Biomass-based sodium-ion battery hard carbon materials, their preparation methods and applications

Abstract

This invention discloses a biomass-based sodium-ion battery hard carbon material, its preparation method, and its application. The preparation method includes: mixing biomass raw materials, an oxidation pore-forming reagent, and water until homogeneous to obtain a precursor dispersion; allowing the precursor dispersion to stand and drying to obtain a hard carbon precursor; pre-carbonizing the hard carbon precursor at 650-900℃ for 1-5 h; cooling to room temperature to obtain a pre-carbonized material; acid washing to remove impurities to obtain an oxidation pore-forming activation material; and deeply carbonizing the oxidation pore-forming activation material at 1150-1450℃ for 1-8 h; cooling to room temperature to obtain the biomass-based sodium-ion battery hard carbon material. The biomass-based sodium-ion battery hard carbon material obtained by this invention has the advantages of high first-cycle charge specific capacity, high first-cycle discharge specific capacity, high ramp capacity, high first-cycle coulombic efficiency, and high cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a biomass-based sodium-ion battery hard carbon material, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries, with their significant cost advantages, low-temperature characteristics, and high safety, show great promise in applications such as low-speed electric vehicles, grid-scale energy storage, power tools, and smart homes. Their industrialization can not only optimize the energy storage system layout but also potentially alleviate the current tight supply of lithium resources. From a technical perspective, sodium-ion batteries still face the challenge of energy density bottlenecks. Because sodium ions have a larger ionic radius than lithium ions, their insertion / extraction kinetics in traditional graphite anodes are limited, resulting in generally lower energy densities for mainstream sodium-ion batteries compared to lithium-ion batteries. Against this backdrop, innovative breakthroughs in electrode material systems have become a key path to improving the energy density of sodium-ion batteries, with the performance optimization of anode materials being particularly important. As a core component determining the overall battery's operating voltage and capacity, parameters such as the sodium storage mechanism, plateau voltage characteristics, and specific capacity of the anode material directly constrain the upper limit of sodium-ion battery energy density.

[0003] Common anode materials, such as hard carbon materials, possess comprehensive advantages including low voltage plateau, high sodium storage capacity, and low raw material cost. Hard carbon materials are carbon-based materials that maintain a non-graphitized structure during high-temperature deep carbonization. Their microstructure exhibits unique short-range ordered graphite microcrystals and long-range disordered stacking characteristics, and their hierarchical porous structure provides an ideal transport channel for rapid sodium insertion / extraction. Hard carbon precursors mainly include three categories: biomass-based hard carbon precursors, coal-based hard carbon precursors, and resin-based hard carbon precursors. Among them, the acid washing and impurity removal process for coal-based hard carbon precursors is complex and costly, resulting in relatively low specific capacity for batteries prepared from coal-based hard carbon precursors. While batteries prepared from resin-based hard carbon precursors have high specific capacity, controllable structure, and good batch stability, the raw material cost is too high and they are difficult to break. Biomass-based hard carbon precursors have natural advantages such as low raw material costs, and their acid washing and crushing are relatively simple. However, due to intrinsic structural factors, the specific capacity of batteries prepared from biomass-based hard carbon precursors is still difficult to meet the requirements of high capacity and high slope.

[0004] Effectively regulating the microstructure of biomass-based hard carbon precursors and constructing localized structures with predominantly open pores on the surface and predominantly closed pores inside is of great significance for improving the electrochemical performance of biomass-based hard carbon anodes. For example, invention patent CN117003237A discloses a method for preparing hard carbon using inorganic acid activation-high-temperature carbonization to close microporous structures. This method utilizes inorganic acids (phosphoric acid / sulfuric acid / nitric acid) to erode the biomass precursor to form micropores during the activation stage at 400-700°C, followed by high-temperature carbonization at 1000-1600°C to collapse the open pore walls and transform them into closed pores. This invention patent uses a strong oxidizing acid as a pore-forming agent.

[0005] Chinese patent application CN118929634A discloses a method for preparing hard carbon that combines activation-based pore formation with coating modification. The method involves pre-carbonizing biomass with an activator (such as Na2CO3 / KOH) at 250-900℃ to form open pores, then sealing the pores with a coating agent such as polyacrylic acid, and finally carbonizing at high temperature (1100-1600℃) to form closed pores. This invention uses a strong alkaline reagent as the activator.

