Numerical and Experimental Study of Meniscus Behavior in Slot-Die Coating of Lithium-Ion Battery Electrodes with Substrate Heating

Instabilities of the coating bead meniscus often lead to coating defects during the slot-die coating process for lithium-ion battery electrode films. In this study, a substrate heating module was introduced to investigate the evolution of the upstream meniscus and associated defect mechanisms under nonisothermal conditions, through a combination of numerical simulations and experimental analysis. First, a temperature-coating window was established based on the capillary number and the minimum wet film thickness, revealing how the synergistic effect between substrate temperature and coating gap governs the boundaries of operational parameters. Second, the influence of substrate temperature on the morphology and position of the upstream meniscus, as well as its impact on edge defect formation, was systematically analyzed. A critical threshold region for wet film thickness variation was identified under the combined effects of temperature and coating gap. Finally, the dynamic evolution of air entrainment defects within the coating bead region was elucidated, with three distinct regimes─threading, bubbling, and transitional flows─experimentally validated. The results demonstrate that substrate heating effectively expands the coating window, and the influence of coating gap and substrate temperature exhibits a quasi-periodic response due to the coupling between the downstream negative pressure field and meniscus dynamics. Moreover, appropriate combinations of substrate temperature and coating gap were found to reduce the apparent dynamic contact angle and mitigate edge height variations. This work provides practical engineering guidance for optimizing thermally assisted electrode manufacturing processes.