Mechanically enhanced battery separator prepared by hot-pressing electrospun polyvinylidene fluoride@polymethyl methacrylate membranes with different fiber orientations in adjacent layers

Compared with commercial polyolefin membranes, electrospun polymeric membranes have the advantages of higher porosity and better electrolyte wettability, but their poor mechanical performance limits their industrial use as battery separators. In this work, a layer-to-layer electrospinning is used for fabrication of PVdF@PMMA membranes, in which fibers in adjacent layers are arranged at a certain angle (0 degrees, 30 degrees, 60 degrees, 90 degrees). The as-electrospun membranes are further hot-pressed to boost their mechanical strength. Various techniques are employed to evaluate the membranes, such as scanning electron microscopy, differential scanning calorimetry, contact angle measurement, electrochemical impedance spectroscopy, and linear sweep voltammetry. The results show that polymethyl methacrylate partially melts during the hot-pressing treatment, causing adjacent fibers in the membranes to bridge. The obtained membranes show different tensile strength values with the various angles between fibers. When the angle is 30 degrees, the tensile strength can reach 22.09 MPa and higher porosity (74.68%), greater liquid electrolyte absorption (612.36%) than that of commercial polyolefin membrane are harvested. The lithium-ion cell assembly with the membrane separator exhibits a discharge capacity reaching 142 mAh g(-1) and an excellent capacity retention of 90.7%. This present study provides an innovative and promising approach for the fabrication of high-performance battery separator by electrospinning.