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by Eva Fox November 11, 2019

We all know and understand that the heart of every electric vehicle is a battery. But the problem is that a complete discharge and recharging every day creates a large load on the battery and destroys its components faster. That is why it is so important to understand this issue.

Elon Musk's tweet, in April 2019, caused a lot of questions and reasoning:

 

 

Of course, some people regarded this statement as false. But this is Elon Musk and he always gets things done.

In September, a group of battery researchers at Dalhousie University, which has an exclusive agreement with Tesla, published a paper in The Journal of the Electrochemical Society describing a lithium-ion battery that “should be able to power an electric vehicle for over 1 million miles” while losing less than 10 percent of its energy capacity during its lifetime.

Led by physicist Jeff Dahn, one of the world’s foremost lithium-ion researchers, the Dalhousie group showed that its battery significantly outperforms any similar lithium-ion battery previously reported. They noted their battery could be especially useful for self-driving robotaxis and long-haul electric trucks, two products Tesla is developing.

The lithium-ion batteries described in the paper use lithium nickel manganese cobalt oxide, or NMC, for the battery’s positive electrode (cathode) and artificial graphite for its negative electrode (anode). The electrolyte, which ferries lithium ions between the electrode terminals, consists of a lithium salt blended with other compounds. 

NMC/graphite chemistries have long been known to increase the energy density and lifespan of lithium-ion batteries. But no one except Tesla has been able to achieve so positive results. The blend of electrolyte and additives is what ends up being the subject of trade secrets.

Dahn’s team achieved its huge performance boosts through lots and lots of optimizing of those familiar ingredients, and by tweaking the nanostructure of the battery’s cathode. Instead of using many smaller NMC crystals as the cathode, this battery relies on larger crystals.This “single-crystal” nanostructure is less likely to develop cracks when a battery is charging. Cracks in the cathode material cause a decrease in the lifetime and performance of the battery.

Through its partnership with Tesla, Dahn’s team was tasked with creating lithium-ion batteries that can store more energy and have a longer lifetime than commercially available batteries.

The energy density of a lithium ion battery is one of the most important qualities in consumer electric cars like Tesla’s Model 3. Customers want to be able to drive long distances on a single charge. Tesla’s newer cars can get up to 370 miles per charge, which is well beyond the range of electric vehicles from other companies. In fact, based on the average American commute, Dahn estimates that most EV owners use only about a quarter of a charge per day. But to make a fleet of robotaxis or an empire of long-haul electric trucks, Tesla will need a battery that can handle full discharge cycles every day.

As Dahn and his team detailed in their benchmarking paper, “one does not need to make a trade-off between energy density and lifetime anymore.” The team’s results show that their batteries could be charged and depleted more than 4,000 times and lose only about 10 percent of their energy capacity. For the sake of comparison, a paper from 2014 showed that similar lithium-ion batteries lost half their capacity after only 1,000 cycles.

“Four thousand cycles is really impressive,” says Greg Less, technical director at the University of Michigan’s Energy Institute battery lab. “A million-mile range is easily doable with 4,000 cycles.”

Shirley Meng, who runs the Laboratory for Energy Storage and Conversion at the UC San Diego, says many electric vehicle companies are pursuing batteries with higher nickel content than what Dahn’s paper and patent describe. That approach can boost the energy density of a battery. Meng says the next step is to merge those higher-density designs with some high-performing mix of electrolytes and additives. Whether it’s the formula Dahn’s group perfected is an open question.

“I believe the ultimate goal of Jeff’s team is to demonstrate ultralong life in a high-nickel-content cathode, but perhaps they need a completely different mixture of the electrolyte additive cocktail,” Meng says. “I don’t think the same formula will work, and that’s why they released all the formulations.”

Whatever design ends up making it into production at Tesla’s massive Gigafactory, the signs are clear: A million-mile battery will be here soon.

The research team believes that the one million-mile mark is just the beginning; they expect Tesla’s fancy, new, patented battery will actually outperform this expected benchmark.


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