Defect-engineered Sulfur Vacancy Modified NiCo 2 S 4-x Nanosheet Anchoring Polysulfide for Improved Lithium Sulfur Batteries.

The low conductivity of sulfur and the shuttle effect of lithium polysulfides (LiPSs) are the two intrinsic obstacles that limit the application of lithium-sulfur batteries (LSBs). Herein, a sulfur vacancy introduced NiCo 2 S 4 nanosheet array grown on carbon nanofiber (CNF) membrane (NiCo 2 S 4-x /CNF) is proposed to serve as a self-supporting and binder-free interlayer in LSBs. The conductive CNF skeleton with a non-woven structure can effectively reduce the resistance of the cathode and accommodate volume expansion during charge-discharge process. The bonding between CNF matrix and NiCo 2 S 4 nanosheet is enhanced by in situ growth, ensuring fast electron transfer. Besides, the sulfur vacancies in NiCo 2 S 4 enhance the chemisorption of LiPSs, and the highly active sites at vacancies can accelerate the LiPSs conversion kinetics. LSB paired with NiCo 2 S 4-x /CNF interlayer achieved improved stability in 500 cycles at 0.2 C and long life of 3000 cycles at 3 C. More importantly, a high areal capacity of 9.69 mAh cm -2 is achieved with a sulfur loading of 10.8 mg cm -2 and a low electrolyte to sulfur (E/S) ratio of 4.8. This work provides insight into the sulfur vacancy in catalysis design for LiPSs conversion and demonstrates a promising direction for electronic defect engineering in material design for LSBs.