Solubility Challenges in Battery Electrolytes

This review provides a foundational understanding of solubility to support researchers in navigating challenges in battery electrolyte development. We survey recent strategies aimed at controlling, and typically maximizing, solubility in electrochemical systems, with a focus on redox flow and metal-ion batteries. The review begins with an accessible overview of solubility concepts, methods for accurately determining solubility for battery-relevant materials, and solubility prediction. We then discuss how solubility can be tuned by modifying the electrolyte solution structure or by tailoring the molecular structure of the active material itself, and we examine emerging strategies to decouple electrolyte capacity from solubility in flow batteries. In the context of metal and metal-ion batteries, we highlight the role of solvation structures in concentrated electrolytes and their influence on both bulk and interfacial properties. Finally, trade-offs associated with high-concentration formulations, such as increased viscosity and reduced ionic conductivity, are considered in light of their impact on practical deployment. We conclude with a forward-looking perspective on solubility as a central design parameter in battery electrolyte research.