title: Direct atomic-scale confirmation of three-phase storage mechanism in Li₄Ti₅O₁₂ anodes for room-temperature sodium-ion batteries.
abstract: Room-temperature sodium-ion batteries attract increasing attention for large-scale energy storage applications in renewable energy and smart grid. However, the development of suitable anode materials remains a challenging issue. Here we demonstrate that the spinel Li4Ti5O12, well-known as a 'zero-strain' anode for lithium-ion batteries, can also store sodium, displaying an average storage voltage of 0.91 V. With an appropriate binder, the Li4Ti5O12 electrode delivers a reversible capacity of 155 mAh g(-1) and presents the best cyclability among all reported oxide-based anode materials. Density functional theory calculations predict a three-phase separation mechanism, 2Li4Ti5O12+6Na(+)+6e(-)↔Li7Ti5O12+Na6LiTi5O12, which has been confirmed through in situ synchrotron X-ray diffraction and advanced scanning transmission electron microscope imaging techniques. The three-phase separation reaction has never been seen in any insertion electrode materials for lithium- or sodium-ion batteries. Furthermore, interfacial structure is clearly resolved at an atomic scale in electrochemically sodiated Li4Ti5O12 for the first time via the advanced electron microscopy.
authors.affiliation: Key Laboratory for Renewable Energy, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Sun
authors.forename: Liang
authors.initials: L
authors.lastname: Zhao
authors.forename: Huilin
authors.initials: H
authors.lastname: Pan
authors.forename: Xia
authors.initials: X
authors.lastname: Lu
authors.forename: Lin
authors.initials: L
authors.lastname: Gu
authors.forename: Yong-Sheng
authors.initials: YS
authors.lastname: Hu
authors.forename: Hong
authors.initials: H
authors.lastname: Li
authors.forename: Michel
authors.initials: M
authors.lastname: Armand
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Ikuhara
authors.forename: Liquan
authors.initials: L
authors.lastname: Chen
authors.forename: Xuejie
authors.initials: X
authors.lastname: Huang