Rational design of Lithium-Sulfur battery cathodes based on differential Atom Electronegativity

Abstract

Lithium-sulfur (Li-S) batteries show advantages for next-generation energy storage due to their high theoretical energy density and cost effectiveness. Despite tremendous efforts, rational cathode design for mitigating the shuttling of soluble lithium polysulfides (LiPSs) between electrodes and improving reversible capacity remains a challenge because effective characteristic descriptor for sulfur cathodes is not established. In this work, the surface electron affinity (defined as electron-acceptance ability of solid-state surface) is firstly established as a quantitative screening principle forcathode materials. We find that those materials with the -2.66 ~ -7.96 eV surface electron affinities do not only prevent LiPSs from dissolving but also exhibit good electronic conductivity. The design principle is verified by our comparative electrochemical characterizations that TiO (ΔVSEA = -4.42 eV) performs a lower capacity-decay rate than TiS2 (-1.12 eV) TiC (-10.86 eV) and TiN (-14.55 eV).The design principle is verified by available experimental data reported in the previous literatures and our comparative experimental studies. The optimum binding strength of LiPSs on cathodes is identified in the range of 1.65 ~ 2.90 eV. Furthermore, differential atom electronegativity is defined as a more universal descriptor for experimentally and theoretically screening high-performance cathodes of Li-S battery. We find that divalent metal oxides (MO) with M:O = 1:1 and tetravalent transition metal sulfides, selenides and carbides (M:X = 1:2) could promote battery performance in maintaining high reversible capacity. These findings provide important insight towards the understanding of interfacial adsorption mechanism in electrochemical systems and establishing design principles for future discovery of improved cathodes for Li-S batteries.