A molybdenum-doped sodium ion battery hard carbon negative electrode material and its preparation method

Abstract

The present invention relates to a molybdenum-doped hard carbon negative electrode material for sodium ion batteries and a preparation method thereof. It is the first time to propose the use of transition metal molybdenum as a doping element to achieve microcrystal adjustment of hard carbon, aiming to improve the electrochemical performance and practical application of hard carbon. The specific preparation process includes the following steps: S1 adds a hard carbon precursor, a molybdenum source doping phase, and a carbon-forming catalyst to a certain volume of deionized water solution, and stirs them at room temperature for a certain period of time to completely dissolve them; S2 transfers the mixed solution in S1 to a polytetrafluoroethylene reactor for hydrothermal treatment, and after the reaction is completed, centrifuges, washes, and dries the generated product; S3 performs high-temperature pyrolysis on the dried product in S2 in an inert atmosphere to obtain a molybdenum-doped hard carbon material. The present invention introduces molybdenum as a doping phase into the hard carbon material, effectively improving the reversible capacity and rate performance of the sodium ion battery negative electrode material, while also having high coulombic efficiency and cycle performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary batteries, specifically to the technical field of sodium ion battery negative electrodes, and in particular to a molybdenum-doped sodium ion battery hard carbon negative electrode material and a preparation method thereof. Background Art

[0002] With the rapid growth of the global population and the rapid improvement of living standards leading to increased energy consumption, energy demand is expected to increase by 90% by 2035. Among current energy storage technologies, lithium-ion batteries dominate the energy storage battery field due to their high voltage, high capacity, and excellent cycle performance. However, the uneven distribution of lithium resources worldwide and the extremely limited reserves in my country have greatly limited their application. Compared with lithium, sodium is more evenly distributed in the Earth's crust, has more abundant reserves, is easily mined, and is low-cost, making sodium-ion batteries a promising application in large-scale energy storage.

[0003] Hard carbon, also known as non-graphitizable carbon, is difficult to graphitize at temperatures above 2500°C. It is composed of disordered graphite nanosheets, randomly distributed graphitized regions, and a rich porous structure. Due to its low operating voltage, high capacity, and low cost, hard carbon is considered the most commercially promising anode material for sodium-ion batteries. However, because the radius of Na+ is much larger than that of Li+, the ion migration rate in the electrode is relatively slow, and the insertion and extraction processes are more complex, resulting in low reversible capacity and poor rate performance for hard carbon.

[0004] Hunan NaNengShiDai Technology Development Co., Ltd. disclosed a metal quantum dot / hard carbon negative electrode material and its preparation method in CN116169288A, which belongs to the field of secondary battery material technology. The metal type in the material is one or more of Fe, Cu, Co, Mn, and Mo. The preparation method of the metal quantum dot / hard carbon negative electrode material is as follows: dissolving a soluble metal salt and an organic complexing agent in deionized water or an organic solvent to obtain a metal organic framework material; mixing the prepared metal organic framework material, a sulfur source, and a carbon source and performing a high-temperature heat treatment to obtain a metal sulfide quantum dot / hard carbon negative electrode material; finally, placing the material in an electrolytic cell for electrolytic desulfurization to obtain the final product of the metal quantum dot / hard carbon negative electrode material. The prepared metal quantum dot / hard carbon negative electrode material has uniform quantum dot distribution and the hard carbon material has uniform size. When used in a secondary battery negative electrode material, it exhibits excellent electrochemical storage performance.

[0005] The Shenzhen Institute of Advanced Technology (SIT) disclosed a hard carbon anode material, its preparation method, and application in CN116706034A. The hard carbon anode material comprises a hard carbon matrix, heteroatoms, and metal single atoms. The metal single atoms are doped into the hard carbon matrix via the heteroatoms, wherein the heteroatoms include at least one of nitrogen, phosphorus, or sulfur, and the metal single atoms are capable of alloying with sodium. The metal single atoms are doped into the hard carbon matrix through covalent (chemical bonding) interactions with other heteroatoms, achieving single-atom doping. This improves the overall capacity and rate performance of sodium-ion batteries at room temperature, while also ensuring capacity retention at low temperatures.

