Renewable Energy Global Innovations features: Superior Sodium Storage in Na2Ti3O7 Nanotube Arrays through Surface Engineering

Significance Statement

Sodium-ion batteries (SIBs) offer a promising scalable energy storage alternative to current lithium-ion batteries (LIBs). Titanium based SIB anode materials have attracted great interest owing to highly efficient Na storage activity, high stability, and low cost. The Na₂Ti₃O₇ structure is composed of zigzag layers of titanium oxygen octahedral, in which up to 3.5 Na ions per formula unit can be intercalated into the interlayer space and easily exchanged, leading to a capacity of 310 mAh g^–1.

This anode shows a low Na insertion potential (0.3 vs Na), leading to a higher operating voltage and energy density in practical batteries. However, the Na₂Ti₃O₇ still suffers from sluggish Na insertion/extraction kinetics resulting from a large bandgap of 3.7 eV and insufficient cycling stability for substantial Na insertion (>2 Na per unit formula) in the lattice due to the fact that the mechanical strain exists upon Na uptake and that the reactive surface sites cause unwanted electrolyte degradation and irreversible trapping of Na ions.

To attack these critical problems of reaction kinetics and surface trapping, for the first time, Prof. Liang Li’s group and their coworkers reported a novel surface engineering method by combining atomic layer deposition (ALD) and elemental doping (Adv. Energy Mater. 2016, 6, 1502568). The fabrication of the Na₂Ti₃O₇ electrode includes the hydrothermal growing of Na₂Ti₃O₇ nanotube arrays, surface ALD deposition of a thin TiO₂ layer, and subsequent sulfidation.

The nanoarrays exhibited high reversible capacities of 221 mAh g⁻¹ and a superior cycling efficiency and rate capability, retaining 78 mAh g⁻¹ at 10 C (1770 mA g⁻¹) over 10 000 continuous cycles. The full cells consisting of Na₂Ti₃O₇ nanotube anode and Na_2/3(Ni_1/3Mn_2/3)O₂ cathode deliver a specific energy of 110 Wh kg⁻¹.  

About The Author

Prof. Liang Li is a full professor in Soochow University, China. He received the Ph.D. degree from the Institute of Solid State Physics, Chinese Academy of Sciences and won the Excellent President Scholarship in 2006. From 2007-2012, he worked in National University of Singapore, Singapore, National Institute of Advanced Industrial Science and Technology, Japan, National Institute for Materials Science, Japan, and the University of Western Ontario, Canada.

Dr. Li’s research group focuses mainly on the energy conversion and storage devices of low-dimensional nanomaterials. He was awarded by China government as 1000 Youth Talents Plan and Excellent Youth Foundation in 2013 and 2014, respectively. His group web: http://ecs.suda.edu.cn  

Journal Reference

Advanced Energy Materials, 2016, Volume 6, Issue 11.

Jiangfeng Ni¹, Shidong Fu¹, Chao Wu², Yang Zhao¹, Joachim Maier², Yan Yu^2,3,4, Liang Li¹

Show Affiliations

1. College of Physics, Optoelectronics and Energy, Center for Energy Conversion Materials & Physics (CECMP), Soochow University, Suzhou, P. R. China
2. Max Planck Institute for Solid State Research, Stuttgart, Germany
3. Key Laboratory of Materials for Energy Conversion, Chinese Academy of Sciences, Department of Materials Science and Engineering, University of Science and Technology of China, Hefei, P. R. China
4. State Key Laboratory of Fire Science (SKLFS), University of Science and Technology of China, Hefei, Anhui, P. R. China 

Abstract

Sodium-ion batteries have attracted extraordinary attention owing to their low cost and raw materials in abundance. A major challenge of practical implementation is the lack of accessible and affordable anodes that can reversibly store a substantial amount of Na ions in a fast and stable manner. It is reported that surface engineered sodium titanate (Na₂Ti₃O₇) nanotube arrays directly grown on Ti substrates can serve as efficient anodes to meet those stringent requirements. The fabrication of the nanotube arrays involves hydrothermal growing of Na₂Ti₃O₇ nanotubes, surface deposition of a thin layer of TiO₂, and subsequent sulfidation.

The resulting nanoarrays exhibit a high electrochemical Na-storage activity that outperforms other Na₂Ti₃O₇ based materials. They deliver high reversible capacities of 221 mAh g⁻¹ and exhibit a superior cycling efficiency and rate capability, retaining 78 mAh g⁻¹ at 10 C (1770 mA g⁻¹) over 10 000 continuous cycles. In addition, the full cell consisting of Na₂Ti₃O₇ nanotube anode and Na_2/3(Ni_1/3Mn_2/3)O₂ cathode is capable of delivering a specific energy of ≈110 Wh kg⁻¹ (based on the mass of both electrodes). The surface engineering can provide useful tools in the development of high performance anode materials with robust power and cyclability.

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