Elsevier

Solid State Ionics

Volume 179, Issue 40, 31 December 2008, Pages 2379-2382
Solid State Ionics

Nickel sulfide cathode in combination with an ionic liquid-based electrolyte for rechargeable lithium batteries

https://doi.org/10.1016/j.ssi.2008.09.007Get rights and content

Abstract

Nickel sulfides, pure Ni3S2 and a mixture of Ni7S6–NiS, were synthesized through a solvothermal process. The nickel sulfide powders were characterized by X-ray diffraction, scanning electron microscopy, and electrochemical testing. The results showed that the capacity of NiS–Ni7S6 is much higher than that of Ni3S2, when used as the cathode in a lithium cell with an organic solvent-based electrolyte, l M lithium bis(trifluoromethanesulfonyl)amide (LiNTf2) in poly(ethylene glycol) dimethyl ether 500. The NiS–Ni7S6 electrodes were also tested with an ionic liquid electrolyte consisting of 1 M LiNTf2 in N-methyl-N-propyl pyrrolidinium bis(trifluoromethanesulfonyl)amide ([C3mpyr][NTf2]) to compare with organic-solvent based electrolytes. The results revealed that the ionic liquid is a useful solvent for use with this cathode material.

Introduction

Transport is one of the largest sources of greenhouse gas emissions and fossil-fuel consumption. This has led to a growing demand for electric vehicles/hybrid electric vehicles (EV/HEVs) to reduce global warming, air pollution, and the consumption of fossil fuels. For EV/HEV applications, a rechargeable lithium battery is required, with high power, high energy density, and high rate capability, together with a high level of safety. One problem that is retarding the development of large lithium batteries for electric vehicles is that the flammable organic-solvent based electrolytes currently used in commercial lithium batteries still raise safety concerns. Recently, room temperature ionic liquids (RTILs) have attracted attention as potentially safe electrolytes for large-size lithium secondary batteries, owing to their unique properties, such as non-flammability and non-volatility [1]. This non-flammability is effective in preventing batteries from catching fire, and a non-volatile electrolyte prevents batteries from bursting. It has also been shown that some ionic liquids provide a highly stable solid electrolyte interphase (SEI) layer on Li metal, such that stable cycling of Li becomes possible without dendrite growth [2], [3]. Various cathode materials, such as LiCoO2, LiFePO4, and sulfur, have been tested in ionic liquid-based electrolyte. The results showed that the cathode materials were stable in the ionic liquid-based electrolyte, and the capacity retentions were very good during cycling [4], [5], [6], [7]. However, at present, there have still been no reports on the use of RTILs with metal sulfide cathode for lithium metal batteries.

Metal sulfides are known to be promising materials for secondary lithium metal batteries because of their high theoretical capacity. A variety of metal sulfides have been considered for cathode materials in lithium batteries [8], [9], [10], [11], [12], [13], and nickel sulfides, in particular, have been attracting attention because of their high theoretical capacity (590 mAh/g for NiS and 462 mAh/g for Ni3S2) compared with the conventional LiNO2 (275 mAh g 1).

Traditionally, nickel sulfides were synthesized by solid-state reactions at high temperature and by a ball-milling method [14], [15], [16]. Recently, the solvothermal method has been proved to be an effective synthesis technique for preparing nickel sulfides [17], [18] with different morphologies. In this paper, nickel sulfides with a petal-like morphology were synthesized solvothermally with varying S/Ni molar ratios. Pure Ni3S2 and a mixture of NiS–Ni7S6 were obtained and tested as cathode materials with an organic solvent-based electrolyte consisting of l M lithium bis(trifluoromethanesulfonyl)amide (LiNTf2) in poly(ethylene glycol) dimethyl ether 500. A ionic liquid-based electrolyte, l M LiNTf2 in N-methyl-N-propyl pyrrolidinium bis(trifluoromethanesulfonyl)amide ([C3mpyr][NTf2]), was also tested in the NiS–Ni7S6 cells. It was found that the NiS–Ni7S6 cathode material had good cycling stability in this ionic liquid-based electrolyte.

