A preparation method of reconstructing surface functional groups of hard carbon negative electrode

Abstract

The application relates to a preparation method of a reconstructed hard carbon negative electrode surface functional group, and relates to the technical field of negative electrode materials. A natural coconut shell bulk is crushed, washed and dried, and first calcination is carried out to obtain a pre-carbonized biomass carbon material; the biomass carbon material is crushed and sieved to obtain a preliminary biomass carbon material; after acid washing, the preliminary biomass carbon material is washed with deionized water, centrifuged and dried to obtain a pretreated biomass carbon material; second calcination is carried out to obtain a precursor material; the precursor material is mixed with hydrogen peroxide and stirred to carry out pre-oxidation, so as to introduce oxygen-containing functional groups and improve the sodium affinity of the material; 5% of 4-(N, N-diethylamino)-benzoic acid in mass fraction is added to the pre-oxidized material, and the mixture is stirred and evaporated at 80 DEG C; the HC polymer after evaporation is subjected to dehydration reaction in an oxygen-free environment at 140 DEG C, so that the surface functional groups and the sodium storage performance of the hard carbon material are optimized, and a sodium ion battery hard carbon negative electrode material after reconstruction of the hard carbon negative electrode surface functional group is obtained. The method is simple in operation, the raw materials are widely sourced, the cost is low, and the method is beneficial to large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of anode material technology, and in particular to a method for preparing reconstructed functional groups on the surface of hard carbon anodes. Background Technology

[0002] In recent years, hard carbon has been considered one of the most promising materials for sodium-ion batteries due to its advantages of low cost and high specific capacity. While the mature development of graphite anode materials has driven the commercialization of lithium-ion batteries, graphite has almost no sodium storage capacity in sodium-ion batteries. Hard carbon, on the other hand, has a larger interlayer spacing and a large number of mesoporous structures, allowing sodium ions to be rapidly embedded and stored in large quantities, exhibiting excellent performance. However, because the surface of hard carbon reacts with ester electrolytes, the resulting solid electrolyte interphase (SEI) thickness is uneven, and the ester electrolyte can also decompose excessively, leading to problems such as low coulombic efficiency in the first cycle and large irreversible capacity.

[0003] The key to improving the sodium storage performance of hard carbon anode materials lies in achieving a large initial discharge specific capacity while maintaining a high initial coulombic efficiency. Currently, hard carbon as an anode material can achieve reversible specific capacities exceeding 300 mAh / g, but its initial coulombic efficiency remains low. Improving the sodium storage performance of hard carbon anodes through heteroatom doping or microstructure control is far from sufficient. Constructing a suitable SEI to regulate the HC / electrolyte interface chemistry is crucial for enhancing the performance of hard carbon anodes.

[0004] Therefore, this invention is mainly based on the method of reconstructing the functional groups on the surface of hard carbon to coat hard carbon, thereby reducing irreversible capacity by blocking the micropores and closing the pores of hard carbon, so as to improve the initial coulombic efficiency of sodium-ion batteries. Summary of the Invention

[0005] The purpose of this invention is to address the problem of low initial coulombic efficiency of hard carbon as a negative electrode material in sodium-ion batteries. It provides a method for reconstructing the functional groups on the surface of hard carbon anodes, significantly improving the initial coulombic efficiency and reversible specific capacity of hard carbon anode materials through a novel interface control approach. This method is low-cost, simple to operate, and highly efficient, which is beneficial to the commercialization of hard carbon anode materials.

[0006] A method for preparing reconstructed functional groups on the surface of a hard carbon anode includes the following steps:

[0007] 1) First high-temperature calcination: The natural coconut shells are broken into smaller pieces to facilitate cleaning and subsequent processing; the broken coconut shells are cleaned to remove surface stains and impurities; the moisture is dried to ensure that the quality of the final product is not affected by moisture during the calcination process, and then the first high-temperature calcination is carried out to obtain pre-carbonized biomass carbon materials; high-temperature calcination helps to decompose organic matter and initially form carbon structures.

[0008] 2) Preparation of preliminary biomass carbon material: The pre-carbonized biomass carbon material obtained in step 1) is crushed and sieved multiple times to obtain uniform and fine preliminary biomass carbon material;

[0009] 3) Pickling: The preliminary biomass carbon material obtained in step 2) is pickled to remove any possible metallic impurities and further purify the material;

[0010] 4) Pre-treated biomass carbon material: The acid-washed biomass carbon is washed with deionized water to remove excess acid and other unwanted impurities, and then centrifuged and dried to obtain pre-treated biomass carbon material.

