High-Energy-Density Redox Flow Batteries: Mechanisms, Design Strategies, and Recent Progress

The inherent intermittency of energy sources such as solar and wind power hinders the transition to renewable energy, necessitating advanced energy storage solutions. Enhancing energy density is crucial for lowering system costs and enabling large-scale deployment. Redox flow batteries (RFBs) demonstrate significant potential for grid-scale energy storage due to their scalable capacity, high safety, and long cycle life. However, the relatively low energy density of conventional RFBs has hindered their widespread adoption. This review summarizes recent research progress in high-energy-density flow batteries, focusing on key parameters and strategies for enhancing the energy density of aqueous RFBs (ARFBs). Three core strategies are discussed in detail: broadening the cell voltage window, constructing multi-electron transfer systems, and developing high-concentration electrolytes. To overcome the practical challenges (e.g., species crossover, material degradation) associated with implementing these high-energy-density strategies, this review also highlights the critical role of advanced membrane technology as a key enabling component. Finally, the review outlines prospects and challenges for high-energy-density flow batteries, emphasizing the need for further research on material stability, energy efficiency, and cost-effectiveness. Through continued innovation and optimization, high-energy-density flow batteries are expected to become a mainstream technology for grid storage, providing robust support for the efficient utilization of renewable energy.