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Dehydration-Driven Ion Aggregation and the Onset of Gelation in ZnCl2 Solution

Alexei V. Tkachenko1,*, Chuntian Cao2, Amy C. Marschilok3,4,5,6, and Deyu Lu1,†

  • *Contact author: oleksiyt@bnl.gov
  • †Contact author: dlu@bnl.gov
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PRX Energy 5, 033012 – Published 18 August, 2026

DOI: https://doi.org/10.1103/gxkq-6zw4

Abstract

A minimal model of ionic aggregation in concentrated ZnCl2 is developed, guided by molecular dynamics simulations with a machine-learned potential. It explicitly incorporates solvent-site depletion, correlated chloride binding, and allows for loops within Zn–Cl clusters. Dehydration drives two coordination-controlled structural changes: a crossover at Z=2 from predominantly isolated Zn-containing species to Cl-bridged clusters and the onset of gelation near Z≈3. The model reproduces the concentration-dependent trends observed in the molecular dynamics simulations with two fitted parameters, while the cluster-size distribution at the highest concentration is consistent with three-dimensional percolation scaling over the accessible range of cluster sizes.

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Popular Summary

Extremely concentrated electrolytes can behave very differently from ordinary salt solutions, but the microscopic origin of their network formation is often unclear. Here, the authors develop a simple yet quantitatively accurate theory informed by molecular dynamics simulations using a machine-learned potential. The theory shows that water scarcity changes how zinc and chloride ions coordinate: chloride ions increasingly bridge neighboring zinc ions, producing a sharp crossover from mostly isolated complexes to branched clusters. At still higher concentration, these clusters approach a connected, gel-like network. Despite its simplicity, the model reproduces the main concentration-dependent trends in the simulations with only two fitted parameters. The broad distribution of cluster sizes at the highest concentration is also consistent with behavior near a three-dimensional connectivity threshold. This framework links local ion coordination to large-scale network formation and may help explain structure, transport, and gelation in highly concentrated electrolytes relevant to aqueous batteries.

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PRX Energy 5, 033012– Published 18 August, 2026
  • Received 19 December 2025
  • Accepted 24 July 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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