Sodium fluoride doped phenol-containing biomass-based hard carbon material as well as preparation and application thereof

Abstract

The invention discloses a sodium fluoride doped phenol-containing biomass-based hard carbon material as well as a preparation method and application thereof, and belongs to the technical field of sodium ion battery electrode materials. The preparation method comprises the following steps: mixing a phenolic biomass precursor, a fluorine-containing organic matter, a sodium element inorganic compound and a solvent, putting the mixture into a reactor for heating reaction, then drying a synthetic product, and completing carbonization under a high-temperature condition. The hard carbon material prepared by the preparation method realizes uniform dispersion of sodium fluoride by virtue of a hydrogen bond formed by a phenolic hydroxyl group and sodium fluoride, solves the problem that sodium fluoride in a traditional sodium ion battery depends on side reaction of an electrolyte, and has double advantages of excellent sodium ion transmission performance and controllable process. The method has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery electrode materials technology, specifically to a class of sodium fluoride-doped phenolic biomass-based hard carbon materials, their preparation methods, and applications. Background Technology

[0002] Against the backdrop of accelerated global energy transition and surging demand for large-scale energy storage and electric vehicles, low cost and high reliability have become the core driving forces for the commercialization of rechargeable battery technology. Sodium-ion batteries, as a complementary technology to lithium-ion batteries, offer cost advantages stemming from a stable raw material supply chain, low-cost core material design, and compatible production processes, reducing unit capacity cost by approximately 30%. Hard carbon, with its multi-dimensional sodium-ion storage mechanism, has become the mainstream anode material for sodium-ion batteries.

[0003] Recent research has focused on microstructure regulation and electrical performance optimization: researchers have successfully improved the closed-pore density and graphitization degree of hard carbon materials using iron-based catalyst-assisted chemical vapor deposition; and researchers have prepared hard carbon materials with uniform pore distribution and high graphitization degree by controlling the spatiotemporal evolution of the synthesis process through an electrothermal coupling strategy. These research results provide important insights for the development of anode materials for sodium-ion batteries.

[0004] In sodium-ion batteries, sodium fluoride, formed through interfacial reactions during cycling, plays a crucial role in enhancing electrochemical performance by optimizing interfacial stability and improving ionic conductivity. Adjusting the electrolyte composition allows fluorinated electrolytes to decompose and produce sodium fluoride during cycling, thereby forming a uniform and dense solid electrolyte interphase (SEI) film. However, the formation of this sodium fluoride is entirely dependent on post-cycling interfacial reactions. Furthermore, the synthesis of hard carbon requires high temperatures and expensive equipment, significantly increasing production costs and hindering industrial applications. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of sodium fluoride formation relying on electrolyte side reactions and uneven dispersion in electrode materials in existing sodium-ion batteries. This invention provides a class of sodium fluoride-doped phenolic biomass-based hard carbon materials, their preparation methods, and applications. It also provides a self-supporting copper-based electrode, its preparation, and applications. The hard carbon materials prepared by this method achieve uniform sodium fluoride doping and improved sodium ion transport performance, while also offering advantages such as controllable processes and readily available raw materials.

[0006] In proposing the inventive concept of "sodium fluoride-doped phenolic biomass-based hard carbon material," the innovative theoretical basis of this invention lies in three aspects: First, crystalline NaF possesses high Young's modulus, excellent electronic insulation, and resistance to dissolution, enabling the construction of robust and stable inorganic SEI films. This solves the problems of easy damage and poor ion conduction in traditional organic SEI films. Simultaneously, nanoscale crystalline NaF can reduce the sodium ion desolvation activation energy and accelerate interfacial ion transport kinetics. Second, the doping-structure synergistic optimization theory allows NaF doping to introduce defect sites into phenolic hard carbon, increasing the active centers for sodium ion adsorption. Simultaneously, it regulates the carbon interlayer spacing, balancing capacitive storage in the slope region and embedded storage in the plateau region, thereby improving the overall sodium storage capacity. Third, the biomass carbon-based material modification theory allows phenolic hydroxyl groups to form weak interactions with NaF, providing anchoring points for uniform NaF dispersion and achieving optimized interfacial compatibility between the dopant and the carbon matrix.

[0007] The technical difficulties / challenges that this invention needs to overcome are: firstly, the difficulty in controlling the interface of uniform NaF doping; secondly, the difficulty in balancing the doping amount and carbon structure; and thirdly, the difficulty in controlling the pore structure and carbon layer order of hard carbon materials.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] This invention provides a class of sodium fluoride-doped phenolic biomass-based hard carbon materials, wherein the sodium fluoride doping amount in the hard carbon material is 0.2%-2%, and the specific surface area is 1-300 m². 2 / g, porosity 20%-50%, sodium ion diffusion coefficient ≥1×10 - 6 cm 2 / s, which combines good structural stability with ion transport capability.

[0010] The present invention also provides a method for preparing sodium fluoride-doped phenolic biomass-based hard carbon material as described above. The preparation method includes: using phenolic biomass precursors, fluorine-containing organic compounds, sodium element inorganic compounds and solvents as raw materials, and preparing sodium fluoride-doped phenolic biomass-based hard carbon material through steps such as heating, drying, heating and carbonization.

