Asphalt-based sodium negative electrode material and preparation method and application thereof

Abstract

The application provides a pitch-based sodium electric negative electrode material and a preparation method and application thereof, and the preparation method comprises the following steps: step S1: pitch and a template agent are subjected to melt stirring and blending to obtain a melt mixture; step S2: the melt mixture obtained in step S1 is crushed, and pre-oxidation is performed in air or oxygen to obtain a pre-oxidized product; step S3: the pre-oxidized product obtained in step S2 is blended with a dopant, and then heating and carbonization are performed to obtain a carbonized product; step S4: the carbonized product obtained in step S3 is subjected to acid pickling, drying, crushing and screening to obtain pitch-based hard carbon; and step S5: the pitch-based hard carbon obtained in step S4 is subjected to carbon coating through chemical vapor deposition to obtain the pitch-based sodium electric negative electrode material. The pitch-based sodium electric negative electrode material prepared based on the method is used to prepare an electrode sheet, and the electrode sheet is applied to a sodium ion battery, so that high initial coulomb efficiency, capacity and rate performance can be achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of new energy materials, in particular to a pitch-based sodium negative electrode material and a preparation method and application thereof. BACKGROUND

[0002] The resource and environmental problems caused by the large-scale use of fossil fuels are becoming increasingly serious, and the development of cleaner secondary energy is very important for the sustainable development of human society. In recent years, new renewable and sustainable energy, such as solar energy, geothermal energy, wind energy, and tidal energy, has received widespread attention. However, these energy sources are heavily dependent on weather, season, and location, and have the disadvantages of intermittency and instability. Therefore, the development of efficient and convenient large-scale energy storage technology is crucial for the development and utilization of new energy. Sodium-ion batteries are considered to be an ideal solution for large-scale energy storage due to their abundant resources, low cost, and high safety. Therefore, it is crucial to develop high-performance sodium battery electrode materials.

[0003] Among the many negative electrode materials, hard carbon materials have become the first choice for commercial sodium battery negative electrodes due to their high capacity, low sodium intercalation potential, and excellent cycle stability. The precursors for preparing hard carbon are various, including biomass, resin, polymer, pitch, and anthracite. Pitch is an excellent precursor for preparing sodium battery negative electrode materials due to its high carbon yield, abundant raw material sources, and low cost. However, pitch pyrolysis easily forms soft carbon with small interlayer spacing, few defects, and low sodium storage capacity. For example, patent 202210897669.X introduces a method for directly pyrolyzing pitch to prepare soft carbon, and the specific capacity of the obtained pitch-based carbon material is low. Studies have shown that hard carbon structures with high disorder have higher sodium storage capacity. Therefore, it is important to develop pitch-based carbon negative electrodes with amorphous hard carbon structures.

[0004] Oxidation and cross-linking of pitch is a common process to obtain amorphous hard carbon. For example, patent (201710880097.3) prepared pitch-based hard carbon with amorphous structure by low-temperature pre-oxidation combined with high-temperature carbonization. Patent (202211046953.2) also prepared pitch hard carbon by blending pitch and low-residual carbon organic polymer and pre-oxidizing and then high-temperature carbonizing. However, simple pre-oxidation combined with high-temperature carbonization cannot guarantee high energy storage sites and fast ion migration, and the obtained hard carbon material cannot balance high capacity and high rate performance. Therefore, there is still a lack of effective technical means to develop pitch-based hard carbon negative electrodes that can balance high capacity and high rate performance. SUMMARY

[0005] The present application provides a pitch-based sodium electric negative electrode material and a preparation method and application thereof. The pitch-based sodium electric negative electrode material prepared based on the preparation method has high disorder degree, considerable heteroatom content, low surface defects, and nano structure, etc. When the pitch-based sodium electric negative electrode material is applied to a sodium ion battery as an electrode sheet, high capacity, first coulomb efficiency and rate performance can be achieved.

