| dc.description.abstract | Despite the high theoretical capacity of Li-S batteries, a high cell-level energy density and a long cycling life were barely achieved mainly due to a large electrolyte-to-sulfur ratio, polysulfides (PS) shuttle causing the loss of active sulfur, and the formation of passivation layers on the Li anode. To raise the energy density, holding PS in the cathode has been the most popular approach. Still, it has failed particularly when the sulfur loading is high enough to have energy densities similar to those of commercial Li-ion batteries. Here, we attempted a practical approach of achieving high “cell-level” energy densities using lithium polysulfides (LPS) containing electrolytes instead of a pure electrolyte, reducing the electrolyte-to-sulfur ratio and PS diffusion out of the cathode due to concentration differences. Meanwhile, the persistent problems including PS passivation and Li dendrites were suppressed using Li₂S-phobic artificial solid-electrolyte interphase (A-SEI) layers on Li metal. The synergistic effects from the LPS additives and A-SEI have resulted in a superior cell-level volumetric energy density of 650 Wh/L as well as large cumulative energy densities considering cycling life, compared with those in the literature. Our approach provides an important steppingstone to realize commercial Li-S batteries rivaling the current Li-ion batteries.
To further increase the cycling life and stability of the Li-S batteries to get to a higher cumulative energy density, we investigated effects of four different cutoff voltage windows on the anodes, cathodes, and electrolyte, systematically. By means of a good reversibility and less salt decomposition owing to a narrow voltage window of 1.95-2.45 V, a superb capacity retention larger than 90% can be kept for over 150 cycles in a lean electrolyte condition with an electrolyte to sulfur ratio (E/S) ~ 5 μL/mg, which is superior to most of the other reports. More strikingly, based on the actual energy density calculated based on the performance of our cell in the lean electrolyte condition, a considerably low materials cost (~$27/kWh) that is only a half of the commercialized NCM/graphite batteries was obtained. | |
