Biomass-based sodium-ion battery hard carbon material as well as preparation method and application thereof

Abstract

The invention discloses a biomass-based sodium ion battery hard carbon material and a preparation method and application thereof, and the preparation method comprises the following steps: uniformly mixing a biomass raw material, an oxidation pore-forming reagent and water to obtain a precursor dispersion liquid, standing and drying the precursor dispersion liquid to obtain a hard carbon precursor, pre-carbonizing the hard carbon precursor at 650-900 DEG C for 1-5 h, and cooling to room temperature to obtain the biomass-based sodium ion battery hard carbon material. And carrying out acid pickling to remove impurities so as to obtain an oxidation pore-forming activated material, carrying out deep carbonization on the oxidation pore-forming activated material at 1150-1450 DEG C for 1-8 hours, and cooling to room temperature, so as to obtain the biomass-based sodium ion battery hard carbon material. The biomass-based sodium-ion battery hard carbon material obtained by the invention has the advantages of high first-circle charge specific capacity, high first-circle discharge specific capacity, high slope capacity, high first-circle coulombic efficiency and high cycle stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and specifically relates to a biomass-based sodium ion battery hard carbon material and a preparation method and application thereof. Background Art

[0002] Sodium-ion batteries, with their significant cost advantages, low-temperature characteristics, and high safety, show broad prospects in application scenarios such as low-speed electric vehicles, grid-level energy storage, power tools, and smart homes. Their industrial development will not only optimize the layout of energy storage systems, but also has the potential to alleviate the current tight supply of lithium resources. From a technical perspective, sodium-ion batteries currently still face the challenge of an energy density bottleneck. Because sodium ions have a larger ionic radius than lithium ions, their insertion / extraction kinetics in traditional graphite anodes are limited, making the energy density of current mainstream sodium-ion batteries generally lower than that of lithium-ion batteries. In this context, innovative breakthroughs in electrode material systems have become a key path to improving the energy density of sodium-ion batteries, among which the performance optimization of negative electrode materials is particularly important. As the core component that determines the operating voltage and capacity of the entire battery, parameters such as the sodium storage mechanism, platform voltage characteristics, and mass-specific capacity of the negative electrode material directly restrict the upper limit of the energy density of sodium-ion batteries.

[0003] Common negative electrode materials, such as hard carbon materials, have comprehensive advantages such as low voltage platform, high sodium storage capacity and low raw material cost. Hard carbon materials are carbon-based materials that still maintain a non-graphitized structure during high-temperature deep carbonization. Their microstructure presents unique short-range ordered graphite crystals and long-range disordered stacking characteristics. Their multi-level pore structure also provides an ideal transmission channel for rapid sodium deintercalation. 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 pickling and impurity removal process of coal-based hard carbon precursors is complicated and costly, and the specific capacity of batteries prepared from coal-based hard carbon precursors is relatively low. Although 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 pickling, impurity removal 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 manipulating the microstructure of biomass-based hard carbon precursors to create localized structures with predominantly open pores on the surface and closed pores within is crucial for improving the electrochemical performance of biomass-based hard carbon anodes. For example, patent publication CN117003237A discloses a method for preparing hard carbon with closed micropores through inorganic acid activation and high-temperature carbonization. Inorganic acids (phosphoric acid, sulfuric acid, and nitric acid) are used to etch the biomass precursor at 400-700°C during the activation phase to form micropores. Subsequently, high-temperature carbonization at 1000-1600°C collapses the open pore walls into closed pores. This patent utilizes a strong oxidizing acid as a pore-forming agent.

[0005] Patent publication number CN118929634A discloses a method for preparing hard carbon that combines activation pore formation with coating modification. This method involves pre-carbonizing biomass with an activating agent (such as Na2CO3 / KOH) at 250-900°C to form open pores. This pores are then sealed with a coating agent such as polyacrylic acid, and finally carbonized at high temperature (1100-1600°C) to form closed pores. This patent uses a strong alkaline agent as the activating agent.

