Oxygen Reduction Contributing To Charge Transfer During The First Discharge Of The Ceo2-Bi2fe4o9-Li Battery: In Situ X-Ray Diffraction And X-Ray Absorption Near-Edge Structure Investigation

Since pioneering work performed by Rouxel et al. that emphasizes the effects of anions in the ionic intercalation process, the role of oxygen ions in lithium ionic battery electrodes is of great interest since it will give new directions to further enhance the battery capacity. In this paper, Bi2Fe4O9-CeO2 was synthesized and was used as an anode for second lithium batteries application. A large amount of oxygen vacancies exist in both CeO2 and Bi2Fe4O9. In CeO2, oxygen vacancies are mainly located at the 111 plane, and in Bi2Fe4O9, oxygen vacancies are mainly located at the 002 plane. Li+ insertion into Bi2Fe4O9 produced high spin tetrahedral Fe2+, which is Jahn-Teller active and induces shrinkage of the Bi2Fe4O9 lattice and releases O-2. The released O-2 is further reduced and contributes to similar to 70 mAh/g during the first discharge process. The 002 plane of Bi2Fe4O9 is very reactive for oxygen reduction, where there are not only a lot of oxygen vacancies but also tetrahedral Fe3+ ions participating in producing more oxygen vacancies. This work gives new directions for future design of lithium battery electrodes, which can reversibly evolve/reduce O-2, and the O-2/O2- (or O-) redox couple is responsible for charge transfer.