MEAM Ph.D. Thesis Defense: “Coupling Hard and Soft Interfaces to Realize Actuators and Energy Sources that Bring Robots Towards Animal Mobility”

Mobile robots have shown significant advancements in agility, intelligence, and efficiency over the past few decades. However, their endurance and overall performance remain limited by the onboard power supplies. Current power sources typically restrict mobile robots to areas close to the electrical grid and necessitate heavier batteries for extended range. Energy refueling could be significantly challenging in remote and inaccessible regions, and traditional energy harvesting methods have also proven inadequate for sustaining continuous operations.

To address this challenge, we propose a bio-inspired approach: enabling robots to “digest” energy-dense metals for power generation, analogous to how animals process food for energy. This concept builds upon aluminum-air batteries, which operate as miniature chemical plants converting aluminum into electricity. We selected this technology for three key advantages: (1) exceptional energy density for improved endurance compared to conventional lithium batteries; (2) simple anode replacement for rapid refueling without charging stations; and (3) readily available fuel sources from everyday aluminum materials, from beverage cans to construction waste.

This thesis investigates how aluminum-air batteries can benefit the robotics community through four interconnected studies. First, we quantify the energy gap between mobile robots and their biological counterparts through comparative analysis of energy and power density, establishing benchmarks for future battery technologies to achieve biological equivalence. Second, we demonstrate the development of a highly stretchable metal-air battery using sliding electrodes, achieving up to 10-fold improvements in areal capacity and power compared to existing stretchable designs, which could extend the endurance and unleash the potential of various soft robots and wearable technologies. Third, we implement customized metal-air batteries on an Arduino-based robot platform, demonstrating continuous operation through metal oxidation using various aluminum and zinc sources while addressing challenges such as byproduct accumulation, hydrogen production, and water consumption. Finally, we showcase a feasible approach to develop a soft crawler based on this metallivore concept, capable of simultaneous metal digestion and continuous locomotion. By developing this aluminum-air battery-based energy solution, we demonstrate a path toward extending robots’ operational range and endurance beyond current limitations, thereby expanding their potential in remote and complex environments.