Se-dopant Modulated Selective Co-Insertion of H+ and Zn2+ in MnO2 for High-Capacity and Durable Aqueous Zn-Ion Batteries.

Abstract

MnO2 is commonly used as the cathode material for aqueous zinc-ion batteries (AZIBs). The strong Coulombic interaction between Zn ions and the MnO2 lattice causes significant lattice distortion and, combined with the Jahn-Teller effect, results in Mn2+ dissolution and structural collapse. While proton intercalation can reduce lattice distortion, it changes the electrolyte pH, producing chemically inert byproducts. These issues greatly affect the reversibility of Zn2+ intercalation/extraction, leading to significant capacity degradation of MnO2. Herein, we propose a novel method to enhance the cycling stability of δ-MnO2 through selenium doping (Se-MnO2). Our work indicates that varying the selenium doping content can regulate the intercalation ratio of H+ in MnO2, thereby suppressing the formation of ZnMn2O4 by-products. Se doping mitigates the lattice strain of MnO2 during Zn2+ intercalation/deintercalation by reducing Mn-O octahedral distortion, modifying Mn-O bond length upon Zn2+ insertion, and alleviating Mn dissolution caused by the Jahn-Teller effect. The optimized Se-MnO2 (Se concentration of 0.8 at.%) deposited on carbon nanotube demonstrates a notable capacity of 386 mAh g-1 at 0.1 A g-1, with exceptional long-term cycle stability, retaining 102 mAh g-1 capacity after 5000 cycles at 3.0 A g-1.