Ion transport through carbon nanotubes enable highly crystalline Na₃V₂(PO₄)₂F₃ cathode for ultra-stable sodium-ion storage

Highly crystallized Na₃V₂(PO₄)₂F₃ (NVPF) is desired for high-performance sodium-ion battery cathode material. However, the slow growth-rate induced by lack of multi-ion-transport pathway during sol-gel synthesis process makes it especially difficult to produce NVPF cathode with high crystallinity. Herein, we find that the presence of carbon nanotube (CNT) can significantly promote the ion transport during synthesis, which drastically increases the NVPF crystallinity. The CNT assisted synthetic route produces quality cathode material with high structural stability and electronic conductivity. As expected, the optimal NVPF cathode with trace CNT (0.1%) delivers favorable rate performance of 113.7 and 96.0 mAh g⁻¹ at 1 and 20 C-rate, respectively, and impressive cycling stability up to 5000 cycles with a high-capacity retention of 77.3%. Furthermore, kilogram-scale produced NVPF@CNT cathode showed excellent adaptability in NVPF@CNT-1 || NaTi₂(PO₄)₃ full-cell with high-rate capability and cycling stability. This work provides a practicable and simple strategy to fabricate highly crystallized electrode materials for commercial applications.