New perspectives on spatial dynamics of lithiation and lithium plating in graphite/silicon composite anodes

Huge volume expansion, unstable SEI-film evolution and uncontrollable Li plating remain challenging issues for achieving high energy-density and fast charging graphite/silicon anodes. Unfortunately, less reports on Li plating in graphite/silicon anodes have been found up to now. Herein, for the first time, we report that the interfacial polarization of silicon dominates the co-lithiation process with graphite, thus determining the preferential Li-plating sites and SEI film evolution. Interestingly, the disturbance of local electrochemical potential due to consecutive volume variation of silicon upon cycling, indeed keep Li plating sites changing and deteriorate the battery performances. In a typical case of silicon, global electrochemical potential-equilibrium of electrons in silicon can be achieved by regulating Li-ion diffusion kinetic in silicon, thus delaying Li-plating on graphite. Comparing to commercial silicon, P-type photovoltaic silicon exhibits weaker disturbance of local electrochemical potential upon volume variation, resulting in smaller change in Li-plating sites and smaller re-growth SEI film. Therefore, our findings propose a new perspective on the competitive lithiation mechanism and Li plating for graphite/silicon anodes which is highly desirable for designing high-capacity and fast-charging graphite/silicon.