Modified separator engineering with 2D ultrathin Ni3B@rGO: Extraordinary electrochemical performance of the lithium-sulfur battery with enormous-sulfur-content cathode in low electrolyte/sulfur ratio

Abstract

Compared to other batteries, a next-generation lithium-sulfur (Li-S) battery's specific capacity and energy density are relatively high. However, the actual electrochemical performance (particularly for the cell with a high cathode sulfur content and a lean electrolyte/sulfur ratio) falls well short of practical usage requirements. The ultrathin Ni 3 B@rGO-PP is designed in this study as a unique modified separator for Li-S cells. Because of its distinct electronic structure, the modified separator shows outstanding adsorption ability toward polysulfide through the boron element's active sites. Additionally, it has excellent electrocatalytic activity, significantly enhancing the performance of Li-S batteries. After the 100th cycle, the cell with 80 wt% sulfur content can retain 819 mA h g −1 under 0.2 C. Also, when the electrolyte/sulfur ratio is reduced to 15 µL mg −1 and 5 µL mg −1 , respectively, considerable capacity retention of 736.3 mA h g −1 and 615 mA h g −1 is achieved after the 100th cycle at 0.2 C. What's more, for the high sulfur loading (single-side up to 4.5 mg cm −2 ) cathode, the cell obtains a retention capacity of 578 mA h g −1 after the 200th cycle under 0.2 C. The surface engineering strategy with the Ni 3 B@rGO modified coating adopted in this work would open an efficient route to acquire the Li-S battery's outstanding electrochemical capability in the practical application situation. The boron element's active cites provide a unique electronic structure to the Ni 3 B@rGO coating layer, which effectively enhance the adsorption ability toward polysulfide, and further provide excellent electrocatalytic activity during the charging/discharging process, greatly improving the electrochemical performance of Li-S batteries. Thus, the Ni 3 B@rGO-PP exhibits long cycling stability even at a low E/S ratio, fast Li + transportation, and high ionic conductivity. • The Ni 3 B@rGO nanohybrid developed as a novel modified coating on the celgard separator in Li-S batteries. • The Ni3B@rGO-PP show outstanding adsorption ability to LiPSs through B active cites and enhances the cell conductivity. • The Ni 3 B@rGO-PP exhibits excellent anti-self-discharge, high ionic conductivity, and fast Li + transportation. • The Ni3B@rGO-PP presents promising electrochemical performances with a high-sulfur-content cathode (up to 83 wt%).