Preparation method of modified sodium ion battery positive electrode material and battery

Abstract

The preparation method comprises the following steps: S1, dissolving a layered oxide positive electrode material, a nitrogen source and a carbon nano tube in a dispersing agent to obtain a first mixed material, dispersing the first mixed material, and uniformly coating the surface of the layered oxide positive electrode material with the nitrogen source and the carbon nano tube to obtain a precursor; and S2, drying the precursor, and calcining to obtain the modified sodium-ion battery positive electrode material, so that the structural stability and the electronic conductivity of the positive electrode material are improved.

Description

A method for preparing a modified sodium-ion battery cathode material and the battery Technical Field

[0001] This invention belongs to the field of electrochemical energy storage materials technology, and particularly relates to a method for preparing a modified sodium-ion battery cathode material and the battery itself. Background Technology

[0002] With the rapid development of electric vehicles, large-scale energy storage power stations, and portable electronic devices, the global demand for electrochemical energy storage continues to surge. While lithium-ion batteries, as the current mainstream energy storage technology, possess excellent electrochemical performance, they face core challenges such as uneven distribution of lithium resources and high mining costs, which significantly limit their sustainable development in the field of large-scale energy storage.

[0003] Sodium-ion batteries, with their significant advantages of abundant and widely distributed sodium resources and low cost, have become an ideal complement to lithium-ion batteries, showing broad application prospects in long-term energy storage, low-speed electric vehicles, and other fields. The cathode material, as the core component of sodium-ion batteries, directly determines the battery's energy density, cycle life, rate performance, and production cost, and is a key factor restricting the commercialization of sodium-ion batteries. Currently, sodium-ion battery cathode materials mainly include four categories: layered oxides, polyanionic compounds, Prussian blue analogues, and organic compounds. Among these, layered transition metal oxides (chemical formula Na) are particularly important. x MO2 (where M is a transition metal) is considered one of the cathode materials with the greatest potential for industrial application due to its simple synthesis process, high volumetric energy density, and large reversible capacity.

[0004] However, layered oxide cathode materials still suffer from three major technical challenges in practical applications, severely restricting their electrochemical performance: 1. Poor structural stability: Sodium ions have a large radius (1.02 Å), and repeated insertion and extraction during charge and discharge easily lead to irreversible phase transitions in the layered crystal structure, causing material volume expansion and structural collapse, ultimately resulting in rapid capacity decay of the battery; 2. Insufficient interface stability: The surface of layered oxides is prone to side reactions with the electrolyte, leading to electrolyte decomposition and dissolution of transition metal ions, further exacerbating structural damage and shortening battery cycle life; 3. Low electronic conductivity: Layered oxides have poor intrinsic conductivity, and severe polarization occurs under high-rate charge and discharge conditions, limiting the battery's power performance and fast-charging capability.

[0005] To address these issues, researchers have proposed various modification strategies: elemental doping introduces heterogeneous elements such as Al and Mg to suppress crystal phase transitions and improve structural stability; surface coating reduces direct contact between the material and the electrolyte by constructing physical barriers, thus suppressing side reactions. However, single modification strategies have significant limitations and cannot simultaneously solve the multiple problems of layered oxides, such as structural instability, easy interface reactions, and poor conductivity. For example, while carbon coating alone can improve interface stability, it has limited effect on improving conductivity; while adding conductive agents alone can improve electron transport efficiency, it cannot suppress transition metal dissolution and structural collapse.

[0006] Therefore, there is an urgent need to design a method for preparing modified sodium-ion battery cathode materials and a battery to solve the problems mentioned above. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing a modified sodium-ion battery cathode material and a battery, thereby improving the structural stability and electronic conductivity of the cathode material.

[0008] To achieve the above objectives, the present invention provides a method for preparing a modified sodium-ion battery cathode material and a specific technical solution for the battery as follows: A method for preparing a modified sodium-ion battery cathode material includes the following steps: S1, taking a layered oxide cathode material, a nitrogen source, and carbon nanotubes and dissolving them in a dispersant to obtain a first mixed material, dispersing the first mixed material so that the nitrogen source and carbon nanotubes are uniformly coated on the surface of the layered oxide cathode material to obtain a precursor; S2, drying the precursor and then calcining it to obtain the modified sodium-ion battery cathode material.

