Quasi-Gel Polymer\nElectrolyte Interfaced with Electrodes\nthrough Solvent-Swollen Poly(ethylene oxide) for High-Performance\nLithium/Lithium-Ion Batteries

Solid polymer electrolytes (SPEs) are regarded as a superior\nalternative\nto traditional liquid electrolytes of lithium-ion batteries (LIBs)\ndue to their improved safety features. The practical implementation\nof SPEs faces challenges, such as low ionic conductivity at room temperature\n(RT) and inadequate interfacial contact, leading to high interfacial\nresistance across the electrode and electrolyte interfaces. In this\nstudy, we addressed these issues by designing a quasi-gel polymer\nelectrolyte (QGPE), a blend of poly(vinylidene fluoride-<i>co</i>-hexafluoropropylene) (PVDF-HFP), poly(ethylene oxide) (PEO), and\nsuccinonitrile (SN), with the desired mechanical strength, ionic conductivity,\nand interfacial stability through a simple solution casting technique.\nThe QGPE features a thin solvated PEO layer on its surface, which\nwets the electrode, reducing the interfacial resistance and ensuring\na homogeneous Li-ion flux across the interface. The optimized QGPE\nexhibits a good lithium-ion conductivity of 1.14 × 10<sup>–3</sup> S cm<sup>–1</sup> with a superior lithium-ion transference\nnumber of 0.7 at 25 °C. The Li/QGPE/Li symmetric cell exhibits\na highly reversible lithium plating/stripping process for over 1300\nh with minimal voltage polarization of ∼20 mV. The Li/QGPE/LiFePO<sub>4</sub> full cell demonstrates good rate capability and excellent\nlong-term cycling performance at a 0.1 C rate at 25 °C, maintaining\na specific discharge capacity of 148 mAh g<sup>–1</sup> over\n200 cycles. The effectiveness of QGPE for LIBs is proven using a graphite/QGPE/LiFePO<sub>4</sub> 4 × 4 cm pouch cell, showcasing outstanding flexibility\nand tolerance against intentional abuse.