A hard carbon sodium-ion battery negative electrode material made from peanut shells and its preparation method

Abstract

The present invention discloses a hard carbon sodium-ion battery anode material made from peanut shells, which is micron-sized particles containing C, O, Na, and N element hybrid nanoparticles. After ultrasonic dispersion, the material has a disordered packing formed by graphitized regions in the range of 0.6 - 3 nm wrapping pores, and has an average graphite layer spacing of 3.6 - 4.0 Å. The present invention also discloses its preparation method, where peanut shells are placed under an air atmosphere for heating and pre-oxidation, then ground or crushed into powder form, and ethylenediaminetetraacetic acid disodium solution is added. After stirring evenly, it is dried; the dried mixture is calcined and carbonized under a nitrogen atmosphere, and after cooling, a hard carbon sodium-ion battery anode material made from peanut shells is obtained. The hard carbon material obtained by the present invention, as the anode of a sodium-ion battery, when charged and discharged at 0.1C, the initial charging specific capacity can reach 274 - 318 mAh·g-1, and the first-cycle Coulombic efficiency reaches 74% - 84%, solving the problems of low capacity and low initial Coulombic efficiency of hard carbon sodium-ion battery anode materials.

Description

Technical Field

[0001] The present invention relates to a hard carbon sodium battery anode material and a preparation method thereof, belonging to the technical field of electrode materials. Background Art

[0002] Peanut shells, as waste in the edible oil industry, are rich in lignin and can be used to prepare hard carbon materials. However, the carbon materials obtained by directly treating peanut shells at high temperature have low charge-discharge capacities. In the solutions of the prior art, concentrated phosphoric acid is used to soak peanut shells for a long time before calcination to increase active sites, hoping to improve the charge-discharge capacity, but this results in a low initial Coulombic efficiency of the final hard carbon product, only 68%. This may be because the soaking process of phosphoric acid makes the product hard carbon have a large specific surface area, and the strong adsorption of these surfaces to sodium ions will reduce the Coulombic efficiency of the first cycle of the material during charge and discharge, thus dragging down the performance of the positive electrode material, which will make the long-term charge-discharge stability of the full battery poor.

[0003] Therefore, when preparing a hard carbon material used as the anode of a sodium-ion battery from peanut shells, it is necessary to solve the problem of low capacity. While increasing active sites to improve the capacity, it is also necessary to prevent the generation of a large specific surface area to avoid reducing the initial Coulombic efficiency of the material. Summary of the Invention

[0004] In view of the above technical requirements, the present invention provides a preparation method of a hard carbon sodium battery anode material using peanut shells as raw materials, and also provides a hard carbon sodium battery anode material using peanut shells as raw materials prepared by this preparation method, to solve the problems of low capacity and low initial Coulombic efficiency of the material.

[0005] The technical solution of the present invention is: a hard carbon sodium battery anode material using peanut shells as raw materials, the hard carbon sodium battery anode material using peanut shells as raw materials is a micron-sized particle containing mixed nanoparticles of C, O, Na, and N elements, and after ultrasonic dispersion, the hard carbon sodium battery anode material using peanut shells as raw materials has a graphitized region with a scale range of 0.6 - 3 nm wrapping pores to form a disordered accumulation, and has an average graphite layer spacing of 3.6 - 4.0 Å.

[0006] Another technical solution of the present invention is: a preparation method of a hard carbon sodium battery anode material using peanut shells as raw materials, including the steps of: S1, heating and pre-oxidizing peanut shells under an air atmosphere condition; S2, grinding or crushing the pre-oxidized peanut shells into a powder form, adding a disodium ethylenediaminetetraacetate solution, stirring evenly and then drying; S3, calcining and carbonizing the mixture dried in step S2 under a nitrogen atmosphere, and obtaining a hard carbon sodium battery anode material using peanut shells as raw materials after cooling.

