Hybrid Poly(ionic liquid)/Polyhedral Oligomeric Silsesquioxane Artificial Solid Electrolyte Interphase for Lithium Metal Batteries

Abstract

Lithium metal is regarded as a promising anode material for next-generation batteries due to its high theoretical capacity and low electrochemical potential. However, challenges such as unstable solid electrolyte interfaces (SEI) and uncontrolled dendrite growth can result in irreversible capacity loss and safety hazards. In this work, a pre-formed artificial solid electrolyte interface (ASEI) is constructed on lithium metal by in-situ polymerization of an imidazole-based poly (ionic liquid) (Im-IL) and polyhedral oligomeric silsesquioxane (POSS) directly on the lithium surface during a pre-assembly treatment step; in this context, the ASEI refers to this conformal polymeric interfacial coating rather than a layer generated solely by spontaneous Li-electrolyte reactions. The resulting organic-inorganic hybrid polymer layer enhances interface adhesion, simplifies processing, and effectively accommodates volume fluctuations during lithium-ion intercalation and deintercalation, resulting in the modified Im-IL/POSS@Li exhibiting a wide electrochemical stability window and remarkable cycling performance. The Im-IL/POSS@Li|LFP cells in carbonate-based electrolyte show superior capacity retention and lower impedance versus bare Li|LFP, achieving 94.7% capacity retention after 500 cycles and 84.6% after 1000 cycles. Moreover, in an ether-based electrolyte, the Im-IL/POSS@Li|LFP cells achieve 99.6% capacity retention after 200 cycles, compared to only 26.9% for the unmodified counterpart. XPS and SEM analyses reveal suppressed lithium salt decomposition and the formation of dense, conductive interphase on Im-IL/POSS@Li. These results demonstrate that the proposed ASEI strategy not only stabilizes lithium metal anodes but also offers a practical pathway toward safe and longer-lasting high-energy-density batteries.