Polymers vs. liquids, gels and ionic liquid
electrolytes. Any winners?
M. Armand, P.G.Bruce, B. Scrosati, W.Wieczorek
Alistore ERI | www.alistore.eu
Présentation du 15 octobre 2009
Outline
• General status quo of present Li (ion) battery architecture
• Introduction to the field of modern electrolytes (concepts, transport
mechanisms, improvement strategy)
• Role of salt anions
• New types of salts
• Ionic Liquids
• Crystalline Electrolytes (P. Bruce)
• Composites (Ceramic, Anion receptors)
• Conclusions
Alistore ERI | www.alistore.eu
Présentation du 15 octobre 2009
Outline
• General status quo of present Li (ion) battery architecture
• Introduction to the field of modern electrolytes (concepts, transport
mechanisms, improvement strategy)
• Role of salt anions
• New types of salts
• Ionic Liquids
• Crystalline Electrolytes (P. Bruce)
• Composites (Ceramic, Anion receptors)
• Conclusions
Alistore ERI | www.alistore.eu
Présentation du 15 octobre 2009
Strategies for Li Batteries
Inorganic: LiFePO4, Li2Fe(Mn)SiO4
Medium capacity
“high” voltage
Positives:
Organic: Li2+xC6O6
Electrolytes:
Very large capacity
“low” voltage
New solutes, polymer (gels) ± ILs
Inorganic: Si
Very high capacity
Cu mandatory / binders?
Negatives:
Organic dicarboxylates
High capacity, 0.8 V
Al option, s elec ??
Présentation du 15 octobre 2009
Outline
• General status quo of present Li (ion) battery architecture
• Introduction to the field of modern electrolytes (concepts,
transport mechanisms, improvement strategy)
• Role of salt anions
• New types of salts
• Ionic Liquids
• Crystalline Electrolytes (P. Bruce)
• Composites (Ceramic, Anion receptors)
• Conclusions
Alistore ERI | www.alistore.eu
Présentation du 15 octobre 2009
Transport mechanisms
Liquid electrolytes:
transport of solvated
species
Polymer electrolytes:
transport by
solvation / desolvation
No net displacement of the host matrix
Ceramic electrolytes:
transport by ion hopping
Présentation du 15 octobre 2009
Gels
The Donor Number of the polymer repeat units vs. that of the solvent
DNsolvent > DNpolymer
Direct solvent-cation interaction
 solvent drag
DNPVF
DNpolymer > DNsolvent
Direct polymer-cation interaction
 no solvent drag
≈ 0 < DNcarbonates ≈ 15 < DNPEO ≈ 22
Présentation du 15 octobre 2009
Polymer Electrolytes
•
•
Li+
PEO
•
•
•
•
Electrodonor polymers
O,N,S (sufficient donor ability for
complexation)
Sufficient distance between sites
Amorphous
Polyethers good candidates
Low Tg (flexibility)
General classification
Polymer Comlexes
Poymer Gels
Polyelectrolytes (Single Ion Conductors)
Copyrights Marek Marcinek
Présentation du 15 octobre 2009
Solid Polymer Electrolytes Advantages
• non volatility,
• no decomposition at the electrodes,
• no possibility of leaks,
• use of metallic lithium in secondary cells (lithium dendrites growing on
the electrode surface would be stopped by the non-porous and solid
electrolyte),
• lowering the cell price (PEO is cheaper than organic carbonates; it could
be used as a binder for electrodes to improve the compatibility of
consecutive layers; moreover fabrication of such a cell would be easier –
cost),
• strengthening of cells thanks to the all-solid-state construction,
• shape flexibility,
•lowering the cell weight – non-volatile, all-solid-state cells don’t need
heavy steel casing,
• improved shock resistance,
• better overheat and overcharge allowance,
• improved safety!!!
