the enzyme (3 min), and then dry it to obtain the fermented basswood powder material.

[0187] 3. Pretreatment 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 basswood powder to the prepared acidic solution, then heat at 70°C for 2.5 h, and then wash and dry to obtain the pickled basswood powder material.

[0189] 3.2: Prepare a 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 pickled basswood powder material to the prepared first mixed solution, heat at 70°C for 4 h, and then wash, filter and dry to obtain the basswood powder material 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 basswood powder material treated with the first mixed solution, then connect a vacuum pump and seal the vacuum filtration flask, maintain the pressure of the system at about 500 Pa, soak for 8 h under this pressure, and then filter and dry to obtain the basswood powder material treated with the second mixed solution.

[0191] 4. Carbonization and coating:

[0192] 4.1: Place the basswood powder material treated with the second mixed solution in a tube furnace and conduct the first carbonization under a nitrogen atmosphere. The temperature of the first carbonization is selected as 550°C, the heating rate is 5°C / min, the carbonization time is 4 h, then naturally cool to room temperature, and then ultra-finely crush the carbonized powder to D50 of 5 μm to obtain the first carbonized powder.

[0193] 4.2: Dissolve polyvinyl alcohol (PVA1788, 2.5 g) in 50 mL of water. After complete dissolution, add the first carbonized powder and stir well. Then, directly dry it in an oven at 60 °C. Next, place the dried product in a tube furnace and heat it at 250 °C for 1.5 h in a nitrogen environment to obtain the coated carbon material. Then, continue to heat and carbonize it at a heating rate of 8 °C / min until the temperature reaches 1250 °C, and the carbonization time is 6.5 h to obtain the second carbonized powder.

[0194] 5. Post-treatment:

[0195] After pickling (0.5 mol / L dilute hydrochloric acid solution), washing with water, and washing with alcohol, the second carbonized powder is subjected to a ball milling process. The ball milling process includes: putting 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 into the ball milling tank of a ball mill at a mass ratio of 4:1 for intermittent ball milling. The rotational speed of the ball mill is 250 revolutions per minute, the ball milling time for each time is 3 minutes, the cooling time after stopping the mill is 5 minutes, and the total net ball milling time is 4 hours to obtain the hard carbon material.

[0196] 6. Assembly of sodium-ion battery button-type half-cell:

[0197] Take the hard carbon material prepared above as the active material, SP as the conductive agent, and PVDF as the binder, and weigh them according to the mass ratio of hard carbon material:SP:PVDF of 94:3:3. Using NMP as the solvent, prepare a uniformly mixed slurry through a planetary disperser, and then uniformly coat the slurry on a composite copper current collector to obtain a negative electrode plate. Using sodium hexafluorophosphate / EC + DEC as the electrolyte, a sodium sheet as the counter electrode, and a glass fiber (GF / F) as the separator, assemble a CR2025-type button-type sodium-ion half-cell and conduct an electrochemical performance test. The test is carried out in a glove box filled with argon with a water content and an oxygen content both lower than 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. Potassium fluoride is used in Example 1, while lithium bromide is used in Example 2.

[0199] Comparative Example 1:

[0200] Comparative Example 1 includes the following steps:

[0201] 1. Preparation of basswood powder material:

[0202] Weigh about 50 g of basswood raw material; dry the basswood raw material at 60 °C for 8 h, and then use an industrial cutting machine to crush it to 1 - 3 mm; continue to dry the crushed basswood raw material at 60 °C for 12 h to obtain the basswood powder material.

[0203] 2. Preprocessing 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 basswood powder to the prepared acidic solution, then heat at 70°C for 2.5 hours, and then wash and dry to obtain acid-washed basswood powder.

[0205] 3.2: Prepare a first mixed solution, which is 150 mL of ammonia water containing 12 wt% of sodium bromide, with a concentration of 25%. Add the acid-washed basswood powder to the prepared first mixed solution, heat at 70°C for 4 hours, and then wash, filter and dry to obtain the basswood 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 bottle, and add the basswood powder treated with the first mixed solution, then connect a vacuum pump and seal the vacuum filtration bottle, maintain the system pressure at about 500 Pa, soak at this pressure for 8 hours, and then filter and dry to obtain the basswood powder treated with the second mixed solution.

