Short-range graphite-like and closed-pore synergistic hard carbon negative electrode material and preparation method thereof

Abstract

The application provides a short-range graphite-like and closed-pore coordinated hard carbon negative electrode material and a preparation method thereof, aims to regulate the growth of graphite-like microcrystalline structure in the hard carbon, and realizes high-performance sodium ion storage. The preparation of the short-range graphite-like and closed-pore coordinated hard carbon negative electrode material is realized through simple pre-carbonization temperature regulation and atmosphere control at high-temperature carbonization, and the preparation method mainly comprises the following steps: taking biomass bean dregs as raw materials, pre-carbonization treatment is carried out at different temperatures to obtain pre-carbonization materials; then high-temperature treatment is carried out under a hydrogen reduction atmosphere to regulate the growth of graphite-like structure, so that the short-range graphite-like structure and closed-pore coordinated hard carbon negative electrode material are prepared. Through optimization of the reasonable combination of the short-range graphite-like structure and the closed pore, excellent sodium storage performance is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy materials, and particularly relates to a short-range graphite-like and closed-pore coordinated hard carbon negative electrode material and a preparation method thereof. BACKGROUND

[0002] Sodium is the seventh most abundant element on Earth, widely existing in seawater and terrestrial minerals. Compared with lithium resources, sodium resources are more abundant and have lower cost, which makes sodium-ion batteries have potential advantages in large-scale energy storage applications. In the research of sodium-ion batteries, the choice of negative electrode material is crucial because it directly affects the energy density, cycle stability and safety of the battery. Among the numerous candidate materials, hard carbon materials have attracted widespread attention due to their excellent performance.

[0003] Among the preparation raw materials of numerous hard carbon materials, biomass raw materials stand out due to their advantages such as abundant sources, sustainability, environmental friendliness and cost-effectiveness. Using biomass raw materials not only can reduce production costs, but also can reduce environmental pollution caused by large-scale waste incineration. Further, the defects and pores formed in the natural growth process of biomass can still be retained after carbonization treatment. In the subsequent heat treatment stage, these structures can be transformed into closed-pore structures, thereby significantly improving their sodium storage performance and exhibiting excellent sodium storage capacity, which indicates that they have great potential to become a new generation of low-cost and high-performance negative electrode materials for sodium-ion batteries.

[0004] Due to the above characteristics, the formation of graphite domains (carbon layers) and closed pores composed thereof after carbonization of biomass raw materials becomes the research object. Closed pore structure is crucial in the design of hard carbon negative electrode materials for sodium ion batteries, which helps to improve the sodium storage performance in the low voltage platform area of the battery, and thus promotes its potential in commercial applications. However, its formation mechanism is still controversial. Studies have shown that the formation of closed pores in hard carbon may be related to the decomposition of the precursor, the composition and the curling of the carbon layer. In the literature "Understanding the Sodium Storage Behavior of Closed Pores / Carbonyl Groups in Hard Carbon. ACS Nano 2024, 18(32), 21491-21503.", the authors treated the precursor with sulfuric acid to increase the content of carbonyl groups in the precursor, which in turn affected the formation of graphite domains after carbonization, resulting in abundant closed pores. However, this treatment often results in thicker pore walls and increases the long-range ordered graphite structure, which in turn affects the rate performance and faster kinetics. In patents (CN109921020A, CN113666356A), the carbon source precursor is mixed with chemical reagents (such as hydrogen peroxide, nitric acid, sulfuric acid) for treatment to increase the closed pore content, but it often changes other properties of the material, resulting in long-range ordered graphite structure or uneven distribution of closed pores, and thicker pore walls.

[0005] Therefore, there is an urgent need to develop a suitable new method to prepare hard carbon negative electrode materials that meet the requirements of high closed pore content and short-range graphite-like structure. SUMMARY

[0006] The purpose of the present application is to provide a short-range graphite-like and closed pore synergistic hard carbon negative electrode material and a preparation method thereof. The present application uses biomass bean dregs as raw material, without adding any chemical reagents, and obtains a pre-carbonized material by temperature regulation under argon conditions. Then, a short-range graphite-like structure and closed pore synergistic hard carbon negative electrode material is prepared by high temperature treatment under a reducing atmosphere containing hydrogen.

