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||LiNi_0.8Co_0.1Mn_0.1O₂ 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.