Synergistic Anion Confinement in a Poly(Ionic Liquid)/MOF Composite Electrolyte Decouples Ionic Conductivity and Mechanical Strength for High-Performance Solid-State Lithium Metal Batteries.

Poly(ionic liquid)s (PILs) are promising solid electrolyte for solid-state lithium metal batteries, but are fundamentally constrained by the trade-off between ionic conductivity and mechanical strength. To overcome this issue, we design a novel composite Poly(ionic liquid)s based solid electrolyte (CPLE) through the synergistic integration of a main-chain imidazolium-based PIL backbone and a metal-organic framework (MOF-5). The main-chain PIL architecture intrinsically mitigate strong intermolecular ionic interactions, while MOF-5 framework acts as a multi-functional filler that strongly immobilizes TFSI- anions via Lewis acid-base interactions. This dual-anchoring strategy effectively promotes Li salt dissociation, provides additional ion transport pathways, and remarkably enhance the Li+ transference number. Consequently, the CPLE achieves a high room-temperature ionic conductivity of 1.4 mS cm- 1, an exceptional Li+ transference number of 0.7, and a widened electrochemical stability window up to 4.6 V. The strong interfacial interaction between the PIL and MOF-5 also reinforces mechanical strength (1.9 MPa tensile strength). This unique synergy enables outstanding interfacial stability: Li||Li symmetric cells cycle stably for over 2000 h at 0.1 mA cm- 2, and Li||LiFePO4 full cells retain 80% capacity after 700 cycles at 1 C. Crucially, the CPLE is compatible with high-voltage LiNi0.8Co0.1Mn0.1O2 cathodes.