The findings reported here provide a comprehensive investigation of LaSrMnO4 as a cathode material FIBs, integrating experimental and computational approaches to analyze its The results obtained for LaSrMnO₄ and the scientific approach applied may be transferable to other materials within the same class, contributing to the optimization of their electrochemical performance. Furthermore, this work presents the first molecular dynamics simulations for this system, demonstrating that fluoride ions are the only species exhibiting long-range diffusion at operating temperatures. The diffusion mechanism is predicted to be vacancy-driven and confined within the fluoride interstitial layers, with no interlayer diffusion observed under the simulation conditions employed in this study.