Safe lithium-ion battery with ionic liquid-based electrolyte for hybrid electric vehicles

► Ionic liquids (ILs) are safe electrolytes for lithium-ion batteries. ► A graphite/LiFePO4 lithium-ion battery with pyrrolidinium IL-based electrolyte was assembled and tested for hybrid electric vehicle (HEV) application. ► This battery surpasses energy and power targets for HEV even after long cycling.