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Nanostructured Carbons for Supercapacitors: beyond the double-layer concept
CIC Energigune, Vitoria, Spain, March 21 2012
double-layer concept
Patrice SIMON
Université Paul Sabatier CIRIMAT UMR CNRS 5085
Toulouse – [email protected]
Outline
1. Supercapacitors- principles - charge storage mechanism
2. Electrical Double Layer Capacitors2.1 Activated carbons
3. High voltage EDLCs
2.1 Activated carbons2.2 Microporous carbons2.3 Modeling (MD)
1. Why supercapacitors?
� Intermediate performance betweenbatteries and capacitors
Electrochemical Capacitors:
- high power (10-20 kW/kg) - medium energy : 5 Wh/kg- time constant: ~ 5 s
(A. Burke’s talk)
batteries and capacitors
Various types of ECs:- Carbon-based: EDLCs (~90%)- oxydes (pseudo-capacitance)- asymetric and hybrid devices (A. Beliakov’s talk)
Applications: (J. R. Miller’s talk)- power electronics (<100F)- power delivery / energy harvesting: HEV (Citroën, Peugeot, Mazda) , trams…
EDLCs : Double layer capacitance
Electro
de
Electro
lyte
Electrostatic Storage
1.1 Charge storage in EDLCs
Electro
lyte
Cdl≈10-20 µF/cm²
Active material: high surface area carbon (1,500-2,500 m²/g): >100 F/g
2 nm
ff
2 nm10 nm
ActivatedCarbon
CarbonNanotubes
CarbonOnions
Graphene
1. Increase carbon capacitance
1.2 EDLCs : challenges
Next Challenges for Supercapacitors
Incease energy density (E=1/2 C.V²) from 5 to >10 Wh/kg� tdischarge > 10s
1. Increase carbon capacitancework on the carbon / electrolyte interface� understand the ion size /carbon pore size relationship
2. Increase the cell voltage� design carbon structure in conjunction with electrolyte
formulation
Outline
1. Supercapacitors- principles - charge storage mechanism
2. Electrical Double Layer Capacitors2.1 Activated carbons
3. High voltage EDLCs
2.1 Activated carbons2.2 Microporous carbons2.3 Modeling (MD)
2.1 Activated Carbons
Activated Carbon=
Porous carbon
2. Active Materials: high surface area carbon
� high SSA ~1500 m2/g
Activated Carbons(amorphous)
Large Pore SizeDistribution
2.2 Carbide-Derived Carbons
Selective etching of metal from carbide (TiC, SiC, ZrC…)
TiC(s) + 2 Cl2(g) →→→→ TiCl4(g) + C(s)
Why CDCs? � Controled, narrow pore size distribution
Pores from 0.6 to 1.2 nm
900°C
1 nm
1600
1700
1.1
1.2
800°C
0.8 nm
500°C
0.68 nm
1000
1100
1200
1300
1400
1500
1600
0.6
0.7
0.8
0.9
1.0
1.1
500 600 700 800 900 1000
BE
TS
SA
(
m2 /g
)
Average pore size (nm
)
Chlorination temperature (°C)
Selective etching of metal from carbide (TiC, SiC, ZrC…)
TiC(s) + 2 Cl2(g) →→→→ TiCl4(g) + C(s)
Why CDCs? � Very fine pore size control (unimodal)
Pores from 0.6 to 1 nm
900°C
1 nm
2. Carbide-Derived Carbons
800°C
0.8 nm
500°C
0.68 nm
Cellules Labo Electrolyte(C2H5)4N+,BF4
- 1,5M in ACNEt4N+
BF4-
2.1 CDCs in AN+1M (C2H5)4+,BF4-
95% CDC, 5% PTFE sur feuille Alélectrode 4cm2, 15 mg/cm²
Pores smaller thanthe solvated ion
size are accessibleto the ions