[0207] 4. Carbonization and coating:

[0208] 4.1: The basswood powder treated with the second mixed solution is placed in a tubular furnace and carbonized for the first time under a nitrogen environment; the temperature for the first carbonization is selected from 550°C, the heating rate is 5°C / min, the carbonization time is 4 hours, and then naturally cooled to room temperature. The carbonized powder is then ultrafinely ground to a D50 of 5 μm to obtain the first carbonized powder.

[0209] 4.2: Dissolve polyvinyl alcohol (PVA1788, 2.5 g) in 50 mL of water. After it is fully dissolved, add the first carbonized powder into it, stir it thoroughly, and then dry it directly in an oven at 60°C. Then place the dried product in a tubular furnace and heat it at 250°C for 1.5 h under a nitrogen environment to obtain the coated carbon material; then continue to heat and carbonize at a heating rate of 8°C / min to 1250°C for 6.5 h to obtain the second carbonized powder.

[0210] 5. Post-processing:

[0211] After pickling the second carbonized powder with dilute hydrochloric acid solution (0.5 mol / L), washing with water and then with alcohol, a ball milling process is carried out; the ball milling process includes: putting 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 into the ball milling tank of the ball mill at a mass ratio of 4:1 for intermittent ball milling. The rotation speed of the ball mill is 250 revolutions per minute, the ball milling time each time is 3 minutes, the cooling time after stopping the mill is 5 minutes, and the total net ball milling time is 4 hours; a hard carbon material is obtained. The SEM image of the hard carbon negative electrode material of Comparative Example 1 is as Figure 2 shown.

[0212] 6. Assembly of a sodium-ion battery button-type half-cell:

[0213] Taking the above-prepared hard carbon material as the active material, SP as the conductive agent, and PVDF as the binder, weigh them according to the mass ratio of hard carbon material, SP, and PVDF of 94:3:3. Using NMP as the solvent, prepare a uniformly mixed slurry through a planetary disperser, and then uniformly coat the slurry on a composite copper current collector to obtain a negative electrode sheet; using sodium hexafluorophosphate / EC+DEC as the electrolyte, a sodium sheet as the counter electrode, and glass fiber (GF / F) as the separator, assemble a CR2025-type button-type sodium ion half-cell, and conduct electrochemical performance tests. The tests are carried out in a glove box filled with argon with a water content and an oxygen content both lower than 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 basswood powder material:

[0218] Weigh about 50 g of basswood raw material; dry the basswood raw material at 60 °C for 8 h, and then use an industrial cutting machine to crush it to 1 - 3 mm; continue to dry the crushed basswood raw material at 60 °C for 12 h to obtain basswood powder material.

[0219] 2. Solid-state fermentation process:

[0220] After uniformly mixing basswood powder (50 g), corn flour (20 g), soybean meal (15 g), and complex fungal enzymes, add water and ferment at room temperature for 5 days to obtain a fermented mixture; among them, the complex fungal enzymes used include a mixture of cellulase, ligninase, and Bacillus subtilis; among them, the addition amount of Bacillus subtilis is 4×10 13 CFU / kg, and the addition amount of cellulase is 3×10 6U / kg, the addition amount of ligninase was 1.5×10 6 After the fermentation was completed, the fermented mixture was added to 100°C water to inactivate the enzyme (3 min), and then dried to obtain the fermented basswood powder.

[0221] 3. Preprocessing 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 basswood powder to the prepared acidic solution, then heat at 70°C for 2.5 hours, and then wash and dry to obtain an acid-washed basswood 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 bottle, add the acid-washed basswood powder, then connect a vacuum pump and seal the vacuum filtration bottle, maintain the system pressure at about 500 Pa, soak at this pressure for 8 hours, and then filter and dry to obtain the basswood powder treated with the mixed solution.

[0224] 4. Carbonization and coating:

[0225] 4.1: The basswood powder treated with the mixed solution is placed in a tubular furnace and carbonized for the first time under a nitrogen environment; the temperature for the first carbonization is selected from 550°C, the heating rate is 5°C / min, the carbonization time is 4 hours, and then it is naturally cooled to room temperature. The carbonized powder is then ultrafinely ground to a D50 of 5μm to obtain the first carbonized powder.

