Causal Relationship between Potential Shift and Molecular Structure in Concentrated Electrolytes

Understanding the origin of potential shifts in concentrated
electrolytes
is crucial for the design of stable and high-energy-density lithium–metal
batteries. In our previous work, we identified a strong correlation
between experimental electrode potential and Li+–anion
interactions, suggesting the importance of intermolecular structure
beyond conventional molecular properties. In this study, we revisit
this issue from the perspective of causal discovery. We applied the
Linear Non-Gaussian Acyclic Model (LiNGAM) to a data set of 75 electrolyte
solutions containing LiFSI salt and various solvent molecules, using
a comprehensive set of 132 descriptors including molecular properties
(e.g., HOMO, LUMO, binding energy) and intermolecular descriptors
derived from radial distribution functions (RDF) and their integrals
(NDF) from molecular dynamics simulations. To mitigate overfitting
due to high descriptor dimensionality, we employed a genetic algorithm
to select reduced sets of descriptors. LiNGAM analysis revealed that
descriptors associated with Li+–anion spatial distribution,
especially long-range NDF descriptors, exhibit a direct causal effect
with experimentally measured potential values. In contrast, no such
causal relationships were identified for intrinsic molecular properties.
These findings further support the recently proposed advanced theoretical
framework, which incorporates a Debye–Hückel-based model
and identifies the liquid-phase Madelung interaction as a dominant
factor governing the potential shift in highly concentrated electrolytes.
Moreover, we demonstrate that causal discovery methods can reveal
fundamental physical mechanisms underlying electrochemical behavior.