Innovative electrolytes could transform steelmaking and beyond

The lifeblood of any battery is the electrolyte. It is the medium through which positively charged elements (cations) migrate en masse between the positive and negative electrodes. Through this means, batteries discharge to provide energy and charge to store energy. Scientists call this an electrochemical process.

Electrolytes also play a key role in the development of various electrochemical processes. For example, they could be used to convert iron ore into purified iron metal or iron alloys. One challenge is that the electrolyte must remain stable under extreme operating conditions and avoid side reactions that reduce energy efficiency. The advantage of such a process would be to eliminate the energy-intensive blast furnaces used in steel production and thus reduce greenhouse gas emissions.

This is the goal of the new Center for Steel Electrification by Electrosynthesis (C-STEEL), an Energy Earthshot research center.

In a recent paper, Argonne researchers present an innovative approach to designing a new generation of electrolytes for nearly any electrochemical process. The paper is published in the journal Chemistry.

“With this approach, scientists should be able to develop electrolytes not only for electric vehicle batteries, but also for the carbon-free manufacturing of steel, cement and various chemicals,” said Justin Connell, a materials scientist at Argonne and deputy director of C-STEEL.

Electric vehicle battery electrolytes are typically composed of a salt dissolved in a liquid solvent. For example, sodium chloride is a common salt and water is a common solvent. The salt provides the electrolyte with both cations and negatively charged elements (anions) – chlorine in the case of common salt. In batteries, the salt and solvent compositions are much more complicated than this, but the key to their functionality is that the electrolyte is charge neutral because the number of anions and cations is balanced.

Previous research has focused on changing the solvent composition by using a single salt at varying concentrations. “In our opinion, the best path to improving electrolytes is primarily to use different anions for the salt,” Connell said. “Changing the anion chemistry could lead to both more energy-efficient electrochemical processes and a more durable electrolyte.”

In most current electrolytes, the solvent surrounds the active cation as it moves between the electrodes. In conventional lithium-ion batteries for electric vehicles, for example, this cation would be lithium and the anion, a fluorine phosphate (PF₆).

To design new electrolytes for different applications, the Argonne team is looking to pair the active cation with one or more different anions in the electrolyte. When anions partially or completely replace the solvent to surround the cation, scientists call them contact ion pairs.

However, with countless possible contact ion pairings, how can we identify the best match between active anions and cations in a specific application? To this end, the team is pursuing experiments supplemented by calculations using machine learning and artificial intelligence.

The goal is to develop a set of design principles that produce the best contact ion pairs for the electrolyte suited to the steelmaking requirements of C-STEEL.

“With these principles in mind, we hope to discover an affordable and sustainable electrolyte that yields the most efficient process for making iron for steel,” Connell said.

These same principles would apply to electrolytes for other decarbonized electrochemical processes, as well as lithium-ion batteries and beyond.

Besides Connell, authors include Stefan Ilic and Sydney Lavan.