Tactics to optimize conversion-type metal fluoride/sulfide/oxide cathodes toward advanced lithium metal batteries

Considering limited energy density of current lithium metal batteries (LMBs) due to low capacity of traditional intercalation-type cathodes, alternative high-energy cathodes are eagerly demanded. In this regard, conversion-type metal fluoride/sulfide/oxide cathodes have emerged great attention owing to their high theoretical specific capacities, supplying outstanding energy density for advanced LMBs. However, their low ionic/electrical conductivities, huge volume changes, sluggish reaction kinetics, and severe side reactions result in quick capacity fading and poor rate capability of LMBs. Recent research efforts on the conversion-type cathodes have brought new insights, as well as effective approaches toward realizing their excellent electrochemical performances. Here, the recent discoveries, challenges, and optimizing strategies including morphology regulation, phase structure engineering, surface coating, heterostructure construction, binder functionalization, and electrolyte design, are reviewed in detail. Finally, perspectives on the conversion-type metal fluoride/sulfide/oxide cathodes in LMBs are provided. It is believed that the conversion-type cathodes hold a promising future for the next-generation LMBs with high energy density.