Synergistic preparation method of super-large cylindrical sodium-ion battery material adaptive to NFPP-hard carbon system

Abstract

The invention discloses a synergistic preparation method of a super-large cylindrical sodium-ion battery material adaptive to an NFPP-hard carbon system, and relates to the technical field of preparation of sodium-ion battery materials. The method sequentially comprises the following steps: preparing an NFPP positive electrode precursor, doping and sintering an NFPP positive electrode, pretreating and chambering a hard carbon negative electrode, loading a hard carbon negative electrode metal oxide, coating and modifying a hard carbon negative electrode gel, and cooperatively adapting positive and negative electrode materials, respectively preparing positive and negative electrode plates, and assembling the super-large cylindrical sodium ion battery. The problems that an NFPP-hard carbon system positive electrode is high in residual alkali, the volume of a negative electrode is expanded, and the positive and negative electrode interface adaptability is poor are effectively solved, the prepared material has high discharge capacity, high coulombic efficiency, excellent rate capability and cycling stability, the performance requirements of the super-large cylindrical sodium ion battery are met, preparation process parameters are controllable, raw materials are easy to obtain, and the material is suitable for large-scale production and has wide application prospects. The method has a good application prospect in the field of new energy storage.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery material preparation technology, specifically to a method for the synergistic preparation of ultra-large cylindrical sodium-ion battery materials adapted to the NFPP-hard carbon system. Background Technology

[0002] With the rapid development of the new energy industry, sodium-ion batteries have shown broad application prospects in energy storage power stations, electric vehicles, and other fields due to their abundant resources and low cost. NFPP (sodium iron pyrophosphate), as the positive electrode material of sodium-ion batteries, has the characteristics of stable structure and moderate theoretical capacity, while hard carbon has become an ideal negative electrode material due to its low cost and good safety. The NFPP-hard carbon system composed of the two has become the preferred solution for ultra-large cylindrical sodium-ion batteries. However, in the existing technology, this system still has many problems that need to be solved: NFPP positive electrodes are prone to problems such as excessive residual alkali and oxide impurity phase precipitation, which leads to increased interface resistance and decreased cycle performance; hard carbon negative electrodes face defects such as insufficient conductivity and significant volume expansion during cycling, which restricts the fast charging performance and lifespan of the battery; more importantly, existing technologies mostly optimize positive and negative electrode materials separately, lacking synergistic design for the interface compatibility between the two, making it difficult to meet the requirements of high consistency and high stability of ultra-large cylindrical batteries.

[0003] The patent document with patent publication number CN117457887B and patent name "A sodium-ion battery cathode material and its preparation method and sodium-ion battery" mentions the use of O3@P2 core-shell structure cathode material. The air stability and cycle performance of the material are improved by calcination treatment mediated by residual alkali layer. However, it does not optimize the structural characteristics of NFPP cathode and does not consider the synergistic adaptation with hard carbon anode. It cannot solve the interface compatibility problem of NFPP-hard carbon system and is difficult to apply directly to ultra-large cylindrical batteries.

[0004] The patent document CN119263257B, entitled "A Hard Carbon Anode Material for Fast-Charging Sodium-Ion Batteries and Its Preparation Method," mentions modifying hard carbon by loading with nickel-aluminum metal oxides and coating with a composite gel to improve the material's conductivity and cycle stability. However, it does not address the modification and adaptation design of the NFPP cathode, nor does it consider the special requirements of ultra-large cylindrical batteries for the compaction density and interfacial impedance of the cathode and anode materials. When the separately optimized anode material is paired with a conventional NFPP cathode, it is prone to problems such as low system compatibility and limited overall cell performance. In addition, the existing technology also suffers from defects such as complex preparation processes, high costs, and difficulty in large-scale production, which seriously hinder the industrial application of the NFPP-hard carbon system in ultra-large cylindrical sodium-ion batteries. Therefore, developing a synergistic preparation method for the NFPP-hard carbon system to simultaneously solve the performance defects of the cathode and anode and the interface compatibility problem has become an urgent need in the field. Summary of the Invention

[0005] (a) Technical problems to be solved To address the shortcomings of existing NFPP-hard carbon systems, such as excessive residual alkali in the positive electrode, precipitation of oxide impurities, insufficient conductivity of the hard carbon negative electrode, significant cycle volume expansion, poor compatibility of the positive and negative electrode interfaces, and lack of synergistic optimization design, which make it difficult to meet the high capacity, long cycle, and high rate performance requirements of ultra-large cylindrical sodium-ion batteries, this invention provides a method for the synergistic preparation of ultra-large cylindrical sodium-ion battery materials adapted to the NFPP-hard carbon system.

[0006] (II) Technical Solution A method for the synergistic preparation of ultra-large cylindrical sodium-ion battery materials adapted to the NFPP-hard carbon system includes the following steps: S1. Preparation of NFPP cathode precursor: Na-source compound, Fe-source compound, and P-source compound were mixed in a molar ratio of 1.0:0.8-1.2:1.5-2.5, and deionized water was added to prepare a mixed salt solution with a concentration of 0.5-1.5 mol / L. The mixed salt solution and a NaOH solution with a concentration of 1.0-2.0 mol / L were added to the reactor in parallel flow. The pH of the reaction system was controlled at 7.5-9.0, the reaction temperature at 40-60℃, the stirring rate at 300-500 r / min, and the reaction was carried out at a constant temperature for 3-6 h. After the reaction was completed, the precipitate was separated by centrifugation, washed with deionized water 3-5 times, and dried in a vacuum drying oven at 60-80℃ for 8-12 h to obtain the NFPP cathode precursor. S2. Doping and Sintering of NFPP Cathode: The NFPP cathode precursor and dopant are mixed uniformly at a mass ratio of 100:0.5-5.0, placed in a tube furnace, and protected by inert gas. The temperature is raised to 450-600℃ at a heating rate of 2-5℃ / min and held for 3-5 hours for pre-sintering. Then, the temperature is raised to 850-1000℃ at a heating rate of 2-5℃ / min and held for 8-15 hours for secondary sintering. After sintering, the material is cooled to room temperature in the furnace and pulverized through a 400-600 mesh sieve to obtain the doped modified NFPP cathode material. S3. Pretreatment and pore expansion of hard carbon anode: Hard carbon raw material is mixed with hydrochloric acid solution of 5-15% by mass at a solid-liquid ratio of 1g:15-25mL, placed in a three-necked flask, and ultrasonically treated for 30-60min at an ultrasonic power of 200-300W. Then, the temperature is raised to 40-55℃, the stirring rate is 300-400r / min, and the reaction is kept at a constant temperature for 2-4h. After the reaction is completed, the mixture is allowed to stand for 2-3h, centrifuged, and the precipitate is washed with deionized water until the filtrate is neutral. The precipitate is then dried in a vacuum drying oven at 70-90℃ for 6-10h to obtain pore-expanded hard carbon material. S4. Metal oxide loading of hard carbon anode: Zinc salt and aluminum salt are mixed in a molar ratio of 1:0.5-2.0, and deionized water is added to prepare a metal salt mixed solution with a concentration of 0.1-0.5 mol / L; the pore-expanding hard carbon material is added to the metal salt mixed solution, with a mass ratio of hard carbon to metal salt of 10:1-3, and 0.5-1.5% of polyvinylpyrrolidone by the total mass of metal salt is added simultaneously. Nitrogen gas is introduced for protection, the temperature is raised to 80-120℃, the stirring rate is 300-400 r / min, and the reaction is carried out for 4-8 h; after the reaction is completed, the precipitate is separated by centrifugation, washed with deionized water 3-4 times, dried in a vacuum drying oven at 80-100℃ for 6-12 h, and then placed in a tube furnace, heated to 450-600℃ at a heating rate of 1-3℃ / min, held for 3-5 h, and cooled with the furnace to obtain the metal oxide loaded hard carbon material; S5. Gel coating modification of hard carbon anode: Sodium alginate and deionized water are mixed at a mass ratio of 1:100-200, under nitrogen protection, heated to 60-80℃, stirred at a rate of 300-400 r / min, and stirred at this temperature for 1-2 h until completely dissolved; calcium chloride solution is added to adjust the calcium ion concentration of the system to 0.05-0.2 mol / L, and stirring is continued for 20-40 min; subsequently, metal oxide-supported hard carbon material is added, with a mass ratio of hard carbon to sodium alginate of 10: Add 0.5–2.0% aniline and sodium dodecyl sulfate, with the mass ratio of aniline to sodium alginate being 1:0.8–1.5. The amount of sodium dodecyl sulfate is 0.02–0.05% of the total mass of the mixture. Stir for 30–60 min. Finally, slowly add 1.5–3.0% ammonium persulfate solution at a dropping rate of 1–3 drops / s. After the addition is complete, continue stirring for 6–10 h. After the reaction is complete, freeze dry to obtain gel-coated modified hard carbon anode material. S6. Synergistic adaptation treatment of positive and negative electrode materials: Doped modified NFPP positive electrode material and gel-coated modified hard carbon negative electrode material are mixed at a mass ratio of 1:0.8-1.2, placed in an atmosphere furnace, and a nitrogen-oxygen mixed gas with a volume ratio of 90-95:5-10 is introduced. The temperature is raised to 500-700℃ at a heating rate of 2-4℃ / min, held for 2-4h, and cooled to room temperature with the furnace to complete the synergistic interface modification of positive and negative electrode materials. S7. Preparation of positive electrode sheet: The co-treated NFPP positive electrode material, conductive carbon black, and PVDF binder are mixed at a mass ratio of 85-90:5-10:3-5, N-methylpyrrolidone solvent is added, and the mixture is stirred at a stirring rate of 500-800 r / min for 3-6 h to prepare a positive electrode slurry; the positive electrode slurry is uniformly coated on the surface of an aluminum foil current collector with a coating thickness of 80-120 μm, dried in a vacuum drying oven at 100-120℃ for 12-16 h, and then rolled to a compaction density of 2.0-2.5 g / cm³, and cut to obtain a positive electrode sheet for ultra-large cylindrical batteries; S8. Preparation of negative electrode sheet: The co-treated hard carbon negative electrode material, conductive carbon black, and sodium carboxymethyl cellulose are mixed at a mass ratio of 88-92:4-8:2-4, deionized water is added, and the mixture is stirred at a stirring rate of 500-800 r / min for 4-8 h to prepare a negative electrode slurry; the negative electrode slurry is uniformly coated on the surface of an aluminum foil current collector with a coating thickness of 100-150 μm, dried in a vacuum drying oven at 80-100℃ for 12-16 h, and then rolled to a compaction density of 1.2-1.6 g / cm³, and cut to obtain a negative electrode sheet for ultra-large cylindrical batteries; S9. Assembling an ultra-large cylindrical sodium-ion battery: The positive electrode, separator, and negative electrode are stacked sequentially and wound to form an electrode core. The electrode core is then inserted into a cylindrical battery casing with a diameter of 65–500 mm and a height of 100–1200 mm, and an electrolyte is injected. The electrolyte is a NaPF6 solution with a concentration of 1.0–1.5 mol / L, and the solvent is a mixture of ethylene carbonate and dimethyl carbonate with a volume ratio of 1:1–1:2. After injecting the electrolyte, the battery is sealed, formed, and aged. The formation conditions are: constant current charging at 0.05–0.1 C to 4.2 V, standing for 1–2 h, and then constant current discharge at 0.1–0.2 C to 2.0 V. The aging conditions are: standing at 25–40 °C for 24–48 h. This yields an ultra-large cylindrical sodium-ion battery adapted to the NFPP-hard carbon system. This method is particularly suitable for ultra-large cylindrical sodium-ion batteries with a diameter ≥65 mm.

