Biobased Membranes for Redox Flow Batteries

Redox flow batteries (RFBs) are gaining attention as viable candidates for large-scale energy storage due to their scalability, decoupling of power and energy capacity, and potential for long-duration discharge. A critical component of these systems is the membrane, which plays a key role in determining battery performance, capacity retention, and overall cost. However, existing membrane technologies face significant challenges—they often lack either the necessary performance characteristics, durability, environmental sustainability, or are prohibitively expensive, limiting their adoption beyond research environments. In this study, we present a sustainable, low-cost membrane that addresses these limitations, suitable for both organic and vanadium redox flow batteries. By modifying a cellulose-based substrate with ionic liquids, we create a charged biopolymer that meets the performance requirements for battery operation. The membrane was characterized using techniques such as scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and solid-state NMR. Additionally, its functionality was tested in an organic redox flow battery and all-vanadium redox flow batteries. Our results demonstrate the membrane’s adequate ion conductivity and low cross-diffusion of active species. We successfully operated a vanadium-based organic flow battery for 800 cycles and an all-vanadium flow battery for 50 cycles. These findings highlight the potential of sustainable materials, such as cellulose-based membranes, in redox flow batteries, paving the way for their broader application in electrochemical energy storage systems.