Preparation method of biomass-based hard carbon negative electrode material with high first efficiency for sodium-ion battery
By optimizing the structure of biomass-based hard carbon anode materials through hydrothermal methods and high-temperature coating technology, the problems of low initial coulombic efficiency and poor cycle performance of sodium-ion batteries were solved, achieving efficient sodium-ion storage and a stable electrode structure.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHENZHEN JANAENERGY TECH CO LTD
- Filing Date
- 2026-01-31
- Publication Date
- 2026-05-01
AI Technical Summary
Sodium-ion battery biomass-based hard carbon anode materials suffer from low initial coulombic efficiency and poor cycle performance, mainly due to irreversible reactions caused by heteroatom residues, porous structure, and high specific surface area, as well as instability of the SEI film.
Biomass precursors are treated with a hydrothermal method combined with reducing agents and surfactants to form a low-defect spherical structure. A dense carbon layer is then formed through high-temperature coating, optimizing the carbon skeleton and surface coating, and reducing irreversible reactions and the formation of SEI films.
It significantly improves initial coulombic efficiency and cycle stability, reduces specific surface area and internal defects, forms a stable SEI film, and enhances the energy density and cycle life of the battery.
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Figure CN121948423A_ABST
Abstract
Description
A method for preparing biomass-based hard carbon anode material for sodium-ion batteries with high initial efficiency Technical Field
[0001] This invention relates to the field of sodium-ion battery technology, specifically to a method for preparing a high-efficiency sodium-ion battery biomass-based hard carbon anode material. Background Technology
[0002] Hard carbon is a carbon material that cannot be further graphitized, obtained by carbonizing polymers or biomass precursors at high temperatures. Biomass-based hard carbon, in particular, has advantages such as abundant precursor sources (e.g., coconut shells, walnut shells, straw, starch), renewability, low cost, and environmental friendliness, making it very suitable for the low-cost requirements of large-scale energy storage.
[0003] As an anode material for sodium-ion batteries, hard carbon possesses a larger carbon interlayer spacing (typically > 0.37 nm, compared to 0.335 nm for graphite) and numerous micropores and defects, providing ample channels and storage space for the larger Na+ ions. Its "open" structure alleviates volumetric strain during sodium ion insertion / extraction, preventing structural collapse and maintaining excellent cycle stability. Due to its open structure perfectly matching the size of sodium ions, excellent electrochemical performance, and environmental advantages, hard carbon has become the preferred and core anode material for current commercial sodium-ion batteries.
[0004] However, sodium-ion batteries suffer from low initial charge-discharge coulombic efficiency after formation and capacity testing, which is one of the main reasons for their low energy density. During the initial charge-discharge process, the solvent and salt in the electrolyte undergo irreversible decomposition reactions on the hard carbon surface of the negative electrode, generating a solid protective film covering the hard carbon surface, namely the SEI film. This is the main source of initial efficiency loss in carbon-based negative electrodes.
[0005] Currently, the biomass-based hard carbon anode in sodium-ion batteries has the following drawbacks:
[0006] 1. Low initial coulombic efficiency. Firstly, biomass itself contains a large number of heteroatoms such as oxygen, hydrogen, and nitrogen. During carbonization, these heteroatoms remain on the surface and inside the hard carbon in the form of oxygen- or hydrogen-containing functional groups (-OH, -COOH, C=O, etc.). At the low potential of the initial charge-discharge cycle, these functional groups undergo irreversible redox reactions with sodium ions, generating inert products such as Na₂O and Na₂CO₃, permanently consuming Na⁺. Secondly, the natural porous structure of biomass forms numerous open pores, closed pores, and defect sites after carbonization. Some Na⁺ ions, after embedding in extremely small or closed pores, are permanently trapped due to excessively high kinetic barriers and cannot escape. Finally, the extremely high specific surface area of biomass hard carbon provides a huge reaction interface for electrolyte decomposition, leading to a sharp increase in the irreversible sodium consumption required for SEI film formation.
[0007] 2. Poor Cycling Performance. The surface of biomass hard carbon is highly active and uneven, resulting in a fragile and non-dense SEI film structure formed during the initial formation. During long-term cycling, the surface structure of hard carbon is subjected to stress from repeated Na+ insertion / extraction, leading to SEI film damage. The continuously exposed interface and ongoing side reactions with the electrolyte continuously consume Na+, forming a thicker SEI film, resulting in accelerated capacity retention decay and a continuous increase in impedance. Simultaneously, biomass hard carbon contains numerous nanopores and defects with a highly disordered structure. Under long-term cycling, repeated Na+ insertion / extraction generates continuous mechanical stress on these pore walls and defect structures. This stress may cause the micropores and defects to collapse, destroying the original sodium-storing active sites. Na+ precipitates on the negative electrode surface, accelerating battery degradation. Summary of the Invention
[0008] The purpose of this invention is to provide a method for preparing a biomass-based hard carbon anode material for sodium-ion batteries with high initial efficiency, characterized by high initial coulombic efficiency and good cycle stability.
