Tailoring the Ag+ Content within the Tunnels and on the Exposed Surfaces of α-MnO2 Nanowires: Impact on Impedance and Electrochemistry

Abstract

Efficient conduction of both electrons and cations (e.g., Li+) has a profound effect on the current and capacity of lithium-based batteries. With this study, we focus on cathode effects, with the preparation of pure silver hollandite materials with variable silver ion content within (intra-tunnel) and on the surface of α-MnO2 tunneled materials, followed by the measurement and analysis of impedance and electrochemistry data. Specifically, pure AgxMn8O16-y materials with low (x = 1.13) and high (x = 1.54) intra-tunnel silver content are compared with AgxMn8O16-y·aAg2O (a = 0.25, 0.63, 1.43) composites prepared via a new Ag2O coating strategy. When the Ag2O (a = 0, 0.25) content is low, the material with higher intra-tunnel silver (x = 1.53) content delivers up to ∼5-fold higher capacity accounted for by a ∼10-fold lower impedance than its lower intra-tunnel silver (x = 1.13) counterpart. In the presence of high Ag2O content (a = 0.63, 1.43), both composites exhibit comparable impedance but the lower intra-tunnel silver (x = 1.13) composite delivers up to ∼1.5-fold higher capacity than higher intra-tunnel silver composite, highlighting the key role of Li+ transport under those conditions. Our results demonstrate material design strategies which can significantly increase electronic and ionic conductivities.