The effect of interactions and reduction products of LiNO₃, the anti-shuttle agent, in Li-S battery systems

Sulfur cathodes have excellent theoretical properties for use as positive electrodes in rechargeable lithium batteries. However they suffer from an internal redox shuttle process which limit their capacity because the sulfur reduction products, Li_xS_y species, cannot be fully re-oxidized. In order to overcome this problem, lithium nitrate is commonly used as an additive to the electrolyte solution, suppressing the shuttle phenomena in Li-sulfur batteries.We rigorously studied the electrochemical behavior of LiNO₃ in electrolyte solutions and with electrodes relevant to Li-S cells. EQCM UV-Vis and XPS spectroscopies were used in conjunction with standard electrochemical measurements, in order to determine the stability limits of this additive. An irreversible reduction of the nitrate species occurs in Li-S cells resulting in a precipitation of electrolyte solutions decomposition products such as LiF and oxygencontaining polymeric species formed by reactions of the ethereal solutions due to nitrate reduction on the cathode side below 1.9 V vs. Li .We showed that both the reversible capacity and the voltage profile of Li-S cells are significantly improved when the limiting cutoff potentials for the sulfur cathodes is set above the red-ox potential of LiNO₃.