Ag-S co-doped biomass hard carbon negative electrode material and preparation method thereof

Abstract

The invention discloses an Ag-S co-doped biomass hard carbon negative electrode material and a preparation method thereof. The preparation method comprises the following steps: uniformly mixing hard carbon precursor powder with a silver source and a sulfur source to form an Ag-S co-doped compound on the surface of a hard carbon precursor, forming a layer of amorphous carbon through vapor deposition, cooling to room temperature, and screening to obtain the Ag-S co-doped biomass hard carbon negative electrode material. According to the Ag-S co-doped biomass hard carbon negative electrode material, the material capacity and the first coulombic efficiency can be greatly improved, and meanwhile, good rate capability and cycle performance are achieved.

Description

Technical Field

[0001] The present invention belongs to the field of sodium ion battery material preparation, and specifically relates to an Ag-S co-doped biomass hard carbon negative electrode material and a preparation method thereof. Background Art

[0002] With the rapid development of sodium-ion batteries, their application in large-scale energy storage projects has gradually become mainstream. However, the difficulty in scalable mass production of anode materials for sodium-ion batteries has become a key constraint to their development. Currently, hard carbon anode materials for sodium-ion batteries mainly include resin-based, fossil fuel-based, and biomass-based. Although resin-based hard carbon anodes offer advantages such as high specific capacity, excellent electrochemical performance, and good consistency, they are difficult to achieve large-scale application due to high cost and huge pressure to mass produce. Fossil fuel-based hard carbon anodes, while offering a high cost-performance ratio, have average performance and an environmentally unfriendly production process. Biomass-based hard carbon anodes combine high performance with low cost, and biomass itself has rich heteroatoms and a unique microstructure. Hard carbon prepared by carbonizing plant biomass substrates can retain the material structure and pore channels of the plant biomass template, making it an ideal anode material for sodium-ion batteries. However, biomass-based hard carbon anode materials still have some limitations that hinder their development, such as low capacity and low first coulombic efficiency.

[0003] For example, patent CN113206246A discloses a hard carbon negative electrode based on bamboo and camphor wood as raw materials. The biomass raw materials are ultrasonically washed with deionized water, and then dried, pre-carbonized, mixed with heteroatom organic compounds and ball milled, high-temperature carbonized, pickled, and dried to obtain a heteroatom-doped biomass-derived hard carbon material. Although its reversible capacity can reach 303 mAh / g, its first coulombic efficiency is only 70.7%; for example, patent CN115385323A discloses "Heteroatom-doped biomass-derived hard carbon negative electrode material and its preparation method". The biomass precursor is subjected to low-temperature carbonization, grinding, hydrothermal reaction, and high-temperature carbonization and pyrolysis in an air atmosphere to obtain a heteroatom-doped biomass-derived hard carbon negative electrode material. Although its capacity can reach 336.7 mAh / g, its first coulombic efficiency is only 67.43%.

[0004] In response to the above problems, the present invention uses Ag-S co-doping to improve the performance of biomass hard carbon negative electrode materials, providing a biomass-based hard carbon negative electrode material for sodium ion batteries that can improve the first coulombic efficiency, has high energy density and good cycle performance. Summary of the Invention

[0005] The present invention aims to provide an Ag-S co-doped biomass hard carbon negative electrode material.

[0006] Another object of the present invention is to provide a method for preparing Ag-S co-doped biomass hard carbon negative electrode material.

[0007] The preparation method of the present invention comprises the following steps:

[0008] Step S1: placing the biomass precursor in a carbonization device under an inert atmosphere for pyrolysis at a temperature of 200-400°C for 1-6 hours; after pyrolysis, continuously introducing air into the carbonization device, heating the temperature to 400-600°C at a heating rate of 2-10°C / min in an air atmosphere, and maintaining the temperature for 1-8 hours. After pre-oxidation is completed, the precursor Dv50 is crushed to 4-15 μm using a crushing device to obtain a hard carbon precursor powder;

[0009] Step S2: A 1 mol / L mixed solution of a silver source and a sulfur source at a molar concentration ratio of 50-95:5-50 is prepared and placed in a magnetic stirrer together with hard carbon precursor powder to be thoroughly mixed to obtain a precursor slurry. The slurry is dried in a vacuum oven at 80°C for 2 hours. The slurry is transferred to a carbonization device and heated to 500-900°C at a rate of 1-10°C / min under an inert atmosphere and kept at this temperature for 2-8 hours.

