Storage Characteristics of Li-Ion Batteries TECHNOLOGIES GROUP Storage Characteristics of Li Ion...

ELECTROCHEMICAL TECHNOLOGIES GROUP

Storage Characteristics of Li Ion Cells

Storage Characteristics of Li-Ion Batteries

M. C. Smart, K. B. Chin, L. D. Whitcanack and B. V. Ratnakumar

NASA Battery Workshop

Huntsville, AL November 14-16, 2006

(Supported by ESRT Technology Program)



Landers, Rovers and Probes to Outer Planets

GEO SatelliteLEO satellitePlanetary Orbiters• Cruise time : 6-12 Y• Long calendar Life

• Mission Life: 5-10 y• Long Cycle Life

– > 30,000 cycles

• Mission Life: 5-10 y• Long Cycle life

– > 30,000 cycles

• Mission Life: ~10 y• Long Cycle life

– > 2,000 cycles

Why Long-Life Batteries?

ESMD Missions

Pressurized and Unpressurized planetary

landers

Lunar Habitat



Li-Ion Technology Demonstration Strategy • Technology Insertion Criteria

– Flight Heritage preferred• Nickel systems have over 3 decades of flight heritage compared to

less than fifteen years old Li-ion technology (Still evolving) .– Real-time data critical for new technology infusion

• Limited real-time storage data for Li ion system. • Predictions from models and accelerated tests unreliable

– All the failure modes are not yet fully understood.– Unpredictable failure modes, not connected with gradual

degradation, are observed occasionally.

• Our strategy is to evaluate different aerospace prototype cells in real-time tests under related environments.

• Manufacture Control Documents available with the manufacturer.



Outline of Storage Tests• Storage tests at different temperatures

– Two different type of prototype aerospace cells (20 each).• Prismatic 7 Ah cells from Yardney (same chemistry as MER batteries);

First generation low temperature electrolyte.• SAFT DD cells (~ 9.5 Ah)

– Six different storage temperatures (-20, 0, 10, 25, 40 and 55oC). Two cells for each temperature.

– Cells stored on bus as a two-cell module at 7.3 V (for minimizing test stations)

– Periodic measurement of capacity after each 3 months at 25 and 0oC.– EIS at 100% state of charge at 25oC after each three months; Currently

DC impedance is also being monitored– Four cells stored in a similar manner at –20oC and 0oC, without

intermittent capacity/EIS measurements.



SAFT DD Cells- Discharge at RT

0

2

4

6

8

10

12

14

16

0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54Storage Time (Months)

Cap

acity

(AH

r)

-20C Storage Cell SO118 0C Storage Cell SO128

10C Storage Cell SO124 23C Storage Cell SO117


Dsicharge @ 23oC



Storage of SAFT Cells- Discharge at RT

• Over 90% capacity retained after about 54 months at temperatures temperatures < 40oC.

• Tolerant to storage at 55oC

60

70

80

90

100

110

120

0 6 12 18 24 30 36 42 48 54 60

Storage Time (Months)

% In

itial

Cap

acity




DischargeTemperature = 23oC



SAFT DD Cells- Capacity at 0oC After Storage

0

2

4

6

8

10

12

14

0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54


Cap

acity

(AH

r)







Storage of SAFT cells -Discharge at 0oC

• Low temperature performance capability maintained upon storage, upon storage, even at high temperatures.

60

70

80

90

100

110

120

0 6 12 18 24 30 36 42 48 54 60


% In

itial

Cap

acity




Discharge Temperature = 0oC



Storage of YTP Cells -Discharge at 25oC

0

2

4

6

8

10

12

0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51


Cap

acity

(AH

r)

-20C Storage Cell YO74 0C Storage Cell YO89

10C Storage Cell YO88 23C Storage Cell YO82


Temperature = 23oC



YTP Cells - Discharge at 20oC

60

70

80

90

100

110

120

0 6 12 18 24 30 36 42 48 54 60

Time (Months)

% In

itial

Cap

acity





• Over 90% capacity retained after about 54 months at temperatures < 20oC.• Slightly high capacity fade, possibly due to the use of low temperature electrolyte

electrolyte



Storage of YTP Cells -Discharge at 25oC

0

2

4

6

8

10

12

0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51


Cap

acity

(AH

r)




Temperature = 23oC



YTP Cells - Discharge at 0oC

• Over 90% capacity of original LT capacity retained after about 54 months at at temperatures < 20oC.

