Engineering shell thickness of pyridinic-N rich hollow carbon nanospheres for stable and high energy density potassium ion hybrid capacitors

Potassium-ion hybrid capacitors (PIHCs) are candidate devices for large-scale electricity storage due to their attractive combination of high energy density of batteries and high power capacity of supercapacitors. But the much larger ionic size and higher mass of K+ in comparison to that of Li+ and Na+ make it difficult to identify a high capacity and rate capability anode material. Here we fabricate pyridinic-N rich hollow carbon nanospheres (NHCNs) with tunable shell size by a facile core-shell polymerization and carbonization method. By simply regulating the shell thickness, we can control the carbon nanospheres with appropriate surface area and defects/functional groups level, which are critical in determining their potassium storage capability. Due to the high nitrogen content (8.56 at.%), optimal porosity and shell size (similar to 20 nm), the NHCNs-420 exhibits a dominant surface-control behavior of a high capacity of 197.5 mAh g(-1) at a high rate of 5 A g(-1) and long-term stability of 280.3 mAh g(-1) over 2500 cycles at 1 A g(-1), which compares favorably with most previously reported carbon-based electrodes. Moreover, the kinetics matched NHCNs-420//porous carbon PIHC device combines high energy and power density, demonstrating the promise of using NHCNs for potassium-ion storage.

Automated summary

Potassium-ion hybrid capacitors (PIHCs) are potential devices for large-scale energy storage. Researchers have fabricated hollow carbon nanospheres with tunable shell size, which demonstrate high capacity and long-term stability for potassium-ion storage.