Yunasko methodology

Methodology for supercapacitor
performance measurements
Dr. Natalia Stryzhakova
Dr. Yurii Maletin
Dr. Sergiy Zelinskiy

Methodology for supercapacitor performance measurement

References
1.FreedomCAR Ultracapacitor Test Manual. Idaho National Laboratory Report DOE/NEID-11173, September 21, 2004.
2.IEC 62391-2 . Fixed electric double layer capacitors for use in electronic equipment.
Part 2. Sectional specification – Electric double layer capacitors for power application.
3.IEC 62576. Electric double layer capacitors for use in hybrid electric vehicles – Test
methods for electrical characteristics.
4.A. Burke, M. Miller. Testing of Electrochemical Capacitors: Capacitance, Resistance,
Energy Density, and Power Capability. ISEE’Cap09 Conference, Nantes, 2009.
5.A. Burke, M. Miller. Testing of Electrochemical Capacitors: Capacitance,
Resistance, Energy Density, and Power Capability. Idaho National Engineering
Laboratory Report DOE/ID-10491, October 1994.
6.S. Zhao, F. Wu, L. Yang, L. Gao, A. Burke. A measurement method for determination of
dc internal resistance of batteries and supercapacitors. Electrochemistry Communications,
2010, v.12, p.242-245.
7. A. Burke. Testing Large Format Electrochemical Capacitors. Tutorial of ISEECap2011,
Poznan, Poland, June 12, 2011.
2


Main characteristics of
a supercapacitor unit cell
•Rated voltage, Ur (V)
•Capacitance, C (F)
•Internal resistance, R (Ohm)
•Specific energy, E (Wh/kg)
•Specific power, P (W/kg)
•Specific energy vs. Specific power (Ragone plot)
•Resistance and capacitance vs. temperature (-40…+70 ºC)
•Cycle life
•Self discharge
•Calendar life (hours) at rated voltage and high temperature (60 ºC)

3


Test procedures
•Constant current charge/discharge
Capacitance and resistance
Cycle life
•Pulse tests to determine resistance
•Constant power charge/discharge
Ragone Plot for power densities between 100 and at least
1000 W/kg for the voltage between Ur and ½ Ur.
Test at increasing W/kg until discharge time is less than 5
sec. The charging is often done at constant current with a
charge time of at least 30 sec.
•Voltage maintenance
Self discharge test
•Continuous application of rated voltage at high temperature
Endurance test (calendar life estimation)

4


Capacitance
Test procedure: Constant current charge/discharge
USABC test procedure
Normal Test Currents
(Discharge & Charge)
Minimum Test
Current

Test Currents
Test Equipment Limited
to ITEST < IMAX (Discharge & Charge)

0.1 ITEST

0.25 IMAX

0.25 ITEST

0.5 IMAX

0.5 ITEST

0.75 IMAX
Maximum Test
Current

5C

0.1 IMAX
Other Test
Currents

5C

0.75 ITEST

IMAX

ITEST

•Current of 5C corresponds to 12 min discharge
•IMAX can be chosen as the lowest of: (a) the current required to cause an
immediate ( <0.1 s) 20 % voltage drop in a fully charged device at 30 ºC, or
(b) the current required to discharge the device from UMAX to UMIN within 2 s.
•At least 5 cycles at each current value

5


Capacitance
IEC procedure (# 62576)
Single test to determine the capacitor performance at a
single current – so that the efficiency in charge and
discharge to be of 95%.

Ur
I ch =

38 R

I dch ⋅ ∆t
C=
∆U

I dch = U r

40 R

∆U = 0.9U r − 0.7U r
6


Capacitance
UC Davis procedure (ITS, Dr.A.Burke)
1) The nominal charge/discharge current In corresponding
to nominal power density (200 or 400 W/kg)

Pn ⋅ m
In =
Ur
2
2) A set of current values: 0.25, 0.5, 1.0, 2.0, 4.0, 8.0In

I test ⋅ ttest
C=
U r − U min

7


Capacitance
Yunasko procedure
1) A set of current values from 0.2Itest to Itest.; Itest 200 A

I test ⋅ ∆t
C=
∆U

∆U = 0.9(U r − U drop ) − 0.7(U r − U drop )

2) From С = f(I) plot the С0 max capacitance value
(extrapolation to zero current) and -dC/dI value (the slope)
can be found.
NOTE: The -dC/dI slope characterizes the system behavior
at high power loads and depends on electrode material and
system design.
8


Capacitance
Conclusions:
1.Capacitance value depends on test conditions,
though, not dramatically.
2.Testing current conditions differ significantly:
Yunasko supercapacitor cell:
1200F, 0.15 mOhm, 0.12 kg
Procedure

Itest, range, A

USABC

from 2.5 A (5C) to 800 A (Imax)

IEC

450 A

ITS
Yunasko

from 35 A to 280 A
from 40 A to 200 A
9


Internal resistance
1) Equivalent Series Resistance (ESR) - the resistance
due to all the resistive components within the
supercapacitor.
2) Equivalent Distributed Resistance (EDR) includes ESR
and an additional contribution from the charge
redistribution process in the electrode pore matrix
due to non-homogeneous electrode structure, the
process adding significantly to Joule heating: I2Rt.

10


Internal resistance
Test procedure: Constant current method,
sampling rate of 10 ms

∆U 4
ESR =
I dch

∆U 3
EDR =
I dch
11


Internal resistance

ESR is independent of current value.
EDR value depends on testing current
12


Internal resistance
Measurements using the voltage recovery after current interruption
(Maxwell procedure)

13


Internal resistance
Yunasko procedure

14


Internal resistance
Pulse procedure (Arbin)

Rpulse = Average (Voltage at P2 – Voltage at P3) / (2 I).

