Flexible zincophilic polypyrrole paper interlayers for stable Zn metal anodes: Higher surface flatness promises better reversibility

Due to the low redox potential and high volumetric capacity, Zn metal anode is regarded as an ideal anode material for aqueous Zn-ion batteries (AZBs). However, the critical issues of uncontrolled dendrite propagation and side reactions with Zn anodes have hindered their practical applications. Herein, a thin and mesoporous polypyrrole (PPy) paper is proposed as an advanced zincophilic interlayer to tackle these problems. We show that the high surface area of the PPy interlayer promises enhanced reaction kinetics, and the excellent affinity to Zn2+ and uniform pore size distribution render homogeneous Zn2+ flux. Moreover, a compact PPy paper interlayer with high surface flatness can be readily made by mechanical compression, which enables much more intimate contact with the Zn anode at the nanoscale level, facilitating enhanced anti-corrosion property and dendrite-free deposition with nearly full surface coverage during repeated depositing/stripping. Consequently, the modulation of surface flatness engineered PPy paper interlayer enables dendrite-free Zn anode with an outstanding cycling performance at simultaneous high current densities and areal capacities (930 h at 5 mA cm−2 for 5 mAh cm−2). The feasibility of the PPy paper interlayer is verified in PANI/V2O5-based AZBs and activated carbon-based Zn-ion capacitors. Our work provides a facile and sustainable strategy and new insight into constructing efficient interface layers for practical AZBs by surface geometry engineering.