Unveiling the effect and correlative mechanism of series-dilute electrolytes on lithium metal anodes

An emerging development direction for electrolytes is the utilization of low-concentration electrolytes (LCE, generally less than 0.5 M) owing to their promising properties such as better wetting ability, reduced costs, and fast electrochemical kinetics, which have been studied in several battery scenarios. However, the direct assessment of LCEs with Li metal anodes has not yet been done, which would provide new insights to high-energy-density rechargeable lithium metal batteries (LMBs). For this purpose, apparent cycling performances of Li metal anode (LMA) in series-diluted (0.1∼1.0 M) ether-based electrolytes are reported in this study with Li||Li and Li||Cu cells, showing the enhanced performances with the concentration increasing. Moreover, the concentration effect and the underlying mechanism are revealed in detail by using coordinated post-mortem analyses and theoretical simulations, demonstrating that the preferential solvent decomposition in LCEs induces the organic-dominant interfacial layer on LMAs. Such layer demonstrates low interface stability, causing poor cycling performance among various current densities in Li half cells. However, comprehensive results also indicate that LCEs are facing a good opportunity because of the fast interfacial charge transfer kinetics originating from the weak solvation nature. This work elucidates the roles of electrolyte concentration on the LMA and uncovers their correlative mechanism of series-diluted electrolytes. It is a certain breakthrough for this timely research to provide a comprehensive perspective for designing novel low-concentration electrolytes.