Biomass-derived hard carbon sodium-ion battery anode material with high platform capacity and preparation method thereof

Abstract

The application discloses a biomass hard carbon sodium ion battery negative electrode material with high platform capacity and a preparation method thereof, and comprises the following steps: S1, raw material pretreatment to obtain preliminary raw material; S2, alkaline solution treatment: temperature control treatment under alkaline solution condition to obtain biomass raw material after alkaline solution treatment; S3, lignin removal treatment: centrifugation, acid washing, water washing and drying are carried out to obtain biomass raw material from which part of lignin is removed; S4, activator treatment: temperature control reaction in an activator solution, followed by centrifugation and drying to obtain biomass raw material rich in activator; S5, carbonization activation: carbonization activation is carried out to obtain activated material; S6, post-treatment: acid washing, water washing to neutral and drying to obtain low-temperature carbonized material rich in micropore structure; and S7, high-temperature carbonization: high-temperature carbonization is carried out to obtain sodium ion battery hard carbon negative electrode material rich in micropores in the interior. The application has the characteristics of effectively improving platform capacity, high first-week charge-discharge efficiency and low process cost.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion batteries, in particular to a biomass hard carbon sodium ion battery negative electrode material with high platform capacity and a preparation method thereof. BACKGROUND

[0002] With the rapid development of smart grids and electric vehicles, the limited lithium resources cannot meet the social demand. Therefore, sodium ion batteries with low price and rich raw material reserves have become an excellent alternative.

[0003] Hard carbon is the most promising sodium ion battery negative electrode material at present, however, the low platform capacity limits the improvement of the energy density of the sodium ion battery. Since the structure of the hard carbon material is complex and the sodium storage mechanism is still controversial, it is more challenging to develop a sodium ion battery negative electrode material with high platform capacity.

[0004] At present, hard templates such as ZnCl2 and MgCl2 are widely used as activators in the industry. Such activators have weak corrosion, have the advantages of low equipment wear and tear, mild process conditions, etc., but also have defects: such as the activator is difficult to enter the material inside, is easy to stay and enrich on the material surface, and the oxides formed during calcination will gather on the material surface, forming macropores and mesopores, resulting in a large specific surface area of the hard carbon material, a low micropore content, and limited capacity improvement of the hard carbon negative electrode material, and a low first efficiency. SUMMARY

[0005] The purpose of the present application is to provide a biomass hard carbon sodium ion battery negative electrode material with high platform capacity and a preparation method thereof, which has the characteristics of effective platform capacity improvement, high first charge and discharge efficiency and low process cost.

[0006] The present application can be realized by the following technical solutions:

[0007] The present application discloses a preparation method of a biomass hard carbon sodium ion battery negative electrode material with high platform capacity, comprising the following steps:

[0008] S1, raw material pretreatment: crushing and sieving the biomass raw material to obtain a preliminary raw material;

[0009] S2, alkali solution treatment: controlling the temperature of the preliminary raw material obtained in step S1 in an alkali solution to obtain an alkali solution treated biomass raw material;

[0010] S3, lignin removal treatment: centrifuging the alkali solution treated biomass raw material in step S2, then acid washing and water washing to neutral, and finally drying to obtain a biomass raw material with part of the lignin removed;

[0011] S4, activating agent treatment: the biomass material with partially removed lignin obtained in step S3 is reacted in an activating agent solution, followed by centrifugation, drying, to obtain the biomass material rich in activating agent;

[0012] S5, carbonization activation: the biomass material rich in activating agent obtained in step S4 is subjected to carbonization activation, to obtain the activated material;

[0013] S6, post-treatment: the activated material obtained in step S5 is subjected to acid washing and water washing until neutral, and drying, to obtain the low-temperature carbonized material rich in microporous structure;

[0014] S7, high-temperature carbonization: the carbonized material obtained in step S6 is subjected to high-temperature carbonization, to obtain the sodium-ion battery hard carbon negative electrode material rich in micropores inside.

[0015] In step S2, the role of the alkaline solution is to dissolve part of the lignin and break the dense network structure of the biomass material, so that the activating agent used in the subsequent step can fully penetrate into the interior of the biomass material. The structure of the biomass material is very complex and diverse. From the microscopic level, it is mainly composed of lignin, cellulose and hemicellulose. Lignin, cellulose and hemicellulose are often connected to each other to form lignin-carbohydrate complexes. Among them, lignin is a polyphenolic polymer with a three-dimensional network structure formed by phenylpropane structural units connected and randomly coupled by carbon-carbon bonds (C-C) and ether bonds (-O-). Lignin penetrates between cellulose and hemicellulose, acting as a linker between the two, and then forming a very firm network structure. In order to make the activating agent enter the material interior, the alkaline solution is used to take advantage of the dissolution of lignin, to break the tight network structure between cellulose, hemicellulose and lignin without damaging the structure of the material itself, and to create a path for the activating agent to penetrate into the biomass material.

