Short communication Reliable benchmark material for anatase TiO 2 in Li-ion batteries: On the role of dehydration of commercial TiO 2 Edyta Madej a, b , Fabio La Mantia b , Bastian Mei c , Stefan Klink a , Martin Muhler c , Wolfgang Schuhmann a, b , Edgar Ventosa a, * a Analytische Chemie e Elektroanalytik & Sensorik, Ruhr-Universität Bochum, Universitätsstr. 150, 44780 Bochum, Germany b Center for Electrochemical Sciences e CES, Ruhr-Universität Bochum, Universitätsstr. 150, 44780 Bochum, Germany c Laboratory of Industrial Chemistry, Ruhr-Universität Bochum, Universitätsstr.150, 44780 Bochum, Germany highlights  Commercial TiO 2 nanoparticles for Li-ion batteries fails in cyclability.  Li-ions are entrapped inside TiO 2 upon cycling.  Annealing in air of commercial TiO 2 leads to remarkable improvement.  Air-annealed commercial TiO 2 becomes an excellent TiO 2 benchmark material. article info Article history: Received 6 February 2014 Received in revised form 8 April 2014 Accepted 3 May 2014 Available online 14 May 2014 Keywords: Li-ion battery Anatase TiO 2 Benchmark material Cyclability Dehydration abstract Commercially available anatase TiO 2 nanoparticles (ca. 15e20 nm particle size) were investigated as negative electrode material for Li-ion batteries. Despite the high initial specific charge of 200 mAh g 1 at 0.5C, the pristine commercial TiO 2 failed to retain the reversible capacity upon cycling, keeping only 23% of the initial value after 80 cycles. X-ray photoelectron spectroscopy (XPS) results together with elec- trochemical data suggest that the failure in cyclability is of kinetic nature as the loss in specific charge is not completely irreversible. Thermogravimetry analysis revealed that the pristine TiO 2 contained a significant amount of TiO(OH) 2 (ca. 8%) which can be easily removed by dehydration when annealing in air above 250  C. Air-annealing of TiO 2 at 300  C resulted in a remarkable improvement in cyclability retaining 83% of initial specific charge after 80 cycles at 0.5C. No further improvement in cyclability was observed for TiO 2 annealed at 450  C suggesting that the dehydration of TiO(OH) 2 was the primary source of the improvement. Knowing the role of dehydration of TiO 2 allows obtaining a reliable benchmark material via simple air-annealing and becomes a key factor when developing advanced materials from commercial TiO 2 . Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction Energy storage plays a key role in achieving a sustainable energy system. Among different existing technologies, Li-ion batteries (LIBs) are receiving much attention mainly due to their high specific energy density [1e3]. For negative electrodes, titania-based mate- rials offer additional safety, especially at temperatures above 60  C, longer cycle stability and a safe potential gap to lithium electro- plating for high-power applications [4], which may compensate in some cases for their lower energy density. Indeed, batteries employing Li 4 Ti 5 O 12 as negative electrode material have been commercialized [5,6]. TiO 2 has been hence explored as alternative negative electrode material due to its mature synthesis methods and its higher theoretical Li-ion storage capacity of 335 mAh g 1 versus 175 mAh g 1 for Li 4 Ti 5 O 12 . However, the practical specific charge of TiO 2 , which is typically around 160 mAh g 1 , is still far from the theoretical one and unlocking the potential of TiO 2 re- mains a challenge. There are two main limitations that prevent TiO 2 from achieving higher practical specific charge values: 1) the poor electric con- ductivity and 2) the slow Li-ion diffusivity. The conductivity has been successfully improved by e.g. wiring with carbon nanotubes [7], carbon [8] and RuO 2 [9] coatings or introducing different types of doping agents [10]. The slow diffusivity has been addressed by * Corresponding author. Tel.: þ49 234 3228202; fax: þ49 234 3214683. E-mail address: edgar.ventosa@rub.de (E. Ventosa). Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour http://dx.doi.org/10.1016/j.jpowsour.2014.05.018 0378-7753/Ó 2014 Elsevier B.V. All rights reserved. Journal of Power Sources 266 (2014) 155e161