V-Doped CoSe2 Nanowire Catalysts in a 3D-Structured Electrode for Durable Li-S Pouch Cells.

Abstract

Lithium-sulfur (Li-S) batteries have high theoretical energy density and are regarded as a promising candidate for next-generation energy storage systems. However, their practical applications are hindered by the slow kinetics of sulfur conversion and polysulfide shuttling. In particular, large-scale pouch cells show much poor cyclability. Here, we develop a high-efficiency catalyst of V-doped CoSe2 by studying the binary CoSe2-VSe2 system and confirming its effectiveness in accelerating polysulfide conversion. The coin cell tests reveal an initial capacity of 1414 mAh g-1 at 0.1 C and 1049 mAh g-1 at 1 C and demonstrate 1000 times cyclability with a decaying rate of 0.05% per cycle. Furthermore, the assembly and construction of pouch cells were optimized with monolithic three-dimensional (3D) electrodes and a multistacking strategy. Specifically, a 3D metallic scaffold (3MS) was developed to host V-doped CoSe2 nanowires and sulfur. In addition, Janus microspheres of C@TiO2 were synthesized to capture polar polysulfides with their polar part of TiO2 and adsorb nonpolar sulfur with their nonpolar part of carbon. By integrating with 3MS, C@TiO2 microspheres can block all ion channels of 3MS and only allow Li ions in and out. These integral designs and monolithic structures enable multistacking pouch cells with high cyclability. A high-loading pouch cell was demonstrated with a total capacity of 700 mAh. The cell can be cycled for 70 times with a capacity retention of 65.7%. In brief, this work provides an integral strategy of catalyst design and overall 3D assembly for practical Li-S batteries in a large pouch cell format.