Advances in transition metal oxide cathodes for zinc-ion batteries – A review focusing on safety and toxicity

Aqueous Zinc-ion Batteries (AZIBs) have garnered significant attention as promising alternatives to conventional lithium-ion batteries, owing to their inherent advantages such as high energy density, affordability, and non-flammability. Despite their potential, achieving high-performance cathode materials remains a challenge, necessitating a delicate balance between electrochemical properties and considerations of environmental toxicity and human health. This comprehensive review delves into recent advancements in transition metal oxide cathodes, focusing on their potential to address safety, toxicity, cost, and feasibility concerns. The importance of toxicity has emerged prominently in recent years, fueled by increasing awareness of environmental and health impacts associated with energy storage technologies. Meanwhile, feasibility encompasses not only the electrochemical performance of cathode materials but also considerations of scalability, cost-effectiveness, and compatibility with large-scale energy storage applications. The review begins with a brief yet focused overview of Zinc batteries, providing an accurate classification, foundational understanding, and overview of current challenges. It then delves into contemporary concerns surrounding toxicity, cost, and feasibility of transition metal oxide cathode materials. In subsequent sections, various works involving oxide cathodes of Ti, Fe, Mn, and other relevant transition metals are thoroughly examined for their ability to meet these considerations. Lastly, key strategies directed towards mitigation of toxicity issues and cost-effective development of ZIBs is provided along with valuable insights into the future direction of AZIB research and development.