[0226] 4.2: Dissolve polyvinyl alcohol (PVA1788, 2.5 g) in 50 mL of water. After it is fully dissolved, add the first carbonized powder into it, stir it thoroughly, and then dry it directly in an oven at 60°C. Then place the dried product in a tubular furnace and heat it at 250°C for 1.5 h under a nitrogen environment to obtain the coated carbon material; then continue to heat and carbonize at a heating rate of 8°C / min to 1250°C for 6.5 h to obtain the second carbonized powder.

[0227] 5. Post-processing:

[0228] After pickling the second carbonized powder with dilute hydrochloric acid solution (0.5 mol / L), washing with water and then with alcohol, a ball milling process is carried out; the ball milling process includes: putting 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 into the ball milling tank of the ball mill at a mass ratio of 4:1 for intermittent ball milling. The rotational speed of the ball mill is 250 revolutions per minute, the ball milling time each time is 3 minutes, the cooling time after stopping the mill is 5 minutes, and the total net ball milling time is 4 hours; a hard carbon material is obtained. The SEM image of the hard carbon negative electrode material of Comparative Example 2 is as Figure 3 shown.

[0229] 6. Assembly of sodium-ion battery button-type half-cell:

[0230] Taking the above-prepared hard carbon material as the active material, SP as the conductive agent, and PVDF as the binder, weigh them according to the mass ratio of hard carbon material, SP, and PVDF of 94:3:3. Using NMP as the solvent, prepare a uniformly mixed slurry through a planetary disperser, and then uniformly coat the slurry on the composite copper current collector to obtain a negative electrode sheet; using sodium hexafluorophosphate / EC+DEC as the electrolyte, a sodium sheet as the counter electrode, and glass fiber (GF / F) as the separator, assemble a CR2025-type button-type sodium-ion half-cell, and conduct electrochemical performance tests. The tests are carried out in a glove box filled with argon with a water content and an oxygen content both lower than 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 basswood powder material:

[0235] Weigh about 50 g of basswood raw material; dry the basswood raw material at 60 °C for 8 h, and then use an industrial cutting machine to crush it to 1 - 3 mm; continue to dry the crushed basswood raw material at 60 °C for 12 h to obtain basswood powder material.

[0236] 2. Process of solid-state fermentation:

[0237] After uniformly mixing the basswood powder (50 g), corn flour (20 g), soybean meal (15 g), and complex fungal enzyme, add water and ferment at room temperature for 5 days to obtain a fermented mixture; among them, the complex fungal enzyme used contains a mixture of cellulase, ligninase, and Bacillus subtilis; among them, the addition amount of Bacillus subtilis is 4×10 13 CFU / kg, and the addition amount of cellulase is 3×10 6U / kg, the addition amount of ligninase was 1.5×10 6 After the fermentation was completed, the fermented mixture was added to 100°C water to inactivate the enzyme (3 min), and then dried to obtain the fermented basswood powder.

[0238] 3. Preprocessing 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 basswood powder to the prepared acidic solution, then heat at 70°C for 2.5 hours, and then wash and dry to obtain an acid-washed basswood powder.

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

[0241] 4. Carbonization and coating:

[0242] 4.1: The basswood powder treated with the first mixed solution is placed in a tubular furnace and carbonized for the first time under a nitrogen environment; the temperature for the first carbonization is selected from 550°C, the heating rate is 5°C / min, the carbonization time is 4 hours, and then naturally cooled to room temperature. The carbonized powder is then ultrafinely ground to a D50 of 5 μm to obtain the first carbonized powder.

[0243] 4.2: Dissolve polyvinyl alcohol (PVA1788, 2.5 g) in 50 mL of water. After it is fully dissolved, add the first carbonized powder into it, stir it thoroughly, and then dry it directly in an oven at 60°C. Then place the dried product in a tubular furnace and heat it at 250°C for 1.5 h under a nitrogen environment to obtain the coated carbon material; then continue to heat and carbonize at a heating rate of 8°C / min to 1250°C for 6.5 h to obtain the second carbonized powder.

[0244] 5. Post-processing:

[0245] The second carbonized powder is pickled (with 0.5mol / L dilute hydrochloric acid solution), washed with water and then washed with alcohol, and then undergoes a ball milling process; the ball milling process includes: putting the prepared grinding balls (made of agate balls with diameters of 3mm, 5mm, and 10mm, mixed in a mass ratio of 1:2:1) and the carbonized powder into the ball milling tank of the ball mill in a mass ratio of 4:1 for intermittent ball milling. The rotational speed of the ball mill is 250 revolutions per minute, the ball milling time each time is 3 minutes, the cooling time after stopping the mill is 5 minutes, and the total net ball milling time is 4 hours; a hard carbon material is obtained.