[0006] In order to achieve the above-mentioned purpose, the present application adopts the following technical solution:

[0007] The first aspect of the present application provides a preparation method of a pitch-based sodium electric negative electrode material, comprising the following steps:

[0008] Step S1: melt stirring and blending pitch and a template agent to obtain a melt mixture;

[0009] Step S2: pre-oxidizing the melt mixture obtained in step S1 in air or oxygen after crushing to obtain a pre-oxidized product;

[0010] Step S3: blending the pre-oxidized product obtained in step S2 with a dopant and then heating and carbonizing to obtain a carbonized product;

[0011] Step S4: acid washing, drying, crushing and screening the carbonized product obtained in step S3 to obtain a pitch-based hard carbon;

[0012] Step S5: carbon-coating the pitch-based hard carbon obtained in step S4 by chemical vapor deposition to obtain carbon-coated pitch-based hard carbon, i.e. the pitch-based sodium electric negative electrode material.

[0013] The present application improves the disorder degree and defect sites of pitch by pre-oxidation and heteroatom doping, and increases the graphite layer spacing, which is beneficial to obtain high adsorption capacity and intercalation capacity. By blending pitch with a template agent, the pitch skeleton size can be reduced, the oxidation path of pitch can be effectively shortened, and the oxidation crosslinking time can be shortened and the oxidation crosslinking effect can be improved.

[0014] The introduction of a suitable template agent effectively reduces the final carbon skeleton size, which is beneficial to the rapid insertion / deinsertion of sodium ions in sodium electric applications, and can effectively improve the rate performance of the electrode. The pitch with a high softening point is beneficial to improve the reliability and durability of the electric negative electrode material. In some preferred embodiments, in step S1, the softening point of the pitch is 120-250℃, preferably 180-220℃; the template agent is selected from one or more of nano-magnesium oxide, magnesium nitrate, nano-zinc oxide, nano-barium oxide, zinc nitrate, zinc acetate, nano-calcium oxide, nano-calcium carbonate, nano-strontium oxide or strontium nitrate, preferably, the template agent is selected from one or more of nano-calcium carbonate or zinc nitrate.

[0015] In some preferable embodiments, in step S1, the melt blending is carried out in a reaction kettle under an air atmosphere, and the holding temperature is selected to be 250-450°C to ensure sufficient melting of the pitch; preferably, the mass ratio of the pitch to the templating agent is 1:0.5-1:10, and if the amount of the templating agent is too small, the purpose of reducing the size of the carbon skeleton cannot be achieved due to insufficient contact, etc.; and the pitch and the templating agent are melt blended in a specific ratio to obtain a melt mixture with a certain fluidity, so that the templating agent is uniformly distributed in the pitch.

[0016] The melt mixture obtained in step S1 is further heated in air or oxygen for oxidation and crosslinking after being crushed and sieved. The pitch after melt blending and crushing can be rapidly and sufficiently crosslinked with oxygen.

[0017] In some preferable embodiments, in step S2, the particle size of the melt mixture after crushing is 2-20 μm, preferably 3-8 μm; the pre-oxidation temperature is 280-420°C, preferably 350-400°C; and the pre-oxidation time is 4-20 h, preferably 6-12 h.

[0018] The dopant is added during carbonization, and the dopant is fully introduced into the defect lattice, which changes the microstructure of the carbon material and increases the graphite layer spacing, which is beneficial to obtaining high adsorption capacity and intercalation capacity. The amount of the dopant is selected, and the ratio of the N dopant to the S dopant is adjusted at the same time, further optimizing the graphite layer spacing.

[0019] In some preferable embodiments, in step S3, the dopant comprises an N dopant and an S dopant, the N dopant is selected from one or more of cyanuric acid, ammonium chloride, urea, amino acid, aniline, ethylenediamine, triethanolamine, and ammonium bicarbonate; and the S dopant is selected from one or more of sulfur, thiourea, thiosulfate, and mercaptan; preferably, the N dopant is selected from one or more of cyanuric acid, amino acid, and urea, and the S dopant is selected from one or both of sulfur and thiourea.

[0020] In some preferable embodiments, the mass ratio of the pre-oxide in step S2 to the dopant in step S3 is 1:0.5-1:5; preferably, the mass ratio of the N dopant to the S dopant is 1:2-2:1, more preferably 1:1.

[0021] Low-temperature carbonization is adopted, which is beneficial to the pitch-based hard carbon material having a large layer spacing and a low surface area in structure, and is easy to obtain high adsorption capacity. In some preferable embodiments, in step S3, the carbonization is carried out in an argon atmosphere; the carbonization temperature is 600-1200°C, preferably 700-900°C; and the isothermal time for carbonization at the carbonization temperature is 1-6 h, preferably 2 h.

