UC Berkeley

Lithium/sulfur (Li/S) cells have a theoretical specific energy five times higher than that of lithium-ion (Li-ion) cells (2600 vs. ~500Whkg-1). The conventional Li/S cells that use an organic liquid electrolyte are short-lived with low coulombic efficiency due to the polysulfide shuttle. We herein design carbon-coated NanoLi2S (NanoLi2S@carbon) composites, which consist of Li2S nanoparticles as the core and a carbon coating as the shell. The carbon shell prevents the NanoLi2S core from directly contacting the liquid electrolyte, which improves the performance of Li/S cells to provide longer cycle life and high sulfur utilization. The cyclability of Li/S cells is further enhanced by mixing the core-shell NanoLi2S@carbon composites with graphene oxide, which chemically immobilizes polysulfides in the cathode through their functional groups. The resulting Li/S cell shows an initial specific discharge capacity of 1263mAhg-1 (normalized to sulfur) at the C/10 rate and a capacity retention of 65.4% after 200 cycles. The capacity decay mechanism during cycling is also characterized in detail using near edge X-ray absorption fine structure (NEXAFS) spectra. •Li2S@C core-shell nano particle active material developed for sulfur cathodes.•Improved cycle life of Li/S cells demonstrated with Li2S@C cathodes.•High utilization obtained with Li2S@C active material.