[0006] Patent publication number CN118888734A discloses a method for preparing porous sodium selenate composite hard carbon. Selenium oxide reacts with an organic base pore-forming agent (tetrapropylammonium hydroxide) to form a porous sodium selenate skeleton. Hard carbon then fills the pores, forming an amorphous carbon shell via vapor deposition. This patent utilizes a strong base reagent.

[0007] Patent publication number CN119637851A describes a method for pre-oxidizing biomass, such as poplar and willow branches, at 200-500°C, followed by high-temperature carbonization. Dopamine hydrochloride then self-polymerizes in a buffer solution to form a surface coating, followed by secondary carbonization to produce a hard carbon material. Pre-oxidation stabilizes the biomass carbon skeleton structure, while polydopamine coating repairs surface defects and introduces nitrogen doping, reducing electrolyte side reactions while sealing micropores to form a mesoporous structure. This patent relates to a pre-oxidation-coating pore-forming process.

[0008] Patent publication number CN119833630A discloses a method for pore creation using hydrochloric acid pretreatment of peanut shells followed by activation with disodium EDTA. The hydrochloric acid pretreatment shortens lignin chains, while the disodium EDTA introduces N / O heteroatoms and optimizes pore distribution, resulting in a chaotic stacking structure with pores encased in graphite-like regions of 0.6-3 nm. This patent involves a pre-oxidation-coating pore-forming process, and the initial coulombic efficiency is relatively low (74%-84%).

[0009] Patent publication number CN 119612496A discloses a pre-oxidation-pore-forming method using biomass pre-oxidation combined with phosphorus doping via vapor deposition. The method involves pre-oxidation of the biomass feedstock at 200-400°C in an air atmosphere, introducing oxygen-containing free radicals and increasing structural disorder, providing more active sites for subsequent sodium storage. Following pre-oxidation, the feedstock is coated with a phosphorus-containing dopant and asphalt, forming a closed-pore structure during high-temperature carbonization. Furthermore, carbon nanotubes and graphene are generated via transition metal-catalyzed vapor deposition, optimizing pore distribution and shortening ion transport paths. This patent relates to a pre-oxidation-coating pore-forming process.

[0010] In summary, existing methods for preparing hard carbon materials typically involve the use of strong oxidizing acids and bases, as well as complex processes such as pre-oxidation and coating to create pores, making large-scale production difficult. There is an urgent need for a simple, controllable, and environmentally friendly method for preparing hard carbon materials that combines high capacity, high first-cycle coulombic efficiency, and excellent cycling stability. Summary of the Invention

[0011] In view of the shortcomings of the prior art, the object of the present invention is to provide a method for preparing biomass-based hard carbon materials for sodium ion batteries.

[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 purpose of the present invention is achieved through the following technical solutions.

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

[0016] S1, mixing a biomass raw material, an oxidative pore-forming agent, and water until uniformly mixed to obtain a precursor dispersion, allowing the precursor dispersion to stand and drying to obtain a hard carbon precursor, wherein the ratio of the biomass raw material to the oxidative pore-forming agent is 4:(0.5-3.5) by mass, and the oxidative pore-forming agent is at least one of sodium squarate, sodium tartrate, sodium benzoate, sodium percarbonate, and sodium magnesium ethylenediaminetetraacetate;

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

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

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

[0020] In S1, the biomass feedstock, the oxidative pore-forming agent, and water are mixed, first ultrasonically and then 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 standing time is at least 5 hours, and preferably 6 to 12 hours.

[0022] In S1, the particle size of the biomass raw material was 8–15 μm.

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

[0024] S2, pre-carbonizing the hard carbon precursor at 650-900° C. for 1-5 hours (for oxidation pore formation treatment) under a nitrogen or inert gas atmosphere, cooling to room temperature to obtain a pre-carbonized material, and acid-washing and removing impurities to obtain an oxidation pore-forming activated material, wherein the acid-washing and impurity-removing process comprises: immersing the pre-carbonized material in an inorganic acid, reacting the material under stirring for at least 5 hours, allowing the material to stand, washing, and drying;

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

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

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

[0028] In S2, the standing 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, deeply carbonizing the oxidative pore-forming activation material at 1150-1450° C. for 1-8 hours, and cooling to room temperature to obtain a biomass-based sodium ion battery hard carbon material.