Présentation du 15 octobre 2009
Solid Polymer Electrolytes Advantages
The most important and universal properties of polymeric electrolytes
for application in lithium cells:
• chemical and mechanical stabilities over a wide temperature range,
• electrochemical stability of at least 3-4 V versus a Li electrode;
especially important for battery applications
• low activation energies for conduction
• high cationic transport numbers
• good electrode - electrolyte characteristics
• ease of sample preparation.
Présentation du 15 octobre 2009
Polymeric electrolytes modifications
Methods of modification of polymeric electrolytes:
- random copolymers
- block copolymers
- comb-like copolymers
- polymer blends
- addition of liquid plasticizers
- crosslinking (UV, gamma, chemical)
- application of plasticizing salts
- addition of anion receptors:
– soluble Lewis acids
– supramolecular receptors
- polymer-in-salt materials
– well-designed crystalline polymer electrolytes (NEW)
– composites with inorganic fillers
– ceramic-in-polymers
– reversed phase systems (polymer-in-ceramic) (NEW)
Présentation du 15 octobre 2009
Electrolyte solvents
Generally an ideal electrolyte solvent should meet the following criteria:
• be able to dissolve lithium salts to sufficient concentration
• its viscosity should be low so fast ion transport can occur within electrolyte
• be inert to all cell components especially anode and cathode materials
• it should remain liquid in a wide temperature range (low melting and high
boiling temperature are desirable)
Présentation du 15 octobre 2009
Electrolyte solvents
The role of electrolyte is two, or sometimes threefold:
•It should provide ionic contact between electrodes allowing to close the circuit when the cell is
operational
•It should assure electronic and spatial separation of the positive and negative electrode in order to avoid
short-circuit and as a result – self discharge of the cell, which in some cases can be very spectacular (as
those of failed high power Li-ion cells)
•In case of electrochemical systems where electrode components are not the only reactants appearing in
the overall cell reaction, the electrolyte is the source (storage) of the remaining ones.
Présentation du 15 octobre 2009
(a) Optimization of ion conductivity in mixed
solvents: 1.0 M LiClO4 in PC/DME.
(b) Dependence of dielectric constant (ε)
and fluidity (η-1) on solvent composition.
Chemical Reviews, 2004, Vol. 104, No. 10
Alistore ERI | www.alistore.eu
Présentation du 15 octobre 2009
Electrolytes additives
According to the functions targeted, the numerous
chemicals tested as electrolyte additives can be
tentatively divided into the following three distinct
categories:
(1) those used for improving the ion conduction properties in
the bulk electrolytes;
(2) those used for SEI chemistry modifications; and
(3) those used for preventing overcharging of the cells…
….and thus improve SAFETY!!!!
Présentation du 15 octobre 2009
Donor Numbers
DN for solvents: propensity to give electrons pairs
(H of interaction to a reference Lewis acid)
CH2Cl2
2
EC,PC,
AN
THF
P(EO)
DMF
DMSO
Py
3
≈ 15
22
≈ 27
28
40
MeNO
0
The notion of DN for anions :
-
+
DN(X-) > DN(solvent)
 Role of  
-
+
DN(X-) < DN(solvent)
Présentation du 15 octobre 2009
Outline
• General status quo of present Li (ion) battery architecture
• Introduction to the field of modern electrolytes (concepts, transport
mechanisms, improvement strategy)
• Role of salt anions
• New types of salts
• Ionic Liquids
• Crystalline Electrolytes (P. Bruce)
• Composites (Ceramic, Anion receptors)
• Conclusions
Alistore ERI | www.alistore.eu
Présentation du 15 octobre 2009
Anions – „A Letter to Santa”
Properties of the salt used for battery applications are as follows:
• it should be able to completely dissolve in the applied solvent at
desired concentration and ions should be able to transfer through
the solution
•anion should be stable towards oxidative decomposition at the
cathode
• anion should be inert to electrolyte solvent
• both anion and cation should be inert towards other cell
components
• anion should be nontoxic and remains thermally stable at the
battery working conditions
Présentation du 15 octobre 2009
Anions-Role
• Control dissociation and conductivity
• Control transport numbers t+ /t• are an important part of SEI build-up
at +/- electrodes
• Control aluminium corrosion
Présentation du 15 octobre 2009
Classic Anions
ClO4-
BF4-
Explosive !
