Ab initio molecular dynamics for calculating battery voltage

The voltage of a battery can typically be simulated with density functional theory (DFT) by calculating the Gibbs free energy difference between the charged and discharged components. For typical battery chemistries, this can be reasonably approximated with the energies of the cathode and anode, while the electrolyte is considered to experience no net change. However, there are some instances where the electrolyte plays an active role in the operation of the battery. This presentation will describe our efforts to calculate the voltage of batteries in which the state (composition) of the electrolyte changes during the charge/discharge process, which needs to be treated with ab initio molecular dynamics (AIMD) to capture the dynamical nature of liquid electrolyte, and to calculate its contribution to the voltage. In one example, we study a battery that involves dual ion (de)-intercalation of both Na⁺ and ClO₄^- species into the cathode. A second example involves vanadium redox flow batteries in which all electrochemical processes occur within the liquid anolyte and catholyte. The approach described here is transferrable to study numerous other battery chemistries in which the liquid electrolyte plays an active role.