Preparation method of a bimetallic cation-doped and modified starch-based hard carbon material, starch-based hard carbon material and application thereof

Abstract

The present invention provides a preparation method of a bimetallic cation-doped modified starch-based hard carbon material, a starch-based hard carbon material and its application, belonging to the technical field of anode materials for sodium-ion batteries, including: dissolving cellulose, an acid and two metal chlorides in water together to obtain a mixed solution; dispersing starch in the mixture solution, and drying the obtained starch suspension slurry to obtain a precursor powder; performing low-temperature pre-calcination on the precursor powder in an oxygen or air atmosphere to obtain a hard carbon intermediate; placing the hard carbon intermediate in an inert atmosphere for high-temperature calcination to obtain a bimetallic cation-doped modified starch-based hard carbon material. This method uses starch with relatively low cost as the main raw material, and prepares a starch-based hard carbon material with controllable particle size through the doping modification and synergistic effect of bimetallic cations. The prepared starch-based hard carbon material has excellent electrochemical performance and can be used as an anode material for sodium-ion batteries, which is of great significance to the large-scale application of sodium-ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of negative electrode materials for sodium-ion batteries, and particularly relates to a preparation method of a bimetallic cation-doped modified starch-based hard carbon material, a starch-based hard carbon material, and their applications. Background Art

[0002] Among the negative electrode materials for sodium-ion batteries, carbon-based materials have become the first choice for research on sodium storage negative electrode materials due to their advantages such as wide sources, rich resources, and diverse structures. Carbon materials can be further divided into graphite-like carbon materials (mainly graphite), new carbon materials, and amorphous carbon materials according to their different microstructures. Among them, the disordered structure of hard carbon enables it to have more defects and vacancies, that is, more sodium storage active sites; and its layer spacing is relatively large, which is more suitable for the storage and insertion / extraction of sodium ions, and can maintain good stability during the insertion / extraction process of sodium ions. Therefore, compared with other carbon materials and non-carbon materials, hard carbon is more suitable as the negative electrode material for sodium-ion batteries. In addition, due to the excellent innate conditions of hard carbon (wide sources, simple preparation, etc.), it has become the best choice for commercial negative electrode materials for sodium-ion batteries. Therefore, the preparation of high-performance hard carbon negative electrode materials is of great significance for the large-scale application of sodium-ion batteries.

[0003] As an amorphous carbon material, hard carbon is usually composed of a large number of disordered graphite microcrystals and amorphous regions, similar to a "house of cards" structure, without an exact crystal structure model. Therefore, it is relatively difficult to theoretically study the physical and chemical changes during the sodiation / desodiation process of hard carbon. The mechanism models that have been proposed so far include "intercalation-pore filling", "adsorption-intercalation", "adsorption-pore filling", "adsorption-intercalation / pore filling", etc. Generally speaking, the sodium storage behavior of hard carbon materials mainly includes: (1) adsorption on the surface, defect sites, and functional groups; (2) micropore filling; (3) intercalation of graphitic carbon layers. At present, in the academic research and commercial exploration of the preparation of hard carbon materials, the doping of inorganic non-metal anions (N, P, S, O, etc.) is used to improve the sodium storage performance of hard carbon negative electrode materials. However, the doping of inorganic non-metal anions may introduce defects or impurities, thereby affecting the electron transport path of hard carbon materials, leading to a decrease in the chemical stability of the materials. At the same time, this type of doping requires special process steps and technical control, which increases the preparation complexity and also raises the production cost. Summary of the Invention

[0004] In order to obtain a new type of hard carbon negative electrode material, the present invention provides a preparation method of a bimetallic cation-doped modified starch-based hard carbon material. This method uses starch with a relatively low cost as the main raw material, and through the doping modification and synergistic effect of bimetallic cations, a starch-based hard carbon material with controllable particle size is prepared. The prepared starch-based hard carbon material has excellent electrochemical performance and can be used as the negative electrode material for sodium-ion batteries, which is of great significance for the large-scale application of sodium-ion batteries.

[0005] The present invention also provides a bimetallic cation-doped modified starch-based hard carbon material and its application.

