One-pot scalable synthesis of pure phase Ni3S4 quantum dots as a versatile electrode for high performance hybrid supercapacitors and lithium ion batteries

Transition metal based quantum dots (QDs) have great potential for electrode materials of advanced electrochemical energy storage due to their unique structural superiorities. Here, we develop a simple, green and scalable one-pot method for the synthesis of 10-g-scale monodisperse nickel sulfides QDs. Interestingly, the composition of the target QDs products can be precisely regulated through adjustment of the concentration of 6-mercapto-1-hexanol ligands in precursor solution and thus pure phase Ni3S4 QDs are obtained. Benefiting from the advantages of high specific area carrying more metallic active sites and rich pore structure in favor of the diffusion of electrolyte ions, the optimal Ni3S4 QDs manifest extraordinary electrochemical performance as advanced electrodes for both hybrid supercapacitors and lithium ion batteries. Impressively, the constructed hybrid supercapacitor achieves high energy density of 49.3 Wh·kg−1 and power density of 21718 W kg−1 with a robust stability of maintaining 91.7% after 8000 cycles. When applied to anode materials of lithium energy storage, Ni3S4 QDs can deliver a high reversible specific capacity of 647.5 mAh·g−1 at 100 mA g−1 with remarkable cyclic performance of losing only 2% reversible capacity value under 500 cycles.