[0009] This invention can be achieved through the following technical solutions:
[0010] This invention provides a novel method for preparing a high-efficiency biomass-based hard carbon anode material for sodium-ion batteries, comprising the following steps:
[0011] S1. Biomass precursor preparation: Biomass raw materials are crushed to obtain biomass precursors;
[0012] S2. Preparation of hydrothermal precursor: The biomass precursor obtained in step S1 is soaked in acid solution, then washed with water, centrifuged and dried to obtain hydrothermal precursor.
[0013] S3. Preparation of carbonized precursor: The hydrothermal precursor obtained in step S2 is immersed in a mixed solution of reducing agent and surfactant. The mixed solution is transferred to a reaction vessel and heated to react. After cooling to room temperature, it is centrifuged and dried to obtain the pre-carbonized precursor.
[0014] S4. Pre-carbonization: The pre-carbonized precursor obtained in step S3 is subjected to pre-carbonization treatment, followed by crushing and sieving to obtain pre-carbonized material.
[0015] S5. High-temperature coating: The pre-carbonized material obtained in step S4 is coated to obtain a high-temperature carbonization precursor.
[0016] S6. High-temperature carbonization: The coating material obtained in step S5 is subjected to high-temperature carbonization treatment to obtain the sodium-ion battery biomass hard carbon anode material.
[0017] Further, in step S3, the reducing agent is one or more of formic acid, oxalic acid, ascorbic acid, hydrazine hydrate, and sodium sulfite, and the amount added is 5-10 wt% of the hydrothermal precursor. Insufficient reducing agent may result in incomplete reduction of oxygen-containing functional groups in the precursor, leading to a large number of residual oxygen atoms in the hard carbon, increasing defect sites in the carbon skeleton, resulting in more irreversible side reactions in the first round and low coulombic efficiency in the first round; excessive reducing agent may result in over-densification of the carbon skeleton, reducing interlayer spacing, which is not conducive to the insertion and extraction of sodium ions.
[0018] Further, in step S3, the surfactant is one or more of cetyltrimethylammonium bromide, polyvinylpyrrolidone, polyethylene glycol, and sodium dodecyl sulfate, and the amount added is 5-10 wt% of the hydrothermal precursor. Insufficient surfactant addition will lead to uneven dispersion of the biomass precursor, easy aggregation during hydrothermal process, resulting in uneven size distribution of hard carbon particles, or even the formation of large, dense structures; excessive surfactant may form too many pores or superpores, reducing the material density and tap density, thereby reducing the volumetric energy density.
[0019] Further, in step S3, the heating reaction conditions are: reaction temperature of 160-240℃, heating rate of 1-5℃ / min, and holding time of 10-36h. In the hydrothermal preparation of spherical hard carbon anodes, precise control from molecular reaction to physical assembly is achieved through the synergistic addition of reducing agents (such as formic acid and ascorbic acid) and surfactants (such as surfactant CTAB and crosslinking agent glutaraldehyde). The reducing agent, by scavenging reactive oxygen species, directly reducing unstable carbonyl groups, and catalyzing aromatization polymerization, inhibits the oxidation pathway from the chemical source, generating stable aromatic precursors with low oxygen content and low intrinsic defects. Simultaneously, the surfactant guides spherical assembly through soft template guidance and steric hindrance effects, and strengthens the three-dimensional network structure through crosslinking, ensuring the spherical integrity and mechanical stability of the precursor. The synergistic effect of these two agents results in hydrothermal products possessing both a low-defect chemical structure and a highly stable spherical morphology. After subsequent high-temperature carbonization, these are ultimately transformed into spherical hard carbon anode materials with fewer defects, suitable interlayer spacing, high initial efficiency, and excellent cycle performance.
[0020] Further, in step S4, the pre-carbonization conditions are: heating rate of 1-5 ℃ / min, pre-carbonization temperature of 600-1000 ℃, pre-carbonization time of 2-10 h, and protective gas of nitrogen and / or argon.
[0021] Furthermore, in step S5, the coating material is one or more of benzene, toluene, ethanol, pyridine, graphite pitch, coal tar pitch, epoxy resin, and phenolic resin. The coating can close some micropores, reduce the specific surface area of the material, reduce side reactions between the material and the electrolyte, and improve the first-cycle coulombic efficiency and long-cycle stability of the material. The coating amount of the carbon layer is 5-15 wt% of the biomass hard carbon material core, and the coating thickness is 10-500 nm. Specifically, if the coating is too thin, impurities remaining in the biomass hard carbon material core will gradually migrate to the material surface during subsequent carbonization, failing to achieve the purpose of coating; if the coating is too thick, it will increase costs and is not conducive to commercial application.
[0022] Further, in step S6, the conditions for high-temperature carbonization are: a heating rate of 1-5 °C / min, a carbonization temperature of 900-1600 °C, a carbonization time of 2-10 h, and a protective gas of nitrogen and / or argon. Specifically, high-temperature carbonization can promote the collapse of open micropore walls to form closed internal pores, reducing the specific surface area of the material. Excessively high carbonization temperatures can lead to excessive graphitization of the material, narrowing the interlayer spacing, which is detrimental to sodium ion insertion / extraction, thus resulting in poor rate performance.
