TECHNICAL NOTETECHNICAL NOTEELECTRIC DOUBLEELECTRIC DOUBLELAYER CAPACITORSLAYER CAPACITORS®

1 Description of Electric Double Layer
Capacitor
1-1 Basic Concepts
Generally capacitors are constructed with a dielectricplaced between opposed electrodes, functioning as
capacitors by accumulating charges in the dielectricmaterial. Aluminum electrolytic and tantalum electrolytic capacitors, for example, use an aluminum oxide
film and a tantalum oxide film as the dielectric,
respectively.

On the other hand, Electric Double Layer Capacitors
have no visible dielectric in a general sense but utilize
the state referred to as the electric double layer, which
is developed naturally on the interface between
substances, as the function of dielectric.
1-2 Operating Principle
The Electric Double Layer represents the state inwhich positive and negative charges exist at a very
short distance on the boundary where contact occurs
between two different substances (e.g. solid andliquid). By externally applying a voltage below acertain voltage to the boundary, higher charges canbe accumulated. Accordingly, charge and dischargeof electric double layer capacitors utilize adsorption
and desorption of ions to the ionic adsorption layer(Electric Double Layer) formed on the electrodesurface of the activated carbon used for electrodes.

Applying DC voltage externally across the electrodesof the Electric Double Layer allows almost no passageof current up to a certain voltage, exhibiting a
condition like insulation.
However, the application of voltages exceeding thecertain voltage causes electrolysis to occur in theelectrolyte, resulting in abrupt passage of current.
This voltage determines the resistance of voltage ofan Electric Double Layer Capacitor. We use anorganic electrolyte and its standard electrolysis occurs
at the voltage of about 2.5 to 3V.
1-3 Advantages and Disadvantages of Electric
Double Layer Capacitor[Advantages](1) Small size and capacitance in farads (F) available
by utilizing the activated carbon electrode with alarge surface area
(2) No special charging circuit and constrains during
discharge are required.
(3) No effect on the life through overcharging andoverdischarging(4) Environmentally clean energy[Disadvantage](1) The life is limited due to the use of electrolyte.
(2) Series connection is required when used with alow resistance of voltage at a high voltage.
(3) Cannot be used in AC circuits due to high internal
resistance unlike aluminum electrolytic capacitors.

Electrolyte

ActivatedcarbonChargeActivatedcarbonDischarge

Fig.1 Schematic of Principle of Electric Double Layer Capacitor

NOTE : ‌Design, Specifications are subject to change without notice.
It is recommended that you shall obtain technical specifications
from ELNA to ensure that the component is suitable for your use.

CAT.No.2023/2024E

TECHNICALNOTETECHNICALNOTEELECTRIC DOUBLEELECTRIC DOUBLELAYER CAPACITORSLAYER CAPACITORS

1-4 Construction of DYNACAP
The series which consists of coin cells is similar tothat of coin-type batteries as shown in Fig.2.
DYNACAP contains a single cell or two to three cells
stacked in series.
Since these series have a large electrode-to-electrodedistance and a small electrode area exhibiting a large
internal resistance, they are suitable for the memory
backup application that involves microcurrent
discharge.
The cylindrical cell construction as seen in the DZ1 andDZN series has the construction similar to that ofaluminum electrolytic capacitors as shown in Fig.3.

These series have a small electrode-to-electrodedistance, allowing a large electrode area because of
the winding structure. This decreases the internal
resistance, which is primary suitable for applications
requiring high-power such as motor drive and LED
lighting that need high currents.

2 Description of Life Expectancy
Generally, the life of Electric Double Layer Capacitors
is largely affected by the ambient temperature.
The expected life is approximated by the equation asshown below:

Where,Gasket

Activated carbon
electrode

Electrolyte

Separator

CapCaseFig.2 Example of Basic Construction of Coin Cell

Separator®

Expected lifetime at temperature T
Lifetime at temperature
Expected working temperature
Upper category temperature

Note that the above equation does not cover charge
and discharge. In the case of charge and discharge,heat generation occurs inside a capacitor; thetemperature rise by this heat generation must also beconsidered.
The expected life time is a maximum as a guide interms of deterioration of the sealant.
Coin cell type : about ten years
Cylindrical type : about fifteen years

Activated carbon
electrode

Aluminumcase

Seal rubber

Terminal

Fig.3 Example of Basic Construction of Cylindrical Cell

NOTE : ‌Design, Specifications are subject to change without notice.
It is recommended that you shall obtain technical specifications
from ELNA to ensure that the component is suitable for your use.

