Li-ion Pouch Cell Designs;

Are They Ready for Space

Applications?

by

Eric Darcy

NASA-JSC

For the

Large Li-ion Battery Technology and

Application Symposium

of the

Advanced Automotive Battery Conference

8 Feb 2012

Orlando, FL

https://ntrs.nasa.gov/search.jsp?R=20120000040 2018-06-23T15:18:29+00:00Z

Outline Li-ion Pouch Cells

• Various Space Applications

• Pouch cell design evaluation

• Cell lot uniformity, why that’s important – Soft Short Screening

• Performance at 4C Discharge Rates

• Pouch Corrosion

• Forward plans – Cycle life durability

– Seals

– Manufacturing quality

• Conclusions

Current EVA Batteries

Rechargeable EVA Battery Assembly (REBA)

Nickel Metal Hydride (NiMH)

Pistol Grip Tool (PGT) Battery

Nickel Metal Hydride (NiMH)

Helmet Light (EHIP) Battery

Nickel Metal Hydride (NiMH)

Simplified Aid For EVA Rescue (SAFER) Battery

Lithium Manganese Dioxide (Li-MnO2)

Long Life Battery (LLB) for EMU

Lithium ion (Li-ion)

3

Critical Manned Spacecraft Batteries • Spacesuit (Li-ion first flight in 2011)

– 20V, 35Ah, 50 cycle, 5 yr life

– Power all life support systems of the spacesuit

• Robonaut (proposed) – 96V, 26Ah, few cycles, 5 yr life

– Eventually operates side-by-side with spacewalkers

• Orion Crew Exploration Vehicle (201?) – 120V, 30Ah, 3000 cycles, 3 yr life

– 6-man capsule

• International Space Station (Li-ion planned for 2017)

– 120V, 120 Ah, 38,000 cycles, 6.5 yr life

– Main power source during LEO eclipses

• VASIMR (proposed) – 425V, 50 kWh discharged in 15 minutes

– Main power for RF generator firings

• Safety Requirements – Two-fault tolerant to most catastrophic

hazards

– Electrolyte leakage and cell internal shorts hazards controlled by a defined process that applies all reasonable mitigating measures

Assessment of Cell Designs

• All 4 are mature cell designs, made in high volume production lines

• All 4 provide a blend of high power and energy density capability

# Vendor P/N Mass (g)

Rated Discharge Capacity (Ah)

Standard Charge Regime Max Discharge

1 A123 PHEV 480 20 3.6V at C/2 with C/50 taper current limit

80A to 2.0V

2 Dow Kokam

SLPB75106100 165 8 4.2V at C/2 with C/50 taper current limit

32A to 2.7V

3 EIG C020 425 20 4.15V at C/2 with C/50 taper current limit

80A to 2.5V

4 LG Chem P1 383 15 4.15V at C/2 with C/50 taper current limit

60A to 2.8V

Test Plan for Assessment of Cell Designs

• Acceptance Testing – Visual, OCV, AC Impedance, mass, dimensional

– Pouch isolation resistance

– Soft short (OCV bounce back after deep discharge)

• Capacity performance – Capacity/Energy vs rate

• at ambient T, C/5, C/2, C, 2C, 4C with 3 cells per design,

• all charging at manufacturer recommended rate

• Cycling performance – Capacity/Energy vs cycle number

• 4C discharge, C/2 charge at ambient T for >100 cycles

• Evaluate cell design and manufacturing quality – Seal leak rate and compare to 18650 crimp seal rates

• Seal cells in Al laminate bag with dual element impulse heat sealer

• Then thermally cycling (vs not) for 3 weeks

• Sample gas trapped in outer bag

• Measure trace concentrations of electrolyte components via GC/MS to calculate leak rate in volume/time

– Compare leak rates per Wh, seal perimeter

– Corrosion susceptibility

– Destructive Physical Analysis (Tear down)

EIG Cell Discharging at 80A

4.0

3.8

3.6

3.4

3.2

3.0

2.8

2.6

Vo

lta

ge

, V

798796794792790788786784

Elapse Time, min

-80

-60

-40

-20

0

Cu

rren

t, A

Cell Voltage, Current vs TimeEIG 20Ah Cell Design p/n C020s/n 2385, 2386, 23874C (80A) discharge at RT

Voltage 2385 Current 2385 Voltage 2386 Current 2386 Voltage 2387 Current 2387

Comparisons of Demonstrated Performance

• DK has highest specific energy (~160 Wh/kg) at the 4C-rate – However, also has highest temperature rise (28 C)

• EIG has highest energy density (~319 Wh/L) at the 4C-rate – 2nd highest specific energy (~150 Wh/kg)