2.1 CDCs: Capacitance increase in 1M (C2H5)4N
+,BF4- in AN electrolyte
J. Chmiola, G. Yushin, Y. Gogotsi, C. Portet, P.L. Taberna and P. Simon, Science 313, 1760-1763 (2006)
Hypothesis:� micropores accessible thanks to the distortion of the ion solvation shell
High capacitance in micropores; 50% increase
100
110
120
130
140
150
Spe
cific
capa
cita
nce (F/g
)
1.1nm0.80.76nm0.74nm
0.72nm
0.64 nm
0.72nm
0.74nm
0.76nm0.8nm1nm
2.1 CDCs in AN+1M (C2H5)4+,BF4-
High C at high rateLow capacitance loss (<10%)
80
90
100
0 20 40 60 80 100 120
Spe
cific
capa
cita
nce (F/g
)Current density (mA.cm-2 )
1 A.g-13 A.g-1
6 A.g-1
Microporous Carbons: high C AND high P
ESR: 0.6 Ohm.cm² @ 1kHzCDCs with 0.7-0.8 nm pore size
< 0.7 nm <
130
140
150
160
170
Cell Capacitance
Negative electrode
Specific
capacita
nce (F/g
)
Positive electrode
2.1 CDCs in AN+1M (C2H5)4+,BF4-
3-electrode cells
J. Chmiola. C. Largeot, P.L. Taberna, P. Simon and Y. Gogotsi, Angewandte Chemie Int. 120 (18), 2008, 3440
1. Adapt pore size to ion size
2. Ions partially desolvated to accessmicropores
3. Cmax for an optimum pore size
< 0.76 nm <
R. Lin, P.L. Taberna, J. Chmiola, D. Guay, Y. Gogotsi and P. Simon, JECS 158 (2009) A7-A12
100
110
120
130
0.6 0.7 0.8 0.9 1 1.1
Specific
capacita
nce (F/g
)
Pore size (nm)
TFSI- EMI+
Cell Capacitance (F/g)
Positive Electrode (F/g)
Negative Electrode (F/g)
100
120
140
160
180
C (F/g
)
2.2 CDCs in neat EMI,TFISI
60
80
0,6 0,7 0,8 0,9 1 1,1Pore Size (nm)
AC
C. Largeot, C. Portet, J. Chmiola, P.L. Taberna, Y. Gogotsi and P. Simon JACS, 130 (9), 2730 -2731 (2008)
P. Simon, Y. Gogotsi Nature Materials, 7 (2008) 845-854
2. Maximum C at ~ 0,72 nm � when ion size ~ pore size !!!
1. >50% capactiance increase commercial activated carbon (AC)
No solvent, cation size ≈ anion size:
Maximum Capacitance when ion size ~ pore size:
Ions aligned in pores >50% capacitance increase
Carbone
Carbon
e
2.2 Microporous CDCs: summary
Ions aligned in pores � >50% capacitance increase“Double-layer” sub-nanometer pores?
- potential well (K. Kaneko, Carbon 2009) ?
- screening (Kornyshev et al.?) 2009-2011
- exclusion of counter-ions (Shim et al.) ? 2011
~ 50 papiers since 2008
� C increase confirmed
� Modeling experiments needed for:
- understanding the capacitance increase in micropores
- designing new carbon structures with high capacitance
2.2 DFT modeling of EMI,TFSI in slit pores
D. Jiang et al. Nano Letter 11 (Dec. 2011) 5373
2. Very fine and precise control of the carbon pore size is neededto observe the capacitance increase
1. Confirmation of the capacitance increase in micropores
� Constructive superposition of the ionic density profiles
Ionic density profiles of ions near one charged wallCapacitance vs pore width (σ = ion size)
� Oscillation of capacitancevs carbon pore size!
Y. Feng et al, J. Phys. Chem. Lett 2 (Dec. 2011) 2859
2.2 MD modeling of EMI,TFSI in slits pores
� Oscillation of capacitancevs carbon pore size!
