All Fiber Based Electrochemical Capacitor towards Wearable AC Line Filters with Outstanding Rate Capability

Abstract

Due to their high spatial utilization, excellent flexibility and good adaptability, fiber-shaped devices have promising potential for applications in wearable electronics. However, the fiberization process of the component with alternate current (AC) line filtering function is still far from being satisfactory, since it is difficult to arrange an ordered structure in a fiber shape in large-scale manufacturing. This leads to a slow frequency response. Herein, a weavable fiber-shaped electrochemical capacitor (SC) for AC line filtering is made of reduced graphene oxide (rGO) fibers with a highly oriented porous structure by wet-spinning method. The highly consistent orientations of the rich pores greatly improve the ionic accessible sites, ion mobility and the electron transport pathways. As a result, the all-fiber-based SC revealing a high rate performance (500 V s À 1 ) and a fast frequency response (RC time constant~0.241 ms, phase angle~À 80°) is successfully applied to filter � 1.5 V AC to 1.04 V direct current (DC). Notably, the highly flexible SC exhibits an outstanding consistency during the performance test at bending and folding states. This work shows a potential substitution for aluminium electrolytic capacitors (AEC) towards wearable electronic.

History and Perspectives on Ultrafast Supercapacitors for AC Line Filtering

“…Besides the liquid electrolytes, gel electrolytes including hydrogels and ion‐gels were also investigated for quasi‐solid‐state high‐frequency SCs, thereby expanding their applications to stretchable MSCs, [ 74 ] flexible SC or MSCs, [ 44,60,75,76 ] weavable fiber‐shaped SCs, [ 77,78 ] and on‐chip MSCs ( Figure 14 ). [ 55,63–65,82 ] Their 3D polymeric network structure with a liquid phase provides many advantages such as good mechanical properties (flexibility or/and stretchability) and no leakage issues.…”

“…[20,23,111] Therefore, to achieve both sufficiently highfrequency response and high capacitance for 60-Hz AC line filtering, it is desirable for carbon electrode materials to have optimized pore sizes/structures that allow fast ion movement while providing large surface areas for ion adsorption (e.g., Φ = −81° and 13.1 F cm -3 for CNTs). [37][38][39][40][41][42][43][44] Besides the liquid electrolytes, gel electrolytes including hydrogels and ion-gels were also investigated for quasi-solidstate high-frequency SCs, thereby expanding their applications to stretchable MSCs, [74] flexible SC or MSCs, [44,60,75,76] weavable fiber-shaped SCs, [77,78] and on-chip MSCs (Figure 14). [55,[63][64][65]82] Their 3D polymeric network structure with a liquid phase provides many advantages such as good mechanical properties (flexibility or/and stretchability) and no leakage issues.…”

“…[114] PVA-based hydrogels were prepared with acidic (H 2 SO 4 and phosphoric acid (H 3 PO 4 )), alkaline (KOH), and neutral aqueous electrolytes (LiCl). Various quasi-solid-state SCs such as flexible SC or MSCs, [44,60,75,76] stretchable MSCs, [74] weavable fiber-shaped SCs, [77,78] and on-chip MSCs [55,[63][64][65] have been successfully developed with the PVA-based hydrogels (Figure 14). Lian's group investigated the TEAOH salt-based hydrogel electrolytes (TEAOH/PVA and TEAOH/PAM) to achieve stable cell operation of quasi-solid-state SCs under harsh environmental conditions for a wide range of applications.…”

“…[16,30,37,[39][40][41]43,[70][71][72][73] As a result of this finding, the ultrafast SCs achieved a drastic enhancement in the energy density without degrading the fast frequency response. Together with the liquid electrolytes, the gel electrolytes including hydrogels and ion-gels were adopted for developing the quasi-solid-state high-frequency SCs to follow the future trend of advanced electronic devices such as stretchable/flexible SCs or micro-SCs (MSCs), [44,60,[74][75][76] weavable fibershaped SCs, [77][78][79][80][81] and on-chip MSCs. [55,[63][64][65]82] A study on the multi-cell configuration is desirable for high-voltage applications.…”

Vertical Graphene Arrays for AC Line-Filtering Capacitors

“…Given this, a myriad of electrode materials with elaborate structures have been developed to balance the trade-offs between the ion transport property and capacitance density, including the vertically aligned arrays, large porous films, onion-like nanoparticles, edge-oriented coating, and their composite assemblies [17][18][19][20][21][22][23][24][25][26][27][28] . Among them, large porous structures are of advantage for rapid ion transport, which enables the phase angle value at 120 Hz (Φ120) to reach −80° (the Φ120 close to −90° represents a good capacitive behavior) 14, 15,25,26,29,30 .…”