[0006] However, the existing hard carbon doping methods still have limitations, and the research on molybdenum-based materials is not in-depth enough. It is urgent to study new methods to prepare hard carbon negative electrode materials for sodium ion batteries. By using molybdenum-based materials, the microstructure and efficiency of hard carbon can be adjusted at the micro-nano level, the defect concentration of hard carbon can be reduced, the active sites on the hard carbon surface can be increased, and the reversible capacity and first-cycle coulombic efficiency of hard carbon can be improved. Summary of the Invention

[0007] In order to solve the above problems, the present invention proposes for the first time a preparation method using molybdenum as the doping phase and adjusting the microstructure and efficiency of hard carbon negative electrode materials based on the molybdenum base, thereby reducing the defect concentration of hard carbon and increasing the active sites on the hard carbon surface, thereby improving the reversible capacity and first-cycle coulombic efficiency of hard carbon.

[0008] The technical solutions adopted in the present invention are as follows:

[0009] A method for preparing a molybdenum-doped hard carbon negative electrode material for sodium ion batteries comprises the following steps:

[0010] S1. Dissolve the hard carbon precursor, molybdenum source doping phase and carbon forming catalyst in deionized water in a certain proportion, and stir for a certain period of time at room temperature to fully dissolve the three in the deionized water;

[0011] In step S1, the hard carbon precursor is one of glucose, sucrose or fructose; the molybdenum source doping phase is ammonium molybdate or sodium molybdate; and the carbon forming catalyst is ammonium persulfate;

[0012] The molar ratio of the hard carbon precursor, the molybdenum source doping phase and the carbon-forming catalyst ammonium persulfate is 6:(0.1-3):(0.1-2);

[0013] S2. Transfer the mixed solution in S1 to a reactor and perform hydrothermal treatment at 150-240° C. for 6-48 hours. After the reaction is completely cooled to room temperature, the hydrothermal product is centrifuged, washed, and dried.

[0014] S3. The product in S2 is subjected to high-temperature pyrolysis and carbonization under an inert atmosphere, wherein the high-temperature pyrolysis and carbonization temperature is 1000-1700° C. and the high-temperature pyrolysis and carbonization time is 2-12 hours to obtain a molybdenum-doped hard carbon material.

[0015] Furthermore, the molar concentration of glucose is 0.5-1 mol / L, the molar concentration of sucrose is 0.4-1 mol / L, the molar concentration of fructose is 0.5-1 mol / L, the molar concentration of ammonium molybdate or sodium molybdate is 0.1-0.2 mol / L, and the molar concentration of the carbon-forming catalyst ammonium persulfate is preferably 0.05-0.1 mol / L.

[0016] Furthermore, the molar ratio of the hard carbon precursor, the molybdenum source doping phase and the carbon-forming catalyst ammonium persulfate is 6:(0.1-3):0.5.

[0017] Furthermore, the molar ratio of the hard carbon precursor, the molybdenum source doping phase and the carbon-forming catalyst ammonium persulfate is 6:1:0.5.

[0018] Furthermore, the hydrothermal reaction temperature of the mixed solution in step S2 is preferably 160-200° C., and the hydrothermal reaction time is preferably 10-24 h.

[0019] Furthermore, in step S3, the high-temperature pyrolysis carbonization temperature is preferably 1200-1500° C., and the high-temperature pyrolysis carbonization time is preferably 2-6 hours.

[0020] A molybdenum-based doped sodium ion battery hard carbon negative electrode material prepared according to the above-mentioned method for preparing a molybdenum-based doped sodium ion battery hard carbon negative electrode material.

[0021] A method for preparing an electrode sheet of a hard carbon negative electrode material for a sodium ion battery comprises the following steps: mixing the aforementioned molybdenum-based doped hard carbon negative electrode material for a sodium ion battery with acetylene black and sodium carboxymethyl cellulose in a certain proportion and grinding them uniformly; then adding deionized water and stirring them uniformly to obtain an electrode slurry; then using a coating machine to evenly coat the electrode slurry on a copper foil; transferring the copper foil to a vacuum oven and drying it at 60-100°C for 8-24 hours; and finally using a sheet punching machine to cut disc electrodes to obtain a hard carbon negative electrode material electrode sheet.

[0022] Furthermore, the mass ratio of the molybdenum-based doped hard carbon material to acetylene black and sodium carboxymethyl cellulose is 8:1:1, the drying temperature of the electrode slurry is 70-80° C., and the drying time of the electrode slurry is 12-18 hours.