[0007] The short-range graphite-like microcrystalline structure of the hard carbon negative electrode material prepared by the present application provides more sodium intercalation sites, and the abundant closed pores provide good platform capacity, thereby achieving excellent sodium storage performance.

[0008] In order to achieve the above-mentioned application purposes, the technical solutions of the present application are as follows:

[0009] A preparation method of a short-range graphite-like and closed pore synergistic hard carbon negative electrode material, comprising the following steps:

[0010] (1) After washing the bean dregs with distilled water, dry them in a forced air drying oven;

[0011] (2) The dried bean dregs are placed in a tube furnace and pre-carbonized under an argon or nitrogen atmosphere to obtain pre-carbonized material I;

[0012] (3) The pre-carbonized material I obtained in step (2) is washed with dilute hydrochloric acid and deionized water until the washing liquid is neutral to obtain pre-carbonized material II;

[0013] (4) The pre-carbonized material II obtained in step (3) is placed in a high-temperature furnace and high-temperature carbonized under an atmosphere containing hydrogen reduction, wherein the short-range graphite domain microcrystals of the pre-carbonized material II continue to grow and bend to form closed pores, and part of the short-range graphite domain microcrystals stop growing, thereby obtaining a hard carbon negative electrode material rich in short-range graphite and closed pores.

[0014] Preferably, the drying temperature of the bean dregs in step (1) is 80 ℃, and the drying time is 12 h.

[0015] It should be noted that the pre-carbonization temperature affects the development of the carbon layer and the formation of closed pores, ultimately affecting the performance of the material; and the pre-carbonization treatment time should not be too long, otherwise the carbon layer will be too thick, which will affect the specific capacity or the first coulombic efficiency of the hard carbon material.

[0016] Preferably, the pre-carbonization temperature in step (2) is between 450-850 ℃, and the pre-carbonization time is 2-5 h, ensuring that the components of the bean dregs are fully carbonized and decomposed. A too high pre-carbonization temperature will bring additional energy consumption and excessive development of the carbon layer, while a too low pre-carbonization temperature may result in incomplete carbonization of the hard carbon material in the subsequent high-temperature treatment. This incomplete carbonization may damage the reversible specific capacity of the hard carbon material, thereby affecting the overall electrochemical performance of the material.

[0017] Further preferably, the pre-carbonization temperature in step (2) is 700-750 ℃, and the pre-carbonization time is 2 h.

[0018] Preferably, the pre-carbonization temperature in step (2) is 700-750 ℃, and the pre-carbonization time is 2 h.

[0019] Preferably, the dilute hydrochloric acid concentration in step (3) is 1-2 mol / L, and the acid washing time is 6 h, ensuring the complete removal of impurities in the pre-carbonized material.

[0020] The deionized water washing process in step (3) is repeated by using deionized water to filter and wash, and the washing number is preferably 3-10 times to ensure the removal of hydrochloric acid.

[0021] Preferably, the high-temperature carbonization temperature in the step (4) is 1000-1600 ℃, the heating rate is 2-10 ℃ / min, and the holding time is 2-5 h. The growth of the graphite-like structure is controlled according to the high-temperature carbonization temperature range, so as to ensure that the length of the graphite-like structure is appropriate.

[0022] Further preferably, the high-temperature carbonization temperature in the step (4) is 1350-1400 ℃, and the time is 2 h.

[0023] Preferably, the protective gas for high-temperature carbonization in the step (4) is any one of hydrogen, hydrogen-argon, and hydrogen-nitrogen.

[0024] The application also provides a short-range graphite-like and closed-pore coordinated hard carbon negative electrode material, which is prepared by the above preparation method.

[0025] The application also provides an application of the short-range graphite-like and closed-pore coordinated hard carbon negative electrode material as a sodium ion battery negative electrode material.

