A method for preparing a negative electrode material, the negative electrode material and a sodium-ion battery

Abstract

This application discloses a method for preparing a negative electrode material, the negative electrode material itself, and a sodium-ion battery. The method for preparing the negative electrode material includes the following steps: (1) mixing a biomass-based carbon source and a zinc source, dispersing them in deionized water, adding hydrogen peroxide, stirring, and heating to obtain a precursor; (2) crosslinking the precursor with a resin-based carbon source to form an intermediate with a three-dimensional network structure; (3) carbonizing the intermediate under an inert atmosphere to form a negative electrode material. The method for preparing this negative electrode material is simple, low-cost, and suitable for production; the obtained negative electrode material can enhance the coulombic efficiency, cycle stability, and rate performance of the electrode.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery technology, and in particular to a method for preparing a negative electrode material, the negative electrode material, and a sodium-ion battery. Background Technology

[0002] Due to the increasingly serious environmental and energy crises, there is an urgent need to develop renewable and sustainable energy sources such as wind and solar power. Developing large-scale energy storage systems is crucial to addressing these intermittent energy conversion problems. Sodium-ion batteries are considered the most promising alternative to lithium-ion batteries for large-scale energy storage applications because of their low cost, abundant natural sodium resources, and similar rocking-chair operation. Significant progress has been made in the practical application of sodium-ion battery cathodes over the past decade, including polyanionic compounds, layered oxides, and Prussian analogs. For anodes, various materials, such as carbonaceous materials, alloy metals, and metal chalcogenides, have been extensively explored. However, due to their complex preparation processes and inherent electrochemical defects, most candidate materials exhibit serious limitations in large-scale applications. Carbonaceous materials are considered the most promising anode materials because they are low-cost, easy to prepare, and reproducible. Unlike the successful application of graphite in traditional lithium-ion batteries, the narrow carbon interlayer spacing (0.335 nm) and thermodynamic instability of graphite intercalation compounds hinder sodium ion intercalation. Currently, it is generally accepted that graphite cannot be directly used as the anode material for sodium-ion batteries. Hard carbon consists of interlaced graphite microcrystalline layers, abundant micropores, and defects. It has a relatively large interlayer spacing, can store a large number of sodium ions, and has a large reversible capacity. Furthermore, due to the increasing demands on batteries, and to meet the requirements of full-cell batteries in practical applications, there is an urgent need for high-performance anode materials for sodium-ion batteries. Summary of the Invention The purpose of this invention is to provide a method for preparing a negative electrode material, the negative electrode material itself, and a sodium-ion battery. The method for preparing the negative electrode material is simple, low-cost, and suitable for production. The resulting negative electrode material can enhance the coulombic efficiency, cycle stability, and rate performance of the electrode.

[0003] To achieve the objectives of this invention, the following technical solution is adopted: A method for preparing a negative electrode material includes the following steps: (1) Mix the biomass-based carbon source and zinc source, disperse them in deionized water, add hydrogen peroxide, stir, and heat to obtain the precursor; (2) The precursor is crosslinked with a resin-based carbon source to form an intermediate with a three-dimensional network structure; (3) The intermediate is carbonized in an inert atmosphere to form a negative electrode material.

[0004] In an embodiment of the present invention, the biomass-based carbon source is cellulose, the resin-based carbon source is phenolic resin, and the weight ratio of cellulose to phenolic resin is 0.5 to 2:1.

[0005] In embodiments of the present invention, the zinc source includes one or more of zinc chloride, zinc acetate, and zinc oxalate.

[0006] In an embodiment of the present invention, the weight ratio of the zinc source to the biomass-based carbon source is 0.05-0.5:1.

[0007] In an embodiment of the present invention, step (1) specifically involves: uniformly mixing the zinc source and the biomass carbon source, dispersing them in deionized water, adding hydrogen peroxide, stirring, and then heating at 80~110°C for 2-4 hours. After filtration and drying, the precursor is obtained.

[0008] In an embodiment of the present invention, step (2) specifically involves: uniformly dispersing the precursor, phenol source, formaldehyde solution and catalyst in a solvent, followed by hydrothermal polymerization at 100-120°C for 12-24 hours, and then washing and drying to obtain the intermediate; The phenol source is at least one of phenol, 2-aminophenol, 2,6-diaminophenol, and 4-aminophenol; the molar ratio of the phenol source to the formaldehyde is 1:2~5.

[0009] In an embodiment of the present invention, in step (3), the inert atmosphere is at least one of nitrogen, argon and helium.

[0010] In an embodiment of the present invention, the carbonization treatment is carried out at a temperature of 1100-1400℃ for 2-5 hours, with a heating rate of 2-5℃ / min and a gas flow rate of 50-100 mL / min.

[0011] Preferably, the catalyst is ammonia water with a concentration of 23-26 wt%, and the formaldehyde is added in the form of a formaldehyde solution with a concentration of 1-1.2 g / ml, and the mass ratio of the formaldehyde solution to the ammonia water is 20-50:1.

[0012] Preferably, the solvent comprises ethanol and water, wherein the mass ratio of ethanol to water is 1:1-2.

