The design strategy of metal-organic frameworks for artificial solid-electrolyte interface layer in aqueous zinc ion battery

Abstract

As the demand for lithium-ion batteries increases in a variety of applications, there are some needs to improve the safety issue. Aqueous zinc ion battery is one of the next-generation batteries that can eliminate the risks of lithium-ion batteries, and have the advantage of using a water-based electrolyte for higher safety and increased capacity due to the use of zinc metal as the cathode. However, aqueous zinc ion batteries suffer from lifespan such as hydrogen generation reactions and corrosion and dendritic growth. Various research efforts have been made to address these issues, and the creation of an artificial SEI layer has shown the highest performance among the existing approaches in terms of cost benefits and compatibility with current systems. Materials used as artificial SEI layers include inorganic materials and polymers. However, inorganic materials suffer from crystalline grain boundaries and a lack of design versatility due to their simple structure, while polymers suffer from fewer problems, but are hydrophobic, which reduces the performance of the electrode, and hydrophilic, which dissociates in water. Metal-organic frameworks are an excellent platform to combine the stability of inorganic materials with the tunability of polymers. Also, they can provide channels for ions to move through their porous structure. In this study, we synthesized a metal-organic framework with a stable zirconium-based metal node as a secondary synthetic unit, and organic linkers with polar groups as the material for an artificial SEI layer. Through various experiments, the zinc metal anode with artificial SEI layer showed excellent reversibility in the electroplating/stripping of zinc ions compared to the bare zinc metal anode. Subsequently, the effect of the metal-organic framework on the kinetics of the zinc metal anode was analyzed. The organic ligands in the channels of the metal-organic backbone act as zincophilic groups to mitigate the concentration polarization that occurs during the electroplating/stripping of zinc ions. Furthermore, full cell experiments with β-MnO2 cathode confirmed that these advantages are indeed under the desired voltage range. As a result, we proposed a design strategy for metal-organic frameworks as a candidate material for artificial protective layers, through the combination of organic ligands and secondary synthetic units, have the advantages of both inorganic materials and polymers and can provide ion diffusion channel, additionally.