High-initial-activity low-temperature fast-charging sodium ion battery and preparation method thereof

Abstract

The application discloses a high-initial-efficiency low-temperature fast-charging sodium ion battery and a preparation method thereof, and relates to the field of sodium ion batteries.The modified hard carbon fiber negative electrode with disordered curved carbon layer structure is prepared by taking a thermoplastic resin as a precursor, performing melt spinning, hexamethylenetetramine crosslinking, oxidation and high-temperature carbonization; meanwhile, the diaphragm base film is modified by polydopamine and loaded with nanoparticles to obtain a modified diaphragm with high liquid affinity and high ion selectivity. The application realizes the synergistic adaptation of the negative electrode and the diaphragm, constructs an efficient sodium ion transmission channel, and the first coulombic efficiency of the negative electrode can reach 95%, the initial efficiency of the full battery is 93%, the discharge performance is excellent at an extreme low temperature of-20 DEG C, and the long cycle stability is significantly improved at-10 DEG C, thereby effectively breaking through the problem that the traditional sodium ion battery cannot simultaneously achieve high initial efficiency and wide temperature fast charging.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion batteries, and in particular to a high-efficiency, low-temperature, fast-charging sodium-ion battery and its preparation method. Background Technology

[0002] Sodium-ion batteries, with their abundant and widely distributed sodium resources, low cost, and excellent safety, and their similar working principle to lithium-ion batteries, can serve as a replacement for lithium-ion batteries. However, the radius of sodium ions (0.95 Å) is much larger than that of lithium ions, resulting in slow diffusion kinetics within the bulk electrode material and high charge transfer resistance at the electrode / electrolyte interface. This problem is even more pronounced at low temperatures. Sodium-ion batteries typically operate within a temperature range of -20°C to 55°C. When the ambient temperature drops below -20°C, the batteries exhibit problems such as rapid reversible capacity decay, charging difficulties, significantly increased polarization, and a sharp decline in cycle stability, failing to meet the usage requirements of special scenarios such as high-altitude, cold regions, and polar regions. Meanwhile, hard carbon, as the mainstream anode material for sodium-ion batteries, always faces an inherent trade-off between initial coulombic efficiency (ICE) and rate performance. Current technologies, such as porosimetry and high specific surface area modifications to improve rate performance, often exacerbate irreversible electrolyte decomposition, leading to a significant reduction in ICE. Conversely, densification and low specific surface area modifications to improve ICE sacrifice ion transport channels, worsening rate performance and low-temperature adaptability. Therefore, achieving both high initial efficiency and low-temperature adaptability while maintaining high power characteristics is crucial for advancing the industrialization of sodium-ion batteries.

[0003] To address the aforementioned issues, existing technologies primarily focus on optimization from a single dimension, resulting in the following limitations: For instance, at the anode material optimization level, current technologies often optimize hard carbon anode performance through precursor modification, heteroatom doping, and pore structure control. For example, reducing the pyrolysis heating rate and pre-oxidation treatment can increase the initial coulombic efficiency of hard carbon to 85%–90%, but significantly degrades rate performance. Etching to create pores and heteroatom doping can improve the rate performance of hard carbon, but this drastically increases the specific surface area, generally resulting in an initial coulombic efficiency below 85%, and further exacerbates interfacial side reactions at low temperatures, leading to severe capacity decay. More critically, existing modification schemes cannot overcome the triangular constraint of "high initial efficiency (half-cell initial efficiency > 92%, full-cell > 90%) - high rate (≥ 10C) - low temperature (-20℃ capacity retention ≥ 85%) adaptation," making it difficult to simultaneously meet these three core performance requirements. Regarding separator optimization: Traditional commercial separators inherently suffer from strong hydrophobicity, poor electrolyte wettability, low sodium ion transport number, and poor thermal stability. At low temperatures, the separator's affinity for the electrolyte further decreases, and the resistance to ion transmembrane transport increases exponentially, becoming a core bottleneck for battery low-temperature performance. Furthermore, existing modification methods such as ceramic coating and polymer grafting can only improve the wettability and thermal stability of the separator to a limited extent; they cannot achieve selective ion transport, and the increase in sodium ion transport number is limited, failing to fundamentally solve the concentration polarization problem at low temperatures. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a high initial efficiency low temperature fast-charging sodium-ion battery and its preparation method, aiming to solve the problems of low initial coulombic efficiency, difficulty in low temperature charging and discharging, and poor rate performance of existing sodium-ion batteries.

[0005] To achieve the above objectives, the present disclosure adopts the following technical solution: In a first aspect, this disclosure provides a high-efficiency, low-temperature, fast-charging sodium-ion battery, comprising a positive electrode, a negative electrode, a modified separator, and an electrolyte; The negative electrode sheet includes a negative electrode active material, which includes modified hard carbon with nanopores. The interlayer spacing of the modified hard carbon is 0.380-0.386 nm, which can provide a low-barrier fast insertion and extraction channel for sodium ions, improve ion diffusion kinetics, and improve rate and low-temperature performance.

[0006] The average pore size of the nano-closed pores is 1.2-1.3 nm, which can provide sufficient and uniform sodium ion storage sites, ensuring high reversible capacity, while avoiding the problems of interfacial side reactions and increased transport resistance caused by pore size that is too large or too small.

[0007] The modified hard carbon has a BET specific surface area of ​​1.0-2.0 m². 2 / g is used to reduce irreversible decomposition of the electrolyte, reduce sodium loss during SEI film formation, and effectively improve initial coulombic efficiency. The synergistic matching of these three factors enables the modified hard carbon anode to simultaneously possess high initial efficiency, excellent rate performance, and good low-temperature adaptability.

[0008] The modified diaphragm is obtained by grafting functionalized nanoparticles onto a diaphragm base membrane after interfacial modification with polydopamine. The functionalized nanoparticles include a nanoparticle matrix and cationic or anionic groups loaded thereon.

[0009] By modifying the interface of polydopamine and combining it with anionic or cationic grafted nanoparticles, a modified membrane with high wettability, high ion transference number, and high thermal stability can be constructed to solve the problem of high resistance to ion transmembrane transport at low temperatures.