[0023] Further, in step S2, the acid solution is one or more of hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, and hydrofluoric acid, and the amount of acid solution added is 5-20 wt%; the stirring time is 10-24 h, the drying temperature is 80-110℃, and the drying time is 10-24 h. Biomass raw materials contain some metallic impurities. During the high-temperature carbonization process of hard carbon materials, these metallic impurities react with carbon to form various inorganic salts. During charge and discharge, these impurities come into contact with the electrolyte, catalyzing the irreversible decomposition of the electrolyte, leading to poor cycle stability. Acid washing can remove residual metallic and non-metallic impurities from the material, improving the cycle stability of the material.
[0024] Furthermore, in step S1, the biomass raw material is one or more of the following: sawdust, walnut shells, coffee shells, nut shells, straw, coconut shells, bamboo, and leaves.
[0025] Furthermore, in step S5, the surface coating method is chemical vapor deposition, liquid phase coating, or molten liquid phase coating, and the coating equipment is fluidized bed vapor deposition equipment, rotary kiln vapor deposition equipment, spray drying and mechanical fusion coating machine.
[0026] This invention provides a method for preparing a high-efficiency biomass-based hard carbon anode material for sodium-ion batteries, which has the following beneficial effects:
[0027] First, the high coulombic efficiency in the first cycle is achieved by adding a reducing agent during the hydrothermal process to effectively remove oxygen-containing functional groups such as carboxyl and carbonyl groups from the precursor surface. The addition of surfactants guides the formation of a dense and smooth spherical structure, significantly reducing the specific surface area of the material and thus greatly reducing the sodium ions consumed in forming the solid electrolyte interphase (SEI) film during the first charge and discharge process. At the same time, the crosslinking and aromatization processes strengthen the carbon skeleton, reduce the concentration of internal defects, and the surface coating reduces the concentration of surface defects, reducing irreversible side reactions between the material and the electrolyte. Ultimately, the material forms a thin and stable SEI film in the first cycle and directs more sodium ions to reversible sodium storage sites, improving the coulombic efficiency in the first cycle.
[0028] Secondly, it exhibits excellent cycling stability. The low-defect, stable spherical hard carbon core pre-constructed by the hydrothermal method effectively buffers bulk volume changes, while the dense outer carbon coating acts as a physical barrier, directly suppressing continuous side reactions between the electrolyte and the core, stabilizing the formation of the SEI film at the interface, and constraining the expansion and rupture of the core during cycling. Simultaneously, the coating layer enhances interparticle electron conduction. This dual protection mechanism, from the inside out, jointly maintains the structural integrity and interfacial stability of the electrode during long-term cycling, thereby significantly improving capacity retention and cycle life. Attached Figure Description
[0029] Figure 1 is a SEM image of the biomass hard carbon anode prepared in Example 1;
[0030] Figure 2 shows the long-cycle test curve of a sodium-ion battery made of biomass hard carbon and polyanionic poly(NFPP) cathode material prepared in Example 1 under constant current charge-discharge at 1C current density. Detailed Implementation
[0031] To enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention will be further described in detail below with reference to embodiments.
[0032] This invention provides a novel method for preparing a high-efficiency biomass-based hard carbon anode material for sodium-ion batteries, comprising the following steps:
[0033] S1. Biomass precursor preparation: Biomass raw materials are crushed to obtain biomass precursors;
[0034] S2. Preparation of hydrothermal precursor: The biomass precursor obtained in step S1 is soaked in acid solution, then washed with water, centrifuged and dried to obtain hydrothermal precursor.
[0035] S3. Preparation of carbonized precursor: The hydrothermal precursor obtained in step S2 is immersed in a mixed solution of reducing agent and surfactant. The mixed solution is transferred to a reaction vessel and heated to react. After cooling to room temperature, it is centrifuged and dried to obtain the pre-carbonized precursor.
[0036] S4. Pre-carbonization: The pre-carbonized precursor obtained in step S3 is subjected to pre-carbonization treatment, followed by crushing and sieving to obtain pre-carbonized material.
[0037] S5. High-temperature coating: The pre-carbonized material obtained in step S4 is coated to obtain a high-temperature carbonization precursor.
[0038] S6. High-temperature carbonization: The coating material obtained in step S5 is subjected to high-temperature carbonization to obtain a sodium-ion battery biomass-based hard carbon anode material.
[0039] Further, in step S3, the reducing agent is one or more of formic acid, oxalic acid, ascorbic acid, hydrazine hydrate, and sodium sulfite, and the amount added is 5-10 wt% of the hydrothermal precursor.
[0040] Further, in step S3, the surfactant is one or more of cetyltrimethylammonium bromide, polyvinylpyrrolidone, polyethylene glycol, and sodium dodecyl sulfate, and the amount added is 5-10 wt% of the hydrothermal precursor.
[0041] Furthermore, in step S3, the conditions for the heating reaction are: reaction temperature of 160-240℃, heating rate of 1-5℃ / min, and holding time of 10-36h.
[0042] Further, in step S4, the pre-carbonization conditions are: heating rate of 1-5 ℃ / min, pre-carbonization temperature of 600-1000 ℃, pre-carbonization time of 2-10 h, and protective gas of nitrogen and / or argon.
[0043] Further, in step S5, the coating material is one or more of benzene, toluene, ethanol, pyridine, graphite pitch, coal tar pitch, epoxy resin, and phenolic resin; the coating amount of the carbon layer is 5-15 wt% of the core of the biomass hard carbon material, and the coating thickness is 10-500 nm.
