Dresden 2014 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 14: Functional Materials III - Li ion batteries
MM 14.1: Vortrag
Montag, 31. März 2014, 15:45–16:00, IFW A
Studying the phase growth in LFP thin films — •Fabian Wunde1, Frank Berkemeier1, and Guido Schmitz2 — 1Institut für Materialphysik Universität Münster — 2Institut für Materialwissenschaft Universität Stuttgart
Lithium Iron Phosphate (LFP) is one of the state of the art cathode materials for lithium ion batteries. In this work, LFP thin films between 100 and 300 nm are deposited by ion beam sputtering. These films exhibit a reasonable electrochemical capacity and excellent cycle life stability, which makes them capable for fundamental research, like diffusion studies. Therefore, detailed cyclic voltammetry (CV) measurements are carried out on the films.According to Randles and Sevcik, the peakcurrent of the CV diagrams is found to be proportional to the squareroot of the scan rate, but studies on LFP films of different thickness also show a proportionality to the film thickness. The latter differs from the theory of Randles and Sevcik and is expected to be due to the two-phase nature of LFP, forming a lithium-rich and a lithium-poor phase.Therefore, we numerically study the growth and descent of the two phases, by means of finite differences methods, using a discrete diffusion model and chemical potentials obtained from the regular solution. Within these studies, the time-dependence of the lithium content of the LFP is evaluated, and correlated to the experimental data.