Heterojunction Vacancies-Promoted High Sodium Storage Capacity and Fast Reaction Kinetics of the Anodes for Ultra-High Performance Sodium-Ion Batteries

Transition metal sulfides as anode materials for sodium-ion batteries (SIBs) have the advantage of high capacity. However, their cycle-life and rate performance at ultra-high current density is still a thorny issue that limit the applicability of these materials. In this paper, the carbon-embedded heterojunction with sulfur-vacancies regulated by ultrafine bimetallic sulfides (vacancy-CoS₂/FeS₂@C) with robust interfacial C-S-Co/Fe chemical bonds is successfully synthesized and explored as an anode material for sodium-ion battery. By changing the ratio of two metal cations, the concentration of anion sulfur vacancies can be in-situ adjusted without additional post-treatment. The as-prepared vacancy-CoS₂/FeS₂@C anode material offers ultrahigh rate performance (285.1 mAh g⁻¹ at 200 A g⁻¹), and excellent long-cycle stability (389.2 mAh g⁻¹ at 40 A g⁻¹ after 10000 cycles), outperforming all reported transition metal sulfides-based anode materials for SIBs. Both in-situ and ex-situ characterizations provide strong evidence for the evolution mechanism of the phases and stable solid-electrolyte interface (SEI) on the vacancy-CoS₂/FeS₂@C surface. The density functional theory calculations show that constructing heterojunction with reasonable concentration of vacancies can significantly increase the anode electronic conductivity. Notably, the assembled vacancy-CoS₂/FeS₂@C//Na₃V₂(PO₄)₃/C full-cell shows a capacity of 226.2 mAh g⁻¹ after 400 cycles at 2.0 A g⁻¹, confirming this material's practicability.