Structural and electrochemical behaviour of bilayer manganite LaSr₂Mn₂O6.96 cathode for all-solid-state fluoride ion batteries

In this study, we explore the potential of the RP-type bilayer manganite LaSr2Mn2O6.96 as an intercalation-based cathode material for all-solid-state fluoride ion batteries (FIBs). Structural changes of LaSr2Mn2O6.96 during fluoride intercalation and de-intercalation were analyzed via ex-situ X-ray diffraction, revealing that F- insertion induces the formation of three distinct tetragonal phases. To understand the complex behavior of these phases, we examined the changes in the Mn oxidation state and coordination environment using X-ray absorption spectroscopy and magnetic measurements. Under stack pressure (20 kN), electrochemical cycling of LaSr2Mn2O6.96 in the potential range of 1 V to -1 V exhibited a continuous increase in specific capacity from capacity of ∼ 30 mAh/g to ∼ 68 mAh/g over 200 cycles, with ∼99% coulombic efficiency and no signs of capacity fading. This makes the bilayer manganite LaSr2Mn2O6.96 a promising candidate for a cycling stable cathode for all-solid-state FIBs, especially under the application of stack pressure.