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

摘要

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 atcurrent densities of 0.1, 10 and 100 mA cm~(-2). Voltage-time plotsshow evidence for instabilities manifesting themselves as voltagespikes. SEM imaging of cycled electrodes crucially shows noevidence for dendrite formation capable of leading to short circuitconditions, under all cycling regimes. SEM study shows evidencefor surface corrosion. Based on the SEM study and cyclingbehavior a corrosion based equivalent circuit is presented andfitted to impedance data. SEM and impedance data are used todescribe the changes in the voltage-time plots and ascribe thevoltage spikes observed to changes in the lithium metal surface andsubsequent corrosion. FTIR spectroscopy was used to analyzelithium electrodes after cycling. Evidence for IL surfacecoordination and LiOH formation was found.