A controlled process of atomic-scale material design via temperature-mediated grain refinement of NiCo2O4 rods for capacitive energy storage

We report on a controlled process of atomic-scale material design based on calcination-temperature-induced structural variation and its influence on capacitive energy storage characteristics of spinel-structured NiCo2O4 rods (NCOR). Precisely, morphology-tuned NCOR were grown through a facile solvothermal process followed by a controlled calcination. The meticulous thermal-kinetics study revealed that the activation energy of 269.53 kJ/mol could transform the hydroxides into oxides completely. The precipitate was annealed at variable temperatures (350, 450 and 550 °C) to incorporate structural changes with variation in size of the crystallites. NCOR-450 consisting of fine-sized nanocrystallites coated on a flexible graphite foil exhibited a maximum gravimetric specific capacitance of 326.1 F/g at a constant current density of 0.5 A/g. The comparatively smaller crystallites lead to attractive capacitances as the temperature-induced grain-growth-correlated electrical properties influence the electrochemical properties significantly.