Controllable Fabrication and Tuned Electrochemical Performance of Potassium Co-Ni Phosphate Microplates as Electrodes in Supercapacitors.

Abstract

Most reported pristine phosphates, such as NH4MPO4·H2O (M = Co, Ni), are not very stable as supercapacitor electrodes because of their chemical properties. In this work, KCoxNi1-xPO4·H2O microplates were fabricated by a facile hydrothermal method at low temperature and used as electrodes in supercapacitors. The Co and Ni content could be adjusted, and optimal electrochemical performance was found in KCo0.33Ni0.67PO4·H2O, which also possessed superior specific capacitance, rate performance, and long-term chemical stability compared with NH4Co0.33Ni0.67PO4·H2O because of its unique chemical composition and microstructure. Asymmetric supercapacitor cells based on KCo0.33Ni0.67PO4·H2O and active carbon were assembled, which produce specific capacitance of 34.7 mA h g-1 (227 F g-1) under current density of 1.5 A g-1 and retain 82% as initial specific capacitance after charging and discharging approximately 5000 times. The assembled asymmetric supercapacitor cells (ASCs) exhibited much higher power and energy density than most previously reported transition metal phosphate ASCs. The KCoxNi1-xPO4·H2O electrodes fabricated in this work are efficient, inexpensive, and composed of naturally abundant materials, rendering them promising for energy storage device applications.