[0007] Another technical solution of the present invention is: a preparation method of a hard carbon sodium battery negative electrode material using peanut shells as raw materials, comprising the steps of: S0. Placing peanut shells in a hydrochloric acid solution and heating, then separating the solid substance from the solution, washing, and drying; S1. Placing the peanut shells dried in step S0 in an air atmosphere and heating for pre-oxidation; S2. Grinding or crushing the pre-oxidized peanut shells into powder form, adding a disodium ethylenediaminetetraacetate solution, stirring evenly, and drying; S3. Calcining and carbonizing the mixture dried in step S2 in a nitrogen atmosphere, and obtaining a hard carbon sodium battery negative electrode material using peanut shells as raw materials after cooling.

[0008] In the technical solution of the preparation method of the hard carbon sodium battery negative electrode material using peanut shells as raw materials, further, in step S1, the pre-oxidation temperature is 200 - 300 °C.

[0009] Further, in step S2, the proportion of disodium ethylenediaminetetraacetate in the disodium ethylenediaminetetraacetate solution to the mass of the powdered peanut shells is 2% - 8%.

[0010] Further, in step S3, the temperature of calcining and carbonizing in the nitrogen atmosphere is 1200 - 1400 °C, and the calcining and carbonizing treatment time is 0.5 - 5 h.

[0011] Further, in step S0, the concentration of the hydrochloric acid is 0.5 - 2 mol / L, the heating temperature is 60 - 150 °C, and the heating time is 0.5 - 5 h.

[0012] The advantages of the present invention compared with the prior art are as follows:

[0013] (1) Disodium ethylenediaminetetraacetate added during the preparation process contains nitrogen, oxygen, and sodium elements. Among them, the oxygen element may increase the disorder degree of the final hard carbon material and provide active sites; the nitrogen element not only provides active sites but may also improve the conductivity of the material; the sodium element will be reduced to elemental sodium in a reducing atmosphere and evaporated at high temperature. This process may generate sodium ion channels, facilitating the entry of sodium ions into the material interior after being reduced during the charge and discharge of the sodium battery negative electrode. These factors make the product hard carbon have a higher charge and discharge capacity compared with the hard carbon material produced by directly calcining peanut shells.

[0014] (2) The process of adding disodium ethylenediaminetetraacetate mentioned above does not produce sewage, and the addition ratio is very low, so it has little impact on the cost of the product hard carbon.

[0015] (3) Calcining peanut shells after adding disodium ethylenediaminetetraacetate will not increase the specific surface area of the product hard carbon, thus avoiding the reduction of the first-cycle Coulombic efficiency during the charge and discharge of the product as a sodium ion battery negative electrode.

[0016] (4) The pre - treatment process with hydrochloric acid can cause partial hydrolysis of lignin in peanut shells, shortening and reducing the size of its structural segments, which helps to fully contact with disodium ethylenediaminetetraacetate added subsequently at the microscopic level. As a result, the hard carbon of the product can further provide a higher charge - discharge specific capacity, and this hydrochloric acid treatment step does not reduce the Coulombic efficiency of the first charge - discharge cycle of the product hard carbon.

[0017] (5) The hard - carbon sodium - ion negative electrode material prepared from peanut shells in the present invention, when the assembled sodium - ion half - cell is at 0.1C (1C = 300 mA g -1 ) can provide an initial charge specific capacity of 264 - 318 mAh·g -1 . The Coulombic efficiency of the first cycle is between 74% - 84%, and the capacity retention rate is 84% - 91% after 50 stable cycles. These characteristics make the material suitable for practical energy storage applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is the powder X - ray diffraction (XRD) pattern of the hard - carbon sodium - ion negative electrode material prepared from peanut shells in Example 1.

[0019] Figure 2 It is the powder X - ray diffraction (XRD) pattern of the hard - carbon sodium - ion negative electrode material prepared from peanut shells in Example 4.

[0020] Figure 3 It is the powder X - ray diffraction (XRD) pattern of the hard - carbon sodium - ion negative electrode material prepared from peanut shells in Example 5.