[0023] A sodium ion battery hard carbon negative electrode material electrode sheet prepared according to the above-mentioned method for preparing a sodium ion battery hard carbon negative electrode material electrode sheet.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] A hard carbon precursor is combined with a molybdenum-based doping phase using a hydrothermal method, and the addition of a carbon-forming catalyst, ammonium persulfate, is proposed for the first time. Ammonium persulfate can accelerate the hydrothermal reaction rate of monosaccharides or polysaccharides, while controlling the hydrothermal temperature and time to prepare micro-nanostructured carbon spheres. During the high-temperature pyrolysis and carbonization process, the molybdenum group performs microcrystalline adjustment on the graphitized structure of the hard carbon material, achieving carbon atom recombination, continuously reducing the porosity on the surface of the carbon spheres, reducing the defect concentration of the carbon spheres, and increasing the tap density of the hard carbon. The molybdenum-based doped hard carbon material prepared by the present invention exhibits excellent electrochemical performance when used as an electrode material for sodium ion batteries, solving the problems of low reversible capacity and poor first-cycle coulombic efficiency of sodium ion batteries. At the same time, the preparation process of the present invention is simple, cost-effective, and has broad application prospects in large-scale industrial mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0027] Figure 1 This is the SEM image of the molybdenum-doped hard carbon negative electrode material prepared in Example 2.

[0028] Figure 2 This is the charge and discharge curve of the molybdenum-doped hard carbon negative electrode material prepared in Example 2 at a current density of 50 mA / g.

[0029] Figure 3 This is a rate performance diagram of the molybdenum-doped hard carbon negative electrode material prepared in Example 2 at a current density of 0.05A / g-1A / g.

[0030] Figure 4 This is the charge and discharge curve of the molybdenum-doped hard carbon negative electrode material prepared in Example 2 at a current density of 0.05A / g-1A / g.

[0031] Figure 5 This is a long cycle diagram of the molybdenum-doped hard carbon negative electrode material prepared in Example 2 at a current density of 200 mA / g. DETAILED DESCRIPTION

[0032] In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention and to make the above-mentioned objects, features and advantages of the present invention more obvious and understandable, the specific implementation methods of the present invention are further described below.

[0033] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0034] Example 1

[0035] S1: Glucose, ammonium molybdate, and ammonium persulfate were added to an aqueous solution at a molar ratio of 6:1:0.5, and stirred at room temperature for 30 minutes to fully dissolve them, to prepare 60 mL of a 0.6 mol / L glucose mixed solution.

[0036] S2 transferred 60 mL of 0.6 mol / L glucose mixed solution into the reactor and subjected it to hydrothermal reaction at 180 °C for 15 h. After the reactor was completely cooled, it was removed and the hydrothermal product was washed three times by centrifugation with deionized water and once with anhydrous ethanol, and then transferred to a 60 °C oven for drying for 12 h.

[0037] S3: The dried hydrothermal product is transferred to a high-temperature tube furnace, subjected to high-temperature pyrolysis and carbonization in an argon atmosphere, heated to 1100°C at a heating rate of 5°C / min, and kept warm for 3 hours to obtain a molybdenum-doped hard carbon material.

[0038] Example 2

[0039] S1: Glucose, ammonium molybdate, and ammonium persulfate were added to an aqueous solution at a molar ratio of 6:1:0.5, and stirred at room temperature for 30 minutes to fully dissolve them, to prepare 60 mL of a 0.6 mol / L glucose mixed solution.

[0040] S2 transferred 60 mL of 0.6 mol / L glucose mixed solution into the reactor and subjected it to hydrothermal reaction at 180 °C for 15 h. After the reactor was completely cooled, it was removed and the hydrothermal product was washed three times by centrifugation with deionized water and once with anhydrous ethanol, and then transferred to a 60 °C oven for drying for 12 h.

[0041] S3: The dried hydrothermal product is transferred to a high-temperature tube furnace, subjected to high-temperature pyrolysis and carbonization in an argon atmosphere, heated to 1300°C at a heating rate of 5°C / min, and kept warm for 3 hours to obtain a molybdenum-doped hard carbon material.

[0042] Example 3

[0043] S1: Glucose, ammonium molybdate, and ammonium persulfate were added to an aqueous solution at a molar ratio of 6:1:0.5, and stirred at room temperature for 30 minutes to fully dissolve them, to prepare 60 mL of a 0.6 mol / L glucose mixed solution.

[0044] S2 transferred 60 mL of 0.6 mol / L glucose mixed solution into the reactor and subjected it to hydrothermal reaction at 180 °C for 15 h. After the reactor was completely cooled, it was removed and the hydrothermal product was washed three times by centrifugation with deionized water and once with anhydrous ethanol, and then transferred to a 60 °C oven for drying for 12 h.

