Sodium-ion battery coal pitch-based carbon negative electrode material as well as preparation method and application thereof

Abstract

The invention discloses a sodium-ion battery coal pitch-based carbon negative electrode material obtained through a modified coal pitch double-crosslinking strategy, and a preparation method and application thereof, and belongs to the technical field of sodium-ion batteries. The preparation process comprises the following steps: firstly, heating and mixing medium-temperature coal pitch, terephthalyl alcohol and boric acid to obtain modified asphalt; weighing strong phosphoric acid, uniformly mixing with water and ethanol, then fully mixing with the modified asphalt, and drying to obtain a cross-linked sample; and carrying out pre-oxidation treatment on a cross-linked sample in air, then preheating in argon, naturally cooling to room temperature, repeatedly washing with water to be neutral, and finally carrying out high-temperature carbonization treatment to obtain the coal pitch-based negative electrode material. According to the present invention, the rich and cheap raw materials are adopted so as to obtain the high specific capacity from the coal tar pitch with characteristics of low cost and high carbon yield;

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium-ion batteries, and particularly relates to a sodium-ion battery coal-tar pitch-based carbon negative electrode material, a preparation method thereof, and an application thereof. Background Art

[0002] With the rapid development of new energy technologies, the shortage and increasing cost of lithium resources have prompted people to seek alternative energy storage solutions. Sodium-ion batteries have gradually attracted the attention of the scientific research community and the industrial community due to their multiple advantages such as rich resources and low prices. The development of high-performance sodium-ion batteries largely depends on the progress of electrode materials, especially in the negative electrode aspect. However, the choices in the negative electrode aspect are still limited. Therefore, the development of high-quality and low-cost negative electrode materials is the key to the development of sodium-ion batteries.

[0003] Compared with various negative electrode materials, such as carbon materials, alloys, metal oxides, etc. Coal-tar pitch is a low-cost coal chemical resource with advantages such as rich production and high carbon yield, and is a good raw material for preparing carbon negative electrodes. Pitch-derived carbon materials have shown high capacity and good rate performance in electrochemical devices such as lithium-ion batteries and supercapacitors. At the same time, S. Wenzel, T. Hara, J. Janek, P. Adelhelm, Room-temperature sodium-ionbatteries: improving the rate capability of carbon anode materials bytemplating strategies, Energy Environ. Sci. 4 (2011) 3342–3345. first reported a sodium-ion battery negative electrode derived from pitch, which can provide 130 mA h g -1 at 0.074 A g -1 capacity. L. Song,S. Liu, B. Yu, C. Wang, M. Li, Anode performance of mesocarbon microbeads forsodium-ion batteries, Carbon 95 (2015) 972–977. reported mesocarbon microbeads derived from coal-tar pitch, whose reversible storage capacity is 140 mA h g -1 at 0.1 A g -1 .

[0004] However, due to the strong π-π interaction during the liquid-phase carbonization process, the performance of these asphalt-derived sodium-ion battery anodes leads to an increase in the graphitization degree of coal tar pitch and a decrease in the interlayer spacing. The electrochemical performance is far inferior to that of commercial lithium-ion batteries. Therefore, it is necessary to convert the planar aromatic molecules of asphalt into three-dimensional molecules to weaken the π-π interaction between aromatic compounds, reduce the graphitization trend, and thereby improve the electrochemical performance of asphalt-based carbon materials. Summary of the Invention

[0005] In order to overcome the shortcomings of the strong π-π interaction in the liquid-phase carbonization process of asphalt-derived carbon materials in the above-mentioned prior art, which leads to an increase in the graphitization degree of coal tar pitch and a decrease in the interlayer spacing, thereby causing a decline in the electrochemical performance of sodium-ion batteries, the purpose of the present invention is to provide a sodium-ion battery coal tar pitch-based carbon anode material, its preparation method and application, to improve the shortcoming of the low sodium storage capacity of coal tar pitch-based sodium battery anode materials.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions: The first object of the present invention is to provide a preparation method of a sodium-ion battery coal tar pitch-based carbon anode material, which is characterized by including the following steps: S1. Mix and heat medium-temperature coal tar pitch, terephthalyl alcohol and boric acid to obtain modified asphalt; S2. Mix concentrated phosphoric acid, water and ethanol evenly to form a mixed solution, and fully disperse the modified asphalt obtained in S1 in the mixed solution to form a dispersion, and dry the dispersion to obtain crosslinked modified asphalt; S3. First pre-oxidize the crosslinked modified asphalt, then perform a preheating treatment, and then cool it to room temperature. After washing, the pre-oxidized crosslinked modified asphalt is obtained; S4. Perform high-temperature carbonization treatment on the pre-oxidized crosslinked modified asphalt, and the sodium-ion battery coal tar pitch-based carbon anode material is obtained.

