Decision-oriented assessment of redox flow batteries for grid-scale energy storage: Scalability, system complexity, and intelligent operation

Redox flow batteries (RFBs) are widely regarded as promising candidates for grid-scale, long-duration energy storage due to their intrinsic safety, decoupled scaling of power and energy, and long cycle life. However, despite decades of intensive research and significant advances in electrolyte chemistry, electrode design, and system modeling, commercial deployment remains limited and concentrated in a small number of mature chemistries, indicating that performance-oriented optimization alone is insufficient to ensure deployability. In this review, we introduce a decision-oriented assessment framework-Scalability-Complexity-Intelligence (SCI) - to systematically evaluate RFB technologies based on their readiness for long-term operation, tolerance to system-level complexity, and the conditional value of intelligent control. Electrolyte chemistries, electrode and membrane components, modeling strategies, and hybrid system architectures are examined through a unified lens that emphasizes durability, manufacturability, operational predictability, and levelized cost of storage. The analysis demonstrates that many proposed RFB concepts achieve promising laboratory metrics at the expense of escalating system complexity, undermining scalability and long-term reliability, whereas technologies characterized by intrinsic chemical stability, transparent degradation behavior, and simplified system architectures exhibit stronger alignment with deployment realities. Advanced modeling, digital twins, and AI-assisted control are shown to deliver meaningful benefits primarily in chemically stable and operationally predictable systems, where intelligence enhances reliability rather than compensating for fundamental material or architectural limitations. By explicitly distinguishing deployable solutions from conditionally viable pathways and systemically constrained concepts, this review provides actionable guidance for researchers, system designers, and energy stakeholders seeking to translate redox flow battery innovation into reliable grid-scale energy storage infrastructure.