Alkanethiol-Passivated Ge Nanowires as High-Performance Anode Materials for Lithium-Ion Batteries: The Role of Chemical Surface Functionalization

Abstract

We demonstrate that dodecanethiol monolayer passivation can significantly enhance the anode performance of germanium (Ge) nanowires in lithium-ion batteries. The dodecanethiol-passivated Ge nanowires exhibit an excellent electrochemical performance with a reversible specific capacity of 1130 mAh/g at 0.1 C rate after 100 cycles. The functionalized Ge nanowires show high-rate capability having charge and discharge capacities of ∼555 mAh/g at high rates of 11 C. The functionalized Ge nanowires also performed well at 55 °C, showing their thermal stability at high working temperatures. Moreover, full cells using a LiFePO(4) cathode were assembled and the electrodes still have stable capacity retention. An aluminum pouch type lithium cell was also assembled to provide larger current (∼30 mA) for uses on light-emitting-diodes (LEDs) and audio devices. Investigation of the role of organic monolayer coating showed that the wires formed a robust nanowire/PVDF network through strong C-F bonding so as to maintain structure integrity during the lithiation/delithiation process. Organic monolayer-coated Ge nanowires represent promising Ge-C anodes with controllable low carbon content (ca. 2-3 wt %) for high capacity, high-rate lithium-ion batteries and are readily compatible with the commercial slurry-coating process for cell fabrication.