Unraveling the Function Mechanism of N-Doped Carbon-Encapsulated NaV(PO) Cathode toward High-Performance Sodium-Ion Battery with Ultrahigh Cycling Stability.

The NASICON-type NaV(PO) (NVP) is recognized as a potential cathode material for Na-ion batteries (SIBs). Nevertheless, its inherent small electronic conductivity induces limited cycling stability and rate performance. Carbon coating, particularly N-doped carbon, has been identified as an effective strategy to address these challenges. Hence, N-doped carbon-coated NVP was successfully produced by a straightforward high-temperature solid-phase method, and the mechanism of N-doped carbon coating in regulating the electrochemical kinetics of NVP was unraveled. The N-doped carbon layer establishes a robust conductive network that interconnects the active particles, facilitating electron transfer within the electrode. SEM images after cycling show that the uniform carbon coating mitigated NVP agglomeration, thereby reducing undesired side reactions between electrode and electrolyte. The discharge capacities of NVP/N-C2 electrodes at 0.1, 0.2, 0.5, 1, 2, 5, and 10 reach 116.0, 114.6, 112.6, 111, 108.7, 104.2, and 99.4 mAh g, respectively. Even at 20, the discharge capacity remains up to 92.2 mAh g, which is approximately 80% of the discharge capacity at 0.1. When the rate returns to 0.1, the NVP/N-C2 cathode still exhibits a discharge capacity of 115.9 mAh g, showing excellent electrochemical reversibility. This study presents a viable approach for fabricating NVP with a N-doped carbon coating, showcasing enhanced sodium storage properties.