[0016] In step S4, the purpose of adding the activating agent is to form oxides during the subsequent low-temperature carbonization stage, and the pores are formed after the generated oxides are removed by acid washing. In order to make the formed pore structure a microporous structure, the mass fraction of inorganic salts or organic salts containing zinc, magnesium and calcium needs to be controlled at 5%~20%, so that the activating agent can enter the material interior uniformly and sufficiently, and at the same time, the problem of activating agent enrichment is avoided, and then the dispersed oxides are generated in the material interior, so that the material produces abundant microporous structure.

[0017] Further, in step S2, the alkaline solution is one or two or more of a sodium hydroxide solution, a sodium carbonate solution, a sodium bicarbonate solution, a potassium hydroxide solution, a potassium carbonate solution, a barium hydroxide solution, and a calcium hydroxide solution, and the concentration of the alkaline solution is 2-10 mol / L; the temperature control reaction conditions are: a temperature of 60-120°C and a time of 2-10 h. Specifically, if the concentration of the alkaline solution is too low, i.e., too little lignin is dissolved, the tight network structure connected by the lignin cannot be broken, directly affecting the penetration of the activator into the material interior, resulting in poor activation effect; if the concentration of the alkaline solution is too high, i.e., the lignin is completely dissolved, the structure of the material will collapse, and the interlayer spacing will be greatly reduced, affecting the insertion and extraction of sodium ions, and ultimately causing a significant decline in battery performance.

[0018] Further, in step S4, the activator is one or two or more of zinc chloride, magnesium chloride, calcium chloride, zinc nitrate, magnesium nitrate, zinc acetate, magnesium acetate, calcium acetate, zinc gluconate, magnesium gluconate, calcium gluconate, zinc citrate, magnesium citrate, and calcium citrate, and the amount of the activator added is 5-20 wt.% of the amount of the biomass raw material added, and the temperature control reaction conditions are: a temperature of 50-80°C and a time of 5-20 h. Specifically, if the amount of the activator added is too high, the activator is easily enriched in the material interior, resulting in too much or too large oxides formed at the same site, causing macroporous and mesoporous structures and reducing the performance of the battery; if the amount of the activator added is too low, the activator entering the material interior is less, the oxides generated are less, and the pore structure formed is less, which is not significant for capacity improvement.

[0019] Further, in step S5, the carbonization activation conditions are: a temperature rising rate of 2-10 ℃ / min, a temperature of 300-600°C, and a treatment time of 2-5 h; and the protective gas is nitrogen and / or argon. Specifically, the carbonization activation temperature affects the effect of the present application: if the carbonization activation temperature is too low, the activator cannot be completely converted into a metal oxide, resulting in that the activator cannot be completely removed in the subsequent acid washing step; if the carbonization activation temperature is too high, the carbon material is carbonized to a high degree, resulting in pore collapse and closure, which is also not conducive to the removal of the activator in the subsequent acid washing step.

[0020] Further, in step S7, the high-temperature carbonization conditions are: a temperature rising rate of 0.5-5 ℃ / min, a carbonization temperature of 1200-1600 ℃, and a carbonization time of 2-10 h. Specifically, the high-temperature carbonization temperature needs to be 1200-1600 ℃, and the purpose is to close the original microporous structure of the low-temperature carbonized material at high temperature in the high-temperature carbonization stage, to form a closed pore structure. Such structure can not only store sodium to improve the capacity, but also make the material have a smaller specific surface area, thereby not affecting the first cycle efficiency of the hard carbon negative electrode material. If the high-temperature carbonization temperature is too low, the microporous structure in the low-temperature carbonized material cannot be completely closed, resulting in a larger specific surface area of the material, which affects the first cycle efficiency of the material; if the high-temperature carbonization temperature is too high, the graphitization degree of the carbon material will be higher, and the interlayer spacing will be smaller, which is not conducive to the embedding and extraction of sodium ions, and will have a negative impact on the performance of the material.

[0021] Further, in steps S3 and S6, the acid washing solution is one or two or more of hydrochloric acid, nitric acid solution, hydrofluoric acid, formic acid, acetic acid, and phytic acid with a mass fraction of 2-10%.

[0022] Further, in step S4, the filtered activator filtrate is calibrated to the required concentration after filtration, and the filtrate can be recycled to increase economic benefits.

[0023] Further, in step S1, the biomass raw material is one or two or more of walnut shell, coconut shell, apricot shell, coffee shell, peanut shell, fruit peel, reed, wood chip, bamboo chip, sunflower stem, corn straw, and wheat straw, and starch.

[0024] Another aspect of the present application is to protect a biomass hard carbon sodium ion battery negative electrode material, which is prepared by the above preparation method.

[0025] The biomass hard carbon sodium ion battery negative electrode material with high platform capacity and the preparation method thereof have the following beneficial effects:

[0026] First, the platform capacity is effectively improved. In the present application, alkali dissolution is combined with hard template activation to form a rich microporous structure in the interior of the biomass material, greatly improving the low potential platform capacity of the hard carbon negative electrode material.

[0027] Second, the first cycle charge-discharge efficiency is high. The preparation method of the present application produces a large number of micropores, non-macropores and mesopores. The microporous structure is easy to close after high-temperature carbonization, so that the material has a small specific surface area. The hard carbon material with a small specific surface area has a higher first cycle efficiency and processability.

