Positive electrode material for aqueous sodium-ion battery, positive electrode and aqueous sodium-ion battery

Abstract

The application provides a positive electrode material, a positive electrode and a water-based sodium ion battery for the water-based sodium ion battery, the positive electrode material comprising a positive electrode active material with sodium defects and a positive electrode additive, the positive electrode active material comprising a Prussian blue analogue, and the positive electrode additive comprising an organic sodium salt. The application can effectively supplement the loss of sodium ions of the positive electrode active material caused by sodium defects in the water-based battery system by using the specific positive electrode active material Prussian blue analogue and the positive electrode additive in combination, and the two synergistically act, greatly improving the energy density, cycle stability and rate performance of the water-based sodium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a positive electrode material for aqueous sodium-ion batteries, a positive electrode, and an aqueous sodium-ion battery. Background Technology

[0002] Batteries, as an energy storage medium, have received widespread attention due to their environmental friendliness and convenience. Rechargeable lithium-ion batteries, in particular, have garnered significant interest due to their high conversion efficiency and energy density. However, the uneven distribution and high cost of lithium resources have raised concerns about their scarcity, especially regarding their potential unsustainability in large-scale energy storage applications. With the rise of large-scale energy storage, and considering the high abundance and low price of sodium resources in the Earth's crust, as well as the similarity in working principle between sodium-ion and lithium-ion batteries, sodium-ion batteries have become an important supplement to lithium-ion batteries. Room-temperature aqueous sodium-ion batteries possess moderate energy density and have gained widespread attention due to their environmental friendliness, safety, and ease of operation. Aqueous sodium batteries, in particular, offer more relaxed production conditions, eliminating the need for strict control of water and oxygen during assembly, and significantly reducing the cost of aqueous electrolytes. Furthermore, the ionic conductivity of aqueous electrolytes is higher than that of organic electrolytes, facilitating higher charge-discharge rates.

[0003] CN110336026A discloses a method for preparing an aqueous sodium-ion battery cathode material and an aqueous sodium-ion battery. The cathode material is prepared by thoroughly mixing and grinding sodium and manganese sources, followed by calcination at a certain temperature. The raw materials are inexpensive, the operation is simple, and the prepared cathode material exhibits a high charge-discharge specific capacity of 85 mAh / g, good cycle stability, and high overall electrochemical performance. CN106328917B discloses an aqueous rechargeable sodium battery cathode material and an aqueous sodium battery. In this patent, NaMnTiMO is used as the main active material for the cathode. The resulting aqueous rechargeable sodium battery exhibits stable performance, high power density, long cycle life, and is safe, environmentally friendly, and low-cost. CN109888411A discloses a high-rate, long-cycle, wide-temperature-range aqueous sodium-ion full battery. The positive electrode material of this aqueous sodium-ion battery is a commercially available nickel-based material, the negative electrode material is sodium-based phosphate, and the electrolyte is an aqueous sodium salt solution. Energy storage and conversion are achieved through a dual-ion mixing mechanism of the positive and negative electrodes, thereby improving the rate performance and cycle performance.

[0004] However, compared to the wide electrochemical window of non-aqueous sodium-ion batteries, aqueous sodium-ion batteries have a narrow electrochemical window due to hydrogen and oxygen evolution issues, which is a major drawback of aqueous batteries. Therefore, high-capacity, low-cost cathode materials with chemical stability in water are the preferred choices for aqueous sodium-ion battery cathodes. Consequently, only a few cathode materials, such as Prussian blue analogs, have potential applications in aqueous sodium-ion battery cathodes. However, these materials often suffer from sodium defects; while the initial coulombic efficiency in a half-cell is greater than 100%, the negative electrode cannot provide additional sodium ions in a full-cell, resulting in a low coulombic efficiency, which severely restricts the practical application of aqueous sodium-ion batteries. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention aims to provide a positive electrode material, a positive electrode, and an aqueous sodium-ion battery for use in aqueous sodium-ion batteries. The present invention combines a specific positive electrode active material, a Prussian blue analogue, with a positive electrode additive. The synergistic effect of these two additives effectively compensates for sodium ion loss in the positive electrode active material caused by sodium defects in the aqueous battery system, significantly improving the energy density, cycle stability, and rate performance of the aqueous sodium-ion battery.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a cathode material for an aqueous sodium-ion battery, the cathode material comprising a cathode active material having sodium defects and a cathode additive, the cathode active material comprising a Prussian blue analogue and the cathode additive comprising an organic sodium salt.

