Biomass-based closed-pore hard carbon material, method for preparing same, and sodium-ion battery negative electrode material

Abstract

The application belongs to the technical field of sodium ion battery negative electrode materials, and particularly relates to a biomass-based closed-pore hard carbon material and a preparation method thereof and a sodium ion battery negative electrode material. The biomass is preheated and treated to be converted into a hard carbon precursor with carbonization capacity. The hard carbon precursor has a firm structural framework in structure and contains abundant ultramicropores. The hard carbon precursor is subjected to joule heat treatment, and instant high-temperature carbonization rapidly generates the biomass-based closed-pore hard carbon material with adjustable closed pores, carbon layer spacing and defect structure. The biomass-based closed-pore hard carbon material prepared by the method has significantly improved storage performance for sodium ions, high initial coulombic efficiency and high reversible capacity. The method is simple to operate, and raw materials are easy to obtain. The biomass-based closed-pore hard carbon material not only has abundant closed pores, but also has moderate layer spacing, overcomes the deficiencies of the prior art in preparation and performance, and has a wide application prospect in the energy storage field.

Description

Technical Field

[0001] This invention belongs to the technical field of sodium-ion battery anode materials, specifically based on biomass-based closed-pore hard carbon materials, their preparation methods, and sodium-ion battery anode materials. Background Technology

[0002] Hard carbon materials have attracted widespread attention as anode materials for sodium-ion batteries due to their unique structural characteristics. However, hard carbon materials prepared using existing techniques often face problems such as suboptimal pore structure, unsuitable carbon layer spacing, and insufficient defect control, which directly affect the energy density and cycle performance of sodium-ion batteries. Furthermore, commonly used closed-pore generation techniques, such as chemical activation and chemical vapor deposition, are complex, time-consuming, and energy-intensive, making them difficult to meet the needs of industrial production.

[0003] It is evident that biomass materials, due to their abundant sources, low cost, and environmental friendliness, have become important precursors for the preparation of hard carbon materials. However, biomass-derived hard carbon materials prepared by traditional methods often suffer from low yields due to insufficient carbonization processes or difficulties in structural control. Furthermore, the pore structure and carbon interlayer spacing are unfavorable for sodium ion storage. In particular, the lack of simple and effective strategies to simultaneously control pore closure, defects, and carbon interlayer spacing limits the practical application of biomass-based hard carbon materials.

[0004] Existing technologies also disclose rapid preparation methods for hard carbon anode materials, such as CN116462176A, entitled: "An Ultra-Fast Preparation Method for Hard Carbon Anode Materials for Sodium-Ion Batteries"; the disclosed preparation method for hard carbon anode materials is as follows: (1) drying and pulverizing biomass raw materials to obtain a hard carbon precursor; (2) purifying and drying the hard carbon precursor, the purification process being water washing, alcohol solution washing, acid solution washing, and alkali solution washing, and purifying at 20-80℃ for 3-24h to obtain a purified hard carbon precursor; (3) subjecting the purified hard carbon precursor to ultra-fast heat treatment based on the Joule heating effect in a protected environment to obtain a hard carbon anode material. The method in this patent document is simple, has a short carbonization time, and can still maintain good electrochemical performance, but this patent does not provide closed-pore or even pore structure data, so it is impossible to judge its technical effect.