[0022] In some preferred embodiments, in step S4, the carbonized product is washed with 0.5-2M excess of hydrochloric acid or sulfuric acid for 24 hours, filtered, washed with water until the filtrate is neutral, the filter cake is collected and dried at a temperature of 80-120℃ until the mass of the filter cake no longer decreases; the particle size of the pulverized carbide is 2-20μm, preferably 3-8μm.

[0023] The surface is coated with a layer of soft carbon by chemical vapor deposition, which effectively reduces the surface area and the content of surface defects, and at the same time improves the electrical conductivity, which is beneficial to improve the initial coulombic efficiency and reversible capacity. In some preferred embodiments, in step S5, the conditions of the chemical vapor deposition include: the vapor deposition temperature is 700-1000℃, the flow rate of the organic gas is 10-300sccm, and the treatment time is 20min-2h; the organic gas for chemical vapor deposition is one or more of methane, acetylene, ethanol, ethylene, toluene, benzene, and methanol.

[0024] The second aspect of the present application provides a pitch-based sodium electric negative electrode material prepared by the above method.

[0025] The third aspect of the present application provides a pitch-based sodium electric negative electrode material prepared by the above method or the use of the pitch-based sodium electric negative electrode material described above in a sodium ion battery, for example, as a negative electrode material in a sodium ion battery.

[0026] The technical solution provided by the present application has the following beneficial effects:

[0027] The present application improves the disorder degree and defect site of pitch by pre-oxidation and heteroatom doping, increases the graphite layer spacing, and is beneficial to obtain high adsorption capacity and intercalation capacity. By blending pitch with a template agent, the size of the pitch skeleton can be reduced, which can effectively shorten the oxidation path of the pitch, and is beneficial to shorten the oxidation crosslinking time and improve the oxidation crosslinking effect. The introduction of a suitable template agent effectively reduces the size of the carbon skeleton, which is beneficial to the rapid insertion / deinsertion of sodium ions in sodium battery applications, and can effectively improve the rate performance of the electrode.

[0028] The rate performance refers to the discharge performance of the battery at different currents. In the present application, the rate performance of the negative electrode carbon is evaluated by testing the specific capacity at different currents (0.02-5A / g). The higher the specific capacity retention rate is, the better the rate performance of the material is. The initial coulombic efficiency is the ratio of the first charge capacity to the discharge capacity.

[0029] In preferred embodiments, low-temperature carbonization and chemical vapor deposition are combined, which is beneficial to further improve the performance of the pitch-based hard carbon material manufactured by the present application, so that it has a large interlayer spacing, a low surface area, an observable heteroatom content, a low number of surface defects, and can better balance high capacity and high rate, and further improve the initial coulombic efficiency.

[0030] The preparation method of the asphalt-based sodium electric negative electrode material has the characteristics of rich raw materials, low price, and easy-to-implement mass production. The asphalt-based sodium electric negative electrode material prepared based on the method has structural advantages such as high disorder degree, considerable heteroatom content, nano skeleton, and low surface defects. As a sodium electric negative electrode, the first coulombic efficiency is 78% to 89%, the reversible capacity is 260-320 mAh / g, and the specific capacity under a large current (5 A / g) is 115-150 mAh / g. DETAILED DESCRIPTION

[0031] The application will be further described below through specific examples. The examples described in the application are only used to illustrate the application and do not mean that the scope of the application is limited to the examples.

[0032] In the following examples, the preparation method of the asphalt-based sodium electric negative electrode material specifically includes the following steps:

[0033] Step S1: melt stirring and blending asphalt and a template agent to obtain a melt mixture;

[0034] The softening point of the asphalt is 120-250°C, and is preferably 180-220°C; the template agent is selected from one or more of nano-magnesium oxide, magnesium nitrate, nano-zinc oxide, nano-barium oxide, zinc nitrate, zinc acetate, nano-calcium oxide, nano-calcium carbonate, nano-strontium oxide, or strontium nitrate; preferably, the template agent is selected from one or more of nano-calcium carbonate or zinc nitrate.

[0035] The melt blending is carried out in an air atmosphere in a reaction kettle at a temperature of 250-450°C; preferably, the mass ratio of the asphalt to the template agent is 1:0.5 to 1:10.

