1 Bernard LESTRIEZ Les Les r r ô ô les cl les cl é é s s des des polym polym è è res dans res dans les les é é lectrodes lectrodes composites de composites de batterie batterie Li ion Li ion Colloque du GFP du 18 Mai 2010, Paris Institut des Matériaux Jean Rouxel
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1
Bernard LESTRIEZ
Les Les rrôôles clles clééss des des polympolymèères dansres dans les les éélectrodeslectrodescomposites de composites de batteriebatterie Li ionLi ion
Colloque du GFP du 18 Mai 2010, Paris
Institut des Matériaux Jean Rouxel
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The (+) or (The (+) or (--) composite electrode.) composite electrode.
Mixing the Active material withElectron-conductive agent (CB powder) ⇒ e- conductivityLiquid electrolyte within the porosity ⇒ Li+ conductivityPolymeric binder B ⇒ Cohesion and Adhesion
Polyacrylic acid (PAA), for adhesion strength to the current collector
Carboxymethyl cellulose (CMC), rheological aid
Liquid ElectrolyteCH2
CH2
O
OC=O
CH2
CH2
O
OC=O
CH3
LiPF6
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OutlineOutline
1. The usual and new binder combinations
2. Role of the binder on the processing
3. Role of the binder on the electronic conductivity
4. Role of the binder on the ionic conductivity
5. Role of the binder on the mechanical properties
6. Role of the binder on the SEI layer
7. Conclusions and Prospects
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ProcessingProcessing
Battery assembly
Calendaring
Drying
Liquid electrolyte
Typical speed for this machine: 5 m / min
Mixing AM+CB+B in a solvent
From CEA
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Instabilities in electrode slurriesInstabilities in electrode slurries
Measurement of settling rate (closed tubes)
Settling
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30 µm
30 µm
Under Shear
At Rest
Instabilities in electrode slurriesInstabilities in electrode slurries
Aggregation SEM (retrodiffusion mode)
Carbon
Active material
15Li, C.C., et al., 2006, J. Electrochem. Soc.
Dispersants for the aqueous processingDispersants for the aqueous processing (6000 g/mol)
Electronic conductivity
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a)
b)
2%m HPMC
1%m CMC
ThickenersThickeners
Porcher et al., J. Electrochem. Soc. 2009
HPMC does not prevent settling
COO-
COO-
COO-
COO-
COO-
COO-
COO-
260 nm
CMC (DS O.7, 250.000 g/mol)
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ThickenersThickeners
-50
0
50
100
150
200
0.01 0.1 1 10 100
Spe
cific
Cap
acity
(mA
h/g)
Discharge Rate (C)
HPMC2.7mAh.cm-2
CMC3.0mAh.cm-2
Thin0.4mAh.cm-2
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1
10
100
0 200 400 600 800 1000Time (s)
G' &
G'' (
Pa)
G'' CMCG' CMC
G'' HPMC G' HPMC
tf : G’ = G’’
HPMC ⇒ liquid-like
CMC ⇒ solid-like
ThickenersThickeners
Re-structuration of the slurries after constant shear.
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OutlineOutline
1. The usual and new binder combinations
2. Role of the binder on the processing
3. Role of the binder on the electronic conductivity
4. Role of the binder on the ionic conductivity
5. Role of the binder on the mechanical properties
6. Role of the binder on the SEI layer
7. Conclusions and Prospects
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The electronic conductivityThe electronic conductivity
e- electronic conductivity follows a percolation (ΦC) process
Wired AM particlesWired AM particles
D. Guy et al., 2006, J. Electrochem Soc
Below ΦC
Above ΦC
ΦC
Dependence of ΦC on processing and aspect ratio of the conductive additive.
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The percolation thresholdThe percolation threshold
ΦC dependence role of the binder during the processing.
PEOPEO/PVdF-HFP
PEO/EC+PC
PEO/PVdF-HFP/EC+PC
PEO/PVdF-HFP/EC+PC+LiFSI
PEOPEO/PVdF-HFP
PEO/EC+PC
PEO/PVdF-HFP/EC+PC
PEO/PVdF-HFP/EC+PC+LiFSI
Guy, D., et al., 2006, J. Electrochem. Soc.
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The The tunneling tunneling mechanismmechanism
P. Sheng, Phys. Rev. B 1980. I. Balberg, Carbon, 2002 (thermal fluctuation-induced tunneling model).
D. Guy, et al., 2006, J. Electrochem. Soc.
33 66w (nm), mean extrapolated valuew (nm), mean extrapolated value
Γ (mg of binder / m2 of CB surface)
log σ = log (σCB) - a Γ
ww
CB Binder
Tunnel junctions
Logρ ∝ w ∝ Γ
for Φ > ΦC
Narrow distribution of insulating gaps
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OutlineOutline
1. The usual and new binder combinations
2. Role of the binder on the processing
3. Role of the binder on the electronic conductivity
4. Role of the binder on the ionic conductivity
5. Role of the binder on the mechanical properties
6. Role of the binder on the SEI layer
7. Conclusions and Prospects
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The ionic conductivityThe ionic conductivity
oc κεκ β=
Li+ ionic conductivity κc
Influence the rate performance
A property difficult to measure.
κ0 bulk conductivity of the liquid electrolyte
ε void volume fraction of the porous electrode filled with electrolyte
β pore tortuosity
Patel, K.K., et al., 2003, J. Power Sources. Doyle, M., et al., 1996, J. Electrochem. Soc. Arora, P., et al., 2000, J. Power Sources. Doyle M., et al., 2003, J. Electrochem. Soc. W. Yu et al., 2006, J. Electrochem. Soc.