Shackling the aqueous electrolyte via metal-organic frameworks to realize high energy density zinc-ion batteries

Abstract

Ocean-like free water in conventional aqueous electrolytes leads to narrow operating voltage and parasitic reactions in rechargeable aqueous Zn ion batteries (AZIBs), which is highly undesirable. Herein, a quasi-solid aqueous electrolyte (QSAE) with a typical bulk liquid electrolyte confined inside the sub-nanoscale channels of metal-organic framework (MOFs) is proposed to tackle this issue. Detailed experiments and theoretical calculations suggest that the unfavored side reactions, e.g., corrosion, hydrogen evolution reaction, and dendrite growth on zinc surface can be effectively depressed and the electrochemical window can be expanded to 2.51 V (based on OER), achieved by the proposed MOF-QSAE because of the tailored solvation structure of Zn2+ and the restrained activity of water molecules in MOF-QSAE. Thanks to the unexpected merits of MOF-QSAE, a fabricated Zn|MOF-QSAE|V2O5 full cell exhibits an ultra-high coulombic efficiency (average value≈99.98 %) and cycle stability (capacity retention: 81.89 % after 2000 cycles). The Zn|MOF-QSAE|V2O5 full cell can even work at a low temperature of −10 ℃ for 4000 cycles without obvious performance degradation. In addition, a high-voltage AZIBs based on zinc hexacyanoferrate (ZnHCF) cathode yields an average operating voltage of more than 1.70 V and a high energy density of ≈102 Wh kg−1, further validating the practicality of the MOF-QSAE. The proposed new type of QSAE could pave a new way for the commercialization of aqueous batteries.