Solid-state rigid-rod polymer composite electrolytes with nanocrystalline lithium ion pathways

A critical challenge for next-generation lithium-based batteries lies in development of electrolytes that enable thermal safety along with the use of high-energy-density electrodes. We describe molecular ionic composite electrolytes based on an aligned liquid crystalline polymer combined with ionic liquids and concentrated Li salt. This high strength (200 MPa) and non-flammable solid electrolyte possesses outstanding Li+ conductivity (1 mS cm−1 at 25 °C) and electrochemical stability (5.6 V versus Li|Li+) while suppressing dendrite growth and exhibiting low interfacial resistance (32 Ω cm2) and overpotentials (≤120 mV at 1 mA cm−2) during Li symmetric cell cycling. A heterogeneous salt doping process modifies a locally ordered polymer–ion assembly to incorporate an inter-grain network filled with defective LiFSI and LiBF4 nanocrystals, strongly enhancing Li+ conduction. This modular material fabrication platform shows promise for safe and high-energy-density energy storage and conversion applications, incorporating the fast transport of ceramic-like conductors with the superior flexibility of polymer electrolytes.