Resilient Three-Dimensional Graphene/CoS ₂ –SnS ₂ Heterostructures for Flexible Solid-State Supercapacitors

Metal sulfides have garnered extensive interest owing to their superior electrochemical properties. However, their practical application as electrode materials is severely hindered by sluggish electrical conductivity and drastic volume expansion during cycling. While blending carbonaceous materials with metallic sulfides boosts overall capabilities through structural synergy, engineering heterogeneous sulfide assemblies that concurrently exhibit efficient charge-transfer pathways and durable interfacial connections continues to be a formidable obstacle. Herein, a 3DG/CoS 2 –SnS 2 composite was designed and synthesized, in which cubic CoS 2 –SnS 2 heterostructures are anchored onto a three-dimensional graphene (3DG) support. The core mechanism lies in the difference in band structures between CoS 2 and SnS 2, which triggers the formation of an internal electric field at the heterogeneous boundary, thereby significantly accelerating the transport kinetics of both ions and electrons. Simultaneously, the 3D graphene network serves not only as a highway for rapid electron conduction but also as a resilient mechanical framework to effectively accommodate the volumetric swelling experienced by the electroactive components throughout repeated electrochemical cycling. Benefiting from the synergistic effects of the aforementioned dual strategies, the 3DG/CoS 2 –SnS 2 composite exhibits good electrochemical performance. It achieved a specific capacitance of 1100.2 F g –1 at a current density of 1 A g –1 and retains 85.8% of its initial capacitance after 10,000 cycles even at 5 A g –1 . Furthermore, the asymmetric supercapacitor (ASC) assembled with activated carbon (denoted as 3DG/CoS 2 –SnS 2 //AC) demonstrates good performance, achieving an energy density of 24.23 Wh kg –1 at a power density of 750 W kg –1, along with a capacity retention of 88.5% after 10,000 cycles at 5 A g –1 .