In situ monitoring of dual-salt synergy in the cathode and anode processes in lithium metal batteries

Lithium metal batteries (LMBs) with high-capacity cathode materials are considered the high-energy storage devices of the future. The nature of the electrode–electrolyte interphase (EEI) is an important parameter affecting LMBs performance and lifetime, and the addition of lithium salts is considered an effective strategy to stabilize the electrode interface. Understanding its regulatory mechanism and structural evolution is vital for unraveling the “structure–performance” relationship. Here, we utilize in situ atomic force microscopy to unravel the dynamic processes of EEI formation regulated by dual salts effect on both NCM622 cathode and Li anode in working batteries. On the cathode side, the double-layer cathode electrolyte interphase (CEI) formation processes of a LiDFOB-mediated film and a LiPF 6 -induced nanoparticles (NPs) layer are successively detected upon charging. On the Li anode side, the morphological evolution of uniform Li deposition and a wrinkled LiF-rich solid electrolyte interphase (SEI) film after Li stripping mediated by the LiDFOB salt were directly tracked. The on-site formed EEI layers reduce interfacial impedance and endow the battery with improved cycling stability as well as excellent rate capability. These straightforward insights disclose the morphological/chemical evolution of CEI and SEI mediated by lithium salts, providing guidance on the optimal design for a stable electrode/electrolyte interface. • The dynamic evolution of electrode–electrolyte interphase formation regulated by dual salts on both the NCM622 cathode and Li anode is directly tracked by in situ AFM. • Real-time observation reveals a bilayer CEI, with an inner LiDFOB-derived film and outer LiPF 6 -induced nanoparticles, alongside a LiF-rich SEI on anode. • The on-site formed electrode–electrolyte interphase contributes to optimizing the interfacial stability and battery performance.