[0010] The modification principle of the modified separator is as follows: The polydopamine interface layer effectively enables the functionalized nanoparticles to firmly bond with the base membrane, solving the problem of easy detachment of traditional ceramic coatings, while improving the hydrophilicity of commercial conventional separators; the nanoparticle matrix modified by grafting anionic or cationic groups has good ion selectivity, which can effectively regulate the electrochemical performance of the battery interface. The grafted functionalized groups ionize in the electrolyte to form fixed negative charge sites. Through the Donnan repulsion effect, the sulfonate anions attached to the separator, based on the principle of electrostatic repulsion, repel and restrict the negatively charged electrolyte anions in the electrolyte, effectively inhibiting the transmembrane migration of anions. At the same time, it has a directional adsorption effect on sodium ions, and a directional traction effect on the sodium ions, the charge carriers of the battery, optimizing the interfacial characteristics and ion transport kinetics of the separator, while improving high-temperature safety performance. The addition of modified groups not only improves electrolyte affinity, but also optimizes the solvation structure, reduces the resistance to ion transmembrane transport, promotes the dissociation of electrolyte salts, and constructs efficient ion channels.

[0011] The following are preferred technical solutions of this disclosure, but are not intended to limit the technical solutions provided by this disclosure. The technical objectives and beneficial effects of this disclosure can be better achieved through the following technical solutions.

[0012] As a preferred technical solution of this disclosure, the modified hard carbon is a modified hard carbon fiber with a diameter of 10-50μm, such as 10μm, 20μm, 30μm, 40μm or 50μm, but is not limited to the listed values. Other values ​​not listed above are also applicable.

[0013] When the diameter of the modified hard carbon fiber is >50μm, the diffusion path of the sodium ion bulk phase is extended exponentially, directly affecting the rate capability and low-temperature fast charging performance. At the same time, when the diameter of the modified hard carbon fiber is too large, there is a gradient difference in the thermal conductivity and pyrolysis small molecule escape rate between the surface and core of the modified hard carbon fiber during carbonization, making it difficult to form closed pores with low specific surface area and uniform size. When the diameter of the modified hard carbon fiber is <10μm, the specific surface area increases rapidly, irreversible side reactions are aggravated, the preparation is difficult, and the stability of the microcrystalline structure decreases.

[0014] As a preferred technical solution of this disclosure, the porosity of the modified membrane is 40%-50%, such as 40%, 42%, 45%, 47% or 50%, but is not limited to the listed values. Other values ​​not listed above are also applicable.

[0015] As a preferred technical solution of this disclosure, the air permeability of the modified diaphragm is 150-240s / 100mL, such as 150s / 100mL, 180s / 100mL, 220s / 100mL or 240s / 100mL, but is not limited to the listed values. Other values ​​not listed above are also applicable.

[0016] As a preferred technical solution of this disclosure, the contact angle of the modified diaphragm is ≤30°, such as 30°, 28°, 24° or 20°, but is not limited to the listed values. Other values ​​not listed above are also applicable.

[0017] The aforementioned physical and chemical properties ensure that the modified separator has sufficient mechanical strength and structural stability while enabling rapid and thorough electrolyte wetting, reducing ion transport resistance, and forming efficient and stable sodium ion transmembrane channels. Moderate porosity and permeability can prevent pore blockage or insufficient permeability, balancing ion transport efficiency and battery safety performance. The low contact angle can improve the electrolyte affinity of the modified separator at low temperatures, alleviate concentration polarization, and jointly ensure the stable operation of sodium-ion batteries in fast charging and low-temperature environments.

[0018] As a preferred technical solution of this disclosure, the particle size of the nanoparticle matrix is ​​5-20nm, such as 5nm, 10nm, 15nm or 20nm, but is not limited to the listed values. Other values ​​not listed above are also applicable.

[0019] This limited particle size range allows the nanoparticle matrix to be uniformly dispersed and stably attached to the surface of the membrane, avoiding the agglomeration problem that easily occurs when the particle size is less than 5nm, and also preventing the nanoparticle matrix from clogging the pores of the membrane when the particle size is greater than 20nm.

[0020] As a preferred technical solution of this disclosure, the nanoparticles include one of two-dimensional transition metal carbide / nitride nanoparticles (MXene particles), silica nanoparticles, and metal-organic framework materials (MOF).

[0021] By selecting the aforementioned nanoparticles, their high specific surface area, tunable interfacial properties, and good dispersibility can be fully utilized. Through surface functionalization grafting, the hydrophilicity, ion selectivity, and thermal stability of the separator can be synergistically improved. This not only creates an efficient directional transport channel for sodium ions but also enhances the bonding force between the nanoparticles and the base film, preventing coating peeling. Thus, from the interfacial transport level, it ensures the realization of low-temperature fast charging and high initial efficiency of the battery.

[0022] As a preferred technical solution of this disclosure, the cationic groups include amino (-NH2) and quaternary ammonium salts (-N). + R3), imidazole group (-C3H3N2) + ), pyridyl (-C5H4N) + Any one of the following: the anionic group includes any one of sulfonic acid group (-SO3H), carboxyl group (-COOH), phosphonic acid group (-PO3H2), and perfluorosulfonic acid group (-CF2SO3H).

[0023] Secondly, this disclosure also provides a method for preparing a high-efficiency, low-temperature, fast-charging sodium-ion battery, comprising the following steps: S100. Preparation of the positive electrode sheet: A positive active material, a first conductive agent, a first binder, and a first solvent are mixed to obtain a positive active slurry. The positive active slurry is coated onto a positive current collector and rolled into shape. The raw material ratio of the positive active slurry is: positive active material : first conductive agent : first binder = 90%-97% : 1.5%-5% : 1.5%-5%; the double-sided surface density of the positive slurry coating is 70 g / m². 2 -500g / m 2 The compaction density of the positive electrode sheet is 1.3 g / cm³. 3 -3.3g / cm 3 .

[0024] S200. Preparation of negative electrode active materials: S201. Melt spinning: Thermoplastic resin fibers are prepared by melt spinning of thermoplastic resin; S202. Crosslinking treatment: The thermoplastic resin fiber is immersed in an aqueous solution containing 15-20 wt% hydrochloric acid (e.g., 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt% or 20 wt%) and 12-18 wt% hexamethylenetetramine (e.g., 12 wt%, 14 wt%, 16 wt% or 18 wt%), heated to 110-130 ℃ (e.g., 110 ℃, 115 ℃, 120 ℃, 125 ℃ or 130 ℃) at a heating rate of 10-25 ℃ / h, and kept at a constant temperature for 1-3 h (e.g., 1 h, 1.5 h, 2 h, 2.5 h or 3 h) to complete the crosslinking reaction.

[0025] In this crosslinking step, hexamethylenetetramine decomposes under the catalysis of hydrochloric acid and fully crosslinks with resin molecules under heating conditions, constructing a stable and continuous methylene bridge spatial network structure inside the fiber, effectively fixing the resin skeleton and inhibiting excessive graphitization and disordered growth of pore structure during subsequent carbonization.