[0007] Preferably, in the step S1, the dosage of terephthalyl alcohol is 5-50 wt% of the mass of medium-temperature coal tar pitch, and the dosage of boric acid is 0.5-5 wt% of the mass of medium-temperature coal tar pitch.

[0008] Further preferably, in the step S1, the heating temperature is 140°C to 160°C, and the mixing and heating reaction time is 2 to 3 h.

[0009] Preferably, in S2, the concentration of concentrated phosphoric acid is 68 wt% to 89 wt%, and the mass ratio of modified asphalt, concentrated phosphoric acid, water and absolute ethanol is 2:(1.11-1.46):1.17:1:(0.75-1.5).

[0010] Further preferably, in S2, the drying temperature of the dispersion is 80°C to 130°C, and the drying time is 12 h to 15 h.

[0011] Preferably, in the step S3, the pre-oxidation treatment of the crosslinked modified asphalt is specifically to heat it to 300 °C at a heating rate of 5 °C / min in an oxidizing atmosphere, hold for 3 h, and then take it out after natural cooling to room temperature.

[0012] Preferably, in the step S3, the preheating treatment of the crosslinked modified asphalt is specifically to heat it to 450 - 750 °C at a heating rate of 3 - 7 °C / min under the protection of an inert atmosphere, hold for 1.5 - 3 h, and then cool it to 250 - 350 °C at a cooling rate of 1 - 4 °C / min, and take it out after natural cooling to room temperature.

[0013] Preferably, in the step S4, the high-temperature carbonization treatment is specifically to heat it to 1000 - 1400 °C at a heating rate of 1 - 5 °C / min under the protection of an argon atmosphere, hold for 2 - 4 h, and then cool it to 250 - 350 °C at a cooling rate of 1 - 4 °C / min, and take it out after natural cooling to room temperature.

[0014] The second object of the present invention is to provide a sodium-ion battery coal tar pitch-based carbon negative electrode material prepared by the above preparation method.

[0015] The third object of the present invention is to provide a sodium-ion battery negative electrode sheet, which is prepared by grinding a slurry obtained by mixing the aforementioned sodium-ion battery coal tar pitch-based carbon negative electrode material, Ketjen black, and polyvinylidene fluoride in a mass ratio of 8:1:1 in N-methylpyrrolidone, and then coating and drying the slurry on a copper foil.

[0016] The fourth object of the present invention is to provide the application of the sodium-ion battery coal tar pitch-based carbon negative electrode material as a sodium-ion battery negative electrode material.

[0017] Compared with the prior art, the present invention has the following beneficial effects: In the product of the present invention, a coal-tar pitch-based carbon negative electrode material obtained by a modified coal-tar pitch double-crosslinking strategy is prepared. First, the formation of an ordered structure in the carbonized structure is prevented by modified coal-tar pitch. Further, by adding concentrated phosphoric acid and pre-oxidation treatment, etc., the sodium storage performance of the coal-tar pitch-based carbon negative electrode material is improved by double-crosslinking of P and O. In step S1 of the present invention, medium-temperature coal-tar pitch is mixed and reacted with p-xylene glycol (PXG) and boric acid. After modification, the asphalt can effectively weaken the strong π-π interaction between molecules during the carbonization process, prevent the formation of a carbon ordered structure, and increase the content of the carbon disordered structure, thereby improving the electrochemical performance of the carbon negative electrode. In step S2 of the present invention, by adding concentrated phosphoric acid, water, and ethanol to the modified asphalt, it helps that during the subsequent pre-oxidation process, phosphoric acid and oxygen-containing functional groups will increase more binding sites, and more effectively transport and improve the sodium ion storage capacity. In step S3 of the present invention, a large number of micropores are introduced into the whole structure through preheating and cleaning treatment, thereby promoting the improvement of electrochemical activity. Through high-temperature carbonization treatment, the micropores coalesce to form more sites, thereby enhancing the sodium storage capacity. The coal-tar pitch-based carbon negative electrode material prepared by this method can obtain 312.27 mA h g -1 at a current density of 20 mA g -1 of high sodium storage capacity. Description of the Drawings

