Fatigue of Batteries - Technische Universität Darmstadt...in operando techniques for life-time...

KIT – University of the State of Baden-Wuerttemberg and National Research Center of the Helmholtz Association

HELMUT EHRENBERG INSTITUTE FOR APPLIED MATERIALS – ENERGY STORAGE SYSTEMS (IAM-ESS)

www.iam.kit.edu/ess

Investigations on Fatigue of Li-ion batteries



www.iam.kit.edu/ess


Introduction into Fatigue of Li-ion batteries: General aspects

Materials challenges and the cell level

in operando techniques for life-time studies:

Neutron tomography and diffraction on 18650-type batteries

Conclusion

Institute for Applied Materials -

Energy Storage Systems (IAM-ESS)

3

Fatigue:

Degradation of performance with operation

Number of charge/discharge cycles or time

Cap

acity

Failure

Conditioning/Formation (e.g. SEI)

Operation: Fatigue and Ageing

17.09.2014

Loss of capacityIncrease of internal resistanceVoltage fade…



4

Failure modes: „Thermal runaway“

Serious safety concerns at the EOL (end of life)

17.09.2014

Li0.5CoO2 1/2 LiCoO2 + 1/6 Co3O4 + 1/6 O2T ≥ 200°C

Li1-xCoO2 is intrinsically unstable in the overcharged state (x > 0.5)

Enhanced materials for safer operation (NCM, NCA)Design freezing (~7 y in cars, ~10 y in planes)



5

Safety aspects: energy within a Li-ion battery

17.09.2014

A charged Li-ion battery stores about the same energyas a stick of dynamite of the same size!



6

A charged Li-ion battery stores about the same energyas a stick of dynamite of the same size!

> 2000 Cycles(80% Capacity)

0.5 Cycle(0% Capacity)

17.09.2014

Safety aspects: energy within a Li-ion battery



7

a

c

Functional materialsComponents

DeviceApplication

Fatigue: Multi length-scale complexity

17.09.2014



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Conclusion



9

„Anode“

LixC6Electrolyte

Li1-xCoO2„Cathode“

Separator „Short cuts“„Loss of porosity“„Dendrite formation“

„Decomposition“(oxidation or reduction)

„Ionic conductivity“

„Dissolution“

„Redox reactions“(atomic rearrangements)

„Lattice strain“

17.09.2014

Li-ion batteries: Materials challenges

Cu Al

All components suffer from „Ageing“ & „Fatigue“Materials interactions: „Solid Electrolyte Interface/Interphase“, SEI

„Metal dissolution“, „Loss of adhesion“



10 17.09.2014

Li-ion batteries: contributions to fatigue

Vetter, J., et al., Ageing mechanisms in lithium-ion batteries.J. Power Sources 147 (2005) 269-281.



11

Electrode-specific contributions to fatigue

17.09.2014

2,7 V3,6 V4,0 V e- e-

Li O CNi, Co, Al

NCA against Lithium

Graphite against Lithium

Lithium exchanged [mAh/cm2]0 0.5 1

3

2

1

0

4

3

2

1

Relative shift of the states-of-charge of cathode and anode results in capacity losses on full-cell level (example: NCA against graphite)



12


17.09.2014

Not-fatigued (aged) graphite

ChargeNCA against Lithium

“Fatigued” graphite against Lithium

Lithium exchanged [mAh/cm2]

Overvoltages from the negative electrode result in a higher level of Li-extraction from the positive electrode and, therefore,more pronounced fatigue.



13


17.09.2014

NCA againstLithium referenceNCA againstgraphiteGraphite againstLithium referenceNCA againstLithiumGraphite againstLithium


Cyclovoltamograms of full cells with reference electrode (NCA againstgraphite) in combination with half-cell data (NCA and graphit against Li).



