Electrostatic self-assembly of MXene and edge-rich CoAl layered double hydroxide on molecular-scale with superhigh volumetric performances

It is highly desirable to design and synthesize two-dimensional nanostructured electrode materials with high electrical conductivity, large electrolyte-accessible surface area and more exposed active sites for energy storage applications. Herein, MXene/CoAl-LDH heterostructure has been prepared through electrostatic ordered hetero-assembly of monolayer MXene and edge-rich CoAl-LDH nanosheets in a face-to-face manner on molecular-scale for supercapacitor applications. Benefiting from the unique structure, strong interfacial interaction and synergistic effects between MXene and CoAl-LDH nanosheets, the electrical conductivity and exposed electrolyte-accessible active sites are significantly enhanced. The as-prepared MXene/CoAl-LDH-80% (ML-80) film exhibits high volumetric capacity of 2472 C cm−3 in 3 M KOH electrolyte with high rate capability of 70.6% at 20 A g−1. Notably, to the best of our knowledge, the high volumetric capacity is the highest among other previously reported values for supercapacitors in aqueous electrolytes. Furthermore, our asymmetric supercapacitor device fabricated with ML-80 and MXene/graphene composite as cathode and anode, respectively, exhibits impressive volumetric energy density of 85.4 Wh L−1 with impressive cycling stability of 94.4% retention ratio after 30,000 continuous charge/discharge cycles.