To date, there have been some studies and reports on AZIBs based on conversion reactions, but the systematic overview and in-depth discussion of these studies are still lacking. In fact, conversion-type cathodes have been studied extensively in other battery systems, such as LIBs and sodium-ion batteries, and several reviews have presented the reaction mechanism and research progress of the conversion reaction in different batteries. Furthermore, the conversion-type cathode materials commonly used in AZIBs, such as S, I 2 and Br 2, have significant competitiveness over their counterparts for intercalation-type cathodes in light of their more abundant resources and lower cost. In contrast to intercalation-type cathodes, conversion-type cathodes accomplish the process of energy storage via the “conversion reaction” of zinc ions, which tends to realize a higher specific capacity and energy density. Hence, there is an urgent need to develop AZIBs with higher energy densities. Despite many advantages, the energy densities of AZIBs are still far behind those of commercial LIBs, owing to the narrow electrochemical window of water-based electrolytes and the limited specific capacity of intercalation-type cathodes, thereby impeding the industrialization of AZIBs. These cathode materials generally complete the process of energy storage through the intercalation of zinc ions. The most studied AZIBs usually employ zinc foil as an anode, ZnSO 4, Zn(OTF) 2 and other weakly acidic solutions as electrolytes and manganese-based, vanadium-based, Prussian blue analogs, organics and other materials as cathodes. Even more importantly, the high hydrogen evolution overpotential of metallic zinc can significantly reduce the rate of hydrogen evolution, which enables zinc metal to be used directly as an anode in ABs. a standard hydrogen electrode) of zinc metal. In particular, aqueous zinc-ion batteries (AZIBs) have considerable practical potential because of their natural abundance, eco-friendliness, non-toxicity, high theoretical specific capacity (5855 Ah L -1 and 820 Ah kg -1) and moderate redox potential (-0.763 V vs.
In recent years, alkali metal (Li, Na and K )-ion batteries and multivalent metal (Mg, Ca, Zn and Al )-ion batteries have drawn increasing attention.
Based on the aforementioned advantages, the development of high-performance ABs has become a global scientific research area for energy storage. In addition, the high ionic conductivity and good interfacial compatibility of aqueous electrolytes endow ABs with fast reaction kinetics and outstanding rate capability. Furthermore, their insensitivity to the environment allows them to be manufactured in air atmospheres, which can improve the production efficiency and reduce the manufacturing costs simultaneously. Given the benefit of water-based electrolytes, aqueous batteries (ABs) have the merits of high safety and low cost and toxicity. The flammability, pollution and expensiveness of organic electrolytes hinder the further application of LIBs and therefore require us to seek safer and cleaner low-cost alternatives. Nevertheless, commercial LIBs generally employ organic electrolytes, such as ethers or esters. Lithium-ion batteries (LIBs), as ubiquitous advanced secondary batteries, have been successfully applied to mobile communications, consumer electronics, electric vehicles and numerous other fields. Due to the intermittent characteristics of renewable energy resources, such as solar, wind and tidal energy, advanced energy storage technology has become an essential element for establishing new energy systems in the future.
Considering that the current energy and environmental crisis is becoming increasingly prominent, it is imperative to establish new low-carbon and eco-friendly energy systems.
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