[0045] S3: The dried hydrothermal product is transferred to a high-temperature tube furnace, subjected to high-temperature pyrolysis and carbonization in an argon atmosphere, heated to 1500°C at a heating rate of 5°C / min, and kept warm for 3 hours to obtain a molybdenum-doped hard carbon material.

[0046] Example 4

[0047] S1: Glucose, ammonium molybdate, and ammonium persulfate were added to an aqueous solution at a molar ratio of 6:2:0.5, and stirred at room temperature for 30 minutes to fully dissolve them, to prepare 60 mL of a 0.6 mol / L glucose mixed solution.

[0048] S2 transferred 60 mL of 0.6 mol / L glucose mixed solution into the reactor and subjected it to hydrothermal reaction at 180 °C for 15 h. After the reactor was completely cooled, it was removed and the hydrothermal product was washed three times by centrifugation with deionized water and once with anhydrous ethanol, and then transferred to a 60 °C oven for drying for 12 h.

[0049] S3: The dried hydrothermal product is transferred to a high-temperature tube furnace, subjected to high-temperature pyrolysis and carbonization in an argon atmosphere, heated to 1300°C at a heating rate of 5°C / min, and kept warm for 3 hours to obtain a molybdenum-doped hard carbon material.

[0050] Example 5

[0051] S1: Glucose, ammonium molybdate, and ammonium persulfate were added to an aqueous solution at a molar ratio of 6:1:0.5, and stirred at room temperature for 30 minutes to fully dissolve them, to prepare 60 mL of a 0.6 mol / L glucose mixed solution.

[0052] S2 transferred 60 mL of 0.6 mol / L glucose mixed solution into the reactor and subjected it to hydrothermal reaction at 200 °C for 15 h. After the reactor was completely cooled, it was removed and the hydrothermal product was washed three times by centrifugation with deionized water and once with anhydrous ethanol, and then transferred to a 60 °C oven for drying for 12 h.

[0053] S3: The dried hydrothermal product is transferred to a high-temperature tube furnace, subjected to high-temperature pyrolysis and carbonization in an argon atmosphere, heated to 1300°C at a heating rate of 5°C / min, and kept warm for 3 hours to obtain a molybdenum-doped hard carbon material.

[0054] Example 6

[0055] S1: Glucose, ammonium molybdate, and ammonium persulfate were added to an aqueous solution at a molar ratio of 6:1:0.5, and stirred at room temperature for 30 minutes to fully dissolve them, to prepare 60 mL of a 0.6 mol / L glucose mixed solution.

[0056] S2 transferred 60 mL of 0.6 mol / L glucose mixed solution into the reactor and subjected it to hydrothermal reaction at 150 °C for 15 h. After the reactor was completely cooled, it was removed and the hydrothermal product was washed three times by centrifugation with deionized water and once with anhydrous ethanol, and then transferred to a 60 °C oven for drying for 12 h.

[0057] S3: The dried hydrothermal product is transferred to a high-temperature tube furnace, subjected to high-temperature pyrolysis and carbonization in an argon atmosphere, heated to 1300°C at a heating rate of 5°C / min, and kept warm for 3 hours to obtain a molybdenum-doped hard carbon material.

[0058] Example 7

[0059] S1: Glucose, ammonium molybdate, and ammonium persulfate were added to an aqueous solution at a molar ratio of 6:1:0.5, and stirred at room temperature for 30 minutes to fully dissolve them, to prepare 60 mL of a 0.6 mol / L glucose mixed solution.

[0060] S2 transferred 60 mL of 0.6 mol / L glucose mixed solution into the reactor and subjected it to hydrothermal reaction at 160 °C for 15 h. After the reactor was completely cooled, it was removed and the hydrothermal product was washed three times by centrifugation with deionized water and once with anhydrous ethanol, and then transferred to a 60 °C oven for drying for 12 h.

[0061] S3: The dried hydrothermal product is transferred to a high-temperature tube furnace, subjected to high-temperature pyrolysis and carbonization in an argon atmosphere, heated to 1300°C at a heating rate of 5°C / min, and kept warm for 3 hours to obtain a molybdenum-doped hard carbon material.

[0062] Example 8

[0063] S1: Glucose, ammonium molybdate, and ammonium persulfate were added to an aqueous solution at a molar ratio of 6:1:0.5, and stirred at room temperature for 30 minutes to fully dissolve them, to prepare 60 mL of a 0.6 mol / L glucose mixed solution.

