
AsianScientist (Aug. 17, 2017) – Researchers in China have engineered bendable batteries that can run on body-inspired liquids such as normal IV saline solution and cell-culture medium. They published their findings in the journal Chem.
Many wearable devices and medical implants run on batteries. For portability, the batteries for these devices should be lightweight, durable and safe. However, most batteries currently used are bulky, rigid and contain hazardous material that can cause harm should battery leakage occur.
“Current batteries like the lithium-ion ones used in medical implants generally come in rigid shapes,” said Professor Wang Yonggang who led the experiments with Professor Peng Huisheng, both from Fudan University. “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.”
In this study, the authors designed alternatives to lithium-ion batteries by focusing on the mechanical-stress demands of wearable electronics such as smartwatches and the safety requirements of implantable electronics.
Safety measures for wearable and implantable batteries have generally involved structural reinforcement to prevent hazardous chemicals from leaking out. Instead, the researchers replaced those toxic and flammable liquids for cheap sodium ion solutions that are less harmful, even to the environment.
Among those solutions, normal saline and cell-culture medium that contains amino acids, sugars and vitamins in addition to sodium ions stood out as ideal biocompatible electrolytes. They cause no harm to the surface or interior of the body and therefore are considered biocompatible and suitable for implantable devices.
Since thick reinforcement structures were no longer required to prevent electrolyte leakage, the researchers were able to make the batteries more flexible. They designed two types of flexible batteries—a 2D ‘belt’-shaped battery for which they adhered thin electrode films to a net of steel strands, and a 1D fiber-shaped battery for which they embedded nanoparticles of electrode material around a carbon nanotube backbone.
Besides testing biocompatible fluids, the authors 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, both battery types 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.
The batteries’ performance held up when the authors 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 also noticed a unique property of their fiber-shaped battery. The same carbon nanotubes that made up the skeleton of the 1D battery also accelerated the conversion of dissolved oxygen into hydroxide ions, a process that harms battery effectiveness but could be used 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.”
The article can be found at: Guo et al. (2017) Multi-functional Flexible Aqueous Sodium-Ion Batteries with High Safety.
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Source: Cell Press; Photo: Shutterstock.
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