60

70

80

90

100

110

120

0 6 12 18 24 30 36 42 48 54 60

Time (Months)

% In

itial

Cap

acity




Discharge Temperature = 0oC



Mid-point voltages - Discharge at 0oC

3.53

3.55

3.57

3.59

3.61

3.63

0 3 6 9 12 15 18 21 24 27 30Storage Time (Months)

Mid

-Poi

nt V

olta

ge (V

)

-20C Storage Temperature 0C Storage Temperature

10C Storage Temperature RT Storage Temperature

40C Storage Temperture 55C Storage Temperature

Discharge @ 0oC

3.42

3.44

3.46

3.48

3.5

3.52

3.54

3.56

3.58

3.6

0 3 6 9 12 15 18 21 24 27 30


Mid

-Pio

nt V

olta

ge (V

)

-20C Storage Temperature 0C Storage Temperature

10C Storage Temperature RT Storage Temperature

40C Storage Temperture 55C Storage Temperature

Discharge @oC

SAFT Yardney

• Stable mid-point voltages with a maximum of 20-30 mV depression after 27 months.• Consistent with relatively higher capacity fade, mid-point voltages are lower for YTP cells, once gain

attributable to low temperature electrolytes.



2.5

2.7

2.9

3.1

3.3

3.5

3.7

3.9

4.1

4.3

0 2 4 6 8

Discharge Capacity (AHr)

Cel

l Vol

tage

(V)

Discharge Capacity Prior To Storage at 23C

Discharge Capacity Prior To Storage at 0C

Discharge Capacity After 6 Month Storage






Cell Stored on the Buss at 50% SOC at 10oC

1.4 Amp Charge current (C/5) to 4.1 VTaper Cut-Off at 0.140 A (C/50)

1.4 Amp Discharge Current (C/5) to 3.0 V

Discharge Characteristics

2.0

2.5

3.0

3.5

4.0

4.5

0 1 2 3 4 5 6 7 8 9 10Discharge Capacity (AHr)

Cel

l Vol

tage

(V)

Initial Characterization Discharge Capacity Prior To Storage Discharge Capacity After 6 Month Storage Discharge Capacity After 12 Month Storage Discharge Capacity After 18 Month Storage Discharge Capacity After 24 Month Storage Discharge Capacity After 30 Month Storage Discharge Capacity After 36 Month Storage

Stored on the Buss at 50% SOC at 10oC

Yardney cells

Yardney Cells

Discharge at 23oC Discharge at 0oC



Cells on Uninterrupted Storage at 10oC SAFT Cells

2.0

2.5

3.0

3.5

4.0

4.5

0 1 2 3 4 5 6 7 8 9 10 11Discharge Capacity (AHr)

Cel

l Vol

tage

(V)

Discharge Capacity Prior To Storage at 23C Discharge Capacity Prior To Storage at 0C Discharge Capacity at 0C After 33 Month Storage

Cell Stored on the Buss at 50% SOCTemperature = 10oC



Discharge at 0oC

2.0

2.5

3.0

3.5

4.0

4.5

0 1 2 3 4 5 6 7 8 9 10 11Discharge Capacity (AHr)

Cel

l Vol

tage

(V)

Discharge Capacity Prior To StorageDischarge Capacity After 33 Month Storage

Cell Stored on the Buss at 50% SOCTemperature = 10oC



Initial Capacity = 9.7637 Ahr Capacity after 33 Months = 9.6106 Ahr (98.43 %)

Discharge at 23oC



2.0

2.5

3.0

3.5

4.0

4.5

0 1 2 3 4 5 6 7 8 9 10Discharge Capacity (AHr)

