Electrodeposition of nickel sulfur composite cathodes for lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have emerged as one of the most promising next generation energy storage systems due to their high theoretical specific energy and the natural abundance of sulfur. However, the polysulfide shuttle effect, poor electrical conductivity, and volumetric expansion during cycling have hindered the commercialization of Li-S batteries. This study focuses on developing Ni-S composite cathodes through controlled electrodeposition to overcome these limitations. The study investigates the influence of key electrodeposition parameters - including thiourea concentration (50-100 g/L), current density (-25 to -100 mA/cm²), deposition time (15-60 minutes), and dispersant additives (polyethyleneimine, PEI and sodium dodecyl sulfate, SDS) - on the composition, morphology, and electrochemical performance of Ni-S composites. Using a modified Watts bath as the electrolyte, the electrodeposition process was optimized to achieve high sulfur loading and uniform distribution. SEM/EDS, TGA, linear sweep voltammetry (LSV), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic cycling were employed to evaluate the composites. Results indicate that a thiourea concentration of 75 g/L yields optimal sulfur incorporation (12.78 wt%), and lower current densities (-25 mA/cm²) favor higher sulfur content. The addition of PEI and SDS significantly improves particle homogeneity and reduces agglomeration, though it leads to brittle coatings. Electrochemical testing reveals distinct redox behavior in Ni-S cathodes, with characteristic peaks at 1.8 V and 1.3 V corresponding to NiS formation and conversion reactions. The optimized cathode delivers an initial discharge capacity of 204 mAh/gS at a C/10 rate. While these results demonstrate the potential of electrodeposited Ni-S composites for Li-S batteries, further optimization is required to improve cycling stability and capacity retention. This work provides valuable insights into the relationship between electrodeposition parameters and cathode performance, contributing to the development of practical, high-energy-density Li-S battery systems.