[0031] In S3, the temperature is raised to 1150-1450°C at a rate of 1-5°C / min.

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

[0033] In S3, deep carbonization is preferably performed at 1250-1350°C for 1-8 h.

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

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

[0036] In the above technical solution, the first-cycle charging capacity of the sodium-ion battery is 320~385mAh / g, the first-cycle coulombic efficiency is greater than 90%, and the slope capacity is 108~161 mAh / g.

[0037] Application of sodium magnesium ethylenediaminetetraacetate in improving the slope 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) The present invention selects a high-efficiency oxidation pore-forming agent based on the carbonization behavior of the biomass raw material structure, and proposes a pre-carbonization-deep carbonization process, thereby avoiding the use of strong oxidizing acid and strong base pore-forming agents and the complicated process of pre-oxidation-coating pore-forming in the traditional method, and prepares a biomass-based sodium ion battery hard carbon material with high first-cycle charge capacity, high first-cycle discharge capacity, and high slope capacity. Generally, the slope capacity is positively correlated with the adsorption process of sodium ions by the hard carbon material. Since the reaction kinetics of the adsorption process is higher than that of the embedding and filling process, the high slope capacity usually reflects that the hard carbon material has better rate performance. The preparation method of the present invention can not only realize oxidation pore formation at low temperature, improve the cross-linking degree of the biomass raw material, avoid the formation of a large number of graphitized domains, thereby improving the first-cycle charge capacity and first-cycle discharge capacity, but also can expand the interlayer spacing of the hard carbon material by pillaring the carbon layer through the alkali metal ions or alkaline earth metal ions in the oxidation pore-forming agent, thereby improving the slope capacity of the hard carbon material. The entire process is simple and has important practical significance 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 in the present invention has the advantages of high first-cycle charge capacity, high first-cycle discharge capacity, high slope 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 charge capacity of 363.63 mAh / g, a first-cycle coulombic efficiency of 92.03%, and a slope capacity of 160.68 mAh / g, further reflecting the advanced nature of the oxidation pore-forming process in the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a first cycle charge and discharge test chart of a CR2032 button cell prepared using the biomass-based sodium ion battery hard carbon material of Example 1;

[0043] Figure 2 This is a first cycle charge and discharge test chart of a CR2032 button cell prepared using the biomass-based sodium ion battery hard carbon material of Example 2;

[0044] Figure 3 This is a first cycle charge and discharge test chart of a CR2032 button cell prepared using the biomass-based sodium ion battery hard carbon material of Example 3;

[0045] Figure 4 This is a first cycle charge and discharge test chart of a CR2032 button cell prepared using the biomass-based sodium ion battery hard carbon material of Example 4;

[0046] Figure 5 This is a first cycle charge and discharge test chart of a CR2032 button cell prepared using the biomass-based sodium ion battery hard carbon material of Example 5;

[0047] Figure 6 This is a first cycle charge and discharge test chart of a CR2032 button cell prepared using the biomass-based sodium ion battery hard carbon material of Example 6;

[0048] Figure 7 This is a first cycle charge and discharge test chart of a CR2032 button cell prepared using the biomass-based sodium ion battery hard carbon material of Example 7;

[0049] Figure 8 This is a first cycle charge and discharge test chart of a CR2032 button battery prepared based on the biomass-based sodium ion battery hard carbon material of Comparative Example 1;

[0050] Figure 9 This is a first cycle charge and discharge test chart of a CR2032 button battery prepared based on the biomass-based sodium ion battery hard carbon material of Comparative Example 2;

[0051] Figure 10 This is a first cycle charge and discharge test chart of a CR2032 button battery prepared based on the biomass-based sodium ion battery hard carbon material of Comparative Example 3;

[0052] Figure 11 This is a first cycle charge and discharge test chart of a CR2032 button cell prepared using the biomass-based sodium ion battery hard carbon material of Example 8;

[0053] Figure 12This is a first cycle charge and discharge test chart of a CR2032 button cell prepared using the biomass-based sodium ion battery hard carbon material of Example 9;

