dr. natalia stryzhakova dr. yurii maletin dr. sergiy zelinskiy

Dr. Natalia StryzhakovaDr. Yurii MaletinDr. Sergiy Zelinskiy

Methodology for supercapacitor performance measurements

References1.FreedomCAR Ultracapacitor Test Manual. Idaho National Laboratory

Report DOE/NE-ID-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.

Methodology for supercapacitor performance measurement

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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)

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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


CapacitanceTest procedure: Constant current

charge/dischargeUSABC test procedure

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Normal Test Currents (Discharge & Charge)

Test Currents Test Equipment Limited

to ITEST < IMAX (Discharge & Charge)

Minimum Test Current

5C 5C

Other Test Currents

0.1 IMAX 0.1 ITEST

0.25 IMAX 0.25 ITEST

0.5 IMAX 0.5 ITEST

0.75 IMAX 0.75 ITEST

Maximum Test Current

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


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Test procedure: Constant current charge/dischargeIEC 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%.

RUI r

ch 38 RUI r

dch 40

U

tIC dch

rr UUU 7.09.0

Capacitance


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

2r

nn U

mPI

2) A set of current values: 0.25, 0.5, 1.0, 2.0, 4.0, 8.0In

minUU

tIC

r

testtest

Capacitance


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Test procedure: Constant current charge/dischargeYunasko procedure 1) A set of current values from 0.2Itest to Itest.; Itest 200 A

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.

U

tIC test

)(7.0)(9.0 droprdropr UUUUU

Capacitance


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 from 35 A to 280 A

Yunasko from 40 A to 200 A


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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.


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Internal resistance

dchI

UESR 4

dchI

UEDR 3

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


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Internal resistance

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


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Internal resistance

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


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Internal resistance

Yunasko procedure


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Internal resistance

Pulse procedure (Arbin)


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

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Internal resistance

Comparison of different procedures:


Yunasko cells

C, F

Resistance, mOhm

pulse ESR interruption

E-type 1500 0.242 0.225 0.265

P-type 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.

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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)

Specific energy and power

The efficiency η:

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


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Test procedure: Constant power tests, Ragone plot



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


)/(36002

2

max kgWhm

CUE r

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

)/(36008

3 2

kgWhm

CUE ravail


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Maximum power (matched impedance power) - the power that can

be delivered to the load of the same resistance as a supercapacitor.


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

)/(25.0 2

max kgWRm

UP r

Rm

UP r

16

)1(9 2

NOTE: YUNASKO normally uses the η value of 0.95

Power density according to IEC 62391-2:

RmU

mIUUU

P ed

26 12.02

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


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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.

Self-discharge test

%100r

end

U

UB

where B is the voltage maintenance rate (%)


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Self-discharge test - example

%100r

end

U

UB

where B is the voltage maintenance rate (%)


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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)

Cycle-life test


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Cycle-life test – SC example


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

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Cycle-life test – hybrid capacitor example


0 2000 4000 6000 8000 1000060

80

100

120

140

160

180

Q/Q

0 (R

/R0)

, %

Cycle number

Charge/discharge 20A CC Q/Q

0 R/R

0

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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:

1. Constant-Current Charge/Discharge (In) 2. ESR (from constant-current test data) 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

Temperature Performance


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Temperature performance


EDLC Hybrid

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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.

1. Constant-Current Charge/Discharge (In) 2. ESR (from constant-current test data) 3. Constant Power Discharge (200 W/kg, 1000 W/kg)

Endurance test


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Endurance test


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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)

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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dr. natalia stryzhakova dr. yurii maletin dr. sergiy zelinskiy

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