The Structure–Property Investigation of Bi_1–<i>x</i>Ce_<i>x</i>FeO₃ (<i>x</i> = 0, 0.05)–Li Battery: <i>In Situ</i> XRD and XANES Studies

BiFeO₃ and Bi_0.95Ce_0.05FeO₃ were synthesized via a coprecipitation technique. During the synthesis process, the phase transitions were monitored via <i>in situ</i> synchrotron X-ray diffraction (XRD). The Ce addition increased the formation temperature of BiFeO₃ phase, while greatly suppressed the particle size growth. Ce_0.05Bi_0.95FeO₃ was further employed for lithium battery application, and good electrochemical cycling performance was observed between 1.15 and 3.0 V. Ce addition not only increased the discharge capacity but also displayed 0.15 V higher discharge voltage (in the second cycle), compared with BiFeO₃. After 2 Li ions insertion, Bi ions are reduced to metallic Bi and separated out of the perovskite lattice. In the following charge process, metallic Bi can be oxidized back to its ionic state. Elevated discharge voltage was observed in the second discharge process. <i>a</i>/<i>b</i>-axis lattice parameters are mainly changed by Li intercalation/deintercalation, and <i>c</i>-axis lattice parameters are heavily affected by the ionic species in the <i>c</i>-axis. There are two distinct conduction pathways: one is the ionic conduction along the <i>a</i>/<i>b</i>-plane, and the other is the electronic conduction along the <i>c</i>-axis