[0011] 5) Second high-temperature calcination: The pretreated biomass carbon material from step 4) is subjected to a second high-temperature calcination to further optimize the carbon structure and obtain precursor material;

[0012] 6) Pre-oxidation treatment: Mix the precursor material obtained in step 5) with hydrogen peroxide solution (H2O2 solution) and stir to carry out pre-oxidation to introduce oxygen-containing functional groups. These functional groups can improve the affinity of the material for sodium ions, thereby improving its sodium storage performance in sodium-ion batteries.

[0013] 7) Preparation of HC polymer: 5% by mass of 4-(N,N-diethylamino)-benzoic acid was added to the pre-oxidized material, and the mixture was stirred and evaporated to dryness at 80°C to obtain HC polymer;

[0014] 8) Obtaining hard carbon anode material: The HC polymer after evaporation in step 7) is subjected to dehydration reaction in an oxygen-free environment at 140℃ to optimize the surface functional groups and sodium storage performance of the hard carbon material, and obtain sodium-ion battery hard carbon anode material (DEBA-HC) after reconstructing the surface functional groups of the hard carbon anode.

[0015] In step 1), the natural coconut shell is replaced with one of the following: bamboo, walnut shell, orange peel, peanut shell, macadamia nut shell, or straw; the drying process can be carried out overnight in an oven at 120°C.

[0016] In step 1), the first high-temperature calcination is carried out in an inert gas, the temperature of the first high-temperature calcination is 400-600℃, the heating rate of the first high-temperature calcination is 2-10℃, and the holding time is 1-6h; preferably, the first high-temperature calcination is carried out in a tube furnace at 600℃, the heating rate is 5℃ / min, and the holding time is 2h.

[0017] In step 2), the pre-carbonized biomass carbon material obtained in step 1) is crushed and sieved. The specific steps are as follows: First, the pre-carbonized biomass carbon material is coarsely crushed using an ore crusher and then preliminarily sieved using a 300-500 mesh sieve. The sieved pre-carbonized biomass carbon material is then finely crushed using a mechanical mill-airflow pulverizer and sieved a second time using a 600-1000 mesh sieve to obtain preliminary biomass carbon material. Preferably, the preliminary sieve is a 500 mesh sieve, and the second sieve is an 800 mesh sieve.

[0018] In step 3), the reagent used for pickling is one of hydrochloric acid, hydrofluoric acid, sulfuric acid, and nitric acid.

[0019] In step 3), the acid washing involves mixing the preliminary biomass carbon material obtained in step 2) with a 5% concentrated hydrochloric acid solution for acid washing.

[0020] The 5% concentrated hydrochloric acid solution was prepared by mixing 2 ml of 12 mol / L concentrated hydrochloric acid and 38 ml of deionized water; the preliminary biomass carbon material was mixed with the 5% concentrated hydrochloric acid solution at a solid-liquid mass ratio of 1:4.

[0021] The specific steps are as follows: Take 10g of the preliminary biomass carbon material after secondary sieving and put it into a container with a capacity of 100ml. Add 40g of the prepared hydrochloric acid solution at a solid-liquid mass ratio of 1:4 and acid wash for 4 hours to allow the hydrochloric acid to fully contact the coconut shell powder and complete the acid washing process.

[0022] In step 4), the centrifugation speed is 10,000 rpm and the centrifugation time is 10 min; the number of centrifugations can be 3; the drying is carried out in an oven at 120℃ for 6 hours.

[0023] In step 5), the second high-temperature calcination can be carried out in a tube furnace at 1100-1400℃, 0.16L / min Ar, and a heating rate of 2-5℃ / min, with carbonization and holding for 2-12 hours; preferably at 1200℃, 0.16L / min Ar, and a heating rate of 5℃ / min, with carbonization and holding for 4 hours.

[0024] In step 6), the hydrogen peroxide is a 3% H2O2 solution; the pre-oxidation time can be 12h; the mass percentage of H2O2 in the precursor is 10% to 20%, the solid-liquid ratio is 0.2 to 1, and the treatment time is 12 to 24h.

[0025] In step 7), the stirring can be carried out on a magnetic stirrer, with the temperature set at 80°C and the speed at 300 rpm for 12 hours; the 4-(N,N-diethylamino)-benzoic acid can be replaced with caffeic acid (CA) or gallic acid.