[0010] Step S3: The product obtained in step S2 is washed 2-5 times with 0.5-3 mol / L acid solution, and then washed with deionized water until the product is neutral. After drying in a vacuum oven at 80°C for 2h, the material is transferred to a carbonization equipment. Under an inert atmosphere, the temperature is first increased to 300-550°C at 2-10°C / min and kept warm for 1-4h, then increased to 550-900°C and kept warm for 1-4h, and finally increased to 800-1300°C and kept warm for 1-4h. Then, the inert gas is stopped and the carbon source gas is changed to a gas flow rate of 50-300mL / min. Amorphous carbon is deposited on the surface of the material for 2-8h, cooled to room temperature with the furnace, and sieved to obtain Ag-S co-doped biomass hard carbon negative electrode material.

[0011] The biomass precursor in step S1 of the present invention is one or more of coconut shell, bamboo, walnut shell, peanut shell, and almond shell; the crushing equipment is one or more of air flow mill, mechanical mill, roller mill, and grinder.

[0012] Preferably, the biomass precursor in step S1 of the present invention is coconut shell; and the pulverizing equipment is a jet mill.

[0013] The silver source in step S2 of the present invention is one or more of silver nitrate, silver acetate, silver cyanide, and silver fluoride; the sulfur source is one or more of thiourea, sodium thiosulfate, sulfadiazine, ammonium sulfate, and allyl mercaptan.

[0014] Preferably, the silver source in step S2 of the present invention is silver nitrate; and the sulfur source is thiourea.

[0015] The acid solution in step S3 of the present invention is one or more of hydrochloric acid, hydrofluoric acid, nitric acid, and acetic acid; and the carbon source gas is one or more of methane, acetylene, ethylene, propane, and propylene.

[0016] Preferably, the acid solution in step S3 of the present invention is hydrochloric acid; and the carbon source gas is methane.

[0017] The carbonization equipment of the present invention is one or more of a tube furnace, a pit furnace, a rotary furnace and a box furnace.

[0018] Preferably, the carbonization equipment of the present invention is a tubular furnace.

[0019] The inert gas described in the present invention is argon.

[0020] Preferably, the pyrolysis temperature in step S1 of the present invention is 330°C, and the pyrolysis time is 3 hours; the heating rate is 3°C / min, the temperature is raised to 550°C, and the holding time is 3 hours; the precursor Dv50 is crushed to 8-9 μm.

[0021] Preferably, the molar concentration ratio of the silver source to the sulfur source in step S2 of the present invention is 60:40; the heating rate is 5°C / min, the temperature is raised to 800°C, and the holding time is 5 hours.

[0022] Preferably, the method for washing the product of step S2 in step S3 of the present invention is: washing the product obtained in step S2 three times with 1 mol / L acid solution; the heating method is: first heating to 550°C at 5°C / min and keeping warm for 1 hour, then heating to 850°C and keeping warm for 1 hour, and finally heating to 1200°C and keeping warm for 2 hours; the carbon source gas flow rate is 100 mL / min; and the time for depositing amorphous carbon on the material surface is 3 hours.

[0023] The Ag-S co-doped biomass hard carbon negative electrode material is prepared by the preparation method of the present invention.

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

[0025] The present invention uniformly mixes a silver source, a sulfur source, and a hard carbon precursor to form an Ag-S co-doped compound on the surface of the hard carbon precursor, and then forms a layer of amorphous carbon through vapor deposition. The synergistic effect of the dual processes of Ag-S co-doping and vapor deposition can not only significantly expand the graphite interlayer spacing of the hard carbon and reduce the sodium ion embedding barrier, but also improve electronic conductivity and accelerate charge transfer. The co-doping of Ag-S increases the density of defect sites, promoting the adsorption and intercalation of sodium ions. At the same time, the uniform carbon layer on the surface of the material can reduce the irreversible sodium loss caused by the high specific surface area, inhibit the side reaction between the electrolyte and the defect sites, and form a stable SEI film. Therefore, not only the material capacity and initial efficiency are improved, but also the rate performance and cycle performance of the material are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 SEM image of the Ag-S co-doped biomass hard carbon anode material prepared in Example 1;

[0027] Figure 2 SEM image of the Ag-S co-doped biomass hard carbon negative electrode material prepared in Example 2. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described in detail below through specific embodiments.

