Manipulating Zn-ion flux by two-dimensional porous g-C3N4 nanosheets for dendrite-free zinc metal anode

Zinc metal anode is a promising choice in aqueous zinc ion batteries (ZIBs) due to its high volumetric capacity, low toxicity, and natural abundance. However, zinc dendrite growth severely compromises the practicability of zinc metal anode in large-scale utilizations of ZIBs. As a key component of ZIB, separator plays an important role in regulating zinc ion flux and thus has a direct impact on zinc dendrite growth. However, little attention has been paid on the the effect of separator on dendrite growth. Herein, we report a modified separator by coating a layer of g-C3N4 nanosheets onto commercial cellulose fiber separator via a simple drop casting route. The porous two-dimensional g-C3N4 nanosheets act as ion redistributors to induce homogenous zinc ion flux, thus the g-C3N4 coated separator enables a dendrite-free zinc deposition and improves the reversibility of zinc metal anodes. As a result, the Zn||Zn symmetric cell using the g-C3N4 coated separator exhibits a 300-fold improvement in cycling lifetime of over 590 h at 3 mA cm−2 and the coulombic efficiency of Zn||Cu asymmetric cell with g-C3N4 coated separator maintains at 99.2% at 1 mA cm−2 for over 750 cycles, which are better than most of the reported ZIBs to date.