Towards Li-Air and Li-S Batteries: Understanding the Morphological Changes of Lithium Surfaces during Cycling at a Range of Current Densities in an Ionic Liquid Electrolyte

Abstract

The repetitive cycling of lithium metal electrodes in Li metal | ionic liquid electrolytes | Li metal coin cells was investigated. Lithium metal electrodes achieved 800 charge-discharge cycles at current densities of 0.1, 10 and 100 mA cm-2. Voltage-time plots show evidence for instabilities manifesting themselves as voltage spikes. SEM imaging of cycled electrodes crucially shows no evidence for dendrite formation capable of leading to short circuit conditions, under all cycling regimes. SEM study shows evidence for surface corrosion. Based on the SEM study and cycling behavior a corrosion based equivalent circuit is presented and fitted to impedance data. SEM and impedance data are used to describe the changes in the voltage-time plots and ascribe the voltage spikes observed to changes in the lithium metal surface and subsequent corrosion. FTIR spectroscopy was used to analyze lithium electrodes after cycling. Evidence for IL surface coordination and LiOH formation was found.