unexpected negative impact of additives on degradation...
TRANSCRIPT
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© C
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Unexpected negative impact of additives on degradation mechanisms in commercial
Graphite/NMC lithium-ion pouch-cells
E.Bekaert§, F. Aguesse§, T. Waldmann*, M. Kasper*, N. Ghanbari *, C.
Chabrol#, S. Genies#, B. Pilipili Matadi#, L. Daniel#, M. Wohlfahrt-
Mehrens*
34th International Battery Seminar &
Exhibit
Fort Lauderdale, 23rd March 2017
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*
#
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1. CIC EnergiGUNE
2. Motivation
3. Batteries post-test analyses
4. Cell Characteristics
5. Analysis of the components
6. Proposition of degradation mechanism
7. Conclusion
Opening Date: Sept 2011
About 80 researchers
Electrochemical and Thermal Energy Storage
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Where are we...?
Vitoria-Gasteiz, capital of the Basque Country
Basic research Applied research Industrial dev.
CIC Visioning… Mission & vision definitionR&D value chain: CIC´s role and cooperation scheme in the Basque Environment.
UNIVERSITIES
TECH. CENTRES
Ma
in p
laye
rsPa
rtn
ers
COMPANIES
TECH. CENTRES
UNIVERSITIES
TRL1-3 TRL 4-5 TRL 6-84
5Confidential
✓ Synthesis laboratories (solid state and organic chemistry)
✓ Characterization laboratory (ICP-AES, TGA/DSC, FTIR, UV-vis…)
✓ Platforms (solid state NMR, XRD, EM…)
✓ Testing laboratory (potentiostats, Maccor, climatic chamber)
✓ Dry room (prototyping)
✓ Computational studies group
Research infrastructure:
CIC Visioning… top research facilities
Role of the storage - complexity of applications
Interdisciplinary of the energy storage
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Scales of Power
10000
1
10
100
1000
10k10 100 1k 100k
Cu
rren
t (A
)
Voltage (V)
Consumer Products
Aerospace
Military
Traction
Ships
UtilityHybrid Electric
Vehicles
Utility
Performance and Aging will be different for each single type of device, for each application and technologies.
* Courtesy of US DOT
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Post –Mortem analyses for validation
Motivation What is the driving force for post-mortem analysis?
❖ Better understanding of the reasons of a battery failure
❖ What are the main aging degradation mechanisms ?
❖ How can we use this knowledge to improve cell manufacturing ?
❖ Determination of the condition of use for an extended life.
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Batteries post-test analysisCritical steps for efficient analysis
1º) Observe
2º) Open
3º) Analyse
First aging before opening :
Steps for post-test analysis* :
▪ Calendar aging vs cycling aging
▪ Different SOC, DOD
▪ Cycling environment (temperature, humidity,
etc.)
