Ion‐Specific Acetate‐Mn2+ Coordination for Accelerating Desolvation Kinetics in Aqueous Mn‐Ion Battery

The unique d¹⁰ configuration of Mn²⁺ provides exceptional coordination ability, making it highly sensitive to acetate ligands (Ac⁻). This ion-specific coordination enables Ac⁻ to replace one H₂O molecule in the inner hydration shell of Mn²⁺ through ligand exchange. The resulting [MnAc(H₂O)₅]⁺ configuration accelerates the desolvation kinetics of Mn²⁺, enhancing the energy storage performance of aqueous Mn-ion batteries.

Abstract

Aqueous manganese ion batteries (AMIBs) are promising candidates for large-scale energy storage because of their inherent safety and low cost. As a representative transition metal ion, Mn²⁺ features a half-filled 3d⁵ electron configuration that enables diverse coordination geometries and a broader scope for battery optimization. Here, the ion-specific coordination between Mn²⁺ and acetate ions (Ac⁻) to adjust the d-electron configuration of Mn²⁺ and induce a distorted water-deficient hydration shell is demonstrated. The coordination chemistry of Mn²⁺ allows Ac⁻ to break the octahedral geometry of [Mn(H₂O)₆]²⁺ through ligand exchange, facilitating the de-solvation kinetics and interfacial transfer of Mn²⁺. This regulating effect is distinct from that observed in Zn²⁺ solvation, highlighting the ion-specific pairing resulting from the d-electron configurations of transition metals. As expected, incorporating Ac⁻ ligands in aqueous manganese-based electrolytes enhances the Mn²⁺ storage performance of perylenetetracarboxylic diimide (PTCDI) anode in terms of both capacity and stability. An all-organic AMIB is then assembled by using tetrachloro-1,4-benzoquinone (TCBQ) as the cathode, which exhibits an average discharge plateau voltage of 1.1 V, a capacity of 98 mAh g⁻¹ at a current density of 1.0 A g⁻¹, and an impressive capacity retention of 96.3% over 1000 cycles.