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.