SKM 2023 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 5: Materials in Energy Conversion: Mechanical Properties and Solid State Batteries

MM 5.2: Vortrag

Montag, 27. März 2023, 10:30–10:45, SCH A 215

Design of zero strain cathode materials based on colquiriite-type Li_xCa(M,M’)F₆ — •Aljoscha Felix Baumann^1,2, Daniel Mutter², Daniel Urban^1,2, and Christian Elsässer^1,2 — ¹Freiburger Materialforschungszentrum, Stefan-Meier-Straße 21, 79104 Freiburg im Breisgau — ²Fraunhofer-Institut für Werkstoffmechanik IWM, Wöhlerstr. 11, 79108 Freiburg

The long-term stability of Li ion batteries can be negatively affected by mechanical stresses in the microstructure of the cathode material during charge/discharge cycles. Therefore, materials are of great interest which show a zero-strain (ZS) behavior, i.e. a negligible volume change during insertion or extraction of Li ions. For specific compounds of the material class of colquiriites, Li_xA^IIM^IIIF₆, ZS behavior was predicted theoretically and measured experimentally for different Li concentration ranges. In this work we investigate the effect of the electrochemically active cation M^III (M = Ti, V, Cr, Mn, Fe, Co, Ni) on the volume change during (de-)lithiation. Using density-functional theory we calculated the equilibrium volumes at different Li concentrations. The analysis of the electronic and magnetic structures and the calculation of local structural parameters indicate that the total volume change depends mainly on the counteracting effects of expanding fluorine octahedra around the M ions due to the changing oxidation state, and a decrease of repulsion between fluorine anions due to the inserted Li ions. The trends in the properties along the period of the 3d transition metals provide a guideline for a design of new ZS cathode materials in solid solutions of type Li_xCa(M,M’)F₆.