Biaxial Stretching Array Based on High-Energy-Efficient MXene-Based Al-Ion Micro-supercapacitor Island and Editable Stretchable Bridge
Yudong Wu, Mingzai Wu, Derek Ho, Haibo Hu
Abstract
Employment of multivalent charge carriers with higher charge density to replace frequently used univalent ones can effectively increase the areal capacitance of micro-supercapacitors utilizing few-layered MXene self-assembled electrodes. However, their larger charge density and ionic size usually lead to a sluggish extraction/insertion dynamic between MXene interlayers with limited free space, greatly offsetting the benefits. Herein, we show how to facilitate de-/intercalation of high-valence charge carriers (Al3+) by using polypyrrole-coated bacterial cellulose (BC@PPy) nanospacers to expand MXene interlayer space. Together with the longitudinal electron transport path between interlayers synchronously constructed by the conductive PPy shell, a significant 496% areal capacitance enhancement (232.79 mF cm–2) is realized in the fabricated symmetric Al3+-ion micro-supercapacitors (AMSCs) with the obtained MXene/BC@PPy hybrid film electrodes employing polyacrylamide/1 M AlCl3·6H2O hydrogel electrolyte relative to the cell with pure MXene film electrodes (39.02 mF cm–2). Further benefiting from a high output voltage of 1.2 V, the AMSCs acquire an areal energy density up to 45.3 μW h cm–2. As a device demonstration, we further fabricate a biaxially stretchable AMSC array, simulate its spatial strain distribution during biaxial stretching, and characterize its electrochemical and mechanical properties up to an extreme areal strain of 300%. The proposed rational fabrication paradigm achieves a new level of combined energy density, stretch performance, and architectural simplicity, which presents a route toward a commercially viable stretchable micro energy-storage system with high energy efficiencies.