(401i) High Energy Density Picoliter-Scale Zn-Air Batteries for Colloidal Robotics

The recent interest in microscopic autonomous systems, including microrobots, colloidal state machines and smart dust has created a need for microscale energy storage and harvesting. However, macroscopic materials for energy storage have noted incompatibilities with micro-fabrication techniques, creating significant challenges to realizing microscale energy systems. Herein, we photolithographically pattern a microscale Zn/Pt/SU-8 system to generate the highest energy density microbattery at the picoliter (10^-12 L) scale. The device scavenges ambient or solution dissolved oxygen for a Zn oxidation reaction, achieving an energy density ranging from 760 to 1070 Wh L^-1 at scales below 100 μm lateral and 2 μm thickness in size. The parallel nature of photolithography processes allows 10,000 devices per wafer to be released into solution as colloids with energy stored onboard. Within a volume of only 2 pL each, these primary microbatteries can deliver open circuit voltages of 1.05 ± 0.12 V with total energies ranging from 5.5 ± 0.3 to 7.7 ± 1.0 μJ and a maximum power near 2.7 nW. We demonstrate that such systems can reliably power a micron-sized memristor circuit, providing access to non-volatile memory. We also cycle power to drive the reversible bending of microscale bimorph actuators at 0.05 Hz for mechanical functions of colloidal robots. Additional capabilities such as powering two distinct nanosensor types and a clock circuit are also demonstrated. The high energy density, low volume and simple configuration promise the mass fabrication and adoption of such picoliter Zn-air batteries for micron-scale, colloidal robotics with autonomous functions.