[0008] This invention uses an organic sodium salt as a positive electrode additive in combination with a Prussian blue analogue that has sodium defects. On the one hand, the positive electrode additive can efficiently compensate for the sodium defects in the positive electrode active material itself, and can also replenish the sodium ions needed for the formation of the SEI film and other side reactions, thereby improving the energy density and coulombic efficiency of the battery. On the other hand, compared with the positive electrode materials used in oil-based sodium-ion batteries in the prior art, this invention uses a specific positive electrode active material and positive electrode additive in an aqueous sodium-ion battery. The organic sodium salt decomposes to produce gas, and the release of the gas can form impact pores on the positive electrode surface, which is conducive to the penetration of electrolyte and improves the transport efficiency of Na ions. Moreover, the decomposition products do not contain... In solid products, the gases generated by the decomposition of cathode additives are easily discharged in open-system aqueous sodium-ion batteries, eliminating safety concerns related to gas generation. However, in oil-based systems, the decomposition products are difficult to discharge, and even if venting is performed during the formation stage, the operation is relatively difficult and not easily implemented, resulting in relatively poor cycle performance of the cathode additives. Furthermore, Prussian blue analogues contain interstitial water. In aqueous sodium-ion batteries, when combined with cathode additives, the interstitial water is not consumed, resulting in structural stability. However, in oil-based systems, when Prussian blue analogues interact with cathode additives, the consumption of interstitial water can easily lead to structural collapse, reducing the electrochemical performance of the cathode material.

[0009] The present invention has a simple process and a highly usable system. It can effectively compensate for the sodium ion loss caused by sodium defects in the cathode material of aqueous battery systems, and greatly improve the energy density, cycle stability and rate performance of the whole battery. It has significant implications for the future application of aqueous sodium-ion batteries in the field of large-scale energy storage.

[0010] Preferably, the mass of the positive electrode additive is 1 to 30% of the mass of the positive electrode active material, for example, it can be 1%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28% or 30%, etc., preferably 10 to 20%.

[0011] Preferably, the chemical formula of the Prussian blue analogue is Na. a A[B(CN)6] b X 1-b·cH₂O, where 0 ≤ a ≤ 2, for example, it can be 0, 0.2, 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, or 2, etc.; 0 < b < 1, for example, it can be 0.2, 0.4, 0.6, or 0.8, etc.; c > 0, for example, it can be 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, etc.; A and B independently include any one or a combination of at least two of Fe, Co, Ni, Mn, Cu, and Mg, for example, it can be a combination of Fe and Co, a combination of Ni and Mn, a combination of Cu and Mg, or a combination of Fe, Co, and Ni, etc.; X is a sodium defect.

[0012] In the present invention, "independently" means that the selection of the two does not interfere with each other. For example, A and B independently include any one or a combination of at least two of Fe, Co, Ni, Mn, Cu, and Mg, which means that when A is a combination of Fe and Co, B can be Fe, can be a combination of Fe and Co, or can be a combination of Mn and Cu. The selection of A and B does not interfere with each other.

[0013] As a preferred technical solution of the cathode material of the present invention, the Prussian blue analogue is Na a Fe[Fe(CN)₆] b X 1-b ·cH₂O.

[0014] In the present invention, when Na a Fe[Fe(CN)₆] b X 1-b ·cH₂O is used in combination with a cathode additive as the cathode material of an aqueous sodium-ion battery, the effect is the best. Na a Fe[Fe(CN)₆] b X 1-b The sodium defect in ·cH₂O is generated by the oxidation of Fe. In an aqueous sodium-ion battery, based on the principle of charge balance, this sodium defect is easily filled with sodium released by the cathode additive; for Prussian blue analogues with more water defects, if the defects are caused by the occupation of interstitial water, when sodium supplementation is carried out in an aqueous sodium-ion battery, it is difficult for sodium to fill the sodium defects formed by the occupation of interstitial water. Therefore, when Na a Fe[Fe(CN)₆] b X 1-b ·cH₂O is used in combination with a cathode additive to prepare a cathode material for an aqueous sodium-ion battery, the effect is the best.

