A low-temperature sodium-ion battery and its preparation method

Abstract

This invention belongs to the field of sodium-ion battery technology, and relates to a low-temperature sodium-ion battery and its preparation method. By controlling the electrolyte and the sequentially stacked positive electrode, separator, and negative electrode, this invention significantly shortens the ion transport channel between the electrodes and the electrolyte, significantly enhances the contact between the electrodes and the separator, reduces interfacial resistance, improves the low-temperature cycle performance of the battery, and extends its lifespan. This invention improves the internal electron and ion transport speed of the battery under cold conditions through a low-temperature electrolyte, enabling the battery to have better charge and discharge performance at -20°C. This allows the sodium-ion battery to exhibit excellent kinetic characteristics in low-temperature environments, resulting in outstanding performance over a wide temperature range and promoting the commercial application of sodium-ion batteries in low-temperature environments.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, and relates to a low-temperature sodium-ion battery and its preparation method. Background Technology

[0002] Sodium-ion batteries, as an ideal candidate for next-generation large-scale energy storage devices, have attracted widespread attention due to their low cost. However, the practical effectiveness of sodium-ion batteries is significantly limited by geographical and environmental factors, especially in high-altitude and cold regions. In these low-temperature environments, sodium-ion batteries face a series of severe technical challenges. First, the electrochemical reaction kinetics become extremely slow at low temperatures, directly affecting the battery's charge and discharge efficiency. Second, the stability of the electrode-electrolyte interface decreases significantly at low temperatures, leading to increased interfacial resistance and further deteriorating the overall battery performance. Furthermore, the diffusion rate of sodium ions in electrode materials slows down considerably, especially in the negative electrode material. This not only reduces the battery's energy density but may also lead to serious safety issues, such as internal short circuits. These factors combined significantly reduce the performance of sodium-ion batteries in low-temperature environments, making them unsuitable for practical applications.

[0003] To address these challenges, researchers are actively exploring new solutions, with the rational design of electrolytes and electrode materials considered key to optimizing the low-temperature performance of sodium-ion batteries. For example, by adjusting the electrolyte composition and introducing specific additives, the freezing point of the electrolyte can be effectively lowered, increasing its conductivity at low temperatures and thus improving the battery's low-temperature charge-discharge performance. Simultaneously, selecting electrode materials with high specific surface area and good conductivity can accelerate sodium ion transport, reduce side reactions at the electrode / electrolyte interface, and improve the battery's cycle stability and safety. Furthermore, the development of novel electrode materials, such as hard carbon and sodium titanate, which exhibit excellent electrochemical performance at low temperatures, also provides new possibilities for the application of sodium-ion batteries in extreme environments.

[0004] Nevertheless, most low-temperature sodium-ion batteries currently on the market can only discharge in low-temperature environments, and their discharge capacity is relatively low, far from meeting practical needs. More importantly, these batteries have not yet achieved low-temperature charging capabilities, which severely limits the widespread application of sodium-ion batteries in cold regions. Summary of the Invention

[0005] The purpose of this invention is to address the aforementioned problems in the prior art by proposing a low-temperature sodium-ion battery that can achieve excellent charge and discharge performance under low-temperature conditions.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A low-temperature sodium-ion battery, comprising an electrolyte and a positive electrode, a coated separator, and a negative electrode stacked sequentially, wherein the electrolyte comprises the following raw materials in parts by weight: 0.5-1.0 parts NaFP6, 0.3-0.8 parts NaFSI, 0.5-1.5 parts vinylene carbonate, 1-3 parts fluorovinyl carbonate, 1-2 parts ethylene sulfate, 0.5-1.5 parts 1,3-propanesulfonyl lactone, 0.5-1.5 parts sodium difluorooxalate borate, 0.5-1.5 parts triborate ester, and 2-5 parts organic solvent.

