The Role of Fluorine in Polyanionic Cathode Materials for Sodium‐Ion Batteries

With the growing global demand for renewable energy and the increasing scarcity of lithium resources, sodium-ion batteries have received extensive attention and research as a potential alternative. Among many cathode materials for sodium-ion batteries, polyanion materials are favored for their high operating voltage, stable cycling performance, and good safety. However, the low electronic conductivity and low energy density of polyanionic materials limit their potential for large-scale commercial applications. To overcome this challenge, various strategies have been explored to improve their electrochemical performance. Among them, fluorine doping has been proven to be an effective means. In this study, we have systematically explored the effects of trace fluorine doping and mass fluorine substitution on the structure, dynamics, and electrochemistry of polyanionic cathode materials for sodium-ion batteries and deeply analyzed their reaction mechanisms. The analysis results show that trace fluorine doping can effectively improve the electronic conductivity of the material, thus enhancing its electrochemical performance. A large amount of fluorine substitution can effectively improve the voltage plateau of the material, thus enhancing its energy density. However, the environmental and safety challenges associated with the introduction of fluorine should also be addressed. Overall, the introduction of fluorine in polyanionic cathode materials can further optimize the electronic structure and electrochemical performance, thus realizing the wide application of high-performance sodium-ion batteries and making them a competitive battery technology.