From smartwatches and phones to drones, many modern devices depend on small, rechargeable energy storage systems.
But when these products reach the end of their lives, their batteries can be difficult to recycle and often contribute to the growing problem of electronic waste.
Researchers have now developed a different approach: a compact supercapacitor designed from the beginning to be easily taken apart and reused.
The new device can store and release electrical energy while using materials that can be separated in a simple water-based solution.
In experiments, researchers reused key components to build new supercapacitors that performed about as well as the original.
The study was reported in ACS Energy Letters.
Many portable electronic products currently rely on lithium-ion batteries. These batteries can store large amounts of energy, but they have disadvantages. Their electrolytes can be flammable, and recycling them is complicated because their different layers and materials are often difficult to separate.
Researchers Tse Nga Ng, Nandu Koripally and their colleagues wanted to create a more sustainable alternative for lightweight energy storage.
Their solution uses zinc ions and a water-based, nonflammable electrolyte. The researchers also incorporated reusable electrically conductive materials and an adhesive that holds the device together during use but can later be dissolved.
The supercapacitor contains a zinc-and-copper anode and a cathode made from activated carbon fiber. Between them is a solid electrolyte containing a zinc chloride solution. The layers are joined using a special resin that forms strong bonds when heated.
Importantly, those bonds can be broken when the device is placed in a mildly acidic, water-based liquid. This allows the different layers to separate without complicated recycling equipment.
To demonstrate that the technology could power a real device, the researchers built four supercapacitors into the wings of a small model glider. The supercapacitors powered a motor connected to a propeller. With the motor operating, the glider traveled farther than it did without external power.
The researchers then tested whether the energy storage device could truly be recycled. They placed one supercapacitor in the mildly acidic solution, and within about 30 minutes its layers separated.
They recovered the carbon-fiber cathode and used it to build another supercapacitor with a new electrolyte and zinc anode. They then repeated the recycling process and reused the same carbon fibers again.
Across the original device and two rounds of reuse, the carbon fibers completed more than 172,000 charging and discharging cycles while maintaining similar electrical performance.
The researchers say the results show that high performance and easier recycling do not necessarily have to compete with each other.
Designing energy storage devices so their parts can be repaired, separated and reused could reduce the amount of valuable material thrown away. If approaches like this can eventually be produced on a larger scale, future electronics and lightweight machines could become easier to recycle while still getting the power they need.
