Lead-halide perovskites are promising materials for opto-electronic applications. Recent reports indicated that their mechanical and electronic properties are strongly affected by the lattice vibrations. Herein we report far-infrared spectroscopy measurements of CH3NH3Pb(I/Br/Cl)3 thin films and single crystals at room temperature and a detailed quantitative analysis of the spectra. We find strong broadening and anharmonicity of the lattice vibrations for all three halide perovskites, which indicates dynamic disorder of the lead-halide cage at room temperature. We determine the frequencies of the transversal and longitudinal optical phonons, and use them to calculate the static dielectric constants, polaron masses, electron-phonon coupling constants, and upper limits for the phonon-scattering limited charge carrier mobilities. Our findings place an upper limit in the range of 200 cm 2 V −1 s −1 for the room temperature charge carrier mobility in MAPbI3 single crystals, and are important for the basic understanding of charge transport processes and mechanical properties in metal halide perovskites.

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Building a lithium-ion cell with a third reference electrode which is stable and does not disturb the cell characteristics promises deep insights into the cell performance and aging behavior. In this study, a lithium titanium oxide coated aluminum mesh is introduced into lab size 28 mAh pouch cells, which allows the cells to be braced as usual. The influence of inserting the coated mesh together with an additional separator is analyzed using electrochemical impedance spectroscopy and cyclic aging tests. Cells with this reference electrode show small deviations in the Nyquist plot and an increased capacity fade compared to the standard cells. Nonetheless, these 3-electrode cells already allowed C-rate performance tests in a fresh and aged cell state. According to this, the charge current profiles for fresh and aged cells are optimized as step wise protocols to improve the utilization of the anode overpotential reserve while avoiding lithium plating. In order to realize this, the aged cells require a 60% slower protocol. This work shows that the overpotentials on the anode side increase during aging, which makes the cells more susceptible to lithium plating. However, compared to a constant current charge, a reduction in charging time of 30% is possible.

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