Na2FePO4F@C composite material, its preparation and application in sodium-ion batteries

Abstract

The application belongs to the field of sodium ion battery cathode materials, and particularly relates to a preparation method of Na2FePO4F@C composite material, which comprises the following steps: heat treating mixed raw materials of a precursor of Na2FePO4F and a synergic carbon source to obtain the Na2FePO4F@C composite material; the synergic carbon source comprises component a and component b in a weight ratio of 1:0.4-2, wherein the component a is CMC, and the component b is a small-molecule hydroxyl-containing compound; the application further comprises the material prepared by the preparation method and application of the material; and the process can improve the high-rate stability and high-temperature cycle stability of the prepared material.

Description

Technical fields:

[0001] This invention belongs to the field of battery materials technology, specifically relating to a positive electrode active material for sodium-ion batteries. Background technology:

[0002] Lithium-ion batteries, with their advantages of high energy density, high stability, and long lifespan, have rapidly captured the portable electronics market and are increasingly penetrating the electric transportation sector. However, the low reserves and uneven geographical distribution of lithium resources in the Earth's crust have led to a continuous rise in lithium prices during the widespread adoption of lithium-ion batteries, resulting in persistently high prices. Therefore, the application of lithium-ion batteries in large-scale energy storage is limited. Sodium and lithium belong to the same group and share some similar physicochemical properties, but sodium has a larger radius than lithium. Many materials and material construction theories suitable for lithium-ion batteries are difficult to apply to sodium-ion batteries, making it difficult to achieve similar technical effects. This is the main reason why lithium-ion batteries are widely used while sodium-ion batteries have not achieved widespread commercialization.

[0003] Iron-based composite phosphates stand out among sodium-ion electrode materials due to the abundant availability and low cost of iron (Fe) in the Earth's crust, making them one of the most commercially promising cathode materials for sodium-ion batteries. Iron-based composite phosphates mainly include sodium iron phosphate and sodium fluorophosphate, but sodium iron phosphate and sodium fluorophosphate have poor electrical conductivity, and existing technologies typically perform carbon coating on them. For example, Chinese patent document CN116845215A discloses a secondary carbon-coated sodium pyrophosphate composite material and its preparation method. Another example is Chinese patent document CN114242968A, which discloses a carbon-coated sodium fluorophosphate material, its preparation method, and its applications.

[0004] While existing carbon-coating processes can improve conductivity to some extent, unlike other conventional iron-based composite phosphates, sodium fluorophosphate (Na2FePO4F@C) has a layered structure, making it difficult to improve its tap density and requiring higher conductivity. Furthermore, due to the lattice doping of F, it is prone to the formation of numerous impurity phases during preparation, necessitating sintering at relatively mild temperatures. However, the suitable sintering conditions make it difficult to construct a carbon-coated structure with high conductivity, which is also detrimental to the material's tap density. Therefore, for Na2FePO4F@C materials, current technologies still struggle to simultaneously achieve the requirements of impurity phase control, high tap density, and high conductivity composites, leaving significant room for improvement in the electrochemical performance, particularly high-temperature cycling performance. Summary of the Invention:

[0005] To address the problems in the preparation of existing Na2FePO4F@C materials, the primary objective of this invention is to provide a method for preparing Na2FePO4F@C composite materials, aiming to improve the compatibility of Na2FePO4F phase control and carbon layer construction methods, thereby preparing materials that combine excellent phase purity, electrical conductivity, tap density, and electrochemical performance.

[0006] The second objective of this invention is to provide the Na2FePO4F@C composite material prepared by the aforementioned method and its application in the cathode of a sodium-ion battery.

[0007] A third objective of this invention is to provide a sodium-ion battery comprising the Na2FePO4F@C composite material, as well as its positive electrode and positive electrode material.

[0008] Na₂FePO₄F possesses a unique layered microstructure, which demands higher tap density and conductivity. However, due to lattice doping of F, impurity phases easily appear during the preparation of Na₂FePO₄F, making it difficult to construct the desired high-tap and high-conductivity structure. Existing techniques primarily optimize this by adjusting the amount of carbon composite. However, this approach cannot effectively solve the problems of low tap density and insufficient conductivity in the layered structure; instead, it may reduce the effective capacity and negatively impact electrochemical stability, especially during high-temperature cycling.

