One day, cities will be connected with hundreds of tiny sensors to track everything from pollution to traffic to weather. The 5G cell boxes will transmit ultra-fast wireless internet capable of downloading an entire movie to a phone in seconds. Advanced wearable sensors that could be woven into a shirt will track your gait, your heart rate and even the chemicals in your sweat.
There is only one thing holding back the realization of that future: the battery.
“The technology is close to being ready, it’s just the power source that isn’t there yet.” Shirley Meng, a professor of nanoengineering and materials science at the University of California, San Diego, told The Daily Beast. “For something like wearable sensors, you need something that’s flexible and safe enough to wear directly on your body in a wide range of temperatures.”
The dominant battery technology for consumer devices is lithium ion, found in everything from mobile phones to electric vehicles. While lithium-ion batteries pack a lot of power into a small package, they also rely on a liquid electrolyte that can be flammable when overheated or damaged. (Remember those that explode samsung phones?) That means careful storage and a hard case, which isn’t exactly conducive to a sweat-management shirt.
That has some companies searching for new battery technology so agile it can be bent and twisted, with a manufacturing process that can be carried out on a T-shirt sieve press instead of a gigafactory. Made of zinc, a more common metal than lithium, these batteries can be printed in as many shapes and sizes as stickers.
Alameda-based Imprint Energy is one of the companies working on flexible solid-state zinc batteries. Co-founder and CEO Christine Ho began working on lithium-ion batteries as a student researcher at the University of California, Berkeley, but realized the world needed an alternative, one that didn’t rely on mining takes place outside of the U.S. (according to a white house reportChina controls 60 percent of global lithium production.)
In January, Imprint launched a new battery design, ZinCore, which packs ten times more power than previous models into a cell just one millimeter wide. Crucially, Ho told The Daily Beast, batteries also have a broader temperature range. While most batteries slow down significantly in the cold, the new version can withstand temperatures as low as -35 degrees Celsius (-31 degrees Fahrenheit), meaning it can be used to track and trace products that need to be cooled like COVID vaccines.
Ho likened battery manufacturing to “packaging dirt” because of how common the components are. “Most of the components of our batteries are vitamins,” he said.
And without a hard case, those batteries can be shrunk, bent, and twisted to fit into all sorts of tiny devices. Imprint currently targets two main markets. They can be used to power 5G cells and Internet of Things (IoT) sensors for smart cities. Imprint is also working with shipping companies on smart tags, which could send a location signal to valuable products or monitor the temperature in sensitive items like seafood or ice cream. Amid concerns about election security, Ho said, smart labels on paper ballot shipments powered by a wafer-thin battery could offer peace of mind.
“Batteries are typically the largest real estate item on a smart tag,” Ho said. “Ours can be almost invisible because it is so small.” But Imprint’s ambitions are not just to remain miniature.
“Our ultimate mission is to become the de facto green, sustainable and safe alternative to lithium-ion,” said Ho. “This could be designed for large-scale applications. Someone could design this into cell phones, put batteries into walls, put them into really big structural things that have never had power before.”
Zinc batteries were once thought to be an old-fashioned technology. Because they couldn’t be easily recharged but the components were cheap, they were mostly used as waste power sources. Most consumers found them in hearing aids, where they could be easily disposed of. Now zinc batteries are “hot,” said Chunsheng Wang, director of the Extreme Battery Research Center at the University of Maryland.
Unlike lithium-ion, which is based on rare minerals and carries significant safety risks, zinc batteries are “intrinsically safe and readily available,” Wang said. The biggest drawback, however, has been in recharging. When traditional zinc batteries are reversed to extract and store energy, zinc can accumulate in certain places where electricity is strongest at the anode, forming dendrites that eventually short-circuit the cells. While limitations vary by chemistry and design, batteries generally can’t last more than a few hundred cycles.
Researchers, including Wang, have worked on modifying the electrolyte to reduce that damage and allow faster recharging. One Hanyang University study in the Republic of Korea reported a high performance zinc-air cell that was stable for 30,000 cycles.
The applications, proponents say, could become more widespread due to the flexibility of the technology. There is promise for energy storage for renewable energy production as an alternative to large lithium-ion projects. Companies like Zinc8 are adapting zinc-air batteries for large-scale energy storage that could power the electricity grid; the company recently announced a pilot project in a Queens apartment complex, after a pilot at the University at Buffalo in 2021.
However, the chemical advantages also make them work on a small scale. Meng’s UCSD lab worked with hearing aid battery company ZPower (now renamed riot power) in silver-zinc oxide batteries whose parts could be essentially condensed in the form of ink. They could then be silk-screened into thin films with an electrode in between to make a battery less than 1 millimeter. according to a 2020 article published in Joulethat battery produced at least five times the power of the same size lithium-ion battery, though recharging was still limited.
Furthermore, the chemical advantages that make zinc safer also facilitate its mass production. “Lithium ion cannot tolerate water in the manufacturing process and needs this very good case,” Meng explained. “For us it is much easier to manufacture outdoors. You don’t need to build a dry room.”
That opens the door to many opportunities, with batteries that can be mass-printed with ink barrels, in all shapes and sizes.
“The first big hurdle is the change in mindset,” Meng said. “With all the research that has been done on lithium batteries, very little progress has been made on zinc. People think that zinc chemistry is done. That is so wrong.
Imprint’s Ho said the company will announce a manufacturing partner soon, building on the company’s existing screen printing work with an eye to flexibility. “There is not going to be an AA battery for IoT devices,” he said, meaning the ability to change size, shape, and wattage ratio on a daily, or even hourly, basis may open up new markets.
“We get contacted all the time about every possible application, from contact lenses to mass deployments throughout the building. And many of them can change the earth or change lives,” said Ho. “I remember when lithium ion was introduced 45 years ago to see how it now spreads to vehicles and consumer electronics. I think a similar journey will happen with this chemistry.”