Abstract
In this paper, metal sulfide materials have been explored for the first time as a new choice of bifunctional cathode electrocatalyst materials for non-aqueous lithium-air batteries (LABs). Nickel sulfides with two different morphologies of flower-like (f-NiS) and rod-like (r-NiS) are successfully synthesized using a hydrothermal method with and without the assistance of cetyltrimethyl ammonium bromide. As LAB cathode catalysts, both f-NiS and r-NiS demonstrate excellent catalytic activities towards the formation and decomposition of Li2O2, resulting in improved specific capacity, reduced overpotentials and enhanced cycling performance when compared to those of pure Super P based electrode. Moreover, the morphology of NiS materials can greatly affect LAB performance. Particularly, the f-NiS is more favorable than r-NiS in terms of their application in LABs. When compared to both r-NiS and pure super P materials as LAB cathode materials, this f-NiS catalyst material can give the highest capacity of 6733 mA h g−1 and the lowest charge voltage of 4.24 V at the current density of 75 mA g−1 and also exhibit an quite stable cycling performance.
Highlights
Specific capacity, reduced discharge/charge overpotentials, and enhanced cycling performance
The growth of such a flower-like nickel sulfide (f-NiS) could be explained in terms of the diffusion-limited aggregation (DLA) process and the cage effect[30], which should be induced by the addition of cetyltrimethyl ammonium bromide (CTAB)
The capacities of the f-NiS based Lithium-air batteries (LABs) at several elevated current densities are considerably larger than those of the rod-like nickel sulfide (r-NiS) based one. These results indicate that both NiS based electrodes have enhanced specific capacities, reduced overpotentials and improved rate capability when compared to those of the Super P electrode, and the f-NiS is more favorable than r-NiS as the cathode catalyst material
Summary
Synthesis of flower-like and rod-like Nickel Sulfides.The synthesis of flower-like nickel sulfide (f-NiS)was referred to a previous report[30], the typical process was as follows: 1.7 mmol Ni(NO3)2·6H2O, 1.8 mmol NaSCN and 2.58 mmol cetyltrimethyl ammonium bromide (CTAB) were dissolved in 80 ml ultrapure water to form a solution. Synthesis of flower-like and rod-like Nickel Sulfides. The synthesis of flower-like nickel sulfide (f-NiS). Was referred to a previous report[30], the typical process was as follows: 1.7 mmol Ni(NO3)2·6H2O, 1.8 mmol NaSCN and 2.58 mmol cetyltrimethyl ammonium bromide (CTAB) were dissolved in 80 ml ultrapure water to form a solution. When the solution became clear and bright green, the autoclave was heated to 220 °C and maintained at this temperature for 24 hours. After cooling down to room temperature, the flower-like nickel sulfide (f-NiS) was collected by centrifugation and washed thoroughly with distilled water and ethanol alternate for several times followed by a drying step in vacuum at 80 °C overnight. To synthesize rod-like nickel sulfide (r-NiS), the same procedure was employed but without using CTAB
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