MnO2 ultrathin films deposited by means of magnetron sputtering: Relationships between process conditions, structural properties and performance in transparent supercapacitors

This study focuses on the relationships between the process parameters during magnetron sputter deposition of MnO2 and the resulting film properties. Three MnO2 phases were identified - gamma, beta and lambda and the dependence of MnO2 phase presence on the oxygen content in the sputtering atmosphere was found. Selected MnO2 phases were subsequently applied as ultrathin coatings on top of nanostructured ZnO electrodes for transparent super capacitors with LiCI-based gel electrolyte. The films containing X-MnO2 exhibited both the highest optical transparency of 62% at 550 nm as well as the highest specific capacitance in the supercapacitor structure, equal to 73.1 mu F/cm(2). Initially lower, the capacitance was elevated by charge-discharge conditioning. (C) 2016 The Authors. Published by Elsevier Ltd.