Preparation method of new substance derived hard carbon negative electrode material

Abstract

The invention relates to a preparation method of a new substance derived hard carbon negative electrode material, which comprises the following steps of: under an ultrasonic condition, cleaning mistletoe stems with deionized water, drying, crushing for later use, performing pre-carbonization and acid pickling treatment, absolutely mixing with thiourea, and further performing carbonization treatment to obtain a hard carbon material. According to the method, two-step carbonization is adopted, pre-carbonization is performed firstly, then carbonization is performed, carbon elements in the raw materials are fixed in solid carbon as much as possible, and the yield is increased; thiourea is added in the material preparation process, active adsorption sites of the material are improved, pore forming is assisted, and after two-step carbonization and heteroatom doping, the capacity and initial coulombic efficiency of the biomass hard carbon material are effectively improved. The problems that an existing biomass hard carbon material is few in reversible sodium ion adsorption active sites, low in tilt capacity and low in initial coulombic efficiency are solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of sodium ion battery negative electrode active materials, and relates to a preparation method of a new biomass-derived hard carbon negative electrode material. BACKGROUND

[0002] The safety performance and service life of a sodium ion battery depend on a negative electrode material, and at the same time, greatly affect the reaction kinetics and energy density of the battery.

[0003] Straw burning and automobile exhaust emission have caused great concern about global warming and environmental pollution. Therefore, carbon-based materials have become a negative electrode material of a sodium ion battery due to their good environmental protection. Hard carbon material is widely concerned due to its simple preparation, wide source and low price, and its large interlayer spacing and rich layered porous structure effectively avoid the volume expansion caused by the embedding / extraction of sodium ions in the negative electrode. Therefore, hard carbon material is a very ideal negative electrode material of a sodium ion battery. The low voltage platform of hard carbon material plays an important role in improving the energy density of the whole battery, and has a great influence on the practical application of the sodium ion battery.

[0004] Hard carbon material is mainly prepared by pyrolysis of polymers, organic matter and biomass. Common precursors of hard carbon include polymers (such as phenolic resin, furfural) and sugar (such as glucose, sucrose and biomass material). However, polymers and organic compounds are high in cost and low in yield, and therefore are not suitable for large-scale production of hard carbon. Biomass-derived hard carbon material has the advantages of environmental protection, low cost and good reversibility. However, due to the different structures of hard carbon prepared from different biomass materials, the selection of biomass material has a great influence on the electrochemical performance of the sodium ion battery. In addition, the low sodium ion diffusion kinetics hinders the fast charge and discharge performance of the hard carbon material, resulting in poor rate performance and cycle stability, and the hard carbon material also has a low specific capacity, which greatly restricts the development of the hard carbon material.

[0005] In order to solve the above technical problems, the microstructure of the hard carbon material can be adjusted, for example, prepared into a three-dimensional internet-like structure, to provide a path for the transmission of sodium ions, improve the reaction kinetics, or introduce active sites by doping heteroatoms (N, O, P, S), thereby improving the specific capacity of the sodium ion battery. So far, S atoms do not cause serious volume expansion when introduced into carbon materials because their radius is similar to that of C, and N atoms can expand the interlayer spacing when introduced into carbon materials because their radius is larger, thus providing more space for the storage of sodium ions. Therefore, there must be a doping material containing S atoms and N atoms, and there must be a new precursor with a porous structure that is beneficial to the intercalation storage of sodium ions. SUMMARY

[0006] Objectives of the invention

[0007] The purpose of the present application is to provide a new biomass-derived hard carbon negative material preparation method. The prepared new biomass-derived hard carbon negative material is doped with thiourea, which can expand the interlayer distance of the hard carbon material, increase the active sites, and improve the capacity of the sodium ion battery in the low voltage platform area, as well as the rate performance and cycle stability.

[0008] Technical scheme

[0009] A new biomass-derived hard carbon negative material preparation method, comprising the following steps:

[0010] Step one: clean the mistletoe stems, dry them, and then cool them to room temperature naturally before crushing them into powder;

[0011] Step two: the powder crushed in step one is heated to 300-500°C under nitrogen atmosphere for 1-3 hours, naturally cooled to room temperature, then acid-washed to remove impurities, filtered through a filter membrane, dried, and naturally cooled to room temperature to obtain a pre-carbonized material;

[0012] Step three: grind the thiourea into thiourea powder, mix the thiourea powder with the pre-carbonized material obtained in step two at a mass ratio of (0.5-3):1, and stir evenly;

[0013] Step four: heat the material stirred evenly in step three to 1000-1400°C under nitrogen atmosphere for 1-3 hours, and naturally cool to room temperature to obtain a new biomass-derived hard carbon negative material.