[0005] The publication number is CN118771351A, and the title is: A method for rapidly preparing hard carbon anode material and the resulting product and sodium-ion battery. The method for preparing hard carbon anode material disclosed therein is as follows: (1) the pre-treated biomass material is carbonized at low temperature under an inert atmosphere to obtain pre-carbonized material; (2) the pre-carbonized material is mixed with an activator and then subjected to Joule heating treatment under an inert atmosphere. The activator is at least one of sodium hydroxide, sodium carbonate, potassium hydroxide and potassium carbonate; and the carbon material after ultrafast Joule heating treatment is acid washed, water washed and dried to obtain hard carbon anode material. This patent document discloses a method that, on the one hand, involves etching a microporous structure onto the surface of a carbon material through alkali activation, followed by high-temperature treatment to increase the closed-pore content of the material, thereby providing more sites for sodium storage and resulting in excellent electrochemical performance of the prepared hard carbon material. On the other hand, instantaneous high-temperature Joule heating treatment rapidly heats the carbon material to a certain high temperature, accelerating the decomposition of the raw materials and preventing the rapid accumulation of metal impurities at high temperatures, which is beneficial for subsequent impurity removal. Furthermore, instantaneous high-temperature Joule heating accelerates the diffusion of the alkali activator, promoting a more complete activation reaction and resulting in a more uniform size and distribution of the etched pore structure. This is beneficial for uniform stress distribution during the charge-discharge process of the hard carbon material, improving the cycle stability of the material. However, activation and acid washing are common processing methods in the preparation of carbon materials. Although they can significantly increase the specific surface area and porosity of hard carbon anode materials, they also bring technical drawbacks such as material loss, uncontrollable pore size distribution, and high production costs. During the activation process, the action of strong alkalis or salt activators can cause excessive corrosion of the hard carbon anode material, while further cleaning with acid washing may exacerbate the damage to the pore structure, leading to reduced yield and uneven pore size distribution of the hard carbon anode material. In addition, the multiple treatment steps greatly increase time and operating costs, and also place higher demands on the environmental protection treatment of waste liquid. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a biomass-based closed-cell hard carbon material, its preparation method, and a sodium-ion battery anode material. The invention involves preheating the biomass to transform the fragile biomass into a hard carbon precursor. This precursor possesses a high carbonization capacity structural framework and abundant micropores. Subsequently, the hard carbon precursor undergoes Joule heat treatment to rapidly generate a biomass-based closed-cell hard carbon material with adjustable pore size, carbon layer spacing, and defect structure. The biomass-based closed-cell hard carbon material prepared using the method of this invention significantly improves sodium ion storage performance, exhibiting high initial coulombic efficiency and high reversible capacity, overcoming the technical defects of existing preparation methods and the resulting hard carbon anode materials.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] The preparation method of biomass-based closed-pore hard carbon materials includes the following steps:

[0009] Biomass was preheated and pretreated under an inert atmosphere to obtain a hard carbon precursor with a high carbonization capacity structural framework and abundant micropores.

[0010] Under an inert atmosphere, the hard carbon precursor is instantaneously heated by Joule heat treatment to rapidly generate closed nanopores, thus obtaining a biomass-based closed-pore hard carbon material.

[0011] Preferably, the preheating conditions are: heating at 350-600℃ for 1-6 hours. The heating temperature is crucial because the main thermal decomposition peak of cellulose is at 300-400℃. Carbonization time is not a primary influencing factor, as long as carbonization is uniform. However, excessively long carbonization times may cause some micropores to close or collapse, affecting the distribution of the pore structure and specific surface area, and also impacting the effectiveness of the subsequent Joule heat treatment.

[0012] Preferably, the heating rate for preheating is 2-20℃ / min. If the heating rate is too fast, the pore structure of the biomass-based closed-cell hard carbon material may be uneven, affecting the subsequent formation of closed pores. A slower heating rate consumes more energy and allows the biomass-based closed-cell hard carbon material to gradually decompose and shrink, forming a denser carbon structure, resulting in a reduction in the number of micropores in the hard carbon precursor.

[0013] Preferably, the instantaneous heating temperature is 1000-2000℃.

[0014] Preferably, the pulse width of Joule heating is instantaneous, ≤60s. "Instantaneous" typically refers to a rapid heating process within an extremely short time (milliseconds or even microseconds); the number of pulses is 1-5, meaning it can undergo 1-5 instantaneous heating cycles. The impact of pulse width: Pulse width (the duration of each pulse) determines the heating intensity and duration experienced by the material within a short time, directly affecting the material's microstructure. Short pulse width: Shorter pulse widths result in instantaneous high-temperature heating followed by rapid cooling. This rapid heating-cooling process can introduce more defects and closed-pore structures into the material while maintaining its amorphous characteristics. Short pulses help suppress graphitization tendency and maintain the disordered structure of hard carbon, thus making them suitable for electrochemical applications requiring high capacity and closed-pore structures. Long pulse width: Longer pulse widths mean longer heating times, resulting in more time for structural rearrangement within the material. This promotes the formation of a more ordered structure of carbon atoms, tending towards graphitization. This heating method typically leads to a reduction in closed pores and a weakening of the microporous structure in the material, making it more suitable for applications requiring high conductivity, but it may reduce the specific surface area and closed pore structure of the material.

