Assessment on the Self-Discharge Behavior of Lithium-Sulfur Batteries with LiNO₃-Possessing Electrolytes

It is generally understood that the reduction of nitrate on the metallic Li surface aids in the formation of a solid-electrolyte interphase. LiNO₃ is, therefore, frequently used as an electrolyte additive to help suppress the polysulfide redox shuttle in lithium-sulfur (Li-S) batteries. Although LiNO₃ enables cycling of cells with considerably improved Coulombic efficiency and cyclic performance, the self-discharge behavior has largely been neglected. We present in this work a basic but systematic study to assess self-discharge of Li-S batteries with electrolytes possessing LiNO₃. Comparative electrochemical tests and interfacial analysis reveal that the redox shuttle is fast enough to cause cells to self-discharge at a relatively rapid rate with limited concentration of the LiNO₃ additive. Despite the capacity loss of a full-charged cell under rest for one day can be controlled to 2% with LiNO₃ concentration as high as 0.5 M, the development of a practically viable Li-S technology looks like a daunting challenge. Further increasing LiNO₃ would potentially cause more irreversible reduction of LiNO₃ on the cathode during the first discharge. Therefore, a possible pathway for a long shelf life and low self-discharge is offered as well by the synergic protection of the separator and stabilization of the Li anode surface. The cell using a nanosized Al₂O₃-coated microporous membrane and a LiNO₃-possessing electrolyte exhibits an extremely suppressed self-discharge, providing an alternative perspective for the practical use of Li-S batteries.