Cel

l Vol

tage

(V)

Discharge Capacity Prior To Storage Discharge Capacity After 33 Month Storage



2.0

2.5

3.0

3.5

4.0

4.5

0 1 2 3 4 5 6 7 8 9 10 11

Discharge Capacity (AHr)C

ell V

olta

ge (V

)

Discharge Capacity Prior To Storage at 23C Discharge Capacity Prior To Storage at 0C Discharge Capacity at 0C After 33 Month Storage



• Capacity before storage at 0oC = 8. 6 Ah (88.5 % of Initial RT Value)

• Capacity at 0oC after 33 Months = 8.5 Ah(87.3 % of Initial RT Value)

Discharge at 0oCDischarge at 23oC

• Capacity before storage = 9.6Ah• Capacity after 33 Months = 9.5 Ah (98.5 %)

SAFT CellsCells on Uninterrupted Storage at -20oC

• Similar good performance from YTP cells subjected uninterrupted storage



Calendar Life Analysis and Projections



Mechanisms for Permanent capacity loss upon storage

• Li Loss– SEI growth (mainly at the anode) – SAFT analysis– isolation– sequestering

• Host material degradation– phase change (at the cathode? Yazami et al)– isolation/fracture– blocked sites

• Increased resistance– particle-particle – Separator– Receding carbon diluent in the cathode (LBL)– Reduced surface area/ Increased charge-transfer

• Other parasitic reactions– electrolytes/solvents (Oxidation: depends on state of charge)– Additives and impurities



SAFT ApproachCorrosion rate proportional to the electronic conductivity of SEI:

The SEI thickness increases due to the corrosion as:

• Plots of Storage period vs capacity loss, assumed entirely due to corrosion; Good correlation.

• May be improved by analyzing effects of increased SEI thickness on electrode kinetics (Ohmic and diffusion)



Scott’s (Medtronic’s) Approach Decoupling Calendar (T) and Cycle (C) dependence

• Reported better correlation with exponential dependence than parabolic

Scott et al, ECS October 2005.



Calendar Life Analysis

• Data fit to exponential dependence: Slightly better correlation correlation than parabolic dependence

• Available capacity : Initial capacity x exp -(fade factor x Number of days)

Number of days)

Storage of SAFT 9 AH Cells on Bus at 50% SOC

y = 100e-0.000043875407624x

y = 100e-0.000037559891266xy = 100e-0.000129771199732x

y = 100e-0.000132476307304x

70

75

80

85

90

95

100

105

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Storage Time (days)

% In

itial

Cap

acity

Discharge at 23oC

55oC

23oC



Yardney-Capacity Fade Rate

y = 0.000042987788974e0.021797242345331x

0.00E+00

4.00E-05

8.00E-05

1.20E-04

1.60E-04

2.00E-04

-30 -20 -10 0 10 20 30 40 50 60

Temp, oC

Fade

Fac

tor

Discharge at 23oC

• Capacity Fade at 55oC is higher than expected from (Arrhenius) extrapolation



Yardney Capacity Fade Rate (Arrhenius)

-4.80E+00

-4.60E+00

-4.40E+00

-4.20E+00

-4.00E+00

-3.80E+00

3 3.2 3.4 3.6 3.8 4

1000/T

Fade

Fac

tor

• Activation energy for the process contributing capacity fade may be calculated.



