Composite sodium-supplementing materials, preparation methods, electrodes and batteries

Abstract

This invention relates to a composite sodium-replenishing material, its preparation method, an electrode, and a battery. The composite sodium-replenishing material comprises a matrix, a sodium-replenishing agent body, and a conductive reinforcement. The matrix is ​​porous carbon fiber; the sodium-replenishing agent body is distributed on the surface and within the pores of the matrix; the conductive reinforcement is partially embedded within the sodium-replenishing agent body and partially located on its outer surface. The preparation method of the composite sodium-replenishing material includes the following steps: hydrothermal treatment of a dispersion; the dispersion comprises porous carbon fibers, sodium salt, and a conductive reinforcement. The composite sodium-replenishing material of this invention can improve the initial efficiency and capacity retention of sodium-ion batteries.

Description

Technical Field

[0001] This invention relates to a composite sodium-supplementing material, its preparation method, an electrode, and a battery. Background Technology

[0002] Sodium-ion batteries, as an alternative to lithium-ion batteries, have attracted widespread attention due to their abundant resources, low cost, and environmental friendliness, especially in the field of large-scale energy storage. However, sodium-ion batteries generally suffer from low initial coulombic efficiency, mainly because side reactions such as the formation of a solid electrolyte interphase (SEI) film at the negative electrode during the first charge and discharge process consume a large amount of sodium ions, leading to irreversible capacity loss. To alleviate this problem, sodium-replenishing materials are often introduced into the positive electrode to release sodium ions during the initial charging process. + It compensates for negative electrode losses and improves the initial efficiency and capacity retention of the entire battery.

[0003] Currently, using inorganic sodium salts (such as Na₂CO₃, Na₃PO₄, Na₂S, etc.) as sodium replenishment sources is a common strategy. These salts are low in cost, high in sodium content, and have good thermal stability, and can release sodium ions under specific voltages. Existing sodium replenishment technologies mostly employ the method of physically mixing sodium salts with positive electrode materials or conductive agents to prepare composite materials. Although the process is simple, it generally suffers from problems such as uneven sodium salt distribution, weak interfacial bonding, and insufficient conductivity, which affect the sodium ion release efficiency and the structural stability of the material.

[0004] Building upon this foundation, researchers have explored the structural design of various sodium-supplementing materials. For instance, CN117199360A discloses a method for preparing a sodium carbonate / carbon composite cathode sodium-supplementing additive. This method involves preparing defect-rich Na₂CO₃ crystals through high-temperature quenching, followed by mechanical ball milling to mix them with a conductive carbon matrix, forming a composite structure. The aim is to reduce the sodium salt decomposition potential and enhance electronic conductivity. This method represents a typical sodium-supplementing strategy based on defect modulation and physical composite methods; however, the overall structure is still constructed using a powder dispersion method, resulting in limited particle stability and spatial coordination.

[0005] CN116826060A employs a combination of electrospinning and carbonization to produce a fibrous composite sodium-supplementing material by blending a polymer with sodium salt, spinning the resulting fibers, and then heat-treating. This structure exhibits good electrical conductivity and facilitates electrolyte wetting, thus improving the sodium salt release rate to some extent. However, this method requires carbonization at high temperatures of 400-1000℃, which carries the risk of thermal decomposition or loss of the inorganic sodium salt, affecting its effective loading and release controllability. Furthermore, the sodium salt is already incorporated into the system before spinning, making precise control of particle size and spatial distribution difficult. Summary of the Invention

[0006] The technical problem this invention aims to solve is to overcome the deficiencies in the prior art and provide a composite sodium-replenishing material, a preparation method, an electrode, and a battery. The composite sodium-replenishing material of this invention can improve the initial efficiency and capacity retention rate of sodium-ion batteries.

[0007] The present invention solves the above-mentioned technical problems through the following technical solution:

[0008] In a first aspect, the present invention provides a composite sodium supplement material, which includes a matrix, a sodium supplement agent body and a conductive reinforcement, wherein the matrix is ​​porous carbon fiber;

[0009] The sodium supplement body is distributed on the surface and within the pores of the matrix; the conductive reinforcement is partially embedded inside the sodium supplement body and partially located on the outer surface of the sodium supplement body.

[0010] In this invention, the material of the sodium supplement body is conventionally chosen in the art, such as sodium-containing carbon oxides.

