How is it possible that mobile phones can do so much—summon cars, order groceries, make video-calls, count footsteps—and yet still drain power so quickly? For devices that are so mind-bogglingly smart, the constant charging that’s required seems painfully outdated. Why hasn’t anyone built a better phone battery?

“To have a battery that can last for a week or longer, you’re looking for a more energy-dense battery—that’s the fundamental thing you’re searching for,” said Venkat Srinivasan, a materials scientist who directs the Energy Storage and Distributed Resources Division at the Lawrence Berkeley National Lab.

Energy density refers to the amount of energy stored within a battery. To extend a battery charge on a cell phone or laptop to weeklong lengths would require researchers to, say, double the energy density of a battery within the next couple of years. Recent improvements to phone batteries have increased energy density by about 5 to 6 percent each year—which translates to a few extra hours on a smartphone or laptop.  

“I don’t think that there will be new technologies coming out tomorrow that suddenly it seems we are doubling the energy,” said Srinivasan. “When new technology comes in, it will be introduced in a phased fashion.”

Breakthroughs in battery technology are relatively rare. The last one came in the 1990s, with the advent of rechargeable lithium-ion batteries. “Batteries are very complex objects,” said Michael Toney, a materials scientist at the SLAC National Accelerator Laboratory.  “The complexity makes it very hard to get any sort of sustained improvement.”

The prospect of doubling an iPhone’s battery lifetime within the next five years is not unreasonable, Toney says, but anything more than that would require a dramatic development. He’s part of a team that observes batteries as they charge and discharge as a way to better predict how long they’ll last—and how battery technology might be improved.

In addition to looking for ways to increase the amount of time between charges, there’s also cycle life to consider—that is, how many times a battery can be charged and discharged completely until a battery starts to diminish, typically to 80 percent of its original capability. According to Apple, an iPhone can handle 500 charge cycles before this point, while MacBooks and iPads can complete about 1,000 cycles apiece.

Improving the batteries of the future will require optimizing the amount of energy stored in the battery, while also accounting for portability, weight, and volume. One way to make a more powerful battery that’s still relatively small would be to find new materials that can hold more ions by volume. (The conventional battery in a cell phone or laptop has a liquid electrolyte that shuttles lithium ions and electrons back and forth between the two materials as the battery is charged and discharged.) Silicon is one candidate to replace anodes that are today composed of graphite. “But we don’t just dump silicon into the battery and hope it works because it doesn’t work,” said Srinivasan. “Instead we introduce silicon bit by bit into existing anode material.” The thinking goes: Additions will slowly improve the battery’s energy density until researchers get to the point where there is significantly more silicon in the battery and less graphite in it.

On the cathode end, sulfur will most likely replace currently used metal oxides, such as cobalt oxide. Another area for improvement, according to Srinivasan, would involve using magnesium instead of lithium in a battery. Recent research shows magnesium can have double the charge-speed and can hold twice the amount of charge as lithium. (Aluminum is another likely contender as well because it can hold three times the amount of electrons as lithium.) But the use of these materials is still being explored in lab settings, and it will take a while before they are introduced into the market and then widely used.  

Researchers are also exploring how they might add more power to batteries by squeezing out the components that do not store energy so that the active parts can be made bigger, increasing energy density and giving consumers a longer-lasting charge.

Many national labs and research institutions get funding to work towards battery breakthroughs, but most of that funding goes toward improving electric vehicles, not necessarily mobile devices. But because battery density, cycle life, and safety are important components of building a better electronic, sometime the technology can be scaled down to mobile devices. Scaling is also a question of economics. The cost of a battery in a mobile device is small, but in an automobile the battery could be a significant fraction of the sticker price. So cobalt oxide, which is the cathode material in most cell phone batteries, is too expensive to be used in a vehicle. But scaling down faces problems as well. Solid-state batteries, which have no liquid components, are a key aspect in the future of electric car batteries. But according to Linda Nazar, a chemist at the University of Waterloo in Canada who also works on batteries used to power next generation electric cars, that technology is too far in the developmental stage for mobile devices. The problems include not only economics, and research funding, but also safety.  

“When you pack that much energy into a small packet then safety becomes a problem as well,” said Nazar. She notes that some of the advances in that field, such as more efficient solid-state batteries, may not be able to be effectively scaled down for use in mobile devices. The demands on mobile device batteries have increased in recent years, and batteries have improved to meet those demands. “You see this in your laptops—as soon as you put a higher-capacity battery in the device, then of course there’s the opportunity to have that battery do more things.”

Researchers are already building better batteries, but change comes slowly—almost imperceptibly. “What they notice is that they have a faster processor, or a brighter screen than two years ago,” Nazar said said. “Batteries have certainly improved for mobile devices. It’s just that people haven’t necessarily noticed.”