Mille-Crêpe-like Metal Phosphide Nanocrystals/Carbon Nanotube Film Composites as High-Capacitance Negative Electrodes in Asymmetric Supercapacitors
Nan Zhang, Junyuan Xu, Bin Wei, Junjie Li, Isilda Amorim, Rajesh Thomas, Sitaramanjaneya Mouli Thalluri, Zhongchang Wang, Weiya Zhou, Sishen Xie, Lifeng Liu
Abstract
Transition metal phosphides (TMPs) are emerging as high-performance and promising electrode materials for use in asymmetric supercapacitors (ASCs). Herein, we demonstrate that cobalt phosphide (CoP) nanocrystals supported on carbon nanofibers (CoP/CNF) can serve as negative electrode materials in ASCs and show outstanding specific capacitance 748 F g–1 at 2 A g–1 and superior long-term cycle stability, outperforming conventional carbon-based and nearly all TMP-based negative electrode materials reported previously. A binder-free mille-crêpe-like negative electrode is fabricated by loading CoP/CNF onto an ultrathin, interconnected carbon nanotube (CNT) film current collector, followed by folding the film multiple times, which exhibits a high total mass (active materials and current collector) based specific capacitance of 200.0 F g–1 at 1 A g–1, due to the lightweight of the CNT film collector. Furthermore, we fabricate an all-phosphide ASC (APASC) using CoP/CNF/CNT as the negative electrode and NiP/CNF/CNT as the positive electrode, which delivers a specific capacitance of 163.8 F g–1 and shows excellent long-cycle stability up to 50000 cycles. The APASC’s capacitance can be further improved to 209 F g–1 if a bimetallic CoNiP/CNF/CNT positive electrode is used. The APASC holds substantial promise for use in the next generation energy storage systems.