The high abundance of both sulfur and sodium on earth makes room-temperature sodium-sulfur (Na-S) batteries a low-cost, environmentally benign, sustainable energy storage technology.¹ High reactivity and instability of the Na-metal anode and the formation and migration of sodium polysulfides (NaPSs) at the sulfur cathode need to be mitigated to make this technology viable. The root cause of these issues can be the traced to the electrolytes that are conventionally used.

To simultaneously solve the issues mentioned above, we utilize a localized high concentration electrolyte (LHCE).² LHCE is prepared by diluting a concentrated salt solution with an inert solvent. The resulting unique solvation structure of the electrolyte favors the decomposition of the sodium salt to yield a thin, robust, ion-conducting SEI on both the anode and the cathode. This enables highly efficient and reversible stripping and plating at the Na-metal anode. At the sulfur cathode, this SEI changes the sulfur redox pathway by preventing the formation of NaPSs and steers it towards a quasi-solid-state conversion reaction. These benefits significantly prolong the life of the battery and bring the Na-S technology a step closer to viability.

References

1. A. Manthiram and X. Yu, Small, 11, 2108–2114 (2015).
2. J. He, A. Bhargav, W. Shin, and A. Manthiram, J. Am. Chem. Soc., 143, 20241–20248 (2021).