[0007] Preferably, the process further includes a secondary doping step for the S2-1.NFPP cathode: after the secondary sintering of S2, the cooled material is mixed with ZrO2 powder at a mass ratio of 100:0.3 to 2.0, and placed in a high-energy ball mill. The ball milling speed is 800 to 1200 r / min, and the ball milling time is 2 to 4 h. After the ball milling is completed, the material is kept at 700 to 800°C under inert gas protection for 2 to 3 h, and then cooled with the furnace to obtain the secondary doped modified NFPP cathode material. The particle size of the ZrO2 powder is 50 to 200 nm.

[0008] Preferably, the process further includes S5-1. Plasma treatment step after gel coating: After the freeze-drying in S5, the gel-coated modified hard carbon material is placed in a plasma treatment instrument, argon gas is introduced, the plasma power is adjusted to 100-200W, the treatment time is 10-30min, and the treatment pressure is 10-30Pa; after the treatment, the material is taken out and dried in a vacuum drying oven at 60-80℃ for 2-4h to obtain the plasma-modified hard carbon anode material.

[0009] Preferably, the Na source compound in S1 is one or more of sodium carbonate, sodium bicarbonate, or sodium hydroxide; the Fe source compound is one or more of ferrous sulfate, ferrous chloride, or ferrous nitrate; the P source compound is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, or phosphoric acid; and during the preparation of the mixed salt solution, sodium citrate, accounting for 0.1 to 0.5% of the total mass of the mixed salt, is added as a complexing agent.

[0010] Preferably, the dopant in S2 is one or more of CaCO3, Li2CO3, and K2CO3; the inert gas is nitrogen or argon, and the gas flow rate is 50-100 mL / min; the heating rate for pre-sintering is 3 °C / min, and the heating rate for secondary sintering is 4 °C / min; the particle size of the pulverized NFPP cathode material is 1-5 μm.

[0011] Preferably, the hard carbon raw material in S3 is one or more of coconut shell-based hard carbon, pitch-based hard carbon, or biomass-based hard carbon; the mass fraction of the hydrochloric acid solution is 8-12%; the ultrasonic treatment power is 250W and the ultrasonic time is 45min; the constant temperature reaction temperature is 50℃ and the stirring rate is 350r / min; the vacuum drying temperature is 80℃ and the drying time is 8h.

[0012] Preferably, the zinc salt in S4 is one or more of zinc nitrate hexahydrate, zinc chloride, or zinc sulfate; the aluminum salt is one or more of aluminum nitrate nonahydrate, aluminum chloride, or aluminum sulfate; the concentration of the metal salt mixed solution is 0.2–0.4 mol / L; the mass ratio of hard carbon to metal salt is 10:1.5–2.5; the amount of polyvinylpyrrolidone added is 0.8–1.2% of the total mass of metal salt; the reaction temperature is 100°C, the stirring rate is 350 r / min, and the reaction time is 6 h; the heating rate of the tube furnace calcination is 2°C / min, the calcination temperature is 500–550°C, and the holding time is 4 h.

[0013] Preferably, in step S5, the mass ratio of sodium alginate to deionized water is 1:150-180; the concentration of calcium chloride solution is 0.5-1.0 mol / L, and the calcium ion concentration in the system after its addition is 0.1-0.15 mol / L; the mass ratio of hard carbon to sodium alginate is 10:1.0-1.5; the mass ratio of aniline to sodium alginate is 1:1.0-1.2; the amount of sodium dodecyl sulfate is 0.03-0.04% of the total mass of the mixed system; the mass fraction of ammonium persulfate solution is 2.0-2.5%, and the dropping rate is 2 drops / s; the freeze-drying temperature is -40 to -20℃, and the drying time is 24-36 h.

[0014] Preferably, the volume ratio of the nitrogen-oxygen mixture in S6 is 92:8; the heating rate is 3℃ / min; the co-processing temperature is 550~650℃; the holding time is 3h; and the gas flow rate during the co-processing is 80~120mL / min.

[0015] Preferably, in step S7, the solid content of the positive electrode slurry is 40-60%; the coating thickness is 90-110 μm; the vacuum drying temperature is 110℃, and the drying time is 14 h; the compaction density after rolling is 2.2-2.4 g / cm³; in step S8, the solid content of the negative electrode slurry is 35-55%; the coating thickness is 120-140 μm; the vacuum drying temperature is 90℃, and the drying time is 14 h; the compaction density after rolling is 1.3-1.5 g / cm³; in step S9, the concentration of the electrolyte is 1.2 mol / L, and the volume ratio of ethylene carbonate to dimethyl carbonate in the solvent is 1:1.5; the charging current during formation is 0.08 C, and the discharging current is 0.15 C; the aging temperature is 30-35℃, and the aging time is 36 h; the diameter of the battery casing is 70-80 mm, and the height is 105-115 mm.

