3D CNTs/Graphene‐S‐Al 3 Ni 2 Cathodes for High‐Sulfur‐Loading and Long‐Life Lithium–Sulfur Batteries

Biendicho

et al. 2019

Adv Funct Materials

178

150

Urchin-shaped NiCo 2 Se 4 (u-NCSe) nanostructures as efficient sulfur hosts are synthesized to overcome the limitations of lithium-sulfur batteries (LSBs). u-NCSe provides a beneficial hollow structure to relieve volumetric expansion, a superior electrical conductivity to improve electron transfer, a high polarity to promote absorption of lithium polysulfides (LiPS), and outstanding electrocatalytic activity to accelerate LiPS conversion kinetics. Owing to these excellent qualities as cathode for LSBs, S@u-NCSe delivers outstanding initial capacities up to 1403 mAh g −1 at 0.1 C and retains 626 mAh g −1 at 5 C with exceptional rate performance. More significantly, a very low capacity decay rate of only 0.016% per cycle is obtained after 2000 cycles at 3 C. Even at high sulfur loading (3.2 mg cm −2 ), a reversible capacity of 557 mAh g −1 is delivered after 600 cycles at 1 C. Density functional theory calculations further confirm the strong interaction between NCSe and LiPS, and cytotoxicity measurements prove the biocompatibility of NCSe. This work not only demonstrates that transition metal selenides can be promising candidates as sulfur host materials, but also provides a strategy for the rational design and the development of LSBs with long-life and high-rate electrochemical performance.

Section: Resultsmentioning

confidence: 99%

Combined High Catalytic Activity and Efficient Polar Tubular Nanostructure in Urchin‐Like Metallic NiCo₂Se₄ for High‐Performance Lithium–Sulfur Batteries

Biendicho

et al. 2019

Adv Funct Materials

178

150

“…Nanostructured porous carbon materials were first investigated as lithium polysulfide traps by way of physical confinement. Such materials as graphene, carbon nanosheets, carbon spheres, carbon nanotubes, and microporous carbon materials, provide excellent electron transport networks for sulfur intermediates of the redox reaction and high specific surface areas to accommodate volumetric expansion [29][30][31][32][33][34][35][36][37][38][39]. Enhancement of lithium polysulfide redox kinetics requires electrochemically available polysulfides once the polysulfides are adsorbed on the carbon materials.…”

Section: Introductionmentioning

confidence: 99%

Lotus Root-Like Nitrogen-Doped Carbon Nanofiber Structure Assembled with VN Catalysts as a Multifunctional Host for Superior Lithium–Sulfur Batteries

et al. 2019

Lithium–sulfur batteries (LSBs) are regarded as one of the most promising energy-recycling storage systems due to their high energy density (up to 2600 Wh kg−1), high theoretical specific capacity (as much as 1672 mAh g−1), environmental friendliness, and low cost. Originating from the complicated redox of lithium polysulfide intermediates, Li–S batteries suffer from several problems, restricting their application and commercialization. Such problems include the shuttle effect of polysulfides (Li2Sx (2 < x ≤ 8)), low electronic conductivity of S/Li2S/Li2S2, and large volumetric expansion of S upon lithiation. In this study, a lotus root-like nitrogen-doped carbon nanofiber (NCNF) structure, assembled with vanadium nitride (VN) catalysts, was fabricated as a 3D freestanding current collector for high performance LSBs. The lotus root-like NCNF structure, which had a multichannel porous nanostructure, was able to provide excellent (ionically/electronically) conductive networks, which promoted ion transport and physical confinement of lithium polysulfides. Further, the structure provided good electrolyte penetration, thereby enhancing the interface contact with active S. VN, with its narrow resolved band gap, showed high electrical conductivity, high catalytic effect and polar chemical adsorption of lithium polysulfides, which is ideal for accelerating the reversible redox kinetics of intermediate polysulfides to improve the utilization of S. Tests showed that the VN-decorated multichannel porous carbon nanofiber structure retained a high specific capacity of 1325 mAh g−1 after 100 cycles at 0.1 C, with a low capacity decay of 0.05% per cycle, and demonstrated excellent rate capability.

“…In addition, the N-CNTs not only promote the electronic conductivity but also buffer the volume expansion of elemental sulfur. Therefore, a remarkable increase in the discharge capacity, rate performance and cyclic stability of the lithium-sulfur battery is achieved [76].…”

Section: Resultsmentioning

confidence: 99%

A Co9S8 microsphere and N-doped carbon nanotube composite host material for lithium-sulfur batteries

Angulakshmi

Journal of Alloys and Compounds

et al. 2020

Lithium-sulfur batteries have emerged as extraordinarily favorable energy storage devices due to their high specific capacity and energy density, safety and low cost. Unfortunately, the wide applications of lithium-sulfur batteries are hampered by several issues, such as the low electronic conductivity and slow redox kinetics, serious volumetric expansion and polysulfide "shuttle effect". To overcome these issues, in our work, we design and synthesize a composite sulfur host material of Co9S8 microspheres and N-doped carbon nanotubes, where the metallic sulfide Co9S8 with a good conductivity enables the immobilization of the polar lithium polysulfides owing to the strong polar chemisorptive capability, and the one dimensional N-doped carbon nanotubes can provide channels for fast electron and lithium-ion transport. As the lithium polysulfides are well confined, and the redox conversions are promoted, the Co9S8@N-CNTs/S-based lithium-sulfur battery possesses a superior energy storage performance, exhibiting a large specific capacity of 1233 mAh g -1 at 0.1 C and an outstanding cyclic performance, with a low decay of 0.045% per cycle and a Coulombic efficiency of more than 99% after 1000 cycles. Keywords: Metal sulfides; N-doped carbon nanotube; Cathode material; Lithium-sulfur battery. tightly attached to the N-CNTs is formed. In this composite, the polar metal sulfide Co9S8 enables a superior lithium polysulfide absorptivity via the polar chemical bond, which decreases polysulfide dissolution and the shuttle effect and increases the specific capacity and cyclic performance, while the N-doped carbon nanotubes can assist to increase the electronic conductivity and enlarge the interface between the electrode and electrolyte to further enhance the rate performance. Meanwhile, the N-CNTs/S composite and the Co9S8@N-CNTs/S composites with different contents of N-CNTs have been studied and compared. The unique Co9S8@N-CNTs composite-based sulfur cathode displays an outstanding overall electrochemical performance, making it promising for applications in 6 lithium-sulfur batteries. Experimental Preparation of Co9S8 and Co9S8@N-CNTsThe Co9S8@N-CNTs composite host was prepared using a solvothermal process. First, 27 mg of the N-CNTs was ultrasonically dispersed into 30 mL of ethylene glycol and 10 mL of distilled water to form a suspension. CoCl2· 6H2O (0.7138 g) and thiourea (0.4567 g) were added with stirring, and the ratio of CoCl2:thiourea was fixed as 60:40. The obtained solution was then subjected to a hydrothermal reaction for 12 h at 180 C. The product was filtered, adequately washed, and vacuum-dried for 24 h at 80 C. The obtained precursor was annealed for 3 h at 500 °C in H2/Ar (10%:90%). The obtained sample is denoted as Co9S8@N-CNTs. The pristine Co9S8 material was also prepared using the same processes but without adding the N-CNTs. The other Co9S8@N-CNTs composites with different contents of N-CNTs (13.5 mg and 40.5 mg) were prepared by a similar procedure. Hereafter, these obtained samples with different N...