ReductiveCarbonas an Additive Enables the High Capacityand Durability of NASICON Structured Sodium-Ion Batteries

Sodium-ion batteries are gaining attention for their lower cost, higher earth abundance, improved safety, and wider distribution compared to lithium-ion batteries. Among the promising cathode materials, the vanadium-free sodium superionic conductor (NASICON) stands out due to its sustainability, low cost, and excellent rate performance. Notably, Na₃MnTi(PO₄)₃ WC offers the potential for three-electron reactions, increasing its capacity. However, its application is limited by poor ionic conductivity and the lack of scalable, low-cost synthesis strategies. Additionally, the degradation mechanisms over long-term cycling remain unclear, with no effective solutions to improve durability. Here we report a facile synthesis method using reductive carbon, which enhances both the capacity and long-term cycling performance. The introduced carbon reduces particle size, improving sodium ion diffusion pathways and electronic conductivity. As a result, the assembled coin cell achieved a specific capacity of 123 mAh g^–1 at 0.1C, with 92% capacity retention at 2C after 1000 cycles. Analysis revealed that carbon prevents manganese oxidation during synthesis, supporting better sodium ion intercalation and deintercalation kinetics. Additionally, the carbon layer helps prevent the leaching of transition metal ions, ensuring a stable cycling performance. This approach provides an efficient strategy to improve the electrochemical performance and durability of Na₃MnTi(PO₄)₃ WC, advancing its use in sodium-ion batteries.