[0014] Further, in step one, the mistletoe stems are cleaned with deionized water under ultrasonic conditions at 40-50 kHz for 3-5 hours, then dried in a vacuum oven at a temperature of 100-110°C for more than or equal to 1 hour, and then crushed into powder with a particle size of 0.5-1 um using a cell wall crusher.

[0015] Further, in step two, the acid-washing to remove impurities uses a dilute hydrochloric acid solution, which is prepared by mixing deionized water with hydrochloric acid with a concentration of 35%-40% at a volume ratio of 33:7.

[0016] Further, in step two, the filter membrane is a microporous filter membrane with a particle size of 0.45 um, and the filtration is performed under a pressure of -0.09 to -0.11 MPa. Then, the obtained material is placed in a vacuum oven and dried at a temperature of 100-110°C for 10-12 hours.

[0017] Further, in the third step, the thiourea powder has a particle size of 0.5-1 um, and the thiourea powder is mixed with the pre-carbonized material obtained in the second step in a stirrer with a rotation speed of 417-500 r / min, and the stirring time is not less than 1 h.

[0018] Further, the fourth step is performed in a rotary carbonization furnace, and the rotary carbonization furnace comprises a furnace body, a rotating drum, a motor and resistance wires, the resistance wires are arranged in the furnace body, the motor is arranged on one side outside the furnace body, the motor shaft of the motor is connected with the rotating drum in the furnace body, the furnace body is provided with an air inlet pipe and an air outlet, the end of the air inlet pipe is located at the two ends of the rotating drum and faces the inside of the rotating drum, and the furnace body is provided with a furnace door; the material after uniform stirring in the third step is put into the rotating drum of the rotary carbonization furnace, and the rotating drum is rotated continuously; after being kept at 1000-1400 DEG C for 1-3 h in a nitrogen atmosphere, the material in the rotating drum is a new biomass-derived hard carbon negative material.

[0019] Further, the resistance wires are connected with a resistance wire power supply control device outside the furnace body through power supply lines.

[0020] Further, the motor is fixed on a pad block, the pad block is fixed on one side of the furnace body, the motor shaft of the motor is located on the inner side of the pad block and is connected with a proximal shaft through a shaft coupling, the proximal shaft passes through the furnace body and is connected with a rotating shaft through a shaft coupling, support frames are fixedly arranged at the two ends of the rotating drum, the rotating shaft passes through and is clamped and fixed with the two support frames, the end of the rotating shaft away from the motor is connected with a distal shaft through a shaft coupling, the distal shaft passes through the furnace body, and bearings are arranged between the proximal shaft, the distal shaft and the furnace body.

[0021] Further, the rotating drum has a rotation speed of 50-80 r / h.

[0022] The new biomass-derived hard carbon negative material prepared by the method is used as a negative electrode of a sodium ion battery.

[0023] Advantages and effects

[0024] The two-step carbonization, pre-carbonization and then carbonization, is adopted in the application, so that the carbon elements in the raw material are fixed in the solid carbon as much as possible, and the yield is increased; the thiourea is added in the material preparation process, the active adsorption sites of the material are improved, and pore formation is assisted; after two-step carbonization and heteroatom doping, the capacity and initial coulombic efficiency of the biomass hard carbon material are effectively improved. The mistletoe-derived hard carbon negative material with a relatively low specific surface area is synthesized by taking the mistletoe as a precursor, and the two-step carbonization method and thiourea doping are combined, so that the closed micropores and sulfur atoms are introduced into the hard carbon material, and the problems of the existing biomass hard carbon material, such as few reversible sodium ion adsorption active sites, low inclined capacity and low initial coulombic efficiency, are solved. BRIEF DESCRIPTION OF DRAWINGS

[0025] The application will be further described below in conjunction with the accompanying drawings and specific embodiments. The scope of protection of the application is not limited to the following content.