[0006] The present invention is achieved through the following technical solutions:

[0007] The present invention provides a preparation method of a bimetallic cation-doped modified starch-based hard carbon material, and the preparation method includes:

[0008] Dissolve cellulose, an acid, and two metal chlorides in water together to obtain a mixed solution;

[0009] Disperse starch in the mixture solution to obtain a starch suspension slurry;

[0010] Dry the starch suspension slurry to obtain a precursor powder;

[0011] Perform low-temperature pre-calcination on the precursor powder in an oxygen or air atmosphere to obtain a hard carbon intermediate;

[0012] Place the hard carbon intermediate in an inert atmosphere for high-temperature calcination to obtain a bimetallic cation-doped modified starch-based hard carbon material;

[0013] Wherein, the mass ratio of the starch to the cellulose is (3-10):1;

[0014] The two metal chlorides include any two of manganese chloride, sodium chloride, lithium chloride, copper chloride, zinc chloride, aluminum chloride, potassium chloride, calcium chloride, and magnesium chloride.

[0015] Further, the step of dissolving cellulose, an acid, and two metal chlorides in water together to obtain a mixed solution specifically includes:

[0016] Dissolve cellulose, an acid, metal chloride A, and metal chloride B in water together to obtain a transparent mixed solution;

[0017] Wherein, in the mixed solution, the mass concentration of the cellulose is 0.1-1 g / L, the molar concentration of the metal chloride A is 0.01-0.1 mol / L, and the molar concentration of the metal chloride B is 0.01-0.1 mol / L.

[0018] Further, the acid includes at least one of phosphoric acid, hydrochloric acid, nitric acid, sulfuric acid, perchloric acid, and acetic acid;

[0019] In the mixed solution, the molar concentration of the acid is 0.1-1 mol / L.

[0020] Further, the starch includes at least one of corn starch, mung bean starch, potato starch, wheat starch, sweet potato starch, lotus root starch, pea starch, coconut starch, and soluble starch;

[0021] The cellulose includes at least one of microcrystalline cellulose, polycellulose, lignin fiber, methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose;

[0022] The solid content of the starch suspension slurry is 5-60 wt%.

[0023] Further, drying the starch suspension slurry to obtain a precursor powder specifically includes:

[0024] Spray-drying the starch suspension slurry to obtain a precursor powder.

[0025] Preferably, the fan frequency of the spray drying is 10-60 Hz, the feeding rate is 10-2000 mL / h, the inlet air temperature is 100-275 °C, and the outlet air temperature is 60-200 °C.

[0026] Further, low-temperature pre-burning the precursor powder in an oxygen or air atmosphere to obtain a hard carbon intermediate specifically includes:

[0027] Low-temperature pre-burning the precursor powder in an oxygen or air atmosphere, the low-temperature pre-burning temperature is 80-300 °C, and the heat preservation time is 1-15 h to obtain a hard carbon intermediate.

[0028] Further, placing the hard carbon intermediate in an inert atmosphere for high-temperature calcination to obtain a bimetallic cation-doped modified starch-based hard carbon material specifically includes:

[0029] Placing the hard carbon intermediate in an inert atmosphere for high-temperature calcination, the high-temperature calcination includes a first stage and a second stage. The calcination temperature in the first stage is 500-750 °C, and the duration is 1-6 h. The calcination temperature in the second stage is 900-1500 °C, and the duration is 1-7 h to obtain a bimetallic cation-doped modified starch-based hard carbon material;

[0030] Among them, the inert atmosphere includes any one of nitrogen, argon, argon-hydrogen mixture, and nitrogen-hydrogen mixture.

[0031] Based on the same inventive concept, the present invention provides a bimetallic cation-doped modified starch-based hard carbon material, and the starch-based hard carbon material is prepared by the preparation method of the above-mentioned bimetallic cation-doped modified starch-based hard carbon material.

[0032] Based on the same inventive concept, the present invention also provides an application of a bimetallic cation-doped modified starch-based hard carbon material in the preparation of an anode material for a sodium-ion battery.

[0033] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0034] 1. The preparation method of a bimetallic cation-doped modified starch-based hard carbon material of the present invention uses starch with a relatively low cost as the main raw material, and realizes the doping of bimetallic ions by a simple solution method. Through the doping modification and synergistic effect of bimetallic cations, a starch-based hard carbon material with controllable particle size is prepared. It has the advantages of simple process, low cost, environmental friendliness and being conducive to batch production. The prepared starch-based hard carbon material has excellent electrochemical performance, and has the advantages of controllable particle size, low cost and easy industrialization. It can be used as an anode material for sodium-ion batteries, which is of great significance for the large-scale application of sodium-ion batteries.

