New progress has been made in the research of aqueous sodium-ion batteries

Recently, the team of Wang Chengxin/Yang Gongzheng of the School of Materials Science and Engineering of Sun Yat-sen University proposed a surface cation in situ capture strategy for the first time, which solved the problems of unstable cathode structure and poor battery cycle stability of aqueous sodium-ion batteries. The results were published in Nature – Communications.

Due to the characteristics of safety, environmental protection and abundant resources, aqueous sodium-ion batteries have shown great application prospects in the field of large-scale energy storage. Among the existing chemical systems, manganese-based Prussian blue has the highest working voltage (3.5 volts) and theoretical specific capacity (about 160 mAh per gram), which is an ideal aqueous sodium-ion battery cathode material. However, how to effectively inhibit or mitigate the negative effects of the Taylor effect of Jiang Taylor has become one of the biggest scientific problems in the field of aqueous sodium-ion batteries.

The team found that manganese-based Prussian blue gradually changed from monoclinic phase to cubic phase during charging, and finally changed to tetragonal phase. In the process of cubic-quadrilateral phase transition, the Taylor effect of ginger caused by high spin trivalent manganese ions causes the disproportionation reaction of manganese, so that part of the manganese is dissolved in the electrolyte with divalent manganese ions. When a trace amount of sodium ferrocyanide is introduced into the electrolyte as an additive, the cyanide ions electromigrate to the surface of the positive electrode during the charging process, which can capture the dissolved manganese ions on the surface and rapidly nucleate and epitaxial to grow manganese Prussian blue in situ, thereby eliminating the hidden danger of degradation of the positive electrode structure at the source.

(a, b) Schematic diagram of electrolyte modification strategy and comparison of (c-e) modification effect. Photo courtesy of the research team

Experiments show that manganese-based Prussian blue still maintains a complete morphology and uniform elemental distribution after long cycles under the electrolyte system introduced with additives. Advanced electron energy loss spectroscopy was used to further reveal the uniform distribution of manganese elements and valence states at the atomic scale, indicating that the dissolution of manganese was well inhibited. Based on this novel surface modification method, the cathode exhibits a specific capacity of 157 and 125 mA per gram at a current density of 0.5 and 10 amps per gram, respectively, with an average operating voltage of nearly 1.4 volts. The aqueous sodium-ion full battery was assembled with the organic anode material (3,4,9,10-tetraformyldiimide) with an energy density of up to 94 watt-hours per kilogram, and the capacity holding rate reached 73.4% after 15,000 charge-discharge cycles at a current density of 2 amps per gram.

This research work has made important breakthroughs in the two key indicators of cycle life (previously generally less than 3000 cycles) and energy density (usually less than 60 watt-hours per kilogram), which is of great significance for the practical development of aqueous sodium-ion batteries.

The reviewers spoke highly of the work and said, “This is an interesting and very important research work on improving the stability of manganese-based Prussian blue cathode materials for aqueous sodium-ion batteries.” (Source: China Science News Zhu Hanbin)

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