**Abstract**

In addition to the accelerated development of standard and novel types of rechargeable batteries, for electricity storage purposes, more and more attention has recently been paid to supercapacitors as a qualitatively new type of capacitor. A large number of teams and laboratories around the world are working on the development of supercapacitors, while their ever-improving performances enable wider use. The major challenges are to improve the parameters of supercapacitors, primarily energy density and operating voltage, as well as the miniaturization, optimization, energy efficiency, economy, and environmental acceptance. This chapter provides an overview of new techniques and technologies of supercapacitors that are changing the present and future of electricity storage, with special emphasis on self-powering sensor and transmitter systems. The latest achievements in the production, modeling, and characterization of supercapacitor elements (electrode materials, electrolytes, and supporting elements) whose parameters are optimized for long-term self-supply of low power consumers (low voltage, high energy density, and low leakage current, etc.) are considered.

**Keywords:** supercapacitors, innovation, energy storage, application

### **1. Introduction**

For decades, science has been intensively researching electrochemical systems that exhibit extremely high capacitance values (in the order of hundreds of Fg<sup>1</sup> ), which were previously unattainable. The early researches have shown the unsuspected possibilities of supercapacitors and traced a new direction for the development of electrical energy storage systems [1]. In recent times, with the development of new materials and technologies, very large developed surfaces and very small inter-electrode distances have been achieved. In many materials, enormous pseudocapacitance is also expressed, which achieves extremely large capacitances (several orders of magnitude larger than standard capacitors), so such systems are called supercapacitors (supercapacitors or, more rarely, ultracapacitors) [2].

There are two types of supercapacitors, depending on the energy storage mechanism: electric double-layer capacitors and pseudocapacitors [3]. In the first case, it is an electrostatic principle, and in the second one, the charge storage is caused by fast redox reactions [4]. Some electrode materials have both one and the other mechanism, thus so-called hybrid capacitors are formed on their basis.

High needs for powering isolated systems (sensor networks and IoT), covering peaks of electricity consumption, filtration, and new more efficient topologies in power electronics require further development and improvement of supercapacitor properties. More on this topic is given in Section 2 of this chapter.

New technologies and new materials in this area are presented in Section 3 of this chapter. Fabrication, modeling, and characterization are presented in Section 4.

Supercapacitors are widely used due to their high-power density, that is, fast charge and discharge, and a huge number of charge/discharge cycles [5]. Increasing the performance of supercapacitors opens up new fields of application and attention will be paid to this in Section 5. The growth of the industry in this area causes a drop in prices, which will be discussed in Section 6.

### **2. Need for supercapacitors**

Since the energy harvesting from renewable energy sources is highly actual today, the studies are also focused on the diverse methods for storing this energy in the form of electricity. Supercapacitors are one of the most efficient energy storage devices. As they have many advantages, supercapacitors are continuously being used in devices and systems that are eager for a high-power supply, opposite to the batteries. Recently actual, supercapacitors' applications are driven by their high performance and market potential, placing them in many fields of interest, such as industrial control, power, transportation, consumer electronic products, national defense, communications, medical equipment, electric and hybrid vehicles [6–8].

Nowadays, with the rapid development of intelligent electronic devices, have placed flexible energy storage devices in the focus of researchers. The industry requires energy storage that are flexible and optimized but endowed with high electrochemical properties [8–10]. The advantages of the supercapacitors, such as charge-discharge cycle life, size and weight, and environmentally oriented, suiting them for various applications. Supercapacitors are being used more and more as applications require storing and releasing high amounts of energy in short periods. Current industry applications include the automotive industry, hybrid transportation systems around the world, grid stabilization, utility vehicles, and rail-system power models [11].

