An innovation to revive water-based flow batteries?

Thus David Reber, a young researcher at EMPA, intends to completely decouple energy storage from electrolytic solutions

Batteries: David Reber, a young researcher at EMPA in Switzerland, intends to completely decouple energy storage from the electrolyte solution to modernize traditional water-based flow battery concepts
EMPA researcher David Reber aims to completely decouple energy storage from the electrolyte solution in water-based flow batteries (Photo: EMPA)

Two colored liquids bubbling through tubes: is this what the batteries of the future will look like?
David Reber, a researcher at the Federal Materials Testing and Research Laboratory of Switzerland, has decided to answer this question over the next four years with the support of an “Ambition” grant from the Swiss National Science Foundation.
In what way, it is easy to say.
So-called redox flow batteries have been known since the 70s.
In chemistry, oxidation-reduction or redox (a word composed of the English “reduction”, i.e. reduction, and “oxidation”, i.e. oxidation) indicates all those chemical reactions in which the oxidation number of the atoms changes, therefore in which there is a passage of electrons from one chemical species to another
Unlike traditional lithium-ion batteries, they store energy not in solid electrodes, but in tanks containing liquid electrolyte solutions.
The charging and discharging process does not take place in the tanks themselves, but the electrolytes are pumped through an electrochemical cell.

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Batteries: David Reber, a young researcher at EMPA in Switzerland, intends to completely decouple energy storage from the electrolyte solution to modernize traditional water-based flow battery concepts
One of the goals of David Reber, a researcher at the Federal Materials Testing and Research Laboratory of Switzerland, is to develop a better type of flow battery
(Photo: EMPA)

Current redox impractical for smartphones, PCs or cars, but promising for stationary storage

Liquid batteries are impractical for cell phones, laptops or cars.
But they are very promising for stationary storage solutions.
Because energy is stored outside of the actual cell, flow batteries can benefit from simple and targeted scaling.
A larger electrochemical cell causes the battery to charge and discharge faster, while larger electrolyte tanks allow it to store more energy.
“As we use more renewable energy, we will need large-scale energy storage, including in urban areas”, says Reber.
Another point in favor of flow batteries: If you use water-based electrolytes, they are virtually non-flammable, unlike conventional lithium-ion batteries.

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Batteries: David Reber, a young researcher at EMPA in Switzerland, intends to completely decouple energy storage from the electrolyte solution to modernize traditional water-based flow battery concepts
For David Reber, water-based flow batteries, non-toxic and scalable, are in theory a good solution for storing renewable energy in urban areas
(Photo: EMPA)

Outsourced energy density because usually 10 times lower than solid state batteries?

However, the tech It hasn't caught on yet.
Reber knows the main problem: “Flow batteries have an energy density about ten times lower than batteries made from solid storage materials,” explains.
The more storage material that can be dissolved in the electrolyte, the higher the energy density of a flow battery.
“However, high concentrations thicken the solution and it takes much more energy to pump it into the cell”, explains the researcher.

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Batteries: David Reber, a young researcher at EMPA in Switzerland, intends to completely decouple energy storage from the electrolyte solution to modernize traditional water-based flow battery concepts
EMPA researcher David Reber wants to remedy the very low energy density of water-based flow batteries by redesigning their materials
(Photo: EMPA)

The idea is not a better solubility of storage materials, but rather a "hybrid" between redox and lithium ion batteries

David now wants to solve precisely this problem in his work at EMPA's Materials for Energy Conversion laboratory, with an unusual approach.
While most flow battery projects focus on improved solubility of storage materials, David wants to completely decouple energy storage from the electrolyte solution.
“My vision is to develop a sort of hybrid between a flow battery and a lithium ion battery”, explains Reber.
To this end, it intends to add solid storage materials, such as those used in cell phone batteries, to the flow battery reservoir.
“If the dissolved material and the solid storage material are exactly matched, they can transfer energy to each other.”
"This allows us to combine the scalability of flow batteries with the high energy density of batteries with solid storage materials."

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Batteries: the Materials for Energy Conversion sector of the Federal Materials Testing and Research Laboratory (EMPA) in Dübendorf in the Swiss canton of Zurich
The headquarters of the Materials for Energy Conversion sector of the Federal Materials Testing and Research Laboratory (EMPA) in Dübendorf in the Swiss canton of Zurich
(Photo: EMPA)

Looking for suitable material: a chelate, an organic molecule with multiple arms, capable of "enveloping" a metal ion?

First, however, researchers must find suitable pairs of materials that allow energy exchange and remain stable for an extended period of time.
“Ideally, a redox flow battery should be able to operate for around 20 years”, explains the researcher.
The compatibility of a pair of materials depends on the so-called redox potential of the substances: at what voltage they donate or accept electrons.
“I already have several possible couples in mind”says David.
And if a promising pair isn't quite compatible, its redox potentials can be manipulated with some chemical modifications.
One of Reber's ideas is to use a chelate as a dissolved storage material: a multi-armed organic molecule, which “envelops” a metal ion.
Depending on the number of arms of the organic molecule, the so-called “ligand”, the redox potential changes.
In biochemistry, a ligand (from the Latin "ligare", to bind) is defined as a molecule capable of binding a biomolecule and forming a complex capable of carrying out or inducing a biological function.
David has already conducted research on chelate-based redox flow batteries during his postdoctoral period at the University of Colorado Boulder in the United States of America, for which he will receive the prestigious “Battery Division Postdoc Award” at the meeting annual meeting of the Electrochemical Society in Gothenburg, Sweden.

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Batteries: David Reber, a young researcher at EMPA in Switzerland, intends to completely decouple energy storage from the electrolyte solution to modernize traditional water-based flow battery concepts
Flow batteries separate the charging process from energy storage and could be an excellent solution for stationary storage needs in urban areas
(Photo: EMPA)

Compact flow batteries, with a flexible form factor, much easier to integrate into urban areas

At the end of the “Ambition” financing period, which will last four years by decision of the SNSF, he hopes to have a well-functioning battery with further solid storage.
“If this approach works, the potential applications are very different”, he claims.
For example, compact flow batteries with a flexible form factor would be much easier to integrate into urban areas.
“Pumps and some pipes would be enough”, concludes the researcher from the Federal Materials Testing and Research Laboratory of Switzerland.

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Batteries: David Reber, a young researcher at EMPA in Switzerland, intends to completely decouple energy storage from the electrolyte solution to modernize traditional water-based flow battery concepts
David Reber wants to use a chelate as a dissolved storage material: a multi-armed organic molecule, which "envelops" a metal ion (Photo: EMPA)