Gradient Perovskite Ionic–Electronic Heterointerphases for Deep Cycling Mg Metal Anodes

Abstract

Abstract Direct use of metals with low redox potential and high capacity as anodes can enable high energy density batteries. Mg metal has been considered as an ideal anode for its high critical current density and earth‐abundance, but its development has been impeded by the lacking of Mg‐compatible yet cost‐effective electrolyte. Artificial layers that prevent direct Mg‐electrolyte contact while permit Mg 2+ to transport through, mitigate the anode–electrolyte incompatibility and allow industrial Li battery electrolyte analog to implement. However, charge transport through these artificial layers remains elusive, let alone to quantitatively design the layer thickness, components, and their distribution. Here it is shown that by using a gradient mixed ion‐electron conducting layer, which is prepared by a transferable perovskite film, the ion/electron transport path can be individually and continually tuned. It is found that a high Coulombic efficiency of 99.2% can be obtained for Mg anode in 0.5 M Mg(TFSI) 2 /DME electrolyte. It is also shown that long cycling full cells with a low N/P ratio (N/P ≈ 3.42 for Mg|Mo 6 S 8 , N/P ≈ 2.06 for Mg|Cu 2‐x S) can be achieved. It is suggested that rational interfacial engineering will open new way to design practical Mg metal batteries.