Characterisation of Defluorination Reaction and Solid Electrolyte Interphase in Fluoride-Shuttle Battery Anode MgF2

Abstract

Fluoride-shuttle batteries using fluoride ion transfer have been extensively investigated for producing post-lithium-ion batteries. One of the key issues hampering the development is the low capacity utilisation rate in anodes, causing a significant reduction in battery performance. To improve the utilisation rate, it is necessary to clarify the unexplained parts regarding the (de)fluorination behaviour to optimise the electrode design. Here, we demonstrated the characterisation of Mg metal formations and the solid electrolyte interphase (SEI) in defluorinated MgF2 anode. Mg was mainly formed in the region with electron and F ion conductivities, implying that these conductivity paths must be efficiently increased to further improve the utilisation rate. Nanosized Mg metals were formed even in the region with poor electron conductivity, implying that an efficient (de)fluorination process could be achieved by designing the electrode configuration or/and elemental composition. The influence of SEI in battery performance have currently been neglected because the problems of low utilisation rate are more serious. However, as research progresses, the control of the SEI composition and its properties should be an important investigation to further improve fluoride-shuttle battery performances.