HKUST-1 derived CuS_x@C nanocomposites with TiO₂coating and rich sulfur vacancies for excellent high-rate long-life sodium-ion batteries

Transition metal sulfides are expected as potential conversion-type anodes for sodium-ion batteries (SIBs) due to their high theoretical capacity and natural abundance, but they are limited by the large volume changes upon cycling, poor electronic conductivity and the polysulfide shuttle effects. Herein, we demonstrate the confinement of copper sulfide (CuS_x) into porous carbon matrices with simultaneous TiO₂ coating and rich sulfur vacancies (denoted as TiO₂/CuS_x@C), via the facile CS₂ sulfurization of TiO₂-precoated HKUST-1 metal-organic framework (MOF). During the carbonization/sulfurization process, the TiO₂ coating facilitates to maintain the conformal octahedral morphology of HKUST-1, which converts into ultrafine CuS_x nanoparticles that embedded into the MOF-derived carbon matrices with simultaneous N/S-doping. Owing to the synergistic interaction of the polar C-N/C-S bonds, TiO₂ hybridization and sulfur vacancies, the shuttle of polysulfides is efficiently suppressed and the charge transfer coefficients are great improved. Consequently, the TiO₂/CuS_x@C demonstrates superior long-life cycling stability and outstanding high-rate capability, delivering a high capacity of 174.5 mA h g⁻¹at an ultra-high-rate of 20 A g⁻¹for more than 10000 cycles. Furthermore, the TiO₂/CuS_x@C||Na₃V₂(PO₄)₃ cell displays superior cycling and rate performances with 110.7 mA h g⁻¹at 5 A g⁻¹after 1000 cycles, proving its potential for practical application.