Carbon Nanotube and Cellulose-Based Energy Storage

Trevor J. Simmons, SangHyun Lee, TaeJoon Park, Daniel P. Hashim, Robert J. Linhardt, Pulickel M. Ajayan*Rensselaer Polytechnic Institute, Troy, NY

*Rice University, Houston, TX

• Discovered in 1991 by Sumio Iijima• Graphene sheets rolled into tubes• Single and multiple wall CNTs exist• Can be semiconducting or metallic• High tensile strength, highly flexible• High surface area, high aspect ratio• Thermally and chemically stable• Can be grown as vertically aligned arrays

Brief Background on Carbon Nanotubes

Wikipedia.org

Cellulose

• Composed of glucose units with β-glycosidic linkage• Main constituent of wood, dried plant matter, paper• Highly fibrous, non-conductive, porous

Why Cellulose?

• Low Cost • Physical Properties

Strong, lightweight, flexible

• Substitute for Petrochemicals• Low Environmental Impact

‘Green Chemistry’ avoids volatile organic solvents

• Renewable FeedstockAgriculture by-product, recycled matter

Problems with Cellulose

• Poor solubility in most solvents• Requires extensive chemical activation

(e.g.: formation of cellulose acetate to make soluble)

• Extraction from native materials(e.g.: lignocellulosic materials such as wood)

Ionic Liquids provide a solution to these problems

Room Temperature Ionic Liquids

• Composed of almost entirely ions• Essentially exist as ‘molten salts’• Very low vapor pressure• High thermal and chemical stability• Remain Liquid over a wide temp. range• Can replace volatile organic solvents• Highly recoverable and recyclable

Total number of Ionic Liquid Publications and Patents 1990-2006

El Seoud et al., Biomacromolecules, Vol. 8, No. 9, 2007

Electrospun Fibers from RTIL

TJ Park et al., ACS symposium series books, Polysaccharide Materials: Performance by Design, 2007

Cellulose Film Electrospun Cellulose Fibers

Vertically Aligned MWNT Arrays from CVD

FerroceneXylene

Argon

800 °C

SiO2 Substrate

Quartz Tube Furnace

Xylene-Ferrocene MWNT

Completed Nanotube Material on SilicaDeposition of Cellulose from RTIL

Cellulose dissolved in RTIL

RTIL in Cellulose

Ethanol

[Cl] -

[CH3COO] -

[PF6] -

emim

bmim

Anions (-) Cations (+)RTIL of Interest:

[bmim]Cl

[bmim]PF6

[emim]CH3COO

• Comparison between [Bmim][Cl] and [Emim][acetate]

E. Uerdingen (BASF) “Current status in ionic liquids technology”, ERC symposium in Korea.

Composite Material Removed from Substrate

Titanium Metal DepositionGold Metal Deposition

CelluloseIn RTIL

IonicDiffusion

Pushparaj et al., PNAS, 2007, 104, 34

Mechanism of Charge Separation

Super-Capacitor Device

Applied Voltage

Improved infiltration of cellulose will enable enhanced capacitance

Electric Double Layer

Cellulose-based Lithium Battery

Why Replace Existing Li-Batteries?

• Price - If you disagree, can you please buy me some?

• Weight - a majority of a device weight is the battery

• Reliance on Petrochemical Polymers• Short lifetime in non-optimal conditions• Hazards posed by dangerous reactions:

Lithium Metal Volatile Organic ElectrolyteBurns on contact with air/moisture Flammable, thermally unstable

According to the US Consumer Product Safety Commission there were 339 incidents of:

“overheating, emitting smoke and fumes or exploding since 2003.”

Benefits of Cellulose Battery Design

• Inexpensive, scalable process• Low-toxicity materials• Non-flammable electrolyte• Avoids use of highly reactive lithium metal

MWNT LiCoO2

Cu

Cur

rent

Col

lect

or

Al C

urre

nt C

olle

ctor

Au/Ti Cellulose

Anode(-) Cathode(-)

Cellulose with TiO2 and Li+

20-50 μm

Anode(MWNT)60-100 μm

Cathode(LiCoO2)

Au200-400 nm

Ti20-100 nm

Layer Thickness(not drawn to scale)

cellulosewith TiO2

Anode(MWNT)

Cathode(LiCoO2)

Al c

urre

nt c

olle

ctor

Charging

+

+

++

+

+

+

+

+

+

Li+

+

AnodexLi+ + Cn → LixCn

Li+ insertion

CathodeLiCoO2 → Li1-xCoO2 + xLi+

Co oxidation

Cn + LiCoO2 → LixCn + Li1-xCoO2

e-

Cellulose and Electrolyte(LiTFSI and [CrBim]TFSI)

Intercalated Li

LiCoO2Cathode

Li

Li

Li

CelluloseCurrentCollector

+

+

+

electron

lithium ion

-

-

-

-

Li

Li

Li

Intercalated lithium lithiumcobalt oxide

Carbon Nanotubes

Charging

AnodeLixCn→ xLi+ + Cn

Li+ extraction

CathodeLi1-xCoO2 + xLi+ →LiCoO2

Co reduction

LixCn + Li1-xCoO2 → Cn + LiCoO2

cellulosewith TiO2

Anode(MWNT)

Cathode(LiCoO2)

Al c

urre

nt c

olle

ctor

Cellulose and Electrolyte(LiTFSI and [CrBim]TFSI)

++

+

++

++

+

++

+

++

+

Li++

+

e-

Discharging

LiCoO2CathodeCellulose

CurrentCollector

-

-

-

-

-

-

Li

Li

Li

Intercalated lithium

Carbon Nanotubes

+

+

+ Li

Li

Li

lithiumcobalt oxide

lithium ionDischarging

Lithium Intercalation

Expansion of graphene sheets can lead to exfoliation

Lithium Intercalation

MWNT cannot expand like graphite, and rupturing can occur

Flexible nanocompositeEnergy device

Voltage(V)

Capacity Specific Energy(Wh/Kg)

Specific Power(W/Kg)

Operating temperature

(o K)Thin film Paper

battery(Liquid electrolyte)

3.6 110 mAh/g 300 140 273- 333

Supercapacitor(RTIL electrolyte)

2.2 80 F/g 13 1500 195 - 450

Flexible nanocomposite energy devices

Conclusions• Ionic Liquids are excellent cellulose solvents• RTILs can be easily recycled and reused• Cellulose is an alternative to high-dielectric

synthetic polymers based on petrochemicals• Carbon nanotubes can replace graphite as a

high surface area electrode material• Super-capacitors and Li-Ion batteries can be

made from cellulose, RTILs, and CNT

AcknowledgementsAdvisors

Dr.Pulickel AjayanDr.Robert LinhardtDr.Robert VajtaiDr.Fuming Zhang

Co-Workers

Dr.Sang Hyun LeeTae Joon ParkDr.Justin BultDaniel HashimDr.Ashavani KumarDr.Victor PushparajDr. M. ShaijumonDr. Swastik Kar

Funding Sources• NSF award DMR-0303174

• NSF Materials World Network: Fabrication of Polymer Composites and Sensors Using Doped Nanotubes (DMR-0801012)

• NSF-funded Nanoscale Science and Engineering Center on directed assembly of nanostructures.

• NYSTAR New York State Office of Science, Technology,and Academic Research

• National Institutes of Health grant AI06578

Results of Electrochemical Tests

Pushparaj et al., PNAS, 2007, 104, 34