Post on 19-May-2020
The Long-Term Performance of Small-cell Batteries Without Cell-
Balancing Electronics
C. Pearson, C. Thwaite, D. Curzon (AEA Technology)
G. Rao (NASA/GSFC)
https://ntrs.nasa.gov/search.jsp?R=20080015775 2020-05-19T13:25:36+00:00Z
Contents
Background− The AEA small-cell approach− Cell uniformity history
Selected test data− Old
Geosynchronous-Earth-Orbit (GEO) Standard testSTRV lifetest
− OngoingMars ExpressNASA/GSFC Low-Earth-Orbit(LEO)/GEO
Other data
Background: AEA Small Cell Approach
•Standard Sony 18650 commercial cells
•Space Qualified
•Ensure continued uniformity
•Lot Acceptance Test (LAT)
•Screen cells
•Match cells
•No cell balancing
p strings define the capacity
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Background: Cell Uniformity History
Tests ~8 yrs ago showed Sony HC do not imbalanceAEA developed a theory (ESPC 2002)− Self-discharge (SD) decreases with state-of-charge (SOC)− Cells diverge to a state of dynamic equilibrium− Equilibrium spread depends on cell SD uniformity
Balancing model verified against test dataShort-term measures of SD difficult in Sony cells− Very small values, depends on technique
Long-term evidence supports lower SD at low SDBattery testing best proof of performance− Typically mission specific tests
Selected Test Data: Old Data
GEO Standard Test− Commenced October 1998
AEA - 6s2p modulesFixed 60% depth-of-discharge (DOD)0°C, 20°C, 40°C0.12C charge and taper to 25.2V0.5C discharge3 years pre-test storage: 50%SOC, 20°CUnmatched cells
GEO Standard 20°C End-of-Discharge (EOD) Voltages
20°C Battery shorted after 350 cyclesDespite battery abuse, cells remain uniform for further 2000 cycles
2.3
2.5
2.7
2.9
3.1
3.3
3.5
3.7
Cycle Number
Cel
l End
of D
isch
arge
Vol
tage
(V)
Cell 1 Cell 2 Cell 3 Cell 4 Cell 5 Cell 6
Cell 7 Cell 8 Cell 9 Cell 10 Cell 11 Cell 12
0 5.6 11.1 16.7 22.2 27.8 GEO Mission - Equivalent Years
GEO Standard 0°C EOD Voltages
0, 40°C tests showed uniform cell performance
Selected Test Data: Old Data (cont’d)
QM lifetest for STRV Geo Transition Orbit (GTO) missionNo cell matching6s2p battery20°C 44% DODCharge at C/9 to 24V (4V per cell)Discharge at C/5250 cycles per month, test lasted 4 months
STRV Lifetest: Cell Uniformity
Strong evidence of self-balancing mechanism
0
0.01
0.02
0.03
0.04
0.05
0.06
0 200 400 600 800 1000 1200
Cycle Number
Cel
l Vol
tage
Sta
ndar
d D
evia
tion
(V)
End of Charge Data
End of Discharge Data
STRV: Cell Uniformity Prediction
Characteristic self-balancing correctly predictedConservative standard deviation predictions
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0 1000 2000 3000 4000 5000 6000
Time (mins) for Full Data / Cycle Number for End of Phase Data
Cel
l Vol
tage
Sta
ndar
d D
evia
tion
(V)
ST Dev of EMF
EoC Standard Deviation)
EoD Standard Deviation)
Selected Test Data: Ongoing
