In Situ TEM Investigation of Electron Irradiation Induced Metastable States in Lithium-Ion Battery Cathodes: Li2FeSiO4 versus LiFePO4

Energy storage and conversion in Li-ion batteries involve dynamic Li storage and transport through a series of electrochemical metastable states (or quasi-equilibrium configuration). Therefore, an investigation of these metastable states is helpful to fully understand the lithium storage mechanism. An accurate understanding of the storage mechanism is a key factor in the design and optimization of the next-generation high-performance batteries. Here, we report the results obtained from electron irradiation-induced phase transitions in Li2FeSiO4 and LiFePO4 by electron microscopy. During prolonged irradiation, the crystalline Li2FeSiO4 particles experienced a transition from a monocrystalline structure to an amorphous phase, with a subsequent recrystallization process (monoclinic to orthorhombic phase). The fine structure of the electron energy loss (ELNES) spectra showed the electron beam-sensitive characteristic of Li2FeSiO4 that included the electron beam-induced mass loss (composition changes), formati...