Poly(lactic acid) block improves ambient-temperature ionic conductivity of pentablock copolymer electrolyte

Abstract

A polystyrene-b-poly(lactic acid)-b-poly(ethylene oxide)-b-poly(lactic acid)-b-polystyrene pentablock copolymer electrolyte (PSLE) is successfully prepared by ring-opening polymerization (ROP) of DL-lactide (DL-LA) with poly(ethylene oxide) (PEO) followed by atom transfer radical polymerization (ATRP) with styrene. Poly(lactic acid) (PLA) block made by the polymerization of DL-LA can not only reduce the crystallinity of PEO, but also balance the coordination properties of Li+, while polystyrene (PS) block acts as a hard block to improve the mechanical properties of PSLE. Here, the obtained PSLE achieves high ionic conductivity (1.3 × 10−4 S cm−1) under ambient temperature and wide electrochemical stable window (4.2 V). In addition, the PSLE shows outstanding stability, allowing the Li/PSLE/Li cell to cycle stably for more than 600 h at 0.1 mA cm−2 without an increase in polarization voltage. And LiFePO4/PSLE/Li cell shows an initial discharge capacity of 159 mA h g−1 and keeps a capacity retention of 94.6 % after 200 cycles at 0.1C under ambient temperature. The LiNi0.6Co0.2Mn0.2O2/PSLE/Li cell also delivers good cycling performance. These results suggest that multiblock copolymer electrolyte is very promising material for the preparation of solid polymer electrolytes (SPEs) suitable for lithium metal batteries.