Storage Characteristics of Li-Ion Batteries - NASA Battery Workshop

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

(Supported by ESRT Technology Program)

NASA Battery Workshop Huntsville, AL November 14-16, 2006 ELECTROCHEMICAL TECHNOLOGIES GROUP


Why Long-Life Batteries?

Landers, Rovers and Planetary Orbiters Probes to Outer Planets • Mission Life: 5-10 y • Cruise time : 6-12 Y • Long Cycle Life • Long calendar Life –

> 30,000 cycles

LEO satellite • Mission Life: 5-10 y • Long Cycle life –

> 30,000 cycles

GEO Satellite • Mission Life: ~10 y • Long Cycle life –

> 2,000 cycles

ESMD Missions Pressurized and Lunar Habitat Unpressurized planetary landers ELECTROCHEMICAL TECHNOLOGIES GROUP


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.

ELECTROCHEMICAL TECHNOLOGIES GROUP


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 16 o

Capacity (AHr)

Dsicharge @ 23 C

14

-20C Storage Cell SO118

0C Storage Cell SO128

12





10 8 6 4 2 0 0

3

6

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


Storage Characteristics of Li Ion Cells Storage of SAFT Cells- Discharge at RT 120

110 o

% Initial Capacity

DischargeTemperature = 23 C

100

90

80

70







60 0

6

12

18

24

30

36

42

48

54

60

Storage Time (Months)

• Over 90% capacity retained after about 54 months at temperatures temperatures < 40oC. • Tolerant to storage at 55oC ELECTROCHEMICAL TECHNOLOGIES GROUP


SAFT DD Cells- Capacity at 0oC After Storage 14

o








12

Capacity (AHr)

10

8

6

4

2

0 0

3

6

9

12

15

18

21

24

27

30

33

36

39

42

45

48

51

54



Storage Characteristics of Li Ion Cells Storage of SAFT cells -Discharge at 0oC 120

110 o

% Initial Capacity

Discharge Temperature = 0 C 100

90

80







70

60 0

6

12

18

24

30

36

42

48

54

60


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

Storage Characteristics of Li Ion Cells Storage of YTP Cells -Discharge at 25oC 12

o

Temperature = 23 C

Capacity (AHr)

10

8

-20C Storage Cell YO74

0C Storage Cell YO89





6

4

2

0 0

3

6

9

12

15

18

21

24

27

30

33

36

39

42

45

48

51



Storage Characteristics of Li Ion Cells YTP Cells - Discharge at 20oC 120 o


% Initial Capacity

110

100

90

80 -20C Storage Cell YO74






70

60 0

6

12

18

24

30

36

42

48

54

60

Time (Months)

• 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 ELECTROCHEMICAL TECHNOLOGIES GROUP

Storage Characteristics of Li Ion Cells Storage of YTP Cells -Discharge at 25oC 12

o

Temperature = 23 C

Capacity (AHr)

10

8







6

4

2

0 0

3

6

9

12

15

18

21

24

27

30

33

36

39

42

45

48

51



Storage Characteristics of Li Ion Cells YTP Cells - Discharge at 0oC 120

o

Discharge Temperature = 0 C

% Initial Capacity

110

100

90

80

70







60 0

6

12

18

24

30

36

42

48

54

60

Time (Months)

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

Storage Characteristics of Li Ion Cells Mid-point voltages - Discharge at 0oC SAFT 3.63

Yardney

3.6

o

Discharge @ 0 C

Discharge @oC 3.58 3.56

Mid-Piont Voltage (V)

Mid-Point Voltage (V)

3.61

3.59

3.57 -20C Storage Temperature

0C Storage Temperature


RT Storage Temperature

3.55 40C Storage Temperture

3.54 3.52 3.5 3.48

-20C Storage Temperature


3.46


RT Storage Temperature

40C Storage Temperture



3.44 3.42

3.53 0

3

6

9

12

15

18


21

24

27

30

0

3

6

9

12

15

18

21

24

27

30


• 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.



Discharge Characteristics Discharge at 23oC

Discharge at 0oC 4.3

4.5

o

o

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

Stored on the Buss at 50% SOC at 10 C 4.1

Yardney Cells

4.0

1.4 Amp Charge current (C/5) to 4.1 V Taper Cut-Off at 0.140 A (C/50) 1.4 Amp Discharge Current (C/5) to 3.0 V

3.9

Cell Voltage (V)

Cell Voltage (V)

3.7

3.5

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

3.0

2.5

3.5 Discharge Capacity Prior To Storage at 23C

3.3

Discharge Capacity Prior To Storage at 0C Discharge Capacity After 6 Month Storage

3.1

Discharge Capacity After 12 Month Storage

2.9

Discharge Capacity After 18 Month Storage Discharge Capacity After 24 Month Storage

