Ball milling modification of perovskite LaNiO3 powders for enhancing electrochemical pseudocapacitor

Abstract

A perovskite LaNiO3 powder was prepared via a sol–gel method. The powder has a particle size of 0.28 μm and a rhombohedral crystal structure. Electrochemical performance of the as-prepared LaNiO3 electrodes is as low as 9.94 F g−1 at the discharged current density of 5 A g−1. Ball milling treatments of the LaNiO3 powders in dry-air, ethanol and DI water reduce the particle sizes and greatly improve their specific capacitances to 27.10, 64.23 and 76.87 F g−1, respectively. X-ray diffraction detects a second phase formation of La(OH)3 in LaNiO3 ball-milled in DI water. Energy dispersive X-ray spectra and X-ray photoelectron spectroscopy results suggest that the charge process of the LaNiO3 electrode attracts OH− ions to the LaNiO3 electrode and oxidizes Ni2+ to Ni3+. In contrast, the discharge process releases OH− ions from the LaNiO3 electrode and reduces Ni3+ back to Ni2+. Electrochemical impedance spectroscopy shows that the DI-ball-milled LaNiO3 powders have lower series resistance (Rs = 0.207 Ω) and charge-transfer resistance (Rct = 0.18 Ω,) than the as-prepared LaNiO3 powders (Rs = 0.205 Ω and Rct = 0.99 Ω).