Conductive Ti3C2Tx networks to optimize Na3V2O2(PO4)2F cathodes for improved rate capability and low-temperature operation

Abstract

Na₃V₂O₂(PO₄)₂F (NVOPF) is gaining attention as a high-energy cathode candidate for sodium-ion batteries owing to its wide operating voltage, high energy density and excellent thermal stability. However, its intrinsic poor electrical conductivity results in its current sodium-storage performance being far below expectations. Herein, two-dimensional Ti₃C₂T_x MXene nanosheets with excellent electrical conductivity are introduced to construct an interconnected conductive framework to tightly encapsulate NVOPF nanoparticles. The Ti₃C₂T_x nanosheets ensure superior electronic contacts, along with inhibiting the agglomeration of NVOPF nanoparticles, thus accelerating electron and ion transfer during sodium-ion de/intercalation and maximizing the storage capacity. As a result, the optimized NVOPF/Ti₃C₂T_x cathode exhibits high rate capabilities (111 mA h g⁻¹ at 0.2 C and 78 mA h g⁻¹ at 20 C), with an impressively high capacity retention of 74.8% over a wide temperature range (from −20 to 20 °C). Additionally, the assembled sodium-ion full cell provides a highly reversible capacity of 116 mA h g⁻¹ at 1 C, with a capacity retention of 67.2% after 100 cycles. These inspiring results provide new insights for improving the charge-transfer kinetics of the NVOPF cathode and this methodology may be extended to other cathode materials.