A Photolithographable Electrolyte for Deeply Rechargeable Zn Microbatteries in On-Chip Devices.

Zn batteries are promising candidates for microscale applications due to their impressive compatibility with various microfabrication processes. However, the full potential of Zn batteries has been hampered by dendrite growth and chemical corrosion of the Zn anode, particularly at the microscale. Despite previous attempts in electrolyte engineering, achieving successful patterning of electrolyte microscale devices has remained challenging. Here, we enable successful patterning using photolithography by incorporating caffeine into a UV-crosslinked polyacrylamide hydrogel electrolyte. Caffeine passivates the Zn anode, preventing chemical corrosion, while its coordination with Zn 2+ ions forms a Zn 2+ -conducting complex that transforms into ZnCO 3 and 2ZnCO 3 ·3Zn(OH) 2 over cycling. The resulting Zn-rich interphase product significantly enhances Zn reversibility. In on-chip microbatteries, the resulting solid-electrolyte interphase allows the Zn||MnO 2 full cell to cycle for over 700 cycles with an 80% depth of discharge. Integrating the photolithographable electrolyte into multilayer microfabrication creates a microbattery with a three-dimensional Swiss-roll structure that occupies a footprint of 0.136 mm 2 . This tiny microbattery retains 75% of its capacity (350 μAh cm -2 ) for 200 cycles at a remarkable 90% depth of discharge. Our findings offer a promising solution for enhancing the performance of Zn microbatteries, particularly for on-chip microscale devices, and have significant implications for the advancement of autonomous microscale devices. This article is protected by copyright. All rights reserved.