[0015] Preferably, the organic sodium salt includes any one or a combination of at least two of Na2C3O3, Na2C4O4, Na2C2O4, Na2C3O5, sodium phenolate, trisodium cyanurate, sodium ascorbate, sodium urate, and sodium alginate. For example, it can be a combination of Na2C3O3 and Na2C4O4, a combination of Na2C4O4 and Na2C2O4, a combination of Na2C3O5 and sodium phenolate, a combination of trisodium cyanurate and sodium ascorbate, or a combination of Na2C3O5, sodium ascorbate, sodium urate, and sodium alginate, etc., preferably Na2C2O4.

[0016] The preferred organic sodium salts of this invention produce gaseous products during decomposition, which are easily discharged from aqueous sodium-ion batteries, resulting in good safety performance and high usability. Furthermore, the preferred organic sodium salts of this invention work even better when used in combination with Prussian blue analogues, with the two working synergistically to improve the energy density and cycle stability of aqueous sodium-ion batteries.

[0017] Preferably, the positive electrode material further includes a conductive agent and a binder.

[0018] Preferably, the conductive agent comprises acetylene black and / or carbon nanotubes.

[0019] Preferably, the adhesive comprises polytetrafluoroethylene.

[0020] In a second aspect, the present invention provides a positive electrode comprising the positive electrode material according to the first aspect.

[0021] The cathode prepared using the cathode material of this invention has good energy density, cycle stability and rate performance, and is suitable for aqueous sodium-ion batteries.

[0022] Preferably, the positive electrode further includes a conductive agent and a binder.

[0023] Preferably, the conductive agent comprises acetylene black and / or carbon nanotubes.

[0024] Preferably, the adhesive comprises polytetrafluoroethylene.

[0025] By way of example, the present invention provides a method for preparing the above-mentioned positive electrode, the method comprising:

[0026] The positive electrode active material with sodium defects of the present invention is thoroughly mixed with the positive electrode additive to obtain the positive electrode material. Then, the positive electrode material, conductive agent and binder are ground and mixed evenly, and rolled to form a film of uniform thickness. After drying the film in a vacuum drying oven at 120°C for 5 hours, it is cut into square electrode sheets to obtain the positive electrode.

[0027] The preparation method of this invention is simple and easy to operate, and the prepared cathode material has excellent applications in aqueous sodium-ion batteries.

[0028] Thirdly, the present invention provides an aqueous sodium-ion battery, comprising a positive electrode, a negative electrode and an aqueous electrolyte, wherein the positive electrode is the positive electrode described in the second aspect.

[0029] The aqueous sodium-ion battery prepared using the cathode described in this invention has good safety performance. Compared with the oil-based closed system, it does not produce safety problems such as swelling and has better energy density, cycle stability and rate performance.

[0030] Preferably, the negative electrode comprises sodium titanium phosphate and / or transition metal oxides.

[0031] Preferably, the transition metal oxide includes TiO2.

[0032] Preferably, the aqueous electrolyte includes any one or at least two aqueous solutions of Na2SO4, NaClO4, NaOTF and TEAOTF, such as aqueous solutions of Na2SO4 and NaClO4, NaClO4 and NaOTF, NaOTF and TEAOTF, or aqueous solutions of Na2SO4, NaClO4, NaOTF and TEAOTF, etc.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) In this invention, organic sodium salt is used as a positive electrode additive in combination with Prussian blue analogues that have sodium defects. The combination structure is stable and can efficiently compensate for the sodium defects of the positive electrode active material itself. It can also replenish the sodium ions required by the formation of the SEI film and other side reactions, thereby improving the energy density and coulombic efficiency of the battery. At the same time, the organic sodium salt of this invention decomposes to produce gas, which can form impact pores on the positive electrode surface, which is conducive to the penetration of electrolyte and improves the transport efficiency of Na ions. Moreover, the decomposition products do not contain solid products. The gas produced by the decomposition of the positive electrode additive is easy to discharge in the open aqueous sodium-ion battery, which has high safety and good stability.

[0035] (2) The process of this invention is simple, the positive electrode active material is cheap, the system has strong availability, and it can effectively supplement the sodium ion loss caused by sodium defects in the positive electrode material in the aqueous battery system, greatly improving the energy density, cycle stability and rate performance of the whole battery. It has significant implications for the future application of aqueous sodium ion batteries in the field of large-scale energy storage. Attached Figure Description

[0036] Figure 1 These are charge-discharge curves of aqueous sodium-ion batteries from Embodiment 1 and Comparative Example 1 of the present invention.

