Ti-substituted tunnel-type Na₀.₄₄MnO₂ oxide as a negative electrode for aqueous sodium-ion batteries.

Yuesheng Wang,Ruimin Qiao,Xiao-Qing Yang,Byungju Lee,Zhenzhong Yang,Xiqian Yu,Xuejie Huang,Shuyin Xu,Yong-Sheng Hu,Kisuk Kang,Jue Liu,Hong Li,Liquan Chen,Lin Gu,Wanli Yang

doi:10.1038/ncomms7401

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.

Highlights

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
Major diffraction peaks can be indexed with space group of Pbam. (Note that some minor impurities were found in some substituted samples, which we were unable to index.)[38] Lattice parameter evolution of Na0.44[Mn1-xTix]O2 (x 1⁄4 0.17, 0.22, 0.34, 0.39, 0.56) is shown in Supplementary Table 1
The morphology of the sample was revealed as a rod-like shape with a length of ca. 10 mm and a diameter of ca. 1 mm by scanning electron microscopy (SEM) observation as shown in the Supplementary Fig. 2

Summary

Introduction

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. 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. 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. Renewable energies such as solar and wind powers are being developed rapidly these days, critically demanding the development of large-scale energy storage in order to smooth the integration of their energies into the grid and improve the grid’s reliability. The site occupancy of substituted Ti in the crystal structure is clearly demonstrated on an atomic scale and the sodium storage mechanism is revealed by multiple advanced characterization techniques

Methods

Results

Conclusion