[0044] Furthermore, in step S6, the conditions for high-temperature carbonization are: a heating rate of 1-5 ℃ / min, a carbonization temperature of 900-1600 ℃, a carbonization time of 2-10 h, and a protective gas of nitrogen and / or argon.
[0045] Further, in step S2, the acid solution is one or more of hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, and hydrofluoric acid, and the amount of acid solution added is 5-20 wt%; the stirring time is 10-24 h, the drying temperature is 80-110℃, and the drying time is 10-24 h.
[0046] Furthermore, in step S1, the biomass raw material is one or more of the following: sawdust, walnut shells, coffee shells, nut shells, straw, coconut shells, bamboo, and leaves.
[0047] Furthermore, in step S5, the surface coating method is chemical vapor deposition, liquid phase coating, or molten liquid phase coating, and the coating equipment is fluidized bed vapor deposition equipment, rotary kiln vapor deposition equipment, spray drying and mechanical fusion coating machine.
[0048] Example 1
[0049] This embodiment relates to a high-efficiency sodium-ion battery biomass-based hard carbon anode material, the preparation method of which includes the following steps:
[0050] S1. Preparation of biomass precursors: Biomass raw materials are crushed to obtain biomass precursors; specifically, biomass raw materials are sawdust, walnut shells, and coffee shells.
[0051] S2. Preparation of hydrothermal precursor: The biomass precursor obtained in step S1 is soaked in an acid solution, then washed with water, centrifuged and dried to obtain the hydrothermal precursor; specifically, the acid solution is hydrochloric acid and phosphoric acid, and the amount of acid solution added is 20 wt%; the stirring time is 17 h, the drying temperature is 800 ℃, and the drying time is 24 h.
[0052] S3. Preparation of carbonized precursor: The hydrothermal precursor obtained in step S2 is immersed in a mixed solution of reducing agent and surfactant. The mixed solution is transferred to a reaction vessel and heated for reaction. After cooling to room temperature, it is centrifuged and dried to obtain the pre-carbonized precursor. Specifically, the reducing agent is formic acid and oxalic acid, and the amount added is 10 wt% of the hydrothermal precursor. The surfactant is hexadecyltrimethylammonium bromide and polyvinylpyrrolidone, and the amount added is 8 wt% of the hydrothermal precursor. The heating reaction conditions are: reaction temperature of 160℃, heating rate of 5℃ / min, and holding time of 23h.
[0053] S4. Pre-carbonization: The pre-carbonized precursor obtained in step S3 is subjected to pre-carbonization treatment, followed by crushing and sieving to obtain pre-carbonized material; specifically, the pre-carbonization conditions are: heating rate of 5 ℃ / min, pre-carbonization temperature of 800 ℃, pre-carbonization time of 2 h, and protective gas of nitrogen.
[0054] S5. High-temperature coating: The pre-carbonized material obtained in step S4 is coated to obtain a high-temperature carbonization precursor; specifically, the coating material is benzene and toluene; the coating amount of the carbon layer is 15 wt% of the core of the biomass hard carbon material, and the coating thickness is 10-500 nm; the surface coating method is chemical vapor deposition, and the coating equipment is a fluidized bed vapor deposition equipment.
[0055] S6. High-temperature carbonization: The coating material obtained in step S5 is subjected to high-temperature carbonization to obtain a biomass-based hard carbon anode material for sodium-ion batteries. Specifically, the conditions for high-temperature carbonization are: heating rate of 5 ℃ / min, carbonization temperature of 1300 ℃, carbonization time of 3 h, and nitrogen as the protective gas.
[0056] Example 2
[0057] This embodiment relates to a high-efficiency sodium-ion battery biomass-based hard carbon anode material, the preparation method of which includes the following steps:
[0058] S1. Preparation of biomass precursors: Biomass raw materials are crushed to obtain biomass precursors; specifically, biomass raw materials are straw, coconut shells, bamboo, and leaves.
[0059] S2. Preparation of hydrothermal precursor: The biomass precursor obtained in step S1 is soaked in acid solution, then washed with water, centrifuged and dried to obtain hydrothermal precursor; specifically, the acid solution is hydrochloric acid and sulfuric acid, and the amount of acid solution added is 10 wt%; the stirring time is 10 h, the drying temperature is 110 ℃, and the drying time is 17 h.
[0060] S3. Preparation of carbonized precursor: The hydrothermal precursor obtained in step S2 is immersed in a mixed solution of reducing agent and surfactant. The mixed solution is transferred to a reaction vessel and heated for reaction. After cooling to room temperature, it is centrifuged and dried to obtain the pre-carbonized precursor. Specifically, the reducing agent is ascorbic acid and sodium sulfite, with an addition amount of 8 wt% of the hydrothermal precursor; the surfactant is polyvinylpyrrolidone, polyethylene glycol, and sodium dodecyl sulfate, with an addition amount of 8 wt% of the hydrothermal precursor; the heating reaction conditions are: reaction temperature of 160℃, heating rate of 5℃ / min, and holding time of 23h.
