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.