[0036] Step S2: after the melt mixture obtained in step S1 is crushed, pre-oxidation is carried out in air or oxygen to obtain a pre-oxidized product;

[0037] The particle size of the crushed melt mixture is 2-20 μm, and is preferably 3-8 μm; the pre-oxidation temperature is 280-420°C, and is preferably 350-400°C; the pre-oxidation time is 4-20 h, and is preferably 6-12 h.

[0038] Step S3: after the pre-oxidized product obtained in step S2 is blended with a dopant, carbonization is carried out by heating to obtain a carbonized product;

[0039] The dopant comprises an N dopant and an S dopant, the N dopant is selected from one or more of triazine, ammonium chloride, urea, amino acid, aniline, ethylenediamine, triethanolamine, ammonium bicarbonate; the S dopant is selected from one or more of sulfur, thiourea, thiosulfate, mercaptan; preferably, the N dopant is selected from one or more of triazine, amino acid, urea, and the S dopant is selected from one or two of sulfur and thiourea.

[0040] The mass ratio of the pre-oxide in step S2 and the dopant in step S3 is 1:0.5-1:5; preferably, the mass ratio of the N dopant and the S dopant is 1:2-2:1, more preferably 1:1.

[0041] The carbonization is carried out in an argon atmosphere; the carbonization temperature is 600-1200℃, preferably 700-900℃; the constant temperature time at the carbonization temperature is 1-6h, preferably 2h.

[0042] Step S4: The carbonide obtained in step S3 is subjected to acid pickling, drying, crushing, and screening to obtain pitch-based hard carbon;

[0043] The acid pickling is carried out using 0.5-2M excess hydrochloric acid or sulfuric acid for 24h, and then the filter cake is collected after filtration and water washing until the filtrate is neutral, and dried at a drying temperature of 80-120℃ until the mass of the filter cake no longer decreases; the particle size of the crushed carbonide is 2-20μm, preferably 3-8μm.

[0044] Step S5: The pitch-based hard carbon obtained in step S4 is subjected to carbon coating by chemical vapor deposition to obtain the pitch-based sodium electro-negative electrode material.

[0045] The conditions of the chemical vapor deposition include: a vapor deposition temperature of 700-1000℃, a flow rate of the organic gas of 10-300sccm, and a treatment time of 20min-2h; the organic gas for the chemical vapor deposition is one or more of methane, acetylene, ethanol, ethylene, toluene, benzene, and methanol.

[0046] Reagents and instruments:

[0047] Reagents:

[0048] The pitch is a refined pitch such as tar pitch, coal liquefaction pitch, or petroleum pitch after deashing.

[0049] Nanometer magnesium oxide, melamine, sulfur, ethanol, zinc acetate, urea, thiourea, toluene, nanometer calcium oxide (50±5nm), aspartic acid, acetylene (99.9999%), benzene, nanometer calcium carbonate (80±10nm), and sodium thiosulfate are commercially available.

[0050] Instruments:

[0051] Method and equipment for testing performance of asphalt-based sodium electric negative electrode material

[0052] Equipment: battery test system CT2001A Wuhan Lan Electric.

[0053] Test method: The obtained asphalt-based sodium electric negative electrode material is made into an electrode sheet through a coating process, a sodium sheet is used as a counter electrode, a 1M NaClO4 / ethylene carbonate (EC) / diethyl carbonate (DEC) / fluoroethylene carbonate (FEC) solution is used as an electrolyte, a button cell is assembled, and constant current charge and discharge tests are performed. After setting a certain current value, the measured battery is continuously charged and discharged to obtain important information such as the specific capacity and coulombic efficiency that the electrode can provide. In addition, by setting different parameters, the rate performance and other battery data of the battery can be further tested. The voltage window is 0.01-3V, and the current density is 0.03-5Ag -1 , and the test process follows the principle of discharging first and then charging.

