This video was created in partnership  with Bill Gates, inspired by his new book   “How to Avoid a Climate Disaster.” You can find  out more about how we can all work together   to avoid a climate disaster in the link below.   [♩INTRO].

Renewable energy is the future. The cost just keeps going down, and for   lots of countries, the goal is to transition  to as much renewable energy as possible.   But for some of the more popular options,  like solar and wind power, there’s a problem:   the supply is inconsistent.

Maybe it’s cloudy for a few days,   or there’s not much wind for a while.  But people still need electricity. The solution might seem obvious — just build  batteries and save extra power for when you need it. But it’s not that simple, because  battery technology hasn’t come far enough.

You can try building enormous arrays of them,   but at a certain point, it’s just too expensive. And it turns out, there are some very good   reasons why making improvements is  hard. But scientists are on it.

Also, quick aside: It might seem like new  laptops and phones have better battery life   every year, but that’s mostly from  improvements to the rest of the device.   They allow manufacturers to  cram in bigger batteries and   better processors that draw less power. Some of the best battery tech we have is   what’s known as lithium-ion. It’s what’s in your  phone, your laptop — maybe even your electric car.

These batteries have three main parts:  . Two sides that store electric charge, and  an electrolyte separator between them. One side is the cathode, usually made  of a chemical compound called a lithium   metal oxide.

The compound is a combination of  lithium, oxygen, and some metals — like cobalt. The other side is the anode, and it’s most often  made of sheets of crystalline carbon, a.k.a.   graphite. The same stuff that’s in pencils.

And finally, separating these two sides is the   electrolyte. This is a material that’s designed  to allow positively-charged lithium ions to pass   through, but not negatively-charged electrons. When you charge a battery, lithium ions from   the cathode are released and  travel through the separator,   where they’re stored in the graphite anode.

Then, when you use the battery to power  something, the opposite happens: The lithium ions are released by the   anode and pass through to the cathode. Ultimately, this creates an imbalance where   there’s more negative charge in the anode  and more positive charge in the cathode. To balance things out, the electrons in  the anode travel to rejoin their lithium   friends in the cathode.

But since they can’t pass  through the separator, they take the only route   available — through the device you’re powering. In general, the more ions  you can fit in a battery,   the more energy it will be able to store. And part of why lithium-ion batteries are so   popular is that lithium ions are very small,  even for ions.

So you can store more of them   without increasing the battery’s size and weight. In other words, they have a high energy density.   And researchers have been working to  increase it even more, so that we can   use batteries for bigger projects — like power  storage, and also bigger electric vehicles.  But that’s not simple.   For instance, one way to increase  the energy density of a battery   would be to have an anode that can store more lithium ions when the battery is charged.   And there are materials like that! Like, silicon can hold more lithium ions than   graphite.

But because of the way it’s structured,  those extra ions also make it expand. The expansion cracks through a protective layer  around the anode, and the battery loses a bit of  its silicon — and its capacity — the next time you   charge it. So the battery doesn’t last as long.

Another main way researchers are trying  to increase energy density is by improving   the cathode. But that’s equally tricky. Two main things you need from a good cathode   are a high energy density, and  also a high conductivity.   In other words, you need a bunch  of ions, but they also need to   move fast to generate that current.

Unfortunately, many cathode materials   with high energy density and high conductivity  tend to be less stable and less safe. They also   tend to be less sustainable, because they often  use metals that are less abundant on Earth.   So like with anodes, a lot of research  has focused on energy density.   One way to improve the cathodes here might be  to use a metal oxide with more nickel in it,   and less of the harder-to-find cobalt. Because of the way nickel ions are structured,   they can lose more electrons than some  of the other metals used in cathodes,   giving the battery a higher energy density.

Problem is… this super-charged nickel isn’t   exactly stable. So it tends to react  with other parts of the battery,   messing with its structure and again,  destroying the battery’s capacity over time.   Now, researchers are working on ways to  prevent this — and on ways to improve   anodes. So there is hope for the future!

Progress has just been slow, and we’re not   quite at the point where it’s practical  to build huge battery arrays to support   all our solar and wind power. We’re getting closer, though. And to   supplement this research, other scientists are  also looking into other types of batteries that   rely on different kinds of chemistry and physics.

Because in the end, improving batteries is a   tough problem. But it’s also an important one —  because in many ways, the future of our planet   also depends on the future of batteries. Really, though, many of the solutions to climate   change are complicated.

It’s a big problem with  a lot of pieces — but it’s not a hopeless one.   If you want to learn more about how we could  actually get to a world with net-zero greenhouse   gas emissions, you might like Bill Gates’s  new book, “How to Avoid a Climate Disaster.”   It talks about batteries, but also about how  we feed ourselves, how we heat and cool our   buildings, how we get around, and more — and  how we could do those things more responsibly,   from an individual to a government level. You can find out more about how we can all   work together to avoid a climate  disaster in the link below. [♩OUTRO].