Mars Express (MEX) Realistic Lifetest (RL)Milestones − Test started on Dec 5, 1999 − Mars Cruise ended on Aug 16, 2000− 1st Martian year end on Jun 6, 2002− 2nd Martian year end on Mar 10, 2004Hardware Description:− 12Ah test module, 6s-8p− Individual cell voltage monitoring− Same voltage, 1/4 capacity of flight
battery− Same batch of cells as flight batteryTest temperature:− 20°C (max interface temp)
MEX Battery: Voltage
MEX RL Test Profile: SummaryCycle Type Bat tery Discharge Peak
DODPrimary
Mission Cycles(One Mars
Year)
ExtendedMission Cycles
(Two MarsYears)
Low Cycle 0 Wh < 25 Wh 2.5% 1800 4300
Standard Cycle 25 Wh < 100 Wh 10% 1990 3130
High Cycle 100 Wh < 250 Wh 24% 1000 1340
Extreme Cycle 250 Wh < 350 Wh 34% 240 510
Total number of Cycles 5030 8980
Each orbit has up to 5 battery discharges Two periods each Martian-year with no eclipses
MEX Cell Uniformity: Storage Phase
Cell voltage range ~5mVCell voltage standard deviation ~1mV
3.8580
3.8600
3.8620
3.8640
3.8660
3.8680
3.8700
3.8720
3.8740
3.8760
3.8780
0 50 100 150 200 250Storage (days)
Volta
ge (V
)
0
0.0005
0.001
0.0015
0.002
0.0025
0.003
0.0035
0.004
0.0045
0.005
Standard Deviation (V)
Cell Voltages (V)
Sta
ndar
d D
evia
tion
(V))
MEX Cell Uniformity: Martian Orbit
EOC Voltages – range <5mVCell voltage standard deviation ~1mV
4.1300
4.1350
4.1400
4.1450
4.1500
4.1550
4.1600
4.1650
4.1700
4.1750
4.1800
4.1850
4.1900
500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600
Test Stage (days)
Cel
l Vol
tage
(V)
0
0.0005
0.001
0.0015
0.002
0.0025
0.003
0.0035
0.004
0.0045
0.005
Standard Deviation (V)
Cell Voltages (V)
Sta
ndar
d D
evia
tion
(V))
MEX Cell Uniformity: EOD Voltages
4 EODV measurements: beginning 3 years into testRange <100mV, standard deviation ~20mVUniformity maintained over 4 year test
2.6500
2.6750
2.7000
2.7250
2.7500
2.7750
2.8000
2.8250
2.8500
2.8750
2.9000
30/12/2002 30/03/2003 28/06/2003 26/09/2003 25/12/2003 24/03/2004
Date
EOD
Vol
tage
(V)
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0.05
Standard Deviation (V)
Cell Voltages (V)
Sta
ndar
d D
evia
tion
(V))
1100 1200 1300 1400 1500 1600 Test Stage (Days)
Selected Test Data: Ongoing (cont’d)
NASA/GSFC LEO/GEO Test NASA/GSFC Funded, performedat AEAMixed profile− LEO 30%DOD− GEO (up to 72%DOD) with
solstice periods 8s4p battery (4x8s1p)Monitoring:− Individual cell voltage− Individual pack temperature
Test Will Continue
NASA/GSFC LEO/GEO Test
Stage Orbit Type Days Stage Orbit Type Days1 SCM (AEA 01 & GSFC 01) 2 16 GEO Eclipse cycles 42 days 422 Impedance measurement 01 3 17 SCM (GSFC 07) 13 LEO 30% DOD 450 Cycles 28 18 GEO Solstice 140 days 1404 SCM (AEA 02) 1 19 SCM (GSFC 08) 25 LEO 30% DOD 450 Cycles 28 20 Impedance measurement 02 06 SCM (AEA 03 & GSFC 02) 1 21 LEO 30% DOD 450 Cycles 287 GEO Eclipse cycles 42 days 42 22 SCM (GSFC 09) 18 SCM (GSFC 03) 1 23 LEO 30% DOD 450 Cycles 289 GEO Solstice 140 days 140 24 SCM (GSFC 10) 1
