Pretreatment of Li metal anode with electrolyte additive for enhancing Li cycleability

A Li sheet electrode was galvanostatically cycled only once as a pretreatment process in a binary electrolyte, propylene carbonate (PC) with dimethyl carbonate (DMC), containing Li bis(perfluoroethylsulfonyl)imide [Li(C2F5SO2)2N] in the presence of an additive, aluminum iodide (AlI3). The Li electrode pretreated in this manner showed a high cycleability in the subsequent cycles even after it was transferred to an electrolyte without any additives; its cycleability was higher than that of a Li electrode without the pretreatment. This means that the primary Li cycle in the presence of the additive can provide an enhanced Li cycleability no longer with the need for additives during the subsequent cycles. The enhancement effect was significant under various charge–discharge conditions, i.e., depth of discharge (DoD) and current density, when an appropriate amount of AlI3 was applied to the pretreatment process. Aluminum derived from the pretreatment was found to remain at the Li electrode still in charge–discharge cycles. Such residual Al in Li, inevitably composing Li alloy, contributes to stabilize the properties of Li electrode interface, e.g., an interfacial resistance, thereby enhancing the charge–discharge cycling efficiency of Li. Thus, the pretreatment of Li metal anode with a single cycle in Li(C2F5SO2)2N/PC-DMC electrolyte containing an appropriate amount of AlI3 can provide a durable Li interface with better Li cycleability even in an electrolyte without AlI3 under various charge–discharge conditions.