[0026] Figure 1 SEM image of the comparative material;

[0027] Figure 2 EDS image of the material of Example 2;

[0028] Figure 3 Long cycle performance graph of the material of Example 2 at a current density of 1A / g;

[0029] Figure 4 Cycle performance graph of the comparative material, the material of Example 2 at a current density of 0.1A / g

[0030] Figure 5 Rate performance graph of the comparative material, the material of Example 2;

[0031] Figure 6 XRD graph of the comparative material, the material of Example 2;

[0032] Figure 7 Rotary carbonization furnace structure schematic diagram;

[0033] Figure 8 Side view structure schematic diagram of Figure 7

[0034] Figure 9 Support frame structure schematic diagram.

[0035] Explanation of reference signs: 1. furnace body, 2. rotating drum, 3. motor, 4. rotating shaft, 5. support frame, 6. cushion block, 7. bearing, 8. coupling, 9. distal shaft, 10. air inlet pipe, 11. resistance wire, 12. resistance wire power supply control device, 13. new biomass-derived hard carbon negative electrode material, 14. furnace door, 15. air outlet, 16. proximal shaft. DETAILED DESCRIPTION

[0036] A preparation method of a new biomass-derived hard carbon negative electrode material, comprising the following steps:

[0037] Step one: wash mistletoe stems with deionized water under ultrasonic conditions at 40-50 kHz for 3-5 h, then dry in a vacuum oven at a temperature of 100-110℃ for greater than or equal to 1 h, naturally cool to room temperature, and then crush into a powder with a particle size of 0.5-1 um using a cell wall breaking machine;

[0038] ​Step 2: The powder crushed in step 1 is heated to 300-500°C under a nitrogen atmosphere for 1-3 hours. After cooling naturally to room temperature, it is pickled and impurities removed using a dilute hydrochloric acid solution, which is a mixture of deionized water and 35%-40% hydrochloric acid in a volume ratio of 33:7. The powder is then filtered through a microporous filter membrane with a particle size of 0.45 μm at a pressure of -0.09 to -0.11 MPa. The resulting material is then dried in a vacuum oven at 100-110°C for 10-12 hours, and then cooled naturally to room temperature to obtain a pre-carbonized material.

[0039] Step 3: Grind thiourea into thiourea powder, mix the thiourea powder with the pre-carbonized material obtained in step 2 at a mass ratio of (0.5-3):1, and stir evenly; the thiourea powder particle size is 0.5-1 μm, and the thiourea powder and the pre-carbonized material obtained in step 2 are stirred in a stirrer at a speed of 417-500 r / min for not less than 1 hour;

[0040] Step 4: The material stirred in step 3 is kept at 1000-1400° C. for 1-3 hours under a nitrogen atmosphere, and then naturally cooled to room temperature to obtain a new biomass-derived hard carbon negative electrode material.

[0041] like Figures 7-9 As shown (the figure is only a schematic diagram, not a realistic one-to-one drawing), step four is carried out in a rotary carbonization furnace, which includes a furnace body 1, a rotating drum 2, a motor 3 and a resistance wire 11. The resistance wire 11 is arranged in the furnace body 1, and the motor 3 is arranged on one side outside the furnace body 1. The motor shaft of the motor 3 is connected to the rotating drum 2 in the furnace body 1. The furnace body 1 is provided with an air inlet pipe 10 and an air outlet 15. The ends of the air inlet pipe 10 are located at both ends of the rotating drum 2 and face the inside of the rotating drum 2. When the air inlet pipe 10 is connected to an external nitrogen bottle, the incoming nitrogen can be blown directly toward the material inside the drum 2, preferentially blowing out the air inside the drum 2. The furnace body 1 is provided with a furnace door 14. The material, after being evenly mixed in step 3, is placed into the drum 2 of the rotary carbonization furnace, which rotates continuously at a speed of 50 to 80 revolutions per hour. After being kept at 1000 to 1400°C for 1 to 3 hours in a nitrogen atmosphere, the material inside the drum 2 becomes the new biomass-derived hard carbon negative electrode material 13. The resistance wire 11 is connected to the resistance wire power supply control device 12 outside the furnace body 1 via a power cord. The resistance wire power supply control device 12 is a conventional switch device connected to an AC power supply, including a power supply and a switch. The power supply, switch, and resistance wire 11 are connected in series. The motor 3 is also connected to the power supply when in use.

