The instability of Zn anode caused by severe dendrite growth and side reactions has restricted the practical applications of aqueous zinc-ion batteries (AZIBs). Herein, an enamel-like layer of nanohydroxyapatite (Ca5(PO4)3(OH), nano-HAP) is constructed on Zn anode to enhance its stability. Benefiting from the ion exchange between Zn2+ and Ca2+, the adsorption for Zn2+ in enamel-like nano-HAP (E-nHAP) layer can effectively guide Zn deposition, ensuring homogeneous Zn2+ flux and even nucleation sites to suppress Zn dendrites. Meanwhile, the low pH of acidic electrolyte can be regulated by slightly soluble nano-HAP, restraining electrolyte corrosion and hydrogen evolution. Moreover, the E-nHAP layer features high mechanical flexibility due to its enamel-like organic-inorganic composite nanostructure. Hence, symmetric cells assembled by E-nHAP@Zn show superior stability of long-term cycling at different current densities (0.1, 0.5, 1, 5, and 10 mA cm-2). The E-nHAP@Zn∥E-nHAP@Cu cell exhibits an outstanding cycling life with high Coulombic efficiency of 99.8% over 1000 cycles. Notably, the reversibility of full cell based on CNT/MnO2 cathode can be effectively enhanced. This work shows the potential of drawing inspiration from biological nanostructure in nature to develop stable metal electrodes.
Keywords: aqueous Zn-ion batteries; electrolyte pH regulation; enamel-like nanostructure; ion exchange adsorption; nanohydroxyapatite.