[0006] Chinese patent application CN118888734A discloses a method for preparing porous sodium selenate composite hard carbon. The method involves reacting selenium oxide with an organic base pore-forming agent (tetrapropylammonium hydroxide) to generate a porous sodium selenate framework. After the hard carbon fills the pores, an amorphous carbon shell is deposited via vapor deposition. This patent uses a strong base reagent.

[0007] The invention patent with publication number CN119637851A describes a process where biomass such as willow branches is pre-oxidized at 200-500℃ followed by high-temperature carbonization. Dopamine hydrochloride is then used to self-polymerize in a buffer solution to form a surface coating layer. Finally, a secondary carbonization process is performed to obtain a hard carbon material. The pre-oxidation stabilizes the biomass carbon framework structure, while the polydopamine coating repairs surface defects and introduces nitrogen doping, reducing electrolyte side reactions and simultaneously sealing micropores to form a mesoporous structure. This invention patent relates to a pre-oxidation-coating pore-forming process.

[0008] Patent CN119833630A discloses a method for creating pores by pretreating peanut shells with hydrochloric acid followed by activation with disodium EDTA. The hydrochloric acid pretreatment shortens the lignin chain segments, while the disodium EDTA introduces N / O heteroatoms and optimizes the pore distribution, forming a chaotic stacked structure with 0.6–3 nm graphite-like regions encapsulating the pores. This patent involves a pre-oxidation-coating pore-creating process, but the initial coulombic efficiency is relatively low (74%–84%).

[0009] Chinese patent application CN 119612496A discloses a pre-oxidation-pore-forming method combining biomass pre-oxidation with phosphorus doping via vapor deposition. The method involves pre-oxidizing biomass raw materials at 200-400°C in an air atmosphere to introduce oxygen-containing free radicals and increase structural disorder, providing more active sites for subsequent sodium storage. After pre-oxidation, the biomass raw materials are coated with a phosphorus-containing dopant, forming a closed-pore structure during high-temperature carbonization. Furthermore, carbon nanotubes and graphene are generated via transition metal-catalyzed vapor deposition to optimize pore distribution and shorten ion transport paths. This patent relates to a pre-oxidation-coating pore-forming process.

[0010] In summary, existing technologies for preparing hard carbon materials generally involve the use of strong oxidizing acids and strong bases, as well as complex processes such as pre-oxidation and coating pore-forming, making large-scale production difficult. There is an urgent need in this field to develop a simple, controllable, and environmentally friendly method for preparing hard carbon materials, which can achieve high capacity, high first-cycle coulombic efficiency, and excellent cycling stability. Summary of the Invention

[0011] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing biomass-based sodium-ion battery hard carbon materials.

[0012] Another object of the present invention is to provide a biomass-based sodium-ion battery hard carbon material obtained by the above preparation method.

[0013] Another object of the present invention is to provide the application of the above-mentioned biomass-based sodium-ion battery hard carbon material in sodium-ion batteries.

[0014] The objective of this invention is achieved through the following technical solution.

[0015] A method for preparing a biomass-based sodium-ion battery hard carbon material includes the following steps:

[0016] S1, mix biomass raw material, oxidation pore-forming reagent and water until uniform to obtain precursor dispersion, let the precursor dispersion stand and dry to obtain hard carbon precursor, the ratio of biomass raw material to oxidation pore-forming reagent by mass is 4: (0.5~3.5), and the oxidation pore-forming reagent is at least one of sodium squartzate, sodium tartrate, sodium benzoate, sodium percarbonate and sodium magnesium ethylenediaminetetraacetate;

[0017] In S1, the ratio of biomass raw material to oxidative pore-forming reagent by mass is preferably 4:(1~3), and more preferably 4:(2.2~2.8).

[0018] In S1, the biomass raw material is one or a mixture of several of the following: fruit shells, bamboo powder, coconut shells, wood, and reed.

[0019] In S1, the ratio of biomass feedstock to water by mass is 1:(5~20).

[0020] In step S1, the biomass feedstock, oxidizing pore-forming reagent, and water are mixed, and then ultrasonicated and stirred until homogeneous. The ultrasonication time is 0.5 to 2 hours, and the stirring time is at least 6 hours.

[0021] In S1, the settling time is at least 5 hours, and the settling time is preferably 6 to 12 hours.

[0022] In S1, the particle size of the biomass feedstock is 8~15 μm.

