Evaluation of High Power Energy Storage Devices for Use in Compact Pulsed Power

Systems

Biju Shrestha, Peter Novak, and David Wetz (PhD)University of Texas at Arlington

College of EngineeringElectrical Engineering Department

416 Yates Street537 Nedderman Hall

Arlington, Texas 76019-0016biju.shrestha@mavs.uta.edu

Motivation

• High density energy storage is needed for driving naval pulsed power applications

• Electrochemical energy storage devices have either possessed a high energy density or a high power density, but not both

• Advancement in the development of electrode materials and electrolytes has helped to increase energy density and power density in electrochemical cells.

• These higher densities allow them to drive fast, high current pulsed power applications

• We seek to discover the aging and power limitations of high power cells when they are discharged repeatedly at elevated rates (tens to hundreds of times their rated C values)

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JM Energy Lithium Ion Capacitor Presentation, ULTIMO, http://www.jmenergy.co.jp/en/product.html, JM Energy Corporation, Copyright(C), July 2010.

Pulsed Power

100 ms pulsed discharge–Current normalized to cell mass

–Power normalized to cell mass

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Ragone chart comparison of the 1C energy density and the 100 ms pulsed power density

High C Rate Pulsed Applications

•The ability to source high C pulsed currents makes them potential prime power sources for applications such as– Compact Marx Generators– Laser Systems– EM Launchers– Seed Current Sources– Grid energy storage– Hybrid/electric vehicles

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Architecture

http://www.apelc.com/marx5.html

http://www.freedomsphoenix.com/News/106436-2012-02-29-new-navy-railgun-tests-leading-to-ship-superweapon-by-2020.htm?EdNo=001&From=

http://forums.nasioc.com/forums/showthread.php?t=2353156

http://www.hybridcarsdata.com/what-are-hybrid-cars/

Lithium-Ion Battery Aging

• Much research has been done to understand the physical processes that occur inside of lithium-ion batteries as they are cycled and aged at their nominal power rating.

• On the negative electrode side, the main parameters are SEI layer stability, SEI structure/composition and polluting agents. On the positive electrode side, the key factors seem to be material structure evolution and organic solvent oxidation[1],[2].

• The development of very high power Li-ion cells is still quite recent and, to our knowledge, there have been no documented research efforts detailing the effect extremely elevated discharge rate cycling has on capacity and power fade.

• This research attempts to study the effect of very high rate pulsed discharge (> 80C, 50% duty cycle 10 kHz) coupled with 1C charge rate, at room temperature without added cooling to the cells.

[1] Guy Sarre, Ph Blanchard, M. Broussely, ‘Aging of Lithium-ion batteries’, Journal of Power Sources, 127 (2004) 65-71.[2] M. Broussely, Ph. Biensan, F. Bonhomme, Ph. Blanchard, S. Herreyre, K. Nechev, R.J. Staniewicz, ‘Main aging mechanisms in Li ion batteries’, Journal

of Power Sources, 146 (2005), 90-96.5

EIS Study of Lithium-ion Batteries

Impedance spectra of fully discharged lithium-ion batteries with different cycle numbers at a 1C rate: (a) 0; (b) 40; (c) 286 cycles.

Source: J. Li, E. Murphy, J. Winnick, And P.A. Kohl, “Studies on the cycle life of commercial lithium ion batteries during rapid charge-discharge cycle,” Journal of Power Sources, 2001.

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High C Pulsed load

• Designed to discharge up to 10 kA peak pulsed current

• 10 kHz switching frequency• Variable inductance loop to adjust the

discharge rise time • Can be easily modified to achieve lower

(more standard) discharge rates if needed• Incorporates several safety features in the

event of thermal runaway

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Data Acquisition

• Cell voltage is monitored using a differential probe.

• Cell current is monitored using both a Rogowski coil and custom current viewing resistor (CVR).

• National instrument data acquisition system (PXIe-6361) is used with BNC-2110 connector.

• Temperature data is collected using a 0.076 mm K-type thermocouple and 16 channel NI-9213 thermocouple module in a cDAQ-9171 (up to 100 S/s for one channel).