The storing of energy is one of the main applications of supercapacitors. Following their outstanding power characteristics, supercapacitors are vital for the energy sector and their stationary applications. Additionally, the low maintenance requirements, as well as the extreme conditions that supercapacitors are able to withstand, make them suitable for renewable energy-related applications [12, 13]. Furthermore, the supercapacitors provide substantial benefits to railway electricity systems and the aerospace industry, since these sectors are trying to achieve a more electric power supply [13, 14]. Furthermore, many systems in the industrial sector are using supercapacitors, including small vehicles, such as forklifts, shovel trucks, agricultural machinery, excavators, mining shovels, harbor cranes, and industrial lasers. Consumer electronics are relying on supercapacitors, especially in real-time clock or memory backup, power failure backup, storage applications in which supercapacitors are used instead of batteries, and high load assistance to the primary electrical energy storage systems [13].

### **3. New technologies and materials for supercapacitors**

Supercapacitors are increasingly used for energy storage due to their large number of charge and discharge cycles, high power density, minimal maintenance, long life

span, and environmental friendliness [15]. The only disadvantage over batteries, the lower energy density, is decreasing more and more thanks to the intensive development of new technologies and new materials. Hybrid electrodes that combine doublelayer (electrostatic) capacitance and pseudo (redox) capacitance are increasingly being used [16].

The latest nanotechnologies have given rise to nanomaterials, such as 2D graphene, 1D CNT, and 0D fullerene [17]. There is a high trend in the research of carbon-based electrode materials (CNT, graphene, fullerene and their composites with metal oxides, etc.), copper sulfide and other metals, and metal oxides, all in combination with appropriate electrolytes.

For years, the authors of this chapter have researched the possibility of using natural copper minerals, primarily chalcosine [18] and coveline [19].

The latest research in the field of perovskite oxide applications for supercapacitor electrode materials deserves special attention. Perovskite oxides based on lanthanum, strontium, and cerium, etc. are being researched [20].

The researches with polymer materials are of great interest as well, which, in addition to high power density, also has an acceptable energy density (**Figure 1**). Conductive polymers are materials that contain a conjugated double bond, which places them in the group of materials that exhibit good electrical conductivity. Apart from showing electrical conductivity, these materials are characterized by redox reactions that take place when the electrode is polarized in a certain potential range. As a consequence of the redox reaction, constant currents are recorded in a wide range of potentials, which indicates the continuous development of the redox reaction in the

**Figure 1.** *Ragone plot shows the energy vs. power density comparison of supercapacitors with the other energy storage devices [21].*

**Figure 2.** *Comparison of various materials according to their specific parameter for supercapacitor applications [21].*

investigated potential range. The resulting response is similar to the electrochemical response of charging/discharging the double layer and therefore these reactions are called pseudocapacitive reactions. This property enables the application of these materials in supercapacitors. In order to further improve the properties of conducting polymers, attempts are being made to increase their electrical conductivity and porosity [21].

In **Figure 2** a comparative review of current supercapacitor electrode materials has been provided. Carbon materials have a specific capacitance of up to 300 F/g, while polymer and metal oxide materials can have over 1000 F/g. Composites of two or more of the above materials can have a very high specific capacitance of over 2000 F/g. Recently, the predominant approach is the development of binary or ternary nanocomposites of different capacitive materials to determine and optimize the structures and physical and mechanical properties of the electrode materials, in order to achieve improved supercapacitor performance. However, the properties of composite electrodes, in addition to the individual active components, also depend on the morphology and characteristics of the interphase [21].

Special, often complex technologies are developed for the production of superior electrode material. In **Figure 3** one of them is shown. A schematic diagram of the entire process of MnNi2O4@MnNi2S4 electrode materials is presented. Ni2+ and Mn2+ form Mn-Ni precursors in the reactor and are then calcined at high temperature to produce oxides. Then, under the influence of sodium sulphide, ion exchange is carried out at the appropriate temperature, i.e. oxygen is replaced by sulphur, which is less electronegative. A core-shell structure is formed without changing the morphology of the oxide. Metal ions react with KOH electrolyte in the Faraday redox reaction [22].

*Supercapacitors: The Innovation of Energy Storage DOI: http://dx.doi.org/10.5772/intechopen.106705*

**Figure 3.** *The schematic diagram of the construction process for MnNi2O4@MnNi2S4 electrode [22].*
