Our group is engaged in the development of new materials and reactions toward high-energy-density and safe rechargeable batteries. Through our unique strategy of controlling the coordination states of ions and solvent molecules in electrolyte materials, we are developing new functions and properties that are not found in conventional electrolytes. We are also pursuing the possibility of new rechargeable batteries by utilizing the developed electrolyte materials. Our research achievements include the development of high-voltage lithium-ion batteries by widening the potential window of electrolytes (Nature Communications 2016, Nature Energy 2019), rapid charging of lithium-ion batteries using unique electrode/electrolyte interphases (Journal of the American Chemical Society 2014), development of safe lithium-ion batteries using flame-retardant and fire-extinguishing organic electrolytes (Nature Energy 2018), discovery of alkaline metal salt hydrate melts and development of high-voltage aqueous batteries using hydrate melt electrolytes (Nature Energy 2016, Angewandte Chemie 2019), and design and synthesis of a new electrolyte solvent that is both flame-retardant and voltage-resistant (Nature Energy 2020). We will continue to explore unknown functions and properties of electrolyte materials and develop new rechargeable batteries that contribute to solving energy and environmental issues.