[0026] Compared with the prior art, the advantages of the present invention are:

[0027] This invention utilizes the dehydration condensation reaction between the -COOH bonds on 4-(N,N-diethylamino)benzoic acid (4-DEBA) and the -OH bonds on the oxidized HC surface to successfully graft 4-DEBA uniformly onto the HC surface. The 4-DEBA molecules also form a self-crosslinking structure (4-DEBA modification layer) through their own -COOH and -OH bonds during the dehydration reaction. The thickness and uniformity of the 4-DEBA modification layer on the HC surface can be adjusted by controlling the amount of 4-DEBA added; a suitable thickness does not affect ion transport performance. The grafting of the 4-DEBA modification layer reduces the specific surface area of ​​hard carbon, which helps reduce irreversible capacity loss caused by the reaction between the negative electrode material and the electrolyte. Furthermore, the modification of the HC surface functional groups by the 4-DEBA modification layer gives the HC better electrolyte affinity, enabling rapid ion transport and a stable electrode / electrolyte interface. The presence of the surface polymer effectively hinders the decomposition of the electrolyte solvent, improving the initial coulombic efficiency of the sodium-ion battery and providing more reversible active sites for sodium storage, thus enhancing the battery's sodium storage performance. In addition, this method is simple to operate, requires minimal preparation environment, uses widely available coconut shell charcoal, and is inexpensive, making it suitable for large-scale industrial production. Attached Figure Description

[0028] Figure 1 The figure shows the N2 adsorption-desorption curves of the hard carbon anode material (DEBA-HC) prepared in Example 1 of this invention. In the figure, the horizontal axis represents relative pressure, and the vertical axis represents the adsorption amount.

[0029] Figure 2 This is an X-ray diffraction pattern of the hard carbon anode material (DEBA-HC) prepared in Example 1 of this invention. In the figure, the horizontal axis represents the 2θ angle, and the vertical axis represents the intensity.

[0030] Figure 3 The graph shows the cycling performance of the hard carbon anode material (DEBA-HC) prepared in Example 1 of this invention in a sodium-ion battery at a current density of 30 mA / g. In the graph, the horizontal axis represents capacity, and the vertical axis represents voltage.

[0031] Figure 4 The figures show the nitrogen adsorption-desorption curves and specific surface area results of the biomass hard carbon material after surface coating in Example 2 of this invention. In the figures, the horizontal axis represents relative pressure, and the vertical axis represents adsorption amount.

[0032] Figure 5 The figure shows the first-week charge-discharge performance of the surface-coated modified hard carbon material in Example 2 of this invention. In the figure, the horizontal axis represents capacity and the vertical axis represents voltage.

[0033] Figure 6 The graph shows the charge-discharge curves of the uncoated carbon material in Comparative Example 1 after being assembled into a half-cell during the first week. In the figure, the horizontal axis represents capacity, and the vertical axis represents voltage. Detailed Implementation

[0034] The following embodiments will further illustrate the present invention in conjunction with the accompanying drawings, but the scope of protection of the present invention is not limited to the following embodiments.

[0035] Example 1

[0036] A method for preparing sodium-ion battery anode materials by surface coating of biomass hard carbon includes the following steps:

[0037] (1) After breaking the natural coconut shell into large pieces, wash it with tap water and dry it overnight in an oven at 120℃. Then, calcine it for the first time in a tube furnace at 600℃ to obtain pre-carbonized biomass carbon material. The heating rate is 5℃ / min and the temperature is maintained for 2 hours.

[0038] (2) The pre-carbonized biomass carbon material in step (1) is coarsely crushed using an ore crusher and sieved through a 500-mesh sieve. The sieved coconut shell is then finely crushed using a mechanical mill-airflow pulverizer and sieved through an 800-mesh sieve to obtain preliminary biomass carbon material.

[0039] (3) Take 10g of coconut shell powder after double sieving and put it into a beaker with a capacity of 100ml. Add 40g of hydrochloric acid solution (2ml 12mol / L HCl, 38ml deionized water) diluted to 5% concentrated hydrochloric acid solution at a solid-liquid mass ratio of 1:4 and acid wash for 4h.

[0040] (4) Transfer all the acid-washed coconut shells to 50ml centrifuge tubes, weigh and balance them, put them into a centrifuge, set the centrifugation speed to 10000 rpm, centrifugation time to 10 min, and pour out the solution in the tube after centrifugation.

[0041] (5) Add deionized water to the centrifuge tube in step (4), weigh and balance it, wash and centrifuge it 3 times according to the above centrifugation parameters, and dry it in an oven at 120°C for 6 hours to obtain clean pretreated biomass carbon material.

[0042] (6) Take out 3g of the pretreated biomass carbon material from step (5) and calcine it for the second time in a tube furnace at 1400℃, 0.16L / min Ar, and a heating rate of 5℃ / min. After high-temperature carbonization and holding for 4h, the biomass carbon material precursor is obtained after natural cooling.

[0043] (7) Take 2g of the biomass carbon material precursor from step (6) into a beaker with a capacity of 10ml, add 5ml of hydrogen peroxide solution (3wt% H2O2 solution) for pre-oxidation for 12h;

[0044] (8) Add 5% by mass of p-4-(N,N-diethylamino)-benzoic acid (4-DEBA) to the beaker in step (7), place the beaker on a magnetic stirrer, set the temperature to 80°C and the speed to 300 rpm, stir for 12 hours, and obtain the evaporated HC polymer.