[0016] Preferably, the present invention further includes the steps of controlling and stabilizing residual alkali in the NFPP positive electrode, modifying the multi-level structure of the hard carbon negative electrode, and synergistic heat treatment of the positive and negative electrode interfaces, the specific operations of which are as follows: S2-2. Control and Stabilization of Residual Alkali in NFPP Cathode: The NFPP cathode material treated with S2 or S2-1 is mixed with a 1-3% (w / w) dilute citric acid solution at a liquid-solid ratio of 1g:20-30mL. The mixture is stirred and washed at 40-50℃ for 1-2 hours, centrifuged until neutral, and then vacuum dried to control the residual alkali content of the cathode material to ≤0.5wt%. The cathode material with controlled residual alkali is then mixed with a TiO2-Al2O3 composite stabilizing agent at a mass ratio of 100:0.2-1.0. The mixture is heated to 300-500℃ at a rate of 1-3℃ / min and held for 2-4 hours under inert gas protection in a tube furnace. After cooling, the doped and stabilized NFPP cathode material is obtained. S5-2. Modification of the hierarchical structure of hard carbon anode: The hard carbon anode material treated with S5 or S5-1 is mixed with glucose porous carbon precursor at a mass ratio of 100:5-15. Polyethylene glycol pore-forming agent accounting for 2-8% of the total mass of the mixture is added, and deionized water is added at a ratio of 1g:10-20mL. The mixture is hydrothermally reacted at 160-200℃ for 6-10h in a hydrothermal reactor. After drying, it is calcined at 600-800℃ for 3-5h under nitrogen protection at a rate of 2-4℃ / min. After cooling, the modified hard carbon anode material with a microporous-mesoporous hierarchical pore structure is obtained. S6-1. Synergistic thermal treatment of the positive and negative electrode interfaces: The NFPP positive electrode material obtained in S2-2 and the hard carbon negative electrode material obtained in S5-2 are mixed at a mass ratio of 1:0.8 to 1.2 and placed in an atmosphere furnace. A nitrogen-hydrogen mixed gas with a volume ratio of 95 to 98:2 to 5 is introduced at a flow rate of 60 to 100 mL / min. The temperature is first raised to 150 to 200℃ at a rate of 2℃ / min for 1 to 2 hours, then raised to 400 to 600℃ at a rate of 2 to 3℃ / min and held for 1.5 to 3 hours. Finally, an inert gas is introduced and the furnace is cooled to room temperature to complete the deep synergistic thermal treatment of the positive and negative electrode interfaces.

[0017] (iii) Beneficial technical effects Compared with existing technologies, the beneficial effects of this invention are: In terms of the cathode, this invention effectively reduces the residual alkali content of the NFPP cathode by precisely controlling the stoichiometry of sodium and dopant elements, combined with a two-stage sintering process, and suppresses the formation of oxide impurity phases. At the same time, it improves the crystal structure stability and ion conduction efficiency of the material, enabling the cathode to have both high capacity and excellent cycle stability. This solves the problems of high interfacial impedance and rapid performance decay of traditional NFPP cathodes from the source.

[0018] For the anode, the pore structure of the hard carbon material is optimized through synergistic modification of pore expansion treatment, metal oxide loading and composite gel coating, and the conductivity is significantly improved. At the same time, the composite gel network effectively suppresses volume expansion during cycling and avoids electrode pulverization. This allows the hard carbon anode to maintain high capacity while having good structural stability and fast charging performance, making up for the performance shortcomings of traditional hard carbon materials.

[0019] The synergistic adaptation of positive and negative electrode materials is the core design and key step of this invention. Through a co-calcination process under a specific nitrogen-oxygen mixed atmosphere, a stable interfacial transition layer is formed on the surface of the positive and negative electrode materials, which fundamentally enhances the interfacial compatibility of the positive and negative electrode materials, significantly reduces the interfacial impedance, realizes the efficient transport of ions and electrons in the electrochemical process, and significantly improves the initial coulombic efficiency of the battery. This further improves the cycle stability of the whole battery, making the electrochemical performance of the two highly matched, significantly improving the rate performance and energy density of the whole battery, and perfectly adapting to the structural and performance requirements of ultra-large cylindrical sodium-ion batteries.

[0020] Furthermore, the preparation process of this invention is clear and the parameters are controllable. The raw materials used are readily available, and there is no need for complex and expensive equipment. It balances product performance with the needs of large-scale production, thereby reducing production costs. At the same time, the process is environmentally friendly and conforms to the concept of green manufacturing. In summary, this invention effectively solves the problems of poor positive and negative electrode performance, poor interface compatibility, and difficulty in adapting to ultra-large cylindrical batteries in the existing NFPP-hard carbon system. It provides key technical support for the industrialization of high-performance sodium-ion batteries and has significant practical application value. Attached Figure Description

[0021] Figure 1 This is a flowchart of the method for synergistic preparation of ultra-large cylindrical sodium-ion battery materials proposed in this invention; Figure 2 These are bar charts showing the electrochemical core performance of different embodiments and comparative examples; Figure 3 This is a line graph comparing the interface impedance and initial coulomb efficiency of different embodiments and comparative examples; Figure 4 This is a line graph showing the 1C cycle capacity retention rate of Example 2 and the comparative example. Detailed Implementation

[0022] according to Figures 1 to 4 The specific embodiments of the present invention are as follows: The following describes in detail the technical solution of the synergistic preparation method of ultra-large cylindrical sodium-ion battery materials adapted to the NFPP-hard carbon system of the present invention, with three embodiments and one comparative example. All operations comply with the industry standards for lithium-ion battery material preparation. The ambient temperature is controlled at 22±2℃, the relative humidity is 45%-55%, and the entire process is carried out in a sterile and dry environment. The purity of all reagents used is ≥99.0%, and the equipment parameters strictly follow the scope defined in the claims to ensure the repeatability and reliability of the technical solution.

[0023] General Raw Materials, Reagents and Equipment Instructions Core raw material parameters: Sodium source compounds: sodium carbonate with a purity of 99.5% and a particle size of 100-200 mesh, and sodium bicarbonate with a purity of 99.2%; Fe source compounds: ferrous sulfate with a purity of 99.0% and a water of crystallization content of ≥98%, and ferrous chloride with a purity of 99.3%; P-source compounds: 99.5% pure ammonium dihydrogen phosphate and 99.0% pure diammonium hydrogen phosphate; Dopant: Calcium carbonate with a purity of 99.4% and a particle size of 50-100 nm, lithium carbonate with a purity of 99.6%, and potassium carbonate with a purity of 99.3%; Hard carbon raw materials: coconut shell-based hard carbon with a specific surface area of ​​100-150 m² / g and a particle size of 5-10 μm, and pitch-based hard carbon with a specific surface area of ​​80-120 m² / g. Metal salts: Zinc nitrate hexahydrate (99.0% purity), aluminum acetate tetrahydrate (99.1% purity), and zinc chloride (99.2% purity); Gel coating materials: sodium alginate with a viscosity of 200-300 mPa·s, aniline with a purity of 99.0%, sodium dodecyl sulfate with a purity of 98.5%, and ammonium persulfate with a purity of 98.0%; Electrolyte raw materials: sodium hexafluorophosphate (99.9% purity), ethylene carbonate (99.9% purity), and dimethyl carbonate (99.9% purity).

[0024] Key equipment parameters: Reactor: 5L capacity, temperature control accuracy ±1℃, stirring speed 0~1000r / min, adjustable pH monitoring range 0~14; Tube furnace: Temperature control range: room temperature - 1200℃; Heating rate: 0.5~10℃ / min; Atmosphere control accuracy: ±1%; Ultrasonic equipment: power 0-500W, frequency 20-80kHz, timer 0-120min; Vacuum drying oven: Temperature control range: room temperature - 200℃; Vacuum degree: ≤10Pa; Coating machine: coating thickness accuracy ±5μm, coating speed 0.1~1m / s; Battery testing system: charge / discharge voltage range 0~5V, current accuracy ±0.1%, cyclic testing capability 0~10000 cycles.

[0025] Example 1: Basic formulation, Ca-doped NFPP + zinc-aluminum bimetallic supported hard carbon Raw material ratio: The raw material usage and specifications for preparing 1 kg of positive electrode material and 1 kg of negative electrode material in a single batch are as follows: Raw materials required for step S1: 320g sodium carbonate, 99.5% purity, 150 mesh particle size; 480g ferrous sulfate, 99.0% purity, 98.5% water of crystallization content; 350g ammonium dihydrogen phosphate, 99.5% purity; 2.1g sodium citrate, 99.0% purity, used as a complexing agent.

[0026] Raw materials required for step S2: 15g of calcium carbonate, 99.4% purity, 80nm particle size.

[0027] Raw materials required for step S3: 1000g coconut shell-based hard carbon, with a specific surface area of ​​120m² / g and a particle size of 8μm; 20L hydrochloric acid solution, with a mass fraction of 8%.

[0028] Raw materials required for step S4: 80g zinc nitrate hexahydrate, 99.0% purity; 80g aluminum acetate tetrahydrate, 99.1% purity; 1.2g polyvinylpyrrolidone, molecular weight 40000.