[0013] On the other hand, the present invention also provides a negative electrode material, which is prepared by the negative electrode material preparation method described above, wherein the content of Zn in the negative electrode material is 0.5~1.0 wt%.

[0014] In another aspect, the present invention also provides a sodium-ion battery comprising a negative electrode sheet, the negative electrode sheet comprising the negative electrode material as described above.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: The preparation method of the negative electrode material of the present invention is simple, low in cost, and suitable for production. The preparation method modifies the functional groups of the biomass-based carbon source through hydrothermal reaction, enhances the cross-linking degree between the precursor and the resin-based carbon source, and obtains the negative electrode material after carbonization. The carbon yield of direct carbonization of biomass-based carbon source is low. By introducing resin-based carbon source, the structural stability of the material can be enhanced through cross-linking with the resin-based carbon source, thereby achieving a high yield of hard carbon material.

[0016] The negative electrode material prepared by this invention can enhance the coulombic efficiency, cycle stability, and rate performance of the electrode. This negative electrode material contains biomass-based hard carbon, resin-based hard carbon, and Zn dispersed within the hard carbon material. The three-dimensional interconnected network structure of the biomass-based hard carbon facilitates electron and ion transport, while the resin-based hard carbon has a stable carbon structure that alleviates stress released during material deformation during charging and discharging. The cross-linking of biomass-based hard carbon and resin-based hard carbon further enhances the structural stability of the material, effectively alleviating stress released during material deformation during charging and discharging, and further improving the rate performance and cycle life. The presence of Zn can induce a local electric field to achieve rapid Na+ conversion. + It also catalyzes the formation of a solid electrolyte interface rich in inorganic matter, enhancing the cycle stability and rate performance of the electrode. Attached Figure Description

[0017] Figure 1 The images shown are TEM and HAADF-STEM images of the negative electrode material obtained in Example 1. Figure 2 The images show the Raman spectra of the negative electrode materials obtained in Example 1 and Comparative Example 4. Detailed Implementation

[0018] To better understand and implement this application, the technical solutions of this application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only some of the embodiments of this application, and not all of them.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0020] Unless otherwise stated, all numerical values ​​for the amounts of expressed components, reaction conditions, etc., used in the specification and claims are to be understood as being modified by the term "about". Therefore, unless otherwise indicated, the numerical parameters set forth herein are approximate values ​​that can be varied to obtain the desired performance.

[0021] For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] The word “and / or” as used in this article refers to one or all of the elements mentioned.

[0023] The terms "include" and "contain" as used in this article cover both cases where only the mentioned elements exist and cases where other unmentioned elements exist in addition to the mentioned elements.

[0024] Hard carbon is considered the most mature and commercially promising anode material for sodium-ion batteries, with biomass-based carbon sources and phenolic resins being the main materials used in its synthesis. However, biomass-based hard carbon faces challenges such as low carbon yield and poor coulombic efficiency; resin-based hard carbon faces difficulties in pore structure adjustment and high cost; and hard carbon materials as a whole also suffer from low specific capacity and poor rate performance, all of which require further improvement.

[0025] The purpose of this invention is to provide a method for preparing a negative electrode material that can enhance the coulombic efficiency, cycle stability, and rate performance of the electrode. This preparation method is simple, low-cost, and suitable for production. The following is a detailed description of this application.

[0026] Preparation method of negative electrode material This invention provides a method for preparing a negative electrode material, which includes the following steps: (1) Mix the biomass-based carbon source and zinc source, disperse them in deionized water, add hydrogen peroxide, stir, and heat to obtain the precursor; (2) The precursor is crosslinked with a resin-based carbon source to form an intermediate with a three-dimensional network structure; (3) The intermediate is carbonized in an inert atmosphere to form a negative electrode material.

[0027] This preparation method first modifies the functional groups of a biomass-based carbon source through a hydrothermal reaction, incorporating oxygen-containing functional groups (-COOH) capable of coordinating with zinc ions. Subsequently, the precursor is cross-linked with a resin-based carbon source, which further encapsulates zinc, forming a three-dimensional network structure intermediate. The presence of the oxygen-containing functional group (-COOH) effectively promotes the cross-linking of the precursor and the resin-based carbon source. Finally, the intermediate is carbonized to form a hard carbon substrate from the biomass and resin-based carbon sources. The oxygen-containing functional groups anchor zinc, forming single-atom sites, resulting in the anode material. This invention achieves a simple and efficient electrode synthesis through a straightforward method, which is of great significance for improving the electrochemical performance of sodium-ion battery anode materials.

[0028] Direct carbonization of biomass-based carbon sources yields a low carbon efficiency. Introducing resin-based carbon sources enhances the structural stability of the material through cross-linking, thereby achieving a high yield of hard carbon materials. Simultaneously, the presence of Zn induces a local electric field to facilitate rapid Na+ carbonization. + The process facilitates electron and ion transport and catalyzes the formation of a solid electrolyte interface rich in inorganic matter, enhancing the electrode's cycle stability and rate performance. Furthermore, the three-dimensional interconnected network structure of biomass-based hard carbon facilitates electron and ion transport. Crosslinking of biomass-based hard carbon with resin-based hard carbon further improves the material's structural stability, effectively mitigating stress released during material deformation during charge and discharge, thus further improving the material's rate performance and cycle life. In addition, this preparation method is simple, low-cost, and suitable for production.

