Computational Simulation Research On Alkali-ion Battery Cathode MoF₆

Due to its high energy density,high electrode potential,good cycle performance and environmentally friendliness,lithium-ion battery has received considerable attention as an ideal chemical battery.The great success of the lithium-ion battery,making the research of sodium ion battery and corresponding electrode material have also gained a wide range of attention in recent years.Molybdenum fluoride is expected to use its multiple redox pairs to achieve multi-electron reversible exchange,thereby achieving sodium/lithium ion battery higher reversible specific capacity.At the same time,due to the "induced effect",fluorine element is a strong electronegativity expected to significantly improve the potential of transition metal,thereby enhancing the battery operating voltage.Considering the above factors,MoF6 is expected to be a novel cathode material for lithium/sodium ion batteries.Based on the Bond Valence-based force field model,we construct the interaction potentials and explore the potential energy surfaces in the MoF6 structures to find the suitable intercalation positions for the sodium/lithium ions.Combined with the first principles calculations,the structural evolution and the internal mechanism of the material during the intercalation process are investigated.In two different MoF6 experimental structures(Im-3m,Pnma),the AxMoF6 structures with different Na/Li contents are predicted.The relationship between the formation energy,the voltage and the Na/Li content x is studied.The results show that MoF6 octahedra have significant effects on the stability of the structure.The structure with lower distortion shows to be more energetically stable.Considering the relatively small volume change during the intercalation process and high voltage,MoF6 could be a potential cathode material for both sodium ion and lithium ion batteries.The investigation on the intercalation process of polyvalent metal fluoride MoF6 would provide important insights for the experimental and theoretical research of polyvalent metal fluoride as cathode material.