Ion dynamics of the LixMn2O4 cathode in thin-film solid-state batteries revealed by in situ Raman spectroscopy

Abstract

In situ Raman spectroscopy is a powerful tool to elucidate the lithium-ion dynamics in solid-state batteries. Thus, in this work, in situ Raman spectroscopy of thin-film batteries is used to study the structural changes of LixMn2O4 during battery operation. Thin-film batteries with Li/Li3PO4/LiMn2O4 structures are fabricated, and in situ Raman measurements are performed from both the front and back sides of the thin-film battery. The LixMn2O4 in the thin-film batteries present characteristic Raman spectra originating from the α, β, and λ phases. Notably, the Raman intensity of LixMn2O4 shows hysteresis during charging and discharging when observed from the front-surface configuration, whereas only small hysteresis is observed when measured from the back surface. This behavior is explained by the lithium diffusion and phase transition behavior in LixMn2O4. The value of diffusion coefficients estimated from the simulations are in good agreement with those previously obtained using thin-film batteries.