Conductive Ti 3 C 2 T x networks to optimize Na 3 V 2 O 2 (PO 4 ) 2 F cathodes for improved rate capability and low-temperature operation.

Na 3 V 2 O 2 (PO 4 ) 2 F (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 Ti 3 C 2 T x MXene nanosheets with excellent electrical conductivity are introduced to construct an interconnected conductive framework to tightly encapsulate NVOPF nanoparticles. The Ti 3 C 2 T 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/Ti 3 C 2 T 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.