First principle study of the electrochemical properties of Li2FeSiS4

First principle calculations have been performed to evaluate the effect of S substitution for O on the electrochemical performance of Li2FeSiO4. Basing on the Li2FeSiO4 structure, the hypothetical models of Li2FeSiS4 have been analyzed. The deinsertion voltage associated to Fe3+/Fe4+ redox couple is predicted to decrease from 4.80 V (Li2FeSiO4) to 3.24 V (Li2FeSiS4). From the point of view of electronic conductivity, Li2FeSiS4 is expected to have a better current rate capacity than Li2FeSiO4. The calculations also indicate that S substitution significantly improve the material ductility, preventing the probable structural collapse of silicate materials during charge–discharge cycles. In the light of our calculated results the high electrochemical performance of silicate cathode materials would be achieved in Li2FeSiS4.

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