Toward Membrane-Free Flow Batteries

Flow batteries have long been considered as a competitive candidate for large-scale energy storage owing to their advantages of high power density, long lifespan, and decoupling of energy density/power. However, high membrane and maintenance costs hinder their further development and application. To lower the cost and improve maintainability, membrane-free flow battery systems were developed. In this review, we summarize three types of membrane-free flow batteries, laminar flow batteries, immiscible flow batteries, and deposition–dissolution flow batteries, and systematically analyze the design principles, reaction mechanisms, and battery structure. Finally, we highlight the current bottlenecks and development trends for membrane-free flow batteries.