Ex Situ Raman Mapping of LiMn 2 O 4 Electrodes Cycled in Lithium-Ion Batteries.

In this study, we focus on the large-scale ex situ Raman mapping of LiMn 2 O 4 (LMO) electrodes maintained at varying states of charge. A comprehensive statistical analysis has been conducted at an area of ca. 3660 μm 2 on more than 3100 collected spectra for each LMO electrode sample. High-definition ex situ Raman maps provide profound insight into the lithiation process, offering an additional perspective on the mechanism of LMO intercalation. These maps clearly depict the coexistence of two phases, with evident phase transitions and state-of-charge gradients. The set of spectra with various state-of-charge has been successfully deconvoluted taking into account the two-phase character of the ongoing reaction. In addition, we performed the study on the samples operated for 50 cycles at the high C-rates and tracked their delithiation state and impurity formation. This technique serves as a complementary visualization and analytical tool alongside other bulk-type methods employed in battery diagnostics. Importantly, this ex situ Raman mapping approach is applicable to any electrode material exhibiting a Raman response.