Dendrite-Free Electrodeposition and Reoxidation of Lithium-Sodium Alloy for Metal-Anode Battery

Two ionic liquids, EMI-AlCl4 and N1114-TFSI, that support both lithium and sodium deposition/dissolution were studied as potential electrolytes for lithium metal batteries. In both cases, lithium's dendritic growth was suppressed by adding a small amount of sodium to a lithium electrolyte. This results in a co-deposition or alloying process that hinders dendrite growth. SEM images show a significant difference in morphology obtained by the addition of sodium. A smooth deposit was not enough for stable cycling of the lithium anode because of lithium's reactivity with the electrolyte. Vinylene carbonate (VC) was added to the N1114-TFSI to form a stable SEI layer. Cyclic voltammetry and chronopotentiometry was carried out on tungsten and stainless steel electrodes to obtain efficiency measurements. The combination of a small amount of sodium in the electrolyte, along with VC as an SEI former, lead to significant improvements in cycling performance and efficiency.