Publication Date:
2016-05-27
Description:
Li 2 S is the final product of lithiation of sulfur cathodes in lithium-sulfur (Li-S) batteries. In this work, we study formation and diffusion of defects in Li 2 S. It is found that for a wide range of voltages (referenced to metal Li) between 0.17 V and 2.01 V, positively charged interstitial Li (Li + ) is the most favorable defect type with a fixed formation energy of 1.02 eV. The formation energy of negatively charged Li vacancy ( V L i − ) is also constant, and it is only 0.13 eV higher than that of Li + . For a narrow range of voltages between 0.00 V and 0.17 V, the formation energy of neutral S vacancy is the lowest and it decreases with decreasing the cell voltage. The energy barrier for Li + diffusion (0.45 eV), which takes place via an exchange mechanism, is 0.18 eV higher than that for V L i − (0.27 eV), which takes place via a single vacancy hopping. Considering formation energies and diffusion barriers, we find that ionic conductivity in Li 2 S is due to both Li + and V L i − , but the latter mechanism being slightly more favorable.
Print ISSN:
0003-6951
Electronic ISSN:
1077-3118
Topics:
Physics
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