Bifunctional interface engineering of fluorinated cosmetic cotton separators: Synergistic Zn2+ kinetics and hydrophobic shielding for ultra-stable Zn anodes

Abstract

Though considered as a highly promising energy storage technology, aqueous zinc-ion batteries (AZIBs) still face challenges such as poor cycling stability and low Coulombic efficiency (CE) due to side reactions and dendrite growth on the Zn anode surface during electrochemical processes. To overcome the above issues, commercial cosmetic cotton (CP) was functionalized by polyvinylidene fluoride (PVDF) to fabricate a PVDF-CP composite separator. CP (main component being cellulose) possesses high porosity, excellent mechanical properties and low price, and the cheap PVDF plays bifunctional roles in stabilizing Zn anode interface. The β-phase PVDF in the separator forms a uniform electronegative region, endowing the separator with outstanding functionality: It constructs Zn2+ transport channels and thus accelerates ion migration, as well as restricting the disordered diffusion of Zn2+, which effectively boosts Zn deposition kinetics. Furthermore, the PVDF-CP separator inherits PVDF's hydrophobicity and establishes a stable hydrophobic interface that can prevent water from accessing the Zn electrode, thereby significantly alleviating water-induced parasitic reactions. Consequently, the multifunctional synergistic effects of the PVDF-CP composite separator observably promote electrochemical performance of AZIBs, and Zn||Zn symmetric cells assembled with the PVDF-CP separator obtain a cycling lifespan of over 2810 h. Zn||Cu asymmetric cells demonstrate 1000 reversible cycles with a high average CE of 99.0%, showcasing the stable Zn plating/stripping behavior. Besides, Zn||NVO full cells exhibit exceptional cycling stability, retaining 88.0% capacity (155.0 mAh g-1) after 2300 cycles at 5 A g-1.