[0028] Third, the process cost is low. The preparation method of the present application can make the activator enter the interior of the biomass material to play a role, reduce the amount of activator, greatly increase the use efficiency of the activator, and reduce the production cost. Attached Figure Description

[0029] Figure 1 The first-week charge-discharge curve of Application Example 1;

[0030] Figure 2 The first-week charge-discharge curves for application Example 2;

[0031] Figure 3 The first-week charge-discharge curves are for Comparative Example 1.

[0032] Figure 4 The first-week charge-discharge curves are for Comparative Example 2. Detailed Implementation

[0033] To enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention will be further described in detail below with reference to embodiments.

[0034] This invention discloses a method for preparing a high-capacity biomass hard carbon sodium-ion battery anode material, comprising the following steps:

[0035] S1. Raw material pretreatment: The biomass raw materials are crushed and sieved to obtain preliminary raw materials;

[0036] S2, Alkaline solution treatment: The preliminary raw material obtained in step S1 is subjected to temperature-controlled treatment under alkaline solution conditions to obtain alkaline solution-treated biomass raw material;

[0037] S3. Lignin removal treatment: The biomass raw material treated with alkaline solution in step S2 is centrifuged, then acid washed, washed with water until neutral, and finally dried to obtain biomass raw material with some lignin removed.

[0038] S4. Activator treatment: The biomass raw material with some lignin removed obtained in step S3 is reacted in an activator solution under controlled temperature, followed by centrifugation and drying to obtain biomass raw material rich in activator.

[0039] S5. Carbonization and activation: Carbonize and activate the biomass raw material rich in activator obtained in step S4 to obtain activated material;

[0040] S6. Post-processing: The activated material obtained in step S5 is acid-washed, water-washed to neutral, and dried to obtain a low-temperature carbonized material rich in microporous structure.

[0041] S7. High-temperature carbonization: The carbonized material obtained in step S6 is subjected to high-temperature carbonization to obtain a sodium-ion battery hard carbon anode material with rich micropores inside.

[0042] Further, in step S2, the alkaline solution is one or two or more of a sodium hydroxide solution, a sodium carbonate solution, a sodium bicarbonate solution, a potassium hydroxide solution, a potassium carbonate solution, a barium hydroxide solution, and a calcium hydroxide solution, and the concentration of the alkaline solution is 2-10 mol / L; the temperature control reaction condition is that the temperature is 60-120℃ and the time is 2-10 h.

[0043] Further, in step S4, the activator is one or two or more of zinc chloride, magnesium chloride, calcium chloride, zinc nitrate, magnesium nitrate, zinc acetate, magnesium acetate, calcium acetate, zinc gluconate, magnesium gluconate, calcium gluconate, zinc citrate, magnesium citrate, and calcium citrate, and the amount of the activator added is 5-20 wt.% of the amount of the biomass raw material; the temperature control reaction condition is that the temperature is 50-80℃ and the time is 5-20 h.

[0044] Further, in step S5, the carbonization activation condition is that the temperature increasing rate is 2-10 ℃ / min, the temperature is 300-600℃, and the treatment time is 2-5 h; the protective gas is nitrogen and / or argon.

[0045] Further, in step S7, the high-temperature carbonization condition is that the temperature increasing rate is 0.5-5 ℃ / min, the carbonization temperature is 1200-1600℃, and the carbonization time is 2-10 h.

[0046] Further, in steps S3 and S6, the acid washing solution is one or two or more of a hydrochloric acid solution, a nitric acid solution, a hydrofluoric acid, a formic acid, an acetic acid, and a phytic acid with a mass fraction of 2-10%.

[0047] Further, in step S4, the activated agent filtrate after filtration is added to the required concentration after being calibrated.

[0048] Further, in step S1, the biomass raw material is one or two or more of walnut shells, coconut shells, apricot shells, coffee shells, peanut shells, fruit peels, reeds, wood chips, bamboo chips, sunflower stalks, corn stalks, and starch.

[0049] Another aspect of the application is to protect a biomass hard carbon sodium ion battery negative electrode material prepared by the above method. Example 1

[0050] This embodiment relates to a biomass hard carbon sodium ion battery negative electrode material with high platform capacity, and a preparation method thereof includes the following steps:

[0051] S1, raw material pretreatment: crushing and sieving the biomass raw material to obtain a preliminary raw material. Specifically, the biomass raw material is walnut shells, coconut shells, apricot shells.

[0052] S2, alkaline solution treatment: the primary raw material obtained in step S1 is treated under alkaline solution conditions to obtain a biomass raw material after alkaline solution treatment. Specifically, the alkaline solution is a sodium hydroxide solution, and the concentration of the alkaline solution is 10 mol / L; the temperature control reaction conditions are: temperature 90℃, time 2h.

[0053] S3, lignin removal treatment: the biomass raw material after alkaline solution treatment in step S2 is centrifuged, then washed with acid and water to neutral, and finally dried to obtain a biomass raw material with part of the lignin removed. Specifically, the acid washing solution is 10% hydrochloric acid by mass fraction.