[0064] S2 transferred 60 mL of 0.6 mol / L glucose mixed solution into the reactor and subjected it to hydrothermal reaction at 240 °C for 15 h. After the reactor was completely cooled, it was removed and the hydrothermal product was washed three times by centrifugation with deionized water and once with anhydrous ethanol, and then transferred to a 60 °C oven for drying for 12 h.

[0065] S3: The dried hydrothermal product is transferred to a high-temperature tube furnace, subjected to high-temperature pyrolysis and carbonization in an argon atmosphere, heated to 1300°C at a heating rate of 5°C / min, and kept warm for 3 hours to obtain a molybdenum-doped hard carbon material.

[0066] Example 9

[0067] S1: Glucose, ammonium molybdate, and ammonium persulfate were added to an aqueous solution at a molar ratio of 6:1:0.5, and stirred at room temperature for 30 minutes to fully dissolve them, to prepare 60 mL of a 0.6 mol / L glucose mixed solution.

[0068] S2 transferred 60 mL of 0.6 mol / L glucose mixed solution into the reactor and subjected it to hydrothermal reaction at 200 °C for 15 h. After the reactor was completely cooled, it was removed and the hydrothermal product was washed three times by centrifugation with deionized water and once with anhydrous ethanol, and then transferred to a 60 °C oven for drying for 12 h.

[0069] S3: The dried hydrothermal product is transferred to a high-temperature tube furnace, subjected to high-temperature pyrolysis and carbonization in an argon atmosphere, heated to 1000°C at a heating rate of 5°C / min, and kept warm for 3 hours to obtain a molybdenum-doped hard carbon material.

[0070] Example 10

[0071] S1: Glucose, ammonium molybdate, and ammonium persulfate were added to an aqueous solution at a molar ratio of 6:1:0.5, and stirred at room temperature for 30 minutes to fully dissolve them, to prepare 60 mL of a 0.6 mol / L glucose mixed solution.

[0072] S2 transferred 60 mL of 0.6 mol / L glucose mixed solution into the reactor and subjected it to hydrothermal reaction at 180 °C for 15 h. After the reactor was completely cooled, it was removed and the hydrothermal product was washed three times by centrifugation with deionized water and once with anhydrous ethanol, and then transferred to a 60 °C oven for drying for 12 h.

[0073] S3: The dried hydrothermal product is transferred to a high-temperature tube furnace, subjected to high-temperature pyrolysis and carbonization in an argon atmosphere, heated to 1700°C at a heating rate of 5°C / min, and kept warm for 3 hours to obtain a molybdenum-doped hard carbon material.

[0074] Example 11

[0075] S1: Glucose, ammonium molybdate, and ammonium persulfate were added to the aqueous solution in a molar ratio of 6:0.1:0.5, and stirred at room temperature for 30 minutes to fully dissolve them, to prepare 60 mL of a 0.6 mol / L glucose mixed solution.

[0076] S2 transferred 60 mL of 0.6 mol / L glucose mixed solution into the reactor and subjected it to hydrothermal reaction at 180 °C for 15 h. After the reactor was completely cooled, it was removed and the hydrothermal product was washed three times by centrifugation with deionized water and once with anhydrous ethanol, and then transferred to a 60 °C oven for drying for 12 h.

[0077] S3: The dried hydrothermal product is transferred to a high-temperature tube furnace, subjected to high-temperature pyrolysis and carbonization in an argon atmosphere, heated to 1300°C at a heating rate of 5°C / min, and kept warm for 3 hours to obtain a molybdenum-doped hard carbon material.

[0078] Example 12

[0079] S1: Glucose, ammonium molybdate, and ammonium persulfate were added to the aqueous solution at a molar ratio of 6:0.5:0.5, and stirred at room temperature for 30 minutes to fully dissolve them, to prepare 60 mL of a 0.6 mol / L glucose mixed solution.

[0080] S2 transferred 60 mL of 0.6 mol / L glucose mixed solution into the reactor and subjected it to hydrothermal reaction at 180 °C for 15 h. After the reactor was completely cooled, it was removed and the hydrothermal product was washed three times by centrifugation with deionized water and once with anhydrous ethanol, and then transferred to a 60 °C oven for drying for 12 h.

[0081] S3: The dried hydrothermal product is transferred to a high-temperature tube furnace, subjected to high-temperature pyrolysis and carbonization in an argon atmosphere, heated to 1300°C at a heating rate of 5°C / min, and kept warm for 3 hours to obtain a molybdenum-doped hard carbon material.