[0015] The impact of pulse count: The pulse count determines the cumulative number of heat treatments and the total energy input, playing a crucial role in the overall material properties. Fewer pulses: With fewer pulses, the heat treatment is more concentrated on instantaneous high temperatures. This results in more micropores and defects, forming a loose hard carbon structure, which facilitates electrolyte penetration and improves electrochemical activity. Simultaneously, a low pulse count does not cause severe carbon rearrangement, maintaining a high closed-pore ratio and amorphous structure, but the material's structural uniformity may be low. More pulses: As the pulse count increases, the material has time for partial cooling between pulses, and the overall cumulative heating effect is more significant. This increases the material's order and density, tending to reduce the carbon interlayer spacing, making the material more compact and stable. However, if the carbon interlayer spacing is too low, the diffusion and intercalation of sodium ions will be significantly restricted, leading to a decrease in sodium intercalation capacity and affecting the battery's reversible capacity. Therefore, the pulse count needs to be adjusted specifically based on the hard carbon precursor. In particular, the mentioned hard carbon precursors are applicable within the 1-5 pulse count range, and this range can be appropriately broadened to meet different performance requirements. This flexible pulse control helps optimize the structural properties of biomass-based closed-cell hard carbon materials, further improving their sodium storage performance. In this invention, shorter pulse widths and fewer pulse counts are used to maintain the high closed-cell and defect characteristics of biomass-based closed-cell hard carbon materials through rapid heating-cooling effects, making them suitable for electrochemical energy storage applications.

[0016] Preferably, the biomass is selected from cellulose nanocrystals, corn cobs, bamboo, hazelnut shells, or coconut shells.

[0017] Preferably, corn cobs, bamboo, hazelnut shells or coconut shells are crushed to a particle size ≤75μm before use, that is, crushed and passed through a 200-mesh sieve.

[0018] This invention also protects the biomass-based closed-cell hard carbon material prepared by the above preparation method.

[0019] Preferably, the interlayer spacing of the biomass-based closed-cell hard carbon material is 0.35-0.44 nm.

[0020] The present invention also protects a sodium-ion battery anode material made of a biomass-based closed-pore hard carbon material.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. This invention uses biomass as raw material. First, a preheating pretreatment at 350-600℃ is performed to obtain a hard carbon precursor with a high carbonization capacity structural framework and abundant micropores. Then, the hard carbon precursor is subjected to Joule heat treatment at 1000-2000℃, undergoing instantaneous high-temperature carbonization to rapidly generate closed nanopores, and quickly producing biomass-based closed-pore hard carbon materials with adjustable closed pores, carbon interlayer spacing, and defect structures. This invention proposes an innovative control method, specifically a closed-pore control method for biomass-derived hard carbon materials based on Joule heating. This method combines preheating pretreatment and Joule heating technology, adjusting the preheating pretreatment temperature and the Joule heating temperature to control the pore structure and interlayer spacing of the biomass-based closed-pore hard carbon material, thereby optimizing sodium ion storage performance and enabling the rapid preparation of high-performance biomass-based closed-pore hard carbon materials.

[0023] 2. This invention provides an efficient and simple preparation method. Compared with existing preparation methods, by simply adjusting the preheating and Joule heat treatment temperatures, it is possible to generate hard carbon materials with abundant closed pores, suitable carbon layer spacing, and controllable defect structures while shortening the preparation time and reducing energy consumption.

[0024] 3. The biomass-based closed-cell hard carbon material of this invention exhibits a high initial coulombic efficiency of 93.1% and a high first-cycle reversible capacity of 367 mAh g. -1 It is particularly suitable for high-energy-density sodium-ion batteries and has broad application prospects in the field of energy storage.

[0025] 4. The method of the present invention is versatile and can be applied to the rapid conversion of a variety of biomass raw materials, including cellulose nanocrystals, coconut shells, hazelnut shells, corn cobs and bamboo, providing a new approach for the preparation of high-performance hard carbon materials, and showing broad adaptability and industrialization potential.

