(355h) Aramid Nanofiber Separators for Energy Storage

Catastrophic battery failure can lead to serious injuries and enormous costs in damages. This is a major problem preventing the advancement of energy storage devices and materials. One approach to mitigate or prevent battery failure is multifunctional materials for energy and power devices. These materials can be used as an electrode, electrolyte, or separator while simultaneously withstanding extreme environments such as mechanical forces or high temperatures. However, research in multifunctional energy storage materials has typically focused on the electrode. Thermally and mechanically robust separators offer an alternative approach for preventing battery failure under extreme conditions such as high temperatures and loads. Unfortunately, a robust separator must also maintain adequate ion transport properties and require easy processability to be a feasible replacement for commercial energy storage separators. Aramid nanofibers (ANFs), a nanoscale building block derived from Kevlar^® fibers, have been used as a mechanical reinforcement filler for composite materials and have shown promise in battery separators. Here, we fabricate pure ANF separators through the dissolution of bulk Kevlar^® fibers and vacuum-assisted self-assembly. Thermogravimetric analysis shows a high 5 wt% decomposition temperature of 457.1 ^oC while differential scanning calorimetry shows no thermal behaviors up to 400 ^oC. The ANF separator also possesses high Young’s modulus of 8.8 GPa and strength of 252.6 MPa. The ANF separators performs well in a LiFePO₄ vs Li metal battery with a capacity of ~140 mAh g^-1. Finally, we compare the pure ANF separator to the common commercially available separators of Celgard and Dreamweaver. ANF separators allow for producing safer batteries under extreme conditions while being easily processable and are a promising alternative to current commercial separators.