[0054] Figure 13 This is a first cycle charge and discharge test chart of a CR2032 button cell prepared using the biomass-based sodium ion battery hard carbon material of Example 10;

[0055] Figure 14 This is a first cycle charge and discharge test chart of a CR2032 button cell prepared using the biomass-based sodium ion battery hard carbon material of Example 11;

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

[0057] Figure 16 This is an 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 This is a test chart of the cycle performance of the sodium ion battery prepared based on the biomass-based sodium ion battery hard carbon material of Comparative Example 2 and Example 4. DETAILED DESCRIPTION

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

[0061] The raw material information involved in the following examples and comparative examples is as follows: Drug name purity Manufacturer Sodium magnesium EDTA analytically pure Shanghai MacLean Biochemical Technology Co., Ltd. Sodium percarbonate analytically pure Beijing Inokai Technology Co., Ltd. Sodium squarate analytically pure Shanghai Aladdin Biochemical Technology Co., Ltd. Sodium tartrate analytically pure Shanghai Haohong Biopharmaceutical Technology Co., Ltd. Sodium benzoate analytically pure Shanghai Haohong Biopharmaceutical Technology Co., Ltd. hydrochloric acid Premium Pure Tianjin Kairuisi Fine Chemical Co., Ltd. Styrene-butadiene rubber solution 40wt% Suzhou Duoduo Chemical Technology Co., Ltd. carbon nanotubes analytically pure Shanghai MacLean Biochemical Technology Co., Ltd.

[0062] Unless otherwise specified, the reagents, materials and instruments used in the present invention are conventional reagents, conventional materials and conventional instruments and can be obtained commercially.

[0063] In the following embodiments, a method for assembling a sodium ion battery (CR2032 button cell) includes: using a biomass-based hard carbon electrode sheet as a working electrode, a sodium sheet as a counter electrode, a Whatman glass fiber membrane as a separator, and an electrolyte of NaPF6-DIGLYME electrolyte (the NaPF6-DIGLYME electrolyte includes: an electrolyte sodium hexafluorophosphate (NaPF6) and a 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 is purchased from Suzhou Duoduo Chemical Technology Co., Ltd.), and packaging in a glove box (the content of O2 and H2O in the glove box is less than 0.01 ppm) to obtain a CR2032 button cell;

[0064] The preparation method of a biomass-based hard carbon electrode sheet includes: uniformly mixing a hard carbon material, a sodium carboxymethyl cellulose (CMCNa) aqueous solution, carbon nanotubes, and a styrene-butadiene rubber (SBR) solution (the ratio of the hard carbon material, CMCNa in the sodium carboxymethyl cellulose (CMCNa) aqueous solution, carbon nanotubes, and SBR in the styrene-butadiene rubber (SBR) solution is 92.5:1.5:3:3 by mass), stirring for 6 hours to obtain a slurry. The slurry is evenly coated on a copper foil using a spatula, dried in a drying oven at 120°C for 6 hours, rolled, and punched to obtain a 12 mm diameter disc as a 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 to 11 and Comparative Examples 1 to 3 below. For each hard carbon material, a corresponding sodium ion battery is obtained. The concentration of CMCNa in the sodium carboxymethyl cellulose (CMCNa) aqueous solution is 1 wt%, and the concentration of SBR in the styrene-butadiene rubber (SBR) solution is 40 wt%.

[0065] In the following examples, CR2032 button batteries were tested on a BlueDian battery tester with a voltage window of 0.005-2 V and a test temperature of room temperature.

[0066] In the present invention, 1C=300 mA / g.

