Sandwich-structured anode enables high stability and enhanced zinc utilization for aqueous Zn-ion batteries

Constructing a current collector is a promising approach to modifying the zinc anode. However, most collectors exhibit top zinc deposition patterns, leading to unsatisfactory zinc utilization and instability. To address this issue, we have developed a new sandwich deposition approach in which a boron nitride layer (BN layer) is applied onto Cu foils as the current collector, which allows us to achieve the sandwich-structured anode (BN-ZnCu). Through experimental characterization and theoretical calculations, the deposition mechanisms of Zn2+ have been explored and verified. The insulating BN layer, the upper layer of the anode, acts as the protective barrier of deposited zinc and accelerates the transmission of zinc ions. The zincophilic Cu substrate, the bottom layer of the anode, promotes Zn deposition without dendrites. Under the synergistic effect of the BN layer and substrate, the sandwich-structured anode enables superior reversibility with 99.49 % coulombic efficiency over 700 cycles and realizes 66.7 % zinc utilization at 4 mAh cm-2. Moreover, the assembled BN-Zn-Cu||CNT/MnO2 cells display high stability with an average fading of 0.06 % per cycle for 600 cycles. Our work verifies the feasibility of sandwich-structured anodes in enhancing the performance of aqueous zinc-ion batteries, providing an innovative idea for the structural design of metal anodes.