Lithium storage study on MoO3-grafted TiO2 nanotube arrays

Appl Nanosci DOI 10.1007/s13204-016-0526-y ORIGINAL ARTICLE Lithium storage study on MoO3-grafted TiO2 nanotube arrays Tauseef Anwar1 • Li Wang1 • Li Jiaoyang1 • Wang Chen2 • Rizwan Ur Rehman Sagar3 • Liang Tongxiang2 Received: 8 January 2016 / Accepted: 27 February 2016 Ó The Author(s) 2016. This article is published with open access at Springerlink.com Abstract Titanium dioxide nanotube arrays (TNAs) were fabricated via anodic ionization. Porous MoO3 was grafted on TNAs with the help of hydrothermal method. Scanning electron microscopy and X-ray powder diffraction was utilized for the confirmation of one dimensional morphology and phase identification. The porous MoO3 nanoflake-grafted TNAs (MoO3/TNAs) electrode was used as anode material in lithium ion battery (LIB) and it was found that the areal specific capacity of MoO3/TNAs (*797 lAh cm-2) was three times higher than those of anatase TNAs (*287 lAh cm-2) and porous MoO3 (*234 lAh cm-2) at 50 lA cm-2. Keywords Molybdenum oxide  Titanium dioxide nanotube arrays (TNAs)  Anode  Lithium-ion batteries (LIBs) Electronic supplementary material The online version of this article (doi:10.1007/s13204-016-0526-y) contains supplementary material, which is available to authorized users. & Liang Tongxiang 1 Beijing Key Lab of Fine Ceramics, Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084, People’s Republic of China 2 State Key Lab of New Ceramic and Fine Processing, Tsinghua University, Beijing 100084, People’s Republic of China 3 Nanshan District Key Lab for Biopolymers and Safety Evaluation, College of Materials Science and Engineering, Shenzhen University, Shenzhen 518060, People’s Republic of China Introduction Lithium ion battery (LIB) is one of the most reliable power sources for portable electronic devices. The improved performance of microbatteries is highly necessary for modern microelectronic devices such as PC memory, microelectromechanical systems (MEMS), medical implants, hearing aids, ‘‘smart’’ cards, RF-ID tags, remote sensors and energy harvesters, etc. (Kyeremateng 2014; Matiko et al. 2014; Patil et al. 2008; Pikul et al. 2013). The requirement of high-performance LIBs encourages scientists to develop new anode materials with capacity higher than graphite (Reddy et al. 2013; Wu et al. 2012a; Wu and Hong 2014; Xiong et al. 2014). TiO2 is a promising material for lithium storage due to its low volume expansion, environmental benignity and widespread availability. Amongst the various nanostructures of TiO2 (Armstrong et al. 2006; Cao et al. 2010; Liu et al. 2012; Qiu et al. 2010; Ren et al. 2012; Wang et al. 2011), titanium dioxide nanotube arrays (TNAs) (Guo et al. 2012) are favorable due to their high specific surface area, high porosity, vertical orientation which accommodate volume expansion and also provide short lithium ion diffusion path (Wu et al. 2012b). However, the areal specific capacity, even for the optimized TNAs, is found to be low (Tauseef Anwar et al. 2015). Three different methods have been proposed to enhance the specific capacity: (1) doping TNAs with metal or nonmetal elements (Kyeremateng et al. 2013b; Liu et al. 2008, 2009); (2) coating TNAs with conductive reagents (Guan and Wang 2013; Kim et al. 2010; Zhang et al. 2009); (3) modify TNAs with oxide materials that have larger capacities [SnO2 (Meng et al. 2013), Co3O4 (Fan et al. 2013; Kyeremateng et al. 2013a), Nb2O5 (Yang et al. 2013) and Fe2O3 (Yu et al. 2013)] to yield hybrid or composite structures. 123 Appl Nanosci MoO3 is an anode material candidate due to its high theoretical capacity (1117 mAh g-1). The orthorhombic phase layered structure of a-MoO3 hosts Li? by insertion and deinsertion reaction. However, the electrochemical properties of TNAs could be further enhanced with the extra porous hybrid material such as MoO3 (Fan et al. 2013; Guan et al. 2014a, b; Kyeremateng et al. 2013a; Meng et al. 2013; Wang et al. 2013; Xue et al. 2011; Zhu et al. 2015). Considering low electronic conductivity and high volume expansion, Yu et al. (2014) synthesized porous MoO3 thin films and elucidated better performance as compared to bulk MoO3. Zhao et al. (2013) synthesized porous MoO3 thin films via electro-deposition which exhibit a high capacity of 650 mAh g-1 at high current density of 3 A g-1. Yu et al. synthesized porous MoO3 nanosheets by hydrothermal method at Ti substrate and the nanosheets showed specific capacity of 750 mAh g-1 at 1C-rate. There are rare reports on the MoO3/TNAs as anode material in LIBs. However, different fabrication of coating MoO3 on TNAs led difference in their electrochemical properties. The hydrothermal synthesis for the grafting of MoO3 nanoflakes at TNAs was used first time. The fabrication method and porosity would play important role for future electrochemical properties of material. Herein, TNAs were grown at Ti substrate and consecutive annealing transforms TNAs in anatase phase. The porous MoO3 were grafted using a facile hydrothermal method which facilitate high yield product (Fig. 1) (Fan et al. 2015a, b; Gong et al. 2015). The grafting of porous Fig. 1 Schematic illustration of the formation of MoO3/TNAs composite: (I) Ti substrate; (II) formation of TNAs on Ti substrate; (III) grafting MoS2 on TNAs via hydrothermal reaction (IV) formation of MoO3/TNAs 123 MoO3 nanoflakes at TNAs was controlled via hydrothermal reaction time. The electrochemical properties were optimized by controlling thickness of MoO3 with hydrothermal duration. There are several benefits of utilizing MoO3/ TNAs as electrode in LIBs. Firstly, TiO2 with zero strain (ca. 4 % volume change after lithiation) is an ideal material to optimize cycle stability and rate performance. Secondly, the nanosize and intrinsic characteristics of porous MoO3 will provide both reversible large capacity and good electrical conductivity. Thirdly, the specific architectural feature of binder-free single-crystalline TiO2 nanotube array will simplify the electrode fabrication process. Fourthly, TiO2 nanotube array provides direct electron transport pathway between active material and current collector and also facilitate uniform deposition of porous MoO3 with large areal mass loading. In contrast to the advantages, there are disadvantages as well, firstly, to get synergic capacity of both anatase TNAs and porous MoO3 the potential window must be higher (0.005–3 V). Secondly, the solid electrolyte interface (SEI) layer is inevitable which leads to high capacity fading. Experimental section Synthesis of MoO3/TNAs Prior to anodic oxidation, titanium foil (0.125-mm-thick foil, 99.7 % purity, Sigma Aldrich) was degreased by Appl Nanosci sonication in acetone, ethanol and deionized water in turn, then dried in air. The electrochemical cell for anodization was a two-electrode cell, consisting of Ti foil as working electrode and platinum foil as counter electrode. Electrochemical anodization experimen (...truncated)