[0018] Figure 1 XRD diagrams of Example 3, Comparative Example 1, and Comparative Example 2 of the present invention; Figure 2 Raman diagrams of Example 3, Comparative Example 1, and Comparative Example 2 of the present invention; Figure 3 First charge-discharge curve comparison diagrams of Example 3, Comparative Example 1, and Comparative Example 2 of the present invention; Figure 4 Rate performance data diagrams of Example 3, Comparative Example 1, and Comparative Example 2 of the present invention; Figure 5 Long cycle test curve diagrams of Example 3, Comparative Example 1, and Comparative Example 2 of the present invention; Detailed Embodiments In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0019] It should be noted that the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, or product that includes a series of steps or units does not have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, or products.

[0020] The present invention will be further described in detail below with reference to the accompanying drawings: The object of the present invention is to improve the disadvantage of low sodium storage capacity of coal tar pitch-based sodium battery negative electrode materials, so as to provide a high-performance coal tar pitch-based carbon negative electrode material for sodium ion batteries. By using low-cost and resource-rich coal tar pitch as a carbon precursor, modifying the coal tar pitch, phosphoric acid cross-linking, and high-temperature carbonization and other treatments, the results show that it can not only provide a large number of active sites, but also promote the insertion / extraction of sodium ions by expanding the layer spacing, thereby improving the electrochemical performance of sodium ion batteries. The object of the present invention is achieved by the following method: A preparation method of a coal tar pitch-based carbon negative electrode material for sodium ion batteries obtained by a modified coal tar pitch double cross-linking strategy, the preparation method comprising the following steps: S1. Mix and heat medium-temperature coal tar pitch, p-xylene glycol, and boric acid to obtain modified pitch; S2. Mix concentrated phosphoric acid, water, and ethanol evenly to form a mixed solution, disperse the modified pitch obtained in S1 in the mixed solution to form a dispersion, and dry the dispersion to obtain cross-linked modified pitch; S3. First pre-oxidize the cross-linked modified pitch, then perform a preheating treatment, and then cool to room temperature. After washing, the pre-oxidized cross-linked modified pitch is obtained; S4. Perform high-temperature carbonization treatment on the pre-oxidized cross-linked modified pitch to obtain the coal tar pitch-based carbon negative electrode material for sodium ion batteries.

[0021] Among them, in step S1, p-xylene glycol is used as a chemical cross-linking agent and boric acid is used as an acidic catalyst to chemically cross-link the medium-temperature coal tar pitch, inhibit graphitization, and increase the layer spacing, which is beneficial to sodium ion storage. The cross-linking agent forms a carbocation in an acidic environment and undergoes an electrophilic substitution reaction with polycyclic aromatic hydrocarbon compounds. The aromatic nuclei are condensed by methylene linkages to form a modified pitch with a large layer spacing, a more complex cross-linking degree, and a more thorough cross-linking degree as a precursor of the carbon electrode material.

[0022] In some preferred embodiments, in S1, the dosage of p-xylene glycol is 5-50 wt% of the mass of the medium-temperature coal tar pitch, and the optimal range is 5-20 wt%; the dosage of boric acid is 0.5-5 wt% of the mass of the medium-temperature coal tar pitch, and the optimal range is 0.5-1 wt% to avoid side reactions caused by excessive boric acid; the optimal mass ratio of medium-temperature coal tar pitch, p-xylene glycol, and boric acid is 10:2:1.

[0023] Preferably, the temperature of the chemical cross-linking reaction in S1 is 140°C to 160°C, and can be, for example, but not limited to, 140°C, 145°C, 150°C, 155°C or 160°C. In the above acidic reaction environment, cross-linking is preferably completed at 140°C to 180°C, the optimal reaction temperature is 150°C, the reaction time is 2 to 3 h, the optimal reaction time is 3 h, and the reaction temperature and reaction time are balanced to ensure that the cross-linking reaction proceeds fully.

[0024] In some preferred embodiments, the chemical cross-linking process of S1 is carried out in an oil bath to improve the reaction efficiency and deepen the degree of chemical cross-linking reaction.

