I have been following battery technology pretty closely, as this is a key technology for the transition to green energy. The most obvious application is in battery electric vehicles (BEVs). The second most obvious application is in grid storage. But also there are all the electronic devices that we increasingly depend on day-to-day. That same battery technology that powers your Tesla also powers your laptop and your smartphone.

As I have discussed before, a useful battery technology needs to simultaneously have a suite of features (with different priorities depending on application) – good energy density (energy storage per volume) specific energy (energy per mass, also called gravimetric density), stability, fast charge and discharge, many rechargeable life-cycles, useful over a large range of temperatures, and made from material that is ideally non-toxic, recyclable, cheap and abundant. The current lithium-ion batteries are actually very good. They have been incrementally improving over the last two decades, allowing for the BEV revolution to really get under way.

But they have some downsides. They are just at the edge of energy density for aviation applications. They use some difficult to source raw material, like nickel and cobalt. They can occasionally catch fire (although are getting safer). And they are still pretty expensive. Further, we are really stretching the lithium supply chain if we want to build millions of cars and lots of grid storage. Fortunately, the key role that battery technology is playing in the green revolution is widely appreciated in the industry, and there has been a tremendous investment in accelerating battery development. Here are a few potential advances I have been keeping an eye on.

The first is actually not potential, but already in production. I interviewed for the SGU this week (the episode will come out Saturyday) the COO of Amprius, who have started production (actual production) of a lithium ion battery with twice the energy density and specific energy of the current batteries being used in BEVs –  500 Wh/kg, 1300 Wh/L vs about 240/650 for a current Tesla battery. So yeah – double. That is not an incremental advance, that’s a pretty big leap. These numbers have been independently verified, so they seem legit.

The innovation is something I first heard about over a decade ago (that is how long these laboratory innovations take to work their way through the technology pipeline. The big change is using silicon anodes instead of graphite. Current batteries are pretty much at the limit of how many lithium ions the graphite can hold. Silicon, however, has 10 times the capacity as graphite. The problem has been that silicon swells and cracks when it stores charge as lithium ions, but Amprius spent about 14 years to figure out how to solve this problem, and they did. Their silicon anode lithium ion batteries have twice the energy storage capacity, and there is still head room with this technology. They estimate they will eventually be able to double that again.

As they ramp up production they are first selling these batteries to the aviation industry (mostly for drones), where the higher energy density is at a premium. But this can also have a dramatic effect on the adoption of electric aircraft for short distance commercial flights. They are also building a new factory and anticipate that their batteries will find their way into electric cars sometime around 2026. Essentially, the switch to silicon anodes will allow lithium ion battery technology to continue to improve for decade at least, and get us to not only double current energy density but to 3-4 times, which is more than enough for BEVs to have all the range they need with smaller lighter batteries. Hopefully they will be cheaper also, but that will depend on mass production.

A potentially competing technology for BEVs is solid lithium batteries. These still use lithium as the charge carrier, but in solid state form rather than liquid. This makes the batteries more stable – they won’t have a tendency to catch fire. The estimate is that out of the gate they will have twice the energy storage capacity as current lithium ion batteries. This is less impressive now that Amprius is producing their battery, but still the whole not-catching-fire thing is a plus. The greater stability at higher temperature does mean that the batteries can be packed tighter, increasing their potential energy density. Further, they can take advantage of the same silicon technology as the Amprius batteries.

However – solid state lithium batteries still have some technological hurdles to overcome, and it remains to be seen how long it will take to figure out how to mass produce them. Until it happens, it’s possible that this will be a deal-killer for this technology. They have to solve this fast or else may simply be eclipsed by existing lithium ion batteries that have an established manufacturing infrastructure.

The third possible battery breakthrough is sodium-based batteries (instead of lithium). Sodium is a cheaper and more abundant material than lithium, and is also a relatively light element. Right now most of the research into sodium battery technology is happening in China, but again, until they get over the production finish line, it’s hard to predict how this technology will pan out.

The big advantage of sodium-based batteries is in raw material. As I said, they use the more abundant sodium, which is also easier to recycle. They also do not depend on cobalt or nickel, so have significant raw material advantages over lithium batteries. Their primary downside, however, is that they are less energy dense than lithium batteries. This means we will probably never see a sodium-based battery in cars or planes.

However – they could be ideal for grid storage, where energy density is much less important. What matters most for grid storage is cost and raw materials, not energy density. You can have building-sized arrays of batteries for grid storage. Even in your home, you can theoretically have a refrigerator-sized battery in your basement or garage. As long as it’s relative inexpensive, that trumps size.

If industry can bring sodium batteries over the finish line, then we can envision a path forward for green technology in which all battery-based grid storage uses sodium batteries. This would relieve any strain on the supplies of lithium, nickel, and cobalt, which can then be used exclusively for vehicles and portable devices. Battery-based grid storage then becomes a much more viable option, in my opinion.

There are many other avenues of battery research ongoing, but these are the three that I think are most likely to impact the industry in the short term. It’s always possible for a wild card to change the game, but as new tech takes about a decade to develop commercially, we will generally see these new technologies coming. It is reassuring to see that battery advances are coming, as critical as they are to the green energy revolution.