[0067] Examples 1 to 5

[0068] A method for preparing a biomass-based sodium ion battery hard carbon material comprises the following steps:

[0069] S1, coarsely crushing, ball-milling, and sieving a biomass raw material (fruit shell: walnut shell), mixing the sieved biomass raw material (particle size 8-15 μm), an oxidative pore-forming agent, and water, first sonicating and then stirring until uniform (sonication time is 1 hour, stirring time is 6 hours) to obtain a precursor dispersion, allowing the precursor dispersion to stand for 8 hours, and drying in a vacuum oven at 80°C for 12 hours to obtain a hard carbon precursor, wherein the ratio of the biomass raw material to the oxidative pore-forming agent is X (see Table 1 for X) by mass, the ratio of the biomass raw material to water by mass is 1:10, and the oxidative pore-forming agent is sodium magnesium ethylenediaminetetraacetate;

[0070] S2, under an argon atmosphere, placing a hard carbon precursor in a tube furnace, heating it to 825°C at a heating rate of 3°C / min and pre-carbonizing it at 825°C for 2 hours to perform oxidation pore formation treatment, cooling it to room temperature to obtain a pre-carbonized material, pickling and removing impurities to obtain an oxidation pore-forming activated material, wherein the pickling and removing impurities include: soaking the pre-carbonized material in an inorganic acid, reacting it under stirring for 5 hours, standing it for 8 hours, filtering it, washing it to neutrality, and drying it in an oven at 80°C for 12 hours, the inorganic acid is hydrochloric acid, the concentration of HCl in the hydrochloric acid is 4 M, and the ratio of the pre-carbonized material to the inorganic acid is 1:10 by mass;

[0071] S3. Under an argon atmosphere, the oxidative pore-forming activated material is placed in a tubular furnace, heated to 1300°C at a rate of 3°C / min, and deeply carbonized at 1300°C for 3 hours, and then cooled to room temperature to obtain a biomass-based sodium ion battery hard carbon material. 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 to room temperature with the furnace.

[0072] Table 1 Biomass-based hard carbon materials for sodium-ion batteries X Example 1 4：1 Example 2 4：1.5 Example 3 4：2 Example 4 4：2.5 Example 5 4：3

[0073] Example 6

[0074] A method for preparing a biomass-based sodium ion battery hard carbon material is basically the same as Example 4, except that the deep carbonization temperature of S3 is different. Example 6 is: heating to 1400°C at a rate of 3°C / min and deep carbonizing at 1400°C for 3 h.

[0075] Example 7

[0076] A method for preparing a biomass-based sodium ion battery hard carbon material is basically the same as Example 4, except that the deep carbonization temperature of S3 is different. Example 7 is: heating to 1200°C at a rate of 3°C / min and deep carbonizing at 1200°C for 3 h.

[0077] Comparative Example 1

[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 "sodium magnesium ethylenediaminetetraacetate" is replaced by "magnesium oxide".

[0079] Comparative Example 2

[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 magnesium ethylenediaminetetraacetate" is replaced by "disodium ethylenediaminetetraacetate".

[0081] Comparative Example 3

[0082] A method for preparing a biomass-based sodium ion battery hard carbon material comprises: placing fine powder of a raw material of acid-washed fruit shells in a muffle furnace under an air atmosphere, performing a pre-oxidation treatment 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 tubular furnace, heating it to 825°C at a rate of 3°C / min and keeping 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 along with the furnace to obtain the biomass-based sodium ion battery hard carbon material. Among them, the method for obtaining fine powder of pickled fruit shell raw material includes: coarsely crushing, ball milling and screening the biomass raw material (fruit shell: walnut shell), soaking the sieved biomass raw material (particle size of 8~15 μm) in hydrochloric acid, reacting for 5 hours under stirring conditions, standing for 8 hours, filtering and washing to neutrality, and drying in an 80°C oven for 12 hours to obtain fine powder of pickled fruit shell raw material, wherein 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.

[0083] Example 8

[0084] 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 ethylenediaminetetraacetic acid" is replaced by "sodium squarate".

[0085] Example 9

[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 ethylenediaminetetraacetic acid" is replaced by "sodium tartrate".

[0087] Example 10

[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 magnesium ethylenediaminetetraacetic acid" is replaced by "sodium benzoate".

[0089] Example 11

[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 ethylenediaminetetraacetic acid" is replaced by "sodium percarbonate".

