Single-Ion Conducting Polymer Electrolytes Based on Random Polyurethane-Urea with Different Diisocyanate Structures for Lithium Batteries

Polyurethane-urea ionomers based on poly(ethylene oxide) (PEO) with various hard segment contents were synthesized from diisocyanates with different symmetries and planarities. The influence of the random copolymer microphase structure (including the phase separation morphology and hydrogen bonding behavior) on the ion states and ion migration was investigated. The soft phase could maintain a low glass transition temperature to yield samples with good ionic conductivity when the hard segment was less than 48 wt %. Furthermore, the hard phase and hydrogen bonds could provide good mechanical strength. Fourier transform infrared spectroscopy and small-angle X-ray scattering confirmed that ionomers with a smaller degree of phase separation had a high fraction of ions in isolated ion pairs. Coupled with faster segmental dynamics and ion mobility from the depressed T_g, the polyurethane-urea ionomer simultaneously showed high strength and ionic conductivity. After plasticization, the prepared single-ion conductor was successfully tested in lithium cells, demonstrating outstanding discharge capacity (166 mAh g^-1), Coulombic efficiency (96.5%), and retention (92.6% after 100 cycles) at 0.1 C and high temperature.