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

Abstract

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 (PμSCs) 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 PμSCs 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 PμSC device displays excellent electrochemical performance, including high energy and power density (energy density of 13.28 mWh/cm3 at a power density of 4.5 W/cm3), 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.

Textile-based supercapacitors for flexible and wearable electronic applications

“…The physical properties of all the inks were carefully optimized to ensure the stable ink formation for a drop-on-demand printer. The viscosity and surface tension of water-based solutions were modified to the requirements of printable inks by using ethylene glycol and ethanol as detailed in our previous study 18 . The rheological properties of the inks were carefully optimized by controlling the Ohnesorge number (Oh) 33 .…”

“…The energy density is directly proportional to the working potential and capacitance of the supercapacitor device 15 . Therefore, much research attention has focused on improving the potential range and energy density, either by using asymmetric cell assembly or by adopting the battery-supercapacitors hybrid electrode materials 16 – 18 . Recently, enormous efforts have been made for the realization of a hybrid combination of electric double layer capacitive (EDLC) material and pseudocapacitive/ battery-type material to combine the characteristic feature and potential ranges of both 17 , 19 .…”

“…Although the textile substrates are highly compatible with the inkjet printing process, some limitations of the inkjet printing process hinder its full utilization for practical applications. These limitations include the requirement of inks with rigid physical properties, the requirement of compatible post-treatment processes and size restriction of the ink particles 9 , 18 , 33 . The metal oxides are the promising energy storage materials and preparation of printable metal oxide inks with the required rheological properties pose a lot of difficulty due to their improper dispersion in most of the non-toxic solvents.…”

Sand‐Milling Exfoliation of Structure Controllable Graphene for Formulation of Highly Conductive and Multifunctional Graphene Inks

“…[ 1,2 ] The emerging advanced printing techniques allow low‐cost, large‐scale, additive‐manufacturing of flexible electronics such as, sensors, [ 3 ] electronic textiles, [ 4 ] photodetectors, [ 5 ] and energy devices. [ 6 ] To date, these printing methods include but are not limited to, flexographic printing, inkjet printing, gravure printing, and screen printing based on conductive inks. [ 7 ] The major challenge of most electronic devices is the capability to obtain interconnected and highly conductive patterns as well as the synthesis of highly conductive inks at low‐cost.…”

Nano-finishing of MEMS-based platforms for optimum optical sensing

“…Surface roughness is one of the important parameters which significantly affects the surface properties of a device. 25–27 During the fabrication of channels through wet etching, the surface roughness of the etched channel is not very conducive for performing optical studies. In the current case, there is a layer of low refractive index material being planned as cladding within the channels.…”