RESEARCH PAPER Electrochemical activity of rock-salt-structured LiFeO 2 / Li 4/3 Ti 2/3 O 2 nanocomposites in lithium cells J. Morales Æ J. Santos-Pen ˜a Æ R. Tro ´coli Æ S. Franger Received: 20 June 2008 / Accepted: 21 August 2008 Ó Springer Science+Business Media B.V. 2008 Abstract a-LiFeO 2 prepared as nanoparticles exhib- its substantially increased electrochemical activity in lithium cells. Thus, in the first half-cycle, the nanoferrite provides a capacity close to 70 mAh g -1 (i.e. approximately 0.25 mol lithium ions is deinserted from the lithium ferrite network), which is several times higher than the values for other ferrites. Even higher capacities have been observed for solid solu- tions of a-LiFeO 2 and rock-salt lithium titanate. In this work, we prepared nanocomposites with improved electroactivity in the first half-cycle. Also, we com- pared their electrochemical properties with those of nanosized lithium ferrite and lithium titanate. Based on them, explanation for their disparate behaviour involving a protective role of the titanate coating from unwanted reactions with the electrolyte is provided. Keywords a-LiFeO 2  Li 4/3 Ti 2/3 O 2  Nanocomposites  Lithium ion batteries  Positive electrode  Electrochemical impedance spectroscopy  Energy storage Introduction The use of environmentally friendly materials as electrodes for lithium ion batteries has become man- datory with a view to developing clean renewable technologies for the future. LiCoO 2 was used as a positive electrode material at the early stages of the rocking-chair cell concept despite its high cost and toxicity; however, this shortcoming fostered a research for alternative compounds based on other transition metals such as Fe, which is less expensive and toxic than Co. Various types of iron-containing systems including oxides, vanadates and borates were investi- gated, and special emphasis was placed on compounds from the olivine structural family (e.g. Li 3 Fe 2 (PO 4 ) 3 (Nanjundaswamy et al. 1996; Masquelier et al. 1998) and the now in vogue LiFePO 4 (Padhi et al. 1997; Franger et al. 2002, 2003a, 2004; Caballero et al. 2006; Morales et al. 2007). Five different polymorphs of lithium ferrite, LiFeO 2 , were also studied as potential alternatives to Li–Co–O positive electrodes (Kanno et al. 1997; Lee et al. 2002, 2003a, b; Sakurai et al. 1997, 1998; Matsumura et al. 2002; Wang et al. 2004; Morales and Santos-Pen ˜a 2007). The use of these ferric materials as electrodes is subject to major constraints arising from their low cycling efficiency and also low operating voltage (Kanno et al. 1997; Lee et al. 2002, 2003, 2003b; Sakurai et al. 1997, 1998; Matsumura et al. 2002; Wang et al. 2004). However, Li–Fe–O systems provide similar capacities to those of LiCoO 2 and LiFePO 4 . In recent work (Morales and J. Morales  J. Santos-Pen ˜a (&)  R. Tro ´coli Departamento de Quı ´mica Inorga ´nica e Ingenierı ´a Quı ´mica, Edificio Marie Curie, Campus de Rabanales, Universidad de Co ´rdoba, 14071 Cordoba, Spain e-mail: iq2sanpe@uco.es S. Franger Laboratoire de Physico-Chimie de l’Etat Solide, UMR CNRS 8182, ICMMO, Universite ´ Paris XI, 91405 Orsay, France 123 J Nanopart Res DOI 10.1007/s11051-008-9490-0