LiMn2O4-based spinels have been extensively studied as positive electrode materials for lithium-ion batteries. Our investigations have shown that, by using the Pechini process, the performance of these materials can be improved significantly through adjustments to the synthesis conditions and composition by means of selective doping. This paper reports the results of neutron and ex situ X-ray diffraction studies performed to examine the structural changes that occur during lithium ion insertion into various LiMn,O4 compositions. It appears that an ordering intercalation of lithium ions occurs in the lithium concentration range of 0.15-0.35, followed by a second-order phase transformation when the lithium population is close to 0.5, leading to a random lithium insertion into a single-spinel phase from x = 0.5 to 1.0. * Electrochemical Society Student Member. * * Electrochemical Society Active Member.agreement with many literature reports,4"°13 including results obtained from the ionic modeling of various lithium manganese spinel compounds.'3 However, the reason is not cleat One goal of this study was to explore the intrin-

In the past ten years, LiMn2O4 ‐based spinels have been extensively studied as positive electrode materials for lithium‐ion batteries. Our ongoing investigations have shown that the Pechini process, a low temperature synthetic method that often yields inorganic oxides of excellent phase purity and well‐controlled stoichiometry, is very effective for preparing LiMn2O4 ‐based cathode materials. It also has been shown that different firing temperatures and the selective doping of LiMn2O4 both produce materials with different electrochemical characteristics that merit further exploration.

Atomic force microscopy, a powerful, high-resolution imaging technique for determining the structure of surfaces in gaseous and liquid environments, was used to examine the reactivity of an electropolished surface of a naturally aged aluminum-copper-magnesium alloy (2024-T3) in aqueous hydrochloric acid (0.01, 0.1, and 1 M). When first exposed to acid, the matrix dissolved uniformly. Dissolution then accelerated and pits formed predominately in the vicinity of the secondphase precipitates. The pits developed into characteristic intergranular damage: i.e., elongated pits (incipient corrosion cracks) along grain boundaries. Postexperimental ex situ energy dispersive x-ray analysis and Auger electron spectroscopy were employed to characterize the composition of the various surface features of corroded samples.

consists mainly of chromium oxide enrichment and an increase of the thickness of the inner oxide layer at constant total film thickness. The main modification responsible for the increased resistance to pitting is attributed to this chromium oxide enrichment.

The morphological features of 2024-T3 aluminum alloy were delineated using atomic force microscopy (AFM) during separate and combined actions of corrosion and fatigue.In-situ AFM corrosion studies in hydrochloric acid environments without mechanical deformation showed accelerated dissolution in the vicinity of second phase precipitates leading to intergranular corrosion. During fatigue in air, AFM images revealed steps along grain boundaries, as well as parallel extrusions and intrusions during the early stages of fatigue life. At later stages of mechanical deformation persistent slip bands (PSBs) were observed on the sample's surface. Cracks were observed to nucleate and propagate along PSBs. For experiments where samples were subjected to the simultaneous action of a corrosive environment and mechanical deformation, intergranular cracking was observed during the early stages of fatigue life. The corrosive environment was observed to accelerate the crack nucleation process.