[0054] S4, activator treatment: the biomass raw material with part of the lignin removed obtained in step S3 is subjected to temperature control reaction in an activator solution, then centrifuged and dried to obtain a biomass raw material rich in activator. Specifically, the filtered activator filtrate is calibrated to the desired concentration after filtration, and the activator is zinc chloride and magnesium chloride. The amount of activator added is 20 wt.% of the amount of biomass raw material added, and the temperature control reaction conditions are: temperature 65℃, time 5h.

[0055] S5, carbonization activation: the biomass raw material rich in activator obtained in step S4 is subjected to carbonization activation to obtain an activated material. Specifically, the carbonization activation conditions are: heating rate 10 ℃ / min, temperature 450℃, treatment time 2h; the protective gas is nitrogen and argon.

[0056] S6, post-treatment: the activated material obtained in step S5 is washed with acid and water to neutral, and dried to obtain a low-temperature carbonized material rich in microporous structure. Specifically, the acid washing solution is 10% hydrochloric acid by mass fraction.

[0057] S7, high-temperature carbonization: the carbonized material obtained in step S6 is subjected to high-temperature carbonization to obtain a sodium ion battery hard carbon negative electrode material rich in micropores inside. Specifically, the high-temperature carbonization conditions are: heating rate 5 ℃ / min, carbonization temperature 1400℃, carbonization time 2h. Example 2

[0058] This embodiment relates to a biomass hard carbon sodium ion battery negative electrode material with high platform capacity, and a preparation method thereof includes the following steps:

[0059] S1, raw material pretreatment: the biomass raw material is crushed and sieved to obtain a primary raw material. Specifically, the biomass raw material is walnut shell, coconut shell, wheat straw, and starch.

[0060] S2, alkali solution treatment: the preliminary raw material obtained in step S1 is treated under the condition of an alkali solution to obtain a biomass raw material after alkali solution treatment. Specifically, the alkali solution is potassium carbonate solution, barium hydroxide solution, calcium hydroxide solution, and the concentration of the alkali solution is 6 mol / L; the temperature control reaction conditions are: temperature 60℃, time 10h.

[0061] S3, lignin removal treatment: the biomass raw material after alkali solution treatment in step S2 is centrifuged, then washed with acid and water to neutral, and finally dried to obtain a biomass raw material with part of the lignin removed. Specifically, the acid washing solution is 5% acetic acid and phytic acid by mass fraction.

[0062] S4, activator treatment: the biomass raw material with part of the lignin removed obtained in step S3 is reacted in an activator solution under temperature control, then centrifuged and dried to obtain a biomass raw material rich in activator. Specifically, the filtered activator filtrate is calibrated to the desired concentration, the activator is zinc citrate, magnesium citrate, calcium citrate, the amount of activator added is 12 wt.% of the biomass raw material, and the temperature control reaction conditions are: temperature 50℃, time 20h.

[0063] S5, carbonization activation: the biomass raw material rich in activator obtained in step S4 is subjected to carbonization activation to obtain an activated material. Specifically, the carbonization activation conditions are: heating rate 6 ℃ / min, temperature 300℃, treatment time 5h; the protective gas is nitrogen.

[0064] S6, post-treatment: the activated material obtained in step S5 is washed with acid and water to neutral, and dried to obtain a low-temperature carbonized material rich in microporous structure. Specifically, the acid washing solution is 6% nitric acid solution by mass fraction.

[0065] S7, high-temperature carbonization: the carbonized material obtained in step S6 is subjected to high-temperature carbonization to obtain a sodium ion battery hard carbon negative electrode material rich in micropores inside. Specifically, the high-temperature carbonization conditions are: heating rate 3 ℃ / min, carbonization temperature 1200℃, carbonization time 10h. Example 3

[0066] This embodiment relates to a biomass hard carbon sodium ion battery negative electrode material with high platform capacity, and a preparation method thereof includes the following steps:

[0067] S1, raw material pretreatment: the biomass raw material is crushed and sieved to obtain a preliminary raw material. Specifically, the biomass raw material is corn straw, wheat straw, and starch.

[0068] S2, alkaline solution treatment: the preliminary raw material obtained in step S1 is treated under alkaline solution conditions to obtain a biomass raw material after alkaline solution treatment. Specifically, the alkaline solution is sodium hydroxide solution, barium hydroxide solution, calcium hydroxide solution, and the concentration of the alkaline solution is 2 mol / L; the temperature control reaction conditions are: temperature 120℃, time 6h.

[0069] S3, lignin removal treatment: the biomass raw material after alkaline solution treatment in step S2 is centrifuged, then washed with acid and water to neutral, and finally dried to obtain a biomass raw material from which part of the lignin is removed. Specifically, the acid washing solution is formic acid, acetic acid, and phytic acid with a mass fraction of 2%.

