Stretchable and Biodegradable Batteries with High Energy and Power Density

Realizing a sustainable, technologically advanced future will necessitate solving the electronic waste problem.^[1] Biodegradable forms of electronics offer a viable path through their environmental benignity. With both the sheer number of devices produced every day as well as their areas of application ever increasing, new concepts of degradable batteries able to sustain the high power demands of modern electronics must be developed. Simultaneously, integration of electronics in close interaction with its user or powering soft robotic devices necessitates high degrees of compliance, rendering stretchable batteries indispensable. With the first stretchable battery demonstrated by our group in 2010, we since advance such concepts towards environmentally benign materials.^[2] We demonstrate a concept for merging intrinsically stretchable materials with engineered stretchability by kirigami-patterning on a component level. With this method, we achieve high-power biodegradable batteries with reversible elasticity up to 35% when stretched uniaxially and 20% for biaxial extension. Using a combination of molybdenum metal foils, a molybdenum trioxide paste and magnesium metal foils as electrode materials, a peak power output of 196 µW cm^-2 and an energy density of 1.72 mWh cm^-2 is realized. The biodegradable batteries are used to power an on-skin biomedical sensor patch, enabling monitoring of sodium concentration in sweat. We designed a flexible circuit board in a small form factor allowing the collection of sensor data, while solely being powered by our biodegradable battery. The whole device is non-obtrusive and comfortable to the wearer. This concept provides a versatile route for high-power biodegradable batteries, enabling untethered soft electronic devices in a sustainable future.<br/><br/>[1] Hartmann, F., Baumgartner, M., Kaltenbrunner, M., “Becoming Sustainable, The New Frontier in Soft Robotics”. <i>Adv. Mater.</i> 2021, 33, 2004413<br/>[2] S. Bauer, S. Bauer-Gogonea, I. Graz, M. Kaltenbrunner, C. Keplinger, R. Schwödiauer, “25th anniversary article: a soft future: from robots and sensor skin to energy harvesters”, <i>Advanced Materials 26(1)</i>, 149-162, 2014