[0011] In some specific embodiments of the present invention, the material of the sodium supplement body is a sodium-containing carbon oxide compound with a cyclic or chain structure, such as sodium carbonate, sodium oxalate, or sodium squartzate.

[0012] In this invention, the material of the conductive reinforcement is conventionally chosen in the art, such as graphene. The graphene can be formed by in-situ reduction of graphene oxide.

[0013] In this invention, the mass ratio of the porous carbon fiber to the sodium supplement body can be 1:(0.3-3), for example 1:(2.5-3).

[0014] In this invention, the mass ratio of the conductive enhancer to the sodium supplement body can be 1:(10-30), for example 1:(16.7-20).

[0015] In this invention, the diameter of the porous carbon fiber can be 600-1200 nm, for example 700 nm, 850 nm or 1050 nm.

[0016] In this invention, the average pore size of the porous carbon fiber can be 50-500 nm, preferably 100-300 nm, for example 155 nm, 190 nm or 235 nm.

[0017] In this invention, the length of the porous carbon fiber can be 10 μm-5 mm, preferably 100-1000 μm, for example 100 μm, 200 μm, 400 μm, 800 μm or 900 μm;

[0018] In some specific embodiments of the present invention, the length of the porous carbon fiber is 100-400 μm, 200-800 μm or 400-900 μm.

[0019] In this invention, the porosity of the porous carbon fiber can be 40%-80%, preferably 60%-80%, for example 65%, 68%, 70%, 73%, 74% or 78%.

[0020] In some specific embodiments of the present invention, the porosity of the porous carbon fiber is 65%-70%, 68%-73%, or 74%-78%.

[0021] In this invention, the porous carbon fiber can be prepared by the following steps: S1, electrospinning the polymer spinning solution to obtain the spun fiber; the polymer spinning solution includes a polymer precursor and a template agent; S2, heat-treating the spun fiber.

[0022] In step S1, the polymer precursor may be selected from one or more of polyacrylonitrile, polyvinyl alcohol, and polyamide polyvinylpyrrolidone.

[0023] In step S1, the template agent may be polymethyl methacrylate and / or polystyrene;

[0024] In step S1, the solvent of the polymer spinning solution can be an organic solvent, such as N,N-dimethylformamide.

[0025] In step S1, the mass ratio of the polymer precursor to the template agent can be 1:(0.1-1), preferably 1:(0.2-0.6), for example 1:0.3, 1:0.4 or 1:0.5.

[0026] In step S1, the solid content of the polymer spinning solution can be 9wt%-50wt%, preferably 10wt%-50wt%, for example 20wt%.

[0027] In step S1, the voltage of the electrospinning treatment can be 15-25kV, for example 18kV, 20kV or 22kV.

[0028] In step S1, the receiving distance of the electrospinning process can be 15-20 cm, for example, 16 cm, 17 cm or 18 cm.

[0029] In step S1, the feed rate of the electrospinning treatment can be 0.3-1 mL / h, for example, 0.5 mL / h, 0.6 mL / h or 0.7 mL / h.

[0030] In step S2, the heat treatment may sequentially include drying, pre-oxidation, and carbonization. The drying atmosphere may be a vacuum. The drying temperature may be 60-80℃. The drying time may be 12-24 hours. The pre-oxidation atmosphere may be an oxidizing atmosphere, such as air. The pre-oxidation temperature may be 200-250℃, for example, 230℃. The pre-oxidation time may be 2-3 hours. The carbonization atmosphere may be an inert atmosphere, such as a nitrogen atmosphere or a rare gas atmosphere. The carbonization temperature may be 800-1000℃, for example, 900-950℃. The carbonization time may be 2-4 hours, for example, 2-3 hours.

[0031] Secondly, the present invention provides a method for preparing a composite sodium-supplementing material, which includes the following steps: subjecting a dispersion to hydrothermal treatment; the dispersion includes porous carbon fibers, sodium salt and conductive reinforcing agent.

[0032] In this invention, the sodium salt may be a sodium-containing carbon oxide compound, preferably a sodium-containing carbon oxide compound having a cyclic or chain structure, such as sodium carbonate, sodium oxalate, or sodium squartzate.

[0033] In this invention, the conductive enhancer may be graphene oxide and / or reduced graphene oxide.

