SURFACE AND INTERFACE ANALYSIS Surf. Interface Anal. 27, 1064–1068 (1999) Surface and Bulk Composition of Lithium Manganese Oxides † E. Regan, 1 T. Groutso, 1 J. B. Metson, 1 R. Steiner, 2 * B. Ammundsen, 2 D. Hassell 2 and P. Pickering 2 1 The University of Auckland, Private Bag 92019 Auckland, New Zealand 2 Pacific Lithium Ltd, PO Box 90725 Auckland, New Zealand Lithium manganese oxides, and in particular the spinel-structured LiMn 2 O 4 , have been investigated as potential active cathode materials for lithium ion batteries. Recently both orthorhombic and monoclinic LiMnO 2 have attracted considerable attention. It has been reported that Al doping allows the preparation of monoclinic LiAl x Mn 1-x O 2 under suitable reaction conditions, and furthermore improves the capacity retention of both o-LiAl x Mn 1-x O 2 and m-LiAl x Mn 1-x O 2 . The aim of this study was to elucidate the structural effects of Al doping with particular attention to the surface properties of the material. X-ray diffraction data reveal that Al induces monoclinic stacking faults in orthorhombic LiAl x Mn 1-x O 2 and at Al contents of ~5% the preferred cation ordering becomes that of monoclinic LiAl x Mn 1-x O 2 . X-ray photoelectron spectroscopy measurements show that the Al is homogeneously incorporated throughout the grains up to its solubility limit, and no surface enrichment of Al is observed. The XPS data indicate that Mn in the near-surface region of the material is predominantly present in its Y3 oxidation state, even when annealed to temperatures of up to 250 ° C. Copyright  1999 John Wiley & Sons, Ltd. KEYWORDS: lithium manganese oxide; aluminium doping; crystal structure; surface composition; XPS; x-ray diffraction INTRODUCTION Secondary lithium ion batteries are rapidly becoming the pre-eminent power source for applications in portable elec- tronics applications and offer potential for application in the emerging electric vehicle market. 1 Much effort is being invested in the development of active cathode materi- als for use in lithium battery systems. Suitable active cathode materials should exhibit high open-circuit volt- age vs. lithium, high capacity and good charge/discharge cycleability. The intercalation compounds Li x CoO 2 , Li x NiO 2 and Li x Mn 2 O 4 have been investigated widely in recent years. 2–8 Lithium cobalt oxide ⊲Li x CoO 2 ⊳ cur- rently represents the state-of-the-art and is used almost exclusively in a variety of commercial applications. 9–11 Yet, the achievable reversible capacities of both Li x CoO 2 (¾140 mAh g 1 ) and Li x NiO 2 (¾160 mAh g 1 ) are limited because the material becomes unstable when more than 0.5 Li per transition metal is de-intercalated during charging. 12 This and the fact that cobalt and nickel compounds are expensive and of high toxicity have led to an increased interest in manganese-based materials. Spinel-structured Li x Mn 2 O 4 , although attractive from a cost and toxicity perspective, offers lower capacity (¾120 mAh g 1 ) and suffers from rapid capacity fade when used at elevated temperatures in the range 50–70 ° C, which are commonly experienced in many portable electronics applications. 13 * Correspondence to: R. Steiner, Pacific Lithium Ltd, PO Box 90725 Auckland Mail Centre, Auckland, New Zealand. E-mail: rudolf@pacificlithium.co.nz † Paper presented at the AXAA-99 Conference, 8 – 12 February 1999, Melbourne, Australia. Contract/grant sponsor: Technology New Zealand. Recently the trivalent manganese compound LiMnO 2 was identified as a potential cathode material. It usually crystallises in an orthorhombic (o-LiMnO 2 ) structure (space group Pmnm), but the preparation of a layered form of LiMnO 2 crystallizing in monoclinic structure (space group C2/m) has been reported by Bruce et al. 14 – 20 Because monoclinic LiMnO 2 (m-LiMnO 2 ) is not usually thermodynamically stable, Bruce et al. 20 prepared it via an ion-exchange reaction where ˛-NaMnO 2 was refluxed with LiCl or LiBr in an alcohol solution. It is the structural analogy of m-LiMnO 2 to LiCoO 2 and LiNiO 2 that has attracted additional attention. Since then, Chiang et al. 21 have reported the stabilization of m-LiMnO 2 by Al dop- ing, allowing the preparation of the material via a more conventional synthesis technique. Chiang et al. also found that Al doping improves the electrochemical properties of o-LiMnO 2 , in particular its cycleability at elevated temperatures. The aim of this study is to elucidate the structural effects of Al doping on both the orthorhombic and the monoclinic polymorphs, with particular attention to the surface properties of the material. X-ray diffraction (XRD) was used to probe the bulk structure and x-ray photo- electron spectroscopy (XPS) was used to investigate the manganese oxidation state at the surface as well as the aluminium distribution. Grain morphology was studied by means of scanning electron microscopy. EXPERIMENTAL Materials of the empirical formula LiAl x Mn 1x O 2 (0  x  0.1) were prepared at Pacific Lithium Ltd. CCC 0142–2421/99/121064–05 $17.50 Received 11 February 1999 Copyright  1999 John Wiley & Sons, Ltd. Revised 28 June 1999; Accepted 30 June 1999