Stabilizing Liquid Electrolytes in a Porous PVDF Matrix Incorporated with Star Polymers with Linear PEG Arms and CycloPEG Cores
Porous membranes fabricated from poly(vinylidene fluoride) (PVDF) and a star polymer with linear poly(ethylene glycol) (PEG) arms and cycloPEG cores were fabricated via the phase-separation method. The porous gel polymer electrolytes (PGPEs) were obtained by immersing the porous membranes in the electrolyte solution. When the additive amount of star polymer was up to 20 wt %, the prepared membrane had the largest porosity and the pores were uniformly distributed in the membrane. The star polymer can not only decrease the crystallization of PVDF and enhance the absorption of liquid electrolyte but also offer ion conduction channels (cycloPEG cores). Therefore, the PGPE with 20 wt % star polymers exhibited competitive ionic conductivities of 1.27 mS cm–1 at 30 °C and 2.89 mS cm–1 at 80 °C. To stabilize the liquid electrolyte in the holes of porous membranes, a gelator was introduced in the liquid electrolyte to form gelled porous gel polymer electrolytes (GPGPEs), and the leakage of liquid electrolytes was thus remarkably reduced. The ionic conductivity of GPGPEs with 20 wt % star polymer and 1.5 wt % gelator was importantly improved at high temperatures (6.02 mS cm–1 at 80 °C). We systematically investigated the electrochemical performances of PGPEs without star polymer, PGPEs with star polymer, and GPGPEs with star polymer. The incorporation of star polymers with linear PEG arms and cycloPEG cores into the PGPEs and GPGPEs significantly improved the electrochemical performances of the lithium metal/LiFePO4 cell assembled with the PGPEs or GPGPEs.
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