A biomass hard carbon material and its preparation method and application

Abstract

The present application belongs to the technical field of sodium ion batteries, and specifically relates to a biomass hard carbon material, a preparation method thereof, and an application thereof. The preparation method of the biomass hard carbon material comprises the following steps: sintering a biomass raw material to obtain a sintered material, and then ball-milling the sintered material to obtain a ball-milled product; adding an acid washing solution to the ball-milled product, heating and stirring, washing, immersing the material obtained after washing in an alkaline washing solution, stirring at room temperature, washing, and obtaining a washed product; adding a chelating agent to the washed product, heating and stirring, filtering, washing, and drying to obtain a chelated product; wet-mixing the chelated product with a modified material, drying, and sintering to obtain a biomass hard carbon material. The biomass hard carbon material obtained by the preparation method of the present application has a low impurity content and a low porosity, and can realize the normalization of components of biomass materials from different batches, thereby improving the electrochemical properties of the biomass hard carbon material.

Description

Technical Field

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

[0002] Due to the rapid development of clean energy, the demand for large-scale, efficient and inexpensive energy storage systems is growing. Lithium-ion batteries have the characteristics of high energy density and long cycle life and have been widely used in portable electronic products and electric vehicle markets. However, the limited and uneven geographical distribution of lithium resources restricts its application in large-scale energy storage. Sodium-ion batteries (SIBs) as a potential alternative have attracted widespread attention due to their abundant resources and similar working mechanism to lithium-ion batteries. However, the atomic diameter of sodium ions is larger than that of lithium ions, and they cannot form binary intercalated graphite in carbonate electrolyte systems, so it is not easy to form intercalated graphite in SIBs. Therefore, it is necessary to explore other low-cost, larger interlayer spacing anode materials.

[0003] Biomass hard carbon has attracted great attention in SIBs due to its low cost, wide availability, environmental friendliness, and highly disordered structure. It also has unique structures such as mesopores and multipores, which can easily accommodate sodium ions, resulting in a higher sodium storage capacity. These advantages have made hard carbon a promising material for SIBs. However, due to factors such as the growth environment, biomass hard carbon itself contains a large amount of impurity elements such as sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), and silicon (Si). Furthermore, the content of these impurity elements varies due to factors such as regional environment and individual differences. These differences lead to different structures, components, and electrochemical properties of biomass hard carbon produced from different batches, making the industrial application of biomass hard carbon materials difficult. Therefore, measures need to be taken to normalize the composition of biomass hard carbon. To date, there are few reports that consider the differences in the composition of biomass hard carbon from different batches. Summary of the Invention

[0004] The present application aims to provide a biomass hard carbon material and its preparation method and application. The biomass hard carbon material prepared by the preparation method of the present application contains fewer impurities and can achieve excellent electrochemical performance.

[0005] In order to achieve the above objectives, the present application adopts the following technical solution: a method for preparing a biomass hard carbon material, comprising the following steps:

[0006] The biomass raw material is sintered to obtain a sintered material, and then the sintered material is ball-milled to obtain a ball-milled product;

[0007] Adding an acid washing solution to the ball milled product, heating and stirring, washing, immersing the washed material in an alkaline washing solution, stirring at room temperature, washing, and obtaining a washed product;

[0008] Adding a chelating agent to the washed product, heating and stirring, filtering, washing, and drying to obtain a chelated product;

[0009] The chelated product is wet-mixed with the modified material, dried, and sintered to obtain the biomass hard carbon material.

[0010] As a preferred embodiment of the method for preparing the biomass hard carbon material described in the present application, the biomass raw material includes at least one of coconut shell, lychee wood, bamboo chips, cotton, and rice husk.

[0011] As a preferred embodiment of the method for preparing the biomass hard carbon material described in the present application, the mass ratio of the chelating product to the modified material is (1-5):1.

[0012] As a preferred embodiment of the method for preparing the biomass hard carbon material described in the present application, the modified material includes at least one of phenolic resin and soluble starch.

[0013] As a preferred embodiment of the method for preparing the biomass hard carbon material described herein, the pickling solution has a pH < 7 and a concentration of 0.5 to 3 mol / L. More preferably, the pickling solution comprises at least one of sulfuric acid, hydrochloric acid, phosphoric acid, and nitric acid.

