Operando Experiments and Modeling on the Dynamics and Heterogeneity of Composite Electrodes in Batteries

The composition dynamics regulate the accessible capacity and rate performance of rechargeable batteries. Heterogeneous Li reactions can lead to non-uniform electrochemical activity and amplify mechanical damage in the cell. We develop operando optical microscopy as a laboratory tool to map the spatial composition heterogeneity in a solid-solution cathode for Li-ion batteries. We observe that the active particles charge asynchronously with reaction fronts propagating on the particle surfaces during the 1st charging, while the subsequent (dis)charge cycles transition to a synchronous behavior for the same group of particles. Such transition is understood by computational modeling which incorporates the dependence of Li diffusivity and interfacial reaction on the state of charge. Furthermore, we use synchrotron experiments to visualize the morphological defects at multi-scales ranging from the macroscopic composite, particle ensembles, to individual single particles. We find that the interfacial failure reconstructs the conductive network and redistribute the electrochemical activities that render a dynamic nature of electrochemistry and mechanics evolving over time in the composite electrodes.