Anthracite-based carbon negative electrode material and preparation method thereof

Abstract

The invention discloses an anthracite-based carbon negative electrode material and a preparation method thereof.The method comprises the steps that anthracite and sodium nitrate are mixed and then subjected to ball milling treatment, then phosphoric acid is added into the ball-milled mixture for reflux treatment, the mixture is washed till the pH value is 3, and phosphorus-doped anthracite is obtained; and carrying out carbonization treatment on the phosphorus-doped anthracite in an inert atmosphere to prepare the anthracite-based carbon negative electrode material. The preparation method effectively solves the technical problems of low specific capacity and low initial coulombic efficiency when a coal-based carbon material is used as a sodium-ion battery negative electrode material in the prior art through mutual cooperation of the steps of raw material selection and pretreatment, phosphoric acid doping modification and carbonization treatment.

Description

Technical Field

[0001] The invention belongs to the technical field of negative electrode materials for sodium ion batteries and relates to an anthracite-based carbon negative electrode material and a preparation method thereof. Background Art

[0002] As a new type of energy storage device, sodium-ion batteries have received extensive attention and research. Compared with traditional lithium-ion batteries, sodium-ion batteries have many advantages, such as abundant sodium resources, low cost, high specific capacity and safety. The negative electrode materials of sodium-ion batteries mainly include metal compounds, alloy materials, carbon materials, etc. Among them, carbon materials have become the mainstream choice due to their rich variety, low price, high conductivity, and stable structure. Carbon materials have a wide range of raw materials, such as coal, graphite, coal tar, biomass, etc., which can be used to produce carbon materials. In addition, coal has become a high-quality carbon precursor because of its high carbon content, low cost, high carbon yield, and wide use in industry.

[0003] Among them, anthracite material is a carbon material with fewer defects and relatively high crystallinity, but the narrow interlayer space hinders the deintercalation of sodium ions, and the availability of active sites is limited, and the sodium ion storage capacity is generally low. Li Yunming et al. prepared an anthracite sodium anode by a one-step carbonization method, which has a specific capacity of 222mAh / g at a current density of 30mA / g and a first coulombic efficiency of 81% ("Advanced sodium-ion batteries using superior low costpyrolyzed anthracite anode: towards practical applications", Li Yunming, Hu Yongsheng, etc., Energy Storage Materials, Vol. 5, pp. 191-197, October 2016). This study proves the potential of anthracite, but coal-based carbon-carbon materials still have the problems of low specific capacity and unsatisfactory first coulombic efficiency, which limits their application in the field of high energy density batteries. Anthracite as a negative electrode material for sodium ion batteries needs to further improve its sodium storage capacity. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention provides an anthracite-based carbon negative electrode material and a preparation method thereof, thereby solving the technical problems in the prior art of low specific capacity and low first coulombic efficiency when the coal-based carbon-carbon material is used as the negative electrode material of the sodium ion battery.

[0005] The present invention is achieved through the following technical solutions: A method for preparing anthracite-based carbon negative electrode material comprises the following steps: S1: mixing anthracite and sodium nitrate, and then ball-milling the mixture. Then, phosphoric acid is added to the mixture after the ball milling, and the mixture is refluxed, and then washed to a pH value of 3 to obtain phosphorus-doped anthracite. S2: Carbonizing the phosphorus-doped anthracite in an inert atmosphere to obtain the anthracite-based carbon negative electrode material.

[0006] Preferably, the mass ratio of anthracite to sodium nitrate is 1:(3-5).

[0007] Preferably, during the ball milling process, the rotation speed is 500 rpm and the time is 2 to 3 hours.

[0008] Preferably, the ratio of the ball-milled mixture to phosphoric acid is 3 g: (10-20) mL.

[0009] Preferably, during the reflux treatment, the temperature is 100-120° C. and the time is 2-4 h.

[0010] Preferably, the carbonization treatment process is specifically as follows: firstly, the temperature is raised to 300-400°C, kept warm for 2-4 hours, and then the temperature is raised to 800-1200°C, kept warm for 2-3 hours.

[0011] Preferably, during the carbonization process, the heating rate is 2°C / min.