[0011] In one specific embodiment, the preparation method specifically includes the following steps:

[0012] The first step is to mix raw materials such as phenolic biomass precursors, fluorine-containing organic compounds, sodium-containing inorganic compounds, and solvents;

[0013] The second step is to heat the raw materials mixed in the first step to obtain the synthetic product;

[0014] The third step involves drying and heating the synthesized product obtained in the second step to complete carbonization, thereby preparing sodium fluoride-doped phenolic biomass-based hard carbon material.

[0015] In the first step, the phenolic biomass precursor refers to the product obtained by mixing phenolic compounds with biomass and then heat-treating it.

[0016] Wherein, the phenolic compound refers to a compound having the structure of Formula 1:

[0017] Formula 1

[0018] Where n = 0-22; m = 0-46; R = -O, -OH, -SO3H, -SO3Na, -SH.

[0019] The biomass includes one or more of the following: lignocellulose, starch, polysaccharides, glucose, fructose, galactose, mannose-maltose, lactose, cellobiose, furfural, and 5-hydroxymethylfurfural; preferably, it is glucose.

[0020] The mass ratio of the phenolic compound to the biomass is 10:1 to 1:10; preferably, it is 3:1 to 1:3.

[0021] The temperature used in the heat treatment is 50-200℃.

[0022] In the first step, the preferred phenolic biomass precursor is cashew phenol glucose resin.

[0023] In the first step, the fluorinated organic compound includes one or more of fluorinated olefins, fluorinated aromatics, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP); preferably, it is polyvinylidene fluoride (PVDF), and the molecular weight of the polyvinylidene fluoride is 1 million to 2 million.

[0024] In the first step, the inorganic sodium compound includes one or more of sodium hydroxide, sodium carbonate, and sodium bicarbonate; preferably, it is sodium hydroxide.

[0025] In the first step, the solvent includes one or more of ethanol, methanol, isopropanol, ethylene glycol, etc.; preferably, it is ethanol with a volume fraction ≥99.5%.

[0026] In the first step, the mass / volume ratio of the phenolic biomass precursor, the fluorine-containing organic compound, the sodium element inorganic compound, and the solvent is (2-3g):(2-3g):(0.1-0.2g):(4-5mL); preferably, it is 2g:2g:0.1g:4mL.

[0027] In the first step, the mixing time is 1-2 hours.

[0028] In the first step, the mixing process adopts magnetic stirring, with a stirring rate of 300-500 r / min and a stirring time of 30-60 minutes, to ensure that the raw materials are evenly dispersed.

[0029] In the second step, the heating temperature is 160-200℃; preferably, it is 180℃.

[0030] In the second step, the heating time is 18-24 hours; preferably, it is 24 hours.

[0031] In the third step, the drying method includes one or more of vacuum drying, forced air drying, and freeze drying; preferably, it is vacuum drying.

[0032] The parameters / conditions and preferred parameters for each drying method are as follows: 1. Vacuum drying (preferred): Vacuum degree controlled at -0.08~-0.1MPa, drying temperature at 60~80℃, drying time at 4~8h; preferred parameters are vacuum degree -0.095MPa, temperature 80℃, and time 8h. Under these conditions, the vacuum environment accelerates the evaporation of ethanol solvent, the low-oxygen atmosphere prevents the oxidation of phenolic precursors, and the moderate temperature prevents NaF from migrating and agglomerating due to local overheating, while ensuring the initial formation of the internal pore structure of the material. 2. Blower air drying: Air velocity at 1~3m / s, drying temperature at 70~90℃, drying time at 8~12h; preferred parameters are air velocity at 2m / s, temperature at 80℃, and time at 10h. 3. Freeze-drying: Pre-freezing temperature is -40~-20℃, pre-freezing time is 2~4h, vacuum degree is -0.09~-0.1MPa, sublimation drying temperature is 20~40℃, and total drying time is 12~24h; the preferred parameters are pre-freezing temperature -30℃, pre-freezing time 3h, vacuum degree -0.098MPa, sublimation temperature 30℃, and total drying time 18h. This method can preserve the porous structure of the material to the greatest extent, but the cost is relatively high, and it is suitable for small-batch preparation in the laboratory or for scenarios with extremely high requirements for pore structure.

[0033] The third step is preferably performed by heating in a nitrogen atmosphere.

[0034] The nitrogen atmosphere has a nitrogen purity of ≥99.99%, and the nitrogen flow rate is controlled at 50-100 mL / min during carbonization to avoid material oxidation.

[0035] In the third step, the heating rate is 2-10℃ / minute; preferably, it is 5℃ / minute.

[0036] In the third step, the heating temperature is 800-1600℃; preferably, it is 1000℃.

[0037] In the third step, the heating time is 1-2 hours; preferably, it is 1 hour.