[0026] S203. Oxidation treatment: The cross-linked thermoplastic resin fiber is kept in a vacuum environment at a temperature of 180-220℃ (e.g., 180℃, 190℃, 200℃, 210℃ or 220℃, etc.) for 2-4 hours (e.g., 2 hours, 2.5 hours, 3 hours, 3.5 hours or 4 hours, etc.) to complete the dehydration and dehydrogenation reaction, and obtain the cross-linked-oxidized phenolic resin precursor.

[0027] This step is used to promote the conversion of -C-OH groups in the resin fiber to -C=O groups, so as to avoid the rapid increase in the specific surface area of ​​the material due to the generation of a large amount of gas by the dehydration of hydroxyl groups during subsequent high-temperature carbonization; at the same time, moderate oxidation can stabilize the resin skeleton structure and further enhance the compactness and regularity of the cross-linking network.

[0028] S204. Carbonization treatment: The cross-linked oxidized phenolic resin precursor is heated to 1000-1500℃ (e.g., 1000℃, 1100℃, 1200℃, 1300℃, 1400℃ or 1500℃, etc.) at a heating rate of 1-6℃ / min under an inert atmosphere, and kept at a constant temperature for 1-4h (e.g., 1h, 1.5h, 2h, 2.5h, 3h, 3.5h or 4h, etc.), and then naturally cooled to obtain the modified hard carbon fiber.

[0029] This step allows the precursor to be fully carbonized and form a stable amorphous carbon structure; slow heating helps small molecules escape smoothly, avoiding structural collapse and abnormal increase in specific surface area, while controlling the carbon interlayer spacing and closed pore morphology to obtain modified hard carbon fibers with large interlayer spacing, uniform closed pores and low specific surface area.

[0030] This invention utilizes melt spinning synthesis technology combined with a hexamethylenetetramine (HMTA) crosslinking-oxidation strategy to multidimensionally regulate the structure of resin-derived hard carbon, thereby preparing a modified hard carbon anode material that simultaneously possesses ultra-high initial coulombic efficiency, excellent rate performance, and low-temperature kinetics, breaking through the trade-off between initial efficiency and rate performance.

[0031] The modification principle of the negative electrode active material is as follows: Hexamethylenetetramine (HMTA) has high reactivity with aromatic rings, and as a spatial crosslinking agent, it effectively promotes the occurrence of substitution reaction. The resin-based material can provide a structural platform with a large number of continuous crosslinking sites, which is conducive to the formation of stable methylene bridges (-CH2-), thereby realizing the formation of closed pores and structural stability. By controlling the spatial cross-linking and oxidation of the precursor, the carbon interlayer spacing is expanded while effectively suppressing excessive graphitization of hard carbon during high-temperature carbonization, providing a low-barrier channel for the rapid insertion / extraction of sodium ions. Simultaneously, the resulting disordered, bent carbon layers can encapsulate smaller, more uniform, and abundant closed nanopores, effectively limiting excessive pore growth. This provides ample storage sites for sodium ions, ensuring high reversible capacity, while avoiding excessive electrolyte decomposition caused by open-pore structures. More importantly, the pre-oxidation reaction in this modification scheme promotes the conversion of -C-OH to -C=O groups. This process prevents a sharp increase in specific surface area due to the release of large amounts of gas from -C-OH dehydration during carbonization, significantly reducing irreversible sodium consumption during the formation of the solid electrolyte interphase (SEI) membrane, effectively achieving ultra-high initial coulombic efficiency.

[0032] S300. Preparation of the negative electrode sheet: The negative electrode active material, the second conductive agent, the second binder, and the second solvent are mixed to obtain a negative electrode active slurry. The negative electrode active slurry is coated onto the negative electrode current collector and rolled into shape. The raw material ratio of the negative electrode active slurry is: negative electrode active material: second conductive agent: second binder = 87%-96%: 1%-5%: 3%-8%. The double-sided surface density of the negative electrode slurry coating is 30 g / m². 2 -190g / m 2 The compaction density of the negative electrode sheet is 0.8 g / cm³. 3 -1.1g / cm 3 .

[0033] S400. Preparation of the modified diaphragm: S401. Pretreatment of the diaphragm base membrane: Immerse the diaphragm base membrane in a dopamine hydrochloride (concentration 1-4 mg / mL)-tris(hydroxymethyl)aminomethane hydrochloride buffer (5-20 mM) system and react at room temperature for 24-48 h (e.g., 24 h, 30 h, 36 h, 42 h or 48 h, etc.) to allow polydopamine to spontaneously deposit on the surface of the diaphragm base membrane, forming a uniform and firm interfacial transition layer, improving the hydrophilicity of the diaphragm base membrane and enhancing its bonding force with the inorganic nanoparticle matrix; then wash and vacuum dry at 75-90℃ (e.g., 75℃, 80℃, 85℃ or 90℃, etc.) for 12-24 h (e.g., 12 h, 15 h, 18 h, 21 h or 24 h, etc.) to obtain a polydopamine modified base membrane.

[0034] S402. Preparation of functionalized nanoparticles: The nanoparticle matrix is ​​dispersed in an organic solvent, a grafting agent is added, and the mixture is refluxed at 80°C under a protective atmosphere for 5-8 hours (e.g., 5 hours, 6 hours, 7 hours, or 8 hours) to graft thiol groups (-SH) onto the surface of the nanoparticle matrix, providing reaction sites for subsequent sulfonation; after the reaction is complete, the mixture is centrifuged and washed; it is then vacuum dried at 80°C for 10-20 hours (e.g., 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, or 20 hours) to obtain the product; the product is then sulfonated to introduce sulfonic acid functional sites, imparting ion selectivity and high electrolyte wettability to the membrane, reducing ion transmembrane resistance, and obtaining sulfonic acid functionalized modified nanoparticles.

[0035] S403. Impregnation and loading: The sulfonic acid functionalized modified nanoparticles are prepared into a dispersion, and the polydopamine modified base membrane is impregnated in the dispersion for 20-60 min (e.g., 20 min, 30 min, 40 min, 50 min, or 60 min, etc.); then it is washed and vacuum dried to make the nanoparticle matrix uniformly and stably attached to the membrane surface, and finally a modified membrane with high wettability, high ion transference number, and high thermal stability is obtained.

[0036] S500. Assemble the positive electrode, the negative electrode, the modified separator, and the electrolyte to obtain the above-mentioned high-efficiency low-temperature fast-charging sodium-ion battery.