[0014] As a preferred embodiment of the method for preparing the biomass hard carbon material described herein, the alkaline washing solution is a solution with a pH greater than 7 and a concentration of 2 to 5 mol / L. More preferably, the alkaline washing solution comprises at least one of potassium hydroxide and sodium hydroxide.

[0015] As a preferred embodiment of the method for preparing the biomass hard carbon material described in the present application, the mass ratio of the chelating agent to the washing product is 1:(5-40).

[0016] As a preferred embodiment of the method for preparing the biomass hard carbon material described in the present application, the chelating agent is at least one of ethylenediaminetetraacetic acid (EDTA) and disodium ethylenediaminetetraacetic acid solution (EDTA-2Na).

[0017] As a preferred embodiment of the method for preparing the biomass hard carbon material described in the present application, the concentration of the chelating agent is 0.02 to 0.1 mol / L.

[0018] As a preferred embodiment of the method for preparing the biomass hard carbon material described in the present application, the ball-milled product is heated and stirred after acid washing at a temperature of 60 to 90° C., a time of 2 to 5 hours, and a stirring speed of 300 to 600 rpm.

[0019] As a preferred embodiment of the method for preparing the biomass hard carbon material described in the present application, the stirring time at room temperature is 2 to 5 hours, and the stirring speed is 300 to 600 rpm.

[0020] As a preferred embodiment of the method for preparing biomass hard carbon materials described in the present application, the washing product is heated and stirred after adding the chelating agent at a temperature of 80 to 120° C., a processing time of 1 to 6 hours, and a stirring speed of 300 to 600 rpm.

[0021] As a preferred embodiment of the method for preparing the biomass hard carbon material described in the present application, the drying temperature is 80-90° C., and the drying time is 8 hours to 12 hours.

[0022] As a preferred embodiment of the method for preparing the biomass hard carbon material described in the present application, the washing conditions are all to use water as the solvent for washing until neutrality.

[0023] As a preferred embodiment of the preparation method of the biomass hard carbon material described in this application, the conditions for sintering the biomass raw material are as follows: under the protection of an inert atmosphere, the sintering temperature is 400-800°C, the heating rate is 5-10°C / min, and the sintering time is 4-8h; the inert atmosphere includes nitrogen, argon, etc.

[0024] As a preferred embodiment of the method for preparing the biomass hard carbon material described in the present application, the ball milling speed is 300 to 600 rpm, and the ball milling time is 1 to 3 hours.

[0025] As a preferred embodiment of the method for preparing the biomass hard carbon material described in the present application, the Dv50 particle size of the ball-milled product is 10 to 15 microns.

[0026] As a preferred embodiment of the method for preparing the biomass hard carbon material described in the present application, the wet mixing solvent includes at least one of anhydrous ethanol and deionized water.

[0027] As a preferred embodiment of the method for preparing the biomass hard carbon material described in the present application, the drying temperature is 60° C. to 80° C., and the drying time is 6 hours to 10 hours.

[0028] As a preferred embodiment of the preparation method of the biomass hard carbon material described in this application, the chelating product and the modified material are mixed and dried and then sintered under the protection of an inert atmosphere, with a sintering temperature of 1200-1600°C, a heating rate of 0.5-4°C / min, and a sintering time of 2-6h.

[0029] More preferably, the inert atmosphere includes nitrogen, argon, etc.

[0030] The present application also claims protection for a biomass hard carbon material produced by the preparation method.

[0031] This application also claims protection for a use of the biomass hard carbon material in the preparation of sodium ion batteries.

