2020 Fiscal Year Annual Research Report

Exploration of Ultra-High Voltage Cathodes for Rechargeable Batteries

Research Project

Project/Area Number	20F20038
Research Institution	The University of Tokyo
Principal Investigator	山田淳夫東京大学, 大学院工学系研究科(工学部), 教授 (30359690)
Co-Investigator(Kenkyū-buntansha)	DWIBEDI DEBASMITA 東京大学, 工学(系)研究科(研究院), 外国人特別研究員
Project Period (FY)	2020-04-24 – 2022-03-31
Keywords	Battery / Cathode / High-Voltage / Capacity / Polyanion / Insertion host
Outline of Annual Research Achievements	The research in 2020 fy dwelled on new high voltage electro-active materials with increased operating voltages and capacities. Putting polyanionic system known for their high voltages attributes as anvil, we unveiled a special category of anion engineering strategy that allowed us to identify polyanionic solid solutions of (VO)2SO4PO4. The combine incorporation of oxy, sulphate and phosphate anions not only rendered stable framework for alkali ion (Li/Na) insertion with a superior cycling performance but also exploited inductive effect to provide a high voltage insertion host. Further, Vanadium as a cation redox centre in the system provided multiple redox activity and thus a desirable capacity for the system.
Current Status of Research Progress	Current Status of Research Progress 2: Research has progressed on the whole more than it was originally planned. Reason Due to COVID situation, the experiments hit a low. However, with these newly developed cathode systems I am conducting an in-depth physico-chemical and electrochemical analysis for a deeper understanding of the electrochemical properties of each compound from the atomic scale to the bulk materials and device development. The stability of electrodes and electrolytes as well as their interfaces is crucial to achieve long cycle life and good safety features. In parallel, I am trying to improve the cycling performance and electrode stability via particle downsizing and carbon coating. I am also varying the mixing ratio of the two oxy polyanions to gauge the structural and electrochemical performance change.
Strategy for Future Research Activity	The obvious direct extension of the work would be a combine structural and electrochemical investigation, to gauge the observed multiple redox activity. To this end, I am planning to use synchrotron sources and extended X-ray fine structure (EXAFS) to effectively gauge each redox and structural state. Further, I will be using energy migration calculation for energy landscape of the system. Finally, I will comply all these results for journal publication. In parallel, I will conduct the similar research to investigate various unknown compositions differing cationic redox couples (e.g., Co3+/Co2+, Ni3+/Ni2+, Fe3+/ Fe2+ etc.) to gauge electroactive systems. Also, we will test these materials with super concentrated electrolyte and additives to provide the best cathode/electrolyte couple.