Vendor PN

4C rate

Energy

Average

mass

Specific

Energy Length Width Thickness Volume

Energy

Density

Wh g Wh/kg mm mm mm L Wh/L

A123 PHEV 55.01 509.6 107.9 227 161 7.2 0.26314 209.1

DK SLPB75106100 26.34 165.0 159.6 102 106 7.8 0.08433 312.3

EIG C020 64.48 429.4 150.2 216 130 7.2 0.20218 318.9

LG P1 51.62 382.5 135.0 226 165 5.5 0.2051 251.7

4C specific energy and energy density comparison

Variations in as Received OCVs

0.00%

0.50%

1.00%

1.50%

2.00%

2.50%

A B C D

Sdev%

Range%

3s Range%

Vendor

A

B

C

D

Variations in as received Mass

0.00%

0.50%

1.00%

1.50%

2.00%

2.50%

3.00%

3.50%

A B C

Sdev%

Range%

3s Range%

Vendor

A

B C

Soft Short (Large Cell Design)

3.025

3.03

3.035

3.04

3.045

3.05

3.055

3.06

0.00 5.00 10.00 15.00

N2-596-Y-1

N2-596-Y-2

N2-596-Y-3

N2-596-Y-4

N2-596-Y-5

N2-596-Y-6

N2-596-Y-7

N2-596-Y-8

N2-596-Y-9

N2-596-Y-10

3.025

3.03

3.035

3.04

3.045

3.05

3.055

3.06

3.065

3.07

0.00 5.00 10.00 15.00

N2-596-Y-11

N2-596-Y-12

N2-596-Y-13

N2-596-Y-14

N2-596-Y-15

N2-596-Y-16

N2-596-Y-17

N2-596-Y-18

N2-596-Y-19

N2-596-Y-20

V

o

l

t

s

,

V

V

o

l

t

s

,

V

Days Days

4 cells out of 20 had declining OCV between days 10 and 14

14-day OCV bounce back after deep discharge (constant voltage to 3.0V)

Vendor A OCV Bounce Back 3.0

2.9

2.8

2.7

OC

V,

V

14121086420

Days

OCV recovery vs days after deep CV discharge at minimum operating voltage to a taper current limit of C/50, while at 23 degC.Cells with declining OCVs have soft (high impedance) short

Vendor C OCV Bounce Back 3.04

3.02

3.00

2.98

2.96

2.94

2.92

2.90

OC

V,

V

2520151050

Days

OCV recovery vs days after deep CV discharge at minimum operating voltage to a taper current limit of C/50, while at 23 degC.Cells with declining OCVs have soft (high impedance) short.

DPA Results of Failing Cells

• Cells failing the OCV bounce back test were from lots

made on consecutive days

– Cells made on other dates passed all acceptance tests

• OCV bounce back test after deep discharge (soft short

test) was effective at non-destructively identifying cells

with defects (in case of worst performing cell, defect was

confirmed by DPA)

– 2 large halos detected on one anode,

• one with a crystalline piece of FOD consisting of Fe, Mg, Si, Al

• And with a small piece of Al NOD

SEM/EDS

1 2 3 4 5 6 7 8 9 10

keV

0

10

20

30

40

50

60

70

80

90

cps/eV

C

O F

Mg

Al

Si P

S K Fe

Fe

Cu

Cu

Crystalline FOD consists of Fe, Mg, Al, and Si

SEM/EDS of NOD

• Piece of Al debris on anode

• Found near the bigger FOD

1 2 3 4 5 6 7 8 9 10

keV

0

10

20

30

40

50

60

70

80

cps/eV

C

N

O

F

Al

Si

Cl

Cl

Ca

Ca

Cu Cu Zr

Zr Zr

S S

K

K

Na

Pouch Corrosion • Procedure

– Polarize Al layer of pouch to the negative potential of the cell

– All four cell designs tested for up to 2 months

• Results – Within 2 weeks, the

pouch corrosion sites on Vendor D cell developed several wide, black blisters

– The cell pouch no longer appeared tightly fitted around the cell electrode stack

Pouch Corrosion (cont)

• Vendor C Results – Within 4 weeks, the pouch

corrosion sites on cell developed, one black and one small, gray blister, both on the corners

– The cell pouch no longer appeared tightly fitted around the cell electrode stack

• Results on the other 2 designs – No evidence of pouch

corrosion after 2 months

• What cell design attributes do pouch corrosion resistant cells have that the others don’t?

Other Examples of Pouch Corrosion

• Defective inner isolation layer of

the laminate pouch results in

corrosion of the Al layer

• Polarizing the Al layer to the (-)

terminal is a quick test method

Nylon layer

Melt extrusion

Corrosion site Butter-Cup Side

Flat side

Polyethylene layers

Corrosion spots

Cross section of corrosion spot

Photo courtesy of NREL

Conclusions To Date

• Current Li-ion pouch cells designs for electric vehicle market are

offering

– Over 150 Wh/kg and 300 Wh/L at 15 minute (4C) discharge rates

• Verified by test with 2 cell designs

• Soft short test (or OCV bounce back test) is an excellent

discriminator of manufacturing quality

– Preventing battery assembly with cells with charge retention issues

– Help precluding battery assembly with cells with latent defects

• DPA’s are also an excellent way to assess manufacturing quality

• Two cell designs were resistance to our pouch corrosion test

• Planned testing will determine their readiness for the demands of

crewed spacecraft

– Manufacturing quality

– Effectiveness of the seals

– Durability of performance