[0054] Example 1

[0055] The asphalt with a softening point of 120°C and nano-magnesium oxide are blended at a mass ratio of 1:0.5 in a reaction kettle at 250°C for 2 hours; then the above-mentioned melt mixture is crushed to about 4-8μm, heated to 340°C in air for 8 hours for pre-oxidation; then the above-mentioned pre-oxidized product is blended with a dopant (melamine:sulfur = 1:1, mass ratio) at a mass ratio of 1:5, and carbonized in an argon atmosphere at 700°C for 2 hours; then the obtained carbonized product is acid washed with 2M excess hydrochloric acid for 24h, filtered, washed with water until the filtrate is neutral, the filter cake is collected and dried at 80°C for 12 hours, and crushed to 4-8μm to obtain an asphalt-based hard carbon. Finally, ethanol is used as an organic source, and the above-mentioned asphalt-based hard carbon is coated with carbon by chemical vapor deposition at a flow rate of 60sccm at 800°C for 20min to obtain an asphalt-based sodium electric negative electrode material.

[0056] The above-mentioned asphalt-based sodium electric negative electrode material is made into an electrode sheet through a coating process, and tested by assembling a sodium ion battery, which has a specific capacity of 280mAh / g, a first coulombic efficiency of 78%, and a capacity of 130mAh / g at 5A / g.

[0057] Example 2

[0058] The pitch with softening point of 250℃ and zinc acetate were blended in a mass ratio of 1:4 in a reaction kettle at 300℃ for 4 hours by melt stirring; then the above melt mixture was crushed to about 6-12 μm, and pre-oxidized in air at 280℃ for 20 hours; then the above pre-oxidized product was blended with a dopant (urea: thiourea = 2:1, mass ratio) in a mass ratio of 1:1, and carbonized in an argon atmosphere at 1200℃ for 2 hours; then the obtained carbonized product was washed with 0.5M excess sulfuric acid for 24 hours, filtered, washed with water until the filtrate was neutral, the filter cake was collected and dried at 120℃ for 24 hours, and crushed to 8-12 μm to obtain pitch-based hard carbon. Finally, the pitch-based hard carbon was coated with carbon by chemical vapor deposition using toluene as an organic source at a flow rate of 10 sccm at 700℃ for 20 min to obtain pitch-based sodium battery anode material.

[0059] The pitch-based sodium battery anode material obtained in Example 2 was made into an electrode sheet by a coating process according to Example 1, and tested by assembling a sodium ion battery, and the specific capacity reached 260 mAh / g, the first coulombic efficiency reached 89%, and the capacity at 5 A / g reached 115 mAh / g.

[0060] Example 3

[0061] The pitch with softening point of 170℃ and nano calcium oxide were blended in a mass ratio of 1:10 in a reaction kettle at 250℃ for 2 hours by melt stirring; then the above melt mixture was crushed to about 10-20 μm, and pre-oxidized in air at 400℃ for 6 hours; then the above pre-oxidized product was blended with a dopant (aspartic acid: sulfur = 1:2, mass ratio) in a mass ratio of 1:2, and carbonized in an argon atmosphere at 1000℃ for 6 hours; then the obtained carbonized product was washed with 0.5M excess sulfuric acid for 24 hours, filtered, washed with water until the filtrate was neutral, the filter cake was collected and dried at 100℃ for 18 hours, and crushed to 6-10 μm to obtain pitch-based hard carbon. Finally, the pitch-based hard carbon was coated with carbon by chemical vapor deposition using acetylene as an organic source at a gas flow rate of 100 sccm at 900℃ for 60 min to obtain pitch-based sodium battery anode material.

[0062] The pitch-based sodium battery anode material obtained in Example 3 was made into an electrode sheet by a coating process according to Example 1, and tested by assembling a sodium ion battery, and the specific capacity reached 290 mAh / g, the first coulombic efficiency reached 80%, and the capacity at 5 A / g reached 135 mAh / g.

[0063] Example 4

[0064] The asphalt with softening point of 200°C and nano calcium oxide were blended in a mass ratio of 1:4 in a reaction kettle at 300°C for 3 hours by melt stirring; then the melt mixture was crushed to about 5-10 μm, heated to 420°C in air for 4 hours for pre-oxidation; then the pre-oxidized product was blended with a dopant (melamine: thiourea = 2:1 in mass ratio) in a mass ratio of 1:5, and carbonized in an argon atmosphere at 800°C for 2 hours; then the obtained carbonized product was acid washed with 2M excess hydrochloric acid for 24 hours, filtered, washed with water until the filtrate was neutral, the filter cake was collected and dried at 120°C for 18 hours, crushed to 3-5 μm, to obtain asphalt-based hard carbon. Finally, the asphalt-based hard carbon was coated with carbon by chemical vapor deposition using benzene as an organic source at a flow rate of 60 sccm at 700°C for 60 min, to obtain an asphalt-based sodium battery negative electrode material.

