In situ AFM of interfacial evolution at magnesium metal anode

Magnesium (Mg) metal batteries have attracted increased attention due to their high theoretical energy densities, low cost and high safety. However, severe capacity degradation induced by irreversible Mg deposition/stripping processes limits the long-term durability of Mg metal batteries. Direct visualization of the dynamic processes of Mg deposition/stripping is of great significance to intensively understand the degradation mechanism. Herein, we systematically investigated the morphological changes during Mg deposition and stripping at the nanoscale by in situ atomic force microscopy (AFM) in diglyme (DEG)/ ionic liquid (IL) system. The formation processes of sphere-shaped and crystallized Mg, as well as their stripping processes are directly observed. In the combination with in situ optical imaging, we found that the irreversible stripping process of deposited Mg results in the loss of active materials, potentially leading to severe capacity fading and poor cycling stability. Our results provide direct insights into the interfacial evolution at the nanoscale and the structure–reactivity correlation, which offer useful information for the design of high performance Mg metal batteries.