Boosting sodium-storage properties of hierarchical Na3V2(PO4)3@C micro-flower cathodes by tiny Cr doping: The effect of “four ounces moving a thousand pounds”

Na 3 V 2 (PO 4 ) 3 (NVP), as a great potential cathode candidate for Na-ion batteries (NIBs), has attracted enormous interest due to its three-dimensional (3D) large open framework for convenient Na + transport, yet its practical application is still limited by its inferior electron conductivity and sluggish Na + diffusion kinetics. Herein, the tiny Cr doped hierarchical NVP micro-flower cathodes (i.e., Na 3 V 2− x Cr x (PO 4 ) 3 @C, x ≤ 0.1), which are self-assembled with single-crystal nanoflake subunits in-situ coated with carbon nano-shell, are designed and fabricated via a scalable avenue. The optimized cathode, i.e., Na 3 V 1.94 Cr 0.06 (PO 4 ) 3 @C (NVCP-6), was endowed with more electro-active Na(2) sites and higher electronic/ionic conductivity for efficient sodium storage. Benefiting from these competitive merits, the NVCP-6, when evaluated as a cathode towards NIBs, exhibits an ultrahigh-rate capability of 99.8 mAh·g −1 at 200 C and superior stability of 82.2% over 7300 cycles at 50 C. Furthermore, the NVCP-6 based full NIBs display remarkable electrochemical properties in terms of both high-rate capacities and long-duration cycling properties at different temperatures (−20–50 °C). The contribution, i.e., the design of “four ounces can move a thousand pounds”, here will promote the practical industrial application of NVP towards advanced NIBs.