  In lithium ion batteries, Li+ intercalation and processes associated with
passivation of electrodes are governed by applied voltages, which are in turn
associated with free energy changes of Li+ transfer (Delta G_t) between the
solid and liquid phases. Using ab initio molecular dynamics (AIMD) and
thermodynamic integration techniques, we compute Delta G_t for the virtual
transfer of a Li+ from a LiC(6) anode slab, with pristine basal planes exposed,
to liquid ethylene carbonate confined in a nanogap. The onset of delithiation,
at Delta G_t=0, is found to occur on LiC(6) anodes with negatively charged
basal surfaces. These negative surface charges are evidently needed to retain
Li+ 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+/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.