[0025] In some preferred embodiments, using ethanol as a polar solvent in S2 can reduce the viscosity of the modified asphalt, promote the uniform dispersion of the modified asphalt in the mixed solution. Concentrated phosphoric acid can provide a weak acidic environment, further stabilize the cross-linked structure through protonation, and inhibit oxidation side reactions. The mixed system of water and ethanol can dissolve unreacted boric acid and by-products, and impurities are removed by subsequent drying. The concentration of concentrated phosphoric acid is 68 wt% to 89 wt%, and can be, for example, but not limited to, 69 wt%, 70 wt%, 75 wt%, 76 wt%, 80 wt%, 81 wt%, 85 wt% or 89 wt%. The mass ratio of the amounts of modified asphalt, concentrated phosphoric acid, water and absolute ethanol is 2:(1.11 - 1.46):1.17:1:(0.75 - 1.5). When the concentration of concentrated phosphoric acid is selected as 85 wt%, the mass ratio of the amounts of modified asphalt, concentrated phosphoric acid, water and absolute ethanol is 2:1.17:1:0.75. In some preferred embodiments, the drying temperature of the dispersion in S2 is 80°C to 130°C, and can be, for example, but not limited to, 80°C, 90°C, 100°C, 110°C, 120°C or 130°C, and the drying time is 12 to 15 h, and can be, for example, but not limited to, 12 h, 13 h or 14 h. In this solution, when the drying temperature is controlled at about 120°C, the optimal drying duration is 12 h. Coordinating and controlling the drying temperature and drying time within a reasonable range can avoid decomposition caused by overheating and destruction of the cross-linked structure.

[0026] In some preferred embodiments, the pre-oxidation treatment in S3 is carried out in an oxidizing atmosphere, such as in an air or oxygen atmosphere. The temperature of the pre-oxidation is 200 - 400 °C, for example, it can be, but is not limited to, 200 °C, 250 °C, 300 °C, 350 °C, 400 °C; the heating rate is 3 - 7 °C / min, for example, it can be, but is not limited to, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min or 7 °C / min. The holding time is 2 - 4 h, for example, it can be, but is not limited to, 2 h, 2.5 h, 3 h, 3.5 h or 4 h. Most preferably, it is heated to 300 °C at a heating rate of 5 °C / min for pre-oxidation and held for 3 h, and then taken out after natural cooling to room temperature.

[0027] In some preferred embodiments, the preheating treatment in S3 is carried out in a protective atmosphere. The further preheating temperature is 450 - 750 °C, for example, it can be, but is not limited to, 450 °C, 500 °C, 550 °C, 600 °C, 650 °C, 700 °C, 750 °C. The heating rate is 3 - 7 °C / min, for example, it can be, but is not limited to, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min or 7 °C / min. The holding time is 1.5 - 3 h, for example, it can be, but is not limited to, 1.5 h, 2 h, 2.5 h or 3 h; most preferably, it is heated to 600 °C at a heating rate of 5 °C / min and held for 2 h. After preheating, it is cooled down. The cooling rate is 1 - 4 °C / min to cool down to 250 - 350 °C, and then taken out after natural cooling to room temperature. Most preferably, it is cooled down to 300 °C at a cooling rate of 3 °C / min and taken out after natural cooling to room temperature.

[0028] After the further preheating in S3 is completed and cooled to room temperature, the sample is washed. It can be washed with water until the pH = 7 and then dried. The present invention has no special limitation on the process of the water washing, and it can be carried out by using the process well-known to those skilled in the art.

[0029] In some preferred embodiments, the temperature of the high-temperature carbonization in S4 is 1000 - 1400 °C, for example, it can be, but is not limited to, 1000 °C, 1100 °C, 1200 °C, 1300 °C, 1400 °C. The heating rate is 1 - 5 °C / min, for example, it can be, but is not limited to, 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min or 5 °C / min. The carbonization holding time is 2 - 4 h, for example, it can be, but is not limited to, 2 h, 2.5 h, 3 h, 3.5 h or 4 h. The high-temperature carbonization is preferably carried out in a tube furnace. Preferably, it is heated to 1200 °C at a heating rate of 3 °C / min for carbonization and held for 3 h. After the holding is completed, it is cooled down at a cooling rate of 1 - 4 °C / min to 250 - 350 °C, and then taken out after natural cooling to room temperature. Most preferably, it is cooled down to 300 °C at a cooling rate of 3 °C / min and taken out after natural cooling to room temperature.

