Electrochemical properties of monolithic nickel sulfide electrodes for use in sodium batteries
Graphical abstract
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).
References (14)
- et al.
Nickel sulfide cathode in combination with an ionic liquid-based electrolyte for rechargeable lithium batteries
Solid State Ionics
(2008) - et al.
Electrochemical properties of Na/Ni3S2 cells with liquid electrolytes using various sodium salts
Curr. Appl. Phys.
(2011) - et al.
The addition of iron to Ni3S2 electrode for sodium secondary battery
Curr. Appl. Phys.
(2011) - et al.
Electrochemical properties of NiS as a cathode material for rechargeable lithium batteries prepared by mechanical alloying
J. Alloys Compd.
(2003) - et al.
Electrochemical characteristics of cathode materials NiS2 and Fe-doped NiS2 synthesized by mechanical alloying for lithium-ion batteries
Powder Technol.
(2012) - et al.
The discharge properties of Na/Ni3S2 cell at ambient temperature
J. Power Sources
(2008) - et al.
Ammonium sulfide treatment of HgCdTe substrate and its effects on electrical properties of ZnS/HgCdTe heterostructure
Thin Solid Films
(2005)