Colossal Reversible Volume Changes in Lithium Alloys

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Abstract
It is uncommon to consider strains in a stiff solid approaching or exceeding 100% even though some materials exhibit large volume changes during chemical reactions. We used in situ atomic force and optical microscopy to study, for the first time, the colossal volume changes that occur as lithium is electrochemically added and removed from lithium alloy films. When lithium is first added to alloy films on rigid substrates, the films expand perpendicular to the substrate. When lithium is removed, the films shrink both perpendicular and parallel to the substrates, leading to crack patterns similar to those found in dried mud. Subsequently, the formed particles expand and contract reversibly without further cracking as lithium is added and removed from the alloy. Time lapsed “movies” of this process can be found at www.physics.dal.ca/∼dahn/ECS_Letters.html © 2001 The Electrochemical Society. All rights reserved.