[0029] Raw materials required for step S5: 10g sodium alginate, viscosity 250mPa·s; 5g calcium chloride, purity 99.0%, prepared as a 0.8mol / L solution; 12g aniline, purity 99.0%; 0.8g sodium dodecyl sulfate, purity 98.5%; 15g ammonium persulfate, purity 98.0%, prepared as a 2.0% solution.

[0030] Raw materials required for step S7: 70g conductive carbon black, specific surface area 800m² / g; 30g PVDF binder, molecular weight 500,000.

[0031] Raw materials required for step S8: 25g sodium carboxymethyl cellulose, viscosity 500mPa·s.

[0032] Raw materials required for step S9: 120g sodium hexafluorophosphate, 99.9% purity; 500mL ethylene carbonate, 99.9% purity; 750mL dimethyl carbonate, 99.9% purity.

[0033] Detailed preparation steps S1. Preparation of NFPP cathode precursor: Sodium carbonate, ferrous sulfate, and ammonium dihydrogen phosphate were mixed in a molar ratio of 1.0:1.0:2.0, and deionized water was added to prepare a 1.0 mol / L mixed salt solution. Sodium citrate was added as a complexing agent. The mixed salt solution and a 1.5 mol / L NaOH solution were added to the reactor in parallel flow. The pH of the reaction system was controlled at 8.2, the reaction temperature at 50℃, the stirring rate at 400 r / min, and the reaction was carried out at a constant temperature for 4 h. The following reaction occurred during the reaction: 2Na2CO3 + 3FeSO4 + 2(NH4)2HPO4 → Na4Fe3(PO4)2P2O7 + 2CO2↑ + 4NH3↑ + 3H2SO4 + H2O. After the reaction, the precipitate was separated by centrifugation, washed four times with deionized water, and dried in a vacuum drying oven at 70℃ for 10 h to obtain the NFPP cathode precursor.

[0034] S2. Doping and Sintering of NFPP Cathode: NFPP cathode precursor and calcium carbonate were mixed uniformly at a mass ratio of 100:1.5 and placed in a tube furnace. Nitrogen gas was introduced for protection at a flow rate of 80 mL / min. The temperature was increased to 500℃ at a rate of 3℃ / min and held for 4 hours for pre-sintering. Subsequently, the temperature was increased to 900℃ at a rate of 3℃ / min and held for 12 hours for secondary sintering. After sintering, the mixture was cooled to room temperature in the furnace and pulverized through a 500-mesh sieve using a high-speed pulverizer to obtain Ca-doped modified NFPP cathode material with a particle size of 2–4 μm.

[0035] S3. Pretreatment and Pore Enlargement of Hard Carbon Anode: Coconut shell-based hard carbon was mixed with 8% hydrochloric acid solution at a solid-liquid ratio of 1g:20mL in a three-necked flask and ultrasonically treated for 45min at 250W. The mixture was then heated to 45℃, stirred at 350r / min, and reacted at this temperature for 3h. After the reaction, the mixture was allowed to stand for 2.5h, centrifuged, and the precipitate was washed with deionized water until the pH of the filtrate reached 7.0. The precipitate was then dried in a vacuum drying oven at 80℃ for 8h to obtain the pore-enlarged hard carbon material, with a specific surface area increased to 180m² / g.

[0036] S4. Metal Oxide Loading of Hard Carbon Anode: Zinc nitrate hexahydrate and aluminum acetate tetrahydrate were mixed in a molar ratio of 1:1, and deionized water was added to prepare a 0.3 mol / L metal salt mixed solution. Pore-expanding hard carbon material was added to the metal salt mixed solution at a mass ratio of hard carbon to metal salt of 10:2. Simultaneously, 1.0% (by mass) of polyvinylpyrrolidone (PVP) of the total metal salt mass was added. Nitrogen gas was introduced for protection at a flow rate of 50 mL / min. The temperature was raised to 100 °C, and the stirring rate was 350 r / min for 6 h. After the reaction, the mixture was centrifuged, and the precipitate was washed three times with deionized water and dried in a vacuum drying oven at 90 °C for 10 h. Subsequently, it was placed in a tube furnace and heated to 500 °C at a heating rate of 2 °C / min, held at that temperature for 4 h, and then cooled with the furnace to obtain the zinc-aluminum bimetallic oxide-loaded hard carbon material.

[0037] S5. Gel-coated modification of hard carbon anode: Sodium alginate and deionized water were mixed at a mass ratio of 1:150, protected with nitrogen, heated to 70℃, stirred at a stirring rate of 350 r / min, and stirred at a constant temperature for 1.5 h until completely dissolved. Calcium chloride solution was added to adjust the calcium ion concentration of the system to 0.12 mol / L, and stirring was continued for 30 min. Subsequently, metal oxide-supported hard carbon material was added, with a mass ratio of hard carbon to sodium alginate of 10:1.2. Aniline and sodium dodecyl sulfate were then added, with a mass ratio of aniline to sodium alginate of 1:1.1. The amount of sodium dodecyl sulfate was 0.035% of the total mass of the mixture, and stirring was continued for 45 min. Finally, a 2.0% ammonium persulfate solution was slowly added dropwise at a dropping rate of 2 drops / s. After the addition was complete, stirring was continued for 8 h. After the reaction was completed, the mixture was freeze-dried at -30℃ for 30 h to obtain the gel-coated modified hard carbon anode material.

[0038] S6. Synergistic adaptation treatment of positive and negative electrode materials: The doped modified NFPP positive electrode material and the gel-coated modified hard carbon negative electrode material are mixed at a mass ratio of 1:1.0 and placed in an atmosphere furnace. A nitrogen-oxygen mixed gas with a volume ratio of 92:8 is introduced at a gas flow rate of 100 mL / min. The temperature is increased to 600℃ at a heating rate of 3℃ / min and held for 3 hours. The mixture is then cooled to room temperature with the furnace to complete the synergistic interface modification of the positive and negative electrode materials.

[0039] S7. Preparation of positive electrode sheet: The co-treated NFPP positive electrode material, conductive carbon black, and PVDF binder are mixed at a mass ratio of 88:7:5. N-methylpyrrolidone solvent is added, and the mixture is stirred at a stirring rate of 600 r / min for 4 h to prepare a positive electrode slurry with a solid content of 50%. The positive electrode slurry is uniformly coated on the surface of an aluminum foil current collector using a coating machine to a coating thickness of 100 μm. It is then dried in a vacuum drying oven at 110℃ for 14 h, and subsequently rolled to a compaction density of 2.3 g / cm³ using a roller press. The resulting sheets are then cut into circular electrode sheets with a diameter of 67–77 mm using a cutting machine to obtain a positive electrode sheet for ultra-large cylindrical batteries.

[0040] S8. Preparation of negative electrode sheet: The co-treated hard carbon negative electrode material, conductive carbon black, and sodium carboxymethyl cellulose are mixed at a mass ratio of 90:6:4, deionized water is added, and the mixture is stirred at a stirring rate of 700 r / min for 6 h to prepare a negative electrode slurry with a solid content of 45%. The negative electrode slurry is uniformly coated on the surface of an aluminum foil current collector using a coating machine to a coating thickness of 130 μm. It is then dried in a vacuum drying oven at 90℃ for 14 h, and subsequently rolled to a compaction density of 1.4 g / cm³ using a roller press. The resulting sheets are then cut into circular electrode sheets with a diameter of 69–79 mm using a cutting machine to obtain a negative electrode sheet for ultra-large cylindrical batteries.

[0041] S9. Assembling the ultra-large cylindrical sodium-ion battery: The positive electrode, polypropylene separator, and negative electrode are stacked sequentially and wound using a winding machine to form an electrode core with a diameter of 65–75 mm and a height of 100–110 mm. The electrode core is then inserted into a cylindrical battery casing with a diameter of 70–80 mm and a height of 105–115 mm, and an electrolyte is injected. The electrolyte is a 1.2 mol / L NaPF6 solution, with a solvent of a mixture of ethylene carbonate and dimethyl carbonate at a volume ratio of 1:1.5. After electrolyte injection, the casing is sealed, and then formation treatment is performed in a formation cabinet: constant current charging at 0.08 C to 4.2 V, standing for 1.5 h, followed by constant current discharge at 0.15 C to 2.0 V; after formation, aging treatment is performed at 32℃ for 36 h to obtain an ultra-large cylindrical sodium-ion battery adapted to the NFPP-hard carbon system.

[0042] Example 2: Ca-Li dual-doped NFPP + secondary doping modification Raw material ratio: The raw material usage and specifications for preparing 1 kg of positive electrode material and 1 kg of negative electrode material in a single batch are as follows: Raw materials required for step S1: 350g sodium bicarbonate, 99.2% purity, 120 mesh particle size; 420g ferrous chloride, 99.3% purity; 380g diammonium hydrogen phosphate, 99.0% purity; 2.3g sodium citrate, 99.0% purity, used as a complexing agent.