[0023] In S1, the drying temperature is 60~100°C, and the drying time is at least 6 hours.

[0024] S2, under a nitrogen or inert gas atmosphere, the hard carbon precursor is pre-carbonized at 650~900℃ for 1~5 h (to perform oxidation pore-forming treatment), cooled to room temperature to obtain pre-carbonized material, acid-washed to remove impurities, to obtain oxidation pore-forming activated material, wherein the acid washing to remove impurities includes: immersing the pre-carbonized material in inorganic acid and reacting it under stirring conditions for at least 5 hours, allowing it to stand, washing, and drying;

[0025] In S2, the inorganic acid is a mixture of acid molecules and water, and the acid molecules are one or more of HCl, HNO3 and H2SO4. The concentration of the acid molecules in the inorganic acid is 1~6 M, preferably 3~4 M.

[0026] In S2, the ratio of pre-carbonized material to inorganic acid by mass parts is 1:(2~20).

[0027] In S2, the drying temperature is 60~100°C, and the drying time is at least 6 hours.

[0028] In S2, the settling time is 6 to 12 hours.

[0029] In S2, the heating rate to 650~900℃ is 1~5℃ / min.

[0030] S3. Under a nitrogen or inert gas atmosphere, the oxidized pore-forming activating material is deeply carbonized at 1150~1450℃ for 1~8 h, and then cooled to room temperature to obtain a biomass-based sodium-ion battery hard carbon material.

[0031] In S3, the heating rate to 1150~1450℃ is 1~5℃ / min.

[0032] In S3, the method of cooling to room temperature includes: first reducing the temperature to 500-700°C at a rate of 3-5°C / min, and then cooling it to room temperature along with the furnace.

[0033] In S3, deep carbonization at 1250~1350℃ for 1~8 h is preferred.

[0034] The above preparation method yields biomass-based sodium-ion battery hard carbon material.

[0035] A sodium-ion battery, comprising: the biomass-based sodium-ion battery hard carbon material.

[0036] In the above technical solution, the sodium-ion battery has a first-cycle charge specific capacity of 320~385mAh / g, a first-cycle coulombic efficiency of more than 90%, and a ramp capacity of 108~161 mAh / g.

[0037] Application of magnesium sodium ethylenediaminetetraacetate in improving the ramp capacity of sodium-ion batteries.

[0038] In the above technical solution, the slope capacity of the sodium-ion battery is 160.68 mAh / g.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) Based on the carbonization habit of the biomass raw material's bulk structure, this invention selects a highly efficient oxidizing pore-forming reagent and proposes a pre-carbonization-deep carbonization process. This avoids the use of strong oxidizing acids and strong bases for pore-forming reagents and the complicated processes of pre-oxidation-coating pore-forming in traditional methods, thus preparing biomass-based sodium-ion battery hard carbon materials with high first-cycle charging specific capacity, high first-cycle discharging specific capacity, and high slope capacity. Generally, slope capacity is positively correlated with the adsorption process of sodium ions by hard carbon materials. Since the reaction kinetics of the adsorption process are higher than those of the intercalation and filling processes, a high slope capacity usually reflects that the hard carbon material has superior rate performance. The preparation method of this invention can not only achieve oxidation pore-forming at low temperatures and improve the cross-linking degree of biomass raw materials, avoiding the formation of a large number of graphitized domain regions, thereby improving the first-cycle charging specific capacity and the first-cycle discharging specific capacity, but also expand the interlayer spacing of the hard carbon material by using alkali metal ions or alkaline earth metal ions in the oxidation pore-forming reagent to support the carbon layer, thereby improving the slope capacity of the hard carbon material. The entire process is simple and has significant practical implications for the large-scale preparation of high-performance biomass-based hard carbon materials for sodium storage.

[0041] (2) The biomass-based sodium-ion battery hard carbon material obtained by the present invention has the advantages of high first-cycle charging specific capacity, high first-cycle discharging specific capacity, high ramp capacity, high first-cycle coulombic efficiency and high cycle stability. The sodium-ion battery prepared based on the biomass-based sodium-ion battery hard carbon material can achieve a first-cycle charging specific capacity of 363.63 mAh / g, a first-cycle coulombic efficiency of 92.03%, and a ramp capacity of 160.68 mAh / g, further demonstrating the advanced nature of the oxidation pore-forming process in the present invention. Attached Figure Description

[0042] Figure 1 The image shows the first charge-discharge test of the CR2032 coin cell prepared based on the biomass-based sodium-ion battery hard carbon material of Example 1.

