Freestanding cathode design for lithium-sulfur batteries: CoP/Co-PCNF sandwich structure to enhance adsorption and catalysis for polysulfides

Abstract

Lithium-sulfur (Li-S) batteries are exceedingly restrained in practical application originating from the shuttling of soluble lithium polysulfides (LiPSs), despite their superelevated theoretical specific capacity as well as energy density. Herein, a flexible carbon nanofiber membrane in situ embedded with Co, CoP nanoparticles (Co-PCNF, CoP/Co-PCNF) was designed to fabricate a unique sandwich structure, as a free-standing cathode for Li-S batteries. These innovative Li-S batteries deliver an initial capacity of 993.5 mAh g−1 at 1 C, along with a substantial capacity of 814.18 mAh g−1 even over 300 cycles, which corresponds to a low capacity decay of only 0.06% per cycle. Besides, with a sulfur content of 4.5 mg cm−2, an initial discharge capacity of 700.1 mAh g−1 was realized at 0.2 C with an excellent capacity retention rate of 91% over 200 cycles, prominent in long-cycle Li-S batteries. In this aspect, rosy cycling stability was achieved because of the impeded shuttle effect by the synergistic effect of Co and CoP compared with Co-PCNF sandwich structure as well as traditional aluminum foil. Moreover, underlying the DFT calculation, the enhanced overlap of electronic state ascribed to the conversion of fraction Co nanoparticles to CoP, triggering the adsorption capacity of CoP/Co-PCNF crucially higher than that of Co-PCNF. This observation paves ways into implementing the CoP/Co-PCNF sandwich structure as a free-standing cathode for the high-performance Li-S batteries.