Stick‐and‐Use Flexible K‐Ion Microbatteries with Ultrahigh Power Density and Long Lifespan Via Electron‐Ion Synergistic Tailoring

ABSTRACT Rechargeable micro batteries (MBs) with compatible sizes, high integration, and great energy storage potential have become a pressing need for future microelectronics and microrobots. However, current MBs struggle to balance high energy and high power while lacking applicable convenience. Hence, in this work, a novel kind of stick‐and‐use soft K‐ion 3D MBs is designed via a scalable additive manufacturing. Aided by electropolymerization, as‐3D‐printed micro‐cathode in MBs achieves an outstanding cycling stability over 10 000 cycles. For full MB devices, an ultrahigh power density of 50.2 mW cm −2 along with a long lifespan over 3 000 charge‐discharge cycles is simultaneously exhibited. Through theoretical and experimental analysis, the obtained excellent performance is attributed to the rational surface modification and 3D microstructure advance, resulting in stabilized interfacial electrochemistry and tailored ion‐electron transport, respectively. Notably, through a unique 3D stacking, our MBs reach an exceptional areal capacity of 7.01 mAh cm −2 and energy density of 5.9 mWh cm −2 . With the soft and miniature characteristics, these MBs can be easily stuck onto various microelectronic devices for direct use, where ensuring a stable and enduring operation. These results demonstrate a strong potential of MBs as a reliable microscale power source for next‐generation microsystems with high energy demands.