Fluorine doping of cathode materials for rechargeable batteries

Abstract

In the continuing search for alternative cathode materials for rechargeable batteries with improved electrochemical performances, there is a need for a versatile approach that will address concerns regarding low reversible capacity, poor capacity retention, low operating voltage and structural instability. So far, a lot of investigation was focused on cation doping. On the other hand, there is much less investigation on anion doping of cathode materials. Taking olivine-type LiFePO4 and layered NaxCoO2 as example materials for lithium- and sodium- ion batteries, respectively, the influence of fluorine doping on both the structure and the electrochemical performances was examined. The crystal structure refinement revealed that fluorine incorporation preserves the parent structure. Furthermore, small oxygen replacement by fluorine ions changes electronic structure and consequently modifies electrical properties.