[0026] Advantages:

[0027] (1) The hard carbon negative electrode material provided by the application has a developed closed-pore structure and a short-range graphite-like structure, and exhibits a better sodium storage capacity than traditional hard carbon negative electrode materials. In addition, the number of open pores in the material is reduced, which helps to improve the first coulombic efficiency. The first coulombic efficiency is as high as 88.1%, and the first charge specific capacity is 335.2 mAh / g.

[0028] (2) The preparation method of the hard carbon negative electrode material provided by the application uses biomass bean dregs as a raw material, and through pre-carbonization temperature treatment, the material triggers the curling of the carbon layer during the carbonization process, thereby promoting the formation of more thin-walled closed-pore structures.

[0029] (3) The preparation method of the hard carbon negative electrode material provided by the application has the advantages of wide raw material sources and simple process, which makes it very suitable for large-scale industrial manufacturing environment. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is an HRTEM graph of Example 1 of the application.

[0031] Figure 2 It is the first charge-discharge curve of the hard carbon negative electrode material prepared in Example 1 of the application for a sodium ion battery at a current density of 20 mA / g.

[0032] Figure 3 It is the rate performance of the hard carbon negative electrode material prepared in Example 1 of the application for a sodium ion battery.

[0033] Figure 4XRD pattern of Example 1 and Comparative Example 1 of the present application.

[0034] Figure 5 Raman pattern of Example 1 and Comparative Example 1 of the present application.

[0035] Figure 6 HRTEM pattern of Example 3 of the present application.

[0036] Figure 7 HRTEM pattern of Example 6 of the present application. DETAILED DESCRIPTION

[0037] The present application aims to provide a short-range graphite-like and closed-pore synergistic hard carbon negative electrode material and a preparation method thereof. The present application takes biomass okara as raw material, and obtains pre-carbonized material through temperature regulation under argon condition without adding any chemical reagent. Then, the short-range graphite-like and closed-pore synergistic hard carbon negative electrode material is prepared through high-temperature treatment under hydrogen, hydrogen-argon or hydrogen-nitrogen mixed gas condition.

[0038] The short-range graphite-like microcrystalline structure of the hard carbon negative electrode material prepared by the present application makes it have more sodium intercalation sites, and the rich closed pores provide good platform capacity, thereby realizing excellent sodium storage performance.

[0039] The present application provides a short-range graphite-like and closed-pore synergistic hard carbon negative electrode material and a preparation method thereof, which comprises the following steps:

[0040] (1) A certain amount of okara is weighed, washed with distilled water, and then dried in a forced air drying oven;

[0041] (2) The dried okara is placed in a tube furnace, and pre-carbonization is carried out under argon or nitrogen atmosphere to obtain pre-carbonized material I;

[0042] (3) The pre-carbonized material I obtained in step (2) is washed with dilute hydrochloric acid solution and deionized water until the solution is neutral to obtain pre-carbonized material II;

[0043] (4) The pre-carbonized material II obtained in step (3) is placed in a high-temperature furnace and subjected to high-temperature carbonization under hydrogen, hydrogen-argon or hydrogen-nitrogen atmosphere, wherein the short-range graphite domain microcrystals of the pre-treatment material continue to grow and bend to form closed pores, and at the same time, part of the short-range graphite domain microcrystals stop growing, thereby obtaining a hard carbon negative electrode material rich in short-range graphite-like and closed-pore synergistic.

[0044] Example 1

[0045] A short-range graphite-like and closed-pore synergistic hard carbon negative electrode material and a preparation method thereof, the preparation method comprising the following steps:

[0046] Step 1, 500 g of bean dregs was weighed and washed with distilled water, then placed in a forced air drying oven, the drying temperature was 80℃, and the drying time was 12 h, to remove impurities and moisture;

[0047] Step 2, 10 g of dried and treated bean dregs was placed in a tube furnace, heated to 750℃ at a heating rate of 5℃ / min under an argon or nitrogen atmosphere, and the holding time was 2 h. After cooling to room temperature, the pre-carbonized material I was taken out and washed. The 750℃ carbonization for 2 h was mainly to ensure that the cellulose was fully pyrolyzed.