[0029] Example 1

[0030] Step S1: placing the biomass precursor coconut shell in an argon inert atmosphere for pyrolysis at 280°C for 4 hours in a tube furnace; after pyrolysis, continuously introducing air into the tube furnace, heating the temperature to 450°C at a rate of 3°C / min in an air atmosphere, and maintaining the temperature for 5 hours. After pre-oxidation, the precursor Dv50 is crushed to 8-9 μm using a jet mill to obtain a hard carbon precursor powder;

[0031] Step S2: Prepare a 1 mol / L mixed solution of silver nitrate and thiourea at a molar concentration ratio of 50:50, put it into a magnetic stirrer together with the hard carbon precursor powder and mix thoroughly to obtain a precursor slurry. Dry the slurry in a vacuum oven at 80°C for 2 h, then transfer it to a tubular furnace, and in an argon inert atmosphere, heat it to 700°C at a rate of 3°C / min and keep it warm for 5 h.

[0032] Step S3: The product obtained in step S2 was washed three times with a 1 mol / L hydrochloric acid solution, and then washed with deionized water until the product was neutral. After drying in a vacuum oven at 80°C for 2 h, the material was transferred to a tubular furnace. Under an argon inert atmosphere, the temperature was first increased to 450°C at a rate of 5°C / min and kept warm for 2 h, then increased to 700°C and kept warm for 2 h, and finally increased to 1100°C and kept warm for 2 h. Subsequently, the argon gas was stopped and replaced with methane at a gas flow rate of 100 mL / min. Amorphous carbon was deposited on the surface of the material for 4 h. After cooling to room temperature with the furnace, the Ag-S co-doped biomass hard carbon negative electrode material was obtained by screening.

[0033] Example 2

[0034] Step S1: placing the biomass precursor bamboo in an argon inert atmosphere for pyrolysis at 280°C for 4 hours; after pyrolysis, continuously introducing air into the tube furnace, heating the mixture to 450°C at a heating rate of 5°C / min in an air atmosphere, and maintaining the temperature for 5 hours. After pre-oxidation, the precursor Dv50 is crushed to 11-12 μm using a mechanical grinder to obtain a hard carbon precursor powder;

[0035] Step S2: Prepare a 1 mol / L mixed solution of silver nitrate and thiourea at a molar concentration ratio of 60:40, put it into a magnetic stirrer together with the hard carbon precursor powder and mix thoroughly to obtain a precursor slurry. Dry the slurry in a vacuum oven at 80°C for 2 h, then transfer it to a tubular furnace, and in an argon inert atmosphere, heat it to 700°C at a rate of 3°C / min and keep it warm for 5 h.

[0036] Step S3: The product obtained in step S2 was washed three times with a 1.5 mol / L nitric acid solution, and then washed with deionized water until the product was neutral. After drying in a vacuum oven at 80°C for 2 h, the material was transferred to a tubular furnace. Under an argon inert atmosphere, the temperature was first increased to 450°C at 5°C / min and kept warm for 2 h, then increased to 700°C and kept warm for 2 h, and finally increased to 1200°C and kept warm for 2 h. Subsequently, the argon gas was stopped and replaced with methane at a gas flow rate of 150 mL / min. Amorphous carbon was deposited on the surface of the material for 4 h. After cooling to room temperature with the furnace, the Ag-S co-doped biomass hard carbon negative electrode material was obtained by screening.

[0037] Example 3

[0038] Step S1: placing the biomass precursor coconut shell in an argon inert atmosphere for pyrolysis at 330°C for 3 hours in a rotary kiln; after pyrolysis, continuously introducing air into the rotary kiln, heating the temperature to 550°C at a rate of 5°C / min in an air atmosphere, and maintaining the temperature for 3 hours. After pre-oxidation, the precursor Dv50 is crushed to 8-9 μm using a roller mill to obtain a hard carbon precursor powder;

[0039] Step S2: Prepare a 1 mol / L mixed solution of silver nitrate and sulfadiazine at a molar concentration ratio of 50:50, put it into a magnetic stirrer together with the hard carbon precursor powder and mix thoroughly to obtain a precursor slurry. Dry the slurry in a vacuum oven at 80°C for 2 h, then transfer it to a rotary kiln, and heat it to 800°C at a rate of 5°C / min under an argon inert atmosphere and keep it warm for 3 h.

