Toward
First Principles Prediction of Voltage Dependences
of Electrolyte/Electrolyte Interfacial Processes in Lithium Ion Batteries
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Abstract
In lithium ion batteries, Li<sup>+</sup> intercalation into electrodes
is induced by applied voltages, which are in turn associated with
free energy changes of Li<sup>+</sup> transfer (Δ<i>G</i><sub><i>t</i></sub>) between the solid and liquid phases.
Using <i>ab initio</i> molecular dynamics (AIMD) and thermodynamic
integration techniques, we compute Δ<i>G</i><sub><i>t</i></sub> for the virtual transfer of a Li<sup>+</sup> from
a LiC<sub>6</sub> anode slab, with pristine basal planes exposed,
to liquid ethylene carbonate confined in a nanogap. The onset of delithiation,
at Δ<i>G</i><sub><i>t</i></sub> = 0, is
found to occur on LiC<sub>6</sub> anodes with negatively charged basal
surfaces. These negative surface charges are evidently needed to retain
Li<sup>+</sup> inside the electrode and should affect passivation
(“SEI”) film formation processes. Fast electrolyte decomposition
is observed at even larger electron surface densities. By assigning
the experimentally known voltage (0.1 V vs Li<sup>+</sup>/Li metal)
to the predicted delithiation onset, an absolute potential scale is
obtained. This enables voltage calibrations in simulation cells used
in AIMD studies and paves the way for future prediction of voltage
dependences in interfacial processes in batteries