Regulating pore structure of aramid nanofiber (ANF) separators for lithium–sulfur (Li–S) batteries

Abstract

Excellent ionic conductivity and mechanical robustness are significant for separators of Li–S batteries. Aramid nanofiber (ANF) has been widely used in separators due to their excellent mechanical properties and high-temperature resistance. However, pure ANF separator possesses a dense pore structure resulting from the closely intertwined nanofibrous network, leading to inferior ionic conductivity. Herein, we propose a strategy of inhibiting of hydrogen bonding (IHB) among nanofibers to regulate the pore structure of ANF separators via employing pore-forming agent, solvation, and differentiated drying methods. Notably, a graph theoretical methodology (structural GT) is introduced to analyze the percolating network of ANF separator, revealing that the higher average nodal connectivity, the more abundant and homogeneous porous structure and higher conductivity. Excitingly, the pore size and the ionic conductivity of ANF separator by supercritical carbon dioxide drying (S-ANFs) is 44 nm and 0.171 mS/cm, which is 5 times and 1.9 times higher than pure ANF separator, respectively. Moreover, the ANF separator is dimensionally stable under 200 °C, demonstrating its desirable security under extreme conditions. Finally, the half-cell equipped resultant S-ANFs exhibits outstanding cycling stability (566 mAh/g after 200 cycles at 0.5 C) and Coulombic efficiency (99.25%). This work provides an efficient strategy to regulate the pore structure of ANF separator.