14


17.09.2014

Highly fatigued Capacity loss

Cathode 28,5 % ± 1,3 %1)

Cell balancing 9,7 % ± 0,7 %1)

Aged cell Capacity loss

Cathode -


Fatigued Capacity loss

Cathode 9,0 % ± 1,3 %1)


1) Maximum deviation within three experimentsLithium exchanged [mAh/cm2]

Anode excess



15

in operando observation of anode excess

17.09.2014


Anode excess

2θ/°

newfatigued4.20V4.15V4.10V4.05V4.00V3.95V

3.90Vocv

Neutron diffraction:

More intermediate LiC12 in the „fully“ charged state due to fatigue, i.e.less Li in the anode in fatigued statedue to „anode excess“.



16

Reveal working and degradation mechanisms

Idealized model systems

(Single processes)Real energy storage devices

(high level of complexity)

17.09.2014

e.g. UHV conditionsXPS, TEM

in operando studies



17

Cycle life testing and fatigue analysis

17.09.2014

O. Dolotko, J. Electrochem. Soc. 159 (2012) A2082

Commercial Li-ion cell of 18650-type (2600 mAh, 3.0 - 4.2 V)„Fresh“ - single cycle„Fatigued“ at 25°C and 50°C (200, 400, 600, 800, 1000 cycles)Cycling 3.0 - 4.2 V, CCCV, 1C



18

Cycle-life testing and fatigue analysis

17.09.2014


Commercial Li-ion cell of 18650-type (2600 mAh, 3.0 - 4.2 V)

0 200 400 600 800 10001900

2000

2100

2200

2300

2400

2500

2600

21.9 %

25°C 50°C

Cap

acity

, mA

h

Number of cycles

12.8 %



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Conclusion



20

in operando techniques for life-time studies

Pronounced materials interactions: real battery conditions essentialSpecific degradation mechanisms:

Correlation between effects and causeInfluence of load profile

Proceeding of fatigueCell design concepts

Non-destructive methodsPenetration capabilityTime- and spatial resolutionDetailed information (minor changes)Sensitivity to light elements (H, Li, C, O)Complementary post mortem analysis

17.09.2014

High-energy synchrotron &neutron radiation



21

Neutron radiography and tomography

17.09.2014

ANTARES (research reactor FRM-II), L/D=800Field of view 100x100 mm2 ~ 100 µm pixel resolution

penetration with different distribution of attenuation

object 180x 2D neutron transmission images

Radontransformation

A. Senyshyn et al., J. Power Sources 2 (2012) 126

3D reconstruction



22


17.09.2014

Verticalcut

Horizontalcut

Visualisation by assignment of absorption levels to a false-color scheme




23


17.09.2014




24

Selected examples

X-ray tomography reveals shifts with SOC

17.09.2014

Discharged Charged

Displacement in radial direction: 80 µm to 100 µmDisplacement in axial direction: up to 80 µm



25

Selected examples

Neutron tomography: electrolyte level changes during charge/discharge

17.09.2014

charged discharged



26

Selected examples

Combined neutron tomography & diffraction

17.09.2014

Fresh Cell Fatigued Cell (1000 cycles)

see „Highlights“ @ http://www.iam.kit.edu/ess



27

Neutron Powder Diffraction

17.09.2014

20

40

60

80

100

20 40 60 80 100 120 140-505

observed calculated difference Bragg position

7)6)5) 4)

3)

Angle 2θ, degs.

Nor

mal

ised

inte

nsity

, %

1)

"fresh" Li-ion battery(charged to 4.20V)λ=1.5482(1) A

(b) (1) - cathode (LixCoO2)

(2) - anode (graphite)

(3) - anode (LiC12)

(4) - anode (LiC6)

(5) - current collector (Cu)

(6) - current collector (Al)

(7) - steel housing (Fe)

Measured at SPODI, FRM II, Garching




28

Anode: Ratio of LiC6 and LiC12 in charged state

17.09.2014

Phase fraction of LiC6is lower for the fatigued 25 °C cell, while the LiC12 value is higher.

Reduction of lithium inside the anode:25 °C � 26 %50 °C � 15 %


More intermediate LiC12 in the „fully“ charged state due to fatigue, i.e.less Li in the anode in fatigued state due to „anode excess“ by shift ofthe voltage window.Elevated temperature: less overvoltage and less fatigue.



