Sodium-driven Rechargeable Batteries: An Effort towards Future Energy Storage

Due to the crucial impact of Li-ion batteries commercialized in 1991, the author had an opportunity to contribute to the research development of lithium battery materials beginning in 1997. These research experiences further provided motivation and opened up a new research field targeting the demonstration of non-aqueous Na-ion batteries later in the career. In 2009, the author's research group successfully demonstrated 3-volt class charge and discharge of a Na-ion battery, and the increased motivation led to a brand-new 4-volt class K-ion battery. This article overviews our systematic studies of lithium-, sodium-, and potassium-driven redox systems, which synergistically induce accelerated development of new materials for next-generation rechargeable batteries. Our achievement update of layered oxide and hard carbon electrode materials is also described as an effort towards high-energy Na-ion batteries.