A nitrogen and boron co-doped pre-sodium-preliminary negative electrode material, a preparation method and application thereof

Abstract

The application provides a nitrogen and boron co-doped pre-sodiated negative electrode material and a preparation method and application thereof, and the preparation method comprises the following steps: (1) mixing hard carbon and nitrogen-containing organic matter, and performing primary sintering to obtain a nitrogen-doped hard carbon material; (2) mixing the nitrogen-doped hard carbon material and a pre-sodiated material, and performing secondary sintering to obtain a pre-sodiated negative electrode material; wherein the pre-sodiated material comprises NaBH4 and / or Na2B4O7. The hard carbon material and the nitrogen-containing organic matter are sintered once to form a nitrogen-doped hard carbon material, the capacity of the material is improved, then specific pre-sodiated material is added to perform secondary sintering, and the purposes of boron doping and pre-sodiation are simultaneously achieved. The method is simple, safe, and no by-product is generated, no impurities are additionally introduced, the capacity and rate performance of the material are improved through nitrogen and boron element co-doping, the first coulomb efficiency of the material is improved through pre-sodiation, and finally, the prepared pre-sodiated negative electrode material has excellent rate performance and first coulomb efficiency.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a nitrogen-boron co-doped pre-sodium-doped anode material, its preparation method, and its application. Background Technology

[0002] Sodium is abundant and inexpensive on Earth, giving sodium-ion batteries a significant competitive advantage over lead-acid and nickel-cadmium batteries in energy storage. This has attracted widespread attention in both academic and industrial fields, making it a promising alternative to lithium-ion batteries in electrochemical devices. In the lithium-ion and sodium-ion battery sectors, carbon-based anodes are considered among the most suitable anode materials due to their good conductivity, low cost, and excellent cycle performance. Hard carbon materials, with their unique layered structure, are currently the most commercially viable sodium-ion anode material among all carbon-based materials. However, hard carbon anodes still suffer from low initial coulombic efficiency (40–70%) and poor rate performance, hindering large-scale industrial application. Therefore, developing hard carbon anodes with higher initial efficiency and rate performance is crucial.

[0003] The use of heteroatomic doping can effectively improve the rate performance of hard carbon materials. Patent CN113644269 A discloses a method for preparing nitrogen-doped hard carbon materials. Specifically, it involves a hydrothermal reaction of glucose to form carbon microspheres, followed by mixing a nitrogen-containing precursor with the carbon microspheres and calcining at high temperature to obtain nitrogen-doped hard carbon materials. The resulting hard carbon materials significantly improve the sodium storage performance of conventional hard carbon, increase the conductivity of hard carbon materials, and improve their rate performance in sodium-ion batteries. However, this patent still does not significantly improve the problem of low initial coulombic efficiency of hard carbon materials.

[0004] The main reason for the low first-charge efficiency of hard carbon is the binding of sodium ions at the defect sites of hard carbon during the first charge and the irreversible consumption caused by the formation of a solid electrolyte interphase (SEI) film on the surface of hard carbon during the first charge. Commonly used pre-sodiuming methods include: 1. Contact pre-sodiuming method: Patent CN 111952532 B discloses a mechanical pre-sodiuming method, in which sodium metal sheets are flatly bonded to the battery negative electrode material in a glove box under certain environmental protection conditions, and then pressed by equipment to completely embed the sodium metal sheets into the negative electrode material, thus obtaining a pre-sodiumed sodium-ion secondary battery negative electrode material. The prepared material has a significantly improved first charge and discharge efficiency; however, this pre-sodiuming method has high environmental requirements for the entire process and poses certain safety hazards. II. Electrochemical Method: Patent CN 114207866 A discloses a method for pre-sodiuming the negative electrode using an electrochemical method. This patent achieves the purpose of pre-sodiuming the negative electrode by assembling the negative electrode and sodium metal sheet into a simple battery and electrochemically charging it in an electrolyte. This method can significantly improve the initial efficiency of the negative electrode, but it involves disassembling and reassembling the battery, which is a relatively cumbersome process and has very strict environmental requirements. III. Chemical Reaction Method: The chemical reaction method involves pre-sodiuming the negative electrode material or sheet by immersing it in an organic sodium-modifying reagent to achieve sodium compensation, and then assembling it into a battery. Patent CN 112635709 B discloses a sodium-ion battery negative electrode SEI film forming agent and pre-sodiuming method. This patent uses a polycyclic aromatic sodium solution to react with the sodium-ion negative electrode to form a stable SEI film on one side on the surface of the negative electrode before the battery is charged and discharged, and at the same time, sodium ions are pre-embedded into the negative electrode to improve the first efficiency of sodium ions. However, the reagents used in this method are often highly toxic and have very strict environmental requirements, otherwise the pre-sodiumed negative electrode is very likely to lose its activity.