[0037] Beneficial effects: This invention provides a high-efficiency, low-temperature, fast-charging sodium-ion battery and its preparation method, which has the following advantages: 1. This invention utilizes melt spinning combined with hexamethylenetetramine crosslinking, oxidation, and carbonization processes to prepare a modified hard carbon anode with disordered, curved carbon layers, uniformly closed nanopores, and low specific surface area. The interlayer spacing, pore size, and specific surface area are controlled at 0.380-0.386 nm, 1.2-1.3 nm, and 1.0-2.0 nm, respectively. 2The / g range provides a low-barrier fast insertion / extraction channel for sodium ions, and can reduce the irreversible decomposition of electrolyte and irreversible sodium loss of SEI film. The first coulombic efficiency is significantly improved to 95%, achieving high first efficiency and high rate capability from the intrinsic material properties, while improving sodium ion diffusion kinetics and interface stability at low temperature.

[0038] 2. This invention uses polydopamine interface modification and sulfonic acid-functionalized nanoparticle loading to prepare a modified separator, so that the separator porosity, air permeability, and electrolyte contact angle are controlled at 40%-50%, 150-240s / 100mL, and ≤30°, respectively, and the nanoparticle size is limited to 5-20nm. This solves the problems of traditional separators such as strong hydrophobicity, poor wettability, low ion transference number, easy coating peeling, and easy pore blockage. It improves ion selectivity and transmembrane transport efficiency, fundamentally alleviates concentration polarization under high current and low temperature, and ensures that the battery can still be stably fast charged and efficiently discharged at an extreme low temperature of -20℃.

[0039] 3. This invention achieves efficient synergy between modified hard carbon anode and modified separator, constructing a sodium ion transport channel of "rapid diffusion in bulk phase - rapid transfer at interface - efficient transmembrane transport", enabling the battery to simultaneously possess four core advantages: high initial efficiency, ultra-fast charging, wide temperature range adaptability, and long cycle stability. It has excellent low-temperature discharge capacity retention at -20℃, and no significant attenuation after 600 cycles at -10℃. The battery's initial coulombic efficiency can reach 93%, with small charge and discharge polarization and high reversible capacity, which can meet the stringent usage requirements of high-altitude and cold regions, large-scale energy storage, start-stop power supplies and other scenarios.

[0040] 4. The preparation process of this invention is simple and controllable, highly compatible, and easy to scale up: melt spinning can achieve kilogram-level mass production of hard carbon materials, and the separator adopts room temperature impregnation loading, without the need to modify the existing production line. It has low equipment investment, high production efficiency, and significant cost advantages, and has extremely strong industrial application potential. It can effectively promote the industrialization of high-safety, low-cost, wide-temperature-range sodium-ion batteries. Attached Figure Description

[0041] Figure 1 This is a SEM image of the modified hard carbon fiber obtained in this invention. Figure 2 This is a SEM image of the modified diaphragm prepared according to the present invention; Figure 3 This is a test diagram of the contact angle between the modified diaphragm prepared in this invention and the electrolyte; Figure 4 This is a comparison of the interlayer spacing between Example 1 (the modified hard carbon anode material prepared in this invention) and Comparative Example 1 (conventional commercial hard carbon material). Figure 5 The image shows a comparison of the specific surface area between Example 1 (the modified hard carbon anode material prepared in this invention) and Comparative Example 1 (a conventional commercial hard carbon material). Figure 6 A comparison graph showing the electrochemical performance of coin cells assembled in Example 1 (the modified hard carbon anode material prepared in this invention) and Comparative Example 1 (conventional commercial hard carbon material). Figure 7 This is a comparison chart of the first charge-discharge performance of Example 1 (the sodium-ion battery of the polyanion system prepared by the present invention) and Comparative Example 1 (a conventional commercial hard carbon assembled battery). Figure 8 This is a comparison graph showing the discharge performance of Example 1 (the sodium-ion battery with polyanion system prepared in this invention) and Comparative Example 1 (a conventional commercial battery) at a low temperature of -20°C. Figure 9 This is a comparison chart of the cycle performance of Example 1 (the sodium-ion battery of the polyanion system prepared by the present invention) and Comparative Example 1 (a conventional commercial battery) at a low temperature of -10℃. Detailed Implementation

[0042] To better understand the above-mentioned objectives, features, and advantages of this disclosure, the solutions disclosed herein will be further described below. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0043] Numerous specific details are set forth in the following description in order to provide a full understanding of this disclosure, but this disclosure may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only some, and not all, of the embodiments of this disclosure.

[0044] This invention provides a high-efficiency, low-temperature, fast-charging sodium-ion battery, comprising a positive electrode, a negative electrode, a modified separator, and an electrolyte; the negative electrode comprises a negative electrode active material, which includes modified hard carbon with nanopores; the modified separator comprises a separator base film, a polydopamine interface layer disposed on the separator base film, and functionalized nanoparticles grafted onto the polydopamine interface layer; the functionalized nanoparticles comprise a nanoparticle matrix and cationic or anionic groups supported on the nanoparticle matrix.

[0045] The following are the sources of raw materials used in each embodiment: phenolic resin (purity ≥99%) was purchased from Shandong Laiwu Runda New Material Co., Ltd.; hexamethylenetetramine (HMTA, hexamethylenetetramine, purity ≥99.5%), hydrochloric acid, silica nanoparticles (99.5%), and dopamine hydrochloride were all purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; tris(hydroxymethyl)aminomethane hydrochloride buffer, toluene solution, hydrogen peroxide (H2O2), and sulfuric acid were all purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; (3-mercaptopropyl)trimethoxysilane was purchased from Sigma Aldrich; and the polypropylene diaphragm was provided by Celgard.

[0046] Example 1 This embodiment provides a high-efficiency, low-temperature, fast-charging sodium-ion battery. Referring to the specific embodiment of the high-efficiency, low-temperature, fast-charging sodium-ion battery, its preparation method is as follows: The preparation method of S100 modified hard carbon includes the following steps: S101. Melt spinning: Phenolic resin is spun through a melt spinning device at 250°C (to avoid resin degradation due to excessive temperature or breakage due to excessively low temperature) and a spinning speed of 2500 rpm to prepare phenolic resin fibers.

[0047] S102. Crosslinking treatment: Immerse the phenolic resin fiber in an aqueous solution containing 18wt% hydrochloric acid and 16wt% hexamethylenetetramine, heat it to 120℃ at a heating rate of 15℃ / h, and keep it at the same temperature for 3h to complete the crosslinking reaction.