Toxic !
PF6-
AsF6-
SbF6-
Tendency to decompose according to equilibrium:
LiBF4  BF3 + <LiF>
LiPF6   PF5 + <LiF>
Fast reaction above 80°C
 Destruction of electrolyte and interfaces
Présentation du 15 octobre 2009
Conceptual Approach to Anion Design
“O” is not a favorable building block:
Strong Li—O interactions  ion pairing, ≠ ClO4-, BOBIf O present, F or CnF2n+1 is required
“N, C” are favorable:
Weak interactions Li—N but easy oxidation
Présentation du 15 octobre 2009
Diagonally Opposed Interests?
Organic chemistry
Enhance the activity of anions (SN)
+
+
Electrochemistry
Maximize the conductivity
-
-
Ionic processes
-
-
I- = 2,2 Å
Li+
 design of
polyatomic
anions
Présentation du 15 octobre 2009
Outline
• General status quo of present Li (ion) battery architecture
• Introduction to the field of modern electrolytes (concepts, transport
mechanisms, improvement strategy)
• Role of salt anions
• New types of salts
• Ionic Liquids
• Crystalline Electrolytes (P. Bruce)
• Composites (Ceramic, Anion receptors)
• Conclusions
Alistore ERI | www.alistore.eu
Présentation du 15 octobre 2009
Hückel anions…
Aromaticity 4n + 2 «  » electrons
X = N, C-CN, CRF, S(O)RF
pKA = 10-60
pKA = 10-20
Gain of > 1 eV by resonance
See P. Johansson et al
Physical Chemistry Chemical Physics, volume 6, issue 5, (2004).
Présentation du 15 octobre 2009
Cyanocarbons
pKA < -10!!
Stronger than 100% sulfuric acid
pKA < -3 corrodes glass
Présentation du 15 octobre 2009
Hückel anions…
DCTA
Stable to 3.8 V (La Sapienza, KZ)
inexpensive
Gives quite fluid ILs
Présentation du 15 octobre 2009
Gas Phase Ion Pair Dissociation Energies
Ion pair (g)
LiTDI
<
LiPDI
LiTDI
Li+ (g) + Anion- (g)
<
LiPDI
LiDCTA
LiDCTA
LiTFSI
<
LiTFSI
<
LiPF6
LiPF6
Excellent Theoretical Prediction
MP2/6-31G(d)
Scheers et al. 2009
Présentation du 15 octobre 2009
Most Stable Lithium Imidazole
Configurations
1.93 Å
1.88 Å
1.87 Å
1.92 Å
LiTDI
LiPDI
B3LYP/6-311+G(d)
Scheers et al. 2009
Présentation du 15 octobre 2009
LiTDI
(2-trifluoromethyl-4,5-dicyanoimidazole lithium
salt)
Important Benefits
•Easy, low-demanding, inexpensive, one-step, high yield
syntheses;
•Salts are pure, stable in air atmosphere, non-hygroscopic,
stable up to 250°C, easy to handle;
Présentation du 15 octobre 2009
New salts - Synthetized Examples
Présentation du 15 octobre 2009
Exemplary Electrolyte Conductivities
(20°C)
Présentation du 15 octobre 2009
New Salts - Anodic limit (Pt, ECDMC)
Real Chance to be >4V Class Battery
Présentation du 15 octobre 2009
Anodic limit (Al, EC-DMC)
Real Chance to be >4V Class Battery
Présentation du 15 octobre 2009
