Fabrication of three-dimensional hierarchical NiCo-LDH micro-flowers for enhanced charge storage in battery-type supercapacitors

Abstract

Layered double hydroxides (LDHs) show great advantage in supercapacitors (SCs) due to their unique layered structure and high theoretical capacity. However, their poor electrical conductivity and structural instability hinder their practical application. Metal-organic framework materials (MOFs) can be utilized to construct transition metal derived materials with adjustable morphology and high electrochemical properties. In this study, we first synthesized flower-like NiCo-based MOFs (NiCo-BTC) using a one-step solvothermal reaction. The formation process followed a sequence of “nucleation-growth-etching” corresponding to Ostwald's maturation theory. Subsequently, novel hierarchical NiCo-LDHs micro-flowers were constructed through treating the NiCo-BTC in an alkaline solution. The morphology of NiCo-LDHs was optimized by adjusting the ratio of Ni to Co, so as to achieve excellent electrochemical properties due to the hierarchical flower-like structure and the bimetallic synergistic effect. As a result, Ni3Co1-LDH exhibited a high specific capacitance of 1978.2 F/g at 1 A/g, excellent rate capability of 82.80 % at 40 A/g and good cycle stability with 70.6 % capacitance retention after 10,000 cycles at a high current density of 10 A/g. Furthermore, the asymmetric SC (ASC) based on Ni3Co1-LDH//AC exhibited high specific capacitance of 162.4 F/g at 1 A/g and excellent energy density of 54.8 Wh/kg at power density of 779.4 W/kg. In addition, the ASC demonstrated remarkable cycle stability with a capacitance retention of 96.5 % after 3500 cycles. The successful synthesis of 3D hierarchical NiCo-LDHs micro-flowers offers an effective approach to developing highly promising electrodes for SCs.