[0026] 5. Improving the yield of biomass-based closed-cell hard carbon materials is a key objective of improving the carbonization process in order to achieve higher material utilization and industrial application potential. This invention optimizes the Joule heat treatment technology through preheating pretreatment. This invention significantly improves the yield of biomass-based closed-cell hard carbon materials, making the production process more efficient and reducing the loss of biomass-based closed-cell hard carbon materials. Attached Figure Description

[0027] Figure 1 The diagrams show the pore structure of the biomass-based closed-pore hard carbon materials in Examples 1, 6-7, and Comparative Example 1.

[0028] Figure 2 This is a comparison chart of the total carbonization yield of biomass-based closed-cell hard carbon materials in Examples 1-5 and Comparative Examples 1-5.

[0029] Figure 3 This is a high-resolution transmission electron microscope image of the biomass-based closed-pore hard carbon material from Example 1.

[0030] Figure 4 The sodium storage performance diagrams for the biomass-based closed-cell hard carbon material in Example 10 and the biomass-based hard carbon material in Comparative Example 1 are shown.

[0031] Figure 5 The closed-cell volume diagrams are for examples 1, 8-9, and Comparative Example 6, showing the closed-cell hard carbon materials based on biomass. Detailed Implementation

[0032] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods.

[0033] In this invention, biomass is first preheated, i.e., heated to 350-600℃ at a heating rate of 2-20℃ / min and held for 1-6 hours under an inert atmosphere to obtain a framework with high carbonization capacity and abundant ultra-microporous hard carbon precursor. The structure of the hard carbon precursor can be controlled by adjusting the preheating atmosphere, heating rate, holding temperature, and holding time.

[0034] The preheated hard carbon precursor is placed in a Joule heating device for instantaneous high-temperature treatment to form a biomass-based closed-pore hard carbon material with abundant closed pores, suitable carbon layer spacing and defect structure. The structure of the biomass-based closed-pore hard carbon material is controlled by adjusting the Joule heating temperature, pulse width and pulse number.

[0035] The suitable interlayer spacing for carbon is generally in the range of 0.37 nm to 0.40 nm. This spacing is larger than the standard interlayer spacing of graphite (approximately 0.335 nm), and has the following advantages:

[0036] 1. Sodium ion intercalation and diffusion: A suitable, larger interlayer spacing provides smoother intercalation and diffusion channels for sodium ions, reducing diffusion resistance. This is crucial for sodium ion storage performance because sodium ions have a larger radius than lithium ions, and a wider spacing is more suitable for their intercalation.

[0037] 2. Closed-cell filling and stability: Wider interlayer spacing helps to form a stable closed-cell structure, allowing sodium ions to be stored more effectively in the closed pores and improving the low potential plateau capacity.

[0038] 3. Cyclic stability: Appropriate interlayer spacing can also buffer the volume changes during sodium ion insertion and release, reduce structural stress, extend the service life of biomass-based closed-cell hard carbon materials, and improve cycle performance.

[0039] Defective structures can increase specific surface area, which is beneficial for the adsorption of sodium ions.

[0040] The technical solution of the present invention will be further studied using examples and comparative examples. The specific research methods and results are shown below:

[0041] Example 1

[0042] The preparation method of biomass-based closed-pore hard carbon materials includes the following steps:

[0043] S1. Preheating and pretreatment: Cellulose nanocrystals are placed in a tube furnace and heated to 600°C at a heating rate of 5°C / min. The temperature is maintained for 3 hours under a nitrogen atmosphere to obtain a hard carbon precursor rich in micropores.

[0044] S2. Joule thermal carbonization: The hard carbon precursor is placed in a Joule thermal carbonization device, instantaneously heated to 1500℃, and then directly cooled to obtain a biomass-based closed-cell hard carbon material, denoted as HC600-J-1500.

[0045] Example 2

[0046] The preparation method of biomass-based closed-pore hard carbon materials includes the following steps:

[0047] S1. Preheating and pretreatment: Wash, dry and crush coconut shells to a particle size of ≤75μm to obtain coconut shell powder. Heat the coconut shell powder to 600℃ in a tube furnace at a heating rate of 5℃ / min and keep it at that temperature for 3h under a nitrogen atmosphere to obtain a hard carbon precursor rich in micropores.