[0065] The asphalt-based sodium battery negative electrode material obtained in Example 4 was made into an electrode sheet by a coating process according to Example 1, and was tested by assembling a sodium ion battery, and the specific capacity reached 320 mAh / g, the first coulombic efficiency reached 84%, and the capacity at 5 A / g reached 150 mAh / g.

[0066] Example 5

[0067] The asphalt with softening point of 220°C and nano calcium carbonate were blended in a mass ratio of 1:6 in a reaction kettle at 350°C for 2 hours by melt stirring; then the melt mixture was crushed to about 6-12 μm, heated to 380°C in air for 6 hours for pre-oxidation; then the pre-oxidized product was blended with a dopant (melamine: sodium thiosulfate = 1:2 in mass ratio) in a mass ratio of 1:3, and carbonized in an argon atmosphere at 700°C for 2 hours; then the obtained carbonized product was acid washed with 1M excess sulfuric acid for 24 hours, filtered, washed with water until the filtrate was neutral, the filter cake was collected and dried at 120°C for 18 hours, crushed to 3-5 μm, to obtain asphalt-based hard carbon. Finally, the asphalt-based hard carbon was coated with carbon by chemical vapor deposition using ethylene as an organic source at a gas flow rate of 300 sccm at 1000°C for 2h, to obtain an asphalt-based sodium battery negative electrode material.

[0068] The asphalt-based sodium battery negative electrode material obtained in Example 5 was made into an electrode sheet by a coating process according to Example 1, and was tested by assembling a sodium ion battery, and the specific capacity reached 310 mAh / g, the first coulombic efficiency reached 85%, and the capacity at 5 A / g reached 140 mAh / g.

[0069] Comparative Example 1

[0070] The pitch with softening point of 180°C was crushed to about 6-12 μm, and pre-oxidized at 280°C for 12 hours in air; then the pre-oxidized product was blended with the dopant (urea: thiourea = 1:1, mass ratio) at a mass ratio of 1:2, and carbonized at 800°C in argon atmosphere for 2 hours; then the obtained carbonized product was acid washed with 1M excess hydrochloric acid for 24 hours, filtered, washed with water until the filtrate was neutral, the filter cake was collected and dried at 120°C for 18 hours, crushed to 3-5 μm, to obtain pitch-based hard carbon. Finally, the pitch-based hard carbon obtained above was coated with carbon by chemical vapor deposition using ethanol as organic source at a flow rate of 50 sccm, deposited at 800°C for 30 min, to obtain pitch-based sodium battery anode material.

[0071] The pitch-based sodium battery anode material obtained in Comparative Example 1 was made into electrode sheet by coating process, and tested by assembling sodium ion battery, the specific capacity reached 290 mAh / g, the first coulombic efficiency reached 85%, and the capacity at 5 A / g reached 56 mAh / g. Since no template agent was added to mix with the pitch in Comparative Example 1, the capacity of the sodium ion battery at large current (5 A / g) was low, and the capacity retention rate (i.e. rate) of the sodium ion battery at large current was significantly decreased.

[0072] Comparative Example 2

[0073] The pitch with softening point of 200°C was blended with nano calcium carbonate at a mass ratio of 1:5 in a reaction kettle at 400°C for 1 hour; then the melt mixture was crushed to about 6-12 μm, and pre-oxidized at 350°C for 4 hours in air; then the pre-oxidized product was carbonized at 700°C in argon atmosphere for 1 hour; then the obtained carbonized product was acid washed with 1M excess hydrochloric acid for 24 hours, filtered, washed with water until the filtrate was neutral, the filter cake was collected and dried at 100°C for 18 hours, crushed to 3-5 μm, to obtain pitch-based hard carbon. Finally, the pitch-based hard carbon obtained above was coated with carbon by chemical vapor deposition using toluene as organic source at a flow rate of 100 sccm, deposited at 900°C for 20 min, to obtain pitch-based sodium battery anode material.