[0012] Preferably, after the carbonization treatment is completed, the temperature is lowered to 300°C at a cooling rate of 3°C / min, and then naturally cooled to room temperature to obtain the anthracite-based carbon negative electrode material.

[0013] An anthracite-based carbon negative electrode material is prepared by the above method.

[0014] A sodium ion battery comprises the above-mentioned anthracite-based carbon negative electrode material; the sodium ion battery has a specific capacity of 203.5~288.5mA h / g and a first coulombic efficiency of 31.5%~40.2%.

[0015] Compared with the prior art, the present invention has the following beneficial technical effects: The invention discloses a method for preparing an anthracite-based carbon negative electrode material. In the first aspect, the method first selects anthracite as a carbon source. Anthracite has a high fixed carbon content and a low ash content, and is an ideal raw material for preparing high-performance negative electrode materials. The anthracite has a relatively hard texture, micropores and a suitable microcrystalline interlayer spacing, which is conducive to the embedding and de-embedding of sodium ions without causing significant structural expansion. Secondly, the method adds sodium nitrate during the ball milling process. When the anthracite and sodium nitrate are mixed and rubbed, the sodium nitrate exhibits a certain degree of oxidation effect, which can effectively remove impurities in the coal, such as aluminum oxide and silicon dioxide. The presence of these impurities will affect the electrochemical properties of the negative electrode material. At the same time, the sodium nitrate can also destroy the macromolecular aromatic skeleton structure of the coal, reduce its cross-linking density, reduce the fatty side chain structure and the heterocyclic structure, and make the structure of the coal looser, which is conducive to subsequent processing and modification. Then, the ball mill is added with sodium nitrate. Phosphoric acid is added to the milled mixture for reflux treatment, which can introduce P atoms for doping modification. The introduction of P atoms can change the electronic structure and chemical properties of coal-based carbon materials, increase the active sites of the materials, improve the conductivity and ion mobility of the materials, and facilitate the rapid embedding and de-embedding of sodium ions. At the same time, P atom doping can also stabilize the structure of the material, reduce the volume expansion and contraction during the charge and discharge process, thereby improving the cycle stability of the material; finally, the phosphorus-doped anthracite is carbonized in an inert atmosphere to further change the structure and properties of the material. The carbonization treatment can improve the graphitization and disorder of the material, forming a structure with a large interlayer spacing and a high degree of amorphism. The structure with a large interlayer spacing is conducive to the embedding and de-embedding of sodium ions, and improves the specific capacity of the material. At the same time, the structure with a high degree of amorphism can increase the active sites of the material and improve the reaction activity of the material. All of these are conducive to improving the electrochemical performance of the negative electrode material.

[0016] The anthracite-based carbon negative electrode material prepared by this method has the structural characteristics of large interlayer spacing and high amorphous degree, which is conducive to the embedding and de-embedding of sodium ions, thereby improving the specific capacity of the material. At the same time, the doping modification of P atoms increases the active sites of the material, further improving the specific capacity. The introduction of P atoms can stabilize the structure of the material, reduce the volume expansion and contraction during the initial charge and discharge process, thereby reducing the capacity loss during the initial charge and discharge process and improving the initial coulombic efficiency. In addition, the graphitized structure and amorphous structure formed by the carbonization treatment are also conducive to improving the conductivity and ion mobility of the material, further improving the initial coulombic efficiency. The preparation method effectively solves the technical problems of low specific capacity and low initial coulombic efficiency when coal-based carbon materials are used as negative electrode materials for sodium ion batteries in the prior art through the synergy of raw material selection and pretreatment, phosphoric acid doping modification and carbonization treatment steps.

