mat-electrochemical-window

Electrochemical Stability Window (ECW) Calculation

Goal

To determine the intrinsic electrochemical stability window (ECW) of a material, specifically bounding the reduction ($V_{\text{red}}$) and oxidation ($V_{\text{ox}}$) potentials against a mobile working ion (e.g., Li/Li+), using a standard zero-Kelvin phase diagram.

This explicitly implements the standard thermodynamic approach for solid electrolytes defined in: Zhu, Y., He, X. & Mo, Y. "Origin of Outstanding Stability in the Lithium Solid Electrolyte Materials: Insights from Thermodynamic Analyses Based on First-Principles Calculations". ACS Appl. Mater. Interfaces 7, 23685–23693 (2015).

[!TIP] Coupling with Stability: ECW calculation relies entirely on the same generic computed energies and PhaseDiagram used for determining $E_{hull}$. You can uniquely combine this with the mat-stability skill to calculate both intrinsic thermodynamic stability and electrochemical stability in the same step using the same unified convex hull.

Methodology

The electrochemical stability window of a phase represents the voltage range over which it is thermodynamically stable against reduction by (e.g., lithiation) or oxidation (e.g., delithiation) of the target ion.

In pymatgen, this exact analytical bounding is extracted using PhaseDiagram.get_transition_chempots(mobile_element).

1. Calculate Global Phase Diagram boundaries: For the composition of the target phase, identifying the critical chemical potentials ($\mu_{\text{Li}}$) where stable facets on the phase diagram intersect.
2. Identify the stable Region: Evaluating an intermediary point in each discrete chemical potential band on the GrandPotentialPhaseDiagram to check if the exact composition is structurally present on the extended hull. If the material is metastable (E_hull > 0), its intrinsic ECW is always exactly [0.0 V, 0.0 V].
3. Reference Scale Conversion: The bounds are translated from absolute chemical potentials into voltages versus the pure standard state metal: $V = -(\mu_{\text{Li}} - \mu_{\text{Li, ref}})$.