Thermal conductive aramid nanofiber/surface-decorated alumina microsphere composite separator

The development of lithium-sulfur (Li–S) batteries is hindered by inhomogeneous Li plating and irreversible loss of active materials. In this work, a thermal conductive and electrocatalytic aramid nanofiber (ANF) composite separator containing surface-decorated alumina (Al₂O₃) microspheres is prepared through a simple filtration approach using ZnO nanosheets decorated Al₂O₃ microspheres (Al₂O₃@ZnO) as the thermal conductive filler and electrocatalyst. Compared with the separators fabricated by surface modification of commercial polyolefin separators, the as-prepared ANF/Al₂O₃@ZnO composite separator features homogeneous compositions and ensures uniform thermal distribution in both the through-plane and in-plane directions of the membrane. By rationally designing the structure of Al₂O₃@ZnO and adjusting the mass ratio of Al₂O₃@ZnO to ANF, excellent thermal conduction networks are formed by overlapping the ZnO nanosheets. Hence, the prepared ANF/Al₂O₃@ZnO composite separator possesses higher thermal conductivity than ANF/Al₂O₃ composite separator, which benefits uniform thermal distribution and homogeneous Li plating within the battery. Moreover, the electrocatalytic ZnO nanosheets catalyze the conversion of lithium polysulfides, efficiently inhibiting the shuttle effect and improving sulfur utilization. When subjected to a temperature gradient, the ANF/Al₂O₃@ZnO composite separator assembled cells display high initial capacity, low decay rate, and superb cycle stability. This novel composite separator integrates both thermal conductive and electrocatalytic functional components with the heat-resistant ANF matrix, offering a new design strategy of separator towards high-performance Li–S batteries.