Ž . Journal of Power Sources 89 2000 232–236 www.elsevier.comrlocaterjpowsour Structural aspects of electrochemically lithiated SnO: nuclear magnetic resonance and X-ray absorption studies Y. Wang a , J. Sakamoto b,1 , S. Kostov a , A.N. Mansour c , M.L. denBoer a, ) , S.G. Greenbaum a , C.-K. Huang b , S. Surampudi b a Physics Department, Hunter College of City UniÕersity of New York, New York, NY 10021, USA b Electrochemical Technologies Group, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA c NaÕal Surface Warfare Center, 9500 MacArthur BouleÕard, West Bethesda, MD 20817, USA Received 24 September 1999; accepted 14 October 1999 Abstract We have compared the local structure of electrochemically lithiated SnO with SnrLi alloys using 7 Li to study the environment of the Li ion and extended X-ray absorption fine structure to study the environment of the Sn ion. Although a widely accepted simple model suggested that the electrochemically lithiated SnO should be similar to SnrLi alloys of corresponding composition, we find this is true only at low Li concentrations. The addition of more Li to the structure produces, for both the Li and the Sn, features which are difficult to reconcile with the simple model, and suggest the presence of direct Sn–O interactions. q 2000 Elsevier Science S.A. All rights reserved. Keywords: SnO; Nuclear magnetic resonance; X-ray absorption 1. Introduction Tin compounds and especially oxides have attracted recent interest as high capacity anodes in lithium ion w x batteries 1–7 . The compound SnO, which has been con- sidered as a possible anode material, has the additional advantage of serving as a useful model of the more chemically complex composite tin oxide glasses. A widely used model of the reaction of lithium with SnO involves initially reduction of the Sn and subsequently alloying of w x the Sn, according to 1,2 : SnO q x Li Li O q SnLi . 1 Ž. 2 xy2 Although there is a large irreversible Li capacity associ- ated with the Li O phase, the latter appears to improve 2 cyclability as compared to elemental Sn, which undergoes large volumetric changes on Li alloying. Recently pub- wx w x lished results from our laboratory 4 and others 5–7 have ) Corresponding author. Tel.: q 1-212-772-5258. Ž . E-mail address: mdenboer@hunter.cuny.edu M.L. denBoer . 1 Current address: Department of Materials Science, University of California at Los Angeles, Los Angeles, CA 90095, USA. shed additional light on the electrochemical lithiation of 7 Ž . SnO, via Li nuclear magnetic resonance NMR and X-ray absorption spectroscopy at the Sn K-edge. The two methods are complementary in that the former yields information regarding the local environment of the Li q ions while the latter is sensitive to the local Sn environ- ment. In these previous studies, it was found that the Ž. simple reaction mechanism 1 is valid only under limited circumstances; large structural differences between the ideal SnLi alloy and the electrochemically lithiated mate- w x rial were observed at high Li content 4–7 . In this paper, we present more detailed measurements than those in our wx initial communication 4 , which provide additional evi- dence for differences in alloy formation at high Li content. 2. Experimental Lithium was electrochemically titrated into SnO as wx Ž 2 . described elsewhere 4 under galvanostatic 20 m Arcm conditions. Reference SnLi alloys were synthesized by x direct reaction of the elements. Appropriate amounts of elemental lithium and tin obtained commercially were weighed. Tin contained in a molybdenum crucible was 0378-7753r00r$ - see front matter q 2000 Elsevier Science S.A. All rights reserved. Ž . PII: S0378-7753 00 00434-1