High-Performance Battery-Type Supercapacitors Based on Self-Oriented Growth of Nanorods/Nanospheres Composite Assembled on Self-Standing Conductive GO/CNF Frameworks
Nipa Roy, Gutturu Rajasekhara Reddy, Mohan Reddy Pallavolu, Ramesh Reddy Nallapureddy, Merum Dhananjaya, Arla Sai Kumar, Arghya Narayan Banerjee, Bong‐Ki Min, Hasi Rani Barai, Sang Woo Joo
Abstract
MnO x -based materials have limited capacity and poor conductivity over various voltages, hampering their potential for energy storage applications. This work proposes a novel approach to address these challenges. A self-oriented multiple-electronic structure of a 1D-MnO 2 -nanorod/2D-Mn 2 O 3 -nanosphere composite was assembled on 2D-graphene oxide nanosheet/1D-carbon nanofiber (GO/CNF) hybrids. Aided by K + ions, the MnO 2 nanorods were partially converted to Mn 2 O 3 nanospheres, while the GO nanosheets were combined with CNF through hydrogen bonds resulting in a unique double binary 1D–2D mixed morphology of MnO 2 /Mn 2 O 3 -GO/CNF hybrid, having a novel mechanism of multiple Mn ion redox reactions facilitated by the interconnected 3D network. The morphology of the MnO 2 nanorods was controlled by regulating the potassium ion content through a rinsing strategy. Interestingly, pure MnO 2 nanorods undergo air-annealing to form a mixture of nanorods and nanospheres (MnO 2 /Mn 2 O 3 ) with a distinct morphology indicating pseudocapacitive surface redox reactions involving Mn 2+, Mn 3+, and Mn 4+ . In the presence of the GO/CNF framework, the charge storage properties of the MnO 2 /Mn 2 O 3 -GO/CNF composite electrode show dominant battery-type behavior because of the unique mesoporous structure with a crumpled morphology that provides relatively large voids and cavities with smaller diffusion paths to facilitate the accumulation/intercalation of charges at the inner electroactive sites for the diffusion-controlled process. The corresponding specific capacity of 800 C g –1 or 222.2 mAh g –1 at 1 A g –1 and remarkable cycling stability (95%) over 5000 cycles at 3 A g –1 were considerably higher than those of the reported electrodes of similar materials. Moreover, a hybrid supercapacitor device is assembled using MnO 2 /Mn 2 O 3 -GO/CNF as the positive electrode and activated carbon as the negative electrode, which exhibits a superior maximum energy density (∼25 Wh kg –1 ) and maximum power density (∼4.0 kW kg –1 ). Therefore, the as-synthesized composite highlights the development of highly active low-cost materials for next-generation energy storage applications.