| 저자(한글) |
Asakura, Daisuke,Hosono, Eiji,Niwa, Hideharu,Kiuchi, Hisao,Miyawaki, Jun,Nanba, Yusuke,Okubo, Masashi,Matsuda, Hirofumi,Oshima, Masaharu,Harada, Yoshihisa |
| 초록 |
Improving the energy density and power density of electrode materials for Li-ion batteries (LIBs) is highly important to further develop electric and hybrid-electric vehicles. For the improvements, understanding the charge-discharge mechanisms from a viewpoint of the electronic structure is indispensable. Recently, electronic-structure analyses of the electrode materials using soft x-ray spectroscopy have been of particular importance. In this study we demonstrate operando Mn L 3 soft x-ray emission spectroscopy (XES) for LiMn 2 O 4 [1] which is a typical cathode material of LIB. We developed an operando cell consisting of the LiMn 2 O 4 cathode, a counter electrode and an electrolyte solution [2] by modifying the in situ cell for fuel cell catalysts [3]. The charge-discharge experiments were performed by cyclic voltammetry. The operando XES experiments were carried out using ultrahigh-resolution x-ray emission spectrometer [4] at BL07LSU of SPring-8. The XES spectra were analyzed by theoretical analyses based on the configuration-interaction full-multiplet (CIFM) calculation [5-7]. In the operando Mn L 3 XES study for LiMn 2 O 4 , we revealed that the open-circuit voltage (OCV) state is almost the same as the initial state consisting of the Mn 3+ and Mn 4+ states. For the charged state, the Mn L 3 XES spectrum largely changed corresponding to the oxidation of Mn 3+ to Mn 4+ state at the Mn 3+ site for the OCV. The spectrum for the discharged state almost returned to the spectrum for the OCV, while the small difference indicates that the Mn 3+ state is slightly enhanced for the discharged state. Thus, the Mn 3 d electronic states were reversibly changed for the charge-discharge process [2]. Moreover, charge-transfer (CT) effects between the Mn 3 d and O 2 p orbitals for each valence state were clarified. For the Mn 4+ state, a negative CT energy was determined by the CIFM calculation, suggesting a very strong CT effect from the O 2 p to Mn 3 d orbitals. In the presentation, XES and soft X-ray absorption spectroscopy studies for other electrode materials will also be reported, and the relationship between the electronic structure and electrochemical performance will be discussed. References [1] M. M. Thackeray, Prog. Solid St. Chem. 25 , 1 (1997). [2] D. Asakura et al ., Electrochem. Commun. 50 , 93 (2015). [3] H. Niwa et al ., Electrochem. Commun. 35 , 57 (2013). [4] Y. Harada et al ., Rev. Sci. Instrum. 83 , 013116 (2012). [5] Y. Nanba et al ., J. Phys. Chem. C 116 , 24896 (2012). [6] Y. Nanba et al ., Phys. Chem. Chem. Phys. 16 , 7031 (2014). [7] D. Asakura et al ., J. Phys. Chem. Lett. 5 , 4008 (2014). |