[0009] Furthermore, the layered oxide cathode material is Na. x MO2, where M is at least one of Co, Ni, Mn, and Fe.

[0010] Furthermore, the layered oxide cathode material is NaNi. 0.5 Co 0.5 O2, NaNi 0.5 Mn 0.5 O2, Na 0.6 Ni 0.2 Mn 0.6 Co 0.2 O2, Na 0.7 Fe 0.5 Mn 0.5 At least one of O2 or NaCoO2.

[0011] Furthermore, the mass ratio of the layered oxide cathode material, nitrogen source, and carbon nanotubes is 5:(0.4~0.75):0.1.

[0012] Further, step S1, dispersing the first mixed material includes the following steps: ultrasonically dispersing the first mixed material for 10 to 30 minutes, and then dispersing it through a ball mill at a speed of 300 to 400 r / min for 4 to 6 hours.

[0013] Further, in step S2, the calcination includes the following steps: placing the dried precursor in a tube furnace, introducing inert gas, heating it to 300-400℃ at a heating rate of 3-5℃ / min and holding it at that temperature for 1-2 hours, and then heating it to 600-800℃ at a heating rate of 5-10℃ / min and holding it at that temperature for 2-4 hours.

[0014] Furthermore, the nitrogen source is at least one of pyrrole, imidazole, pyridine, melamine, or polyaniline.

[0015] Furthermore, the mass ratio of the nitrogen source to the layered oxide cathode material is 8%, 10%, 12%, or 15%.

[0016] Furthermore, the dispersant is one of deionized water, ethanol, or ultrapure water.

[0017] A modified sodium-ion battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The positive electrode is prepared by coating an aluminum foil current collector with a mixture of positive electrode material obtained by the above-mentioned method for preparing positive electrode material of modified sodium-ion battery, conductive agent carbon black, and binder polyvinylidene fluoride in a mass ratio of 8:1:1. The negative electrode is a metallic sodium sheet.

[0018] The modified sodium-ion battery cathode material preparation method and battery of the present invention have the following advantages: the nitrogen-doped carbon coating layer can act as a physical barrier, isolating the active material from direct contact with the electrolyte and suppressing side reactions; at the same time, nitrogen atoms form strong coordination bonds with transition metals in the layered oxide, effectively suppressing the extraction of transition metal ions from the lattice, avoiding material volume expansion and structural collapse during charging and discharging, significantly improving battery cycle stability, with a capacity retention rate of up to 95% after 100 cycles at 1C. Nitrogen atoms in the nitrogen-doped carbon layer can generate a large number of defects and active sites, synergistically constructing a continuous three-dimensional conductive network with carbon nanotubes, significantly reducing electron transport resistance, improving the material's electronic conductivity, and enhancing battery rate performance, with a maximum 101 mAh / g discharge specific capacity and a capacity retention rate of 78%. Attached Figure Description

[0019] Figure 1 is a schematic flowchart of the preparation method of the modified sodium-ion battery cathode material of the present invention; Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of the invention and form different embodiments. For example, in the claims, any of the claimed embodiments can be used in any combination.

[0022] The following describes a method for preparing a modified sodium-ion battery cathode material and a battery according to the present invention, with reference to Figure 1.

[0023] A method for preparing a modified sodium-ion battery cathode material, as shown in Figure 1, includes the following steps: S1, dissolving layered oxide cathode material, nitrogen source, and carbon nanotubes in a dispersant to obtain a first mixed material; dispersing the first mixed material to uniformly coat the nitrogen source and carbon nanotubes on the surface of the layered oxide cathode material to obtain a precursor; specifically, the carbon nanotubes, as a highly efficient conductive agent, can form a continuous conductive network with the nitrogen-doped carbon layer. Through the in-situ nitrogen-doped carbon coating and carbon nanotube synergistic modification strategy, the structural stability and electronic conductivity of the cathode material are simultaneously improved, while possessing the advantages of simple process, convenient operation, and rapid formation. This low cost makes it suitable for large-scale industrial production. The nitrogen-doped carbon coating layer acts as a physical barrier, isolating the active material from direct contact with the electrolyte and suppressing side reactions. At the same time, nitrogen atoms form strong coordination bonds with the transition metals in the layered oxide, effectively inhibiting the extraction of transition metal ions from the lattice, avoiding material volume expansion and structural collapse during charging and discharging, and significantly improving battery cycle stability. The nitrogen atoms in the nitrogen-doped carbon layer can generate a large number of defects and active sites, which work together with carbon nanotubes to construct a continuous three-dimensional conductive network, greatly reducing electron transport resistance, improving the material's electronic conductivity, and improving battery rate performance.

