Unconventional Dendrite-Free Deposition of Mg Metal Anodes at Low Temperatures.

Temperature plays a critical role in governing the plating behavior of metallic anodes by regulating ionic conductivity of the electrolyte, desolvation energy, and charge transfer processes in the solid-electrolyte interphase (SEI). While low temperature commonly triggers dendritic growth on metallic anodes (e.g., Li, Na, and Zn), the temperature effect on Mg plating/stripping behaviors remains unknown thus far. Herein, we report an unconventional temperature-dependent deposition behavior of Mg anodes that tends to form dendrite-free deposits at low temperatures. Integration of cryo-transmission electron microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy reveals that the SEI layer formed at low temperatures has an ultrathin thickness (∼2-3 nm) and is enriched in high-modulus inorganic compounds, which facilitates the uniform deposition of Mg anodes. As a result, the Mg metal anode realizes an exceptional average Coulombic efficiency up to 99.92% over 2000 cycles at -20°C. This study demonstrates the unconventional deposition behavior of Mg metal anodes at low temperatures, underpinning their potential for low-temperature applications and advancing the fundamental understanding of metal deposition.