Physics-Based Assessment of EV Battery Degradation in V2G Services using a Coupled Electrical-Electrochemical- Thermal-Fluid Model

Abstract

Vehicle-to-grid (V2G) allows electric vehicles to provide grid ancillary services, but its impact on battery degradation remains unclear. Current V2G literature relies predominantly on computationally efficient, but limited, semi-empirical methods at constant temperatures, while high-fidelity models are too computationally intensive for long-term simulations. This research bridges this gap by developing a coupled physics-based thermal-electrochemical framework to accurately model battery degradation without the high computational cost of Computational Fluid Dynamics (CFD) models. A Single Particle Model with electrolyte dynamics (SPMe) is augmented with heat generation and side reaction kinetics. This is integrated with a Lumped Parameter Thermal Network (LPTN) and a 1D thermal-fluid Thermal Management System (TMS) model utilising empirical flow correlations. The single-cell framework is validated against experimental voltage and surface temperature data of cylindrical 21700 LG M50 cells under 0.1C, 0.5C, 1C and 1.5C constant current discharge experiments, while the pack-level LPTN and TMS are validated using CFD data from a module consisting of 28 cylindrical 21700 LG M50 cells with serpentine channel cooling under 1C and 5C constant current discharge experiments.

Validation confirms that the reduced-order multi-physics framework accurately replicates pack-level thermal-fluid behaviour (R² > 0.94) at a fraction of the computational cost required for full volumetric meshing. Utilising this framework, subsequent ablation studies demonstrate that, for relatively mild load profiles (< 0.1C), thermal and electrical coupling yields virtually no divergence in macroscopic degradation compared to simple isothermal models. Meaningful degradation spread only emerges at more aggressive currents (> 0.75C), where localised heat generation distinctly accelerates temperature-dependent solid electrolyte interphase (SEI) growth. Finally, long-term V2G simulations demonstrate that standard Frequency Containment Reserve (FCR) services impose a negligible thermal and degradative burden on the battery pack. Even under more extreme stress-test scenarios with tenfold power limits, heat generation remains minimal, failing to approach the thresholds required to trigger active cooling. Therefore, this research concludes that for standard V2G frequency regulation, the implementation of complex, anticipative thermal management strategies offers no tangible benefit, and standard reactive cooling logic is entirely sufficient to preserve pack health.