[0021] Figure 4 It is the scanning electron microscope (SEM) image of the hard - carbon sodium - ion negative electrode material prepared from peanut shells in Example 1.

[0022] Figure 5 It is the scanning electron microscope (SEM) image of the hard - carbon sodium - ion negative electrode material prepared from peanut shells in Example 4.

[0023] Figure 6 It is the scanning electron microscope (SEM) image of the hard - carbon sodium - ion negative electrode material prepared from peanut shells in Example 5.

[0024] Figure 7 It is the transmission electron microscope (TEM) image and element distribution map of the hard - carbon sodium - ion negative electrode material prepared from peanut shells in Example 1. The sample powder of Example 1 was first ultrasonically treated in absolute ethanol, and then dispersed on the surface of the copper grid before taking the transmission electron microscope photograph.

[0025] Figure 8TEM image and elemental distribution map of the hard carbon sodium-ion battery anode material made from peanut shells obtained in Example 4. The sample powder of Example 4 was first ultrasonically treated in absolute ethanol, then dispersed on the surface of a copper grid and then subjected to TEM imaging.

[0026] Figure 9 TEM image and elemental distribution map of the hard carbon sodium-ion battery anode material made from peanut shells obtained in Example 5. The sample powder of Example 5 was first ultrasonically treated in absolute ethanol, then dispersed on the surface of a copper grid and then subjected to TEM imaging.

[0027] Figure 10 Variable rate cycling effect diagram of the sodium-ion half-cell assembled with the hard carbon sodium-ion battery anode material made from peanut shells obtained in Example 1 and a sodium sheet.

[0028] Figure 11 Variable rate cycling effect diagram of the sodium-ion half-cell assembled with the hard carbon sodium-ion battery anode material made from peanut shells obtained in Example 4 and a sodium sheet.

[0029] Figure 12 Variable rate cycling effect diagram of the sodium-ion half-cell assembled with the hard carbon sodium-ion battery anode material made from peanut shells obtained in Example 5 and a sodium sheet.

[0030] Figure 13 Variable rate cycling effect diagram of the sodium-ion half-cell assembled with the hard carbon material obtained by directly calcining peanut shells in the comparative example and a sodium sheet.

[0031] Figure 14 Comparison diagram of the long-term cycling effects of the sodium-ion half-cells of Examples 1-9 and the comparative example at a rate of 0.1C. Detailed implementation mode

[0032] The present invention will be further described below in conjunction with examples, but it is not intended to limit the present invention.

[0033] Example 1:

[0034] (1) Peanut shells were placed under an air atmosphere and heated for pre-oxidation at a pre-oxidation temperature of 250°C;

[0035] (2) The pre-oxidized peanut shells were ground or crushed into powder form. Disodium ethylenediaminetetraacetate accounting for 5% of the mass of the powdered peanut shells was dissolved in distilled water to form a clear solution, which was then added to the above peanut shell powder and stirred evenly, and the mixed system was dried;

[0036] (3) Place the mixture of dried peanut shell powder and disodium ethylenediaminetetraacetate under an N2 atmosphere, heat it to 1300 °C and maintain this temperature for 2 hours, and then cool it to obtain the hard carbon sodium-ion battery anode material using peanut shells as the raw material. This material can provide a first-cycle charge specific capacity of 274 mAh·g -1 at 0.1 C. The first-cycle Coulombic efficiency is 77%, and the capacity after 50 cycles at 0.1 C is 231 mAh·g -1 , and the capacity retention rate is 84%.

