Simultaneous Enhancement of Interface Stability and Ionic Transport by Li⁺ and BH₄^- in Magnesium-Based Energy Storage

Magnesium-based batteries present a promising alternative to lithium-ion systems due to the high abundance, volumetric capacity, and dendrite-free nature of magnesium. However, existing magnesium battery electrolytes often encounter significant limitations, including high overpotentials, limited ionic conductivity, and electrode passivation, which hinder their practical application. In this work, we report a Mg(TFSI)₂/diglyme (G2) electrolyte enhanced with 0.3 M lithium borohydride (LiBH₄), which demonstrates a marked improvement in both electrochemical stability and efficiency through the dual role of Li⁺ and BH₄^- ions. Our findings show that Li⁺ ions effectively boost ionic conductivity, enabling rapid Mg²⁺ transport, while BH₄^- anions stabilize the electrode interface by forming a robust, passivation-resistant solid electrolyte interphase (SEI) layer. This electrolyte formulation achieves high Coulombic efficiency and extended cycling stability, as validated in both symmetric Mg//Mg, asymmetric Mg//Cu and full Mg//V₂S₃ cells. Additionally, molecular dynamics simulations provide insight into the coordination environment of Mg²⁺ and Li⁺ ions, confirming the distinct contributions of Li⁺ and BH₄^- to the electrolyte's enhanced performance. This study highlights the practical applicability of LiBH₄-modified Mg-based electrolytes in next-generation energy storage systems, offering a scalable pathway for developing efficient, durable magnesium batteries.