Ultrathin and Strong Electrospun Porous Fiber Separator

Abstract

An ideal separator of lithium-ion battery (LIB) should have a zero ionic resistance. Low ionic resistance (high ionic conductivity) will greatly help to realize very fast ion diffusion and superhigh rate capability of LIBs. The most effective technique to achieve low ionic resistance of separator is to reduce its thickness or increase its porosity. Paradoxically, the low thickness and high porosity will inevitably decrease the mechanical strength of separators. Inspired by the hierarchical structures of abalone shell, we demonstrate in this work an ultrathin silica-anchored layered (PVdF/PE/PVdF) porous fiber separator prepared via electrospinning. The separator displays both ultrathin thickness (∼20 μm thick) and high mechanical strength of ∼11.2 MPa, as well as high porosity, which results in high electrolyte uptake (∼380%) and ionic conductivity (∼2.5 mS cm–1). When such thin separator was deployed in a LiFePO4/Li cell, and the cell can deliver an initial discharge capacity of 134.3 mA h g–1 at a high rate of 10 C and maintain a capacity of 129.2 mA h g–1 after 300 charge–discharge cycles, showing excellent high-rate performance. More interestingly, this study demonstrates a pathway for the development of ultrathin and high-mechanical-strength electrospun separators for high-rate Li-ion batteries.