Nanoflake-Assembled\nHierarchical Na3V2(PO4)3@C Microspheres for Ultrafast\nand Highly Durable Sodium Storage

The Na superionic conductor (NASICON)-type Na3V2(PO4)3 (NVP) is considered a potential\ncommercial cathode for sodium ion batteries (SIBs) owing to its distinctive\nopen 3D framework. However, NVP exhibits an unsatisfactory capacity\nat high rates and long-cycle instability due to its poor intrinsic\nconductivity. Herein, hierarchical flower-like NVP microspheres are\nsynthesized via solvothermal reactions and subsequent annealing. The\nmicrosphere surface is coated with a dense and highly conductive carbon\nlayer through the addition of polyvinylpyrrolidone (PVP). The cathode\ndemonstrates exceptional cycling stability, maintaining a discharge\ncapacity of 84.3 mA h g–1 over 10 000 cycles\nat 40 C. Despite functioning as an anode, it maintains a 55.9 mA h\ng–1 discharge capacity at 10 C, demonstrating remarkable\nstability with negligible capacity degradation even after undergoing\napproximately 2000 cycles. Additionally, the symmetrical NVP-based\nfull 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\nfurther accelerates the development of electrodes for ultrafast and\nhighly durable SIBs.