Measurement of the Entropy of Reaction as a Function of State of Charge in Doped and Undoped Lithium Manganese Oxide

Potentiometric measurements of the entropy and enthalpy of reaction at 298 K as a function of state of charge for and are presented. Lithium resides on nearest neighbor or next-nearest neighbor sublattices in lithium manganese oxide. The entropy of reaction is positive when a sublattice is nearly empty and negative when a sublattice is nearly full, and ranges from 0.25 to in the undoped spinel and from 0.1 to in the doped spinel. The potentiometric method includes a correction for self-discharge. Potentiometric measurements of entropy are compared to calorimetric measurements. The potentiometric method is most accurate for thermally thin cells, while calorimetric methods require large cells to improve the signal-to-noise ratio. © 2001 The Electrochemical Society. All rights reserved.