Coupled electrochemical–thermal modelling of early-stage degradation processes in lithium-rich disordered rocksalt cathodes

offer high theoretical capacity but exhibit complex electrochemical and thermal interactions during early operation. Here, a coupled electrochemical-thermal model based on the Doyle-Fuller-Newman framework is developed to investigate the initial interplay between interfacial kinetics, transport, and heat generation under galvanostatic discharge. The model incorporates solid electrolyte interphase (SEI) growth, lithium plating, and spatially resolved heat production to examine the onset of degradation-related processes within a single discharge cycle. Simulations predict SEI thickening to ∼30 nm within 0.4 h, lithium plating onset near 0.25 h, and localized thermal hotspots reaching ∼360 K at the cathode mid-plane. Sensitivity analysis identifies SEI kinetics and anode exchange current density as dominant factors influencing early performance loss. These results highlight the electrochemical-thermal feedback mechanisms active during early-stage operation and provide a physically grounded framework for interpreting the initial degradation behaviour of lithium-rich DRX cathodes.