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. This third paper in a three-part series focuses on composites of Sn2Fe and SnFe3C made by mechanical alloying of elemental powders. The Sn2Fe and SnFe3C grains which comprise the powder particles were about 10 nm in size. Seven samples of composition Sn2Fe, 25% (by weight) Sn2Fe/75% SnFe3C, 24% Sn2Fe/72% SnFe3C/4% C, 36% Sn2Fe/63% SnFe3C/1% C, 45% Sn2Fe/55% SnFe3C, 66% Sn2Fe/34% SnFe3C, and SnFe3C were studied. Using in situ X-ray diffraction and electrochemical methods, the reversible reaction of Li with these materials was studied. The Sn2Fe in these materials is an active phase, that is, it reacts completely to form Li4.4Sn and Fe, and the SnFe3C is an inactive phase, that is, it reacts with very little Li. Thus, since there is a two-phase tie line connecting an inactive and an active phase in the Sn-Fe-C ternary phase diagram, and the fact that mechanical alloying generally produces materials with very small grains, it is possible to produce composites with controlled amounts of active and inactive phases. The best material we have made gives a volumetric capacity of about 1600 mAh/cm(3), has an average voltage near 0.4 V vs. Li metal, and shows stable cycling for over 80 charge-discharge cycles. Materials like this may ultimately replace graphite as the anode of choice for the Li-ion battery. (C) 1999 The Electrochemical Society. S0013-4651(98)04-054-3. All rights reserved.
