Using Howardevansite Framework Adaptivity to Explore the Li2O-Fe2O3-V2O5 Phase Diagram.

An iron vanadate in the Li2O-Fe2O3-V2O5 ternary phase diagram was successfully synthesized by using β-Cu3Fe4(VO4)6 framework adaptivity. The three Cu2+ ions in Howardevansite β-Cu3Fe4(VO4)6 were substituted by 1.5 Li+ and 1.5 Fe3+ to form Li1.5Fe5.5(VO4)6. The structure was determined based on single-crystal X-ray diffraction data, which showed that it crystallizes in the triclinic P1̅ space group. The structure consists of zigzag chains formed of iron octahedra and distorted trigonal bipyramids running along the [10-1] direction and connected into a 3D framework by the VO4 tetrahedra. The framework can accommodate Li+ ions. Magnetic susceptibility revealed the presence of high spin Fe3+ ions in the material. Li1.5Fe5.5(VO4)6 was tested in electrochemistry and can reversibly insert up to 5.5 Li+ ions, with a theoretical capacity of 146 mA h/g, making it a suitable insertion positive electrode material. During galvanostatic discharge, a maximum capacity of 128 mA h/g and a reversible capacity of 78 mA h/g were obtained after 100 cycles at C/10.