[0040] Step S3: The product obtained in step S2 was washed twice with a 3 mol / L hydrochloric acid solution, and then washed with deionized water until the product was neutral. After drying in a vacuum oven at 80°C for 2 h, the material was transferred to a rotary kiln. Under an argon inert atmosphere, the temperature was first increased to 550°C at 5°C / min and kept warm for 1 h, then increased to 850°C and kept warm for 1 h, and finally increased to 1200°C and kept warm for 2 h. Subsequently, the argon gas was stopped and replaced with ethylene at a gas flow rate of 100 mL / min. Amorphous carbon was deposited on the surface of the material for 6 h. After cooling to room temperature with the furnace, the Ag-S co-doped biomass hard carbon negative electrode material was obtained by screening.

[0041] Example 4

[0042] Step S1: placing the biomass precursor coconut shell in an argon inert atmosphere for pyrolysis at 330°C for 3 hours in a tube furnace; after pyrolysis, continuously introducing air into the tube furnace, heating the temperature to 550°C at a rate of 3°C / min in an air atmosphere, and maintaining the temperature for 3 hours. After pre-oxidation, the precursor Dv50 is crushed to 8-9 μm using a jet mill to obtain a hard carbon precursor powder;

[0043] Step S2: Prepare a 1 mol / L mixed solution of silver nitrate and thiourea in a molar concentration ratio of 60:40, put it into a magnetic stirrer together with the hard carbon precursor powder and mix thoroughly to obtain a precursor slurry. Dry the slurry in a vacuum oven at 80°C for 2 h, then transfer it to a tubular furnace, and in an argon inert atmosphere, heat it to 800°C at a rate of 5°C / min and keep it warm for 5 h.

[0044] Step S3: The product obtained in step S2 was washed three times with a 1 mol / L hydrochloric acid solution, and then washed with deionized water until the product was neutral. After drying in a vacuum oven at 80°C for 2 h, the material was transferred to a tubular furnace. Under an argon inert atmosphere, the temperature was first increased to 550°C at 5°C / min and kept warm for 1 h, then increased to 850°C and kept warm for 1 h, and finally increased to 1200°C and kept warm for 2 h. Subsequently, the argon gas was stopped and replaced with methane at a gas flow rate of 100 mL / min. Amorphous carbon was deposited on the surface of the material for 3 h. After cooling to room temperature with the furnace, the Ag-S co-doped biomass hard carbon negative electrode material was obtained by screening.

[0045] Example 5

[0046] Step S1: placing the biomass precursor bamboo in an argon inert atmosphere for pyrolysis at 380°C for 2 hours in a pit furnace; after pyrolysis, continuously introducing air into the pit furnace, heating the temperature to 450°C at a rate of 5°C / min in an air atmosphere, and maintaining the temperature for 3 hours. After pre-oxidation, the precursor Dv50 is crushed to 8-9 μm using a jet mill to obtain a hard carbon precursor powder;

[0047] Step S2: Prepare a 1 mol / L mixed solution of silver nitrate and thiourea at a molar concentration ratio of 50:50, put it into a magnetic stirrer together with the hard carbon precursor powder and mix thoroughly to obtain a precursor slurry. Dry the slurry in a vacuum oven at 80°C for 2 h, then transfer it to a pit furnace, and in an argon inert atmosphere, heat it to 850°C at a rate of 5°C / min and keep it warm for 4 h.

[0048] Step S3: The product obtained in step S2 was washed three times with 1 mol / L acetic acid solution, and then washed with deionized water until the product was neutral. After drying in a vacuum oven at 80°C for 2 h, the material was transferred to a pit furnace. Under an argon inert atmosphere, the temperature was first increased to 350°C at 5°C / min and kept warm for 2 h, then increased to 600°C and kept warm for 2 h, and finally increased to 1000°C and kept warm for 2 h. Then, the argon gas was stopped and acetylene was introduced instead with a gas flow rate of 100 mL / min. Amorphous carbon was deposited on the surface of the material for 6 h. After cooling to room temperature with the furnace, the Ag-S co-doped biomass hard carbon negative electrode material was obtained by screening.