Fade factors from RT and LT DischargesCapacity Fade Rate

0.00E+00

2.00E-05

4.00E-05

6.00E-05

8.00E-05

1.00E-04

1.20E-04

1.40E-04

-30 -20 -10 0 10 20 30 40 50 60

Temp, oC

Fade

Fac

tor

Disch@ 0oC

Disch@ 20oC

SAFT Capacity Fade Rate

-5.0

-4.8

-4.6

-4.4

-4.2

-4.0

-3.8

3 3.2 3.4 3.6 3.8 4

Temp, oCFa

de F

acto

r

Disch@ 20oC

Disch@ 0oC

• Fade factor calculated from capacities at 0oC is surprisingly lower than those obtained from RT discharges



Fade Factors for SAFT and YTP Cells

• High fade factor, attributable to the use of low temperature electrolytes

Capacity Fade Rate

0.00E+00

4.00E-05

8.00E-05

1.20E-04

1.60E-04

2.00E-04

-30 -20 -10 0 10 20 30 40 50 60

Temp, oC

Fade

Fac

tor

Discharge at 23oC

SAFT

YTP



Projected Calendar Life of Li Ion Cells

• Possible to get > 80% capacity after 10 years of storage at <25oC.• Tests on going for further validation of the projections.

Projected capacities of SAFT cells at various storage temperatures

55

65

75

85

95

105

0 365 730 1095 1460 1825 2190 2555 2920 3285 3650 4015 4380

Storage time, days

Ava

ilabl

e ca

paci

ty, %

BO

L A

h

20 40 55

0 10 -20

55oC performance is less than projected

Verified thus far



Projected Calendar Life of Li Ion Cells

• Possible to get > 80% capacity after 10 years of storage at <25oC.• Tests on going for further validation of the projections.

Projected capacities of YTP cells at various storage temperatures

50

60

70

80

90

100

0 365 730 1095 1460 1825 2190 2555 2920 3285 3650 4015 4380

Storage time, days

Ava

ilabl

e ca

paci

ty, %

BO

L A

h



EIS as a function of storage

0.000

0.010

0.020

0.030

0.040

0.000 0.010 0.020 0.030 0.040

3 Month Storage6 Month Storage9 Month Storage12 Month Storage18 Month Storage27 Month Storage

Storage Temperature = 0oC

Z'

Storage at 0oC

0.000

0.010

0.020

0.030

0.040

0.050

0.060

0.070

0.000 0.010 0.020 0.030 0.040 0.050 0.060 0.070

Initial3 Month Storage6 Month Storage9 Month Storage12 Month Storage15 Month Storage18 Month Storage24 Month Storage27 Month Storage

Storage Temperature = 55 oC

Z'

Storage at 55oC

YTP CellsYTP Cells

• Increasing series impedance with storage, more noticeable at high temperatures.• Marginal increase in the low frequency loop, but no change in the high frequency loop.• Analyses based on two relaxation loops.



0.00

0.20

0.40

0.60

0.80

1.00

1.20

0.00 0.50 1.00Z' (Ohms)

-Z"

(Ohm

s)Anode MeasurementCathode MeasurementTotal Cell MeasurementSum of anode and cathode

Temperature = 23oC

EIS of Individual Electrodes

• Cathode impedance significant at lower impedances.

• Consistent with the DC polarization behavior of lower limiting current

current densities for cathode, compared to anode.

3 Electrode cell- Type 1



Chf

Rlf

Clf

Rhf

Rs

• EIS data analyzed using Zsimpwin program.

• Good fit with the experimental data.

Z , Msd.Z , Calc.

unknown.txtModel : R(CR)(C(RW)) Wgt : Modulus

Z ', ohm1.80E-021.60E-021.40E-021.20E-021.00E-028.00E-036.00E-034.00E-032.00E-030.00E+00

- Z ''

, oh

m

1.00E-02

9.00E-03

8.00E-03

7.00E-03

6.00E-03

5.00E-03

4.00E-03

3.00E-03

2.00E-03

1.00E-03

0.00E+00

EIS Data Analysis

YTP Cells



23oC: y = 6.4001e0.0012x

40oC: y = 7.1628e0.0011x

0oC: y = 7.1272e0.0012x

-20oC: y = 6.1728e0.0013x

55oC: y = 7.9463e0.0013x

5

10

15

20

25

0 200 400 600 800 1000Storage Days,

Serie

s R

esis

tanc

e, m

Ohm

s

EIS Data Analysis-1

Series Resistance

• Series resistance increases more noticeably at 55oC.

• No change in the resistance of the high frequency loop.

