Stress‐Induced Dual‐Carbon Coating of Na ₃ V ₂ (PO ₄ ) ₂ F ₃ Cathode for Sodium‐Ion Batteries

Na ₃ V ₂ (PO ₄ ) ₂ F ₃ (NVPF) has emerged as a promising candidate for SIBs cathode, but faces severe challenges, primarily due to fluorine loss and phase instability. These issues result in the formation of undesirable phases, such as Na ₃ V ₂ (PO ₄ ) ₃ and VF ₃ , which significantly alter the electrochemical behavior of NVPF by the presence of low‐voltage plateaus (≈3.4 V). Herein, a polytetrafluoroethylene (PTFE)‐assisted sintering method that mitigates these issues is demonstrated, enabling the synthesis of phase‐pure NVPF. PTFE plays a key role in this process: its viscoelastic properties induce internal stress to suppress fluorine volatilization, while its decomposition compensates fluorine loss and facilitates the formation of another carbon layer. The optimized NVPF‐4%P cathode delivers impressive capacities of 119 and 101.7 mAh g ⁻¹ at 0.5 and 50 C, respectively, and exhibits a long lifespan of 500 cycles with 82.1% capacity retention at 10 C. Additionally, in a full‐cell configuration paired with a NaTi ₂ (PO ₄ ) ₃ anode, the system still presents excellent electrochemical performance and its potential for high‐power applications. These results demonstrate that the PTFE‐assisted dual‐carbon coating not only mitigates fluorine loss but also ensures excellent electrochemical performance, providing a promising route for the development of high‐performance SIBs cathode materials.