Operando Optical Microscopy of Dead Lithium Growth in Anode-Less Configuration

There is an increasing demand to improve battery safety and performance as part of the global push to convert the small electronics and transportation sector to infrastructures based on electricity. This work follows the deposition of lithium metal in anode-less conditions by an operando optical microscope using a transparent indium tin oxide-polyethylene terephthalate (ITO-PET) window as the current collector in a readily-available electrochemical set-up. The mechanism of Li metal nucleation strongly depends on the selected current densities (C/40 and 2C). After the deposition of the solid electrolyte interface (SEI), Li nucleates from mossy to needle morphology. Moreover, layer-by-layer growth of dead Li in voids is monitored by following its accumulation upon cycling. Dead Li deposits in residual hollow structures, especially when high current densities are applied. These optical observations are coupled with computer vision analyses to evaluate the average size of the Li deposits: smaller Li nuclei plate when high C-rate is applied. The results here described provide insights into a new electrochemical cell concept that enables to elucidate the influence of spatial inhomogeneities of the lithophilic ITO-PET surface on the mechanism of Li nucleation and plating.