Cycling LiMn2O4 4.3 V (EC-DMC)
Swagelok cell , Al plunger
Promising Cycling Performance…
Présentation du 15 octobre 2009
Ragone Signature
..as well as Rate Capability and Power/Energy relation
Présentation du 15 octobre 2009
Conductivity in PEO
SS / PEO20LiX / SS
0.01
1E-3
1E-4
-1
conductivity /  cm
-1
cooling scan
1E-5
1E-6
DCTA
LiDCTA
PDI
LiPDI
TDI
LiTDI
1E-7
1E-8
2.5
2.6
2.7
2.8
2.9
3.0
3.1
1000/T / K
3.2
3.3
3.4
3.5
-1
Présentation du 15 octobre 2009
T (°C)
127 111
0.01
10
-2
10
-3
10
-4
10
-5
10
-6
10
-7
97
84
72
60
49
39
30
21
13
P(EO)20LiCF3SO3
(Scm )
1E-4
1E-5
PEO
A
PEO2020LiTDI
PEO
LiPDI
PEO 20 B
20
1E-6
2.6
2.8
3.0
1000 / T
-1
N
PEO20LiBOB/ LiBF4
Hot-Pressing
0.01
T / °C
111,5 84 60,1 39,4 21
2,6
2,7
2,8
2,9
3,0
3,1
3,2
3,3
3,4
3,5
0.01
T / °C
111,5 84 60,1 39,4 21
1000/T (K )
PEO20LiCF3SO3+ ZrO2SA
Casting
T/°C
111,5 84 60,1 39,4 21
0.01
Conducibilità / Scm
-1
1E-3
1E-4
1E-5
1E-4
PEO20 LiDCTA
1E-5
PEO20 LiBF4
1E-8
2.4 2.6 2.8 3.0 3.2 3.4 3.6
-1
-1
1000T / K
1E-7
1E-3
1E-4
1E-5
1E-6
1E-6
1E-7
1E-3
-1
Conducibilità / Scm
-1
N
+
Li
2,5
-1
PEO20LiDCTA
Hot-Pressing
CN
N
K
3.2
Conducibilità / Scm
NC
P(EO)20LiDCTA
-1
PEO20LiTDI
PEO20LiPDI
Hot-Pressing
Conductivity
S / cm
1E-3
1E-6
PEO20 LiBOB
PEO20 LiBF4
1E-8
2.4 2.6 2.8 3.0 3.2 3.4 3.6
-1
-1
1000T / K
1E-7
x: 0%
x: 10%
1E-8
2.4 2.6 2.8 3.0 3.2 3.4 3.6
-1
-1
1000T / K
Présentation du 15 octobre 2009
Charge profile 4.3 V cut-off, Al collector
Présentation du 15 octobre 2009
Anodic stability
Li / PEO20LiX / Super P
current / mA/cm
2
0.20
DCTA
LiDCTA
PDI
LiPDI
TDI
LiTDI
Anodic
breakdown
voltage vs.
Li
0.15
0.10
0.05
P(EO)20LiDCTA
3.6V
P(EO)20LiPDI
4.0V
P(EO)20LiTDI
4.0V
0.00
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
Potential / V
Présentation du 15 octobre 2009
Interphase resistance - PEO
Li / PEO20LiX / Li
LiDCTA
-100
-60
2h
7h
2d
7d
-100
-40
-20
-80
LiTDI
4.5h
1d
5d
12d
-60
-40
-20
0
0
0
40
80
120
160
200
0
40
80
Zreal / Ohm
2h
7h
2d
7d
-80
-60
120
160
Zreal / Ohm
LiPDI
-100
Zimm / Ohm
Zimm / Ohm
-80
4.5h
1d
5d
12d
Zimm / Ohm
2h
7h
2d
7d
4.5h
1d
5d
12d
-40
-20
0
0
40
80
120
160
200
Zreal / Ohm
Présentation du 15 octobre 2009
200
Cycling behaviour
Présentation du 15 octobre 2009
% of capacity at C/20
Rate capability (PEO)
Présentation du 15 octobre 2009
New imidazole-derived salts
• Easy, low-demanding, inexpensive, one-step, high yield
syntheses;
• Salts are pure, stable in air atmosphere, non-hygroscopic, stable
up to 250°C, easy to handle;
• 20°C ionic conductivity exceeds:
• 10-3 S∙cm-1 in PC, 10-4 S∙cm-1 in PEGDME500
• 10-6 S∙cm-1 in PEO (10-4 S∙cm-1 at 50°C)
• 6 mS∙cm-1 in EC:DMC
