Layered ternary sulfide CuSbS2 nanoplates for flexible solid-state supercapacitors

Abstract

Layer-structured materials are advantageous for supercapacitor applications owing to their ability to host a variety of atoms or ions, large ionic conductivity and high surface area. In particular, ternary or higher-order layered materials provide a unique opportunity to develop stable supercapacitor devices with high specific capacitance values by offering additional redox sites combined with the flexibility of tuning the interlayer distance by substitution. CuSbS₂ is a ternary layered sulfide material that is composed of sustainable and less-toxic elements. We report the results of a systematic study of CuSbS₂ nanoplates of varying thickness (4.3 ± 1.4 to 105 ± 5.5 nm) for use as supercapacitors along with the effect of ionic size of electrolyte ions on the specific capacitance and long-term cycling performance behavior. We have obtained specific capacitance values as high as 120 F g⁻¹ for nanoplates with thickness of 55 ± 6.5 nm using LiOH electrolyte. Electronic structure calculations based on density functional theory predict that with complete surface coverage by electrolyte ions a specific capacitance of over 1160 F g⁻¹ is achievable using CuSbS₂, making it a very attractive layer-structured material for supercapacitor applications. Additionally, the calculations indicate that lithium ions can be intercalated between the van der Waals layers without significantly distorting the CuSbS₂ structure, thereby further enhancing the specific capacitance by 85 F g⁻¹. Quasi-solid-state flexible supercapacitor devices fabricated using CuSbS₂ nanoplates exhibit an aerial capacitance value of 40 mF cm⁻² with excellent cyclic stability and no loss of specific capacitance at various bending angles. Moreover, the supercapacitors are operable over a wide temperature range. We have further compared the electrochemical behavior of CuSbS₂ with other non-layered phases in the system, namely Cu₃SbS₃, Cu₃SbS₄ and Cu₁₂Sb₄S₁₃ that clearly highlight the importance of the layered structure for enhancing charge storage.