Highly Stretchable and Elastic Polymer Electrolytes with High Ionic Conductivity and Li‐Ion Transference Number for High‐Rate Lithium Batteries

Comprehensive Summary The ever‐growing demand for wearable electronics drives the development of stretchable lithium‐ion batteries (LIBs) with fast charging capability, in which stretchable polymer electrolytes (PEs) with high ionic conductivity and lithium‐ion transference numbers ( ) are highly desirable. Herein, we report a highly stretchable and elastic PE with high ionic conductivity and , which is applicable in high‐rate and stretchable LIBs. The PE was fabricated by incorporating polyethylene glycol (PEG) and lithium salts into polyurethane networks, wherein α‐cyclodextrin (α‐CD) acts as the cross‐linker. The PEG chains are cross‐linked by covalent and noncovalent bonds, and some PEG chains enter into the cavity of α‐CD to form PEG/α‐CD inclusions. These structural features effectively suppress crystallization of the PEG chains, hinder movement of the counterions of Li + , and endow PE with satisfactory mechanical robustness. The PE with a tensile strength (0.61 MPa) exhibits a large strain at break (840%) and excellent elasticity, possessing a high ionic conductivity (5.0 × 10 –4 S·cm –1 ) and a high (0.52). The Li‖LiFePO 4 battery assembled with the PE delivers a high capacity of 75 mAh·g –1 even at the high rate of 16 C. The battery can be stably cycled for 300 and 200 cycles at 1 C and 4 C, respectively.