Supercapacitor (EDLC) Basics (Part 1):
What Is a Supercapacitor (EDLC)?

6/23/2015
Basic

Category: Capacitor Room

1.Introduction

In recent years, Murata has launched new kinds of capacitors in addition to its multilayer ceramic capacitors in order to offer solutions for even more applications. Two specific products are its polymer aluminum electrolytic capacitors, which were introduced in a previous article, and the supercapacitor (also known as EDLC, Electrical Double Layer Capacitor in academic parlance), which we are introducing here.

In Part 1, we will introduce our supercapacitors , describe their structure and characteristics, and note how they compare to other capacitors and batteries.


2.What is a supercapacitor?

2-1. Structure of the supercapacitor

Unlike a ceramic or electrolytic capacitor, a supercapacitor (EDLC) does not have a dielectric. Instead, it uses the "electrical double layer" that is formed at the interface of the solid (electrode) and liquid (electrolyte).

Figure 1 is a representation of the structure of the supercapacitor. A typical supercapacitor is composed of electrodes and electrolytes (including electrolyte salt) and a separator (to prevent contact between the positive and negative electrodes). The electrodes are positioned on the electricity collectors and coated with activated carbon powder. 

An electrical double layer is formed at each interface where the active carbon powder contacts the electrolyte. When you charge the supercapacitor, the negative ions and vacancies on the positive electrode side and the positive ions and the electrons on the negative electrode side are arranged across the interface. This state of arrangement of ions and electrons (vacancies) is called an "electrical double layer." 

Because this layer is formed by the physical movement of ions, there is no chemical reaction involved as there is with batteries. This gives the supercapacitor a superior charge-discharge cycle life. The reason for using activated carbon on the electrode is to increase its surface area. Very fine pores on the activated carbon surface greatly increase the surface area of the electrode. Since the greater the surface area, the greater the charge that can be stored, the supercapacitor is able to achieve very high capacitance.


This time "Supercapacitor (EDLC) Basics (Part 1): What Is an   Supercapacitor (EDLC)?

Figure 1. Structure of Supercapacitor(EDLC)


Supercapacitors are found in a variety of basic shapes and structures, as illustrated in Figure 2. Our supercapacitors are the laminate type. Below we will explain how this compares to other shapes.

This time "Supercapacitor (EDLC) Basics (Part 1): What Is an   Supercapacitor (EDLC)?

Figure 2. Supercapacitor Shapes


2-2. Features of Murata's supercapacitors

2-2 (1). Main features of our supercapacitors

  • Small and slim package (starting at LWT: 14.0mm×21.0mm×3.2mm)
  • Low ESR! High power, high capacitance (DMF series example: 45mΩ, 5 5V, 470mF)
Enables high-current, high-power input and output compared to batteries and conventional supercapacitors.
For details, see 2-2 (2) and (3).
  • Excellent charge-discharge cycle life
As mentioned in 2-1, since the charging/discharging mechanism does not involve a chemical reaction, it is possible to charge and discharge more than 100,000 times.
  • High reliability
Thanks to our excellent package sealing and optimization of electrochemical systems, there is very little performance degradation compared to other supercapacitors. For details, see 2-2 (3).


2-2 (2). Comparison to other capacitors and batteries

Figure 3 characterizes the supercapacitor in comparison to other capacitor technologies, with the horizontal axis representing capacitance, and the vertical axis representing rated voltage. Ceramic capacitors support a wide range of voltages, but the capacitance is several hundred μF at most. Our supercapacitors, on the other hand, have very high capacitance compared to other capacitor technologies, ranging from hundreds of mF to more than 1F.


This time "Supercapacitor (EDLC) Basics (Part 1): What Is an   Supercapacitor (EDLC)?

Figure 3. Capacitances and Voltages of Murata's Capacitor Technologies in Comparison to Supercapaitors(EDLCs).


Next, we will describe the energy and power of supercapacitors when compared with electrolytic capacitors and batteries. In Figure 4, the energy density on the horizontal axis represents how much charge can be stored, and the power density on the vertical axis represents how much electricity can be released instantaneously. 

Batteries can store a large charge, but the amount of power that can be released instantaneously is small. Conversely, electrolytic capacitors can release a large charge instantaneously, but the charge that can be stored is small. The performance of our supercapacitors lies in between. That is, their energy is high compared to other capacitors, while their power is high compared to batteries.


This time "Supercapacitor (EDLC) Basics (Part 1): What Is an   Supercapacitor (EDLC)?

Figure 4. Comparison of Power Density and Energy Density


2-2 (3). Comparison to other supercapacitors

There are various types of supercapacitors, as mentioned in 2-1 and illustrated in Figure 2. Figure 5 compares the discharge performance of supercapacitors of each shape, with the discharge current on the vertical axis, and the discharge time on the horizontal axis. The coin-type capacitor is characterized by a long, slow trickle of current. This is the conventional supercapacitor. In the laminate type, a large current flows instantaneously. Our supercapacitors are this type. The cylinder type is somewhere in between. In other words, our supercapacitors are ideal for applications requiring large amounts of power all at once.


This time "Supercapacitor (EDLC) Basics (Part 1): What Is an   Supercapacitor (EDLC)?

Figure 5. Comparison of the Discharge Performance of Various Supercapacitors


As mentioned earlier, our supercapacitors have high reliability. Typically, supercapacitors suffer from aging degradation caused by external moisture. Another problem that occurs is failure due to the electrolyte drying up. Murata's supercapacitors have addressed these problems. Because moisture penetrates inside the package from the sealed area, Murata's supercapacitors are designed with a smaller sealed area to prevent the infiltration of moisture (Figure 6).

It therefore suffers little moisture damage, unlike the cylinder-type supercarpacitors, which are significantly affected by moisture. The minimized sealed area design also serves to prevent the evaporation of the electrolyte that causes dry-up failure. This has enabled a very high level of reliability compared to conventional supercapacitors.


This time "Supercapacitor (EDLC) Basics (Part 1): What Is an   Supercapacitor (EDLC)?

Figure 6. Package and Reliability Comparison of Cylinder-Type supercapacitor and Murata supercapacitor


3.Conclusion

Our supercapacitors deliver high power and high energy in a small, slim package.
They are highly reliable and can be used in a wide variety of applications.
For a detailed introduction to the products and how to use them, please visit the Products page. For more detailed information, see the technical notes and application notes.
In " Supercapacitor (EDLC) Basics (Part 2)," we will cover specific applications and methods of using supercapacitors.

Department Responsible: High Performance Power Device Department, Murata Manufacturing Co., Ltd.
High Performance Power Device Dept