9 * T. Waldmann and al J. Electrochem. Soc. 2016 volume 163, issue 10, A2149-A2164
Cell Characteristics Li-ion battery for high performance application
Selected system :
❖ NMC/graphite chemistry
❖ 16 Ah nominal capacity
❖ Pouch-cell
Separator:Z-folding
Stack of electrode
➢ Pristine battery as received from the manufacturer➢ 29 cells calendar aging
Selected cells for post-test:
Post test cells were chosen on the resultof the aging
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Post test study: Pristine cell
• Flaky graphite• no core-shell structure• SEI on top of electrode (not visible in SEM)
• spherical layered oxide + graphite• Lix(Ni0.41Mn0.37Co0.22)O2
• no core-shell structure• polycristalline material
• separator: Polyethylene• main electrolyte components
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Pristine: electrolyte composition
Main Solvant :
EC: Ethylene Carbonate
EMC : Ethyl Methyl Carbonate
Additives➢ 7%wt BP: Biphenyl (overcharge protection)
➢ 5%wt FEC: Fluoroethylene carbonate (SEI stabilisation)
➢ 2%wt VC: Vinylene carbonate (SEI stabilisation)
➢ 0.1%wt PS: Propane Sultone ( thermal stability)
1M LiPF6 in EC/EMC (1/1) + additives :
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Cell aging: Degradation of the performances during calendar aging
SOH based on CC-CV capacity measurement during Check Ups at 25ºC
Trends:SOH vs. time decreases faster with• higher SOC• higher temperature
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Post-test cell:
5ºC - SOC=100%
25ºC - SOC=100%
45ºC - SOC=100%
60ºC - SOC=100%
Influence of the temperature duringcalendar aging:
T[ºC] SOC[%] 50 90 100 Total
60 x2 x2 x3 7
45 x2 x3 x3 8
25 x3 x3 x3 9
5 x2 x3 5
Total 9 8 12 29
Aging Evaluation of the electrodes:
By comparing the resistance R* of the semi-loop
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No changefor E+
Increase ofresistancefor E-
✓ Interfacial impedance ↗ for the negative electrode✓ The positive electrode impedance is approximately constant
Deterioration of the graphite resistive properties is evidenced.Interfacial impedance increase is related to :- SEI growing- Li-plating deposit
Pag. 15
Battery opening and first analysisVisual observations
Fresh cell5ºC/ SOC=100% 25ºC/
SOC=100%45ºC/
SOC=100%
60ºC/ SOC=100%
Po
siti
veN
ega
tive
Sep
arat
or
color changes of cathode in case of Li deposition on anode
Li deposition
uncolor area of separator
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Battery opening and first analysisOrigin of Lithium deposition*
Li deposition
No Li deposition but uncolor area
with Check Ups
Without Check Ups
Gas Evolution Under Temperature
16* A. Iturrondobeitia and al, Post-Mortem Analysis of Calendar Aged 16 Ah NMC/Graphite Pouch Cells for EV Application, The Journal of Physical Chemistry, submitted
Positive Electrode: XRD
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SEM :
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✓ no relevant structural changes✓ no trace of cubic phase (NMC
cycling aging)✓ Lattice parameter variation in
agreement with literature*
✓ no morphological changes or alteration✓ some particles present cracks
✓ decrease of Li on cathodes✓ decrease of Mn on anodes
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ICP-OES:
Negative Electrode:
✓ increase of Li on anodes✓ presence of Mn on anodes
XRD
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SEM anode:
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✓ no relevant structural changes✓ no significant enlargement of the line (002) of
graphite✓ White deposite recover:decomposition
products due to side reaction during aging such as Li2CO3, LiF, Li3PO4 or Li4P2O7
✓ growth of the layer on top of the stable SEI
ICP-OES:
Li
P
O
C
Cu
Depth [µm]
Inte
nsi
ty (
a.u
.)
surf
ace
bu
lk
colle
cto
r
Depth-resolved multi-elemental analysis
Grimm-type discharge source
Calibration necessary~ 1 µm/min
2.5 mm
a) ECS Electrochem. Lett. 4 (2015) A100–A102.b) J. Phys. Chem. C. 120 (2016) 22225–22234.19
Development of GD-OES method for graphite anodes
Aging mechanism of calendar aging(Kokam Cell, 45ºC+60ºC, SOC=100%)
No metallic
Li
13.38 mass%
metallic Li
Calendar aging tests at 60°C
No metallic
Li
4.50 mass%
metallic Li
Calendar aging tests at 45°C
✓ Graphite electrodes harvested after calendar aging tests showed local white depositions.
✓ Performing GD-OES on different positions of each electrode revealed local deposition of metallic Li.
✓ Metallic Li is estimated across the first micrometer (based on the previously defined assumption).
a) ECS Electrochem. Lett. 4 (2015) A100–A102.b) J. Phys. Chem. C. 120 (2016) 22225–22234.
