Recent development in MOFs and their derivatives for battery electrodes

Utilization of renewable energy sources boosts the demand for advanced energy storage systems due to environmental concerns on fossil fuels. Compared to other systems, electrochemical energy storage systems are efficient, reliable, and compact and have been used in a wide range of applications from large-scale energy storage to electric vehicles and portable electronics in our daily life. During the past few decades, Li-ion batteries (LIBs) are dominant in consumer electronics market for reliable cycle life and relatively high energy density. However, due to the limit of Li resources, the increasing market demand for LIBs significantly drives the rise of cost. For large-scale energy storage, it is necessary to explore low-cost batteries based on Na, K, Mg, Zn, and Al. Apart from their abundance, they also possess redox potentials that are low enough or even close to that of Li and high specific capacities, in both gravimetric and volumetric terms. The increasing demand for high-density energy storage shifts the focus from metal-ion batteries to metal batteries that directly use metals as anodes and high-energy-density chemicals (such as O2 and S) as cathodes. The application of these battery technologies also faces big challenges. One the one hand, the use of metal anodes in a practical battery may cause safety hazards, especially in the liquid electrolyte battery: dendritic sodium growth due to its uneven deposition upon charging and further growth of dendrites may puncture the separator, leading to a short circuit eventually. On the other hand, the O2 and S cathode reactions have sluggish kinetics that results in large overpotentials. Additionally, S cathodes suffer severe “shuttle effect,” resulting in low Coulombic efficiency. Aqueous batteries have been regarded as the most promising alternative to LIBs for large-scale energy storage considering safety, productivity, and economic and ecological aspects. The aqueous electrolytes eliminate safety concerns, such as fire or explosion, even with a short circuit of batteries. The insensitivity of electrolytes to moisture and oxygen also guarantees simple battery assembly in ambient atmosphere, giving rise to high-efficiency battery manufacture. Among the aqueous batteries, Zn-based batteries have shown their considerable potential in practical applications benefiting from the direct utilization of Zn metal. Zn metal has high theoretical capacity (820 mAh g−1), low toxicity, high safety, and low cost. However, they also suffer from several issues that need to be addressed. The development of aqueous ZIBs is plagued by the scarcity of suitable cathode materials for Zn-ion storage. Moreover, Zn batteries face the problem of dendrite formation in anode and side reactions during plating/stripping, and this problem results in poor cycle life, capacity fade, and safety problems.