Advanced materials for electrochemical capacitors

A proposed contribution to a CU capacitor consortium

Stephen Creager, Dennis Smith, Darryl DesMarteau, Luis Echegoyen

Department of Chemistry, Clemson University

Also, Dr. Oleg Borodin, University of Utah

Steve Creager Electrochemistry & Carbon

Darryl DesMarteau Fluoropolymers;

ionic liquid electrolytes

Dennis Smith Polymers & Carbon

Luis Echegoyen Fullerenes; Carbon

Nano-onions

Oleg BorodinResearch Professor, U Utah.

Computational approaches to liquid structure / dynamics

Supercapacitors / Ultracapacitors

Images from the Energy Storage Association, California

http://www.electricitystorage.org/technologies.htm

Accessed July 2, 2003

Electrode requirements:

• High electrical conductivity

• High surface area (for high capacitance)

• High porosity (for electrolyte penetration and fast response)

• Wide voltage stability window

Electrolyte requirements:

• High ionic conductivity

• Low viscosity

• Low volatility / flammability

• Wide voltage stability window

Advanced Materials for Electrochemical Capacitors

• Electrode materials; Nanoporous / nanostructured carbon– Carbon aerogels (e.g. resorcinol / formaldehyde)– Fullerenes / Nanotubes / Carbon Nano-Onions– Hi-carbon-yield glassy carbon precursors (“BODA”).

• Electrolyte materials; Room-temperature ionic liquids (RTILs) – Ammonium / phosphonium cations– Fluorosulfonimide anions– No solvent

• Small-scale testing– Three-electrode cells / potentiostatic control– Voltammetry / impedance spectroscopy– Galvanostatic charging / discharging

OH

OH

+

H H

O

OH

HO

CH2OCH2

CH2OCH2 CH2

CH2

H2COCH2

CH2OCH2

CH2

OH

OH

OH

OH

OH

OH

OH

OHOH

HO

OHHO

HO

HO

2

Carbon aerogels via the resorcinol / formaldehyde (RF) method

Na2CO3, heat

1 day each at

ambient, 50oC,

90oC

Solvent

removal,

carbonize

1100oC

Monomers Crosslinked polymer (sol) Nanoporous carbon aerogel

Carbon aerogel typical properties:

Surface area 500 – 600 m2/g (BET)

Pore sizes 0.3 – 20 nm (BHJ)

Macroscopic density after pyrolysis,

approx. 0.5 g / cm3

Free volume, approx. 70 %

Left, cyclic voltammograms of 2.0 mg of large particle (~90 micrometer) of RF 30

carbon aerogel (sample S-12) on sticky carbon electrode, plotted as a dependence of

specific capacitance on different scan rates vs. voltage profiles. The electrolyte was

aqueous 1M H2SO4.

Right, frequency dependence of 2.0 mg of RF 30 carbon aerogel large particle (~90

micron) in 1 M of H2SO4 electrolyte, at DC potential of 0.4 V, AC amplitude of 80 mV,

and frequency range from 100 to 0.001 Hz.

0

10

20

30

40

50

60

70

80

-3.5 -2.5 -1.5 -0.5 0.5 1.5

Log f (Hz)

C (

F/g

)

71 F/g

-100-80

-60-40

-20020

4060

80100

0.40.420.440.460.480.5

E (V)

C (

F/g

)

Scan rate=0.001 V/s

Scan rate=0.002 V/s

Scan rate=0.005 V/s

Scan rate= 0.01 V/s

Scan rate=0.02 V/s

Scan rate 0.05 V/s

Scan Rate=0.1 V/s

76.3 F/g

Specific capacitance (C) values were calculated from the imaginary part of Nyquist

impedance plots according to the equation; C= -1/(2f * Zim), where f is the frequency

and Zim is the imaginary (out-of-phase) portion of the impedance.

Specific capacitance of non-templated CAG materials

1100oCDryingNa2CO3,

heat

RF Monomers Wet RF Sol

OH

OHH H

O

2+

Dry RF Sol Carbon aerogel

Preparation of templated carbon aerogels via the RF method

Templated Carbon Aerogel

Etching to remove templating agent

Q: Why templating? A: To promote rapid electrolyte access to the full interior surface area of the

carbon electrode!

Hierarchical porosity; Large pores & small pores

FE-SEM of Templated RF 20 CAG after carbonization and etching with 30 % HF

to remove silica template.

