Advanced porous composite membrane with ability to regulate zinc deposition enables dendrite-free and high-areal capacity zinc-based flow battery

Zinc-based flow battery (ZFB) is well suited for stationary energy storage due to its features of high energy density and low cost. However, the zinc dendrite issue seriously affects the performance and lifespan of ZFBs. Herein, a novel porous polyolefin/polyethylene glycol (PEG) composite membrane is designed and prepared for ZFBs. The PEG coating on the membrane surface and pore walls acts as both an ion conductor to Zn2+ ions and a passivation layer to zinc atoms. The PEG coating accelerates the uniform Zn2+ concentration distribution and decreases the membrane resistance. Moreover, this insulating and passivated coating achieves even electric field distribution on the anode surface, avoiding the continual deposition of newly reduced zinc atoms on deposited zinc. Consequently, the prepared porous composite membrane enables dendrite-free zinc platting processes. As a result, the porous composite membrane enables a zinc symmetric flow battery with a high coulombic efficiency of 99.38% and a lifespan of over 120 cycles at a current density of 40 mA cm−2. Moreover, the ZFB with the resultant membrane realizes a high working current density of 160 mA cm−2, and a high areal capacity of 60 mAh cm−2, much superior to those of the porous polyolefin matrix (40 mAh cm−2, 40 mAh cm−2). Therefore, the designed advanced porous composite membrane can significantly increase the power density and lifespan of ZFBs, facilitating their further development.