[0005] In summary, current pre-sodiumization methods suffer from drawbacks such as insufficient simplicity, poor safety performance, and stringent environmental requirements. Therefore, providing a method for preparing hard carbon materials that is simple to process, has low environmental requirements, and can simultaneously improve the rate performance and initial coulombic efficiency of the material is of great significance to the research and development of sodium-ion batteries. Summary of the Invention

[0006] To address the problems existing in the prior art, the present invention aims to provide a nitrogen-boron co-doped pre-sodium-treated anode material, its preparation method, and its applications. The present invention involves a single sintering process of hard carbon material and nitrogen-containing organic matter to form a nitrogen-doped hard carbon material, thereby increasing the material's capacity. Then, a specific pre-sodium-treated material is added for a second sintering, simultaneously achieving boron doping and pre-sodium treatment. The method is simple, safe, and produces no byproducts or introduces additional impurities. The co-doping of nitrogen and boron elements improves the material's capacity and rate performance, while pre-sodium treatment enhances the material's initial coulombic efficiency. The resulting pre-sodium-treated anode material exhibits both excellent rate performance and initial coulombic efficiency.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing a nitrogen-boron co-doped pre-sodium-doped anode material, the method comprising:

[0009] (1) Hard carbon and nitrogen-containing organic matter are mixed and sintered in one step to obtain nitrogen-doped hard carbon material;

[0010] (2) Mix the nitrogen-doped hard carbon material and the pre-sodium material described in step (1) and sinter them for a second time to obtain the pre-sodiumized anode material;

[0011] The pre-sodium material includes NaBH4 and / or Na2B4O7.

[0012] This invention mixes hard carbon materials and nitrogen-containing organic compounds, and forms nitrogen-doped hard carbon materials through a single sintering process involving atomic rearrangement. Then, a specific pre-sodium material is added for a second sintering, simultaneously achieving boron doping and pre-sodiumization. This results in a nitrogen-boron co-doped pre-sodiumized anode material that exhibits both excellent rate performance and high initial coulombic efficiency. The technical principle of this invention is as follows:

[0013] First, nitrogen atoms are electron donors and can attract sodium ions to increase battery capacity during battery charging. In this invention, nitrogen-containing organic matter and hard carbon are sintered together once. Compared with inorganic nitrogen sources, the decomposition of nitrogen-containing organic matter is more conducive to nitrogen doping. Furthermore, the pre-doping of nitrogen into hard carbon can promote subsequent boron doping, allowing boron to replace part of the nitrogen element and be more easily doped into hard carbon, thus exerting a synergistic effect of nitrogen and boron to jointly improve the rate performance of the material.

[0014] Secondly, this invention involves a secondary sintering of nitrogen-doped hard carbon material obtained from a single sintering process with specific pre-sodium materials NaBH4 and / or Na2B4O7. The pre-sodium material serves as both a pre-sodiumizing agent and a boron source, simultaneously achieving boron doping and pre-sodiumization. This prevents the introduction of impurities when adding pre-sodium reagents and boron sources separately. The preparation method is simple, safe, and produces no byproducts, eliminating the need for impurity removal. Pre-sodiumization effectively improves the initial coulombic efficiency of the material. Simultaneously, boron, as an electron acceptor, attracts electrons, enhancing battery capacitance. This invention fully leverages the synergistic effect between nitrogen, boron, and pre-sodium through a specific preparation method. The resulting pre-sodiumized anode material exhibits both excellent rate performance and high initial coulombic efficiency, providing a new technical route for the development and application of sodium-ion batteries.

[0015] Preferably, based on the total mass of the hard carbon and nitrogen-containing organic matter as 100 wt%, the content of the nitrogen-containing organic matter is 10 to 90 wt%, for example, it can be 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, or 90 wt%, etc., preferably 10 to 40 wt%.