[0030] In the embodiment of the present invention, preheating and high-temperature carbonization are carried out under an inert atmosphere, and the inert atmosphere is preferably one or more of Ar, N2 or He.

[0031] The present invention also provides a coal tar pitch-based carbon negative electrode material for a sodium ion battery prepared by any of the above schemes.

[0032] The present invention also provides a sodium ion battery negative electrode sheet using the above-mentioned sodium ion battery coal tar pitch-based carbon negative electrode material.

[0033] The present invention also provides the use of the above-mentioned coal tar pitch-based carbon negative electrode material for sodium ion batteries as a negative electrode material for sodium ion batteries.

[0034] In the present invention, unless otherwise specified, all raw materials are commercially available products known to those skilled in the art. The technical scheme adopted by the present invention is described in detail below in conjunction with the embodiments.

[0035] Example 1 10 g of medium-temperature coal tar was mixed with 2 g of terephthalic acid (PXG) and 1 g of boric acid, placed in a three-necked flask, heated and mixed in an oil bath, and reacted at 150°C for 3 h to obtain modified asphalt. 5.85 g of concentrated phosphoric acid (85 wt%) was weighed and mixed evenly with 5 ml of water and 5 ml of anhydrous ethanol, and then 10 g of modified asphalt was weighed and dispersed in the above solution, mixed thoroughly, and placed in a vacuum oven and dried at 120°C for 12 h to obtain a cross-linked product.

[0036] The obtained cross-linked product was placed in a tubular furnace, heated to 300°C at a heating rate of 5°C / min in an air atmosphere, kept warm for 3 hours, and naturally cooled to room temperature; then, heated to 600°C at a heating rate of 5°C / min under the protection of an argon atmosphere, kept warm for 2 hours, cooled to 300°C at a cooling rate of 3°C / min, naturally cooled to room temperature, and repeatedly washed with water until neutral; finally, heated to 1000°C at a heating rate of 3°C / min under the protection of an argon atmosphere, kept warm for 3 hours, cooled to 300°C at a cooling rate of 3°C / min, and naturally cooled to room temperature to obtain the coal tar-based carbon negative electrode material.

[0037] Example 2 10 g of medium-temperature coal tar was mixed with 2 g of terephthalic acid (PXG) and 1 g of boric acid, placed in a three-necked flask, heated and mixed in an oil bath, and reacted at 150°C for 3 h to obtain modified asphalt. 5.85 g of concentrated phosphoric acid (85 wt%) was weighed and mixed evenly with 5 ml of water and 5 ml of anhydrous ethanol, and then 10 g of modified asphalt was weighed and dispersed in the above solution, mixed thoroughly, and placed in a vacuum oven and dried at 120°C for 12 h to obtain a cross-linked product.

[0038] The obtained cross-linked product was placed in a tubular furnace. In an air atmosphere, it was heated to 300 °C at a heating rate of 5 °C / min, held for 3 h, and then naturally cooled to room temperature. Subsequently, under the protection of an argon atmosphere, it was heated to 600 °C at a heating rate of 5 °C / min, held for 2 h, cooled to 300 °C at a cooling rate of 3 °C / min, and then naturally cooled to room temperature. It was repeatedly washed with water until neutral. Finally, under the protection of an argon atmosphere, it was heated to 1200 °C at a heating rate of 3 °C / min, held for 3 h, cooled to 300 °C at a cooling rate of 3 °C / min, and then naturally cooled to room temperature to obtain the coal tar pitch-based carbon negative electrode material.

[0039] Example 3 10 g of medium-temperature coal tar pitch was mixed with 2 g of p-xylene glycol (PXG) and 1 g of boric acid, placed in a three-necked flask, and heated and mixed in an oil bath at 150 °C for 3 h to obtain a modified pitch. 5.85 g of concentrated phosphoric acid (85 wt%) was weighed, mixed evenly with 5 ml of water and 5 ml of absolute ethanol. Then, 10 g of the modified pitch was weighed, dispersed in the above solution, mixed thoroughly, and placed in a vacuum oven to be dried at 120 °C for 12 h to obtain a cross-linked product.

