Dual-Site Modulation of Mg Desolvation Beyond the Primary Solvation Shell in Magnesium Battery Electrolytes.

High overpotential and instability of Mg anode reactions limit the development of halide-free Mg battery electrolytes. Here, we report 7-aminoindole (7AID), a predominantly noncoordinating additive that modulates solvation via CH-π and hydrogen-bonding interactions with both Mg-bound and free ether solvents. These outer-shell and bulk-phase interactions weaken Mg···solvent binding, enhance solvent mobility, and lower the desolvation barrier. As a result, Mg plating/stripping overpotentials are significantly reduced and interfacial stability is improved. Compared to strongly coordinating additives, this approach suppresses parasitic reactions and enables more stable cycling. This work presents a solvation-targeted additive design paradigm beyond the primary coordination shell for advancing multivalent battery electrolytes.