Ruddlesden–Popper Y2Ti2O5S2/SWCNT composite anode: durable cycling and ultrafast lithium-ion storage for hybrid supercapacitors

Abstract

Y₂Ti₂O₅S₂ (YTOS) is a unique cation-deficient Ruddlesden–Popper structured material composed of alternating perovskite-like slabs (TiO₅S octahedra) and rock-salt [Y₂S₂]²⁺ layers. Despite its potential for lithium-ion storage, research on YTOS as an energy storage material remains limited, underscoring its novelty and unexplored capabilities. The addition of 1 wt% single-walled carbon nanotubes (SWCNTs) significantly improved the electrochemical performance of YTOS, resulting in enhanced capacity, superior output characteristics, and improved cycle stability compared to the pristine material. The resulting composite demonstrates superior rate capability (up to 230C) and outstanding cycleability, retaining 95% of its capacity even after 1000 cycles. Operando XRD and Ti K-edge XAFS analyses reveal fully reversible orthorhombic-tetragonal phase transitions and stable Ti³⁺/Ti⁴⁺ redox activity during 500 cycles, while unchanged Y K-edge spectra confirm the structural stability conferred by the yttrium sublattice. Hybrid supercapacitor full cell assemblies with activated carbon (YTOS‖AC) display minimal polarization and remarkable durability over 10 000 cycles at 10C, highlighting the material's suitability for high-power capability. This work presents a promising approach for developing high-performance energy storage materials, as the YTOS anode offers both high energy density and excellent cycle life, making it an excellent candidate for advanced lithium-ion batteries and hybrid supercapacitors.