This paper introduces polyphosphoric acid (PPA) as a solvent-free protic liquid electrolyte for batteries. Unlike conventional liquid electrolytes which have limitations in electrochemical window, operating temperature, volatility, and flammability, PPA exhibits nonflammability, a wide electrochemical stability window (>2.5 V), low volatility, and a wide working temperature range (>400 °C). Using a MoO3/LiVPO4F rocking-chair battery, the authors demonstrate stable operation from 0 °C to 250 °C, achieving a high power density of 4975 W kg−1 at 100 °C. This solvent-free electrolyte offers a promising pathway for safe and stable batteries operating under extreme conditions.

Mochou Liao, Xiao Ji, Yongjie Cao, Jie Xu, Xuan Qiu, Yihua Xie, Fei Wang, Chunsheng Wang, Yongyao Xia