[0048] Step 3, the pre-carbonized material I obtained in step 2 was placed in a 1 mol / L hydrochloric acid solution for washing treatment until the washing liquid was neutral, and the washing time was 6 h. Then it was washed with deionized water until the washing liquid was neutral. Then it was placed in a forced air drying oven and dried at 60℃ for 12 h to obtain a relatively pure pre-carbonized material II.

[0049] Step 4, the pure pre-carbonized material II obtained in step 3 was placed in a high-temperature tube furnace and heated to 900℃ at a heating rate of 5℃ / min under a hydrogen reducing atmosphere, and then heated to 1400℃ at a heating rate of 2℃ / min. The holding time was 2 h. After cooling to room temperature, the short-range graphite-like and closed-pore collaborative hard carbon material was prepared. Experimental verification showed that 1400℃ for 2 h was the optimal condition for regulating the structure of short-range graphite. Prolonged time or high temperature would lead to excessive development of graphite domains, and short time or low temperature would lead to insufficient development of graphite domains.

[0050] The short-range graphite-like and closed-pore collaborative hard carbon material prepared above was used as an active material for battery negative electrode material for the preparation of sodium ion batteries.

[0051] According to the mass ratio of 80% : 10% : 10%, 80 mg of hard carbon material, 10 mg of acetylene black, and 10 mg of sodium alginate SA were weighed, and an appropriate amount of deionized water was added dropwise. After stirring for 20 min, a uniform slurry was obtained. A 100 μm doctor blade was used to uniformly coat the slurry on a copper (Cu) foil, which was then placed in a forced air drying oven and dried for 12 h. The Cu foil with active material was cut into a circular electrode sheet and reserved for use.

[0052] The assembly of the button cell was carried out in an Ar-filled glove box. The prepared electrode sheet was used as the negative electrode, the commercial electrolyte 1.0 M NaPF6 in DME = 100 Vol% was used as the electrolyte, and a Na metal sheet was used as the counter electrode to assemble a 2032 button cell.

[0053] Figure 1This is the HRTEM image of the short-range graphite-like and closed-pore synergistic hard carbon negative electrode material prepared in Example 1 of the present invention; as can be seen from the figure, it can be clearly seen that there is a short-range graphite-like microcrystalline structure with high conductivity; at the same time, the short-range graphite-like domains are cross-linked with each other to construct a rich closed-pore structure, which is conducive to sodium storage in the platform area.

[0054] Figure 2 This is the first cycle charge and discharge curve of Example 1 of the present invention. As shown in the figure, at a current density of 20 mA / g, the first cycle coulombic efficiency is 88.1%, and the first cycle charge capacity is 335.2 mAh / g. The platform capacity contributes 230.9 mAh g -1 , accounting for 68.9%. The high platform capacity share is attributed to the synergistic effect of the short-range graphite-like microcrystal structure and closed pores.

[0055] Figure 3 This is the rate performance of Example 1 of the present invention; As can be seen from the figure, at 1 A g -1 The reversible specific capacity is 222.8 mAh g -1 The excellent rate capability can be attributed to the small interlayer spacing and short-range graphite-like microcrystalline structure, which give it high electrical conductivity.

[0056] Comparative Example 1

[0057] Step 1: Weigh 500 g of bean dregs, wash them with an appropriate amount of distilled water, and place them in a forced air drying oven at 80°C for 12 h to remove impurities and moisture;

[0058] Step 2: Take 10 g of dried bean dregs and place them in a tube furnace. Heat them to 750 °C at a heating rate of 5 °C / min under an argon or nitrogen atmosphere, keep them at this temperature for 2 h, cool them to room temperature, and take them out to obtain pre-carbonized material 1 for washing. Carbonization at 750 °C for 2 h is mainly to ensure sufficient pyrolysis of cellulose.

[0059] Step 3: The pre-carbonized material 1 obtained in step 2 is placed in a 1 mol / L hydrochloric acid solution for washing for 6 hours, and then washed with deionized water until the washing solution is neutral; and then placed in a blast drying oven at 60°C for 12 hours to obtain a relatively pure pre-carbonized material 2;

[0060] Step 4: Place the pure pre-carbonized material obtained in step 3 in a high-temperature tube furnace, first heat it to 900 °C at a heating rate of 5 °C / min under an argon or nitrogen atmosphere, and then heat it to 1400 °C at a heating rate of 2 °C / min. The holding time is 2 h. After cooling to room temperature, take it out to obtain a hard carbon material.

