Metal chelate induced: In situ wrapping of Ni₃S₂ nanoparticles into N, S-codoped carbon networks for highly efficient sodium storage

Carbon-confined transition metal sulfides (TMS@C), featured with excellent redox reversibility, good electrical conductivity and high theoretical capacity, are considered to be promising anode materials for sodium-ion batteries (SIBs). Unfortunately, a large amount of additional S sources are involved in traditional preparation strategies, such as S powder, thiourea, l-cysteine, etc., resulting in the release of dangerous and poisonous H₂S or residues of free S in final products. Therefore, developing a facile approach for eco-friendly synthesis of TMS@C remains a big challenge. Herein, a novel approach is developed to realize the facile fabrication of TMS@C from metal-dithiooxamide chelate (MDC) without additional S sources, which effectively reduces the release of H₂S and avoids the residue of free S. In this strategy, dithiooxamide (DTO) with superior coordination ability coordinates with Ni²⁺ for the fine generation of the Ni-MDC precursor that is converted to N, S-codoped carbon-confined Ni₃S₂ nanoparticles (Ni₃S₂@NSC) after an in situ self-carbonization and self-sulfidation process. Benefiting from the rich heteroatoms in DTO, high doping contents of N and S in the carbon matrix can be obtained. When evaluated as an anode material for SIBs, Ni₃S₂@NSC exhibits excellent sodium storage performance with high reversible capacity (458.1 mA h g^-1 after 100 cycles at 0.1 A g^-1), superior rate capability (323.3 mA h g^-1 at 2 A g^-1) and robust long-term cycling stability (392.6 mA h g^-1 after 300 cycles at 0.5 A g^-1), which outperform those of nickel sulfide-based electrodes reported so far. More importantly, the strategy by employing MDC as a versatile precursor and template in this work should be promisingly applied in the fabrication of other heteroatom-doped TMS@C for efficient energy storage and conversion.