[0048] S2. Joule thermal carbonization: The hard carbon precursor is placed in a Joule thermal carbonization device, instantaneously heated to 1500℃, and then directly cooled to obtain a biomass-based closed-cell hard carbon material.

[0049] Example 3

[0050] The preparation method of biomass-based closed-pore hard carbon materials includes the following steps:

[0051] S1. Preheating and pretreatment: Wash, dry and crush the corn cobs to obtain corn cob powder with a particle size ≤75μm. Heat the corn cob powder to 600℃ in a tube furnace at a heating rate of 5℃ / min and keep it at that temperature for 3h under an argon atmosphere to obtain a hard carbon precursor rich in micropores.

[0052] S2. Joule thermal carbonization: The hard carbon precursor is instantaneously heated to 1500℃ in a Joule thermal carbonization device and then directly cooled to obtain a biomass-based closed-cell hard carbon material.

[0053] Example 4

[0054] The preparation method of biomass-based closed-pore hard carbon materials includes the following steps:

[0055] S1. Preheating and pretreatment: Wash, dry and crush the bamboo to obtain bamboo powder with a particle size ≤75μm. Heat the bamboo powder to 600℃ in a tube furnace at a heating rate of 5℃ / min and keep it at that temperature for 3h under a nitrogen atmosphere to obtain a hard carbon precursor rich in micropores.

[0056] S2. Joule thermal carbonization: The hard carbon precursor is placed in a Joule thermal carbonization device, instantaneously heated to 1500℃, and then directly cooled to obtain a biomass-based closed-cell hard carbon material.

[0057] Example 5

[0058] The preparation method of biomass-based closed-pore hard carbon materials includes the following steps:

[0059] S1. Preheating and pretreatment: Wash, dry and crush the hazelnut shells to obtain hazelnut shell powder with a particle size ≤75μm. Heat the hazelnut shell powder to 600℃ in a tube furnace at a heating rate of 5℃ / min and keep it at that temperature for 3h under a nitrogen atmosphere to obtain a hard carbon precursor rich in micropores.

[0060] S2. Joule heating carbonization: The hard carbon precursor is placed in a Joule heating device and heated instantaneously at 1500℃, then directly cooled to obtain a biomass-based closed-cell hard carbon material.

[0061] Example 6

[0062] The preparation method of biomass-based closed-pore hard carbon materials includes the following steps:

[0063] S1. Preheating and pretreatment: Cellulose nanocrystals are placed in a tube furnace and heated to 350°C at a heating rate of 5°C / min. The temperature is maintained for 3 hours under a nitrogen atmosphere to obtain a hard carbon precursor rich in micropores.

[0064] S2. The hard carbon precursor is placed in a Joule heating carbonization device, instantaneously heated at 1500℃, and then directly cooled to obtain a biomass-based closed-cell hard carbon material, denoted as HC350-J-1500.

[0065] Example 7

[0066] The preparation method of biomass-based closed-pore hard carbon materials includes the following steps:

[0067] S1. Preheating and pretreatment: Cellulose nanocrystals are placed in a tube furnace and heated to 400°C at a heating rate of 5°C / min. The temperature is maintained for 3 hours under a nitrogen atmosphere to obtain a hard carbon precursor rich in micropores.

[0068] S2. The hard carbon precursor is placed in a Joule heating carbonization device, heated instantaneously at 1500℃, and then directly cooled to obtain a biomass-based closed-cell hard carbon material, denoted as HC400-J-1500.

[0069] Example 8

[0070] The preparation method of biomass-based closed-pore hard carbon materials includes the following steps:

[0071] S1. Preheating and pretreatment: Cellulose nanocrystals are placed in a tube furnace and heated to 600°C at a heating rate of 5°C / min. The temperature is maintained for 3 hours under a nitrogen atmosphere to obtain a hard carbon precursor rich in micropores.

