Enhancing Solid Booster Utilization in Redox-targeted Flow Batteries with Non-fluorinated Binders

Redox-targeted flow batteries (RTFBs) are promising for large-scale energy storage but suffer from poor solid booster utilization. This study examines how binder selection affects the reaction rate between a LiFePO₄/FePO₄ solid booster composite and a dissolved [Fe-(CN)₆]^4-/3- redox mediator. The porosity and hydrophilicity of LiFePO₄ composites correlate with booster utilization, determined by galvanostatic cell cycling and by <i>in situ</i> UV-Vis spectroscopy. Compared with state-of-the-art polyvinylidene difluoride composites, booster pellets containing non-fluorinated, biodegradable polycaprolactone or cellulose acetate binders exhibit up to 175% higher LiFePO₄ conversion rates and improved capacity utilization at cycling rates up to 10 mA cm^-2. Solid-material utilization directly correlates with binder hydrophilicity, establishing it as a key design parameter for RTFBs and offering a straightforward path toward more efficient and non-fluorinated booster formulations.