Bimetallic UiO‐66(Zr/Ti)‐Ionic Liquid Grafted Fillers with Intensified Lewis Acidity for High‐Performance Composite Solid Electrolytes

Enhancing the incorporation of highly accessible Lewis acid sites on fillers is crucial for achieving exceptional electrochemical performances in composite solid electrolytes (CSEs). Typically, they can provide a vital role in improving CSEs performance by interacting with lithium salt anions and the polymer matrix through Lewis acid–base interactions. To address this technological need, in this work, a novel filler of bimetallic UiO‐66(Zr/Ti)‐ionic liquid grafted composite (BUIL) is developed to enhance its inherent electrochemical properties. The bimetallic structure, which introduces structural defects, along with the grafted ionic liquid, abundantly creates accessible Lewis acid sites. This modification of the intrinsic Lewis acidity results in a remarkable enhancement of CSEs performances. The incorporation of BUIL in CSEs leads to a significant increase in ionic conductivity (0.458 mS cm−1) and lithium‐ion transference number (0.668) at 30 °C. Furthermore, LiFePO4/CSEs/Li cells demonstrate a high specific capacity of 148.5 mAh g−1 at a current density of 1 C, which is stably maintained over 880 cycles. Overall, the innovative synthetic approach in producing multifunctional fillers for CSEs shows strong potential for enhancing the performance of advanced lithium metal batteries. A bimetallic UiO‐66(Zr/Ti)‐ionic liquid grafted (BUIL) filler is developed to enhance the effectiveness of Lewis acid–base interactions as a filler. By incorporating the bimetallic structure and the grafted ionic liquid, the BUIL filler provides a greater number of accessible Lewis acid sites. As a result, the BUIL filler significantly increased the dissociation of lithium salt and greatly reduced the crystallinity of the polymer matrix, eventually improving the performance of composite solid electrolytes.