[0048] S103. Oxidation treatment: The cross-linked phenolic resin fiber is kept in a vacuum environment at 220°C for 3 hours to complete the dehydration and dehydrogenation reaction, and obtain the cross-linked-oxidized phenolic resin precursor.

[0049] S104. Carbonization treatment: The cross-linked-oxidized phenolic resin precursor is placed in a tube furnace and heated to 1300℃ at a heating rate of 4℃ / min under an inert atmosphere. It is then held at the same temperature for 3 hours and allowed to cool naturally to obtain cross-linked-oxidized modified hard carbon.

[0050] The preparation method of the S200 modified diaphragm includes the following steps: S201. Base membrane pretreatment: The polypropylene base membrane was cleaned with anhydrous ethanol and dried, and then immersed in a dopamine hydrochloride (concentration of 2.5 mg / mL)-tris(hydroxymethyl)aminomethane hydrochloride buffer (10 mM) system and reacted at room temperature for 48 h; then it was cleaned and vacuum dried at 80 °C for 20 h to obtain the polydopamine modified base membrane.

[0051] S202. Preparation of Functionalized Silica Nanoparticles: Dry silica nanoparticles (10 nm in diameter) were dispersed in a toluene solution (mass ratio of silica nanoparticles to toluene 1:220). A grafting agent (3-mercaptopropyl)trimethoxysilane (concentration of grafting agent in toluene 40 mmol / L) was added, and the mixture was refluxed at 80 °C for 6 h under nitrogen protection. After the reaction was complete, the mixture was centrifuged and washed to remove unreacted grafting agent and impurities. Finally, it was vacuum dried at 80 °C for 15 h. The obtained product was dispersed in an aqueous hydrogen peroxide solution, oxidized by stirring at room temperature, then acidified with sulfuric acid, centrifuged, washed, and vacuum dried to obtain sulfonic acid-functionalized modified silica nanoparticles.

[0052] S203. Impregnation and loading: Sulfonic acid functionalized modified silica nanoparticles were dispersed in a water-ethanol mixed solvent to prepare a 1.5 wt% dispersion; a polydopamine-modified polypropylene membrane was immersed in the dispersion and impregnated by shaking at room temperature for 40 min. After completion, it was washed and vacuum dried to obtain anion-grafted silica functionalized modified polypropylene membrane.

[0053] The preparation method of S300 high-efficiency low-temperature fast-charging sodium-ion battery includes the following steps: S301. Preparation of the positive electrode sheet: A positive electrode active slurry is obtained by mixing polyanionic positive electrode active material NVP (provided by Beijing Xibei Power Technology Co., Ltd.), a first conductive agent SP, and a first binder PVDF. The raw material ratio of the positive electrode active slurry is positive electrode active material : first conductive agent : first binder = 93% : 2% : 5%. The positive electrode active slurry is then coated onto the positive electrode current collector, with a double-sided areal density of 200 g / m². 2 The positive electrode sheet is then rolled to achieve a compaction density of 1.7 g / cm³. 3 .

[0054] S302. Preparation of the negative electrode sheet: A negative electrode active material, a second conductive agent SP, and a second binder PVDF are mixed to obtain a negative electrode active slurry. The raw material ratio of the negative electrode active slurry is negative electrode active material : second conductive agent : second binder = 93% : 2% : 5%. Then, the negative electrode active slurry is coated onto the negative electrode current collector. The double-sided areal density of the negative electrode slurry coating is 76 g / m². 2 The negative electrode sheet is then rolled to achieve a compaction density of 0.97 g / cm³. 3 .

[0055] S303. The positive and negative electrode sheets are separated by a modified separator, arranged in a regular pattern, and then stacked or wound multiple times. Specifically, this embodiment uses a stacking method.

[0056] S304. Connect the positive electrode tab to the positive current collector and the negative electrode tab to the negative current collector; place the sodium-ion battery semi-finished product in a vacuum oven at 55°C and bake for 24 hours.

[0057] After electrolyte injection, sealing, formation, aging, and capacity testing, the S305 battery is obtained as a high-efficiency, low-temperature, fast-charging sodium-ion battery.

[0058] Example 2 This embodiment provides a high-efficiency, low-temperature, fast-charging sodium-ion battery. Referring to the specific embodiment of the high-efficiency, low-temperature, fast-charging sodium-ion battery, its preparation method is as follows: The preparation method of S100 modified hard carbon includes the following steps: S101. Melt spinning: Phenolic resin is spun through a melt spinning device at 230°C (to avoid resin degradation due to excessive temperature or breakage due to excessively low temperature) and a spinning speed of 2800 rpm to prepare phenolic resin fibers.

[0059] S102. Crosslinking treatment: Immerse the phenolic resin fiber in an aqueous solution containing 15wt% hydrochloric acid and 13wt% hexamethylenetetramine, heat it to 110℃ at a heating rate of 25℃ / h, and keep it at the same temperature for 2h to complete the crosslinking reaction.

[0060] S103. Oxidation treatment: The cross-linked phenolic resin fiber is kept in a vacuum environment at 180°C for 4 hours to complete the dehydration and dehydrogenation reaction, and obtain the cross-linked-oxidized phenolic resin precursor.

[0061] S104. Carbonization treatment: The cross-linked-oxidized phenolic resin precursor is placed in a tube furnace and heated to 1000℃ at a heating rate of 2℃ / min under an inert atmosphere. It is then held at the same temperature for 4 hours and allowed to cool naturally to obtain cross-linked-oxidized modified hard carbon.

[0062] The preparation method of the S200 modified diaphragm includes the following steps: S201. Base membrane pretreatment: The polypropylene base membrane was cleaned with anhydrous ethanol and dried, and then immersed in a dopamine hydrochloride (concentration of 4 mg / mL)-tris(hydroxymethyl)aminomethane hydrochloride buffer (20 mM) system and reacted at room temperature for 30 h; then it was cleaned and vacuum dried at 80 °C for 12 h to obtain the polydopamine modified base membrane.

[0063] S202. Preparation of Functionalized Silica Nanoparticles: Dry silica nanoparticles (15 nm in diameter) were dispersed in a toluene solution (mass ratio of silica nanoparticles to toluene 1:180). A grafting agent (3-mercaptopropyl)trimethoxysilane (concentration of grafting agent in toluene 50 mmol / L) was added, and the mixture was refluxed at 80 °C for 5 h under nitrogen protection. After the reaction was complete, the mixture was centrifuged and washed to remove unreacted grafting agent and impurities. Finally, it was vacuum dried at 80 °C for 15 h. The resulting product was dispersed in an aqueous hydrogen peroxide solution, oxidized by stirring at room temperature, then acidified with sulfuric acid, centrifuged, washed, and vacuum dried to obtain sulfonic acid-functionalized modified silica nanoparticles.

