Application of metal-organic frameworks to the interface of lithium metal batteries

Lithium metal batteries (LMBs) are representative systems for high-energy-density batteries. The design of LMBs with high capacity and high cycle stability is imperative. However, the development of LMBs is hindered by typical interface-related problems such as lithium dendrite growth, incompatible separator interfaces, and unstable cathode interfaces because of the inhomogeneous ionic flux and composition distribution. The intrinsic instability significantly hinders electron/ion transfer at the interface, causing serious issues such as dendrite growth, volume changes, low coulombic efficiency, dead lithium, interface deterioration, capacity degradation, and loss of safety. Metal-organic frameworks (MOFs) are organic-inorganic hybrid materials with a stable highly porous structure, which can allow for highly efficient gas adsorption, separation and purification, catalysis, etc., in addition to facilitating their application in nanomedicine and other fields. In recent years, MOFs have attracted much attention in the field of LMBs as a possible solution to the typical interface problems abovementioned. The porous structure and open metal sites (OMs) of MOFs provide an excellent interface structure for uniform and high ionic conductivity. As additional bonus, the stable structure provides high mechanical strength with different functional groups and metal sites, resulting in significant versatility of functionality for interface stabilization. MOFs are usually synthesized by hydrothermal/solvothermal, microwave-assisted, electrochemical, and spray-drying methods. The excellent properties of MOFs have prompted researchers to pursue their rational design and modification. Much progress has been made in this direction, and exemplary investigations have been performed to solve the abovementioned interfacial problems encountered with LMBs. Consequently, metallic lithium deposition frameworks, artificial solid electrolyte interface films, electrolyte additives, separator materials, cathode materials for lithium-sulfur batteries, and lithium-air batteries have been developed. However, there is a long way to go before the commercialization of batteries based on MOF materials. In practical, more complex electrochemical reactions occur at the lithium-metal interface, and the operating conditions (temperature, over charging/discharging, external stress, etc.) vary widely. Moreover, MOFs as electrode materials have intrinsic drawbacks, including structural collapse, pore blockage, and low inherent conductivity during the cycles. Based on these interfacial challenges, in LMBs, it introduces the structural characterization and optimization of MOFs and the key chemical components that determines the MOFs of structure (central atom, organic ligand, etc.). Subsequently, we summarized the growth mechanism of lithium dendrites and discussed the applications of MOFs and their derivatives to battery cathodes, separators, anodes, and electrolytes. The manuscript contents would be a guide to solve the problem of unstable interfaces in LMBs by the use of MOFs. Furthermore, the prospects and rational design of MOF-based materials are discussed.