[0037] Example 2:

[0038] (1) Place peanut shells under an air atmosphere and heat them for pre-oxidation at a pre-oxidation temperature of 200 °C;

[0039] (2) Grind or crush the pre-oxidized peanut shells into powder form. Dissolve disodium ethylenediaminetetraacetate accounting for 2% of the mass of the powdered peanut shells in distilled water to form a clear solution, add it to the above peanut shell powder, stir evenly, and dry the mixed system;

[0040] (3) Place the mixture of dried peanut shell powder and disodium ethylenediaminetetraacetate under an N2 atmosphere, heat it to 1200 °C and maintain this temperature for 5 hours, and then cool it to obtain the hard carbon sodium-ion battery anode material using peanut shells as the raw material. This material can provide a first-cycle charge specific capacity of 264 mAh·g -1 at 0.1 C. The first-cycle Coulombic efficiency is 75%, and the capacity after 50 cycles at 0.1 C is 226 mAh·g -1 , and the capacity retention rate is 86%.

[0041] Example 3:

[0042] (1) Place peanut shells under an air atmosphere and heat them for pre-oxidation at a pre-oxidation temperature of 300 °C;

[0043] (2) Grind or crush the pre-oxidized peanut shells into powder form. Dissolve disodium ethylenediaminetetraacetate accounting for 8% of the mass of the powdered peanut shells in distilled water to form a clear solution, add it to the above peanut shell powder, stir evenly, and dry the mixed system;

[0044] (3) Place the mixture of dried peanut shell powder and disodium ethylenediaminetetraacetate under an N2 atmosphere, heat it to 1400 °C and maintain this temperature for 0.5 hours, and then cool it to obtain the hard carbon sodium-ion battery anode material using peanut shells as the raw material. This material can provide a first-cycle charge specific capacity of 271 mAh·g -1 at 0.1 C. The first-cycle Coulombic efficiency is 75%, and the capacity after 50 cycles at 0.1 C is 238 mAh·g -1 , and the capacity retention rate is 88%.

[0045] Example 4:

[0046] (1) Add peanut shells into an acid-resistant container, add 1 mol / L HCl solution to submerge the peanut shells, seal the container and heat it at 100 °C for 2 hours. After cooling, separate the solid matter, wash it and then dry it.

[0047] (2) Place the dried peanut shells obtained above under air atmosphere and heat them for pre-oxidation, with the pre-oxidation temperature being 250 °C.

[0048] (3) Grind or crush the pre-oxidized peanut shells into powder form. Dissolve disodium ethylenediaminetetraacetate accounting for 5% of the mass of the powdered peanut shells in distilled water to form a clear solution, add it to the above peanut shell powder and stir evenly, and then dry the mixed system.

[0049] (4) Place the mixture of the dried peanut shell powder and disodium ethylenediaminetetraacetate under N2 atmosphere, heat it to 1300 °C and maintain this temperature for 2 hours, and then cool it to obtain the hard carbon sodium-ion battery anode material using peanut shells as the raw material. This material can provide a first-cycle charge specific capacity of 296 mAh·g -1 at 0.1C, the first-cycle Coulombic efficiency is 84%, and the capacity is 255 mAh·g -1 after 50 cycles at 0.1C, and the capacity retention rate is 86%.

[0050] Example 5:

[0051] (1) Add peanut shells into an acid-resistant container, add 1 mol / L HCl solution to submerge the peanut shells, seal the container and heat it at 80 °C for 2 hours. After cooling, separate the solid matter, wash it and then dry it.

[0052] (2) Place the dried peanut shells obtained above under air atmosphere and heat them for pre-oxidation, with the pre-oxidation temperature being 250 °C.

[0053] (3) Grind or crush the pre-oxidized peanut shells into powder form. Dissolve disodium ethylenediaminetetraacetate accounting for 5% of the mass of the powdered peanut shells in distilled water to form a clear solution, add it to the above peanut shell powder and stir evenly, and then dry the mixed system.

[0054] (4) Place the mixture of the dried peanut shell powder and disodium ethylenediaminetetraacetate under N2 atmosphere, heat it to 1300 °C and maintain this temperature for 2 hours, and then cool it to obtain the hard carbon sodium-ion battery anode material using peanut shells as the raw material. This material can provide a first-cycle charge specific capacity of 318 mAh·g -1 at 0.1C, the first-cycle Coulombic efficiency is 74%, and the capacity is 287 mAh·g -1 after 50 cycles at 0.1C, and the capacity retention rate is 90%.

