Gene Berdichevsky believes in batteries. As employee number seven at Tesla, he helmed the team that designed the lithium-ion battery pack for the company’s first car, the Roadster, which convinced the world to take electric vehicles seriously. A decade later, EVs can hold their own against your average gas guzzler, but there’s still a large trade-off between the shelf life of their batteries and the amount of energy packed into them. If we want to totally electrify our roads, Berdichevsky realized, it would require a fundamentally different approach.

In 2011, Berdichevsky founded Sila Nanotechnologies to build a better battery. His secret ingredient is nanoengineered particles of silicon, which can supercharge lithium-ion cells when they’re used as the battery’s negative electrode, or anode. Today, Sila is one of a handful of companies racing to bring lithium-silicon batteries out of the lab and into the real world, where they promise to open new frontiers of form and function in electronic devices ranging from earbuds to cars.

The long-term goal is high-energy EVs, but the first stop will be small devices. By this time next year, Berdichevsky plans to have the first lithium-silicon batteries in consumer electronics, which he says will make them last 20 percent longer per charge. As the lustrous feedstock for the digital hearts of most modern gadgets, silicon and lithium are a dynamic duo on par with Batman and Robin. Crack open your favorite portable device—be it a phone, laptop, or smartwatch—and you’ll find a lithium-ion battery eager to provide electrons, plus a silicon-soaked circuit board that routes them where they need to go. But if you combine the metals in a battery, it can create all sorts of problems.

Several lithium-ion cell prototypes containing Sila Nanotechnologies' silicon anode. Courtesy of SilaNanoTech

When a lithium-ion battery is charging, lithium ions flow to the anode, which is typically made of a type of carbon called graphite. If you swap graphite for silicon, far more lithium ions can be stored in the anode, which increases the energy capacity of the battery. But packing all these lithium ions into the electrode causes it to swell like a balloon; in some cases, it can grow up to four times larger.

The swollen anode can pulverize the nanoengineered silicon particles and rupture the protective barrier between the anode and the battery’s electrolyte, which ferries the lithium ions between the electrodes. Over time, crud builds up at the boundary between the anode and electrolyte. This both blocks the efficient transfer of lithium ions and takes many of the ions out of service. It quickly kills any performance improvements the silicon anode provided.