**1. Introduction**

The rapid technological advancements in this era demand the provision of electricity for the maintenance. In addition, the household requirements for the electricity are also in its peak of demand. The current energy resources like coal and oil are irreversible and depleting at a faster rate. On the other hand, the developments of renewable energy resources like solar and wind energies are limited by the intermittent nature and it demands the provision of energy storages to be accompanied which leads to the high cost of the resulting commercial energy modules resulting in a less attractiveness in the market. In addition, the disposal issues generated by the energy storages like traditional batteries are a major concern for the environment. On the other hand, green on-chip energy storages offer an efficient, cost-effective platform for integrated miniaturized devices, energy-harvesting, self-reliant residential and commercial buildings.

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Micro-supercapacitors (MSCs) are a recent addition to the environmentally friendly energy storages with higher charge-discharge transfer rates on the contrary to traditional batteries [1]. The batteries whose lifetime is restricted due to the involvement of electrochemical redox reaction create the issues of additional storage and disposal space where MSCs which can be fabricated on any substrates utilize the electrostatic interactions of electrode-electrolyte materials.

source is tightly focused to a diffraction limited focal spot, using an objective made of different numerical apertures (NAs) forming a high intensity of laser beam. The transparency at the wavelength and spot size uniformity of the used laser beam as well as the sample uniformity is highly necessary to obtain good quality structures. However, due to the high-intensity generation from the tight focusing conditions, the non-linear process is triggered at the focal spot, which can lead to the photo-polymerization [9], microexplosion [10], photoreduction [11] and micro-machining process [12] in the material leaving remaining area unmodified. The sample moves with the help of three-dimensional (3D) translation stage according to the pre-

In the following sections, a detailed understanding of the DLW process on various electrode

The electrodes of MSC require high active surface area, long-term stability, resistance to electrochemical oxidation or reduction, the capability of multiple cycling materials, optimum pore size distribution, minimized ohmic resistance with the contacts, sufficient electrode-

Materials such as carbon and its derivatives like porous activated carbon, carbon nanotubes, carbon aerogels or carbon-metal composites have a higher surface area of 100–220 m2 g−1 and they exhibit excellent stability but limited capacitance [4]. For activated carbons, only about 10–20% of the theoretical capacitance can be achieved due to the micropores that are inaccessible by the electrolyte [13]. The carbon nanotubes do not exhibit satisfactory capacitance

materials [15]. In addition, both faces of graphene sheets are readily accessible by the electrolyte. However, in practical applications, the surface area of graphene will be much reduced

Laser-scribed graphene (LSG), obtained from the DLW in graphene oxide (GO) material, is a cost-effective tunable alternative to graphene. The LSG films are used to fabricate MSC and other integrable applications and first reported from Ajayan's group with the use of carbon

work is followed by the Kaner's group in 2012 through the production of high-performance

Furthermore, two famous works came in the following years: The first work demonstrates the fabrication of all solid state MSCs using ionic gel electrolyte with interdigitated electrodes.

) laser beam by adopting the design concept from capacitors [6] in 2011. This

, which sets the upper limit of EDLC capacitance of all carbon-based

/g and the intrinsic

Direct Laser Writing of Supercapacitors http://dx.doi.org/10.5772/intechopen.73000 105

electrolyte solution contact interface, mechanical integrity and less self-discharge [1].

unless a conducting polymer [14] is used to form a pseudocapacitance.

LSG sandwich energy storages using a DVD burner [16].

Graphene is a form of carbon with the high surface area up to 2675 m2

programmed pattern design. The schematic of the DLW setup is given in **Figure 1**.

**3. Direct laser writing of micro-supercapacitors**

materials for MSCs is discussed.

*3.1.1. Laser-scribed graphene and its derivatives*

**3.1. Electrode materials**

capacitance of 21 μF/cm<sup>2</sup>

due to agglomeration.

dioxide (CO<sup>2</sup>

The performance of MSC is determined by the available active electrode material and the voltage window of the electrolyte [2]. Based on the electrode-electrolyte interactions, the supercapacitors are divided into three major types: (i) electrochemical double layer capacitor (EDLC), (ii) pseudocapacitors and (iii) hybrid supercapacitors. EDLC works based on the electrostatic interaction between electrode and electrolyte ions where pseudocapacitors involve the redox reaction between electrodes and electrolyte ions similar to the batteries. A strong pseudocapacitance is not desirable in many applications due to the slow response time and high capacitance decay rate [3]. Hybrid supercapacitors combine the EDLC and pseudocapacitance effects in the performance which can be used to compensate the drawbacks of current commercial supercapacitors to become a replacement for the batteries.

Several methods are used for the fabrication of various kind of supercapacitors. The main categories are chemical techniques based on the nanomaterials [4] and electron beam lithography (EBL) [5]. The lesser integrability for flexible applications and cost involved in the fabrication of these techniques make them less desirable for industrial scale production of commercial applications. The recent reports on the use of direct laser writing (DLW) technique for the supercapacitor fabrication [6] is a fast and reliable single-step method with the possible integration of all substrates.