[0009] To address this problem, after in-depth research and exploration, the present invention proposes the following improvement scheme:

[0010] A method for preparing Na2FePO4F@C composite material involves heat-treating a mixture of precursor raw materials for forming Na2FePO4F and a synergistic carbon source.

[0011] The synergistic carbon source comprises component a and component b in a weight ratio of 1:0.4 to 2, wherein component a is CMC and component b is a small molecule hydroxyl-containing compound.

[0012] To address the challenges of simultaneously improving phase purity, layered structure conductivity, and tap density during the preparation of Na2FePO4F, this invention provides a novel solution through a chemical bridging mechanism between components a and b. By combining components a and b and controlling their ratio, a synergistic effect is unexpectedly achieved. Based on chemical bridging interactions such as hydrogen bonds, a connection pathway between the active material and carbon can be constructed, thereby resolving the impurity phase problem easily caused by F doping in Na2FePO4F and improving its tap density. Furthermore, it facilitates improved electron and sodium ion conduction pathways, thus synergistically improving the capacity, high-rate performance, and cycling performance, especially high-temperature cycling stability of the prepared material.

[0013] In this invention, the combination of components a and b and their proportions is key to synergistically improving the tap density of Na2FePO4F, its layered structure, and its electron-ion conduction network, thereby synergistically improving its capacity, cycling performance, and especially its high-temperature performance.

[0014] In this invention, the precursor raw materials include stoichiometric amounts of Na source, Fe source, phosphorus source and fluorine source;

[0015] In this invention, the iron source is selected from at least one of ferric phosphate, ferrous oxalate, ferrous sulfate, ferric nitrate, and iron oxide red;

[0016] In this invention, the sodium source is selected from at least one of sodium carbonate, sodium bicarbonate, sodium citrate, sodium acetate, and sodium phosphate;

[0017] In this invention, the phosphorus source is selected from at least one of sodium phosphate, iron phosphate, phosphoric acid, ammonium dihydrogen phosphate, and sodium dihydrogen phosphate;

[0018] In this invention, the fluorine source is selected from at least one of sodium fluoride, ammonium fluoride, and iron fluoride;

[0019] In this invention, the stoichiometric ratio of iron, sodium, phosphorus and fluorine in the precursor raw materials is 1:2:1:1.

[0020] In this invention, component b is at least one selected from citric acid, malic acid, tartaric acid, sodium citrate, and glucose; preferably glucose. Research in this invention shows that using glucose as component b unexpectedly exhibits better synergy with component a, further addressing the preparation problems related to the physicochemical structure of Na2FePO4F, and further improving the electrochemical performance of the prepared material, such as its high-temperature cycling stability.

[0021] Preferably, the weight ratio of component a to component b is 1:0.5 to 1.5, more preferably 1:0.9 to 1.1. This invention demonstrates that, based on the preferred components a and b, further optimization of their ratio can synergistically improve the high-rate cycling stability and high-temperature cycling stability of the obtained material.

[0022] In a preferred embodiment of the present invention, components a and b are premixed before being mixed with the precursor raw material for subsequent processing. The premixing temperature is preferably 20–70°C, more preferably 45–65°C. The premixing time can be 0.3–2.5 h, more preferably 0.5–2 h. Studies have shown that premixing components a and b helps to further improve their physicochemical compatibility, and can further improve the high-rate stability and high-temperature cycling stability of the prepared material.

[0023] Unlike conventional approaches that focus on increasing carbon content, this invention, based on the unique chemical synergy of components a and b at the stated ratio, can unexpectedly achieve superior performance, particularly better high-temperature cycling stability, even at lower carbon content.

[0024] In this invention, the synergistic carbon source is 1% to 10% of the weight of the precursor raw material, more preferably 4% to 6%.

[0025] In this invention, the precursor raw material and the synergistic carbon source liquid are dry-mixed to obtain the mixed raw material; or, the precursor raw material and the synergistic carbon source liquid are mixed and then spray-dried to obtain the mixed raw material.

[0026] In this invention, the liquid phase mixing method is high-energy liquid phase mixing, and can further be at least one of ball milling and sand milling;

[0027] In this invention, the rotation speed during the high-energy mixing stage is 500-2500 rpm, and the grinding time is 2-4 hours.

[0028] In this invention, the inlet temperature of the spray drying process is 100-250°C, the drying time is 2-10 hours, and the carrier gas is dry air.