[0045] (9) The HC polymer obtained in step (8) is subjected to a dehydration reaction at 140°C in an oxygen-free environment to obtain a sodium-ion battery hard carbon anode material (DEBA-HC).

[0046] Figure 1 To obtain the nitrogen adsorption-desorption curves for the surface-coated carbon material, the specific surface area was found to be 2.3728 m². 2 / g, the lower specific surface area indicates that the coating of 4-DEBA reduces defects on the HC surface, and open pores are transformed into closed pores. Figure 2 The X-ray diffraction pattern of the surface-coated carbon material is shown in the figure. Two amorphous carbon characteristic peaks are located at 24.3° and 43.6°, which correspond to the (002) and (100) crystal planes of hard carbon, respectively. The interplanar spacing of the (002) crystal plane of hard carbon (DEBA-HC) is calculated to be 0.367 nm by Bragg equation, indicating that the introduction of 4-DEBA did not change the structure of the raw material hard carbon and did not cause damage to the internal structure. Figure 3 The first-cycle charge-discharge curves of the half-cell assembled from surface-coated carbon materials were obtained according to the sodium-ion battery test standard at a current density of 30 mA / g. The modified hard carbon achieved an initial discharge specific capacity of 298 mAh / g and an initial coulombic efficiency of 87%. The high coulombic efficiency indicates that the preparation method of this biomass carbon material contributes to the improvement of sodium storage performance in sodium-ion batteries.

[0047] Example 2

[0048] A method for preparing sodium-ion battery anode materials by surface coating of biomass hard carbon includes the following steps:

[0049] (1) After breaking the bamboo into large pieces, wash it with tap water and dry it overnight in an oven at 120℃. Then, calcine it for the first time in a tube furnace at 500℃ to obtain pre-carbonized biomass carbon material. The heating rate is 2℃ / min and the temperature is maintained for 2h.

[0050] (2) The pre-carbonized biomass carbon material in step (1) is coarsely crushed using an ore crusher and sieved through a 500-mesh sieve. The sieved bamboo is then finely crushed using a mechanical mill-airflow pulverizer and sieved through an 800-mesh sieve to obtain preliminary biomass carbon material.

[0051] (3) Take 10g of bamboo powder after sieving twice and put it into a beaker with a capacity of 100ml. Add 40g of hydrochloric acid solution (2ml 12mol / L HCl, 38ml deionized water) diluted to 5% concentrated hydrochloric acid solution according to the solid-liquid mass ratio of 1:4 and acid wash for 4h.

[0052] (4) Transfer all the pickled bamboo to a 50ml centrifuge tube, weigh and balance it, then put it into a centrifuge, set the centrifugation speed to 10000 rpm and the centrifugation time to 10 min, and pour out the solution in the tube after centrifugation.

[0053] (5) Add deionized water to the centrifuge tube in step (4), weigh and balance it, wash and centrifuge it 3 times according to the above centrifugation parameters, and dry it in an oven at 120°C for 6 hours to obtain clean pretreated biomass carbon material.

[0054] (6) Take out 3g of the pretreated biomass carbon material from step (5) and calcine it for the second time in a tube furnace at 1100℃, 0.16L / min Ar, and a heating rate of 4℃ / min. After high-temperature carbonization and holding for 2h, the biomass carbon material precursor is obtained after natural cooling.

[0055] (7) Take 2g of the biomass carbon material precursor from step (6) into a beaker with a capacity of 10ml, add 4ml of hydrogen peroxide solution (4wt% H2O2 solution) for pre-oxidation for 12h;

[0056] (8) Add 5% by mass of caffeic acid (CA) to the beaker in step (7), place the beaker on a magnetic stirrer, set the temperature to 80°C and the speed to 300 rpm, stir for 12 hours to obtain the evaporated HC polymer.

[0057] (9) The HC polymer obtained in step (8) is subjected to a dehydration reaction at 140°C in an oxygen-free environment to obtain a sodium-ion battery hard carbon anode material (CA-HC).

[0058] Figure 4 The nitrogen adsorption-desorption curve of the carbon material after surface coating of biomass hard carbon made from moso bamboo in Example 2 is shown, and the specific surface area obtained is 2.9 m². 2 / g, the lower specific surface area indicates that the coating of CA reduces defects on the HC surface, and open pores are transformed into closed pores. Figure 5The first-cycle charge-discharge curves of a half-cell assembled from surface-coated carbon materials were obtained according to sodium-ion battery testing standards at a current density of 30 mA / g. The modified hard carbon achieved an initial discharge specific capacity of 314 mAh / g and an initial coulombic efficiency of 89%. The high coulombic efficiency indicates that the preparation method of this biomass carbon material alleviates the irreversible reaction between the negative electrode and the electrolyte, which helps to improve the sodium storage performance of sodium-ion batteries.