[0035] 2. The preparation method of a bimetallic cation-doped modified starch-based hard carbon material of the present invention. In the mixed solution prepared by this method, cellulose is dissolved in the multi-metal salt solution as a glucose polymer with a smaller molecular weight. These small molecules form a soluble complex structure with metal ions. During the high-temperature calcination process, these complex structures will coat the hard carbon surface formed by starch with metal ions, thereby realizing a certain degree of suppression of the foaming phenomenon of starch during the high-temperature pyrolysis process. The present invention uses starch and cellulose mixed together as the hard carbon precursor. Among them, starch with a wide source and uniform composition provides the main hard carbon skeleton. After cellulose is dissolved, it forms a complex structure with metal ions and can coat the starch surface, which is beneficial to improving the rate performance of hard carbon.

[0036] 3. A bimetallic cation-doped modified starch-based hard carbon material of the present invention. Through the doping of metal ions, during the carbonization and pyrolysis process, the metal ions will form an M-Nx-C (M represents metal, N is nitrogen, C is carbon, and x represents the quantity) structure to repair the defects on the hard carbon surface, providing more effective active sites. At the same time, the presence of metal ions increases the interlayer spacing and closed pore diameter of the hard carbon material, thereby effectively improving the sodium storage capacity and the first Coulomb efficiency of hard carbon. Moreover, the present invention uses bimetallic ion doping, and utilizes the bimetallic synergistic effect to repair the problem of large defects in the hard carbon itself while suppressing the graphitization of hard carbon, and inhibits the decomposition of the electrolyte, forming a dense and uniform SEI film on the hard carbon surface. The reversible discharge capacity of the starch-based hard carbon material of the present invention reaches 400 mAh / g, and the first Coulomb efficiency is greater than 90%, having excellent electrochemical performance. Description of the Drawings

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0038] Figure 1 XRD pattern of the hard carbon anode material prepared in Examples 1-4 of the present invention.

[0039] Figure 2 Charge-discharge curve of the hard carbon anode material prepared in Example 1 of the present invention.

[0040] Figure 3 Charge-discharge curve of the hard carbon anode material prepared in Example 2 of the present invention.

[0041] Figure 4 Charge-discharge curve of the hard carbon anode material prepared in Example 3 of the present invention.

[0042] Figure 5 Charge-discharge curve of the hard carbon anode material prepared in Example 4 of the present invention. Detailed implementation manners

[0043] The following will specifically describe the present invention in combination with the detailed implementation manners and examples, and the advantages and various effects of the present invention will be presented more clearly therefrom. Those skilled in the art should understand that these detailed implementation manners and examples are used to illustrate the present invention, rather than limiting the present invention.

[0044] Throughout the specification, unless otherwise specifically stated, the terms used herein should be understood as having the meanings commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. In case of contradiction, this specification shall prevail.

[0045] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can all be obtained through market purchases or can be prepared by existing methods.

[0046] The technical principle of the present invention is as follows:

[0047] A preparation method of a bimetallic cation-doped and modified starch-based hard carbon material of the present invention, the preparation method comprising:

[0048] S1. Dissolve cellulose, an acid, and two metal chlorides in water together to obtain a mixed solution;

[0049] S2. Disperse starch in the mixture solution to obtain a starch suspension slurry;

[0050] S3. Dry the starch suspension slurry to obtain precursor powder;

[0051] S4. Perform low-temperature pre-calcination on the precursor powder in an oxygen or air atmosphere to obtain a hard carbon intermediate;

[0052] S5. Place the hard carbon intermediate under an inert atmosphere for high-temperature calcination to obtain a bimetallic cation-doped modified starch-based hard carbon material;

[0053] Wherein, the mass ratio of the starch to the cellulose is (3-10):1;

[0054] The two metal chlorides include any two of manganese chloride, sodium chloride, lithium chloride, copper chloride, zinc chloride, aluminum chloride, potassium chloride, calcium chloride, and magnesium chloride.