[0008] This invention effectively reduces the viscosity of the electrolyte using 1,3-propanesulfonyl lactone, thereby maintaining high ionic conductivity at low temperatures. Secondly, the use of organic solvents and NaFSI and NaFP6 significantly lowers the melting point of the electrolyte, ensuring it remains liquid at extremely low temperatures and guaranteeing ion migration and charge transfer. Furthermore, fluoroethylene carbonate and ethylene sulfate can form a LiF-rich SEI (solid electrolyte interface) film on the electrode surface. This SEI film has low electronic impedance and high sodium ion conductivity, contributing to improved electrode stability and battery cycle life. Sodium difluorooxalate borate not only forms a stable SEI film but also does not contain hydrofluoric acid, thus increasing the charge transfer rate, reducing battery polarization at low temperatures, and further improving battery charge-discharge efficiency. Therefore, this invention, through the rational selection and proportioning of these additives, can significantly improve the physical and chemical properties of the electrolyte, such as reducing viscosity, lowering the freezing point, and forming a stable SEI film, thereby working together to improve battery performance in low-temperature environments. This optimized electrolyte design not only improves the battery's discharge capacity and cycle stability under cold conditions, but also significantly enhances the battery's overall performance, making it more suitable for applications in high-altitude and cold regions.

[0009] In the aforementioned low-temperature sodium-ion battery, the organic solvent includes at least three of the following: dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, ethyl acetate, and ethylene carbonate.

[0010] In the aforementioned low-temperature sodium-ion battery, the positive electrode comprises an aluminum foil with a thickness of 12-15 μm and a positive electrode active material layer coated on the surface of the aluminum foil. The positive electrode active material comprises the following raw materials in parts by weight: 90-96 parts sodium nickel iron manganese oxide, 0.3-0.8 parts Ketjen black, 1-1.8 parts carbon black, 0.5-0.9 parts carbon nanotubes, and 1.5-2 parts polyvinylidene fluoride.

[0011] In the aforementioned low-temperature sodium-ion battery, the sodium nickel iron manganese oxide (D50) has a particle size of 5-6 μm.

[0012] In the aforementioned low-temperature sodium-ion battery, the areal density of the positive electrode active material layer coated on the aluminum foil surface is 11-13 mg / cm³. 2 .

[0013] In the aforementioned low-temperature sodium-ion battery, the negative electrode comprises a carbon-coated aluminum foil with a thickness of 12-15 μm and a negative electrode active material layer coated on the surface of the carbon-coated aluminum foil. The negative electrode active material comprises the following components by mass percentage: 94-96 parts hard carbon, 0.3-0.5 parts Ketjen black, 1-1.5 parts carbon black, 0.5-0.6 parts carbon nanotubes, 1.5-1.8 parts polyvinylidene fluoride, 1-1.3 parts styrene-butadiene rubber, and 0.5-1.5 parts polyacrylic acid.

[0014] Preferably, the particle size of hard carbon D50 is 3-8 μm.

[0015] In the aforementioned low-temperature sodium-ion battery, the areal density of the negative electrode active material layer coated on the surface of the carbon-coated aluminum foil is 6-8 mg / cm³. 2 .

[0016] This invention controls the areal density of the positive and negative electrodes, primarily in the following aspects: First, a lower areal density means thinner electrodes, which not only directly reduces the diffusion distance of sodium ions in the electrode material but also improves the distribution and wetting of the electrolyte in the electrodes, helping to increase the ionic conductivity of the electrolyte, thereby reducing the battery's internal resistance and improving the battery's charge-discharge efficiency, especially under low-temperature conditions. Second, thinner electrodes help reduce polarization at low temperatures because the migration path of sodium ions in the electrode material is shorter, resulting in lower internal resistance and thus improving the battery's low-temperature discharge capacity and cycle stability. Finally, a lower areal density means less active material, thereby reducing the damage to the material structure caused by sodium ion cyclic insertion / extraction, especially under low-temperature conditions where sodium ion cyclic insertion / extraction can cause greater damage to the material structure. Through these measures, this invention significantly improves the performance and reliability of sodium-ion batteries in low-temperature environments.

[0017] In the aforementioned low-temperature sodium-ion battery, the separator is a coated separator with a thickness of 10-15 μm.