[0043] Figure 2 The image shows the first charge-discharge test of the CR2032 coin cell prepared based on the biomass-based sodium-ion battery hard carbon material of Example 2.

[0044] Figure 3 The image shows the first charge-discharge test of the CR2032 coin cell prepared based on the biomass-based sodium-ion battery hard carbon material of Example 3.

[0045] Figure 4 The image shows the first charge-discharge test of the CR2032 coin cell prepared based on the biomass-based sodium-ion battery hard carbon material of Example 4.

[0046] Figure 5 The image shows the first charge-discharge test of the CR2032 coin cell prepared based on the biomass-based sodium-ion battery hard carbon material of Example 5.

[0047] Figure 6 The image shows the first charge-discharge test of the CR2032 coin cell prepared based on the biomass-based sodium-ion battery hard carbon material of Example 6.

[0048] Figure 7 The image shows the first charge-discharge test of the CR2032 coin cell prepared based on the biomass-based sodium-ion battery hard carbon material of Example 7.

[0049] Figure 8 The image shows the first charge-discharge test of the CR2032 coin cell prepared based on the biomass-based sodium-ion battery hard carbon material of Comparative Example 1.

[0050] Figure 9 The image shows the first charge-discharge test of the CR2032 coin cell prepared based on the biomass-based sodium-ion battery hard carbon material of Comparative Example 2.

[0051] Figure 10 The image shows the first charge-discharge test of the CR2032 coin cell prepared based on the biomass-based sodium-ion battery hard carbon material of Comparative Example 3.

[0052] Figure 11 The image shows the first charge-discharge test of the CR2032 coin cell prepared based on the biomass-based sodium-ion battery hard carbon material of Example 8.

[0053] Figure 12The image shows the first charge-discharge test of the CR2032 coin cell prepared based on the biomass-based sodium-ion battery hard carbon material of Example 9.

[0054] Figure 13 The image shows the first charge-discharge test of the CR2032 coin cell prepared based on the biomass-based sodium-ion battery hard carbon material of Example 10.

[0055] Figure 14 The image shows the first charge-discharge test of the CR2032 coin cell prepared based on the biomass-based sodium-ion battery hard carbon material of Example 11.

[0056] Figure 15 SEM image of the biomass-based sodium-ion battery hard carbon material prepared in Comparative Example 2;

[0057] Figure 16 SEM image of the biomass-based sodium-ion battery hard carbon material prepared in Example 4;

[0058] Figure 17 XRD images of the biomass-based sodium-ion battery hard carbon materials prepared in Comparative Example 2 and Example 4;

[0059] Figure 18 The graph shows the cycle performance test results of sodium-ion batteries prepared based on the biomass-based sodium-ion battery hard carbon materials of Comparative Example 2 and Example 4. Detailed Implementation

[0060] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0061] The raw material information involved in the following examples and comparative examples is as follows:

[0062] Drug Name purity Manufacturer Sodium magnesium ethylenediaminetetraacetate Analytical Pure Shanghai McLean Biochemical Technology Co., Ltd. Sodium percarbonate Analytical Pure Beijing Innocare Technology Co., Ltd. Sodium squartz Analytical Pure Shanghai Aladdin Biochemical Technology Co., Ltd. Sodium tartrate Analytical Pure Shanghai Haohong Biomedical Technology Co., Ltd. Sodium benzoate Analytical Pure Shanghai Haohong Biomedical Technology Co., Ltd. hydrochloric acid Superior Pure Tianjin Kairuis Fine Chemical Co., Ltd. Styrene-butadiene rubber solution 40wt% Suzhou Duoduo Chemical Technology Co., Ltd. carbon nanotubes Analytical Pure Shanghai McLean Biochemical Technology Co., Ltd.

[0063] Unless otherwise specified, the reagents, materials and instruments used in this invention are all conventional reagents, materials and instruments, and can be obtained commercially.

