Thermodynamic properties and composites design principles of metal fluoride as active cathode material for lithium batteries

As part of the energy network, batteries still have limited applications due to their low capacity and low energy density. Metal fluorides (MFs), with the advantages of high specific energy and high output voltage, are promising active cathode materials for high-specific-energy batteries in the future. However, a comprehensive understanding of their thermodynamic and physicochemical properties based on current research progress is needed to facilitate their applications. In this paper, we evaluate the thermodynamic performance of 55 MFs battery systems from main-group elements, transition elements, and inner-transition elements. We analyze the distribution patterns in the periodic table of metal elements with superior electrochemical performance and explain why transition metal fluorides (TMFs) are suitable for cathode materials. Then we explain the main challenges in practical applications and how composite materials can address these shortcomings. Finally, from the perspective of designing composite materials, we summarize and analyze the composition and structures of recently reported TMFs-based composites while establishing the principles of composition matching and structure matching. Furthermore, we propose general rules that need to be observed in the design of composite materials.