Interfacial Chemistry of Silicone Nanofilament‐Grafted Montmorillonite Enables Li + Selective Transport in Composite Solid‐State Electrolytes for Wide‐Temperature Lithium Metal Batteries

Designing fast and selective Li + transport in composite solid‐state electrolytes (CSEs) remains challenging, as conventional fillers modify polymer crystallinity but exert limited control over the interfacial chemistry that governs ion selectivity. Herein, we demonstrate that constructing continuous polymer/filler interphases with appropriate anion‐binding and Li + ‐coordination characteristics substantially enhances the interfacial contribution to Li + transport in PEO‐based CSEs. To validate this transport behavior, neuron‐like hybrid fillers are synthesized by grafting vinyl silicone nanofilaments onto montmorillonite nanosheets and further functionalized with tunable terminal groups (─CH 3 , ─OH, ─NH 2 , ─COOH) to form active interphases in a poly(ethylene oxide) matrix. Among these functional groups, the ─COOH interface promotes Li + ‐TFSI– dissociation, lowers desolvation barriers, and enables continuous Li + ‐selective migration along the interphase, delivering an ionic conductivity of 6.9 × 10 −4 S cm −1 and a Li + transference number of 0.62 at 30°C. Benefiting from the enhanced interfacial contribution to ion transport, Li|LiFePO 4 cells retain 97.2% capacity after 1100 cycles at 1.0 C and 30°C and remain operable at 0°C. Pouch cells remain functional even after being physically damaged. This work highlights the critical role of interfacial chemistry in enabling Li + ‐selective transport and provides general mechanistic insights for designing high‐performance CSEs over a wide temperature range.