[0016] In this invention, a suitable amount of nitrogen-containing organic matter can fully exert the synergistic effect with boron. When the content of nitrogen-containing organic matter is too high, it will cause the hard carbon capacity to be low and the side reactions to increase during the charging and discharging process after the battery is assembled. When the content of nitrogen-containing organic matter is too low, the nitrogen doping effect is not obvious.

[0017] Preferably, based on a total mass of 100wt% for the nitrogen-doped hard carbon material and the pre-sodium material, the content of the pre-sodium material is 1 to 20wt%, for example, it can be 1wt%, 2wt%, 4wt%, 6wt%, 8wt%, 10wt%, 12wt%, 14wt%, 16wt%, 18wt%, or 20wt%, etc.

[0018] In this invention, mixing pre-sodium material with nitrogen-doped hard carbon material in a suitable ratio is more conducive to improving the first-efficiency and rate performance of hard carbon anode. When the content of pre-sodium material is too high, it will reduce the specific capacity of hard carbon anode. When the content of pre-sodium material is too low, the pre-sodium effect is not obvious.

[0019] Preferably, the nitrogen-containing organic compound includes any one or a combination of at least two of urea, melamine, dicyandiamide, polyacrylonitrile, and polyaniline. For example, it may be a combination of urea and melamine, a combination of dicyandiamide and polyacrylonitrile, a combination of dicyandiamide, polyacrylonitrile, and polyaniline, or a combination of urea, melamine, dicyandiamide, and polyacrylonitrile, etc.

[0020] As a preferred technical solution of the preparation method described in this invention, the temperature of the first sintering in step (1) is 500-600℃, for example, it can be 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃ or 600℃, etc. When the temperature of the first sintering is too low, it is difficult to achieve the purpose of carbonization of hard carbon materials. When the temperature of the first sintering is too high, the specific surface area of ​​the material will decrease, and the nitrogen content will decrease, affecting the electrical properties of the material.

[0021] Preferably, the sintering time in step (1) is 1 to 4 hours, for example, it can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours.

[0022] Preferably, the gas in the atmosphere of the first sintering in step (1) includes an inert gas.

[0023] Preferably, the inert gas in the atmosphere of the primary sintering in step (1) includes argon and / or helium.

[0024] Preferably, the flow rate of the gas in the atmosphere during the first sintering in step (1) is 1 to 5 L / min, for example, it can be 1 L / min, 2 L / min, 3 L / min, 4 L / min or 5 L / min, etc.

[0025] As a preferred technical solution of the preparation method described in this invention, the secondary sintering temperature in step (2) is 450-650℃, for example, it can be 450℃, 480℃, 500℃, 520℃, 540℃, 560℃, 580℃, 600℃, 620℃ or 650℃, etc.; when the secondary sintering temperature is too high, the specific surface area of ​​the material will decrease, affecting the electrical properties of the material; when the secondary sintering temperature is too low, it is difficult to achieve the purpose of boronization.

[0026] Preferably, the secondary sintering time in step (2) is 2 to 6 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours.

[0027] Preferably, the gas in the atmosphere of the secondary sintering in step (2) includes an inert gas.

[0028] Preferably, the inert gas in the atmosphere of the secondary sintering in step (2) includes argon and / or helium.

[0029] Preferably, after the secondary sintering in step (2), the product of the secondary sintering is further cooled and cleaned.

[0030] As a preferred embodiment of the preparation method of the present invention, the preparation method includes:

[0031] (1) Hard carbon and nitrogen-containing organic matter are mixed and sintered at 500-600°C for 1-4 hours. The gas in the atmosphere of the first sintering includes argon and / or helium, and the flow rate of the gas is 1-5 L / min, to obtain nitrogen-doped hard carbon material.

[0032] Of which, based on a total mass of hard carbon and nitrogen-containing organic matter of 100 wt%, the content of nitrogen-containing organic matter is 10 to 90 wt%;

[0033] (2) Mix the nitrogen-doped hard carbon material and the pre-sodium material described in step (1), and sinter them at 450-650°C for 2-6 hours. The gas in the atmosphere of the second sintering includes argon and / or helium. After cooling, clean the material to obtain the pre-sodium anode material.

[0034] The pre-sodium material includes NaBH4 and / or Na2B4O7, and the content of the pre-sodium material is 1 to 20 wt%, based on a total mass of 100 wt% of the nitrogen-doped hard carbon material and the pre-sodium material.

[0035] In a second aspect, the present invention provides a nitrogen-boron co-doped pre-sodium anode material, wherein the pre-sodium anode material is prepared by the preparation method described in the first aspect.

