Unraveling nanoscale interfacial kinetics in battery cathodes through operando tip-enhanced Raman spectroscopy

Abstract

Understanding interfacial phenomena at the micro- and nanoscale is essential for improving the performance of energy storage technologies such as lithium-ion batteries. However, probing the chemical and structural evolution of buried interfaces during operation remains a major experimental challenge. Here, we present the first implementation of operando Tip-Enhanced Raman Spectroscopy (TERS) to track nanoscale lithium-ion dynamics in working battery electrodes. Using LiMn₂O₄ and LiFePO₄ thin films as model systems, we demonstrate that TERS can determine grain- and grain-boundary-specific behavior with spatial and temporal resolution. In LiMn₂O₄, we observe a delayed appearance of the λ-MnO₂ phase at grain boundaries during delithiation, which is consistent with faster Li⁺ diffusion in these regions and is supported in this work by 2D finite-element simulations. In contrast, LiFePO₄ exhibits reduced spectral visibility under operando conditions, yet systematic background modulation enables tracking of surface-level redox processes. These results establish operando TERS as a powerful technique for probing local ionic transport and interfacial chemistry in complex energy materials, with broad implications for the design and optimization of next-generation battery systems.