Prospect and Status of Polyanionic Lithium Cobalt Silicates as High Energy‐Density and Safe Cathode Materials for Lithium‐Ion Batteries

Lithium cobalt silicate Li2CoSiO4 (LCSO) is a promising but challenging high energy-density cathode for lithium-ion battery. Herein, recent studies of synthesis-structure-performance of LCSO are reported, in which carbon coating, element doping, and nanostructure designs are incorporated in a two-step synthesis starting with hydrothermal reaction. The initial performance is significantly improved with respect to previous reports in literature with the charge and discharge capacities now reaching 330 and 220 mAh g(-1), respectively. The discharge voltage platform is compatible with the 4 V window of the nonaqueous organic electrolytes and presents no structural-change-induced voltage drops. The striking finding from the study of LCSO is the oxygen redox activity amid the second lithium deintercalation process, in which peroxo formation dominates the charge compensation to the high-voltage lithium capacity. First-principles modeling reveals an intrinsic and general relation between oxygen redox and cationic disorder in bulk compounds. Thus, LCSO is a new prototype of polyanionic materials with oxygen redox, which is the foundation of high-capacity Li-rich cathodes. This review is also aimed to narrate the progresses of LCSO within a broad domain of Li3PO4-based polyanionic structures that support the development of solid-state electrolytes for all solid-state batteries.