[0034] In this invention, the mass ratio of the porous carbon fiber to the sodium salt can be 1:(0.3-3), for example 1:(2.5-3).

[0035] In this invention, the mass ratio of the conductive enhancer to the sodium salt can be 1:(10-30), for example 1:(16.7-20).

[0036] In this invention, the concentration of the porous carbon fiber in the dispersion can be 6-20 mg / mL, for example 10 mg / mL.

[0037] In this invention, the temperature of the hydrothermal treatment can be 120-180℃, for example 150℃, 160℃ or 180℃.

[0038] In this invention, the hydrothermal treatment time can be 6-12 hours, for example, 8 hours, 10 hours or 12 hours.

[0039] In this invention, after the hydrothermal treatment, washing and drying can be performed. The washing preferably uses ethanol and / or water. The drying temperature is preferably 60-80°C, for example, 70-80°C.

[0040] Thirdly, the present invention provides a composite sodium supplement material prepared by the method described above.

[0041] Fourthly, the present invention provides an electrode sheet comprising a positive electrode active material and a composite sodium-supplementing material as described above.

[0042] In this invention, the mass ratio of the positive electrode active material to the composite sodium supplement material is preferably (8-30):1, more preferably (15-20):1, for example 16.4:1.

[0043] Fifthly, the present invention provides a battery comprising the electrodes as described above.

[0044] In a sixth aspect, the present invention provides an application of the battery as described above, wherein the charge / discharge voltage range is 2-4.3V, preferably 2-4V.

[0045] The positive and progressive effects of this invention are as follows:

[0046] (1) The composite sodium supplement material of the present invention has a matrix, a sodium supplement agent body and a conductive reinforcement interconnected to form a three-dimensional conductive network of interpenetrating "fiber-sheet" structure, which integrates multiple functions such as matrix support, electronic conduction and interface stabilization, establishes an efficient ion / electron transport channel, reduces the electrochemical impedance of the material, and helps to reduce the electrochemical decomposition potential of the composite sodium supplement material.

[0047] (2) The composite sodium supplement material of the present invention utilizes porous carbon fiber as the matrix skeleton, which has significant one-dimensional features and larger pore size, providing sufficient containment space and loading sites for the sodium supplement body, ensuring uniform distribution under high loading, and can also precisely control the size and spatial distribution of the sodium supplement body through physical confinement, significantly improving the mechanical integrity and electrochemical performance of the composite sodium supplement material.

[0048] (3) The composite sodium supplement material of the present invention can be constructed by electrospinning to form a three-dimensional porous carbon fiber skeleton; during the carbonization process, the template agent is pyrolyzed or ablated to form pores, and finally a matrix with high specific surface area and porous structure is obtained, while ensuring that the pore size of the porous carbon fiber is adjustable.

[0049] (4) The preparation method of the present invention utilizes hydrothermal method to grow sodium salt particles in situ on the substrate surface, which enhances the interfacial bonding force between sodium salt and porous carbon fiber, effectively improving the structural stability and sodium ion release efficiency during the sodium supplementation process; during this period, graphene oxide can be reduced to graphene in situ, which helps to construct a three-dimensional conductive network.

[0050] (5) The preparation method of the present invention is carried out under mild conditions, which effectively avoids the thermal decomposition and volatilization loss of sodium salt caused by traditional high-temperature carbonization, significantly improves the loading retention rate of sodium source, and the process is simple and has good controllability.

[0051] (6) The present invention has good adjustability and universality, clear process route, readily available raw materials, potential for large-scale production, and is widely applicable to the field of sodium-ion batteries, with broad application prospects. Attached Figure Description

[0052] Figure 1 This is a transmission electron microscope image of the composite sodium-supplementing material in Example 1. Detailed Implementation

[0053] The present invention will be further illustrated by way of embodiments below, but the present invention is not limited to the scope of the embodiments described herein.

[0054] The specific information of the raw materials used in the following examples and comparative examples is as follows:

[0055] Polyacrylonitrile, PAN, M w ≈150,000.

[0056] Polymethyl methacrylate, PMMA, M w ≈120,000.

[0057] Polyvinylpyrrolidone, PVP, M w ≈1,300,000.

[0058] Polyamide, PA, Nylon 6, M w ≈80,000.

[0059] Polystyrene, PS, M w ≈200,000.

[0060] Commercial porous carbon powder NCP, purchased from Pioneer Nano, model XFP10, with an average pore size of 50 nm.

