Spatial shift of Li nucleation onto electrically conductive SEI residues

Residual solid electrolyte interphase (rSEI) accumulates during cycling, yet how it evolves and regulates battery failure remains unclear. Here, we quantify the structure, composition, and transport properties of rSEI formed in carbonate- and ether-based electrolytes. We find that rSEI is a dynamically evolving composite interphase rather than an inert corrosion residue. As dead lithium (Li) accumulates, it drives a percolation transition that increases rSEI electronic conductivity. This transport evolution shifts Li nucleation from the Cu current collector to the rSEI surface, where newly deposited Li is readily disconnected and converted into dead Li. This failure mode occurs before electrolyte dry-out and can be mitigated by chemically or electrochemically dissolving the rSEI. Our findings establish rSEI transport evolution as a key origin of battery failure and a target for interphase engineering.