High-performance magnesium metal batteries via switching the passivation film into a solid electrolyte interphase

Abstract

Magnesium-ion batteries have been regarded as a promising alternative to the lithium-ion batteries due to their high theoretical capacity, relatively high potential, and magnesium abundance. However, the contradiction between the plating/stripping of Mg²⁺ and the electrolytes’ oxidative stability has hampered the Mg-ion battery's development for energy storage applications. Here, we designed an amorphous MgO-wrapped Zn-skeleton as a unique current collector for an anode-free Mg battery to allow reversible Mg²⁺ plating/stripping in oxidatively stable electrolytes. The significant lattice mismatch between hexagonal Zn and MgO induces dislocations, leading to a highly defective interphase. This layer behaves as a mixed ionic-electronic conductor, rendering Mg nanoparticles upon electroplating. Combined with a large surface area, the proposed current collector considerably improved the charge transfer kinetics and lowered the cell impedance for Mg²⁺ plating/stripping by 1/20 of the typical Mg metal. Moreover, the Mg²⁺ interphase conduction was two orders of magnitude higher (∼10⁻¹¹ S cm⁻¹) compared to the widely known passivating layer (<10⁻¹³ S cm⁻¹). This special design enables Mg–Li hybrid batteries with non-corrosive electrolytes to exhibit a high-operating-voltage of 2.82 V vs. Mg/Mg²⁺ and an energy density of 412.5 W h kg⁻¹.