[0043] Raw materials required for step S2: 10g calcium carbonate, 99.4% purity, 80nm particle size; 5g lithium carbonate, 99.6% purity.

[0044] Raw materials required for step S2-1: 12g of zirconium oxide powder, 99.5% purity, 100nm particle size.

[0045] Raw materials required for step S3: 1000g of pitch-based hard carbon with a specific surface area of ​​100m² / g and a particle size of 6μm; 18L of hydrochloric acid solution with a mass fraction of 10%.

[0046] Raw materials required for step S4: 70g zinc chloride, 99.2% purity; 75g aluminum chloride, 99.0% purity; 1.1g polyvinylpyrrolidone, molecular weight 40000.

[0047] Raw materials required for step S5: 12g sodium alginate, viscosity 280mPa·s; 6g calcium chloride, purity 99.0%, prepared as a 0.9mol / L solution; 13g aniline, purity 99.0%; 0.9g sodium dodecyl sulfate, purity 98.5%; 16g ammonium persulfate, purity 98.0%, prepared as a 2.2% solution.

[0048] Raw materials required for step S7: 65g conductive carbon black, with a specific surface area of ​​900m² / g; 35g PVDF binder, with a molecular weight of 500,000.

[0049] Raw materials required for step S8: 22g sodium carboxymethyl cellulose, viscosity 450mPa·s.

[0050] Raw materials required for step S9: 125g sodium hexafluorophosphate, 99.9% purity; 550mL ethylene carbonate, 99.9% purity; 825mL dimethyl carbonate, 99.9% purity.

[0051] Detailed preparation steps S1. Preparation of NFPP cathode precursor: Sodium bicarbonate, ferrous chloride, and diammonium hydrogen phosphate were mixed in a molar ratio of 1.0:1.1:2.2, and deionized water was added to prepare a 1.2 mol / L mixed salt solution. Sodium citrate was added as a complexing agent. The mixed salt solution and a 1.8 mol / L NaOH solution were added to the reactor in parallel flow. The pH of the reaction system was controlled at 8.5, the reaction temperature at 55℃, the stirring rate at 450 r / min, and the reaction was carried out at a constant temperature for 3.5 h. The reaction equation is: 4NaHCO3 + 3FeCl2 + 2(NH4)2HPO4 → Na4Fe3(PO4)2P2O7 + 4CO2↑ + 4NH3↑ + 6HCl + 2H2O.

[0052] After the reaction was completed, the precipitate was separated by centrifugation, washed four times with deionized water, and dried in a vacuum drying oven at 75°C for 9 hours to obtain the NFPP cathode precursor.

[0053] S2. Doping and Sintering of NFPP Cathode: The NFPP cathode precursor was mixed uniformly with calcium carbonate and lithium carbonate at a mass ratio of 100:1.0:0.5, placed in a tube furnace, and protected by argon gas at a flow rate of 90 mL / min. The temperature was increased to 550℃ at a rate of 3.5℃ / min and held for 3.5 h for pre-sintering. Subsequently, the temperature was increased to 950℃ at a rate of 3.5℃ / min and held for 10 h for secondary sintering. After sintering, the material was cooled to room temperature in the furnace, pulverized, and passed through a 500-mesh sieve to obtain the Ca-Li dual-doped NFPP cathode material.

[0054] S2-1. Secondary doping steps of NFPP cathode: The cooled Ca-Li dual-doped NFPP material and ZrO2 powder were mixed at a mass ratio of 100:1.2 and placed in a high-energy ball mill. The ball milling speed was 1000 r / min and the ball milling time was 3 h. After the ball milling was completed, the mixture was kept at 750℃ under argon protection for 2.5 h with an argon flow rate of 80 mL / min and cooled with the furnace to obtain the secondary doped modified NFPP cathode material.

[0055] S3. Pretreatment and Pore Enlargement of Hard Carbon Anode: Pitch-based hard carbon was mixed with a 10% hydrochloric acid solution at a solid-liquid ratio of 1g:18mL in a three-necked flask and ultrasonically treated for 40 min at an ultrasonic power of 280W. The mixture was then heated to 50℃, stirred at 380 r / min, and reacted at this temperature for 2.5 h. After the reaction, the mixture was allowed to stand for 2.5 h, centrifuged, and the precipitate was washed with deionized water until the pH of the filtrate reached 7.0. The filtrate was then dried in a vacuum drying oven at 85℃ for 7 h to obtain the pore-enlarged hard carbon material, with a specific surface area increased to 160 m² / g.

[0056] S4. Metal Oxide Loading of Hard Carbon Anode: Zinc chloride and aluminum chloride were mixed in a molar ratio of 1:0.9, and a 0.4 mol / L metal salt mixed solution was prepared by adding deionized water. Pore-expanding hard carbon material was added to the metal salt mixed solution at a mass ratio of hard carbon to metal salt of 10:1.8. Simultaneously, 0.9% (by mass of the total metal salt) of polyvinylpyrrolidone was added. Nitrogen gas was introduced for protection at a flow rate of 60 mL / min. The temperature was raised to 110 °C, and the stirring rate was 380 r / min for 5 h. After the reaction, the mixture was centrifuged, and the precipitate was washed three times with deionized water and dried in a vacuum drying oven at 95 °C for 9 h. Then, it was placed in a tube furnace and heated to 550 °C at a heating rate of 2.5 °C / min, held at that temperature for 3.5 h, and cooled with the furnace to obtain the zinc-aluminum bimetallic oxide-loaded hard carbon material.

[0057] S5. Gel-coating modification of hard carbon anode: Sodium alginate and deionized water were mixed at a mass ratio of 1:160, protected with nitrogen, heated to 75℃, stirred at a stirring rate of 380 r / min, and stirred at a constant temperature for 1.2 h until completely dissolved. Calcium chloride solution was added to adjust the calcium ion concentration of the system to 0.14 mol / L, and stirring was continued for 25 min. Subsequently, metal oxide-supported hard carbon material was added, with a mass ratio of hard carbon to sodium alginate of 10:1.5. Aniline and sodium dodecyl sulfate were then added, with a mass ratio of aniline to sodium alginate of 1:1.2. The amount of sodium dodecyl sulfate was 0.038% of the total mass of the mixture, and stirring was continued for 50 min. Finally, a 2.2% ammonium persulfate solution was slowly added dropwise at a dropping rate of 2 drops / s. After the addition was complete, stirring was continued for 7 h. After the reaction was completed, the mixture was freeze-dried at -25℃ for 28 h to obtain the gel-coated modified hard carbon anode material.

[0058] S6. Synergistic adaptation treatment of positive and negative electrode materials: The secondary doped modified NFPP positive electrode material and the gel-coated modified hard carbon negative electrode material were mixed at a mass ratio of 1:1.1 and placed in an atmosphere furnace. A nitrogen-oxygen mixed gas with a volume ratio of 92:8 was introduced at a gas flow rate of 110 mL / min. The temperature was increased to 650℃ at a heating rate of 3.5℃ / min and held for 2.5 h. The mixture was then cooled to room temperature with the furnace to complete the synergistic interface modification of the positive and negative electrode materials.

[0059] S7. Preparation of positive electrode sheet: The co-treated NFPP positive electrode material, conductive carbon black, and PVDF binder are mixed at a mass ratio of 87:8:5. N-methylpyrrolidone solvent is added, and the mixture is stirred at a stirring rate of 650 r / min for 3.5 h to prepare a positive electrode slurry with a solid content of 52%. The positive electrode slurry is uniformly coated on the surface of an aluminum foil current collector using a coating machine to a coating thickness of 95 μm. It is then dried in a vacuum drying oven at 115℃ for 13 h, and subsequently rolled to a compaction density of 2.4 g / cm³ using a roller press. The resulting sheets are then cut into circular electrode sheets with a diameter of 67–77 mm using a cutting machine to obtain the positive electrode sheet for ultra-large cylindrical batteries.

[0060] S8. Preparation of negative electrode sheet: The co-treated hard carbon negative electrode material, conductive carbon black, and sodium carboxymethyl cellulose were mixed at a mass ratio of 89:7:4, deionized water was added, and the mixture was stirred at a stirring rate of 750 r / min for 5 h to prepare a negative electrode slurry with a solid content of 48%. The negative electrode slurry was uniformly coated on the surface of an aluminum foil current collector using a coating machine to a coating thickness of 125 μm. It was dried in a vacuum drying oven at 95℃ for 13 h, and then rolled to a compaction density of 1.5 g / cm³ using a roller press. It was then cut into circular electrode sheets with a diameter of 69–79 mm using a cutting machine to obtain a negative electrode sheet for ultra-large cylindrical batteries.

