Effect of Current Density on Morphology of Lithium Electrodeposited in Ionic Liquid-Based Electrolytes

The morphology of electrodeposited lithium in room-temperature ionic liquids was investigated by ex situ SEM observations, and the dependence of the distribution of the electrodeposited lithium nuclei on current density was discussed with respect to the lithium-ion diffusion coefficient. It was concluded that the deposits are better distributed with a decreased size when the current density is increased in the current range where the deposition is charge-transfer controlled. Under a larger current density at which the deposition is diffusion controlled, larger dendritic deposits are observed, although deposits are well distributed over a large area. Under so large current density that the diffusion of lithium ions is slower than the lithium ion reduction, the electrode potential becomes highly negative. Abovementioned tendency is very common for the electrodeposition of noble metals from an aqueous solution, but it was firstly presented for lithium metal. It is probably due to very low reactivity of the ionic liquid used with lithium in this study.