[0061] S4. Pre-carbonization: The pre-carbonized precursor obtained in step S3 is subjected to pre-carbonization treatment, followed by crushing and sieving to obtain pre-carbonized material; specifically, the pre-carbonization conditions are: heating rate of 3 ℃ / min, pre-carbonization temperature of 600 ℃, pre-carbonization time of 10 h, and protective gas of argon.
[0062] S5. High-temperature coating: The pre-carbonized material obtained in step S4 is coated to obtain a high-temperature carbonization precursor; specifically, the coating material is benzene, pyridine, graphite pitch, and phenolic resin; the coating amount of the carbon layer is 10wt% of the core of the biomass hard carbon material, and the coating thickness is 10-500nm; the surface coating method is liquid phase coating, and the coating equipment is spray drying.
[0063] S6. High-temperature carbonization: The coating material obtained in step S5 is subjected to high-temperature carbonization to obtain a biomass-based hard carbon anode material for sodium-ion batteries. Specifically, the conditions for high-temperature carbonization are: heating rate of 3 ℃ / min, carbonization temperature of 900 ℃, carbonization time of 10 h, and argon as the protective gas.
[0064] Example 3
[0065] This embodiment relates to a high-efficiency sodium-ion battery biomass-based hard carbon anode material, the preparation method of which includes the following steps:
[0066] S1. Preparation of biomass precursors: Biomass raw materials are crushed to obtain biomass precursors; specifically, biomass raw materials are sawdust, walnut shells, and leaves.
[0067] S2. Preparation of hydrothermal precursor: The biomass precursor obtained in step S1 is soaked in acid solution, then washed with water, centrifuged and dried to obtain hydrothermal precursor; specifically, the acid solution is phosphoric acid and sulfuric acid, and the amount of acid solution added is 5 wt%; the stirring time is 24 h, the drying temperature is 95 ℃, and the drying time is 10 h.
[0068] S3. Preparation of carbonized precursor: The hydrothermal precursor obtained in step S2 is immersed in a mixed solution of reducing agent and surfactant. The mixed solution is transferred to a reaction vessel and heated for reaction. After cooling to room temperature, it is centrifuged and dried to obtain the pre-carbonized precursor. Specifically, the reducing agent is oxalic acid and ascorbic acid, and the amount added is 5 wt% of the hydrothermal precursor. The surfactant is polyethylene glycol and sodium dodecyl sulfate, and the amount added is 10 wt% of the hydrothermal precursor. The heating reaction conditions are: reaction temperature of 200℃, heating rate of 1℃ / min, and holding time of 36h.
[0069] S4. Pre-carbonization: The pre-carbonized precursor obtained in step S3 is subjected to pre-carbonization treatment, followed by crushing and sieving to obtain pre-carbonized material; specifically, the pre-carbonization conditions are: heating rate of 1℃ / min, pre-carbonization temperature of 1000℃, pre-carbonization time of 6 h, and protective gas of nitrogen and argon.
[0070] S5. High-temperature coating: The pre-carbonized material obtained in step S4 is coated to obtain a high-temperature carbonization precursor; specifically, the coating material is graphite pitch, coal pitch, epoxy resin, and phenolic resin; the coating amount of the carbon layer is 5wt% of the core of the biomass hard carbon material, and the coating thickness is 10-500nm; the surface coating method is molten liquid phase coating, and the coating equipment is a mechanical fusion coating machine.
[0071] S6. High-temperature carbonization: The coating material obtained in step S5 is subjected to high-temperature carbonization to obtain a biomass-based hard carbon anode material for sodium-ion batteries. Specifically, the conditions for high-temperature carbonization are: heating rate of 1 ℃ / min, carbonization temperature of 1600 ℃, carbonization time of 6 h, and protective gases of nitrogen and argon.
[0072] Example 4
[0073] This embodiment relates to a high-efficiency sodium-ion battery biomass-based hard carbon anode material, the preparation method of which includes the following steps:
[0074] S1. Preparation of biomass precursors: Biomass raw materials are crushed to obtain biomass precursors; specifically, biomass raw materials are sawdust, walnut shells, straw, coconut shells, and bamboo.
[0075] S2. Preparation of hydrothermal precursor: The biomass precursor obtained in step S1 is soaked in an acid solution, then washed with water, centrifuged and dried to obtain the hydrothermal precursor; specifically, the acid solution is hydrochloric acid and nitric acid, and the amount of acid solution added is 16 wt%; the stirring time is 14 h, the drying temperature is 100 ℃, and the drying time is 13 h.
[0076] S3. Preparation of carbonized precursor: The hydrothermal precursor obtained in step S2 is immersed in a mixed solution of reducing agent and surfactant. The mixed solution is transferred to a reaction vessel and heated for reaction. After cooling to room temperature, it is centrifuged and dried to obtain the pre-carbonized precursor. Specifically, the reducing agent is formic acid, oxalic acid, and ascorbic acid, with an addition amount of 6 wt% of the hydrothermal precursor; the surfactant is hexadecyltrimethylammonium bromide and polyvinylpyrrolidone, with an addition amount of 8 wt% of the hydrothermal precursor; the heating reaction conditions are: reaction temperature of 19℃, heating rate of 4℃ / min, and holding time of 26h.
