| 研究実績の概要 |
The goal of this JSPS fellowship is to identify new high-potential cathode materials for sodium-ion batteries. To this end, we studied the electrochemical properties of a Na-based heteropolyanionic SO4-PO3F solid-solution Na2Fe(SO4)2-x(PO3F)x.2H2O. The PO3F unit has not been studied as a polyanion for cathode materials so far and we were interested in its inductive effect and its impact on electrochemical performances. Galvanostatic cycling revealed elevated redox potentials for the PO3F polyanion. This would open the pathway to a new class of high-potential cathode materials. However, one drawback of this functional group is its low thermal stability. Therefore, we try to find additional synthesis routes to ensure an easy and reproducible preparation method of this compound.
A second project consists of the electrochemical and structural characterization of a Na-based layered oxide containing Ti4+ and Co2+, which displays a large hysteresis during Na (de)intercalation suggesting a spin transition of Co2+ upon oxidation. We are using a multi-angle approach with complementing characterization methods such as ex situ soft and hard X-ray absorption, magnetic measurements and galvanostatic intermittent titration technique (GITT) experiments to understand the underlying redox mechanism. Furthermore, we performed Density Functional Theory calculations to complement the experimental work with a theoretical viewpoint. The respective publication is under preparation.
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