[0032] This application uses coconut shells and the like as biomass raw materials, taking into account the different types of impurities. First, because the biomass raw materials contain a large amount of organic carbon such as lignin, cellulose and hemicellulose, the unstable organic carbon can be converted into inorganic carbon through the process of high-temperature sintering. This process can promote the rearrangement of the structure and discharge most of the tar. Secondly, the impurities on the surface of the biomass material and the metal elements in the particles are removed by acid washing and alkali washing, and the residual metal elements, especially Na, K, Ca, Mg and other elements, are further removed through interaction with the chelating agent. The combined action of the three can remove most of the impurities. Finally, the carbon structure is repaired and closed by adding a modifying material and carbonizing it at high temperature, effectively reducing the porosity of the obtained biomass hard carbon material and obtaining a hard carbon material with excellent performance. The purpose of using hot acid washing in this application is to accelerate the reaction rate, and the reason for using normal temperature alkali washing is that the material after one sintering still retains the characteristics of cellulose. If hot alkali is used for washing, the reaction between cellulose and hot alkali will cause chain breaking and decomposition, thereby reducing the yield. The present application adopts the advantage of a specific order of acid washing, alkali washing, and then carbonization: in addition to removing some impurities, acid washing and alkali washing will also destroy the carbon structure, introduce oxygen-containing functional groups, increase porosity and defect level, and promote structural repair and pore closing after high-temperature carbonization, thereby reducing porosity. Conversely, if pore closing is performed first and then acid washing and alkali washing are performed, some impurities can be removed, but the structure will be destroyed again, thereby affecting performance.

[0033] Compared with the prior art, this application has the following beneficial effects:

[0034] (1) The present application adopts a treatment method of a specific sequence of sintering, impurity removal, and high-temperature carbonization to synergistically remove most of the impurity elements, reduce the porosity, and normalize the components of different batches of biomass materials, thereby improving the electrochemical properties of hard carbon.

[0035] (2) The biomass hard carbon material preparation method used in this application can be used to normalize various batches of biomass materials and has a wide range of applicability. In addition, normalization has practical significance for improving the electrochemical performance of hard carbon and is expected to be used in industrialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is the SEM image of the biomass hard carbon material prepared in Example 2 of this application. DETAILED DESCRIPTION

[0037] The following will be combined with the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments of the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0038] In the Examples and Comparative Examples, the experimental methods used are conventional methods unless otherwise specified, and the materials and reagents used are all commercially available unless otherwise specified.

[0039] Example 1: Biomass hard carbon material and preparation method thereof

[0040] The litchi wood was placed in a box-type furnace and heat treated for 8 hours at a temperature of 400°C and a heating rate of 5°C / min under N2 atmosphere to obtain a sintered material. The sintered material was then ball-milled at a speed of 300 rpm for 3 hours to obtain a ball-milled product with a Dv50 particle size of 10 to 15 microns.

[0041] The ball milled product was immersed in a 0.5 mol / L H2SO4 solution, heated and stirred, the speed was adjusted to 300 rpm, the heating temperature was set to 90 ° C, and heated and stirred for 5 hours. After the process was completed, it was washed with water and filtered until the pH of the filtrate reached 7 and then the filtration was terminated. The obtained material was immersed in a 2 mol / LKOH solution, stirred at room temperature, the speed was adjusted to 300 rpm, and stirred for 5 hours. After the process was completed, it was washed with water and filtered until the pH of the filtrate reached 7 and then the filtration was terminated to obtain a washed product;

[0042] 0.02 mol / L EDTA-2Na solution was added to the washed product, and the mixture was heated and stirred at a speed of 300 rpm and a heating temperature of 80°C for 6 h. The product was then washed with water and filtered until the pH of the filtrate reached 7. The product was then placed in an 80°C oven and dried for 12 h to obtain a chelated product. The mass ratio of the EDTA-2Na solution to the washed product was 1:5.

[0043] The chelating product was dispersed in a phenolic resin ethanol solution (the mass ratio of the chelating product to the phenolic resin was 5:1), heated and stirred until the ethanol was evaporated, and then the mixed materials were placed in a high-temperature furnace and sintered together under the protection of a N2 atmosphere. The treatment temperature was 1200°C, the heating rate was 0.5°C / min, and the carbonization was carried out for 6 hours to obtain a biomass hard carbon material.

[0044] Example 2: Biomass hard carbon material and preparation method thereof

[0045] The coconut shell was placed in a box furnace and heat treated for 6 hours at a temperature of 600°C and a heating rate of 5°C / min under N2 atmosphere to obtain a sintered material. The sintered material was then ball-milled at a speed of 520 rpm for 1 hour to obtain a ball-milled product with a Dv50 particle size of 10 to 15 microns.