[0091] At 0.1C, the sodium ion battery (CR2032 button cell) prepared from the biomass-based sodium ion battery hard carbon materials of Examples 1 to 11 and Comparative Examples 1 to 3 was subjected to the first cycle charge and discharge test, and the voltage window was 0.005~2 V (vs. Na / Na + ), the test results are as follows Figures 1 to 14 (exist Figures 1 to 14 In the figure, “first efficiency” represents the first-cycle Coulomb efficiency) and as shown in Table 2.

[0092] Table 2

[0093] The first cycle charge and discharge test diagrams of the sodium ion battery prepared based on the biomass-based sodium ion battery hard carbon material of Examples 1 to 7 are as follows: Figures 1 to 7 As shown; the first cycle charge and discharge test diagrams of the sodium ion battery prepared based on the biomass-based sodium ion battery hard carbon material of Comparative Examples 1 to 3 are respectively as shown Figures 8 to 10 As shown; the first cycle charge and discharge test diagrams of the sodium ion battery prepared based on the biomass-based sodium ion battery hard carbon material of Examples 8 to 11 are respectively as shown Figures 11 to 14 shown.

[0094] In Examples 1 to 5, the mass ratios of the biomass raw material and the oxidative pore-forming agent are different. Comparing the test results of Examples 1 to 5, it can be seen that as the proportion of the oxidative pore-forming agent (sodium magnesium ethylenediaminetetraacetic acid) gradually increases, the first-cycle charging capacity of the sodium ion battery shows a trend of first increasing and then decreasing. When the mass ratio of the biomass raw material and the oxidative pore-forming agent is 4:2.5 (Example 4), the first-cycle charging capacity of the sodium ion battery prepared based on the biomass-based sodium ion battery hard carbon material of Example 4 reaches the maximum, and the slope capacity also reaches the maximum.

[0095] In Example 4 and Examples 6-7, the mass ratio of the biomass raw material and the oxidative pore-forming agent is the same, but the deep carbonization temperature is different (the deep carbonization temperature of Example 4 is 1300°C, the deep carbonization temperature of Example 6 is 1400°C, and the deep carbonization temperature of Example 7 is 1200°C). Comparing the test results of Example 4 and Examples 6-7, it can be seen that as the deep carbonization temperature increases, the first cycle charge capacity of the sodium ion battery shows an increasing trend from 350.80 mAh / g to 384.98 mAh / g, while the ramp capacity does not show an increasing trend, but reaches a maximum value (160.68 mAh / g) at 1300°C. When the temperature of deep carbonization is 1400 ° C, the slope capacity of the sodium ion battery obtained by preparing the biomass-based sodium ion battery hard carbon material based on Example 6 is only 112.20 mAh / g, which makes it have shortcomings in core performances such as fast charging and discharging, high power output, cycle life, and environmental adaptability, and it is difficult to meet the application requirements of high-demand scenarios such as electric vehicles and energy storage systems. This is because as the temperature of deep carbonization increases, high temperature promotes the closure of open pores on the surface of the biomass-based sodium ion battery hard carbon material, thereby increasing the platform capacity and reducing the slope capacity. Although the slope capacity of the sodium ion battery obtained by preparing the biomass-based sodium ion battery hard carbon material based on Example 7 is acceptable, due to the relatively low temperature of deep carbonization, the closed pores of the biomass-based sodium ion battery hard carbon material are insufficiently developed, resulting in its first-cycle charge capacity not being as high as that in Example 4.

[0096] The deep carbonization temperature of Example 4, Comparative Example 1, Comparative Example 2, Example 8, Example 9, Example 10 and Example 11 is all 1300°C, but the oxidation pore-forming agents used are different. By comparing Example 4, Comparative Example 1, Comparative Example 2, Example 8, Example 9, Example 10 and Example 11, it can be seen 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 after oxidation pore-forming treatment of sodium magnesium ethylenediaminetetraacetic acid) is significantly improved. It can be seen that the Na in sodium magnesium ethylenediaminetetraacetic acid is significantly improved. + / 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.

[0097] Comparative Example 3 adopts the traditional air pre-oxidation pore-forming process and does not use an oxidative pore-forming agent. 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 charge capacity of 363.63 mAh / g and a slope capacity of 160.68 mAh / g, which is significantly better than Comparative Example 3, further confirming the gain effect of the oxidative pore-forming agent of the present invention on the reversible capacity and slope capacity.