[0049] Example 6

[0050] Step S1: placing the biomass precursor coconut shell in an argon inert atmosphere for pyrolysis at 380°C for 2 hours in a tube furnace; after pyrolysis, continuously introducing air into the tube furnace, heating the temperature to 550°C at a rate of 5°C / min in an air atmosphere, and maintaining the temperature for 3 hours. After pre-oxidation, the precursor Dv50 is crushed to 11-12 μm using a mechanical grinder to obtain a hard carbon precursor powder;

[0051] Step S2: Prepare a 1 mol / L mixed solution of silver nitrate and thiourea at a molar concentration ratio of 70:30, put it into a magnetic stirrer together with the hard carbon precursor powder and mix thoroughly to obtain a precursor slurry. Dry the slurry in a vacuum oven at 80°C for 2 h, then transfer it to a tubular furnace, and in an argon inert atmosphere, heat it to 850°C at a rate of 5°C / min and keep it warm for 4 h.

[0052] Step S3: The product obtained in step S2 was washed three times with a 2 mol / L nitric acid solution, and then washed with deionized water until the product was neutral. After drying in a vacuum oven at 80°C for 2 h, the material was transferred to a tubular furnace. Under an argon inert atmosphere, the temperature was first increased to 550°C at 5°C / min and kept warm for 1 h, then increased to 850°C and kept warm for 1 h, and finally increased to 1200°C and kept warm for 2 h. Subsequently, the argon gas was stopped and replaced with propylene at a gas flow rate of 50 mL / min. Amorphous carbon was deposited on the surface of the material for 6 h. After cooling to room temperature with the furnace, the Ag-S co-doped biomass hard carbon negative electrode material was obtained by screening.

[0053] Example 7

[0054] Step S1: placing the biomass precursor coconut shell in an argon inert atmosphere for pyrolysis at 240°C for 6 hours in a pit furnace; after pyrolysis, continuously introducing air into the pit furnace, heating the temperature to 400°C at a rate of 2°C / min in an air atmosphere, and maintaining the temperature for 8 hours. After pre-oxidation, the precursor Dv50 is crushed to 4-8 μm using a mechanical grinder to obtain a hard carbon precursor powder;

[0055] Step S2: Silver sulfate and sodium thiosulfate are prepared into a 1 mol / L mixed solution with a molar concentration ratio of 85:15, and the mixture is put into a magnetic stirrer together with the hard carbon precursor powder and mixed thoroughly to obtain a precursor slurry. The slurry is dried in a vacuum oven at 80°C for 2 h, and then transferred to a pit furnace. In an argon inert atmosphere, the temperature is increased to 500°C at a rate of 2°C / min and kept warm for 8 h.

[0056] Step S3: The product obtained in step S2 was washed 5 times with 0.5 mol / L hydrofluoric acid, and then washed with deionized water until the product was neutral. After drying in a vacuum oven at 80°C for 2 h, the material was transferred to a pit furnace. In an argon inert atmosphere, the temperature was first raised to 300°C at 2°C / min and kept warm for 4 h, then raised to 550°C and kept warm for 4 h, and finally raised to 800°C and kept warm for 4 h. Then, the argon gas was stopped and replaced with acetylene at a gas flow rate of 50 mL / min. Amorphous carbon was deposited on the surface of the material for 8 h. After cooling to room temperature with the furnace, the Ag-S co-doped biomass hard carbon negative electrode material was obtained by screening.

[0057] Example 8

[0058] Step S1: placing the biomass precursor walnut shell in an argon inert atmosphere for pyrolysis at 400°C for 1 hour in a rotary kiln; after pyrolysis, continuously introducing air into the rotary kiln, heating the temperature to 600°C at a rate of 10°C / min in an air atmosphere, and maintaining the temperature for 1 hour. After pre-oxidation, the precursor Dv50 is crushed to 12-15 μm using a roller mill to obtain a hard carbon precursor powder;

[0059] Step S2: Prepare a 1 mol / L mixed solution of silver nitrate and sulfadiazine at a molar concentration ratio of 50:50, put it into a magnetic stirrer together with the hard carbon precursor powder and mix thoroughly to obtain a precursor slurry. Dry the slurry in a vacuum oven at 80°C for 2 h, then transfer it to a rotary kiln, and heat it to 900°C at a rate of 10°C / min under an argon inert atmosphere and keep it warm for 2 h.

