Bi-MOF Modulating MnO2 Deposition Enables Ultra-Stable Cathode-Free Aqueous Zinc-Ion Batteries

Abstract

The Mn-based materials are considered as the most promising cathodes for zinc-ion batteries (ZIBs) due to their inherent advantages of safety, sustainability and high energy density, however suffer from poor cyclability caused by gradual Mn2+ dissolution and irreversible structural transformation. The mainstream solution is pre-adding Mn2+ into the electrolyte, nevertheless faces the challenge of irreversible Mn2+ consumption results from the MnO2 electrodeposition reaction (Mn2+ → MnO2). This work proposes a “MOFs as the electrodeposition surface” strategy, rather than blocking it. The bismuth (III) pyridine-3,5-dicarboxylate (Bi-PYDC) is selected as the typical electrodeposition surface to regulate the deposition reaction from Mn2+ to MnO2. Because of the unique less hydrophilic and manganophilic nature of Bi-PYDC for Mn2+, a moderate MnO2 deposition rate is achieved, preventing the electrolyte from rapidly exhausting Mn2+. Simultaneously, the intrinsic stability of deposited R-MnO2 is enhanced by the slowly released Bi3+ from Bi-PYDC reservoir. Furthermore, Bi-PYDC shows the ability to accommodate H+ insertion/extraction. Benefiting from these merits, the cathode-free ZIB using Bi-PYDC as the electrodeposition surface for MnO2 shows an outstanding cycle lifespan of more than 10 000 cycles at 1 mA cm-2. This electrode design may stimulate a new pathway for developing cathode free long-life rechargeable ZIBs.