Hyperbranched Solid Polymer Electrolyte Based on Polyzwitterions and Polyimide for Lithium-Ion Batteries

Compared with traditional liquid electrolytes, solid polymer electrolytes have good formability, lightweight, and safety; especially, poly(ethylene oxide) (PEO)-based polymer electrolytes have strong dissociation capability with alkali salts. However, linear PEO-based polymers are easy to crystallize. The crystal domains of the PEO-based polymers will greatly hinder the transportation of ions. In this study, A2 and B3 monomers were first synthesized by click chemistry. Then, a series of hyperbranched polyelectrolytes (HBPEs) were synthesized by esterification using an A2 + B3 monomer. Finally, a certain amount of HBPEs was mixed with poly(amic acid) solution to prepare HBPE composite membranes. It is found that the PI-HBPE30-G3 composite membrane has superior thermal stability, good mechanical properties, and high ionic conductivity at 80 °C. Moreover, the PI-HBPE30-G3 composite membrane exhibits superior electrochemical performance. The fabricated LiFePO4|PI-HBPE30-G3|Li cell shows excellent cycling performance. The discharge capacity is maintained at 137 mA h g–1 at 0.2C after 200 cycles, and the Coulombic efficiency is virtually invariant above 99% at room temperature. This paper highlights a hyperbranched polymer electrolyte that can be used in next-generation safe power devices.