The Perfect Electrolyte Sandwich

photo-de-jeff-dahn

French

The battery of the future will need to be efficient, safe, long-lasting, cheap, and ethically sourced. 

That’s a long list, but Jeff Dahn, a pioneer in the development of lithium-ion (Li-ion) batteries, is in a good position to find the recipe. Earlier this year, his research group at Dalhousie University in Halifax, Nova Scotia, renewed its industrial research partnership with Tesla. 

“The goal is to completely move away from fossil fuels,” says Dahn. 

Batteries store energy for later use, but charging and discharging them thousands of times is tough on the materials that compose them. If Li-ion batteries for electric vehicles did not degrade after many years of operation, they could be used to store energy while they are parked. This practice is called vehicle-to-grid. They could contribute to grid-scale energy storage from renewables. “We need to be able to use solar and wind energy even though it’s not there all the time,” explains Dahn. 

Even though Li-ion technology has become more affordable in recent years, its cost remains a substantial barrier to mass adoption. One way to reduce cost is to make the batteries last longer, which is done by altering their chemical makeup.

“A battery is like a sandwich,” explains Dahn. The meat of the sandwich is the electrolyte, an ionically conducting liquid. Lithium ions travel through this liquid to and from the positive and negative electrodes, or bread slices. The ions react with the electrolyte and electrodes, which can make the battery degrade over time. Better batteries, therefore, depend on a mix of additives in the electrolyte and electrode surface coatings that minimize these reactions.

This requires an understanding of how materials interact at the atomic level. Promising materials found experimentally in Dahn’s lab are targeted for further analysis via computer simulation. “You start with a box of atoms,” explains Marc Cormier, a PhD student in Dahn’s lab. “Using the principles of quantum mechanics, you can learn the physical properties of a collection of atoms.” 

Such an analysis is computationally demanding and would take a long time to run on a regular desktop, so Cormier depends on CCF resources to crunch the numbers. He uses the Vienna Ab initio Simulation Package (VASP), a computer program that models atomic scale materials, which he runs on the national ARC platform.  

“A material is like a beach,” says Cormier. “Take a handful of sand and look at the grains. Learn about that handful, and you learn about the whole beach.”

This deep dive into the fundamental building blocks of materials has implications that go beyond energy efficiency, as they also enable us to address ethical concerns regarding how they are sourced. 

Such is the case with cobalt. “The positive electrode determines how much energy you can store, and it’s the most expensive part of a lithium-ion cell.” says Cormier. In many Li-ion cells, the positive electrode contains cobalt. The issue is that roughly 60% of cobalt mining in the world is done in the Democratic Republic of the Congo, where unsafe work practices and child labour are not properly put in check.

Experimentally, Dahn’s group and others around the world have shown that cobalt is not required in these materials, with a few minor tradeoffs associated with its removal. 

By analyzing the element through theoretical modeling, Cormier hopes to better understand its role in the battery and, if removed, how the battery can still perform as desired. This, in turn, may lead to the production of clean batteries free of exploitation.

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