[0064] S203. Impregnation and loading: Sulfonic acid functionalized modified silica nanoparticles were dispersed in a water-ethanol mixed solvent to prepare a 2wt% dispersion; a polydopamine-modified polypropylene membrane was immersed in the dispersion and impregnated by shaking at room temperature for 60 min. After completion, it was cleaned and vacuum dried to obtain anion-grafted silica functionalized modified polypropylene membrane.

[0065] The preparation method of S300 high-efficiency low-temperature fast-charging sodium-ion battery is the same as in Example 1.

[0066] Example 3 This embodiment provides a high-efficiency, low-temperature, fast-charging sodium-ion battery. Referring to the specific embodiment of the high-efficiency, low-temperature, fast-charging sodium-ion battery, its preparation method is as follows: The preparation method of S100 modified hard carbon includes the following steps: S101. Melt spinning: Phenolic resin is spun through a melt spinning device at 260°C (to avoid resin degradation due to excessive temperature or breakage due to excessively low temperature) and a spinning speed of 2100 rpm to prepare phenolic resin fibers.

[0067] S102. Crosslinking treatment: Immerse the phenolic resin fiber in an aqueous solution containing 20wt% hydrochloric acid and 18wt% hexamethylenetetramine, heat it to 130℃ at a heating rate of 20℃ / h, and keep it at the same temperature for 3h to complete the crosslinking reaction.

[0068] S103. Oxidation treatment: The cross-linked phenolic resin fiber is kept in a vacuum environment at 200°C for 2 hours to complete the dehydration and dehydrogenation reaction, and obtain the cross-linked-oxidized phenolic resin precursor.

[0069] S104. Carbonization treatment: The cross-linked-oxidized phenolic resin precursor is placed in a tube furnace and heated to 1500℃ at a heating rate of 6℃ / min under an inert atmosphere. It is then held at the same temperature for 2 hours and allowed to cool naturally to obtain cross-linked-oxidized modified hard carbon.

[0070] The preparation method of the S200 modified diaphragm includes the following steps: S201. Base membrane pretreatment: The polypropylene base membrane was cleaned with anhydrous ethanol and dried, and then immersed in a dopamine hydrochloride (concentration of 1 mg / mL)-tris(hydroxymethyl)aminomethane hydrochloride buffer (5 mM) system and reacted at room temperature for 24 h; then cleaned and vacuum dried at 90 °C for 24 h to obtain the polydopamine modified base membrane.

[0071] S202. Preparation of Functionalized Silica Nanoparticles: Dry silica nanoparticles (5 nm in diameter) were dispersed in a toluene solution (mass ratio of silica nanoparticles to toluene 1:240). A grafting agent (3-mercaptopropyl)trimethoxysilane (concentration of grafting agent in toluene 25 mmol / L) was added, and the mixture was refluxed at 80 °C for 8 h under nitrogen protection. After the reaction was complete, the mixture was centrifuged and washed to remove unreacted grafting agent and impurities. Finally, it was vacuum dried at 80 °C for 20 h. The obtained product was dispersed in an aqueous hydrogen peroxide solution, oxidized by stirring at room temperature, then acidified with sulfuric acid, centrifuged, washed, and vacuum dried to obtain sulfonic acid-functionalized modified silica nanoparticles.

[0072] S203. Impregnation and loading: Sulfonic acid-functionalized silica nanoparticles were dispersed in a water-ethanol mixed solvent to prepare a 1wt% dispersion; a polydopamine-modified polypropylene membrane was immersed in the dispersion and impregnated by shaking at room temperature for 20 min. After completion, it was cleaned and vacuum dried to obtain anion-grafted silica-functionalized polypropylene membrane.

[0073] The preparation method of S300 high-efficiency low-temperature fast-charging sodium-ion battery is the same as in Example 1.

[0074] Comparative Example 1 This comparative example provides a sodium-ion battery, which is the same as the high-efficiency low-temperature fast-charging sodium-ion battery in Example 1, except that: the negative electrode active material is a conventional hard carbon material, specifically, the conventional hard carbon material is a commercially available hard carbon material (model: Type-2, purchased from Kuraray Co., Ltd.); the separator is not modified and is a conventional polypropylene separator (purchased from Celgard). That is, this comparative example is a battery made of conventional hard carbon and conventional separator.

[0075] Comparative Example 2 This comparative example provides a sodium-ion battery, which is the same as the high-efficiency low-temperature fast-charging sodium-ion battery in Example 1, except that the negative electrode active material is a conventional hard carbon material. Specifically, the conventional hard carbon material is a commercially available hard carbon material (model: Type-2, purchased from Kuraray Co., Ltd.).

[0076] Comparative Example 3 This comparative example provides a sodium-ion battery, which is the same as the high-efficiency low-temperature fast-charging sodium-ion battery in Example 1, except that the negative electrode active material is obtained by the preparation method of Example 1, and the separator is an unmodified conventional polypropylene base film.

[0077] Comparative Example 4 This comparative example provides a sodium-ion battery, which is the same as the high-efficiency low-temperature fast-charging sodium-ion battery in Example 1, except that: the negative electrode active material is prepared by the same method as in Example 1, and the separator is only modified with polydopamine on the base film without the introduction of functionalized nanoparticles.

[0078] Performance testing (a) Morphological characteristics Figure 1 Scanning electron microscope (SEM) images of the cross-linked-oxidative modified hard carbon material prepared in Example 1 are shown. As can be seen from the images, the material exhibits a micron-sized fiber morphology, with the fiber diameter falling within the 10-50 μm range specified in this invention. This demonstrates that the modification scheme provided by this invention can achieve control over the fiber morphology and size.

[0079] Figure 2Scanning electron microscope (SEM) images of the modified membrane material prepared in Example 1 are shown. As can be seen from the images, the polypropylene base membrane exhibits a three-dimensional network porous structure. The nano-silica particles (a number of white dots) are uniformly dispersed and firmly attached to the surface of the base membrane fibers. There is no obvious agglomeration, accumulation, or blockage of the base membrane pores. This indicates the synergistic effect of polydopamine interface modification and sulfonic acid functionalized nanoparticle loading, which ensures that the membrane has suitable porosity and interconnected pores.

