Ultrafine Na3V2(PO4)3@C with boosted interfacial charge transfer kinetics for low-temperature (-40 °C) Na-ion battery

Energy storage devices with good temperature-dependent performance is stringently needed due to the growing energy demand. The abundant sodium reservoir and smaller Stokes diameter of Na+ make sodium ion batteries (SIBs) promising alternative to lithium-ion batteries for commercial application. Nevertheless, the large ionic radius of Na+ brings challenges to ion insertion/extraction kinetics and structural stability of electrode materials, especially at low temperatures. In this study, ultrafine Na3V2(PO4)(3)@C core-shell nanorod structure (NVP@C-CS-Nanorod), in which NVP with a diameter of 5 nm is the core and a 3 nm thick carbon layer with ordered graphitic lattice acts as the shell, is efficiently prepared by a microwave-mediated surfactant-free method. Glycerol is the only morphology tuning reagent and carbon source. NVP precursor and glycerol concentrations as well as the heating temperature and mode are key factors affecting the molecular self-assembly to guide the formation of the ultrafine core-shell morphology. The product maintains 71 mA h g(-1) (similar to 86 % capacity retention) after 200 cycles at 1 C and -40 degrees C. As demonstrated by theoretical calculations, the superior low-temperature performance is derived from the lowered activation energy of Na migration through cross-linked interfaces between the ultrafine NVP nanorod and graphitized carbon shell.