[0024] S2. After drying the precursor, calcination is performed to obtain a modified sodium-ion battery cathode material.

[0025] Specifically, the drying conditions are as follows: drying in a forced-air oven at 60~80℃ for 6~8 hours. This condition can completely remove the moisture in the precursor and avoid the generation of water vapor during calcination, which could cause the carbon layer to crack.

[0026] Furthermore, the layered oxide cathode material is Na.x MO2, where M is at least one of Co, Ni, Mn, and Fe.

[0027] Optionally, the layered oxide cathode material is NaNi. 0.5 Co 0.5 O2, NaNi 0.5 Mn 0.5 O2, Na 0.6 Ni 0.2 Mn 0.6 Co 0.2 O2, Na 0.7 Fe 0.5 Mn 0.5 At least one of O2 or NaCoO2, such materials possess high reversible capacity and excellent ion transport performance, making them preferred materials for the cathode of sodium-ion batteries.

[0028] Furthermore, the mass ratio of the layered oxide cathode material, nitrogen source, and carbon nanotubes is 5:(0.4~0.75):0.1. This ratio ensures uniform coating of the nitrogen source and carbon nanotubes while preventing the agglomeration of conductive agents.

[0029] Further, step S1, dispersing the first mixed material includes the following steps: ultrasonically dispersing the first mixed material for 10 to 30 minutes, and then dispersing it through a ball mill at a speed of 300 to 400 r / min for 4 to 6 hours.

[0030] Specifically, the process of dispersing the first mixed material is as follows: the first mixed material is first ultrasonically dispersed for 10 to 30 minutes to break up material agglomeration using the cavitation effect of ultrasound and achieve preliminary mixing; then it is dispersed in a ball mill at a speed of 300 to 400 r / min for 4 to 6 hours. The ball milling process adopts a working mode of rotating for 20 minutes and resting for 5 minutes, which can ensure that the nitrogen source and carbon nanotubes are tightly and uniformly wrapped on the surface of the layered oxide, and avoid the destruction of the material crystal structure caused by long-term ball milling.

[0031] Further, in step S2, the calcination includes the following steps: placing the dried precursor in a tube furnace, introducing inert gas, heating it to 300-400℃ at a heating rate of 3-5℃ / min and holding it at that temperature for 1-2 hours, and then heating it to 600-800℃ at a heating rate of 5-10℃ / min and holding it at that temperature for 2-4 hours.

[0032] Specifically, an inert gas, such as nitrogen, argon, or helium, is introduced as a protective gas. The temperature is increased to 300-400℃ at a rate of 3-5℃ / min and held for 1-2 hours. This stage is the low-temperature pre-nitriding stage, which allows the nitrogen source to initially decompose and combine with carbon to form a nitrogen-doped carbon precursor. The temperature is then increased to 600-800℃ at a rate of 5-10℃ / min and held for 2-4 hours. This stage is the high-temperature carbonization and nitrogen doping stage, which forms a stable nitrogen-doped carbon coating layer and ensures that the carbon nanotubes are tightly bonded to the carbon layer to construct a conductive network. The introduction of the inert gas prevents the material from being oxidized at high temperatures, ensuring the stability of the modification effect.

[0033] Furthermore, the nitrogen source is at least one of pyrrole, imidazole, pyridine, melamine or polyaniline. This type of nitrogen source has a high nitrogen content, can form a stable nitrogen-doped carbon layer after pyrolysis, and can form strong coordination bonds with transition metals.

