Synergistic design of g-C3N4-supported CNTs: experimental and DFT insights for enhanced electrochemical performance in flexible Li–S batteries†

Abstract

In addressing the shuttle effect and sluggish redox kinetics of lithium polysulfides (LiPSs) in lithium–sulfur batteries, we developed a novel heterostructure combining 1D carbon nanotubes (CNTs) grown on a 2D sheet of graphitic carbon nitride (g-C₃N₄) to improve conversion reaction kinetics and LiPS adsorption capacity. The high pyridine N content in g-C₃N₄ facilitates homogeneous Li ion deposition and enhances affinity between Li and N atoms. Extensive experimental characterization and density functional theory (DFT) calculations validated the interaction between g-C₃N₄-CNT/S and LiPSs. In pouch cell evaluation, the hybrid g-C₃N₄-CNT/S cathode, with ∼70% sulfur loading, demonstrated outstanding rate performance, delivering ∼895 mA h g⁻¹ at 0.1C and retaining ∼500 mA h g⁻¹ even at 1.5C under lean electrolyte conditions (E/S ∼5 μl mg⁻¹). Long-term stability over 250 cycles, with a capacity retention of 86% and a coulombic efficiency (CE) of 90.4%, was achieved, even with an elevated sulfur loading of 6.2 mg cm⁻². Post-mortem investigation using X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS) elucidated surface chemistry changes and elemental composition alterations, highlighting the formation of various reaction products during charge–discharge cycles. This study underscores the cost-effective heterostructure strategy's potential for advancing LiSBs in practical applications.