Elsevier

Electrochimica Acta

Volume 202, 1 June 2016, Pages 131-139
Electrochimica Acta

Improved Electrochemical Performance of Biomass-Derived Nanoporous Carbon/Sulfur Composites Cathode for Lithium-Sulfur Batteries by Nitrogen Doping

https://doi.org/10.1016/j.electacta.2016.03.176Get rights and content

Abstract

A two-step method with high-efficiency is developed to prepare nitrogen doped activated carbons (NACs) with high surface area and nitrogen content. Based on the method, series of NACs with similar surface area and pore texture but different nitrogen content and nitrogen group species are successfully prepared. The influence of nitrogen doping on electrochemical performance of carbon/sulfur composites cathode is studied deeply under the conditions of similar surface area and pore texture. It presents the directly experimental demonstration that both nitrogen content and nitrogen group species play crucial roles on electrochemical performance of carbon/sulfur composites cathode. NAC/sulfur composites show the much improved cycling performance, which is about 3.5 times as that of nitrogen free carbon. Improved electrochemical performance is due to synergistic effects between nitrogen content and effective nitrogen groups, which enables effective trapping of lithium polysulfides within carbon framework. Besides, it is found that oxygen groups exist in carbon materials obviously influence electrochemical performance of cathode, which could be ignored in most of studies. Based on above, it can be concluded that enhanced chemisorption to lithium polysulfides by functional groups modification is the effective route to improve the electrochemical performance of Li-S battery.

Introduction

Lithium-sulfur (Li-S) batteries have attracted intensive attention as the next-generation energy storage devices for electrical energy storage (EES) systems, owing to their high theoretical capacity of 1672 mAh g−1 and energy density of 2600 Wh kg−1 compared with traditional Li-ion batteries [1]. Besides, sulfur is abundant, low-cost and environmentally benign.

Despite these considerable advantages, the practical utility of Li–S batteries is challenging to realize due to several issues. First, electronic insulation nature of sulfur necessitates contact with large amounts of conductors e.g. conductive carbon, thus lowering the whole energy density of batteries. Second, reaction intermediates (lithium polysulfides, Li2Sx, 2 < x  8) stemming from electrochemical reaction of sulfur are prone to dissolve and diffuse into the electrolyte, which leads to the loss of active materials accompanied with shuttle phenomenon, thus resulting in capacity fading and poor coulombic efficiency [2].

Many strategies have been explored to solve above-mentioned problems, including novel cathode materials [3], [4], [5], [6], [7], lithium anode protection [8], [9], [10], [11], electrolytes modification [12], [13], [14] and cell configuration design [15], [16], [17]. Among them, nanoporous carbon hosts are especially promising, since they not only improve the sulfur utilization by forming carbon/sulfur nano-composites with good conductivity; but also they can hinder dissolution of lithium polysulfides by adsorption of nanopores, thus effectively suppressing the shuttle phenomenon [3], [4], [5], [7]. Ji et al. first presents the idea of sulfur-mesoporous carbon composite synthesized by a melt-diffusion process [3]. Sulfur is successfully encapsulated within the mesoporous space utilizing large pore volume and uniform mesoporous structure of CMK-3 carbon, finally high reversible capacity with good efficiency in Li–S batteries is exhibited for the first time.

However, above-mentioned designs are limited by weak interaction between sulfur and carbon host, which is basically based on physisorption. In addition, sulfur and lithium polysulfides always contact with electrolyte during the electrochemical process, inevitably prone to dissolve into organic electrolyte. Consequently, the achieved cycling performance is unsatisfactory. Recently, it is well reported that functional carbons especially nitrogen (N) doped carbons have the strong ability to chemically adsorb sulfur and lithium polysulfides compared with physisorption [18], [19], [20], [21]. Chemisorption enables uniform distribution and redeposition of sulfur, which thus improves electronic conductivity of composites and effectively confines the diffusion of lithium polysulfides within the carbon framework. For example, Wang and co-workers use nitrogen doped mesoporous carbon spheres as a conductive framework for sulfur and take advantage of chemical interaction between nitrogen groups and lithium polysulfides, thus resulting in the good electrochemical performance [18], [19]. Archer et al. utilize the chemical interaction between the nitrile group of polyacrylonitrile (PAN) and lithium polysulfides to obtain high capacities and excellent coulombic efficiency [20].

Generally, nitrogen doping carbons are mainly achieved by two strategies, i.e. chemical synthesis using nitrogen organic precursor [18], [19], [20] and chemical activation of nitrogen containing carbides [22], [23]. However, nanoporous structure of obtained carbons would be varied after nitrogen doping via above-mentioned methods (e.g. surface area and pore volume are 1475 m2 g−1 and 2.08 cm3 g−1 for nitrogen free sample; 824 m2 g−1 and 1.38 cm3 g−1 after doping nitrogen [19]). Basically, the improved electrochemical performance by nitrogen doping is based on synergistic effects of porous structure and nitrogen doping in most of studies. Up to date, there are few reports about systematic studies about effects of nitrogen doping under the conditions of unchanged surface area and pore texture.

