Interface-Controlled Rhombohedral Li3V2(PO4)3 Embedded in Carbon Nanofibers with Ultrafast Kinetics for Li Ion Batteries.

We here present a unique composite assembly of rhombohedral Li3V2(PO4)3 and carbon nanofiber, which simultaneously facilitates Li ion transport as well as electron transfer. For the synthesis of this composite, the inorganic precursors were confined in electron-spun nanofibers and then, through controlled annealing, Na3V2(PO4)3 particulates were grown with controllable crystallite size and partially embedded into carbon nanofibers with precisely controlled diameter. The rhombohedral Li3V2(PO4)3 could be successfully obtained by ion exchange from Na to Li in the prepared Na3V2(PO4)3. The final rhombohedral Li3V2(PO4)3 particles anchored onto the carbon nanofibers exhibited excellent electrochemical performance with fast kinetics for Li ion batteries. Suprisingly, it maintains 69 mAh/g and 41 mAh/g of capacity even at 100C as cathode and anode. Several advanced characterizations revealed that its high kinetics could be a synergistic effect of the distinctive microstructure of the composite and the structural superiority of highly symmetric rhombohedral Li3V2(PO4)3 over its monoclinic phase for Li ion transport.