Super-concentrated alkali hydroxide electrolytes for rechargeable Zn batteries

TL;DR

This paper introduces super-concentrated alkaline electrolytes for rechargeable zinc batteries, significantly reducing parasitic reactions and enabling high capacity and long-lasting performance.

Contribution

The study demonstrates the use of 15 M KOH electrolytes to suppress parasitic reactions and enhance zinc battery performance through novel electrolyte chemistry and insights from simulations.

Findings

Electrolyte with 15 M KOH shows >2.5 V electrochemical window

High ZnO solubility (>1.5 M) and ionic conductivity (>0.27 S/cm)

Batteries achieve over 110 hours of operation

Abstract

Rechargeable Zn batteries offer safe, inexpensive energy storage, but when deeply discharged to compete with lithium-ion batteries, they are plagued by parasitic reactions at the Zn anodes. We apply super-concentrated alkaline electrolytes to suppress two key parasitic reactions, hydrogen evolution and ZnO passivation. An electrolyte with 15 M KOH displays a broad electrochemical window (>2.5 V on Au), a high ZnO solubility (>1.5 M), and an exceptionally high ionic conductivity (>0.27 S/cm at 25 C). Spectroscopies and ab-initio molecular dynamics simulation suggest K+-OH- pairs and a tightened water network to underpin the stability. The simulation further reveals unique triggered proton hopping that offsets the lack of water wires to sustain the conductivity. Low hydrogen evolution, confirmed via online mass spectroscopy, and slow passivation enable a NiOOH||Zn battery to deliver a cumulative capacity of 8.4 Ah cm-2 and a Zn-air battery to last for over 110 hours.