Here’s what you’ll learn when you read this story:

• Batteries have powered the clean energy revolution, but their chemistry can make them too slow and too bulky for applications that demand massive power bursts in seconds.
• A decades-old technology called the supercapacitor is getting a second look as AI data centers, public transport systems, and renewable energy grids create sudden, unpredictable increases in power demand that batteries struggle to meet.
• In the future, pairing supercapacitors with batteries could offer a cheaper, longer-lasting, and more flexible solution than batteries alone.

When cloud cover parks itself over a solar farm or an AI data center receives a sudden surge in computing requests, the grid has seconds—or less—to compensate before those disturbances can cascade into larger failures. And our current energy infrastructure isn’t enough to handle these complexities, which the ever-growing energy demands of the future will only multiply.

But imagine a solution that allows lightning-fast charging whenever it’s needed. An electric bus could top up its energy in 15-second bursts, never having to stop for a full battery replenishment, for instance. Batteries are excellent for storing energy, but not so great at delivering bursts of power or charging quickly. As the boom in AI data centers and renewable energy pushes demand to new extremes, the world will need a solution that does both.

Increasingly, engineers are turning to an old solution to handle these spiky new demands. Developed in the 1950s, supercapacitors are like batteries that deliver large bursts of power and last for decades with minimal wear and tear. While they have long occupied a niche role in industrial equipment and consumer electronics, many engineers think they may become more important as renewable energy, AI, and electrified transport put new stress on the grid. Pairing a supercapacitor’s power with a lithium-ion’s deep energy reserves might be one key solution our grid needs.

“The world is slowly electrifying everything,” says Yury Gogotsi, professor in the Department of Materials Science and Engineering at Drexel University. “So that means we need a variety of ways of harvesting and storing electrical energy.”

Gogotsi says that different energy needs require specialized solutions. “There is no such thing as one size fits all in energy storage and harvesting,” he says. Supercapacitors are better suited than batteries for tasks with a demand for intermittent spikes of energy or that need to happen very quickly. The distinction between the two comes down to how they handle charge. In lithium-ion batteries, ions physically move into the crystalline structure of their material, and energy is harvested as their chemical bonds form and break. The process allows a ton of energy to be stored, but it takes time due to the movement of atoms and causes wear and tear on the physical structure over time.

Supercapacitors work differently. The charges park themselves on the outside of the electrode, effectively using electrostatic attraction. Because they’re not moving into the crystal structure, there’s very little degradation over time, and they charge and discharge in a fraction of the time a battery takes. The tradeoff is that they can’t store as much energy.

This ability to respond reliably and instantaneously is why the technology is already being deployed in a number of high-stakes applications. In one example, the Airbus A380 jumbo jet uses these supercapacitors to power the aircraft’s 16 emergency doors. In the event of a catastrophic failure, the doors must blow open instantly. Whereas a traditional battery might have degraded over years of just sitting there, the supercapacitors can be counted on to work reliably.

Gogotsi and others think that the real benefit will be to use supercapacitors in parallel with batteries to bridge gaps in power demand.

“Delivering high power to stabilize the network for two to three seconds. This is really where supercapacitors can make a difference,” says Patrice Simon, professor of materials science at the University of Toulouse in France.

Supercapacitors are increasingly used to power public transport systems, he says. A system of electric buses in Switzerland uses supercapacitors that charge during brief stops—sometimes as short as 15 seconds—along their routes. This instantaneous charging allows the buses to run all day without long breaks and reduces strain from sudden power draws on the grid. In this application, the energy needs are small but frequent, which works well with the supercapacitor’s capabilities.

As Gogotsi mentioned, in some cases, the best approach is not to choose between batteries and supercapacitors, but to combine them. This is exactly the design of the world’s first large grid-scale hybrid installations unveiled in China this year, which comprises a hybrid configuration of lithium iron phosphate batteries and supercapacitors. Battery storage allows the system to save energy for later, when it is needed to smooth out spikes in electricity demand and avoid overwhelm, such as during a heat wave when everyone turns on their air conditioners at once. And the supercapacitors deliver minute- to millisecond-level responses, allowing the system to react instantly and keep the grid running steadily.

Could this combination turn blackouts off for good? Don’t get rid of your candles just yet, says Gogotsi. Blackouts will still occur due to infrastructure damage during storms, for example, when a tree takes down power lines or lightning strikes a transformer. Blackouts that are caused by strain on the grid, however, will be a thing of the past.