• T+ at ionic conductivity maximum reaches:
• 0.45 in PC, 0.40 in EC-DMC,
0.25 in PEGDME500 (but overall max 0.62);
• Stable over time against Li;
• Stable up to 4.4 V vs. Li against metallic lithium anode;
• Stable up to 5.0 V vs. Li against aluminum;
• Much smaller association rate than commercially available salts;
Présentation du 15 octobre 2009
Outline
• General status quo of present Li (ion) battery architecture
• Introduction to the field of modern electrolytes (concepts, transport
mechanisms, improvement strategy)
• Role of salt anions
• New types of salts
• Ionic Liquids
• Crystalline Electrolytes (P. Bruce)
• Composites (Ceramic, Anion receptors)
• Conclusions
Alistore ERI | www.alistore.eu
Présentation du 15 octobre 2009
Ionic Liquids (IL) 1/3
Typical cations used in ionic liquids:
1) Imidazole cation
2) Alkylpyridine cation
3) Dialkylpyrrole cation
Ionic liquid with lithium
cation example
Présentation du 15 octobre 2009
The basic IL
V = 142.5 Å3
V = 107.3 Å3
V = 88.4 Å3
Présentation du 15 octobre 2009
First Alkali metal IL? K(CF3SO2NSO2F)
99°C
Eutectics, re-investigation of “polymer in salt” (Angell)
Présentation du 15 octobre 2009
Outline
• General status quo of present Li (ion) battery architecture
• Introduction to the field of modern electrolytes (concepts, transport
mechanisms, improvement strategy)
• Role of salt anions
• New types of salts
• Ionic Liquids
• Crystalline Electrolytes (P. Bruce)
• Composites (Ceramic, Anion receptors)
• Conclusions
Alistore ERI | www.alistore.eu
Présentation du 15 octobre 2009
Crystalline Solid Polymer Electrolytes 1/2
T/ °C
-4.0
60
50
40
3.0
3.1
3.2
30
20
1
log(/S cm )
-4.5
-5.0
-5.5
-6.0
-6.5
-7.0
-7.5
-1
1000 T
Fig.1 The structure of PEO6:LiAsF6. Left, view of the structure showing rows of Li+ ions
perpendicular to the page. Right, view of the structure showing the relative position of the chains
and their conformation (hydrogens not shown). Thin lines indicate coordination around the Li+
cation.
3.3
/K
1
Fig.2 Conductivity of crystalline polymer electrolytes. Red - PEO6:LiAsF6; green PEO6:Li(AsF6)0.9(SbF6)0.1; magenta - PEO6:(LiSbF6)0.99(Li2SiF6)0.01; blue PEO6:(LiAsF6)0.95(LiTFSI) 0.05; black - (PEO0.75G40.25)6:LiPF6. G4 – tetraglyme,
CH3O(CH2CH2O)4CH3.
Présentation du 15 octobre 2009
3.4
Crystalline Solid Polymer Electrolytes 2/2
Fig.3 The structure of PEO8:NaAsF6. Left, view of the structure showing rows of
Na+ ions perpendicular to the page. Right, view of the structure showing the relative
position of the chains and their conformation (hydrogens not shown). Thin lines
indicate coordination around the Na+ cations.