[0064] The following embodiments describe a method for assembling a sodium-ion battery (CR2032 coin cell): using a biomass-based hard carbon electrode sheet as the working electrode, a sodium sheet as the counter electrode, a Whatman glass fiber membrane as the separator, and a NaPF6-DIGLYME electrolyte (NaPF6-DIGLYME electrolyte includes: electrolyte sodium hexafluorophosphate (NaPF6) and solvent diethylene glycol dimethyl ether (DIGLYME), the concentration of sodium hexafluorophosphate in the NaPF6-DIGLYME electrolyte is 1 mol / L, and the NaPF6-DIGLYME electrolyte was purchased from Suzhou Duoduo Chemical Technology Co., Ltd.), and encapsulating the battery in a glove box (the content of O2 and H2O in the glove box is less than 0.01 ppm) to obtain the CR2032 coin cell.

[0065] The preparation method of the biomass-based hard carbon electrode sheet includes: uniformly mixing hard carbon material, sodium carboxymethyl cellulose (CMCNa) aqueous solution, carbon nanotubes, and styrene-butadiene rubber (SBR) solution (by mass parts, the ratio of CMCNa, carbon nanotubes, and SBR in the hard carbon material, sodium carboxymethyl cellulose (CMCNa) aqueous solution, and SBR in the SBR solution is 92.5:1.5:3:3), stirring for 6 hours to obtain a slurry, uniformly coating the slurry onto copper foil using a scraper, drying it in a drying oven at 120°C for 6 hours, rolling and punching to obtain a disc with a diameter of 12 mm as the biomass-based hard carbon electrode sheet. The hard carbon material is one of the biomass-based sodium-ion battery hard carbon materials prepared in Examples 1-11 and Comparative Examples 1-3 below, and a corresponding sodium-ion battery is obtained based on each hard carbon material. The concentration of CMCNa in the sodium carboxymethyl cellulose (CMCNa) aqueous solution is 1 wt%, and the concentration of SBR in the SBR solution is 40 wt%.

[0066] In the following embodiments, the CR2032 button cell was tested on a Blue Battery Tester with a voltage window of 0.005~2 V and a test temperature of room temperature.

[0067] In this invention, 1C = 300 mA / g.

[0068] Examples 1-5

[0069] A method for preparing a biomass-based sodium-ion battery hard carbon material includes the following steps:

[0070] S1. The biomass raw material (fruit shell: walnut shell) is coarsely crushed, ball-milled, and sieved. The sieved biomass raw material (particle size of 8~15 μm), oxidation pore-forming reagent and water are mixed, ultrasonicated and then stirred until uniform (ultrasonication time is 1 hour and stirring time is 6 hours) to obtain a precursor dispersion. The precursor dispersion is allowed to stand for 8 hours and then dried in a vacuum oven at 80°C for 12 hours to obtain a hard carbon precursor. The ratio of biomass raw material to oxidation pore-forming reagent by mass is X (X is shown in Table 1). The ratio of biomass raw material to water by mass is 1:10. The oxidation pore-forming reagent is sodium magnesium ethylenediaminetetraacetate.

[0071] S2, Under an argon atmosphere, the hard carbon precursor is placed in a tube furnace and heated to 825°C at a heating rate of 3°C / min. It is then pre-carbonized at 825°C for 2 hours for oxidation pore-forming treatment. After cooling to room temperature, the pre-carbonized material is obtained. It is then acid-washed to remove impurities, resulting in an oxidation pore-forming activated material. The acid washing and impurity removal process includes: immersing the pre-carbonized material in an inorganic acid and reacting it under stirring for 5 hours, allowing it to stand for 8 hours, filtering and washing it until neutral, and drying it in an oven at 80°C for 12 hours. The inorganic acid is hydrochloric acid with a HCl concentration of 4 M. The ratio of pre-carbonized material to inorganic acid is 1:10 by mass.

[0072] S3. Under an argon atmosphere, the oxidized pore-forming activation material is placed in a tube furnace and heated to 1300°C at a rate of 3°C / min and deeply carbonized at 1300°C for 3 hours. After cooling to room temperature, a biomass-based sodium-ion battery hard carbon material is obtained. The method of cooling to room temperature includes: first reducing the temperature to 600°C at a rate of 4°C / min, and then cooling it to room temperature with the furnace.

[0073] Table 1

[0074] Biomass-based sodium-ion battery hard carbon materials X Example 1 4：1 Example 2 4：1.5 Example 3 4：2 Example 4 4：2.5 Example 5 4：3

[0075] Example 6

[0076] A method for preparing a biomass-based sodium-ion battery hard carbon material is basically the same as that in Example 4, except that the deep carbonization temperature in S3 is different. In Example 6, the temperature is increased to 1400℃ at a rate of 3℃ / min and deep carbonized at 1400℃ for 3 hours.