[0059] Example 3

[0060] A method for preparing sodium-ion battery anode materials by surface coating of biomass hard carbon includes the following steps:

[0061] (1) After crushing the natural macadamia nut shells into small pieces, wash them with tap water and dry them overnight in an oven at 120°C. Then, calcine them for the first time in a tube furnace at 400°C to obtain pre-carbonized biomass carbon material. The heating rate is 5°C / min and the temperature is maintained for 2 hours.

[0062] (2) The pre-carbonized biomass carbon material in step (1) is coarsely crushed using an ore crusher and sieved through a 400-mesh sieve. The sieved macadamia nut shell powder is then finely crushed using a mechanical mill-airflow pulverizer and sieved through a 700-mesh sieve to obtain preliminary biomass carbon material.

[0063] (3) Take 10g of macadamia nut shell powder after sieving twice and put it into a beaker with a capacity of 100ml. Add 40g of hydrochloric acid solution (2ml 12mol / L HCl, 38ml deionized water) diluted to 5% concentrated hydrochloric acid solution at a solid-liquid mass ratio of 1:4 and acid wash for 4h.

[0064] (4) Transfer all the acid-washed macadamia nut shells to a 50ml centrifuge tube, weigh and balance them, then put them into a centrifuge. Set the centrifugation speed to 10,000 rpm and the centrifugation time to 10 min. After centrifugation, pour out the solution in the tube.

[0065] (5) Add deionized water to the centrifuge tube in step (4), weigh and balance it, wash and centrifuge it 3 times according to the above centrifugation parameters, and dry it in an oven at 120°C for 6 hours to obtain clean pretreated biomass carbon material.

[0066] (6) Take out 3g of the pretreated biomass carbon material from step (5) and calcine it for the second time in a tube furnace at 1300℃, 0.16L / min Ar, and a heating rate of 2℃ / min. After high-temperature carbonization and holding for 12h, the biomass carbon material precursor is obtained after natural cooling.

[0067] (7) Take 2g of the biomass carbon material precursor from step (6) into a beaker with a capacity of 10 ml, add 2ml of hydrogen peroxide solution (5wt% H2O2 solution) for pre-oxidation for 12h;

[0068] (8) Add 5% by mass of p-4-(N,N-diethylamino)-benzoic acid (4-DEBA) to the beaker in step (7), place the beaker on a magnetic stirrer, set the temperature to 80°C and the speed to 300 rpm, stir for 12 hours, and obtain the evaporated HC polymer.

[0069] (9) The HC polymer obtained in step (8) is subjected to a dehydration reaction at 140°C in an oxygen-free environment to obtain a sodium-ion battery hard carbon anode material (DEBA-HC).

[0070] Results Test: The carbon material coated on the surface in Example 3 was assembled into a half cell. According to the sodium-ion battery test standard, the first-cycle charge-discharge curve at a current density of 30 mA / g showed that the modified hard carbon could achieve a first-cycle discharge specific capacity of 304 mAh / g and the first-cycle coulombic efficiency was improved to 92.1%. The high coulombic efficiency indicates that the preparation method of this biomass carbon material helps to alleviate the irreversible reaction between the negative electrode and the electrolyte, and at the same time leads to the improvement of sodium storage performance of sodium-ion batteries.

[0071] Example 4

[0072] A method for preparing sodium-ion battery anode materials by surface coating of biomass hard carbon includes the following steps:

[0073] (1) After breaking the bamboo into large pieces, wash it with tap water and dry it overnight in an oven at 120℃. Then, calcine it for the first time in a tube furnace at 500℃ to obtain pre-carbonized biomass carbon material. The heating rate is 2℃ / min and the temperature is maintained for 2h.

[0074] (2) The pre-carbonized biomass carbon material in step (1) is coarsely crushed using an ore crusher and sieved through a 500-mesh sieve. The sieved bamboo is then finely crushed using a mechanical mill-airflow pulverizer and sieved through an 800-mesh sieve to obtain preliminary biomass carbon material.

[0075] (3) Take 10g of bamboo powder after sieving twice and put it into a beaker with a capacity of 100ml. Add 40g of hydrochloric acid solution (2ml 12mol / L HCl, 38ml deionized water) diluted to 5% concentrated hydrochloric acid solution according to the solid-liquid mass ratio of 1:4 and acid wash for 4h.

[0076] (4) Transfer all the pickled bamboo to a 50ml centrifuge tube, weigh and balance it, then put it into a centrifuge, set the centrifugation speed to 10000 rpm and the centrifugation time to 10 min, and pour out the solution in the tube after centrifugation.