[0029] In embodiments of the present invention, the biomass-based carbon source includes at least one selected from cellulose, lignin, starch, chitosan, and chitin. In some preferred embodiments, the biomass-based carbon source is cellulose. Cellulose materials can more effectively and uniformly disperse Zn on the material.

[0030] In embodiments of the present invention, the resin-based carbon source includes at least one selected from phenolic resin, polyimide resin, epoxy resin, and furan resin. In some preferred embodiments, the resin-based carbon source is phenolic resin.

[0031] In some preferred embodiments, the biomass-based carbon source is cellulose, and the resin-based carbon source is phenolic resin. The cellulose is subjected to a hydrothermal reaction with a Zn source, resulting in Zn being loaded onto the cellulose. 2+ The electrostatic interaction between metal cations and phenolic hydroxyl groups in phenolic resin, along with the hydrothermal reaction of cellulose to obtain carboxyl functional groups, under the dual effect, better achieves the composite of phenolic resin and precursor (Zn@cellulose) in the cross-linking stage, thus enhancing the overall stability of the material.

[0032] Furthermore, the weight ratio of cellulose to phenolic resin is 0.5 to 2:1. Examples of such ratios include 0.5:1, 0.7:1, 1:1, 1.2:1, 1.5:1, 1.7:1, and 2:1. Excessive cellulose content reduces the yield of hard carbon materials; insufficient cellulose content affects the synthesis effect; and within the specified range, a better yield of hard carbon materials is achieved, along with improved cross-linking between cellulose and phenolic resin, resulting in superior performance of the generated anode material.

[0033] In embodiments of the present invention, the zinc source includes one or more of zinc chloride, zinc acetate, and zinc oxalate.

[0034] In embodiments of the present invention, the weight ratio of zinc source to biomass-based carbon source is 0.05-0.5:1. Exemplary examples include weight ratios of 0.05:1, 0.08:1, 0.1:1, 0.2:1, 0.25:1, 0.3:1, 0.35:1, 0.4:1, and 0.5:1. Appropriate amounts of zinc source and biomass-based carbon source enable monodisperse loading of Zn onto the biomass-based carbon source, preventing agglomeration. This results in uniform dispersion of Zn in the anode material at the single-atom level, while ensuring sufficient Zn for better anode material performance. Better uniformity of Zn dispersion at the single-atom level provides more active sites; furthermore, high atomic utilization generates a uniformly distributed local electric field, enabling faster Na+ extraction. + It also catalyzes the formation of a strong inorganic-rich solid electrolyte interface, significantly improving the cycle stability and rate performance of the electrode.

[0035] In an embodiment of the present invention, step (1) specifically involves uniformly mixing the zinc source and the biomass carbon source, dispersing them in deionized water, adding hydrogen peroxide, stirring, and then heating at 80~110°C for 2-4 hours. After filtration and drying, the precursor is obtained.

[0036] For example, the heating temperatures are 80℃, 85℃, 90℃, 97℃, 100℃, 105℃, 110℃, etc. Heating the zinc source and the biomass carbon source at 80~110℃ can not only better promote the monodisperse loading of Zn on the biomass carbon source and prevent Zn from forming agglomerates, but also ensure the reaction rate, shorten the reaction time, and allow the reaction to proceed fully. When the temperature is too high, Zn is prone to form agglomerates, which is not conducive to dispersion; when the temperature is too low, the reaction efficiency is low and the reaction time is long.

[0037] Preferably, hydrogen peroxide is added in the form of a hydrogen peroxide solution with a concentration of 20-30%, and the mass ratio of biomass-based carbon source to hydrogen peroxide solution is 1-2:10.

[0038] Preferably, the dispersion ratio of the biomass-based carbon source in deionized water is 1g:(20-50)mL.

[0039] In an embodiment of the present invention, step (2) specifically involves: uniformly dispersing the precursor, phenol source, formaldehyde solution and catalyst in a solvent, and then carrying out a hydrothermal polymerization reaction at 100-120°C for 12-24 hours. After washing and drying, the intermediate is obtained.

[0040] For example, the hydrothermal polymerization reaction temperature is 100℃, 105℃, 108℃, 110℃, 112℃, 116℃, 120℃, etc. When the temperature is selected between 100-120℃, a moderately cross-linked three-dimensional network structure can be formed, resulting in a negative electrode material with better performance.

[0041] Preferably, the phenol source is at least one selected from phenol, 2-aminophenol, 2,6-diaminophenol, and 4-aminophenol.

[0042] Preferably, the molar ratio of phenol source to formaldehyde is 1:2 to 5. For example, the molar ratio of phenol source to formaldehyde is 1:2, 1:2.5, 1:3, 1:3.2, 1:3.8, 1:4, 1:4.5, 1:5, etc.

[0043] Preferably, the catalyst is ammonia water with a concentration of 23-26 wt%, and the formaldehyde is added in the form of a formaldehyde solution with a concentration of 1-1.2 g / ml, and the mass ratio of the formaldehyde solution to the ammonia water is 20-50:1.