[0070] S4, activator treatment: the biomass raw material from which part of the lignin is removed obtained in step S3 is subjected to temperature control reaction in an activator solution, then centrifuged and dried to obtain a biomass raw material rich in activator. Specifically, the filtered activator filtrate is calibrated to the desired concentration after filtration, and the activator is calcium acetate, zinc gluconate, magnesium gluconate, and calcium citrate. The amount of activator added is 5 wt.% of the biomass raw material, and the temperature control reaction conditions are: temperature 80℃, time 12h.

[0071] S5, carbonization activation: the biomass raw material rich in activator obtained in step S4 is subjected to carbonization activation to obtain an activated material. Specifically, the carbonization activation conditions are: heating rate 2 ℃ / min, temperature 600℃, treatment time 2-5h; and the protective gas is argon.

[0072] S6, post-treatment: the activated material obtained in step S5 is washed with acid and water to neutral, and dried to obtain a low-temperature carbonized material rich in microporous structure. Specifically, the acid washing solution is hydrochloric acid, formic acid, and acetic acid with a mass fraction of 2%.

[0073] S7, high-temperature carbonization: the carbonized material obtained in step S6 is subjected to high-temperature carbonization to obtain a sodium ion battery hard carbon negative electrode material rich in micropores inside. Specifically, the high-temperature carbonization conditions are: heating rate 0.5 ℃ / min, carbonization temperature 1600℃, carbonization time 6h. Example 4

[0074] This embodiment relates to a biomass hard carbon sodium ion battery negative electrode material with high platform capacity, and a preparation method thereof includes the following steps:

[0075] S1, raw material pretreatment: the biomass raw material is crushed and sieved to obtain a preliminary raw material. Specifically, the biomass raw material is walnut shell, coconut shell, apricot shell, coffee shell, peanut shell, and starch.

[0076] S2, alkaline solution treatment: the preliminary raw material obtained in step S1 is treated under alkaline solution conditions to obtain a biomass raw material after alkaline solution treatment. Specifically, the alkaline solution is sodium bicarbonate solution, potassium hydroxide solution, potassium carbonate solution, barium hydroxide solution, and the concentration of the alkaline solution is 4 mol / L; the temperature control reaction conditions are: temperature 80℃, time 8h.

[0077] S3, lignin removal treatment: the biomass raw material after alkaline solution treatment in step S2 is centrifuged, then washed with acid and water to neutral, and finally dried to obtain a biomass raw material with part of the lignin removed. Specifically, the acid washing solution is 4% hydrochloric acid, formic acid, or acetic acid by mass fraction.

[0078] S4, activator treatment: the biomass raw material with part of the lignin removed obtained in step S3 is subjected to temperature control reaction in an activator solution, then centrifuged and dried to obtain a biomass raw material rich in activator. Specifically, the filtered activator filtrate is calibrated to the desired concentration after filtration, and the activator is calcium acetate, zinc gluconate, magnesium gluconate, or calcium citrate. The amount of activator added is 10 wt.% of the biomass raw material, and the temperature control reaction conditions are: temperature 70℃, time 12h.

[0079] S5, carbonization activation: the biomass raw material rich in activator obtained in step S4 is subjected to carbonization activation to obtain an activated material. Specifically, the carbonization activation conditions are: heating rate 4 ℃ / min, temperature 400℃, and treatment time 4 h; the protective gas is nitrogen or argon.

[0080] S6, post-treatment: the activated material obtained in step S5 is washed with acid and water to neutral, and dried to obtain a low-temperature carbonized material rich in microporous structure. Specifically, the acid washing solution is 3% hydrochloric acid or formic acid by mass fraction.

[0081] S7, high-temperature carbonization: the carbonized material obtained in step S6 is subjected to high-temperature carbonization to obtain a sodium-ion battery hard carbon negative electrode material rich in micropores inside. Specifically, the high-temperature carbonization conditions are: heating rate 2 ℃ / min, carbonization temperature 1300℃, and carbonization time 5 h. Example 5

[0082] This embodiment relates to a biomass hard carbon sodium-ion battery negative electrode material with high platform capacity, and a preparation method thereof includes the following steps:

[0083] S1, raw material pretreatment: the biomass raw material is crushed and sieved to obtain a preliminary raw material. Specifically, the biomass raw material is walnut shell, coconut shell, apricot shell, coffee shell, peanut shell, fruit peel, reed, wood chip, bamboo chip, sunflower stem, corn straw, wheat straw, and starch.

[0084] S2, alkali solution treatment: the preliminary raw material obtained in step S1 is treated under the condition of an alkali solution to obtain a biomass raw material after alkali solution treatment. Specifically, the alkali solution is a sodium hydroxide solution, a sodium carbonate solution, a sodium bicarbonate solution, a potassium hydroxide solution, a potassium carbonate solution, a barium hydroxide solution, a calcium hydroxide solution, and the concentration of the alkali solution is 4 mol / L; the temperature control reaction conditions are: temperature 70℃, time 7h.

[0085] S3, lignin removal treatment: the biomass raw material after alkali solution treatment in step S2 is centrifuged, then washed with acid and water to neutral, and finally dried to obtain a biomass raw material from which part of the lignin is removed. Specifically, the acid washing solution is a hydrochloric acid solution with a mass fraction of 7%, and a nitric acid solution.

