Role of Ferroelectric InSe in Polysulfide Shuttling and Charging/Discharging Kinetics in Lithium/Sodium-Sulfur Batteries.

Lithium-sulfur (Li-S) and sodium-sulfur (Na-S) batteries, with the advantages of ultrahigh energy density, natural abundance, and ecofriendliness, are regarded as next-generation rechargeable batteries. However, polysulfide shuttling and sluggish charging/discharging kinetics in sulfur cathodes severely hamper their practical applications. In this study, via employing first-principles calculations, we investigate two-dimensional ferroelectric InSe as a promising additive to overcome these obstacles. Our studies reveal the following findings: (1) the InSe monolayer has a modest adsorption strength to soluble polysulfides, which not only eliminates the notorious shuttle effect but also prevents polysulfide dissolution; (2) InSe is able to significantly reduce the free energy barriers of sulfur reduction reaction and the decomposition barriers of LiS and NaS, thus greatly enhancing the charging and discharging efficiency; and (3) due to the strong binding ability, the polarization downward (P↓) surface always outperforms the polarization upward (P↑) surface during charging/discharging processes, enabling the effective control of battery performance by ferroelectric switching. Given these advantages, it is expected that ferroelectric InSe and similar ferroelectric additives will open a new route to enhance Li-S and Na-S battery performance.