[0077] (5) Add deionized water to the centrifuge tube in step (4), weigh and balance it, wash and centrifuge it 3 times according to the above centrifugation parameters, and dry it in an oven at 120°C for 6 hours to obtain clean pretreated biomass carbon material.

[0078] (6) Take out 3g of the pretreated biomass carbon material from step (5) and calcine it for the second time in a tube furnace at 1100℃, 0.16L / min Ar, and a heating rate of 4℃ / min. After high-temperature carbonization and holding for 2h, the biomass carbon material precursor is obtained after natural cooling.

[0079] (7) Take 2g of the biomass carbon material precursor from step (6) into a beaker with a capacity of 10ml, add 4ml of hydrogen peroxide solution (4wt% H2O2 solution) for pre-oxidation for 12h;

[0080] (8) Add gallic acid (GA) with a mass fraction of 5% to the beaker in step (7), place the beaker on a magnetic stirrer, set the temperature to 80°C and the speed to 300 rpm, stir for 12 hours to obtain the evaporated HC polymer.

[0081] (9) The HC polymer obtained in step (8) is subjected to a dehydration reaction at 140°C in an oxygen-free environment to obtain sodium-ion battery hard carbon anode material (GA-HC).

[0082] Results Test: In Example 4, gallic acid was used for coating. The coated carbon material was assembled into a half-cell. According to the sodium-ion battery test standard, the first-cycle charge-discharge curve at a current density of 30 mA / g showed that the modified hard carbon could achieve a first-cycle discharge specific capacity of 301 mAh / g and a first-cycle coulombic efficiency of 91.9%, which is similar to the results of carbon coating with caffeic acid. This also shows that the carbon material coated with gallic acid can help alleviate the irreversible reaction between the negative electrode and the electrolyte, and at the same time help improve the sodium storage performance of sodium-ion batteries.

[0083] Example 5

[0084] A method for preparing sodium-ion battery anode materials by surface coating of biomass hard carbon includes the following steps:

[0085] (1) After breaking the bamboo into large pieces, wash it with tap water and dry it overnight in an oven at 120℃. Then, calcine it for the first time in a tube furnace at 500℃ to obtain pre-carbonized biomass carbon material. The heating rate is 2℃ / min and the temperature is maintained for 2h.

[0086] (2) The pre-carbonized biomass carbon material in step (1) is coarsely crushed using an ore crusher and sieved through a 500-mesh sieve. The sieved bamboo is then finely crushed using a mechanical mill-airflow pulverizer and sieved through an 800-mesh sieve to obtain preliminary biomass carbon material.

[0087] (3) Take 10g of bamboo powder after sieving twice and put it into a beaker with a capacity of 100ml. Add 40g of hydrofluoric acid solution (2ml 22.5mol / L HF, 38ml deionized water) diluted to 5% of the original concentrated hydrofluoric acid solution at a solid-liquid mass ratio of 1:4 and acid wash for 4h.

[0088] (4) Transfer all the pickled bamboo to a 50ml centrifuge tube, weigh and balance it, then put it into a centrifuge, set the centrifugation speed to 10000 rpm and the centrifugation time to 10 min, and pour out the solution in the tube after centrifugation.

[0089] (5) Add deionized water to the centrifuge tube in step (4), weigh and balance it, wash and centrifuge it 3 times according to the above centrifugation parameters, and dry it in an oven at 120°C for 6 hours to obtain clean pretreated biomass carbon material.

[0090] (6) Take out 3g of the pretreated biomass carbon material from step (5) and calcine it for the second time in a tube furnace at 1100℃, 0.16L / min Ar, and a heating rate of 4℃ / min. After high-temperature carbonization and holding for 2h, the biomass carbon material precursor is obtained after natural cooling.

[0091] (7) Take 2g of the biomass carbon material precursor from step (6) into a beaker with a capacity of 10ml, add 4ml of hydrogen peroxide solution (4wt% H2O2 solution) for pre-oxidation for 12h;

[0092] (8) Add gallic acid (GA) with a mass fraction of 5% to the beaker in step (7), place the beaker on a magnetic stirrer, set the temperature to 80°C and the speed to 300 rpm, stir for 12 hours to obtain the evaporated HC polymer.

[0093] (9) The HC polymer obtained in step (8) is subjected to a dehydration reaction at 140°C in an oxygen-free environment to obtain sodium-ion battery hard carbon anode material (GA-HC).

[0094] Results Test: The carbon material with surface coating in Example 4 was assembled into a half-cell. According to the sodium-ion battery test standard, the first-cycle charge-discharge curve at a current density of 30 mA / g showed that the modified hard carbon achieved a first-cycle discharge specific capacity of 297 mAh / g and a first-cycle coulombic efficiency of 91.2%. The results of acid washing with hydrofluoric acid were similar to those of acid washing with hydrochloric acid, indicating that surface coating played the same role and did not affect the change of acid. This further demonstrates that the preparation method of this biomass carbon material helps to alleviate the irreversible reaction between the negative electrode and the electrolyte, and at the same time leads to the improvement of sodium storage performance of sodium-ion batteries.