[0018] In the aforementioned low-temperature sodium-ion battery, the coated separator consists of an oily PVDF layer, a polypropylene layer, a ceramic layer, and another oily PVDF layer from the inside out, wherein the thickness ratio of the oily PVDF layer, polypropylene layer, ceramic layer, and oily PVDF layer is 0.5-1.5: 5-15: 1-3: 0.5-1.5.

[0019] Preferably, the thicknesses of the oil-based PVDF layer, the polypropylene layer, the ceramic layer, and the oil-based PVDF layer are 0.5-1.5um, 5-15um, 1-3um, and 0.5-1.5um, respectively.

[0020] The adhesive-coated separator of this invention helps improve the adhesion between the separator and the organic materials in the electrodes, improves the contact between the positive and negative electrodes and the separator, shortens the sodium ion transport channel, and greatly reduces polarization, thereby improving the low-temperature performance of the battery. In addition, the ceramic in the separator enhances the separator's puncture resistance, preventing short circuits caused by sodium dendrites piercing the separator during long-term battery cycling.

[0021] The present invention also provides a method for preparing the above-mentioned low-temperature sodium-ion battery, the method comprising the following steps:

[0022] S1. The positive electrode, negative electrode and separator are stacked in a Z-shaped manner to form a battery cell;

[0023] S2. Then, positive and negative electrode tabs are ultrasonically welded onto the positive and negative electrode plates respectively, and the battery cell is placed in the aluminum-plastic film shell for baking.

[0024] S3. Then, electrolyte is injected into the cell, sealed and left to stand, then it undergoes formation and capacity testing, and finally aged to obtain a sodium-ion battery.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. By controlling the electrolyte and the sequentially stacked positive electrode, separator, and negative electrode, this invention significantly shortens the ion transport channel between the electrode and the electrolyte, significantly enhances the contact between the electrode and the separator, reduces interfacial resistance, improves the low-temperature cycle performance of the battery, and extends the battery's service life.

[0027] 2. This invention introduces superconducting carbon black Ketjenblack into the positive and negative electrodes, which can form a conductive network with the active material, promote electron transport and storage, and thus reduce the internal resistance of the electrode; the porous structure of carbon black can serve as a support for the active material, increase the specific surface area of ​​the electrode, and improve the contact area between the electrolyte and the electrode material.

[0028] 3. This invention improves the internal electron and ion transport speed of the battery under cold conditions by using a low-temperature electrolyte, enabling the battery to have better charge and discharge performance at -20℃. This allows sodium-ion batteries to exhibit excellent kinetic characteristics in low-temperature environments, resulting in outstanding performance over a wide temperature range and promoting the commercial application of sodium-ion batteries in low-temperature environments. Detailed Implementation

[0029] The following are specific embodiments of the present invention, which further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0030] Example 1:

[0031] S1. Prepare the electrolyte raw materials according to the following mass proportions: 0.7 parts NaFP6, 0.5 parts NaFSI, 1 part vinylene carbonate, 2 parts fluorovinyl carbonate, 1.5 parts ethylene sulfate, 1 part 1,3-propanesulfonyl lactone, 1 part sodium difluorooxalate borate, 1 part triborate ester and 3 parts organic solvent.

[0032] The organic solvents are methyl ethyl carbonate, propylene carbonate, and ethyl acetate in a mass ratio of 1:1:1.

[0033] S2, NaFP 6、 NaFSI and organic solvents are mixed in a reactor, then the remaining raw materials are added and the mixture is stirred and mixed again, and finally protected with argon gas.

[0034] S3. Prepare the positive electrode active material raw materials according to the following mass proportions: 95.5 parts sodium nickel iron manganese oxide with a D50 particle size of 5 μm, 0.6 parts Ketjen black, 1.4 parts carbon black, 0.7 parts carbon nanotubes, and 1.8 parts polyvinylidene fluoride.

[0035] S4. Sodium nickel iron manganese oxide, Ketjen black, carbon black, carbon nanotubes, and polyvinylidene fluoride are mixed into a slurry and uniformly coated onto an aluminum foil with a thickness of 13 μm, resulting in a coating surface density of 12 mg / cm³. 2 After drying, rolling, and cutting, positive electrode sheets are obtained.

