Substrate‐Free and Shapeless Planar Micro‐Supercapacitors

Abstract

Micro‐supercapacitors (MSCs), albeit powerful, are unable to broaden their potential applications primarily because they are not as flexible and morphable as electronics. To address this problem, a universal strategy to fabricate substrate‐free, ultrathin, shapeless planar‐MSCs with high‐performance tenability under serious deformation is put forward. These represent a new class of “all‐inside‐one” film supercapacitors, achieved by encapsulating two‐dimensional interdigital microelectrodes within chemically cross‐linked polyvinyl‐alcohol‐based hydrogel electrolyte containing graphene oxide (GO). GO nanosheets significantly improve ionic conductivity, enhance the capacitance, and boost robustness of hydrogel electrolyte. Consequently, the entire MSC, while being only 37 µm thick, can be crumpled and its shape can self‐adjust through fluid channel ten times smaller than its original size without any damage, demonstrating shapelessness. Using MXene as active material, high single‐cell areal capacitance of 40.8 mF cm−2 is achieved from microelectrodes as thin as 5 µm. Furthermore, to demonstrate wide applicability of this protocol, screen‐printed graphene‐based highly integrated MSCs connecting nine cells in series are fabricated to stably output a high voltage of 7.2 V while crumpling them from 0.11 to 0.01 cm−3, manifesting superior performance uniformity. This protocol allows the coexistence of high performance with incredible flexibility that may greatly diversify MSCs' applications.

Conductive Hydrogel‐Based Electrodes and Electrolytes for Stretchable and Self‐Healable Supercapacitors

“…[ 170 ] For the miniaturization and high‐density integration of future electronics, micro‐SCs (MSCs), with in‐plane interdigital configuration and small size, is touted as a promising candidate for energy supply. [ 225 ] By direct laser writing (DLW) of the multilayered‐graphenes and coating with acidic PVA‐H 2 SO 4 electrolyte, a MSC was constructed, delivering high specific capacitance (36.8 F cm −3 ), excellent cyclic stability (capacitance retention of ≈96% after 20 000 charge/discharge cycles), and superior mechanical bendability, capable of integration into flexible integrated electronics. [ 226 ] Generally, plenty of water in hydrogel electrolytes is apt to freeze and constrain ion diffusion at subzero temperatures, and their configurations are unstable under high temperature, causing a narrow operation temperature range.…”

“…Reproduced with permission. [ 225 ] Copyright 2019, Wiley. d) Slidable polymer network consisted of two types of dynamic cross‐linking sites in PEI‐PVA‐Bn hydrogel.…”

Recent developments of advanced micro-supercapacitors: design, fabrication and applications

“…It has the merits of rapidness, simplicity and low cost, and there are various types of substrates that can be directly printed on. Therefore, this method is quite suitable for MSCs manufacturing, especially in mass production [36][37][38] . The common strategy of screen printing involves printing active electrode materials and current collector separately.…”

Laser fabrication of functional micro-supercapacitors

“…In another hand, flexible and lightweight on-chip MSCs with excellent mechanical and electrochemical performances can satisfy the needs of wearable and portable electronics [117][118][119][120][121][122]. However, it is difficult to fabricate the polymer-based devices under extreme reaction conditions, which can be easily achieved by using the non-contact laser processing [123][124][125].…”