Gel electrolytes show certain advantages over conventional liquid and solid electrolytes, but their mechanical strength and surface adhesion to the electrode remain to be improved. To address the challenges, we design and fabricate herein the core-shell nanofiber mats in situ on the LiFePO4 electrode as matrices for gel electrolytes, in which the core is poly(m-phenylene isophthalamide) (PMIA) nanofiber and the shell are composite of Al2O3 nanoparticles and poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP). The mechanical property of the core-shell polymeric nanofiber mats and their surface interaction with LiFePO4 electrode are characterized complementarily using dynamic thermomechanical analysis and scanning electron microscopy. The electrochemical properties of the gel electrolytes based on the as-prepared matrices after being loaded with lithium salt solution are studied systematically on half coin cells. It is found that the ultimate strength of the core-shell PMIA@PVdF-HFP/Al2O3 mat can reach 6.70 MPa, 2 times higher than that of the PVdF-HFP/Al2O3 nanofiber mat. Meanwhile, the shell PVdF-HFP/Al2O3 can ensure manifest surface affinity to the LiFePO4 electrode and enhance lithium-ion conductance. Thus, the as-assembled LiFePO4 half coin cells using PMIA@PVdF-HFP/Al2O3 gel electrolyte show good electrochemical performances, especially the long cycle stability with the capacity retention of 96.6% after 600 cycles under 1C.
Keywords: core−shell polymeric nanofibers; electrochemical properties; gel electrolytes; interfacial interaction; mechanical strength.