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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
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
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…
Institute for Applied Materials -
Energy Storage Systems (IAM-ESS)
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)
Institute for Applied Materials -
Energy Storage Systems (IAM-ESS)
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!
Institute for Applied Materials -
Energy Storage Systems (IAM-ESS)
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
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Energy Storage Systems (IAM-ESS)
7
a
c
Functional materialsComponents
DeviceApplication
Fatigue: Multi length-scale complexity
17.09.2014
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
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)
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“
Institute for Applied Materials -
Energy Storage Systems (IAM-ESS)
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.
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Energy Storage Systems (IAM-ESS)
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)
Institute for Applied Materials -
Energy Storage Systems (IAM-ESS)
12
Electrode-specific contributions to fatigue
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.
Institute for Applied Materials -
Energy Storage Systems (IAM-ESS)
13
Electrode-specific contributions to fatigue
17.09.2014
NCA againstLithium referenceNCA againstgraphiteGraphite againstLithium referenceNCA againstLithiumGraphite againstLithium
Lithium exchanged [mAh/cm2]
Cyclovoltamograms of full cells with reference electrode (NCA againstgraphite) in combination with half-cell data (NCA and graphit against Li).
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Energy Storage Systems (IAM-ESS)
14
Electrode-specific contributions to fatigue
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 -
Cell balancing 2,1 % ± 0,01 %1)
Fatigued Capacity loss
Cathode 9,0 % ± 1,3 %1)
Cell balancing 10,0 % ± 2,0 %1)
1) Maximum deviation within three experimentsLithium exchanged [mAh/cm2]
Anode excess
Institute for Applied Materials -
Energy Storage Systems (IAM-ESS)
15
in operando observation of anode excess
17.09.2014
Lithium exchanged [mAh/cm2]
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“.
Institute for Applied Materials -
Energy Storage Systems (IAM-ESS)
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
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Energy Storage Systems (IAM-ESS)
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
Institute for Applied Materials -
Energy Storage Systems (IAM-ESS)
18
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)
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 %
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
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)
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
Institute for Applied Materials -
Energy Storage Systems (IAM-ESS)
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
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Energy Storage Systems (IAM-ESS)
22
Neutron radiography and tomography
17.09.2014
Verticalcut
Horizontalcut
Visualisation by assignment of absorption levels to a false-color scheme
A. Senyshyn et al., J. Power Sources 2 (2012) 126
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Energy Storage Systems (IAM-ESS)
23
Neutron radiography and tomography
17.09.2014
A. Senyshyn et al., J. Power Sources 2 (2012) 126
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Energy Storage Systems (IAM-ESS)
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
Institute for Applied Materials -
Energy Storage Systems (IAM-ESS)
25
Selected examples
Neutron tomography: electrolyte level changes during charge/discharge
17.09.2014
charged discharged
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Energy Storage Systems (IAM-ESS)
26
Selected examples
Combined neutron tomography & diffraction
17.09.2014
Fresh Cell Fatigued Cell (1000 cycles)
see „Highlights“ @ http://www.iam.kit.edu/ess
Institute for Applied Materials -
Energy Storage Systems (IAM-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
O. Dolotko, J. Electrochem. Soc. 159 (2012) A2082
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Energy Storage Systems (IAM-ESS)
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 %
O. Dolotko, J. Electrochem. Soc. 159 (2012) A2082
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.
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Energy Storage Systems (IAM-ESS)
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
Institute for Applied Materials -
Energy Storage Systems (IAM-ESS)
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
O. Dolotko, J. Electrochem. Soc. 159 (2012) A2082
unstable operation
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Energy Storage Systems (IAM-ESS)
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
Institute for Applied Materials -
Energy Storage Systems (IAM-ESS)
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
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Energy Storage Systems (IAM-ESS)
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
Institute for Applied Materials -
Energy Storage Systems (IAM-ESS)
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
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Energy Storage Systems (IAM-ESS)
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.
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
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)
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.
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Energy Storage Systems (IAM-ESS)
38
Acknowledgement
17.09.2014
Natalia BramnikSusana DarmaOleksandr DolotkoMarkus HerklotzKarin KleinerMichael LangMartin MühlbauerKristian NikolowskiLars RiekehrAnatoliy SenyshynFlorian Sigel
&
all SFB members
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