Reversible Mg metal anode in conventional electrolyte enabled by durable heterogeneous SEI with low surface diffusion barrier

The popularization of Mg metal batteries (MMBs) is plagued by Mg anode usually suffering from severe passivation and exhibiting an extremely high overpotential in conventional electrolytes. Here, a solvent-assisted additive displacement strategy is proposed to design a durable and heterogeneous solid electrolyte interphase (SEI) with low surface diffusion barrier, composed of MgCl2-rich top layer and organosilicon-dominated bottom layer. This SEI can tolerate long-term anode cycling and therefore permanently protect Mg anode against passivation in conventional electrolyte. Different from traditional SEI with porosity accumulation, this hybrid SEI is condensable with the attenuation of monolithic MgCl2 into nanodomains, which are infused and embedded in the Si-O and Si-C reinforced organic matrix, without the compromise of Mg-ion diffusion. This anti-passivation strategy enables a highly reversible Mg metal anode (over 600 cycles) in Mg(TFSI)2 based electrolyte with the enhanced interfacial kinetics, reduced overpotential (∼350 mV), large critical current density (5.6 mA cm−2) and excellent compatibility with conversion cathode without extra electrolyte additive. This work opens the avenue for the construction of highly tolerant and conductive SEI to displace fragile and passivated SEI to inspire the application of “simple” salt electrolyte in MMBs.