In situ growth of LiFePO 4 nanorod arrays under hydrothermal condition Fei Teng, Sunand Santhanagopalan, Ryan Lemmens, Xiaobao Geng, Pragneshkumar Patel, Dennis Desheng Meng * Department of Mechanical Engineering–Engineering Mechanics, MichiganTechnological University, Houghton, MI 49931, USA article info Article history: Received 17 November 2009 Received in revised form 5 January 2010 Accepted 3 February 2010 Available online 11 February 2010 Keywords: LiFePO 4 Nanorod arrays In situ Hydrothermal Anodized alumina oxides abstract A novel in situ combinatorial method has been developed to fabricate LiFePO 4 nanorod arrays, during which anodized alumina oxide (AAO) was employed as the template and ethylene glycol/water medium is used to ensure mass transportation rates of different chemicals to match each other. The samples were then characterized by X-ray diffractometer (XRD), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and energy dispersive X-ray spectroscopy (EDX). After being hydrothermally processed at 160  C, the highly-crystallized LiFePO 4 arrays were directly obtained, which are composed of single crystal nanorods with a diameter of 200 nm and a length of 3 mm. The reported synthesis is simple, mild and energy- efficient. A noteworthy advantage over conventional sol–gel–template methods is the elimination of high-temperature annealing. Ó 2010 Elsevier Masson SAS. All rights reserved. 1. Introduction Nanoarrays have attracted significant attention for their appli- cations in energy storage/conversion devices due to large surface areas, short distances for charge and mass transport, reduced internal resistance and high tolerance for volume change [1–4]. For example, the V 2 O 5 nanorod arrays have achieved a capacity 4 times as high as that of thin-film electrodes at high discharge rates [4]. To date, various techniques have been used to fabricate nanoarrays including template synthesis [5,6], vapor deposition [7], chemical solution growth [8], electrochemical deposition [9] and sub-micrometer lithography [10]. Among these methods, AAO- templated synthesis is one of the most widely used methods to fabricate highly-ordered nanoarrays [5,6], which is promising to acquire nanoarrays with high purity and large surface areas [11]. Use of an AAO template has been proven to be a low-cost and high-yield technique for nanoarray synthesis [5,6]. To date, the fabrication of nanoarrays with simple composition, i.e. single or di-element, by AAO templates has been a fairly common practice, which has provided a variety of metal and semiconductor nano- arrays through electrochemical processes [4–6]. However, the fabrication of nanoarrays with complex, multi-element composi- tions cannot be easily achieved by this method, with only a few examples demonstrated [12–19]. This can be attributed to the difficulty in preparing homogeneous and stable precursor. As a result, the compositions of infiltrated precursor sols within the template channels are generally non-stoichiometric, which makes it difficult to obtain single-phase products [12–17,20,21]. Moreover, the sol–gel based methods commonly require post-synthesis annealing at high temperatures to obtain crystallized materials, which consumes large amount of energy. Hence, there are signifi- cant challenges on the synthesis and practical applications of nanoarrays of multi-element materials. As one of the most promising cathode materials, LiFePO 4 has been intensively investigated for large lithium-ion batteries in electrical vehicles (EVs) and hybrid electric vehicles (HEVs) [22–24]. To date, various methods have been used to synthesize LiFePO 4 [25–27]. Sides et al. [28] synthesized LiFePO 4 nanofibers via a solution impregnation polycarbonate membrane method. In their experiment, however, annealing was used to obtain the crystallized materials. It is desirable to develop a simpler route to synthesize highly-crystallized LiFePO 4 nanorod arrays. In this communication, we have overcome the above-mentioned limitations by combining the concepts of mild hydrothermal synthesis with template method to provide a new in situ route for fabricating LiFePO 4 nanoarrays, during which ethylene glycol/water (EG/W) was used as medium. Compared with sol–gel–template methods [12– 17,20,21], our approach shows significant advantages on its mild synthesis environment, low energy-consumption and simplicity, e.g., elimination of additional high-temperature annealing step. * Corresponding author. Tel.: þ1 906 487 2817; fax: þ1 906 487 3551. E-mail address: dmeng@mtu.edu (D.D. Meng). Contents lists available at ScienceDirect Solid State Sciences journal homepage: www.elsevier.com/locate/ssscie 1293-2558/$ – see front matter Ó 2010 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.solidstatesciences.2010.02.017 Solid State Sciences 12 (2010) 952–955