Ternary hybrids of amorphous nickel hydroxide-carbon nanotube-conducting polymer for supercapacitors with high energy density, excellent rate capability, and long cycle life

Abstract

The utilization of Ni(OH)2 as a pseudocapacitive material for high performance supercapacitors is hindered by its low electrical conductivity and short cycle life. A coaxial ternary hybrid material comprising of amorphous Ni(OH)2 deposited on multiwalled carbon nanotubes wrapped with conductive polymer (poly (3,4-ethylenedioxythiophene)-poly(styrenesulfonate)) is demonstrated. A thin layer of disordered amorphous Ni(OH)2 is deposited by an effective “coordinating etching and precipitating” method, resulting in an ultrahigh specific capacitance of 3262 F g−1 at 5 mV s−1 and excellent rate capability (71.9% capacitance retention at 100 mV s−1). More importantly, the polymer layer prevents the degradation of the nanostructure and dis­solution of Ni ion during repeated charge–discharge cycling for 30 000 cycles, a phenomenon which often plagues Ni(OH)2 nanomaterials. Using the ternary Ni(OH)2 hybrid and the reduced graphene oxide/carbon nanotube hybrid as the positive and negative electrodes, respectively, the assembled asymmetric supercapacitors exhibit high energy density of 58.5 W h kg−1 at the power density of 780 W kg−1 as well as long cycle life (86% capacitance retention after 30 000 cycles). The ternary hybrid architecture design for amorphous Ni(OH)2 can be regarded as a general approach to obtain pseudocapacitive materials for supercapacitors with both high energy density, excellent rate capability, and long cycle life.