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

s cel

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out

put:

V

s-p topology

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