In situ Raman spectroscopy of Li CoO2 cathode in Li/Li3PO4/LiCoO2 all-solid-state thin-film lithium battery

Abstract A thin-film battery was fabricated in the structure Li/Li3 PO 4 /LiCoO 2 using pulsed laser deposition technique. The structural changein Lix CoO 2 during battery operation was investigated using in situ Raman spectroscopy. Raman measurements were performed from the front side of the cell beside the lithium anode through the solid electrolyte and from the backside of the cell below the lithium anode through a transparent electrode. The Raman peaks of A 1g and E g modes were observed to shift to lower and higher wavenumbers at around 4 V due to Liextraction and insertion, respectively, according to the structural changebetween H1 and H2 phases of the Lix CoO 2 . The Raman shift for the Lix CoO 2 showed hysteresis during the charging–discharging process when observed from the front side of the cell, although no hysteresis is seen in those measured from the backside. The observed hysteresis is explained as a delay in structural changedue to the chemical diffusion of lithium in the Lix CoO 2 cathode.