[0037] Figure 2These are rate performance diagrams of aqueous sodium-ion batteries from Embodiment 1 and Comparative Example 1 of the present invention.

[0038] Figure 3 These are cycle performance diagrams of aqueous sodium-ion batteries from Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0039] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0040] In this invention, the sodium defect number of the positive electrode active material is obtained from ICP testing of Na and Fe and elemental analysis of C and N. The preparation of the positive electrode active material is as follows: the reactant raw materials are a mixture of a cyanide salt of a transition metal ion and one of its sulfate, nitrate, or chloride salts; the mixture is ball-milled or co-precipitated; the precipitate is washed, filtered, collected, and dried to obtain the product. The preparation of the positive electrode additive is described in patent ZL201910970077.4.

[0041] Example 1

[0042] This embodiment provides a positive electrode material for aqueous sodium-ion batteries. The positive electrode material includes Na, a Prussian blue analogue with sodium defects. 1.56 Fe[Fe(CN)6] 0.84 X 0.16 • 2.13H2O and positive electrode additive sodium squartzate (Na2C4O4), the mass of Na2C4O4 being 11.2% of the mass of the positive electrode active material.

[0043] This embodiment also provides an aqueous sodium-ion battery and its preparation method. The sodium-ion battery includes a positive electrode, a negative electrode, and an aqueous electrolyte. The positive electrode includes the aforementioned positive electrode material, a conductive agent acetylene black, and a binder polytetrafluoroethylene. The preparation method includes:

[0044] (1) Preparation of positive electrode: The above positive electrode material, conductive agent and binder are ground and mixed evenly in a mass ratio of 7:2:1, rolled into a film of uniform thickness, dried in a vacuum drying oven at 120℃ for 5h, and then cut into square electrode sheets for use as positive electrode, denoted as Fe-HCF-1-F;

[0045] (2) Preparation of aqueous sodium-ion battery: Except for replacing the Prussian blue analogue and the positive electrode additive with sodium titanium phosphate (NTP), the preparation of the negative electrode is the same as that of the positive electrode. Using the positive and negative electrodes prepared in this example, and using 1M Na2SO4 aqueous solution as electrolyte, a 2032 button cell is assembled to obtain an aqueous sodium-ion battery.

[0046] Example 2

[0047] This embodiment provides a positive electrode material for aqueous sodium-ion batteries. The positive electrode material includes Na, a Prussian blue analogue with sodium defects. 1.38 Fe[Fe(CN)6] 0.76 X 0.24 • 2.79H2O and sodium oxalate (Na2C2O4) as a positive electrode additive, wherein the mass of Na2C2O4 is 15.0% of the mass of the positive electrode active material.

[0048] This embodiment also provides an aqueous sodium-ion battery and its preparation method, except that the Prussian blue analogue and the positive electrode additive are replaced with Na as described in this embodiment. 1.38 Fe[Fe(CN)6] 0.76 X 0.24 Except for 2.79H2O and Na2C2O4, the rest are the same as in Example 1. In this example, the positive electrode is denoted as Fe-HCF-2-C.

[0049] Example 3

[0050] This embodiment provides a positive electrode material for aqueous sodium-ion batteries. The positive electrode material includes Na, a Prussian blue analogue with sodium defects. 0.88 Cu[Fe(CN)6] 0.9 X 0.1 • 3.79H2O and positive electrode additive Na2C3O5, the mass of Na2C3O5 being 26.5% of the mass of the positive electrode active material.

[0051] This embodiment also provides an aqueous sodium-ion battery and its preparation method. The sodium-ion battery includes a positive electrode, a negative electrode, and an aqueous electrolyte. The positive electrode includes the aforementioned positive electrode material, a conductive agent acetylene black, and a binder polytetrafluoroethylene. The preparation method includes:

[0052] (1) Preparation of positive electrode: The positive electrode material, conductive agent and binder are ground and mixed evenly in a mass ratio of 7:2:1, rolled into a film of uniform thickness, dried in a vacuum drying oven at 120℃ for 5h, and then cut into square electrode sheets for use as positive electrode, denoted as Cu-HCF-1-F;

[0053] (2) Preparation of aqueous sodium-ion battery: Except for replacing the Prussian blue analogue and the positive electrode additive with sodium titanium phosphate (NTP), the preparation of the negative electrode is the same as that of the positive electrode. Using the positive and negative electrodes prepared in this example, and the electrolyte is 9M NaOTF + 22M TEAOTF aqueous solution, a 2032 button cell is assembled to obtain an aqueous sodium-ion battery.