[0040] The obtained cross-linked product was placed in a tubular furnace. In an air atmosphere, it was heated to 300 °C at a heating rate of 5 °C / min, held for 3 h, and then naturally cooled to room temperature. Subsequently, under the protection of an argon atmosphere, it was heated to 600 °C at a heating rate of 5 °C / min, held for 2 h, cooled to 300 °C at a cooling rate of 3 °C / min, and then naturally cooled to room temperature. It was repeatedly washed with water until neutral. Finally, under the protection of an argon atmosphere, it was heated to 1200 °C at a heating rate of 3 °C / min, held for 3 h, cooled to 300 °C at a cooling rate of 3 °C / min, and then naturally cooled to room temperature to obtain the coal tar pitch-based carbon negative electrode material.

[0041] Comparative Example 1 10 g of medium-temperature coal tar pitch was weighed and placed in a tubular furnace. Under the protection of an argon atmosphere, it was heated to 1200 °C at a heating rate of 3 °C / min, held for 3 h, and then cooled to 300 °C at a cooling rate of 3 °C / min, and then naturally cooled to room temperature to obtain the coal tar pitch-based carbon negative electrode material.

[0042] Comparative Example 2 5.85 g of concentrated phosphoric acid (85 wt%) was weighed, mixed evenly with 5 ml of water and 5 ml of absolute ethanol. Then, 10 g of medium-temperature coal tar pitch was weighed, dispersed in the above solution, mixed thoroughly, and placed in a vacuum oven to be dried at 120 °C for 12 h to obtain a cross-linked product.

[0043] The obtained crosslinked product was placed in a tubular furnace. In an air atmosphere, it was heated to 300 °C at a heating rate of 5 °C / min, held for 3 h, and then naturally cooled to room temperature. Subsequently, under the protection of an argon atmosphere, it was heated to 600 °C at a heating rate of 5 °C / min, held for 2 h, cooled to 300 °C at a cooling rate of 3 °C / min, and then naturally cooled to room temperature. It was repeatedly washed with water until neutral. Finally, under the protection of an argon atmosphere, it was heated to 1200 °C at a heating rate of 3 °C / min, held for 3 h, cooled to 300 °C at a cooling rate of 3 °C / min, and then naturally cooled to room temperature to obtain the coal-tar pitch-based carbon negative electrode material.

[0044] Test Example 1 The coal-tar pitch-based carbon negative electrode materials obtained in Example 3, Comparative Example 1, and Comparative Example 2 were subjected to X-ray diffraction testing, and the obtained XRD patterns were as Figure 1 shown.

[0045] Test Example 2 The coal-tar pitch-based carbon negative electrode materials obtained in Example 3, Comparative Example 1, and Comparative Example 2 were subjected to Raman testing, and the obtained Raman patterns were as Figure 2 shown.

[0046] Test Example 3 The coal-tar pitch-based carbon negative electrode materials obtained in Examples 1 to 3 and Comparative Examples 1 to 2 were used as the electrode materials of a sodium-ion battery to verify the electrochemical performance.

[0047] The coal-tar pitch-based carbon negative electrode material, Ketjen black, and polyvinylidene fluoride were mixed at a mass ratio of 8:1:1, ground in an N-methylpyrrolidone solution to obtain a slurry, and the slurry was coated on a copper foil and dried to obtain a negative electrode sheet. Inside a glove box filled with argon, a sodium-ion battery was assembled with a metallic sodium as the counter electrode, the obtained electrode sheet as the working electrode, and a 1 M NaClO4 solution (where the solvent was a 1:1 volume ratio of EC + DMC) as the electrolyte for electrochemical performance testing; the obtained first charge-discharge test curve was as Figure 3 shown, and the test results are shown in Table 1. Under the same test conditions, at current densities of 20, 50, 100, 200, and 500 mA g -1 −1, the rate performance of the sodium-ion batteries prepared in Example 3, Comparative Example 1, and Comparative Example 2 was as Figure 4 shown. Under the same test conditions, at a current density of 100 mA g -1 −1, after 200 charge-discharge cycles, the cycle diagrams of the sodium-ion batteries prepared in Example 3, Comparative Example 1, and Comparative Example 2 were as Figure 5 shown.

