Enabling uniform Li deposition behavior with dynamic electrostatic shield by the single effect of potassium cation additive for dendrite-free lithium metal batteries†

The stabilization of Li metal anodes via dendrite-free Li deposition is a prerequisite for the commercialization of lithium metal batteries (LMBs). Among the various strategies to suppress Li metal anodes, electrolyte modification has been highlighted as a feasible method because it can be easily applied to conventional manufacturing processes. Tremendous efforts have been devoted to achieving dendrite-free Li deposition via various concepts of electrolyte modification. In this study, we first introduce potassium bis(trifluoromethanesulfonyl)imide (KTFSI) as an electrolyte additive for LMBs, which enables an electrostatic shielding effect. In addition, our study focuses solely on the individual effect of the cation (K⁺), excluding the influence of the anion (TFSI⁻), thus not considering the synergetic effect of both the anion and cation. As a result of comprehensive analysis and systematic experiments, we confirmed the effects of the KTFSI concentration on the electrostatic shield and determined the optimal concentration that can successfully suppress Li dendrite growth by controlling the deposition behavior of Li. The potassium cation controls the Li deposition behavior and results in surface stabilization of the Li metal anode, which is visually confirmed in in situ optical microscopy (in situ OM) and field-emission scanning electron microscope (FE-SEM). Consequently, our designed electrolyte showed outstanding performance overall during electrochemical testing, such as the Li | Cu asymmetric cell, Li | Li symmetric cell, and Li | LiFePO₄ (LFP) full cell, compared to the lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) electrolyte.