[0060] Step S3: The product obtained in step S2 was washed twice with 3 mol / L nitric acid, and then washed with deionized water until the product was neutral. After drying in a vacuum oven at 80°C for 2 h, the material was transferred to a rotary kiln. In an argon inert atmosphere, the temperature was first increased to 550°C at 10°C / min and kept warm for 1 h, then increased to 900°C and kept warm for 1 h, and finally increased to 1300°C and kept warm for 1 h. Subsequently, the argon gas was stopped and replaced with methane at a gas flow rate of 300 mL / min. Amorphous carbon was deposited on the surface of the material for 2 h. After cooling to room temperature with the furnace, the Ag-S co-doped biomass hard carbon negative electrode material was obtained by screening.

[0061] Example 9

[0062] Step S1: placing the biomass precursor peanut shells in an argon inert atmosphere for pyrolysis at 380°C for 2 hours. After pyrolysis, air was continuously introduced into the box furnace, and the temperature was raised to 550°C at a heating rate of 5°C / min in an air atmosphere. The temperature was maintained for 3 hours. After pre-oxidation, the precursor Dv50 was crushed to 11-12 μm using a grinder to obtain a hard carbon precursor powder.

[0063] Step S2: Prepare a 1 mol / L mixed solution of silver fluoride and ammonium sulfate in a molar concentration ratio of 60:40, put it into a magnetic stirrer together with the hard carbon precursor powder and mix thoroughly to obtain a precursor slurry. Dry the slurry in a vacuum oven at 80°C for 2 h, then transfer it to a box furnace, and in an argon inert atmosphere, heat it to 850°C at a rate of 5°C / min and keep it warm for 4 h.

[0064] Step S3: The product obtained in step S2 was washed three times with 1 mol / L nitric acid, and then washed with deionized water until the product was neutral. After drying in a vacuum oven at 80°C for 2 h, the material was transferred to a box furnace, and the temperature was first increased to 350°C at 5°C / min in an argon inert atmosphere and kept warm for 2 h, then increased to 600°C and kept warm for 2 h, and finally increased to 1000°C and kept warm for 2 h. Subsequently, the inert gas was stopped and replaced with propane with a gas flow rate of 200 mL / min. Amorphous carbon was deposited on the surface of the material for 4 h. After cooling to room temperature with the furnace, the Ag-S co-doped biomass hard carbon negative electrode material was obtained by screening.

[0065] Example 10

[0066] Step S1: placing the biomass precursor almond shell in an argon inert atmosphere for pyrolysis at 280°C for 4 hours in a tube furnace; after pyrolysis, continuously introducing air into the tube furnace, heating the temperature to 450°C at a rate of 5°C / min in an air atmosphere, and maintaining the temperature for 5 hours. After pre-oxidation, the precursor Dv50 is crushed to 8-9 μm using a jet mill to obtain a hard carbon precursor powder;

[0067] Step S2: Prepare a 1 mol / L mixed solution of silver cyanide and allyl mercaptan at a molar concentration ratio of 70:30, put it into a magnetic stirrer together with the hard carbon precursor powder and mix it thoroughly to obtain a precursor slurry. After mixing, dry it in a vacuum oven at 80°C for 2 hours, then transfer it to a tubular furnace, and heat it to 700°C at a rate of 3°C / min under an inert atmosphere and keep it warm for 5 hours.

[0068] Step S3: The product obtained in step S2 was washed twice with 0.5 mol / L acetic acid, and then washed with deionized water until the product was neutral. After drying in a vacuum oven at 80°C for 2 h, the material was transferred to a tubular furnace, and the temperature was first increased to 450°C at 5°C / min and kept warm for 2 h in an inert atmosphere, then increased to 700°C and kept warm for 2 h, and finally increased to 1200°C and kept warm for 2 h. Subsequently, the inert gas was stopped and propylene was introduced instead with a gas flow rate of 100 mL / min. Amorphous carbon was deposited on the surface of the material for 4 h. After cooling to room temperature with the furnace, the Ag-S co-doped biomass hard carbon negative electrode material was obtained by screening.

[0069] Comparative Example 1

[0070] The difference from Example 1 is that there is no step S2.

[0071] Comparative Example 2

[0072] The difference from Example 1 is that in step S3, the temperature is directly raised to 1100° C. at 5° C. / min and kept at that temperature for 6 h.

