Scalable Micro-fabrication of Flexible, Solid-State, Inexpensive, and High-Performance Planar Micro-supercapacitors through Inkjet Printing

Inkjet printing is becoming one of the most efficient micro-manufacturing techniques to fabricate thin-film devices for flexible electronics applications. The energy storage unit is one of the most critical parts of the electronic devices, and planar micro-supercapacitors (P mu SCs) are the emerging energy storage architecture in miniaturized electronic devices. However, the lack of high-performance energy storage units with the required flexibility, the selection of cost-effective processes, scalability issues related to inexpensive, high-volume manufacturing, and proper design of the device structure are still some of the major challenges for the development of flexible supercapacitors (SCs). To address these issues, we have fabricated fully printed, solid-state, and flexible P mu SCs on cellulose paper substrates. The digitally designed interdigitated electrode patterns are first printed on paper with reduced graphene oxide (rGO) ink to construct a conducting matrix. The negative electrode is printed using activated carbon-Bi2O3 ink and the positive electrode is printed with rGO-MnO2 ink, each on one half of the pre-printed conducting patterns to form an asymmetric design using different nozzles of the same printer. A polyvinyl alcohol-KOH electrolyte ink is printed over the electrode patterns and solidifies to complete the device. Notably, geometric parameters such as the width of the electrode finger and the width of the interspaces between the adjacent fingers were also optimized to achieve the optimum electrochemical performance of the device. Interestingly, the as-prepared P mu SC device displays excellent electrochemical performance, including high energy and power density (energy density of 13.28 mWh/cm(3) at a power density of 4.5 W/cm(3)), excellent rate capability (80% retention of capacitance as the current density increases by 32 times), excellent frequency response (a time constant of 0.09 ms), and high cycle stability (92.2% retention of capacitance after 20 000 cycles). In addition, the presented method is highly scalable, with control over the device thickness, dimensions, size, shape, and implementation through one printing step defined through the computer-aided design layout. The devices also show outstanding flexibility, reproducibility, and repeatability. Therefore, the proposed strategy is beneficial to improve the next generation of printable and flexible energy storage systems.