[0044] Preferably, the solvent comprises ethanol and water, wherein the mass ratio of ethanol to water is 1:1-2.

[0045] In an embodiment of the present invention, in step (3), the inert atmosphere is at least one of nitrogen, argon and helium.

[0046] In an embodiment of the present invention, the carbonization treatment temperature is 1100-1400℃, the time is 2-5 hours, the heating rate is 2-5℃ / min, and the gas flow rate is 50-100 mL / min.

[0047] For example, the carbonization temperature is 1100℃, 1150℃, 1180℃, 1200℃, 1260℃, 1300℃, 1340℃, 1400℃, etc. Both excessively high and excessively low carbonization temperatures will affect the material properties. Excessively high carbonization temperatures may also cause Zn to volatilize, damaging the single-atom structure of Zn.

[0048] Anode material On the other hand, the present invention also provides a negative electrode material, which is prepared by the negative electrode material preparation method described above; in the negative electrode material, the content of Zn is 0.5~1.0 wt%.

[0049] For example, in the anode material, the Zn content is 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.85 wt%, 0.9 wt%, 1.0 wt%, etc. The Zn content has a significant impact on the performance of the anode material. When the Zn content is too high, Zn tends to agglomerate in the material, resulting in poor dispersion and thus affecting the performance of the anode material; when the Zn content is too low, the resulting material has poor performance.

[0050] The negative electrode material prepared by this invention is rich in micropores and includes biomass-based hard carbon, resin-based hard carbon, and Zn dispersed within the hard carbon material. The three-dimensional interconnected network structure of the biomass-based hard carbon facilitates electron and ion transport, while the resin-based hard carbon possesses a stable carbon structure that alleviates stress released during material deformation during charging and discharging. Crosslinking of the biomass-based hard carbon and resin-based hard carbon further enhances the material's structural stability, effectively mitigating stress released during charging and discharging, and further improving the material's rate performance and cycle life. The presence of Zn can induce a local electric field to achieve rapid Na+ conversion. + It also catalyzes the formation of a solid electrolyte interface rich in inorganic substances, enhancing the cycling stability and rate performance of the electrode.

[0051] Sodium-ion batteries In another aspect, the present invention also provides a sodium-ion battery comprising a negative electrode sheet, the negative electrode sheet comprising the negative electrode material as described above.

[0052] In embodiments of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including the negative electrode material. Further, the negative electrode film layer also includes a conductive agent and a binder. The present invention does not impose any particular limitations on the material of the negative electrode current collector or the types of conductive agents and binders in the negative electrode film layer, as long as the purpose of this application can be achieved.

[0053] In an embodiment of the present invention, the sodium-ion battery further includes a positive electrode, an electrolyte, and a separator. The separator is disposed between the positive and negative electrodes, and the electrolyte fills the pores of the separator and wets the positive and negative electrodes. During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes; the electrolyte acts as a conductor between the positive and negative electrodes; the separator, disposed between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through. The present invention does not impose any particular limitations on the positive electrode, electrolyte, and separator, as long as they achieve the purpose of this application.

[0054] The present invention will be further illustrated below with reference to the embodiments: Example 1: The method for preparing the negative electrode material in this embodiment includes the following steps: (1) Disperse 0.5g of zinc chloride and 5g of cellulose in 150ml of deionized water, add 40g of hydrogen peroxide solution with a mass percentage concentration of 25%, stir rapidly for 1 hour, then transfer the mixture to a 200ml high-pressure reactor and heat at 100℃ for 3 hours. After the reaction is completed, filter the material and dry it at 80℃. After drying, the precursor is obtained.

[0055] (2) 6g of phenol, 10ml of formaldehyde solution with a concentration of 1.09g / mL and 3g of precursor were placed in 100ml of ethanol and pure water solvent with a volume ratio of 1:1. The mixture was stirred at room temperature for 1h. Then the mixed solution was poured into the reaction vessel and 0.5ml of 25wt% ammonia solution was added dropwise. The reaction was carried out at 120℃ for 12h. After the reaction was completed, the reaction product was washed with acetone solution several times to remove soluble substances. The precipitate was collected and washed repeatedly with deionized water and anhydrous ethanol and dried in an 80℃ oven to obtain the intermediate.

[0056] (3) Take 5g of intermediate and put it into a tube furnace under nitrogen atmosphere. Heat it to 1300℃ for 3 h at a heating rate of 2℃ / min to obtain high-performance sodium-ion battery anode material.

[0057] Example 2: The method for preparing the negative electrode material in this embodiment includes the following steps: (1) Disperse 0.5g of zinc acetate and 5g of cellulose in 150ml of deionized water, add 40g of hydrogen peroxide solution with a mass percentage concentration of 25%, stir rapidly for 1 hour, then transfer the mixture to a 200ml high-pressure reactor and heat at 110℃ for 2 hours. After the reaction is completed, filter the material and dry it at 80℃. After drying, the precursor is obtained.

