Design of Polymer Electrolytes with Superionic Ion Transport*

Progress toward durable, high-energy density lithium-ion batteries has been hindered by instabilities at electrolyte-electrode interfaces leading to poor cycling stability, and by safety concerns associated with energy-dense lithium metal anodes. Solid polymeric electrolytes (SPEs) can help mitigate these issues, however SPE conductivity is limited by sluggish polymer segmental dynamics. Transport through the free volume of ordered, superionically conductive domains results in decoupling of ion motion and polymer segmental dynamics. Although crystalline domains are conventionally detrimental to ion conduction in SPEs, we demonstrate that semicrystalline polymer electrolytes with labile ion-ion interactions and tailored ion sizes exhibit excellent lithium conductivity (1.6 mS/cm) and selectivity (t+~0.6-0.8). This allows for simultaneous optimization of typically orthogonal properties including conductivity, Li-selectivity, mechanics, and processability.