2.7


Yardney cells


2.0

2.5

0

1

2

3

4

5

6

7

8

9

10

0

2

4

6

8

Discharge Capacity (AHr)




Cells on Uninterrupted Storage at 10oC Discharge at

SAFT Cells

23oC

4.5

Discharge at 0oC

4.5

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

4.0

4.0

3.5

3.5

Cell Voltage (V)

Cell Voltage (V)

Cell Stored on the Buss at 50% SOC o Temperature = 10 C


3.0

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

Discharge Capacity Prior To Storage Discharge Capacity After 33 Month Storage 2.5

2.5


Initial Capacity = 9.7637 Ahr Capacity after 33 Months = 9.6106 Ahr (98.43 %) 2.0

2.0 0

1

2

3

4

5

6

7

8

9

10

11

0

1

2

3

4 5 6 7 Discharge Capacity (AHr)

8

9

10

11




Cells on Uninterrupted Storage at -20oC Discharge at

SAFT Cells

23oC

Discharge at 0oC

4.5

4.5

1.8 Am p Charge current (C/5) to 4.1 V Taper Cut-Off at 0.180 A (C/50) 1.8 Am p Discharge Current (C/5) to 3.0 V

4.0

4.0

3.5

Cell Voltage (V)

Cell Voltage (V)


3.0 Discharge Capacity Prior To Storage

3.5

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

Discharge Capacity After 33 Month Storage 2.5

2.5

2.0 0

1

2

3

4

5

6

7

8

9

10


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

•

2.0 0

1

2

3

4

5

6

7

8

9

10

11


• 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)

Similar good performance from YTP cells subjected uninterrupted storage ELECTROCHEMICAL TECHNOLOGIES GROUP


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 Approach Corrosion 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) ELECTROCHEMICAL TECHNOLOGIES GROUP


Scott’s (Medtronic’s) Approach Decoupling Calendar (T) and Cycle (C) dependence Scott et al, ECS October 2005.

• Reported better correlation with exponential dependence than parabolic ELECTROCHEMICAL TECHNOLOGIES GROUP


Calendar Life Analysis Storage of SAFT 9 AH Cells on Bus at 50% SOC 105 Discharge at 23oC

100

% Initial Capacity

95

23oC

90 85 80

55oC y = 100e-0.000037559891266x

75

y = 100e

y = 100e-0.000132476307304x

70 0

200

y = 100e-0.000129771199732x

-0.000043875407624x

400

600

800 1000 1200 1400 1600 1800 2000

Storage Time (days)

• 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 Characteristics of Li Ion Cells Yardney-Capacity Fade Rate 2.00E-04

Discharge at 23oC y = 0.000042987788974e0.021797242345331x

Fade Factor

1.60E-04 1.20E-04 8.00E-05 4.00E-05 0.00E+00 -30

-20

-10

0

10

20

30

40

50

60

Temp, oC

•

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


Storage Characteristics of Li Ion Cells Yardney Capacity Fade Rate (Arrhenius) -3.80E+00

Fade Factor

-4.00E+00 -4.20E+00 -4.40E+00 -4.60E+00 -4.80E+00 3

3.2

3.4

3.6

3.8

4

1000/T •

Activation energy for the process contributing capacity fade may be calculated. ELECTROCHEMICAL TECHNOLOGIES GROUP


Fade factors from RT and LT Discharges SAFT Capacity Fade Rate

1.40E-04

-3.8

1.20E-04

-4.0

1.00E-04

Fade Factor

Fade Factor

Capacity Fade Rate

o

Disch@ 20 C

8.00E-05 6.00E-05 4.00E-05

-4.2

o

Disch@ 20 C

-4.4 -4.6

Disch@ 0oC

2.00E-05

o

-4.8

Disch@ 0 C

0.00E+00 -30

-20

-10

0

10

20

Temp, oC

30

40

50

60

-5.0 3

3.2

3.4

3.6

3.8

4

Temp, oC

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



Fade Factors for SAFT and YTP Cells Capacity Fade Rate 2.00E-04

o

Discharge at 23 C

Fade Factor

1.60E-04 1.20E-04 YTP

8.00E-05 SAFT

4.00E-05 0.00E+00 -30 -20 -10

0

10

20

30

40

50

60

Temp, oC

•

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


Storage Characteristics of Li Ion Cells Projected Calendar Life of Li Ion Cells Projected capacities of SAFT cells at various storage temperatures

Available capacity, %BOL Ah

105

95

85

75

65

20

40

55

0

10

-20 Verified thus far o

55 C performance is less than projected

55 0

365

730

1095 1460 1825 2190 2555 2920 3285 3650 4015 4380

Storage time, days

• Possible to get > 80% capacity after 10 years of storage at 80% capacity after 10 years of storage at