[0058] (2) 8g of 2-6-diaminophenol, 8ml of formaldehyde solution with a concentration of 1.09g / mL and 3g of material No.1 were placed in 100ml of ethanol and pure water solvent with a volume ratio of 1:1. The mixture was stirred at room temperature for 1h. Then the mixed solution was poured into the reaction vessel and 0.5ml of 25wt% ammonia solution was added dropwise. The reaction was carried out at 120℃ for 12h. After the reaction was completed, the reaction product was washed with acetone solution several times to remove soluble substances. The precipitate was collected and repeatedly washed with deionized water and anhydrous ethanol and dried in an 80℃ oven to obtain the intermediate.

[0059] (3) Take 5g of intermediate and put it into a tube furnace under nitrogen atmosphere. Heat it to 1200℃ at a heating rate of 2℃ / min for 5 h to obtain high-performance sodium-ion battery anode material.

[0060] Example 3: The method for preparing the negative electrode material in this embodiment includes the following steps: (1) Disperse 0.5g of zinc oxalate and 5g of cellulose in 150ml of deionized water, add 40g of hydrogen peroxide solution with a mass percentage concentration of 25%, stir rapidly for 1 hour, then transfer the mixture to a 200ml high-pressure reactor and heat at 100℃ for 2 hours. After the reaction is completed, filter the material and dry it at 80℃. After drying, the precursor is obtained.

[0061] (2) 8g of 2-6-diaminophenol, 8ml of formaldehyde solution with a concentration of 1.09g / mL and 3g of material No.1 were placed in 100ml of ethanol and pure water solvent with a volume ratio of 1:1. The mixture was stirred at room temperature for 1h. Then the mixed solution was poured into the reaction vessel and 0.5ml of 25wt% ammonia solution was added dropwise. The reaction was carried out at 120℃ for 12h. After the reaction was completed, the reaction product was washed with acetone solution several times to remove soluble substances. The precipitate was collected and repeatedly washed with deionized water and anhydrous ethanol and dried in an 80℃ oven to obtain the intermediate.

[0062] (3) Take 5g of intermediate and put it into a tube furnace under nitrogen atmosphere. Heat it to 1300℃ for 3 h at a heating rate of 2℃ / min to obtain high-performance sodium-ion battery anode material.

[0063] Example 4: The method for preparing the negative electrode material in this embodiment includes the following steps: (1) Disperse 0.5g of zinc oxalate and 5g of cellulose in 150ml of deionized water, add 40g of hydrogen peroxide solution with a mass percentage concentration of 25%, stir rapidly for 1 hour, then transfer the mixture to a 200ml high-pressure reactor and heat at 100℃ for 2 hours. After the reaction is completed, filter the material and dry it at 80℃. After drying, the precursor is obtained.

[0064] (2) 8g of 2-diaminophenol, 10ml of formaldehyde solution with a concentration of 1.09g / mL and 3g of material No.1 were placed in 100ml of ethanol and pure water solvent with a volume ratio of 1:1. The mixture was stirred at room temperature for 1h. Then the mixed solution was poured into the reaction vessel and 0.6ml of 25wt% ammonia solution was added dropwise. The reaction was carried out at 110℃ for 16h. After the reaction was completed, the reaction product was washed with acetone solution several times to remove soluble substances. The precipitate was collected and repeatedly washed with deionized water and anhydrous ethanol and dried in an 80℃ oven to obtain the intermediate.

[0065] (3) Take 5g of intermediate and put it into a tube furnace under nitrogen atmosphere. Heat it to 1400℃ at a heating rate of 2℃ / min for 2 hours to obtain high-performance sodium-ion battery anode material.

[0066] Example 5: The only difference between this embodiment and Embodiment 1 is that cellulose is replaced with lignin.

[0067] Example 6: The only difference between this embodiment and Embodiment 1 is that the amount of zinc chloride used is 0.25g. Example 7: The only difference between this embodiment and Embodiment 1 is that the amount of zinc chloride used is 2.5g. Example 8: The only difference between this embodiment and embodiment 1 is that in step (1), the heating temperature is 80°C and the heating time is 4 hours. Example 9: The only difference between this embodiment and embodiment 1 is that in step (1), the heating temperature is 110°C and the heating time is 2 hours. Example 10: The only difference between this embodiment and embodiment 4 is that in step (2), the reaction temperature is 100°C and the reaction time is 24h. Example 11: The only difference between this embodiment and embodiment 4 is that in step (2), the reaction temperature is 120°C and the reaction time is 12h. Example 12: The only difference between this embodiment and Embodiment 1 is that the amount of zinc chloride used is 3.0g.

[0068] Example 13: The only difference between this embodiment and Embodiment 1 is that the amount of zinc chloride used is 0.2g.

[0069] Comparative Example 1: The preparation method of the negative electrode material in this comparative example includes the following steps: (1) 6g of phenol and 6ml of formaldehyde solution with a concentration of 1.09g / mL were placed in 100ml of ethanol and pure water solvent with a volume ratio of 1:1. The mixture was stirred at room temperature for 1h. Then the mixed solution was poured into the reaction vessel and 0.3ml of 25wt% ammonia solution was added dropwise. The reaction was carried out at 110℃ for 16h. After the reaction was completed, the reaction product was washed with acetone solution several times to remove soluble substances. The precipitate was collected and repeatedly washed with deionized water and anhydrous ethanol and then dried in an 80℃ oven to obtain material A.