[0036] S5. Prepare the negative electrode active material raw materials according to the following mass proportions: 94.2 parts hard carbon with D50 particle size distribution of 5um, 0.4 parts Ketjen black, 1.1 parts carbon black, 0.55 parts carbon nanotubes, 1.65 parts polyvinylidene fluoride, 1.1 parts styrene-butadiene rubber, and 1.0 parts polyacrylic acid.

[0037] S6. Mix hard carbon, Ketjen black, carbon black, carbon nanotubes, polyvinylidene fluoride, and styrene-butadiene rubber into a slurry, and uniformly coat it onto a 13µm thick carbon-coated aluminum foil, with a coating surface density of 7mg / cm³. 2 After drying, rolling, and cutting, the negative electrode sheet is obtained.

[0038] S7. The positive electrode sheet, negative electrode sheet and adhesive-coated separator are stacked in a Z-shaped manner to form a battery cell. Then, positive electrode tabs and negative electrode tabs are ultrasonically welded onto the positive electrode sheet and negative electrode sheet respectively. Finally, the battery cell is placed in an aluminum-plastic film shell and baked at 90°C to remove moisture from the battery cell.

[0039] The coated diaphragm consists of an oil-based PVDF layer, a polypropylene layer, a ceramic layer, and another oil-based PVDF layer from the inside out. The thicknesses of the oil-based PVDF layer, the polypropylene layer, the ceramic layer, and the oil-based PVDF layer are 1µm, 9µm, 2µm, and 1µm, respectively.

[0040] S8. Inject 7g / mAh of electrolyte into the cell, seal and let stand, perform capacity testing on the obtained cell, and age it for 24 hours to obtain a sodium-ion battery.

[0041] Example 2:

[0042] S1. Prepare the electrolyte raw materials according to the following mass proportions: 0.5 parts NaFP6, 0.3 parts NaFSI, 0.5 parts vinylene carbonate, 1 part fluorovinyl carbonate, 1 part ethylene sulfate, 0.5 parts 1,3-propanesulfonyl lactone, 0.5 parts sodium difluorooxalate borate, 0.5 parts triborate ester and 2 parts organic solvent.

[0043] The organic solvents are methyl ethyl carbonate, propylene carbonate, and ethyl acetate in a mass ratio of 1:1:1.

[0044] S2, NaFP 6、 NaFSI and organic solvents are mixed in a reactor, then the remaining raw materials are added and the mixture is stirred and mixed again, and finally protected with argon gas.

[0045] S3. Prepare the positive electrode active material raw materials according to the following mass proportions: 90 parts sodium nickel iron manganese oxide with a D50 particle size of 5 μm, 0.3 parts Ketjen black, 1 part carbon black, 0.5 parts carbon nanotubes, and 1.5 parts polyvinylidene fluoride.

[0046] S4. Sodium nickel iron manganese oxide, Ketjen black, carbon black, carbon nanotubes, and polyvinylidene fluoride are mixed into a slurry and uniformly coated onto an aluminum foil with a thickness of 13 μm, resulting in a coating surface density of 12 mg / cm³. 2 After drying, rolling, and cutting, positive electrode sheets are obtained.

[0047] S5. Prepare the negative electrode active material raw materials according to the following mass proportions: 94 parts hard carbon with D50 particle size distribution of 5um, 0.3 parts Ketjen black, 1 part carbon black, 0.5 parts carbon nanotubes, 1.5 parts polyvinylidene fluoride, 1 part styrene-butadiene rubber, and 0.5 parts polyacrylic acid.

[0048] S6. Mix hard carbon, Ketjen black, carbon black, carbon nanotubes, polyvinylidene fluoride, and styrene-butadiene rubber into a slurry, and uniformly coat it onto a 13µm thick carbon-coated aluminum foil, with a coating surface density of 7mg / cm³. 2 After drying, rolling, and cutting, the negative electrode sheet is obtained.

