End-capped polycarbonate-based composite electrolytes filled with Al2O3 for Li battery application

Abstract

Polymer electrolytes are highlighted as alternatives to liquid electrolytes to address safety problems. However, they exhibit limitations in electrochemical performance. In this research, the enhancement of electrochemical properties for composite polymer electrolytes has been investigated through the addition of nano-sized Al₂O₃ and the chemical modification of poly(ethylene carbonate) (PEC) by substituting its terminal hydroxyl group with acetate group, producing PEC-Ac. The introduction of the acetate end group significantly increased the thermal decomposition temperature of the electrolytes, while the addition of Al₂O₃ reduced the glass transition temperature and increased ionic conductivity due to an expanded free volume and enhanced Lewis acid-base interactions. Battery tests demonstrated that PEC-Ac with 80 mol % of LiFSI and 10 wt % of Al₂O₃ maintained a coulombic efficiency near 100 % and exhibited stable polarization voltages around 0.1 V. The discharge capacity was consistently around 150 mAh g⁻¹, approaching the theoretical capacity of 170 mAh g⁻¹. The XPS analysis after charge/discharge cycling confirmed the formation of a stable Li_xAlO_y composite layer, which effectively prevents Li dendrite formation and enhances the overall cycle stability of the battery. This study confirms the significant improvements in the battery performance and cyclability brought about by the strategic modifications of PEC-Ac and the addition of inorganic Al₂O₃, offering valuable insights for the development of advanced battery technologies.