[0029] In this invention, the atmosphere during the heat treatment stage is a protective atmosphere, preferably at least one of nitrogen and inert gas;

[0030] Preferably, the heat treatment temperature is 500–650°C, more preferably 580–620°C, and even more preferably 590–610°C. In this invention, thanks to the combined use of the synergistic carbon source and the combined control of temperature, the high-rate cycling performance and high-temperature cycling performance of the prepared material can be unexpectedly and synergistically improved.

[0031] Preferably, the heat treatment time is 5 to 16 hours, and more preferably 8 to 12 hours;

[0032] Preferably, the rate of heating to the heat treatment temperature is 1 to 10 °C / min, and more preferably 2 to 4 °C / min;

[0033] Preferably, the heat-treated material is subjected to airflow crushing.

[0034] Preferably, the frequency of the feeding motor in the airflow crushing process is 1-15Hz, the frequency of the grinding motor is 150-400Hz, and the grinding air pressure is 0.1-0.8MPa.

[0035] The present invention also provides a Na2FePO4F@C composite material prepared by the above preparation method.

[0036] The preparation method described in this invention can endow the prepared material with special microscopic characteristics, and the material prepared by the method has excellent electrochemical performance, such as excellent high-temperature cycling stability.

[0037] The Na2FePO4F@C composite material of the present invention has a carbon content of 0.5% to 2.5%.

[0038] Preferably, its tap density is 1.2 g / cm³. 3 ~1.7g / cm 3 ;

[0039] Preferably, its specific surface area is 10m². 2 / g~25m 2 / g.

[0040] The present invention also provides an application of the Na2FePO4F@C composite material prepared by the above preparation method, which is used as a positive electrode active material for the preparation of sodium-ion batteries;

[0041] Preferably, the sodium-ion battery is a sodium-ion battery.

[0042] The present invention also provides a positive electrode for a sodium-ion battery, comprising a current collector and a positive electrode material composited thereon, wherein the positive electrode material comprises a positive electrode active material, and the positive electrode active material comprises the Na2FePO4F@C composite material prepared by the preparation method described in the present invention.

[0043] Preferably, the content of the positive electrode active material in the positive electrode material is above 60 wt.%, and more preferably 70 to 90 wt.%.

[0044] Preferably, the positive electrode material may also contain a conductive agent and a binder;

[0045] Preferably, the content of conductive agent and binder is less than 15 wt.%, and more preferably 5 to 10 wt.%.

[0046] The present invention also provides a sodium-ion battery, comprising a battery cell and an electrolyte for soaking the battery cell, wherein the battery cell comprises a positive electrode, a separator and a negative electrode sequentially laminated together, characterized in that the positive electrode comprises a positive electrode active material prepared by the preparation method of the present invention.

[0047] In this invention, the sodium-ion battery, except for the positive electrode portion which contains the positive electrode active material prepared by the method described in this invention, may have other components, structures, and properties that are known or reasonably adjusted based on known principles.

[0048] Beneficial effects:

[0049] To address the challenge of simultaneously managing impurities, conductive networks, and tap density in the preparation of Na2FePO4F@C composite materials, this invention innovatively combines components a and b, further controlling their ratio. This unexpectedly improves the connection pathway between the active material and carbon based on a chemical bridging mechanism, thereby resolving the impurity issue easily caused by F doping in Na2FePO4F and improving its tap density. Furthermore, it enriches and improves the pathways for electron and sodium ion conduction, thus synergistically improving the capacity, high-rate cycling performance, and high-temperature cycling stability of the prepared material. This research also shows that pre-reacting components a and b helps to further enhance their synergistic effect based on their physicochemical characteristics, further improving the high-rate cycling performance and high-temperature cycling stability of the prepared material.

[0050] This invention solves the problem of preparing Na2FePO4F@C composite materials based on a novel approach. Moreover, it can unexpectedly improve the electrochemical performance of the prepared Na2FePO4F@C composite materials, especially helping to improve their cycling stability at high rates and high temperatures. Attached image description:

[0051] Figure 1 This is a SEM image of the material prepared in Example 1 of the present invention.

[0052] Figure 2 The image shows the XRD pattern of the material prepared in Example 1 of this invention. Detailed implementation method:

[0053] Example 1

[0054] (1) Add component b (glucose, 1.25g) and component a (carboxymethyl cellulose 90000, 1.25g) to 1L of pure water and mechanically stir at a stirring rate of 500rpm for 0.5h (the temperature of the process is room temperature, specifically 25~35℃) to obtain carbon composite slurry.