[0034] Furthermore, the mass ratio of the nitrogen source to the layered oxide cathode material is 8%, 10%, 12%, or 15%. This ratio range has been verified by a large number of experiments. It can ensure nitrogen doping efficiency while avoiding excessive nitrogen source that would lead to an excessively thick carbon layer that would affect ion transport.

[0035] Furthermore, the dispersant is one of deionized water, ethanol, or ultrapure water. This type of dispersant is environmentally friendly, non-toxic, and inexpensive, and can ensure uniform dispersion of each component. The amount of dispersant used is preferably 80ml, 90ml, 100ml, 110ml, or 120ml, which can be flexibly adjusted according to the total mass of the mixed materials to ensure the dispersion effect.

[0036] A modified sodium-ion battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The positive electrode is prepared by coating an aluminum foil current collector with a mixture of positive electrode material obtained by the above-mentioned method for preparing positive electrode material of modified sodium-ion battery, conductive agent carbon black, and binder polyvinylidene fluoride in a mass ratio of 8:1:1. The negative electrode is a metallic sodium sheet.

[0037] Specifically, the positive electrode is prepared as follows: the modified sodium-ion battery positive electrode material obtained by the above preparation method, the conductive agent carbon black (SP), and the binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 8:1:1, and an appropriate amount of N-methyl-pyrrolidone (NMP) is added to form a uniform slurry. The slurry is coated on an aluminum foil current collector and then dried under vacuum to form the positive electrode. The negative electrode is made of metallic sodium. Metallic sodium has high theoretical capacity and low electrode potential, making it an ideal negative electrode material for sodium-ion batteries. The electrolyte is a conventional sodium-ion battery electrolyte (such as sodium hexafluorophosphate-carbonate electrolyte), and the separator is a porous polyolefin separator. The batteries are assembled into button cells or pouch cells in a glove box (argon atmosphere, water and oxygen content <1ppm).

[0038] The present invention will be further illustrated by specific embodiments below, but these embodiments do not limit the scope of protection of the present invention.

[0039] Example 1: Take 5g of Na 0.6 Ni 0.2 Mn 0.6 Co 0.2 O2, 0.4 g pyrrole (8% nitrogen source by mass), and 0.1 g carbon nanotubes were dissolved in 100 ml deionized water to obtain a first mixed material. The first mixed material was then ultrasonically dispersed for 20 min, followed by uniform dispersion using a high-energy ball mill at 400 r / min for 6 h, with a 20 min rotation followed by a 5 min rest period, to ensure the nitrogen source and carbon nanotubes uniformly coated the surface of the active material. The uniformly mixed precursor was then subjected to gradient pyrolysis to achieve in-situ nitridation, forming a nitrogen-doped carbon coating layer. The prepared precursor material was dried in a forced-air oven at 60 °C for 8 h. It was then placed in a tube furnace with argon as a protective gas, heated to 350 °C at a rate of 5 °C / min and held for 2 h, followed by a further heating to 700 °C at a rate of 10 °C / min and held for 4 h. After cooling, the modified sodium-ion battery cathode material was obtained.

[0040] The above-mentioned positive electrode material, SP, and PVDF are mixed in a mass ratio of 8:1:1, and an appropriate amount of NMP is added to prepare a slurry. The slurry is coated onto an aluminum foil current collector and dried under vacuum to form a positive electrode sheet. In a glove box, a CR2032 coin cell is assembled using a sodium metal sheet as the negative electrode, a porous polyolefin membrane as the separator, and a carbonate electrolyte as the electrolyte.

[0041] In Example 2, the amount of nitrogen source pyrrole used was 0.5g (10% by mass), and the remaining steps and parameters were the same as in Example 1.

[0042] In Example 3, the temperature for the second calcination step was 750°C, and the remaining steps and parameters were the same as in Example 2.

[0043] In Example 4, the heating rate for the second step of calcination was 5°C / min, and the remaining steps and parameters were the same as in Example 3.

[0044] In Example 5, the amount of nitrogen source pyrrole used was 0.6g (12% by mass), and the remaining steps and parameters were the same as in Example 4.

