Versatile Biopolymers for Advanced Lithium and Zinc Metal Batteries.

Lithium (Li) and zinc (Zn) metals are emerging as promising anode materials for next-generation rechargeable metal batteries due to their excellent electronic conductivity and high theoretical capacities. However, issues such as uneven metal ion deposition and uncontrolled dendrite growth result in poor electrochemical stability, limited cycle life, and rapid capacity decay. Biopolymers, recognized for their abundance, cost-effectiveness, biodegradability, tunable structures, and adjustable properties, offer a compelling solution to these challenges. This review systematically and comprehensively examines biopolymers and their protective mechanisms for Li and Zn metal anodes. It begins with an overview of biopolymers, detailing key types, their structures, and properties. The review then explores recent advancements in the application of biopolymers as artificial solid electrolyte interphases, electrolyte additives, separators, and solid-state electrolytes, emphasizing how their structural properties enhance protection mechanisms and improve electrochemical performance. Finally, perspectives on current challenges and future research directions in this evolving field are provided.