[0072] S2. The hard carbon precursor is placed in a Joule heating carbonization device, instantaneously heated at 1500℃, and then directly cooled to obtain a biomass-based closed-cell hard carbon material, denoted as HC600-J-1000.

[0073] Example 9

[0074] The preparation method of biomass-based closed-pore hard carbon materials includes the following steps:

[0075] S1. Preheating and pretreatment: Cellulose nanocrystals are placed in a tube furnace and heated to 600°C at a heating rate of 5°C / min. The temperature is maintained for 3 hours under a nitrogen atmosphere to obtain a hard carbon precursor rich in micropores.

[0076] S2. The hard carbon precursor is placed in a Joule heating carbonization device and instantaneously heated to 2000℃. After instantaneous heating, it is directly cooled to obtain a biomass-based closed-cell hard carbon material, denoted as HC600-J-2000.

[0077] Example 10

[0078] The preparation method of biomass-based closed-pore hard carbon materials includes the following steps:

[0079] S1. Preheating and pretreatment: Cellulose nanocrystals are placed in a tube furnace and heated to 600°C at a heating rate of 5°C / min. The temperature is maintained for 3 hours under a nitrogen atmosphere to obtain a hard carbon precursor rich in micropores.

[0080] S2. The hard carbon precursor is placed in a Joule thermal carbonization device and heated instantaneously at 1500℃ for 20 seconds, then directly cooled to obtain a biomass-based closed-cell hard carbon material.

[0081] Example 11

[0082] The preparation method of biomass-based closed-pore hard carbon materials includes the following steps:

[0083] S1. Preheating and pretreatment: Cellulose nanocrystals are placed in a tube furnace and heated to 350°C at a heating rate of 2°C / min. The temperature is maintained for 6 hours under a nitrogen atmosphere to obtain a hard carbon precursor rich in micropores.

[0084] S2. The hard carbon precursor is placed in a Joule heating carbonization device and heated instantaneously at 1500℃ for 60 seconds with one pulse to obtain a biomass-based closed-cell hard carbon material.

[0085] Example 12

[0086] The preparation method of biomass-based closed-pore hard carbon materials includes the following steps:

[0087] S1. Preheating and pretreatment: Cellulose nanocrystals are placed in a tube furnace and heated to 600°C at a heating rate of 20°C / min. The temperature is maintained for 1 hour under a nitrogen atmosphere to obtain a hard carbon precursor rich in micropores.

[0088] S2. The hard carbon precursor is placed in a Joule heating carbonization device and instantaneously heated to 2000℃ for 30 seconds with 5 pulses to obtain a biomass-based closed-cell hard carbon material.

[0089] Comparative Example 1

[0090] The preparation method of biomass-based hard carbon materials includes the following steps:

[0091] Cellulose nanocrystals were placed in a Joule heating device and instantaneously heated to 1500℃. After instantaneous heating, they were directly cooled to obtain a biomass-based hard carbon material, denoted as HC25-J-1500.

[0092] Comparative Example 2

[0093] The preparation method of biomass-based hard carbon materials is the same as that of Comparative Example 1, except that cellulose nanocrystals are replaced with coconut shells, and includes the following steps:

[0094] Coconut shells are washed, dried, and pulverized to a particle size of ≤75μm to obtain coconut shell powder. The coconut shell powder is then instantaneously heated at 1500℃ and directly cooled to obtain biomass-based hard carbon material.

[0095] Comparative Example 3

[0096] The preparation method of biomass-based hard carbon materials is the same as that of Comparative Example 1, except that cellulose nanocrystals are replaced with bamboo, and includes the following steps:

[0097] Bamboo is washed, dried and crushed to obtain bamboo powder with a particle size ≤75μm. The bamboo powder is then instantaneously heated at 1500℃ and directly cooled to obtain biomass-based hard carbon material.

[0098] Comparative Example 4

[0099] The preparation method of biomass-based hard carbon materials is the same as that of Comparative Example 1, except that cellulose nanocrystals are replaced with corn cobs, and includes the following steps:

[0100] Corn cobs are washed, dried and crushed to obtain corn cob powder with a particle size ≤75μm. The corn cob powder is then instantaneously heated at 1500℃ and directly cooled to obtain biomass-based hard carbon material.