[0098] Figure 15 and Figure 16 The 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 sizes 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 much different.

[0099] 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 the carbon interlayer spacing of the biomass-based sodium ion battery hard carbon material prepared in Comparative Example 2 is 0.3710 nm, and 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.

[0100] The sodium ion battery prepared from the biomass-based sodium ion battery hard carbon material of Comparative Example 2 and Example 4 was subjected to a cycle performance test and the results were as follows: Figure 18 The cycle performance diagram is shown in Figure 2. Figure 18 As shown, at 0.1C, the second-cycle discharge specific capacity of the sodium ion battery prepared based on the biomass-based sodium ion battery hard carbon material of Comparative Example 2 was only 303.5 mAh / g, and the capacity retention rate after 300 cycles was 95.4% (calculated based on the second-cycle discharge specific capacity); the second-cycle discharge specific capacity of the sodium ion battery prepared based on the biomass-based sodium ion battery hard carbon material of Example 4 was 357.4 mAh / g, and the capacity retention rate after 300 cycles was 95.9% (calculated based on the second-cycle discharge specific capacity), and the capacity retention rate after 1200 cycles was 90.7% (calculated based on the second-cycle discharge specific capacity). Therefore, sodium magnesium ethylenediaminetetraacetate as an oxidative pore-forming agent greatly improves the discharge specific capacity without sacrificing cycle stability.

[0101] Sodium magnesium ethylenediaminetetraacetate has three major advantages as an oxidative pore-forming agent: (1) It directly breaks through the bottleneck of biomass intrinsic capacity by regulating the pore structure, and the oxidation effect increases the cross-linking degree and inhibits graphitization, which significantly improves the reversible charge capacity; (2) the alkali metal ions (Na + ) and alkaline earth metal ions (Mg 2+ ) In carbonization, the carbon layer is supported to expand the interlayer spacing, thereby improving the slope capacity. (3) Some of the N atoms in sodium magnesium ethylenediaminetetraacetic acid can be incorporated into the carbon structure. N doping will increase the surface defect state of the material, thereby helping to improve the Na + Adsorption activity, enhanced slope capacity.

[0102] The above is an exemplary description of the present invention. It should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by other skilled in the art without expending creative labor falls within the scope of protection of the present invention.

Claims

1. A method for preparing a biomass-based sodium ion battery hard carbon material, characterized in that: The following steps are involved: S1, mixing a biomass raw material, an oxidative pore-forming agent, and water until uniformly mixed to obtain a precursor dispersion, allowing the precursor dispersion to stand and drying to obtain a hard carbon precursor, wherein the ratio of the biomass raw material to the oxidative pore-forming agent is 4:(0.5-3.5) by mass, and the oxidative pore-forming agent is at least one of sodium squarate, sodium tartrate, sodium benzoate, sodium percarbonate, and sodium magnesium ethylenediaminetetraacetate; S2, pre-carbonizing the hard carbon precursor at 650-900° C. for 1-5 hours under a nitrogen or inert gas atmosphere, cooling to room temperature to obtain a pre-carbonized material, and acid-washing and removing impurities to obtain an oxidative pore-forming activated material, wherein the acid-washing and impurity-removing step comprises: immersing the pre-carbonized material in an inorganic acid, reacting the material under stirring for at least 5 hours, allowing the material to stand, washing, and drying. S3, under nitrogen or inert gas atmosphere, deeply carbonizing the oxidative pore-forming activation material at 1150-1450° C. for 1-8 hours, and cooling 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 fruit shells, bamboo powder, coconut shells, wood and reed bamboo.

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

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

5. The preparation method according to claim 1, characterized in that In S1, the particle size of the biomass raw material was 8–15 μm.

6. A 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 according to claim 6.

8. The sodium ion battery according to claim 7, characterized in that The first-cycle charge capacity of the sodium-ion battery is 320~385mAh / g, the first-cycle Coulombic efficiency is greater than 90%, and the slope capacity is 108~161 mAh / g.

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