[0038] In one specific embodiment, the preparation method includes: thoroughly mixing cashew phenol glucose resin, polyvinylidene fluoride, sodium hydroxide, and ethanol, placing the mixture in a reactor, and heating it at 180°C for 24 hours; subsequently drying the synthesized product and heating it to 1000°C for 1 hour at a heating rate of 5°C / min under a nitrogen atmosphere to complete carbonization and obtain sodium fluoride-doped hard carbon material. The preferred proportions of the raw materials are: 2g cashew phenol glucose resin, 2g polyvinylidene fluoride, 0.1g sodium hydroxide, and 4mL ethanol. The hydroxyl groups of the cashew phenol glucose resin can form hydrogen bonds with sodium fluoride, thereby achieving uniform dispersion of sodium fluoride within the hard carbon framework.

[0039] The reactor is a hydrothermal reactor lined with polytetrafluoroethylene, and the pressure is controlled at 1-2 MPa during the reaction.

[0040] This invention also provides a sodium fluoride-doped phenolic biomass-based hard carbon material prepared by the method described above. The sodium fluoride doping amount in the hard carbon material is 0.2%-2%, and the sodium fluoride is uniformly dispersed in the hard carbon framework via hydrogen bonds formed by the hydroxyl groups of cashew phenols, with a specific surface area of ​​1-300 m². 2 / g, porosity 20%-50%, sodium ion diffusion coefficient ≥1×10 -6 cm 2 / s, which combines good structural stability with ion transport capability.

[0041] The present invention also provides a sodium-ion battery negative electrode (conventional copper current collector electrode), wherein the sodium-ion battery negative electrode comprises sodium fluoride doped phenolic biomass-based hard carbon material as described above.

[0042] Furthermore, the sodium-ion battery negative electrode also includes conductive agents and binders.

[0043] In a specific embodiment of the present invention, the mass ratio of sodium fluoride-doped phenolic biomass-based hard carbon material: conductive agent: binder ranges from 7:2:1 to 9.4:0.3:0.3, preferably 8:1:1. At this preferred ratio, the hard carbon material can fully utilize its sodium storage activity, the conductive agent forms a continuous conductive network, and the binder ensures the stability of the electrode structure. These three components work synergistically to achieve a balance between high capacity and long cycling time. If the proportion of hard carbon material is less than 7%, the electrode capacity will decrease significantly; if the proportion of hard carbon material is greater than 94%, problems such as poor electrode formability and easy cracking will easily occur.

[0044] In one specific embodiment of the present invention, the conductive agent includes one or more of Super-P (superconducting carbon black), acetylene black (AB), Ketjen black (KB), and carbon fiber (VGCF); preferably, it is Super-P, i.e., with a particle size of 20~40nm and a specific surface area of ​​50~100m². 2 / g, Super-P with conductivity ≥100S / m. Among them, acetylene black has a high cost-performance ratio and is suitable for mass production; Ketjen black has better conductivity (conductivity ≥500S / m) and is suitable for high-rate battery scenarios. It can be selected according to the battery performance requirements. In order to balance cost and performance, this invention prioritizes Super-P.

[0045] In one specific embodiment of the present invention, the binder includes one or more of sodium alginate (SA), sodium carboxymethyl cellulose (CMC), xanthan gum, guar gum, etc.; preferably, it is sodium alginate, that is, sodium alginate with a molecular weight of 100,000 to 300,000, a solid content of ≥98%, and good water solubility (viscosity of 1wt% aqueous solution at 25°C is 500 to 1000 mPa·s). Among them, sodium carboxymethyl cellulose has similar properties to sodium alginate and has strong interfacial bonding with hard carbon materials, making it a commonly used alternative; compared with organic binders such as polyvinylidene fluoride (PVDF), sodium alginate, as a natural polymer material, has the advantages of being environmentally friendly and having low cost (about 1 / 5 of PVDF), and has good dispersibility in aqueous slurries, avoiding the use of toxic solvent NMP, making it the preferred binder of the present invention.

[0046] This invention also provides a method for preparing the sodium-ion battery anode, which uses cashew phenol glucose resin as a carbon source, polyvinylidene fluoride (PVDF) as a dual reagent with both carbon and fluorine source functions, sodium hydroxide as a sodium source, and ethanol as a dispersion medium. First, raw materials are weighed according to a preferred ratio of 2g cashew phenol glucose resin, 2g PVDF, 0.1g sodium hydroxide, and 4mL ethanol. These are placed in a closed reactor and thoroughly stirred to form a homogeneous system. The system is then kept at 180°C for 24 hours to complete the solvothermal reaction. The reaction product is vacuum dried to remove residual solvent. The dried precursor is then placed in a tube furnace under a nitrogen protective atmosphere and heated to 1000°C at a heating rate of 5°C / min for 1 hour to complete carbonization, obtaining sodium fluoride-doped hard carbon material. Finally, the hard carbon... Materials: A slurry was prepared by mixing Super-P and sodium alginate (SA) in a mass ratio of 8:1:1. This slurry was coated onto the surface of a copper foil current collector and then dried and rolled to form a sodium-ion battery anode. The core of this method lies in utilizing the hydroxyl groups of cashew phenol glucose resin to form hydrogen bonds with sodium fluoride, thereby achieving uniform dispersion of sodium fluoride in a hard carbon framework. By simplifying the process steps through the multifunctional integration of PVDF, and combining the precise control of parameters such as temperature and time during solvothermal and carbonization processes, this method effectively solves the problems of uneven dispersion of inorganic dopants, high carbon source cost, and environmental unfriendliness in traditional preparation methods. It significantly improves the specific capacity, cycle stability, and initial coulombic efficiency of the anode material, while also possessing the advantages of being green, environmentally friendly, and low-cost, providing an effective path for the high-performance preparation of sodium-ion battery anodes.