Présentation du 15 octobre 2009
Outline
• General status quo of present Li (ion) battery architecture
• Introduction to the field of modern electrolytes (concepts, transport
mechanisms, improvement strategy)
• Role of salt anions
• New types of salts
• Ionic Liquids
• Crystalline Electrolytes (P. Bruce)
• Composites (Ceramic, Anion receptors, Ceramic „sponges”)
• Conclusions
Alistore ERI | www.alistore.eu
Présentation du 15 octobre 2009
PEO-based electrolytes transference number
Lithium transference numbers for (PEO)20LiClO4 based
composite electrolytes containing 10% by weight of inorganic
filler additives
Type of the
electrolyte
Type of the filler
Temperature/oC
Lithium transference
number
(PEO)20LiClO4
Filler free sample
40
0.31
(PEO)20LiClO4
Al2O3
40
0.61
(PEO)20LiClO4
Al2O3 (1% ASG)
40
0.66
(PEO)20LiClO4
Al2O3 (4% ASG)
40
0.72
(PEO)20LiClO4
Al2O3 (8% ASG)
40
0.77
(PEO)20LiBF4
0
70
0.32
(PEO)20LiBF4
Surface modified ZrO2
70
0.81
Présentation du 15 octobre 2009
Lithium transference numbers
for PEO-LiX-Calix-6-pyrrole electrolytes
Type of the electrolyte
Molar fraction of calix- Temperature/oC
6-pyrrole
Lithium transference
number
(PEO)20LiI
0
70
0.25
(PEO)20LiI
0.125
70
0.56
(PEO)20LiAsF6
0
75
0.44
(PEO)20LiAsF6
0.5
75
0.84
(PEO)20LiBF4
0
70
0.32
(PEO)20LiBF4
0.125
70
0.78
(PEO)20LiBF4
0.25
70
0.81
(PEO)20LiBF4
0.5
70
0.85
(PEO)100LiBF4
0.25
70
0.95
(PEO)100LiBF4
1
70
0.92
(PEO)20LiCF3SO3
0
75
0.45
(PEO)20LiCF3SO3
0.125
75
0.68
Alistore ERI | www.alistore.eu
Présentation du 15 octobre 2009
How does it (probably) work?
1) KI>Kcal>KT
KI-ion pairs formation constant
2) KI>KT>Kcal
KT-ionic tiplets formation
Kcal-calix-anion complex constant
3) Kcal>KI>KT
O
O
O
O
O
ClO4
Calix
-
Li+
ClO4-
ClO4-
Li+
Calix
Li+
Calix
O
Présentation du 15 octobre 2009
PEO-based electrolytes additives stability
Cyclic voltammograms of LiTf:PEO20 membranes with and without
C6P and SiO2 additives at (a)75˚C and (b)90˚C over potential range
of 0-5.0V using SS/PE/SS cell configuration
H. Mazor, D. Golodnitsky, E. Peled, W. Wieczorek, B. Scrosati, J.Power Sources, 178 (2008) 736743
Présentation du 15 octobre 2009
New Types of Ceramic Composites
1/2 – Concept and Structure
Inhibition of
crystallization
Présentation du 15 octobre 2009
New Types of Ceramic Composites
2/2 – Preliminary/First!!!
Electrochemical Testing
Présentation du 15 octobre 2009
Outline
• General status quo of present Li (ion) battery architecture
• Introduction to the field of modern electrolytes (concepts, transport
mechanisms, improvement strategy)
• Role of salt anions
• New types of salts
• Ionic Liquids
• Crystalline Electrolytes (P. Bruce)
• Composites (Ceramic, Anion receptors)
• Conclusions
Alistore ERI | www.alistore.eu
Présentation du 15 octobre 2009
Conclusions
• Anion design is one (most?) of the important aspect of
electrolyte improvement
• Hückel anions offer a cheap alternative and are covalent
(i.e. easy to handle, dry…)!
• CF3 (C2F5) dicyano imidazoles are stable @ 4.6 V and do
not corrode aluminum
• Many tools but still a lot of steps toward
better real life systems
Role of positive input/collaboration
from the industry!
Présentation du 15 octobre 2009
Acknowledgements
The following scientists greatly contributed
to the preparation of this report:
From Warsaw University of Technology:
Marek Marcinek
Leszek Niedzicki
Jarosław Syzdek
From University of St. Andrews:
Yuri Andreev
From Chalmers University:
Per Jacobsson
Patrik Johansson
Johan Scheers
Présentation du 15 octobre 2009