Reynier, Yvan and Graetz, Jason and Swan-Wood, Tabitha and Rez, Peter and Yazami, Rachid and Fultz, Brent (2004) Entropy of Li intercalation in LixCoO2. Physical Review B, 70 (17). Art. No. 174304. ISSN 1098-0121 http://resolver.caltech.edu/CaltechAUTHORS:REYprb04
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The entropy of lithiation of LixCoO2 for 0.5 < x less than or equal to 1.0 was determined from measurements of the temperature dependence of equilibrated voltages of electrochemical cells. Measured changes in the entropy of the lithiation reaction were as large as 9.0 k(B)/atom, and as large as 4.2 k(B)/atom within the "O3" layered hexagonal structure of LixCoO2. Three contributions to the entropy of lithiation for the O3 phase were assessed by experiment and calculation. The phonon entropy of lithiation was determined from measurements of inelastic neutron scattering. Phonon entropy can account for much of the negative entropy of lithiation, but its changes with lithium concentration were found to be small. Electronic structure calculations in the local density approximation gave a small electronic entropy of lithiation of the O3 phase. The configurational entropy from lithium-vacancy disorder was large enough to account for most of the compositional trend in the entropy of lithiation of the O3 phase if ordered structures exist at lithium concentrations of x=1/2 and x=5/6. The electrochemical measurements showed the existence of a two-phase region in the composition range between x=5/6 and 0.95. Electronic structure calculations gave evidence that these phases were metallic and insulating, respectively. Changes of the electronic and configurational entropy were found to be of comparable importance for this metal-insulator transition.
|Additional Information:||©2004 The American Physical Society. Received 26 February 2004; revised 2 July 2004; published 17 November 2004. We thank A. Van der Ven for kindly supplying atom coordinates for many of the relaxed O3 structures. This work was supported by the Department of Energy through the Basic Energy Sciences Grants DE-FG03-00ER15035 and DE-FG02-03ER15425. The work has benefited from the use of the Los Alamos Neutron Science Center at Los Alamos National Laboratory. LANSCE is funded by US Department of Energy under Contract W-7405-ENG-36. We would also like to acknowledge CNRS for financial support.|
|Subject Keywords:||lithium compounds; intercalation compounds; crystal structure; secondary cells; entropy; phonons; density functional theory; vacancies (crystal); metal-insulator transition; electrochemical analysis; electronic density of states|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||09 May 2006|
|Last Modified:||26 Dec 2012 08:51|
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