[0049] S7. The positive electrode sheet, negative electrode sheet and adhesive-coated separator are stacked in a Z-shaped manner to form a battery cell. Then, positive electrode tabs and negative electrode tabs are ultrasonically welded onto the positive electrode sheet and negative electrode sheet respectively. Finally, the battery cell is placed in an aluminum-plastic film shell and baked at 90°C to remove moisture from the battery cell.

[0050] The coated diaphragm consists of an oil-based PVDF layer, a polypropylene layer, a ceramic layer, and another oil-based PVDF layer from the inside out. The thicknesses of the oil-based PVDF layer, the polypropylene layer, the ceramic layer, and the oil-based PVDF layer are 1µm, 9µm, 2µm, and 1µm, respectively.

[0051] S8. Inject 7g / mAh of electrolyte into the cell, seal and let stand, perform capacity testing on the obtained cell, and age it for 24 hours to obtain a sodium-ion battery.

[0052] Example 3:

[0053] S1. Prepare the electrolyte raw materials according to the following mass proportions: 1.0 parts NaFP6, 0.8 parts NaFSI, 1.5 parts vinylene carbonate, 3 parts fluorovinyl carbonate, 2 parts ethylene sulfate, 1.5 parts 1,3-propanesulfonyl lactone, 1.5 parts sodium difluorooxalate borate, 1.5 parts triborate ester and 5 parts organic solvent.

[0054] The organic solvents are methyl ethyl carbonate, propylene carbonate, and ethyl acetate in a mass ratio of 1:1:1.

[0055] S2, NaFP 6、 NaFSI and organic solvents are mixed in a reactor, then the remaining raw materials are added and the mixture is stirred and mixed again, and finally protected with argon gas.

[0056] S3. Prepare the positive electrode active material raw materials according to the following mass proportions: 96 parts sodium nickel iron manganese oxide with a D50 particle size of 5 μm, 0.8 parts Ketjen black, 1.8 parts carbon black, 0.9 parts carbon nanotubes, and 2 parts polyvinylidene fluoride.

[0057] S4. Sodium nickel iron manganese oxide, Ketjen black, carbon black, carbon nanotubes, and polyvinylidene fluoride are mixed into a slurry and uniformly coated onto an aluminum foil with a thickness of 13 μm, resulting in a coating surface density of 12 mg / cm³. 2 After drying, rolling, and cutting, positive electrode sheets are obtained.

[0058] S5. Prepare the negative electrode active material raw materials according to the following mass proportions: 96 parts hard carbon with D50 particle size distribution of 5um, 0.5 parts Ketjen black, 1.5 parts carbon black, 0.6 parts carbon nanotubes, 1.8 parts polyvinylidene fluoride, 1.3 parts styrene-butadiene rubber, and 1.5 parts polyacrylic acid.

[0059] S6. Mix hard carbon, Ketjen black, carbon black, carbon nanotubes, polyvinylidene fluoride, and styrene-butadiene rubber into a slurry, and uniformly coat it onto a 13µm thick carbon-coated aluminum foil, with a coating surface density of 7mg / cm³. 2 After drying, rolling, and cutting, the negative electrode sheet is obtained.

[0060] S7. The positive electrode sheet, negative electrode sheet and adhesive-coated separator are stacked in a Z-shaped manner to form a battery cell. Then, positive electrode tabs and negative electrode tabs are ultrasonically welded onto the positive electrode sheet and negative electrode sheet respectively. Finally, the battery cell is placed in an aluminum-plastic film shell and baked at 90°C to remove moisture from the battery cell.

[0061] The coated diaphragm consists of an oil-based PVDF layer, a polypropylene layer, a ceramic layer, and another oil-based PVDF layer from the inside out. The thicknesses of the oil-based PVDF layer, the polypropylene layer, the ceramic layer, and the oil-based PVDF layer are 1µm, 9µm, 2µm, and 1µm, respectively.

[0062] S8. Inject 7g / mAh of electrolyte into the cell, seal and let stand, perform capacity testing on the obtained cell, and age it for 24 hours to obtain a sodium-ion battery.

