Erschienen in:International Journal of Materials Research
Sprache:
Nicht zu entscheiden
DOI:
10.3139/146.111549
ISSN:
2195-8556;
1862-5282
Entstehung:
Anmerkungen:
Beschreibung:
<jats:title>Abstract</jats:title><jats:p>Thin film battery electrodes of the olivine structure LiFePO<jats:sub>4</jats:sub> and the spinel phase LiMn<jats:sub>2</jats:sub>O<jats:sub>4</jats:sub> 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 LiFePO<jats:sub>4</jats:sub> 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 LiFePO<jats:sub>4</jats:sub> have the character of an ion-conductor of vanishing electronic conductivity.</jats:p>