29

Lithium occupation in LixCoO2 (cathode)

18650 cell, cycling at 1C, 4.2 – 2.0 V, 25 °C

17.09.2014

Capacity loss 21,9%(from electrochemical cycling)

discharged

charged

Active lithium loss(20,8 %)

0 200 400 600 800 100030

35

40

45

50

55

60

65

70

75

80

85

90

95

100Li

occ

upat

ion,

%

Number of cycles

stable

unstableoperation



30

Lithium occupation in LixCoO2 (cathode)

Li occupation in the discharged state higher at 50°C.Safety problems due to low Li-content in the carged state also at highertemperature!

17.09.2014

18650 cell, cycling at 1C, 4.2 – 3.0 V, 25 °C and 50 °C


unstable operation



31

Lattice strain in layered oxides LCO, NCM, NCA

17.09.2014

2.86

2.85

2.84

2.83

a / Å

1 0.5 0.15 0.5 0.85

x Li in LixNi1/3Co1/3Mn1/3O2

14.5

14.4

14.3

14.2

14.1

14.0

c / Å

101

100

99

98

97

Vol

/ Å

3

2.86

2.85

2.84

2.83

2.82

2.81

a / Å

1.0 0.5 0.0 0.5 1.0x Li in LixNi0.8Co0.2O2

14.4

14.2

14.0

13.8

c / Å

100

98

96

94

Vol

/ Å

3

Phase 1 Phase 2

LiNi1/3Co1/3Mn1/3O2Phase behaviour of LiNi0.8Co0.2O2

charge

discharge

Oxidation of oxygen



32

Comparison of lattice strain in LCO, NCM, NCA

17.09.2014

NCA

SOC [%]0 100

NCA

Capacity [mAh]0 350096

102

14.0

14.5

2.88

2.80

V/Å3

c/Å

a/Å



33 17.09.2014

Lattice strain and microstructure: NCM

1 µm

200 nm

N. Kiziltas-Yavuz et al., Electrochim. Acta. 113 (2013) 313

SEM images of as-prepared Li(Ni1/3Co1/3Mn1/3)O2 powder



34 17.09.2014

Lattice strain and microstructure: NCM

300 nm

100 nm

N. Kiziltas-Yavuz et al., Electrochim. Acta. 113 (2013) 313

SEM images of Li(Ni1/3Co1/3Mn1/3)O2 after cycling between 3.0 and 4.2 V



35

Cathode fatigue

17.09.2014

Positive electrode materials are the only source of exchanged Li.Most serious limitation for the energy density of a cell.Restricted stability with respect to the Li-content (except LiFePO4).Details of the electronic structure play a crucial role for

cell voltage,electronic conductivity,stability range, band overlap: oxidation of oxygen,activitiy of specific ions (energy levels)and more…

Structure and composition gradients within one particle/crystallite, for example a NiO-type surface layer in NCA.One-phase or two-phase mechanisms.Significant structural distortions and volume changes.High probability for cracks, especially in blend cathodes, working overa broad voltage range.



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Conclusion



37

Conclusions

17.09.2014

Fatigue of Li-ion batteries has to be addressed on cell level.Capacity losses and internal resistance are determined by materials and balancing.Materials interactions are very pronounced in batteries.No individual optimization of materials, only within specific cells!

Dedicated methods are needed to investigate fatigue under real operation conditions.Data analysis is a specific challenge.Complementary methods are essential.Probably not all basic physical parameters can be measured.

Complex functionalities have to be consideredToo many degrees of freedom: only knowledge-based approaches are promising.



38

Acknowledgement

17.09.2014

Natalia BramnikSusana DarmaOleksandr DolotkoMarkus HerklotzKarin KleinerMichael LangMartin MühlbauerKristian NikolowskiLars RiekehrAnatoliy SenyshynFlorian Sigel

&

all SFB members

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Fatigue of Batteries - Technische Universität Darmstadt...in operando techniques for life-time...

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