[0070] (2) Take 5g of material A and put it into a tube furnace under nitrogen atmosphere. Heat it to 1400℃ for 2 hours at a heating rate of 2℃ / min to obtain sodium-ion battery anode material.

[0071] Comparative Example 2: The preparation method of the negative electrode material in this comparative example includes the following steps: 10g of cellulose was placed in a tube furnace under a nitrogen atmosphere and calcined at 1300℃ for 3 hours at a heating rate of 2℃ / min to obtain sodium-ion battery anode material.

[0072] Comparative Example 3: The preparation method of the negative electrode material in this comparative example includes the following steps: (1) 6g of phenol and 6ml of formaldehyde solution with a concentration of 1.09g / mL were placed in 100ml of ethanol and pure water solvent with a volume ratio of 1:1. The mixture was stirred at room temperature for 1h. Then the mixed solution was poured into the reaction vessel and 0.3ml of 25wt% ammonia solution was added dropwise. The reaction was carried out at 110℃ for 16h. After the reaction was completed, the reaction product was washed with acetone solution several times to remove soluble substances. The precipitate was collected and repeatedly washed with deionized water and anhydrous ethanol and dried in an 80℃ oven to obtain material B. (2) After mixing 5g of material B and 5g of cellulose, the mixture was placed in a tube furnace under a nitrogen atmosphere and calcined at 1400℃ for 2 h at a heating rate of 2℃ / min to obtain sodium-ion battery anode material.

[0073] Comparative Example 4: The preparation method of the negative electrode material in this comparative example includes the following steps: (1) 6g of phenol and 6ml of formaldehyde solution with a concentration of 1.09g / mL were placed in 100ml of ethanol and pure water solvent with a volume ratio of 1:1. The mixture was stirred at room temperature for 1h. Then the mixed solution was poured into the reaction vessel and 0.3ml of 25wt% ammonia solution was added dropwise. The reaction was carried out at 110℃ for 16h. After the reaction was completed, the reaction product was washed with acetone solution several times to remove soluble substances. The precipitate was collected and repeatedly washed with deionized water and anhydrous ethanol and dried in an 80℃ oven to obtain material C. (2) After mixing 5g of material C, 5g of cellulose and 0.5g of zinc acetate, the mixture was placed in a tube furnace under a nitrogen atmosphere and calcined at 1400℃ for 2 h at a heating rate of 2℃ / min to obtain sodium-ion battery anode material.

[0074] Performance testing: 1. Preparation of sodium-ion batteries (1) The negative electrode materials prepared in the above embodiments and comparative examples are used as negative electrode active materials. Carbon black is selected as a conductive agent and CMC as a binder. The mass ratio of the three is: negative electrode active material: conductive agent: CMC = 8:1:1. The three are mixed and stirred for 30 minutes, coated on aluminum foil with a coating thickness of 30 μm, and placed in an oven at 80°C for vacuum drying for 12 hours to obtain a negative electrode sheet.

[0075] (2) Provide a sodium metal sheet as the positive electrode of the counter electrode.

[0076] (3) Provide a glass fiber diaphragm as a separation membrane.

[0077] (4) Provide an electrolyte prepared by dissolving 1.0 mol / L NaPF6 in diethylene glycol dimethyl ether.

[0078] (5) Assemble the negative electrode, separator and positive electrode in the order of negative electrode, separator and positive electrode, and wet them with electrolyte respectively. Assemble them into CR2032 button cell in argon glove box.

[0079] 2. Test methods and conditions (1) The GCD of the button cells made from the negative electrode materials of each embodiment and comparative example was tested using the Land battery testing system within a voltage window of 0.01-2 V. The test conditions are as follows: Initial charge / discharge capacity and coulombic efficiency: At 25 degrees, discharge at a constant current of 0.1C to 0V, the discharge capacity at this time is recorded as the initial discharge capacity; charge at a constant current of 0.1C to 2V, the charging capacity at this time is recorded as the initial charging capacity; initial coulombic efficiency = (initial charge capacity / initial discharge capacity) * 100%.

[0080] Capacity retention rate after 100 cycles: At 25 degrees Celsius, discharge at a constant current of 1.0C to 0V, and record the discharge capacity as the first discharge capacity; then charge at a constant current of 1.0C to 2V, and record the charge capacity as the first charge capacity. This constitutes one cycle, recorded as the first cycle. Repeat this cycle 100 times, then end the test and record the charge capacity on the 100th cycle. Therefore, the capacity retention rate after 100 cycles = (charge capacity on the 100th cycle / charge capacity on the first cycle) * 100%.

[0081] (2) a. The methods for testing the residual carbon content of the negative electrode materials in each embodiment are as follows: To obtain the mass M2 after calcination: The product obtained after high-temperature calcination of the intermediates of each embodiment was immersed in a mixed acid consisting of 5 mol / L HF and 2 mol / L HCl for 4 hours, then rinsed repeatedly with deionized water and dried at 80°C to obtain the mass M2. To obtain the mass M1 before calcination: The intermediates of each embodiment were immersed in a mixed acid consisting of 5 mol / L HF and 2 mol / L HCl for 4 hours, then rinsed repeatedly with deionized water and dried at 80°C to obtain the mass M1. The residual carbon content of the negative electrode material in each embodiment = mass after calcination M2 / mass before calcination M1.

