100k Cycles and Beyond: Extraordinary Cycle Stability for MnO2 Nanowires Imparted by a Gel Electrolyte

We demonstrate reversible cycle stability for up to 200 000 cycles with 94-96% average Coulombic efficiency for symmetrical delta-MnO2, nanowire capacitors operating across a 1.2 V voltage window in a poly(methyl methacrylate) (PMMA) gel electrolyte. The nanowires investigated here have a Au@delta-MnO2 core@shell architecture in which a central gold nanowire current collector is surrounded by an electrodeposited layer of delta-MnO2 that has a thickness of between 143 and 300 nm. Identical capacitors operating in the absence of PMMA (propylene carbonate (PC), 1.0 M LiClO4) show dramatically reduced cycle stabilities ranging from 2000 to 8000 cycles. In the liquid PC electrolyte, the delta-MnO2 shell fractures, delarninates, and separates from the gold nanowire current collector. These deleterious processes are not observed in the PMMA electrolyte.