[0048] Table 1. Electrochemical performance test results of coal-tar pitch-based carbon negative electrode materials prepared under different conditions

[0049] As can be seen from the results in the above table, the sodium-ion battery anode material based on coal tar pitch prepared by the method of the present invention can obtain a specific capacity of 312.27 mA h g- -1 at a current density of 20 mA g 1 ; and still has a specific capacity of 167.46 mA h g -1 after 200 cycles at a current density of 100 mA g -1 , and the capacity retention rate is 84.46%.

[0050] The above content is only to illustrate the technical idea of the present invention, and the protection scope of the present invention cannot be limited thereby. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a coal tar pitch-based carbon negative electrode material for a sodium ion battery, characterized in that: The following steps are involved: S1. Mixing coal tar, terephthalic acid and boric acid at medium temperature and heating to obtain modified asphalt; S2 concentrated phosphoric acid, water and ethanol are mixed to form a mixed solution, the modified asphalt obtained in S1 is fully dispersed in the mixed solution to form a dispersion, and the dispersion is dried to obtain a cross-linked modified asphalt; S3 first pre-oxidize the cross-linked modified asphalt, then preheat, then cool to room temperature, and wash to obtain a pre-oxidized cross-linked modified asphalt; S4. The pre-oxidized cross-linked modified asphalt is subjected to high-temperature carbonization treatment to obtain a coal-tar pitch-based carbon negative electrode material for a sodium ion battery.

2. The method for preparing a coal tar pitch-based carbon negative electrode material for a sodium ion battery according to claim 1, characterized in that: In the step S1, the amount of terephthalic acid used is 5-50wt% of the mass of the medium-temperature coal tar pitch, and the amount of boric acid used is 0.5-5wt% of the mass of the medium-temperature coal tar pitch.

3. The method for preparing a coal tar pitch-based carbon negative electrode material for a sodium ion battery according to claim 1 or 2, characterized in that: In step S1, the heating temperature is 140° C. to 160° C., and the mixing and heating reaction time is 2 to 3 hours.

4. The method for preparing a coal tar pitch-based carbon negative electrode material for a sodium ion battery according to claim 1, characterized in that: The concentration of concentrated phosphoric acid in the S2 is 68wt%~89wt%, and the mass ratio of modified asphalt, concentrated phosphoric acid, water and anhydrous ethanol is 2:(1.11~1.46)1.17:1:(0.75~1.5).

5. The method for preparing the coal tar pitch-based carbon negative electrode material for sodium ion batteries according to claim 1 or claim 4, characterized in that: The drying temperature of the dispersion in S2 is 80° C. to 130° C., and the drying time is 12 h to 15 h.

6. The method for preparing a coal tar pitch-based carbon negative electrode material for a sodium ion battery according to claim 1, characterized in that: In S3, the pre-oxidation treatment of the cross-linked modified asphalt is specifically to heat to 300°C at a heating rate of 5°C / min in an oxidizing atmosphere, keep the temperature for 3 h, and naturally cool to room temperature and take out; The preheating treatment of the cross-linked modified asphalt is specifically to heat the material to 450~750℃ at a heating rate of 3~7℃ / min and keep it at that temperature for 1.5~3h under the protection of an inert atmosphere, then cool it to 250~350℃ at a cooling rate of 1~4℃ / min, and naturally cool it to room temperature before taking it out.

7. The method for preparing a coal tar pitch-based carbon negative electrode material for a sodium ion battery according to claim 1, characterized in that: The high temperature carbonization treatment in S4 is specifically to heat the material to 1000-1400°C at a heating rate of 1-5°C / min and keep the temperature for 2-4h under the protection of an inert atmosphere, then cool the material to 250-350°C at a cooling rate of 1-4°C / min, and naturally cool the material to room temperature before taking it out.

8. A coal tar pitch-based carbon negative electrode material for a sodium ion battery, characterized in that: Prepared by the preparation method according to any one of claims 1 to 8.

9. A negative electrode sheet for a sodium ion battery, characterized in that: The coal tar-based carbon negative electrode material for a sodium ion battery according to claim 9, Ketjen black and polyvinylidene fluoride are ground in N-methylpyrrolidone at a mass ratio of 8:1:1 to obtain a slurry, and the slurry is coated on a copper foil and then dried to obtain the product.

10. Use of the coal tar pitch-based carbon negative electrode material for sodium ion batteries according to claim 8 as a negative electrode material for sodium ion batteries.

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