Highly Reversible Na Storage in Na₃V₂(PO₄)₃ by Optimizing Nanostructure and Rational Surface Engineering

Sodium‐ion batteries (NIBs) have attracted more and more attention as economic alternatives for lithium‐ion batteries (LIBs). Sodium super ionic conductor (NASICON) structure materials, known for high conductivity and chemical diffusion coefficient of Na + (≈10 −14 cm 2 s −1 ), are promising electrode materials for NIBs. However, NASICON structure materials often suffer from low electrical conductivity (<10 −4 S cm −1 ), which hinders their electrochemical performance. Here high performance sodium storage performance in Na 3 V 2 (PO 4 ) 3 (NVP) is realized by optimizing nanostructure and rational surface engineering. A N, B codoped carbon coated three‐dimensional (3D) flower‐like Na 3 V 2 (PO 4 ) 3 composite (NVP@C‐BN) is designed to enable fast ions/electrons transport, high‐surface controlled energy storage, long‐term structural integrity, and high‐rate cycling. The conductive 3D interconnected porous structure of NVP@C‐BN greatly releases mechanical stress from Na + extraction/insertion. In addition, extrinsic defects and active sites introduced by the codoping heteroatoms (N, B) both enhance Na + and e − diffusion. The NVP@C‐BN displays excellent electrochemical performance as the cathode, delivering reversible capacity of 70% theoretical capacity at 100 C after 2000 cycles. When used as anode, the NVP@C‐BN also shows super long cycle life (38 mA h g −1 at 20 C after 5000 cycles). The design provides a novel approach to open up possibilities for designing high‐power NIBs.