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desorption of ions in the electrolyte contained
between its electrodes.
These processes are much quicker than the
chemical reactions that would be found in bat-
tery charging. With supercapacitors having a
low internal resistance, the device can be fully
charged within a few seconds, whereas a lithium
coin cell used in a secondary battery application
could take anywhere betweenfrom ten minutes
to several hours to be fully charged due to far
higher resistance. Also, there is no theoretical
limit to cycle life, whereas a lithium-ion second-
ary cell has a finite lifetime of approximately 500
cycles.
Figure 1: The internal workings of a supercapacitor.
Recent advancements in carbon-based materi-
SUPERCAPACITOR als mean porous electrodes can be designed to
FUNDAMENTALS have a large surface area which results in a high
Firstly, in terms of how they work, many super- capacitance value and small external dimensions.
capacitors use what is known as the Electric Supercapacitor construction using aqueous elec- Figure 3: Performance for selection.
Double-Layer Capacitor (EDLC) layout featuring trolytes are inherently conductive, come with a
two electrodes that are often coated in a car- low environmental impact and offer non-flam- stability (Figure 2). This also means supercapac- Things-based devices, smart utility meters, or
bon-based porous material, andmaterial and mable characteristics, and this yields excellent itors are essentially maintenance-free, whereas medical equipment, through to automotive elec-
separated by an electrolyte that is itself divided performance and strong safety credentials. lithium coin cells need replacing, with regularity tronics and industrial computing for advanced
by a membrane (Figure 1). While batteries rely on depending on the specific application. automation.
a chemical reaction, the supercapacitor is differ- Typically speaking, they also have greater re-
ent in that it stores and releases energy very rap- sistance to moisture absorption than organic In terms of energy density, supercapacitors are Typical applications include taking over the sys-
idly through a process of physical adsorption and compounds, resulting in a longer life with better usually rated at 0.5 to 5 Wh/kg, compared to 30 tem’s real-time clock or volatile memory when
to 270 Wh/kg for a lithium coin cell. But super- the main system power is cut off, such as during
capacitors have a much higher power density, a power outage or when the main system battery
enabling them to deliver large amounts of energy has been removed for replacement.
in a very short time. Supercapacitors offer great-
er flexibility in terms of operating temperature
range – typically performing between -40 and HOW TO CHOOSE THE RIGHT
+85 deg-C, compared to narrower parameters of SUPERCAPACITOR
-20 to +60 deg-C for the lithium coin cell. So, those are the fundamentals of supercapaci-
tors and some of the roles they perform. But how
These kinds of performance characteristics mean do you go about selecting the right device for the
supercapacitors are finding increasing use-cases. required application?
These include backup power duties in a broad
Figure 2: High-Reliability Design: Cell Construction Differences between aqueous and organic-based electrolytes. range of equipment ranging from Internet of Figure 3 represents a good starting point, as it
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