期刊
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH
卷 108, 期 11, 页码 984-998出版社
CARL HANSER VERLAG
DOI: 10.3139/146.111549
关键词
Intercalation compounds; Thin films; Elastic interaction; Ionic transport; Grain boundary transport
资金
- German Science Foundation (DFG) [SPP 1473]
Thin film battery electrodes of the olivine structure LiFe-PO4 and the spinel phase LiMn2O4 are deposited through ion-beam sputtering. The intercalation kinetics is studied by cyclo-voltammetry using variation of the cycling rate over 4 to 5 orders of magnitude. The well-defined layer geometry allows a detailed quantitative analysis. It is shown that LiFePO4 clearly undergoes phase separation during intercalation, although the material is nano-confined and very high charging rates are applied. We present a modified Randles-Sevcik evaluation adapted to phase-separating systems. Both the charging current and the overpotential depend on the film thickness in a systematic way. The analysis yields evidence that the grain boundaries are important short circuit paths for fast transport. They increase the electrochemical active area with increasing layer thickness. Evidence is obtained that the grain boundaries in LiFePO4 have the character of an ion-conductor of vanishing electronic conductivity.
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