Multi-functional Flexible Aqueous Sodium-Ion Batteries with High Safety

Flexible energy storage devices are attracting extensive attention, but most of the reported flexible batteries and supercapacitors use either strong acid or base or toxic flammable organic solutions as electrolytes, which pose potential safety issues when worn by humans or implanted into the body. Here, we present a highly safe family of flexible sodium-ion batteries (SIBs) based on a Na0.44MnO2 cathode, a nano-sized NaTi2(PO4)(3)@C anode, and various aqueous electrolytes containing Na+. The resulting belt-and fiber-shaped aqueous SIBs exhibit high volumetric energy and power density, high flexibility, and long life and thus can be safely applied in wearable electronic devices. When normal saline or cell-culture medium is used as the electrolyte, these SIBs can still work well, indicating potential application in implantable electronic devices. The fiber-shaped electrodes in Na+-containing aqueous electrolytes exhibit an electrochemical deoxygenation function, which could be applied in biological and medical fields.