Sensitive in-operando observation of Li and O transport in thin-film Li-ion batteries

Thin-film batteries often contain oxides in the anode, cathode, and electrolyte materials. In-operando methods capable of Li and O depth profiling are relevant for battery research to study, e.g. diffusion and trapping of constituents. Here, we demonstrate ion beam-based analytical methods with high depth resolution and sensitivity for depth profiling Li and O in thin-film batteries using 10 MeV Li and He ions. Simultaneous depth profiling of Li and O was performed using combined coincidence elastic recoil detection analysis and Rutherford backscattering spectrometry measurements in the battery with 8 MeV He ions, and the Li and O transport was measured in operando. Reversible Li transport was observed from the LMO anode to the NbO cathode on charging and vice versa during discharging. O transport was observed from the LMO anode to the NbO cathode on first charging with 3.5 V but was not observed on further charging and discharging of the battery. Our in-operando measurements allow direct and quantitative observation of Li and O transport during charge-discharge cycles for thin-film batteries.