Coarse-Grained Carbide-Derived Carbon

Supercapacitor Electrodes for Automotive Applications

Boris Dyatkin

A.J. Drexel Nanomaterials Institute & Department of Materials Science and Engineering, Drexel University, Philadelphia, PA, USA

*Current Institution: U.S. Naval Research Laboratory

AABC 2017, Mainz, Germany

Where Can We Use Supercapacitors?

Wind pitch control to maximize wind energy generation

Trams in Germany, powered by supercapacitors, use 30% less energy than their equivalents in other regions.

2 Energy solutions for transportation require low costs and high gravimetric and volumetric energy densities

Metrics and Limitations of Porous Carbon Supercapacitor Electrodes

P. Simon and Y. Gogotsi. Science, 334 (6048), 917 – 918 (2011).

Theoretical surface area limit: 2630 m2/g for single-layer graphene How much energy can 1 sheet store? How expensive is nanostructured

carbon?

For automotive and grid storage solutions, we need:

1. High volumetric energy densities 2. Low cost and simple production 3. High reliability

3

Carbide-Derived Carbons

Gogotsi, Y. et. al. Nature Materials, 2, 591-594 (2003). Presser, V., et. al. Advanced Functional Materials, 21, 810-833 (2011).

• Powders (nm/μm), Fibers, Monolithic Films

• Key Structure Properties

Conformal transformation of carbide to CDC

75-90% porosity

Uniform pore structure

• Possible Carbide Precursors

SiC, TiC, Fe3C, VC, ZnC, ZrC, NbC, Mo2C, WC, Ti3AlC2, Ti2AlC, SiOC, Ti2AlC0.5N0.5…

• Tunable Carbon Structure

1100

50

100

150

200

250

300

350

400

450

Surf

ace

are

a(m

²/g)

Pore size (nm)

TiC-CDC

VC-CDC

B4C-

CDC

Cl2SiC4

T ~ 200 – 1000°C

P ~ 1 atm

4

Key Limitation: high production cost

B A

1. Chlorination @ 500°C

2. Cell assembly

Sintered TiC plate

TiC derived carbon film

TiC Monolith

TiC plate CDC film

Electrolyte + separator

Teflon plates

A

CDC

TiC

5 µm

J. Chmiola, et al., Science, 238 (5977), 480 – 483 (2010).

Direct conversion of monolithic TiC to carbon

High volumetric capacitance is only

observed for micrometer-thin films due to ionic

transport limitations

Organic electrolyte Aqueous electrolyte

Effect of Thickness (Diffusion Length) on Capacitance

5

Coarse-Grained Carbide-Derived Carbons

75 µm

Cl2 (g): 800 ºC, 6 hours, 580 ml/min

H2 (g): 600 ºC, 2 hours, 120 ml/min

12 cm

100 µm

75 µm 250 µm

Electrode film

• Objective Reduce ball-milling of refractory

carbide precursor powders Characterize and analyze CDCs

synthesized from abrasive TiC

• Approach 75 µm, 250 µm TiC particles Standard tube furnace synthesis Powders with similar bulk properties

as typical CDCs

B. Dyatkin, et al. Journal of Power Sources, 306, 32 – 41 (2016). 6

Structure, Porosity, and Composition

1 2 3 4 5 60.0

0.2

0.4

0.6

0.8

1.0

dV

/dr

/ cc n

m-1 g

-1

Pore Diameter / nm

YP50

Coarse-Grained

CDC

1 2 3 40.0

0.2

0.4

0.6

0.8

1.0

Large CDC

(300 m)