[0077] S4. Pre-carbonization: The pre-carbonized precursor obtained in step S3 is subjected to pre-carbonization treatment, followed by crushing and sieving to obtain pre-carbonized material; specifically, the pre-carbonization conditions are: heating rate of 4℃ / min, pre-carbonization temperature of 900℃, pre-carbonization time of 6 h, and protective gas of nitrogen and argon.
[0078] S5. High-temperature coating: The pre-carbonized material obtained in step S4 is coated to obtain a high-temperature carbonization precursor; specifically, the coating material is ethanol, pyridine, epoxy resin, and phenolic resin; the coating amount of the carbon layer is 5-15 wt% of the core of the biomass hard carbon material, and the coating thickness is 10-500 nm; the surface coating method is chemical vapor deposition, and the coating equipment is a rotary kiln chemical vapor deposition equipment.
[0079] S6. High-temperature carbonization: The coating material obtained in step S5 is subjected to high-temperature carbonization to obtain a biomass-based hard carbon anode material for sodium-ion batteries. Specifically, the conditions for high-temperature carbonization are: heating rate of 2 ℃ / min, carbonization temperature of 1200 ℃, carbonization time of 7 h, and protective gases of nitrogen and argon.
[0080] Application Example 1
[0081] This embodiment relates to a high-efficiency sodium-ion battery biomass-based hard carbon anode material, the preparation method of which includes the following steps:
[0082] S1. Preparation of biomass precursor: The raw material of walnut shells is crushed and sieved to obtain biomass precursor;
[0083] S2. Preparation of hydrothermal precursor: Acid washing treatment: The activated material obtained in step S2 is soaked in acid solution, washed with water, centrifuged and dried to obtain the hydrothermal precursor. Specifically, the added acid solution is hydrochloric acid, the amount added is 10wt% of the activated material, the stirring time is 12h, the drying temperature is 80℃ and the drying time is 24h;
[0084] S3. Preparation of the carbonized precursor: The hydrothermal precursor obtained in step S2 is immersed in a mixed solution of a reducing agent and a surfactant. The mixed solution is transferred to a reaction vessel and heated for a period of time. After cooling to room temperature, it is centrifuged and dried to obtain the pre-carbonized precursor. Specifically, the added reducing agent is ascorbic acid, with an addition amount of 15 wt% of the hydrothermal precursor; the added surfactant is PVP, with an addition amount of 10 wt% of the hydrothermal precursor; the hydrothermal reaction temperature is 180℃; and the reaction time is 24 h. Specifically, the centrifugal drying temperature is 80℃; and the drying time is 24 h.
[0085] S4. Pre-carbonization: The pre-carbonization precursor is pre-carbonized at a certain temperature, then crushed and sieved to obtain pre-carbonized material. Specifically, the heating rate is 5 ℃ / min, the pre-carbonization temperature is 600 ℃, the pre-carbonization time is 2 h, and the protective gas is nitrogen.
[0086] S5. High-temperature coating treatment: The dried pre-carbonized material is mixed with petroleum asphalt and coated using a fusion coating machine to obtain a high-temperature carbonization precursor, wherein the amount of petroleum asphalt added is 8.5 wt% of the pre-carbonized material.
[0087] S6. High-Temperature Carbonization: The high-temperature carbonization precursor is subjected to high-temperature carbonization treatment at a certain temperature to obtain biomass hard carbon material with a carbon coating on the surface. Specifically, the heating rate is 5 ℃ / min, the carbonization temperature is 1300 ℃, the carbonization time is 2h, and the protective gas is nitrogen.
[0088] The electrochemical performance of the obtained materials for soft-pack batteries was tested using the following method: Biomass-based hard carbon material, Super P, CMC, and SBR were mixed in a ratio of 94.5:1.5:1.5:2.5 to form a slurry, which was then uniformly coated onto high-growth aluminum foil using a coating machine. Non-ionic polypropylene (NFPP) was used as the positive electrode material, biomass hard carbon as the negative electrode material, and 1 mol / L NaClO4 in EC+DEC (1:1 vol%) was used as the electrolyte. A PP / PE / PP three-layer separator was used. The full cells were subjected to a 0.1C first-cycle charge-discharge test and a 1C constant-current charge-discharge long-cycle test, with a voltage range of 3.4-1.5V.
[0089] Comparative Example 1
[0090] This embodiment relates to a biomass-based hard carbon anode material for sodium-ion batteries, and its preparation method includes the following steps:
[0091] S1. Preparation of biomass precursors: Preparation of biomass precursors: The raw material of walnut shells is crushed and sieved to obtain biomass precursors;
[0092] S2. Preparation of hydrothermal precursor: Acid washing treatment: The activated material obtained in step S2 is soaked in acid solution, washed with water, centrifuged and dried to obtain the hydrothermal precursor. Specifically, the added acid solution is hydrochloric acid, the amount added is 10wt% of the activated material, the stirring time is 12h, the drying temperature is 80℃ and the drying time is 24h;
[0093] S3. Preparation of the carbonized precursor: The hydrothermal precursor obtained in step S2 is immersed in a mixed solution of a reducing agent and a surfactant. The mixed solution is transferred to a reaction vessel and heated for a period of time. After cooling to room temperature, it is centrifuged and dried to obtain the pre-carbonized precursor. Specifically, the added reducing agent is ascorbic acid, with an addition amount of 15 wt% of the hydrothermal precursor; the added surfactant is PVP, with an addition amount of 10 wt% of the hydrothermal precursor; the hydrothermal reaction temperature is 180℃; and the reaction time is 24 h. Specifically, the centrifugal drying temperature is 80℃; and the drying time is 24 h.
