Nanomaterials for implantable batteries to power cardiac devices

Abstract Batteries have been used in various biomedical devices, such as neurostimulator, cardiac pacemaker, and implantable cardiac defibrillator. Compared to applications in electronics and electric vehicles, those implantable batteries need to be extremely safe and stable as they are placed inside human bodies to play vital role in curing human diseases. They also need to have high energy density to save volume and weight in the limited space inside organs such as heart ventricles. Not only that, complete packaging with no leakage possibility and extremely low self-discharge rate are also required to ensure the safe operation of devices without interruption for an 8-10 years battery life. These requirements are considerably demanding and primary batteries are widely used in biomedical batteries to meet those requirements. Especially for cardiology applications, Li-CFx and Li-SVO (silver vanadium oxide) batteries have been used in industry for decades, and several improvements have been made to push overall battery performance to a theoretical limit. With recent progress made in enhanced treatment methods, such as communication functions among multiple leadless pacemakers for more accurate sensing mechanism, those devices require even higher power input in order to drive new functions without losing life expectancy. In this review, we reviewed principles and recent progress on using nanomaterials in these battery systems for biomedical applications, such as how to further improve electrochemical performance and increase reversibility of these battery systems as a potential solution to prolong their longevity inside human bodies.