[0061] Positive electrode active material NFM, NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0062] Conductive carbon black, purchased from TIMCAL, model Super P TM Li.

[0063] PVDF, purchased from Solvay, model Solef® 5130.

[0064] Example 1

[0065] A hydrothermal in-situ composite cathode sodium supplement material based on electrospun porous carbon fiber and its preparation method include the following steps:

[0066] (1) Preparation of porous carbon fiber carrier:

[0067] Polyacrylonitrile and polymethyl methacrylate were mixed at a mass ratio of 10:3, with a total mass of 2.0 g. The mixture was dissolved in 20 g of N,N-dimethylformamide (DMF) and magnetically stirred at room temperature for 12 hours to obtain a uniform spinning solution.

[0068] Fiber membranes were prepared by electrospinning at 25±2℃ and relative humidity <35%, with a voltage of 20 kV, a receiving distance of 16 cm, and a liquid inlet rate of 0.7 mL / h. The resulting fibers were then vacuum dried at 60℃ for 12 hours to remove residual solvent.

[0069] The fiber membrane was then placed in a tube furnace for heat treatment: first, it was heated to 230°C in an air atmosphere at a rate of 3°C / min and pre-oxidized for 2 hours, and then heated to 900°C in an argon atmosphere (flow rate of 100 mL / min) at a rate of 5°C / min and carbonized for 2 hours.

[0070] After the tube furnace cools naturally to room temperature, the product is taken out and ground to finally obtain porous carbon fiber powder with a diameter of 850 nm, an average pore size of 155 nm, a length of about 200-800 μm, and a porosity of about 65%-70%.

[0071] (2) Preparation of sodium salt / graphene / porous carbon fiber composite sodium supplement material

[0072] 600 mg of carbon fiber powder was dispersed in 60 mL of deionized water and ultrasonically treated at 100 W for 10 minutes. Then, 1.8 g of sodium squartzate (Na2C4O4) and 90 mg of graphene oxide (GO) were added sequentially, and the mixture was ultrasonically dispersed in an ice bath for 30 minutes to form a uniform suspension.

[0073] The suspension was transferred to a 100 mL polytetrafluoroethylene-lined high-pressure reactor and reacted at 160 °C for 10 hours.

[0074] After the reaction was completed and the mixture was allowed to cool naturally, the product was rapidly filtered through a Buchner funnel and then washed twice with 40 mL of a 1:1 (v / v) ethanol-water mixture and once with 30 mL of anhydrous ethanol. Finally, it was vacuum dried at 70°C for 12 hours to obtain a blackish-gray sodium squartz-graphene-carbon fiber ternary composite sodium supplement material. Figure 1 Sodium squartz is grown on the surface of porous carbon fibers.

[0075] Example 2

[0076] A hydrothermal in-situ composite cathode sodium supplement material based on electrospun porous carbon fiber and its preparation method include the following steps:

[0077] (1) Preparation of porous carbon fiber carrier:

[0078] Polyvinylpyrrolidone and polymethyl methacrylate were mixed at a mass ratio of 10:4, with a total mass of 2.0 g. The mixture was dissolved in 20 g of N,N-dimethylformamide (DMF) and magnetically stirred at room temperature for 12 hours to obtain a uniform spinning solution.

[0079] Fiber membranes were prepared by electrospinning at 25±2℃ and relative humidity <35%, with a voltage of 22 kV, a receiving distance of 17 cm, and a liquid inlet rate of 0.5 mL / h. The resulting fibers were then vacuum dried at 60℃ for 12 hours to remove residual solvent.

[0080] The fiber membrane was then placed in a tube furnace for heat treatment: first, it was heated to 230°C in an air atmosphere at a rate of 3°C / min and pre-oxidized for 2 hours, and then heated to 900°C in an argon atmosphere (flow rate of 100 mL / min) at a rate of 5°C / min and carbonized for 2 hours.

[0081] After the tube furnace cools naturally to room temperature, the product is taken out and ground to finally obtain porous carbon fiber powder with a diameter of 700 nm, an average pore size of 190 nm, a length of about 400-900 μm, and a porosity of about 68%-73%.

