Insights into the electrochemical properties of germanium-cobalt-indium nanostructures in a wide temperature range

Abstract

Germanium-cobalt-indium (Ge-Co-In) nanostructures are a promising material for negative electrodes of lithium-ion batteries aimed for arctic exploitation. Electrochemical impedance spectroscopy was used for a detailed study of the interaction of Ge-Co-In nanostructures with lithium in a temperature range from ‒35 to +20°C. The discharge capacity at temperatures of 20, 0, ‒10, ‒20, and ‒35°C amounted to 1400, 1228, 1040, 907, and 793 mAh g^‒1, respectively. The impedance spectra measured at various lithiation degrees were found to differ but insignificantly whereas temperature variation resulted in notable changes in the spectra. A normalized charge transfer resistance for Ge-Co-In nanostructures was significantly (more than an order of magnitude) less than for Ge-In nanowires (obtained by the same method, but without the addition of cobalt salt into the electrolysis solution). It is this difference in charge transfer resistance that can explain the difference in the shapes of the impedance spectra for both objects. Also, in contrast to data for Ge-In nanowires, the dependences of the lithium diffusion coefficient in Ge-Co-In nanostructures on potential had a clearly defined minimum. The lithium diffusion coefficient in Ge-Co-In nanostructures slightly exceeded that in Ge-In nanowires, and the activation energy of lithium diffusion in Ge-Co-In nanostructures was marginally less than in Ge-In nanowires.