[0045] In Example 6, the amount of nitrogen source pyrrole used was 0.75g (15% by mass), and the remaining steps and parameters were the same as in Example 4.

[0046] In Example 7, the temperature for the second calcination step was 800°C, and the remaining steps and parameters were the same as in Example 4.

[0047] In Example 8, the nitrogen source was replaced with imidazole (0.5g, 10% by mass), and the remaining steps and parameters were the same as in Example 4.

[0048] In Example 9, the high-energy ball mill rotated at 350 r / min, and the remaining steps and parameters were the same as in Example 4.

[0049] Comparative Example 1: Take 5g of Na 0.6 Ni 0.2 Mn 0.6 Co 0.2 O2, 0.5g glucose (nitrogen-free carbon source, 10% by mass), and 0.1g carbon nanotubes were dissolved in 100ml deionized water and ultrasonically dispersed for 20min. The mixture was then ball-milled at 400r / min for 6h, followed by a 20min rotation and a 5min rest period to obtain the precursor. The precursor was dried at 60℃ for 8h, then placed in a tube furnace with argon gas introduced. The temperature was increased to 350℃ at 5℃ / min and held for 2h, then increased to 750℃ at 5℃ / min and held for 4h. After cooling, nitrogen-free carbon-coated and carbon nanotube-modified cathode materials were obtained. A coin cell was assembled using the same method as in Example 1.

[0050] Comparative Example 2: Take 5g of Na 0.6 Ni 0.2 Mn 0.6 Co 0.2 O2 and 0.5g pyrrole (nitrogen source mass percentage 10%) were dissolved in 100ml deionized water and ultrasonically dispersed for 20min. Then, the mixture was ball-milled at 400r / min for 6h, rotating for 20min and resting for 5min to obtain the precursor. The precursor was dried at 60℃ for 8h and then placed in a tube furnace with argon gas introduced. The temperature was increased to 350℃ at 5℃ / min and held for 2h, then increased to 750℃ at 5℃ / min and held for 4h. After cooling, nitrogen-doped carbon-coated modified cathode material without carbon nanotubes was obtained. A coin cell was assembled according to the same method as in Example 1.

[0051] Electrochemical performance tests were conducted on the coin cells assembled in Examples 1-9 and Comparative Examples 1-2. The test conditions were: voltage range 2.0-4.5V, activation for 2 cycles at a current density of 0.1C, followed by testing the capacity retention rate after 100 cycles at a 1C rate, and the discharge specific capacity and capacity retention rate at a 10C rate (based on the 0.1C discharge specific capacity). The test results are shown in Table 1 below: Table 1, Electrochemical Performance Comparison Table As shown in Table 1, the electrochemical performance of Examples 1-9 is significantly better than that of Comparative Examples 1-2, demonstrating that nitrogen-doped carbon coating and carbon nanotube synergistic modification can simultaneously improve the cycle stability and rate performance of the battery, with an effect far superior to a single modification strategy. Example 4 is the optimal solution, with a 0.1C discharge specific capacity of 135 mAh / g, a 1C capacity retention rate of 95% after 100 cycles, a 10C discharge specific capacity of 101 mAh / g, and a 10C capacity retention rate of 78%, fully demonstrating the synergistic effect of nitrogen-doped carbon coating and carbon nanotube synergistic modification. This indicates that when the nitrogen source mass ratio is 10%, the second-stage calcination temperature is 750℃, and the heating rate is 5℃ / min, the optimal results can be achieved. At that time, the synergistic effect between nitrogen-doped carbon layer and carbon nanotube was the strongest; the performance of Examples 5 and 6 (nitrogen source ratio of 12% and 15%) was slightly lower than that of Example 4, indicating that the amount of nitrogen source is not necessarily better the higher it is. Excessive nitrogen source may lead to an excessively thick carbon layer, which hinders sodium ion transport; the performance of Example 8 (nitrogen source is imidazole) was close to that of Example 4 (nitrogen source is pyrrole), proving that the nitrogen source selected in this invention has good versatility; the performance of Example 9 (ball milling speed of 350 r / min) was slightly lower than that of Example 4 (400 r / min), indicating that appropriately increasing the ball milling speed can improve the coating uniformity of the modifier and optimize the modification effect.

