Used batteries of different typs are seen in a collecting box for recycling at an office in Zurich, Switzerland August 14, 2017. (Xinhua/REUTERS)
WASHINGTON, Aug. 13 (Xinhua) -- You will soon have no need to worry about potentially dangerous solution leakage from bendable batteries that power wearable and implantable devices if a proof-of-concept design by Chinese researchers proves to work well enough.
In a study published this week in the U.S. journal Chem, researchers in China reported flexible batteries that can run on body-friendly liquids such as normal IV saline solution, or salt water, and cell-culture medium.
Co-senior author Yonggang Wang, a chemistry professor at Fudan University, called their design a much safer alternative to the current popular lithium-ion batteries as they met not only the mechanical-stress demands of wearable electronics such as smartwatches, but also the safety requirements of implantable electronics.
"Current batteries like the lithium-ion ones used in medical implants generally come in rigid shapes," said Wang. "Additionally, most of the reported flexible batteries are based on flammable organic or corrosive electrolytes, which suffer from safety hazards and poor biocompatibility for wearable devices, let alone implantable ones."
The researchers, led by Wang and macromolecular science professor Huisheng Peng, swapped out those toxic and flammable liquids for cheap and environmentally friendly sodium-ion solutions such as IV saline solution and cell-culture medium.
Both liquids are safe for implantable devices. The IV saline solution is the same one used to treat patients in the hospital, while the cell-culture medium contains amino acids, sugars, vitamins and sodium ions to mimic the fluid surrounding human cells.
Besides testing biocompatible fluids, the researchers also tested ordinary sodium sulfate, a safe and fairly inert solution, as a liquid electrolyte suitable for use in external wearable devices.
With sodium sulfate solution as the electrolyte, their newly developed batteries outperformed most of the reported wearable lithium-ion batteries in terms of charge-holding capacity, an indicator of how long a battery can function without recharging, and power output for their size.
That performance held up when the researchers folded and bent the batteries to mimic the impact of wrapping a sensor, watch, or similar device around one's arm.
Charge-holding capacity was only marginally reduced for the saline- and cell-culture-based batteries, most likely because they had slightly lower sodium-ion content than the sodium sulfate solution, the researchers said.
There was indeed an undesired side reaction involving their fiber-shaped batteries.
The same carbon nanotubes that made up the skeleton of their batteries can also accelerate the conversion of dissolved oxygen into hydroxide ions, a process that harms battery effectiveness if left uncontrolled.
However, the researchers noted that the process could be adapted to treat cancer and bacterial infections.
"We can implant these fiber-shaped electrodes into the human body to consume essential oxygen, especially for areas that are difficult for injectable drugs to reach," said Wang.
"Deoxygenation might even wipe out cancerous cells or pathogenic bacteria since they are very sensitive to changes in living environment pH. Of course, this is hypothetical right now, but we hope to investigate further with biologists and medical scientists."
