Unveiling solid electrolyte interface morphology and electrochemical kinetics of amorphous Sb₂Se₃/CNT composite anodes for ultrafast sodium storage

Sb₂Se₃ based anodes are widely studied for advanced Na-ion batteries. However, their Na storage performance at high rates is limited to 2000 mA g⁻¹ because of poor kinetics of redox reactions. Here, the heterointerfacial interactions taking place between Sb₂Se₃ and functionalized CNTs are probed to understand the formation of Sb–O–C and Se–C bonds in the amorphous a-Sb₂Se₃/CNT composite using the density functional theory and ab-initio molecular dynamics simulations. The distinct morphologies and thicknesses of solid electrolyte interface layers formed on crystalline c-Sb₂Se₃ and a-Sb₂Se₃/CNT composite electrodes are revealed by advanced cryogenic transmission electron microscopy and their influences on the kinetics of redox reactions in the corresponding electrodes are identified. The structurally robust a-Sb₂Se₃/CNT composite electrode exhibits four orders of magnitude higher Na-ion diffusion coefficient than the crystalline c-Sb₂Se₃ counterpart, giving rise to an exceptional high-rate capacity of 454 mA h g⁻¹ at 12800 mA g⁻¹ and capacity retention of over 62% after 200 cycles at 10000 mA g⁻¹. The full cells containing the composite electrodes present energy and power densities of ∼175 Wh kg⁻¹ at 0.5C and ∼5784 W kg⁻¹ at 80C, respectively, and stable cyclic performance up to 120 cycles.