Research Update: Retardation and acceleration of phase separation evaluated from observation of imbalance between structure and valence in LiFePO4/FePO4 electrode
Kazuya Tokuda,
Tomoya Kawaguchi,
Katsutoshi Fukuda,
Tetsu Ichitsubo,
Eiichiro Matsubara
Affiliations
Kazuya Tokuda
Department of Materials Science and Engineering, Kyoto University, Kyoto 606-8501, Japan
Tomoya Kawaguchi
Department of Materials Science and Engineering, Kyoto University, Kyoto 606-8501, Japan
Katsutoshi Fukuda
Office of Society-Academia Collaboration for Innovation, Kyoto University, Kyoto, 615-8520, Japan
Tetsu Ichitsubo
Department of Materials Science and Engineering, Kyoto University, Kyoto 606-8501, Japan
Eiichiro Matsubara
Department of Materials Science and Engineering, Kyoto University, Kyoto 606-8501, Japan
LiFePO4 is a potential positive electrode material for lithium ion batteries. We have experimentally observed an imbalance between the valence change of Fe ions and the structure change from the LiFePO4 phase to the FePO4 phase during delithiation by simultaneous in situ XRD and XANES measurements in an LiFePO4/FePO4 electrode. The ratio of structure change to valence change clearly indicates that the phase separation from LiFePO4 to FePO4 is suppressed at the beginning of delithiation, while it is accelerated at the latter stage, which is due to the coherent strain caused by the lattice misfit between the two phases.
