Debajyoti Mondal•Gilles Villemure•Chaojie Song

2.2 Synthesis of porous NiS submicrospheres

The USP procedure for the synthesis of nanomaterials wasreported elsewhere [54]. A solution containingNiCl26H2O, Na2S2O35H2O, and colloidal silica was prepared according to a procedure reported in our previouspaper [55]. The solution was loaded to a USP ultrasonic cell, after which the system was purged with Ar for 30 min.Then, the solution was nebulized with an ultrasonic atomizer (2.4 MHz, Sonaer Inc., Farmingdale, NY). Ar(flow rate: 5 L min-1) was used to carry the aerosol mist through a mini tube furnace(Xiamen Tmaxcn Inc.)at 450℃. The product was collected, filtered, washed with DI water, and dried at room temperature. The silica template was removed by etching in a 5 % HF solution. The final product was centrifuged and washed several times with ethanol and deionized water by drying under vacuum at 70℃for 12h.

2.4 Electrochemical tests

The electrode was prepared as follows: 70 wt% porous spherical NiS was mixed with 20 wt% acetylene black and10 wt% poly(vinylidene fluoride) (PVDF). N-Methyl-2-pyrrolidinone was added as a dispersant to form a paste,which was spread onto aluminum foil substrates, and kept at vacuum for drying. The NiS-loaded aluminum foils were cut into 15-mm diameter disks by a TMAX coin cell disc punching machine, which was used as the cathode. All the other components of the CR2032 coin cell including stainless steel spacer, coin cell case, and PP PE separator were from Xiamen TMAX Battery Equipments Limited and assembled in an argon-filled glove box using a house designed and fabricated coin cell crimper CR100. A lithium metal disk was used as the anode. The electrolyte was composed of 1 mol L-1 LiPF6 dissolved in ethylene carbonate/diethyl carbonate with the ratio of 1:1. The charge–discharge cycles of the cells were performed using a Keithley 2400 source meter in a potential range of 1.0–3.0 V at a current density of 50 mA g-1.