Yolk–Shell Structured Assembly of Bamboo‐Like Nitrogen‐Doped Carbon Nanotubes Embedded with Co Nanocrystals and Their Application as Cathode Material for Li–S Batteries

Abstract

Despite their high theoretical specific capacity (1675 mA h g −1 ), the practical application of Li-S batteries remains limited because the capacity rapidly degrades through severe dissolution of lithium polysulfide and the rate capability is low because of the low electronic conductivity of sulfur. This paper describes novel hierarchical yolk-shell microspheres comprising 1D bamboo-like N-doped carbon nanotubes (CNTs) encapsulating Co nanoparticles (Co@BNCNTs YS microspheres) as efficient cathode hosts for Li-S batteries. The microspheres are produced via a two-step process that involves generation of the microsphere followed by N-doped CNTs growth. The hierarchical yolk-shell structure enables efficient sulfur loading and mitigates the dissolution of lithium polysulfides, and metallic Co and N doping improves the chemical affinity of the microspheres with sulfur species. Accordingly, a Co@BNCNTs YS microsphere-based cathode containing 64 wt% sulfur exhibits a high discharge capacity of 700.2 mA h g −1 after 400 cycles at a current density of 1 C (based on the mass of sulfur); this corresponds to a good capacity retention of 76% and capacity fading rate of 0.06% per cycle with an excellent rate performance (752 mA h g −1 at 2.0 C) when applied as cathode hosts for Li-S batteries. Scheme 1. a) Formation mechanism of the Co@BNCNTs YS microsphere and b) schematic of discharge and charge mechanism.

Metal-based nanostructured materials for advanced lithium–sulfur batteries

“…6.2.2 Cobalt. So far, cobalt-based nanostructured materials for Li-S batteries have comprised several Co/carbon composites obtained by thermolysis processes and have been used as either a sulfur host material [341][342][343][344][345][346]351,352,[378][379][380][381] or an interlayer between the cathode and the separator. 350,382,383 Remarkably, for Co- containing Li-S batteries, degradation rates lower than 0.1% per cycle were achieved.…”

“…The performance achieved with cobalt composite materials can be further enhanced by using conductive scaffold materials like graphene and CNTs, which also additionally lowers the charge transfer resistance determined for the conversion reactions. 343,344,351,379 The synergistic effects of N-doped carbon matrices and metallic cobalt nanoparticles or doping atoms as well as enhanced charge transport enable exceptionally low capacity fading over many cycles due to LiPS-adsorption and electrocatalytic properties. By thermolysis of suitable precursors like ZIF-67 (Co) and sometimes chemical etching, Co/N-doped carbon composites in the form of polyhedrons, nanorods, nanobers and nanosheets were obtained and used as a sulfur host material or separator coating.…”

Graphene Oxide Induced Growth of Nitrogen‐Doped Carbon Nanotubes as a 1D/2D Composite for High‐Performance Lithium‐Sulfur Batteries

“…However, the spatial confinement of polysulfides in HCMs is based on relatively weak interactions between nonpolar carbon and the polar polysulfides. Introducing heteroatom dopants, especially the nitrogen dopant, is supposed to enable chemical binding of polysulfides, so that polysulfide shuttle can be effectively inhibited by physical confinement and chemical adsorption in a synergistic manner. For instance, N‐doped carbon nanotubes fabricated by a facile urea treating process have improved absorbability for sulfur species, resulting in high utilization of active materials; hollow carbon nanorods prepared by polydopamine coated Co‐carbonate hydroxide nanorods and N‐doped carbon nanotubes grown from metal organic frameworks have also exhibited the high performance in lithium‐sulfur batteries …”

Recent Advances in Hollow Porous Carbon Materials for Lithium–Sulfur Batteries

“…[99] This grape-cluster-like structure allows the TiO@C/S cathode with 5 mg cm −2 of sulfur to provide a stable capacity of 630 mAh g −1 after 400 cycles at 0.2 C. Since the hard-templating method can make use of core/shell-structured materials as the templates, the yolk/shell-structured HPCM with polar inorganic cores have also been investigated as sulfur-hosting materials. [100][101][102][103] For instance, Lou and co-workers developed a hybrid structure of hollow carbon fiber filled with MnO 2 nanosheets (MnO 2 @HCF) using MnO 2 nanowires as the templates (Figure 8d). [104] Manthiram and co-workers designed yolk/shell-structured Fe 3 O 4 @C nanoboxes with Fe 2 O 3 nanocubes as the templates (Figure 8e).…”