[0101] Comparative Example 5

[0102] The preparation method of biomass-based hard carbon materials is the same as that of Comparative Example 1, except that cellulose nanocrystals are replaced with hazelnut shells, and includes the following steps:

[0103] Hazelnut shells were washed, dried, and crushed to obtain hazelnut shell powder with a particle size ≤75μm. The hazelnut shell powder was then instantaneously heated at 1500℃ and directly cooled to obtain biomass-based hard carbon material.

[0104] Comparative Example 6

[0105] The preparation method of biomass-based closed-pore hard carbon materials includes the following steps:

[0106] S1. Preheating and pretreatment: Cellulose nanocrystals are placed in a tube furnace and heated to 600°C at a heating rate of 5°C / min. The temperature is maintained for 3 hours under a nitrogen atmosphere to obtain a hard carbon precursor rich in micropores.

[0107] S2. The hard carbon precursor is placed in a Joule heating carbonization device and instantaneously heated to 2500℃. After instantaneous heating, it is directly cooled to obtain a biomass-based closed-cell hard carbon material, denoted as HC600-J-2500.

[0108] Examples 1-12 of this invention all yielded biomass-based closed-cell hard carbon materials with abundant and uniform closed pores and suitable interlayer spacing. The following research uses the biomass-based closed-cell hard carbon materials of Examples 1-10 as examples, and compares them with Comparative Examples 1-6. Specific research methods and results are shown below:

[0109] Performance comparison at the same Joule heat treatment temperature (1500℃) with different preheating temperatures:

[0110] Figure 1The diagram shows the pore structure under the same Joule heat treatment but different preheating and pretreatment conditions. Figure 1 The results show that the closed-pore structure inside the biomass-based closed-pore hard carbon material increases with increasing preheating temperature. Higher preheating temperatures (e.g., 600℃) initially generate a large number of micropores, and Joule heat treatment further leads to the formation of more closed nanopores. Compared to the untreated biomass-based hard carbon material in Comparative Example 1, this increase in closed pores significantly improves the sodium ion storage capacity.

[0111] In summary, the structures of biomass-based closed-cell hard carbon materials exhibit significant differences at different Joule heat treatment temperatures. A Joule heat treatment temperature of 1500℃ achieves a good balance between closed-cell structure, interlayer spacing, and defect level, which helps improve sodium ion storage performance. While higher temperatures (2000℃) increase graphitization and conductivity, the reduced amount of closed cells and narrower interlayer spacing are detrimental to sodium ion intercalation and storage.

[0112] The yields of Examples 1-5 and Comparative Examples 1-5 are as follows: Figure 2 As shown, the results indicate that preheating pretreatment can significantly improve the stability of biomass-based closed-cell hard carbon materials, giving them higher carbonization capabilities and thus reducing carbon loss during subsequent Joule heat treatment.

[0113] Figure 3 The pore structure of biomass-based closed-pore hard carbon materials was obtained using transmission electron microscopy (TEM). Figure 3 The results show that the biomass-based closed-pore hard carbon material has sufficient closed pores. These closed pores are surrounded by carbon layers, forming a stable nanostructure that is conducive to the storage of sodium ions.

[0114] Figure 4 This is a comparison of the electrochemical performance of the biomass-based closed-cell hard carbon material of Example 10 and the biomass-based hard carbon material of Comparative Example 1. The electrochemical performance was tested as follows: the biomass-based closed-cell hard carbon material of Example 10 and the biomass-based hard carbon material of Comparative Example 1 were mixed with sodium alginate (mass ratio 95:5) in deionized water, and the slurry was coated onto copper foil. After drying overnight, the mixture was sliced ​​and used as the working electrode. It was then assembled with a sodium sheet to form a half-cell. The electrolyte in the half-cell was 1.0 mol / L. -1 A solution of NaPF6 in diethanol dimethyl ether at 25 mA g -1 Under constant current density, charge-discharge cycles are performed.