[0047] The present invention also provides the application of the sodium fluoride-doped phenolic biomass-based hard carbon material, or the electrode, or the method described above, in the development / design / screening / preparation of hard carbon materials, sodium-ion battery anode materials, sodium-ion battery anodes, sodium-ion batteries, supercapacitors, etc.

[0048] In one specific embodiment, the application includes the use of sodium fluoride-doped phenolic biomass-based hard carbon materials as described above in the anode of sodium-ion batteries. When used as an anode material, it can effectively improve the cycle stability and rate performance of sodium-ion batteries, and is suitable for large-scale application in the field of energy storage batteries.

[0049] The beneficial effects of the present invention through the above technical solution include:

[0050] In existing technologies, sodium fluoride required for sodium-ion batteries is mostly generated through side reactions of electrolyte decomposition during battery cycling. This not only results in low generation efficiency and poor controllability, but also leads to sodium fluoride agglomeration, causing uneven dispersion and severely affecting sodium ion transport performance. Some active doping methods often require complex pretreatment processes or high-temperature, high-pressure reaction conditions, resulting in high energy consumption and cost. This invention utilizes the synergistic effect of cashew phenol glucose resin, polyvinylidene fluoride, and sodium hydroxide to achieve in-situ uniform doping of sodium fluoride in hard carbon materials under conventional hydrothermal and carbonization conditions. This eliminates the need for additional high-energy reaction equipment, resulting in lower energy consumption, a simple preparation process, and controllable reaction cycle. Crucially, the hydrogen bonding between the hydroxyl groups of cashew phenol glucose resin and sodium fluoride effectively inhibits sodium fluoride agglomeration, ensuring uniform dispersion within the hard carbon framework and significantly improving the sodium ion diffusion coefficient of the material. Meanwhile, the raw material cashew phenol glucose resin used in this method is widely available and inexpensive, and polyvinylidene fluoride has both bonding and pore-forming functions. The hard carbon material prepared has a suitable specific surface area and porosity. When used as a negative electrode material for sodium-ion batteries, it can significantly improve the cycle stability and rate performance of the battery and has the potential for large-scale application. Attached Figure Description

[0051] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0052] Figure 1 This is a schematic diagram of the hard carbon preparation method of the present invention.

[0053] Figure 2 This is the X-ray diffraction pattern of the hard carbon obtained by this invention.

[0054] Figure 3 This is a transmission electron microscope image of the hard carbon obtained by this invention.

[0055] Figure 4 This is the X-ray photoelectron spectrum of the hard carbon obtained by this invention.

[0056] Figure 5 Transmission electron microscope image of the electrode of the hard carbon battery assembled by the present invention after cycling at a current density of 0.1 A / g.

[0057] Figure 6 This is an X-ray photoelectron diagram of the electrode of the battery assembled from the hard carbon prepared in this invention after cycling at a current density of 0.1 A / g.

[0058] Figure 7This is an atomic force microscope image of the electrode of the battery assembled from the hard carbon prepared in this invention after cycling at a current density of 0.1 A / g.

[0059] Figure 8 This is a schematic diagram of the comparative sample preparation method of the present invention.

[0060] Figure 9 This is the X-ray diffraction pattern of the comparative sample obtained by this invention.

[0061] Figure 10 This is a transmission electron microscope image of the comparative sample obtained in this invention.

[0062] Figure 11 This is the X-ray photoelectron spectrum of the comparative sample obtained by this invention.

[0063] Figure 12 Transmission electron microscope image of the electrode of the comparative sample prepared in this invention after cycling at a current density of 0.1 A / g.

[0064] Figure 13 This is an X-ray photoelectron energy map of the electrodes of the comparative sample prepared in this invention after cycling at a current density of 0.1 A / g.

[0065] Figure 14 This is an atomic force microscope image of the electrode of the comparative sample prepared in this invention after being cycled at a current density of 0.1 A / g. Detailed Implementation

[0066] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and 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 in this invention.

[0067] The present invention will be described in detail below through specific embodiments, but the scope of protection of the present invention is not limited to these embodiments.

[0068] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0069] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0070] This invention relates to the field of sodium-ion battery electrode materials, specifically to a type of sodium fluoride-doped phenolic biomass-based hard carbon material and its preparation method. The preparation method includes: thoroughly mixing 2 grams of cashew phenol glucose resin, 2 grams of polyvinylidene fluoride, 0.1 grams of sodium hydroxide, and 4 ml of ethanol, placing the mixture in a reactor, and heating at 180°C for 24 hours. The synthesized product is then dried and heated to 1000°C for 1 hour under a nitrogen atmosphere at a heating rate of 5°C / min to complete carbonization. The hard carbon material prepared by this method achieves uniform dispersion of sodium fluoride through hydrogen bonds formed between the cashew phenol hydroxyl groups and sodium fluoride, solving the problem of sodium fluoride formation dependent on electrolyte side reactions in traditional sodium-ion batteries, and possessing both superior sodium ion transport performance and controllable process control.

