Evolution of Hollow N-Doped Mesoporous Carbon Microspheres from Outdated Milk as Sulfur Cathodes for Lithium-Sulfur Batteries

Li-sulfur batteries possess many advantages, such as high theoretical capacities, high energy densities, environmental benignity and natural abundance of sulfur with a high theoretical capacity of 1672 mAh⋅g⁻¹. However, their commercialization has been hindered due to many prevailing issues, including the poor electrical conductivity of sulfur and the high solubility of polysulfide intermediates. We report a facile and scalable, solution-based spray drying technique to synthesize hollow N-doped mesoporous carbon microspheres (HNMCMs) with an exceptionally large surface area of 872 m²⋅g⁻¹ using outdated dairy products as carbon source. The novel electrode prepared from a high loading of sulfur accommodated by the HNMCM hosts delivers high initial discharge capacities of 781 and 682 mAh⋅g⁻¹ at 0.5 and 1 C, respectively. It was further obtained that the capability retention can be retained as high as 79.4% at 1 C after 400 cycles. The excellent cyclic stability and rate capability of the HNMCM/S cathode can be ascribed to the large surface area, high electrical conductivity enhanced by the high content of doped nitrogen and unique hollow microsphere structure of HNMCMs.