Ionothermal Synthesis of Tailor-Made LiFePO 4 Powders for Li-Ion Battery Applications N. Recham, L. Dupont, M. Courty, K. Djellab, D. Larcher, M. Armand, and J.-M. Tarascon* Laboratoire de Re ´actiVite ´ et Chimie des Solides, UniVersite ´ de Picardie Jules Verne, CNRS UMR6007, 33 rue Saint Leu, 80039 Amiens, France ReceiVed December 3, 2008. ReVised Manuscript ReceiVed January 12, 2009 As opposed to ceramic methods, low-temperature solvothermal-hydrothermal methods using liquid media as reaction support are less energy demanding to design new electrode materials; therefore, they tend to replace ceramic routes. Here, we report the use of ionic liquids as both solvent and template to enable the growth of LiFePO 4 (LFP) powders with controlled size and morphology at temperatures at least 200 °C lower than those required for conventional ceramic methods, while showing excellent electrochemical performances versus lithium. An inherent advantage to the use of ionic liquids lies in the feasibility of carrying out the reaction at atmospheric pressure. Besides, the recovery of the powders from the reacting medium is particularly easy, as are the effluents and ionic liquid recycling. Additionally, it is shown that ionic liquids can be used as a structural directing agent to orient crystal growth and obtain powders adopting a single morphology. Needless to say, such a new approach, which is not specific to LiFePO 4 , offers great opportunities for the low-temperature synthesis of new electrode materials. Introduction Because of its attractive energy density and cycle-life performances, it has taken less than 20 years for the Li-ion technology to capture the portable electronic market. The question is: will such a technology be as quick to conquer the staggering upcoming markets of electric transportation (e.g., hybrid electric vehicles) and renewable energies? Although optimism must prevail, several hurdles remain to be cleared, with the top of the list being safety and cost. 1 Chemical advances in any of the cell components, whether they are anodes, electrolytes, or cathodes, can benefit the battery final cost and safety. Solid-state chemists 2 have played the leading role in addressing these issues by bringing to the scene LiFePO 4 (LFP) a material that, besides having the right voltage (3.5 V vs Li + /Li) to present safety attributes, is a natural mineral known as triphyllite made of low cost and abundant elements. Mining and directly using LiFePO 4 is not an option, as both morphology and purity of this material have to be worked out to fight its intrinsically low conductivity and turn it into an attractive electrode material. Because of smart material processing enlisting both carbon coating 3 and particles downsizing processes, 4-6 Li + can presently be reversibly extracted out of LiFePO 4 leading to room temperature capacities of ∼160 mA h g -1 (close to the theoretical value of 170 mA h g -1 ). Besides addressing fundamental aspects regarding the influence of particle size/defects or cationic/anionic substi- tutes on insertion/deinsertion mechanism and capacity/rate performances of LiFePO 4 , a great amount of work is presently aimed at new low-cost processes to make highly electrochemically optimized LiFePO 4 powders. 1 Along that line, low-temperature hydro(solvo)thermal processes, which are energy miser compared with high-temperature ceramic routes, have received increased attention with successful results, among which the hydrothermal approach pursued by Whittingham’s 7,8 or Tajimi’s 9 groups, and more recently by Delacourt et al. 10 The latter shows the feasibility of precipi- tating at atmospheric pressure (e.g., via a solvothermal process) tailor-made LiFePO 4 nanopowders from a DMSO- based aqueous medium containing the suitable precursors (H 3 PO 4 , FeSO 4 , and LiOH). Our group 11 also recently reported a new eco-efficient hydrothermal synthesis of LiFePO 4 with tunable morphologies, which relies on the use of “latent bases” capable of releasing a nitrogen-based base upon heating. Regardless of the specificity of the hydro(sol- vo)thermal approach, the carbon-coating of the resulting powders is always beneficial to their electrochemical performances. * Corresponding author. E-mail: jean-marie.tarascon@sc.u-picardie.fr. (1) Tarascon, J. M.; Armand, M. Nature 2001, 414, 359–367. (2) Padhi, A. K.; Nanjundaswamy, K. S.; Goodenough, J. B. J. Electro- chem. Soc. 1997, 144, 1188–1194. (3) Ravet, N. et al. 196th Meeting of the Electrochemical Society; Honolulu, HI, Oct 17-22, 1999; Electrochemical Society: Pennington, NJ, 1999; abstract # 127. (4) Delacourt, C.; Poizot, P.; Levasseur, S.; Masquelier, C. Electrochem. Solid- State Lett. 2006, 9, A352-A355. (5) Nuspl, G., Wimmer, L., and Eisgruber, M. World Patent WO 2005/ 051840 A1, 2005. (6) Meetong, N.; Huang, H.; Speakman, S.; Carter, W. C.; Chiang, Y. M. AdV. Funct. Mater. 2007, 17, 1115–1123. (7) Chen, J.; Wang, S.; Whittingham, M. S. J. Power Sources 2007, 174, 442–448. (8) Chen, J.; Vacchio, M. J.; Wand, S.; Chernova, N.; Zavalij, P. Y.; Whittingham, M. S. Solid State Ionics 2008, 178, 1676–1693. (9) Jin, B-; Gu, H.-B. Solid State Ionics 2008, 178, 1907–1914. (10) Delacourt, C.; Poizot, P.; Masquelier, C. World Patent, WO 2007/ 0051, 2007. (11) Recham, N.; Laffont, L.; Armand, M.; Tarascon, J. M. Electrochem. Solid-State Lett. 2009, 12 (2), A39-A44. 1096 Chem. Mater. 2009, 21, 1096–1107 10.1021/cm803259x CCC: $40.75  2009 American Chemical Society Published on Web 02/05/2009