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

Monoclinic alpha-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 alpha-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 alpha-Li3V2(PO4)(3) was studied as a function of irradiation power density. Follow-up thermal studies confirm that two structural phase transitions, beta and gamma, occur at elevated temperatures or high irradiation power density before degradation to alpha-LiVOPO4 under an oxygen-rich atmosphere. Calculated and experimentally determined Raman modes for alpha-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.