[0055] In the present invention, an acid is added to the mixed solution because after different metal chlorides are dissolved in water, they will provide Lewis acid to the solution. The addition of a small amount of low-concentration acid can promote the formation of a complex between metal ions and cellulose while providing the required hydrogen ions to the entire system.

[0056] In the present invention, the cellulose is dissolved first and then the starch is added because the starch is also slightly soluble in the metal salt solution and will react under acidic conditions. Adding the starch later ensures the uniformity during the pyrolysis process of the hard carbon precursor and avoids the influence of the reaction on the properties of the hard carbon.

[0057] In the present invention, the precursor powder is prepared by spray drying. Through spray drying, the dissolved cellulose material is uniformly mixed with the starch, and at the same time, the material can be controlled to form uniform spherical particles.

[0058] In the present invention, the low-temperature pre-calcination of the precursor powder in an oxygen or air atmosphere can reduce costs and at the same time inhibit the foaming phenomenon of the starch during the pyrolysis process. The hard carbon intermediate is placed under an inert atmosphere for high-temperature calcination because a gas with oxidation-reduction properties at high temperature carbonization will reduce the fixed carbon content of the hard carbon and react with carbon, and an inert atmosphere is a necessary condition for forming hard carbon.

[0059] In the present invention, the mass ratio of the starch to the cellulose is (3-10):1. The starch and cellulose are mixed together as the hard carbon precursor, which is widely sourced and has a uniform composition.

[0060] In the present invention, the two metal chlorides include any two of manganese chloride, sodium chloride, lithium chloride, copper chloride, zinc chloride, aluminum chloride, potassium chloride, calcium chloride, and magnesium chloride. They have low cost, are environmentally friendly, and have a wide source. The present invention uses dual-metal co-doping and utilizes the synergistic effect of the two metals to suppress the graphitization of hard carbon while also repairing the problem of large defects in the hard carbon itself, inhibiting the decomposition of the electrolyte, and forming a dense and uniform SEI film on the surface of the hard carbon.

[0061] Step S1 specifically includes:

[0062] Dissolve cellulose, an acid, metal chloride A, and metal chloride B in water together to obtain a transparent mixed solution;

[0063] Among them, in the mixed solution, the mass concentration of the cellulose is 0.1 - 1 g / L, the molar concentration of the metal chloride A is 0.01 - 0.1 mol / L, and the molar concentration of the metal chloride B is 0.01 - 0.1 mol / L.

[0064] Furthermore, the acid includes at least one of phosphoric acid, hydrochloric acid, nitric acid, sulfuric acid, perchloric acid, and acetic acid;

[0065] In the mixed solution, the molar concentration of the acid is 0.01 - 1 mol / L.

[0066] In the present invention, the advantage of using cellulose at the above concentration in the mixed solution is that it can form complexes with all metal ions.

[0067] The molar concentration of the acid in the mixed solution is 0.01 - 1 mol / L. Below this range, the ability to supply H + is insufficient. Above this range, the overly strong acidity will affect the sodium storage performance after the starch forms hard carbon and also increase the environmental protection pressure of the process.

[0068] Step S3 specifically includes:

[0069] Perform spray drying on the starch suspension slurry to obtain a precursor powder.

[0070] Preferably, the fan frequency of the spray drying is 10 - 60 Hz, the feeding rate is 10 - 2000 mL / h, the inlet air temperature is 100 - 275 °C, and the outlet air temperature is 60 - 200 °C.

[0071] In the present invention, using the above process parameters for spray drying can facilitate the timely evaporation of the solution moisture and obtain a suitable spherical precursor. If the process parameters are too low, the moisture cannot be evaporated in time, making it difficult to collect the precursor material. If they are too high, it will cause the starch to saccharify and adhere to the surface of the instrument.

[0072] Step S4 specifically includes:

[0073] The precursor powder is subjected to low-temperature pre-sintering in an oxygen or air atmosphere. The low-temperature pre-sintering temperature is 80 - 300 °C, and the heat preservation time is 1 - 15 h to obtain a hard carbon intermediate.