[0046] The ball milled product was immersed in a 0.5 mol / L H2SO4 solution, heated and stirred, the speed was adjusted to 500 rpm, the heating temperature was set to 80 ° C, and heated and stirred for 3 hours. After the process was completed, it was washed with water and filtered until the pH of the filtrate reached 7 and then the filtration was terminated. The obtained material was immersed in a 3 mol / L KOH solution, stirred at room temperature, the speed was adjusted to 500 rpm, and stirred for 4 hours. After the process was completed, it was washed with water and filtered until the pH of the filtrate reached 7 and then the filtration was terminated to obtain a washed product;

[0047] 0.04 mol / L EDTA-2Na solution was added to the washed product, and the mixture was heated and stirred at a speed of 500 rpm and a heating temperature of 110°C for 2 h. The washed product was then washed and filtered until the pH of the filtrate reached 7. The product was then placed in an 80°C oven and dried for 8 h to obtain a chelated product. The mass ratio of the EDTA-2Na solution to the washed product was 1:20.

[0048] The chelated product was dispersed in a phenolic resin ethanol solution (the mass ratio of the chelated product to the phenolic resin was 3:1), heated and stirred until the ethanol was evaporated, and then the mixed materials were placed in a high-temperature furnace and sintered together under the protection of a N2 atmosphere. The treatment temperature was 1500°C, the heating rate was 1°C / min, and the carbonization was carried out for 4 hours to obtain a biomass hard carbon material.

[0049] Example 3: Biomass hard carbon material and preparation method thereof

[0050] Bamboo chips were placed in a box furnace and heat treated for 4 hours at a temperature of 600°C and a heating rate of 5°C / min under N2 atmosphere to obtain a sintered material. The sintered material was then ball-milled at a speed of 600 rpm for 1 hour to obtain a ball-milled product with a Dv50 particle size of 10 to 15 μm.

[0051] The ball milled product was immersed in a 3 mol / L H2SO4 solution, heated and stirred, the speed was adjusted to 600 rpm, the heating temperature was set to 60 ° C, and heated and stirred for 2 h. After the process was completed, it was washed with water and filtered until the pH of the filtrate reached 7 and then the filtration was terminated. The obtained material was immersed in a 5 mol / L KOH solution, stirred at room temperature, the speed was adjusted to 600 rpm, and stirred for 2 h. After the process was completed, it was washed with water and filtered until the pH of the filtrate reached 7 and then the filtration was terminated to obtain a washed product;

[0052] 0.1 mol / L EDTA solution was added to the washed product, and the mixture was heated and stirred at a speed of 600 rpm and a heating temperature of 120°C for 1 hour. The mixture was then washed and filtered until the pH of the filtrate reached 7. The mixture was then dried in an oven at 80°C for 8 hours to obtain a chelated product. The mass ratio of the EDTA solution to the washed product was 1:40.

[0053] The chelating product was dispersed in a phenolic resin ethanol solution (the mass ratio of the chelating product to the phenolic resin was 1:1), heated and stirred until the ethanol was evaporated, and then the mixed materials were placed in a high-temperature furnace and sintered together under the protection of a N2 atmosphere. The treatment temperature was 1600°C, the heating rate was 4°C / min, and the carbonization was carried out for 2 hours to obtain a biomass hard carbon material.

[0054] Example 4: Biomass hard carbon material and preparation method thereof

[0055] The coconut shell was placed in a box furnace and heat treated for 6 hours at a temperature of 600°C and a heating rate of 5°C / min under N2 atmosphere to obtain a sintered material. The sintered material was then ball-milled at a speed of 520 rpm for 1 hour to obtain a ball-milled product with a Dv50 particle size of 12 μm.

[0056] The ball milled product was immersed in a 0.5 mol / L H2SO4 solution, heated and stirred, the speed was adjusted to 500 rpm, the heating temperature was set to 80 ° C, and heated and stirred for 3 hours. After the process was completed, it was washed with water and filtered until the pH of the filtrate reached 7 and then the filtration was terminated. The obtained material was immersed in a 3 mol / L KOH solution, stirred at room temperature, the speed was adjusted to 500 rpm, and stirred for 5 hours. After the process was completed, it was washed with water and filtered until the pH of the filtrate reached 7 and then the filtration was terminated to obtain a washed product;

[0057] 0.06 mol / L EDTA-2Na solution was added to the washed product, and the mixture was heated and stirred at a speed of 500 rpm and a heating temperature of 110°C for 2 h. The washed product was then washed and filtered until the pH of the filtrate reached 7. The filtrate was then dried in an oven at 80°C for 8 h to obtain a chelated product. The mass ratio of the EDTA-2Na solution to the washed product was 1:20.