[0036] The pre-sodium-treated anode material prepared by this invention is mainly composed of hard carbon, which is doped with nitrogen and boron elements. The hard carbon material has been pre-sodium-treated. The material prepared by the process of this invention does not require impurity removal, has no by-products, and has excellent rate performance and high first coulombic efficiency.

[0037] Thirdly, the present invention provides a sodium-ion battery, wherein the negative electrode of the sodium-ion battery comprises a pre-sodiumized negative electrode material co-doped with nitrogen and boron according to the second aspect.

[0038] The sodium-ion battery prepared using the nitrogen-boron co-doped pre-sodium anode material of the present invention has both excellent rate performance and initial coulombic efficiency.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) This invention mixes hard carbon materials and nitrogen-containing organic matter, and forms nitrogen-doped hard carbon materials through a single sintering atomic rearrangement. Then, a specific pre-sodium material is added for a second sintering, achieving both boron doping and pre-sodiumization simultaneously. Nitrogen atoms are electron donors, which can attract sodium ions to increase battery capacity during battery charging. Boron, as an electron acceptor, can attract electrons to improve battery capacitance, i.e., battery rate performance. The synergistic effect of nitrogen and boron significantly improves the capacity and rate performance of the material.

[0041] (2) In this invention, nitrogen-containing organic matter is first sintered with hard carbon, and then a specific pre-sodium material NaBH4 and / or Na2B4O7 are added for secondary sintering. Compared with inorganic nitrogen sources, the decomposition of nitrogen-containing organic matter is more conducive to nitrogen doping. Furthermore, the pre-doping of nitrogen into hard carbon can promote subsequent boron doping, allowing boron to replace part of the nitrogen element and be more easily doped into hard carbon, thus exerting a synergistic effect of nitrogen and boron. The pre-sodium material, as a pre-sodiumizing agent and boron source, can simultaneously achieve boron doping and pre-sodiumization of the material, preventing the introduction of impurities when adding pre-sodium reagent and boron source separately. It has good safety performance, no by-products are generated, and no impurity removal is required. It effectively improves the first coulombic efficiency of the material through pre-sodiumization. The pre-sodiumized anode material finally prepared has both excellent rate performance and high first coulombic efficiency, providing a new technical route for the development and application of sodium-ion batteries.

[0042] (3) The preparation method of the present invention is simple to operate, produces no by-products, has good safety performance, and is easy to scale up. Attached Figure Description

[0043] Figure 1 This is a process flow diagram of the preparation process of the pre-sodium-modified negative electrode material in a specific embodiment of the present invention. Detailed Implementation

[0044] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0045] Example 1

[0046] This embodiment provides a method for preparing a pre-sodium-modified anode material, the preparation process of which is as follows: Figure 1 As shown, it includes:

[0047] (1) Hard carbon and urea with a mass ratio of 85:15 were mixed and argon gas was introduced. The flow rate of argon gas was 3L / min. The mixture was sintered at 600℃ for 2.5h to complete the nitriding. After cooling, nitrogen-doped hard carbon material was obtained.

[0048] (2) The nitrogen-doped hard carbon material from step (1) and NaBH4 are mixed at a mass ratio of 9:1, argon gas is introduced, and the mixture is sintered at 550℃ for 4 hours to complete the boronizing and pre-sodiumizing treatments. After cooling, the mixture is cleaned to obtain the pre-sodiumized anode material.

[0049] Example 2

[0050] This embodiment provides a method for preparing a pre-sodium-modified anode material, the preparation process of which is as follows: Figure 1 As shown, it includes:

[0051] (1) Hard carbon, melamine and dicyandiamide in a mass ratio of 6:2:2 were mixed and a mixed gas of helium and argon in a volume ratio of 1:1 was introduced. The flow rate of the mixed gas was 5L / min. The mixture was sintered at 600℃ for 1h to complete the nitriding. After cooling, nitrogen-doped hard carbon material was obtained.

[0052] (2) The nitrogen-doped hard carbon material from step (1) and Na2B4O7 are mixed at a mass ratio of 95:5, argon gas is introduced, and the mixture is sintered at 450℃ for 6 hours to complete the boronizing and pre-sodiumizing treatments. After cooling, the mixture is cleaned to obtain the pre-sodiumized anode material.

