Thermally Stable Aramid Nanofiber Separators for Energy Storage
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abstract
A battery separator prevents internal short circuiting while also allowing ion transport between the two electrodes. Catastrophic battery failure, which can lead to economic costs in damages and serious injuries, can result from a failed separator due to shrinkage or puncture. Two major causes of this can be lithium dendrite formation and mechanical deformation. This is a major issue preventing the advancement of safe energy storage technologies. Mechanically and thermally robust separators offer an alternative approach for preventing battery failure under extreme conditions such as high loads and temperatures. Unfortunately, a robust separator must also maintain adequate ion transport properties and, in order to be a feasible replacement for commercial energy storage separators, be easily processed. Recently, aramid nanofibers (ANFs), a novel nanoscale building block derived from Kevlar fibers, have been successfully used as a mechanical reinforcement filler for composite materials and show promise as battery separators. Here, we fabricate pure ANF separators through the dissolution of bulk Kevlarfibers and vacuum-assisted self-assembly. We investigate the thermal behavior and degradation of ANF separators at high temperatures as well as mechanical properties of the separator at elevated temperatures. We also characterize ion transport properties and electrochemical performance of a Li-ion battery utilizing the ANF separator. Finally, we compare the pure ANF separator to common commercially available separators. ANF separators may allow for safer batteries under extreme conditions while being easily processable. In particular, ANF separators show excellent thermal stability by exhibiting no thermal events or mechanical deformation up to 400 oC.
