How to Choose the Right Supercapacitor How Supercapacitors Work

First, in terms of how they work, many supercapacitors use a so-called electric double-layer capacitor (EDLC) layout, which has two electrodes, usually coated with a carbon-based porous material, and separated by an electrolyte, which is While batteries rely on chemical reactions, supercapacitors differ in that they store and release energy very rapidly through the process of physically adsorbing and desorbing ions in the electrolyte between electrodes.

Author: Roya Nikjoo

Supercapacitors have become a popular solution where high-density backup power, long cycle life, and short charge and discharge times are required.

However, even for the most experienced engineers, choosing the right type of equipment for the task at hand can be quite complicated. It requires an understanding of a wide range of technical performance characteristics, as well as some tradeoffs to consider in the process.

Before we discuss in further detail how to choose the right supercapacitor for your application, it is necessary to clarify how such devices work and the advantages they offer over other technologies such as coin cells. This information can provide valuable insights into the various roles for which supercapacitors are particularly suited.

Supercapacitor Basics

First, in terms of how they work, many supercapacitors use a so-called electric double-layer capacitor (EDLC) layout, which has two electrodes, usually coated with a carbon-based porous material, and separated by an electrolyte, which is While batteries rely on chemical reactions, supercapacitors differ in that they store and release energy very rapidly through the process of physically adsorbing and desorbing ions in the electrolyte between electrodes.

How to Choose the Right Supercapacitor How Supercapacitors Work
Figure 1: The inner workings of a supercapacitor

These processes are much faster than the chemical reactions that occur in battery charging. Using supercapacitors with low internal resistance, the device can be fully charged in seconds, whereas lithium coin cells used in secondary battery applications can take ten minutes to hours to fully charge due to the much higher resistance. Also, there is no theoretical limit to the cycle life, whereas a lithium ion secondary battery has a limited life of about 500 cycles.

Recent advances in carbon-based materials mean that porous electrodes can be designed with larger surface areas, resulting in higher capacitance values ​​and smaller external dimensions. Supercapacitors using aqueous electrolytes are inherently conductive, have a low environmental impact, and are non-flammable with excellent performance and robust safety.

They are also generally more hygroscopic than organic compounds, resulting in longer life and better stability (Figure 2). This also means that supercapacitors are essentially maintenance-free, whereas lithium coin cells need to be replaced, depending on the specific application.

How to Choose the Right Supercapacitor How Supercapacitors Work
Figure 2: High reliability design: cell construction differences between aqueous and organic electrolytes

In terms of energy density, supercapacitors are typically rated at 0.5 to 5 Wh/kg, while lithium coin cells are rated at 30 to 270 Wh/kg. But supercapacitors have higher power densities, allowing them to deliver large amounts of energy in a very short period of time. Supercapacitors have more flexibility in operating temperature range C compared to narrower parameters, typically operating in the temperature range of -40 to +85°C for lithium coin cells, from -20 to +60°C.

These performance characteristics mean that supercapacitors are finding more and more use cases. These include backup power duties, including IoT-based devices, smart meters or medical devices, and various devices such as automotive electronics and industrial computers for advanced automation.

Typical applications include taking over the system’s real-time clock or volatile memory when the main system power is removed, such as during a power outage or when the main system battery is removed for replacement.

How to choose the right supercapacitor

So those are the basics of supercapacitors and some of the roles they play. But how do you choose the right device for the application you need?

Figure 3 represents a good starting point, as it illustrates some initial considerations from a high-level perspective. For example, if the end application indicates a need for longer backup times, KEMET’s FG, FY, FC, FM and FR series of high impedance solutions would be the best place to start.

Short backup times require low impedance, which means there will be a different set of solutions, mainly from the FA, FE, FS, FT and FM series. Also, if the key application requirement is high power, then a very specific range (such as the HV series) will provide the answer. However, these are important considerations from the start, before applying other ways of thinking.

How to Choose the Right Supercapacitor How Supercapacitors Work
Figure 3: Selecting Properties

In addition to backup time, a more comprehensive list of parameters that need to be defined before selecting a supercapacitor may include minimum and maximum operating voltage required; dimensions required for operating temperature; and mounting type (surface or through-hole). Then, with these details in hand, a relatively simple formula can be applied to roughly calculate the capacitance required for the task at hand.

As an example of the calculation process, in the project example below, a customer requires an ultracapacitor that can withstand 150 hours of backup time under the following conditions:

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