Magnesium-regulated oxygen vacancies of cobalt-nickel layered double hydroxide nanosheets for ultrahigh performance asymmetric supercapacitors

Rational design of layered double hydroxide (LDH) electrodes is of great significance for highperformance supercapacitors (SCs). Herein, ultrathin cobalt-nickel-magnesium layered double hydroxide (CoNiMg-LDH) nanosheets with plentiful oxygen vacancies are synthesized via sacrificial magnesiumbased replacement reaction at room temperature. Self-doping and mild reduction of magnesium can significantly increase the concentration of oxygen vacancies in CoNiMg-LDH, which promotes the electrochemical charge transfer efficiency and enhances the adsorption ability of electrolytes. Density functional theory (DFT) calculations also indicate that Mg2+ doping can decrease the formation energy of oxygen vacancies in CoNiMg-LDH nanosheets, which increases the concentration of oxygen vacancies. Thus, the assembled asymmetric supercapacitor CoNiMg-LDH//Actived Carbon accomplishes a superior capacity of-333 C g-1 (208 F g-1) at 1 A g-1 and presents a gravimetric energy density of 73.9 Wh kg-1 at 0.8 kW kg-1. It presents only 13% capacity loss at 20 A g-1 after 5000 cycles. This discovery emphasizes the positive role of magnesium in regulating oxygen vacancies to improve the performance of supercapacitors, which should be beneficial for extending the scope of superior SCs active materials. (c) 2021 Elsevier Inc. All rights reserved.

Automated summary

In this study, ultrathin CoNiMg-LDH nanosheets with abundant oxygen vacancies were synthesized, and superior performance in supercapacitors was achieved. This highlights the positive role of magnesium in regulating oxygen vacancies.