Highly reversible Mg metal anodes enabled by interfacial liquid metal engineering for high-energy Mg-S batteries

Metallic Mg is a promising anode material for rechargeable magnesium-ion batteries (MIBs) due to its low electrochemical potential and high theoretical capacity. However, low Mg2+ conductivity on the interface of Mg electrode caused by liquid electrolyte passivation hinders its development. In addition, whether Mg dendrites can be formed in Mg metal anodes is controversial. Herein, we find that Mg dendrites can be formed in Mg metal anodes. The diameter of most Mg dendrites is below 100 nm, which is much smaller than Li and Na dendrites. The nanoscale Mg dendrites can easily pierce through the separators with large pore size and cause the internal short circuit of batteries. A simple strategy is proposed to address the issues of Mg metal anodes by painting a liquid metal Ga layer on Mg foil. Metallic Ga can spontaneously alloy with metallic Mg to form a stable, Mg2+-conductive, corrosive-resistant, and magnesiophilic Ga5Mg2 alloy layer. Under the regulation of the Ga5Mg2 alloy layer, a highly reversible, stable, and dendrite-free Mg metal anode is obtained. Enhanced electrochemical performance is achieved both in symmetric cells and Mg-S full cells. This study paves the way for high-energy Mg-metal batteries.