[0017] Secondly, after the present invention uses phosphoric acid for reflux treatment, the pH value of the system is washed to 3. First, washing to a pH value of 3 helps to optimize the doping effect of P atoms. On the one hand, undoped phosphoric acid molecules can be removed by washing to avoid their negative impact on material properties; on the other hand, a pH value of 3 is conducive to the uniform distribution and stable existence of P atoms inside the material, thereby improving the doping efficiency; secondly, this process can firstly effectively remove impurities and contaminants, ensure the purity of the final product, and avoid their impact on the electrochemical properties of the negative electrode material. Thirdly, in the ball milling process of the present invention, the rotation speed is 500 rpm and the time is 2 to 3 hours. Firstly, under this condition, the ball milling medium can fully impact and grind the material, so that the anthracite particles can be effectively refined and their specific surface area can be increased, which is beneficial to the subsequent doping modification and carbonization treatment, and at the same time, impurities in the coal, such as alumina and silica, can be fully removed. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0019] Figure 1 XRD patterns of anthracite-based carbon negative electrode materials and raw material anthracite (WYM) prepared in Examples 1 to 4 of the present invention; Figure 2 This is the XPS spectrum of the anthracite-based carbon negative electrode material prepared in Example 2 of the present invention; Figure 3 The Raman graphs of the anthracite-based carbon negative electrode materials prepared in Examples 1 to 4 of the present invention; Figure 4 The first charge and discharge curve comparison diagram of the sodium ion battery assembled using the anthracite-based carbon negative electrode material prepared in Examples 1 to 4 of the present invention, wherein (a) is Example 1, (b) is Example 2, (c) is Example 3, and (d) is Example 4; Figure 5 The data diagram of the rate performance of the sodium ion battery assembled using the anthracite-based carbon negative electrode material prepared in Examples 1 to 4 of the present invention; Figure 6 It is a long cycle test curve diagram of the sodium ion battery assembled using the anthracite-based carbon negative electrode materials prepared in Examples 1, 2 and 4 of the present invention. DETAILED DESCRIPTION

[0020] In order to enable those skilled in the art to understand the characteristics and effects of the present invention, the following is a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used in the text are the common meanings understood by those skilled in the art for the present invention. In the event of a conflict, the definition in this specification shall prevail.

[0021] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0022] In this article, all features such as values, quantities, contents and concentrations defined in the form of numerical ranges or percentage ranges are for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to have included and specifically disclosed all possible secondary ranges and individual values ​​within the range (including integers and fractions).

[0023] In this document, unless otherwise specified, “includes,” “including,” “contains,” “has,” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0024] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0025] The present invention provides a method for preparing an anthracite-based carbon negative electrode material, comprising the following steps: S1: anthracite and sodium nitrate are mixed, ball-milled at 500 rpm for 2-3 hours, phosphoric acid is added to the ball-milled mixture, refluxed at 100-120° C. for 2-4 hours, and then washed with water until the pH value is 3 to obtain phosphorus-doped anthracite; The mass ratio of the anthracite to sodium nitrate is 1:(3-5).

[0026] The ratio of the ball-milled mixture to phosphoric acid is 3 g: (10-20) mL.

[0027] S2: Carbonizing the phosphorus-doped anthracite in an inert atmosphere to obtain the anthracite-based carbon negative electrode material.

[0028] The carbonization process is specifically as follows: first, the temperature is raised to 300-400°C at a heating rate of 2°C / min, and the temperature is kept for 2-4 hours, and then the temperature is raised to 800-1200°C at a heating rate of 2°C / min, and the temperature is kept for 2-3 hours. After the carbonization treatment is completed, the temperature is lowered to 300°C at a cooling rate of 3°C / min, and then naturally cooled to room temperature to obtain the anthracite-based carbon negative electrode material.

[0029] In addition, the present invention discloses an anthracite-based carbon negative electrode material prepared by the above method. In addition, the present invention also discloses a sodium ion battery, which contains the above-mentioned anthracite-based carbon negative electrode material. The specific preparation process is: the anthracite-based carbon negative electrode material, Ketjen black and polyvinylidene fluoride are mixed in a mass ratio of 8:1:1, ground in an N-methylpyrrolidone solution to obtain a slurry, and the slurry is coated on a copper foil and then dried to obtain a negative electrode sheet.

[0030] Then, in a glove box filled with argon, sodium metal was used as the counter electrode, the obtained negative electrode sheet was used as the working electrode, and NaClO with a concentration of 1 M was used. 4 The solution is the electrolyte for assembling sodium ion batteries. 4 The solvent of the solution is ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1. The specific capacity of the sodium ion battery is 203.5~288.5mA h / g, and the first coulombic efficiency is 31.5%~40.2%.