[0074] In the present invention, the low-temperature pre-sintering temperature of 80 - 300 °C and the heat preservation time of 1 - 15 h are beneficial in that they can inhibit the foaming phenomenon during the carbonization of starch. The purpose of performing the low-temperature pre-sintering in an oxygen or air atmosphere is to pre-oxidize starch and promote the starch cross-linking reaction.

[0075] Step S5 specifically includes:

[0076] The hard carbon intermediate is placed in an inert atmosphere for high-temperature calcination. The high-temperature calcination includes a first stage and a second stage. The calcination temperature in the first stage is 500 - 750 °C, and the duration is 1 - 6 h. The calcination temperature in the second stage is 900 - 1500 °C, and the duration is 1 - 7 h to obtain a double-metal cation-doped and modified starch-based hard carbon material;

[0077] Among them, the inert atmosphere includes any one of nitrogen, argon, argon-hydrogen mixture, and nitrogen-hydrogen mixture.

[0078] In the present invention, the high-temperature calcination is carried out in two stages. The first-stage high temperature is to fully react to completely remove impurities such as tar and gases in the material, and the second-stage high temperature provides a stable reaction environment based on the first stage.

[0079] The benefits of the calcination temperature in the first stage being 500 - 750 °C and the duration being 1 - 6 h are that it can provide sufficient time to remove the generation of impurity gases such as tar in this temperature range. If the calcination temperature is too low, the reaction is incomplete; if it is too high, the reaction is too violent and affects the hard carbon evolution process.

[0080] The benefits of the calcination temperature in the second stage being 900 - 1500 °C and the duration being 1 - 7 h are that it can form a stable hard carbon material.

[0081] Next, the preparation method of a double-metal cation-doped and modified starch-based hard carbon material of the present application will be described in detail in combination with examples and experimental data.

[0082] Example 1

[0083] This example provides a preparation method of a double-metal cation-doped and modified starch-based hard carbon material, including the following steps:

[0084] (1) Weigh 6.8 g of ZnCl 2 , 6.2 g of AlCl 3, add 500 mL of deionized water, and continuously stir at room temperature until the two samples are completely dissolved. Then, add 30 g of cellulose to the solution and dropwise add 10 mL of 0.05 mol / L dilute hydrochloric acid, and continuously stir until the cellulose is completely dissolved. Weigh 180 g of corn starch and add it to the solution in which the cellulose has been dissolved, and continuously stir to obtain a suspension slurry with a solid content of 30 wt%.

[0085] (2) Spray-dry the suspension slurry with a fan frequency of 50 Hz, a feed rate of 360 mL / h, an inlet air temperature of 120 °C, and an outlet air temperature of 80 °C to obtain and collect the dried precursor powder.

[0086] (3) Place the precursor powder in an air atmosphere and pre-calcine it at 200 °C for 8 h at a heating rate of 2 °C / min. Place the low-temperature pre-calcined material in an argon atmosphere and calcine it at 500 °C for 2 h at a heating rate of 2 °C / min, and then raise the temperature to 1400 °C and calcine it for 2 h to obtain the Zn-Al bimetallic ion-doped hard carbon material.

[0087] Example 2

[0088] This example provides a preparation method of a bimetallic cation-doped modified starch-based hard carbon material, including the following steps:

[0089] (1) Weigh 6.8 g of ZnCl 2 , 6.25 g of MnCl 3 , add 500 mL of deionized water, and continuously stir at room temperature until the two samples are completely dissolved. Then, add 30 g of cellulose to the solution and dropwise add 10 mL of 0.05 mol of dilute hydrochloric acid, and continuously stir until the cellulose is completely dissolved. Weigh 180 g of corn starch and add it to the solution in which the cellulose has been dissolved, and continuously stir to obtain a suspension slurry with a solid content of 30 wt%.

[0090] (2) Spray-dry the suspension slurry with a fan frequency of 50 Hz, a feed rate of 360 mL / h, an inlet air temperature of 120 °C, and an outlet air temperature of 80 °C to obtain and collect the dried precursor powder.

[0091] (3) Place the precursor powder in an air atmosphere and pre-calcine it at 200 °C for 8 h at a heating rate of 2 °C / min. Place the low-temperature pre-calcined material in an argon atmosphere and calcine it at 500 °C for 2 h at a heating rate of 2 °C / min, and then raise the temperature to 1400 °C and calcine it for 2 h to obtain the Zn-Mn bimetallic ion-doped hard carbon material.