[0055] (2) Add the precursor raw materials of iron phosphate, sodium fluoride and sodium citrate (the stoichiometric ratio of iron, sodium, phosphorus and fluorine is 1:2:1:1) to the above composite slurry and mechanically stir at a stirring rate of 500 rpm for 0.5 h to obtain a mixed slurry (component a + component b) / precursor raw material ratio of 5%.

[0056] (3) The above slurry was poured into a sand mill with a speed of 2000 rpm for high-energy mixing for 3 hours to obtain the precursor slurry.

[0057] (4) The above precursor slurry was dried by spray drying to obtain the precursor. Drying air was used as the carrier gas, the drying temperature was 250℃, and the drying time was 5h.

[0058] (5) The above precursor was placed in a box furnace (Ar atmosphere) for heat treatment to obtain the material. The heat treatment temperature was 600℃, the heat treatment time was 10h, and the heating rate was 2℃ / min.

[0059] (6) The sintered material was further reduced in particle size by airflow milling to obtain a high-tap-density iron-based composite phosphate material. The airflow milling process included a feeding motor frequency of 10Hz, a grinding motor frequency of 300Hz, and a grinding air pressure of 0.7MPa. SEM and XRD images are shown below. Figure 1 and 2 .

[0060] Example 2

[0061] Compared with Example 1, the only difference is that the ratio of component a and component b in step (1) is changed, while the total amount is the same as in Example 1. The experimental groups are as follows:

[0062] Group A: The weight ratio of component a to component b is 1:0.5;

[0063] Group B: The ratio of component a to component b is 1:1.5;

[0064] All other operations and parameters are the same as in Example 1.

[0065] Example 3

[0066] Compared with Example 1, the only difference is that the type of component b in step (1) is changed, while the amount is the same as in Example 1; the experimental groups are as follows:

[0067] Group A: Component b is citric acid;

[0068] Group B: Component b is tartaric acid;

[0069] Group C: Component b is malic acid;

[0070] All other operations and parameters are the same as in Example 1.

[0071] Example 4

[0072] Compared with Example 1, the only difference is the ratio of (component a + component b) / precursor raw material. All other operations and parameters are the same as in Example 1. The experimental groups are as follows:

[0073] Group A: The ratio of (component a + component b) to precursor raw material is 1%;

[0074] Group B: The ratio of (component a + component b) to precursor raw material is 10%.

[0075] All other operations and parameters are the same as in Example 1.

[0076] Example 5

[0077] Compared with Example 1, the only difference is that the temperature of the heat treatment in step 5 is changed, and the experimental groups are as follows:

[0078] Group A: The heat treatment temperature is 550℃, and the holding time is 12h;

[0079] Group B: The heat treatment temperature is 650℃, and the holding time is 8 hours;

[0080] All other operations and parameters are the same as in Example 1.

[0081] Example 6

[0082] Compared with Example 1, the only difference is that the temperature of the process in step (1) is controlled at 50-55°C. Other operations and parameters are the same as in Example 1.

[0083] Example 7

[0084] Compared with Example 1, the only difference is that the premixing process in step (1) is cancelled, and the raw materials in step 2 are pre-slurried with water, and then equal amounts of raw materials a and b are added. The amount of water, the amount of components a and b, and other operating parameters are the same as in Example 1.

[0085] Comparative Example 1

[0086] Compared with Example 1, the only difference is that in step (1), an equal weight of sericin is used as component a, and all other operations and parameters are the same as in Example 1.

[0087] Comparative Example 2

[0088] Compared with Example 1, the only difference is that in step (1), an equal weight of ethylene resin is used as component a, and all other operations and parameters are the same as in Example 1.

[0089] Comparative Example 3

[0090] Compared with Example 1, the only difference is that in step (1), an equal weight of epoxy resin 900 is used as component a, and all other operations and parameters are the same as in Example 1.

[0091] Comparative Example 4

[0092] Compared with Example 1, the only difference is that in step (1), an equal weight of acrylic acid is used as component a, and all other operations and parameters are the same as in Example 1.

[0093] Comparative Example 5

[0094] Compared with Example 1, the only difference is that in step (1), an equal weight of polyvinylidene fluoride component a is used, and all other operations and parameters are the same as in Example 1.

