Heterogeneous WO2/WS2 microspheres synergized with reduced graphene oxides with high rate capacity for superior sodium-ion capacitors

Abstract

• Heterogeneous WO 2 /WS 2 microspheres wrapped by reduced graphene oxide are prepared. • WO 2 /WS 2 nanosheets shorten Na + diffusion and WO 2 guarantee high electron conductivity. • RGO provide structure protecting layer and alleviate the volume change of WO 2 /WS 2. • WO 2 /WS 2 -rGO electrode exhibits large capacity, high rate and long cycle life. • A 4.0 V sodium-ion capacitor achieves 140 Wh kg −1 at 200 W kg −1. High rate capacity and long-term cycling stability are the pursuing characteristic of a promising anode for sodium-ion capacitors (SICs). However, the sluggish reaction kinetics and aggregation of volume during sodiation/desodiation process are the main obstacles. In this work, we developed a 3D porous WO 2 /WS 2 -rGO network while urchin-like microspheres self-assembled by WO 2 /WS 2 heterogeneous nanosheets and wrapped by rGO network, demonstrating superior rate properties and cycling stability as the anode of sodium-ion batteries (SIBs). The ultrathin WO 2 /WS 2 nanosheets contribute to shorten the Na + diffusion length, while metallic WO 2 guaranteeing high electric conductivity of nanosheet units and rGO network help to construct the fast dual electron transfer pathways during sodiation/desodiation process. Also, rGO network can provide a stable structure protecting layer and alleviate the volume change of WO 2 /WS 2 . Benefiting from these merits, WO 2 /WS 2 -rGO electrode reveals a dominanting capacitive-controlled process especially at the higher scan rates and achieves 100 mAh g −1 at an ultrahigh current density of 25.6 A g −1 as well as maintains 90% capacity retention over 1000 cycles at 1 A g −1 . The SICs comprising of WO 2 /WS 2 -rGO anode and 3D phosphorus-doped carbon (P C) cathode demonstrate outstanding energy density of 140 Wh kg −1 at 200 W kg −1 along with a reasonable stable cycling of 79% capacity retention over 6000 cycles at 5 A g −1 within the voltage of 0.0–4.0 V. The proposed strategy integrates hierarchical heterogeneous structure and effective dual electron transfer network can be applied to develop promising electrode materials for high performance energy storage systems.