Germanium coating boosts lithium uptake in Si nanotube battery anodes

Abstract

Si nanotubes for reversible alloying reaction with lithium are able to accommodate large volume changes and offer improved cycle retention and reliable response when incorporated into battery anodes. However, Si nanotubes electrode exhibits poor rate capability because of its inherently low electron conductivity and Li ion diffusivity. Si/Ge double-layered nanotubes electrode show promise to improve structural stability and electrochemical kinetics, as compared to homogeneous Si nanotube arrays. The mechanism explaining the enhancement in the rate capabilities is here revealed by means of electrochemical impedance methods. Ge shell efficiently provides electrons to the active materials which increase the semiconductor conductivity thereby assisting Li+ ion incorporation. The charge transfer resistance which accounts for the interfacial Li+ ion intake from the electrolyte is reduced by two orders of magnitude, implying the key role of Ge layer as electron supplier. Other resistive processes hindering the electrode charge/discharge process are observed to show comparable values for Si and Si/Ge array electrodes.