A General Electrode Design Strategy for Flexible Fiber Micro‐Pseudocapacitors Combining Ultrahigh Energy and Power Delivery

Herein, a general strategy is proposed to boost the energy storage capability of pseudocapacitive materials (i.e., MnO2) to their theoretical limits in unconventional 1D fiber configuration by rationally designing bicontinuous porous Ni skeleton@metal wire "sheath-core" metallic scaffold as a versatile host. As a proof of concept, the 1D metallic scaffold supported-MnO2 fiber electrode is demonstrated. The proposed "sheath" design not only affords large electrode surface area with ordered macropores for large electrolyte-ion accessibility and high electroactive material loading, but also renders interconnected porous metallic skeleton for efficient electronic and ionic transport, while the metallic "core" functions as an extra current collector to promote long-distance electron transport and electron collection. Benefiting from all these merits, the optimized fiber electrode yields unprecedented specific areal capacitance of 1303.6 mF cm-2 (1278 F g-1 based on MnO2, approaching the theoretical value of 1370 F g-1) in liquid KOH and 847.22 mF cm-2 in polyvinyl alcohol (PVA)/KOH gel electrolyte, 2-350 times of previously reported fiber electrodes. The solid-state fiber micro-pseudocapacitors simultaneously achieve remarkable areal energy and power densities of 18.83 µWh cm-2 and 16.33 mW cm-2, greatly exceeding the existing symmetric fiber supercapacitors, together with long cycle life and high rate capability.