Bifunctional metal-organic coordination interface induced elastic (Cu-F/S, Na-F/S)-rich SEI on hard carbon for durable sodium-ion batteries

Large-scale applications of resource-enriched sodium-ion batteries (SIBs) suffer serious obstacles on the hard carbon (HC) anode due to large interface resistance and continuous electrolyte consumption induced poor cycling stability. Herein, we reported a metal-organic coordination interface (2-mercaptobenzothiazole-Cu) on the HC anode and particles (HC@MBT-Cu) to obtain the desired solid electrolyte interphase (SEI) and reduce the polarization of plateau-region sodium storage for durable SIBs. In the metal-organic coordination interface, Cu cations as catalytic centers coordinated with PF₆⁻ for easier breakage of P–F bonds to form CuF₂ and NaF into SEI. Cu and Na cations coordinate with exocyclic S groups of the decoration interface, promoting the breakage of C–S bonds and obtaining Na₂S and CuS in SEI. Meanwhile, N, S rigid-ring groups contribute to the SEI’s elasticity. Ultimately, thin elastic (Cu-F/S, Na-F/S)-rich SEI (14–18 nm, Cryo-TEM) was constructed with less electrolyte consumption and significantly reduced gas production. As a result, the polarization voltage of HC greatly decreased. The assembled HC@MBT-Cu∥Na₃V₂(PO₄)₃ full cells exhibited 86.4% after 600 cycles and pouch cells had a high-energy density of 175.1 Wh kg⁻¹. This work not only provides new insight into interface engineering but also offers a strategy to enhance the stability of HC particles and anodes, which might promote the development process of SIBs.