Regensburg 2022 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 8: Materials for Storage and Conversion of Energy
MM 8.5: Vortrag
Montag, 5. September 2022, 16:45–17:00, H46
Investigation of volume changes in the colquiriite structure due to Li insertion from first principles — •Aljoscha Baumann1,2, Daniel Mutter2, Daniel Urban1,2, and Christian Elsässer1,2 — 1Freiburger Materialforschungszentrum, Stefan-Meier-Straße 21, 79104 Freiburg — 2Fraunhofer IWM, Wöhlerstraße 11, 79108 Freiburg
The long-term stability of lithium-ion batteries (LIB) is often negatively affected by mechanical stresses in the cathode material during charge/discharge cycles. Materials that show a zero-strain (ZS) behavior, i.e. their volume changes hardly during insertion or extraction of Li ions, are therefore of great interest. For individual compounds of the material class of colquiriites, LiAIIMIIIF6, ZS behavior has already been predicted theoretically and observed experimentally, e.g. for Li1+xCaFeF6, which exhibited a volume change of less than 0.5 % upon insertion of lithium ions up to x=0.8.
In order to identify the mechanism responsible for the ZS behavior we calculated the variation of the equilibrium volume due to varying Li concentration using density-functional theory (DFT). The analysis of the electronic and magnetic structure and local structure parameters at equilibrium volumes indicates that the total volume is influenced by a combination of expanding fluorine octahedra around the transition-metal ions due to the changing oxidation state, the distortion of octahedra around the Ca ions, and a decrease of repulsion between fluorine anions due to the inserted Li ions.