[0054] Example 4

[0055] Except for Na1.56 Fe[Fe(CN)6] 0.84 X 0.16 ·2.13H2O replaced with Na 1.56 Mn[Fe(CN)6] 0.84 X 0.16 Except for 2.13H2O, everything else is the same as in Example 1. The positive electrode prepared in this example is denoted as Mn-HCF-1-F.

[0056] Example 5

[0057] Except for replacing Na2C4O4 with Na2C3O5, everything else is the same as in Example 1.

[0058] Example 6

[0059] Except for replacing the electrolyte with 1M NaClO4, everything else is the same as in Example 1.

[0060] Example 7

[0061] Except that the mass of the positive electrode additive is 5% of the mass of the Prussian blue analogue with sodium defects, everything else is the same as in Example 1.

[0062] Example 8

[0063] Except that the mass of the positive electrode additive is 15% of the mass of the Prussian blue analog with sodium defects, everything else is the same as in Example 1.

[0064] Example 9

[0065] Except that the mass of the positive electrode additive was 20% of the mass of the Prussian blue analogue with sodium defects, everything else was the same as in Example 1.

[0066] Example 10

[0067] Except that the mass of the positive electrode additive was 25% of the mass of the Prussian blue analogue with sodium defects, everything else was the same as in Example 1.

[0068] Comparative Example 1

[0069] Except for the absence of cathode additives in the cathode material, everything else is the same as in Example 1. The cathode prepared in this comparative example is denoted as Fe-HCF-1.

[0070] Comparative Example 2

[0071] Except for the absence of cathode additives in the cathode material, everything else is the same as in Example 2. The cathode prepared in this comparative example is denoted as Fe-HCF-2.

[0072] Comparative Example 3

[0073] Except for the absence of cathode additives in the cathode material, everything else is the same as in Example 3. The cathode prepared in this comparative example is denoted as Cu-HCF-1.

[0074] The sodium-ion batteries prepared according to the embodiments and comparative examples of the present invention were subjected to first-cycle charge-discharge tests and cycle stability tests under the following conditions:

[0075] I. First Week Charge / Discharge Test: Voltage range 0~1.8V (vs Na) + / Na), current is 20mAg -1 (0.2C) and 100mAg -1 (1C), the charging specific capacity and discharging specific capacity of the battery were recorded, and the results are shown in Table 1.

[0076] II. Cyclic stability test: Voltage range 0~1.8V (vs Na) + / Na), current is 100mAg -1 (1C) Record the capacity retention rate after 200 cycles of the battery. The capacity retention rate is obtained by dividing the discharge specific capacity of the 200th cycle by the discharge specific capacity of the first cycle. The results are shown in Table 1.

[0077] Table 1

[0078]

[0079] As can be seen from Examples 1-10 above, the present invention combines a specific positive electrode active material, a Prussian blue analogue, with a positive electrode additive. The two work synergistically to effectively compensate for the sodium ion loss caused by sodium defects in the positive electrode active material in the aqueous battery system, thereby greatly improving the energy density, cycle stability, and rate performance of the aqueous sodium-ion battery.

[0080] A comparison of Examples 1 and 4 shows that Na is used in this invention. 1.56 Fe[Fe(CN)6] 0.84 X 0.16 • The aqueous sodium-ion battery prepared by using 2.13H2O in combination with the positive electrode additive exhibits better electrochemical performance, while Na 1.56 Fe[Fe(CN)6] 0.84 X 0.16 • Due to the defects caused by the oxidation of Fe in 2.13H2O, it works synergistically with the positive electrode additive Na2C4O4 to improve the electrochemical performance of sodium-ion batteries. Therefore, the performance of Example 1 is better than that of Example 4.

[0081] A comparison of Examples 1 and 5 shows that there is an optimal choice for the positive electrode additive in this invention. When Na2C4O4 is used, the discharge capacity is higher. Therefore, Na2C4O4 performs better as an additive than Na2C3O5.

[0082] A comparison of Examples 1 and 6 shows that the electrolytes selected in this invention, specifically 1M NaClO4 and 1M Na2SO4 aqueous solutions, have comparable properties, indicating that the cathode material of this invention has good application potential in aqueous electrolytes.