[0080] (ii) Contact angle The contact angle between the modified diaphragm and the electrolyte was determined. The test method followed the nanofilm contact angle measurement method (GB / T30447-2013). The test results are as follows: Figure 3 As shown.

[0081] As can be seen from the figure, the modified membrane exhibits excellent wettability to the electrolyte, with a contact angle of 23° (within the ≤30° limit of this invention). This indicates that the polydopamine modification and sulfonic acid functionalized nanoparticle loading can improve the hydrophilicity of the membrane surface and effectively enhance the membrane's affinity for the electrolyte under low-temperature conditions.

[0082] (iii) Interlayer spacing and specific surface area The interlayer spacing (e.g., between the cross-linked-oxidative modified hard carbon material prepared in Example 1 and the conventional commercial hard carbon material (Comparative Example 1) was measured. Figure 4 (as shown) and specific surface area (as shown) Figure 5 As shown in the figure, the specific surface area of ​​BET in Comparative Example 1 is 6.3 m². 2 / g, while the specific surface area of ​​the modified hard carbon material of this invention is 1.5m². 2 / g, within the range of 1.0-2.0m as defined in this invention. 2 Within the optimal range of / g, the overall adsorption capacity of the adsorption curve is lower, proving that the cross-linking, oxidation, and carbonization processes effectively seal the surface pores of the material, inhibit the formation of surface defects, and reduce the specific surface area of ​​the material. Combined with Figure 4 Data shows that the carbon interlayer spacing of the hard carbon material of this invention is widened to 0.383 nm, which is greater than the interlayer spacing value of conventional hard carbon (0.365 nm).

[0083] (iv) Electrochemical performance of button cells The electrochemical performance of coin cells was determined. Coin cells were assembled using the modified hard carbon anode material and modified separator prepared in Example 1, and the conventional commercial hard carbon material and conventional separator from Comparative Example 1. The test conditions were: at 25°C, the cells were discharged to 0V at a constant current and constant voltage of 0.1C (cutoff current ≤10μA), and then charged to 1.5V at a constant current of 0.1C. The results are as follows: Figure 6 As shown.

[0084] The results showed that the initial coulombic efficiency (ICE) of Comparative Example 1 was only 89%, while that of Example 1 was improved to 95%. In addition, the material of the present invention has a lower voltage plateau in the low specific capacity range, less voltage polarization during subsequent capacity utilization, and a smoother overall curve.

[0085] (v) Initial charge-discharge performance of sodium-ion batteries The initial charge-discharge performance of sodium-ion batteries was determined under the following conditions: the battery was charged at 1C (1.5A) current and constant voltage to 3.65V in an environment of 25℃, the cutoff current was 0.1C, and the battery was discharged at 1C constant current to 2.0V. The voltage range was 2.0-3.65V. The initial coulombic efficiency was calculated as (initial discharge capacity / initial charge capacity) × 100%.

[0086] The sodium-ion battery prepared in Example 1 was compared with the sodium-ion battery prepared in Comparative Example 1, and the results are as follows: Figure 7 As shown in the figure, the initial coulombic efficiency of the sodium-ion battery in Comparative Example 1 is only 85.7%, while the initial coulombic efficiency of the sodium-ion battery in Example 1 is improved to 93%. From the curve characteristics, the battery of the present invention has a more stable and wider charge-discharge platform, lower voltage polarization, and more fully utilized capacity.

[0087] (vi) Discharge performance of sodium-ion batteries at -20℃ The discharge performance of a sodium-ion battery at -20℃ was determined. The test conditions were as follows: At 25℃, the battery was charged at a constant current and voltage of 1C (1.5A) to 3.65V, with a cutoff current of 0.1C. It was then discharged at a constant current of 1C to 2.0V, and the discharge capacity was recorded as C0. The voltage range was 2.0-3.65V. The battery was then charged at a constant current and voltage of 1C (1.5A) to 3.65V, with a cutoff current of 0.1C. The battery was then placed in a -20℃ environment and left to stand for 8 hours. Finally, it was discharged at a constant current of *C (a specific rate) to 1.5V, and the discharge capacity was recorded as C0. x -20℃ discharge capacity retention rate = C x / C0×100%.

[0088] The sodium-ion battery prepared in Example 1 was compared with the sodium-ion battery prepared in Comparative Example 1, and the results are as follows: Figure 8 As shown in the figure, the two curves correspond to the sodium-ion battery of Comparative Example 1 (a conventional commercial hard carbon-polyanion battery) at 1C rate and the sodium-ion battery of Example 1 (the polyanion battery of this invention) at 2C rate, respectively. Furthermore, even with a higher testing rate, the battery of this invention exhibits a significantly higher discharge plateau than the control group, a smoother voltage decay rate, and superior capacity utilization and overall capacity retention compared to conventional batteries.

[0089] (vii) Cycle performance of sodium-ion batteries at -10℃ The cycle performance of sodium-ion batteries was determined at a low temperature of -10℃. The test conditions were as follows: the battery was subjected to constant current charge-discharge cycles at a specific rate (C) in an environment of -10℃, with a voltage range of 2.0-3.65V. The discharge capacity of the first cycle was recorded as C0, and the discharge capacity after cycling at the specific rate to a certain number of cycles was recorded as C. x Capacity retention rate = C x / C0×100%.

[0090] The sodium-ion battery prepared in Example 1 was compared with the sodium-ion battery prepared in Comparative Example 1, and the results are as follows: Figure 9 As shown in the figure, the two curves correspond to the sodium-ion battery of Comparative Example 1 (a conventional commercial hard carbon-polyanion battery) at a low rate of 0.5C and the sodium-ion battery of Example 1 (the polyanion battery of this invention) at a high rate of 2C, respectively. The data in the figure shows that the capacity of the conventional battery has decreased to less than 80% after only 200 cycles, with an extremely fast capacity decay rate. However, even when the test rate is much higher than that of the control group, the battery of this invention still maintains a high capacity retention rate after 600 long cycles, with a smooth capacity decay and excellent cycle stability throughout the process.

[0091] Specifically, the basic performance comparison data of the batteries prepared in Examples 1-3 and Comparative Examples 1-4 are summarized in Table 1.