[0061] Step 5, the hard carbon material prepared above is used as an active material of a negative electrode material for the preparation of a sodium ion battery, and the specific method is the same as that in Example 1. The assembled half battery has a first coulombic efficiency of 76.5% and a first cycle charge specific capacity of 290.4 mAh / g at a current density of 20 mA / g.

[0062] Figure 4 The XRD pattern of Example 1 and Comparative Example 1 of the application; it can be seen from the figure that the (002) peak of Example 1 moves to a high angle, and the material layer spacing decreases, which confirms the short-range graphite structure observed in the TEM pattern.

[0063] Figure 5 The Raman pattern of Example 1 and Comparative Example 1 of the application; it can be seen from the figure that the degree of disorder of Example 1 is lower than that of Comparative Example 1, which can be attributed to the short-range graphite structure in Example 1.

[0064] Comparative Example 2

[0065] The application provides a preparation method of a biomass-based hard carbon negative electrode material for a sodium ion battery, and the steps include:

[0066] Step 1, 500 g of bean dregs is weighed, washed with appropriate distilled water, and then placed in a forced air drying oven, with a drying temperature of 80 ℃ and a drying time of 12 h, for removing impurities and moisture;

[0067] Step 2, the bean dregs treated in Step 1 is placed in a 1 mol / L hydrochloric acid solution for washing treatment, with a washing time of 6 h, and then washed with deionized water until the washing liquid is neutral; and then placed in a forced air drying oven for drying at 60 ℃ for 12 h, to obtain a relatively pure bean dregs raw material;

[0068] Step 3, 10 g of the dried bean dregs is taken and placed in a high-temperature tube furnace, and first heated to 900 ℃ at a heating rate of 5 ℃ / min under a hydrogen reduction atmosphere, and then heated to 1400 ℃ at a heating rate of 2 ℃ / min, with a holding time of 2 h, and then taken out after cooling to room temperature to obtain a hard carbon material;

[0069] Step 4, the hard carbon material prepared above is used as an active material of a negative electrode material for the preparation of a sodium ion battery, and the specific method is the same as that in Example 1. The assembled half battery has a first coulombic efficiency of 76.5% and a first cycle charge specific capacity of 290.4 mAh / g at a current density of 20 mA / g.

[0070] Example 2

[0071] A short-range graphite and closed pore synergistic hard carbon negative electrode material and a preparation method thereof, the preparation method comprising the following steps:

[0072] Step 1, 500 g of bean dregs was weighed and washed with distilled water, then placed in a forced air drying oven, the drying temperature was 80℃, and the drying time was 12 h, to remove impurities and moisture;

[0073] Step 2, 10 g of dried bean dregs was placed in a tube furnace, and heated to 750℃ at a heating rate of 5℃ / min under an argon or nitrogen atmosphere, and the holding time was 2 h. After cooling to room temperature, the pre-carbonized material I was taken out and washed;

[0074] Step 3, the pre-carbonized material I obtained in step 2 was placed in 1 mol / L hydrochloric acid solution and deionized water for washing treatment, the washing time was 6 h, and then washed with deionized water until the washing liquid was neutral. Then it was placed in a forced air drying oven and dried at 60℃ for 12 h to obtain a relatively pure pre-carbonized material II;

[0075] Step 4, the pure pre-carbonized material II obtained in step 3 was placed in a high-temperature tube furnace and heated to 900℃ at a heating rate of 5℃ / min under a hydrogen atmosphere, and then heated to 1400℃ at a heating rate of 2℃ / min. The holding time was 2 h, and after cooling to room temperature, the short-range graphite and closed-pore collaborative hard carbon negative electrode material was prepared;

[0076] The short-range graphite and closed-pore collaborative hard carbon material prepared above was used as the active material of the battery negative electrode material for the preparation of sodium ion battery.

