Operando Optical Tracking of Single-Particle Ion Dynamics in Batteries

In order to advance lithium-ion battery technologies, particularly fast charging abilities, it is important to understand the non-equilibrium processes occurring in functioning materials under realistic conditions, in real time, and on the nano- to meso-scale. Currently, operando imaging of lithium-ion dynamics requires sophisticated synchrotron X-ray or electron microscopy methods. These techniques do not lend themselves to high-throughput material screening, and often fail to capture the behaviour of individual particles in batteries charging faster than 2C. In this work, we introduce a laboratory-based optical interferometric scattering microscope to resolve lithium-ion transport in battery materials at the single-particle level, and apply it to follow rapid cycling of the archetypical cathode material Li x CoO2. We directly visualise the insulator-metal, solid solution and lithium ordering phase transitions and determine rates of lithium insertion and removal from individual particles, identifying different mechanisms on charge vs. discharge. Finally, we capture the real-time formation of domain boundaries between different crystal orientations associated with the monoclinic lattice distortion at Li0.5CoO2. The high throughput nature of our methodology allows many particles to be sampled across the electrode and enables exploration of the role of defects, morphologies and cycling rate on battery degradation. The imaging concept is general and may be applied to study any active electrode material, and more broadly, any system where the transport of ions is associated with electronic or structural changes. Due to its straightforward lab-based implementation, we hope that this methodology will become an indispensable tool for high-throughput material discovery and mechanistic studies, to complement existing synchrotron-based methodologies. References Merryweather, A.J., Schnedermann, C., Jacquet, Q. et al. Operando optical tracking of single-particle ion dynamics in batteries. Nature 594, 522–528 (2021).