[0082] Example 13

[0083] S1: Glucose, ammonium molybdate, and ammonium persulfate were added to an aqueous solution at a molar ratio of 6:3:0.5, and stirred at room temperature for 30 minutes to fully dissolve them, to prepare 60 mL of a 0.6 mol / L glucose mixed solution.

[0084] S2 transferred 60 mL of 0.6 mol / L glucose mixed solution into the reactor and subjected it to hydrothermal reaction at 180 °C for 15 h. After the reactor was completely cooled, it was removed and the hydrothermal product was washed three times by centrifugation with deionized water and once with anhydrous ethanol, and then transferred to a 60 °C oven for drying for 12 h.

[0085] S3: The dried hydrothermal product is transferred to a high-temperature tube furnace, subjected to high-temperature pyrolysis and carbonization in an argon atmosphere, heated to 1300°C at a heating rate of 5°C / min, and kept warm for 3 hours to obtain a molybdenum-doped hard carbon material.

[0086] Example 14

[0087] S1: Add sucrose, ammonium molybdate, and ammonium persulfate to an aqueous solution at a molar ratio of 6:1:0.5, stir at room temperature for 30 minutes to fully dissolve them, and prepare 60 mL of a 0.6 mol / L glucose mixed solution.

[0088] S2 transferred 60 mL of 0.6 mol / L glucose mixed solution into the reactor and subjected it to hydrothermal reaction at 180 °C for 15 h. After the reactor was completely cooled, it was removed and the hydrothermal product was washed three times by centrifugation with deionized water and once with anhydrous ethanol, and then transferred to a 60 °C oven for drying for 12 h.

[0089] S3: The dried hydrothermal product is transferred to a high-temperature tube furnace, subjected to high-temperature pyrolysis and carbonization in an argon atmosphere, heated to 1300°C at a heating rate of 5°C / min, and kept warm for 3 hours to obtain a molybdenum-doped hard carbon material.

[0090] Example 15

[0091] S1: Fructose, ammonium molybdate, and ammonium persulfate were added to the aqueous solution at a molar ratio of 6:1:0.5, and stirred at room temperature for 30 minutes to fully dissolve them, thereby preparing 60 mL of a 0.6 mol / L glucose mixed solution.

[0092] S2 transferred 60 mL of 0.6 mol / L glucose mixed solution into the reactor and subjected it to hydrothermal reaction at 180 °C for 15 h. After the reactor was completely cooled, it was removed and the hydrothermal product was washed three times by centrifugation with deionized water and once with anhydrous ethanol, and then transferred to a 60 °C oven for drying for 12 h.

[0093] S3: The dried hydrothermal product is transferred to a high-temperature tube furnace, subjected to high-temperature pyrolysis and carbonization in an argon atmosphere, heated to 1300°C at a heating rate of 5°C / min, and kept warm for 3 hours to obtain a molybdenum-doped hard carbon material.

[0094] Example 16

[0095] S1: Glucose, sodium molybdate, and ammonium persulfate were added to an aqueous solution at a molar ratio of 6:1:0.5, and stirred at room temperature for 30 minutes to fully dissolve them, to prepare 60 mL of a 0.6 mol / L glucose mixed solution.

[0096] S2 transferred 60 mL of 0.6 mol / L glucose mixed solution into the reactor and subjected it to hydrothermal reaction at 180 °C for 15 h. After the reactor was completely cooled, it was removed and the hydrothermal product was washed three times by centrifugation with deionized water and once with anhydrous ethanol, and then transferred to a 60 °C oven for drying for 12 h.

[0097] S3: The dried hydrothermal product is transferred to a high-temperature tube furnace, subjected to high-temperature pyrolysis and carbonization in an argon atmosphere, heated to 1300°C at a heating rate of 5°C / min, and kept warm for 3 hours to obtain a molybdenum-doped hard carbon material.

[0098] Comparative Example 1

[0099] S1: Add glucose to deionized water solution and stir at room temperature for 30 minutes to fully dissolve it, and prepare 60 mL of 0.6 mol / L glucose mixed solution.

[0100] S2 transferred 60 mL of 0.6 mol / L glucose solution into the reactor and subjected it to hydrothermal reaction at 180 °C for 15 h. After the reactor was completely cooled, it was removed and the hydrothermal product was washed three times by centrifugation with deionized water and once with anhydrous ethanol, and then transferred to a 60 °C oven for drying for 12 h.

[0101] S3: The dried hydrothermal product is transferred to a high-temperature tube furnace, subjected to high-temperature pyrolysis and carbonization in an argon atmosphere, heated to 1300°C at a heating rate of 5°C / min, and kept warm for 3 hours to obtain a molybdenum-doped hard carbon material.