[0082] (2) Preparation of sodium salt / graphene / porous carbon fiber composite sodium supplement material

[0083] 600 mg of carbon fiber powder was dispersed in 60 mL of deionized water and ultrasonically treated at 300 W for 10 minutes. Then, 1.8 g of sodium oxalate (Na2C2O4) and 90 mg of graphene oxide (GO) were added sequentially, and the mixture was ultrasonically dispersed in an ice bath for another 30 minutes to form a uniform suspension.

[0084] The suspension was transferred to a 100 mL polytetrafluoroethylene-lined high-pressure reactor and reacted at 180°C for 8 hours.

[0085] After the reaction was completed and the product was cooled naturally, it was rapidly filtered through a Buchner funnel and washed twice with 40 mL of 1:1 (v / v) ethanol-water mixture and once with 30 mL of anhydrous ethanol. Finally, it was vacuum dried at 70°C for 12 hours to obtain a blackish-gray sodium oxalate-graphene-carbon fiber ternary composite sodium supplement material.

[0086] Example 3

[0087] A hydrothermal in-situ composite cathode sodium supplement material based on electrospun porous carbon fiber and its preparation method include the following steps:

[0088] (1) Preparation of porous carbon fiber carrier:

[0089] Polyamide and polystyrene were mixed at a mass ratio of 10:5, with a total mass of 2.0 g, and dissolved in 20 g of N,N-dimethylformamide (DMF). The mixture was magnetically stirred at room temperature for 12 hours to obtain a uniform spinning solution.

[0090] Fiber membranes were prepared by electrospinning at 25±2℃ and relative humidity <35%, with a voltage of 18 kV, a receiving distance of 18 cm, and a liquid inlet rate of 0.6 mL / h. The resulting fibers were then vacuum dried at 60℃ for 12 hours to remove residual solvent.

[0091] The fiber membrane was then placed in a tube furnace for heat treatment: first, it was heated to 230°C in an air atmosphere at a rate of 3°C / min and pre-oxidized for 2 hours, and then heated to 950°C in an argon atmosphere (flow rate of 100 mL / min) at a rate of 5°C / min and carbonized for 3 hours.

[0092] After the tube furnace cools naturally to room temperature, the product is taken out and ground to finally obtain porous carbon fiber powder with a diameter of 1050 nm, an average pore size of 235 nm, a length of about 100-400 μm, and a porosity of about 74%-78%.

[0093] (2) Preparation of sodium salt / graphene / porous carbon fiber composite sodium supplement material

[0094] Take 600 mg of carbon fiber powder and disperse it in 60 mL of deionized water. After ultrasonic treatment at 200 W for 10 minutes, add 1.5 g of sodium carbonate (Na2CO3) and 90 mg of graphene oxide (GO) in sequence. Continue to ultrasonically disperse in an ice bath for 20 minutes to form a uniform suspension.

[0095] The suspension was transferred to a 100 mL polytetrafluoroethylene-lined high-pressure reactor and reacted at 150 °C for 12 hours.

[0096] After the reaction was completed and the product was cooled naturally, it was rapidly filtered through a Buchner funnel and then washed twice with 40 mL of 1:1 (v / v) ethanol-water mixture and once with 30 mL of anhydrous ethanol. Finally, it was vacuum dried at 80°C for 12 hours to obtain a light gray sodium carbonate-graphene-carbon fiber ternary composite sodium supplement material.

[0097] Comparative Example 1

[0098] Sodium squartz can be used directly as a sodium supplement.

[0099] Comparative Example 2

[0100] Compared with Example 1, the only difference is that commercial porous carbon powder is used as the sodium salt supporting matrix. The preparation process of the composite sodium supplement material is as follows:

[0101] Disperse 600 mg of commercial porous carbon powder in 60 mL of deionized water, sonicate at 100 W for 10 minutes, then add 1.8 g of sodium squartzate (Na2C4O4) and 90 mg of graphene oxide (GO) in sequence, and continue to sonicate in an ice bath for 30 minutes to form a uniform suspension.

[0102] The suspension was transferred to a 100 mL polytetrafluoroethylene-lined high-pressure reactor and reacted at 160 °C for 10 hours.

[0103] After the reaction was completed and the product was cooled naturally, it was rapidly filtered through a Buchner funnel and then washed twice with 40 mL of 1:1 (v / v) ethanol-water mixture and once with 30 mL of anhydrous ethanol. Finally, it was vacuum dried at 70°C for 12 hours to obtain a blackish-gray sodium squartzate-graphene-NCP ternary composite sodium supplement material.

