Synthesis and electrochemical performance of P2-Na0.67AlxCo1-xO2 (0.0 ≤ × ≤ 0.5) nanopowders for sodium-ion capacitors

Abstract

Layered P2-Na0.67Al x Co 1-x O2 (0.0 ≤ × ≤ 0.5) nanopowders were prepared by solution combustion process. These nanopowders were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy and field emission scanning electron microscopy (FE-SEM) analysis. The electrochemical behaviours of the prepared layered P2-Na0.67Al x Co 1-x O2 nanopowder-based electrodes were investigated by cyclic voltammetry, electrochemical impedances and galvanostatic charge-discharge studies in 1 M Na2SO4 solution. The layered P2-Na0.67Al0.3Co0.7O2 has achieved a high specific capacitance of 260 F g−1 at a constant current density of 1 A g−1. The excellent electrochemical performance of Na0.67Al0.3Co0.7O2 is due to the partial substitution of Al3+ ions for Co3+ ions that leads to decrease in lattice parameter, resulting in the better structural stability during the Na+ ion intercalation/deintercalation reaction process. Moreover, the Na0.67Al0.3Co0.7O2 demonstrates a long cycle life with 80.1 % of its specific capacitance retention even after 5000 continuous charge-discharge process at a constant current density of 1 A g−1.