If electric vehicles are never going to completely supplant the gas guzzlers on the roads of the world, they’re going to need a whole new kind of battery. Despite constant improvements over the past decade in terms of energy density and lithium-ion battery life, cells in newer electric vehicles still lag behind internal combustion engines on just about every measure of performance. Most electric vehicles have a range of less than 500 miles, it takes over an hour to recharge their batteries, cells lose nearly a third of their capacity in a decade, and they pose a serious safety risk in reason for their flammable materials.
The solution to these problems has been known for decades: It’s called a solid-state battery, and it’s based on a deceptively simple idea. Instead of a conventional liquid electrolyte – the substance that carries lithium ions between electrodes – it uses a solid electrolyte. In addition, the negative terminal of the battery, called its anode, is made of pure lithium. This combination would send its energy density through the roof, allowing super fast charging, and eliminate the risk of battery fires. But over the past 40 years, no one has been able to make a solid-state battery that delivers on that promise – until earlier this year, when a secret startup called QuantumScape claims for solving the problem. Now he has the data to prove it.
For the first time on Tuesday, QuantumScape co-founder and CEO Jagdeep Singh publicly revealed the results of the company’s solid-state battery tests. Singh says the battery has solved all of the major challenges that have plagued solid-state batteries in the past, such as incredibly short lifespans and slow charge rate. According to data from QuantumScape, its cell can charge to 80% of its capacity in 15 minutes, it retains more than 80% of its capacity after 800 charge cycles, it is non-combustible, and it has a volumetric energy density of over of 1000 watt hours per hour. liter at cell level, nearly double the energy density of high-end commercial lithium-ion cells.
“We believe we are the first to solve the solid state problem,” Singh told WIRED ahead of the announcement. “No other solid-state system comes close to this.”
QuantumScape’s battery cell is about the size and thickness of a playing card. Its cathode, or positive terminal, is made of nickel-manganese-cobalt oxide, or NMC, a common chemistry in EV batteries today. Its negative electrode, or anode, is made from pure lithium metal, but it is more accurate to say that it has no anode at all, since it is made without one. When the battery discharges during use, all lithium flows from the anode to the cathode. The void left on the anode side – thinner than a human hair – is temporarily compressed like an accordion. The process is reversed when the battery is charged, and the lithium ions re-enter the anode space.
“This anode-less design is important because it’s probably the only way to manufacture lithium metal batteries today with current manufacturing facilities,” says Venkat Viswanathan, mechanical engineer working on lithium metal batteries at the University. Carnegie Mellon and Technical Advisor at QuantumScape. “The lack of anode was a major challenge for the community.”
But the key to QuantumScape’s semiconductor breakthrough is the flexible ceramic separator that sits between the cathode and the anode. It is the material that puts the “solid” in the solid state. Like the liquid electrolyte that sits between the electrodes in a conventional cell, its primary function is to transport lithium ions from one terminal to another as the battery charges and discharges. The difference is that the solid separator also acts as a barrier that prevents lithium dendrites – metallic tendrites that form on lithium metal anodes during charge cycles – from snaking between the electrodes and causing a short circuit.