[0092] Table 1. Comparison of basic performance of batteries obtained in Examples 1-3 and Comparative Examples 1-4

[0093] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0094] The above description is merely a specific embodiment of this disclosure, enabling those skilled in the art to understand or implement it. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A high-efficiency, low-temperature, fast-charging sodium-ion battery, characterized in that, It includes positive electrode, negative electrode, modified separator and electrolyte; The negative electrode sheet includes a negative electrode active material, which comprises modified hard carbon with nanopores. The modified hard carbon has an interlayer spacing of 0.380-0.386 nm and a specific surface area of ​​1.0-2.0 m². 2 / g, wherein the average pore size of the nano-closed pores is 1.2-1.3 nm; The modified membrane includes a membrane base membrane, a polydopamine interface layer disposed on the membrane base membrane, and functionalized nanoparticles grafted onto the polydopamine interface layer; the functionalized nanoparticles include a nanoparticle matrix and cationic or anionic groups loaded on the nanoparticle matrix.

2. The high-efficiency low-temperature fast-charging sodium-ion battery according to claim 1, characterized in that, The modified hard carbon is a modified hard carbon fiber with a diameter of 10-50 μm.

3. The high-efficiency, low-temperature, fast-charging sodium-ion battery according to claim 1, characterized in that, The modified diaphragm has a porosity of 40%-50%, an air permeability of 150-240s / 100mL, and a contact angle ≤30°.

4. The high-efficiency, low-temperature, fast-charging sodium-ion battery according to claim 1, characterized in that, The particle size of the nanoparticle matrix is ​​5-20 nm.

5. The high-efficiency, low-temperature, fast-charging sodium-ion battery according to claim 1, characterized in that, The nanoparticle matrix includes one of two-dimensional transition metal carbide / nitride nanoparticles, silica nanoparticles, and metal-organic framework materials.

6. The high-efficiency, low-temperature, fast-charging sodium-ion battery according to claim 1, characterized in that, The cationic group includes any one of amino, quaternary ammonium salts, imidazole, and pyridinyl groups; the anionic group includes any one of sulfonic acid, carboxyl, phosphonic acid, and perfluorosulfonic acid groups.

7. A method for preparing a high-efficiency, low-temperature, fast-charging sodium-ion battery as described in any one of claims 1-6, comprising the following steps: Preparation of the positive electrode sheet: The positive electrode active material, the first conductive agent, the first binder and the first solvent are mixed to obtain a positive electrode active slurry. The positive electrode active slurry is coated on at least one surface of the positive electrode current collector and dried to obtain the positive electrode sheet. Preparation of the negative electrode sheet: The negative electrode active material, the second conductive agent, the second binder, and the second solvent are mixed to obtain a negative electrode active slurry. The negative electrode active slurry is coated onto at least one surface of the negative electrode current collector and dried to obtain the negative electrode sheet; wherein, The preparation steps of the negative electrode active material include: sequentially cross-linking, oxidizing, and carbonizing thermoplastic resin fiber and cross-linking agent to obtain the modified hard carbon; Preparation of the modified diaphragm: The diaphragm base membrane is reacted with a dopamine acidic solution to obtain a polydopamine modified base membrane; the nanoparticle matrix is ​​modified with cationic or anionic groups to obtain the functionalized nanoparticles; the functionalized nanoparticles are made into a dispersion, and the polydopamine modified base membrane is immersed in the dispersion to obtain the modified diaphragm; The high-efficiency, low-temperature, fast-charging sodium-ion battery is prepared by assembling the positive electrode, the negative electrode, the modified separator, and the electrolyte.

8. The high-efficiency low-temperature fast-charging sodium-ion battery according to claim 7, characterized in that, The preparation steps of the negative electrode active material include: preparing thermoplastic resin fibers by melt spinning of thermoplastic resin; immersing the thermoplastic resin fibers in an acidic aqueous solution containing hexamethylenetetramine and carrying out a crosslinking reaction under heating; subjecting the thermoplastic resin fibers after the crosslinking reaction to a dehydration and dehydrogenation reaction to obtain a crosslinked-oxidized phenolic resin precursor; and carbonizing the crosslinked-oxidized phenolic resin precursor under an inert atmosphere and allowing it to cool naturally to obtain the modified hard carbon. Preferably, the melt spinning temperature is 230-270℃ and the rotation speed is 2000-3000 rpm; Preferably, the acidic aqueous solution containing hexamethylenetetramine is an aqueous solution containing 15-20 wt% hydrochloric acid and 12-18 wt% hexamethylenetetramine; the crosslinking reaction is carried out by heating to 110-130°C at a heating rate of 10-25°C / h and holding at the temperature for 1-3 hours. Preferably, the dehydration and dehydrogenation reaction step is carried out in a vacuum environment at a temperature of 180-220°C for 2-4 hours. Preferably, in the carbonization process, the temperature is raised to 1000-1500°C at a heating rate of 1-6°C / min under an inert atmosphere, and then held at that temperature for 1-4 hours.

9. The high-efficiency, low-temperature, fast-charging sodium-ion battery according to claim 7, characterized in that, The preparation steps of the modified diaphragm include: immersing the diaphragm base membrane in a dopamine hydrochloride buffer system and reacting at room temperature; then washing and vacuum drying under heating conditions to obtain the polydopamine modified base membrane; dispersing the nanoparticle matrix in an organic solvent, adding a grafting agent, and refluxing under a protective atmosphere and heating conditions; after the reaction is completed, centrifuging and washing; vacuum drying under heating conditions to obtain the modified nanoparticle matrix; grafting cationic or anionic groups onto the modified nanoparticle matrix to obtain the functionalized nanoparticles; preparing the functionalized nanoparticles into the dispersion, immersing the polydopamine modified base membrane in the dispersion; then washing and vacuum drying to obtain the modified diaphragm. Preferably, the dopamine hydrochloride buffer system is a dopamine hydrochloride-tris(hydroxymethyl)aminomethane hydrochloride buffer; the reaction time at room temperature is 24-48 hours. Preferably, the polydopamine-modified base film is obtained by vacuum drying at 75-90℃ for 12-24 hours. Preferably, after adding the grafting agent, the reaction is carried out at 80°C for 5-8 hours; Preferably, the polydopamine-modified base film is immersed in the dispersion for 20-60 minutes; Preferably, the modified nanoparticle matrix is ​​obtained by vacuum drying at 80°C for 10-20 hours.

10. The high-efficiency, low-temperature, fast-charging sodium-ion battery according to claim 7, characterized in that, By mass fraction, the amount of positive electrode active material added is 90%-97%, the amount of the first conductive agent added is 1.5%-5%, and the amount of the first binder added is 1.5%-5%; the amount of negative electrode active material added is 87%-96%, the amount of the second conductive agent added is 1%-5%, and the amount of the second binder added is 3%-8%.

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