[0055] Example 6:

[0056] (1) Add peanut shells into an acid-resistant container, add 0.5 mol / L HCl solution to submerge the peanut shells, seal the container and heat it at 60 °C for 5 hours. After cooling, separate the solid matter, wash it and then dry it;

[0057] (2) Place the dried peanut shells obtained above under an air atmosphere and heat them for pre-oxidation, with the pre-oxidation temperature being 300 °C;

[0058] (3) Grind or crush the pre-oxidized peanut shells into powder form. Dissolve disodium ethylenediaminetetraacetate accounting for 2% of the mass of the powdered peanut shells in distilled water to form a clear solution, add it to the above peanut shell powder and stir evenly, and then dry the mixed system;

[0059] (4) Place the mixture of the dried peanut shell powder and disodium ethylenediaminetetraacetate under an N2 atmosphere, heat it to 1300 °C and maintain this temperature for 2 hours, and then cool it to obtain the hard carbon sodium-ion battery negative electrode material using peanut shells as raw materials. This material can provide a first-cycle charge specific capacity of 285 mAh·g -1 at 0.1C, the first-cycle Coulombic efficiency is 78%, and the capacity after 50 cycles at 0.1C is 258 mAh·g -1 , and the capacity retention rate is 91%.

[0060] Example 7:

[0061] (1) Add peanut shells into an acid-resistant container, add 2 mol / L HCl solution to submerge the peanut shells, seal the container and heat it at 150 °C for 0.5 hours. After cooling, separate the solid matter, wash it and then dry it;

[0062] (2) Place the dried peanut shells obtained above under an air atmosphere and heat them for pre-oxidation, with the pre-oxidation temperature being 250 °C;

[0063] (3) Grind or crush the pre-oxidized peanut shells into powder form. Dissolve disodium ethylenediaminetetraacetate accounting for 4% of the mass of the powdered peanut shells in distilled water to form a clear solution, add it to the above peanut shell powder and stir evenly, and then dry the mixed system;

[0064] (4) Place the mixture of the dried peanut shell powder and disodium ethylenediaminetetraacetate under an N2 atmosphere, heat it to 1300 °C and maintain this temperature for 2 hours, and then cool it to obtain the hard carbon sodium-ion battery negative electrode material using peanut shells as raw materials. This material can provide a first-cycle charge specific capacity of 274 mAh·g -1 at 0.1C, the first-cycle Coulombic efficiency is 80%, and the capacity after 50 cycles at 0.1C is 237 mAh·g -1, the capacity retention rate is 86%.

[0065] Example 8:

[0066] (1) Add peanut shells into an acid-resistant container, add 1 mol / L HCl solution to submerge the peanut shells, seal the container and heat it at 100 °C for 2 hours. After cooling, separate the solid matter, wash it and then dry it;

[0067] (2) Place the dried peanut shells obtained above under air atmosphere conditions for heat pre-oxidation, and the pre-oxidation temperature is 200 °C;

[0068] (3) Grind or crush the pre-oxidized and dried peanut shells into powder form. Dissolve disodium ethylenediaminetetraacetate accounting for 8% of the mass of the powdered peanut shells in distilled water to form a clear solution, add it to the above peanut shell powder and stir evenly, and then dry the mixed system;

[0069] (4) Place the mixture of peanut shell powder and disodium ethylenediaminetetraacetate under N2 atmosphere, heat it up to 1200 °C and keep this temperature for 5 hours, and then cool it to obtain the hard carbon sodium-ion battery negative electrode material using peanut shells as raw materials. This material can provide a first-cycle charge specific capacity of 282 mAh·g -1 , the first-cycle Coulombic efficiency is 77%. After cycling 50 times at 0.1C, the capacity is 239 mAh·g -1 , the capacity retention rate is 85%.