0

20

40

60

80

100

-3 -2 -1 0 1 2

Log f (Hz)

C (

F/g

)

2.2 mg of RF 40 Non-Templated

1.8mg of RF40 Templated

0

20

40

60

80

100

-3 -2 -1 0 1 2

Log f (Hz)

C (

F/g

)

2.0 mg of RF 50 Non-Templated

2.8 mg of RF 50 Templated

0

10

20

30

40

50

60

70

80

90

-3 -2 -1 0 1 2

Log f (Hz)

C (

F/g

)

1.3 mg of RF 20 Non-Templated

2.1 mg of RF 20 Templated

0102030405060708090100110120

-3 -2 -1 0 1 2

Log f (Hz)

C (

F/g

)

1.6 mg of RF 30 Non-Templated

1.8 mg of RF 30 Templated

C=78.20 F/g

C=29.33 F/g

C=111 F/g

C=78.20 F/g

C=71.70 F/g

C=93.20 F/gC=81.07 F/g

C=61.67 F/g

Frequency dependence of Templated (S20-23) and Non-Templated (S16-19) CAG in 1 M

H2SO4, at DC potential of 0.4 V, AC amplitude of 80 mV, and frequency range from 100 to

0.001 Hz. Capacitance was evaluated at the lowest frequency of 0.001 Hz.

Specific capacitance of templated CAG samples by impedance spectroscopy

Large pores

HO

X

OH

1) Br2

2) CF3SO2Cl

3) [Pd] / PhCCH

X

Ph

Ph

Ph

Ph

200 oC

X

PhPh

Ph Ph

X

Ph Ph

Ph Ph

X

Ph

Ph

Ph Ph

X

Ph

Ph

Ph

Ph450

oC

M

Processable Intermediate

BODA Monomer Polynaphthalene Network

x yn

z

x y

900-1000 oC

Glassy Carbon

BIS-ORTHO-DIYNYL-ARYLENE (BODA)-DERIVED

POLYNAPHTHALENES AND GLASSY CARBON

Adv. Funct. Mater. 2007, 17, 1237–1246; Carbon 2007, 45(5), 931-935;

Chem. Mater. 2007, 19, 1411-1417.

Etch with HF

giving 3-D (SEM)

periodic array of holes

surrounded by carbon.

Sol-gel prepared closed packed

colloidal silica impregnated with

processable polymer and carbonized

Polymer (BODA) Derived Inverse Carbon Opal Photonic Crystal

300 nm

silica opal

silica + carbon

2 mm

1 cm

1) BODA melt 103 °C

2) Cure 265 °C

3) Pyrolyze 900 °C

4) HF Etch

Green Blue

Green

(515 nm)

(535 nm)

Langmuir 2003, 19, 7153.

BODA-co-CNOs (Carbon Nano-onions)

+ 206°C, 4 d

NMPF3C

F3C

Ph

Ph

PhPh

C(CF3)2

Ph Ph

PhPh

C(CF3)2

PhPh

Ph

Ph

C(CF3)2

Ph Ph

PhPh

x y z

m

Solubilized CNOs

Arno Rettenbacher

CNOsBODA-CNOs CNOs

BODA-CNOs

sonicatedcentrifuged

Chem. Mater. 2007, 19, 1411-1417.

High Resolution TEM of Soluble BODA-Carbon Onions

HRTEM (300 keV) image

of BODA-CNO copolymer

(from CHCl3 solution),

scale bar represents 2 nm.

The first radical addition to

CNO also provides a route

to purify and resolve CNOs

sizes by thermal-oxidative

de-functionalization.

Chem. Mater. 2007, 19(6), 1411

Adv. Funct. Mater. 2007, 17, 1237

RTIL electrolytes

• Certain combinations of cations and anions (often organic) produce salts which remain liquid at ambient temperature.

• These materials have low volatility and flammability, relatively high conductivity, and can have a very wide voltage window.

• They are well suited for use as electrolytes in electrochemical capacitors.

• Clemson has experience in making and characterizing such electrolytes, with special focus on fluorinated materials having high stability, low viscosity, and high ionic conductivity.

Simulated Ionic Liquids; Work of Dr. Oleg Borodin, University of Utah

A set of anions and cations for which many-body polarizable force field has been developed in Phase I of the project. Note, that while pyrrolidinium+ and imidazolium+ cations are shown only with oligoether modifying groups, the force field has been tested for these cations with both oligoether and alkane modifying groups. Different attachment positions of alkyl chains to the imidazolium+ ring have also been tested. N-alkyl-N-methyl-piperidinium cation has also been simulated (not shown)

IL T, K Viscosity (mPa s)