[0092] Example 3

[0093] This example provides a preparation method of a bimetallic cation-doped modified starch-based hard carbon material, including the following steps:

[0094] (1) Weigh 5.8 g of NaCl separately 2 , 6.25 g of MnCl 3 , add them to 500 mL of deionized water, continuously stir at room temperature until the two samples are completely dissolved, then add 30 g of cellulose to the solution and dropwise add 10 mL of 0.05 mol dilute hydrochloric acid, continuously stir until the cellulose is completely dissolved. Weigh another 180 g of corn starch and add it to the solution in which the cellulose has been dissolved, and continuously stir to obtain a suspension slurry with a solid content of 30 wt%.

[0095] (2) Spray-dry the suspension slurry, with the fan frequency of 50 Hz, the feeding rate of 360 mL / h, the inlet air temperature of 120 °C, and the outlet air temperature of 80 °C, to obtain and collect the dried precursor powder.

[0096] (3) Place the precursor powder in an air atmosphere, pre-calcine it at 200 °C for 8 h at a heating rate of 2 °C / min, place the low-temperature pre-calcined material in an argon atmosphere, calcine it at 500 °C for 2 h at a heating rate of 2 °C / min, and then raise the temperature to 1400 °C and calcine it for 2 h to obtain the hard carbon material doped with Na-Mn bimetallic ions.

[0097] Example 4

[0098] This example provides a preparation method of a bimetallic cation-doped modified starch-based hard carbon material, including the following steps:

[0099] (1) Weigh 5.8 g of NaCl and 8.5 g of CuCl separately 2 , add them to 500 mL of deionized water, continuously stir at room temperature until the two samples are completely dissolved, then add 30 g of cellulose to the solution and dropwise add 10 mL of 0.05 mol dilute hydrochloric acid, continuously stir until the cellulose is completely dissolved. Weigh another 180 g of corn starch and add it to the solution in which the cellulose has been dissolved, and continuously stir to obtain a suspension slurry with a solid content of 30 wt%.

[0100] (2) Spray-dry the suspension slurry, with the fan frequency of 50 Hz, the feeding rate of 360 mL / h, the inlet air temperature of 120 °C, and the outlet air temperature of 80 °C, to obtain and collect the dried precursor powder.

[0101] (3) Place the precursor powder in an air atmosphere, pre-calcine it at 200 °C for 8 h at a heating rate of 2 °C / min, place the low-temperature pre-calcined material in an argon atmosphere, calcine it at 500 °C for 2 h at a heating rate of 2 °C / min, and then raise the temperature to 1400 °C and calcine it for 2 h to obtain the hard carbon material doped with Na-Cu bimetallic ions.

[0102] Figure 1XRD pattern of the hard carbon anode materials prepared in Examples 1-4 of the present invention. From Figure 1 it can be seen that: the prepared bimetal-doped hard carbon materials all exhibit typical hard carbon peaks, and a small amount of metal doping cannot be detected by the XRD instrument. It can be found from the figure that the layer spacing calculated by the Bragg equation for the two-theta corresponding to d002 is greater than 0.4 nm.

[0103] Figure 2 Charge-discharge curve of the hard carbon anode material prepared in Example 1 of the present invention. The test method is as follows: the ratio of the electrode materials is: active material: SP: PVDF = 8:1:1. Constant current charging and constant current discharging are used, the current density is 25 mA / g, and the test is carried out at room temperature. From Figure 2 it can be seen that: the initial discharge capacity of the hard carbon anode material is 439.16 mAh / g, the initial charge capacity is 400.36 mAh / g, and the initial Coulomb efficiency is 91.165%.

[0104] Figure 3 Charge-discharge curve of the hard carbon anode material prepared in Example 2 of the present invention. From Figure 2 it can be seen that: the initial discharge capacity of the hard carbon anode material is 432.96 mAh / g, the initial charge capacity is 392.214 mAh / g, and the initial Coulomb efficiency is 90.59%.

[0105] Figure 4 Charge-discharge curve of the hard carbon anode material prepared in Example 3 of the present invention. From Figure 2 it can be seen that: the initial discharge capacity of the hard carbon anode material is 419.569 mAh / g, the initial charge capacity is 379.70 mAh / g, and the initial Coulomb efficiency is 90.498%.