[0070] Example 9:

[0071] (1) Add peanut shells into an acid-resistant container, add 1 mol / L HCl solution to submerge the peanut shells, seal the container and heat it at 100 °C for 2 hours. After cooling, separate the solid matter, wash it and then dry it;

[0072] (2) Place the dried peanut shells obtained above under air atmosphere conditions for heat pre-oxidation, and the pre-oxidation temperature is 250 °C;

[0073] (3) Grind or crush the pre-oxidized peanut shells into powder form. Dissolve disodium ethylenediaminetetraacetate accounting for 5% of the mass of the powdered peanut shells in distilled water to form a clear solution, add it to the above peanut shell powder and stir evenly, and then dry the mixed system;

[0074] (4) Place the mixture of dried peanut shell powder and disodium ethylenediaminetetraacetate under N2 atmosphere, heat it up to 1400 °C and keep this temperature for 0.5 hours, and then cool it to obtain the hard carbon sodium-ion battery negative electrode material using peanut shells as raw materials. This material can provide a first-cycle charge specific capacity of 278 mAh·g -1 , the first-cycle Coulombic efficiency is 77%. After cycling 50 times at 0.1C, the capacity is 242 mAh·g-1 , the capacity retention rate is 87%.

[0075] Comparative example:

[0076] (1) The peanut shells were heated and pre-oxidized under an air atmosphere condition, and the pre-oxidation temperature was 250 °C;

[0077] (2) The pre-oxidized peanut shells were ground or crushed into powder, placed under an N2 atmosphere, heated to 1300 °C and maintained at this temperature for 2 hours, and then cooled to obtain a hard carbon material using the peanut shells of the comparative example as the raw material. This material can provide a first-cycle charge specific capacity of 256 mAh·g -1 , the first-cycle Coulombic efficiency is 72%, and the capacity after 50 cycles is 219 mAh·g -1 , and the capacity retention rate is 86%.

[0078] In order to verify the structural characteristics and performance of the products obtained by the method of the present invention, the structures and performances of the obtained materials were characterized.

[0079] From Figure 1 It can be seen that in the XRD pattern of the hard carbon sodium-ion battery negative electrode material prepared from peanut shells in Example 1, two broad peaks are present at 2 θ angles of 24.1° and 43.7°. The diffraction peak positions are similar to the diffraction peaks of the (002) and (100) crystal planes of graphite (the 2 θ angle positions are 26.5° and 42.8° respectively), but the diffraction peak angle of 24.1° of the sample in Example 1 is lower, corresponding to a wider average layer spacing of the (002) crystal plane, 3.69 Å, while the normal graphite (002) crystal plane layer spacing is 3.35 Å. The wider layer spacing is beneficial for the insertion of sodium ions into the graphite-like interlayer structure and internal pores, providing a higher charge-discharge capacity. Both diffraction peaks in the XRD pattern are broad peaks, indicating that the sample in Example 1 has a disordered structure, which can be considered to be formed by the loose packing of small-scale graphite-like regions.

[0080] From Figure 2 It can be seen that in the XRD pattern of the hard carbon sodium-ion battery negative electrode material prepared from peanut shells in Example 4, two broad peaks are present at 2 θ angles of 23.2° and 43.7°. The diffraction peak at 23.2° corresponds to an average layer spacing of 3.83 Å of the (002) crystal plane. In addition, both diffraction peaks are also broad peaks, and it can also be speculated that the sample in Example 4 also has a disordered structure, formed by the loose packing of small-scale graphite-like regions.

[0081] From Figure 3 It can be seen that in the XRD pattern of the hard carbon sodium-ion battery negative electrode material prepared from peanut shells in Example 5, two broad peaks are present at 2 θThere are two broad peaks at angles of 22.6° and 43.7°. The diffraction peak at 22.6° corresponds to the average layer spacing of the (002) crystal plane of 3.93 Å. In addition, the two diffraction peaks are also broad peaks, and it can also be speculated that the sample of Example 5 also has a disordered structure, formed by the loose packing of small-scale graphitized regions.

