Critical Factors Dictating Reversibility of the Zinc Metal Anode

Abstract

With high energy density and improved safety, rechargeable battery chemistries with a zinc (Zn) metal anode offer promising and sustainable alternatives to those based on lithium metal or lithium ion intercalation/alloying anode materials; however, the poor electrochemical reversibility of Zn plating/stripping, induced by parasitic reactions with both aqueous and non-aqueous electrolytes, presently limits the practical appeal of these systems1. Although recent efforts in rechargeable Zn metal batteries (RZMBs) have achieved certain advancements in Zn metal reversibility2,3, as quantified by the Coulombic efficiency (CE), a standard protocol for CE has not been established, and results across chemistries and systems are often conflicting. More importantly, there is still an insufficient understanding regarding the critical factors dictating Zn reversibility.In this work, a rigorous, established protocol for determining CE of lithium metal anodes4 is transplanted to the Zn chemistry and is used for systematically examining how a series of factors including current collector chemistry, current density, temperature, and the upper voltage limit during stripping affect the measured reversibility of different Zn electrolytes. With support from density functional theory calculations, this standardized Zn CE protocol is then leveraged to identify an important correlation between electrolyte solvation strength toward Zn2+ and the measured Zn CE in the corresponding electrolyte, providing new guidance for future development and evaluation of Zn electrolytes. Figure 1 shows a schematic of proposed method, including initial results for some of the most promising Zn electrolytes reported in the literature. The capability of supporting Zn plating/stripping is differentiated clearly among these selected Zn electrolytes here.Reference1. Blanc, L. E., Kundu, D. & Nazar, L. F. Scientific Challenges for the Implementation of Zn-Ion Batteries. Joule 4, 771–799 (2020).2. Wang, F. et al. Highly reversible zinc metal anode for aqueous batteries. Nat. Mater. 17, 543–549 (2018)3. Naveed, A., Yang, H., Yang, J., Nuli, Y. & Wang, J. Highly Reversible and Rechargeable Safe Zn Batteries Based on a Triethyl Phosphate Electrolyte. Angew. Chemie Int. Ed. 58, 2760–2764 (2019).4. Adams, B. D., Zheng, J., Ren, X., Xu, W. & Zhang, J.-G. Accurate Determination of Coulombic Efficiency for Lithium Metal Anodes and Lithium Metal Batteries. Adv. Energy Mater. 8, 1702097 (2018). Figure 1