Solid State Self-Assembly of Flaky NaV(PO)@Carbon into Spherical Superstructures: Large Production and Boosted Low-Temperature Na Storage Capability.

The application of secondary batteries at wide temperature ranges, particularly at low temperatures (LT), becomes a hotspot in the energy storage field. NaV(PO) (NVP) emerges as a prospective cathodic material for LT sodium-ion batteries (SIBs) due to its robust structure and fast Na-ion transportation. However, conventional NVP electrode materials are hindered by inferior intrinsic electronic conductivity and interfacial deterioration at LT, leading to unsatisfactory rate capability and service life. To address these challenges, a solid state self-assembly of flaky NaV(PO)@carbon into spherical superstructure composite (denoted as SS-NVP@C) is developed, which serves as the cathode for ultra-low temperature (-40 °C) SIBs. Owing to the robust self-assembly spherical superstructures with boosted electronic transfer and fast Na-ion transportation, the SS-NVP@C cathode demonstrates excellent rate performance and prolonged cyclability, especially pragmatical LT adaptability including specific capacity of 92 mA h g at 0.1C, brilliant rate capability of 51 mA h g at 5C, and remaining 84.8% capacity retention over 400 cycles at 0.2C. Furthermore, the growth mechanism of SS-NVP@C is fully investigated, providing a novel manner for the materials design and large-scale production of advanced electrode materials for LT energy storage.