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.