10 SCM (GSFC 04) 2 25 GEO Eclipse cycles 42 days 4211 Impedance measurement 02 1 26 SCM (GSFC 11) 112 LEO 30% DOD 450 Cycles 28 27 GEO Solstice 140 days 14013 SCM (GSFC 05) 1 28 SCM (AEA 04 & GSFC 12) 214 LEO 30% DOD 450 Cycles 28 29 Impedance measurement 04 115 SCM (GSFC 06) 1 TOTAL DAYS IN TEST 735
Test presently ¾ through first GEO solstice period
13 mV
EoD
5mVMax. Cells Dispersion
EoC
13 mV
EoD
5mVMax. Cells Dispersion
EoC
11 mV
EoD
5mVMax. Cells Dispersion
EoC
11 mV
EoD
5mVMax. Cells Dispersion
EoC
36 mV
EoD
5mVMax. Cells Dispersion
EoC
36 mV
EoD
5mVMax. Cells Dispersion
EoC
LEO Cycle 450
3.85
3.90
3.95
4.00
4.05
4.10
4.15
4.20
4.25
4.30
0 20 40 60 80 100
Orbit Time (min)
Cel
l Vol
tage
(V)
0.000
0.002
0.004
0.006
0.008
0.010
0.012
0.014
0.016
0.018
Cel
ls D
ispe
rsio
n (V
)
Cell 1 Cell 2 Cell 3 Cell 4 Cell 5Cell 6 Cell 7 Cell 8 Cell 9 Cell 10Cell 11 Cell 12 Cell 13 Cell 14 Cell 15Cell 16 Cell 17 Cell 18 Cell 19 Cell 20Cell 21 Cell 22 Cell 23 Cell 24 Cell 25Cell 26 Cell 27 Cell 28 Cell 29 Cell 30Cell 31 Cell 32 Discharge Dispersion Charge Dispersion
Discharge Charge
NASA/GSFC LEO/GEO Test:Dispersion - LEO 30% DoD Cycle 450
EoD EoC
Max. Cells Dispersion 13 mV 5mV
LEO Cycle 900
3.85
3.90
3.95
4.00
4.05
4.10
4.15
4.20
4.25
4.30
0 20 40 60 80 100Orbit Time (min)
Cel
l Vol
tage
(V)
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
Cel
ls D
ispe
rsio
n (V
)
Cell 1 Cell 2 Cell 3 Cell 4 Cell 5Cell 6 Cell 7 Cell 8 Cell 9 Cell 10Cell 11 Cell 12 Cell 13 Cell 14 Cell 15Cell 16 Cell 17 Cell 18 Cell 19 Cell 20Cell 21 Cell 22 Cell 23 Cell 24 Cell 25Cell 26 Cell 27 Cell 28 Cell 29 Cell 30Cell 31 Cell 32 Discharge Dispersion Charge Dispersion
Momentary increase due to switching from discharge to charge.
Discharge Charge
NASA/GSFC LEO/GEO Test: Dispersion - LEO 30% DoD Cycle 900
EoD EoC
Max. Cells Dispersion 11 mV 5mV
NASA/GSFC LEO/GEO Test:Dispersion - GEO, 72min Eclipse
p ( )
3.00
3.20
3.40
3.60
3.80
4.00
4.20
0 50 100 150 200Orbit Time (min)
Cel
l Vol
tage
(V)
0.00
0.01
0.02
0.03
0.04
0.05
0.06
Cel
ls D
ispe
rsio
n (V
)
Cell 1 Cell 2 Cell 3 Cell 4 Cell 5Cell 6 Cell 7 Cell 8 Cell 9 Cell 10Cell 11 Cell 12 Cell 13 Cell 14 Cell 15Cell 16 Cell 17 Cell 18 Cell 19 Cell 20Cell 21 Cell 22 Cell 23 Cell 24 Cell 25Cell 26 Cell 27 Cell 28 Cell 29 Cell 30Cell 31 Cell 32 Discharge Dispersion Charge Dispersion
Discharge Charge
Other DataOther customer funded tests− IAI LEO tests− Multiple mission specific lifetests
PROBA− 3 years successful LEO operation
MEX, 11 months in orbit− Didier Loche, ASTRIUM:“The MEX batteries are performing well with no
anomalies and they are well matched. The measured capacity fade of 15%correlates with predictions and the MEX lifetest."
− Test will continue
Acknowledgements