Photonic methods for rapid crystallization of LiMn2O4 cathodes for solid-state thin-film batteries

Abstract

High temperature and prolonged thermal annealing for the crystallization of cathode in thin-film batteries (TFBs) restricts the choice of current collector and substrates and causes lithium loss in the cathode. This work explores photonic-based alternatives for cathode crystallization, specifically xenon flash-lamp annealing (FLA), ultra-violet excimer laser irradiation (UV-laser), and infrared laser (IR) annealing. The effect of these methods is systematically compared to that of thermal annealing in terms of processing time, crystal structure and electrochemical performance of the LiMn2O4 model thin-film cathode. FLA and UV excimer laser can crystallize LMO cathode in short periods of 6 min and 25 min, respectively, compared to the reference (ref.) thermal processing time of 60 min at 600 °C. The performance of the FLA-processed LMO cathodes (crystallinity, capacity, diffusion coefficient) is comparable to that of the thermal ref. with a capacity of 6 μAh cm−2 and 5 μAh/cm−2 at 15 C for FLA and thermal ref. respectively, with the practical limit of the 150 nm LMO film being 9.5 μAh cm−2. A thin-film FTO/LMO/Li3POxNy/Li solid-state battery was assembled and cycled at a high rate of 10 C with only a negligible capacity fade of 3.6% after 200 cycles. FLA can be used as an effective alternative for fast crystallization of thin-film cathodes on temperature-sensitive substrates and is suitable for upscaling processes.