Cationic, electrostatic shielding, ion-sieving nanocellulose separators stabilize zinc metal anodes

A bio-based, electrostatic shielding, ion-sieving separator is proposed by surface amine functionalization of nanocellulose paper to stabilize Zn metal anode, for the first time. Such cationic nanocellulose separator exhibits uniformly and narrowly distributed nanopores with immobilized cationic groups, which yields a homogenous current distribution at the separator/electrode interfaces, inhibits SO42− migration, enhances the Zn2+ transference number to 0.73, and generates a zincophobic repulsion layer to eliminate the "tip effect". Unlike pristine nanocellulose separator, the combination of ion-sieving nanofibrous network and immobilized electrostatic shielding functional groups lead to smoother and more compact Zn deposition/stripping behavior during repeated cycles. Hence, highly reversible Zn metal anodes and durable supercapacitors are realized: the symmetric Zn//Zn cells can last 180 h under a high current density of 20 mA cm−2 with a high capacity of 10 mAh cm−2, and the Zn//activated carbon supercapacitor shows a discharge capacity of 104.3 mA g−1 at 1 A g−1 with a capacity retention ratio of ∼ 80% after 2500 cycles. The surface charge engineering approach constitutes a practical separator modification strategy toward even Zn deposition and a promising route for the development of aqueous Zn-based energy storage devices with improved sustainability and enhanced cycling stability.