Flexible Aqueous Li‐Ion Battery with High Energy and Power Densities

A flexible and wearable aqueous symmetrical lithium-ion battery is developed using a single LiVPO4 F material as both cathode and anode in a "water-in-salt" gel polymer electrolyte. The symmetric lithium-ion chemistry exhibits high energy and power density and long cycle life, due to the formation of a robust solid electrolyte interphase consisting of Li2 CO3 -LiF, which enables fast Li-ion transport. Energy densities of 141 Wh kg-1 , power densities of 20 600 W kg-1 , and output voltage of 2.4 V can be delivered during >4000 cycles, which is far superior to reported aqueous energy storage devices at the same power level. Moreover, the full cell shows unprecedented tolerance to mechanical stress such as bending and cutting, where it not only does not catastrophically fail, as most nonaqueous cells would, but also maintains cell performance and continues to operate in ambient environment, a unique feature apparently derived from the high stability of the "water-in-salt" gel polymer electrolyte.