Synthesis, Structure, Electronic, Ionic, and Magnetic Properties of Li9V3(P2O7)3(PO4)2 Cathode Material for Li-Ion Batteries

Layered monodiphosphate Li9V3(P2O7)(3)(PO4)(2) can be synthesized by direct. reaction using either hydrogen or carbon as the reducing agent at the sintered temperature of 750 degrees C. When the temperature is higher than 800 degrees C, Li9V3(P2O7)(3)(PO4)(2) begins to decompose into Li3V2(PO4)(3) and Li4P2O7. The measurement results of electronic conductivity, magnetization, and electrochemical impedance spectroscopy are reported for the first time. After carbon coating, the electronic conductivity comes to 2.07 x 10(-3) S cm(-1), which is the same order of magnitude as that of carbon-coated LiFePO4 and Li3V2(PO3)(4). Li-ion diffusion coefficient (4.19 x 10(-10) cm(2) s(-1)) for carbon-uncoated Li9V3(P2O7)(3)(PO4)(2) is close to that of LiCoO2 and much higher than that of LiFePO4 center dot Li9V3(P2O7)(3)(PO4)(2) exhibits a paramagnetic behavior in the temperature range of 5-300 K, which is consistent with the result from our X-ray photoelectron spectroscopy analysis where the oxidation state of vanadium is +3 in the Li9V3(P2O7)(3)(PO4)(2) compound. The favorable electronic and ionic properties suggest that Li9V3(P2O7)(3)(PO4)(2) can be a potential cathode material for Li-ion batteries.