Amprius, a battery startup based in Silicon Valley, is making waves with a new kind of lithium-ion battery that stores around 20% more energy than batteries currently on the market. Unlike most battery breakthroughs that we write about on ExtremeTech, this one is actually here today: Amprius is already shipping its batteries to some smartphone makers, and has recently secured $30 million in funding to develop next-generation batteries that will store 50% or more energy than the current Li-ion batteries. This is massive news for mobile computing, but also for electric vehicles, where energy density per kilo (weight of the battery) is a major factor in the development of long-range EVs.

It isn’t often that we get to write about an actual, honest-to-God, on-the-market battery breakthrough — but it’s definitely not a coincidence that the founder of Amprius, Stanford’s Yi Cui, has been the star of more battery stories on ExtremeTech than any other researcher (by some margin). Yi Cui was the mastermind behind the silicon nanotube anode, the transparent lithium-ion battery, and the everlasting water-based battery. None of those techs are ready for commercial use, though. Instead, Amprius is commercializing something that’s a bit simpler: lithium-ion batteries with a silicon anode (negative; cathode is positive), rather than standard-issue graphite (carbon).

We have long known that a silicon anodes are amazing — four lithium ions can bond to a single silicon atom, whereas it takes six carbon atoms to bond to a single lithium ion, resulting in huge energy density — but it has so far proven very difficult to make a reliable one. Basically, silicon absorbs so many lithium ions that it swells to four times its original size, and then shrinks back to its original size when the ions flow back out. This expansion/contraction process causes the anode to be destroyed within just a handful of charge/discharge cycles. (Read: DoE calls for a chemical battery with 5x capacity, within 5 years – can it be done?)

To get around this, it sounds like Amprius has developed a cathode that’s fashioned out of silicon nanoparticles that have been coated in a layer of carbon to make them more rugged. This silicon-carbon cathode isn’t as energy-dense as a pure silicon cathode, but it’s still a significant improvement (10-50%) — and, most significantly, Amprius says its batteries can be produced using existing equipment (this is a huge barrier when trying to deploy any new tech). These batteries retain 80% of their charge after 500 cycles, which isn’t quite up to spec for electric vehicles — Amprius’ next-gen batteries, which it recently raised $30 million in funding for, will aim for 700 to 1000 cycles — but it’s more than good enough for mobile computing. Talking to Technology Review, Amprius CEO Kang Sun says that the company has made “hundreds of thousands” of batteries, and that they’re now being used in portable electronics devices. Amprius’s first-gen batteries store 650 watt-hours per liter; conventional batteries, like the one in your smartphone, generally store between 400 and 620 watt-hours per liter.

That’s the funny thing about batteries: It’s entirely possible that your new smartphone uses an Amprius battery, but you would would never know it. The thing is, it’s not really in anyone’s interest to produce a smartphone that has 50% more battery life than its predecessor. It’s much better (profit-wise) to increment it slowly — enough to beat last year’s phone and your immediate competition, and no more. Higher energy density isn’t just about longer battery life, either: If you have higher energy density, you can achieve the same run time but with a smaller (and lighter) battery, or you can pack in more sensors and faster chips while keeping the battery life the same.

The main point, though, is that in today’s landscape, where we’re slaves to mobile technology, new battery technology is very important indeed.