Spatiochemical Segregation in Porous Lithium–Metal Interphases

The solid–electrolyte interphase (SEI) on lithium metal forms through electrolyte reduction at a dynamically evolving metal surface, yet how its chemistry and spatial organization develop during lithium plating and stripping remains poorly understood. Here, using a 1,2-dimethoxyethane (DME)/1 M lithium bis(fluorosulfonyl)imide (LiFSI) electrolyte system, we show that three-dimensional lithium growth drives spatiochemical segregation of interphase products into chemically heterogeneous domains that are mechanically reorganized during stripping into a porous electrolyte-retaining framework. Correlative X-ray photoelectron spectroscopy, scanning electron microscopy, nanoscale secondary ion mass spectrometry (NanoSIMS), and synchrotron X-ray absorption spectroscopy reveal that FSI–-derived inorganic species, dominated by LiF, become enriched in regions spatially decoupled from oxygen-containing phases near the lithium surface. Stripping-induced contraction compacts these chemically distinct domains into confined intergranular volumes, where supersaturation promotes precipitation and consolidation, yielding a porous SEI that retains electrolyte-derived species within a buried pore network beyond the reach of surface-sensitive probes. Spatiochemical segregation thus couples interfacial reaction pathways to lithium chemo-mechanics, dictating interphase composition, architecture, and permeability. These findings establish a chemo-mechanical framework for SEI evolution and suggest strategies to mitigate electrolyte retention and interphase instability in lithium–metal batteries.