Preparation and performances of ferric sodium silicate coated with nitrogen-doped carbon for sodium-ion batteries based on solid-phase method

As a cathode material in sodium-ion batteries with great potential, Na₂FeSiO₄ has drawn enormous attention due to its low cost and high theoretical capacity. However, the low electronic conductivity greatly restricts its practical application which can be blamed on the mutual isolation of tetrahedrons. Herein, C222₁-Na₂FeSiO₄/nitrogen-doped carbon (NFS/CN) composites were fabricated via the simple solid-state method with urea as the nitrogen source. The nitrogen atoms introduce more defects and develop the electronic structure while ensuring the stability of the carbon layer, which promotes electronic mobility. This cathode shows a high reversible capacity of 134.06 mAh·g⁻¹, and the initial Coulomb efficiency can reach 84.95%. The capacity of NFS/CN-2 is up to 82.7 mAh·g⁻¹ after 50 cycles at the current density of 0.1 C. Furthermore, the structural rearrangement during the first cycle was observed via the ex situ XRD, and the space group was transformed from C222₁ to Pb2₁a. This work exploits a new path for the industrial application of high-capacity cathode materials for rechargeable batteries.