Progress of Biochar Supercapacitors

Junhua Jiang

1st Midwest Biochar Conference June 14, 2013

Acknowledgement

Management team and staff at the ISTC (Nancy Holm, Ed Delso, Xinying Wang, John Scott, et al.)

Illinois Hazardous Waste Research Fund Dr. Lei Zhang and Prof. Frank Chen at the University of South

Carolina

Staff at the Beckman Institute, the Frederick Seitz Materials Research Laboratory, and the Illinois State Geological Survey of the UIUC

Supercapacitor Applications

Traditional market • Electronics: camera, flashlights, PC

cards, portable media players, and automated meter reading equipment

• Telecom and others: Complementing

batteries (uninterruptible power supplies, handle short interruptions)

Emerging market

• Transportation (electric vehicles, buses, aerospace)

• Energy storage

Supercapacitor Energy Storage

Energy storage-conversion Ragone plot Efficiency-lifetime properties

Industry Outlook

2005 2010 2015 20200

2

4

6

US$bn

0.20.5

1.2

5.0

14% CAGR

21% CAGR

33% CAGR

Source: Daiwa forecast

Due to its fast charge-discharge capability (power density), we expect ultracapacitor use to rise along with batteries for future EV and ESS applications.

New materials are being

developed that should lead to the energy density of ultracapacitors increasing.

We forecast the ultracapacitor

market to expand tenfold, from US$0.5bn in 2010 to US$5.0bn by 2020.

CAGR: Compound annual growth rate

Cost Breakdown

Production cost 50%

15%

10%

25% Packaging

Separator

Electrolyte

Electrode

Material cost

Cost is the key market consideration and barrier for mass adoption.

Materials account for a large portion of overall costs compared to other storage

technologies.

Electrodes account for a significant portion of the materials.

Biochar electrode

Human hair

Potential low cost $0.1/kg vs $5/kg for activated carbon

Low carbon footprint Highly developed surface

area (~400 m2 g-1)

Excellent chemical and electrochemical stability

High conductivity High utilization of

surface area

Biochar Electrode

High-Carbon Zero-Ash Biochar

E / KeV

Element Wt % At % K-Ratio

C K 97.64 98.22 0.9637

O K 2.36 1.78 0.0071

Total 100 100

Electrical Conductivity

Sample Conductivity / S cm-1

Biochar 1.0 ~ 50

Vulcan 3 38.0

Vulcan 6 26.2

Black pearls 880 32.0

Black pearls 1300 34.1

Black pearls 2000 7.0

Sterling V 21.2

Graphite 300

t / oC

Porous model

Macropores (> 50 nm)

Mesopores (2 ~ 50 nm)

Micropores (< 2nm)

X-ray Computed Tomography of Corn Cob Biochar

nm diameter pore

nm thickness wall Wood-ring

Chaff

Woody Ring

Pith

CT of Corn Cob Pith

Softwood Biochar

Hardwood Biochar

Original Biochar Supercapacitor

-0.750 -0.500 -0.250 0 0.250 0.500 0.750-3-0.125x10

-3-0.100x10

-3-0.075x10

-3-0.050x10

-3-0.025x10

0

-30.025x10

-30.050x10

-30.075x10

-30.100x10

-30.125x10

E / V

I /

A

5000 scans

Typical supercapacitor responses

Fast charge-discharge bahavior

Good lifetime

Low environmental impact

Low cost

However, specific capacitance is low (10~20 F g-1)

200 mV s-1

Pseudocapacitance

Activity of O-groups

E

I

De

crease

in activity

Activation of Biochar

Black: Untreated

Red: HNO3-treated

-0.500-0.250 0 0.250 0.500 0.750 1.000 1.250-2-0.100x10

-2-0.075x10

-2-0.050x10

-2-0.025x10

0

-20.025x10

-20.050x10

-20.075x10

E / V

I /

A

Current-potential curve

Untreated

HNO3-treated

0 50.0 100.0 150.0 200.0 250.0 300.0-0.500

-0.250

0

0.250

0.500

0.750

1.000

1.250

t / s

E /

V

Constant current charge-discharge

0.5 A g-1

Raman and FTIR Patterns

0 1000 2000 3000 4000

ID/I

G=1.05

ID/I

G=1.18

D+G

D*

G

D

Inte

nsit

y / a

.u.

Wavenumber / cm-1

Untreated

HNO3-treated

Capacity of Biochar in Aqueous Electrolyte

Electrode material Specific capacitance

(F g-1) BET Surface area

(m2 g-1)

Activated Biochar 100 to 300 300~400

Carbon black 100 to 300 1000~2000

Activated carbon 100 to 400 1000~3000

Mesoporous carbon 100 to 200 1500~2500

Reduced graphene oxide 150 to 250 2000~3000

Multiwall carbon nanotube 100 to 150 500~1000

Single-wall carbon nanotube 100 to 200 1500~2000

Source: Zhang & Zhao, ChemSusChem, 5 (2012) 818-841.

Electrolyte Dependence

Solvent Or salt

Anode potential limit / V

Cathode potential limit / V

Potential window /

V

Water -0.20 1.2 1.4

Acetonitrile -2.8 3.3 6.1

Propylene carbonate

-3.0 3.6 6.6

TEABF4 -3.0 3.65 6.65

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5-0.005

-0.004

-0.003

-0.002

-0.001

0.000

0.001

0.002

0.003

0.004

0.005

0.5 M H2SO

4

BMIBF4

1 M KOH

Cu

rre

nr

/ A

Potential / V

1.4 V

2.7 V

*Potential vs SCE.

Source: Aurbach et al, Nonaqueous electrochemistry,

Marcel, 1999

Maximum energy stored

Emax = CV2/2 (V: cell operating voltage)

Specific Capacity of Biochar in non-Aqueous Electrolyte

Electrode material Specific

capacitance (F g-1)

Surface area (m2 g-1)

Biochar in TEABF4 75 400

Biochar in TEAPF6 35 400

Biochar in TBAPF6 30 400

Activated carbon TEABF4 90 to 140 1000 to 1400

Mesoporous carbon in TEABF4 70 to 160 1500 to 2000

Graphene in TEABF4 100 ~3000

Carbon nanotube in TEABF4 80 to 110 ~2000

Source: J. Zhang & X. Zhao, ChemSusChem 5 (2012) 818-841.

Charge Transport Model

0 25 50 75 100 125 150 175 2000

25

50

75

100

125

150

175

200

Z' / ohm

-Z'' / o

hm

AC impedance spectra

R1

Q1

C

ZW R2

Zw: Warburg transport resistance

Medium

BC Cathode

-

-

-

Charged Discharged

Medium

BC Cathode

-

-

-

-

- -

-

-

Charge transport within a single pore

Conclusions

Biochars have finger-print microstructures inherited their corresponding biomass precursors;

Low ash even zero-ash high carbon bichars can be prepared from wood feedstocks;

Biochar supercapacitors have demonstrated promising capacity and durability which are comparable to those of using advanced carbon materials, especially in aqueous media;

Surface activation of biochars substantially increases their capacitance and degree of surface utilization;

Woody biochars with developed surface area, good conductivity, electrochemical stability, and interesting pore network will be promising energy and environmental materials.