[0104] Comparative Example 3

[0105] Compared to Example 1, the only difference is that GO is not added.

[0106] Example 1: Electrochemical Performance Test

[0107] 1. Test objects: Positive electrode sheets made of sodium-supplemented materials in each embodiment and comparative example.

[0108] 2. Testing Method:

[0109] (1) Preparation of the positive electrode sheet:

[0110] The solid mixture components were weighed out according to the following proportions: 82 wt% positive electrode active material NFM, 5 wt% sodium supplement material, 6 wt% conductive carbon black, and 7 wt% PVDF. Then, an appropriate amount of solvent N-methylpyrrolidone (NMP) was added, and the mixture was mixed at high speed to obtain a slurry.

[0111] The slurry is coated onto aluminum foil and dried at 80℃, then sprayed at 80-120 kg / cm². 2 The pressure is applied during rolling. Finally, the electrode sheet is punched into a circular sheet with a diameter of 10 mm and dried in a vacuum oven at 120℃ for 12 hours to obtain the positive electrode sheet. In addition, a blank control is set up, which differs from the above process only in that the components of the solid mixture are changed to 87wt% positive electrode active material NFM, 6wt% conductive carbon black and 7wt% PVDF.

[0112] (2) Charge and discharge test process:

[0113] After weighing the positive electrode, transfer it to the glove box for use as the working electrode. Assemble the CR 2016 coin cell in the glove box in the order of working electrode, separator, and negative electrode. The negative electrode uses Kuraray hard carbon, and the separator is Whatman glass fiber (Whatman GF / D). The electrolyte is a commercial sodium-ion electrolyte for positive electrodes containing 1 M NaPF6 (1 M sodium hexafluorophosphate NaPF6 dissolved in a mixed solvent of ethylene carbonate EC and diethyl carbonate DEC, where the volume ratio of EC to DEC is 1:1). Connect the assembled coin cell to the battery testing system and perform charge-discharge tests within the specified voltage range (2.0-4.0 V or 2.0-4.3 V).

[0114] 3. Test results: See the table below.

[0115]

[0116] In this invention, although the positive electrode uses the basic positive electrode material NFM, the introduction of composite sodium-supplementing material can increase the 0.2 C reversible specific capacity to over 136.5 mAh / g and the capacity retention rate to over 90%, highlighting the significant advantages in compensation efficiency and material structure design.

[0117] The sodium squartz-GO-PAN / PMMA composite sodium-supplementing material in Example 1 has a sodium-supplementing reaction potential of <4.0 V, enabling the battery to operate stably within a milder voltage window of 2.0-4.0 V. The composite sodium-supplementing material achieves a 0.2 C reversible specific capacity of 145.5 mAh / g and retains a capacity of up to 97.5% after 100 cycles, demonstrating superior long-cycle stability.

[0118] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A composite sodium supplement material, characterized by, The sodium supplement body is distributed on the surface and in the pores of the base body; the conductive reinforcing body is partially embedded in the interior of the sodium supplement body and partially located on the outer surface of the sodium supplement body. One or more of the following conditions are satisfied:

2. The composite sodium supplement material of claim 1, wherein, (1) the material of the sodium supplement body is a sodium-containing carbon oxide; preferably, a sodium-containing carbon oxide with a cyclic or chain structure, such as sodium carbonate, sodium oxalate or sodium squarate; (2) the material of the conductive reinforcing body is graphene; (3) the mass ratio of the porous carbon fiber to the sodium supplement body is 1: (0.3-3), for example 1: (2.5-3); (4) the mass ratio of the conductive reinforcing body to the sodium supplement body is 1: (10-30), for example 1: (16.7-20). One or more of the following conditions are satisfied:

3. The composite sodium supplement material of claim 1, wherein, (1) the diameter of the porous carbon fiber is 600-1200 nm, for example 700 nm, 850 nm or 1050 nm; (2) the average pore size of the porous carbon fiber is 50-500 nm, preferably 100-300 nm, for example 155 nm, 190 nm or 235 nm; (3) the length of the porous carbon fiber is 10 μm-5 mm, preferably 100-1000 μm, for example 100 μm, 100-400 μm, 200 μm, 200-800 μm, 400 μm, 400-900 μm, 800 μm or 900 μm; (4) the porosity of the porous carbon fiber is 40%-80%, preferably 60%-80%, for example 65%, 65%-70%, 68%, 68%-73%, 70%, 73%, 74%, 74%-78% or 78%; (5) the porous carbon fiber is prepared by the following steps: S1, electrospinning treatment is performed on a polymer spinning solution to obtain a spinning; the polymer spinning solution comprises a polymer precursor and a template agent; S2, the spinning is subjected to heat treatment. One or more of the following conditions are satisfied:

