cese november 13, 2009 jai prakash center for electrochemical science and engineering department of...

CESE November 13, 2009November 13, 2009

Jai Prakash

Center for Electrochemical Science and EngineeringCenter for Electrochemical Science and Engineering

Department of Chemical and Biological EngineeringDepartment of Chemical and Biological EngineeringIllinois Institute of TechnologyIllinois Institute of Technology

Electrochemical and thermal Electrochemical and thermal characterization of Li-ion batteriescharacterization of Li-ion batteries


Li-ion cell reactionsLi-ion cell reactions

2 m

MCMB

2 m

MCMB

Oxide

1 m

Metal oxide cathodeMetal oxide cathodeLiMOLiMO22

Graphite anodeGraphite anode

LiP

F6

/EC

,DM

C

High volumetric energy/power densitiesHigh volumetric energy/power densities


Limitations of Li-ion cellsLimitations of Li-ion cells

High power performance High power performance Cell impedance)Cell impedance)

Cycle life Cycle life Cell impedanceCell impedance

Thermal safety Thermal safety Structural stability of delithiated oxideStructural stability of delithiated oxide Cell impedance produces heatCell impedance produces heat

CostCost


Typical Changes in Li-ion Cell EIS with TimeTypical Changes in Li-ion Cell EIS with Time

Impedance rise is associated with interfacial arcImpedance rise is associated with interfacial arc

Most of the impedance is attributed to the positive electrodeMost of the impedance is attributed to the positive electrode

EIS for G2.60C55.A215.33.28.26.G.T.

0

0.005

0.01

0.015

0.02

0.025

0.03

0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04

Zreal, ohms

-Zim

ag,

oh

ms

Characterization t = 0

RPT #1 t = 4 weeks

RPT #2 t = 8 weeks

RPT #3 t = 12 weeks

RPT #4 t = 16 weeks

RPT #5 t = 20 weeks

RPT #6 t = 24 weeks

RPT #7 t = 28 weeks

RPT #8 t = 32 weeks

RPT #9 t = 36 weeks

mid-freq min

high freq min

EIS for G2.60C55.A215.33.28.26.G.T.

0

0.005

0.01

0.015

0.02

0.025

0.03

0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04

Zreal, ohms

-Zim

ag,

oh

ms

Characterization t = 0

RPT #1 t = 4 weeks

RPT #2 t = 8 weeks

RPT #3 t = 12 weeks

RPT #4 t = 16 weeks

RPT #5 t = 20 weeks

RPT #6 t = 24 weeks

RPT #7 t = 28 weeks

RPT #8 t = 32 weeks

RPT #9 t = 36 weeks

mid-freq min

high freq min


(003) reflections are weak or absent (003) reflections are weak or absent in oxide surface layersin oxide surface layers

5 nm Surface Film

~ 5-10 nm

HR-TEM of cycled oxide particlesHR-TEM of cycled oxide particles

LiNiO2-typeLixNi1-xO-type


Electrochemical Model ApproachElectrochemical Model Approach

Porous electrode model

Solid electrolyte interface (SEI) and interfacial oxide film included in the model

Diffusion through the electrolyte, SEI film, interfacial oxide, and bulk oxide considered

Butler-Volmer relation used for electrochemical reaction

AC impedance model constructed for Li-ion cell


Governing equations for the AC impedance modelGoverning equations for the AC impedance model

Linear perturbation Linear perturbation

complex analysiscomplex analysis

0 0 0 )' ( R Ij t j tjc c c c c e c c c e

00

c cc c

dDD D c

dc

1 tanh tanh-

tanh tanh

sbbs ibs

si sisbsbs

si sbs ib

si sisb

D j jdU KK D D DdcZ

z F D j D j jK

D D D

Numerical solution of a set of coupled differential equationsNumerical solution of a set of coupled differential equations

Kinetic impedance and lithium diffusion in active particlesKinetic impedance and lithium diffusion in active particles

2 2

2 2( ) ( )( )m

o a a

m

o oa a a am

nk

c

k FcRT j

F Fk k c

RT RT

Z


Simulation and prediction for the positive electrode Simulation and prediction for the positive electrode

0

5

10

15

20

25

0 5 10 15 20 25

Z' (Real) ohm.cm2

Z"

(Im

) o

hm

.cm

2 simulation

Experimental

0123456

0 4 8 12Z' (Real) ohm.cm2

-Z" (

Im)

oh

m.c

m2

4.00 m1.55 m0.37 m

0123456

0 4 8 12Z' (Real) ohm.cm2

-Z" (

Im)

oh

m.c

m2

4.00 m1.55 m0.37 m

0123456

0 5 10 15

-Z"

(Im

) o

hm

.cm

2

DLi Cathode

3.510-9 cm2/s1.710-9 cm2/s

0123456

0 5 10 15

-Z"

