Emerging Carbonyl Polymers as Sustainable Electrode Materials for Lithium-Free Metal-Ion Batteries

Lithium-ion batteries using inorganic electrode materials have been long demonstrated as the most promising power supplies for portable electronics, electric vehicles, and smart grids. However, the increasing cost and descending availability of lithium resources in combination with the limited electrochemical performance and eco-sustainability have created serious concerns with the competitiveness of lithium-ion batteries. There is a pressing need for the discovery of new redox chemistries between the alternative host materials and charge carriers. Organic nonlithium batteries using organic electrodes have recently attracted considerable interests as the future substitutes for energy storage systems, because of their combined merits (e.g., natural abundance, rich chemistry of organics, rapid kinetics, and multielectron redox) of Li-free batteries and organic electrodes. Herein, an overview on the state-of-the-art developments of emerging carbonyl polymers for nonlithium metal-ion batteries is comprehensively presented with a primary focus on polyquinones and polyimides from the perspective of chain engineering. Six distinct categories, including monovalent (Na⁺, K⁺) and multivalent (Mg²⁺, Zn²⁺, Ca²⁺, Al³⁺) metal-ions batteries are individually outlined. Advantages of polymer electrode materials and characteristics of charge storage mechanisms are highlighted. Some key performance parameters such as specific capacity, rate capability, and cycle stability are carefully discussed. Moreover, aqueous nonlithium batteries based on carbonyl polymers are specially scrutinized due to the less reactivity of Li-free metals when exposed in aqueous electrolytes and ambient atmosphere. Current challenges and future prospects of developing polymer-based batteries are proposed finally. This review provides a fundamental guidance for the future advancement of next-generation sustainable batteries beyond lithium-ion batteries.