Hyperbranched polyether boosting ionic conductivity of polymer electrolytes for all-solid-state sodium ion batteries

Polyether, especially, poly (ethylene oxide) has attracted extensive attention in polymer electrolytes since 1973 due to the superior coordination ability with alkali metal ions. However, the ionic conductivity of linear polyether is suppressed by the inherent effortless crystallizability. Here we synthesized hyperbranched polyether for composite polymer electrolytes (named as PMH9-1/1-3 NaTFSI) with an ionic conductivity of 5.7 × 10⁻⁴ S cm⁻¹ at room temperature used in all-solid-state sodium ion batteries (ASIBs). The effect of grafting site on segmental motion and the plasticizing effect of TFSI⁻ anion on polyether are revealed by nuclear magnetic resonance and infrared spectrum characterizations. ASIBs using PMH9-1/1-3 NaTFSI exhibit a high capacity retention ratio of 92% at 0.2C after 300 cycles. Studies on the grafting site on polyether backbone and the plasticizing effect of TFSI⁻ anion make sense to fabricating composite electrolytes with high performance for ASIBs.