Interfacial Insight from Operando XAS/TEM for Magnesium Metal Deposition with Borohydride Electrolytes

Operando soft X-ray absorption spectroscopy (sXAS) and transmission electron microscopy (TEM) of the electrochemical deposition of magnesium metal from borohydride electrolytes is presented. The analysis identifies the active component for the deposition of magnesium metal as the contact-ion pair [Mg­(μ-H)2BH2]+. Additionally, the formation of boron clusters accompanied by H2 -gas formation accompany the deposition of Mg metal, and play a vital role in the formation of a solid-electrolyte interphase (SEI) on the surface. To use Mg metal as a viable anode for future battery systems, understanding the interfacial components and chemistry is key.