• An implantable Na-O2 battery with opened cathode structure has been first developed
• This Na-O2 battery architecture revolutionizes the concept of implantable batteries
• The Na-O2 battery can be easily bent and presents a good electrochemical performance
• The Na-O2 battery devices exhibit excellent bio-compatibility in vivo

Currently, implantable electronics used in clinical practice are powered by conventional batteries that utilize sealed electrodes and electrolytes. Although an open-structured battery could use dissolved O2 and Na+ in the body liquid as active material to provide unlimited capacity, achieving bio-compatibility and stability poses serious challenges. Herein, we propose a Na-O2 battery for in vivo applications that includes a nanoporous gold catalytic cathode and a NaGaSn alloy anode separated by an ion-exchange membrane (Nafion). A laminated battery subcutaneously implanted in rats delivers a power density of 2.6 μW/cm2 at 1.3 V (vs. Na/Na+) and demonstrates excellent bio-compatibility in vivo. Capillaries regenerate well around the cathode, providing a continuous source of O2 for the battery. Our Na-O2 battery revolutionizes the concept of implantable batteries, the consumption of O2 during discharging results in a deoxygenation function, which also offers a new way to combine bio-electronic implants and biotherapy toward the diseases associated with anaerobic environments.