Entropy change characteristics of LiMn0.67Fe0.33PO4 and Li4Ti5O12 electrode materials

Abstract

The combination of LiMn0.67Fe0.33PO4 positive and Li4Ti5O12 negative electrode is studied in terms of its entropy change behavior, which affects the reversible heat generation of a lithium-ion cell. This electrode combination is especially interesting for large applications, as it is proposed to be a very safe choice having still an adequate energy density. The entropy change of LiMn0.67Fe0.33PO4 and Li4Ti5O12 electrode materials is measured at different states of charge using a potentiometric method. The results are compared with conventional electrode materials, LiFePO4 and artificial graphite. The entropy change of LiMn0.67Fe0.33PO4 is found to follow the distinct plateaus of Fe2+/Fe3+ and Mn2+/Mn3+ redox couples and to be clearly different from LiFePO4. This difference is suggested to be due to single-phase solid solution regions, originating from effects of substituting Mn for Fe. For Li4Ti5O12, mostly a constant entropy change typical for a two-phase reaction is observed, except for the region near 0% state of charge. The data from individual electrodes is used to simulate and compare the entropy change behavior and thus the reversible heat generation rate of different electrode combinations.