Single nanowire electrochemical devices.

We report the single nanowire electrode devices designed as a unique platform for in situ probing the intrinsic reason for electrode capacity fading in Li ion based energy storage devices. In this device, a single vanadium oxide nanowire or single Si/a-Si core/shell nanowire was used as working electrode, and electrical transport of the single nanowire was recorded in situ to detect the evolution of the nanowire during charging and discharging. Along with lithium ion intercalation by shallow discharge, the vanadium oxide nanowire conductance was decreased over 2 orders. The conductance change can be restored to previous scale upon lithium ion deintercalation with shallow charge. However, when the nanowire was deeply discharged, the conductance dropped over 5 orders, indicating that permanent structure change happens when too many lithium ions were intercalated into the vanadium oxide layered structures. Different from vanadium oxide, the conductance of a single Si/a-Si core/shell nanowire monotonously decreased along with the electrochemical test, which agrees with Raman mapping of single Si/a-Si nanowire at different charge/discharge states, indicating permanent structure change after lithium ion insertion and extraction. Our present work provides the direct relationship between electrical transport, structure, and electrochemical properties of a single nanowire electrode, which will be a promising and straightforward way for nanoscale battery diagnosis.