Toward High‐Voltage Magnesium Batteries via Molecular Engineering of a Weakly Coordinating Borate Electrolyte

ABSTRACT Rechargeable magnesium batteries (RMBs) have long been considered ideal alternatives to lithium‐ion batteries due to the high theoretical capacity of metallic magnesium anodes and abundant resources. However, developing chloride‐free electrolytes with high voltage stability, ionic conductivity, and excellent interfacial stability remains a core challenge for practical application. Herein, via a dual‐ligand molecular engineering strategy, we designed and synthesized a novel magnesium electrolyte Mg[B(fp)(hfip) 2 ] 2 . The synergistic effect between the perfluoropinacol and hexafluoroisopropanol ligands precisely regulates the electronic structure of the anion and its solvation behavior at the molecular level. This electrolyte exhibits a high ionic conductivity of 13.57 mS cm −1 , an anodic stability of up to 4.2 V (vs. Mg 2+ /Mg), and a t Mg 2+ of 0.70. The Mg||Mg symmetric cell achieves stable cycling for over 2000 h. When paired with the designed TPA‐COF cathode, the full cell breaks the voltage limitation of conventional magnesium batteries, delivering a discharge plateau exceeding 3.0 V and a high energy density of 212 Wh kg −1 . Moreover, it shows excellent rate capability and ultralong cycle life, retaining 76% capacity after 2000 cycles at 3 A g −1 . This work establishes a profound molecular structure‐macroscopic performance connection, providing an innovative pathway for rational electrolyte design in multivalent batteries.