In April, Elon Musk promised a battery that could power Teslas for more than 1 million miles over the course of their lifespan.

In September, a team of battery researchers at Dalhousie University, with support from Tesla, released test results on a battery that "should be able to power an electric vehicle for over 1 million miles." The results, published in a paper in The Journal of the Electrochemical Society, shows the battery degrades at a remarkably slow rate.

While the battery would be an exciting development for battery research and a sure stepping stone for Tesla on the way to a robotaxi fleet, we think there's a lot more Tesla needs to figure out before it has a single battery that powers its cars for a million miles.

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Following is a transcript of the video.

Narrator: The average lifespan of a car is 150,000 miles. Your average driver drives 13,500 miles every year, meaning a car lasts about 11 years. Now, imagine you had a car that could last 400,000 miles. 800,000? How about 1 million miles? Your car could last an entire lifetime. But a million-mile battery is the stuff of fiction... isn't it?

In April, Elon Musk announced Teslas would soon be powered by a battery with a lifespan of more than 1 million miles.

Elon Musk: "The current battery pack is about maybe 300,000 to 500,000 miles. The new battery pack that'll probably go into production next year is designed explicitly for a million miles of operation."

Narrator: In September, a team of battery researchers at Dalhousie University, with support from Tesla, published a paper that describes a very special kind of battery - a battery that it says "should be able to power "an electric vehicle for over 1 million miles." Soon after, Tesla filed a patent for a battery with a similar cell composition to the one in the paper. Many of the Dalhousie researchers, including Jeff Dahn, Xiaowei Ma, and Stephen Glazier, are listed as inventors. So, is this the battery Musk needs? The paper presents the results of years of testing on a new battery cell formula, or chemistry. And the team says the results from tests on the battery are "far superior" than other lithium-ion batteries. So, what's so good about it?

Battery science is an exercise in experimentation. The right tweak in the combination and efficiency of the elements commonly used for batteries could yield big results. In addition to a winning combination, the million-mile battery uses one large crystal instead of many small crystals. This single-crystal nanostructure is less likely to develop cracks when the battery is charging. Cracks cause a decrease in the lifetime and performance of the battery. How'd the new design do? Well, the life of a battery is measured in discharge cycles. Using an amount equal to 100% of the battery's charge is one cycle. Where a typical lithium-ion battery could give you only 1,000 to 2,000 discharge cycles, tests showed the million-mile battery had 95% of its life left after 1,000 discharge cycles and about 90% after 4,000.

You're probably thinking: "That's awesome!" "We've got a great battery here." And you're right. This is an awesome battery. But we're not going to see this version of the battery in a Tesla.

There is one major thing Tesla would have to sort out before it can use a battery like this in its cars. This cell chemistry uses a large amount of cobalt. Cobalt, a popular element in battery development, carries inherent challenges. One, cobalt is finite and running out. So it's very expensive. Two, mining cobalt is hazardous and some cobalt mines have exploited children for labor. Tesla is trying to eliminate cobalt from its batteries entirely.

So, if we don't have a viable battery here, what's the significance of the battery in the paper? Well, it shows that we're close to obtaining a battery that lasts a million miles and is compatible for use in Teslas, one that is cheaper and probably contains less cobalt. A major announcement is on the horizon. Specifically, we're waiting on Tesla's battery and drivetrain investor day, which has been pushed back to early 2020.

The paper and patent represent a big advancement in battery tech and are undoubtedly a preface to the actual million-mile battery composition that will land itself in Teslas in the coming years.