[0094] S4. Pre-carbonization: The pre-carbonization precursor is pre-carbonized at a certain temperature, then crushed and sieved to obtain pre-carbonized material. Specifically, the heating rate is 5 ℃ / min, the pre-carbonization temperature is 600 ℃, the pre-carbonization time is 2 h, and the protective gas is nitrogen.
[0095] S5. High-temperature carbonization: The high-temperature carbonization precursor is subjected to high-temperature carbonization treatment at a certain temperature to obtain biomass hard carbon material with a carbon layer on the surface. Specifically, the heating rate is 5 ℃ / min, the carbonization temperature is 1300 ℃, the carbonization time is 2h, and the protective gas is nitrogen.
[0096] The electrochemical performance of the obtained materials for soft-pack batteries was tested using the following method: Biomass-based hard carbon material, Super P, CMC, and SBR were mixed in a ratio of 94.5:1.5:1.5:2.5 to form a slurry, which was then uniformly coated onto high-growth aluminum foil using a coating machine. Non-ionic polypropylene (NFPP) was used as the positive electrode material, biomass hard carbon as the negative electrode material, and 1 mol / L NaClO4 in EC+DEC (1:1 vol%) was used as the electrolyte. A PP / PE / PP three-layer separator was used. The full cells were subjected to a 0.1C first-cycle charge-discharge test and a 1C constant-current charge-discharge long-cycle test, with a voltage range of 3.4-1.5V.
[0097] Comparative Example 2
[0098] This embodiment relates to a biomass-based hard carbon anode material for sodium-ion batteries, and its preparation method includes the following steps:
[0099] S1. Preparation of biomass precursors: Preparation of biomass precursors: The raw material of walnut shells is crushed and sieved to obtain biomass precursors;
[0100] S2. Preparation of carbonized precursor: Acid washing treatment: The activated material obtained in step S2 is soaked in acid solution, washed with water, centrifuged and dried to obtain the pre-carbonized precursor. Specifically, the added acid solution is hydrochloric acid, the amount added is 10wt% of the activated material, the stirring time is 12h, the drying temperature is 80℃ and the drying time is 24h;
[0101] S3. Pre-carbonization: The pre-carbonization precursor is pre-carbonized at a certain temperature, then crushed and sieved to obtain pre-carbonized material. Specifically, the heating rate is 5 ℃ / min, the pre-carbonization temperature is 600 ℃, the pre-carbonization time is 2 h, and the protective gas is nitrogen.
[0102] S4. High-Temperature Carbonization: The high-temperature carbonization precursor is subjected to high-temperature carbonization treatment at a certain temperature to obtain biomass hard carbon material with a carbon coating on the surface. Specifically, the heating rate is 5 ℃ / min, the carbonization temperature is 1300 ℃, the carbonization time is 2h, and the protective gas is nitrogen.
[0103] The electrochemical performance of the obtained materials for soft-pack batteries was tested using the following method: Biomass-based hard carbon material, Super P, CMC, and SBR were mixed in a ratio of 94.5:1.5:1.5:2.5 to form a slurry, which was then uniformly coated onto high-growth aluminum foil using a coating machine. Non-ionic polypropylene (NFPP) was used as the positive electrode material, biomass hard carbon as the negative electrode material, and 1 mol / L NaClO4 in EC+DEC (1:1 vol%) was used as the electrolyte. A PP / PE / PP three-layer separator was used. The full cells were subjected to a 0.1C first-cycle charge-discharge test and a 1C constant-current charge-discharge long-cycle test, with a voltage range of 3.4-1.5V.
[0104] Figure 1 is a scanning electron microscope image of the biomass hard carbon anode prepared in Application Example 1. The material has a spherical morphology.
[0105] The nitrogen adsorption-desorption test results showed that the specific surface areas of the biomass hard carbon anodes prepared in Example 1, Comparative Example 1, and Comparative Example 2 were 2.19, 6.93, and 11.52 m², respectively. 2 / g.
[0106] Sodium-ion batteries made from biomass hard carbon and polyanionic poly(NFPP) cathode materials prepared by the three methods of Example 1, Comparative Example 1 and Comparative Example 2 were subjected to constant current charge-discharge tests at a current density of 0.1C. The coulombic efficiencies in the first week were 90.65%, 86.71% and 85.62%, respectively.
[0107] Comparative analysis reveals that the hydrothermal method, by transforming biomass precursors into spherical hard carbon microspheres, effectively reduces the specific surface area and open pores of the material. This reduces irreversible sodium ion consumption caused by excessive formation of the solid electrolyte interphase (SEI) film during the initial charge-discharge cycle. Furthermore, the surface carbon coating layer further isolates the electrolyte from the active defects and functional groups on the hard carbon surface, suppressing side reactions and promoting the formation of a dense and stable SEI film. This synergistic effect of "spherical structure design" and "surface coating engineering" optimizes the reversible insertion / extraction process of sodium ions, significantly reducing initial irreversible capacity loss and achieving high initial coulombic efficiency.
