In-situ XAFS measurements of amorphous Li3PO4-doped V2O5 cathode for all-solid-state thin-film Li-ion batteries

(VO-LPO) cathode in an all-solid-state thin-film lithium-ion battery to observe the behavior of Li ions during charge/discharge. The thin-film lithium-ion battery was fabricated by sputtering deposition and consisted of an amorphous multilayer structure with VO-LPO, LiPON, and Si as cathode, electrolyte, and anode, respectively. In X-ray absorption near edge structure (XANES) measurements, the energy shift of the Vanadium K-edge indicated that the valence of V changed from 4.64 to 5.11 in the cathode during charge/discharge processes. This result indicates that Li ions were removed and inserted into the amorphous VO-LPO cathode layer. The pre-edge peak intensity also increased during charging and decreased during discharging. Additionally, extended X-ray absorption fine structure (EXAFS) measurements indicated that the V-O bond distance shifted during charge/discharge process. From these measurements, we clearly observed that the coordination symmetry and structure around V in the amorphous VO-LPO cathode changed with the charge/discharge reaction.