A NaSICon-type phosphate Fe1.5V2(PO4)3/C (FVP/C) was successfully prepared and its crystal structure and electrochemical performance as a negative electrode material for lithium-ion batteries (LIBs) were investigated. The material was synthesized via a sol-gel method and calcined at 800 °C under inert atmosphere. The obtained powder crystallized in the triclinic system with P-1 space group. The structure contains two types of dioctahedral edge-sharing V2O10 groups, while distorted Fe(1)O6 octahedra and trigonal bipyramid Fe(2)O5 were evidenced. The electrochemical performance of FVP/C versus Li+/Li were evaluated in 0.01–3.0 V voltage range. FVP/C exhibited a conversion mechanism and showed good reversible capacities at both high and low rates. The discharge capacities of 463, 307 and 311 mAh g−1 were delivered at 1C, 2C, and 5C after 100 cycles. Moreover, the lithiation/delithiation mechanism in FVP/C was evidenced by Operando diffraction using synchrotron radiations and Ex situ XPS spectroscopy, conforming the amorphization of the studied phosphate and revealing that both vanadium and iron are involved in the redox process upon cycling.