Zero-Strain Na₃ V₂ (PO₄ )₂ F₃ @Rgo/CNT Composite as a Wide-Temperature-Tolerance Cathode for Na-Ion Batteries with...

Sodium-ion batteries (SIBs) are widely considered a hopeful alternative to lithium-ion battery technology. However, they still face challenges, such as low rate capability, unsatisfactory cycling stability, and inferior variable-temperature performance. In this study, a hierarchical Na₃ V₂ (PO₄ )₂ F₃ (NVPF) @reduced graphene oxide (rGO)/carbon nanotube (CNT) composite (NVPF@rGO/CNT) is successfully constructed. This composite features 0D Na₃ V₂ (PO₄ )₂ F₃ nanoparticles are coated by a cross-linked 3D conductive network composed of 2D rGO and 1D CNT. Furthermore, the intrinsic Na⁺ storage mechanism of NVPF@rGO/CNT through comprehensive characterizations is unveiled. The synthesized NVPF@rGO/CNT exhibits fast ionic/electronic transport and excellent structural stability within wide working temperatures (-40-50 °C), owing to the zero-strain NVPF and the coated rGO/CNT conductive network that reduces diffusion distance for ions and electrons. Moreover, the stable integration between NVPF and rGO/CNT enables outstanding structural stability to alleviate strain and stress induced during the cycle. Additionally, a practice full cell is assembled employing a hard carbon anode paired with an NVPF@rGO/CNT cathode, which provides a decent capacity of 105.2 mAh g^-1 at 0.2 C, thereby attaining an ideal energy density of 242.7 Wh kg^-1 . This work provides valuable insights into developing high-energy and power-density cathode materials for SIBs.