Synthesis of Hyperbranched Polyelectrolyte/Polyimide Polymer Electrolyte Membranes for Lithium-Ion Batteries

In this article, the B3 monomer was first synthesized through thiol–ene click chemistry. Then, it was reacted with the A2 monomer, and a certain amount of lithium hydroxide was added to synthesize the third-generation hyperbranched polyelectrolyte (HBPE). The obtained HBPE and tri(4-aminophenoxy) propane (TAPOP) were added to the polyamide acid solution in a certain proportion, and subsequent thermal amidation obtained a series of hyperbranched polyelectrolytes/polyimide polymer electrolytes (PI-TAPOPx-HBPEy). The structures of the synthesized monomers and HBPE were characterized by nuclear magnetic resonance. PI-TAPOPx-HBPEy membranes were characterized through tensile tests, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), and Land test. The results show that PI-TAPOP15-HBPE30 has excellent mechanical properties (92 Mpa at 25 °C) and thermal stability (Tg: 70.1 °C, from DSC). The electrochemical window is around 4.5 V, and the ionic conductivity is around 5.73 × 10−4 S cm−1 at room temperature. The discharge capacity of LiFePO4|PI-TAPOP15-HBPE30|Li cell is 138 mAh g−1 at 0.2C. Moreover, even after 300 cycles at 0.5C, it still maintains a high discharge capacity and Coulombic efficiency (98%). This indicates that PI-TAPOP15-HBPE30 has excellent cyclic stability and can be used as a material for battery energy storage.