Interfacial coatings show promise in stabilizing carbon negative electrodes for lithium-ion batteries. For example, applying nanometer scale Al2O3 coatings on carbon can improve fast-charging, low-temperature battery performance, and cycle life. However, the exact mechanism by which these interfacial films stabilize negative electrodes in lithium-ion batteries remains poorly understood. Here, we show that Al2O3 coatings on carbon negative electrodes undergo structural and chemical changes during the formation of the solid-electrolyte interphase (SEI) at low potentials. During formation, we find a conformal bilayer SEI on Al2O3-coated carbon electrodes, with each layer exhibiting distinct chemistry. Importantly, the SEI structure, chemistry, and uniformity differ substantially between Al2O3-coated carbon electrodes and uncoated carbon electrodes. Our results suggest that performance improvements are not solely due to the presence of the Al2O3 coating. Instead, we propose that the improved SEI structure, chemistry, and uniformity after formation are the key factors contributing to improvements in battery performance.