Sustainable release of Mg(NO3)2 from a separator boosts the electrochemical performance of lithium metal as an anode for secondary batteries†

Lithium metal batteries (LMBs) can alleviate ‘range anxiety’ and have broad prospects due to their high energy densities. However, poor safety and cycling performances of the LMBs due to the unconstrained lithium metal anodes (LMAs) limit their further application. Many solutions have been proposed to address the problems of LMBs, but few studies have focused on cheap separators. Here, a separator modified with conductive Super P and Mg(NO₃)₂ (MN) (SP@MND) is prepared for LMBs. Super P can promote the reaction kinetics of cathodes. MN can be sustainably released from the modified separator into the electrolyte and can dissociate into Mg²⁺ and NO₃⁻, which standardizes the deposition of Li⁺ cations and forms an ionic-conductive protective layer on the LMA, respectively. SP@MND shows an outstanding performance in both ether-based and ester-based electrolytes, and LMAs can exhibit a long cycling life of over 4800 h at 0.5 mA cm⁻² and 0.5 mA h cm⁻² and a high current density of up to 50 mA cm⁻². The assembled LMBs exhibit a low capacity decay rate of 0.059% after 1000 cycles at 3C for a Li//S battery and a high average coulombic efficiency of 99.2% at 10C for the Li//LiFePO₄ one after 1000 cycles. This work provides a solid basis for the production of LMBs with a high ratio of performance to cost.