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theses

We investigated croconic acid disodium salt for potential use as Li-ion battery material. The crystal was shown to be a promising electrode material with a medium to short battery cycle lifetime. We embarked in a thorough computational study based on classical molecular dynamics simulations to characterize this system and identify optimization strategies to improve battery lifetime. Through long-timescale molecular dynamics simulations in the Canonical Ensemble and Isothermal-Isobaric ensembles, we first established that the custom force field that we generated for this system reproduces the known thermodynamics of the Croconic acid disodium salt dihydrate crystal. In a second step, we predict the existence of a quasi-degenerate denser polymorph which is slightly less stable at room temperature and becomes more stable starting T=420K compared to the known crystal structure as determined by X-Ray crystallography. Interestingly, we find that upon adding lithium the system chooses the denser phase even at room temperature. Lithiation of the denser phase leads to moderate volume increases of about 0.75% for each additional 1% lithiation. By extrapolation of the results of the simulations, we conjecture that a phase transition takes place in the very first stages of lithiation. This should initially reduce the volume, resulting in the formation of cracks in the material contributing to a short battery cycle lifetime. We thus propose to assemble batteries based on croconate at an elevated temperature.

ETD_9410

M.S.

Includes bibliographical references

by Rupali Chawla

doi:10.7282/t3-6swr-w246

ETD graduate

The author owns the copyright to this work.