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

Benben Wei,Guofu Zhou,Xin Wang,Chaoqun Shang,Zhihong Chen,Xiaoying Pan,Lingling Shui

doi:10.3390/nano9121724

Benben Wei, Guofu Zhou + Show 5 more

Open Access

https://doi.org/10.3390/nano9121724

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Abstract

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.

Highlights

Lithium–sulfur batteries (LSBs) have attracted tremendous interest in the energy storage field
Nanostructured porous carbon materials were first investigated as lithium polysulfide traps by way of physical confinement
Enhancement of lithium polysulfide redox kinetics requires electrochemically available polysulfides once the polysulfides are adsorbed on the carbon materials

Summary

Introduction

Lithium–sulfur batteries (LSBs) have attracted tremendous interest in the energy storage field. 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 [29–39]. Unsatisfied electrical conductivity of most metal oxides and sulfides is detrimental to the kinetics of sulfur electrochemical conversion, leading to poor cycling performance and low sulfur utilization, as well as poor rate capability [50–53]. As one of the transition metal nitrides, vanadium nitride (VN), with its high electrical conductivity (1.17 × 106 S m−1 at room temperature), can be a good choice to effectively anchor lithium polysulfide intermediates and to restrict the shuttle effect as a polar host, thereby improving sulfur utilization and enhancing cycling stability through high electron mobility and the catalytic effect [63–67]. A highly reversible capacity of 1325 mAh g−1 at 0.1 C with a low capacity decay of 0.05% per cycle was obtained, as well as a favorable rate capability

Preparation of VN Current Collector

Assembly of Li–S Batteries and Symmetric Batteries

Characterization of Materials and Electrochemical Measurements

Results and Discussion