[0082] From Figure 4 the scanning electron microscope image (SEM), it can be seen that the product prepared in Example 1 is mostly micron-sized irregular granular substances, mixed with a small amount of nano-sized particles.

[0083] From Figure 5 the scanning electron microscope image, it can be seen that the product prepared in Example 4 is mostly micron-sized irregular granular substances, mixed with a small amount of nano-sized particles.

[0084] From Figure 6 the scanning electron microscope image, it can be seen that the product prepared in Example 5 is mostly micron-sized irregular granular substances, mixed with a small amount of nano-sized particles.

[0085] Figure 7 In (a) and (b) in, they are transmission electron microscope images of different magnifications of the hard carbon sodium ion negative electrode material using peanut shells as raw materials obtained in Example 1. From Figure 7 the transmission electron microscope image (TEM), it can be seen that after ultrasonic dispersion, disordered packing formed by graphitized regions with a diameter of about 1 - 3 nm wrapping pores can be observed on the lamellar structure of the sample in Example 1, as Figure 7 shown in (b) in. The white dot regions in the figure have a large proportion of transmitted light, indicating that these regions have a low mass thickness and there are pore structures. Figure 7 In the randomly selected sample particles of Example 1 shown in (c) in, uniformly distributed C, O, Na, and N elements can be observed, which are shown in Figure 7 the element distribution maps (d), (e), (f), and (g) in in turn.

[0086] Figure 8 In (a) and (b) in, they are transmission electron microscope images of different magnifications of the hard carbon sodium ion negative electrode material using peanut shells as raw materials obtained in Example 4. From Figure 8 the transmission electron microscope image (TEM), it can be seen that after ultrasonic dispersion, disordered packing formed by graphitized regions with a diameter of about 0.6 - 2.5 nm wrapping pores can be observed on the lamellar structure of the sample in Example 4, as Figure 8 shown in (b) in. Figure 8 In the randomly selected sample particles of Example 4 shown in (c) in, uniformly distributed C, O, Na, and N elements can be observed, which are shown in Figure 8 the element distribution maps (d), (e), (f), and (g) in in turn.

[0087] Figure 9Figures (a) and (b) are transmission electron microscope images of the hard carbon sodium-ion battery anode material made from peanut shells obtained in Example 5. From Figure 9 the transmission electron microscope (TEM) image, it can be seen that after ultrasonic dispersion, chaotic packing formed by graphitized regions with a diameter of approximately 0.6 - 2.5 nm wrapping pores can be observed on the lamellar structure of the sample in Example 5, as shown in Figure 9 Figure (b). Figure 9 Randomly selected particles of the sample in Example 5 shown in Figure (c) can be observed to have uniformly distributed C, O, Na, and N elements, which are sequentially shown in the element distribution maps (d), (e), (f), and (g) in Figure 9 .

[0088] From Figure 10 it can be seen that for the hard carbon sodium-ion battery anode material made from peanut shells prepared in Example 1, when assembled into a half-cell, the initial charge capacity at a 0.1C charge-discharge rate is 274 mAh·g -1 , and the initial Coulombic efficiency is 77%. This material can be charged and discharged at variable rates, with a maximum rate of 5C. When the low rate (0.1C) charge-discharge is restored, the charge capacity returns to 245 mAh·g -1 , slightly lower than the initial charge capacity. Except for fluctuations in the Coulombic efficiency during the first cycle and when switching the current density, the Coulombic efficiency is close to 100% in other cases.

[0089] From Figure 11 it can be seen that for the hard carbon sodium-ion battery anode material made from peanut shells obtained in Example 4, when assembled into a half-cell, the initial charge capacity at 0.1C reaches 296 mAh·g -1 , and the initial Coulombic efficiency reaches 84%. The material can withstand high-rate charge-discharge at 5C. After restoring to the low rate (0.1C), the charge capacity can return to 275 mAh·g -1 . Except for the first cycle and when switching the rate, the Coulombic efficiency is close to 100% in other cases.