0

0.4

0.8

1.2

1.6

2

0 200 400 600 800 1000

Storage Days,H

igh

Freq

uenc

y R

esis

tanc

e, m

Ohm

s

40oC

-20oC

25oC

High Frequency Resistance

YTP CellsYTP Cells



0oC: y = 6.638e0.0008x

-20oC y = 6.6419e0.001x

25oC: y = 5.3644e0.0011x

40oC y = 7.2344e0.0007x

55oC: y = 8.6345e0.0006x

5

10

15

20

0 200 400 600 800 1000

Storage Time, Days,

Seri

es R

esis

tanc

e, m

Ohm

s

EIS Data Analysis- Low Frequency Resistance

• Resistance of the low frequency loop increases with storage.

YTP Cells



0.0000

0.0100

0.0200

0.0300

0.0400

0.0500

0.0000 0.0100 0.0200 0.0300 0.0400 0.0500

Initial

33 Month Storage

Z"

Z'

YTP – After 33 months @ –20oC

0.0000

0.0100

0.0200

0.0300

0.0400

0.0500

0.0000 0.0100 0.0200 0.0300 0.0400 0.0500

Initial

33 Month Storage

Z"

Z'

YTP – After 33 months @ 0oC

• Marginal increase in the series resistance (attributed to electrolyte)• No change in resistance from high frequency loop but slight increase in the increase in the resistance of low frequency loop.• Does it imply that the thickness of the cathode SEI remains the same upon aging, same upon aging, but its charge transfer (kinetic) properties deteriorate?deteriorate?

EIS of cells on Uninterrupted Storage



0.000

0.003

0.006

0.009

0.012

0.015

0.010 0.013 0.016 0.019 0.022 0.025Re, Z, (Ohms)

Im, Z

, (O

hms)

-20oC 40oC

0oC 23oC

10oC

• Two relaxation processes followed by diffusion.

EIS of SAFT CellsAfter 3 months storage

Type 2 Cells



0.00

0.30

0.60

0.90

1.20

1.50

1.80

0.00 0.30 0.60 0.90 1.20 1.50 1.80

Z' (Ohms)

-Z"

(Ohm

s)

1

23

4

3 Electrode cell- SAFT

• Here also, cathode impedance is significant at lower frequencies.

EIS of Individual Electrodes- SAFT Cells



EIS as a function of storage-Type 2 cells

0.000

0.004

0.008

0.012

0.016

0.020

0.000 0.010 0.020 0.030 0.040 0.050 0.060 0.070 0.080

Initial3 Month Storage6 Month Storage9 Month Storage12 Month Storage15 Month Storage18 Month Storage27 Month Storage

Storage Temperature = 0 oC

Z'

0.000

0.005

0.010

0.015

0.020

0.000 0.020 0.040 0.060 0.080 0.100 0.120 0.140 0.160 0.180 0.200

Initial

3 Month Storage6 Month Storage9 Month Storage

12 Month Storage15 Month Storage27 Month Storage

Storage Temperature = 55oC

Z'

Storage at 55oC

SAFT Cells

Storage at 0oC

SAFT Cells

• Scatter in the impedance data, attributed to the cell case being polarized; Also observed under other test conditions and with different types of cells with such design.

• High impedance is an artifact and was not confirmed from DC discharge data.• EIS analysis still possible, while correcting for the high series resistance.



Summary• Lithium ion cells have thus far shown impressive storage

characteristics at low to warm storage temperatures– Over 90% capacity available at ambient and low storage

temperatures.– Retain good low temperature capability after storage.– Marginal increase in the impedance, possibly from cathode

interface.

• Lithium ion batteries show good promise to meet the needs of long-life space missions (or terrestrial applications, e,g biomedical) but require continued validation from such real-time tests.



Acknowledgments

The work described here was carried out at the Jet Propulsion Laboratory (JPL), California Institute of Technology, for the ESRT Space Rated Li-ion Batteries Technology Program, under contract with the National Aeronautics and Space Administration (NASA).

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