[0031] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0032] The following examples use conventional instruments and equipment in the art. The experimental methods in the following examples where specific conditions are not specified are usually carried out under conventional conditions or under conditions recommended by the manufacturer. The various raw materials used in the following examples are conventional commercial products unless otherwise specified, and their specifications are conventional specifications in the art. In the specification of the present invention and the following examples, unless otherwise specified, "%" means weight percentage, "part" means weight part, and ratio means weight ratio.

[0033] Example 1 A method for preparing an anthracite-based carbon negative electrode material comprises the following steps: 1g of anthracite and 3g of sodium nitrate were mixed and put into a ball mill for ball milling (the ball milling speed was 500rpm, the ball-to-material ratio was 20:1, and the time was 3h); after the ball milling was completed, the obtained mixture was put into a three-necked flask, and 16mL of phosphoric acid was added for reflux at a reflux temperature of 110 °C for 4h to obtain pretreated coal. The pretreated coal was washed with deionized water to a pH value of 3 and dried in an oven to obtain anthracite precursor.

[0034] The obtained anthracite precursor was placed in a tubular furnace, and in an argon atmosphere, the temperature was first increased to 350 °C at a heating rate of 2 °C / min for carbonization, and kept warm for 3 hours. Thereafter, the temperature was increased to 800 °C at a heating rate of 2 °C / min for carbonization, and kept warm for 2 hours; the temperature was reduced to 300 °C at a cooling rate of 3 °C / min, and naturally cooled to room temperature to obtain the anthracite-based carbon negative electrode material.

[0035] Example 2 A method for preparing an anthracite-based carbon negative electrode material comprises the following steps: 1g of anthracite and 3g of sodium nitrate were mixed and put into a ball mill for ball milling (the ball milling speed was 500rpm, the ball-to-material ratio was 20:1, and the time was 3h); after the ball milling was completed, the obtained mixture was put into a three-necked flask, and 16mL of phosphoric acid was added for reflux at a reflux temperature of 110 °C for 4h to obtain pretreated coal. The pretreated coal was washed with deionized water to a pH value of 3 and dried in an oven to obtain anthracite precursor.

[0036] The obtained anthracite precursor was placed in a tubular furnace, and in an argon atmosphere, the temperature was first increased to 350 °C at a heating rate of 2 °C / min for carbonization, and kept warm for 3 hours. Thereafter, the temperature was increased to 1000 °C at a heating rate of 2 °C / min for carbonization, and kept warm for 2 hours; the temperature was reduced to 300 °C at a cooling rate of 3 °C / min, and naturally cooled to room temperature to obtain the anthracite-based carbon negative electrode material.

[0037] Example 3 A method for preparing an anthracite-based carbon negative electrode material comprises the following steps: 1g of anthracite and 3g of sodium nitrate were mixed and put into a ball mill for ball milling (the ball milling speed was 500rpm, the ball-to-material ratio was 20:1, and the time was 3h); after the ball milling was completed, the obtained mixture was put into a three-necked flask, and 16mL of phosphoric acid was added for reflux at a reflux temperature of 110 °C for 4h to obtain pretreated coal. The pretreated coal was washed with deionized water to a pH value of 3 and dried in an oven to obtain anthracite precursor.

[0038] The obtained anthracite precursor was placed in a tubular furnace, and in an argon atmosphere, the temperature was first increased to 350 °C at a heating rate of 2 °C / min for carbonization, and kept warm for 3 hours. Thereafter, the temperature was increased to 1100 °C at a heating rate of 2 °C / min for carbonization, and kept warm for 2 hours; the temperature was decreased to 300 °C at a cooling rate of 3 °C / min, and naturally cooled to room temperature to obtain the anthracite-based carbon negative electrode material.

[0039] Example 4 A method for preparing an anthracite-based carbon negative electrode material comprises the following steps: 1g of anthracite and 3g of sodium nitrate were mixed and put into a ball mill for ball milling (the ball milling speed was 500rpm, the ball-to-material ratio was 20:1, and the time was 3h); after the ball milling was completed, the obtained mixture was put into a three-necked flask, and 16mL of phosphoric acid was added for reflux at a reflux temperature of 110 °C for 4h to obtain pretreated coal. The pretreated coal was washed with deionized water to a pH value of 3 and dried in an oven to obtain anthracite precursor.

