Collateral Advantages of a Gel Electrolyte for MnO2 Nanowire Capacitors: Higher Voltage and Reduced Volume

Recently we demonstrated that symmetric, all Au@ delta-MnO2 core@shell nanowire capacitors can achieve cycle stability to 100 000 cycles and beyond in a poly(methyl methacrylate) (PMMA) gel electrolyte. Here we examine the limits of the PMMA gel to confer this extraordinary stability, in terms of the accessible maximum voltage, Vma, and the thickness of the PMMA gel electrolyte layer. Two conclusions are (1) the PMMA gel permits the V-max.,to be increased by 50% from 1.2 V to 1.8 V, allowing the specific energy to be increased 5-6 fold, and (2) the PMMA gel layer thickness can be reduced from 180 pm (previously) to 2 pm while simultaneously utilizing two layers of nanowires and patterning nanowires in each layer at 5X higher density. For this nanowire sandwich architecture, a net increase in volumetric capacity of 600X up to 500 mF/cm(3) can be achieved while retaining cycle stability to 100 000 cycles.