[0082] b. The test methods for residual carbon content in each comparative example are as follows: To obtain the mass M4 after calcination: The product obtained after high-temperature calcination was immersed in a mixed acid consisting of 5 mol / L HF and 2 mol / L HCl for 4 hours, then rinsed repeatedly with deionized water and dried at 80°C to obtain the mass M4 after calcination. Obtain the mass M3 before calcination: In Comparative Example 1, M3 is: Material A is immersed in a mixed acid consisting of 5 mol / L HF and 2 mol / L HCl for 4 hours, then rinsed repeatedly with deionized water, dried at 80°C, and the mass M3 is obtained. In Comparative Example 2, M3 is the mass of cellulose dried at 80°C. In Comparative Example 3, M3 is: Material B is immersed in a mixed acid consisting of 5 mol / L HF and 2 mol / L HCl for 4 hours, then rinsed repeatedly with deionized water and dried at 80°C, and the mass M31 is obtained; Cellulose is dried at 80°C and the mass M32 is obtained; M3 = M31 + M32. In Comparative Example 4, M3 is: material C is immersed in a mixed acid consisting of 5 mol / L HF and 2 mol / L HCl for 4 hours, then rinsed repeatedly with deionized water and dried at 80°C, and the mass M33 is obtained; cellulose is dried at 80°C and the mass M34 is obtained; M3 = M33 + M34. The residual carbon rate of the negative electrode material in each comparative example = weight after calcination M4 / weight of carbon source before calcination M3.

[0083] (3) The negative electrode material obtained in Example 1 was scanned and imaged using a scanning transmission electron microscope (STEM) to obtain TEM images and HAADF-STEM images; The negative electrode materials obtained in Example 1 and Comparative Example 4 were detected using a Raman spectrometer to obtain Raman spectra.

[0084] 3. Performance Test Results (1) The button batteries made using the negative electrode materials of each embodiment and comparative example were subjected to constant current charge-discharge tests at a current density of 0.1C, with a voltage range of 0~2 V. The test results are shown in Table 1.

[0085] Table 1. Initial charge / discharge capacity and initial coulombic efficiency for each embodiment and comparative example.

[0086] The coin cells fabricated using the negative electrode materials prepared in Examples 1-11 all exhibited high initial discharge capacities (over 480 mAh / g) and initial coulombic efficiencies exceeding 88%, while the initial discharge capacity of Comparative Example 4 was only 402.2 mAh / g and the initial coulombic efficiency was 78.5%. This is mainly because the high-performance hard carbon sodium-ion battery negative electrode materials in Examples 1-11, by uniformly dispersing Zn atoms within the hard carbon material, can induce a local electric field to achieve rapid bulk Na+ dissipation. + The process facilitates the transport of electrons and ions, while simultaneously catalyzing the formation of a robust inorganic-rich solid electrolyte interface. This enhances the cycle stability and rate performance of the electrode. Furthermore, the three-dimensional interconnected network structure and large interlayer spacing of the high-performance hard carbon facilitate the transport of electrons and ions. The cross-linking of cellulose and resin further improves the structural stability of the material, effectively alleviating the stress released by material deformation during charging and discharging, thereby further improving the rate performance and extending the cycle life of the material.

[0087] Comparing the test results of Example 1 and Example 5, it can be seen that although the battery obtained by using the negative electrode material prepared by lignin can improve the first charge capacity, first discharge capacity and coulombic efficiency, the improvement effect is not as good as that of cellulose, especially for the first charge capacity and first discharge capacity, the improvement effect is far less than that of cellulose.

[0088] (2) The button batteries made using the negative electrode materials of each embodiment and comparative example were subjected to constant current charge-discharge test at a current density of 300 mA / g, with a voltage range of 0~2V. After 100 cycles, the test results are shown in Table 2.

[0089] Table 2 Capacity retention rates for each embodiment and comparative example

[0090] The button-type half-cells prepared using the negative electrode materials in Examples 1-11 all exhibited high cycle retention rates (greater than 90%). This is mainly because the uniform dispersion of Zn atoms effectively promotes the growth of graphite-like microcrystalline layers, resulting in larger interlayer spacing and good structural stability. Simultaneously, the stable interface facilitates the formation of a dense SEI layer, giving the material excellent cycle stability. In contrast, the capacity retention rate of Comparative Example 2 was only 72.5%. Although Zn was also added in Comparative Example 4, the Zn particles loaded on the material surface agglomerated and peeled off, leading to electrolyte consumption and the formation of a thicker SEI film, resulting in a low capacity retention rate.

[0091] Combining Tables 1 and 2, and comparing the test results of Examples 1, 12, and 13, it can be seen that both excessive and insufficient zinc chloride dosage will affect coulombic efficiency and capacity retention. This is because excessive zinc chloride dosage will affect the dispersion of Zn, leading to Zn agglomeration; while insufficient zinc chloride dosage will also result in poor performance due to a lack of sufficiently monodisperse Zn atoms. Only appropriate dosages of zinc source and biomass-based carbon source can achieve monodisperse loading of Zn on biomass-based carbon source, avoiding agglomeration, thereby ensuring uniform dispersion of Zn in the anode material in the form of single atoms, while ensuring sufficient Zn to better achieve the performance of the anode material.