Section snippets

Experimental

Nickel sulfide powders were synthesized via a simple solvothermal synthesis method [17]. NiCl2 H2O and Na2S2O3 were first added to 35 ml hydrazine hydrate. The molar ratio of NiCl2 H2O to Na2S2O3 was 1:1 and 2:1, respectively, for the two solutions (amount of Na2S2O3: 0.001 mol). Sealed autoclaves containing these precursors were maintained at 170 °C for 24 h and then cooled to room temperature. After cooling, the mixture was centrifuged, and the separated black precipitate was washed

Results and discussion

The X-ray diffraction patterns of the nickel sulfide powders are shown in Fig. 1. When the reaction was carried out in hydrazine hydrate with a 1:1 molar ratio of NiCl2 H2O to Na2S2O3, a mixture with two phases, NiS (JCPDS Card No. 12-0041) and Ni7S6 (JCPDS Card No. 14-0364) was produced (Fig. 1(a)). When the molar ratio was changed to 2:1 (NiCl2 H2O to Na2S2O3), pure Ni3S2 (JCPDS Card No. 30-0863) compound was obtained (Fig. 1(b)). The X-ray diffraction peaks for the prepared nickel sulfide

Conclusions

Nickel sulfides, Ni3S2 and Ni7S6–NiS, were synthesized via a solvothermal method using Teflon lined stainless steel autoclaves. The nickel sulfide particles, consisting of Ni3S2 and NiS–Ni7S6 prepared in hydrazine hydrate, have a petal-like morphology. The capacity of NiS–Ni7S6 was much higher than that of Ni3S2. The NiS–Ni7S6 cells showed good performance with both a novel ionic liquid-based electrolyte, 1M LiNTf2-[C3mpyr][NTf2], and an organic solvent-based electrolyte, 1 M LiNTf2-PEGDME 500.

Acknowledgments

This research was supported by the ARC Center of Excellence funding under grant number CE0561616, administered through the University of Wollongong. We thank Dr. T. Silver for critical reading of the manuscript.

References (22)

  • H. Sakaebe et al.

    Electrochim. Acta

    (2007)
  • B. Garcia et al.

    Electrochim. Acta

    (2004)
  • J.H. Shin et al.

    J. Power Sources

    (2006)
  • E. Markevich et al.

    Electrochem. Commun.

    (2006)
  • J. Wang et al.

    Carbon

    (2008)
  • J. Wang et al.

    Electrochem. Commun.

    (2007)
  • J. Wang et al.

    J. Power Sources

    (2006)
  • A. Debart et al.

    Solid State Sci.

    (2006)
  • S.C. Han et al.

    J. Alloys Compd.

    (2003)
  • Z. Meng et al.

    Mater. Chem. Phys.

    (2002)
  • G. Shen et al.

    J. Solid State Chem.

    (2003)
  • Cited by (73)

    • One-pot synthesis of nanomaterials

      2021, Handbook of Greener Synthesis of Nanomaterials and Compounds: Volume 1: Fundamental Principles and Methods
    • Nickel/sulfur composite electroplated nickel foams for the use as 3D cathode in lithium/sulfur batteries – A proof of concept

      2018, Energy Storage Materials
      Citation Excerpt :

      After the first cycle, low-intensity peaks disappear and the reduction peak with high intensity shifts to a higher voltage (1.4 V). This might be explained by the electrochemical transformation of NiS to Ni3S2 as the CV curve of the Ni3S2 shows just one reduction peak at ca. 1.5 V and an oxidation peak at ca. 2.0 V [17,18]. The cyclic voltammetry of the composite electroplated Ni-foam + Ni/SPTh cathode reveals a complex scenario (Fig. 10b).

    View all citing articles on Scopus
    View full text