Colossal reversible volume changes in lithium alloys

It is uncommon to consider strains in a stiff solid approaching or exceedin g 100% even though some materials exhibit large volume changes during chemi cal 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 perpend icular to the substrate. When lithium is removed, the films shrink both per pendicular and parallel to the substrates, leading to crack patterns simila r to those found in dried mud. Subsequently, the formed particles expand an d contract reversibly without further cracking as lithium is added and remo ved from the alloy. Time lapsed "movies" of this process can be found at ww w.physics.dal.ca/similar to dahn/ECS_Letters.html (C) 2001 The Electrochemi cal Society. [DOI: 10.1149/1.1388178] All rights reserved.