602535 polymer battery.Progress in research on aqueous potassium-ion batteries

　　Aqueous alkali metal ion (Li+/Na+/K+) batteries have become one of the emerging candidate systems for grid energy storage due to their inherent safety. In early studies, researchers made some preliminary explorations into this battery system (Nature Communications 2015, 6,6401; AdvancedEnergyMaterials2015,5,1501005; AdvancedEnergyMaterials2017,7,1701189). Among aqueous alkali metal ion batteries, aqueous potassium ion batteries have more prominent advantages. The main reasons are: first, the content of potassium in the earth's crust is 1290 times that of lithium, which has a great cost advantage; second, the standard electrode of potassium The potential is 0.22V lower than that of sodium, which means that the potassium cathode of the same type of structure has a higher voltage, resulting in a higher energy density for the full battery; thirdly, in an aqueous solution with the same anions and the same concentration, the potassium salt solution The ionic conductivity of lithium salt is much higher than that of lithium salt and sodium salt, which means that using potassium salt solution as electrolyte can make the full battery have faster charge and discharge capabilities. However, due to the dissolution phenomenon of many electrode materials in water and the narrow voltage window of traditional aqueous electrolytes (less than 2V), the selection of electrode materials in aqueous batteries is greatly limited. Therefore, exploring high-performance potassium-based positive electrodes, negative electrodes, and wide voltage window electrolytes has become a core issue that needs to be solved in the field of aqueous potassium-ion batteries. Recently, Jiang Liwei, a doctoral student in Group E01 of the Clean Energy Key Laboratory of the Institute of Physics, Chinese Academy of Sciences/Beijing National Research Center for Condensed Matter Physics, successfully constructed an aqueous potassium-ion full battery under the guidance of researcher Hu Yongsheng and associate researcher Lu Yaxiang, proposing to use Fe Manganese-rich potassium-based Prussian blue KxFeyMn1-y[Fe(CN)6]w·zH2O, which partially replaces Mn, is the positive electrode, and the organic dye perylene brilliant purple red 29 (PTCDI) (CAS: 81-33-4) is the negative electrode, 22 mol/L The aqueous solution of potassium trifluoromethanesulfonate is the electrolyte. The research results were recently published in Nature Energy (Nature Energy, 2019, doi:10.1038/s41560-019-0388-0), and the article is titled Building Aqueous K-Ion Batteries for Energy Storage. For the cathode, the manganese-rich potassium-based Prussian blue material with P21/n space group (Figure 1a-b) has become the first choice for aqueous potassium-ion battery cathode materials due to its stability to water and the advantages of both high voltage and high capacity. However, manganese-rich potassium-based Prussian blue materials have serious dissolution problems when circulating in low-salt concentration electrolytes.

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