[0106] Figure 5 Charge-discharge curve of the hard carbon anode material prepared in Example 4 of the present invention. From Figure 2 it can be seen that: the initial discharge capacity of the hard carbon anode material is 428.787 mAh / g, the initial charge capacity is 389.70 mAh / g, and the initial Coulomb efficiency is 90.884%.

[0107] Finally, it should also be noted that the term "comprises", "comprising" or any other variation thereof is intended to cover a non-exclusive inclusion, such that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device.

[0108] Although the preferred embodiments of the present invention have been described, additional changes and modifications can be made to these embodiments by those skilled in the art once they learn the basic creative concept. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications that fall within the scope of the present invention.

[0109] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a bimetallic cation-doped modified starch-based hard carbon material, characterized in that: The preparation method comprises: dissolving cellulose, acid and two metal chlorides in water to obtain a mixed solution; Dispersing starch in the mixture solution to obtain a starch suspension slurry; Drying the starch suspension slurry to obtain a precursor powder; Pre-calcining the precursor powder in an oxygen or air atmosphere at a low temperature of 80 to 300° C. for a holding time of 1 to 15 hours to obtain a hard carbon intermediate; The hard carbon intermediate is placed in an inert atmosphere for high-temperature calcination, wherein the high-temperature calcination includes a first stage and a second stage, wherein the first stage calcination temperature is 500-750° C. and the duration is 1-6 hours, and the second stage calcination temperature is 900-1500° C. and the duration is 1-7 hours, to obtain a bimetallic cation-doped modified starch-based hard carbon material; Wherein, the mass ratio of the starch to the cellulose is (3-10):1; The two metal chlorides include any two of manganese chloride, sodium chloride, lithium chloride, copper chloride, zinc chloride, aluminum chloride, potassium chloride, calcium chloride and magnesium chloride.

2. The method for preparing a bimetallic cation-doped modified starch-based hard carbon material according to claim 1, characterized in that: The step of dissolving cellulose, acid and two metal chlorides in water to obtain a mixed solution specifically comprises: Dissolving cellulose, acid, metal chloride A and metal chloride B in water to obtain a transparent mixed solution; Wherein, in the mixed solution, the mass concentration of the cellulose is 0.1-1 g / L, the molar concentration of the metal chloride A is 0.01-0.1 mol / L, and the molar concentration of the metal chloride B is 0.01-0.1 mol / L.

3. The method for preparing a bimetallic cation-doped modified starch-based hard carbon material according to claim 1 or 2, characterized in that: The acid comprises at least one of phosphoric acid, hydrochloric acid, nitric acid, sulfuric acid, perchloric acid and acetic acid; In the mixed solution, the molar concentration of the acid is 0.1-1 mol / L.

4. The method for preparing a bimetallic cation-doped modified starch-based hard carbon material according to claim 1, characterized in that: The starch comprises at least one of corn starch, mung bean starch, potato starch, wheat starch, sweet potato starch, lotus root starch, pea starch, coconut starch and soluble starch; The cellulose comprises at least one of microcrystalline cellulose, polymerized cellulose, lignin fiber, methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose and carboxymethyl cellulose; The solid content of the starch suspension slurry is 5-60wt%.

5. The method for preparing a bimetallic cation-doped modified starch-based hard carbon material according to claim 1, characterized in that: The step of drying the starch suspension slurry to obtain a precursor powder specifically comprises: The starch suspension slurry is spray-dried to obtain a precursor powder.

6. The method for preparing a bimetallic cation-doped modified starch-based hard carbon material according to claim 5, characterized in that: The fan frequency of the spray drying is 10-60 Hz, the feed rate is 10-2000 mL / h, the inlet air temperature is 100-275° C., and the outlet air temperature is 60-200° C.

7. A bimetallic cation-doped modified starch-based hard carbon material, characterized in that: The starch-based hard carbon material is prepared by the method for preparing a bimetallic cation-doped modified starch-based hard carbon material according to any one of claims 1 to 6.

8. Use of a bimetallic cation-doped modified starch-based hard carbon material as claimed in claim 7 in the preparation of a negative electrode material for a sodium ion battery.

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