(Im

) o

hm

.cm

2

DLi Cathode

3.510-9 cm2/s1.710-9 cm2/s

0

10

20

30

0 5 10 15 20

-Z"

(Im

) O

hm

.cm2

20 nm oxide layer

10 nm oxide layer

0

10

20

30

0 5 10 15 20

-Z"

(Im

) O

hm

.cm2

20 nm oxide layer

10 nm oxide layer

Oxide layerLi diffusion

Particle size Electrolyte conductivity


Safety Concerns of Li-ion BatteriesSafety Concerns of Li-ion Batteries

• Large-scale batteries for electric and hybrid vehicles

• Thermal runaway

-High power discharge

-Overcharge

-Abusive and cell-shorting conditions

• Heat and pressure build-up within the cell

• Cell fire caused by the flammable electrolyte


Thermal runaway produces fire in Li-ion cellsThermal runaway produces fire in Li-ion cells

Peter Roth (Sandia National Lab)Peter Roth (Sandia National Lab)

18650 Li-ion cell18650 Li-ion cell


Understanding Thermal Runaway in Li-ion Cells: Understanding Thermal Runaway in Li-ion Cells: A Fire TriangleA Fire Triangle


In-situIn-situ studies of thermal effects in Li-ion cells studies of thermal effects in Li-ion cells during normal cycling using IMCduring normal cycling using IMC

Current C/20 C/10 C/5 C/1

Qanode

mJ.cm-2

61 54 27 -74

Qcathode

mJ.cm-2

-84 -93 -110 -214

-30

-20

-10

0

10

20

30

40

50

60

70

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

x in LixNi0.8Co0.15Al0.05O2

Hea

t Rat

e,

uW.c

m-2

-30

-20

-10

0

10

20

30

40

50

60

70

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

x in LixNi0.8Co0.15Al0.05O2

Hea

t Rat

e,

uW.c

m-2

Charge

Discharge


DSC features of Mag-10 anode at various SOCDSC features of Mag-10 anode at various SOC

-17

-15

-13

-11

-9

-7

-5

-3

-1

1

60 110 160 210 260 310 360

Temperature, oC

No

rma

lize

d H

ea

t R

ate

, W

/g

Li0C6

Li0.18C6

Li0.37C6

Li0.57C6

Li0.7C6

Li0.9C6

SEI dec

ompo

sitio

n

SEI dec

ompo

sitio

n


Enthalpy vs. the amount of intercalated lithium in Enthalpy vs. the amount of intercalated lithium in the secondary SEI film formationthe secondary SEI film formation

-3000

-2500

-2000

-1500

-1000

-500

0

0 0.2 0.4 0.6 0.8 1

x in LixC6

de

lta

_H

, J

/g

1600 J/g for Mag-101600 J/g for Mag-10

The formation of a secondary The formation of a secondary SEI film consumes about 0.37 LiSEI film consumes about 0.37 Li


DSC and XRD of DSC and XRD of LiNi0.8Co0.15Al0.5O2 cathode at various SOC

0

1

2

3

4

5

6

7

8

9

50 100 150 200 250 300 350

Temperature, oC

No

rmal

ize

d H

eat

Flo

w (

exo

up

), W

/g

100%

50%

20%

70%

0%

Peak shift

- 941 J/g

- 730 J/g

- 709 J/g

- 352 J/g

- 150 J/g

H (J/g)

0

1000

2000

3000

4000

5000

55 60 65 70 75Angle, 2

Inte

nsit

y, c

ou

nts

25oC

250oC

225oC

200oC

175oC

150oC

100oC

10

7

01

8

11

0

11

3


Thermal studies of LiThermal studies of Li0.360.36NiNi0.80.8CoCo0.150.15AlAl0.050.05OO22 (CDL) With and (CDL) With and

Without Electrolyte using ARCWithout Electrolyte using ARC

Flash point of EC: 150oC

SHR dramatically increased from 150oC is due to the combustion of the electolyte with released O2 from delithiated cathode

0

50

100

150

200

250

300

0 500 1000 1500 2000 2500 3000

Time, min

Tem

per

atu

re,

oC

Electrolyte

CDL w/o electrolyte

CDL w/electrolyte

CDL w/all components


A conceptual road map for the thermal runaway A conceptual road map for the thermal runaway in Li-ion cellsin Li-ion cells

Need nonflammableNeed nonflammableelectrolyteselectrolytes

Cathode SEI/Elect. Cathode SEI/Elect.