[0053] Example 3

[0054] This embodiment provides a method for preparing a pre-sodium-modified anode material, the preparation process of which is as follows: Figure 1 As shown, it includes:

[0055] (1) Hard carbon and polyacrylonitrile with a mass ratio of 8:2 were mixed and a mixture of helium and helium with a volume ratio of 1:1 was introduced. The flow rate of the mixed gas was 1L / min. The mixture was sintered at 500℃ for 4h to complete the nitriding. After cooling, nitrogen-doped hard carbon material was obtained.

[0056] (2) The nitrogen-doped hard carbon material, NaBH4 and Na2B4O7 from step (1) are mixed in a mass ratio of 8:1:1, argon gas is introduced, and the mixture is sintered at 600℃ for 2 hours to complete the boronizing and pre-sodiumizing treatments. After cooling, the mixture is cleaned to obtain the pre-sodiumized anode material.

[0057] Example 4

[0058] Except for the mass ratio of hard carbon to urea of ​​95:5 in step (1), everything else is the same as in Example 1.

[0059] Example 5

[0060] Except for the mass ratio of hard carbon to urea of ​​5:95 in step (1), everything else is the same as in Example 1.

[0061] Example 6

[0062] Except for the mass ratio of nitrogen-doped hard carbon material to NaBH4 in step (2) being 99.2:0.8, everything else is the same as in Example 1.

[0063] Example 7

[0064] Except for the mass ratio of nitrogen-doped hard carbon material to NaBH4 in step (2) being 75:25, everything else is the same as in Example 1.

[0065] Example 8

[0066] Except for the sintering temperature of 450°C in step (1), the rest is the same as in Example 1.

[0067] Example 9

[0068] Except for the sintering temperature of 650°C in step (1), the rest is the same as in Example 1.

[0069] Example 10

[0070] Except for the secondary sintering temperature of 400°C in step (2), the rest is the same as in Example 1.

[0071] Example 11

[0072] Except for the secondary sintering temperature of 700°C in step (2), the rest is the same as in Example 1.

[0073] Comparative Example 1

[0074] Except for step (1) where urea is not added, everything else is the same as in Example 1.

[0075] Comparative Example 2

[0076] Except for step (2), which does not involve the addition of NaBH4, the rest of the steps are the same as in Example 1.

[0077] Comparative Example 3

[0078] This comparative example provides a method for preparing a pre-sodium-modified anode material, including:

[0079] Hard carbon, urea and NaBH4 were mixed and argon gas was introduced at a flow rate of 3 L / min. The mixture was sintered at 550 °C for 2.5 h, cooled and cleaned to obtain a pre-sodium-modified anode material.

[0080] In this comparative example, the mass ratios of hard carbon, urea, and NaBH4 are the same as in Example 1.

[0081] Comparative Example 4

[0082] This comparative example provides a method for preparing a pre-sodium-modified anode material, including:

[0083] (1) Mix hard carbon and NaBH4 in a mass ratio of 9:1, introduce argon gas at a flow rate of 3L / min, and sinter at 550℃ for 4 hours.

[0084] (2) The product after the first sintering in step (1) and urea are mixed at a mass ratio of 1:1, argon gas is introduced, and the mixture is sintered again at 550℃ for 2.5h. After cooling, the mixture is cleaned to obtain the pre-sodium-modified anode material.

[0085] Comparative Example 5

[0086] Except for replacing urea with ammonium nitrate, everything else is the same as in Example 1.

[0087] I. Assembly of Sodium-ion Batteries

[0088] Sodium-ion batteries were prepared using the pre-sodium-modified negative electrode materials from Examples 1-11 and Comparative Examples 1-5 as negative electrode active materials. The mass ratio of the negative electrode materials in the sodium-ion batteries was 92:4:4 for the negative electrode hard carbon active material, binder PAA, and conductive agent acetylene black. The negative electrode materials were mixed evenly with water as a solvent, then coated onto a copper current collector and vacuum dried to obtain the negative electrode. The positive electrode used commercially available Na3V2(PO4)3 with a mass ratio of positive electrode active material, binder polyvinylidene fluoride, and conductive agent SP of 8:1:1. The sodium-modified positive electrode material was mixed evenly with the conductive agent, binder, and solvent NMP, then coated onto aluminum foil current collector and vacuum dried to obtain the positive electrode. The electrolyte was a sodium salt of 1M NaClO4, with a solvent of PC / EC / DMC of 1:1:1 and 2% FEC additive added. The positive electrode, separator, and negative electrode were stacked and installed into a battery case, and electrolyte was injected to obtain the sodium-ion battery.