• Metrohm PGSTAT 302N/FRA Potentiostat with 20 A Current booster is connected. 8

Experimental Setup

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Experimental cell

• Two Saft 3Ah LiNixCOyAl1-x-yO2 (NCA) cells are used:– One is the control cell subjected to standard 1C charge / discharge.– Another is the variable cell subjected to high C pulsed loading.

• Cell chosen due to its:– Low ESR (~1.5mΩ)– Low capacity allows for quicker testing – Scalability to larger cells of similar chemistry

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3Ah Cell Properties

Experimental Test Plan

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Elevated Discharge* 1C Characterization*

*Cell starts at 0% state of charge (SOC) (3.0V)CC = constant currentCV = constant voltage

Metrics for Investigation

• Cell voltage, current, and temperature

• Capacity measurement is performed through integrating current with respect to time (Coulomb Counting)

• Electrochemical Impedance Spectroscopy (EIS) is used to measure changes in the internal resistance. Attempts are being made to correlate these changes to physical changes inside the cell.

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Experiment performed

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1C Cell Characterization

Elevated Discharge of Cell

Cycle = 1

Is Cycle=10?

Incr

ease

Cy

cle

by 1

Variable Cell(201 cycles completed)

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1C Cell Characterization

1C Rated Cycle

Cycle = 2

Is Cycle=10?

Incr

ease

Cy

cle

by 1

Controlled Cell(97 cycles completed)

Profiles: Current and Voltage

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Temperature Profile

• The graph describes the temperature profiles recorded during the 3rd and 201st elevated pulsed discharge experiments performed at room temperature.

• Elevated discharge in cycle 3 took 140 seconds and in cycle 201 took 120 seconds due to combined effects of increased conductivity at higher cell temperature and decrease in cell capacity.

• Room temperature during cycle 201 was approximately 4°C higher than cycle 3.

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1C Discharge Capacity After Elevated Pulsed Discharge

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• Capacity measurements of both the variable and control cells

• 12.70% capacity loss was measured in variable cell after 200 cycles.

• No capacity loss was measured in the control cell after 97 cycles.

• Voltage vs. Capacity recorded from the variable test cell during the periodic 1C discharge procedure

• There is a decrease in cell capacity with increasing cycle number

• It is important to note that as of now this data is representative of only one, research grade, lithium-ion cell

• Repeat experiments are needed to confirm repeatability

Electrochemical Impedance Spectroscopy Result for variable cell

EIS Setup ParametersFrequency: 20kHz to 10mHzAmplitude: 10mVOCP: 4.10V

• Prior to cycle 50, the cell’s conductivity increased as a result of the cell settling in

• After cycle 50, the conductivity started to decrease as the cell started to age

• The medium frequency semicircle① is decreasing slowly, which represents the increase in passive film formation on the electrodes, especially on the cathode.

• The low frequency semicircle② represents the internal charge transfer resistance (both the interfacial and surface film resistances of the cathode and anode).

• The diameter of the low frequency semicircle ② is increasing with cycle life, indicating an increase in total internal resistance of the cell.

Nyquist plots of baseline at 100% SOC

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1 2

Conclusions

• Two Saft 3 Ah NCA lithium-ion cells are being cycled.– The variable cell has been cycled 201 times

• Discharge performed in a pulsed elevated fashion with roughly 83C peak currents at a frequency of 10 kHz with a 50% duty cycle.

• Recharge was performed using a 1C constant current - constant voltage procedure.

– Control cycle has been cycled 97 times at 1C.• Roughly 12.70% capacity fade has been observed in the variable cell.• No capacity fade has been observed on the control cell.• EIS measurements are being used to correlate the aging of the cell to

physical changes internally.• The cells will continue to be cycled until 20% capacity fade is observed in

the same fashion to better understand the rate of capacity fade at higher C rates.

• It is again important to note that as of now this data is representative of only one, research grade, lithium-ion cell and that more work is needed to demonstrate repeatability

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Comprehensive College of Engineering in North TexasComprehensive College of Engineering in North Texas

ACKNOWLEDGEMENTSACKNOWLEDGEMENTS