[0095] Comparative Example 1

[0096] As a blank control, the preparation steps of the hard carbon anode material without surface coating are as follows:

[0097] (1) After breaking the bamboo into large pieces, wash it with tap water and dry it overnight in an oven at 120℃. Then, calcine it for the first time in a tube furnace at 500℃ to obtain pre-carbonized biomass carbon material. The heating rate is 2℃ / min and the temperature is maintained for 2h.

[0098] (2) The pre-carbonized biomass carbon material in step (1) is coarsely crushed using an ore crusher and sieved through a 500-mesh sieve. The sieved bamboo is then finely crushed using a mechanical mill-airflow pulverizer and sieved through an 800-mesh sieve to obtain preliminary biomass carbon material.

[0099] (3) Take 10g of bamboo powder after sieving twice and put it into a beaker with a capacity of 100ml. Add 40g of hydrofluoric acid solution (2ml 22.5mol / L HF, 38ml deionized water) diluted to 5% of the original concentrated hydrofluoric acid solution at a solid-liquid mass ratio of 1:4 and acid wash for 4h.

[0100] (4) Transfer all the pickled bamboo to a 50ml centrifuge tube, weigh and balance it, then put it into a centrifuge, set the centrifugation speed to 10000 rpm and the centrifugation time to 10 min, and pour out the solution in the tube after centrifugation.

[0101] (5) Add deionized water to the centrifuge tube in step (4), weigh and balance it, wash and centrifuge it 3 times according to the above centrifugation parameters, and dry it in an oven at 120°C for 6 hours to obtain clean pretreated biomass carbon material.

[0102] (6) Take out 3g of the pretreated biomass carbon material from step (5) and calcine it for the second time in a tube furnace at 1100℃, 0.16L / min Ar, and a heating rate of 4℃ / min. After high-temperature carbonization and holding for 2h, the hard carbon anode material is obtained after natural cooling.

[0103] Results Testing: The uncoated carbon material from Example 1 was assembled into a half-cell, and the first-week charge-discharge curve at a current density of 30 mA / g was obtained according to the sodium-ion battery testing standard. Figure 6 As shown, the initial discharge specific capacity of hard carbon is only 232.81 mAh / g, and the initial coulombic efficiency is only 79.17%. This indicates that the uncoated carbon material has a rough surface, a large specific surface area, and a wide contact area with the electrolyte, resulting in serious electrolyte loss.

[0104] This invention utilizes the dehydration condensation reaction between the -COOH bonds on 4-(N,N-diethylamino)benzoic acid (4-DEBA) and the -OH bonds on the oxidized HC surface to successfully graft 4-DEBA uniformly onto the HC surface. The 4-DEBA molecules also form a self-crosslinking structure (4-DEBA modification layer) through their own -COOH and -OH bonds during the dehydration reaction. The thickness and uniformity of the 4-DEBA modification layer on the HC surface can be adjusted by controlling the amount of 4-DEBA added; a suitable thickness does not affect ion transport performance. The grafting of the 4-DEBA modification layer reduces the specific surface area of ​​hard carbon, which helps reduce irreversible capacity loss caused by the reaction between the negative electrode material and the electrolyte. Furthermore, the modification of the HC surface functional groups using the 4-DEBA modification layer gives the HC better electrolyte affinity, enabling rapid ion transport and a stable electrode / electrolyte interface. The presence of the surface polymer effectively hinders the decomposition of the electrolyte solvent, improving the initial coulombic efficiency of the sodium-ion battery and providing more reversible active sites for sodium storage, thus improving the battery's sodium storage performance.

[0105] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for preparing reconstructed functional groups on the surface of a hard carbon anode, characterized in that... Includes the following steps: 1) After crushing the natural coconut shells into large pieces, they are washed, dried, and then subjected to a first high-temperature calcination to obtain pre-carbonized biomass carbon material. 2) The pre-carbonized biomass carbon material obtained in step 1) is crushed and sieved to obtain preliminary biomass carbon material; 3) The preliminary biomass carbon material obtained in step 2) is acid-washed to remove any possible metallic impurities and further purify the material; 4) Wash the acid-washed biomass carbon with deionized water to remove excess acid, then centrifuge and dry to obtain pretreated biomass carbon material; 5) The pretreated biomass carbon material from step 4) is subjected to a second high-temperature calcination to obtain the precursor material; 6) Mix the precursor material obtained in step 5) with hydrogen peroxide and stir to pre-oxidize it, so as to introduce oxygen-containing functional groups and improve the sodium affinity of the material. 7) Add 5% by mass of 4-(N,N-diethylamino)-benzoic acid to the pre-oxidized material, stir and evaporate to dryness at 80°C to obtain HC polymer; 8) The HC polymer after evaporation in step 7) is subjected to a dehydration reaction in an oxygen-free environment at 140°C to optimize the surface functional groups and sodium storage performance of the hard carbon material, and obtain a sodium-ion battery hard carbon anode material after reconstructing the surface functional groups of the hard carbon anode.

