Electrochemical performance of SnO 2 :Sb–MWCNT nanocomposites for Li-ion batteries Ozgur Cevher* ,† , Mehmet Oguz Guler, Ubeyd Tocoglu and Hatem Akbulut Sakarya University, Engineering Faculty, Department of Metallurgical and Material Engineering, Esentepe Campus, Sakarya, Turkey SUMMARY In this study, SnO 2 :Sb coating on Cr-coated stainless steel and multiwall carbon nanotube (MWCNT) buckypaper substrates were prepared as anode materials using a radio frequency (RF) magnetron sputtering process for lithium-ion batteries. The nanocomposites were characterized with field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction and electrochemical test facilities. The evaluation of the electrochemical performance in lithium-ion batteries showed that the SnO 2 :Sb–MWCNT nanocomposites have shown reversible discharge capacities of 701 mAh g À1 , 732 mAh g À1 and 753 mAh g À1 for different RF powers (75 W, 100 W and 125 W), respectively, after 100 cycles. The high-capacity retention and cyclability ascribed to the good dispersion, high conductivity and fine particle size of SnO 2 :Sb on MWCNTs. Besides, the MWCNTs in SnO 2 :Sb act as a load carrying buffer component and behave like a flexible reinforcement, alleviating the electrode dilapidation resulted from volume change during the lithium insertion and de-insertion. Copyright © 2014 John Wiley & Sons, Ltd. KEY WORDS SnO 2 ; Sb–MWCNT nanocomposites; deposition with sputtering; Li-ion batteries Correspondence *Ozgur Cevher, Sakarya University, Engineering Faculty, Department of Metallurgical and Material Engineering, Esentepe Campus, Sakarya, Turkey † E-mail: ocevher@sakarya.edu.tr Received 31 December 2012; Revised 3 October 2013; Accepted 10 October 2013 1. INTRODUCTION SnO 2 is an n-type wide band gap semiconductor where in- herent oxygen vacancies act as an n-type dopant [1,2]. The most notable applications are sensors [3], solar cells [4], optoelectronic devices [5] and flat-panel displays [6], etc., due to their high transparency, conductivity [7] and excel- lent catalytic activity [8]. The conductivity and the charge carrier density of SnO 2 films increase greatly when doped with In, F or Sb [9,10]. The charge carrier of SnO 2 is in- duced by oxygen vacancies serving as donors; the forma- tion of too many oxygen vacancies results in decreased film quality. Thus, increasing the conductivity of SnO 2 in a narrow range of oxygen pressure is very difficult. Extrin- sic donors such as Sb (Sb Sn ) provide another charge carrier to increase the conductivity of SnO 2 thin films. In the last decade, a number of doped and undoped tin oxides have been investigated using laser irradiation to tailor surface properties and reduce lattice defects in order to enhance the conductivity of SnO 2 thin films [11–13]. The formation of Sb 3+ at the internal and external interfaces leads to the reduction of conductivity in SnO 2 . From the literature data, it is well known that Sb-doped SnO 2 thin film with suitable doping level (∼5%) has favorable electrical conductivity, high transmittance and low reflection in the visible light range. Its properties can be controlled by adjusting the amounts of dopants and modifying its non-stoichiometry [14]. Rechargeable lithium-ion batteries are commonly used in portable electronics since their compact size, high power and energy densities, charge retention, life cycles and com- petitive cost [15–18]. With the development of portable electronics, numerous studies have focused on the anode materials that have higher Li + storage capacities than the carbonaceous materials [19–21]. Tin oxide has been con- sidered as an attractive candidate for substitution of the conventional graphite anode (372 mAhg À1 ) in lithium ion battery due to its superiorities such as high theoretical ca- pacity (1497 mAhg À1 ), low cost and good environmental benignity. However, a major problem of anode materials for lithium-ion batteries is the significant volume change (ca. 300%) occurring during the alloying and de-alloying processes, which may induce damage to the anodes and cause very poor long-term cyclability. In spite of above mentioned obstacles, it is constantly investigated in the lithium ion batteries due to the severe capacity fades upon cycling even at low densities and may drop down to 80 INTERNATIONAL JOURNAL OF ENERGY RESEARCH Int. J. Energy Res. 2014; 38:499–508 Published online 3 January 2014 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/er.3132 Copyright © 2014 John Wiley & Sons, Ltd. 499