A Superionic Conductive, Electrochemically Stable Dual-Salt Polymer Electrolyte

A phase diagram-guided rational design was introduced to fabricate polymer composite electrolyte, avoiding Edisonian investigations in searching for a polymer electrolyte with high ionic conductivity. The free-standing, flexible, dual-salt-based polymer electrolyte films with superionic conductivity (1.0 mS/cm) at 30°C have been demonstrated. The synergistic effect of salts gave the dual-salt polymer electrolyte outstanding electrochemical stability with a wide electrochemical window of 0–4.5 V (versus Li/Li+). The lithium stripping/plating experiments indicated that the polymer electrolyte could be safely cycled under current density from 0.05 to 0.5 mA/cm2. The dual-salt polymer electrolyte-based cells exhibited excellent average coulombic efficiency of ∼99.99% in the first 370 cycles. The initial capacity at 30°C is 138 mAh/g (0.2 C), which is close to the value achieved by liquid-electrolyte-based cells under similar condition. The capacity retention is 86% after 370 cycles, indicating the long-term stability of the polymer electrolyte.