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

Abstract

The construction of effective nano-microstructures electrode has been a tireless pursuit in the energy storage field. Herein, Controllable construction of diversified morphologies NiCo2O4 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 NiCo2O4 nanostructures in Vpropylene glycol: VH2O = 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 NiCo2O4 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 NiCo2O4 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.