Construction of CoS<sub>2</sub> Reduction Accelerator-Modified Sulfurized Polyacrylonitrile Nanofibers as High-Performance Cathode Materials for Practical Lithium–Sulfur Batteries
Yongbing Li, Runhe He, Hao Liu, Yun Zhang, Haihui Liu, Na Han, Xingxiang Zhang
Abstract
Sulfurized polyacrylonitrile (SPAN) is an attractive cathode material for lithium–sulfur batteries because of its high theoretical energy density, good cyclic stability, and low self-discharging rate. However, the slow reaction kinetics enormously limits the actual capacity and rate performance of SPAN cathodes. In the present work, SPAN nanofibers containing a certain amount of CoS 2 were used to prepare high-performance cathode materials for lithium–sulfur batteries, and the redox kinetics of sulfur conversion was promoted by imparting catalytic activities to SPAN. Specifically, Co was uniformly distributed in CoS 2 -SPAN nanofibers in the form of CoS 2, which reduced the charge transfer impedance in the electrode, accelerated the conversion of short-chain polysulfide to Li 2 S/Li 2 S 2, increased the migration rate of lithium ions, and improved the kinetics of the redox reaction. Hence, after the sulfurization of polyacrylonitrile nanofibers containing 4 wt % of CoCO 3, CoS 2 -SFPAN manifested a high reversible capacity of 762 mAh g –1 composite at 0.2 C, an excellent multiplicative performance of 592 mAh g –1 composite at 4.0 C, and an extremely stable cycle life of more than 500 cycles at 1.0 C. When the cathode was tested under a high areal loading (S) of 5.5 mg cm –2 and a lean electrolyte (E) condition of E/S = 10 μL mg –1, it maintained high reversible capacities of 710 mAh g –1 composite at 0.1 C and 652 mAh g –1 composite at 0.2 C.