Zinc-ion batteries for biomedical applications: Materials engineering, flexible device design, and biocompatibility

The booming development of wearable and implantable biomedical electronics urgently calls for next-generation energy-storage systems that integrate superior safety, mechanical flexibility, miniaturization, and biocompatibility. Lithium-ion batteries remain constrained in biomedical applications by concerns related to flammable organic electrolytes, structural rigidity, and biosafety. Zinc-ion batteries (ZIBs) have therefore emerged as promising candidates owing to their intrinsic safety, low cost, environmental friendliness, and the physiological relevance of zinc as an essential trace element. This review comprehensively summarizes recent advances in biomedical ZIBs, with a core focus on the synergistic optimization of electrochemical performance, mechanical flexibility, and biocompatibility—the three pivotal requirements for biomedical applications. The charge-storage mechanisms and key challenges of representative cathode systems are first discussed, followed by recent strategies for cathode stabilization, zinc-anode interfacial regulation, flexible and biocompatible electrolyte design, and flexible device integration. Particular attention is further paid to the biosafety of biomedical ZIBs, including electrode-derived ion release, electrolyte leakage, degradation products, and in vitro and in vivo biocompatibility evaluation. Representative wearable, implantable, and biodegradable ZIBs are discussed to demonstrate their potential for biomedical electronics. Finally, remaining challenges involving packaging reliability, sterilization compatibility, long-term stability, standardized biosafety evaluation, and clinical translation are outlined to guide the development of high-performance, flexible, and biointegrated ZIBs systems.