[0083] A comparison of Examples 1 and 7-10 shows that, in this invention, when the contents of the positive electrode active material and the positive electrode additive are within a suitable range, the prepared aqueous sodium-ion battery exhibits better performance. However, when the content of the positive electrode additive is too low, the battery's discharge capacity is low because it cannot compensate for the defects of sodium, resulting in a decrease in energy density. Conversely, when the content of the positive electrode additive is too high, the corresponding proportion of active positive electrode material decreases, which also leads to a lower battery capacity and thus a decrease in energy density. Therefore, the initial discharge specific capacity at 0.2C and 1C in Example 7 is slightly worse than that in Example 1, and the initial discharge specific capacity at 0.2C and 1C in Example 10 is also slightly worse than that in Example 1.

[0084] Figure 1 The above shows the charge-discharge curves of the aqueous sodium-ion batteries in Example 1 and Comparative Example 1 of this invention at 0.2C. Figure 2 The graphs show the rate performance of the aqueous sodium-ion batteries in Example 1 and Comparative Example 1. Figure 3 The graphs show the cycle performance of aqueous sodium-ion batteries in Example 1 and Comparative Example 1. By comparing Example 1 with Comparative Example 1, Example 2 with Comparative Example 2, and Example 3 with Comparative Example 3, it can be seen that when the positive electrode additive of the present invention is used in combination with the positive electrode active material, the introduced sodium can compensate for sodium defects and may also be conducive to the formation of SEI film on the negative electrode surface, so that the material can give full play to its electrochemical performance. Therefore, the materials all exhibit good electrochemical performance. For example, after 200 cycles at 1C, the system with positive electrode additive can achieve a capacity retention rate of over 90%, while the system without additive shows a lower capacity when assembled into an aqueous sodium-ion battery.

[0085] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A cathode material for aqueous sodium-ion batteries, characterized in that, The cathode material includes a cathode active material with sodium defects and a cathode additive. The cathode active material includes a Prussian blue analogue, and the cathode additive includes an organic sodium salt. The organic sodium salt decomposes to produce gas; The Prussian blue analogue contains interstitial water; The Prussian blue analog has a chemical formula of Na a A[B(CN)6] b X 1-b • cH2O, wherein 0≤a≤2, 0<b<1, c>0, A and B independently include any one or a combination of at least two of Fe, Co, Ni, Mn, Cu, and Mg, and X is a sodium defect; The organic sodium salt includes any one or a combination of at least two of the following: Na2C3O3, Na2C4O4, Na2C2O4, Na2C3O5, sodium phenolate, trisodium cyanurate, sodium ascorbate, sodium urate, and sodium alginate.

2. The cathode material according to claim 1, characterized in that, The mass of the positive electrode additive is 1 to 30% of the mass of the positive electrode active material.

3. The cathode material according to claim 2, characterized in that, The mass of the positive electrode additive is 10-20% of the mass of the positive electrode active material.

4. The cathode material according to claim 1, characterized in that, The Prussian blue analogue is Na a Fe[Fe(CN)6] b X 1-b ·cH2O.

5. The positive electrode material according to claim 1, characterized in that, The organic sodium salt is Na2C4O4.

6. A positive electrode, characterized in that, The positive electrode includes the positive electrode material according to any one of claims 1-5.

7. The positive electrode according to claim 6, characterized in that, The positive electrode also includes a conductive agent and a binder.

8. The positive electrode according to claim 7, characterized in that, The conductive agent includes acetylene black and / or carbon nanotubes.

9. The positive electrode according to claim 7, characterized in that, The adhesive includes polytetrafluoroethylene.

10. An aqueous sodium-ion battery, comprising a positive electrode, a negative electrode, and an aqueous electrolyte, characterized in that, The positive electrode is the positive electrode according to any one of claims 6-9.

11. The aqueous sodium-ion battery according to claim 10, characterized in that, The negative electrode includes sodium titanium phosphate and / or transition metal oxides.

12. The aqueous sodium-ion battery according to claim 11, characterized in that, The transition metal oxide includes TiO2.

13. The aqueous sodium-ion battery according to claim 10, characterized in that, The aqueous electrolyte includes any one or at least two of Na2SO4, NaClO4, NaOTF, and TEAOTF.

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