[0042] The motor 3 is fixed on the cushion block 6, the cushion block 6 is fixed on one side of the furnace body 1, the motor shaft of the motor 3 is located on the inner side of the cushion block 6 and is connected with the proximal shaft 16 through the shaft coupling 8, the proximal shaft 16 passes through the furnace body 1 and is connected with the rotating shaft 4 through the shaft coupling 8, the support frame 5 is inserted or clamped and fixed on both ends of the rotating drum 2, the rotating shaft 4 passes through and is clamped and fixed with the two support frames 5, the rotating shaft 4 is preferably a polygonal shaft, the end of the rotating shaft 4 away from the motor 3 is connected with the distal shaft 9 through the shaft coupling 8, the distal shaft 9 passes through the furnace body 1, and the proximal shaft 16 and the distal shaft 9 are connected with the furnace body 1 through the bearing 7. The motor 3 is not directly fixed on the furnace body 1 but is fixed on the cushion block 6, which makes the motor more convenient to disassemble and assemble, and disassembling and assembling the motor will not damage and affect the heat preservation performance of the furnace body 1. In addition, the motor shaft does not directly extend into the interior of the furnace body 1 but is sequentially connected with the proximal shaft 16, the rotating shaft 4 and the distal shaft 9 through the shaft couplings 8, so that the heat in the furnace body 1 will not be directly conducted to the motor 3, and the two shaft couplings 8 in the furnace body 1 are convenient to disassemble after the carbonization is completed, and then the rotating drum 2 is taken out of the furnace body 1, and finally the new biomass-derived hard carbon negative material 13 is poured out of the rotating drum 2. The prepared new biomass-derived hard carbon negative material can be used as a negative electrode of a sodium ion battery. It should be noted that the components in the furnace body 1 and partially in the interior need to use materials (preferably ceramic materials) resistant to 1400℃ high temperature, and the bearing 7 and the interior of the furnace body 1 also need to be filled with a certain heat insulation material to ensure the normal rotation of the rotary carbonization furnace.

[0043] In use, the rotating shaft 4 and the rotating drum 2 are detachable. First, the rotating drum 2 is inclined, the material to be carbonized is poured into the rotating drum 2, then the rotating drum 2 is placed horizontally, and then the support frames 5 at both ends of the rotating drum 2 are connected with the rotating shaft 4. Then the whole is put into the furnace body, then the rotating shaft 4 is connected with the distal shaft 9 and the proximal shaft 16 through the shaft couplings 8, the furnace door 14 is closed, and the rotary carbonization furnace can be used. The resistance wire 11 is used for heating, and at the same time the motor 3 provides power for the rotation of the rotating drum 2. After the carbonization is completed, it is naturally cooled to room temperature, the furnace door 14 is opened, the shaft couplings 8 of the rotating shaft 4 and the distal shaft 9 and the proximal shaft 16 are opened, the rotating shaft 4 and the rotating drum 2 are taken out together, the rotating shaft 4 can be extracted or not extracted, the rotating drum 2 is inclined, and the new biomass-derived hard carbon negative material 13 is poured out of the end of the rotating drum 2. If there is a small amount of residue, a soft tool such as a brush can be used to sweep out the remaining material.

[0044] Example 1

[0045] A new biomass-derived hard carbon negative material preparation method comprises the following steps:

[0046] Step one: the mistletoe stems are cleaned with deionized water under the condition of 40-50 kHz ultrasonic for 3-5 h, and then dried in a vacuum oven at a temperature of 100-110 DEG C for more than or equal to 1 h, and naturally cooled to room temperature, and then broken into a powder with a particle size of 0.5-1 um by a cell wall breaking machine;

[0047] Step two: the powder broken in step one is heated at 300-500 DEG C for 1-3 h under a nitrogen atmosphere, and then naturally cooled to room temperature, and then subjected to acid pickling to remove impurities, wherein the acid pickling is performed using a dilute hydrochloric acid solution prepared by mixing deionized water and hydrochloric acid with a concentration of 35-40% at a volume ratio of 33:7, and then subjected to suction filtration through a filter membrane with a pore size of 0.45 um under a pressure of-0.09 to-0.11 MPa, and then dried in a vacuum oven at a temperature of 100-110 DEG C for 10-12 h, and naturally cooled to room temperature to obtain a pre-carbonized material;

[0048] Step three: sulfur hydride is ground into a powder, and the sulfur hydride powder is mixed with the pre-carbonized material obtained in step two at a mass ratio of 0.5:1, and then uniformly stirred, wherein the particle size of the sulfur hydride powder is 0.5-1 um, and the sulfur hydride powder and the pre-carbonized material obtained in step two are mixed in a stirrer at a rotation speed of 417-500 r / min for not less than 1 h;

[0049] Step four: the material uniformly stirred in step three is heated at 1000-1400 DEG C for 1-3 h under a nitrogen atmosphere, and then naturally cooled to room temperature to obtain a new biomass-derived hard carbon negative electrode material, and the material is collected and named as VC-1.

