Ultra-High-Rate Na₃V(PO₃)₃N Cathode with Superior Stability for Fast-Charging Sodium-Ion Batteries

There is an increasing demand for fast-charging Na-ion batteries (SIBs), which requires the battery to be fully charged within a short time and still possess a large capacity. Such properties are commonly determined by the transport of electrons and ions in the electrodes, and a stable structure is also needed. Na3V(PO3)3N is found to have high sodium diffusion coefficients and a small volume change during sodium intercalation/extraction, making it a promising high-rate and fast-charging cathode. However, these intriguing features are unknown yet due to its inferior reaction kinetics. In this work, Na3V(PO3)3N is synthesized by a sol–gel method for the first time, and a carbon nanotube (CNT)-wrapped carbon-coated Na3V(PO3)3N (NVPN/C@CNT) composite structure is constructed. Impressively, the NVPN/C@CNT material shows 70.0% of the theoretical capacity at an ultra-high rate of 50C. The excellent fast-charging property of NVPN/C@CNT is also identified from 1C to 5C. Ex situ X-ray diffraction (XRD) demonstrates that the crystal phase and parameters of the NVPN unit cell remain stable even under a high charging rate, which is the key to the remarkable capability of fast charging. The galvanostatic intermittent titration technique (GITT) and pseudocapacitance calculation are also employed to understand the reaction and kinetics.