[0077] Example 7

[0078] A method for preparing a biomass-based sodium-ion battery hard carbon material is basically the same as that in Example 4, except that the deep carbonization temperature in S3 is different. In Example 7, the temperature is increased to 1200℃ at a rate of 3℃ / min and deep carbonized at 1200℃ for 3 hours.

[0079] Comparative Example 1

[0080] A method for preparing a biomass-based sodium-ion battery hard carbon material is basically the same as that in Example 4, except that "sodium ethylenediaminetetraacetate magnesium" is replaced with "magnesium oxide".

[0081] Comparative Example 2

[0082] A method for preparing a biomass-based sodium-ion battery hard carbon material is basically the same as that in Example 4, except that "sodium magnesium ethylenediaminetetraacetate" is replaced with "disodium ethylenediaminetetraacetate".

[0083] Comparative Example 3

[0084] A method for preparing biomass-based sodium-ion battery hard carbon material includes: placing acid-washed fruit shell raw material fine powder in a muffle furnace under an air atmosphere, pre-oxidizing it at 300°C for 12 hours to obtain a pre-oxidized biomass-based hard carbon precursor; placing the pre-oxidized biomass-based hard carbon precursor in a tube furnace, heating it to 825°C at a rate of 3°C / min and holding it at 825°C for 2 hours; then heating it to 1300°C at a rate of 3°C / min and deeply carbonizing it at 1300°C for 3 hours; then cooling it to 600°C at a rate of 4°C / min; and finally cooling it to room temperature with the furnace to obtain the biomass-based sodium-ion battery hard carbon material. The method for obtaining fine powder of acid-washed fruit shell raw material includes: coarsely crushing, ball milling and sieving the biomass raw material (fruit shell: walnut shell), immersing the sieved biomass raw material (particle size of 8~15 μm) in hydrochloric acid, reacting for 5 hours under stirring, standing for 8 hours, filtering and washing until neutral, and drying in an oven at 80℃ for 12 hours to obtain fine powder of acid-washed fruit shell raw material. The concentration of HCl in the hydrochloric acid is 4 M, and the ratio of biomass raw material to hydrochloric acid is 1:10 by mass.

[0085] Example 8

[0086] A method for preparing a biomass-based sodium-ion battery hard carbon material is basically the same as that in Example 4, except that "sodium magnesium ethylenediaminetetraacetate" is replaced with "sodium squartzate".

[0087] Example 9

[0088] A method for preparing a biomass-based sodium-ion battery hard carbon material is basically the same as that in Example 4, except that "sodium ethylenediaminetetraacetate magnesium sodium" is replaced with "sodium tartrate".

[0089] Example 10

[0090] A method for preparing a biomass-based sodium-ion battery hard carbon material is basically the same as that in Example 4, except that "sodium magnesium ethylenediaminetetraacetate" is replaced with "sodium benzoate".

[0091] Example 11

[0092] A method for preparing a biomass-based sodium-ion battery hard carbon material is basically the same as that in Example 4, except that "sodium magnesium ethylenediaminetetraacetate" is replaced with "sodium percarbonate".

[0093] The sodium-ion batteries (CR2032 coin cells) prepared from the biomass-based sodium-ion battery hard carbon materials of Examples 1-11 and Comparative Examples 1-3 were subjected to their first charge-discharge test at 0.1C, with a voltage window of 0.005~2 V (vs. Na / Na). + The test results are as follows: Figures 1-14 (exist Figures 1-14 In the table, "first efficiency" represents the first coulomb efficiency (as shown in Table 2).

[0094] Table 2

[0095]

[0096] The first charge-discharge test results of sodium-ion batteries prepared based on the biomass-based sodium-ion battery hard carbon materials of Examples 1-7 are shown below. Figures 1-7 As shown; the first charge-discharge test diagrams of sodium-ion batteries prepared based on the biomass-based sodium-ion battery hard carbon materials of Comparative Examples 1 to 3 are respectively shown in the figures. Figures 8-10 As shown; the first charge-discharge test diagrams of sodium-ion batteries prepared based on the biomass-based sodium-ion battery hard carbon materials of Examples 8-11 are respectively shown in the figures. Figures 11-14 As shown.