[0040] The obtained anthracite precursor was placed in a tubular furnace, and in an argon atmosphere, the temperature was first increased to 350 °C at a heating rate of 2 °C / min for carbonization, and kept warm for 3 hours. Thereafter, the temperature was increased to 1200 °C at a heating rate of 2 °C / min for carbonization, and kept warm for 2 hours; the temperature was reduced to 300 °C at a cooling rate of 3 °C / min, and naturally cooled to room temperature to obtain the anthracite-based carbon negative electrode material.

[0041] Comparative Example 1 1g of anthracite and 3g of sodium nitrate were mixed and put into a ball mill for ball milling (the ball milling speed was 300rpm, the ball-to-material ratio was 20:1, and the time was 3h); after the ball milling was completed, the obtained mixture was put into a three-necked flask, and 16mL of phosphoric acid was added for reflux at a reflux temperature of 110 °C for 4h to obtain pretreated coal. The pretreated coal was washed with deionized water to a pH value of 3 and dried in an oven to obtain anthracite precursor.

[0042] The obtained anthracite precursor was placed in a tubular furnace, and in an argon atmosphere, the temperature was first increased to 350 °C at a heating rate of 2 °C / min for carbonization, and kept warm for 3 hours. Thereafter, the temperature was increased to 1000 °C at a heating rate of 2 °C / min for carbonization, and kept warm for 2 hours; the temperature was reduced to 300 °C at a cooling rate of 3 °C / min, and naturally cooled to room temperature to obtain the anthracite-based carbon negative electrode material.

[0043] Comparative Example 2 1g of anthracite and 3g of sodium nitrate were mixed and put into a ball mill for ball milling (where the ball milling speed was 400rpm, the ball-to-material ratio was 20:1, and the time was 3h); after the ball milling was completed, the obtained mixture was put into a three-necked flask, and 16mL of phosphoric acid was added for reflux at a reflux temperature of 110 °C for 4h to obtain pretreated coal. The pretreated coal was washed with deionized water to a pH value of 3 and dried in an oven to obtain anthracite precursor.

[0044] The obtained anthracite precursor was placed in a tubular furnace, and in an argon atmosphere, the temperature was first increased to 350 °C at a heating rate of 2 °C / min for carbonization, and kept warm for 3 hours. Thereafter, the temperature was increased to 1000 °C at a heating rate of 2 °C / min for carbonization, and kept warm for 2 hours; the temperature was reduced to 300 °C at a cooling rate of 3 °C / min, and naturally cooled to room temperature to obtain the anthracite-based carbon negative electrode material.

[0045] Example 5 A method for preparing an anthracite-based carbon negative electrode material comprises the following steps: S1: 1 g of anthracite and 3 g of sodium nitrate were mixed, and the mixture was ball-milled at 500 rpm for 2 h. Then, 10 mL of phosphoric acid was added to the 3 g of the ball-milled mixture, and the mixture was refluxed at 100° C. for 4 h. The mixture was then washed with water until the pH value was 3, thereby obtaining phosphorus-doped anthracite. S2: The phosphorus-doped anthracite is placed in a tubular furnace, and in an argon atmosphere, the temperature is first increased to 300°C at a heating rate of 2°C / min, and kept warm for 4 hours, and then the temperature is increased to 800°C at a heating rate of 2°C / min, and kept warm for 3 hours for carbonization treatment. After the carbonization treatment is completed, the temperature is reduced to 300°C at a cooling rate of 3°C / min, and then naturally cooled to room temperature to obtain the anthracite-based carbon negative electrode material.

[0046] A sodium ion battery was assembled using the anthracite-based carbon negative electrode material prepared in this embodiment, and its specific capacity and first coulombic efficiency were tested. The specific capacity of the sodium ion battery based on the anthracite-based carbon negative electrode material prepared in this embodiment was 204.6 mA h / g, and the first coulombic efficiency was 32.2%.