[0063] Example 4:

[0064] The only difference from Example 1 is that the organic solvent is ethyl methyl carbonate.

[0065] Example 5:

[0066] The only difference from Example 1 is that the organic solvents are only methyl ethyl carbonate and propylene carbonate.

[0067] Example 6:

[0068] The only difference from Example 1 is that the raw materials in the positive and negative electrode active materials do not contain Ketjen black.

[0069] Example 7:

[0070] The only difference from Example 1 is that the areal density of the positive electrode active material layer coated on the aluminum foil surface is 5 mg / cm³. 2 The areal density of the negative electrode active material layer coated on the carbon-coated aluminum foil is 3 mg / cm³. 2 .

[0071] Example 8:

[0072] The only difference from Example 1 is that the areal density of the positive electrode active material layer coated on the aluminum foil surface is 20 mg / cm³. 2 The areal density of the negative electrode active material layer coated on the carbon-coated aluminum foil is 15 mg / cm³. 2 .

[0073] Example 9:

[0074] The only difference from Example 1 is that the diaphragm is a conventional ceramic diaphragm (ceramic diaphragm\135\boehmite\9+3\Xuran-Numi\PE).

[0075] Example 10:

[0076] The only difference from Example 1 is that the sodium nickel iron manganese oxide D50 has a particle size of 10 μm.

[0077] Comparative Example 1:

[0078] The only difference from Example 1 is that the electrolyte raw material does not contain NaFP6.

[0079] Comparative Example 2:

[0080] The only difference from Example 1 is that the electrolyte raw material does not contain NaFSI.

[0081] Comparative Example 3:

[0082] The only difference from Example 1 is that the electrolyte raw material does not contain vinylene carbonate.

[0083] Comparative Example 4:

[0084] The only difference from Example 1 is that the electrolyte raw material does not contain ethylene sulfate.

[0085] Comparative Example 5:

[0086] The only difference from Example 1 is that the electrolyte raw material does not contain 1,3-propanesulfonyl lactone.

[0087] Performance testing:

[0088] (1) Energy density test:

[0089] The sodium-ion batteries prepared in Examples 1-12 and Comparative Examples 1-5 were placed in a 25°C constant temperature chamber and left to stand for 24 hours. They were then charged at a constant current of 0.2C to 3.9V, left to stand for 30 minutes, and discharged at 0.5C to 1.5V. The energy obtained from the discharge, divided by the mass of the battery, is the energy density of the battery.

[0090] (2) Low-temperature discharge performance test at -20℃:

[0091] The sodium-ion batteries prepared in Examples 1-12 and Comparative Examples 1-5 were placed in a -20°C constant temperature chamber and left to stand for 24 hours. They were then charged at a constant current of 0.2C to 3.9V, left to stand for 30 minutes, and discharged at 0.5C to 1.5V. The specific capacity obtained by discharging at this time divided by the mass of the positive electrode active material is the specific capacity at -20°C low temperature discharge.

[0092] (3) Cyclic life test:

[0093] In Examples 1-12 and Comparative Examples 1-5, the sodium-ion batteries were placed in a -20°C constant temperature chamber and left to stand for 24 hours. They were then charged at a constant current of 0.2C to 3.9V, left to stand for 30 minutes, discharged at 0.5C to 1.5V, left to stand for 30 minutes, and the charging process was repeated.

[0094] Table 1: Performance test results of sodium-ion batteries prepared in Examples 1-12 and Comparative Examples 1-5

[0095]

[0096] In summary, by controlling the electrolyte and the sequentially stacked positive electrode, separator, and negative electrode, this invention significantly shortens the ion transport channel between the electrode and the electrolyte, significantly enhances the contact between the electrode and the separator, reduces interfacial resistance, improves the low-temperature cycle performance of the battery, and extends the battery's service life.

