An Innovative Concept of Membrane‐Free Redox Flow Batteries with Near‐Zero Contact Distance Between Electrodes

Abstract Given that the ion‐exchange membrane takes up more than 30% of redox flow battery (RFB) cost, considerable cost reduction is anticipated with the membrane‐free design. However, eliminating the membrane/separator would expose the membrane‐free RFBs to a higher risk of short‐circuits, and the dendrite growth may aggravate this issue. The current strategy based on expanding distances between electrodes is proposed to address short‐circuit issues. Nevertheless, this approach would decrease the energy efficiency (EE) and could not restrain dendrite growth fundamentally. Herein, an inexpensive and electron‐insulating boron nitride nanosheets (BNNSs)‐Nylon hybrid interlayer (BN/Nylon) is developed for general membrane‐free RFBs to achieve “near‐zero distance” contact between electrodes. And the Lewis acid sites (B atoms) in BNNS can interact with the Lewis base anions in electrolytes, enabling a reduced Pb 2+ concentration gradient. Additionally, the ultrahigh thermal conductivity and mechanical strength of BNNSs promote the uniform plating/stripping process of Pb and PbO 2 . Compared with conventional soluble lead RFBs, introducing BN/Nylon interlayers boosts EE by ≈38.2% at 25 mA cm −2 , and extends the cycle life to 100 cycles. This innovative strategy premieres the application of the BN/Nylon interlayer concept, offering a novel perspective for the development of general membrane‐free RFBs.