Insights into the First Multi Transition Element Containing Ruddlesden Popper-Type Cathode for Fluoride Ion Batteries

Abstract

Fluoride ion batteries (FIBs) have emerged as a recent solid-state battery technology, offering an alternative to traditional battery systems. However, the existing FIBs have encountered challenges related to their poor cycling performance and improved electrodes based on fluoride insertion chemistry are highly sought.Here, we investigate Ruddlesden-Popper type La2Ni0.75Co0.25O4+𝛿 as a promising intercalation-based active cathode material for all-solid-state FIBs. We determine the structural changes of La2Ni0.75Co0.25O4+𝛿 during Fluoride intercalation / de-intercalation by X-ray Diffraction (XRD), electrochemical measurements and X-ray absorption spectroscopy to understand the detailed complex reaction behaviour of the phase, focussing on understanding the changes of Ni, Co oxidation states and coordination environments. Under optimized operating conditions, we obtained a cycle life of 120 cycles at a critical cut-off capacity of 40 mAh/g and over 250 cycles under pressure of 452MPa. The average Coulombic efficiencies ranged from 95% to 99% for the cell running under pressure. Thus, La2Ni0.75Co0.25O4+𝛿 corresponds to the most promising cycling-stable high-energy cathode materials for all-solid-state FIBs with the improved capacity.