The development of wearable and implantable electrical devices has been in great demand recently. However, most existing energy storage systems are based on strong corrosive or toxic electrolytes, posing a huge safety hazard as a result of solution leakage.
Here, we have developed a family of safe and flexible belt- and fiber-shaped aqueous sodium-ion batteries (SIBs) by using various Na+-containing aqueous electrolytes, including Na2SO4 solution, normal saline, and cell-culture medium. The resulting SIBs exhibit high flexibility and excellent electrochemical performance and can be safely applied in wearable electronics. Flexible SIBs with normal saline or cell-culture medium as the electrolyte showed excellent performance, indicating potential application in implantable electronic devices.
In addition, the fiber-shaped electrode in normal saline or cell-culture medium electrolyte can consume O2 and change the pH, implying promising application in biological and medical investigations.