A Hybrid Oleic-Acid-Derived Polymer Electrolyte Integrating Single- and Dual-Ion Conducting Systems for Lithium-Ion Batteries

In this work, a hybrid polymer electrolyte integrating single- and dual-ion conducting systems was developed for lithium-ion batteries using bio-based materials, namely oleic-acid derivatives and epoxidized soybean oil, through an in situ polymerization process. The fixed FSI anions in LiEFSOA enhance the selectivity of Li⁺ transport, while the cross-linked network formed by ESO provides mechanical stability, and the LiFSI incorporated into the polymer matrix helps maintain sufficient overall ionic conductivity. In addition, the long C18 oleic chains increase the internal free volume of the matrix, thereby improving segmental mobility within the amorphous phase. The in situ polymerization inside the cell causes intimate interfacial contact between the electrode and electrolyte, achieving an ionic conductivity of 1.05 × 10^-4 S cm^-1 at 30 °C. Electrochemical evaluation using LiFePO₄/FSOA-2/Li cells shows an initial discharge capacity of 149.09 mAh g^-1 and a capacity retention of 81.09% after 100 cycles, and the average coulombic efficiency was 99.62%, demonstrating that the designed FSOA electrolyte exhibits stable cycling performance and competitive capacity. Overall, the combination of eco-friendly materials and a hybrid ion transport strategy provides a promising platform for developing sustainable and high-performance polymer electrolytes for lithium-ion batteries.