[0050] Example 2

[0051] A method for preparing a new biomass-derived hard carbon negative electrode material, comprising the following steps:

[0052] Step one: the mistletoe stems are cleaned with deionized water under the condition of 40-50 kHz ultrasonic for 3-5 h, and then dried in a vacuum oven at a temperature of 100-110 DEG C for more than or equal to 1 h, and naturally cooled to room temperature, and then broken into a powder with a particle size of 0.5-1 um by a cell wall breaking machine;

[0053] Step two: the powder broken in step one is kept at 300-500℃ for 1-3h under nitrogen atmosphere, and then naturally cooled to room temperature. Acid washing is performed to remove impurities using dilute hydrochloric acid solution, which is prepared by mixing deionized water and 35%-40% hydrochloric acid at a volume ratio of 33:7. The solution is filtered through a filter membrane with a pore size of 0.45um under a pressure of-0.09 to-0.11MPa. The obtained material is then dried in a vacuum oven at a temperature of 100-110℃ for 10-12h, and then naturally cooled to room temperature to obtain a pre-carbonized material;

[0054] Step three: sulfur powder is obtained by grinding thiourea, and the sulfur powder is mixed with the pre-carbonized material obtained in step two at a mass ratio of 1:1. The sulfur powder has a particle size of 0.5-1um, and the sulfur powder and the pre-carbonized material are mixed in a stirrer at a rotation speed of 417-500r / min for not less than 1h.

[0055] Step four: the material obtained in step three is kept at 1000-1400℃ for 1-3h under nitrogen atmosphere, and then naturally cooled to room temperature to obtain a new biomass-derived hard carbon negative electrode material. The material is collected and named as VC-2.

[0056] Example 3

[0057] A method for preparing a new biomass-derived hard carbon negative electrode material, comprising the following steps:

[0058] Step one: mistletoe stems are cleaned with deionized water under ultrasonic conditions at 40-50kHz for 3-5h. Then the stems are dried in a vacuum oven at a temperature of 100-110℃ for not less than 1h, and then naturally cooled to room temperature. The stems are then broken into powder with a particle size of 0.5-1um using a cell wall breaking machine.

[0059] Step two: the powder broken in step one is kept at 300-500℃ for 1-3h under nitrogen atmosphere, and then naturally cooled to room temperature. Acid washing is performed to remove impurities using dilute hydrochloric acid solution, which is prepared by mixing deionized water and 35%-40% hydrochloric acid at a volume ratio of 33:7. The solution is filtered through a filter membrane with a pore size of 0.45um under a pressure of-0.09 to-0.11MPa. The obtained material is then dried in a vacuum oven at a temperature of 100-110℃ for 10-12h, and then naturally cooled to room temperature to obtain a pre-carbonized material;

[0060] Step three: grind the thiourea into thiourea powder, mix the thiourea powder with the pre-carbonized material obtained in step two at a mass ratio of 2:1, and stir uniformly; the particle size of the thiourea powder is 0.5-1 um, and the thiourea powder and the pre-carbonized material obtained in step two are stirred and mixed in a stirrer at a rotation speed of 417-500 r / min, and the stirring time is not less than 1 h;

[0061] Step four: the material stirred uniformly in step three is heated at 1000-1400℃ for 1-3 h under a nitrogen atmosphere, and naturally cooled to room temperature to obtain a new biomass-derived hard carbon negative electrode material. Collect the material and name it VC-3.

