Low‐Overpotential LiF Splitting in Lithiated Fluoride Conversion Cathode Catalyzed by Spinel Oxide

Conversion chemistry involving LiF splitting is an appealing route toward high capacity cathodes for Li-ion batteries. In general, cathodes based on LiF splitting need a redox host to provide the driving force for LiF decomposition from the surface. However, most of the systems are still far from practical owing to their limitations, especially the high charge voltage (4.5-5.0 V) needed to fully utilize the capacity and the subsequent low energy efficiency (<80%). The redox host is apparently the key to further reduce the required charge voltage and improve the energy efficiency. Here, a new LiF-NiFe2O4 conversion cathode chemistry is designed and demonstrated with a crystalline spinel oxide redox host. It is demonstrated that the new host effectively improves the surface redox and LiF splitting kinetics, which enable the new cathode to work at much lower charge cutoffvoltage (4.2 V) without compromising the delivered capacity and voltage. The LiF-NiFe2O4 composite thin film is able to be discharged with large capacity of 237 mA h g(-1) with high energy efficiency (88%), substantial pseudocapacitance contribution (>90%), and satisfactory capacity retention. This result indicates LiF splitting chemistry can become practical by carefully tailoring the redox host chemistry and optimizing the composition.