Quantities are normalized regarding the quantity of EC
✓ Dismutation of EMC DEC + DMC
✓ Degradation of EC in EGMC
Analysis of electrolyte:Gas chromatography–mass spectrometry (GC-MS)
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0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
EC+EMC+othercarbonates
VC FEC BP 1,3-PS
fresh
cal at 25°C
cal at 45°C
Biphenyl (BP) is stronglyconsumed
Analysis of electrolyte:
Quantities are normalized regarding the quantity of EC
0%
3%
5%
8%
10%
13%
VC FEC BP 1,3-PS
fresh
cal at 25°C
cal at 45°C
Gas evolution
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Influence of Biphenyl additive
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Biphenyl: (BP)✓ overcharge protection agent✓ irreversible electrochemical reaction in oxidation
BP polymerises on the cathode during overcharge and the liberated protons (H+)
migrate to the anode, generating hydrogen gas (H2)
Proposition of degradation mechanism:1. Initially homogeneous current repartition on the whole surface of the negative electrode during charge/discharge cycles performed at the beginning of the aging.
2. Storage of the cell at a state of charge of 100% and at high temperature
3. Degradation of electrolyte during the storage (high Tº, high Voltage)
4. Production of gas bubbles
5. Mask/isolation of zones on the surface of the graphite
6. Realization of the first intermediate check up to evaluate the loss of capacity : inhomogeneous current repartition on the surface of the graphite electrode during charge and discharge processes : concentration of the polarization on the border of the bubble
7. Appearance of Li-Plating on the border during charge processes
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Electrochemical characterisation:
Bottom
NMC φ 14mm
Separator φ 18mm
Gasket
Lithium φ 16mm
Spacer
Spring
Top
Electrolyte LP30
2032 coin-cell design
Li/NMC
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Electrochemical characterisation:
Bottom
Graphite φ 14mm
Separator φ 18mm
Gasket
Lithium φ 16mm
Spacer
Spring
Top
Electrolyte LP30
2032 coin-cell design
Li/Gr
Conclusion
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Lessons learned: ✓ Main aging mechanism on anode side✓ Check-ups can influence calendar aging tests
✓ Interfacial impedance increase with temperature✓ Lithium deposition during the Check Ups at 25ºC✓ Growth of SEI on anode✓ Dissolution of Mn from cathodes / migration to anodes✓ Consumption of cyclable Li in anode SEI, less Li in cathode, less Li intercalated in an anode✓ Consumption of Biphenyl additive. ✓ Gas evolution due degradation of additives✓ Formation of Inert area
Post-Test Analysis:Multidisciplinary approach :✓ Better understanding of the reasons of a battery failure✓ Determine the main aging degradation mechanisms✓ Provide knowledge to improve cell manufacturing✓ Determination of the condition of use for an extended life.
Li pouch Cell NMC/G:Main degradation phenomena concern the anodes
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Team involved:
Project ManagerDr. Lise Daniel
Disassembling & Electrochemicalcharacterization:Dr Sylvie GenièsDr. Isabel Gordeons-JimenésGrégory Si LarbiDavid Brun-Buisson
Support in all Characterizations:Bramy Pilipili Matadi PhD
XRD:Dr. Claude Chabrol
GCMS:Dr. Jean-Frederic Martin
7Li NMR:Dr. Michel Bardet
XPS/TOF-SIMS/AugerDr. Eric De Vito
Head of departmentDr. Margret Wohlfahrt-Mehrens
Project ManagerDr. Thomas Waldmann
Post MortemMichael Kasper
GD-OES method developmentNiloofar Ghanbari
Project ManagerDr. Emilie Bekaert
Post Mortem:Dr. Frederic AguesseDr. Amaia IturrondobeitiaDr. Emanuele Gucciardi
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Thank youMuchas graciasEskerrik askoMerciDziękujęDhanyawaadM goiBarak llahu fikShukriyaYAKNIYELEY
Emilie Bekaert
Tlf.: (+34) 945 297 108
www.cicenergigune.comhttp://www.cicenergigune.com/visita-virtual/index.htmlVisita 360ºhttp://www.cicenergigune.com/en/areas-investigacion/infraestructuras/ Infraestructuras