[0061] S9. Assembling the ultra-large cylindrical sodium-ion battery: The positive electrode, polypropylene separator, and negative electrode are stacked sequentially and wound using a winding machine to form an electrode core with a diameter of 65–75 mm and a height of 100–110 mm. The electrode core is then inserted into a cylindrical battery casing with a diameter of 70–80 mm and a height of 105–115 mm, and an electrolyte is injected. The electrolyte is a 1.2 mol / L NaPF6 solution, with a solvent of a mixture of ethylene carbonate and dimethyl carbonate at a volume ratio of 1:1.5. After injecting the electrolyte, the casing is sealed, and then formation treatment is performed in a formation cabinet: constant current charging at 0.08 C to 4.2 V, standing for 1.5 h, followed by constant current discharge at 0.15 C to 2.0 V; after formation, aging treatment is performed at 33℃ for 36 h to obtain an ultra-large cylindrical sodium-ion battery adapted to the NFPP-hard carbon system.

[0062] Example 3: K-doped NFPP+ plasma treatment of hard carbon Raw material ratio: The raw material usage and specifications for preparing 1 kg of positive electrode material and 1 kg of negative electrode material in a single batch are as follows: Raw materials required for step S1: 330g sodium carbonate, 99.5% purity, 140 mesh particle size; 450g ferrous sulfate, 99.0% purity, 98.5% water of crystallization content; 360g ammonium dihydrogen phosphate, 99.5% purity; 2.2g sodium citrate, 99.0% purity, used as a complexing agent.

[0063] Raw materials required for step S2: 18g potassium carbonate, 99.3% purity.

[0064] Raw materials required for step S3: 1000g coconut shell-based hard carbon, with a specific surface area of ​​130m² / g and a particle size of 7μm; 22L hydrochloric acid solution, with a mass fraction of 9%.

[0065] Raw materials required for step S4: 90g zinc nitrate hexahydrate, 99.0% purity; 85g aluminum acetate tetrahydrate, 99.1% purity; 1.3g polyvinylpyrrolidone, molecular weight 40,000.

[0066] Raw materials required for step S5: 11g sodium alginate, viscosity 260mPa·s; 5.5g calcium chloride, purity 99.0%, prepared as a 0.7mol / L solution; 12.5g aniline, purity 99.0%; 0.85g sodium dodecyl sulfate, purity 98.5%; 15.5g ammonium persulfate, purity 98.0%, prepared as a 2.1% solution.

[0067] Equipment required for step S5-1: Plasma treatment instrument. There is no specific requirement for the amount used. The equipment parameters are: power 150W and pressure 20Pa.

[0068] Raw materials required for step S7: 75g conductive carbon black, specific surface area 850m² / g; 25g PVDF binder, molecular weight 500,000.

[0069] Raw materials required for step S8: 28g sodium carboxymethyl cellulose, viscosity 550mPa·s.

[0070] Raw materials required for step S9: 115g sodium hexafluorophosphate, 99.9% purity; 480mL ethylene carbonate, 99.9% purity; 720mL dimethyl carbonate, 99.9% purity.

[0071] Detailed preparation steps S1. Preparation of NFPP cathode precursor: Sodium carbonate, ferrous sulfate, and ammonium dihydrogen phosphate were mixed in a molar ratio of 1.0:0.9:2.1, and deionized water was added to prepare a 0.9 mol / L mixed salt solution. Sodium citrate was added as a complexing agent. The mixed salt solution and a 1.6 mol / L NaOH solution were added to the reactor in parallel flow. The pH of the reaction system was controlled at 8.0, the reaction temperature at 48℃, the stirring rate at 380 r / min, and the reaction was carried out at a constant temperature for 4.5 h. The reaction equation is: 2Na2CO3 + 3FeSO4 + 2(NH4)2HPO4 → Na4Fe3(PO4)2P2O7 + 2CO2↑ + 4NH3↑ + 3H2SO4 + H2O. After the reaction, the precipitate was separated by centrifugation, washed four times with deionized water, and dried in a vacuum drying oven at 72℃ for 9.5 h to obtain the NFPP cathode precursor.

[0072] S2. Doping and Sintering of NFPP Cathode: NFPP cathode precursor and potassium carbonate were mixed uniformly at a mass ratio of 100:1.8, placed in a tube furnace, and protected with nitrogen gas at a flow rate of 85 mL / min. The temperature was increased to 480℃ at a rate of 2.5℃ / min and held for 4.5 h for pre-sintering. Subsequently, the temperature was increased to 920℃ at a rate of 2.5℃ / min and held for 11 h for secondary sintering. After sintering, the mixture was cooled to room temperature in the furnace, pulverized, and passed through a 500-mesh sieve to obtain K-doped modified NFPP cathode material with a particle size of 1–3 μm.

[0073] S3. Pretreatment and Pore Enlargement of Hard Carbon Anode: Coconut shell-based hard carbon was mixed with a 9% hydrochloric acid solution at a solid-liquid ratio of 1g:22mL in a three-necked flask. The mixture was ultrasonically treated at 260W for 50min, followed by heating to 48℃ and stirring at 360r / min for 3.2h. After the reaction, the mixture was allowed to stand for 2.8h, centrifuged, and the precipitate was washed with deionized water until the pH of the filtrate reached 7.0. The precipitate was then dried in a vacuum drying oven at 82℃ for 7.5h to obtain the pore-enlarged hard carbon material, with a specific surface area increased to 170m² / g.

[0074] S4. Metal Oxide Loading of Hard Carbon Anode: Zinc nitrate hexahydrate and aluminum acetate tetrahydrate were mixed in a molar ratio of 1:1.1, and deionized water was added to prepare a 0.25 mol / L metal salt mixed solution. Pore-expanding hard carbon material was added to the metal salt mixed solution at a mass ratio of hard carbon to metal salt of 10:2.2. Simultaneously, 1.1% (by mass) of polyvinylpyrrolidone (PVP) of the total metal salt mass was added. Nitrogen gas was introduced for protection at a flow rate of 55 mL / min. The temperature was raised to 95 °C, and the stirring rate was 360 r / min for 7 h. After the reaction, the mixture was centrifuged, and the precipitate was washed three times with deionized water and dried in a vacuum drying oven at 88 °C for 9.5 h. Then, it was placed in a tube furnace and heated to 520 °C at a heating rate of 1.5 °C / min, held at that temperature for 4.5 h, and cooled with the furnace to obtain the zinc-aluminum bimetallic oxide-loaded hard carbon material.

[0075] S5. Gel-coated modification of hard carbon anode: Sodium alginate and deionized water were mixed at a mass ratio of 1:155, protected with nitrogen, heated to 68℃, stirred at a stirring rate of 360 r / min, and kept at this temperature for 1.8 h until completely dissolved. Calcium chloride solution was added to adjust the calcium ion concentration of the system to 0.11 mol / L, and stirring was continued for 35 min. Subsequently, metal oxide-supported hard carbon material was added, with a mass ratio of hard carbon to sodium alginate of 10:1.1. Aniline and sodium dodecyl sulfate were then added, with a mass ratio of aniline to sodium alginate of 1:1.0. The amount of sodium dodecyl sulfate was 0.032% of the total mass of the mixture, and stirring was continued for 48 min. Finally, a 2.1% ammonium persulfate solution was slowly added dropwise at a rate of 2 drops / s. After the addition was complete, stirring was continued for 7.5 h. After the reaction was completed, the mixture was freeze-dried at -35℃ for 32 h to obtain the gel-coated modified hard carbon anode material.

[0076] S5-1. Plasma treatment steps after gel coating: Place the gel-coated modified hard carbon material into a plasma treatment instrument, introduce argon gas, adjust the plasma power to 150W, the treatment time to 20min, and the treatment pressure to 20Pa; after the treatment, take out the material and dry it in a vacuum drying oven at 75℃ for 3h to obtain the plasma-modified hard carbon anode material.

[0077] S6. Synergistic adaptation treatment of positive and negative electrode materials: K-doped modified NFPP positive electrode material and plasma-modified hard carbon negative electrode material were mixed at a mass ratio of 1:0.9 and placed in an atmosphere furnace. A nitrogen-oxygen mixed gas with a volume ratio of 92:8 was introduced at a flow rate of 95 mL / min. The temperature was increased to 580℃ at a heating rate of 2.8℃ / min and held for 3.2 h. The mixture was then cooled to room temperature with the furnace to complete the synergistic interface modification of the positive and negative electrode materials.

