Unveiling the role of electrode-level heterogeneity alleviated in a silicon-graphite electrode under operando microscopy

Reaction heterogeneity is a crucial factor that influences the design of composite electrodes. Silicon–graphite composites exhibit practical use as anodes, but the complex mechanisms in blended electrodes have not been investigated. Considering mechanisms at an electrode level, intra-/interparticle heterogeneity depending on state-of-charge (SOC) becomes problematic due to their complex kinetic properties. We investigate the complex dynamics of a silicon–graphite blended electrode using side-view operando optical microscopy, highlighting the proper mechanisms of SOC heterogeneity. Graphite and silicon simultaneously lithiated during lithiation by competition between redox potentials and interparticle diffusion. During delithiation, the driving force of electrochemical potentials increases, resulting in sequential reactions from graphite to silicon. Different kinetics induces interplay during the competitive reaction, affecting depth heterogeneity. Silicon mitigates the depth heterogeneity of graphite during lithiation due to its rapid surface diffusion and kinetic-derived overpotential. These findings pave new avenues for a more sophisticated design of high-energy Si-graphite anodes.