High‐Energy Symmetric Li‐Ion Battery Enabled by Binder‐Free FeOF‐MXene Heterostructure with Doubly Matched Capacity and Kinetics

Abstract Fluorides are viewed as promising conversion‐type Li‐ion battery cathodes to meet the desired high energy density. FeOF is a typical member of conversion‐type fluorides, but its major drawback is sluggish kinetics upon deep discharge. Herein, a heterostructured FeOF‐MXene composite (FeOF‐MX) is demonstrated to overcome this limitation. The rationally designed FeOF‐MX electrode features a microsphere morphology consisting of closely packed FeOF nanoparticles, providing fast transport pathways for lithium ions while a continuous wrapping network of MXene nanosheets ensures unobstructed electron transport, thus enabling high‐rate lithium storage with enhanced pseudocapacitive contribution. In/ex situ characterization techniques and theoretical calculations, both reveal that the lithium storage mechanism in FeOF arises from a hybrid intercalation‐conversion process, and strong interfacial interactions between FeOF and MXene promote Li‐ion adsorption and migration. Remarkably, through demarcating the conversion‐type reaction with a controlled potential window, a symmetric full battery with prelithiated FeOF‐MX as both cathode and anode is fabricated, achieving a high energy density of 185.5 Wh kg −1 and impressive capacity retention of 88.9% after 3000 cycles at 1 A g −1 . This work showcases an effective route toward high‐performance MXene engineered fluoride‐based electrodes and provides new insights into constructing symmetric batteries yet with high‐energy/power densities.