Ternary metal sulfides have received increased attention in recent years as an alternative to oxides for energy storage applications such as supercapacitors, batteries, fuel cells, and solar cells. Specifically, the thiospinel group of nickel cobalt sulfides (NixCo3-xS4) have shown promise as transformative active materials. Solution-processible nanoparticles of NixCo3-xS4 have advantages for low-cost, fabrication of high-performance energy devices due to their high surface-to-volume ratio, which increases the electrochemically active surface area and shortens the ionic diffusion path. The current literature standards for nickel cobalt sulfide synthesis, often based on hydrothermal or solvothermal methods, are limited by their complexity, expense, and lack of efficiency. These synthesis techniques are difficult to scale-up safely and preclude monitoring the reaction through aliquots making optimization of size and dispersity challenging. Previous work on scalable NixCo3-xS4 synthesis has been unable to achieve a well-controlled morphology and a narrow size dispersion.In this thesis, we report a synthetic method to produce phase pure nickel cobalt sulfide nanoparticles using two inexpensive, earth abundant sulfur sources. With specific focus on a scalable “heat up” synthesis, we have created a method providing a reliable synthetic pathway to produce phase-pure, monodisperse, gram-scale nanoparticles of ternary metal sulfides that are smaller than 15 nm in diameter with less than 15% in their statistical size distribution. Utilizing our synthetic method, we have conducted preliminary studies on the electrochemical properties of our material. Further research will enhance the current capabilities of NixCo3-xS4 nanoparticles to meet the performance demands to improve renewable energy technologies while exploring the application of our synthesis method to alternative ternary metal sulfide systems with various amino acids.