[0092] (3) The residual carbon rate of the negative electrode materials prepared in each embodiment and comparative example was measured, and the results are shown in Table 3.

[0093] Table 3. Residual carbon content of each embodiment and comparative example

[0094] The anode materials prepared using Examples 1-13 exhibit high residual carbon rates, all exceeding 50%. Specifically, the residual carbon rate of cellulose is 15-25%, and that of phenolic resin is 45-50%. In contrast, the residual carbon rate of Comparative Example 2 is only 22.7%. This is mainly because the carbon rate obtained from direct carbonization of cellulose is low, whereas in these embodiments, Zn is loaded onto the biomass-based carbon source. 2+The electrostatic interaction between metal cations and phenolic hydroxyl groups in phenolic resin, and the hydrothermal reaction of biomass-based carbon source to obtain carboxyl functional groups, together achieve better composite of phenolic resin and precursor in the cross-linking stage. The degree of cross-linking between phenolic resin and precursor and residual carbon rate show a positive correlation trend. The higher the degree of cross-linking, the higher the residual carbon rate. Therefore, the embodiments of the present invention show a higher residual carbon rate.

[0095] (4) Obtain the TEM image and HAADF-STEM image of the negative electrode material obtained in Example 1. The results are as follows: Figure 1 As shown in the TEM image, the negative electrode material has a large interlayer spacing and obvious closed-pore structure, which is beneficial to the transport and storage of sodium ions, and improves the material's cycle performance and specific capacity. The HAADF-STEM image shows that Zn atoms are uniformly dispersed in the negative electrode material.

[0096] The Raman spectra of the negative electrode materials obtained in Example 1 and Comparative Example 4 were obtained, and the results are as follows: Figure 2 As shown; the Raman plot shows that Example 1 has a higher degree of graphitization (by comparing the intensity ratio of defect peaks to graphite peaks), indicating that the anode material has fewer defects, which is beneficial to reducing the consumption of lithium ions in the first cycle and improving the first coulombic efficiency of the anode material.

[0097] The technical means disclosed in this application are not limited to those disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principles of this application, and these improvements and modifications are also considered to be within the scope of protection of this application.

Claims

1. A method for producing a negative electrode material, characterized by, Includes the following steps: (1) Mix the biomass-based carbon source and zinc source, disperse them in deionized water, add hydrogen peroxide, stir, and heat to obtain the precursor; (2) The precursor is crosslinked with a resin-based carbon source to form an intermediate with a three-dimensional network structure; (3) The intermediate is carbonized in an inert atmosphere to form a negative electrode material.

2. The method for producing a negative electrode material according to claim 1, wherein The biomass-based carbon source is cellulose, and the resin-based carbon source is phenolic resin. The weight ratio of cellulose to phenolic resin is 0.5 to 2:

1.

3. The method for producing a negative electrode material according to claim 1, wherein The zinc source includes one or more of zinc chloride, zinc acetate, and zinc oxalate.

4. The method of producing a negative electrode material according to claim 1, wherein The weight ratio of the zinc source to the biomass-based carbon source is 0.05-0.5:

1.

5. The method of producing a negative electrode material according to claim 1, wherein The specific steps (1) are as follows: the zinc source and the biomass carbon source are uniformly mixed and dispersed in deionized water, hydrogen peroxide is added and stirred, and then heated at 80~110℃ for 2-4 hours. After filtration and drying, the precursor is obtained.

6. The method of producing a negative electrode material according to claim 1, wherein The specific steps (2) are as follows: the precursor, phenol source, formaldehyde and catalyst are uniformly dispersed in a solvent, and then hydrothermal polymerization is carried out at 100-120℃ for 12-24h. After washing and drying, the intermediate is obtained. The phenol source is at least one of phenol, 2-aminophenol, 2,6-diaminophenol, and 4-aminophenol; the molar ratio of the phenol source to the formaldehyde is 1:2~5.

7. The method for preparing the negative electrode material as described in claim 1, characterized in that, In step (3), the inert atmosphere is at least one of nitrogen, argon and helium; and / or, the carbonization treatment temperature is 1100-1400℃, the time is 2-5 hours, the heating rate is 2-5℃ / min, and the gas flow rate is 50-100 mL / min.

8. The method for preparing the negative electrode material as described in claim 6, characterized in that, The catalyst is ammonia water with a concentration of 23-26 wt%, the formaldehyde is added in the form of a formaldehyde solution with a concentration of 1-1.2 g / ml, and the mass ratio of the formaldehyde solution to the ammonia water is 20-50:1; and / or, the solvent includes ethanol and water with a mass ratio of ethanol to water of 1:1-2.

9. A negative electrode material, which is prepared by the method for preparing a negative electrode material according to any one of claims 1 to 8, wherein the content of Zn in the negative electrode material is 0.5 to 1.0 wt%.

10. A sodium-ion battery, characterized in that, It includes a negative electrode sheet, wherein the negative electrode sheet comprises the negative electrode material as described in claim 9.

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