Efficient utilization of lithium polysulfides in CO2-derived CNT free-standing electrode of Li-S batteries

Abstract

The implementation of a free-standing carbon electrode provides an excellent strategy for the development of lithium-sulfur (Li-S) batteries with a maximized sulfur portion as the electrode does not require auxiliary components including a conducting agent, binder, and current collector. Electrospinning using a polymer is an attractive approach to prepare a free-standing electrode based on high carbon yield, but effective distribution and utilization of sulfur are hindered by the low porosity of the synthesized carbon nanofiber. The present work tackles this problem of electrospinning-based free-standing electrodes by utilizing Ni precursors and CO2 conversion to make porous materials by the resulting entangled CNTs as well as pores in the carbon nanofiber. The newly formed pores greatly improved the utilization of active sulfur materials and the movement of Li ions. While leading to CNT growth and pore formation, the Ni precursor also played a role in shifting nitrogen atoms from the graphene center to the edge-site, which could greatly improve the chemical interaction between lithium polysulfides and Li-ion as also confirmed by DFT calculations. The CNTs in porous carbon fibers, which are synthesized from CO2 and have both morphological and chemical advantages, delivered an areal capacity of 3.34 mAh cm−2 up to the 200th cycle when driven at 0.2C with high content sulfur-based active materials of 6.52 mg cm−2. The CNT free-standing electrode can effectively provide a high capacity of 412 mAh gcathode−1 based on the total cathode weight.