High-performance aqueous symmetric supercapacitors based on Ni6MnO8–MnCO3 composite self-supported electrodes

Abstract

Ni–Mn-based binary oxides are deemed as a promising commercial electrode material for supercapacitors (SCs) due to their low price, environmental friendliness and high theoretical capacitance. However, their low electrical conductivity and narrow potential window limit their electrochemical performance. Herein, we prepare a composite of Ni₆MnO₈ and MnCO₃ grown in situ on activated carbon cloth (NMO-x@ACC, x = 1, 2, 3) at a low temperature as an electrode for aqueous supercapacitors. By a component optimization and morphology control strategy, nano-flake and wheat-shaped NMO-2@ACC (Ni/Mn = 1) shows outstanding capacitance performance up to 1450 mF cm⁻² at 2 mA cm⁻² within the 0–1 V potential window. The assembled NMO-2@ACC aqueous SC displays a wide potential window of 1.8 V in 1 mol L⁻¹ LiNO₃ electrolyte, and the maximum energy density reaches 4.061 mW h cm⁻³. After 6000 cycles, the capacitance remains at 90.1%, showing good stability. In addition, two devices connected in series can light up 72 LEDs for more than 2 minutes, which demonstrates an excellent practical application prospect. This strategy of proportion control and morphology optimization provides a new strategy for the preparation of high-performance Ni–Mn based electrode materials.