Incorporation of Bimetallic Sulfide with Carbon Nitride for Advanced Na-Ion Batteries

Sodium-ion batteries (SIBs) have received tremendous attention owing to their low cost, high working voltages, and energy density. However, the design and development of highly efficient SIBs represent a great challenge. Here, a unique and reliable approach is reported to prepare carbon nitride (CN) hybridized with nickel iron sulfide (NFCN) using simple reaction between Ni-Fe layered double hydroxide and dithiooxamide. The characterization results demonstrate that the hybridization with optimal amount of CN induces local distortion in the crystal structure of the hybrid, which would benefit SIB performance. Systematic electrochemical studies with a half-cell configuration show that the present hybrid structure exhibits a promising reversible specific capacity of 348 mAh g^-1 at 0.1 A g^-1 after 100 cycles with good rate capability. Simulation result reveals that the iron atoms in nickel iron sulfide act as a primary active site to accommodate Na⁺ ions. At last, with a full cell configuration using NFCN and Na₃V₂(PO₄)₂O₂F as the anode and cathode, respectively, the specific capacity appears to be ≈95 mAh g^-1 after 50 cycles at 0.1 A g^-1 condition. This excellent performance of these hybrids can be attributed to the synergistic effect of the incorporated CN species and the high conductivity of nickel-iron sulfide.