[0062] Example 4

[0063] A new biomass-derived hard carbon negative electrode material preparation method includes the following steps:

[0064] Step one: wash the mistletoe stems with deionized water under ultrasonic conditions at 40-50 kHz for 3-5 h, then dry them in a vacuum oven at a temperature of 100-110℃ for more than or equal to 1 h, naturally cool to room temperature, and then crush them into a powder with a particle size of 0.5-1 um using a cell wall breaker;

[0065] Step two: heat the powder crushed in step one at 300-500℃ for 1-3 h under a nitrogen atmosphere, naturally cool to room temperature, and then perform acid washing to remove impurities; the acid washing uses a dilute hydrochloric acid solution prepared by mixing deionized water with a 35%-40% hydrochloric acid solution at a volume ratio of 33:7. Then perform suction filtration using a filter membrane with a pore size of 0.45 um at a pressure of -0.09 to -0.11 MPa, and then dry the obtained material in a vacuum oven at a temperature of 100-110℃ for 10-12 h, and naturally cool to room temperature to obtain a pre-carbonized material;

[0066] Step three: grind the thiourea into thiourea powder, mix the thiourea powder with the pre-carbonized material obtained in step two at a mass ratio of 2:1, and stir uniformly; the particle size of the thiourea powder is 0.5-1 um, and the thiourea powder and the pre-carbonized material obtained in step two are stirred and mixed in a stirrer at a rotation speed of 417-500 r / min, and the stirring time is not less than 1 h;

[0067] Step four: the material stirred uniformly in step three is heated at 1000-1400℃ for 1-3 h under a nitrogen atmosphere, and naturally cooled to room temperature to obtain a new biomass-derived hard carbon negative electrode material. Collect the material and name it VC-3.

[0068] Comparative example 1

[0069] A new biomass-derived hard carbon negative electrode material preparation method includes the following steps:

[0070] Step one: Wash the mistletoe stems with deionized water under the condition of 40-50 kHz ultrasonic for 3-5 h, then dry in a vacuum oven at a temperature of 100-110 °C for more than or equal to 1 h, and cool to room temperature naturally. Then crush the stems into powders with a particle size of 0.5-1 um using a cell wall breaker;

[0071] Step two: Heat the powders obtained in step one to 300-500 °C under a nitrogen atmosphere for 1-3 h, and cool to room temperature naturally. Then perform acid pickling to remove impurities. The acid pickling is performed using a dilute hydrochloric acid solution, which is prepared by mixing deionized water and hydrochloric acid with a concentration of 35%-40% at a volume ratio of 33:7. Then perform suction filtration through a filter membrane with a pore size of 0.45 um at a pressure of -0.09 to -0.11 MPa. Then dry the obtained material in a vacuum oven at a temperature of 100-110 °C for 10-12 h, and cool to room temperature naturally. Thus, a pre-carbonized material is obtained.

[0072] Step three: Take the pre-carbonized material obtained in step two, and heat it to 1000-1400 °C under a nitrogen atmosphere for 1-3 h, and cool to room temperature naturally. Thus, a new biomass-derived hard carbon negative electrode material is obtained. Collect the material and name it VC-contrast.

[0073] As Figures 1-6The biomass hard carbon materials obtained in each example and the comparative example were mixed with acetylene black and sodium alginate in a ratio of 8:1:1, and an appropriate amount of deionized water was added as a solvent, and continuous stirring was performed to obtain a slurry with a certain fluidity. A clean current collector (copper foil) was placed on a clean glass plane, and then the slurry was uniformly coated onto the surface of the current collector using a coater. Finally, the coated battery sheet was placed in a vacuum oven at 105°C for 12h, and the dried electrode sheet was cut into a circular electrode sheet with a diameter of 12mm. The above obtained electrode sheet was used as the negative electrode, a glass fiber circular sheet with a diameter of 19mm was used as the separator, a sodium sheet with a diameter of 12mm was used as the counter electrode, and a 1mol / L sodium perchlorate / ethylene carbonate / dimethyl carbonate solution was selected as the electrolyte. A sodium ion battery was assembled in accordance with the structure of a CR2032 button cell in an argon-filled glove box, and a series of sodium ion batteries were subjected to electrochemical performance test on a blue light test system at a current density of 100mA / g. It was measured that the initial specific capacity of the sodium ion battery made of the biomass hard carbon material prepared in Example 1 was 496.85mAh / g, the first coulombic efficiency was 77%, and the discharge specific capacity after 100 cycles was 336.42mAh / g; it was measured that the initial specific capacity of the sodium ion battery made of the biomass hard carbon material prepared in Example 2 was 586.58mAh / g, the first coulombic efficiency was 76%, and the discharge specific capacity after 100 cycles was 394.80mAh / g; it was measured that the initial specific capacity of the sodium ion battery made of the biomass hard carbon material prepared in Example 3 was 420.48mAh / g, the first coulombic efficiency was 76%, and the discharge specific capacity after 100 cycles was 278.07mAh / g; it was measured that the initial specific capacity of the sodium ion battery made of the biomass hard carbon material prepared in Example 4 was 629.82mAh / g, the first coulombic efficiency was 72%, and the discharge specific capacity after 100 cycles was 227.69mAh / g; it was measured that the initial specific capacity of the sodium ion battery made of the biomass hard carbon material prepared in Comparative Example 1 was 330.97mAh / g, the first coulombic efficiency was 70%, and the discharge specific capacity after 100 cycles was 184.74mAh / g. In summary, the specific capacity of the material VC-2 of sample Example 2 after 100 cycles was 394.80mAh / g, which was the highest, much higher than the 184.74mAh / g of the undoped VC of Comparative Example 1, and the other examples were also better than Comparative Example 1, which proved that the specific capacity of the precursor after sulfur doping was significantly improved after 100 cycles.