MD exp

[emim][Ntf2] 393 4.2 4.4

[C5O2im][Ntf2] 303 51.8 48.4

[C7 mim][Ntf2] 303 65.5 63-66.8

Viscosity of selected ILs from MD simulations using Lees-Edwards boundary conditions and experiments from Smith, G.D.; Borodin, O.; Li, L.; Kim, H.; Liu, Q.; Bara, J. E.; Jin, D. L., AComparison of Ether- and Alkyl-Derivatized Imidazolium-BasedRoom-Temperature Ionic Liquids: A Molecular DynamicsSimulation Study. Phys. Chem. Chem. Phys. (2008)1000/T (K

-1)

2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0

vis

c, m

Pa

s

1

10

100

1000

exp, Watanabe group

MD

[emim][Ntf2]

Other attributes which can be addressed by simulation are as follows: Liquid density, heat of vaporization, ion diffusion, ionic conductivity, and especially, ion polarization and dynamics in electric fields at and away from polarized interfaces.

Viscosity; from Borodin, Utah

Proposed project scope

• Synthesize new high-voltage-limit high-conductivity ionic liquid electrolytes.

• Characterize WRT conductivity, voltage limits and specific capacitance using templated carbon aerogel electrodes.

• Co-ordinate experimental efforts with modelingefforts focusing on polarization of ionic liquid electrolytes

• As progress dictates, work with private-sector partner(s) to scale up materials for larger-scale testing in functional capacitors.

Summary

• Clemson has experience in making and characterizing a wide range of nanoporouscarbon materials and RTIL electrolytes suitable for use in electrochemical capacitors

• Specific projects could leverage this experience in ways that could enable new capacitor technologies and improve existing technologies.

Extra Slides....

Photo-Voltaic Devices with BODA-C60 Films(with Prof. S. Fukuzumi, Osaka University)

Adv. Funct. Mater. 2007, 17, 1237

Illustration of photoelectrochemical cell

and the structure of BODA-co-C60

I3Š

eŠ

h

OTE Pt

eŠ

OTE :

SnO2

optically transparent electrode

X

RR

R R

nx

X = C(CF3)2

R = C6H5

BODA-co-C60

so lu b ilizin g

co m p o n e n t

e le ct r o n -

t r a n sp o r t e r

BODA-co-C60

IŠ

Photocurrent of (a) OTE/SnO2/BODA-co-C60,

(b) OTE/SnO2, and (c) OTE/BODA-co-C60

electrodes under visible light illumination (l >

380 nm) in the absence of any applied bias.

Electrolyte: 0.5 M NaI and 0.01 M I2 in

acetonitrile. Input power: 100 mW cm–2.J. Mater. Chem. 2008, 18, 3237–3241

Electrochemical characterization

Figure 1. The geometric shape of sticky carbon electrode used for primary

measurements of the RF aerogel capacitance.

Second-generation

supercapacitor cell

Specific capacitance and surface area for the S12-S15 series of carbon aerogels, in 1

M H2SO4

Table 5. Specific capacitance results for the S12 - S15 series.

Sample S13 S12 S14 S15

RF value 20 30 40 50

Specific capacitance from slow-scan

CV, 1 mV/sec in 1 M H2SO4, Farads /

gram

49 76 30 31

Specific capacitance from low-

frequency impedance, 10-3

Hz in 1 M

H2SO4, Farads / gram

50 71 37 30

BET specific surface area,

measurements made October 2003

(m2/g)

482 709 494 558

Capacitance/area from low-frequency

impedance, microFarads / cm2

10.4 10.0 7.5 5.4

Pre-carbonized

processable resin

cured at 250 °C

&

pyrolyzed

800-1000 °C

Inverse Carbon Opal

Shah, H.V.; Brittain, S.T.; Huang, Q.; Hwu, S.-J.; Whitesides, G.M., Smith, Jr. D.W Chem. Mater. 1999, 11, 2623.

Perpall, M.W.; Smith, Jr., D.W.; et al. Langmuir 2003, 19, 7153.

Microstructures via Soft LithographyBODA Derivved Carbon Fibers

diameter = 604 m and (right) hollow fiber (O.D. = 612

m, I.D. = 375 m) carbonized at 1000 °C.

Microtransfer molded grating

with 0.5 m lines

Edwards AFB

15-25 m diameter fibers

300 nm

Use of a porous silica monolith as the templating phase

1. Gelation accomplished

by mixing 4 mL TMOS + 10

mL 0.01 M acetic acid +

0.84 g PEG (MW = 10K),

heating to 40oC. (Thanks to

Jamie Norton, Clemson)

2. Backfill with wet RF sol followed by

thermal program ( 1, 1, 1) and Heat

50oC, 48 hrs.

3. Carbonize at 1050oC, 8 hrs.

4. Etch with 30% HF to remove silica

template.

Templated RF-20 carbon aerogel