摘要
The interplay between solvent co-intercalation, solid-electrolyte interface (SEI) formation, and gas evolution at the graphite anode-electrolyte interface plays a critical role in battery performance; yet, it remains poorly understood at the nanoscale. In this study, we introduce ultrasound-based operando atomic force microscopy (AFM), which breaks the spatial-resolution limitation of ultrasound-based techniques, to visualize the dynamics of solvent co-intercalation, SEI formation, and subsurface gas evolution in graphite anodes for lithium-ion batteries. Remarkably, we observe that gas evolution leads to the formation of "subsurface molecular bubbles"-gaseous pockets trapped between graphite layers-that compromise interfacial stability during battery formation cycles. AFM and density functional theory calculation results revealed that these subsurface molecular bubbles are primarily induced by the co-intercalation and decomposition of Li+(EC)(4) solvation complexes. We also found that the solvent co-intercalation and interlayer decomposition effects can be fully suppressed by incorporating a low-permittivity, non-solvating diluent solvent (fluoride benzene) through optimizing the de-solvation energy and the interfacial molecular architectures. By applying this optimized electrolyte in both graphite/Li half-cells and lithium cobalt oxide (LCO)/graphite full-cells, we achieve stable cycling with negligible molecular bubble formation, compact SEI growth, and high coulombic efficiency (>93%) during high-rate (0.5C) battery formation.