Construction diversified morphologies of NiCo2O4 via tuning dielectric solvents as battery-type electrodes for supercapacitors

The construction of effective nano-microstructures electrode has been a tireless pursuit in the energy storage field. Herein, Controllable construction of diversified morphologies NiCo 2 O 4 nanomaterials by tuning the dielectric constant and viscosity of the mixed solvent. We employed different solvent compositions as deionized water (DI), DI:Ethanol (1:1), DI: Isopropanol (1:1), DI: Propylene glycol (1:1), DI: Butanediol (1:1). In mixed aqueous solvents with low dielectric constants of ethanol and isopropanol, metal ions diffuse well and the nanomaterials tend to construct sheet-like nanostructures whereas high viscosity of the propylene glycol and butanediol solution will slow down the rate of metal ion diffusion, which only grow uni-directionally to form rod-like nanostructures. The formed ear-shaped NiCo 2 O 4 nanostructures in V propylene glycol : V H2O  = 1 : 1 mixed solvent have a large specific surface area and provide more electrochemically active sites, which facilitates effectively access electrolytes and thus accelerates the redox reaction rate. The resulting NiCo 2 O 4 nanoears exhibits favorable capacity of 251 mAh g −1 and excellent rate performance with a 73.0% capacity retention at 20 A g −1 . More importantly, the asymmetric supercapacitors assembled with the preferred NiCo 2 O 4 nanoears and active carbon (AC) reveal excellent electrochemical performance at operating potential of 1.6 V, great specific capacity (58.0 mAh g −1 ), energy and power density of 46.4 Wh kg −1 at 801 W kg −1 and a specific capacity retention rate of 90.7% after 5000 cycles. This work provides a new perspective for the controllable construction of new micro-nanostructure materials.