[0071] In the following examples, the cashew phenol used was synthesized from phenol (Maclean's, analytical grade), sodium hydroxide (Sinopharm Chemical Reagent Co., Ltd., analytical grade) and formaldehyde (Maclean's, analytical grade); polyvinylidene fluoride (PVDF) was a commercially available product with a molecular weight of 1.8 million (Aladdin, analytical grade); sodium hydroxide was analytical grade (Sinopharm Chemical Reagent Co., Ltd.); ethanol was anhydrous ethanol with a volume fraction of 99.7% (Sinopharm Chemical Reagent Co., Ltd.); and nitrogen gas had a purity of 99.999% (commercially available industrial nitrogen gas).

[0072] In the following embodiments, the sodium fluoride doping amount was measured by energy-dispersive X-ray spectroscopy (EDS); the specific surface area was determined by the Brunauer-Emmett-Teller (BET) method; the sodium ion diffusion coefficient was measured by intermittent galvanostatic titration (GITT), which involves applying a small current pulse to the electrode and recording the voltage response, and then calculating the diffusion coefficient using Fick's second law; the material phase was characterized by X-ray diffraction (XRD); and the microstructure was observed by scanning electron microscopy (SEM).

[0073] Example 1

[0074] 1. Raw material preparation and mixing: Accurately weigh 2.0g of cashew nut gum resin (where the mass ratio of cashew nut gum to glucose is 2:1), 2.0g of polyvinylidene fluoride, and 0.1g of sodium hydroxide, and place them in a 50mL polytetrafluoroethylene beaker. Add 4.0mL of anhydrous ethanol. Place the beaker on a magnetic stirrer and stir at a rate of 400r / min for 45 minutes until a homogeneous, viscous mixture without obvious particles is formed.

[0075] 2. Hydrothermal Reaction: Transfer the above mixture to a 50mL PTFE-lined hydrothermal reactor and tighten the outer tank. Place the reactor in a constant temperature oven, set the temperature to 180℃, and maintain the temperature for 24 hours. During the reaction, the pressure inside the reactor will naturally rise to approximately 1.5MPa.

[0076] 3. Product Drying: After the reaction is complete, turn off the power to the oven and allow the reactor to cool naturally to room temperature before opening it. Remove the product from the polytetrafluoroethylene liner, break it into small pieces with a particle size ≤5mm, place them in a vacuum drying oven, and dry them at 90℃ and -0.09MPa for 8 hours to remove residual ethanol and trace amounts of water generated during the reaction, obtaining precursor powder.

[0077] 4. High-temperature carbonization: The dried precursor powder was placed in a graphite boat and then placed in a tube furnace. Nitrogen gas was introduced at a flow rate of 50 mL / min, and the furnace was purged for 30 minutes to remove air. A heating program was then set: the temperature was increased from room temperature to 1000℃ at a rate of 5℃ / min, and held at the target temperature for 1 hour. After the holding period, the heating device was turned off, and nitrogen gas was continued to flow until the tube furnace cooled naturally to room temperature, completing the carbonization process and yielding black sodium fluoride-doped phenolic biomass-based hard carbon material.

[0078] The hard carbon material prepared in Example 1 of this invention was characterized for performance: EDS analysis showed that the sodium fluoride doping content in the hard carbon material was 0.9%. BET analysis showed a specific surface area of ​​7.1 m². 2 / g, porosity 42%; GITT test results show sodium ion diffusion coefficient is 1×10⁻⁶. -6 cm 2 The XRD pattern shows characteristic diffuse peaks of hard carbon and weak characteristic peaks of sodium fluoride (111) and (220) crystal planes, indicating that sodium fluoride has been successfully doped and has not agglomerated significantly; the SEM image shows that the material has a porous three-dimensional structure with no obvious aggregation of sodium fluoride particles.

[0079] Example 2

[0080] 1. Raw material preparation and mixing: Weigh 2.0g of cashew phenol glucose resin (where the mass ratio of cashew phenol to glucose is 1:3), 2.0g of polyvinylidene fluoride, and 0.1g of sodium hydroxide, add 4.0mL of anhydrous ethanol, and stir at 300r / min for 60 minutes to form a homogeneous mixture.

[0081] 2. Hydrothermal reaction: Transfer the mixture to a hydrothermal reactor and keep it at 180°C for 24 hours. The pressure inside the reactor is about 1.4 MPa.

[0082] 3. Product drying: After removing the product, crush it and dry it in a vacuum drying oven at 80℃ and -0.09MPa for 7 hours.

[0083] 4. High-temperature carbonization: The precursor is placed in a tube furnace, the nitrogen flow rate is set to 80 mL / min, and after purging for 30 minutes, the temperature is increased to 1000℃ at 5℃ / min and held for 1 hour. After cooling, hard carbon material is obtained, and carbonization is completed, resulting in black sodium fluoride-doped phenolic biomass-based hard carbon material.

