Synthesis and Electrochemical Reaction with Lithium of Mesoporous Iron Oxalate Nanoribbons Marı ´a Jose ´ Aragón, Bernardo León, Carlos Pérez Vicente, and Jose ´ L. Tirado* Laboratorio de Quı ´mica Inorga ´nica, UniVersidad de Co ´rdoba, Edificio C3, Campus de Rabanales, 14071 Co ´rdoba, Spain Received May 16, 2008 Mesoporous FeC 2 O 4 was prepared by dehydration of bulk monoclinic- and micellar orthorhombic FeC 2 O 4 · 2H 2 O precursors at 200 °C. The micellar material shows nanoribbon shaped particles, which are preserved after dehydration. These solids are used as high-capacity lithium storage materials with improved rate performance. The mesoporous nanoribbons exhibit higher capacities close to 700 mA h/g after 50 cycles at 2C (C ) 1 Li h -1 mol -1 ) rate between 0 and 2 V. Introduction In recent years, nanomaterials have burst upon the scene of lithium battery research. New electrode materials have been recently found which provide higher capacities at higher rates by using the advantage of dispersion at the nanoscale and the enhanced stability of one-dimensional nanopar- ticles. 1-3 In parallel, a significant advance in the understand- ing of conversion electrode materials for lithium batteries has taken place. Transition metal oxides 3-6 and, more recently, transition metal fluorides 7,8 are known examples of solids involved in conversion reactions versus lithium. The electrochemical conversion process leads to the reduction of the metal ions to the metallic state together with the formation of lithium oxide or lithium fluoride, respectively. The partial reversibility of these processes makes these solids potential candidates for the negative or positive electrode of advanced lithium-ion batteries, respectively. Recently, we were able to extend this process to submi- crometric particles of manganese carbonate with the calcite structure. 9 This study revealed that MnCO 3 can be used directly as a conversion electrode versus lithium. The discharge of lithium test cells takes place by a different conversion reaction than that observed for the oxide produced during the thermal decomposition of the carbonate, MnO. Similar values of reversible capacity and better capacity retention were observed for the carbonate as compared with the oxide. In this work, the study of oxysalts as conversion electrode material is investigated for a common and inexpensive compound: iron oxalate prepared by a novel synthesis procedure. The use of dehydrated nanoparticles of this compound provides interesting values of capacity at high rates. Experimental Section Two samples of iron(II) oxalate dihydrate were studied. Com- mercial iron oxalate (Panreac, Barcelona) was used as received. The synthesis of FeC 2 O 4 · 2H 2 O nanoparticles was carried out by a reverse micelles procedure from water-in-oil microemulsions. First, two microemulsions (I and II) were obtained under an argon atmosphere as follows. Microemulsion I contained cetyl-trimethy- lammonium bromide (CTAB) as the surfactant, hexanol as the cosurfactant, isooctane as the hydrocarbon phase and 0.3 M iron(II) sulfate solution as the aqueous phase. Microemulsion II has the same constituents as above except for having 0.3 M ammonium oxalate instead of iron sulfate as the aqueous phase. The weight * To whom correspondence should be addressed. E-mail: iq1ticoj@ uco.es. (1) Armstrong, A. R.; Armstrong, G.; Canales, J.; Garcı ´a, R.; Bruce, P. G. AdV. Mater. 2005, 17, 862–865. (2) Chan, C. K.; Peng, H.; Liu, G.; McIlwrath, K.; Zhang, X. F.; Huggins, R. A.; Cui, Y. Nature Nanotech. 2008, 3, 31–35. (3) Li, Y.; Tan, B.; Wu, Y. Nano Lett. 2008, 8, 265–270. (4) Poizot, P.; Laruelle, S.; Grugeon, S.; Tarascon, J. M. J. Electrochem. Soc. 2002, 149, A1212-A1219. (5) Alca ´ntara, R.; Jaraba, M.; Lavela, P.; Tirado, J. L. Chem. Mater. 2002, 14, 2847–2848. (6) Lavela, P.; Otiz, G.; Tirado, J. L.; Zhecheva, E.; Stoyanova, R.; Ivanova, S. J. Phys. Chem. C 2007, 111, 14238–14246. (7) Badway, F.; Mansour, A. N.; Pereira, N.; Al-Sharab, J. F.; Cosandey, F.; Plitz, I.; Amatucci, G. G. Chem. Mater. 2007, 19, 4129–4141. (8) Liao, P.; MacDonald, B. L.; Dunlap, R. A.; Dahn, J. R. Chem. Mater. 2008, 20, 454–461. (9) Arago ´ n, M. J.; Pe ´rez-Vicente, C.; Tirado, J. L. Electrochem. Commun. 2007, 9, 1744–1748. Inorg. Chem. 2008, 47, 10366-10371 10366 Inorganic Chemistry, Vol. 47, No. 22, 2008 10.1021/ic8008927 CCC: $40.75  2008 American Chemical Society Published on Web 10/11/2008