[0089] II. Electrochemical Performance Testing

[0090] (1) Ratio Performance Test

[0091] The sodium-ion battery was charged at 0.5C and discharged at 2C, with a voltage range of 2 to 4.3V. The discharge capacity of the battery was recorded, and the test results are shown in Table 1.

[0092] (2) First Coulomb efficiency test

[0093] The sodium-ion battery was charged and discharged at 0.2C, and the initial charge capacity and initial discharge capacity were recorded. The initial coulombic efficiency was obtained by dividing the initial discharge capacity by the initial charge capacity. The test results are shown in Table 1.

[0094] Table 1

[0095]

[0096]

[0097] As can be seen from Examples 1-11 above, this invention forms nitrogen-doped hard carbon material by sintering hard carbon material and nitrogen-containing organic matter in one step, thereby improving the material capacity. Then, a specific pre-sodium material is added for a second sintering, which simultaneously achieves the purpose of boron doping and pre-sodiumization. The method is simple, safe, and produces no by-products or introduces additional impurities. The capacity and rate performance of the material are improved by co-doping with nitrogen and boron elements, and the first coulombic efficiency of the material is improved by pre-sodiumization. Finally, the pre-sodiumized anode material prepared can achieve a discharge capacity of 92.4 mAh / g at a 2C rate and an first coulombic efficiency of over 95%.

[0098] A comparison of Examples 1 and Examples 4-7 shows that the content of nitrogen-containing organic matter and pre-sodium material in this invention has an optimal range. In Example 4, the content of nitrogen-containing organic matter is too low, resulting in an insignificant pre-sodiumization effect; in Example 5, the content of nitrogen-containing organic matter is too high, resulting in a decrease in the specific capacity of the material; in Example 6, the content of pre-sodium material is too low, resulting in an insignificant pre-sodiumization effect and a low first-time efficiency; in Example 7, the content of pre-sodium material is too high, resulting in a low specific capacity of the material. Therefore, compared with Examples 4-7, Example 1 has a higher discharge capacity at 2C and a better first-time coulombic efficiency.

[0099] A comparison of Examples 1 and Examples 8-11 shows that when the primary and secondary sintering are carried out at suitable temperatures, the resulting pre-sodium-modified anode material exhibits better rate performance and initial coulombic efficiency. In Example 8, the primary sintering temperature was too low, resulting in poor rate performance; in Example 9, the primary sintering temperature was too high; in Example 10, the secondary sintering temperature was too low, affecting the boronization effect; and in Example 11, the secondary sintering temperature was too high, resulting in poor rate performance. Therefore, compared to Examples 8-11, Example 1 demonstrates superior rate performance and initial coulombic efficiency.

[0100] A comparison of Example 1 and Comparative Examples 1-2 shows that the preparation method of this invention, involving nitrogen-boron co-doping and pre-sodiumization, can simultaneously improve the rate performance and initial coulombic efficiency of the material. Comparative Example 1, without the addition of urea and nitrogen doping, cannot fully utilize the synergistic effect of nitrogen and boron, resulting in limited improvement in rate performance and capacity. Furthermore, the lack of pre-doping with nitrogen in Comparative Example 1 hinders the partial substitution of nitrogen by boron for doping into the hard carbon during secondary sintering, making it difficult to achieve sufficient and effective boron doping. Therefore, the rate performance of Comparative Example 1 is significantly worse than that of Example 1. Comparative Example 2, without the addition of NaBH4 and without boron doping and pre-sodiumization, shows significantly lower rate performance and initial coulombic efficiency than Example 1.

[0101] A comparison of Example 1 and Comparative Examples 3-4 shows that the addition of nitrogen-containing organic matter during the first sintering and pre-sodium material during the second sintering in this invention effectively incorporates nitrogen and boron into the hard carbon material while simultaneously achieving pre-sodiumization. This fully leverages the synergistic effect between elements, significantly improving the rate performance and initial coulombic efficiency of the hard carbon. In Comparative Example 3, nitrogen-containing organic matter and pre-sodium material were simultaneously mixed with hard carbon for sintering, failing to achieve nitrogen doping first. Inorganic NaBH4 also hinders the direct doping of boron into the hard carbon, resulting in poor material doping in Comparative Example 3. In Comparative Example 4, NaBH4 was first mixed with hard carbon for sintering, followed by the addition of nitrogen-containing organic matter for nitrogen doping. Similarly, boron in NaBH4 is difficult to directly dope into the hard carbon, thus the rate performance and initial coulombic efficiency of Comparative Examples 3-4 are significantly worse than those of Example 1.

