# Ab initio molecular dynamics investigations of the speciation and reactivity of deep eutectic electrolytes in aluminum batteries

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## Abstract

Deep eutectic solvents (DES) have emerged as an alternative for conventional ionic liquids in aluminum batteries. Elucidating DES composition is fundamental to understand aluminum electrodeposition in the battery anode. Despite numerous experiemental efforts, the speciation of these DES remains elusive. This work shows how \textit{Ab initio} molecular dynamics (AIMD) simulations can shed light on the molecular composition of DES. For the particular example of AlCl$_{3}$:urea, one of the most popular DES, we carried out a systematic AIMD study, showing how an excess of AlCl$_{3}$ in the AlCl$_{3}$:urea mixture promotes the stability of ionic species vs neutral ones and also favors the reactivity in the system. These two facts explain the experimentally observed enhanced electrochemical activity in salt-rich DES. We also observe the transfer of simple $[$AlCl$_{x}$(urea)$_{y}]$ clusters between different species in the liquid, giving rise to free $[$AlCl$_{4}]^{-}$ units. The small size of these $[$AlCl$_{4}]^{-}$ units favors the transport of ionic species towards the anode, facilitating the electrodeposition of aluminum.

Original language English ChemSusChem 14 9 2034-2041 1864-5631 https://doi.org/10.1002/cssc.202100163 Published - 2021

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