Journal of Power Sources 184 (2008) 527–531 Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour Short communication Surface-modified maghemite as the cathode material for lithium batteries James Manuel a , Jae-Kwang Kim a , Jou-Hyeon Ahn a,∗ , Gouri Cheruvally c , Ghanshyam S. Chauhan a , Jae-Won Choi a , Ki-Won Kim b a Department of Chemical and Biological Engineering and Engineering Research Institute, Gyeongsang National University, 900 Gajwa-dong, Jinju 660-701, Republic of Korea b School of Nano and Advanced Materials Engineering and Engineering Research Institute, Gyeongsang National University, 900 Gajwa-dong, Jinju 660-701, Republic of Korea c Polymers and Special Chemicals Division, Vikram Sarabhai Space Centre, Thiruvananthapuram, Kerala, India article info Article history: Received 21 December 2007 Received in revised form 22 February 2008 Accepted 27 February 2008 Available online 6 March 2008 Keywords: Maghemite Cathode material Lithium batteries Inorganic–organic hybrid Polypyrrole abstract The inorganic–organic hybrid maghemite (-Fe 2 O 3 )/polypyrrole (PPy) was synthesized and evaluated as cathode-active material for room temperature lithium batteries. The nanometer-sized core–shell struc- ture of the hybrid consisting of the maghemite core with surface modified by PPy was evidenced from the morphological examination. The cathode fabricated with the as-prepared hybrid material deliv- ered an initial discharge capacity of 233 mAh g -1 and a reversible capacity of ∼62 mAh g -1 after 50 charge–discharge cycles. A much higher performance with an initial discharge capacity of 378 mAh g -1 and a reversible capacity of ∼100 mAh g -1 was achieved with the cathode based on the segregated active material, which was obtained by subjecting the as-prepared hybrid material to an additional ball-milling process. The study demonstrates the promising lithium insertion characteristics of the nanometer-sized core–shell maghemite/PPy particles prepared under optimized conditions for application in secondary batteries. © 2008 Elsevier B.V. All rights reserved. 1. Introduction The field of advanced power sources is presently dominated by the lithium battery technology that caters to a multitude of appli- cations. A lot of research work is being carried out for developing promising cathode materials for lithium batteries. Although sat- isfactory discharge capacity and stable cycle life are provided by LiCoO 2 , there is an increasing demand to replace it by other suitable cathode materials that are non-toxic, inexpensive and more eas- ily available. Sulfur and iron-based compounds which meet these criteria are thus very attractive. Several iron compounds have attracted interest as cathode materials including iron oxides, sulfides and mixed metal oxides like LiFeO 2 and LiFePO 4 . Among these, the iron oxides are par- ticularly attractive from cost and environmental stand points. However, the initial studies with the micrometer-sized crystalline iron oxide as lithium intercalation electrodes were not reported to be promising, because of its poor conductivity [1–4]. Nano- structured cathode materials such as V 2 O 5 [5] and LiMn 2 O 4 [6] were reported to exhibit enhanced electrochemical performance ∗ Corresponding author. Tel.: +82 55 751 5388; fax: +82 55 753 1806. E-mail address: jhahn@gsnu.ac.kr (J.-H. Ahn). compared to their micrometer-sized counterparts. There are many reports on the electrochemical performance of the nano-structured iron oxide materials [7–14]. Xu et al. reported that nano-crystalline Fe 2 O 3 with a structure resembling that of -Fe 2 O 3 exhibited bet- ter Li intercalation properties with improved cyclability compared to the micro-crystalline -Fe 2 O 3 [8]. The enhanced properties of the nano-structured cathodes result from the higher surface area of the active material, shorter diffusion paths for lithium ions and only small dimensional changes go through the particles on cycling. In addition, the structural defects at/near the surface of the nano- crystalline materials lead to many sub-band gap states between the conduction and valance bands, and result in a better adaptation to the structural changes, as reported by Kwon et al. [15]. Maghemite (-Fe 2 O 3 ) is an important crystalline form of Fe(III) oxide. Its nanoparticles have been prepared by different syn- thetic methods [16,17]. The lithium intercalation property of the pristine maghemite is not so attractive mainly due to its low electrical conductivity. Kwon et al. achieved enhanced electro- chemical performance using nano-sized core–shell particles of the inorganic–organic hybrid of -Fe 2 O 3 /polypyrrole (PPy), which was prepared by the surface modification of -Fe 2 O 3 with PPy [15,18]. PPy forms a thin layer over the maghemite particles that facilitates easy transport of electrons and ions, and thus enhances the capacity and cyclability of the cell. In the present study, we report the prepa- 0378-7753/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2008.02.079