Metal-organic-framework-derived 3D crumpled carbon nanosheets with self-assembled CoxSy nanocatalysts as an interlayer for lithium-sulfur batteries

Abstract

Two-dimensional (2D) nanosheets are promising interlayers for enhancing the electrical conductivity and hindering the lithium polysulfide (LPS) shuttling in lithium–sulfur batteries (LSB). However, their dense 2D nature limits the electrolyte infusion and lithium ion transport, thereby decreasing the rate performance. Herein, we demonstrate that three-dimensional (3D) crumpled carbon nanosheets (CCNSs) decorated with a few nanometers of cobalt heterostructures (CoxSy) that are based on a 2D zeolitic imidazolate framework can improve both the LPS adsorption as well as the ion conduction of LSB interlayer. The method is simple and scalable; the 3D composites are fabricated by post-annealing of 2D metal organic frameworks, which are synthesized by a solution process at room temperature without surfactant. Interestingly, the assembly and polarity of cobalt heterostructures can be further manipulated by the annealing condition; this provides a scientific evidence for the nanostructural and compositional combination of polar compounds. Consequently, CoS/Co9S8@CCNS exhibits the best performance with a discharge capacity of 911 mA h g−1 at 0.2C after 100 cycles (150% more than commercial sulfur cell) and the long-term cyclability of 600 mA h g−1 at 1C after 500 cycles. This is attributed to efficient charge transfer as well as effective LPS adsorption and effective catalytic conversion; further, this is achieved by the synergetic effects of well-distributed polar compounds comprising few nanometers in size and optimal polarity on a highly conductive N-doped carbon nanosheet.