[0095] Comparative Example 6

[0096] Compared with Example 1, the only difference is that in step (1), component a is missing, and the total amount of the remaining component b is the same as the total amount of components a and b in Example 1. All other operations and parameters are the same as in Example 1.

[0097] Comparative Example 7

[0098] Compared with Example 1, the only difference is that in step (1), component b is missing, and the total amount of the remaining component a is the same as the total amount of components a and b in Example 1. All other operations and parameters are the same as in Example 1.

[0099] Comparative Example 8

[0100] Compared with Example 1, the only difference is that in step (1), the total amount of components a and b remains unchanged, but their ratio is not controlled within the required range. For example, the ratio of component a to component b is 1:0.3. Other operations and parameters are the same as in Example 1.

[0101] The main steps of the test are as follows:

[0102] (1) The material after the airflow is broken up is subjected to BET test and tap density test.

[0103] (2) Using a 2032 model battery case, the positive electrode is an iron-based composite phosphate electrode (the current collector is aluminum foil, and the active material: conductive carbon: PVDF = 8:1:1), the negative electrode is sodium metal, and the battery is assembled using a glass fiber separator (model Whatman Grade GF / D) and an electrolyte of 1M NaClO4 (pure PC + 5% FEC).

[0104] (3) The settling time was 12 hours, and a program for testing cycle stability was set. The test environment was 25°C room temperature, 5 cycles at 0.1°C, followed by 500 cycles at 5°C. The test environment was 60°C high temperature, 5 cycles at 0.1°C, followed by 500 cycles at 5°C.

[0105] (4) The theoretical specific capacity of Na2FePO4F is 124 mAh / g;

[0106] The test results are shown in Table 1:

[0107] Table 1

[0108]

[0109] In summary, by jointly controlling the types and proportions of components a and b, and leveraging the high hydrophilicity of binding carbon and its strong hydrogen bond donor properties, the long-term cycling stability and high-temperature stability of the material at high rates can be improved. In particular, further pre-reacting components a and b can further enhance their synergistic effect, thereby further improving the high-rate cycling stability and high-temperature performance of the prepared material.

Claims

1. A method for preparing a Na2FePO4F@C composite material, characterized in that, The precursor material for forming Na2FePO4F and the synergistic carbon source are obtained by heat treatment. The synergistic carbon source comprises component a and component b in a weight ratio of 1:0.4~2, wherein component a is CMC and component b is a small molecule hydroxyl-containing compound; The synergistic carbon source is 1% to 10% of the weight of the precursor raw material.

2. The preparation method of the Na2FePO4F@C composite material as described in claim 1, characterized in that, The precursor raw materials include stoichiometric amounts of sodium, iron, phosphorus, and fluorine sources; The iron source is selected from at least one of ferric phosphate, ferrous oxalate, ferrous sulfate, ferric nitrate, and iron oxide red; The sodium source is selected from at least one of sodium carbonate, sodium bicarbonate, sodium citrate, sodium acetate, and sodium phosphate. The phosphorus source is selected from at least one of sodium phosphate, ferric phosphate, phosphoric acid, ammonium dihydrogen phosphate, and sodium dihydrogen phosphate; The fluorine source is selected from at least one of sodium fluoride, ammonium fluoride, and iron fluoride; In the precursor raw materials, the stoichiometric ratio of iron, sodium, phosphorus and fluorine is 1:2:1:

1.

3. The preparation method of the Na2FePO4F@C composite material as described in claim 1, characterized in that, The component b is at least one of citric acid, malic acid, tartaric acid, sodium citrate, and glucose.

4. The preparation method of the Na2FePO4F@C composite material as described in claim 1, characterized in that, The weight ratio of component a to component b is 1:0.5~1.

5.

5. The preparation method of the Na2FePO4F@C composite material as described in claim 4, characterized in that, The weight ratio of component a to component b is 1:0.9~1.

1.

6. The preparation method of the Na2FePO4F@C composite material as described in claim 1, characterized in that, Components a and b are premixed and then mixed with the precursor raw materials for further processing.

7. The preparation method of the Na2FePO4F@C composite material as described in claim 6, characterized in that, The temperature of the premixing treatment is 20~70℃.

8. The method for preparing the Na2FePO4F@C composite material as described in claim 7, characterized in that, The temperature of the premixing process is 45~65℃.

9. The method for preparing the Na2FePO4F@C composite material as described in claim 6, characterized in that, The premixing time is 0.3~2.5h.

