In Situ Raman Study of Phase Stability of α‐Li3V2(PO4)3 upon Thermal and Laser Heating

Monoclinic α-Li3V2(PO4)3 has a complex 3-D metal phosphate framework that provides mobility for all three lithium ions, giving it the highest gravimetric capacity (197 mAh/g) of all the transition-metal phosphates. Along with its high gravimetric capacity, its thermal and electrochemical stability make it of great interest as a cathode material for lithium-ion energy storage devices. Raman spectroscopy has proven to be a unique analytical tool for studying electrode materials of lithium-ion batteries due to its ability to probe structural changes at the level of chemical bonds. In this work, the calculated Raman spectrum of α-Li3V2(PO4)3 provided by density functional theory is presented along with symmetry assignments for all of the calculated and observed modes through Raman microscopy. Furthermore, the phase stability of microcrystalline αLi3V2(PO4)3 was studied as a function of irradiation power density. Follow-up thermal studies confirm that two structural phase transitions, β and γ, occur at elevated temperatures or high irradiation power density before degradation to α-LiVOPO4 under an oxygen-rich atmosphere. Calculated and experimentally determined Raman modes for α-Li3V2(PO4)3 are in good agreement. It is also noted that careful consideration of the irradiation power density employed must be taken into account to prevent misinterpretation of Raman spectral features.