[0058] The chelated product was dispersed in a phenolic resin ethanol solution (the mass ratio of the chelated product to the phenolic resin was 3:1), heated and stirred until the ethanol was evaporated, and then the mixed materials were placed in a high-temperature furnace and sintered together under the protection of a N2 atmosphere. The treatment temperature was 1500°C, the heating rate was 1°C / min, and the carbonization was carried out for 4 hours to obtain a biomass hard carbon material.

[0059] Example 5: Biomass hard carbon material and preparation method thereof

[0060] The coconut shell was placed in a box furnace and heat treated for 6 hours at a temperature of 600°C and a heating rate of 5°C / min under N2 atmosphere to obtain a sintered material. The sintered material was then ball-milled at a speed of 520 rpm for 1 hour to obtain a ball-milled product with a Dv50 particle size of 12 μm.

[0061] The ball milled product was immersed in a 0.5 mol / L H2SO4 solution, heated and stirred, the speed was adjusted to 500 rpm, the heating temperature was set to 80 ° C, and heated and stirred for 3 hours. After the process was completed, it was washed with water and filtered until the pH of the filtrate reached 7 and then the filtration was terminated. The obtained material was immersed in a 3 mol / L KOH solution, stirred at room temperature, the speed was adjusted to 500 rpm, and stirred for 5 hours. After the process was completed, it was washed with water and filtered until the pH of the filtrate reached 7 and then the filtration was terminated to obtain a washed product;

[0062] 0.08 mol / L EDTA-2Na solution was added to the washed product, and the mixture was heated and stirred at a speed of 500 rpm and a heating temperature of 110°C for 2 h. The product was then washed with water and filtered until the pH of the filtrate reached 7. The product was then placed in an 80°C oven and dried for 8 h to obtain a chelated product. The mass ratio of the EDTA-2Na solution to the washed product was 1:20.

[0063] The chelated product was dispersed in a phenolic resin ethanol solution (the mass ratio of the chelated product to the phenolic resin was 3:1), heated and stirred until the ethanol was evaporated, and then the mixed materials were placed in a high-temperature furnace and sintered together under the protection of a N2 atmosphere. The treatment temperature was 1500°C, the heating rate was 1°C / min, and the carbonization was carried out for 4 hours to obtain a biomass hard carbon material.

[0064] Comparative Example 1

[0065] Compared with Example 2, the only difference of this comparative example is that no acid washing, alkali washing or chelating agent treatment is performed.

[0066] The preparation method is as in Example 2.

[0067] Comparative Example 2

[0068] Compared with Example 2, the only difference of this comparative example is that the concentration of the added EDTA-2Na solution is 0.01 mol / L.

[0069] The preparation method is as in Example 2.

[0070] Comparative Example 3

[0071] Compared with Example 2, the only difference of this comparative example is that no EDTA-2Na solution is added.

[0072] The preparation method is as in Example 2.

[0073] Comparative Example 4

[0074] Compared with Example 2, the only difference in this comparative example is that no pickling operation is performed.

[0075] Preparation method: Coconut shells were placed in a box furnace and heat treated for 6 hours at a temperature of 600°C and a heating rate of 5°C / min under N2 atmosphere to obtain a sintered material. The sintered material was then ball-milled at a speed of 520 rpm for 1 hour to obtain a ball-milled product with a Dv50 particle size of 10 to 15 microns.

[0076] The ball-milled product was immersed in a 3 mol / L KOH solution, stirred at room temperature, the speed was adjusted to 500 rpm, and stirred for 4 h. After the process was completed, it was washed with water and filtered until the pH of the filtrate reached 7, and then the filtration was terminated to obtain a washed product;

[0077] 0.04 mol / L EDTA-2Na solution was added to the washed product, and the mixture was heated and stirred at a speed of 500 rpm and a heating temperature of 110°C for 2 h. The washed product was then washed and filtered until the pH of the filtrate reached 7. The filtrate was then dried in an oven at 80°C for 8 h to obtain a chelated product.

[0078] The chelated product was dispersed in a phenolic resin ethanol solution (the mass ratio of the chelated product to the phenolic resin was 3:1), heated and stirred until the ethanol was evaporated, and then the mixed materials were placed in a high-temperature furnace and sintered together under the protection of a N2 atmosphere. The treatment temperature was 1500°C, the heating rate was 1°C / min, and the carbonization was carried out for 4 hours to obtain a biomass hard carbon material.

