High voltage energy storage devices have always been supported by non-aqueous electrolytes, whose intrinsic wide stability window as well as the capability to form protective interphases at extreme potentials ensures the reversibility of electrochemical reactions, but whose high flammability, toxicity and sensitivity to ambient also bring compromises of safety, environment and rigid-format.

Replacing non-aqueous solvents with water could provide an ideal resolution of these issues on materials level, if the water molecules could be electrochemically stabilized at potentials where ordinary aqueous electrolytes decompose. This talk will summarize the efforts in this direction, and the various high voltage aqueous battery chemistries thus enabled.