Xing Ye1,John Boley1
Boston University1
Liquid metals, such as alloys of gallium, have unique mechanical and electrical properties because they behave like liquid at room temperature. These properties make liquid metals an ideal candidate for soft electronics and stretchable conductors. In addition, these metals spontaneously form a thin oxide layer on its surface. Applications that are made possible by this delicate oxide skin include shape reconfigurable electronics, microfluidic devices, and unconventional actuators. This presentation introduces another class of applications of liquid metals as an electrochemical energy source. By mechanically rupturing their surface oxide, liquid metals can form a galvanic cell and convert its chemical energy to electrical energy. When dispersing liquid metals into an ionically-conductive liquid to form emulsions, this hybrid material can provide ~500 mV of open-circuit voltage and ~10 μA of short-circuit current. This approach is further used to make a strain-activated stretchable electrochemical device that can supply up to ~4 μW of power. Protected by the oxide skin naturally, this passivating layer of the liquid metal shields it from self-discharge over time or changes in operating environment. Future applications of this device are demonstrated by supplying energy to a LED or a capacitor during repeated stretches. Strategies to further improve the output power of these devices are also discussed. These findings may unlock new soft battery designs due to the special surface oxide of liquid metals and offer new pathways to harness their inherent energy for self-powered devices.