Energy Storage Device That's Designed To Be Recycled

"Recyclable Zinc Ion Structural Supercapacitor Enabled by Porous Vitrimer" ACS Energy Letters

Smartwatches, phones, and even some drones rely on lightweight, rechargeable energy storage systems. Once those devices wear out, many end up as electronic waste. Now, researchers reporting in ACS Energy Letters have developed a compact supercapacitor that can be quickly disassembled into reusable components. They used the devices to power a glider's propeller and then took apart one supercapacitor and sequentially reused parts in two new ones that performed as well as the original device.

Sustainability and performance do not have to be competing goals." - Nandu Koripally

Many rechargeable devices use lithium-ion technology and contain flammable electrolytes. Additionally, they are hard to recycle because the components don't come apart easily. So, Tse Nga Ng, Nandu Koripally, and colleagues searched for a more sustainable approach for compact energy storage. Their work led them to develop a supercapacitor that used zinc ions in a water-based, non-flammable electrolyte, dissolvable adhesives, and reusable electrically conductive materials.

"We built on our lab's prior work, combining high-energy alternative zinc-ion chemistry and structural supercapacitors to make a recyclable version that enables second-life cells and outperforms prior state-of-the-art devices," says Koripally, the lead author of the study.

For the supercapacitor, the researchers created a zinc metal-copper-foil anode and an activated-carbon-fiber cathode. In between, they placed a solid electrolyte made from a porous resin coated onto a plastic film and soaked in a zinc(II) chloride salt solution. The resin formed strong bonds when heated but broke apart in a slightly acidic liquid. Finally, they fused the layers together with heat, forming a thin device with a 2-volt potential.

As proof of concept, the researchers integrated four supercapacitors into the wings of a model glider. When tossed like a paper airplane, it went 12 feet (3.7 meters) when the propeller's motor was powered by the supercapacitors, compared to 8 feet (3.4 meters) without an external power source.

The researchers then placed one of the supercapacitors in a mildly acidic, water-based solution to disassemble it. Within 30 minutes, the layers separated. The recovered carbon-fiber cathode was reused twice more, each time with fresh solid electrolytes and zinc anodes. From initial fabrication through two rounds of recycling, the carbon fibers successfully completed more than 172,000 charge-discharge cycles and maintained similar electrical performance throughout their lifetime.

These findings demonstrate a promising approach for lightweight energy storage that minimizes electronic waste, the team says.

"Sustainability and performance do not have to be competing goals," says Koripally. "By considering the full material life cycle, we can combine design requirements into one solution to make structural energy storage devices that maintain high performance and are simple to repair and reuse."

The authors acknowledge funding from a National Defense Science and Engineering Graduate Fellowship, the Naval Innovation Science Engineering Center, the National Science Foundation, and the UC San Diego Materials Research Science and Engineering Center.