Nanoflake-Assembled Hierarchical Na₃V₂(PO₄)₃@C Microspheres for Ultrafast and Highly Durable Sodium Storage

The Na superionic conductor (NASICON)-type Na 3 V 2 (PO 4 ) 3 (NVP) is considered a potential commercial cathode for sodium ion batteries (SIBs) owing to its distinctive open 3D framework. However, NVP exhibits an unsatisfactory capacity at high rates and long-cycle instability due to its poor intrinsic conductivity. Herein, hierarchical flower-like NVP microspheres are synthesized via solvothermal reactions and subsequent annealing. The microsphere surface is coated with a dense and highly conductive carbon layer through the addition of polyvinylpyrrolidone (PVP). The cathode demonstrates exceptional cycling stability, maintaining a discharge capacity of 84.3 mA h g –1 over 10 000 cycles at 40 C. Despite functioning as an anode, it maintains a 55.9 mA h g –1 discharge capacity at 10 C, demonstrating remarkable stability with negligible capacity degradation even after undergoing approximately 2000 cycles. Additionally, the symmetrical NVP-based full battery displays a discharge capacity of 63.2 mA h g –1 at 4 C even after 200 stable cycles. It is evident that this study further accelerates the development of electrodes for ultrafast and highly durable SIBs.