High-resolution Li depth profiling in a thin-film all-solid-state battery using TOF-ERDA

A quantitative understanding of the Li distribution inside all-solid-state Li-ion batteries is important for improving the performance of batteries. We constructed a time-of-flight (TOF) elastic recoil detection analysis (ERDA) system for operando measurements of thin-film Li-ion batteries. The TOF-ERDA measurement provides elementally resolved spectra with a depth resolution much higher than that of conventional stopper-foil ERDA. The Li depth profiles in a cathode film and solid electrolyte were obtained quantitatively to a depth of 100 nm using a 9-MeV Cu ion beam with reflection geometry. In this study, we conducted TOF-ERDA for a thin-film battery having a cathode made from LiCoO2, an oxide-based solid electrolyte [lithium aluminum titanium phosphate (LATP)], and an anode made from Fe2(MoO4)3 to demonstrate the ability of the measurement system and reveal the Li distribution near the interface with improved resolution. The depth resolution at the interface (30 nm from the surface) was estimated to be 12–14 nm. We quantitatively obtained the Li density in the LiCoO2 cathode and the variation in the Li distribution around the LiCoO2/LATP interface and inside the LATP electrolyte upon charging/discharging. TOF-ERDA is thus a powerful tool for the high-resolution quantitative depth analysis of Li in thin-film batteries in operando.