[0073] Comparative Example 3

[0074] Different from Example 3, in step S3, there is no need to switch to methane gas, and the temperature is kept at 1200° C. for 2 hours.

[0075] In order to verify the effectiveness of the present invention, the invention team conducted a series of experiments, as follows:

[0076] (1) SEM test

[0077] The Ag-S co-doped biomass hard carbon negative electrode material prepared in Example 1-2 was subjected to SEM testing, and the results were as follows: Figure 1-2 As shown in the figure, it can be seen that the Ag-S co-doped biomass hard carbon negative electrode materials prepared in Examples 1-2 all have a granular structure and a uniform size distribution.

[0078] (2) Button battery test

[0079] The Ag-S co-doped biomass hard carbon negative electrode materials obtained in Examples 1-10 and Comparative Examples 1-3 were respectively assembled into button batteries.

[0080] The preparation method is as follows: 8g of hard carbon negative electrode material, 1g of acetylene black, and 1g of polyvinylidene fluoride (PVDF) are mixed in N-methylpyrrolidone (NMP) and evenly mixed, coated on copper foil, placed in a vacuum drying oven at 110°C for 3h, and then sliced ​​to prepare a sodium ion battery negative electrode sheet; using a sodium sheet as a counter electrode, the above negative electrode sheet and sodium sheet are assembled into a 2032 button cell in an argon-filled glove box, and the electrolyte used is NaClO4 with a concentration of 1mol / L; the electrochemical performance is carried out on a Wuhan Blue Electric CT2001A battery tester, with a charge and discharge voltage range of 0.005V to 2.0V and a charge and discharge rate of 0.1C. At the same time, the rate (2C / 0.1C) and cycle performance (0.2C / 0.2C, 100 times) of its button cell are tested, and the test results are shown in Table 1 below.

[0081] Table 1 Test results

[0082]

[0083] As can be seen from Table 1, ① Example 4 is the best embodiment of the present invention; ② Comparative Example 1 is not doped with Ag or S, and its first charge specific capacity is 294.5 mAh / g and its first coulombic efficiency is 74.3%; Comparative Example 2 adopts a one-step carbonization method for carbonization in step S3, and its first charge specific capacity is 343.7 mAh / g and its first coulombic efficiency is 82.7%; Comparative Example 3 is not subjected to methane gas vapor deposition, and its first charge specific capacity is 321.6 mAh / g and its first coulombic efficiency is 79.6%; Comparing the above three comparative examples with the embodiments, it can be seen that the Ag-S co-doping process, the step-by-step temperature carbonization process and the vapor deposition process in the material are all beneficial to improving the performance of the material. From the Ag-S co-doped biomass hard carbon negative electrode materials prepared in Comparative Examples 1-3 and Examples 1-10, the first charge specific capacity, first efficiency, rate performance, and cycle performance of the materials are significantly improved, which is mainly due to the synergistic effect of the Ag-S co-doping process and the vapor deposition process of the present invention, which is specifically manifested in: First, the co-doping of Ag-S can not only significantly expand the graphite layer spacing of the hard carbon and reduce the sodium ion embedding barrier, but also the addition of Ag can enhance the electronic conductivity and accelerate the charge transfer, and can form a composite active site with S, further increase the defect site density, and promote the adsorption and intercalation of sodium ions; second, a uniform carbon layer is formed on the surface of the material by vapor deposition, which closes some micropores, reduces the irreversible sodium loss caused by the high specific surface area, and at the same time inhibits the side reaction between the electrolyte and the defect sites to form a stable SEI film.

