First-Principles Investigations to Evaluate NiCl2/NiF2 as Cycle-Catalyzed Electrolyte Additives to Improve Li-S Batteries' Performance

The potential application of two electrolyte additives, NiCl2-DME and NiF2-DME, in lithium-sulfur batteries is investigated by density functional theory calculations. The results show that both electrolyte additives can effectively adsorb soluble lithium polysulfide (LiPSs) in the electrolyte. With the progress of the charging-discharge reaction, NiCl2 and NiF2 separate from Li2Sn when it is converted to S-8 and recombine with 1,2-dimethoxy-ethane (DME) to achieve the purpose of cyclic adsorption of polysulfide in the electrolyte. At the same time, NiF2 and NiCl2 also have a catalytic effect in the cycling process. When adsorbed with Li2Sn, the bond length of the Li-S bond in Li2Sn is elongated, which causes the reduction of the Li2Sn activation energy, making it easier to be oxidized, and accelerating the conversion speed of Li2Sn and reducing Li2S, Li2S2 deposition on the surface of the electrode. Therefore, NiCl2-DME and NiF2-DME are ideal dual-function electrolyte additives.