[0084] Performance characterization results: Sodium fluoride doping content is 0.28%, and specific surface area is 18.5 m². 2 / g, porosity 38%, sodium ion diffusion coefficient 2.8×10 -6 cm 2 / s, the material has a porous structure and sodium fluoride is evenly dispersed.

[0085] Example 3

[0086] 1. Raw material preparation and mixing: Weigh 2.0g of cashew phenol glucose resin (where the mass ratio of cashew phenol to glucose is 1:1), 2.0g of polyvinylidene fluoride, and 0.1g of sodium hydroxide, add 4.0mL of anhydrous ethanol, and stir at 500r / min for 30 minutes to form a homogeneous mixture.

[0087] 2. Hydrothermal reaction: Transfer the mixture to a hydrothermal reactor and keep it at 180°C for 24 hours. The pressure inside the reactor is about 2 MPa.

[0088] 3. Product drying: After removing the product, crush it and dry it in a vacuum drying oven at 100℃ and -0.09MPa for 6 hours.

[0089] 4. High-temperature carbonization: The precursor is placed in a tube furnace, the nitrogen flow rate is set to 100 mL / min, and after purging for 30 minutes, the temperature is increased to 1000℃ at 5℃ / min and held for 1 hour. After cooling, hard carbon material is obtained, and carbonization is completed, resulting in black sodium fluoride-doped phenolic biomass-based hard carbon material.

[0090] Performance characterization results: Sodium fluoride doping content is 1.3%, and specific surface area is 240 m². 2 / g, porosity 45%, sodium ion diffusion coefficient 4.2×10 -6 cm 2 / s, the material has a richer pore structure and excellent sodium fluoride dispersion.

[0091] Comparative Example 1

[0092] Physical mixing of materials (mortar mixing): Accurately weigh 2.0g of polyvinylidene fluoride and 0.1g of sodium hydroxide, and place them together in an agate mortar. First, gently grind to initially mix the two raw materials, then increase the grinding intensity and continue grinding for 30 minutes to ensure that the materials are fully in contact and form a mixed powder with uniform particle size and no obvious lumps, thus completing the physical mixing process.

[0093] High-temperature carbonization: The above-ground and mixed powder was directly placed into a graphite boat and then placed in a tube furnace. Nitrogen gas was introduced at a flow rate of 50 mL / min, and the furnace was purged for 30 minutes to completely remove air and prevent oxidation of the material during carbonization. A heating program was then set: the temperature was increased from room temperature to 1000°C at a rate of 5°C / min, and held at the target temperature for 2 hours. After holding, the heating device was turned off, and nitrogen gas was continued until the tube furnace cooled naturally to room temperature, completing the carbonization process and yielding a black control sample carbon material (due to the absence of cashew phenol glucose resin, phenolic biomass components, and the lack of necessary reaction conditions for sodium fluoride formation, no sodium fluoride doping was obtained).

[0094] Performance characterization results: XRD pattern analysis showed only weak, diffuse peaks of amorphous carbon, and no characteristic diffraction peaks of the (111) and (220) crystal planes of sodium fluoride were observed. Both tests confirmed that no sodium fluoride phase was formed in the comparative sample, indicating a sodium fluoride doping content of 0%, a clear difference from the 0.9% doping content in Example 1 of this invention. The main reason for the absence of sodium fluoride formation is that the comparative sample did not contain cashew phenol glucose resin—a key precursor source for sodium fluoride formation in Example 1 of this invention. Physical mixing of polyvinylidene fluoride and sodium hydroxide alone cannot trigger the relevant reactions for sodium fluoride formation.

[0095] BET testing showed that the control sample exhibited superior pore structure characteristics: a specific surface area as high as 770.06 m². 2 / g, which not only far exceeds the 7.1m of Example 1. 2 / g, and the porosity reached 48%, slightly higher than 42% in Example 1. More importantly, the comparative sample showed a single pore size distribution, indicating that its pore structure has good uniformity.

[0096] GITT testing calculated that the sodium ion diffusion coefficient of the control sample was 2 × 10⁻⁶. -7 cm 2 / s. Analysis of the BET test results shows that the high specific surface area and single-pore size distribution of the comparative sample provide ample channels and convenient diffusion paths for sodium ion transport, making its sodium ion diffusion performance superior to that of ordinary carbon materials. However, compared to Example 1 of this invention, due to the lack of sodium fluoride doping to optimize the ion transport interface, its sodium ion diffusion coefficient is still an order of magnitude lower, highlighting the irreplaceable role of sodium fluoride doping in improving the ion transport performance of materials.

[0097] Comparative Example 2

[0098] Physical mixing of materials (mortar mixing): Accurately weigh 2.0g of polyvinylidene fluoride and 0.2g of sodium hydroxide, and place them together in an agate mortar. First, gently grind to initially mix the two raw materials, then increase the grinding intensity and continue grinding for 30 minutes to ensure that the materials are fully in contact and form a mixed powder with uniform particle size and no obvious lumps, thus completing the physical mixing process.

