In situ time-resolved dispersive X-ray absorption fine structure analysis of BaTiO₃-LiCoO₂ composites for lithium ion batteries

In this study, in situ time-resolved dispersive X-ray absorption fine structure (DXAFS) analysis of BaTiO₃LiCoO₂ (BTLC) composites for lithium ion batteries was performed to characterize the cobalt ion valence shift between oxidized and reduced states of driven cells, in an attempt to better understand the contribution of ferroelectric solid electrolyte interfaces (SEIs) to chargedischarge rates. Two types of artificial SEIs, ferroelectric BT and paraelectric Al₂O₃, were compared. The magnitude of the shift in the X-ray absorption energy at the peak of the white line, E₁, during charging and discharging at a 10C rate, increased in the order of bare LC (0.264 eV) < Al₂O₃ 1 mol% (0.497 eV) < BT 1 mol% (1.15 eV); the corresponding discharge capacities of the laminated cells at 10C were as follows: bare LC (11.6mAh/g) < Al₂O₃ (41.8mAh/g) < BT (95.1mAh/g). The increase in E₁, i.e., the oxidation of Co during charging, intensified under a higher applied potential for the BT-decorated composite compared with that of the Al₂O₃-coated specimen. The stronger oxidation of Co for BTLC under application of a large electric field was attributed to the strengthened polarization due to the larger permittivity of BT.