[0077] According to the mass ratio of 80% : 10% : 10%, 80 mg of hard carbon material, 10 mg of acetylene black, and 10 mg of PVDF were weighed, and an appropriate amount of deionized water was added dropwise. Stir for 20 min to form a uniform slurry. A 100 μm doctor blade was used to uniformly coat the slurry on a copper (Cu) foil. The coated Cu foil was placed in a forced air drying oven and dried for 12 h. The Cu foil with active material was cut into a circular electrode sheet and reserved for use.

[0078] The assembly of the button cell was carried out in an Ar-filled glove box. The prepared electrode sheet was used as the negative electrode, the commercial electrolyte 1.0 M NaPF6 in DME = 100 Vol% was used as the electrolyte, and the Na metal sheet was used as the counter electrode to assemble a 2032 button cell.

[0079] The assembled button cell had a first coulombic efficiency of 76.0% and a first charge specific capacity of 330.1 mAh / g at a current density of 20 mA / g.

[0080] Example 3

[0081] A short-range graphite and closed-pore collaborative hard carbon negative electrode material and a preparation method thereof, the preparation method comprising the following steps:

[0082] Step 1, 500 g of bean dregs was weighed and washed with appropriate amount of distilled water, then placed in a forced air drying oven, the drying temperature was 80℃, and the drying time was 12 h, for removing impurities and moisture;

[0083] Step 2, 10 g of dried bean dregs was placed in a tube furnace, and heated to 450℃ at a heating rate of 5℃ / min under argon or nitrogen atmosphere, and the holding time was 2 h, then cooled to room temperature and taken out to obtain pre-carbonized material I for washing;

[0084] Step 3, the pre-carbonized material I obtained in step 2 was placed in 1 mol / L hydrochloric acid solution for washing treatment, the washing time was 6 h, and then washed with deionized water until the washing liquid was neutral; then placed in a forced air drying oven at 60℃ for 12 h to obtain pure pre-carbonized material II;

[0085] Step 4, the pure pre-carbonized material II obtained in step 3 was placed in a high-temperature tube furnace, and first heated to 900℃ at a heating rate of 5℃ / min under hydrogen atmosphere, and then heated to 1600℃ at a heating rate of 2℃ / min, the holding time was 2 h, then cooled to room temperature and taken out to prepare a short-range graphite-like and closed-pore cooperative hard carbon negative electrode material;

[0086] The short-range graphite-like and closed-pore cooperative hard carbon material prepared above was used as the active material of the battery negative electrode material for the preparation of sodium ion battery, and the specific method was the same as that of Example 2.

[0087] Figure 6 The HRTEM image of the hard carbon negative electrode material prepared in Example 3; as can be seen from the figure, the length of the graphite-like microcrystalline structure obviously increases, and the degree of graphitization increases; at the same time, the closed-pore structure is obviously reduced, which is not conducive to sodium storage.

[0088] Example 4

[0089] A short-range graphite-like and closed-pore cooperative hard carbon negative electrode material and a preparation method thereof, the preparation method comprising the following steps:

[0090] Step 1, 500 g of bean dregs was weighed and washed with appropriate amount of distilled water, then placed in a forced air drying oven, the drying temperature was 80℃, and the drying time was 12 h, for removing impurities and moisture;

[0091] Step 2, 10 g of dried bean dregs was placed in a tube furnace, and heated to 650℃ at a heating rate of 5℃ / min under argon or nitrogen atmosphere, and the holding time was 2 h, then cooled to room temperature and taken out to obtain pre-carbonized material I for washing;

[0092] Step 3, the pre-carbonization material obtained in step 2 is placed in a 1 mol / L hydrochloric acid solution for washing treatment, the washing time is 6 h, and then the pre-carbonization material is washed with deionized water until the washing liquid is neutral; then the pre-carbonization material is placed in a blast drying oven for drying at 60 ℃ for 12 h, to obtain a relatively pure pre-carbonization material two;

[0093] Step 4, the pure pre-carbonization material two obtained in step 3 is placed in a high-temperature tube furnace, and first heated to 900 ℃ at a heating rate of 5 ℃ / min under a hydrogen atmosphere, and then heated to 1400 ℃ at a heating rate of 2 ℃ / min, the holding time is 2 h, and then the short-range graphite and closed pore collaborative hard carbon negative electrode material is prepared after cooling to room temperature.