[0099] High-temperature carbonization: The above-ground and mixed powder was directly placed into a graphite boat and then placed in a tube furnace. Nitrogen gas was introduced at a flow rate of 80 mL / min, and the furnace was purged for 30 minutes to completely remove air and prevent oxidation of the material during carbonization. A heating program was then set: the temperature was increased from room temperature to 1000°C at a rate of 5°C / min, and held at the target temperature for 2 hours. After the holding period, the heating device was turned off, and nitrogen gas was continued until the tube furnace cooled naturally to room temperature, completing the carbonization process. The final product was a black control sample carbon material (due to the absence of cashew phenol glucose resin, phenolic biomass components, and the lack of necessary reaction conditions for sodium fluoride formation, no sodium fluoride doping was obtained).

[0100] Performance characterization results: Specific surface area is 640 m² 2 / g, porosity 50%, sodium ion diffusion coefficient 3.6×10 - 7 cm 2 / s

[0101] Comparative Example 3

[0102] Physical mixing of materials (mortar mixing): Accurately weigh 2.0g of polyvinylidene fluoride and 0.1g of sodium hydroxide, and place them together in an agate mortar. First, gently grind to initially mix the two raw materials, then increase the grinding intensity and continue grinding for 30 minutes to ensure that the materials are fully in contact and form a mixed powder with uniform particle size and no obvious lumps, thus completing the physical mixing process.

[0103] High-temperature carbonization: The above-ground and mixed powder was directly placed into a graphite boat and then placed in a tube furnace. Nitrogen gas was introduced at a flow rate of 60 mL / min, and the furnace was purged for 30 minutes to completely remove air and prevent oxidation of the material during carbonization. A heating program was then set: the temperature was increased from room temperature to 1000°C at a rate of 5°C / min, and held at the target temperature for 2 hours. After holding, the heating device was turned off, and nitrogen gas was continued until the tube furnace cooled naturally to room temperature, completing the carbonization process and yielding a black control sample carbon material (due to the absence of cashew phenol glucose resin, phenolic biomass components, and the lack of necessary reaction conditions for sodium fluoride formation, no sodium fluoride doping was obtained).

[0104] Performance characterization results: Specific surface area is 680 m² 2 / g, porosity 50%, sodium ion diffusion coefficient 5.2×10 - 7 cm 2 / s

[0105] Example 4 Test

[0106] Using the hard carbon materials obtained in Examples 1-3 and Comparative Examples 1-3 of this invention as active materials, a negative electrode slurry was prepared with a mass ratio of hard carbon:Super-P:sodium alginate (SA) of 8:1:1. Deionized water was used as the dispersant. After stirring evenly, the slurry was coated onto a copper foil current collector and dried in a vacuum drying oven at 80°C for 12 hours to obtain the hard carbon negative electrode. The active material mass loading of each electrode was controlled to be 1.8-2.2 mg·cm³. -2 .

[0107] All electrochemical performance tests were performed by assembling CR2032 button cells in an argon-filled glove box (water content <0.01 ppm, oxygen content <0.01 ppm). A sodium metal sheet was used as both the counter and reference electrode. The electrolyte was a 1.0 M NaPF6 solution in 1,2-dimethoxyethane (DME) (pure DME as solvent). The separator was made of glass fiber (model: GF / D).

[0108] After the assembled button batteries were left to stand for 8 hours, performance tests were conducted using an electrochemical workstation to measure their specific capacity, initial coulombic efficiency, and cycle stability under constant current charge-discharge conditions of 0.1 A / g. The test voltage range was 0.01–2.0 V. The test results are shown in Table 1.

[0109] Table 1. Electrochemical performance test results of different hard carbon materials

[0110] Example number Initial Coulomb efficiency [%] <![CDATA[Initial discharge specific capacity [mAh g −1 > Embodiment 1 of the present invention 92 335 Embodiment 2 of the present invention 96 320 Embodiment 3 of the present invention 95 315 Comparative Example 1 of the Invention 95 84 Comparative Example 2 of the Invention 98 88 Comparative Example 3 of the present invention 93 90

[0111] As can be seen from the test results in Table 1, the hard carbon material prepared by the method described in this invention exhibits excellent electrochemical performance when applied to the anode of a sodium-ion battery. Specifically, the sample in Example 2 of this invention shows a high initial discharge specific capacity of 320 mAh / g at 0.1 A / g and an initial coulombic efficiency (ICE) of 96%, significantly better than the comparative experimental sample. Compared to existing technologies where hard carbon materials rely on electrolyte side reactions to generate sodium fluoride and suffer from uneven dispersion, this invention utilizes the dual synergistic mechanism of cashew phenol-glucose resin to achieve in-situ uniform doping of sodium fluoride, which not only simplifies the preparation process but also significantly improves the structural stability and ion transport capability of the hard carbon material.

