Engineering a highly conductive honeycomb network on carbon cloth-supported bimetallic sulfide nanorod arrays for flexible solid-state asymmetric supercapacitors with superior performance

Abstract

Bimetallic sulfides represent electrochemical energy storage materials with potentially ultrahigh capacitance but poor rate performance and cycling stability for practical applications. Herein, a highly conductive carbon honeycomb network was successively engineered by repeatedly coating novel graphitic crystallite nanomaterials (GCNs) on hydrothermally grown carbon cloth-supported NiCo₂S₄ (NCS) nanorod arrays. It was found that the usage of GCNs rather than graphene oxide and carbon quantum dots was essential to constructing such carbon honeycomb networks. This honeycomb carbon network resulted in a significant improvement in the capacitance, rate performance, and cycling stability of the carbon cloth-supported xGCNs@NCS electrode. The engineered 3GCNs@NCS material obtained by coating GCNs three times had an ultrahigh capacitance contribution of 95.15 %, a capacity of 2112 F g⁻¹ at 1 A g⁻¹, an excellent rate performance with a capacitance of 1801 F g⁻¹ at 20 A g⁻¹ and exceptional cycling stability with 89.6 % capacitance retention after 10,000 cycles at 10 A g⁻¹. Therefore, the 3GCNs@NCS material can be directly used as a binder- and additive-free electrode. The flexible quasi-solid-state asymmetric supercapacitor assembled with 3GCNs@NCS and a commercially activated carbon delivered energy densities of 50.5 and 40.6 Wh kg⁻¹ at high power densities of 807.7 and 11087 W kg⁻¹, respectively, retaining a capacitance of > 90 %, even after cycling 20,000 times at 5 A g⁻¹. This work demonstrates that conductive honeycomb network-modified NCS nanorod arrays have excellent potential as flexible solid-state supercapacitor electrodes with both high energy and power densities and ultralong lifetimes.