15


Internal resistance
Comparison of different procedures:
Resistance, mOhm

Yunasko
cells

C, F

E-type
P-type

pulse

ESR

interruption

1500

0.242

0.225

0.265

1200

0.091

0.101

0.104

Conclusions:
Internal resistance measurements involve different time
intervals to fix the voltage drop/jump.
Resistance values depend on test conditions, in
particular, on time interval and testing current chosen.
16


Specific energy and power
Test procedure: Constant power tests
1) Power values between 200 and at least 1000 W/kg
2) For each constant power test, the energy is calculated
as E = U×I×Δt during charge and discharge.
The usable specific energy Em (Wh/kg)

The efficiency η:

Ragone plot: a plot illustrating Em (or Ev) vs Pm (or Pv)
17


Test procedure: Constant power tests, Ragone plot

18


Maximum energy stored - the energy that can be
obtained at discharge from the rated voltage to zero:

Emax

CU r2
=
(Wh / kg )
2 × 3600m

Available energy - at discharge from the rated
voltage Ur to Ur/2

Eavail

3CU r2
=
(Wh / kg )
8 × 3600m
19


Maximum power (matched impedance power) - the power that can
be delivered to the load of the same resistance as a supercapacitor .

Pmax

0.25U r2
=
(W / kg )
Rm

Power density according to IEC 62391-2:

Pd =

(U − U 6 + U e ) × I 0.12U
=
2m
Rm

2

where
U6=0.2U (20%)
Ue=0.4U (40%)

The power at efficiency η and at discharge from the rated voltage Ur
to Ur/2:
2

9(1 − η )U r
P =
η
16 Rm

NOTE: YUNASKO normally uses the η value of 0.95
20


Self-discharge test
The time dependence of the capacitor self-dissipation, i.e., the rate of
internal processes that cause the capacitor discharge when not
connected to a load.

U end
B=
× 100%
Ur
where B is the voltage maintenance rate (%)

21


Self-discharge test - example

B=

U end
× 100%
Ur

where B is the voltage maintenance rate (%)

22


Cycle-life test
Stable performance over more than 100,000 charge/discharge cycles is
desired. Constant-current charge and discharge are used.
Typical procedure:
•Condition the capacitor at 25 ± 3°C.
•Charge the device by a current I chosen so that the voltage reaches Ur
in 30 s.
•Maintain voltage Ur of the device for 15 s.
•Then discharge the capacitor to Umin with current I.
•Hold the capacitor at Umin for 50 s.
•Repeat cycling.
Devices shall be characterized initially and after 1000; 4000; 10,000;
40,000; 100,000 cycles.
Characterization tests to be performed at each measurement cycle include:
1. Constant-Current Charge/Discharge (In)
2. ESR (from constant-current test data)
3. Constant Power Discharge (200 W/kg, 1000 W/kg)
23


Cycle-life test – SC example

Cycling a 1200F device between 2.0 and 3.2 V at 60 °C
24


Cycle-life test – hybrid capacitor example

25


Temperature Performance
Temperature influences the energy that can be stored in a device as
well as the power it can deliver.
Typical procedure:
Step 1 - Condition the device at 25±3°C and perform the followed tests:
3. Constant Power Discharge (200 W/kg, 1000 W/kg) .
Step 2 - Condition the capacitor at 60 ± 3°C until thermal equilibrium is
achieved. Perform the above mentioned tests at this temperature.
Step 3 - Condition the capacitor at -30 ± 3°C until thermal equilibrium is
achieved. Perform the above mentioned tests at this temperature .
Step 4 - Condition the capacitor at 25 ± 3°C and repeat the tests listed
above. This test data will provide information about the stability of the
capacitor under thermal cycling conditions.
Step 5 - Perform a visual inspection of the capacitors to identify any
damage or electrolyte leakage caused by the thermal cycle
26


Temperature performance
EDLC

Hybrid

27


Endurance test
This procedure characterizes device life properties and performance
using an accelerated aging condition.
Typical procedure:
•Device properties and performance are measured initially and then
periodically throughout the aging period.
•Age the capacitors in a suitable oven or environmental chamber
maintained at 60 ± 3°C with an applied voltage equal to Ur.
Characterization tests of the devices should be performed at the start of
the test sequence and after 250 ± 10, 500 ± 25, 1000 ± 50, and 2000 ±
100 hours. Measurements are made at 25 ± 3°C.
3. Constant Power Discharge (200 W/kg, 1000 W/kg)

28


Endurance test

29


Conclusions
 There is a need to further standardization of test procedures.
 The largest uncertainty is related with the resistance measurements.
 The effective capacitance of carbon/carbon devices is well-defined
from constant current tests, but varies with the voltage range used; it is
recommended the voltage range of Vr and Vr/2 to be used.
 Further work is needed to define the effective capacitance and
resistance of hybrid capacitors.
 The energy density should be measured at the constant power
discharge; this is especially the case for hybrid capacitors
 Definition and determination of maximum power capability of both
supercapacitors and lithium batteries remains a very confused issue
(A.F. Burke)
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Acknowledgements
Special thanks to my R&D and Design Bureau colleagues:
S.Podmogilny, S.Chernukhin, S.Tychina, D. Gromadsky, O.Gozhenko,
A.Maletin, D.Drobny, and A.Slezin
Our Pilot Plant and Administrative Department:
For the great support, diligence and dedication to work
YUNASKO investment, technical, scientific and industrial partners:
For the great collaboration and support during the projects
Many thanks to Dr. Andrew F. Burke (ITS) and Dr. John R. Miller (JME)
for their measurements and stimulating discussions
Financial support from FP7 Project no. 286210 (Energy Caps) is very much
acknowledged
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THANKS FOR YOUR ATTENTION!

Please visit us at: www.yunasko.com

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Yunasko methodology

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