[0112] Furthermore, the transmission electron microscope (TEM) image of the hard carbon material prepared in Example 2 of this invention after 100 cycles at 0.1 A / g is presented (…). Figure 5 After cycling, the electrode surface was covered with a uniform and dense SEI layer with a thickness of approximately 7 nanometers, indicating that electrolyte degradation and side reactions were effectively suppressed; X-ray photoelectron spectroscopy (XPS) depth analysis confirmed this. Figure 6 The SEI film exhibits a highly uniform distribution of chemical composition and elements from the electrolyte side to the electrode side, providing direct evidence of sodium fluoride's effective participation in interface construction; atomic force microscopy (AFM) images ( Figure 7 The results show that the SEI film maintains a uniform and smooth morphology after 100 cycles, fully verifying the material's excellent interfacial stability. This further verifies the material's excellent structural stability and the synergistic value of cardanol and sodium fluoride. This invention provides a feasible path for the development of high-performance hard carbon anode materials for sodium-ion batteries and also offers a new direction for the application of biomass molecules in electrode materials.

[0113] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0114] As used in this invention, the terms "comprising" and "including" are open-ended expressions, meaning they include the contents specified in this invention but do not exclude other aspects.

[0115] As used in this invention, the term "about" when applied to a value indicates that a slight degree of imprecision is permissible in the calculation or measurement of the value (the accuracy of the value by some means; approximately or reasonably close to the value; almost). If, for some reason, the imprecision specified by "about" is not understood in this conventional sense in the art, then "about" as used in this invention at least indicates variation that may be caused by conventional methods of measuring or using such parameters.

[0116] As used in this invention, the term "and / or" includes any one or more of the related listed items and all combinations thereof.

[0117] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A type of sodium fluoride-doped phenolic biomass-based hard carbon material, characterized in that, The sodium fluoride doping content in the hard carbon material is 0.2-2.0%, and the specific surface area is 1-300 m². 2 / g, porosity 20%-50%, sodium ion diffusion coefficient ≥1×10 -6 cm 2 / s.

2. A method for preparing a sodium fluoride-doped phenolic biomass-based hard carbon material, characterized in that, The method Includes the following steps: The first step is to mix the phenolic biomass precursor, the fluorine-containing organic compound, the sodium-containing inorganic compound, and the solvent; The second step is to heat the raw materials mixed in the first step to obtain the synthetic product; The third step involves drying and heating the synthesized product obtained in the second step to complete carbonization, thereby preparing sodium fluoride-doped phenolic biomass-based hard carbon material.

3. The method according to claim 2, characterized in that, In the first step, the phenolic biomass precursor refers to the product obtained by mixing phenolic compounds with biomass and heat treatment; and / or, the fluorinated organic compound includes one or more of fluorinated olefins, fluorinated aromatics, polyvinylidene fluoride, polytetrafluoroethylene, and polyvinylidene fluoride-hexafluoropropylene copolymer; and / or, the sodium element inorganic compound includes one or more of sodium hydroxide, sodium carbonate, and sodium bicarbonate; and / or, the solvent includes one or more of ethanol, methanol, isopropanol, and ethylene glycol; and / or, the mass / volume ratio of the phenolic biomass precursor, fluorinated polymer, sodium element inorganic compound, and solvent is (2-3g):(2-3g):(0.1-0.2g):(4-5mL).

4. The method according to claim 3, characterized in that, The phenolic compounds refer to compounds having the structure of Formula 1 below: Formula 1 Where n = 0-22; m = 0-46; R = -O, -OH, -SO3H, -SO3Na, -SH; And / or, the biomass includes one or more of lignocellulose, starch, polysaccharides, glucose, fructose, galactose, mannose-maltose, lactose, cellobiose, furfural, and 5-hydroxymethylfurfural; and / or, the mass ratio of the phenolic compound to the biomass is 10:1 to 1:10; and / or, the temperature used for the heat treatment is 50-200°C.

5. The method according to claim 2, characterized in that, In the first step, the mixing process is carried out by magnetic stirring at a speed of 300-500 r / min for 30-60 minutes; and / or the mixing time is 1-2 hours.

6. The method according to claim 2, characterized in that, In the second step, the heating temperature is 160-200℃; and / or, the heating time is 18-24 hours; and / or, In the third step, the drying method includes one or more of vacuum drying, forced air drying, and freeze drying; and / or, the heating rate is 2-10℃ / minute; and / or, the heating temperature is 800-1600℃; and / or, the heating time is 1-2 hours.

7. A sodium fluoride-doped phenolic biomass-based hard carbon material prepared by the method according to any one of claims 2-6.

8. The sodium fluoride-doped phenolic biomass-based hard carbon material according to claim 7, characterized in that, The sodium fluoride doping content in the hard carbon material is 0.2%-2%, and the specific surface area is 1-100 m². 2 / g, porosity 20%-50%, sodium ion diffusion coefficient ≥1×10 -6 cm 2 / s.

9. A sodium-ion battery negative electrode, characterized in that, The sodium-ion battery anode comprises sodium fluoride-doped phenolic biomass-based hard carbon material as described in claim 1 or 7.

10. The application of a sodium fluoride-doped phenolic biomass-based hard carbon material according to claim 1 or 7, or a sodium-ion battery anode according to claim 9, in the development / design / screening / preparation of hard carbon materials, sodium-ion battery anode materials, sodium-ion battery anodes, sodium-ion batteries, and supercapacitors.

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