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

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Ion-exchange membranes constitute over 30% of redox flow battery (RFB) costs.
• Membrane-free RFBs offer cost reduction potential but face challenges like short-circuiting and dendrite growth.
• Current solutions to mitigate short-circuits in membrane-free RFBs often reduce energy efficiency and fail to address dendrite growth.

Purpose of the Study:

• To develop a cost-effective solution for membrane-free RFBs.
• To enhance the safety and performance of membrane-free RFBs by preventing short-circuits and dendrite growth.
• To introduce a novel boron nitride nanosheets-Nylon hybrid interlayer for general membrane-free RFB applications.

Main Methods:

• Fabrication of an inexpensive, electron-insulating boron nitride nanosheets (BNNSs)-Nylon hybrid interlayer (BN/Nylon).
• Implementation of the BN/Nylon interlayer in membrane-free RFBs to enable near-zero electrode distance.
• Investigation of the interlayer's interaction with electrolyte anions and its effect on ion transport and plating/stripping processes.

Main Results:

• The BN/Nylon interlayer effectively prevents short-circuits and dendrite growth in membrane-free RFBs.
• Lewis acid sites in BNNSs reduce the Pb²⁺ concentration gradient by interacting with Lewis base anions.
• The interlayer's thermal and mechanical properties promote uniform Pb and PbO₂ plating/stripping.
• Energy efficiency (EE) increased by approximately 38.2% at 25 mA cm^-2 compared to conventional soluble lead RFBs.
• Cycle life was extended to 100 cycles.

Conclusions:

• The developed BN/Nylon interlayer is a promising strategy for advancing membrane-free RFB technology.
• This approach offers a novel perspective for cost reduction and performance enhancement in general membrane-free RFBs.
• The interlayer facilitates safe and efficient operation by enabling near-zero electrode spacing without compromising performance.