Metal–Organic Framework-Derived Nanoconfinements of CoF2 and Mixed-Conducting Wiring for High-Performance Metal Fluoride-Lithium Battery

Metal fluoride (MF) conversion cathodes theoretically show higher gravimetric and volumetric capacities than Ni- or Co-based intercalation oxide cathodes, which makes metal fluoride–lithium batteries promising candidates for next-generation high-energy-density batteries. However, their high-energy characteristics are clouded by low-capacity utilization, large voltage hysteresis, and poor cycling stability of transition MF cathodes. A variety of reasons is responsible for this: poor reaction kinetics, low conductivities, unstable MF/electrolyte interfaces and dissolution of active species upon cycling. Herein, we combine the synthesis of the metal–organic-framework (MOF) with the low-temperature fluorination to prepare MOF-shaped CoF2@C nanocomposites that exhibit confinement of the CoF2 nanoparticles and efficient mixed-conducting wiring in the produced architecture. The ultrasmall CoF2 nanoparticles (5–20 nm on average) are uniformly covered by graphitic carbon walls and embedded in the porous carbon framework. Within the CoF2@C nanocomposite, the cross-linked carbon wall and interconnected nanopores serve as electron- and ion-conducting pathways, respectively, enabling a highly reversible conversion reaction of CoF2. As a result, the produced CoF2@C composite cathodes successfully restrain the above-mentioned challenges and demonstrate high-capacity utilization of ∼500 mAh g–1 at 0.2C, good rate capability (up to 2C), and long-term cycle stability over 400 cycles. Overall, the presented study not only reports on a simple composite design to achieve high-energy characteristics in CoF2–Li batteries but also may provide a general solution for many other metal fluoride–lithium batteries.