[0078] S7. Preparation of positive electrode sheet: The co-treated NFPP positive electrode material, conductive carbon black, and PVDF binder are mixed at a mass ratio of 89:6:5. N-methylpyrrolidone solvent is added, and the mixture is stirred at a stirring rate of 580 r / min for 4.5 h to prepare a positive electrode slurry with a solid content of 48%. The positive electrode slurry is uniformly coated on the surface of an aluminum foil current collector using a coating machine to a coating thickness of 105 μm. It is then dried in a vacuum drying oven at 108℃ for 15 h, and subsequently rolled to a compaction density of 2.2 g / cm³ using a roller press. The resulting sheets are then cut into circular electrode sheets with a diameter of 67–77 mm using a cutting machine to obtain the positive electrode sheet for ultra-large cylindrical batteries.

[0079] S8. Preparation of negative electrode sheet: The co-treated hard carbon negative electrode material, conductive carbon black, and sodium carboxymethyl cellulose were mixed at a mass ratio of 91:5:4, deionized water was added, and the mixture was stirred at a stirring rate of 680 r / min for 7 h to prepare a negative electrode slurry with a solid content of 42%. The negative electrode slurry was uniformly coated on the surface of an aluminum foil current collector using a coating machine to a coating thickness of 135 μm. It was dried in a vacuum drying oven at 88℃ for 15 h, and then rolled to a compaction density of 1.3 g / cm³ using a roller press. The slurry was then cut into circular electrode sheets with a diameter of 69–79 mm using a cutting machine to obtain a negative electrode sheet for ultra-large cylindrical batteries.

[0080] S9. Assembling the ultra-large cylindrical sodium-ion battery: The positive electrode, polypropylene separator, and negative electrode are stacked sequentially and wound using a winding machine to form an electrode core with a diameter of 65–75 mm and a height of 100–110 mm. The electrode core is then inserted into a cylindrical battery casing with a diameter of 70–80 mm and a height of 105–115 mm, and an electrolyte is injected. The electrolyte is a 1.2 mol / L NaPF6 solution, with a solvent of a mixture of ethylene carbonate and dimethyl carbonate at a volume ratio of 1:1.5. After injecting the electrolyte, the casing is sealed, and then formation treatment is performed in a formation cabinet: constant current charging at 0.08 C to 4.2 V, standing for 1.5 h, and then constant current discharging at 0.15 C to 2.0 V; after formation, aging treatment is performed at 30℃ for 36 h to obtain an ultra-large cylindrical sodium-ion battery adapted to the NFPP-hard carbon system.

[0081] Comparative example: lack of synergistic adaptation treatment, conventional NFPP + hard carbon system Raw material ratio and process parameters: The raw material ratio is the same as in Example 1. Step S6 (co-adaptation treatment of positive and negative electrode materials) is removed from the process steps. The remaining steps and parameters are exactly the same as in Example 1. That is, after the positive and negative electrode materials are prepared, they are directly used for electrode preparation without co-calcination interface modification under a nitrogen-oxygen mixed atmosphere.

[0082] Performance Test Results and Analysis The performance of Examples 1-3 is significantly better than that of the comparative examples, indicating that the synergistic preparation method of the present invention can effectively improve the electrochemical performance of the NFPP-hard carbon system. Example 2, due to the use of Ca-Li dual doping and Zr secondary doping, exhibits the best performance in terms of capacity and cycle stability, with an initial discharge capacity of 175 mAh and a capacity retention of 92.3% after 500 cycles. Example 3, through plasma treatment to optimize the surface properties of hard carbon, shows excellent rate performance and a 5C discharge capacity of 149 mAh. Example 1, as a basic formulation, has balanced performance and meets the needs of conventional applications. The comparative examples, lacking synergistic adaptation treatment of positive and negative electrodes, have an interface impedance as high as 128 mΩ, resulting in a significant decrease in cycle stability and rate performance, with a capacity retention of only 76.8% after 500 cycles, fully demonstrating that synergistic interface modification is the key to improving system compatibility. In addition, the synergistic effect of the positive and negative electrode modification process of the present invention effectively reduces the residual alkali content of NFPP and suppresses the volume expansion of hard carbon, enabling the full cell to have high capacity, long cycle life, and high rate performance, fully adapting to the application requirements of ultra-large cylindrical sodium-ion batteries.

[0083] refer to Figure 2 This figure compares the core electrochemical performance of each embodiment with that of the comparative example. It can be seen that the NFPP-hard carbon system material prepared by the present invention is significantly better than the comparative example without positive and negative electrode synergistic adaptation treatment in terms of initial discharge capacity, high rate discharge capacity and cycle capacity retention. Among them, the electrochemical performance of Example 2 is the best, which fully proves that the synergistic preparation method of the present invention can effectively improve the comprehensive electrochemical performance of the material.

[0084] refer to Figure 3 This figure shows the correlation trend between the interface impedance and the first coulombic efficiency of each experimental group. The interface impedance of each embodiment of the present invention is much lower than that of the comparative example, and the first coulombic efficiency is higher than that of the comparative example. Among them, the interface impedance of Example 2 is the lowest and the first coulombic efficiency is the highest. This shows that the modification process such as the positive and negative electrode synergistic adaptation treatment of the present invention can effectively reduce the interface impedance of the system, improve the charge transfer efficiency of the electrode reaction, and thus improve the first coulombic efficiency.

[0085] refer to Figure 4 This figure compares the capacity retention changes of Example 2 and the comparative example after 500 cycles at a high rate of 1C. Example 2 showed slow capacity decay throughout the cycling process, maintaining 92.3% capacity after 500 cycles, while the comparative example showed significant capacity decay, with only 76.8% remaining after 500 cycles. This indicates that the synergistic preparation method of the present invention can effectively improve the structural stability of the NFPP-hard carbon system, significantly improve the long-cycle performance of the material, and solve the problem of rapid capacity decay during the cycling process of traditional systems.

[0086] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for the synergistic preparation of ultra-large cylindrical sodium-ion battery materials adapted to the NFPP-hard carbon system, characterized in that, Includes the following steps: S1. Preparation of NFPP cathode precursor: Na, Fe, and P source compounds were mixed in a molar ratio of 1.0:0.8-1.2:1.5-2.5 to prepare a 0.5-1.5 mol / L mixed salt solution, which was then added to the reactor in parallel with a 1.0-2.0 mol / L NaOH solution. The mixture was stirred at 40-60℃ and reacted at a constant temperature for 3-6 hours. After centrifugation, the precursor was washed 3-5 times and dried under vacuum. S2. NFPP cathode doping and sintering: The precursor and dopant are mixed at a mass ratio of 100:0.5-5.

0. Under the protection of inert gas in a tube furnace, the temperature is increased at 2-5℃ / min to 450-600℃ for pre-sintering for 3-5 hours, and then the temperature is increased at the same rate to 850-1000℃ for secondary sintering for 8-15 hours. After cooling, the cathode is crushed and passed through a 400-600 mesh sieve to obtain the doped modified NFPP cathode. S3. Hard carbon anode pretreatment for pore expansion: Hard carbon raw material is mixed with 5-15% hydrochloric acid solution at a ratio of 1g:15-25mL, ultrasonically treated for 30-60min, and stirred at 40-55℃ for 2-4h; after standing, centrifuged and washed until neutral, and vacuum dried to obtain pore-expanded hard carbon. S4. Hard carbon anode metal oxide loading: Zinc and aluminum salts are mixed in a 0.1-0.5 mol / L solution at a molar ratio of 1:0.5-2.

0. Polyvinylpyrrolidone is added at a total mass of 0.5-1.5% of the pore-expanding hard carbon and metal salts. The mixture is reacted at 80-120℃ for 4-8 h under nitrogen protection. After washing and drying, the mixture is calcined at 450-600℃ for 3-5 h with the temperature increased at 1-3℃ / min to obtain supported hard carbon. S5. Hard carbon anode gel coating: Sodium alginate and water are mixed at a ratio of 1:100-200, stirred and dissolved at 60-80℃, calcium chloride is added to adjust the calcium ion concentration to 0.05-0.2 mol / L, then supported hard carbon, aniline and 0.02-0.05% sodium dodecyl sulfate by mass of the total system are added; 1.5-3.0% ammonium persulfate solution is added dropwise, reacted for 6-10 h and then freeze-dried to obtain the coated modified hard carbon anode; S6. Positive and negative electrode synergistic adaptation: Positive and negative electrode materials are mixed at a mass ratio of 1:0.8 to 1.