[0074] The pitch-based sodium battery anode material obtained in Comparative Example 1 was made into electrode sheet by coating process, and tested by assembling sodium ion battery, the specific capacity reached 290 mAh / g, the first coulombic efficiency reached 85%, and the capacity at 5 A / g reached 56 mAh / g. Since no template agent was added to mix with the pitch in Comparative Example 1, the capacity of the sodium ion battery at large current (5 A / g) was low, and the capacity retention rate (i.e. rate) of the sodium ion battery at large current was significantly decreased.

[0075] Comparative Example 3

[0076] The pitch with softening point of 180 °C was blended with nano zinc oxide at a mass ratio of 1:3 at 350 °C for 1 hour by melt stirring. Then the melt mixture was crushed to about 6-12 pm, and heated to 350 °C in air for 6 hours for pre-oxidation. Then the pre-oxidized product was blended with dopant (urea: thiourea = 1:1, mass ratio) at a mass ratio of 1:2, and then carbonized at 800 °C in argon atmosphere for 2 hours. Then the obtained carbonized product was acid washed with 2M excess hydrochloric acid for 24 hours, filtered, washed with water until the filtrate was neutral, and the filter cake was collected and dried at 100 °C for 18 hours, crushed to 3-5 pm to obtain pitch-based hard carbon.

[0077] The pitch-based hard carbon obtained in Comparative Example 3 was made into an electrode sheet by a coating process according to Example 1, and tested by assembling a sodium ion battery. The specific capacity reached 340 mAh / g, the first coulombic efficiency reached 43%, and the capacity at 5 A / g reached 120 mAh / g. Since the sodium battery negative electrode material obtained in Comparative Example 3 was not carbon-coated by chemical vapor deposition, the first coulombic efficiency of the sodium ion battery was low.

[0078] Comparative Example 4

[0079] The pitch with softening point of 220 °C was blended with nano calcium oxide at a mass ratio of 1:5 at 350 °C for 1 hour by melt stirring. Then the melt mixture was crushed to about 6-12 pm. Then the material was blended with dopant (aniline: sulfur = 1:1, mass ratio) at a mass ratio of 1:3, and then carbonized at 900 °C in argon atmosphere for 1 hour. Then the obtained carbonized product was acid washed with 1M excess hydrochloric acid for 24 hours, filtered, washed with water until the filtrate was neutral, and the filter cake was collected and dried at 100 °C for 18 hours, crushed to 3-5 pm to obtain pitch-based hard carbon. Finally, the pitch-based hard carbon was carbon-coated by chemical vapor deposition using ethanol as an organic source at a flow rate of 50 sccm at 700 °C for 20 min to obtain a pitch-based sodium battery negative electrode material.

[0080] The pitch-based sodium battery negative electrode material obtained in Comparative Example 4 was made into an electrode sheet by a coating process according to Example 1, and tested by assembling a sodium ion battery. The specific capacity reached 230 mAh / g, the first coulombic efficiency reached 70%, and the capacity at 5 A / g reached 80 mAh / g. Since the melt mixture in Comparative Example 4 was not pre-oxidized, the specific capacity, the first coulombic efficiency, and the capacity at a large current (5 A / g) of the sodium ion battery were all lower than those of the examples.

[0081] Comparative Example 5

[0082] The pitch with softening point of 220 °C was heated to 350 °C in air for pre-oxidation for 6 hours, then carbonization was carried out at 800 °C in argon atmosphere for 2 hours; then the obtained carbonizate was acid washed with 1 M excess hydrochloric acid for 24 h, filtered, washed with water until the filtrate was neutral, the filter cake was collected and dried at 100 °C for 18 hours, crushed to 3-5 μm, to obtain pitch-based hard carbon.

[0083] The pitch-based hard carbon obtained in Comparative Example 5 was made into electrode sheets by coating process, and tested by assembling sodium ion batteries, the specific capacity reached 180 mAh / g, the first coulombic efficiency reached 63%, and the capacity at 5 A / g reached 34 mAh / g. Since Comparative Example 5 lacks the steps of adding a template agent, adding a dopant and carbon coating by chemical vapor deposition, the specific capacity, the first coulombic efficiency and the capacity at large current (5 A / g) of the sodium ion battery are much lower than those of Examples 1-5 of the present application.