Herein, we use a two-step method with high-efficiency developed from former studies about ammonia (NH3) activation [24] to prepare series of nitrogen doped carbons with similar surface area and pore texture but different nitrogen content and nitrogen group species. The influence of nitrogen doping on electrochemical performance is studied deeply under the conditions of similar surface area and pore texture. It presents the directly experimental demonstration that both nitrogen content and nitrogen group species play crucial roles on electrochemical performance of Li-S battery. Improved electrochemical performance is due to synergistic effects between nitrogen content and effective nitrogen groups, which enable effective trapping of lithium polysulfides within carbon framework. Besides, it is found that oxygen groups exist in carbon materials obviously influences electrochemical performance of cathode, which could be ignored in most of studies. Based on above, it can be concluded that enhanced chemisorption to lithium polysulfides by functional groups modification is the effective route to improve the electrochemical performance of Li-S battery.

Section snippets

Carbon materials preparation

Original nanoporous carbon was prepared by potassium hydroxide (KOH) chemical activation with biomass corncob as the carbon source and KOH as the activating agent. Detailed procedures are described according to previous reports [25]. The pristine carbon sample is hereafter denoted as corncob-derived activated carbon (CAC).

Based on CAC, nitrogen doped activated carbons (NACs) were prepared by a two-step method: The first step is nitric acid oxidation: the CAC was impregnated in concentrated

Results and discussion

Original carbon sample named CAC is prepared by KOH chemical activation with biomass corncob as carbon sources according to previous reports [25]. As shown in Fig. 1 and Table 1, CAC possesses high specific surface area (SSA) of 2762 m2 g−1 and pore volume of 1.49 cm3 g−1 with typical microporous characteristic. It is demonstrated by previous studies that oxygen groups exist in biomass play crucial roles on nitrogen doping by using NH3 as nitrogen source [24]. Treating CAC with NH3 leads to the low

Conclusions

In summary, we have developed a two-step method with high-efficiency to prepare nitrogen doped nanoporous carbon materials, where large amounts of oxygen groups are firstly doped into original nanoporous carbon by nitric acid oxidation, then nitrogen doping is further carried out by NH3 treatment, thus obtaining nitrogen doped activated carbons with high nitrogen content. Based on the method, series of nitrogen doped carbons with similar surface area and pore texture but different nitrogen

Acknowledgments

This work was supported by the National High Technology Research and Development Program of China (863 Program) (2012AA053305, 2014AA052501).

References (33)

  • A. Manthiram et al.

    Lithium-sulfur batteries: progress and prospects

    Adv. Mater.

    (2015)
  • Y. Yang et al.

    Nanostructured sulfur cathodes

    Chem. Soc. Rev.

    (2013)
  • X.L. Ji et al.

    A highly ordered nanostructured carbon-sulphur cathode for lithium-sulphur batteries

    Nat. Mater.

    (2009)
  • N. Jayaprakash et al.

    Porous hollow carbon@sulfur composites for high-power lithium-sulfur batteries

    Angew. Chem. Int. Ed.

    (2011)
  • H.L. Wang et al.

    Graphene-wrapped sulfur particles as a rechargeable lithium-sulfur battery cathode material with high capacity and cycling Stability

    Nano. Lett.

    (2011)
  • L. Xiao et al.

    A soft approach to encapsulate sulfur: polyaniline nanotubes for lithium sulfur batteries with long cycle life

    Adv. Mater.

    (2012)
  • Cited by (47)

    • Lignosulfonate for improving electrochemical performance of chitin derived carbon materials as a superior anode for lithium-ion batteries

      2021, Journal of Alloys and Compounds
      Citation Excerpt :

      Moreover, pyridine-N were the predominant cause for highly reversible capacities of LIBs [58]. Quaternary-N could enhance the conductivity by enabling more electrons introduced into the carbon framework [59], while if the content of N-Q was too high, it would result in the bad cycling performance [42]. Meanwhile, the doping of S element could enhance specific surface area (SSA) for providing more reaction sites.

    • N-doped three-dimensional porous carbon materials derived from bagasse biomass as an anode material for K-ion batteries

      2021, Journal of Electroanalytical Chemistry
      Citation Excerpt :

      To analyze the percentage contribution of pseudocapacitance behavior to the materials, variable speed CV tests are subjected to SC and SCNNi within the potential range of 0.01–3 V at 0.1–1 mV s−1, and the results are as shown in Fig. 7(a, b), respectively. Pseudocapacitance is the deposition of an electroactive material at the potential on the surface or in the two-dimensional space of the material, which generates capacitance related to the anode charging potential through reversible chemisorption and desorption [41,42]. Fig. 7 (c) reveals that the peak current and scan rate exhibit a good linear relationship, where k value is more than 0.5 and less than 1.

    View all citing articles on Scopus
    1

    These authors contributed equally to this work.

    View full text