Regensburg 2016 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 21: Frontiers of Electronic Structure Theory: Focus on Topology and Transport
(Joint session of DS, HL, MA, MM, O and TT organized by MM)

TT 21.2: Vortrag

Montag, 7. März 2016, 16:00–16:15, H51

Potential-dependent mechanism of Li diffusion in Li₂S — •Ashkan Moradabadi^1,2 and Payam Kaghazchi¹ — ¹Institut für Chemie und Biochemie, Freie Universität Berlin, Takustr. 3, 14195 Berlin, Germany — ²Institut für Materialwissenschaft, Fachgebiet Materialmodellierung, Technische Universitat Darmstadt, Jovanka-Bontschits-Str. 2, 64287 Darmstadt, Germany

Li-S batteries are promising candidates for large-scale applications such as electrical vehicles. However, the measured discharge capacity is often less than the theoretical one [1,2]. This is mainly due to the slow diffusion of Li through Li₂S shells formed on S₈ cores, which leads to an incomplete conversion of S₈ cores to Li₂S (the final product of lithiation of S₈). In the present work, using density functional calculation, we have investigated mechanism of Li diffusion in Li₂S. At low cell voltages (< 0.93 V), Li diffusion occurs via an exchange mechanism with a high energy barrier of 0.45 eV. However at higher cell voltages, Li diffusion takes place via a vacancy mechanism with a lower energy barrier of 0.27 eV. Our findings can explain the capacity fading in Li-S batteries at high operation rates.

[1] Liang, X.; Hart, C.; Pang, Q.; Garsuch, A.; Weiss, T.; Nazar, L. F.; A highly efficient polysulfide mediator for lithium-sulfur batteries. Nature Communications, 2015, 6, 5682.

[2] Wang, L.; Wang, Y.; Xia, Y.; A high performance lithium-ion sulfur battery based on a Li₂S cathode using a dual-phase electrolyte. Energy Environ. Sci. 2015, 8, 1551.