Mechanically Reinforced PVdF/PMMA/SiO2 Composite Membrane and Its Electrochemical Properties as a Separator in Lithium-Ion Batteries

Compared with commercial polyolefin separators, the poor mechanical performance of electrospun polymeric membranes limits their usage as battery separators. Herein, poly(methyl methacrylate) (PMMA) and SiO2 nanoparticles were introduced into electrospun poly(vinylidene fluoride) (PVdF) membranes to form a PVdF/PMMA/SiO2 nonwoven membrane. A hot-pressing method controlled the thickness of the electrospun membranes and improved their mechanical performance further. SEM tests show that PMMA partly melts in the composite membrane, which bonds neighboring electrospun fibers to reinforce the mechanical strength of the membrane. Uniformly distributed SiO2 nanoparticles on the electrospun fibers could supply higher resistance to mechanical impact. As a result, the composite membrane shows a high tensile strength (32.69 MPa) and high elongation at breakage (137.50%). Differential scanning calorimetry and hot oven tests indicate that the composite membrane has excellent thermal stability. Furthermore, the addition of PMMA and SiO2 can decrease the crystallinity of PVdF and further improve the absorption of liquid electrolyte. According to the results of electrochemical tests, the composite membrane exhibits higher ionic conductivity (4.0 x 10(-3) Scm(-1)) and lower interfacial resistance than those of the Celgard separator. The lithium-ion cell assembled from the composite membrane exhibits more stable cycle performance, higher discharge capacity (158 mA hg(-1)), and excellent capacity retention.