An organometallic salt as the electrolyte additive to regulate lithium polysulfide redox and stabilize lithium anodes for robust lithium-sulfur batteries

Abstract

Lithium-sulfur (Li-S) batteries with high theoretical specific energy are considered to be one of the highly promising next-generation energy storage systems. However, the shuttle effect of lithium polysulfides (LiPSs) and the interfacial instability of Li anodes have seriously hindered the practical application of Li-S batteries. Optimizing the electrolyte composition with additives can significantly improve the battery performance and has attracted great attention. Herein, we propose an organometallic salt, i.e., nickel bromide dimethoxyethane (NiBr₂DME), as an electrolyte additive, which serves as the dual function of regulating LiPSs redox and synchronously stabilizing Li anodes. We reveal that NiBr₂DME can interact with LiPSs via Ni–S and Li–Br bonds, and accelerate the mutual transformation of LiPSs, thus reducing the accumulation of LiPSs in the electrolyte. In addition, NiBr₂DME can form a stable LiBr-containing interfacial layer on the Li metal surface, and promote the uniform electrodeposition of Li⁺ ions, and inhibit the formation of Li dendrites. Thus, Li-S batteries with a concentration of 0.5 mmol L⁻¹ NiBr₂DME show an initial capacity of 919.8 mAh g⁻¹ at 0.2 C, and a high capacity retention of 89.3% after 100 cycles. Even at the 4 C rate, a high discharge capacity of 602.9 mAh g⁻¹ is achieved. Surprisingly, the good cycling performance is maintained under poor electrolyte conditions with sulfur loading of 4.8 mg cm⁻² and electrlyte/sulfur ratio of 5 µL mg⁻¹. This work provides a positive solution to achieve the suppression of shuttle effect, the regulation of LiPSs redox and the stabilization of Li anodes.