Borohydride-Based Interphase Enabling Reversible Magnesium Metal Anode in Conventional Electrolytes

Magnesium (Mg) anodes typically experience electrochemical passivation and dendrite formation with conventional electrolytes during cell storage and operation, which results in a rapid decline in cyclability and shortened lifespans. These concerns supposedly relate to the features of the Mg/electrolyte interface. Herein, we report that Mg(BH4)2-rich artificial hybrid interphase (AHI) fabricated on Mg by a simple cation replacement method effectively ensures electrochemical activity and nondendritic interface. This can be attributed to the synergy of fast Mg2+ transfer, high electronically insulating and structural stability, etc., of AHI, as revealed by experimental and computational findings. The symmetric cell presents a low-voltage polarization of 230 mV and prolonged cycling life of over 1300 h at 1 mA cm–2 in 0.5 M Mg[bis(trifluoromethanesulfonyl)imide (TFSI)]2/dimethoxyethane (DME) electrolyte. Meanwhile, the full cells paired with a Mo6S8 cathode at various rates with desirable stability are also achieved. Our work provides further insight into the design of a versatile non-MgCl2 artificial layer specialized for rechargeable Mg batteries.