Phase-Modified Strongly Coupled δ/ε-MnO 2 Homojunction Cathode for Kinetics-Enhanced Zinc-Ion Batteries.

Rechargeable Zn-MnO 2 batteries using mild water electrolytes have garnered significant interest owing to their impressive theoretical energy density and eco-friendly characteristics. However, MnO 2 suffers from huge structural changes during the cycles, resulting in very poor stability at high charge-discharge depths. Briefly, the above problems are caused by slow kinetic processes and the dissolution of Mn atoms in the cycles. In this paper, a 2D homojunction electrode material (δ/ε-MnO 2 ) based on δ-MnO 2 and ε-MnO 2 has been prepared by a two-step electrochemical deposition method. According to the DFT calculations, the charge transfer and bonding between interfaces result in the generation of electronic states near the Fermi surface, giving δ/ε-MnO 2 a more continuous distribution of electron states and better conductivity, which is conducive to the rapid insertion/extraction of Zn 2+ and H + . Moreover, the strongly coupled Mn-O-Mn interfacial bond can effectively impede dissolution of Mn atoms and thus maintain the structural integrity of δ/ε-MnO 2 during the cycles. Accordingly, the δ/ε-MnO 2 cathode exhibits high capacity (383 mAh g -1 at 0.1 A g -1 ), superior rate performance (150 mAh g -1 at 5 A g -1 ), and excellent cycling stability over 2000 cycles (91.3% at 3 A g -1 ). Profoundly, this unique homojunction provides a novel paradigm for reasonable selection of different components.