Composite solid electrolytes (CSEs) combine the flexibility of polymers with the stability of inorganic electrolytes, making them promising candidates for next-generation solid-state lithium-metal batteries (LMBs). However, their practical application is limited by low room-temperature ionic conductivity, primarily due to poor polymer-inorganic interfacial compatibility that hinders Li+ transport. In this work, we introduce a polymer-compatible ionic liquid (IL) to mediate the interphase between the polymer and ceramic components, simultaneously preventing ceramic particle aggregation for uniform dispersion and activating ceramic-polymer interfaces to construct continuous Li+ transport pathways across ceramic domains and interfacial boundaries. The interfacial engineered CSEs exhibit a substantial enhancement in room-temperature ionic conductivity to 1.64 × 10−3 S cm−1. At the ambient temperature, the Li||Li symmetric cells demonstrate stable and reversible lithium plating/stripping for 4000 h, and the Li||LiFePO4 cell delivers an initial specific capacity of 172.1 mAh g−1 at 0.5C with 90.4% capacity retention after 300 cycles. Furthermore, the Li||LiNi0.8Co0.1Mn0.1O2 cells demonstrate stable performance even under high-voltage operation (4.5 V). This work provides a practical interfacial design strategy for developing high-performance CSEs in the next-generation solid-state LMBs.

Ionic liquids (ILs), together with the confinement strategy, have emerged as promising electrolyte components for advanced lithium-ion batteries due to their nonvolatility, wide electrochemical windows, and excellent thermal stability. However, the influence of IL confinement on solid surfaces on ion-transport behavior remains unclear. In this work, we investigate how IL-loading confined to the surface of SiO2, modulating the confined IL-layer thickness, affects the electrolyte properties and Li⁺ transport, where the IL confined on SiO2 served as a filler in preparing a PEO-based composite electrolyte. It was found that electrolytes with optimized IL thickness exhibit improved ionic conductivity, Li⁺ transference number, and cycling performance. Specifically, insufficient IL thickness reduces the Li⁺ transport area (insufficient confinement), leading to slow ion transport, whereas excessive IL thickness results in bulk-like behavior, primarily influenced by physical ion crowding, thereby reducing the ion transport rates. This slow ion transport ultimately leads to a decline in electrolyte properties and cycling performance. When achieving the optimized confinement thickness, the surface-induced lithium salt dissociation and available transport space reach a synergistic balance, at which point the Li⁺ transport rate reaches its optimum, thus improving performance. For example, the optimized electrolyte demonstrates significantly enhanced ionic conductivity and interfacial stability. Consequently, the assembled LiFePO4//Li coin cells achieve a 77.7% capacity retention after 700 cycles at 0.5 C. These findings suggest that modulating the IL confinement thickness offers a viable approach to optimizing the ion-conduction channels, providing useful insights into IL–solid interfacial interactions and references for designing high-performance solid-state electrolytes. 

Quasi-solid polymer electrolytes (QSPEs) are promising electrolytes for next-generation high-energy-density lithium metal batteries, benefiting from their flexibility and intimate interfacial contact with electrodes. However, conventional QSPEs encounter challenges such as limited Li+ mobility and poor mechanical properties. Herein, we design a multiple-crosslinked ionogel electrolyte, featuring a high Li+ transference number of 0.74, superior stability against oxidation up to 4.8 V, and high mechanical strength (0.8 MPa) simultaneously. The ionogel electrolyte constructs rapid Li+ conductive pathways and promotes the formation of lithium fluoride (LiF), lithium nitride (Li3N), and lithium sulfide (Li2S)-enriched passivation layers during Li deposition, greatly enhancing the reversibility of lithium metal deposition. Consequently, the Li‖Li cell demonstrates superior lithium plating/stripping stability for 5000 h, and the Li‖LiFePO4 cell shows stable cycling performance with 80% capacity retention after 1000 cycles at a rate of 0.5C. Remarkably, the high-voltage Li‖NCM532 cell maintains about 76% of its capacity over 200 cycles at 4.2 V.