� Constructive superposition of the ionic density profiles from each wall
2. Precise control of the carbon pore size needed
1. Confirmation of the capacitance increase in micropores; trend OK
Models using ideal carbon structures (CNTS, graphite, graphene) confirms C increase but fail to reproduce the experimental C values
Starting point:
1) Use of “real” CDC structures( from RMC simulations)
IFPn: T. De Bruin, J. Jover-Azpurua,
PECSA (UMPC): M. Salanne, B. Rotenberg, C. Merlet
Collaboration with
2.3 MD modeling of BMI,PF6 in CDCs
1) Use of “real” CDC structures( from RMC simulations)
2) MD simulation including electrolyte tank
3) Constant potential at carbon electrode; local charge on carbon
depends on adsorbed ions
CDC 900°C CDC 1200°CBMI, PF6
electrolyte = EMI-PF6 (100°C)
CDC CDC
Potentiel appliqué
2.3 MD modeling of BMI,PF6 in CDCs
1. Electrolyte accède aux pores même à Ψ=0V2. Echanges d’ions avec l’électrolyte !!!3. Nombre de coordination diminue pour les ions (“desolvation”)
C. Merlet, B. Rotenberg, P.A. Madden, P.-L. Taberna, Y. Gogotsi, P. Simon and M. Salanne, Nature Materials (April 2012)
électrolyte = EMI-PF6 (100°C)
CDC CDC
Potential
2.3 MD modeling of BMI,PF6 in CDCs
1. Electrolyte is inside pores even at Ψ=0V2. Ion exchange with the electrolyte bulk !3. Coordination number of ions decreases inside the pores (“desolvation”)
C. Merlet, B. Rotenberg, P.A. Madden, P.L. Taberna, Y. Gogotsi, P. Simon, M. Salanne, Nature Materials (in press)
E=0.5V E=0,5V E=-0.5V
2.3 MD modeling of BMI,PF6 in CDCs
1) Small number of co-ions with counter ions vs graphite
2) One ion per pore observed!
2.3 MD modeling of BMI,PF6 in CDCs
Ions get closer to the carbonsurface for CDCs than for graphite
Charge (per V) per carbon atom largerfor CDCs than for graphite
Capacitance increase comes from partial « desolvation », closerapproach of ions and the absence of the overscreening effect because
of ions confinement
� In progress….
C. Merlet, B. Rotenberg, P.A. Madden, P.L. Taberna, Y. Gogotsi, P. Simon, M. Salanne, Nature Materials (April 2012)
1. Increase carbon capacitance
1.2 EDLCs : challenges
Next Challenges for Supercapacitors
Incease energy density (E=1/2 C.V²) > 10 Wh/kg� tdischarge > 10s
1. Increase carbon capacitancework on the carbon / electrolyte interface� understand the ion size /carbon pore size relationship
2. Increase the cell voltage� approach: adapt carbon structure to electrolytes
3. Ionic Liquid mixtures
1) Ionic Liquid mixtures: PIP-PYR/FSI
(A)
Flow (End
oUp)
NC
C
C
CC
CC
CC +
C
CC
C
C
C
C
C
C
N
+
(I) PIP13FSI
(II) PYR14FSI-18
6
-30-72
(B)
Con
duc
tivity
(S c
m-1)
60.1 12.6 -23.2 -50.9 -73.2
T (°C)
10-610-510-410-310-210-1
50% PIP13FSI / 50% PYR14FSImixture: no melting down to -80°CConductivity:
Heat
Flow (
CC
S
O
S
OO
O
N
FF
_
(III) PIP13-PYR14-FSI
-30
-45
Temperature (°C)
-72
-100 -50 0 50 100
Con
duc
tivity
PIP13FSIPYR14FSIPIP13-PYR14
-FSI
103/T (103K-1)
10-910-810-710-6
2.5 3 3.5 4 4.5 5
Poster Rongying Lin
2) Carbons
High surface area, fully accessible:1. Onion-Like Carbons (OLCs)2. NTC grown onto Al foil (PECVD)
Onion-Like Carbon
3. Exohedral Carbons with IL mixture
OLCs
3. OLC et CNT with IL mixture
CNTs
R. Lin, P.-L. Taberna, et al.J Chem. Phys. Let.19 (2011) 2396-2401
Ionic Liquids and exohedral carbons: - 3.7V Voltage window at room T- from -50°C up to 100°C (2.9V) ; - BUT small capacitance (100 mF/cm², 5 mg)
3. OLC et CNT avec mélange de IL
IL mixture and exohedral carbons: cell voltage improvement and wider T operation range
� Key is the carbon / electrolyte interface
R. Lin, P.-L. Taberna, et al.J Chem. Phys. Let.19 (2011) 2396-2401
Graphene for SCs:
Zhu, et al., Science 12 May 2011
3.2 Activated graphene
SSA = 3000 m²/g, pore size: 1.5 nm
High C (150 F/g) and accessible surface
But:- low electrode loading: 1 mg/cm² (1 µm-thick films)- low graphene density � low C vol.