[0094] Step 5, the short-range graphite and closed pore collaborative hard carbon material prepared above is used as an active substance of a battery negative electrode material for the preparation of a sodium ion battery, and the specific method is the same as that in Example 2.

[0095] Example 5

[0096] A short-range graphite and closed pore collaborative hard carbon negative electrode material and a preparation method thereof, the preparation method comprising the following steps:

[0097] Step 1, 500 g of bean dregs is washed with an appropriate amount of distilled water and then placed in a blast drying oven, the drying temperature is 80 ℃, and the drying time is 12 h, to remove impurities and water;

[0098] Step 2, 10 g of the dried bean dregs is placed in a tube furnace, and heated to 850 ℃ at a heating rate of 5 ℃ / min under an argon or nitrogen atmosphere, the holding time is 2 h, and then the pre-carbonization material one is obtained after cooling to room temperature, and then washed;

[0099] Step 3, the pre-carbonization material one obtained in step 2 is placed in a 1 mol / L hydrochloric acid solution for washing treatment, the washing time is 6 h, and then the pre-carbonization material is washed with deionized water until the washing liquid is neutral; then the pre-carbonization material is placed in a blast drying oven for drying at 60 ℃ for 12 h, to obtain a relatively pure pre-carbonization material two;

[0100] Step 4, the pure pre-carbonization material two obtained in step 3 is placed in a high-temperature tube furnace, and first heated to 900 ℃ at a heating rate of 5 ℃ / min under a hydrogen atmosphere, and then heated to 1400 ℃ at a heating rate of 2 ℃ / min, the holding time is 2 h, and then the short-range graphite and closed pore collaborative hard carbon negative electrode material is prepared after cooling to room temperature.

[0101] The short-range graphite and closed pore collaborative hard carbon material prepared above is used as an active substance of a battery negative electrode material for the preparation of a sodium ion battery, and the specific method is the same as that in Example 2.

[0102] Example 6

[0103] A short-range graphite-like and closed-pore synergistic hard carbon negative electrode material and a preparation method thereof, the preparation method comprising the following steps:

[0104] Step 1, 500 g of bean dregs was weighed and washed with appropriate amount of distilled water, and then placed in a forced air drying oven, the drying temperature was 80 DEG C, and the drying time was 12 h, for removing impurities and moisture;

[0105] Step 2, 10 g of the dried bean dregs was taken and placed in a tube furnace, and heated to 900 DEG C at a heating rate of 5 DEG C / min under argon or nitrogen atmosphere, the holding time was 2 h, and then cooled to room temperature and taken out to obtain pre-carbonized material one, which was washed;

[0106] Step 3, the pre-carbonized material one obtained in step 2 was placed in 1 mol / L hydrochloric acid solution for washing treatment, the washing time was 6 h, and then washed with deionized water until the washing liquid was neutral; and then placed in a forced air drying oven and dried at 60 DEG C for 12 h to obtain relatively pure pre-carbonized material two;

[0107] Step 4, the pure pre-carbonized material two obtained in step 3 was placed in a high-temperature tube furnace, and first heated to 900 DEG C at a heating rate of 5 DEG C / min under hydrogen atmosphere, and then heated to 1000 DEG C at a heating rate of 2 DEG C / min, the holding time was 2 h, and then cooled to room temperature and taken out to obtain the short-range graphite-like and closed-pore synergistic hard carbon negative electrode material;

[0108] The short-range graphite-like and closed-pore synergistic hard carbon material prepared above was used as an active substance of a battery negative electrode material for the preparation of a sodium ion battery, and the specific method was the same as that of Example 2.

[0109] Figure 7 The HRTEM diagram of the hard carbon negative electrode material prepared in Example 6; it can be seen from the diagram that the obvious reduction of the graphite-like microcrystalline structure can be obviously seen, the degree of graphitization is reduced, resulting in lower conductivity; at the same time, the open pores cannot be closed to form closed pore structure, thereby resulting in the reduction of sodium storage capacity.

