High-Resolution Nanoanalytical Insights into Particle Formation in SnO 2 /ZnO Core/Shell Nanowire Lithium-Ion Battery Anodes.

Tin oxide (SnO 2 )/zinc oxide (ZnO) core/shell nanowires as anode materials in lithium-ion batteries (LIBs) were investigated using a combination of classical electrochemical analysis and high-resolution electron microscopy to correlate structural changes and battery performance. The combination of the conversion materials SnO 2 and ZnO is known to have higher storage capacities than the individual materials. We report the expected electrochemical signals of SnO 2 and ZnO for SnO 2 /ZnO core/shell nanowires as well as unexpected structural changes in the heterostructure after cycling. Electrochemical measurements based on charge/discharge, rate capability, and electrochemical impedance spectroscopy showed electrochemical signals for SnO 2 and ZnO and partial reversibility of lithiation and delithiation. We find an initially 30% higher capacity for the SnO 2 /ZnO core/shell NW heterostructure compared to the ZnO-coated substrate without the SnO 2 NWs. However, electron microscopy characterization revealed pronounced structural changes upon cycling, including redistribution of Sn and Zn, formation of ∼30 nm particles composed of metallic Sn, and a loss of mechanical integrity. We discuss these changes in terms of the different reversibilities of the charge reactions of both SnO 2 and ZnO. The results show stability limitations of SnO 2 /ZnO heterostructure LIB anodes and offer guidelines on material design for advanced next-generation anode materials for LIBs.