title: Ti-substituted tunnel-type Na₀.₄₄MnO₂ oxide as a negative electrode for aqueous sodium-ion batteries.
abstract: The aqueous sodium-ion battery system is a safe and low-cost solution for large-scale energy storage, because of the abundance of sodium and inexpensive aqueous electrolytes. Although several positive electrode materials, for example, Na₀.₄₄MnO₂, were proposed, few negative electrode materials, for example, activated carbon and NaTi₂(PO₄)₃, are available. Here we show that Ti-substituted Na₀.₄₄MnO₂ (Na₀.₄₄[Mn₁-xTix]O₂) with tunnel structure can be used as a negative electrode material for aqueous sodium-ion batteries. This material exhibits superior cyclability even without the special treatment of oxygen removal from the aqueous solution. Atomic-scale characterizations based on spherical aberration-corrected electron microscopy and ab initio calculations are utilized to accurately identify the Ti substitution sites and sodium storage mechanism. Ti substitution tunes the charge ordering property and reaction pathway, significantly smoothing the discharge/charge profiles and lowering the storage voltage. Both the fundamental understanding and practical demonstrations suggest that Na₀.₄₄[Mn₁-xTix]O₂ is a promising negative electrode material for aqueous sodium-ion batteries.
authors: Key Laboratory for Renewable Energy, Beijing Key Laboratory for New Energy Materials and Devices, Laboratory of Advanced Materials and Electron Microscopy, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors: Yuesheng
authors: Y
authors: Wang
authors: Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors: Jue
authors: J
authors: Liu
authors: Department of Materials Science and Engineering, Seoul National University, Seoul 151-742, Republic of Korea.
authors: Byungju
authors: B
authors: Lee
authors: Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors: Ruimin
authors: R
authors: Qiao
authors: Key Laboratory for Renewable Energy, Beijing Key Laboratory for New Energy Materials and Devices, Laboratory of Advanced Materials and Electron Microscopy, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors: Zhenzhong
authors: Z
authors: Yang
authors: Key Laboratory for Renewable Energy, Beijing Key Laboratory for New Energy Materials and Devices, Laboratory of Advanced Materials and Electron Microscopy, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors: Shuyin
authors: S
authors: Xu
authors: Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors: Xiqian
authors: http://orcid.org/0000-0001-8513-518X
authors: X
authors: Yu
authors: Key Laboratory for Renewable Energy, Beijing Key Laboratory for New Energy Materials and Devices, Laboratory of Advanced Materials and Electron Microscopy, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors: Lin
authors: L
authors: Gu
authors: Key Laboratory for Renewable Energy, Beijing Key Laboratory for New Energy Materials and Devices, Laboratory of Advanced Materials and Electron Microscopy, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors: Yong-Sheng
authors: http://orcid.org/0000-0002-8430-6474
authors: YS
authors: Hu
authors: Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors: Wanli
authors: http://orcid.org/0000-0003-0666-8063
authors: W
authors: Yang
authors: Department of Materials Science and Engineering, Seoul National University, Seoul 151-742, Republic of Korea.
authors: Kisuk
authors: K
authors: Kang
authors: Key Laboratory for Renewable Energy, Beijing Key Laboratory for New Energy Materials and Devices, Laboratory of Advanced Materials and Electron Microscopy, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors: Hong
authors: http://orcid.org/0000-0002-8659-086X
authors: H
authors: Li
authors: Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors: Xiao-Qing
authors: XQ
authors: Yang
authors: Key Laboratory for Renewable Energy, Beijing Key Laboratory for New Energy Materials and Devices, Laboratory of Advanced Materials and Electron Microscopy, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors: Liquan
authors: L
authors: Chen
authors: Key Laboratory for Renewable Energy, Beijing Key Laboratory for New Energy Materials and Devices, Laboratory of Advanced Materials and Electron Microscopy, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
authors: Xuejie
authors: X
authors: Huang