[0090] From Figure 12 it can be seen that for the hard carbon sodium-ion battery anode material made from peanut shells obtained in Example 5, when assembled into a half-cell, the initial charge capacity at 0.1C reaches 318 mAh·g -1 , and the initial Coulombic efficiency reaches 74%. The material can withstand high-rate charge-discharge at 5C. After restoring to the low rate (0.1C), the charge capacity can return to 303 mAh·g -1 . Except for the first cycle and when switching the rate, the Coulombic efficiency is close to 100% in other cases.

[0091] From Figure 13 it can be seen that for the hard carbon material obtained by directly calcining peanut shells in the comparative example, when assembled into a half-cell, the initial charge capacity at 0.1C is 255 mAh·g -1, the initial Coulombic efficiency is 72%. When the sample undergoes high-rate charge and discharge and returns to 0.1C, the charge specific capacity is 230 mAh·g -1 .

[0092] From Figure 14 It can be seen that compared with the comparative examples, Examples 1 to 3 (i.e., the peanut shell hard carbon materials only processed through steps S1 to S3) have higher charge specific capacities. After 50 cycles, the charge capacity retention rate ranges from 84% to 88%; on this basis, for Examples 4 to 9 with the additional pre-step S0 hydrochloric acid treatment, the charge specific capacity of the material as the sodium battery anode is further improved. After 50 cycles, the charge capacity retention rate ranges from 85% to 91%. In addition, the decrease in the charge specific capacity between the 10th and 11th cycles shown in all the examples and comparative examples in the figure is due to the high-rate charge and discharge between 0.2C and 5C as shown in Figures 10 - 13 ; if the influence of high-rate charge and discharge is excluded, the capacity retention rate after 50 cycles can be further increased by about 2%. In addition, since all tests use a sodium foil as the counter electrode, it is extremely easy to form sodium dendrites and affect the test stability; therefore, it is speculated that the hard carbon material of the present invention will have further improvement in long-term charge and discharge stability and capacity retention rate when applied to a full battery.

Claims

1. A preparation method of a hard carbon sodium-ion battery negative electrode material using peanut shells as a raw material, characterized in that, Including the steps: S0. Place peanut shells in a hydrochloric acid solution and heat in a sealed container. Then separate the solid substance from the solution, wash and dry it. The concentration of the hydrochloric acid solution is 0.5 - 2 mol / L, the heating temperature is 60 - 150 °C, and the heating time is 0.5 - 5 h; S1. Place the peanut shells dried in step S0 under an air atmosphere for pre-oxidation heating; S2. Grind or crush the pre-oxidized peanut shells into a powder, add a disodium ethylenediaminetetraacetate solution, stir evenly and dry it. The mass ratio of disodium ethylenediaminetetraacetate in the disodium ethylenediaminetetraacetate solution to the mass of the powdered peanut shells is 2% - 8%; S3. Place the mixture dried in step S2 under a nitrogen atmosphere for calcination and carbonization, and obtain a hard carbon sodium-ion battery anode material based on peanut shells after cooling. The hard carbon sodium-ion battery anode material based on peanut shells is a micron-sized particle containing mixed nanoparticles of C, O, Na, and N elements. After ultrasonic dispersion, the hard carbon sodium-ion battery anode material based on peanut shells has a graphitized region with a scale range of 0.6 - 3 nm wrapping pores to form a disordered packing, and has an average graphite layer spacing of 3.6 - 4.0 Å.

2. The preparation method of the hard carbon sodium-ion battery negative electrode material using peanut shells as raw materials according to claim 1, characterized in that, In step S1, the pre-oxidation temperature is 200 - 300 °C.

3. The preparation method of the hard carbon sodium-ion battery negative electrode material using peanut shells as raw materials according to claim 1, characterized in that, In step S3, the temperature for calcination and carbonization under the nitrogen atmosphere is 1200 - 1400 °C, and the calcination and carbonization treatment time is 0.5 - 5 h.

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