Multicycle operando Raman spectroscopy reveals reversible and irreversible transitions in LiNiO2 electrodes

Abstract

Operando Raman spectroscopy of the delithiation and lithiation of LiNiO₂ positive electrodes is reported over the first three cycles. Optimisation of the operando electrochemical Raman cell configuration facilitated the characterisation of composite electrodes across multiple cycles with high relevance for practical Li-ion cell chemistry. Tracking the E_g and A_1g Raman modes highlighted localised irreversible changes, particularly correlated to first-cycle inefficiencies in LiNiO₂, followed by reversible band shifts and intensity changes upon subsequent cycles. Furthermore, trends in both the band position and intensities were related to the state of lithiation (x(Li) in Li_xNiO₂) and the phase transitions through hexagonal and monoclinic phases (H1, M, H2 and H3).