Inert Filler Selection Strategies in Li-Ion Gel Polymer Electrolytes

The main role of inert fillers in polymer electrolytes is to enhance ionic conductivity. However, lithium ions in gel polymer electrolytes (GPEs) conduct in liquid solvent rather than along the polymer chains. So far, the main role of inert fillers in improving the electrochemical performance of GPEs is still unclear. Here, various low-cost and common inert fillers (Al₂O₃, SiO₂, TiO₂, ZrO₂) are introduced into GPEs to study their effects on Li-ion polymer batteries. It is found that the addition of inert fillers has different effects on ionic conductivity, mechanical strength, thermal stability, and, dominantly, interfacial properties. Compared with other gel electrolytes containing SiO₂, TiO₂, or ZrO₂ fillers, those with Al₂O₃ fillers exhibit the most favorable performance. The high performance is ascribed to the interaction between the surface functional groups of Al₂O₃ and LiNi_0.8Co_0.1Mn_0.1O₂, which alleviates the decomposition of the organic solvent by the cathode, resulting in the formation of a high-quality Li⁺ conductor interfacial layer. This study provides an important reference for the selection of fillers in GPEs, surface modification of separators, and cathode surface coating.