A Non-Expendable Leveler as Electrolyte Additive Enabling Homogenous Lithium Deposition.

Li metal anodes are extensively studied owing to their unparalleled advantages in achieving high energy density. However, safety issues originating from dendritic Li growth are always a huge hindrance for applications in Li metal batteries (LMBs). In this study, a functional additive, 4,6-dimethyl-2-mercaptopyrimidine (DMP), which is a typical leveler in the copper electroplating industry, is selected to suppress Li dendrite formation. Various Li-metal-based batteries are systematically investigated and they show stable performances, such as excellent cycling stability above 800 h at 3 mA cm in Li||Li cells and 400 cycles with high coulombic efficiencies (CEs >98%) at 1 mA cm in Li||Cu cells. Furthermore, a comprehensive verification of the protective mechanism induced by the DMP leveling agent shows that the leveler updated the Li solvation structure and occupied the inner Helmholtz plane of the Li anode. The planar DMP molecular layer absorbed on the surface of the Li metal can suppress side reactions and modify the Li deposition behavior via steric hindrance, inducing homogeneous Li deposition. Interestingly, the DMP leveler does not participate in the formation of the solid electrolyte interphase. This study can stimulate further ideas on non-depleting but effective levelers as electrolyte additives for high-performance LMBs.