Structural combination of polar hollow microspheres and hierarchical N-doped carbon nanotubes for high-performance Li-S batteries

• Published in: Nanoscale Vol. 12; no. 3; pp. 2142 - 2153
• Main Authors: Lee, Jun Yeob, Park, Gi Dae, Choi, Jae Hun, Kang, Yun Chan
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 23.01.2020
• Subjects: Bamboo; Carbon; Carbon nanotubes; Cobalt ferrites; Construction materials; Current density; Cycles; Dispersion; Dissolution; Electrodes; Electronegativity; Microspheres; Nonuniformity; Polysulfides; Silicon dioxide; Slurries; Structural hierarchy; Trapping
• ISSN: 2040-3364; 2040-3372
• DOI: 10.1039/c9nr09807k

Hierarchical structured materials constructed with conductive carbon materials have been extensively studied as S host materials for Li-S batteries. However, their outwardly developed hierarchical structures, which do not contain structures or materials to inhibit polysulfide dissolution, lead to the dissipation of dissolved polysulfides and poor dispersion properties during the slurry-making process, which results in non-uniformity in the cathodes. Herein, an assembly of polar materials (hollow structured SiO 2 microspheres) and electrically conductive hierarchical N-doped bamboo-like carbon nanotubes (b-NCNTs) is designed as an efficient S host material for minimizing the dissolution of polysulfides during Li-S battery operations. Highly aligned and packed b-NCNTs are grown in hollow structured SiO 2 microspheres. The SiO 2 layer coated on the surface of the hollow CoFe 2 O 4 microspheres plays a key role in the synthesis of easily dispersible hierarchical b-NCNTs microspheres (b-NCNTs@SiO 2 ). The S-loaded b-NCNTs@SiO 2 electrodes show better cycling stability than S-loaded b-NCNTs electrodes. The polysulfide trapping of the polar SiO 2 layer and the well-developed b-NCNTs minimize the dissolution of polysulfides during cycling. In addition, the introduction of electronegative N atoms into the b-NCNTs lattice enhances their polysulfide trapping ability. The S-loaded b-NCNTs@SiO 2 electrodes exhibit stable discharge capacities of >771 mA h g −1 over 195 cycles at a current density of 0.5 C and a high reversible capacity of 486 mA h g −1 even at a high current density of 5.0 C. Herein, unique and novel structured microspheres with a porous SiO 2 layer as a shell and well-aligned inner-grown N-doped CNTs comprising CoFe 2 nanocatalyst alloy were synthesized by a modified Stöber method and chemical deposition.