Insight into different-microstructured ZnO/graphene-functionalized separators affecting the performance of lithium–sulfur batteries

Abstract

Improvements in cyclability and rate capability of lithium–sulfur batteries (LSBs) are imperative for their further practical applications. In this study, we integrated the excellent conductivity of graphene and chemical adsorption of ZnO to confine polysulfides by applying a film of ZnO/graphene on a membrane to functionalize separators. To determine the effect of microstructures of polar materials on the electrochemistry of a sulfur cathode in terms of dimensions and hollow structures, different ZnO structures were designed, which could guide the effective functionalization of separators. Systematic electrochemical testing results indicated that 1D ZnO nanotubes and 3D ZnO hollow octahedra were composed of smaller nanoparticles, which could provide sufficient active sites to adsorb polysulfides by chemisorption. The voids in channels and hollow structures could locally condense the polysulfides, thus promoting reaction kinetics. Besides, the 1D channels could orientationally accelerate the electron transport and shorten the ion transport distance to further improve reaction kinetics. These advantages were not shown by 0D ZnO nanoparticles. Hence, 1D ZnO/2D graphene (1D/2D)-functionalized membranes played the role of restricting the shuttle effect of polysulfides better than 3D ZnO/2D graphene (3D/2D) separators, and the 0D/2D separator exhibited the worst restriction over polysulfides. The cells with 1D/2D separators exhibited excellent cycling performance (927 mA h g⁻¹ at 1C after 200 cycles) and high rate capacity (754 mA h g⁻¹ at 6.0C).