We have prepared intermetallic phases and mixtures of such phases in the Sn-Fe-C Gibbs＇ triangle by mechanical alloying methods or by direct melting of elemental powders. This first paper in a three-part series focuses on the materials which fall on the two-phase line collecting Sn2Fe and C. Using in situ X-ray diffraction, Mossbauer spectroscopy, and electrochemical methods, we show that Sn2Fe reacts with Li in Li/Sn2Fe cells to form lithium-tin alloys and very small metallic iron grains. The experimental capacity for this reaction is about 800 mAh/g, as expected. During the first charge of such cells about 650 mAh/g of Li can be extracted up to 1.5 V vs. Li. The density of these materials is near 7 g/cm(3), so first-cycle volumetric capacities near 4500 Ah/L have been attained. It was our hope that the formed iron would act as an electrically conductive, inactive matrix to support the Li-Sn alloy grains and that good cycling behavior would result. However, the extended cycling life of these materials between 1.5 and 0.0 V is poor. On the other hand, reasonable cycle life is obtained if the cycling range is restricted to between 0.0 and 0.55 V, but in this case, the irreversible capacity is about 600 mAh/g and the reversible capacity only about 200 mAh/g. We show strategies to overcome these difficulties in the next papers in this series.