Ultrasonic-disrupted electrodeposition of gradient Ni-Co-Mn oxide electrodes for stage-wise energy storage in asymmetric supercapacitors

Abstract

To overcome the challenge of building stage-wise energy storage devices with tunable charge distribution, a novel electrodeposition method was developed using ultrasonic disruption. This technique enabled the fabrication of nickel–cobalt–manganese (Ni-Co-Mn) ternary oxide electrodes with vertically graded structures. The gradient was created by sequentially depositing four layers under varying ultrasonic power densities (10–40 W·cm−2) and substrate tilt angles (15°-45°). By precisely adjusting these parameters, a series of vertically graded NCM-x electrodes was synthesized. Among them, the NCM-11 sample, prepared using a power density (P) equal to 30 W·cm−2 and a tilt angle of 35°, revealed the most favorable morphology and electrochemical performance. Characterization using TEM and XPS confirmed the uniform distribution of NiO, Co3O4, and MnO2 phases. BET analysis exhibited a specific surface area equaling 56.97 m2·g−1. Electrochemical measurements revealed that NCM-11 delivered a high specific capacitance equal to 1430.7F·g−1 at 1 mA·cm−2, retaining 1334.9F·g−1 even at 15 mA·cm−2, with excellent cyclic stability, maintaining 93.3 % of its capacitance following 5000 cycles. When assembled into an asymmetric supercapacitor (NCM-11//AC), the device achieved an energy density equal to 45.6 Wh·kg−1 at P = 830.7 W·kg−1, and 30.8 Wh·kg−1 at P = 2440.3 W·kg−1. It also demonstrated exceptional long-term stability, maintaining 96.2 % of its capacitance following 5000 cycles. These findings showcase the prospective value of ultrasonic-assisted, gradient-controlled electrodeposition for developing high-performance supercapacitor electrodes.