2. A nitrogen-oxygen mixed gas of 90 to 95:5 to 10 is introduced into an atmosphere furnace and heated to 500 to 700°C and held for 2 to 4 hours. After cooling, the interface modification is completed. S7. Preparation of positive electrode sheet: Mix the synergistically treated NFPP positive electrode material, conductive carbon black, and PVDF binder, add N-methylpyrrolidone solvent, and stir for 3-6 hours to prepare positive electrode slurry; uniformly coat the positive electrode slurry on the surface of aluminum foil current collector, vacuum dry it, roll it to pressure, and cut it to obtain positive electrode sheet for ultra-large cylindrical battery. S8. Preparation of negative electrode sheet: Mix the co-treated hard carbon negative electrode material, conductive carbon black, and sodium carboxymethyl cellulose, add deionized water, and stir for 4-8 hours to prepare negative electrode slurry; uniformly coat the negative electrode slurry on the surface of aluminum foil current collector, vacuum dry it, and roll it to a compaction density of 1.2-1.6 g / cm³, and cut it to obtain a negative electrode sheet for ultra-large cylindrical batteries; S9. Assemble the battery: The positive and negative electrode sheets and the separator are wound into an electrode core, which is then inserted into a cylindrical battery case with a diameter of 65-500 mm and a height of 100-1200 mm, and injected with 1.0-1.5 mol / L NaPF6 electrolyte. After sealing, the battery undergoes formation and aging treatments to obtain the finished battery.

2. The method for synergistic preparation of ultra-large cylindrical sodium-ion battery materials adapted to the NFPP-hard carbon system according to claim 1, characterized in that, It also includes a secondary doping step for the S2-1.NFPP cathode: after the secondary sintering of S2, the cooled material is mixed with ZrO2 powder at a mass ratio of 100:0.3 to 2.0 and placed in a high-energy ball mill for 2 to 4 hours; after ball milling, the material is cooled with the furnace to obtain the secondary doped modified NFPP cathode material.

3. The method for synergistic preparation of ultra-large cylindrical sodium-ion battery materials adapted to the NFPP-hard carbon system according to claim 1, characterized in that, It also includes S5-1. Plasma treatment step after gel coating: After the freeze-drying of S5, the gel-coated modified hard carbon material is placed in a plasma treatment instrument, the plasma power is adjusted to 100-200W, and the treatment time is 10-30min; after the treatment, the material is taken out and vacuum dried to obtain the plasma-modified hard carbon anode material.

4. The method for synergistic preparation of ultra-large cylindrical sodium-ion battery materials adapted to the NFPP-hard carbon system according to claim 1, characterized in that, The Na source compound mentioned in S1 is one or more of sodium carbonate, sodium bicarbonate, or sodium hydroxide; the Fe source compound is one or more of ferrous sulfate, ferrous chloride, or ferrous nitrate; the P source compound is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, or phosphoric acid; during the preparation of the mixed salt solution, sodium citrate, accounting for 0.1 to 0.5% of the total mass of the mixed salt, is added as a complexing agent.

5. The method for synergistic preparation of ultra-large cylindrical sodium-ion battery materials adapted to the NFPP-hard carbon system according to claim 1, characterized in that, The dopant mentioned in S2 is one or more of CaCO3, Li2CO3, and K2CO3; the inert gas is nitrogen or argon, and the gas flow rate is 50-100 mL / min; the heating rate for pre-sintering is 3℃ / min, and the heating rate for secondary sintering is 4℃ / min; the particle size of the pulverized NFPP cathode material is 1-5 μm.

6. The method for synergistic preparation of ultra-large cylindrical sodium-ion battery materials adapted to the NFPP-hard carbon system according to claim 1, characterized in that, The hard carbon raw material described in S3 is one or more of coconut shell-based hard carbon, pitch-based hard carbon, or biomass-based hard carbon; the mass fraction of the hydrochloric acid solution is 8-12%; the ultrasonic treatment power is 250W and the ultrasonic time is 45min; the isothermal reaction temperature is 50℃ and the stirring rate is 350r / min; the vacuum drying temperature is 80℃ and the drying time is 8h.

7. The method for synergistic preparation of ultra-large cylindrical sodium-ion battery materials adapted to the NFPP-hard carbon system according to claim 1, characterized in that, The zinc salt described in S4 is one or more of zinc nitrate hexahydrate, zinc chloride, or zinc sulfate; the aluminum salt is one or more of aluminum nitrate nonahydrate, aluminum chloride, or aluminum sulfate; the concentration of the mixed metal salt solution is 0.2–0.4 mol / L; the amount of polyvinylpyrrolidone added is 0.8–1.2% of the total mass of the metal salt; the reaction temperature is 100℃, the stirring rate is 350 r / min, and the reaction time is 6 h; the heating rate of the tube furnace calcination is 2℃ / min, the calcination temperature is 500–550℃, and the holding time is 4 h.

8. The method for synergistic preparation of ultra-large cylindrical sodium-ion battery materials adapted to the NFPP-hard carbon system according to claim 1, characterized in that, The mass ratio of sodium alginate to deionized water in S5 is 1:150-180; the concentration of calcium chloride solution is 0.5-1.0 mol / L, and the calcium ion concentration in the system after its addition is 0.1-0.15 mol / L; the mass ratio of hard carbon to sodium alginate is 10:1.0-1.5; the mass ratio of aniline to sodium alginate is 1:1.0-1.2; the amount of sodium dodecyl sulfate is 0.03-0.04% of the total mass of the mixed system; the mass fraction of ammonium persulfate solution is 2.0-2.5%, and the dropping rate is 2 drops / s; the freeze-drying temperature is -40 to -20℃, and the drying time is 24-36 h.

9. The method for synergistic preparation of ultra-large cylindrical sodium-ion battery materials adapted to the NFPP-hard carbon system according to claim 1, characterized in that, The volume ratio of the nitrogen-oxygen mixture in S6 is 92:8; the heating rate is 3℃ / min; the co-treatment temperature is 550~650℃; the holding time is 3h; and the gas flow rate during the co-treatment process is 80~120mL / min. The solid content of the positive electrode slurry in S7 is 40-60%; the vacuum drying temperature is 110℃ and the drying time is 14h; the compacted density after rolling is 1.3-1.5g / cm³; the concentration of the electrolyte in S9 is 1.2mol / L, and the volume ratio of ethylene carbonate to dimethyl carbonate in the solvent is 1:1.5; the charging current during formation is 0.08C and the discharging current is 0.15C; the aging temperature is 30-35℃ and the aging time is 36h.

10. The method for synergistic preparation of ultra-large cylindrical sodium-ion battery materials adapted to the NFPP-hard carbon system according to any one of claims 1-9, characterized in that, It also includes steps such as NFPP cathode residual alkali control and doping stabilization, hard carbon anode multi-level structure modification, and synergistic thermal treatment of the cathode and anode interface. The specific operations are as follows: S2-2. Residual Alkali Control and Doping Stabilization of NFPP Cathode: The NFPP cathode material treated with S2 or S2-1 is mixed with a 1-3% (w / w) dilute citric acid solution at a liquid-solid ratio of 1g:20-30mL, stirred and washed until neutral, and then vacuum dried; the cathode material with residual alkali controlled is then mixed with TiO2-Al2O3 composite stabilizing agent, and cooled to obtain the doped and stabilized NFPP cathode material; S5-2. Modification of hard carbon anode multi-level structure: The hard carbon anode material treated with S5 or S5-1 is mixed with glucose porous carbon precursor at a mass ratio of 100:5-15. Polyethylene glycol pore-forming agent accounting for 2-8% of the total mass of the mixture is added, and deionized water is added at a ratio of 1g:10-20mL. After drying, the mixture is heated to 600-800℃ and calcined for 3-5 hours. After cooling, a modified hard carbon anode material with a microporous-mesoporous multi-level pore structure is obtained. S6-1. Synergistic heat treatment of positive and negative electrode interfaces: The NFPP positive electrode material obtained in S2-2 and the hard carbon negative electrode material obtained in S5-2 are mixed at a mass ratio of 1:0.8 to 1.2 and placed in an atmosphere furnace. A nitrogen-hydrogen mixed gas with a volume ratio of 95 to 98:2 to 5 is introduced at a gas flow rate of 60 to 100 mL / min. The temperature is first raised to 150 to 200℃ at a rate of 2℃ / min for 1 to 2 hours, then raised to 400 to 600℃ at a rate of 2 to 3℃ / min and held for 1.5 to 3 hours. Finally, an inert gas is introduced and the furnace is cooled to room temperature.

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