Observation of Microstructural Evolution in Li Battery Cathode Oxide Particles by In Situ Electron Microscopy

We developed a simple approach to carry out in situ electron microscopy of single Li-ion battery cathode particles during electrochemical cycling. We focused on Li(Ni0.8Co0.15Al0.05)O2-based cathode materials because life-cycle tests suggest a strong contribution of the cathode material to changes in cell impedance. In situ scanning electron microscopy was carried out operando during cycling and at various stages by interrupted cycling. Our work revealed several important aspects of cathode oxide particle dynamics: significant separations develop between grains even during the very first charge (oxide delithiation) and electrolyte penetration through that crack network all the way into the particle interior. Comparing these results to post-test microstructural characterization of oxide particles subjected to extensive cycling confirms the occurrence of these processes in practical cells and suggests that the physical separation and isolation of grains may contribute to performance degradation of lithium-ion cells.