[0086] S4, activator treatment: the biomass raw material from which part of the lignin is removed obtained in step S3 is subjected to temperature control reaction in an activator solution, then centrifuged and dried to obtain a biomass raw material rich in activator. Specifically, the filtered activator filtrate is calibrated to the desired concentration after filtration, and the activator is magnesium citrate or calcium citrate. The amount of activator added is 8 wt.% of the amount of biomass raw material added, and the temperature control reaction conditions are: temperature 70℃, time 7h.

[0087] S5, carbonization activation: the biomass raw material rich in activator obtained in step S4 is subjected to carbonization activation to obtain an activated material. Specifically, the carbonization activation conditions are: heating rate 7 ℃ / min, temperature 500℃, treatment time 4 h; the protective gas is nitrogen and argon.

[0088] S6, post-treatment: the activated material obtained in step S5 is washed with acid and water to neutral, and dried to obtain a low-temperature carbonized material rich in microporous structure. Specifically, the acid washing solution is a hydrochloric acid solution with a mass fraction of 5%.

[0089] S7, high-temperature carbonization: the carbonized material obtained in step S6 is subjected to high-temperature carbonization to obtain a sodium-ion battery hard carbon negative electrode material rich in micropores inside. Specifically, the high-temperature carbonization conditions are: heating rate 2 ℃ / min, carbonization temperature 1400℃, carbonization time 3 h.

[0090] Application Example 1

[0091] This example relates to a biomass hard carbon sodium-ion battery negative electrode material with high platform capacity. The preparation method comprises the following steps:

[0092] S1, raw material pretreatment: the coconut shell raw material is crushed and sieved to 100 mesh to obtain a coconut powder raw material.

[0093] S2, alkali solution treatment: the sieved coconut powder in step S1 is soaked in a potassium hydroxide solution with a concentration of 2.5 mol / L, and heated in a water bath to 80℃ for 2h.

[0094] S3, lignin removal treatment: after centrifugal drying of the coconut powder treated by alkali in step S2, 2% hydrochloric acid solution was added for washing, then pure water was used to wash the coconut powder to neutral, and finally dried at 80°C for 12h.

[0095] S4, activator treatment: the coconut powder with partially removed lignin obtained in step S3 was soaked in 8% zinc chloride solution, water bath at 80°C for 10h; then centrifugal dried, and dried at 80°C for 12h.

[0096] S5, activated carbonization: the dried coconut powder in step S4 was heated to 500°C at a rate of 5°C / min under nitrogen atmosphere, and kept for 4h.

[0097] S6, post-treatment: the coconut powder after low-temperature carbonization in step S5 was washed with 2% hydrochloric acid solution, then washed to a pH value of 7, and finally dried.

[0098] S7, high-temperature carbonization: the dried coconut powder in step S6 was heated to 1200°C at a rate of 2°C / min under nitrogen atmosphere, and kept for 5h, to obtain the final hard carbon negative electrode material.

[0099] The obtained material was subjected to electrochemical performance test according to the following method: hard carbon material, Super P, CMC, SBR were mixed into a slurry in a mass ratio of 94:1.5:2:2.5, then the black slurry was coated on a copper foil using a 60 um four-side coater, and the film was dried in a 100°C vacuum drying box for 2 hours. The electrode film was punched into a 12mm diameter circle using a sheet punching machine, and a metal sodium was used as the counter electrode, 1mol / L NaClO4 EC+DEC (1:1vol%) was used as the electrolyte, and a PP double-layer separator was used as the separator, to assemble a CR2032 type button cell in a glove box. The above button cell was subjected to constant current charge and discharge test, the current density was 0.1C (1C=300 mAh / g), and the voltage range was 2-0.005 V.

[0100] Application Example 2

[0101] This example relates to a biomass hard carbon sodium-ion battery negative electrode material with high platform capacity. The preparation method comprises the following steps:

[0102] S1, raw material pretreatment: the reed raw material was crushed and sieved to 100 mesh to obtain reed powder raw material.

[0103] S2, alkali solution treatment: the sieved reed powder in step S1 was soaked in 6mol / L sodium carbonate solution, and heated to 100°C in a water bath for 6h.

[0104] S3, lignin removal treatment: after centrifugal drying of the reed powder treated by alkali in step S2, the reed powder was washed with 2% nitric acid solution, then washed with pure water to neutral, and finally dried at 80°C for 12h.

[0105] S4, activator treatment: the reed powder with part of lignin removed obtained in step S3 was soaked in 5% magnesium citrate solution, water bath at 80°C for 10h, then centrifugal dried, and finally dried at 80°C for 12h.

[0106] S5, activation and carbonization: the dried reed powder in step S4 was heated to 600°C at a rate of 5°C / min under nitrogen atmosphere, and kept for 2h.

[0107] S6, post-treatment: the reed powder carbonized at low temperature in step S5 was washed with 2% nitric acid solution, then washed with water to a pH value of 7, and finally dried.

[0108] S7, high-temperature carbonization: the dried reed powder in step S6 was heated to 1300°C at a rate of 2°C / min under nitrogen atmosphere, and kept for 3h to obtain the final hard carbon negative electrode material.

