室温固相反应助力制备氮硫共掺杂碳限域的FeCoS2复合物用于高性能钠离子电池负极

利用室温固相自组装反应制备Co (Ⅱ)和Fe (Ⅱ)双席夫碱配合物，随后在硫粉存在下中温热处理，使该配合物同时发生热解碳化和固相硫化反应，从而获得N、S共掺杂碳限域的FeCoS₂纳米复合物(记为FeCoS₂⊂NSC)。通过粉末X射线衍射、透射电镜、X射线光电子能谱和热重分析技术分别对纳米复合物的物相、形貌结构、组分和含量等进行物理表征，并通过循环伏安、恒电流充放电技术测试其电化学储钠性能。研究结果表明，最优化条件下制备的复合物(FeCoS₂⊂NSC-7001)中FeCoS₂粒子的平均尺寸约为3.4 nm，且被均匀限域在N、S共掺杂的碳基体中；该复合物作为钠离子电池负极时，在0.1 A·g^-1的电流密度下经过300次充放电循环，其可逆充电比容量仍高达310.4 mAh·g^-1；即使在5 A·g^-1的大电流密度下，其充电比容量也高达146.0 mAh·g^-1，呈现优异的电化学储钠性能。

Room-temperature solid-state reaction-assisted strategy to fabricate nanocomposites of N, S-codoped carbon confined FeCoS2 as high-performance anode materials for sodium-ion batteries

In this work, a facile and cost-effective solid-state reaction method for the synthesis of the nanocomposites (denoted as FeCoS₂⊂NSC) of N, S-codoped carbon-confined FeCoS₂ nanocrystalline was presented. By directly mixing cobalt acetate tetrahydrate, ferrous acetate, o-vanillin and o-phenylenediamine with a molar ratio of 1∶1∶4∶2 at ambient temperature in the presence of sulfur powder, a self-assembly solid state reaction took place to give rise to the complexes of Co(Ⅱ) and Fe(Ⅱ) with a bis-Schiff base, which were evenly distributed in the sulfur powder surroundings. After subsequent annealing at an elevated temperature, simultaneous carbonization and sulfidization occurred, resulting in the in-situ formation of ultrafine FeCoS₂ nanoparticles confined in N, S-codoped carbon matrices. The phase, morphology, composition, and content of each component in the nanocomposite were determined by powder X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The electrochemical sodium storage performance was tested by the cyclic voltammetry and galvanostatic charge-discharge techniques. The results showed that the average size of the FeCoS₂ particles in the optimized nanocomposite (FeCoS₂ ⊂ NSC-7001) was ca. 3.4 nm, which was uniformly confined in the N, S-codoped carbon matrices. When FeCoS₂⊂NSC-7001 was used as an anode material for sodium-ion batteries, it exhibited excellent electrochemical energy storage performance in terms of long-term cycling stability and rate capability. An anode prepared with FeCoS₂ ⊂ NSC-7001 nanocomposite exhibited significantly improved sodium-ion storage performance, where a large reversible charging capacity of 310.4 mAh·g^-1 was obtained after 300 cycles at a current density of 0.1 A·g^-1. Even when such an anode was cycled at a current density of 5 A·g^-1, a reversible specific charging capacity of 146.0 mAh·g^-1 can still be achieved, showing excellent electrochemical sodium storage performance.