Electrolyte-dependent physico-chemical interfacial kinetics shape degradation pathways and lifetime in lithium-ion batteries

Abstract Electrolyte-dependent lifetime variability remains a major obstacle to sustainable deployment of lithium-ion batteries, contributing to premature retirement, increased material demand and uncertainty in lifecycle assessment. However, most continuum degradation models represent the electrolyte through bulk transport, without capturing its role in interfacial degradation. Here, we use customised multi-layer pouch cells with varied ethylene carbonate:dimethyl carbonate ratio, lithium hexafluorophosphate concentration and electrolyte amount to examine how electrolyte conditions shape degradation trajectories under accelerated degradation. Within this formulation framework, changing the solvent ratio leads to distinct lifetime trajectories across otherwise comparable cells. Electrochemical diagnostics, gas analysis and post-mortem interfacial characterisation show that this divergence is associated with electrolyte-sensitive interphase growth, parasitic reactions and spatially heterogeneous surface degradation. We incorporate electrolyte-dependent transport and thermodynamic properties into a physics-based degradation model. A transport-only implementation does not reproduce the observed separation in capacity-retention trajectories. Introducing a minimal electrolyte-sensitive refinement through an effective interphase transport parameter improves agreement in the ethylene-carbonate-rich case. These results identify electrolyte-sensitive interfacial degradation as a necessary modelling dimension for reliable lifetime prediction.