[0109] The obtained material was subjected to electrochemical performance test according to the following method: hard carbon material, Super P, CMC, and SBR were mixed into a slurry at a mass ratio of 94:1.5:2:2.5, then the black slurry was coated on a copper foil using a 60 um four-side coater, and the film was dried in a vacuum drying oven at 100°C for 2h. The electrode film was punched into a circular sheet with a diameter of 12mm using a sheet punching machine, a metal sodium was used as the counter electrode, 1mol / L NaClO4 EC+DEC (1:1vol%) was used as the electrolyte, and a PP double-layer separator was used as the separator to assemble a CR2032 type button cell in a glove box. The button cell was subjected to constant current charge and discharge test, the current density was 0.1C (1C=300 mAh / g), and the voltage range was 2-0.005 V. Comparative Example 1

[0110] This example relates to a biomass hard carbon sodium ion battery negative electrode material. The preparation method comprises the following steps:

[0111] S1, raw material pretreatment: the coconut shell raw material was crushed and sieved to 100 mesh to obtain coconut powder raw material.

[0112] S2, lignin removal treatment: the sieved coconut powder in step S1 was soaked in 8% zinc chloride solution, water bath at 80°C for 10h.

[0113] S3, Activator Treatment: The coconut powder soaked in zinc chloride solution in step S2 was centrifuged and dried at 80°C for 12h.

[0114] S4, Activation Carbonization: The dried coconut powder in step S3 was heated to 500°C at a rate of 5°C / min under nitrogen atmosphere and kept for 4h.

[0115] S5, Post-treatment: The coconut powder after low-temperature carbonization in step S4 was washed with 2% hydrochloric acid solution, then the pH value was washed to 7 with water, and finally dried.

[0116] S6, High-temperature carbonization: The dried coconut powder in step S5 was heated to 1200°C at a rate of 2°C / min under nitrogen atmosphere and kept for 5h to obtain the final hard carbon negative electrode material.

[0117] The obtained material was tested for electrochemical performance according to the following method: hard carbon material, Super P, CMC, SBR were mixed into a slurry in a mass ratio of 94:1.5:2:2.5, then the black slurry was coated on a copper foil using a 60 um four-side coater, and the film was dried in a 100°C vacuum drying oven for 2 hours. The electrode film was punched into a 12mm diameter circle using a sheet punching machine, with metal sodium as the counter electrode, 1mol / L NaClO4 EC+DEC (1:1vol%) as the electrolyte, and PP double-layer separator as the separator, to assemble a CR2032 type button cell in a glove box. The above button cell was tested for constant current charge and discharge, with a current density of 0.1C (1C=300 mAh / g) and a voltage range of 2-0.005 V. Comparative Example 2

[0118] This example relates to a biomass hard carbon sodium ion battery negative electrode material. Its preparation method comprises the following steps:

[0119] S1, Raw material pretreatment: The coconut shell raw material was crushed and sieved to 100 mesh to obtain coconut powder raw material.

[0120] S2, Alkaline solution treatment: The sieved coconut powder in step S1 was soaked in a 2.5mol / L potassium hydroxide solution, heated to 80°C in a water bath for 2h.

[0121] S3, Lignin removal treatment: The coconut powder after alkaline treatment in step S2 was centrifuged and washed with a 2% hydrochloric acid solution, then washed to neutral with pure water, and finally dried at 80°C for 12h.

[0122] S4, Activation carbonization: The dried coconut powder in step S3 was heated to 500°C at a rate of 5°C / min under nitrogen atmosphere and kept for 4h.

[0123] S5, post-treatment: the coconut powder after low-temperature carbonization in step S4 is washed with a 2% hydrochloric acid solution, then the PH value is washed to 7, and finally dried.

[0124] S6, high-temperature carbonization: the dried coconut powder in step S5 is heated to 1200°C at 2°C / min under a nitrogen atmosphere and kept for 5h to obtain the final hard carbon negative electrode material.

[0125] The obtained material is tested for electrochemical performance according to the following method: the hard carbon material, Super P, CMC, and SBR are mixed into a slurry at a mass ratio of 94:1.5:2:2.5, the black slurry is coated on a copper foil using a 60 um four-side coater, and then the film is dried in a 100°C vacuum drying oven for 2 hours. The electrode film is punched into a 12mm diameter circle using a sheet punching machine, a metal sodium is used as the counter electrode, 1mol / L NaClO4 EC+DEC (1:1vol%) is used as the electrolyte, and a PP double-layer separator is used as the separator to assemble a CR2032 type button cell in a glove box. The above button cell is tested for constant current charge and discharge, the current density is 0.1C (1C=300 mAh / g), and the voltage range is 2-0.005 V.

[0126] To effectively evaluate the technical effects of the application, application examples 1-2 and comparative examples 1-2 are tested and compared as follows:

[0127] The first cycle charge specific capacity of the hard carbon electrode in application example 1, application example 2, comparative example 1, and comparative example 2 is 328.07, 336.64, 294.44, and 282.07 mAh / g respectively, and the constant current test results show that the hard carbon material in application examples 1 and 2 can exhibit high capacity and high initial efficiency after being treated by the combination of alkali treatment and activator activation, while the hard carbon material in comparative example 1 only activated without prior alkali treatment exhibits low capacity; the material in comparative example 2 only alkali treated exhibits low capacity.

