Degradation mechanisms and stability engineering in organic redox flow batteries: From molecular design to system-level control

초록

Organic redox flow batteries (ORFBs) are promising for scalable long-duration energy storage due to their molecular tunability and decoupled energy-power characteristics. However, their practical deployment is limited by insufficient long-term stability arising from the interplay between molecular reactivity, species transport, and operating conditions. This review provides a mechanism-oriented overview of degradation pathways, including intrinsic molecular reactions (radical coupling, nucleophilic attack, and disproportionation), transport-driven losses (crossover), and high state-of-charge instability. Recent advances in stability engineering are summarized across multiple scales. Molecular strategies such as charge delocalization, steric protection, intramolecular hydrogen bonding, and charge distribution tuning are discussed alongside system-level approaches, including electrolyte regeneration, rebalancing, symmetric configurations, and polymeric electrolytes. We highlight thatORFB performance is governed by trade-offs among energy density, transport, and stability, requiring integrated optimization. Finally, future directions are proposed toward mechanism-informed design and practical evaluation under application-relevant conditions, providing guidance for the development of durable ORFB systems.

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