Flexible high-energy asymmetric supercapacitors based on MnO@C composite nanosheet electrodes

Abstract

Developing asymmetric supercapacitors (ASCs) is a promising alternative to achieve both wide voltage windows and high energy densities to meet the application requirements of hybrid vehicles and renewable energy systems. However, a major limitation of high performance asymmetric supercapacitors lies in negative electrode materials which possess relatively low specific capacitance compared to positive electrode materials. Herein, a novel MnO@C composite nanosheet array directly grown on conductive carbon cloth as a negative electrode is prepared successfully, which exhibits a large specific capacitance of 662.9 F g⁻¹ at a current density of 3.7 A g⁻¹ and an areal capacitance of 716 mF cm⁻² at a current density of 4 mA cm⁻². Afterward, a flexible ASC is successfully assembled with Co₃O₄ nanosheets and MnO@C nanosheets as the positive electrode and negative electrode, respectively. The optimized ASC achieves a high operating voltage of 1.7 V and displays intriguing performances with a high specific capacitance of 166 F g⁻¹, an exceptional energy density of 59.6 W h kg⁻¹ and superior rate capability and cycling stability. In addition, the ASC exhibits superior flexibility and mechanical stability even under severe bending states. The ASC based on MnO@C nanosheets as a promising candidate for high performance supercapacitors may pave the way for applications in high performance energy storage systems.