[0074] The mistletoe material has a porous microstructure, which has obvious advantages for sodium ion intercalation storage, and the thiourea doping used in the preparation method also provides a nitrogen and sulfur source for the carbon material, increases the active sites of the sodium ion battery, and expands the interlayer spacing.

[0075] In summary, the present application adopts two-step carbonization, pre-carbonization and then carbonization, so that the carbon elements in the raw materials are fixed in solid carbon as much as possible to increase the yield; thiourea is added in the material preparation process to improve the active adsorption sites of the material and assist in pore making, and after two-step carbonization and heteroatom doping, the capacity and initial coulombic efficiency of the biomass hard carbon material are effectively improved. The mistletoe derived hard carbon negative electrode material with relatively low specific surface area is synthesized by taking mistletoe as a precursor, and by combining the two-step carbonization method and thiourea doping, closed micropores and sulfur atoms are introduced into the hard carbon material, solving the problems of existing biomass hard carbon materials, such as few reversible sodium ion adsorption active sites, low inclined capacity and low initial coulombic efficiency.

[0076] Further description of Figures 1-6 is as follows: from Figure 1 it can be seen that the surface morphology is a porous structure, and such structure provides sites for sodium ion storage.

[0077] Figure 2 It is illustrated that the nitrogen and sulfur elements in thiourea are doped uniformly.

[0078] Figure 3 The long cycle of sample VC-2 at a current density of 1A / g. The specific capacity of VC-2 can still reach 83.2 mAh / g after 3000 cycles, indicating that it has the ability to perform super-long cycle.

[0079] Figure 4 The cycle performance diagram of VC-2 at a current density of 0.1A / g for VC-contrast. The discharge specific capacity of VC-2 after 100 cycles is 394.80 mAh / g, which is much higher than that of VC-contrast without doping, which is 184.74 mAh / g.

[0080] Figure 5 It can be seen that the discharge specific capacity of sample VC-2 is 429.1 mAh / g when the current density is returned to 0.1A / g, which is almost close to 434.3 mAh / g in the tenth cycle, proving that VC-2 has good reversible stability.

[0081] From Figure 6 it can be seen that the two carbon basic characteristic peaks are obvious, and by comparison, the relative intensity of the characteristic peaks of VC-contrast is obviously higher than that of VC-2, and the higher the relative peak intensity of the characteristic peaks, the more the material tends to be crystalline, and the weak relative peak intensity of VC-2 indicates that the introduction of thiourea creates surface defects, which is more conducive to the storage of sodium ions.

[0082] Obviously, the above embodiments of the present application are merely example for clearly explaining the present application, and are not intended to limit the embodiments of the present application. For those skilled in the art, on the basis of the above description, other different forms of changes or variations can also be made, and here all the embodiments cannot be exhausted, and any obvious changes or variations derived from the technical solutions of the present application still fall within the protection scope of the present application.

