Biocompatible Symmetric Na-Ion Microbatteries with Sphere-in-Network Heteronanomat Electrodes Realizing High Reliability and High Energy Density for Implantable Bioelectronics.

The prolonged life expectancy accelerates the development of implantable bioelectronic devices. However, conventional batteries with limited lifetime, rigid architecture, and inferior energy density greatly restrict their applications in patient's body. Herein, a novel flexible symmetric Na-ion microbattery based on the heteronanomat electrode and the biocompatible electrolyte has been developed. The film electrodes with sphere-in-network architecture are synthesized by simultaneously electrospinning and electrospraying followed by carbonization. The combined technologies allow a uniform incorporation of active materials/C spheres into the carbon nanofiber matrix, which results in the heteronanomat electrodes with robust structure, fast electron/ion transport, and compact mass loading. The flexible microbatteries are fabricated based on the interdigitated microelectrodes and the biocompatible electrolytes, which provides a new implantable power source for bioelectronics. As a proof-of-concept study, the symmetric sodium-ion microbatteries are constructed from the heteronanomat bifunctional electrodes (based on NaVTi(PO)) and the biocompatible electrolyte. The high reversibility, fast kinetics, and high energy density of the symmetric system in the biocompatible electrolytes reveal their superior performance in bioenvironments. Moreover, the high capacity retention (over 98%) and the high stability of microbattery implanted in a living SD rat for a month further demonstrate its high reliability for long-term in vivo diagnosis. Therefore, this work not only presents a new sphere-in-net heteronanomat structure for fabricating high-performance electrode but also gives significant contributions to develop high-energy-density and high safety biocompatible power sources of implantable bioelectronics.