Ultrathin Paper Microsupercapacitors for Electronic Skin Applications

Abstract

Ultrathin devices are rapidly developing for skin‐compatible medical applications and wearable electronics. Powering skin‐interfaced electronics requires thin and lightweight energy storage devices, where solution‐processing enables scalable fabrication. To attain such devices, a sequential deposition is employed to achieve all spray‐coated symmetric microsupercapacitors (μSCs) on ultrathin parylene C substrates, where both electrode and gel electrolyte are based on the cheap and abundant biopolymer, cellulose. The optimized spraying procedure allows an overall device thickness of ≈11 µm to be obtained with a 40% active material volume fraction and a resulting volumetric capacitance of 7 F cm−3. Long‐term operation capability (90% of capacitance retention after 104 cycles) and mechanical robustness are achieved (1000 cycles, capacitance retention of 98%) under extreme bending (rolling) conditions. Finite element analysis is utilized to simulate stresses and strains in real‐sized μSCs under different bending conditions. Moreover, an organic electrochromic display is printed and powered with two serially connected μ‐SCs as an example of a wearable, skin‐integrated, fully organic electronic application.

Scalable Paper Supercapacitors for Printed Wearable Electronics

“…23,24 Using CNF as a nanoscale binder provides a nanoporous polymeric scaffold, high surface area, and porosity, leading to high mass loadings throughout the film, and therefore opens a pathway to spray coat nanomaterials with a high control capability on the electrode thickness. 10,25,26 A variety of different conductive polymers with pseudocapacitive properties, such as polyaniline (PANI), polypyrrole (PPy), and PEDOT, have been incorporated into flexible scaffolds (paper, fibrils, etc.) to form electrodes for flexible batteries and supercapacitors.…”

“…PEDOT:PSS has been used to scale up batch processes with paper-based materials to achieve the goals of fully printed paper energy storage systems, demonstrated in use cases and flexible electronics applications. 10,26,37 Following these efforts, considerable attention has been given to understanding and optimizing the interface and bulk morphology of PEDOT electrodes. Recently, the morphological change during drying and film formation and shift in the π−π stacking distance of PEDOT, as well as changes in the device performance metrics, i.e., conductivity and mobility, have been investigated via the effect of additives (cosolvents, surfactants) and method of printing.…”

Upscalable ultra thick rayon carbon felt based hybrid organic‐inorganic electrodes for high energy density supercapacitors

“…Supercapacitors, an important energy storage device that facilitates the digitalization, electrification, and sustainability of the society, are finding increasing usage in a variety of applications ranging from electric vehicles to consumer electronics 1,2 . In recent years, the continuous advancements in wearable electronics boosted the needs for flexible and small foot print power sources 3,4 . For various applications, especially when there is only a limited area available for the placement of the supercapacitor, thick electrodes are desirable since they can provide, with equal occupied surface area, higher amount of energy than more traditional thin electrodes.…”

“…1,2 In recent years, the continuous advancements in wearable electronics boosted the needs for flexible and small foot print power sources. 3,4 For various applications, especially when there is only a limited area available for the placement of the supercapacitor, thick electrodes are desirable since they can provide, with equal occupied surface area, higher amount of energy than more traditional thin electrodes. Furthermore, thick electrodes have the advantage of allowing savings in terms of the amount of collector and packaging material.…”

“…Furthermore, thick electrodes have the advantage of allowing savings in terms of the amount of collector and packaging material. [5][6][7] Additive thick layer manufacturing, for example, spray coating, 4,8 screen printing, [9][10][11][12] and slot die coating, 13 has been shown to be a valuable and versatile approach for the manufacturing of supercapacitors; unfortunately, this approach inherits some significant limitations when it comes to thick electrodes with thicknesses of only few 100 s μm achievable; thicker films often suffer from poor adhesion to the substrate, poor porosity, and are more susceptible to structural damages (eg, cracking). Consequently, when aiming at supercapacitors with millimeter thick electrodes, other materials and manufacturing methods have been explored.…”