[0097] In Examples 1-5, the mass ratio of biomass raw material to oxidizing pore-forming reagent was different. Comparing the test results of Examples 1-5, it can be seen that as the proportion of oxidizing pore-forming reagent (sodium magnesium ethylenediaminetetraacetate) gradually increases, the first-cycle charging specific capacity of sodium-ion battery shows a trend of first increasing and then decreasing. When the mass ratio of biomass raw material to oxidizing pore-forming reagent is 4:2.5 (Example 4), the first-cycle charging specific capacity of sodium-ion battery prepared based on the biomass-based sodium-ion battery hard carbon material of Example 4 reaches the maximum, and the ramp capacity also reaches the maximum.

[0098] In Examples 4 and 6-7, the mass ratio of biomass raw material and oxidative pore-forming reagent was the same, but the deep carbonization temperature was different (the deep carbonization temperature in Example 4 was 1300℃, in Example 6 it was 1400℃, and in Example 7 it was 1200℃). Comparing the test results of Examples 4 and 6-7, it can be seen that as the deep carbonization temperature increases, the specific capacity of the sodium-ion battery in the first charge cycle increases from 350.80 mAh / g to 384.98 mAh / g. However, the ramp capacity does not increase, but reaches its maximum value (160.68 mAh / g) at 1300℃. When the deep carbonization temperature is 1400℃, the slope capacity of the sodium-ion battery prepared based on the biomass-based sodium-ion battery hard carbon material of Example 6 is only 112.20 mAh / g, which results in shortcomings in core performance aspects such as fast charging and discharging, high power output, cycle life, and environmental adaptability, making it difficult to meet the application requirements of high-demand scenarios such as electric vehicles and energy storage systems. This is because as the deep carbonization temperature increases, the high temperature promotes the closure of open pores on the surface of the biomass-based sodium-ion battery hard carbon material, thereby increasing the plateau capacity and reducing the slope capacity. Although the slope capacity of the sodium-ion battery prepared based on the biomass-based sodium-ion battery hard carbon material of Example 7 is acceptable, the relatively low deep carbonization temperature leads to insufficient pore development in the biomass-based sodium-ion battery hard carbon material, resulting in a lower first-cycle charge specific capacity than that of Example 4.

[0099] The deep carbonization temperature for Examples 4, 1, 2, 8, 9, 10, and 11 was all 1300°C, but the oxidation pore-forming reagents used were different. A comparison of Examples 4, 1, 2, 8, 9, 10, and 11 shows that, at the same deep carbonization temperature, the performance (especially the slope capacity) of the sodium-ion battery prepared based on the biomass-based sodium-ion battery hard carbon material of Example 4 (obtained through oxidation pore-forming treatment with sodium magnesium ethylenediaminetetraacetate) is significantly improved. This indicates that the Na in sodium magnesium ethylenediaminetetraacetate... + / Mg 2+ The pillaring effect and the adsorption effect of N atom doping play an important role in improving the slope capacity of hard carbon materials.

[0100] Comparative Example 3 used a traditional air pre-oxidation pore-forming process without using an oxidation pore-forming reagent. Comparing Comparative Example 3 with Example 4, it can be seen that the sodium-ion battery prepared based on the biomass-based sodium-ion battery hard carbon material of Example 4 has a first-cycle charging specific capacity of 363.63 mAh / g and a ramp capacity of 160.68 mAh / g, which is significantly better than Comparative Example 3. This further confirms the effect of the oxidation pore-forming reagent of the present invention on the gain of reversible capacity and ramp capacity.

[0101] Figure 15 and Figure 16 SEM images of the biomass-based sodium-ion battery hard carbon material prepared in Comparative Example 2 and the biomass-based sodium-ion battery hard carbon material prepared in Example 4 are shown respectively. Figure 15 and Figure 16 It can be seen that the particle size of the biomass-based sodium-ion battery hard carbon material prepared in Comparative Example 2 and the biomass-based sodium-ion battery hard carbon material prepared in Example 4 are not significantly different.

[0102] Figure 17 The XRD images of the biomass-based sodium-ion battery hard carbon materials prepared in Comparative Example 2 and Example 4 show that, according to the (002) peak, the carbon interlayer spacing of the biomass-based sodium-ion battery hard carbon material prepared in Comparative Example 2 is 0.3710 nm, while the carbon interlayer spacing of the biomass-based sodium-ion battery hard carbon material prepared in Example 4 is as high as 0.4004 nm.

