Guest Pre-Intercalation Strategy to Boost the Electrochemical Performance of Aqueous Zinc-Ion Battery Cathodes

The growing demand for electric vehicles, communication devices, and grid-scale energy storage systems urgently calls for the development of rechargeable batteries. Although lithium-ion batteries have dominated the new energy market for decades, there are challenges limiting their development, such as the high cost of lithium, as well as the toxicity and flammability of the organic electrolyte. In recent years, aqueous zinc-ion batteries (ZIBs) have gained much attention due to their advantages of high safety, high capacity, low cost, and nontoxicity. Materials based on multivalent vanadium and manganese have shown great potential for application as cathodes that are compatible with the metallic zinc anode in ZIBs. However, the commercialization of ZIBs has been hindered by the choice of cathodes, since the cathode materials show unsatisfactory energy densities and suffer from severe structural collapse, dissolution of the electrode components, sluggish reaction kinetics and detrimental side reactions during cycling. This stalemate was broken when a Zn2+/H2O co-inserted V2O5 (Zn0.25V2O5 center dot nH(2)O) material was first reported in 2016, and it showed much higher cycling stability and capacity than those of V2O5. The Zn2+ and water molecules pre-intercalated into the interlayer served as pillars to maintain the crystal structure and increase the interplanar spacing, leading to high structural stability and fast Zn2+ diffusion. Since then, several guest ions (Li+, Na+, K+, Ca2+, NH4+, PO43-, N3-, etc.) and molecules (H2O, polyethylene dioxythiophene (PEDOT), polyaniline (PANI, etc.) have been widely used to improve the electrochemical performance of aqueous ZIB cathodes, especially with manganese-based and vanadium-based materials. It is demonstrated that pre-intercalation of the guest ions or molecules can effectively optimize the electronic structure, regulate the interplanar spacing, and improve the reaction kinetics of the host. The local coordination structure of the host with pre-intercalated guest ions/molecules directly influences the zinc-ion storage performance. For example, sodium vanadates with a tunneled structure generally show better cycling stability than those with a layered structure due to their stronger Na-O bonds, since the O atoms on their layer surfaces are only single-connected. Manganese dissolution could be greatly suppressed by intercalation of the large potassium ions into tunneled alpha-MnO2, where solid K-O bonds act as pillars to be connected with Mn polyhedrons, and thus strengthen the structure. New mechanisms underlying reduction/displacement reactions could also be revealed in vanadates upon the introduction of Ag+ and Cu2+. Thus, we believe that guest pre-intercalation is a promising method for optimizing the zinc-ion storage performance of the appropriate cathodes and is worthy for further exploration. Here we have reviewed the recent advances in manganese-based and vanadium-based cathodes via the guest pre-intercalation strategy, discussed the related advantages and challenges. The future research direction for these two kinds of aqueous ZIB cathodes is also prospected.

Automated summary

The research on aqueous zinc-ion batteries (ZIBs) has gained significant attention in recent years due to their advantages of high safety, high capacity, low cost, and nontoxicity. Strategies such as the use of Zn2+/H2O co-inserted V2O5 material and the pre-intercalation of other guest ions or molecules have been effective in improving the electrochemical performance of cathode materials. Pre-intercalation of guest ions or molecules can optimize the electronic structure of the host, regulate the interplanar spacing, and enhance the reaction kinetics, showing promise for future advancements in zinc-ion storage.