[0052] The modification method of this invention solves the core pain points of layered oxide cathode materials through synergistic effects. It has a simple process, excellent performance, and important industrial application value.

[0053] The modified sodium-ion battery cathode material preparation method of the present invention adopts conventional ultrasonic dispersion, high-energy ball milling and gradient calcination equipment. The process steps are simple and the operation is easy. It can be directly adapted to existing battery material production lines without large-scale equipment modification. The raw materials used are inexpensive and widely available. The production process is environmentally friendly and pollution-free, which meets the economic and environmental requirements of industrial production.

[0054] The modified cathode material prepared by this method can significantly improve the cycle stability and rate performance of sodium-ion batteries, and is suitable for various scenarios such as large-scale energy storage power stations, low-speed electric vehicles, and portable electronic devices. The corresponding modified sodium-ion batteries have cost advantages and performance competitiveness, which can meet the market demand for high-performance and low-cost energy storage products, and have broad industrial application prospects and economic value.

[0055] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a modified sodium-ion battery cathode material, characterized in that, Includes the following steps: S1. Take layered oxide cathode material, nitrogen source, and carbon nanotubes and dissolve them in a dispersant to obtain a first mixed material. Disperse the first mixed material so that the nitrogen source and carbon nanotubes are uniformly coated on the surface of the layered oxide cathode material to obtain a precursor. S2. Dry the precursor and calcine it to obtain a modified sodium-ion battery cathode material.

2. The method for preparing the modified sodium-ion battery cathode material according to claim 1, characterized in that, The layered oxide cathode material is Na. x MO2, where M is at least one of Co, Ni, Mn, and Fe.

3. The method for preparing the modified sodium-ion battery cathode material according to claim 2, characterized in that, The layered oxide cathode material is NaNi. 0.5 Co 0.5 O2, NaNi 0.5 Mn 0.5 O2, Na 0.6 Ni 0.2 Mn 0.6 Co 0.2 O2, Na 0.7 Fe 0.5 Mn 0.5 At least one of O2 or NaCoO2.

4. The method for preparing the modified sodium-ion battery cathode material according to claim 1, characterized in that, The mass ratio of the layered oxide cathode material, nitrogen source, and carbon nanotubes is 5:(0.4~0.75):0.

1.

5. The method for preparing the modified sodium-ion battery cathode material according to claim 1, characterized in that, Step S1, dispersing the first mixed material includes the following steps: ultrasonically dispersing the first mixed material for 10-30 minutes, and then dispersing it through a ball mill at a speed of 300-400 r / min for 4-6 hours.

6. The method for preparing the modified sodium-ion battery cathode material according to claim 1, characterized in that, In step S2, calcination includes the following steps: the dried precursor is placed in a tube furnace, an inert gas is introduced, the temperature is raised to 300-400℃ at a heating rate of 3-5℃ / min and held for 1-2 hours, and then the temperature is raised to 600-800℃ at a heating rate of 5-10℃ / min and held for 2-4 hours.

7. The method for preparing the modified sodium-ion battery cathode material according to claim 1, characterized in that, The nitrogen source is at least one of pyrrole, imidazole, pyridine, melamine, or polyaniline.

8. The method for preparing the modified sodium-ion battery cathode material according to claim 7, characterized in that, The mass ratio of the nitrogen source to the layered oxide cathode material is 8%, 10%, 12%, or 15%.

9. The method for preparing the modified sodium-ion battery cathode material according to claim 1, characterized in that, The dispersant is one of deionized water, ethanol, or ultrapure water.

10. A modified sodium-ion battery, characterized in that, The battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The positive electrode is prepared by coating an aluminum foil current collector with a positive electrode material obtained by the preparation method of the modified sodium-ion battery positive electrode material according to any one of claims 1 to 9, a conductive agent carbon black, and a binder polyvinylidene fluoride in a mass ratio of 8:1:

1. The negative electrode is a sodium metal sheet.

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