Green and Sustainable Hydrogen-Anchored Solvent Enabling Stable Aqueous Zn Batteries

TL;DR

This paper introduces a novel electrolyte formulation using 5-methyl-2-pyrrolidone and chaotropic ions to stabilize aqueous Zn batteries, reducing side reactions and dendrite growth for improved longevity and performance.

Contribution

The study presents a new electrolyte strategy combining low salt concentration with a polar cosolvent and chaotropic ions, enhancing Zn battery stability and performance.

Findings

Battery lifetime exceeded 2000 hours at 1 C

Zn deposition favored the (002) plane without dehydration

Enhanced stability across various cathodes and current densities

Abstract

Aqueous zinc (Zn) batteries provide many benefits, including high theoretical capacity, a low redox potential, and the abundance of Zn in Earth's crust. However, the benefits are often compromised by severe side reactions and dendrite growth, limiting their practical application. To mitigate these drawbacks, many studies have focused on high-concentration electrolytes to desolvate the Zn2+ solvation shell from water and to reduce the amount of free water. In this study, a methodology is proposed to achieve the benefits of highly concentrated electrolytes while using low salt concentrations. 5-methyl-2-pyrrolidone (5MP) was introduced as a safe and polar cosolvent capable of anchoring free water molecules through hydrogen bonding, enabled by its carbonyl and secondary amine groups. Additionally, by adding a co-salt containing a chaotropic ion, it is possible to disrupt the water network, enabling the development of high-performance aqueous Zn batteries. The synergy between anchoring water molecules and disrupting the overall water network proved to be an effective strategy for enhancing the overall Zn battery performance in a symmetric Zn cell, with lifetimes exceeding 2000 hours and 1400 hours at 1 C and 5 C, respectively. Analysis of the recovered Zn anode confirmed that the combination of 5MP and chaotropic ions enabled Zn deposition along the energetically favorable (002) plane, with no signs of surface dehydration observed by in situ Raman spectroscopy. Furthermore, long-term stability tests using a carbonyl-rich COF- and NaVO-based cathodes at various current densities further demonstrated the benefits of this approach. This work showcases the universality of a diluted electrolyte in combination with 5MP and chaotropic ions, bridging the gap between laboratory research and real-world applications.