Abstract
Cobalt sulphide nanoparticles are encapsulated in nitrogen-rich carbon cages via a simple and scalable method. Insight into sodium storage mechanism is systematically studied via in situ TEM and XRD techniques. The sodium-ion capacitor device achieved high energy densities of 101.4 and 45.8 Wh kg(−1) at power densities of 200 and 10,000 W kg(−1), respectively, holding promise for practical applications. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s40820-020-0391-9) contains supplementary material, which is available to authorized users.