Elsevier

Materials Research Bulletin

Volume 58, October 2014, Pages 190-194
Materials Research Bulletin

Electrochemical properties of monolithic nickel sulfide electrodes for use in sodium batteries

https://doi.org/10.1016/j.materresbull.2014.05.008Get rights and content

Highlights

  • We succeeded in preparing monolithic Ni3S2 integrated electrode through the sulfuration.

  • The sulfuration is a facile and useful method to synthesize metal sulfides with nanostructure.

  • As-prepared monolithic Ni3S2 electrodes showed very stable and cycle performance over charge/discharge cycling.

Abstract

Monolithic nickel sulfide electrodes were prepared using a facile synthesis method, sulfuration and annealing. As-prepared Ni3S2 electrodes were characterized by X-ray diffractometry and field emission scanning electron microscopy. Thermal stability was determined by thermal gravimetric analysis and differential scanning calorimetry. Electrochemical properties were measured by galvanostatic charge and discharge cycling for Na-ion batteries. Three kinds of Ni3S2 electrodes were prepared by varying the sulfuration time (5, 15 and 25 min). The electrochemical results indicated that the capacities increased with an increase in sulfuration time and the cycle performance was stable as a result of monolithic integration of nanostructured Ni3S2 on Ni plates, leading to low interfacial resistance.

Introduction

Fossil fuel consumption has increased greenhouse gas emissions in the atmosphere, causing serious environmental problems such as global warming and pollution. There is an urgent need to develop alternative power sources such as solar and wind powers, which are called green energies. However, the energy supply generated from renewable sources is inconsistent and unpredictable. To secure an alternative energy supply, it is necessary to develop rechargeable batteries that can store and release energy on demand.

Currently available lithium ion batteries that use lithium metal oxide (LiMO2, M = Co, Mn, Ni) and graphite can offer high power, high energy density, cycle life, and high rate capability to small mobile devices [1], [2], [3], but are limited when it comes to new emerging applications such as electrical energy storage systems (ESS), electric vehicles (EVs), and hybrid electric vehicles (HEVs), because of cost and safety. Instead, a wide range of metal sulfides has been proposed as candidates for cathode materials that provide high theoretical capacities at low cost [4], [5], [6]. Among the metal sulfides, nickel sulfide has the advantages of good electronic conductivity, environment-friendly, low cost, and high energy capacity. Nickel sulfide is a material with a multiphase such as Ni3S2, Ni3+xS2, Ni4S3+x, Ni6S5, and Ni7S6. Among these phases Ni3S2 is electrochemically active, chemically stable, and compatible with organic solvents [4,7].

Traditionally, bulk Ni3S2 produced by ball-milling is contaminated and has low crystallinity [8]. A high-purity and nano-structured Ni3S2 can be synthesized through a variety of methods such as H2S gas reacting with nickel nano-particles on graphene or the soft solution chemical route [9,10].

In this study, a facile method was employed to prepare nanostructured Ni3S2 on a nickel plate [11]. As some authors have proposed, it is expected that the synthesis of materials with an integrated nanostructure will have high surface areas and good ionic conductivity, as well as the benefits of not having a binder or conductive agent [12], [13], [14]. Monolithically integrated Ni3S2 on Ni plates was characterized using field emission electron microscopy (FE-SEM) and X-ray diffractometry (XRD). Thermal analysis was conducted to measure weight loss and phase transition temperature. Electrochemical measurements of monolithic Ni3S2 electrodes were taken for sodium ion batteries.

Section snippets

Experimental

Nickel (Ni) plates were polished to remove oxidation layers before the sulfuration process. For nickel sulfuration, a solution was prepared by adding sulfur (S, Sigma–Aldrich) to ammonium sulfide ((NH4)2Sx, Kanto Chemical). Ni plates were soaked in the solution, which was heated up to 70 °C. Sulfuration proceeded for durations of 5 min, 15 min, and 25 min. The decolorized nickel plates were removed promptly from the solution, washed with ethanol, and then dried in an oven for 24 h. The sulfurated

Results and discussion

Fig. 1 presents X-ray diffraction patterns of bare and sulfurated Ni plates. Both patterns show a sharp peak at 44.5°, corresponding to the (1 1 1) plain in the Ni cubic structure (JCPDS Card no. 87-0712). After sulfuration of Ni, two very broad peaks were observed at approximately 25° and 30°. Nickel-based compounds such as NiS, NiS2, and Ni3S2 and sulfur lie in these 2 theta ranges. The pattern (b) of the sulfurated Ni plate indicates the sulfuration process can produce nickel sulfide compounds

Conclusion

In this study, monolithic Ni3S2 electrodes were synthesized using the facile sulfuration method and annealing. As-prepared electrodes had a monolithically integrated petal structure on the Ni plate. Electrochemical properties showed that monolithic Ni3S2 had a lower interfacial resistance and stable operation without capacity decay. For the Ni3S2 sulfurated for 25 min, the initial discharge capacity was 220 μA h/cm2. From characterization and electrochemical measurements, sulfuration is confirmed

Acknowledgments

This research was supported by Project 2012R1A1A2007143 and The Human Resource Training Project for Regional Innovation through the National Research Foundation of Korea (NRF) by the Ministry of Education and Projects 2012R1A2A2A02015831, 2013R1A2A1A01015911, and 2012R1A2A1A01006546 for Regional Innovation through the National Research Foundation of Korea (NRF) by the Ministry of Science, ICT & Future Planning (MSIP).

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