Study on structure and electrochemical properties of carbon-coated monoclinic Li3V2(PO4)3 using synchrotron based in situ X-ray diffraction and absorption

• Phase transition mechanism of Li3V2(PO4)3 cathode material has been analyzed by in situ XRD.
• Redox processes of Li3V2(PO4)3 cathode material has been analyzed by in situ XAS.
• The structural changes and their relationship with electrochemical properties of Li3V2(PO4)3 cathode material has been explained.

Monoclinic Li3V2(PO4)3, is a highly promising cathode material for lithium–ion rechargeable batteries. It has good ion mobility and high lithium capacity due to its ability to reversibly extract all three lithium ions. Here, we present, a systematic investigation of phase transitions and volume variations that occur during lithium extraction from the carbon-coated monoclinic phase of Li3V2(PO4)3 by synchrotron based in situ X-ray diffraction and X-ray absorption spectroscopy. This monoclinic Li3V2(PO4)3 illustrates complex behavior of four successive two-phase transitions upon extraction of all three lithium ions between 3.0 and 4.8 V vs. Li/Li+. Each XRD pattern of the intermediate compositions can be fully indexed in the monoclinic space group P21/n, with net volume reduction of 6.47%. In situ V K-edge XANES in combination with study of structural parameters is applied to find the vanadium valence state at plateau regions, which highlights the variations in electrochemical potential constraining to extraction of lithium ion from different crystal sites.