Metal-organic framework derived N-doped CNT@ porous carbon for high-performance sodium- and potassium-ion storage

Abstract

Considering the lack of lithium resources, sodium- and potassium-ion storage systems possess great potential for large scale energy storage. However, the slow charge storage kinetics of graphite hinders the intercalation of large sodium and potassium ions, leading to low capacity and poor cycling stability. Herein, we report a nitrogen-doped carbon nanotube coated porous carbon derived from the metal-organic framework precursor for boosting the sodium and potassium ion storage. The carbon product tested as anode deliverers a high specific capacity of 320/339 mAh g−1 at 0.05 A g−1 in sodium/potassium ion batteries. Ex-situ X-ray diffraction studies indicate that the dominant charge storage mechanism in the carbon is based on adsorption, rather than intercalation. In addition, kinetics analysis further confirms that the capacitive-controlled capacity is dominant in the carbon electrode. To further illustrate the merits of metal-organic framework derived nanoporous materials, hybrid sodium and potassium ion capacitors are assembled by using the carbon anode and cathode both from metal organic frameworks. A high energy density of 118/126 W h kg−1 can be achieved for sodium/potassium ion capacitors. The present work provides a new strategy to design nanostructured carbons for high-performance metal-ion capacitors based on earth-abundant metals besides lithium.