Recently, the research group led by Professor Sun Dalin and Song Yun from the Institute of Smart Materials and Future Energy at Fudan University, working in tandem with Professor Xiang Yuxuan's and Professor Zhu Yizhou's teams from Westlake University, employed solid-state nuclear magnetic resonance (NMR), synchrotron radiation X-ray diffraction (SR-XRD), and cryo-electron microscopy (cryo-EM) techniques. For the first time, they unveiled the existence of a LiF-LiH solid solution phase within the solid electrolyte interphase (SEI) of lithium-ion batteries. This breakthrough defies conventional wisdom, presenting a fresh perspective on the rapid ion transport mechanism in high-performance secondary batteries and shedding new light on the design of electrode-electrolyte interfaces. Their research indicates that the lithium-ion diffusion energy barrier in the LiH-LiF solid solution phase is notably lower than that in pure LiF, thereby enabling swift lithium-ion movement. Lithium metal symmetric cells coated with this LiH-LiF solid solution phase demonstrated a deposition potential at 10 mA cm^-2 that was merely half of that observed in cells coated with pure LiF, and their cycle life was prolonged by over tenfold.