Low temperature molten salt synthesis of anatase TiO 2 and its electrochemical properties M.V. Reddy a,b, ⁎, S. Adams b, ⁎⁎, Galen Tiong Ji Liang c , Ian Foo Mingze c , Huynh Van Tu An c , B.V.R. Chowdari a a Department of Physics, National University of Singapore, 117542, Singapore b Department of Materials Science and Engineering, National University of Singapore, 117576, Singapore c NUS High School of Mathematics and Science, 129957, Singapore abstract article info Article history: Received 17 May 2013 Received in revised form 13 November 2013 Accepted 16 November 2013 Available online xxxx Keywords: TiO 2 Nanoparticles Molten salt method Electrochemical properties Intercalation anode This study investigates the electrochemical properties of TiO 2 nanoparticles that were obtained using molten salt method (MSM) synthesis when applied as anodic material for lithium-ion batteries. TiO 2 nanoparticles were syn- thesized from 0.62LiNO 3 :0.38LiOH molten salt at 180 °C for 2 h in air followed by reheating at 300 °C for 2 h in air. Another separate sample was prepared in addition to molten salt and urea was added then heated at 180 °C for 2 h. X-ray diffraction studies showed a single anatase phase, with characteristic lattice parameter values of a = 3.81 Å and c = 9.46 Å. Cyclic voltammetry studies on the TiO 2 nanoparticles show main cathodic and anod- ic redox peaks at ~1.7 and ~1.9 V respectively. Further galvanostatic discharge–charge cycling studies were performed on all samples at a current rate of 30 mA/g. TiO 2 nanoparticles synthesized at 180 °C for 2 h and treated with urea delivered a high reversible capacity of ~275 mAh/g, whereas TiO 2 reheated at 300 °C displayed a capacity of ~215 mAh/g. In both compounds capacity fading was found to be at 9.8 to 15% between 5 and 60 cycles. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Rechargeable Li-ion batteries have been garnering increasing atten- tion in recent years. Such batteries operate on the principle of Li-intercalation/de-intercalation of ions [1,2]. In order to improve the capacity and safety of lithium batteries, considerable research has been done into alternative components, especially new electrode materials and novel material synthesis that enhance the storage perfor- mance of the batteries [2]. The reaction mechanisms involved in anode materials are broadly classified into intercalation/de-intercalation, alloying–de-alloying, conversion and alloying & conversion reactions [2]. Ti-containing oxides like Li 4 Ti 5 O 12 [2–4], various polymorphs of TiO 2 [2,5–10], N,F co-doped TiO 2 [11] and other complex oxides [2] undergo intercalation–de-intercalation reaction in the voltage range, 1.0–3.0 V vs. Li. TiO 2 is one well-known material used in various applications such as photo-catalysts [5], solar cells [12], and electrode materials for lithium ion batteries [2]. Nanostructured TiO 2 can be prepared with various methods which are summarized in recent reviews [2,5]. Literature studies showed that electrochemical performance depends on preparation and reaction conditions like temperature and time. TiO 2 can be prepared by a variety of methods, among these is the molten salt method (MSM), which is a particularly versatile and efficient method to synthesize nano/submicron/micron sized particles [13–18], offering the advantages of high diffusivity owing to the molten reaction medium without the need for mechanical mixing. Previously, Reddy et al studied the TiO 2 nanoparticles using KNO 3 :LiNO 3 molten salt at 410 °C [19] and very recently prepared TiO 2 nanoparticles using 0.88LiNO 3 :0.12LiCl at 280 °C and 0.5MNaNO 3 :0.5MKNO 3 at 510 °C [20]. For academic inter- est, here we report low temperature synthesis of TiO 2 using a novel LiNO 3 :LiOH molten salt at 180 °C. To our knowledge, we are reporting, for the first time, the preparation of TiO 2 by the molten salt method. 2. Experimental TiO 2 nanoparticles were prepared from a 1:10 mixture of titanium oxysulfate TiOSO 4 ∙ xH 2 SO 4 xH 2 O (Aldrich, 99%) in flux medium, which consists of a 0.62:0.38 M mixture of LiNO 3 (ALFA AESAR, 99%) and LiOH (Fisher Scientific, 99%). Three batches of TiO 2 were prepared by the molten salt method. For the first batch, the mixture was heated in an alumina crucible at 180 °C for 2 h in air. The final product was addi- tionally stirred in a beaker with distilled water and subsequently fil- tered through a vacuum pump to remove soluble excess Li salts. The residue was then dried in air at 70 °C. To study the effect of urea in the preparation of TiO 2 , 5 g of urea (Aldrich, 99%) was also added to the Ti-oxysulfate: LiOH:LiNO 3 mixture at 180 °C for 2 h in air and other steps are similar to batch 1, for clarity we refer to batch 2. Here urea acts as a nice oxidizer, it improves the oxidation state, pore volume and diameter of TiO 2 , and also partially can dope nitrogen into the Solid State Ionics xxx (2013) xxx–xxx ⁎ Correspondence to: M.V. Reddy, Department of Physics, National University of Singapore, 117542, Singapore. ⁎⁎ Corresponding author. E-mail addresses: msemvvr@nus.edu.sg (M.V. Reddy), mseasn@nus.edu.sg (S. Adams). SOSI-13176; No of Pages 4 0167-2738/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ssi.2013.11.030 Contents lists available at ScienceDirect Solid State Ionics journal homepage: www.elsevier.com/locate/ssi Please cite this article as: M.V. Reddy, et al., Low temperature molten salt synthesis of anatase TiO 2 and its electrochemical properties, Solid State Ionics (2013), http://dx.doi.org/10.1016/j.ssi.2013.11.030