Enhanced Li⁺ transport across the organic–inorganic interface in composite solid electrolytes via a confined solvation strategy

Polymer-based composite solid electrolytes (CSEs), incorporating fast Li⁺-conducting ceramic phases, leverage the advantages of both components to become one of the most promising next-generation solid electrolyte configurations. However, the interfacial incompatibility between the organic and inorganic components inevitably creates significant barriers to the interfacial Li⁺ transport, representing a key challenge in further enhancing the ionic conductivity of CSEs. Herein, we pioneered a confined solvation strategy by growing a metal-organic framework (MOF) layer impregnated with ionic liquid (IL) on the surface of Li_0.33La_0.557TiO₃ (LLTO) fibers, and subsequently incorporating the composite fibers into a polyethylene oxide (PEO) matrix to fabricate a novel CSE (signed as LLTO/ZIF-8@IL/PEO). Benefiting from the unique porous structure and attraction of the metal centers toward anions of MOF, IL is tightly confined within the MOF framework, while retaining its liquid-like high ionic conductivity and interfacial wetting ability at the nano scale. As a result, the Li⁺ transport efficiency is substantially improved across the PEO-LLTO fiber interface to enable a high ionic conductivity of 1.07 × 10⁻³ S·cm⁻¹ at 60 °C for LLTO/ZIF-8@IL/PEO. The corresponding pouch cell with a LiFePO₄ (LFP) cathode (22 mg loading) and a lithium metal anode can successfully charge a mobile phone and deliver a stable capacity of 135.02 mAh·g⁻¹ at 0.2 C over 100 cycles. This confined solvation strategy offers a universal and efficient approach for improving the Li⁺ transport across the polymer-ceramic interface in CSEs.