[0128] In addition, the specific surface area of the hard carbon electrode in application example 1, application example 2, comparative example 1, and comparative example 2 is 7.04, 6.83, 35.31, and 7.72 m 2 / g respectively, and the corresponding first cycle efficiency is 91.40, 93.21, 86.28, and 90.78 respectively, and application examples 1 and 2 have low specific surface area and high first cycle efficiency after being treated by alkali treatment combined with activator activation; the material in comparative example 1 without prior alkali treatment has high specific surface area and low first cycle efficiency. This shows that the alkali treatment combined with activation treatment process in the application can make the hard carbon material achieve high capacity and high initial efficiency at the same time.

[0129] The above embodiments are merely specific embodiments of the present application and are described in more detail and in a specific manner, but should not be construed as limiting the scope of the patent rights of the present application. It should be noted that, for those of ordinary skill in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, and these obvious replacement forms all belong to the protection scope of the present application.

Claims

1. A method for preparing a high-capacity biomass hard carbon sodium-ion battery anode material, characterized in that... Includes the following steps: S1. Raw material pretreatment: The biomass raw materials are crushed and sieved to obtain preliminary raw materials; S2, Alkaline solution treatment: The preliminary raw material obtained in step S1 is subjected to temperature-controlled treatment under alkaline solution conditions; the temperature-controlled reaction conditions are: temperature 60-120℃, time 2-10h, to obtain biomass raw material after alkaline solution treatment; S3. Lignin removal treatment: The biomass raw material treated with alkaline solution in step S2 is centrifuged, then acid washed, washed with water until neutral, and finally dried to obtain biomass raw material with some lignin removed. S4. Activator treatment: The biomass raw material with partially removed lignin obtained in step S3 is reacted in an activator solution under controlled temperature, followed by centrifugation and drying to obtain biomass raw material rich in activator; the activator is one or more of zinc chloride, magnesium chloride, calcium chloride, zinc nitrate, magnesium nitrate, zinc acetate, magnesium acetate, calcium acetate, zinc gluconate, magnesium gluconate, calcium gluconate, zinc citrate, magnesium citrate, and calcium citrate. The amount of activator added is 5-20 wt.% of the amount of biomass raw material added, and the temperature control reaction conditions are: temperature 50-80℃ and time 5-20h; S5. Carbonization and activation: Carbonize and activate the biomass raw material rich in activator obtained in step S4 at an activation temperature of 300-600℃ for 2-5 hours to obtain activated material. S6. Post-processing: The activated material obtained in step S5 is acid-washed, water-washed to neutral, and dried to obtain a low-temperature carbonized material rich in microporous structure. S7. High-temperature carbonization: The carbonized material obtained in step S6 is subjected to high-temperature carbonization at a temperature of 1200-1600℃ for 2-10 hours to obtain a sodium-ion battery hard carbon anode material rich in micropores.

2. The method for preparing the high-platform-capacity biomass hard carbon sodium-ion battery anode material according to claim 1, characterized in that: In step S2, the alkaline solution is one or more of the following: sodium hydroxide solution, sodium carbonate solution, sodium bicarbonate solution, potassium hydroxide solution, potassium carbonate solution, barium hydroxide solution, and calcium hydroxide solution, and the concentration of the alkaline solution is 2-10 mol / L.

3. The method for preparing the high-platform-capacity biomass hard carbon sodium-ion battery anode material according to claim 1, characterized in that: In step S5, the carbonization activation conditions are: heating rate 2-10 ℃ / min; protective gas is nitrogen and / or argon.

4. The method for preparing the high-platform-capacity biomass hard carbon sodium-ion battery anode material according to claim 1, characterized in that: In step S7, the conditions for high-temperature carbonization are: heating rate of 0.5-5 ℃ / min.

5. The method for preparing the high-platform-capacity biomass hard carbon sodium-ion battery anode material according to claim 1, characterized in that: In steps S3 and S6, the pickling solution is one or more of the following: hydrochloric acid, nitric acid, hydrofluoric acid, formic acid, acetic acid, and phytic acid, with a mass fraction of 2-10%.

6. The method for preparing the high-platform-capacity biomass hard carbon sodium-ion battery anode material according to claim 1, characterized in that: In step S4, the activator filtrate after calibrating its concentration is replenished to the required concentration.

7. The method for preparing the high-platform-capacity biomass hard carbon sodium-ion battery anode material according to claim 1, characterized in that: In step S1, the biomass raw material is one or more of the following: walnut shells, coconut shells, apricot shells, coffee shells, peanut shells, fruit peels, reeds, wood chips, bamboo chips, sunflower stalks, corn stalks, wheat stalks, and starch.

8. A biomass hard carbon sodium-ion battery anode material, characterized in that: It is prepared by any one of the preparation methods in claims 1-7.

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