[0079] Comparative Example 5

[0080] Compared with Example 2, the only difference of this comparative example is that no modifying material is added.

[0081] The preparation method is as in Example 2.

[0082] Comparative Example 6

[0083] Compared with Example 2, the only difference of this comparative example is that the mass ratio of the chelated product to the modified material is 6:1.

[0084] The preparation method is as in Example 2.

[0085] Comparative Example 7

[0086] Preparation method:

[0087] The coconut shell was placed in a box furnace and heat treated for 6 hours at a temperature of 600°C and a heating rate of 5°C / min under N2 atmosphere to obtain a sintered material. The sintered material was then ball-milled at a speed of 520 rpm for 1 hour to obtain a ball-milled product with a Dv50 particle size of 10 to 15 microns.

[0088] The ball-milled product was dispersed in a phenolic resin ethanol solution (the mass ratio of the ball-milled product to the phenolic resin was 3:1), heated and stirred until the ethanol was evaporated, and then the mixed materials were placed in a high-temperature furnace and co-sintered under N2 atmosphere at a treatment temperature of 1500°C and a heating rate of 1°C / min. Carbonization was performed for 4 hours to obtain a washed product 1;

[0089] The washed product 1 was immersed in a 0.5 mol / L H2SO4 solution, heated and stirred, the speed was adjusted to 500 rpm, the heating temperature was set to 80°C, and heated and stirred for 3 hours. After the process was completed, it was washed with water and filtered until the pH of the filtrate reached 7 and then the filtration was terminated. The obtained material was immersed in a 3 mol / LKOH solution, stirred at room temperature, the speed was adjusted to 500 rpm, and stirred for 4 hours. After the process was completed, it was washed with water and filtered until the pH of the filtrate reached 7 and then the filtration was terminated to obtain a chelated product 1;

[0090] 0.04 mol / L EDTA-2Na solution was added to the chelated product 1, and the mixture was heated and stirred at a rotation speed of 500 rpm and a heating temperature of 110°C for 2 hours. The mixture was then washed with water and filtered until the pH of the filtrate reached 7, and the filtration was terminated. The mixture was placed in an 80°C oven and dried for 8 hours to obtain a biomass hard carbon material. The mass ratio of the EDTA-2Na solution to the chelated product 1 was 1:20.

[0091] Compared with Example 2, the only difference of this comparative example is that the ball-milled product after high-temperature sintering is first treated with a modified substance and then subjected to acid washing and alkali washing steps.

[0092] Test Example 1

[0093] 1. Determination of impurity content

[0094] The impurity content of the biomass hard carbon materials prepared in Examples 1-5, Comparative Examples 1-5, and Comparative Example 7 was measured using an ICP-AES device. The experimental data are shown in Table 1. As can be seen from Table 1, the impurity content of the products prepared in the Examples is significantly lower than that in Comparative Examples 1-4, especially in Example 2.

[0095] Table 1 Impurity content of each sample

[0096]

[0097]

[0098] 2. Electrochemical performance test

[0099] The electrochemical performance of the biomass hard carbon materials prepared in Examples 1 to 5 and Comparative Examples 1 to 7 was tested using a blue electric test system and other equipment. The experimental results are shown in Table 2.

[0100] Table 2 Electrochemical performance data of each sample

[0101]

[0102] From the data in Table 2, it can be seen that the biomass hard carbon materials prepared in Examples 1 to 5 of the present application have good electrochemical properties, and the first charge and discharge efficiency can reach up to 88.5%.

[0103] In Comparative Example 1, only high-temperature sintering treatment was performed, and the electrochemical properties of the obtained biomass hard carbon material were poor; in Comparative Examples 2 to 3, the concentration of the chelating agent added was too low or no chelating agent was added, and the electrochemical properties of the obtained hard carbon material were worse than those of the embodiment; in Comparative Example 4, no acid washing operation was performed, and the first charge specific capacity and the first discharge specific capacity of the obtained biomass hard carbon material were both lower than those of the embodiment; in Comparative Example 5, no modifying material was added, and the mass ratio of the chelating product to the modifying material in Comparative Example 6 was not appropriate, and the electrochemical properties of the obtained hard carbon material were worse than those of the embodiment; in Comparative Example 7, the order of acid washing, alkali washing and modifying material treatment was different, resulting in the obtained biomass hard carbon material having poor electrochemical properties.