[0108] Figure 2 shows the long-cycle test curves of a sodium-ion battery fabricated using biomass hard carbon prepared in Example 1 and polyanionic polymeric poly(NFPP) cathode material under constant current charge-discharge at 1C current density. The biomass hard carbon prepared by the hydrothermal method has the advantages of low defects and a stable spherical core. The carbon coating enables the formation of a dense SEI film on the hard carbon surface, effectively suppressing repeated rupture / regeneration of the SEI film during long-cycle operation. This comprehensively protects the structural integrity and interface stability of the electrode during long-term cycling, thereby significantly improving the battery's cycle life.
[0109] The above embodiments are merely specific examples of the present invention, and their descriptions are quite specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these obvious substitutions all fall within the protection scope of the present invention.
Claims
1. A method for preparing a high-efficiency sodium-ion battery biomass-based hard carbon anode material, characterized in that... Includes the following steps: S1. Biomass precursor preparation: Biomass raw materials are crushed to obtain biomass precursors; S2. Preparation of hydrothermal precursor: The biomass precursor obtained in step S1 is soaked in acid solution, then washed with water, centrifuged and dried to obtain hydrothermal precursor; S3. Preparation of carbonization precursor: The hydrothermal precursor obtained in step S2 is soaked in a mixed solution of reducing agent and surfactant, the mixed solution is transferred to a reaction vessel and heated to react, cooled to room temperature and then centrifuged and dried to obtain pre-carbonized precursor; S4. Pre-carbonization: The pre-carbonized precursor obtained in step S3 is subjected to pre-carbonization treatment, then crushed and sieved to obtain pre-carbonized material; S5. High-temperature coating: The pre-carbonized material obtained in step S4 is coated to obtain a high-temperature carbonization precursor; S6. High-temperature carbonization: The coated material obtained in step S5 is subjected to high-temperature carbonization to obtain a sodium-ion battery biomass hard carbon anode material.
2. The method for preparing the first high-efficiency sodium-ion battery biomass-based hard carbon anode material according to claim 1, characterized in that: In step S3, the reducing agent is one or more of formic acid, oxalic acid, ascorbic acid, hydrazine hydrate, and sodium sulfite, and the amount added is 5-10 wt% of the hydrothermal precursor.
3. The method for preparing the first high-efficiency sodium-ion battery biomass-based hard carbon anode material according to claim 1, characterized in that: In step S3, the surfactant is one or more of cetyltrimethylammonium bromide, polyvinylpyrrolidone, polyethylene glycol, and sodium dodecyl sulfate, and the amount added is 5-10 wt% of the hydrothermal precursor.
4. The method for preparing the first high-efficiency sodium-ion battery biomass-based hard carbon anode material according to claim 1, characterized in that: In step S3, the conditions for the heating reaction are: reaction temperature of 160-240℃, heating rate of 1-5℃ / min, and holding time of 10-36h.
5. The method for preparing a high-efficiency sodium-ion battery biomass-based hard carbon anode material according to claim 1, characterized in that: In step S4, the pre-carbonization conditions are: heating rate of 1-5 ℃ / min, pre-carbonization temperature of 600-1000 ℃, pre-carbonization time of 2-10 h, and protective gas of nitrogen and / or argon.
6. The method for preparing the first high-efficiency sodium-ion battery biomass-based hard carbon anode material according to claim 1, characterized in that: In step S5, the coating material is one or more of benzene, toluene, ethanol, pyridine, graphite pitch, coal tar pitch, epoxy resin, and phenolic resin; the coating amount of the carbon layer is 5-15 wt% of the core of the biomass hard carbon material, and the coating thickness is 10-500 nm.
7. The method for preparing the first high-efficiency sodium-ion battery biomass-based hard carbon anode material according to claim 1, characterized in that: In step S6, the conditions for high-temperature carbonization are: heating rate of 1-5 ℃ / min, carbonization temperature of 900-1600 ℃, carbonization time of 2-10 h, and protective gas of nitrogen and / or argon.
8. The method for preparing the first high-efficiency sodium-ion battery biomass-based hard carbon anode material according to claim 1, characterized in that: In step S2, the acid solution is one or more of hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, and hydrofluoric acid, and the amount of acid solution added is 5-20 wt%; the stirring time is 10-24 h, the drying temperature is 80-110℃, and the drying time is 10-24 h.
9. The method for preparing the first high-efficiency sodium-ion battery biomass-based hard carbon anode material according to claim 1, characterized in that: In step S1, the biomass raw material is one or more of the following: sawdust, walnut shells, coffee shells, nut shells, straw, coconut shells, bamboo, and leaves.
10. The method for preparing the first high-efficiency sodium-ion battery biomass-based hard carbon anode material according to claim 1, characterized in that: In step S5, the surface coating method is chemical vapor deposition, liquid phase coating, or molten liquid phase coating, and the coating equipment is fluidized bed vapor deposition equipment, rotary kiln vapor deposition equipment, spray drying and mechanical fusion coating machine.