[0084] Although the present invention has been described in detail above using general explanations, specific embodiments, and experiments, it will be apparent to those skilled in the art that modifications and improvements may be made based on the present invention. Therefore, such modifications and improvements, which do not depart from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. A method for preparing an Ag-S co-doped biomass hard carbon negative electrode material, characterized in that: The preparation method comprises the following steps: Step S1: placing the biomass precursor in a carbonization device under an inert atmosphere for pyrolysis at a temperature of 200-400°C for 1-6 hours; after pyrolysis, continuously introducing air into the carbonization device, heating the temperature to 400-600°C at a heating rate of 2-10°C / min in an air atmosphere, and maintaining the temperature for 1-8 hours. After pre-oxidation is completed, the precursor Dv50 is crushed to 4-15 μm using a crushing device to obtain a hard carbon precursor powder; The biomass precursor is one or more of coconut shell, bamboo, walnut shell, peanut shell, and almond shell; The pulverizing equipment is one or more of a jet mill, a mechanical mill, a roller mill, and a grinder; Step S2: A 1 mol / L mixed solution of a silver source and a sulfur source at a molar concentration ratio of 50-95:5-50 is prepared and placed in a magnetic stirrer together with hard carbon precursor powder to be thoroughly mixed to obtain a precursor slurry. The slurry is dried in a vacuum oven at 80°C for 2 hours. The slurry is transferred to a carbonization device and heated to 500-900°C at a rate of 1-10°C / min under an inert atmosphere and kept at this temperature for 2-8 hours. The silver source is one or more of silver nitrate, silver acetate, silver cyanide, and silver fluoride; The sulfur source is one or more of thiourea, sodium thiosulfate, sulfadiazine, ammonium sulfate, and allyl mercaptan; Step S3: The product obtained in step S2 is washed 2-5 times with 0.5-3 mol / L acid solution, and then washed with deionized water until the product is neutral. After drying in a vacuum oven at 80°C for 2h, the material is transferred to a carbonization device. Under an inert atmosphere, the temperature is first increased to 300-550°C at 2-10°C / min and kept warm for 1-4h, then increased to 550-900°C and kept warm for 1-4h, and finally increased to 800-1300°C and kept warm for 1-4h. Subsequently, the inert gas is stopped and replaced with a carbon source gas at a gas flow rate of 50-300 mL / min. Amorphous carbon is deposited on the surface of the material for 2-8h, and then cooled to room temperature with the furnace. Screening is performed to obtain Ag-S co-doped biomass hard carbon negative electrode material; The acid solution is one or more of hydrochloric acid, hydrofluoric acid, nitric acid, and acetic acid; The carbon source gas is one or more of methane, acetylene, ethylene, propane, and propylene; The carbonization equipment is one or more of a tube furnace, a pit furnace, a rotary furnace, and a box furnace.

2. The method for preparing an Ag-S co-doped biomass hard carbon negative electrode material according to claim 1, characterized in that: The pyrolysis temperature in step S1 is 330°C and the pyrolysis time is 3 hours; The heating rate is 3°C / min, the temperature is raised to 550°C, and the holding time is 3h; The precursor Dv50 was crushed to 8-9 μm.

3. The method for preparing an Ag-S co-doped biomass hard carbon negative electrode material according to claim 1, characterized in that: In step S1, the biomass precursor is coconut shell; and the pulverizing equipment is a jet mill.

4. The method for preparing an Ag-S co-doped biomass hard carbon negative electrode material according to claim 1, characterized in that: The molar concentration ratio of the silver source to the sulfur source in step S2 is 60:40; The heating rate is 5°C / min, the temperature is raised to 800°C, and the holding time is 5 hours.

5. The method for preparing an Ag-S co-doped biomass hard carbon negative electrode material according to claim 1, characterized in that: The silver source in step S2 is silver nitrate; The sulfur source is thiourea.

6. The method for preparing an Ag-S co-doped biomass hard carbon negative electrode material according to claim 1, characterized in that: The method for washing the product obtained in step S2 in step S3 is as follows: washing the product obtained in step S2 with 1 mol / L acid solution three times; The heating method is as follows: first heating to 550°C at 5°C / min and keeping the temperature for 1 hour, then heating to 850°C and keeping the temperature for 1 hour, and finally heating to 1200°C and keeping the temperature for 2 hours; The carbon source gas flow rate is 100 mL / min; The time for depositing amorphous carbon on the surface of the material is 3 hours.

7. The method for preparing an Ag-S co-doped biomass hard carbon negative electrode material according to claim 1, characterized in that: The acid solution in step S3 is hydrochloric acid; The carbon source gas is methane.

8. The method for preparing an Ag-S co-doped biomass hard carbon negative electrode material according to claim 1, characterized in that: The carbonization equipment is a tubular furnace.

9. The method for preparing an Ag-S co-doped biomass hard carbon negative electrode material according to claim 1, characterized in that: The inert gas is argon.

10. An Ag-S co-doped biomass hard carbon negative electrode material, characterized in that: Prepared by the preparation method according to any one of claims 1 to 9.

Images