Ionic buffer layer design for stabilizing Zn electrodes in aqueous Zn-based batteries

Abstract

Aqueous Zn-based batteries (AZBs) are hindered by issues associated with the Zn electrodeposition process (ZEDP) on electrode surfaces, including passivation, dendrite formation, and hydrogen evolution. One of the important reasons is the drastic fluctuation in the concentration of Zn²⁺ ions on the electrode surface during the charging and discharging process. In this work, an electrolyte with Zn²⁺ ion buffer layer (EZIBL) is proposed to regulate the ZEDP. First, numerical simulations and corresponding experiments are conducted to assess the impact of different thicknesses of the Zn²⁺ ion buffer layer (ZIBL) on the variation in Zn²⁺ ion concentration, from which the optimal thickness of the ZIBL is determined. Then, the regulation role of EZIBL in the cycling process is demonstrated by a Zn-Cu half cell. Further, combined with the potential profile of the symmetric cell and the experimental phenomena, the regulation role of EZIBL in ZEDP is systematically explained at the mechanistic level through the analysis of key parameters. Finally, a full battery composed of Zn-LiMn₂O₄ is assembled to evaluate the practical applicability of the EZIBL in real battery cycles, which shows great enhancement in capacity retention and coulombic efficiency. This work proposes the design of the EZIBL used to regulate the ZEDP and provides a simple, low-cost regulation method for the development of high-performance AZBs.