[0102] Comparative Example 2

[0103] S1: Glucose, ammonium molybdate, and ammonium persulfate were added to the aqueous solution at a molar ratio of 6:0:0.5, and stirred at room temperature for 30 minutes to fully dissolve them, to prepare 60 mL of a 0.6 mol / L glucose mixed solution.

[0104] S2 transferred 60 mL of 0.6 mol / L glucose mixed solution into the reactor and subjected it to hydrothermal reaction at 180 °C for 15 h. After the reactor was completely cooled, it was removed and the hydrothermal product was washed three times by centrifugation with deionized water and once with anhydrous ethanol, and then transferred to a 60 °C oven for drying for 12 h.

[0105] S3: The dried hydrothermal product is transferred to a high-temperature tube furnace, subjected to high-temperature pyrolysis and carbonization in an argon atmosphere, heated to 1300°C at a heating rate of 5°C / min, and kept warm for 3 hours to obtain a molybdenum-doped hard carbon material.

[0106] Comparative Example 3

[0107] S1: Glucose, ammonium molybdate, and ammonium persulfate were added to the aqueous solution in a molar ratio of 6:1:0, and stirred at room temperature for 30 minutes to fully dissolve them, to prepare 60 mL of a 0.6 mol / L glucose mixed solution.

[0108] S2 transferred 60 mL of 0.6 mol / L glucose mixed solution into the reactor and subjected it to hydrothermal reaction at 180 °C for 15 h. After the reactor was completely cooled, it was removed and the hydrothermal product was washed three times by centrifugation with deionized water and once with anhydrous ethanol, and then transferred to a 60 °C oven for drying for 12 h.

[0109] S3: The dried hydrothermal product is transferred to a high-temperature tube furnace, subjected to high-temperature pyrolysis and carbonization in an argon atmosphere, heated to 1300°C at a heating rate of 5°C / min, and kept warm for 3 hours to obtain a molybdenum-doped hard carbon material.

[0110] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited thereto. The technical solution of the present invention is to improve and optimize the preparation conditions of the hard carbon material under the same conditions, and all of them fall within the protection scope of the present invention.

[0111] Application and performance testing

[0112] The hard carbon materials of the above-described embodiments and comparative examples are used as the negative electrode active material for sodium ion batteries to prepare pole pieces. The specific method is as follows: the molybdenum-based doped sodium ion battery hard carbon negative electrode material is mixed with acetylene black and sodium carboxymethyl cellulose in a mass ratio of 8:1:1 and ground evenly, and then deionized water is added to stir the mixture evenly to obtain an electrode slurry. The electrode slurry is then evenly coated on a copper foil by a coating machine, and the copper foil is transferred to a vacuum oven and dried at 70°C for 16 hours. Finally, a disc electrode is cut with a punching machine to obtain a hard carbon negative electrode material electrode sheet, and a sodium ion button battery is prepared in a glove box, and the button battery is subjected to electrochemical performance testing.

[0113] Table 1 shows the electrochemical performance comparison of the examples and the comparative examples. Compared with the comparative examples, the hard carbon negative electrode materials prepared using the preparation method of the present invention have higher reversible capacity and first-cycle coulombic efficiency. In particular, the reversible capacity of the molybdenum-doped hard carbon in Example 2 reaches 289 mAh / g, and the first-cycle coulombic efficiency reaches 82.3%. Figure 1 This is the SEM image of the hard carbon in Example 2. It can be observed from the image that the prepared product is a micro-nano spherical structure. Figure 2 This is the charge and discharge curve of the molybdenum-doped hard carbon negative electrode material prepared in Example 2 at a current density of 50 mA / g. It can be observed from the figure that except for the first cycle charge and discharge curve, the second and third cycle charge and discharge curves are highly overlapped, indicating that a stable SEI layer is formed on the hard carbon surface, proving that the molybdenum-based doped hard carbon negative electrode material has excellent cycle stability and reversibility. Figure 3 and Figure 4This is the rate performance diagram of the hard carbon negative electrode material in Example 2. It can be seen from the figure that hard carbon still has good cycle stability at different current densities, especially the reversible capacity of 120 mAh / g at a current density of 1 A / g, suggesting its advantage in fast energy storage. Figure 5 The capacity retention rate of the hard carbon negative electrode material exceeds 100% after 59 cycles at a current density of 200 mA / g, showing good cycle stability.