Initial CDC (75 m)

dV

dr-1

/ c

c n

m-1 g

-1

Pore Diameter / nm

Milled CDC

200 300 400 500 600 7000

20

40

60

80

100

Temperature / C

Rem

ain

ing

Mass / %

0.0

0.3

0.6

0.9

1.2

1.5

1.8

dT

G / %

C

-1

1000 1500 2000 2500 3000

D+G2D

G

Norm

aliz

ed R

am

an Inte

nsity

Raman Shift / cm-1

D

Coarse-Grained CDC

CDC Micropowder• Microporous structure High porosity: 1830 m2/g, 0.78 cm3/g Nanostructured, well-ordered pores (dav = 7.8 Å) Similar porosity as CDC micropowders and activated

carbon

• Total conversion (99.5+%) • Graphitization resembles comparable CDCs

B. Dyatkin, et al. Journal of Power Sources, 306, 32 – 41 (2016). 7

Particle Structure

3 6 9 12 15

-2

0

2

4

6

8

G(r

) /

Å-2

r / Å

75 m CDC

[002] Graphite

d-spacing

5, 6, 7 member rings

Micropowder CDC

0.01 0.1 10.01

0.1

1

10

100

1000

Inte

nsi

ty (

Q)

/ Å

2

CDC: 75 m powder

CDC: 20 nm powder

CDC: 1.0 m powder

Q / Å-1

• Short-range carbon ordering of coarse-grained CDCs closely resembles structure of micropowders

• Pore wall graphitization and ring structure independent of particle size

X-Ray PDF SANS

• Identical behaviors in Guinier regime (0.2 Å-1 < Q < 0.7 Å-1) Slit pore structures nearly identical

for coarse and nanosized CDCs

• Changes in Porod regime (low-Q) • Surface roughness and external

surface changes

B. Dyatkin, et al. Journal of Power Sources, 306, 32 – 41 (2016). 8

High Capacitance in Organic Electrolyte

10 100 10000

25

50

75

100

125

Sweep Rate / mV s-1

Ca

pa

cita

nce

/ F

g-1

0.0

0.2

0.4

0.6

0.8

1.0

Co

ars

e-G

rain

ed C

DC

: C

/C0Coarse-Grained

CDC

YP50

• High capacitance and rate handling of coarse-grained CDCs that exceeds micropowder performance

• High mass loading (6.23 mg/cm2) and electrode conductivity (0.16 S∙cm-1)

• High volumetric energy densities and high Csp even for 1 mm thick films! 1 10 100 1000

0

2

4

6

8

10

Are

al C

ap

acita

nce

/ F

cm

-2

Sweep Rate / mV s-1

1 mm thick

electrode

90 m thick electrode

250 m thick

electrode

0.0 0.5 1.0 1.5 2.0 2.5

-120

-60

0

60

120

72 µm

YP50: 10 mV s-1

Capacitance / F

g-1

Voltage / V

250 mV s-1

10 mV s-1

50 mV s-1

100 mV s-1

10 100 10000

25

50

75

100

125

Sweep Rate / mV s-1

Capa

citance / F

g-1

0.0

0.2

0.4

0.6

0.8

1.0

Co

ars

e-G

rain

ed C

DC

: C

/C0Coarse-Grained

CDC

YP50

Sweep Rate Csp: CDC

2 mV/s 134 F/g

20 mV/s 120 F/g

100 mV/s 111 F/g

1000 mV/s 59 F/g

B. Dyatkin, et al. Journal of Power Sources, 306, 32 – 41 (2016). 9

1.5 M [NEt4

+][BF4-]

in CH3CN

Particle Size and Solvent Effects: RTIL Electrolyte

B. Dyatkin, et al. Journal of Power Sources, 306, 32 – 41 (2016).

10 100 10000

30

60

90

120

150

Neat

[EMIm+][TFSI

-]

YP50 in neat [EMIm+][TFSI-]

Capacitance / F

g-1

Sweep Rate / mV s-1

50% [EMIm+][TFSI-] /

50% CH3CN

0 10 20 30 40 500

10

20

30

40

50

Solv. [EMm+][TFSI

-]

Neat [EMm+][TFSI

-]

