Solvent-Enriched Separator–Electrolyte Interface Stabilizes 4.7 V Ni-Rich Layered Cathodes

Elevating the charging cutoff voltage is critical for practical lithium metal batteries (LMBs); however, this strategy is severely hampered by solvent parasitic reactions. Despite advances in electrode/electrolyte interface engineering, solvent molecules near the interface remain attracted by cathodic parasitic-reaction sites, resulting in solvent decomposition. Here, we propose a separator-adsorbed solvent strategy, establishing a separator–electrolyte interface enriched with adsorption sites that prevents solvent molecules from being captured by cathodic parasitic-reaction sites. The selected polytetrafluoroethylene (PTFE) separator serves to interact with positively charged regions of carbonate solvents. This combination facilitates robust separator–solvent interactions, including C–H···F weak hydrogen bonds and n → π* interactions. Significantly, these interactions generate numerous solvent adsorption sites at the separator–electrolyte interface, which compete with the active cathode surface for solvent molecules. This enables the solvent molecules to escape the attraction of cathodic parasitic-reaction sites and preferentially accumulate on the separator surface, thereby significantly suppressing solvent decomposition and stabilizing the cathode interface. The gel polymer electrolyte with a polytetrafluoroethylene separator (GPE–PTFE) enables a 4.4 V Li||LiNi0.8Co0.1Mn0.1O2 cell to achieve a high-capacity retention rate, maintaining 80% capacity over 671 cycles, nearly double the 368 cycles achieved using a polyethylene (PE) separator. Under an ultrahigh cutoff voltage of 4.7 V, the capacity retention reaches 90% after 100 cycles. This work proposes a paradigm for realizing ultrahigh-voltage LMBs through the separator–electrolyte interface.