[0104] The above experiments show that the interaction between the various steps in the preparation method of the biomass hard carbon material of the present application can effectively remove the impurity content in the prepared biomass hard carbon material, reduce the porosity, and achieve normalization of the components of different batches of biomass materials, thereby improving the electrochemical properties of the hard carbon material.

[0105] The above embodiments are merely illustrative of the principles and effects of this application and are not intended to limit this application. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of this application. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical concepts disclosed in this application shall be covered by the claims of this application.

Claims

1. A method for preparing a biomass hard carbon material, characterized in that: The following steps are involved: The biomass raw material is sintered to obtain a sintered material, and then the sintered material is ball-milled to obtain a ball-milled product; Adding an acid washing solution to the ball milled product, heating and stirring, washing, immersing the washed material in an alkaline washing solution, stirring at room temperature, washing, and obtaining a washed product; Adding a chelating agent to the washed product, heating and stirring, filtering, washing, and drying to obtain a chelated product; The mass ratio of the chelating agent to the washing product is 1:(5~40); the chelating agent is at least one of ethylenediaminetetraacetic acid and disodium ethylenediaminetetraacetic acid solution; the concentration of the chelating agent is 0.02~0.1mol / L; the chelating product and the modified material are wet-mixed, dried, and sintered to obtain a biomass hard carbon material; the mass ratio of the chelating product to the modified material is (1~5):1; the modified material includes at least one of phenolic resin and soluble starch.

2. The preparation method according to claim 1, wherein The biomass raw material includes at least one of coconut shells, lychee wood, bamboo scraps, cotton, and rice husks.

3. The preparation method according to claim 1, wherein At least one of the following (1) to (2): (1) The pickling solution is a solution with a pH value less than 7, and the concentration of the pickling solution is 0.5 to 3 mol / L; (2) The alkaline washing solution is a solution with a pH value greater than 7, and the concentration of the alkaline washing solution is 2 to 5 mol / L.

4. The preparation method according to claim 3, wherein At least one of the following (1) to (2): (1) The pickling solution includes at least one of sulfuric acid, hydrochloric acid, phosphoric acid, and nitric acid; (2) The alkaline washing solution includes at least one of potassium hydroxide and sodium hydroxide.

5. The preparation method according to claim 1, wherein At least one of the following (1) to (2): (1) After acid washing, the ball-milled product is heated and stirred at a temperature of 60 to 90° C. for 2 to 5 hours at a stirring speed of 300 to 600 rpm; (2) The stirring time at room temperature is 2 to 5 hours, and the stirring speed is 300 to 600 rpm.

6. The preparation method according to claim 1, wherein At least one of the following (1) to (3): (1) After adding the chelating agent to the washed product, the temperature of the heated stirring is 80-120° C., the treatment time is 1-6 hours, and the stirring speed is 300-600 rpm; (2) The drying temperature is 80-90° C. and the drying time is 8-12 hours; (3) The washing conditions are all to use water as the solvent to wash until neutral.

7. The preparation method according to claim 1, wherein At least one of the following (1) to (3): (1) The biomass raw material is sintered under an inert atmosphere at a temperature of 400 to 800° C., a heating rate of 5 to 10° C. / min, and a sintering time of 4 to 8 hours; (2) The ball milling speed is 300-600 rpm, and the ball milling time is 1-3 hours; (3) The Dv50 particle size of the ball milled product is 10 to 15 microns.

8. The preparation method according to claim 1, wherein At least one of the following (1) to (3): (1) The wet mixing solvent includes at least one of anhydrous ethanol and deionized water; (2) The drying temperature is 60°C to 80°C and the drying time is 6 hours to 10 hours; (3) The chelating product and the modified material are mixed and dried and then sintered under the protection of an inert atmosphere at a sintering temperature of 1200 to 1600° C., a heating rate of 0.5 to 4° C. / min, and a sintering time of 2 to 6 hours.

9. A biomass hard carbon material obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the biomass hard carbon material according to claim 9 in preparing sodium ion batteries.

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