Molecular dynamics simulation. Molecular dynamics simulations were performed to investigate the molecular structure of bulk and interfacial region on the cathode, using MD package GROMACS . The schematic of system are shown in Figures and. For the electrode-electrolyte system, the constant potential method was implemented in GROMACS and further developed for asymmetric electrode systems. The force field for the electrolyte is developed by Dzubiella et al. , which can satisfactorily reproduce density, dielectric constant, viscosity, and diffusion coefficient of LiTFSI/LiNO 3 /DME/DOL mixtures measured by experiments. The parameters for the van-der-Waals potential of LiCoO 2 cathode are taken from the UFF force field , and those for Li metal anode are taken from ref . While the structure and intrinsic charge of Li metal anode and LiCoO 2 cathode are optimized using the density functional theory (DFT) with results shown in Figure . The details for simulations are presented in Note S1. ). The nearly linear shape for the onset potential shift with additive anion radius suggests that the geometric size of anion matters to the ion interfacial packing. The dashed line is a guide for the eyes.