0
50
100
150
200
C (
F.g
-1)
Cellule Swagelok, 2 mg/cm²;5%PTFE-95%grahene, T=25°C
@ 20 mV/s
3.2 Activated graphene in IL mixture
-200
-150
-100
-50
0 0.5 1 1.5 2 2.5 3 3.5
C (
F.g
E (V)
a) 3,7V @ 25°Cb) C=170 F/g
High voltage and high C!!!
@ 20 mV/s
Cellule Swagelok, 2 mg/cm²;5%PTFE-95%grahene, T=25°C – 60°C
@ 100 mV/s
3.2 Activated graphene in IL mixture
a) 3V for 25°C<T< 80°Cb) C=170 F/g
@ 100 mV/s
ESR of 5-10 ohm.cm²
High C and low ESR @ 80°C
3.2 Activated graphene in IL mixture
a) Cycled @ -40°C and -50°Cb) C=100 – 120 F/g
High ESR but still SC working
Validation of the approach: high C (150 F/g) and ∆∆∆∆E > 3V (3,7V@RT)
3.2 Graphene: hype or reality?
Graphene interesting for thin-film, small size devices; not really for Grid storage or HVE/EV applications!!!!
P. Simon and Y. Gogotsi, Science 334 (Nov. 2011) 917-918
4. Conclusions
1. Capacitance increase in micropores due to - desolvation,- absence of over-screening - closer approach of ions to carbon surface
Microporous Carbons (CDCs) for EDLCs
2. Influence of the solvent ?� coupling in-situ NMR and modelling
1. Eutectic mixture of ILs: ∆T of 150°C
2. Activated graphene : high C and ∆E (3.7V @ RT)
� Multiple combinations possible for optimizing C and ∆E
Mastering carbon / electrolyte interface
Thanks
P.L. Taberna, B. DaffosJ. Ségalini, R. Lin, E. Iwama, C. Lecoeur (CIRIMAT)
Y. Gogotsi (Drexel university, Philadelphia)
MAICANANO project programme Blanc (2010-2012)
EADS Foundation Chair of Excellence “NanoMultifonctionnels Embarqués”(2012-2016)
ERC 2011 Advanced Grant “IONACES”2012-2016, project n°291543
1.2 Applications transports : tramways
Source : Alstom
Module SCs :1) récupération de l’énergie de freinage
2) autonomie de traction sur 100s m
Collaboration Alstom / Batscap
Autres tramways à Madrid, Cologne, Mainz (…)
=
Carbone activé : matériau désordonné
+Graphite
Feuillet de graphène
2.1 Carbone activé
Carbones activés
Distribution de taille de pore
Photo MET d’un CA
A. Terzyk et al., Phys. Chem. Chem. Phys., 2007, 9, 5919
Collecteursde courant
Carbone activéElectrolyte
Anion del’électrolyte
Carbone activé
1.1 Stockage des charges
+
2.5 V-2.7 V
Séparateur
- Charbon actif (1500 m2/g) : 100 F/g- Electrolyte organique : ΔV=2.5V- Tfonctionnement : -40°C;+80°- Milions de cycles de charge/décharge
Credit: Argone Nal Lab
1.2 Applications
Alterno/démarreur ET récupération freinagemicro-hybride e-Hdi pour Citroen C3, C4, C5 diesel (2012)
• -15 % gasoil• CO2 < 130g par km
http://www.citroen.fr/citroen-ds4/technologies/#/citroen-ds4/technologies/
http://www.leblogauto.com/2011/11/mazda-i-eloop-place-au-supercondensateur.html
Mazda: i-ELOOP concept
http://www.turbo.fr/peugeot/peugeot-308/essai-auto/410344-essai-peugeot-308/
Peugeot: e-HDI sur 308 1.6 HDi 110 ch
2. Active Materials: high surface area carbon
Onion Like Carbon Carbon Nanotubes Graphene
Activated Carbon Carbon-DerivedCarbides
Templated Carbons
