Energy storage devices play important roles in smart electronics, such as e-skin [
Photonics Research, Volume. 8, Issue 4, 577(2020)
Laser fabrication of graphene-based supercapacitors
Supercapacitors (SCs) have broad applications in wearable electronics (e.g., e-skin, robots). Recently, graphene-based supercapacitors (G-SCs) have attracted extensive attention for their excellent flexibility and electrochemical performance. Laser fabrication of G-SCs exhibits obvious superiority because of the simple procedures and integration compatibility with future electronics. Here, we comprehensively summarize the state-of-the-art advancements in laser-assisted preparation of G-SCs, including working mechanisms, fabrication procedures, and unique characteristics. In the working mechanism section, electric double-layer capacitors and pseudo-capacitors are introduced. The latest advancements in this field are comprehensively summarized, including laser reduction of graphene oxides, laser treatment of graphene prepared from chemical vapor deposition, and laser-induced graphene. In addition, the unique characteristics of laser-enabled G-SCs, such as structured graphene, graphene hybrids, and heteroatom doping graphene-related electrodes, are presented. Subsequently, laser-enabled miniaturized, stretchable, and integrated G-SCs are also discussed. It is anticipated that laser fabrication of G-SCs holds great promise for developing future energy storage devices.
1. INTRODUCTION
Energy storage devices play important roles in smart electronics, such as e-skin [
From the point of view of materials, graphene has high mechanical flexibility, strength, electrical conductivity, and surface area [
Figure 1.Progress in laser fabrication of G-SCs. The structured graphene image, adapted from Ref. [56]; the graphene hybrid image, adapted from Ref. [57]; heteroatom doping graphene image, adapted from Ref. [58]; the miniaturized SC image, adapted from Ref. [59]; the stretchable SC image, adapted from Ref. [60]; the integrated SC image, adapted from Ref. [61].
2. LASER FABRICATION OF GRAPHENE-BASED SCs
In this section, we summarize the working mechanism of SCs, including EDLCs and pseudo-capacitors and review laser-enabled fabrication of G-SCs, including LRGO-SCs, LCVDG-SCs, and LIG-SCs.
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A. Working Mechanism of SCs
The working mechanism of laser fabrication of G-SCs is divided into two types: EDLCs and pseudo-capacitors [
Figure 2.Working mechanism of SCs including (a) EDLCs and (b) pseudo-capacitors; adapted from Ref. [62].
As shown in Fig.
B. LRGO-Based SCs
Graphene oxide (GO) is an important derivative of graphene, which bears plenty of oxygen-containing groups (OCGs) on the plane of graphene [
Figure 3.(a) Schematic illustration of LRGO, adapted from Ref. [67]; (b) schematics and photos of planar and sandwiched LRGO electrodes on GO paper; (c) CV plots of planar and sandwich SCs (scan rate, 40 mV/s); (d) impedance spectra for the in-plane and sandwich devices; (b)–(d) adapted from Ref. [87].
As a typical example, Zhang
Laser carving is capable of being applied on RGO-based materials. Different from laser reduction and patterning, after laser carving processes, unwanted RGOs were removed [
C. LCVDG-Based SCs
Although GO can be reduced to recover conductivity by laser technologies, LRGO suffers from limited electrical conductivity. To produce graphene with high conductivity, CVDG is considered as an effective method for developing high-quality graphene. Typically, Cu or Ni foils under a gas mixture of and are used as a catalytic substrate for graphene growth [
Figure 4.(a) Scheme for the preparation of graphene-based microsupercapacitors (G-MSCs); (b) CV curves of G-MSCs on PET substrates and (c) corresponding areal and volumetric capacitances at different scan rates; adapted from Ref. [59].
D. LIG-Based SCs
Figure 5.(a) Diagram of LIG converted from PI; (b) scanning electron microscope (SEM) image of the as-prepared owl-shaped LIG pattern; scale bar, 1 mm; (c) Raman spectra and (d) XRD patterns of LIG and PI; (e) high-resolution transmission electron microscope (HRTEM) image of LIG; scale bar, 5 nm; (f) transmission electron microscope (TEM) image of selected area of LIG, scale bar, 5 Å; adapted from Ref. [101].
Particularly, based on the similar preparation mechanism, LIG process has been extended using diverse materials such as wood [
3. UNIQUE CHARACTERISTICS OF LASER-ENABLED G-SCs
In this section, the unique characteristics of laser-enabled G-SCs are summarized, including the ease of developing structured graphene and graphene hybrids, heteroatom doping of graphene-based electrode materials, and fabricating miniaturized, stretchable, integrated SCs.
A. Structured Graphene-Based Electrode Materials
Currently, to improve the surface area of graphene-based electrodes and the contact area between electrode and electrolyte, two kinds of structured graphene-based electrode materials have been well studied, including porous structures and grating structures. The porous structures are attributed to LRGO- or LIG-based electrode materials because of the gas generation during laser processing, whereas grating structures are mainly based on LRGO via the laser holography technique.
Figure 6.(a) Diagram of LSG-based electrochemical capacitors, adapted from Ref. [106]; (b) schematic illustration of fabricating LRGO films with 1D grating structures by the TBLI technique; (c) SEM image; (d) atomic force microscope (AFM) image of LRGO films with 1D grating-like structures; (b)–(d) adapted from Ref. [56].
B. Graphene Hybrid-Based Electrode Materials
Though graphene shows great superiority in developing high-performance SCs, the insufficient capacity of pristine graphene and graphene analogues-based SCs is prominent. Therefore, various studies have been carried out to fabricate graphene-based hybrid materials for performance improvement [
As for laser-reducing the GO/active materials composite into the RGO-based hybrid materials, for example, Liu
Figure 7.(a) Photo of molybdenum carbide-graphene (MCG) fabricated by DLW on paper substrate; (b) schematic illustration of the MCG fabrication process; (c) CV curves of interdigital SC; (d) CV curves of single, parallel, and series sandwich-structure devices measured at a scan rate of 100 mV/s; adapted from Ref. [57].
