Graphene wrapped Cobalt/Tin bimetallic sulfides composites with abundant active facets and extended interlayer spacing for stable sodium/potassium storage

Abstract

In this work, graphene wrapped Cobalt/Tin bimetallic sulfides composites (Co1Sn6.75-sulfides/rGO, CSSG) were prepared via soft template-assisted solvothermal reactions, the electrostatic assembly and high-temperature calcination strategies. Compared with pure SnS, Co1Sn6.75-sulfides show extended interlayer spacings and abundant active facets, which can accelerate the intercalation/extraction of Na+/K+ and improve the diffusion kinetics. Graphene can increase the electrical conductivity of composites and induce the formation of stable electrode/electrolyte interfaces. Therefore, CSSG exhibit superior cycle performance (391.7 mAh/g at 2.0 A/g after 1000 cycles, 240 mAh/g at 5.0 A/g over 5000 cycles) and outstanding rate capability (326.3 mAh/g at 10.0 A/g) for sodium ion half-cells. In addition, Na3V2(PO4)3||CSSG full-cells deliver a high reversible capacity of 339.3 mAh/g at 0.5 A/g after 100 cycles. Similarly, CSSG still exhibits high cycle capacities for potassium ion half-cells (306.6 mAh/g at 0.5 A/g after 1000 cycles). A variety of analysis methods and ex-situ characterizations are adopted to explore the diffusion kinetics of Na+/K+ and potassium storage mechanism. The structural evolution of CSSG during the long-term cycle process for sodium storage is investigated to analyze the capacity growth and attenuation.