[0047] Example 6 A method for preparing an anthracite-based carbon negative electrode material comprises the following steps: S1: 1 g of anthracite and 5 g of sodium nitrate were mixed, and the mixture was ball-milled at 500 rpm for 3 h. Then, 20 mL of phosphoric acid was added to 3 g of the ball-milled mixture, and the mixture was refluxed at 120° C. for 2 h. The mixture was then washed with water until the pH value was 3, thereby obtaining phosphorus-doped anthracite. S2: The phosphorus-doped anthracite is placed in a tubular furnace, and in an argon atmosphere, the temperature is first increased to 400°C at a heating rate of 2°C / min, and kept warm for 2 hours, and then the temperature is increased to 1200°C at a heating rate of 2°C / min, and kept warm for 2 hours for carbonization treatment. After the carbonization treatment is completed, the temperature is reduced to 300°C at a cooling rate of 3°C / min, and then naturally cooled to room temperature to obtain the anthracite-based carbon negative electrode material.

[0048] A sodium ion battery was assembled using the anthracite-based carbon negative electrode material prepared in this embodiment, and its specific capacity and first coulombic efficiency were tested. The specific capacity of the sodium ion battery based on the anthracite-based carbon negative electrode material prepared in this embodiment was 275.5 mA h / g, and the first coulombic efficiency was 39.5%.

[0049] Example 7 A method for preparing anthracite-based carbon negative electrode material comprises the following steps: S1: 1 g of anthracite and 4 g of sodium nitrate were mixed, and the mixture was ball-milled at 500 rpm for 2.5 h. Then, 15 mL of phosphoric acid was added to 3 g of the ball-milled mixture, and the mixture was refluxed at 110° C. for 3 h. The mixture was then washed with water until the pH value was 3, thereby obtaining phosphorus-doped anthracite. S2: The phosphorus-doped anthracite is placed in a tubular furnace, and in an argon atmosphere, the temperature is first increased to 350°C at a heating rate of 2°C / min, and kept warm for 3 hours, and then the temperature is increased to 1000°C at a heating rate of 2°C / min, and kept warm for 2.5 hours for carbonization treatment. After the carbonization treatment is completed, the temperature is reduced to 300°C at a cooling rate of 3°C / min, and then naturally cooled to room temperature to obtain the anthracite-based carbon negative electrode material.

[0050] A sodium ion battery was assembled using the anthracite-based carbon negative electrode material prepared in this embodiment, and its specific capacity and first coulombic efficiency were tested. The specific capacity of the sodium ion battery based on the anthracite-based carbon negative electrode material prepared in this embodiment was 264.5 mA h / g, and the first coulombic efficiency was 36.2%.

[0051] In order to characterize the performance of the anthracite-based carbon negative electrode material prepared by the present invention, the following tests were performed: The anthracite-based carbon negative electrode materials obtained in Examples 1 to 4 and the raw material anthracite (WYM) were subjected to X-ray diffraction tests. The test results are as follows: Figure 1 As shown in the figure, it can be seen that the original SiO in anthracite can be effectively removed by adding sodium nitrate and ball milling. 2 and impurities such as alumina.

[0052] Figure 2This is the XPS spectrum of the anthracite-based carbon negative electrode material prepared in Example 2 of the present invention. As can be seen from the figure, the spectrum shows that the sample is mainly composed of C, O and P, confirming that P is successfully incorporated into the sample.

[0053] The anthracite-based carbon negative electrode materials obtained in Examples 1 to 4 were subjected to Raman testing, and the obtained Raman graphs are as follows: Figure 3 As shown in the figure, it can be seen that as the temperature increases, I D / I G The value gradually decreases, indicating that the higher the degree of graphitization, the fewer the defects; and the degree of graphitization is related to the conductivity of the material. The higher the degree of graphitization, the better the conductivity.