4. The composite sodium supplement material of claim 3, wherein, (1) in step S1, the polymer precursor is selected from one or more of polyacrylonitrile, polyvinyl alcohol and polyamide polyvinylpyrrolidone; (2) in step S1, the template agent is polymethyl methacrylate and / or polystyrene; (3) in step S1, the solvent of the polymer spinning solution is an organic solvent, for example N,N-dimethylformamide; (4) in step S1, the mass ratio of the polymer precursor to the template agent is 1: (0.1-1), preferably 1: (0.2-0.6), for example 1: 0.3, 1: 0.4 or 1: 0.5; (5) in step S1, the solid content of the polymer spinning solution is 9wt%-50wt%, preferably 10wt%-50wt%, for example 20wt%; (6) in step S1, the voltage of the electrospinning treatment is 15-25 kV, for example 18 kV, 20 kV or 22 kV; ​ (7) In step S1, the receiving distance of the electrospinning treatment is 15-20 cm, for example 16 cm, 17 cm or 18 cm; (8) In step S1, the liquid feeding rate of the electrospinning treatment is 0.3-1 mL / h, for example 0.5 mL / h, 0.6 mL / h or 0.7 mL / h; (9) In step S2, the heat treatment comprises drying, pre-oxidation and carbonization in sequence.

5. The composite sodium supplement material of claim 4, wherein, One or more of the following conditions are met: (1) The drying atmosphere is vacuum; (2) The drying temperature is 60-80℃; (3) The drying time is 12-24 h; (4) The pre-oxidation atmosphere is an oxidizing atmosphere, for example air atmosphere; (5) The pre-oxidation temperature is 200-250℃, for example 230℃; (6) The pre-oxidation time is 2-3 h; (7) The carbonization atmosphere is an inert atmosphere, for example nitrogen atmosphere or noble gas atmosphere; (8) The carbonization temperature is 800-1000℃, for example 900-950℃; (9) The carbonization time is 2-4 h, for example 2-3 h.

6. A method for preparing a composite sodium supplement material, characterized by, It comprises the following steps: The dispersion liquid is subjected to hydrothermal treatment; the dispersion liquid comprises porous carbon fibers, a sodium salt and a conductive enhancer.

7. The method of claim 6, wherein the sodium supplementing composite material is prepared by mixing the sodium supplementing composite material with water, and then drying the mixture. One or more of the following conditions are met: (1) The sodium salt is a sodium-containing carbon oxide; preferably a sodium-containing carbon oxide having a cyclic or chain structure, for example sodium carbonate, sodium oxalate or sodium squarate; (2) The conductive enhancer is graphene oxide and / or reduced graphene oxide; (3) The mass ratio of the porous carbon fibers to the sodium salt is 1: (0.3-3), for example 1: (2.5-3); (4) The mass ratio of the conductive enhancer to the sodium salt is 1: (10-30), for example 1: (16.7-20); (5) In the dispersion liquid, the concentration of the porous carbon fibers is 6-20 mg / mL, for example 10 mg / mL; (6) The temperature of the hydrothermal treatment is 120-180℃, for example 150℃, 160℃ or 180℃; (7) The time of the hydrothermal treatment is 6-12 h, for example 8 h, 10 h or 12 h; (8) After the hydrothermal treatment, washing and drying are performed; the washing preferably uses ethanol and / or water; the drying temperature is preferably 60-80℃, for example 70-80℃.

8. A composite sodium supplement material prepared by the method of claim 6 or 7.

9. A pole piece characterized by, It comprises a positive electrode active material and the composite sodium supplement material of any one of claims 1-5 and 8; the mass ratio of the positive electrode active material to the composite sodium supplement material is preferably (8-30): 1, more preferably (15-20): 1, for example 16.4:

1.

10. A battery, characterized by It comprises the electrode sheet of claim 9.

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