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 LiVPO4F 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 Li2CO3‐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. A flexible and wearable aqueous lithium‐ion battery is introduced based on a unique “water‐in‐salt” gel polymer electrolyte and single electrode material with far superior energy density to reported aqueous energy‐storage devices at the same power level. The full cell can operate in open air, exhibiting ambient insensitivity, high safety, and unprecedented tolerance to against mechanical stress.