KTiOPO4-structured electrode materials for metal-ion batteries: A review

Abstract The success story of the triphylite-type LiFePO4 immediately boosted the development of numerous classes of polyanion-based electrode materials for metal-ion batteries. A number of advantages including thermal and structural stability, polyanionic inductive effect, and variety of crystal types and chemical compositions render these materials attractive for grid and large-scale applications ensuring high safety standards, environmental friendliness and cost benefits. In this review, we focus on a specific family of polyanion-based electrode materials adopting the KTiOPO4-type structure that captured particular attention recently due to the unique 3D-framework. This framework features thermal, structural and long-term electrochemical cycling stability, fast ionic transport, possibility to accommodate two alkali ions per transition metal cation enabling multi-electron transitions, and unprecedented high electrode potentials for a specific redox couple among all known polyanion materials. The recent advances and overview of KTiOPO4-type and related positive and negative electrode materials for metal-ion batteries are presented with a special emphasis on the interrelations between crystal structure peculiarities and electrochemical properties.