Abstract
BiFeO3 was studied as electrode material for lithium battery applications. The voltage profile of BiFeO3 vs Li battery displays three discharge plateaus around 1.3, 0.7 and 0.4 V (vs Li/Li+) and the first discharge capacity is about 1000 mAh/g, with a cutoff voltage of 0.05 V. If the cutoff voltage is limited to 0.7 V, much better capacity retention is achieved. The structural changes of BiFeO3 during electrochemical cycling process were investigated using synchrotron-based in situ XRD and XANES. Lithium ions were inserted into BiFeO3 during the discharge process. The whiteline of Bi LIII-edge XANES spectra gradually decreased during the discharge process with their LIII edge position concomitantly shifted towards lower energy position. However, the Fe K-edge XANES spectrum of the fully discharged product is similar to that of the pristine one and displays no shifts. This indicates that Bi ions are responsible for charge transfer during the electrochemical cycling process. The reduction of Bi3+ to Bi0 as the gradual insertion of Li ions, is a three-step reduction process. Li2Bi alloy formation was observed at the end of the discharge process, which is not fully reversible towards lithium intercalation/extraction and decomposes to metallic Bi.
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