[0115] Figure 4 The results show that the biomass-based closed-pore hard carbon material in Example 1 exhibits an initial coulombic efficiency of 93.1% and a first-cycle reversible capacity of 367 mAh g⁻¹ in a sodium-ion battery.-1 Comparative Example 1: The initial coulombic efficiency of the biomass-based hard carbon material was 64.7%, and the first-cycle reversible capacity was 142 mAh g. -1 Compared with Comparative Example 1, the electrochemical performance of Example 1 was significantly improved.

[0116] Comparison of performance at different Joule heat treatment temperatures with the same preheating temperature (600℃):

[0117] Figure 5 Diagrams of closed-cell structures under different Joule heat treatments and the same preheating pretreatment conditions. Figure 5 The results show that a lower preheating temperature (1000℃) generates fewer closed-cell structures. As the preheating temperature increases, the number of closed pores increases significantly, with larger pore sizes and more uniform distribution, indicating that rapid thermal shock at this temperature effectively promotes the conversion of micropores into closed pores. However, due to the carbon layer rearrangement caused by high temperatures, the interlayer spacing further decreases when the temperature reaches 2000℃ and 2500℃. This increases the graphitization degree of the biomass-based closed-cell hard carbon material, resulting in a more compact structure that restricts the insertion and extraction of sodium ions, adversely affecting its electrochemical performance.

[0118] Compared with the prior art publication number CN118771351A, entitled "A Method for Rapid Preparation of Hard Carbon Anode Material and the Obtained Product and Sodium-ion Battery", the initial coulombic efficiency and reversible capacity of the present invention are higher than any embodiment of publication number CN118771351A. This indicates that under the preparation conditions of the present invention, by controlling the preheating pretreatment and Joule thermal carbonization conditions, superior electrochemical performance is achieved, resulting in better technical effects.

[0119] Furthermore, to strike a balance between performance and production costs, this invention introduces an optimized preheating pretreatment scheme. Compared to traditional activation and acid washing methods, this preheating pretreatment scheme can control the pore structure with fewer processing steps, effectively improving yield and the proportion of closed-cell materials. This preheating pretreatment enhances the carbonization ability of biomass-based closed-cell hard carbon materials by controlling temperature and time, making the structure more heat-resistant and reducing excessive decomposition during Joule heat treatment. Simultaneously, this scheme avoids the strong corrosive effects of activators and potential pore damage during acid washing, resulting in a more uniform pore size distribution in the biomass-based closed-cell hard carbon materials. This facilitates the construction of closed-cell structures and improves the specific capacity and first-cycle coulombic efficiency of biomass-based closed-cell hard carbon materials. In addition, it reduces the operation time and cost required by the multiple processing steps in patent CN118771351A, and reduces wastewater discharge, thereby significantly reducing production costs while improving the performance of biomass-based closed-cell hard carbon materials, achieving an effective balance between performance and economy.

[0120] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing closed-cell hard carbon materials based on biomass, characterized in that, Includes the following steps: In an inert atmosphere, biomass is heated to 350-600 °C at a heating rate of 2-20 °C / min and held at that temperature for 1-6 h for preheating pretreatment to obtain a hard carbon precursor with a carbonization-capable structural framework and ultra-micropores. In an inert atmosphere, the hard carbon precursor is instantaneously heated by Joule heat treatment at 1000-2000 ℃ to rapidly generate closed nanopores, thus obtaining a biomass-based closed-pore hard carbon material. The biomass is cellulose nanocrystals.

2. The method for preparing biomass-based closed-cell hard carbon material according to claim 1, characterized in that, Preheating treatment is performed at 600℃.

3. The method for preparing biomass-based closed-cell hard carbon material according to claim 1, characterized in that, It was subjected to Joule heat treatment at 1500℃.

4. The method for preparing biomass-based closed-cell hard carbon material according to claim 1, characterized in that, The pulse width of the Joule heat treatment is instantaneous, with a pulse width ≤ 60 s and a pulse count of 1-5 times.

5. A biomass-based closed-cell hard carbon material prepared by the preparation method according to any one of claims 1-4.

6. The biomass-based closed-cell hard carbon material according to claim 5, characterized in that, The interlayer spacing of biomass-based closed-pore hard carbon materials is 0.35-0.44 nm.

7. A sodium-ion battery anode material, characterized in that, Made from the biomass-based closed-cell hard carbon material as described in claim 5.

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