While Tesla continues to innovate with its automotive lithium-ion battery cells and General Motors seeks to join the fray with its forthcoming "Ultium" battery tech, there's one game-changing innovation that has, so far, proven elusive: solid-state battery cells. For decades, it's been known that using a solid electrolyte instead of a liquid one has the potential to extend battery longevity, increase energy density within a given battery cell volume, and drastically improve recharging times.

None of that is new information, and yet up until now, no battery manufacturer has quite been able to crack the code, yielding a solid-state battery that meets every target, in a way that can be manufactured at scale. Now, though, a ten-year-old startup named "QuantumScape" might have done it.

That's good news for Volkswagen, which earlier this year increased its stake in the solid-state battery startup to represent a total investment of $300 million. Volkswagen of course hasn't announced any future product plans involving QuantumScape's solid-state batteries, but there are plenty of possibilities; for now, the automaker's only pure-electric vehicle for sale in the US market is the Volkswagen ID.4, but there are plenty more models planned for the coming years.

The trick behind QuantumScape's success is a new, flexible ceramic separator between the anode and the cathode that takes the place of the liquid electrolyte, keeping dendrites from extending and touching to create a short - something that leads to degradation in a typical lithium-ion battery. The material was actually invented several years ago, but perfecting it and making it manufacturable at scale has been a challenge. Its properties give it an edge over the polymers typically used in li-ion batteries, which can't adequately prevent dendrites from forming, and the hard ceramics used in other solid-state designs, which are too brittle to last.

In a presentation this week, QuantumScape revealed some of the data showing just how promising its solid-state battery tech is. The cells can regain 80 percent of their total charge capacity in less than 15 minutes, the company says, where conventional li-ion batteries can only hope for 50 percent or less in that time, and they retain 80 percent of their original capacity over the course of 800 charge/discharge cycles - the equivalent of about 240k miles.

Most promising of all, however, is the energy density; QuantumScape's cell has an advertised volumetric energy density of about 1,000 Watt-hours per liter, which is roughly double that of the best li-ion battery cells.

Volkswagen is hoping to put an EV with solid-state battery technology on the road by 2025, which is - perhaps not coincidentally - around the same timeline Toyota has set itself. With QuantumScape's latest breakthrough, the automaker might just have gotten one big step closer to achieving that goal.