Flexible and rigid polyurethane based polymer electrolyte for high‐performance lithium battery

Abstract The development of new polymer electrolytes is greatly significant due to the improvement of the energy density and safety of lithium batteries. Comparing with a single polymer electrolyte, the composite polymer electrolyte has better performance, especially some based on the concept of rigid–flexible coupling polymer electrolytes. In this study, a series of polyurethane with various proportion of soft and rigid segments are synthesized and used as a composite polymer electrolyte (C‐PU) together with cellulose membrane. The optimized polymer electrolyte C‐PU20 (with 20 wt% of the hard segment) exhibits high ionic conductivity of 2.4 mS/cm at 25°C and wide electrochemical stability window up to 4.8 V. Moreover, the C‐PU20 electrolyte for LiFePO 4 /Li cell shows more fantastic cycling performance with capacity retention of 96% after 300 cycles at 0.5 C and better C‐rate capability compared with the pristine cellulose membrane. All the findings indicate that the C‐PU20 electrolyte is a very prospective polymer electrolyte for high‐performance lithium batteries.