Operando hard X-ray photoelectron spectroscopy of LiCoO2 thin film in an all-solid-state lithium ion battery

• Published in: Electrochemistry communications 2020-09, Vol.118, p.106790, Article 106790
• Main Authors: Kiuchi, Hisao, Hikima, Kazuhiro, Shimizu, Keisuke, Kanno, Ryoji, Toshiharu, Fukunaga, Matsubara, Eiichiro
• Format: Article
• Language: English
• Subjects: All-solid-state battery; Hard X-ray photoelectron spectroscopy; In situ; LiCoO2; Operando; Thin film
• ISSN: 1388-2481; 1873-1902
• DOI: 10.1016/j.elecom.2020.106790

[Display omitted] •Operando HAXPES was developed for the evaluation of an all-solid-state battery.•The electronic structures of all elements exhibited reversible changes.•The Fermi level shift of LiCoO2 occurred during battery charging.•The electronic structure changes of both Co and O of LiCoO2 were observed. A novel electrochemical setup for operando hard X-ray photoelectron spectroscopy (HAXPES) was proposed to investigate the bulk-sensitive electronic structure of cations and anions in the active materials of an all-solid-state Li-ion battery. A model all-solid-state thin film cell was prepared by depositing a LiCoO2 positive electrode and an Al current collector on the front of the solid electrolyte substrate, and a Li3PO4 buffer solid electrolyte and a Li negative electrode on the back side, to give a structure of Al (10 nm)/LiCoO2 (35 nm)/Li1+x+yAlx(Ti, Ge)2−xSiyP3−yO12 (180 μm)/Li3PO4 (500 nm)/Li (1000 nm). The reversible changes of the core levels (Al 1s, P 1s, Li 1s, Co 2p3/2, O 1s) and the valence bands in the charged (4.2 V)/discharged (3.0 V) states were observed without disassembling the LiCoO2 thin film cell inside the vacuum chamber. The operando HAXPES spectra acquired during the charge–discharge process revealed that the reversible changes in the Co 2p3/2 and O 1s spectra were attributed to the participation of cobalt cations and oxygen anions from LiCoO2 in the redox mechanism.