O2 Evolution

T> 85oC

Solvent/Salt H = 200 J/g H = 300 J/g

LiNi0.8Co0.2O2 /Elect. H = 500 J/g

T > 180oC

T > 200oC

T > 660oC

LixC6 /PVDF/O2 /Elect.H = 1500 J/g Fire

Aluminum MeltdownH = -395J/g

High Rate Abusive Conditions Internal Shorts

Anode SEI/Elect.H = 350 J/g

T> 85oC

Solvent/Salt H = 200 J/g

T > 140oCT > 140oC H = 300 J/g


T > 180oC

oC

T > 660oC





Need stable cathodeNeed stable cathode

Need nonflammableNeed nonflammableelectrolyteselectrolytes

Cathode SEI/Elect. Cathode SEI/Elect.

O2 Evolution

T> 85oC



T > 180oC

T > 200oC

T > 660oC





T> 85oC


T > 140oCT > 140oC H = 300 J/g


T > 180oC

oC

T > 660oC





T> 85oC



T > 180oC

T > 200oC

T > 660oC





T> 85oC


T > 140oCT > 140oCT > 140oCT > 140oC H = 300 J/g


T > 180oC

oC

T > 660oC





Need stable cathodeNeed stable cathode

Stable SEI filmsStable SEI films


Approaches to improve thermal safety of Li-ion cells Approaches to improve thermal safety of Li-ion cells

Use of additives to form stable SEI film » Stable SEI film decomposes at higher temperature

» Avoids the secondary SEI formation

» Delay the initiation of thermal runaway

Thermally stable cathodes» Stable spinel oxides

» Core-shell cathodes (Hanyang university)

Nonflammable electrolytes» Flame retardant additives

» Nonflammable solvents


Effects of VC, VEC and LiBOB additives on the Effects of VC, VEC and LiBOB additives on the thermal behavior of anode thermal behavior of anode

-5

-4

-3

-2

-1

0

60 110 160 210 260 310 360

Temperature (oC)

Hea

t ra

te,

Exo

up

(W

/g)

2wt % VEC

2 wt % VC

2wt % LiBOB

No additive

-2

-1

0

60 80 100 120 140 160 180 200Temperature (oC)

Hea

t ra

te,

Exo

up

(W

/g) 2wt % VEC

2 wt % VC

2wt % LiBOB

No additive


Electrolyte modification: FR additivesElectrolyte modification: FR additives

Cathode

0

0.8

1.6

2.4

3.2

4

50 100 150 200 250 300Temperature, oC

Hea

t F

low

, W/g

EX

O U

P

Without HMTPWith 1.5 wt% of HMTP

216 oC

241 oC

0

0.5

1

1.5

2

50 100 150 200 250 300

Temperature, oC

Hea

t F

low

, W/g

EX

O U

P

Without HMTPWith 1.5 wt% of HMTP

235 oC

243 oC

120 oC131 oC

Anode

N

PN

P

NP

OCH3

OCH3H3CO

H3CO

OCH3H3CO

Hexa-methoxy-cyclo-tri-phosphazene(HMTP)

N

PN

P

NP

OCH3

OCH3H3CO

H3CO

OCH3H3CO

Hexa-methoxy-cyclo-tri-phosphazene(HMTP)


Core-Shell approach to improve thermal safetyCore-Shell approach to improve thermal safety

50 100 150 200 250 300-25

0

25

50

75

100

125

150

175

200

225

Temperature (oC)

Delayed Reaction

Thermal Runaway Start

Core Shell cellCore cell

Sel

f H

eat

Rate

(oC

/min

) Temperature (oC)50 100 150 200 250 300-25

0

25

50

75

100

125

150

175

200

225

Temperature (oC)

Delayed Reaction

Thermal Runaway Start

Core Shell cellCore cell

Sel

f H

eat

Rate

(oC

/min

) Temperature (oC) 50 100 150 200 250 300 3501E-3

0.01

0.1

1

10

100

1000

Thermal runaway delayed by ~50oC delay

Reaction start (Cathode + Electrolyte)

Anode reaction (Decomposition of SEI)

Core ShellCore

Self

He

at

Rate

(o C

/min

)

Temperature (oC)

5050ooC delayC delay ARCARC

0

10

20

30

40

50 100 150 200 250 300 350 400

Temperature (oC)

Core-Shell charged to 4.3V

SOA cathode Charged to 4.3V

0

10

20

30

40

50 100 150 200 250 300 350 400

Heat

Flo

w (W

/g)

Core-Shell charged to 4.3V

SOA cathode Charged to 4.3V

5050ooC delayC delay

DSCDSC

Shell

Core

Shell

Core

Li[NiLi[Ni0.50.5MnMn0.50.5]O]O22

LiNiLiNi0.80.8CoCo0.10.1MnMn0.10.1OO22


AcknowledgmentsAcknowledgments

Dr. Evren Gunen Dr. H. Bang Dr. Hui Yang Dr. C. Lee

Dr. D. Dess (ANL) Dr. K. Amine (ANL) Prof. Y. K. Sun (Hanyang U., S.

Korea

cese november 13, 2009 jai prakash center for electrochemical science and engineering department of...

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