Ultrathin carbon nanosheets for highly efficient capacitive K-ion and Zn-ion storage

Abstract

Porous carbon has attracted extensive attention as an electrode material for various energy storage devices considering its advantages such as high theoretical capacitance/capacity, high conductivity, low cost and earth abundance. However, there still exist limitations hindering its practical applications, such as the tedious fabrication process, limited metal-ion transport kinetics and undesired structural deformation under harsh electrochemical conditions. Herein, we report a facile strategy, with calcium gluconate as the carbon source, to fabricate ultrathin porous carbon nanosheets. The as-prepared Ca-900 electrode delivers excellent K-ion storage performance including high reversible capacity (413.7 mA h g⁻¹), superior rate capability (161.8 mA h g⁻¹ at an ultrahigh current density of 5.0 A g⁻¹) and ultra-stable long-term cycling stability (a high capacity retention ratio of ∼75.0% after 5500 cycles at 5.0 A g⁻¹). Similarly, when being applied in Zn-ion hybrid capacitors, the Ca-900 electrode exhibits a high energy density of 75.22 W h kg⁻¹, illustrating the application potential. Moreover, the origin of the fast and smooth metal-ion storage is also revealed by carefully designed consecutive CV measurements. Both K-ion/Zn-ion storage mechanisms are preliminarily revealed through ex situ measurements. Overall, considering the facile preparation strategy, unique structure, application flexibility and in-depth mechanistic investigations, it can be seen that this work will deepen the fundamental understanding of potassium-ion batteries and serve as a reference for the development of porous carbon materials for other highly efficient energy storage devices.