Rational Design of β-NiOOH Nanosheet-Sheathed CNTs as a Highly Efficient Electrocatalyst for Practical Li-S Batteries

The shuttle effects of polysulfide intermediates (LiPSs) and sluggish kinetics during sulfur reduction reaction (SRR) process severely exacerbate the electrochemical performances of Li-S batteries. Herein, a unique nanocatalyst comprising β-NiOOH nanosheets uniformly implanted on the surface of carbon nanotubes (CNT@NiOOH) was designed and synthesized for sulfur cathodes. The β-NiOOH nanosheets have great capability of adsorbing LiPSs as well as superior catalytic activity for accelerating LiPS conversion, providing a more efficient method to restrain shuttle effects and improve the kinetics of SRR. Moreover, the nanometer-scale epitaxial growth and uniform distribution of β-NiOOH on CNTs provide a multidimensional catalytic skeleton with sufficient accessible active surfaces, unimpeded LiPS diffusion pathways, and resultant high utilization of active sites. Simultaneously, stable electron transportation pathways are also obtained by being synthesized on CNTs to avoid the faultiness of poor electron conductivity of β-NiOOH. These conspicuous advantages contribute to fully exert the catalytic and LiPS anchoring potential of CNT@NiOOH, bringing about the ultralong cycle performance and excellent capacity reversibility at a high discharge rate. Reticular CNT@NiOOH frameworks are assembled with the sulfur composite materials (SCMs) by a self-assembly method, and a super-high capacity of 813.3 mA h g^-1 after 400 cycles at 0.5 C with a small capacity degradation of 0.07% per cycle is achieved. Furthermore, the 3 A h pouch-type cell with the SCM/CNT@NiOOH cathode attains a super-high energy density of about 320 W h kg^-1 and shows a superior capacity retention as high as 75.9% after 50 cycles at 0.2 C. This work provides a promising method to accelerate the SRR process and restrain the shuttle effects for practical long-life and high-capacity Li-sulfur batteries.