Materials with New Design for Improved Lithium Ion Batteries
JP 10 (subproject 3 part 1, Prof. Florian Mertens): Rational Tuning and Thermodynamic Characterisation of Lithium Silicides and Lithium Iron Phosphate as Electrode Materials for Lithium Ion Batteries - Nano-Scaling Guided by Calorimetric, Thermokinetic and Theoretical Investigations
After its discovery as a cathode material in 1997 by Padhi et al. , LiFePO4 has attracted much interest and many investigations were carried out to characterize this olivine like compound for the use in lithium ion batteries. Especially kinetic and thermodynamic studies will give insight into lithiation and delithiation processes and mechanisms, mimicking charge and discharge within the battery cell. In contrast to many electrochemical tests and similar to the wet chemical analyses, the lithiation and delithiation of orthorhombic LiFePO4 is investigated and modeled. This approach will allow a better understanding of growth mechanisms and phase transitions in insertion type electrode materials and might also be generalised to other insertion electrode materials.
For our kinetic experiments, we developed a couple of methods (electrolytic conductivity, mass spectrometry, PXRD, ion chromatography, UV-Vis spectroscopy, titration calorimetry) to detect the progress of the intercalation/deintercalation processes or to interrupt the reaction at a given point in time. Fundamental formal kinetics (activation energy, order of reaction) are accompanied by a nucleation like description of lithium insertion as well as thermokinetic studies (titration calorimetry).
The thermodynamic behaviour of the system is investigated with heat capacity measurements and the determination of the LiFePO4-FePO4 transition enthalpy.
All experiments are carried out in dependence on the lithium content, particle size and carbon-coating.
 A. K. Padhi, K. S. Nanjundaswamy, J. B. Goodenough J. Electrochem. Soc. 144, 1997, 1188-1194
Prof. F. Mertens
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