[0114] Table 1 Electrochemical performance of the examples and comparative examples (current density 50 mAg -1 )

[0115]

[0116]

[0117] The embodiments of the present invention are described in detail above, but the present invention is not limited to the described embodiments. It is apparent to those skilled in the art that various changes, modifications, substitutions, and variations made to these embodiments without departing from the principles and spirit of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for preparing a molybdenum-doped hard carbon negative electrode material for sodium ion batteries, characterized in that: The steps include: S1, dissolving the hard carbon precursor, the molybdenum source doping phase, and the carbon-forming catalyst in deionized water in a certain proportion, and stirring for a certain period of time at room temperature to fully dissolve the three in the deionized water; In step S1, the hard carbon precursor is one of glucose, sucrose or fructose; the molybdenum source doping phase is ammonium molybdate or sodium molybdate; and the carbon forming catalyst is ammonium persulfate; The molar ratio of the hard carbon precursor, the molybdenum source doping phase and the carbon-forming catalyst ammonium persulfate is 6:(0.1-3):(0.1-2); S2. Transfer the mixed solution in S1 to a reactor and perform hydrothermal treatment at 150-240° C. for 6-48 hours. After the reaction is completely cooled to room temperature, the hydrothermal product is centrifuged, washed, and dried. S3. The product in S2 is subjected to high-temperature pyrolysis and carbonization under an inert atmosphere, wherein the high-temperature pyrolysis and carbonization temperature is 1000-1700° C. and the high-temperature pyrolysis and carbonization time is 2-12 hours to obtain a molybdenum-doped hard carbon material.

2. The method for preparing a molybdenum-doped sodium ion battery hard carbon negative electrode material according to claim 1, characterized in that: The molar concentration of glucose is 0.5-1 mol / L, the molar concentration of sucrose is 0.4-1 mol / L, the molar concentration of fructose is 0.5-1 mol / L, the molar concentration of ammonium molybdate or sodium molybdate is 0.1-0.2 mol / L, and the molar concentration of the carbon-forming catalyst ammonium persulfate is 0.05-0.1 mol / L.

3. The method for preparing a molybdenum-doped sodium ion battery hard carbon negative electrode material according to claim 1, characterized in that: The molar ratio of the hard carbon precursor, the molybdenum source doping phase and the carbon-forming catalyst ammonium persulfate is 6:(0.1-3):0.

5.

4. The method for preparing a molybdenum-doped sodium ion battery hard carbon negative electrode material according to claim 1 or 3, characterized in that: The molar ratio of the hard carbon precursor, the molybdenum source doping phase and the carbon-forming catalyst ammonium persulfate is 6:1:0.

5.

5. The method for preparing a molybdenum-doped sodium ion battery hard carbon negative electrode material according to claim 1, characterized in that: The hydrothermal reaction temperature of the mixed solution in step S2 is 160-200° C., and the hydrothermal reaction time is 10-24 h.

6. The method for preparing a molybdenum-doped sodium ion battery hard carbon negative electrode material according to claim 1, characterized in that: In step S3, the high-temperature pyrolysis carbonization temperature is 1200-1500° C., and the high-temperature pyrolysis carbonization time is 2-6 hours.

7. A molybdenum-based doped hard carbon negative electrode material for sodium ion batteries prepared by the method for preparing a molybdenum-based doped hard carbon negative electrode material for sodium ion batteries according to any one of claims 1 to 6.

8. A method for preparing a hard carbon negative electrode material electrode sheet for a sodium ion battery, characterized in that: The molybdenum-based doped sodium ion battery hard carbon negative electrode material according to claim 7 is mixed with acetylene black and sodium carboxymethyl cellulose in a certain proportion and ground evenly, and then deionized water is added and stirred evenly to obtain an electrode slurry, and then the electrode slurry is evenly coated on a copper foil by a coating machine, and transferred to a vacuum oven for drying at 60-100°C for 8-24h, and finally a disc electrode is cut with a punching machine to obtain a hard carbon negative electrode material electrode sheet.

9. The method for preparing a hard carbon negative electrode material for a sodium ion battery according to claim 8, characterized in that: The mass ratio of the molybdenum-based doped hard carbon material to acetylene black and sodium carboxymethyl cellulose is 8:1:1, the drying temperature of the electrode slurry is 70-80° C., and the drying time of the electrode slurry is 12-18 hours. 10 . A hard carbon negative electrode material electrode sheet for sodium ion batteries prepared by the method for preparing a hard carbon negative electrode material electrode sheet for sodium ion batteries according to any one of claims 8 to 9 .

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