Ultrathin Carbon Nanosheets for Highly-efficient Capacitive K-ion and Zn-ion Storage
Porous carbon has attracted extensive attentions as the electrode material for various energy storage devices considering its advantages like high theoretical capacitance/capacity, high conductivity, low cost and earth abundant inherence. However, there still exists limitations hindering its practical applications, such as the tedious fabrication process, limited metal-ion transport kinetics and undesired structure deformation at 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 mAh g-1), superior rate capability (161.8 mAh 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 high energy desntiy of 75.22 Wh kg-1, illuminating the applicable potentials. 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 mechanism investigations, this work will deepen the fundamental understandings of potassium-ion batteries and serve as references for the development of porous carbon materials in other high-efficient energy storage devices.