Hierarchical Design of Cross‐Linked NiCo2S4 Nanowires Bridged NiCo‐Hydrocarbonate Polyhedrons for High‐Performance Asymmetric Supercapacitor

Abstract Engineering core‐shell materials with rationally designed architectures and components is an effective strategy to fulfill the high‐performance requirements of supercapacitors. Herein, hierarchical candied‐haws‐like NiCo 2 S 4 @NiCo(HCO 3 ) 2 core‐shell heterostructure (NiCo 2 S 4 @HCs) is designed with NiCo(HCO 3 ) 2 polyhedrons being tightly strung by cross‐linked NiCo 2 S 4 nanowires. This rational design not only creates more electroactive sites but also suppresses the volume expansion during the charge–discharge processes. Meanwhile, density functional theory calculations ascertain that the formation of NiCo 2 S 4 @HCs heterostructure simultaneously facilitates OH − adsorption/desorption and accelerates electron transfer within the electrode, boosting fast and efficient redox reactions. Ex situ X‐ray diffraction and Raman measurements reveal that gradual phase transformations from NiCo(HCO 3 ) 2 to NiCo(OH) 2 CO 3 and then to highly‐active NiCoOOH take place during the cycles. Therefore, NiCo 2 S 4 @HCs demonstrates an ultrahigh capacitance of 3178.2 F g −1 at 1 A g −1 and a remarkable rate capability of 2179.3 F g −1 at 30 A g −1 . In addition, the asymmetric supercapacitor NiCo 2 S 4 @HCs//AC exhibits a high energy density of 69.6 W h kg −1 at the power density of 847 W kg −1 and excellent cycling stability with 90.2% retained capacitance after 10 000 cycles. Therefore, this novel structural design has effectively manipulated the interface charge states and guaranteed the structural integrity of electrode materials to achieve superior electrochemical performances.