Mn[B(HFIP)4]2: A Weakly Coordinating Electrolyte for Mn Metal Batteries

Abstract Mn metal batteries (MnMBs) are promising for stationary applications owing to the low cost and low working potential of Mn anodes. However, developing electrolytes that combine high ionic conductivity with low-overpotential Mn plating/stripping remains challenging because of the trade-off between salt dissociation and desolvation. Herein, we propose a weakly coordinating electrolyte, Mn[B(HFIP)4]2 (HFIP: hexafluoroisopropyl), for advanced MnMBs. The [B(HFIP)4]– anion, featuring full electron delocalization and steric hindrance, promotes complete salt dissociation in low-dielectric-constant ethers, yielding a pure ether-coordinated Mn2+ electrolyte with high ionic conductivity (4.7–8.5 mS/cm at 20 °C) and a wide electrochemical window (>3 V). Weak ether-Mn2+ coordination facilitates desolvation, affording a record-low Mn plating/stripping overpotential (<100 mV at 0.5 mA/cm2) and dendrite-free 3D growth. Coupling Mn anodes with polytriphenylamine or activated carbon cathodes enables quick-charge full cells, demonstrating the potential of anion engineering for high-performance multivalent metal batteries.