[0103] The sodium-ion batteries prepared based on the biomass-based sodium-ion battery hard carbon materials of Comparative Example 2 and Example 4 were subjected to cycle performance testing, and the results were as follows: Figure 18 The cycle performance graph is shown below. Figure 18 As shown, at 0.1C, the sodium-ion battery prepared based on the biomass-based sodium-ion battery hard carbon material of Comparative Example 2 has a second-cycle discharge specific capacity of only 303.5 mAh / g, and a capacity retention rate of 95.4% after 300 cycles (calculated based on the second-cycle discharge specific capacity). The sodium-ion battery prepared based on the biomass-based sodium-ion battery hard carbon material of Example 4 has a second-cycle discharge specific capacity of 357.4 mAh / g, a capacity retention rate of 95.9% after 300 cycles (calculated based on the second-cycle discharge specific capacity), and a capacity retention rate of 90.7% after 1200 cycles (calculated based on the second-cycle discharge specific capacity). Therefore, sodium magnesium ethylenediaminetetraacetate, as an oxidation pore-forming agent, significantly improves the discharge specific capacity without sacrificing cycle stability.

[0104] Sodium magnesium ethylenediaminetetraacetate (EDTA) has three major advantages as an oxidizing pore-forming reagent: (1) It can directly break through the intrinsic capacity bottleneck of biomass by regulating the pore structure, and the oxidation effect can improve the degree of crosslinking and inhibit graphitization, thus significantly improving the reversible charging capacity; (2) Sodium magnesium ethylenediaminetetraacetate contains alkali metal ions (Na+, Na ... + ) and alkaline earth metal ions (Mg 2+ In carbonization, the carbon layers are pillared to expand the interlayer spacing, thereby increasing the slope capacity. (3) Some N atoms in sodium magnesium ethylenediaminetetraacetate can be incorporated into the carbon structure. N doping will enhance the surface defect states of the material, thereby helping to improve the Na + Adsorption activity enhances slope capacity.

[0105] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing a biomass-based sodium-ion battery hard carbon material, characterized in that, Includes the following steps: S1, mix biomass raw material, oxidation pore-forming reagent and water until uniform to obtain precursor dispersion, let the precursor dispersion stand and dry to obtain hard carbon precursor, the ratio of biomass raw material to oxidation pore-forming reagent by mass is 4: (1.5~3.5), and the oxidation pore-forming reagent is at least one of sodium squartzate, sodium tartrate, sodium benzoate and sodium magnesium ethylenediaminetetraacetate; S2, under a nitrogen or inert gas atmosphere, the hard carbon precursor is pre-carbonized at 650~900℃ for 1~5 h, cooled to room temperature to obtain pre-carbonized material, acid-washed to remove impurities, to obtain oxidized pore-forming activated material, wherein the acid washing to remove impurities includes: immersing the pre-carbonized material in inorganic acid and reacting it under stirring conditions for at least 5 hours, allowing it to stand, washing, and drying. S3. Under a nitrogen or inert gas atmosphere, the oxidized pore-forming activating material is deeply carbonized at 1150~1350℃ for 1~8 h, and then cooled to room temperature to obtain a biomass-based sodium-ion battery hard carbon material.

2. The preparation method according to claim 1, characterized in that, In S1, the biomass raw material is one or a mixture of several of the following: fruit shells, bamboo powder, coconut shells, wood, and reed.

3. The preparation method according to claim 1, characterized in that, In S1, the ratio of biomass feedstock to water by mass is 1:(5~20).

4. The preparation method according to claim 1, characterized in that, In S2, the ratio of pre-carbonized material to inorganic acid by mass parts is 1:(2~20).

5. The preparation method according to claim 1, characterized in that, In S1, the particle size of the biomass feedstock is 8~15 μm.

6. Biomass-based sodium-ion battery hard carbon material obtained by the preparation method according to any one of claims 1 to 5.

7. A sodium-ion battery, characterized in that, include: The biomass-based sodium-ion battery hard carbon material as described in claim 6.

8. The sodium-ion battery according to claim 7, characterized in that, The sodium-ion battery has a first-charge specific capacity of 320~385mAh / g, a first-charge coulombic efficiency of over 90%, and a ramp capacity of 108~161 mAh / g.

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