[0084] Obviously, the above examples are only examples for clarity and do not limit the embodiments. Based on the above description, other different forms of changes or variations can also be made by those skilled in the art. All embodiments do not need to be exhausted here. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method for preparing a pitch-based sodium anode material, characterized in that, The preparation method includes the following steps: Step S1: Melt and mix the asphalt with the template agent to obtain a molten mixture; the template agent is selected from one or more of nano magnesium oxide, nano zinc oxide, nano barium oxide, zinc acetate, nano calcium oxide, nano calcium carbonate, or nano strontium oxide; Step S2: After pulverizing the molten mixture obtained in step S1, pre-oxidize it in air or oxygen to obtain a pre-oxide; Step S3: After blending the preoxide obtained in step S2 with the dopant, heat and carbonize to obtain a carbide; Step S4: The carbide obtained in step S3 is acid washed, dried, crushed and sieved to obtain pitch-based hard carbon; Step S5: The asphalt-based hard carbon obtained in step S4 is carbon-coated by chemical vapor deposition to obtain carbon-coated asphalt-based hard carbon, which is the asphalt-based sodium electrode anode material.

2. The method for preparing the pitch-based sodium anode material according to claim 1, characterized in that, In step S1, the softening point of the asphalt is 120~250℃.

3. The method for preparing the pitch-based sodium anode material according to claim 2, characterized in that, In step S1, the softening point of the asphalt is 180~220℃.

4. The method for preparing the pitch-based sodium anode material according to claim 1 or 2, characterized in that, In step S1, the melt blending is carried out in a reactor under an air atmosphere at a temperature of 250~450℃; the mass ratio of the asphalt to the template agent is 1:0.5~1:

10.

5. The method for preparing the pitch-based sodium anode material according to claim 1, characterized in that, In step S2, the particle size of the pulverized molten mixture is 2~20μm; the pre-oxidation temperature is 280~420℃; and the pre-oxidation time is 4~20h.

6. The method for preparing the pitch-based sodium anode material according to claim 5, characterized in that, In step S2, the particle size of the pulverized molten mixture is 3~8μm; the pre-oxidation temperature is 350~400℃; and the pre-oxidation time is 6~12h.

7. The method for preparing the pitch-based sodium anode material according to claim 1, characterized in that, In step S3, the dopant comprises an N dopant and an S dopant. The N dopant is selected from one or more of melamine, ammonium chloride, urea, amino acids, aniline, ethylenediamine, triethanolamine, and ammonium bicarbonate. The S dopant is selected from one or more of sulfur, thiourea, thiosulfate, and thiols.

8. The method for preparing the pitch-based sodium anode material according to claim 7, characterized in that, The N dopant is selected from one or more of melamine, amino acids, and urea, and the S dopant is selected from one or two of sulfur and thiourea.

9. The method for preparing the pitch-based sodium anode material according to claim 7, characterized in that, The mass ratio of the pre-oxide in step S2 to the dopant in step S3 is 1:0.5 to 1:5; wherein the mass ratio of the N dopant to the S dopant is 1:2 to 2:

1.

10. The method for preparing the pitch-based sodium anode material according to claim 9, characterized in that, The mass ratio of the N dopant to the S dopant is 1:

1.

11. The method for preparing the pitch-based sodium anode material according to claim 1 or 6, characterized in that, In step S3, carbonization is carried out in an argon atmosphere at a temperature of 600-1200°C; the carbonization isothermal time at the carbonization temperature is 1-6 hours.

12. The method for preparing the pitch-based sodium anode material according to claim 11, characterized in that, In step S3, the carbonization temperature is 700~900℃; the carbonization isothermal time at the carbonization temperature is 2h.

13. The method for preparing the pitch-based sodium anode material according to claim 1, characterized in that, In step S4, the particle size of the pulverized carbide is 2~20μm; In step S5, the conditions for chemical vapor deposition include: a vapor deposition temperature of 700-1000℃, an organic gas flow rate of 10-300 sccm, and a deposition time of 20 min-2 h; the organic gas used for chemical vapor deposition is one or more of methane, acetylene, ethanol, ethylene, toluene, benzene, and methanol.

14. The method for preparing the pitch-based sodium anode material according to claim 13, characterized in that, In step S4, the particle size of the pulverized carbide is 3~8μm.

15. A pitch-based sodium anode material prepared by the method according to any one of claims 1-14.

16. The use of the pitch-based sodium anode material prepared by the method according to any one of claims 1-14 or the pitch-based sodium anode material according to claim 15 in a sodium-ion battery.