Slurry-Based Electrochemical Flow Systems: Fundamentals, Performance, and Engineering

Electrochemical energy storage (EES) systems have emerged as a promising technology to enable efficient energy storage and subsequent conversion to electrical power in the coming years. Flow batteries, characterized by the physical separation of electrolytes and electrodes, uniquely decouple power generation from energy capacity, allowing for a flexible design and scalable deployment. Within this paradigm, researchers have proposed replacing conventional electrolytes and static electrodes with highly conductive, flowable slurries composed of electrically conductive nanoparticles and functionally active nanomaterials. These innovations have given rise to advanced systems such as semi-solid flow batteries (SSFBs) and electrochemical flow supercapacitors (EFCs). Slurry-based electrodes, when engineered with high concentrations of active species, demonstrate exceptional potential, achieving energy densities exceeding 500 Wh/kg, significantly surpassing current lithium-ion batteries, and offering at least a 10-fold increase over traditional flow systems. This leap in performance hinges on the development of cost-effective methods to scale production while maintaining competitive energy densities. Consequently, slurry technologies are now being leveraged across a diverse range of EES devices, positioning them as next-generation solutions for flow batteries and supercapacitors that utilize varied redox chemistries and configurations. However, the practical implementation of slurry systems faces challenges due to uncertainties stemming from complex interdependencies among material properties, slurry rheology, and operational parameters. This Review critically evaluates recent advancements in slurry technology, emphasizing the impact of material chemistry and slurry characteristics (e.g., viscosity, conductivity, and stability) on electrochemical performance. It also discusses cutting-edge developments in modeling approaches and cell design optimization for slurry-based flow cells. Finally, the Review identifies key research priorities and outlines necessary steps to bridge existing gaps, including the need for standardized testing protocols, improved understanding of long-term stability, and innovations in cost-effective manufacturing. Addressing these challenges will be pivotal in realizing the full potential of slurry-based EES technologies for large-scale, high-density energy storage applications.