10. The method for preparing the Na2FePO4F@C composite material as described in claim 9, characterized in that, The premixing time is 0.5~2h.

11. The method for preparing the Na2FePO4F@C composite material as described in claim 1, characterized in that, The precursor raw material and the synergistic carbon source liquid are dry-mixed to obtain the mixed raw material; or, the precursor raw material and the synergistic carbon source liquid are mixed and then spray-dried to obtain the mixed raw material.

12. The method for preparing the Na2FePO4F@C composite material as described in claim 11, characterized in that, The liquid phase mixing method described is high-energy liquid phase mixing.

13. The preparation method of the Na2FePO4F@C composite material as described in claim 12, characterized in that, The liquid phase mixing method is at least one of ball milling and sand milling.

14. The method for preparing the Na2FePO4F@C composite material as described in claim 12, characterized in that, The rotation speed during the high-energy liquid-phase mixing stage is 500-2500 rpm, and the time is 2-4 h.

15. The method for preparing the Na2FePO4F@C composite material as described in claim 11, characterized in that, The inlet temperature in the spray drying process is 100~250 ℃, the drying time is 2~10 h, and the carrier gas is dry air.

16. The method for preparing the Na2FePO4F@C composite material according to any one of claims 1 to 15, characterized in that, The atmosphere during the heat treatment stage is a protective atmosphere.

17. The method for preparing the Na2FePO4F@C composite material as described in claim 16, characterized in that, The atmosphere during the heat treatment stage is at least one of nitrogen and an inert gas.

18. The method for preparing the Na2FePO4F@C composite material as described in claim 16, characterized in that, The heat treatment temperature is 500~650 ℃.

19. The method for preparing the Na2FePO4F@C composite material as described in claim 16, characterized in that, The heat treatment time is 5 to 16 hours.

20. The method for preparing the Na2FePO4F@C composite material as described in claim 16, characterized in that, The rate of heating to the heat treatment temperature is 1~10℃ / min.

21. The method for preparing the Na2FePO4F@C composite material as described in claim 1, characterized in that, The heat-treated material is then subjected to airflow crushing.

22. The method for preparing the Na2FePO4F@C composite material as described in claim 21, characterized in that, The feeding motor frequency for the airflow crushing process is 1~15 Hz, the grinding motor frequency is 150~400 Hz, and the grinding air pressure is 0.1~0.8 MPa.

23. A Na2FePO4F@C composite material prepared by the preparation method according to any one of claims 1 to 22.

24. The Na2FePO4F@C composite material prepared by the method described in claim 23, characterized in that, The carbon content ranges from 0.5% to 2.5%. Its tap density is 1.2 g / cm³. 3 ~1.7 g / cm 3 ; Its specific surface area is 10 m² 2 / g ~25 m 2 / g.

25. The application of a Na2FePO4F@C composite material prepared by the preparation method according to any one of claims 1 to 22, characterized in that, It is used as a positive electrode active material in the preparation of sodium-ion batteries.

26. The application as described in claim 25, characterized in that, The sodium-ion battery mentioned is a sodium-ion battery.

27. A positive electrode for a sodium-ion battery, comprising a current collector and a positive electrode material composited on its surface, said positive electrode material comprising a positive electrode active material, characterized in that, The positive electrode active material comprises the Na2FePO4F@C composite material prepared by the preparation method according to any one of claims 1 to 22.

28. The positive electrode of the sodium-ion battery as described in claim 27, characterized in that, The content of the positive electrode active material in the positive electrode material is above 60 wt.%.

29. The positive electrode of the sodium-ion battery as described in claim 28, characterized in that, The content of the positive electrode active material in the positive electrode material is 70~90 wt.%.

30. The positive electrode of the sodium-ion battery according to any one of claims 27 to 29, characterized in that, The positive electrode material also includes a conductive agent and a binder.

31. The positive electrode of the sodium-ion battery as described in claim 30, characterized in that, The content of conductive agent and binder is below 15 wt.%.

32. The positive electrode of the sodium-ion battery as described in claim 31, characterized in that, The content of conductive agent and binder is 5~10 wt.%.

33. A sodium-ion battery, comprising a battery cell and an electrolyte soaking the battery cell, wherein the battery cell comprises a positive electrode, a separator, and a negative electrode sequentially laminated together, characterized in that, The positive electrode described herein is the positive electrode according to any one of claims 27 to 32.

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