Nanostructured Li 2 S Cathodes for Silicon-Sulfur Batteries.

Lithium-sulfur batteries are regarded as an advantageous option for meeting the growing demand for high-energy-density storage, but their commercialization relies on solving the current limitations of both sulfur cathodes and lithium metal anodes. In this scenario, the implementation of lithium sulfide (Li ₂ S) cathodes compatible with alternative anode materials such as silicon has the potential to alleviate the safety concerns associated with lithium metal. In this direction, here, we report a sulfur cathode based on Li ₂ S nanocrystals grown on a catalytic host consisting of CoFeP nanoparticles supported on tubular carbon nitride. Nanosized Li ₂ S is incorporated into the host by a scalable liquid infiltration-evaporation method. Theoretical calculations and experimental results demonstrate that the CoFeP-CN composite can boost the polysulfide adsorption/conversion reaction kinetics and strongly reduce the initial overpotential activation barrier by stretching the Li-S bonds of Li ₂ S. Besides, the ultrasmall size of the Li ₂ S particles in the Li ₂ S-CoFeP-CN composite cathode facilitates the initial activation. Overall, the Li ₂ S-CoFeP-CN electrodes exhibit a low activation barrier of 2.56 V, a high initial capacity of 991 mA h g _{Li 2 S} ^-1 , and outstanding cyclability with a small fading rate of 0.029% per cycle over 800 cycles. Moreover, Si/Li ₂ S full cells are assembled using the nanostructured Li ₂ S-CoFeP-CN cathode and a prelithiated anode based on graphite-supported silicon nanowires. These Si/Li ₂ S cells demonstrate high initial discharge capacities above 900 mA h g _{Li 2 S} ^-1 and good cyclability with a capacity fading rate of 0.28% per cycle over 150 cycles.