Les rôles clés des polymères dans les électrodes ... · PDF fileLes...

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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

CB/Binder network

AM

AM : 90 %wCB : 5 %wB : 5 %wB : 5 %wPorosity 30–40 %v50-100 µm

LiLi++

LiLi++

LiLi++

Liqu

id e

lect

rolyte

ee--

ee--

ee--

Curr

ent

colle

ctor

3

The different contributions (simulation)The different contributions (simulation)

Srinivasan, V., and Newman, J. 2004, J. Electrochem. Soc.

ee--

ee--

ee--

Curr

ent

colle

ctor

LiLi++

Sepa

rato

r /

Liqu

id e

lect

rolyte

LiLi++

LiLi++

LixFePO4 // Li cell

x.LiLi++ + FePO4 + x.ee-- → LixFePO4

2C, 75µm

∑= IRU i

4


ee--

ee--

ee--

Curr

ent

colle

ctor

LiLi++

Liqu

id e

lect

rolyte

LiLi++

LiLi++ee--

2C, 75µm

5

ee--

LiLi++


2C, 75µm

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PEO

PVdF-HFP (LiPLIon)PEO/EC+PC

PEO/PVdF-HFP/EC+PC

PEO/PVdF-HFP/EC+PC+LiFSI

PEO

PVdF-HFP (LiPLIon)PEO/EC+PC

PEO/PVdF-HFP/EC+PC


What is the role of the binder ?What is the role of the binder ?

Lithium Lithium trivanadatetrivanadate ; ; LiTFSILiTFSI ; 2; 2--3.3V; 3.3V; 20°C; 20°C; SwagelokSwagelok test cell, C/5 ratetest cell, C/5 rate

D. Guy, et al., Advanced Materials, 2004.

+ 50%

For a unique AM…

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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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1. Binders are polymers1. Binders are polymers

Original (NON-aqueous) BindersPoly(vinylidene fluoride) ⇒ standard industrial binder Li-Ion batteries, < 5 V

Poly(vinylidene fluoride–co-hexafluoropropylene) ⇒ Bellcore technology , < 5 V

Poly(tetra fluoro ethylene) ⇒ wet process for laboratory , < 5 V

Poly(ethylene oxyde) ⇒ dry LMP batteries, < 4 V vs Li°/Li+

Poly(methyl methacrylate) ⇒ gel, < 4.6 V

Dias, F.B., et al., 2000, J. Power Sources. Quatartone, E., et al., 1998, Solid State Ionics. Tarascon, J.M., et al., 1996, Solid State Ionics.

-100

-80

-60

-40

-20

0

20 120 220 320 420 520Température (°C)

Pert

e de

mas

se (%

)

PVdF-HFP poudre

PEO poudreW

eigh

t loss

%PEO

PVdF-HFPC CH2

COOCH3

CH3 n

-(CH2-CH2-O)n-

-(CH2-CF2)n-

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A big issue Environment, cost, safety concerns => switch from nonnon--aqueousaqueous to aqueousaqueousprocessing techniques

Drawbacks:• Stability of the AM in water ?

• Water elimination

Aqueous Binders for aqueous processing

NN--methylmethyl--22--pyrrolidonepyrrolidone

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Styrene-butadiene rubber latex(SBR latex), elastomer (binder).

-(CH2-CH)n-(CH2-CH=CH-CH2)p-

-(CH2-CH)n-

HO-C=O

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








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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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-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


Re-structuration of the slurries after constant shear.

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OutlineOutline








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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


PEOPEO/PVdF-HFP

PEO/EC+PC

PEO/PVdF-HFP/EC+PC


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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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.

70-µm LiFePO4 electrode

18.721.961 M LiPF6 in EC/DME = 3:7

7.243.661 M LiPF6 in EC/DEC = 3:7

κ0mS/cm

ηmPa s

Viscosity and conductivity of

electrolyte at 25°C.

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[(-CH2-CH=CH-CH2-)m-(CH2-CH)n- [(-CH2-CH-C-O-C8H17-)m-(CH2-CH)n-

CNO

Styrene-butadiene copolymer 2-ethylhexyl acrylate-acrylonitrile copolymer

SBR 2EHA-AN

The The wettabilitywettability

Kaneko M., et al., 2007, J. Solid State Electrochem.

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Mechanical properties: the binder's jobMechanical properties: the binder's job

Adhesion to the current collector

Cohesion of the composite electrode by particle-to-particle bridging

TEM image : Anne-Claire GAILLOT (IMN)

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Modelling ?Modelling ?

Σ = number ofbridging chains

f = forceof the bond

Model of the Mechanical toughness in polymer-based composite materials for aeronautics, automotive… applications:

Strength of composite Strength of interface σ = f Σ

C. Creton (ESPCI), J.F. Gérard (INSA Lyon), L. Léger (Coll. France),

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Role of the binder on the mechanical propertiesRole of the binder on the mechanical properties

W. Porcher., et al. 2010, J. power Sources.

The calendaring

mass of binder per total surface area of the grains

(mg / m²)Σ = number ofbridging chains

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The assembly

(SEM of fractured surface Particle delamination)

Strain at break is less than 2% with PVdF.

Particle delamination from the PVdF matrix is a mechanism for stress relief.

S. Babinec., et al. J. power Sources, 174 (2007) 508.

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Yoo, M., et al. 2003, Chem. Mater. Yoo, M., et al. 2004, Chem. Mater. Yoo, M., et al. 2003, Polymer.

Graphite and amorphous carbons negative composite electrode

PVdF F atoms H atoms from graphite ⇒ scrapping load < 1,000gweak hydrogen bonds

PVdF F atoms C atoms from amorphous carbon ⇒ scrapping load > 10,000gsemi-ionic / covalent bonds

The scratch testf = forceof the bond

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The SEI / The SEI / interphase interphase layer (5 layer (5 –– 10 nm)10 nm)

From M. Winter

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Improvement of efficiency with aqueous bindersImprovement of efficiency with aqueous binders

Graphite in 1 mol dm−3 LiClO4 EC:DMCImprovement of efficiency:

- more uniform covering of graphite grains with Polyacrylate than with PVdF

- COO- groups enhancement of the de-solvation / intercalation of Li+ ions

Komaba S. et al., Electrochem. Solid-State Lett., 2009 ; J. Power Sources, 2009.

SEM after first cycle

Li carbonates

XPS of Graphite before cycling

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ConclusionConclusion

Polymers for Li-Ion electrodes

- Binder

- Processing aid (dispersant, thickener)

- Participate in the electronic wiring

- Participate in the ionic wiring

- Participate in SEI formation and efficiency

Critical dependence on the nanometer scale,

-Poorly defined !

-Properties of polymers in ultra thin layers are different from the bulk !

-Studies to be done on well defined polymers

⇒Strong need for fundamental research

“TODAY” !TEM image : Philippe MOREAU (IMN)

CF

CBAM

B

Electrolyte

5%w ⇔ 1-2%v

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AcknowledgementsAcknowledgements

D. Guyomard, J. Gaubicher, P. Moreau, N. Dupré, J-C. Badot, R. Bouchet,

M. Deschamps, J-L. Monfort, A. Nazri, S. Levasseur,

D. Guy, E. Ligneel, W. Porcher, C. Fongy, K. Seid, V. Gaudefroy, P. Mongondry, S. Desaever, D.

Mazouzi

for friendly and fruitful discussions.

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