Nanoparticles of SnO Produced by Sonochemistry as Anode Materials for Rechargeable Lithium Batteries Doron Aurbach,* Alex Nimberger, Boris Markovsky, Elena Levi, Elena Sominski, and Aharon Gedanken Department of Chemistry, Bar-Ilan University, Ramat Gan 52900, Israel Received February 6, 2002. Revised Manuscript Received July 25, 2002 Nanoparticles of SnO were synthesized sonochemically in mildly basic SnCl 2 solutions. The amorphous product thus obtained could be transformed to a nanocrystalline phase by heating to 200 °C. Composite electrodes comprised (by weight) of 80% SnO, 10% graphite flakes (conductive additive), and 10% polymeric binder (an optimal composition) were tested as anodes for rechargeable Li batteries. The nanocrystalline SnO was found to be much more effective as an active material for electrodes than the initial amorphous phase. These electrodes could reach nearly their theoretical capacity (=790 mAh/g, SnO) in electrochemical lithiation-delithiation processes versus a Li counter electrode in nonaqueous Li salt solutions. However, there is still a long way to go to the possible use of SnO as an anode material in practical batteries. This is due to its high irreversible capacity (Li 2 O formation and surface film precipitation due to reactions of lithium-tin compounds with solution species) and gradual capacity decrease during repeated charge-discharge cycling. Possible reasons for this capacity fading are discussed. The tools for this study included electron microscopy (both TEM and SEM), thermal analysis (DSC), XRD, FTIR and impedance spectroscopies, and standard electrochemical techniques. I. Introduction The development of high energy density rechargeable lithium batteries has been one of the greatest challenges of modern electrochemistry during the last three de- cades. However, the use of metallic lithium as an anode in secondary batteries was found to be very problematic. This is due to the fact that there is no way to avoid continuous reactions between highly reactive lithium deposits (formed during charging of a lithium battery) and the solution components. 1 Hence, major problems in rechargeable batteries based on lithium metal anodes are the loss of solution upon charge-discharge cycling that considerably limits the cycle life of these batteries and dendrite formation during Li deposition, which may short the batteries and thus create severe safety prob- lems upon their current use. 2 Successful alternatives to lithium anodes in recharge- able batteries were found to be lithiated carbonaceous materials, mainly graphite. 3 Indeed, the development of lithiated carbon anodes and lithiated transition metal oxide cathodes (e.g., LiMn 2 O 4 , LiCoO 2 , LiNiO 2 ), both reversibly inserting lithium into nonaqueous electrolyte solutions, paved the way to the invention and com- mercialization of rechargeable lithium ion batteries based on the “rocking chair” concept. 4 These batteries, which are now practical and are conquering increasingly more power source markets, can indeed be considered as one of the most impressive successes of the electro- chemistry technological community in recent years. However, although changing from lithium metal to lithiated graphite means a gain in stability, safety, and cycle life of rechargeable Li batteries, it is at the expense of loss of capacity (372 mAh/g for fully lithiated graphite, LiC 6 , compared with 3800 mAh/g for lithium metal). Thereby, there is a continuous driving force for the development of alternative anode materials for both lithium and lithiated graphite, with which the capacity is much higher than that of lithiated graphite yet the safety features are acceptable (i.e., much better com- pared with metallic lithium). Natural candidates as alternatives for Li anodes in rechargeable Li batteries are lithium alloys, which can be formed and decomposed electrochemically, reversibly, in nonaqueous electrolyte solutions. Indeed, there are many reports on binary and ternary Li alloys that were tested as Li battery anodes. 5-7 Of special importance in this respect are the Li-Sn compounds because lithium can be inserted electro- chemically, reversibly, into tin to form alloys of high Li content up to Li 17 Sn 4 , corresponding to a theoretical capacity of 790 mAh/g. 8 We should mention that the * Corresponding author. E-mail address: aurbach@mail.biu.ac.il. (1) Aurbach, D.; Zinigrad, E.; Teller, H.; Dan, P. J. Electrochem. Soc. 2000, 147, 2486-2493. (2) Yamaki, J. I.; Tobishima, S. I. In Handbook of Battery Materials; Besenhard, J. O., Ed.; Wiley VCH: Weinheim, 1999; Part 3, Chapter 3. (3) Kinoshita, K. In Handbook of Battery Materials; Besenhard, J. O., Ed.; Wiley VCH: Weinheim, 1999; Part 2, Chapter 8. (4) Winter, M.; Novak, P.; Monier, A. J. Electrochem. Soc. 1998, 145, 428-436. (5) Dahn, J. R.; Courtney, I. A.; Mao, O. Solid State Ionics 1998, 111, 289-294. (6) Huggins, R. A. In Handbook of Battery Materials; Besenhard, J. O., Ed.; Wiley VCH: Weinheim, 1999; Part 4, Chapter 4. (7) Mohamedi, M.; Lee, S.-J.; Takahashi, D.; Nishizawa, M.; Itoh, T.; Uchida, I. Electrochim. Acta 2001, 46, 1161-1168. (8) Winter, M.; Besenhard, J. O. Electrochim. Acta 1999, 45, 31- 50. 4155 Chem. Mater. 2002, 14, 4155-4163 10.1021/cm021137m CCC: $22.00 © 2002 American Chemical Society Published on Web 10/01/2002