[0246] 6. Assembly of sodium-ion battery button-type half-cell:

[0247] Taking the hard carbon material prepared above as the active material, SP as the conductive agent, and PVDF as the binder, weigh them according to the mass ratio of hard carbon material, SP, and PVDF of 94:3:3. Using NMP as the solvent, prepare a uniformly mixed slurry through a planetary disperser, and then uniformly coat the slurry on the composite copper current collector to obtain a negative electrode sheet; using sodium hexafluorophosphate / EC+DEC as the electrolyte, a sodium sheet as the counter electrode, and glass fiber (GF / F) as the separator, assemble a CR2025-type button-type sodium-ion half-cell, and conduct electrochemical performance tests. The tests are carried out in a glove box filled with argon with both the water content and oxygen content lower than 1ppm.

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

[0249] Example 4:

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

[0251] Example 5:

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

[0253] Example 6:

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

[0255] Example 7:

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

[0257] Electrochemical performance test of half-cells:

[0258] The products of Examples 1-7 and Comparative Examples 1-3 were subjected to a constant current discharge at 0.1C to 0.01V first and then at 0.2C to 0.01V in a voltage range of 0-2V, followed by standing for 20 min and then a constant current charge at 0.1C to 2V; their electrochemical performance was tested; the specific values are shown in Table 1 below.

[0259] Table 1

[0260]

[0261]

[0262] Comparing the values in Table 1 and Figure 1 and Figure 2 , it can be seen that Comparative Example 1, which does not include the solid-state fermentation process, lacks through-holes and a connecting structure in its structure compared to Example 1 using the solid-state fermentation process, and its electrochemical performance is also significantly weaker than that of the examples; in the present disclosure, the enzyme-fungi co-fermentation decomposes part of the lignin in the linden wood structure, thereby forming a large number of through-holes and connecting structures, providing sufficient space for the loading and expansion of SnS x . Comparing the values in Table 1 and Figure 1 and Figure 3 , it can be seen that Comparative Example 2, which does not include pretreatment with the first mixed solution (alkali metal halide salt + ammonia water), forms larger SnS x particles compared to Example 1 pretreated with the first mixed solution, and its electrochemical performance also decreases; in the present disclosure, the combined use of lithium metal halide and ammonia water is to remove the lignin on the surface of the through-holes in the wood structure and keep the wood fiber channels unobstructed, thereby providing better sites for the deposition of SnS x . Therefore, in Comparative Example 2, which does not include pretreatment with the first mixed solution, larger SnS x particles are formed on the surface of the wood fiber channels after sintering, which will cause uneven expansion during charge and discharge, affecting its electrochemical performance. In addition, it is worth noting that the electrochemical performance of Example 1 is further improved compared to Examples 2 and 3 because the alkali metal halide salt used in Example Ⅰ contains fluorine element. Therefore, while removing the lignin on the surface of the through-holes in the wood structure, fluorine element is introduced, and thus fluorine atoms are doped into the finally obtained hard carbon material, so its electrochemical performance is further improved.

[0263] Other embodiments of the present invention will be readily apparent to those skilled in the art upon consideration of the specification and practice of the disclosure herein. The present invention is intended to cover any variations, uses, or adaptations of the invention following the general principles of the invention and including known common general knowledge or conventional technical means in the technical field of the present invention that are not disclosed herein.

Claims

1. A preparation method of a hard carbon anode material for a sodium-ion battery, characterized in that, The preparation method includes the following steps: Step 1: Provide a biomass raw material, dry and crush the biomass raw material, and then dry it again to obtain biomass powder; Step 2: Subject the biomass powder to co-fermentation of bacteria and enzymes to obtain fermented biomass powder; Step 3: Immerse the fermented biomass powder in an acidic solution to obtain pickled biomass powder; Step 4: Immerse the pickled biomass powder in a 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 a 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: Perform first carbonization on the biomass powder treated with the second mixed solution to obtain a carbon material after the first carbonization; Step 7: Blend the carbon material after the first carbonization with a coating agent and heat to obtain a coated carbon material; Step 8: Subject the coated carbon material to second carbonization and post-treatment to obtain the hard carbon negative electrode material for the sodium-ion battery.

