Enhanced Na‐Ion Electrochemical Performance through Cu Doping‐Mediated Sb₂Se₃ Phase Transformation into CuSbSe₂ with Improved Kinetics

This work investigates the influence of structural and electronic modification on the electrochemical performance of conversion and alloying materials. The CuSbSe₂, a promising 2D layered conversion, and alloying material is being investigated with references to parent pristine Sb₂Se₃ and a doped version of later Sn_0.2Sb_1.8Se₃ for their sodium-ion battery performance. The CuSbSe₂ with layered structure is well known to accommodate lattice distortions via inter-layer movement, potentially mitigating distortions brought about by the Alkali ion (Na in this case) insertion. In contrast, the parent conversion-cum-alloying material Sb₂Se₃ with its one-dimensional crystal structure leads to structural disintegration during battery operation. The Sn-doped analog, Sn_0.2Sb_1.8Se₃, comparatively exhibits enhanced kinetics owing to the reduced long-range order. The 2D layered, CuSbSe₂ despite exhibiting 2D long-range order exhibits superior electrochemical performance owing to the favorable electronic and structural features. The CuSbSe₂ exhibits a reversible capacity of 881 mAh g^-1 compared to 516 mAh g^-1 for Sn_0.2Sb_1.8Se₃ and 429 mAh g^-1 for Sb₂Se₃, with an improved Coulombic efficiency as well. The transient electrochemical investigations of Electrochemical Impedance Spectroscopy (EIS) and Galvanostatic intermittent titration techniques (GITT) reveal that better performance exhibited by CuSbSe₂ may well be attributed to kinetics owing to enhanced diffusion coefficients in the intercalation and conversion regime.