[0102] By comparing Example 1 and Comparative Example 5, it can be seen that the nitrogen-containing organic material used in this invention can achieve better nitrogen doping. In Comparative Example 5, an inorganic nitrogen source is used for doping, which has a poor doping effect and is not conducive to subsequent mixing and sintering with NaBH4. Therefore, the rate performance and first-time efficiency of the material in Comparative Example 5 are worse than those in Example 1.

[0103] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a nitrogen-boron co-doped pre-sodium-doped anode material, characterized in that, The preparation method includes: (1) Hard carbon and nitrogen-containing organic matter are mixed and sintered in one step to obtain nitrogen-doped hard carbon material; (2) Mix the nitrogen-doped hard carbon material and the pre-sodium material described in step (1) and sinter them for a second time to obtain the pre-sodiumized anode material; The pre-sodium material includes NaBH4 and / or Na2B4O7; Based on a total mass of 100 wt% of the hard carbon and nitrogen-containing organic matter, the content of the nitrogen-containing organic matter is 10-90 wt%; The temperature of the first sintering is 500-600℃; the temperature of the second sintering is 450-650℃.

2. The preparation method according to claim 1, characterized in that, Based on a total mass of 100 wt% of the hard carbon and nitrogen-containing organic matter, the content of the nitrogen-containing organic matter is 10-40%.

3. The preparation method according to claim 1 or 2, characterized in that, Based on a total mass of 100 wt% for the nitrogen-doped hard carbon material and the pre-sodium material, the content of the pre-sodium material is 1-20 wt%.

4. The preparation method according to claim 1, characterized in that, The nitrogen-containing organic compound includes any one or a combination of at least two of urea, melamine, dicyandiamide, polyacrylonitrile, and polyaniline.

5. The preparation method according to claim 1, characterized in that, The sintering time in step (1) is 1 to 4 hours.

6. The preparation method according to claim 1, characterized in that, The inert gas in the atmosphere of the first sintering step (1) includes argon and / or helium.

7. The preparation method according to claim 1, characterized in that, The flow rate of the gas in the atmosphere during the first sintering step (1) is 1 to 5 L / min.

8. The preparation method according to claim 1, characterized in that, The secondary sintering time in step (2) is 2 to 6 hours.

9. The preparation method according to claim 1, characterized in that, The gas in the atmosphere of the secondary sintering in step (2) includes an inert gas.

10. The preparation method according to claim 1, characterized in that, The inert gas in the atmosphere of the secondary sintering in step (2) includes argon and / or helium.

11. The preparation method according to claim 1, characterized in that, After the secondary sintering in step (2), the product of the secondary sintering is further cooled and cleaned.

12. The preparation method according to claim 1, characterized in that, The preparation method includes: (1) Hard carbon and nitrogen-containing organic matter are mixed and sintered at 500-600°C for 1-4 hours. The gas in the atmosphere of the first sintering includes argon and / or helium, and the flow rate of the gas is 1-5 L / min, to obtain nitrogen-doped hard carbon material. Of which, based on a total mass of hard carbon and nitrogen-containing organic matter of 100 wt%, the content of nitrogen-containing organic matter is 10 to 90 wt%; (2) Mix the nitrogen-doped hard carbon material and the pre-sodium material described in step (1), and sinter them at 450-650°C for 2-6 hours. The gas in the atmosphere of the second sintering includes argon and / or helium. After cooling, clean the material to obtain the pre-sodium anode material. The pre-sodium material includes NaBH4 and / or Na2B4O7, and the content of the pre-sodium material is 1 to 20 wt%, based on a total mass of 100 wt% of the nitrogen-doped hard carbon material and the pre-sodium material.

13. A nitrogen-boron co-doped pre-sodium-doped anode material, characterized in that, The pre-sodium-modified anode material is prepared using the preparation method according to any one of claims 1-12.

14. A sodium-ion battery, characterized in that, The negative electrode of the sodium-ion battery includes the nitrogen-boron co-doped pre-sodiumized negative electrode material according to claim 13.

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