Synergistic Effects of Separator Architecture and Electrolyte Chemistry on the Electrochemical Stability of Lithium Ion Batteries With Li–Mn Rich Cathodes and µ‐Si Anodes

High‐voltage, high‐capacity lithium ion batteries (LIBs) combining cobalt‐free lithium manganese‐rich (LMR) cathodes with pure silicon (µ‐Si) anodes offer a promising route toward more sustainable and cost‐effective energy storage. In this study, the capacity fading behavior of LMR||µ‐Si cells is correlated with the poor wettability of the conventional polyolefin Celgard 2500 separator, which leads to non‐uniform electrolyte distribution and localized Li metal deposition on the µ‐Si surface. Consequently, cells with Celgard separators exhibit rapid degradation, with capacity roll‐over occurring after less than 75 cycles. In contrast, replacing Celgard 2500 with an electrospun polyacrylonitrile (PAN) membrane enhances cycling stability, retaining 80% of the initial capacity after approximately 230 cycles, due to improved electrolyte wetting and mechanical contact with µ‐Si anode. Further optimization of the electrolyte composition, using N, N ‐dimethylsulfamoyl fluoride (DMFSA) as co‐solvent with fluoroethylene carbonate (FEC), extends LMR||µ‐Si cell lifetime to more than 400 cycles, regardless of the separator type. These findings highlight the synergistic influence of separator selection and electrolyte formulation in stabilizing interphases at both electrodes. A holistic materials design approach is therefore essential for advancing the performance and durability of next‐generation LMR||µ‐Si‐based LIBs cells.