2. The method for preparing reconstructed functional groups on the surface of a hard carbon anode as described in claim 1, characterized in that... In step 1), the natural coconut shell is replaced by one of the following: bamboo, walnut shell, orange peel, peanut shell, macadamia nut shell, and straw; the drying is carried out overnight in an oven at 120°C; the first high-temperature calcination is carried out in an inert gas atmosphere, the temperature of the first high-temperature calcination is 400-600°C, the heating rate of the first high-temperature calcination is 2-10°C / min, and the holding time is 1-6 hours.

3. The method for preparing reconstructed functional groups on the surface of a hard carbon anode as described in claim 2, characterized in that... The first high-temperature calcination was carried out in a tube furnace at 600℃, with a heating rate of 5℃ / min and a holding time of 2 hours.

4. The method for preparing reconstructed functional groups on the surface of a hard carbon anode as described in claim 1, characterized in that... In step 2), the pre-carbonized biomass carbon material obtained in step 1) is crushed and sieved. The specific steps are as follows: First, the pre-carbonized biomass carbon material is coarsely crushed using an ore crusher and then preliminarily sieved using a 300-500 mesh sieve. The sieved pre-carbonized biomass carbon material is then finely crushed using a mechanical mill-airflow pulverizer and sieved a second time using a 600-1000 mesh sieve to obtain preliminary biomass carbon material.

5. The method for preparing reconstructed functional groups on the surface of a hard carbon anode as described in claim 4, characterized in that... The initial screening passed through a 500-mesh sieve; the secondary screening passed through an 800-mesh sieve.

6. The method for preparing reconstructed functional groups on the surface of a hard carbon anode as described in claim 1, characterized in that... In step 3), the reagent used for pickling is one of hydrochloric acid, sulfuric acid, or nitric acid.

7. The method for preparing reconstructed functional groups on the surface of a hard carbon anode as described in claim 1, characterized in that... In step 3), the acid washing involves mixing the preliminary biomass carbon material obtained in step 2) with a 5% concentrated hydrochloric acid solution for acid washing. The 5% concentrated hydrochloric acid solution was prepared by mixing 2 ml of 12 mol / L concentrated hydrochloric acid and 38 ml of deionized water; the preliminary biomass carbon material was mixed with the 5% concentrated hydrochloric acid solution at a solid-liquid mass ratio of 1:

4. The specific steps are as follows: Take 10g of the preliminary biomass carbon material after secondary sieving and put it into a container with a capacity of 100ml. Add 40g of the prepared hydrochloric acid solution at a solid-liquid mass ratio of 1:4 and acid wash for 4 hours to allow the hydrochloric acid to fully contact the coconut shell powder and complete the acid washing process.

8. The method for preparing reconstructed functional groups on the surface of a hard carbon anode as described in claim 1, characterized in that... In step 4), the centrifugation speed is 10,000 rpm and the centrifugation time is 10 min; the number of centrifugations is 3; the drying is carried out in an oven at 120℃ for 6 h.

9. The method for preparing reconstructed functional groups on the surface of a hard carbon anode as described in claim 1, characterized in that... In step 5), the second high-temperature calcination is carried out in a tube furnace at 1100-1400℃, 0.16L / min Ar, and a heating rate of 2-5℃ / min, and the carbonization is held for 2-12 hours.

10. The method for preparing reconstructed functional groups on the surface of a hard carbon anode as described in claim 9, characterized in that... The second high-temperature calcination was carried out in a tube furnace at 1200℃, 0.16L / min Ar, and a heating rate of 5℃ / min, with carbonization and holding at that temperature for 4 hours.

11. The method for preparing reconstructed functional groups on the surface of a hard carbon anode as described in claim 1, characterized in that... In step 6), the hydrogen peroxide is a 3% H2O2 solution; the pre-oxidation time is 12h; the mass percentage of H2O2 in the precursor is 10% to 20%, the solid-liquid ratio is 0.2 to 1, and the treatment time is 12 to 24h.

12. The method for preparing reconstructed functional groups on the surface of a hard carbon anode as described in claim 1, characterized in that... In step 7), the stirring is carried out on a magnetic stirrer, with the temperature set at 80°C and the speed at 300 rpm, for 12 hours.

13. The sodium-ion battery hard carbon anode material prepared by the preparation method according to any one of claims 1 to 12.

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