CAT.No.2023/2024E

TECHNICAL NOTETECHNICAL NOTEELECTRIC DOUBLEELECTRIC DOUBLELAYER CAPACITORSLAYER CAPACITORS

3 Calculation Method of Discharge Time
3-1 Approximating the Discharge Time of Basic
Constant Current DischargeThe discharge time at the constant current of acapacitor can be calculated by the followingequation.
t = (C×∆V)/IWhere,t : Discharge time (sec.)
C : Capacitor capacitance (F)∆V : Working voltage range (V)I : Discharge current (A)As an example, we calculate the discharge time whena capacitor of the CB1 series 5.5V 1F is charged with
5V and discharged to 3V at a constant current of 1mA. Since the working voltage range ∆V is 2Vfrom 5 − 3V, t = (1F × 2V)/0.001A from the above
equation, and the discharge time can be calculated
as 2,000 seconds (about 33 minutes). Note thatthe actual discharge time may be different because
this equation does not cover the effect of theself-discharge and the IR drop by internal resistancedescribed below.
3-2 Effect of Self-discharge at Microcurrents
When backup is made by discharge with a microcurrent below some μA especially for the memory
backup application and the like, the discharge timemust be determined while taking into account the selfdischarge as shown in Fig.4.
The value closer to the actual discharge curve isobtained by adding the voltage drop through the selfdischarge determined from the voltage retention
characteristic test to the discharge curve given by
calculation.
Note that the value of self-discharge varies by
the charge time, charging current and an ambient
temperature.

3-3 Effect of IR Drop at Large Currents
When a large Current discharge and a capacitor witha high internal resistance are used, the effect of IR
drop by the product of the internal resistance and thecurrent must be considered as shown in Fig.5.
Moreover, the maximum discharge current of theproduct (coin cell series) of a memory backup use
recommends below 1 mA/F (at20 ℃).
When a large current is required in a very short time,or a large instantaneous current flows at the start ofdischarge, the voltage drop indicated with ∆V1 counts.
However, when the discharge continues as it is, thedischarge curve indicates in a manner showing a slow
diffusion and then keeps a constant straight line.
We also make calculation including ∆V2 of theintersection extending from the initial discharge andthe discharge straight line section including thediffusion curve when indicating the DC internalresistance.

EV2

V1Voltage®

ChargeDischarge

Fig.5 Example of Discharge Curve involving IR Drop

Due to IR drop, the shape of the discharge curve
varies by the internal resistance and ambient
temperature for each series.

Voltage

Discharge curve given by calculation

Actual discharge curve

TimeFig.4 Example of Discharge Curve involving Self-Discharge
NOTE : ‌Design, Specifications are subject to change without notice.
It is recommended that you shall obtain technical specifications
from ELNA to ensure that the component is suitable for your use.

CAT.No.2023/2024E

TECHNICALNOTETECHNICALNOTETECHNICAL NOTEELECTRIC DOUBLEELECTRIC DOUBLELAYER CAPACITORSLAYER CAPACITORS®
®

ELECTRICDOUBLE
4 Series-parallel connection packaged
products.

LAYER CAPACITORSElectric Double Layer Capacitors have a low operating
voltage per cell.
To deal with this, ELNA is ready to offer series packaging for high operating voltages to meet to various needs.

Please consult
with us on optimization and design.
4 Moisture-proof
provision

Packagedlayer
item
If a electric double
capacitor is used in a heat-and-high-humidity environment, the characteristic willdeteriorate.
Please consult when using in a heat and high humidlty environment.

5 Regarding Recovery Voltage
Examplepackaged item
After charging and then discharging the electric double layer capacitor,
andof further
causing short-circuit
to the terminals and leave them alone, the voltage between the two terminals will rise again after some
In case of a low voltage (up to about 24 V) for the DZ and DZN series with relatively low capacitance,interval. This
voltage is called recovery voltage.
we are preparing simple packaged products.
This voltage
cause
the equalization
bad influence
thelow-voltage
drivencomponents(CPU,etc.) orNomay
full-scale
voltagecircuittohas
beenequipped yet,but comparatively
low cost
andmemory,
flexible layout
damage of canthebe
capacitor
realized. with soldering.
Discharging before use is safer. It is important especially when using it by series connection.
Moreover,5 itApplications
is possible making the terminals in short-circuit condition at& Benefitsof Electric
Double Layer Capacitor
the production stage. PleaseFeaturesconsult us
for adequate
procedures.

6 Applications

Features & Benefits of Electric Double Layer Capacitor

Electric Double Layer Capacitors

CAT.No.2013/2014E

NOTE : ‌Design, Specifications are subject to change without notice.
It is recommended that you shall obtain technical specifications
from ELNA to ensure that the component is suitable for your use.

212

NOTE

Design, Speciﬁcations are subject to change without notice.
Ask factory for technical speciﬁcations before purchase and/or use.

CAT.No.2023/2024E

6E
6-1