Water-Based Wonders: Exploring Recent Progress in Aqueous Lithium-Ion Batteries

Aqueous lithium-ion batteries have recently attracted more attention due to their environmental friendliness and safety. Strategies to improve the energy density and cycle life of these batteries are being pursued. The development of aqueous Li-ion batteries over the past 10 years is discussed in the current review. The issue of a narrow electrochemical stability window is addressed by engineering different water-based electrolyte systems, including hydrate melt, water-in-bisalt, water-in-salt, and ether-in-water. The incorporation of cost-effective, innovative electrolyte additives effectively expands the electrochemical stability window, suppresses side reactions, and thereby enhances the performance of aqueous Li-ion batteries. The structural and electrochemical properties of anode materials, including vanadium-, titanium-, and molybdenum-based materials, as well as newly emerging materials, are reviewed. Phosphates and binary metal oxides are promising anode materials for aqueous Li-ion batteries due to their stability in aqueous media and high lithium storage capacity from redox-active transition metals. Their robust structure and ability to undergo multielectron redox reactions make them suitable for safe and efficient energy storage. As for cathodes, traditional materials like LiCoO2, LiMn2O4, and LiFePO4 are water-compatible, while doped and co-doped LiMnPO4) stands out for its superior structural and electrochemical performance. Performance enhancements can be achieved through carbon compositing, surface coatings, and electrolyte optimization, which improve cycling stability and reduce ion dissolution. Research may be carried out to further enhance the performance of aqueous Li-ion batteries by utilizing titanium and steel as current collectors for the anode and cathode. Collectively, these strategies help to narrow the performance gap between aqueous and conventional Li-ion battery systems.