As for depositing active materials after laser reduction of GO or LIG processing, for example, Ghoniem
C. Heteroatom Doping-Based Graphene Electrode Materials
Heteroatom doping has attracted much research interest in tailoring the characteristics of graphene for improving electrochemical properties because heteroatomic defects and functional groups will be introduced to graphene, leading to alteration of the electronic structure [
Figure 8.(a) Illustration of the preparation of boron-doped LIG MSCs (B-LIG-MSCs); (b) B 1s spectrum and (c) N 1s spectrum of B-LIG; (d) CV curves of LIG-MSC and B-LIG-MSC; scan rate 0.1 V/s; (e) galvanostatic charge-discharge (GCD) curves of LIG-MSC and B-LIG-MSC; current density
D. Miniaturized Graphene-Based SCs
As for laser-enabled miniaturized G-SCs, there are two functions of laser technologies. One of the most obvious advantages of laser-enabled G-SCs is the miniaturization of MSCs with the resolution of micrometers [
Figure 9.(a) Fabrication process for miniaturized SCs by using a femtosecond laser; (b) RGO electrode arrays with a spacing of 2 μm; (c) optical microscope image of microelectrolyte droplets covering the electrode; CV plots of RGO MSC with interelectrode spacing of (d) 2 μm and (e) 550 μm; adapted from Ref. [61].
E. Stretchable Graphene-Based SCs
Currently, in order to meet the huge requirements of wearable intelligent electronic devices, stretchable G-SCs have been achieved based on laser-enabled graphene [
Figure 10.(a) Schematic illustration of a highly stretchable SC using LIG electrode onto elastomeric substrate; (b) device structure; CV plots of SCs under (c) stretching and (d) bending tests; scan rate 10 V/s; adapted from Ref. [60].
F. Integrated with Other Devices
Figure 11.(a) Illustration of an integrated device including SCs and sensors; (b) photograph of the integrated device; (c) charging and discharging curve of the MG-MSCs and discharging curves of the MG-PANI MSCs; (d) leakage currents of MSCs; adapted from Ref. [59].
4. SUMMARY AND OUTLOOK
There has been much research progress since laser-enabled graphene has been successfully prepared. In this review, we summarized the working mechanism of SCs, laser fabrication of G-SCs, and the unique characteristics of laser-enabled G-SCs.
As for the working mechanism of SCs, there are two kinds of mechanism, including EDLCs and pseudo-capacitors. Because of the high conductivity and surface area, laser-enabled graphene, including LRGO, LCVDG, and LIG, has been adopted to fabricate electrodes of SCs. Compared with the graphene prepared via mechanical exfoliation, laser-based graphene is able to prepare large-area films with high electrical conductivity, flexibility, and high chemical/physical stability. They work based on the EDLCs. Lasers also have the ability to develop doped graphene and graphene hybrids. The heteroatom doping-based graphene and graphene hybrid-based SCs can be attributed to the pseudo-capacitors.
In order to obtain high device performance, lasers have been adopted to fabricate structured graphene to improve contact area between graphene and electrolytes. Porous and grating structures have been developed for graphene. Porous structures can be fabricated by LRGO and LIG because of gas generation. The grating structures can be fabricated via laser interference. Lasers can also be used to fabricate graphene hybrids and heteroatom doping graphene for higher device performance. Graphene hybrids have been developed via laser-reduced GO composite or depositing active materials after LRGO of LIG processing. The active materials contain abundant active sites, which is helpful in improving electrochemical performance. As for doping graphene, the heteroatom doping can increase the hole charge density.
In addition to developing high electrochemical performance, lasers play an important role in developing miniaturized, stretchable, and integrated devices. Thanks to its high-resolution ability, a femtosecond laser can be used to develop miniaturized SCs. As for stretchable G-SCs, they can be fabricated for stretching substrates or stretching structures via LIG or a laser cutting process. In addition, it is worth noting that graphene is a versatile material for developing electronic devices, which are able to develop integrated SCs. For example, fabricated SCs arrays improve energy storage ability and shed light on possible practical uses.
Though many successes have been achieved in this field, there are still urgent problems to be solved. First, to satisfy the huge demand for electrodes, mass production of high-quality graphene is still challenging. Then, introduction of essential functional groups and surface modification during the device fabrication still require long and arduous processes. In addition, developing easy and effective device fabrication methods towards miniaturized, integrated, and multifunctional devices is still a great challenge. What is more, exploring new materials and electrolyte factors should also be taken into account. Finally, laser processing efficiency should be considered for practical applications. To address this limitation, spatial light modulators and concurrent processing technologies have been widely used to improve processing efficiency. In short, the development of laser-enabled G-SCs may stimulate rapid progress in various wearable devices for future applications.
To summarize, laser-enabled G-SCs are still a promising method for developing high-performance energy storage devices. The method combines advanced fabrication technologies with unique material properties that will stimulate the rapid progress of wearable devices.
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Xiu-Yan Fu, Zhao-Di Chen, Dong-Dong Han, Yong-Lai Zhang, Hong Xia, Hong-Bo Sun. Laser fabrication of graphene-based supercapacitors[J]. Photonics Research, 2020, 8(4): 577
Category: Optical and Photonic Materials
Received: Nov. 15, 2019
Accepted: Jan. 30, 2020
Published Online: Mar. 31, 2020
The Author Email: Dong-Dong Han (handongdong@jlu.edu.cn), Yong-Lai Zhang (yonglaizhang@jlu.edu.cn)