Synergetic effects of cation and anion of Mg(NO3)2 as electrolyte additives in stabilizing Li metal anode

Abstract

The fabrication of a uniform solid electrolyte interface (SEI) with high robustness and ionic conductivity has long been necessary for Li metal anodes with high-performance; however, realizing such a design remains challenging. In this work, we applied magnesium nitrate (Mg(NO₃)₂) as an additive and γ-butyrolactone (GBL) as a solubility mediator to optimize an ester-based electrolyte for Li metal anodes. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS) results revealed that the Mg(NO₃)₂ in the 0.1 Mg(NO₃)₂-GBL electrolyte spontaneously reacted with the Li metal anodes to form a continuous Li–Mg alloy with Li₃N phases dominating the SEI on the anode. The formed SEI induced a homogenous Li plating/stripping behavior on the anode surface, which improved the charge/discharge performance of the anode and inhibited Li dendritic growth. Furthermore, owing to the high ionic conductivity and large young's modulus of the inorganic phases in the optimized SEI, the Li metal anode maintained a stable and flat surface morphology even after cycling for 3000 h without any dendrite-induced issues, thus guaranteeing a long lifespan for the corresponding battery system. In addition, the symmetrical cell using only 10 μL of 0.1 Mg(NO₃)₂-GBL electrolyte maintained constant voltage hysteresis in the range of 12–18 mV over 620 h before the voltage swelled, suggesting such a superior electrolyte under a restricted condition.