[0054] The anthracite-based carbon negative electrode materials obtained in Examples 1 to 4 and Comparative Examples 1 to 4 were used as negative electrode materials for sodium ion batteries to verify the electrochemical performance. The specific process is as follows: Preparation of the negative electrode of sodium ion battery: anthracite-based carbon negative electrode material, ketjen black and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1, ground in N-methylpyrrolidone solution to obtain slurry, coated on copper foil and dried to obtain a negative electrode sheet. In an argon-filled glove box, sodium metal was used as the counter electrode, the obtained electrode sheet was used as the working electrode, and NaClO with a concentration of 1M was used as the negative electrode sheet. 4 The solution (the solvent is ethylene carbonate EC + dimethyl carbonate DMC with a volume ratio of 1:1) is used as the electrolyte to assemble a sodium ion battery and conduct electrochemical performance tests; The first charge and discharge test curves of the sodium ion battery assembled using the anthracite-based carbon negative electrode material prepared in Examples 1 to 4 are as follows: Figure 4 The test results are shown in Table 1. Figure 4 It can be seen that the anthracite-based sodium negative electrode material prepared by the method of the present invention can obtain a sodium storage capacity of 288.49 mAh / g at a current density of 20 mA / g under the conditions of Example 2; and after 200 cycles at a current density of 100 mA / g, it still has a specific capacity of 135.76 mAh / g, and the capacity retention rate is 84.70%.

[0055] Table 1 Electrochemical performance test results of anthracite-based carbon negative electrode materials prepared under different conditions

[0056] Under the same test conditions, when the current density is 20, 50, 100, 200, 500 mA / g, the rate performance of the sodium ion battery assembled using the anthracite-based carbon negative electrode material prepared in Examples 1 to 4 is obtained as follows: Figure 5As shown in the figure, it can be seen that the sodium ion battery obtained by the technical solution of the present invention maintains a good capacity value at a high current density and has good rate performance.

[0057] Under the same test conditions, the charge and discharge cycles were repeated for 200 cycles at a current density of 100 mA / g, and the cycle diagram of the sodium ion battery assembled using the anthracite-based carbon negative electrode material prepared in Examples 1 to 4 was obtained as follows: Figure 6 As shown in the figure, it can be seen that the sodium ion battery prepared in the present invention has good specific capacity and capacity retention rate, especially after heat treatment at 1000°C, its specific capacity is 135.76mAh / g, and after 200 cycles, the capacity retention rate is 84.70%. The method provided by the present invention can improve anthracite-based carbon materials with poor sodium storage performance, and further improve the reversible specific capacity and cycle stability of coal-based carbon materials.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing anthracite-based carbon negative electrode material, characterized in that: The following steps are involved: S1: mixing anthracite and sodium nitrate, and then ball-milling the mixture. Then, phosphoric acid is added to the mixture after the ball milling, and the mixture is refluxed, and then washed to a pH value of 3 to obtain phosphorus-doped anthracite. S2: Carbonizing the phosphorus-doped anthracite in an inert atmosphere to obtain the anthracite-based carbon negative electrode material.

2. The method for preparing an anthracite-based carbon negative electrode material according to claim 1, characterized in that: The mass ratio of the anthracite to sodium nitrate is 1:(3-5).

3. The method for preparing an anthracite-based carbon negative electrode material according to claim 1, characterized in that: During the ball milling process, the rotation speed is 500 rpm and the time is 2 to 3 hours.

4. The method for preparing an anthracite-based carbon negative electrode material according to claim 1, characterized in that: The ratio of the ball-milled mixture to phosphoric acid is 3 g: (10-20) mL.

5. The method for preparing an anthracite-based carbon negative electrode material according to claim 1, characterized in that: During the reflux treatment, the temperature is 100-120°C and the time is 2-4h.

6. The method for preparing an anthracite-based carbon negative electrode material according to claim 1, characterized in that: The carbonization treatment process is specifically as follows: firstly, the temperature is raised to 300-400°C, kept warm for 2-4 hours, and then the temperature is raised to 800-1200°C, kept warm for 2-3 hours.

7. The method for preparing an anthracite-based carbon negative electrode material according to claim 1, characterized in that: During the carbonization process, the heating rate is 2°C / min.

8. The method for preparing an anthracite-based carbon negative electrode material according to claim 1, characterized in that: After the carbonization treatment is completed, the temperature is lowered to 300°C at a cooling rate of 3°C / min, and then naturally cooled to room temperature to obtain the anthracite-based carbon negative electrode material.

9. An anthracite-based carbon negative electrode material, characterized in that: Prepared by the method according to any one of claims 1 to 8.

10. A sodium ion battery, characterized in that: It comprises an anthracite-based carbon negative electrode material as described in claim 9; the specific capacity of the sodium ion battery is 203.5~288.5mA h / g, and the first coulombic efficiency is 31.5%~40.2%.

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