Insight into the solid-liquid electrolyte interphase between Li6.4La3Zr1.4Ta0.6O12 and LiPF6-based liquid electrolyte

• LLZTO can provide protection Li metal anode in hybrid electrolyte cells. • Solid-liquid electrolyte interphase is essential, but obtains little attention. • Freshly-dissociated surface furthest present the intrinsic SLEI characteristics. • LiF generated from LiPF 6 decomposition and HF corrosion is the SLEI main component. • Trace water in LE can facilitate the formation of SLEI and deteriorate Li + transfer. Garnet-type Li 7 La 3 Zr 2 O 12 (LLZO) solid electrolyte (SE) has been widely used as a promising material providing protection for Li anode in lithium-ion and hybrid-electrolyte cells due to its high ionic conductivity and superior stability against Li metal. So far much efforts have been expended on addressing the issues at LLZO/Li metal interface, but relatively little attention was placed on the interface between LLZO and liquid electrolyte (LE), while this interface is also crucial for the successful implementation of protected Li metal batteries. Herein, we devote an effort to clarifying the characteristics of the SLEI between Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) and LiPF 6 -based LE. Furthermore, the reaction mechanism and improved approaches are particularly emphasized and discussed. The presence of trace water in LE plays an important role in the formation of SLEI, as it can accelerate the H + /Li + exchange of LLZTO and self-decomposition of LiPF 6 . LiF generated from LiPF 6 decomposition and HF corrosion is confirmed as the main component of SLEI via X-ray photoelectron spectroscopy (XPS) depth profiling. The thickness of the SLEI increase with time, the maximum thickness is about 40 nm after immersion in LE for 48 h. We expect that this systematic methodology can serve as a reference for investigating various SLEI for broader applications.