Prussian Blue Analogue-Derived Cobalt Sulfide Nanoparticles Embedded in N/S-Codoped Carbon Frameworks as a High-Performance Anode Material for Sodium-Ion Batteries

Metal sulfides display considerable theoretical capacities as anode materials in sodium-ion batteries (SIBs), but their application is limited by their large volume expansion, sluggish charge-transfer kinetics, and poor cycling performances. In this study, unlike the traditional coprecipitation method to prepare the Prussian blue analogue (PBA), PBA with a tremella-like microflower structure is first synthesized by the hydrothermal method under the synergistic effect of trisodium citrate dihydrate (TSC, Na(3)C(6)H(5)O(7)middot2H(2)O) and K-3[Co(CN)(6)], and two kinds of cobalt sulfide nanoparticles embedded in N/S-codoped carbon frameworks (namely, Co3S4@C-N/S and Co9S8@C-N/S) are successfully synthesized by a subsequent solid sulfidation process. Herein, N/S-codoped carbon frameworks improve the electronic conductivity and provide more active sites for sodium storage. As the anode material in SIBs, the Co3S4@C-N/S 1.8-based anode exhibits an excellent initial charge/discharge specific capacity of 685.3/745.2 mAh g(-1) with a high initial Coulombic efficiency of 91.97% at 0.1 A g(-1) and a superior cycling performance (599.1 mAh g(-1) in the 600th cycle at 1 A g(-1) with a capacity retention of 89.4%). However, the Co9S8@C-N/S 1.8-based anode also delivers considerable initial Coulombic efficiency (86.1% at 0.1 A g(-1)) with high cycling stability (391.9 mAh g(-1) even in the 1200th cycle at 2 A g(-1) with a capacity retention of 78.1%). This study provides a material synthesis route for high-performance anode materials used in SIBs and other alkali metal-ion batteries.