Claims

1. A method for preparing a new biomass-derived hard carbon negative electrode material, characterized by: The steps are as follows: Step 1: Clean and dry the mistletoe stems, cool them to room temperature, and then crush them into powder. Step 2: The powder crushed in step 1 is heated at 300-500° C. under a nitrogen atmosphere for 1-3 hours, cooled naturally to room temperature, then acid-washed to remove impurities, filtered through a filter membrane, dried, and cooled naturally to room temperature to obtain a pre-carbonized material; Step 3: Grind thiourea into thiourea powder, mix the thiourea powder with the pre-carbonized material obtained in step 2 in a mass ratio of (0.5-3):1, and stir evenly; Step 4: The material stirred in step 3 is kept at 1000-1400° C. for 1-3 hours under a nitrogen atmosphere, and then naturally cooled to room temperature to obtain a new biomass-derived hard carbon negative electrode material.

2. The method for preparing a new biomass-derived hard carbon negative electrode material according to claim 1, characterized in that: In the step 1, the mistletoe stems are cleaned with deionized water under 40-50 kHz ultrasonic conditions for 3-5 hours, then dried in a vacuum oven at a temperature of 100-110° C. for greater than or equal to 1 hour, naturally cooled to room temperature, and then crushed into powder with a particle size of 0.5-1 μm using a wall breaking machine.

3. The method for preparing a new biomass-derived hard carbon negative electrode material according to claim 1, characterized in that: In the step 2, the pickling and impurity removal is performed using a dilute hydrochloric acid solution, which is prepared by mixing deionized water and hydrochloric acid with a concentration of 35% to 40% in a volume ratio of 33:

7.

4. The method for preparing a new biomass-derived hard carbon negative electrode material according to claim 1, characterized in that: In the step 2, the filter membrane is a microporous filter membrane with a particle size of 0.45 μm, and the filtration is performed under a pressure of -0.09 to -0.11 MPa. The obtained material is then placed in a vacuum oven and dried at a temperature between 100 and 110° C. for 10 to 12 hours.

5. The method for preparing a new biomass-derived hard carbon negative electrode material according to claim 1, characterized in that: In the step 3, the particle size of the thiourea powder is 0.5 to 1 μm, and the thiourea powder and the pre-carbonized material obtained in the step 2 are stirred and mixed in a stirrer with a rotation speed of 417 to 500 r / min for a stirring time of not less than 1 hour.

6. The method for preparing a new biomass-derived hard carbon negative electrode material according to claim 1, characterized in that: The step 4 is carried out in a rotary carbonization furnace, which includes a furnace body (1), a rotating drum (2), a motor (3) and a resistance wire (11). The resistance wire (11) is arranged in the furnace body (1), the motor (3) is arranged on one side outside the furnace body (1), and the motor shaft of the motor (3) is connected to the rotating drum (2) in the furnace body (1). The furnace body (1) is provided with an air inlet pipe (10) and an air outlet (15). The ends of the air inlet pipe (10) are located at both ends of the rotating drum (2) facing the inside of the rotating drum (2). The furnace body (1) is provided with a furnace door (14). The material after being evenly stirred in step 3 is placed in the rotating drum (2) of the rotary carbonization furnace, rotated continuously, and kept warm at 1000-1400°C for 1-3 hours under a nitrogen atmosphere. The material in the rotating drum (2) is a new biomass-derived hard carbon negative electrode material (13).

7. The method for preparing a new biomass-derived hard carbon negative electrode material according to claim 6, characterized in that: The resistance wire (11) is connected to a resistance wire power supply control device (12) outside the furnace body (1) via a power line.

8. The method for preparing a new biomass-derived hard carbon negative electrode material according to claim 6, characterized in that: The motor (3) is fixed on a pad (6), which is fixed on one side of the furnace body (1). The motor shaft of the motor (3) is located on the inner side of the pad (6) and is connected to the proximal shaft (16) through a coupling (8). The proximal shaft (16) passes through the furnace body (1) and is connected to the rotating shaft (4) through the coupling (8). The support frame (5) is fixedly arranged at both ends of the rotating drum (2). The rotating shaft (4) passes through and is fixedly engaged with the two support frames (5). The end of the rotating shaft (4) away from the motor (3) is connected to the distal shaft (9) through the coupling (8). The distal shaft (9) passes through the furnace body (1). A bearing (7) is connected between the proximal shaft (16), the distal shaft (9) and the furnace body (1).

9. The method for preparing a new biomass-derived hard carbon negative electrode material according to claim 8, characterized in that: The rotating drum (2) has a rotation speed of 50 to 80 revolutions per hour.

10. The biomass-derived hard carbon negative electrode material prepared by the method according to claim 1 is used as a negative electrode of a sodium ion battery.

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