Degradation and SEI Evolution in Alloy Anodes Revealed by Correlative Liquid-Cell Electrochemistry and Cryogenic Microscopy

Abstract Understanding solid–liquid interfaces at high spatial and chemical resolution is crucial for advancing electrochemical energy storage technologies, yet remains challenging due to the difficulty of capturing dynamic processes while preserving fragile interfacial chemistries. In lithium-ion batteries, interfacial phenomena such as lithium alloying, solid–electrolyte interphase (SEI) formation, and electrode degradation play a decisive role in capacity retention and failure mechanisms, but are difficult to observe in their native state due to lithium’s high mobility, reactivity, and low atomic number. Here, we integrate operando liquid-cell transmission electron microscopy (LCTEM) with cryogenic atom probe tomography (cryo-APT) to directly resolve the evolution of a platinum alloy anode at the solid–liquid interface during electrochemical cycling. Operando imaging reveals the evolution of mossy lithium plating, unstable SEI growth, and progressive electrode cracking over successive cycles. Complementary cryo-APT analysis of the preserved interface identifies carbonate-containing interfacial species, lithium enrichment at the electrode–electrolyte interface, and lithium localization within the electrode microstructure. Together, these observations provide mechanistic insight into how SEI instability drives heterogeneous lithium deposition, structural degradation, and early-cycle capacity loss. This correlative framework enables direct linkage of electrochemical dynamics with near-atomic-scale chemistry, establishing a broadly applicable approach for investigating reactive interfaces in next-generation energy materials.