Cryogenic nanoscale visualization of intrinsic magnesium deposition in magnesium metal batteries.

Magnesium metal batteries are considered promising candidates for next-generation energy storage systems due to the high volumetric capacity, intrinsic safety and natural abundance of magnesium. Yet, the fundamental mechanisms that govern the magnesium deposition and the formation of surface interphases remain poorly understood, largely due to the complexity of battery chemistry and the lack of reliable techniques to probe these processes at the atomic scale. Here we show that, by using cryogenic transmission electron microscopy, different magnesium deposition morphologies (e.g., whisker-shaped or seaweed-shaped) in conventional single-salt electrolytes converge to an intrinsic hexagonal platelet shape once surface passivation is decoupled from magnesium plating. This characteristic shape persists across different electrolyte chemistries, suggesting that suppressing surface passivation eliminates the influence of electrolyte composition on magnesium deposition morphology. These findings reveal the intrinsic nature of magnesium electrodeposition and establish a mechanistic link between interfacial chemistry and morphological evolution. Our work highlights a fundamental principle for controlling magnesium deposition behavior, paving the way for the rational design of stable, high-performance magnesium-based batteries.