2. The preparation method according to claim 1, characterized in that, The preparation method satisfies at least one of the following conditions:

1. (1) The biomass raw material is selected from one or more of straw, basswood, pine, buckwheat husk, coconut shell, palm fruit shell, walnut fruit shell, almond fruit shell, hawthorn fruit core and cottonseed core; 2. (2) 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; 3. (3) In the co-fermentation of bacteria and enzymes in Step 2, the bacterial strains used are selected from Bacillus subtilis, Bacillus licheniformis, cellulose-decomposing bacteria, brown rot fungi or white rot fungi; 4. (4) In Step 3, the acidic solution is selected from an aqueous mixed solution of sodium chlorite and glacial acetic acid; 5. (5) In Step 4, the first mixed solution is ammonia water containing at least one alkali metal halide, and 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; 6. (6) 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 stannous oxalate, stannous chloride, stannic chloride, sodium stannate, stannous tartrate, stannous sulfate; the sulfur-containing compound is selected from thiourea or ammonium sulfide; 7. (7) In Step 6, the temperature of the first carbonization is selected from 450°C - 650°C, and the time of the first carbonization is selected from 2 - 5 h; 8. (8) 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 - 1.5 h; 9. (9) In Step 8, the temperature of the second carbonization is selected from 850°C - 1450°C, and the time of the second carbonization is selected from 4 - 8 h.

3. The preparation method according to claim 1 or 2, characterized in that, Step 1 includes: Step 1-1: Provide a biomass raw material, which is selected from one or more of straw, basswood, pinewood, buckwheat husk, coconut fruit shell, palm fruit shell, walnut fruit shell, almond fruit shell, hawthorn fruit pit and cottonseed pit; Step 1-2: Dry the biomass raw material at 50°C - 65°C for 6 - 12 h, and then crush it to 1 - 5 mm; Step 1-3: Continue to dry the crushed biomass raw material at 50°C - 65°C for 6 - 12 h 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 uniformly stirring the biomass powder, corn flour, soybean meal and compound bacterial enzyme, add water and ferment at room temperature for 3 - 6 days to obtain a fermented mixture; wherein, the compound bacterial enzyme contains at least one strain selected from Bacillus subtilis, Bacillus licheniformis, cellulose-decomposing 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°C - 100°C to inactivate the enzyme to 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, which is an aqueous solution containing 1.5 - 3 wt% of sodium chlorite and 0.1 - 0.3 wt% of glacial acetic acid; Step 3-2: Add the fermented biomass powder to the prepared acidic solution, then heat at 65°C - 75°C for 2 - 3 h, and then wash and dry to obtain the pickled 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 ammonia water containing 10 - 20 wt% of potassium fluoride, and the concentration of the ammonia water is selected from 10% - 25%; Step 4-2: Add the pickled biomass powder to the prepared first mixed solution, heat at 60°C - 80°C for 3 - 5 h, 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% of stannous chloride and 5 - 10 wt% of thiourea; Step 5-2: Add the biomass powder treated with the first mixed solution to the prepared second mixed solution, soak in an environment below normal pressure for 6 - 12 h, and then filter and dry 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 in a tubular furnace and carry out the first carbonization under the protection of an inert gas; the temperature of the first carbonization is selected from 450°C - 650°C and the time is selected from 2 - 5 h; Step 6-2: After crushing the product obtained in Step 6-1, carry out an ultrafine crushing process so that the D50 value of the powder is 4 - 6 μm to obtain 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 into the polymer solution, and directly dry it at 50°C - 65°C after stirring to obtain the product of Step 7-2; Step 7-3: Place the product of Step 7-2 in a tube furnace, and heat it at 200°C - 300°C for 1 - 1.5 h 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 second carbonization under the protection of an inert gas; the temperature of the second carbonization is selected from 850°C - 1450°C, and the time is selected from 4 - 8 h; obtain the carbon material after the second carbonization; Step 8-2: After the carbon material after the second carbonization undergoes second pickling and ball milling processes, obtain the hard carbon anode material for the sodium-ion battery.

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