[0110] The performance of the battery assembled by the material obtained in the above examples and comparative examples was tested, and the results are shown in Table 1.

[0111] Table 1 Related performance parameters of the assembled half battery

[0112]

[0113] From the above examples and comparative examples, it can be seen that in Example 1, the bean dregs are carbonized at high temperature, and the reversible specific capacity of the material can reach 335.2 mAh / g and the first coulombic efficiency can reach 88.1%. In Comparative Example 2, the bean dregs are not pre-carbonized, resulting in a high content of surface defects of the material after high-temperature carbonization. The long graphite layer hinders the formation of closed pores, and the effective closed pores are not formed, thereby affecting the first coulombic efficiency and the specific capacity. In Example 2, compared with Example 1, only the binder is replaced by PVDF, and the first efficiency of the obtained hard carbon material is reduced, and the specific capacity changes unobviously. Further increasing the pre-carbonization treatment temperature, in Example 6 of the present application, since the pre-carbonization treatment temperature is not controlled in the optimal range, which leads to the growth of the carbon layer being too long, which will hinder the formation of closed pores, and the first coulombic efficiency is about 70%, and the reversible specific capacity is only 251.8 mAh / g.

[0114] In summary, the preparation method proposed in the present application relies on the matching of the component ratio and each process step. It is this synergistic effect that endows the biomass-based hard carbon material with excellent electrochemical properties. If any condition deviates from the range specified in the present application, the performance of the hard carbon material may be reduced.

[0115] The above description shows the basic principles, main features and advantages of the present application. It should be understood by those skilled in the art that the present application is not limited by the above examples, and the above examples and descriptions in the specification are only the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection required by the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a short-range graphitic and closed-pore synergistic hard carbon negative electrode material, characterized by, Comprising the following steps: (1) After washing the bean dregs with distilled water, dry them in a forced air drying oven; (2) Place the dried bean dregs in a tube furnace and pre-carbonize them under an argon or nitrogen atmosphere to obtain pre-carbonized material one; (3) Wash the pre-carbonized material one obtained in step (2) with dilute hydrochloric acid and deionized water until the washing liquid is neutral to obtain pre-carbonized material two; (4) Place the pre-carbonized material two obtained in step (3) in a high-temperature furnace and perform high-temperature carbonization under a hydrogen-containing reducing atmosphere to obtain a hard carbon negative electrode material rich in short-range graphite and closed pores; The pre-carbonization temperature in step (2) is 700-750 ℃, and the pre-carbonization time is 2 h; The high-temperature carbonization protective gas in step (4) is hydrogen; The high-temperature carbonization temperature in step (4) is 1000-1600 ℃, the heating rate is 2-10 ℃ / min, and the holding time is 2 h.

2. The preparation method of the short-range graphite-like and closed-pore synergistic hard carbon negative electrode material according to claim 1, characterized in that, The bean dregs drying temperature in step (1) is 80 ℃, and the drying time is 12 h.

3. The preparation method of the short-range graphite-like and closed-pore synergistic hard carbon negative electrode material according to claim 1, characterized in that, The pre-carbonization heating rate in step (2) is 2-10 ℃ / min.

4. The preparation method of the short-range graphite-like and closed-pore synergistic hard carbon negative electrode material according to claim 1, characterized in that, The dilute hydrochloric acid concentration in step (3) is 1-2 mol / L, and the acid pickling time is 6 h.

5. The preparation method of the short-range graphite-like and closed-pore synergistic hard carbon negative electrode material according to claim 1, characterized in that, The deionized water washing process in step (3) is repeated filtration washing with deionized water, and the washing number is 3-10 times.

6. The preparation method of the short-range graphite-like and closed-pore synergistic hard carbon negative electrode material according to claim 1, characterized in that, The high-temperature carbonization temperature in step (4) is 1350-1400 ℃, and the time is 2 h.

7. A short-range graphite and closed pore coordinated hard carbon negative electrode material prepared by the preparation method of any one of claims 1-6.

8. The application of the short-range graphite and closed pore coordinated hard carbon negative electrode material of claim 7 in sodium ion battery negative electrode materials.

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