Mechanistic insights of Mg²⁺-electrolyte additive for high-energy and long-life zinc-ion hybrid capacitors

• Main Authors: Wang, Pinji, Xie, Xuesong, Xing, Zhenyue, Chen, Xianhong, Fang, Guozhao, Lu, Bingan, Zhou, Jiang, Liang, Shuquan, Fan, Hong Jin
• Other Authors: School of Physical and Mathematical Sciences
• Format: Article
• Language: English
• Published: 2022
• Subjects: Science::Physics; Cation Additives; Aqueous Electrolytes
• Online Access: https://hdl.handle.net/10356/155768
• Institution: Nanyang Technological University

An electrolyte cation additive strategy provides a versatile route for developing high-energy and long-life aqueous zinc-ion hybrid capacitors. However, the mechanisms of energy storage and Zn anode protection are still unclear in Zn-based systems with dual-ion electrolytes. Here, a dual charge storage mechanism for zinc-ion hybrid capacitors with both cations and anions adsorption/desorption and the reversible formation of Zn4SO4(OH)6·xH2O enabled by the Mg2+ additive in the common aqueous ZnSO4 electrolyte are proposed. Theoretical calculations verify that the self-healing electrostatic shield effect and the solvation-sheath structure regulation rendered by the Mg2+ additive account for the observed uniform Zn deposition and dendrite suppression. As a result, an additional energy storage capacity of ≈50% compared to that in a pure 2 m ZnSO4 electrolyte and an extended cycle life with capacity retention of 98.7% after 10 000 cycles are achieved. This work highlights the effectiveness of electrolyte design for dual-ion carrier storage mechanism in aqueous devices toward high energy density and long cycle life.