[0097] The embodiments described herein cover any points not exhaustively within the scope of the technical claims of this invention, as well as new technical solutions formed by equivalent substitutions of one or more technical features in the embodiments. These are all within the scope of the claims of this invention. Furthermore, in all listed or unlisted embodiments of this invention, each parameter in the same embodiment merely represents an instance (i.e., a feasible solution) of its technical solution, and there is no strict coordination or limitation relationship between the parameters. The parameters can be substituted for each other without violating axioms and the claims of this invention, unless otherwise stated.

[0098] The technical means disclosed in this invention are not limited to those described above, but also include technical solutions composed of any combination of the above technical features. The above descriptions are specific embodiments of this invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention.

[0099] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A low-temperature sodium-ion battery, characterized in that, The low-temperature sodium-ion battery comprises an electrolyte and a positive electrode, a coated separator, and a negative electrode stacked sequentially. The electrolyte comprises the following raw materials in parts by weight: 0.5-1.0 parts NaFP6, 0.3-0.8 parts NaFSI, 0.5-1.5 parts vinylene carbonate, 1-3 parts fluorovinyl carbonate, 1-2 parts ethylene sulfate, 0.5-1.5 parts 1,3-propanesulfonyl lactone, 0.5-1.5 parts sodium difluorooxalate borate, 0.5-1.5 parts triborate ester, and 2-5 parts organic solvent. The positive electrode comprises an aluminum foil with a thickness of 12-15 μm and a positive electrode active material layer coated on the surface of the aluminum foil. The positive electrode active material comprises the following raw materials in parts by weight: 90-96 parts sodium nickel iron manganese oxide, 0.3-0.8 parts Ketjen black, 1-1.8 parts carbon black, 0.5-0.9 parts carbon nanotubes, and 1.5-2 parts polyvinylidene fluoride. The negative electrode comprises a carbon-coated aluminum foil with a thickness of 12-15 μm and a negative electrode active material layer coated on the surface of the carbon-coated aluminum foil. The negative electrode active material comprises the following components by mass percentage: 94-96 parts hard carbon, 0.3-0.5 parts Ketjen black, 1-1.5 parts carbon black, 0.5-0.6 parts carbon nanotubes, 1.5-1.8 parts polyvinylidene fluoride, 1-1.3 parts styrene-butadiene rubber, and 0.5-1.5 parts polyacrylic acid.

2. The low-temperature sodium-ion battery according to claim 1, characterized in that, The organic solvent includes at least three of the following: dimethyl carbonate, ethyl methyl carbonate, ethyl methyl carbonate, propylene carbonate, ethyl acetate, and ethylene carbonate.

3. The low-temperature sodium-ion battery according to claim 1, characterized in that, The particle size of sodium nickel iron manganese oxide D50 is 5-6 μm.

4. A low-temperature sodium-ion battery according to claim 1, characterized in that, The areal density of the positive electrode active material layer coated on the aluminum foil surface is 11-13 mg / cm³. 2 .

5. A low-temperature sodium-ion battery according to claim 1, characterized in that, The areal density of the negative electrode active material layer coated on the surface of carbon-coated aluminum foil is 6-8 mg / cm³. 2 .

6. A low-temperature sodium-ion battery according to claim 1, characterized in that, The diaphragm is a coated diaphragm with a thickness of 10-15 μm.

7. A low-temperature sodium-ion battery according to claim 1, characterized in that, The coated diaphragm consists of an oil-based PVDF layer, a polypropylene layer, a ceramic layer, and another oil-based PVDF layer from the inside out. The thickness ratio of the oil-based PVDF layer, polypropylene layer, ceramic layer, and oil-based PVDF layer is 0.5-1.5: 5-15: 1-3: 0.5-1.

5.

8. A method for preparing a low-temperature sodium-ion battery as described in claim 1, characterized in that, The method includes the following steps: S1. The positive electrode, negative electrode and separator are stacked in a Z-shaped manner to form a battery cell; S2. Then, positive and negative electrode tabs are ultrasonically welded onto the positive and negative electrode plates respectively, and the battery cell is placed in the aluminum-plastic film shell for baking. S3. Then, electrolyte is injected into the cell, sealed and left to stand, then it undergoes formation and capacity testing, and finally aged to obtain a sodium-ion battery.

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