-Im

(Z

) /

Ohm

s

Re(Z) / Ohms

Milled CDCInitial CDC

0 3 60

3

6

-Im

(Z

) / O

hm

s

Re(Z) / Ohms

0.0 0.5 1.0 1.5 2.0 2.5-150

-100

-50

0

50

100

150

YP50 in neat [EMIm+][TFSI-]

Ca

pa

cita

nce

/ F

g-1

Voltage / V

50%[EMIm+][TFSI-] /

50% CH3CN

Neat [EMIm+][TFSI-]

• Neat [EMIm+][TFSI-] ionic liquid exhibits high capacitance Added solvent improves ionic mobility Solvated [EMIm+][TFSI-] capacitance exceeds

100 F/g Coarse-grained pores show same solvated ion

dynamics in milled CDC (10 um particles) Neat [EMIm+][TFSI-] more mobile in micropowders

75 µm75 µm

10

Electrochemical Stability in Coarse-Grained Carbons

0.0 0.5 1.0 1.5 2.0 2.5 3.0

-0.8

-0.4

0.0

0.4

0.8

Curr

ent

/ m

A

Voltage / V

0 10 20 30 40 50 600

10

20

30

40

50

60

-Im

(Z)

(Ohm

s)

Re(Z) (Ohms)

Initial 75 m CDC

Cycled to 3.5 V

3 60

3

-Im

(Z)

(Oh

ms)

Re(Z) (Ohms)

• Extended Cyclability and Potential Window • Minimal external surface minimizes

breakdown in neat RTIL • Ion confinement increases voltage window

from 2.5 V to 3.1 V • Breakdown mostly inside pores

2 mV/s

0 2000 4000 6000 8000 100000

20

40

60

80

100

Capacitance / F

g-1

Cycle Numer

1.0 A/g

B. Dyatkin, et al. Journal of Power Sources, 306, 32 – 41 (2016). 11

CDCs With Larger Diameters

• High capacitance in 1.5 M [NEt4+][BF4

-] in CH3CN 250 µm films are ~1 particle thick; 16 mg/cm2 loading Minimal bulk diffusion limitation Even higher capacitance than 75 µm films of comparable thickness

10 100 10000

30

60

90

120

1.5

1.0

0.5

Are

al C

apacitance / F

cm

-2

Capacitance / F

g-1

Sweep Rate / mV s-1

300 m CDC

75 m CDC

2.0

0.0 0.5 1.0 1.5 2.0 2.5

-120

-80

-40

0

40

80

120 20 mV s-1

10 mV s-1

Capacitance / F

g-1

Voltage / V

50 mV s-1

100 mV s-1

75 m CDC,

250 m film

10 mV s-1

B. Dyatkin, et al. Journal of Power Sources, 306, 32 – 41 (2016). 12

Key Advantages of Coarse-Grained Carbon Electrodes

0.1 µm

2 µm

75 µm

1. Microporosity and high surface areas (over 1500 m2/g)

2. Less expensive electrode materials 3. High capacitance and voltage window 4. High film loading: films can be made as

thick as 1 mm (automotive, transportation)

BUT WHY?

0.0 V +2.5 V 0.0 V -2.5 V

Electrosorption dominated by local ion-ion rearrangement, not bulk diffusion

B. Dyatkin, et al. Journal of Power Sources, 306, 32 – 41 (2016). Richey, F., Dyatkin, B., et al. J. Am. Chem. Soc., 135, 12818 (2013).

13

Acknowledgements 1. Nanomaterials Group (Drexel)

- Prof. Yury Gogotsi

2. Materials Research Centre

- Oleksiy Gogotsi, Yulya Zozulya,

Bohdan Malinovskiy

3. Oak Ridge National Laboratory - Hsiu-Wen Wang, Katharine L. Page

4. Universite Toulouse - Prof. Patrice Simon

14

Thank you!

BorisDyatkin@gmail.com http://nano.materials.drexel.edu

Funding: 1. Department of Energy Fluid Interface Reactions,

Structures and Transport (FIRST) Center 2. DOE SCGSR Research Fellowship