Novel Carbon Materials for Electrochemical Applications

Giselle SandíChemistry Division

In 1785 Luigi Galvani observed, while dissecting a frog, that the frog’s legs would twitch whenever touched by a steel rod

Topics of Discussion The Rocking Chair Model: Lithium

Ion Batteries Types of Electrodes

Anodes of Choice Synthesis and Characterization of

Novel Carbon Materials Electrochemical Performance New Directions Acknowledgments

System Net Electrochemical ReactionRechargeable CellsLead-Acid PbO2 + Pb + 2H2SO4 2PbSO4 +

2H2ONickel-Cadmium 2NiOOH + Cd + 2H2O 2Ni(OH)2

+ Cd(OH)2

Nickel-Hydrogen 2NiOOH + H2 2Ni(OH)2

Lithium-Ion Li+ + xC + e- LiCx

Non-RechargeableCellsLeclanché or dry cell Zn + 2MnO2 ZnOMn2O3

Alkaline cell Zn + 2 MnO2 ZnO + Mn2O3

Silver-Zinc Ag2O2 + 2Zn + 2H2O 2Ag +2Zn(OH)2

Zinc-Air 2Zn + O2 + 2H2O 2Zn(OH)2

Fuel Cell 2H2 + O2 2H2OLithium-Iodine 2Li + I2 2LiILithium-SulfurDioxide

2Li + 2SO2 Li2S2O4

Lihium-ThionylChloride

4Li + 2SOCl2 4LiCl + S+ SO2

Lithium-ManganeseDioxide

Li + Mn(IV)O2 LiMn(III)O2

Lithium-CarbonMonofluoride

xLi +(CF)x xLiF + xC

Examples of Batteries Commercially Available

0 50 100 150 200 250

Energy Density (Wh/kg)

Lithium-Ion (High Energy)

Lithium-Ion (Long Life)

Silver-Cadmium

Nickel-Hydrogen

Lead -Acid (Automotive)

Nickel Cadmium (High Energy)

Lead -Acid (High Energy)

Nickel-Cadmium (Sealed)

Alkaline Manganese

Comparison of the energy density of the most common rechargeable batteries

e-e-

Li = Anode Cathode

Problems with metallic Li

The Rocking Chair ModelCharge

Discharge

ElectrolyteCathode Anode

Li+

Li+

Li+

Li+

Types of ElectrodesCathode materials Anode materials Transition metal oxides and chalcogenidesUni-dimensional structures: TiS3, NbSe3

Bi-dimensional structures Metal sulfides of Ti, Nb, Ta, Mo, and WMetal oxides of V, Cr, Fe, Co, Ni and Mn

Three-dimensional structureManganese oxides: -MnO2 (Mn2O4)

Organic molecules

Polymers

Pitches

Cokes

Natural graphite

Fullerenes

Synthetic carbons

Practical Considerations Selection of a suitable electrolyte

To minimize the decomposition that occurs during the lithiation of the carbon formation of a passivating layer

Liquid electrolytes: LiPF6/EC/DEC Polymer electrolytes

Low surface area carbons Amount of lithium consumed in the formation of the

passivating layer is proportional to the surface areaof the carbon

The Novel Approach

Silicate layer ++

++

++

++

Intercalation

Hydroxyl cation

-nH2O

Pore

At the beginning….

Pillared clay (PILC)

Carbon Precursors

C

H H

HH

C CC

H H

H

H

C

H

Mechanism similar to Schllreaction: 2 ArH Ar-Ar + H2

AlCl3

H+

Incorporation of liquid monomerfollowed by low temperaturepolymerization reaction

Linear polymer

Condensationpolymer similarto phenoplasts

Gaseous hydrocarbon is deposited in the PILC layers and pyrolized

H

O

O O

Loading Methods

pyrolize at 700 °Cunder N2, dissolvein HF, and reflux inHCl

overnight dry

Pyrene

N2

Styrene

PILC

To vacuum Wash out excess and dry

Styrene

N2

C2H4 orC3H6

C2H4 or C3H6

Characterization Techniques X-ray powder diffraction Thermal gravimetric analysis Scanning electron microscopy Transmission electron microscopy Scanning tunneling microscopy Near-edge X-ray absorption fine structure Small angle neutron scattering Small angle X-ray scattering NMR techniques Electrochemical techniques

Angle 2 2

0 10 20 30 40 50

Re

lati

ve

Inte

ns

ity

Styrene, 3.50 DEthylene, 3.58 DTrioxane, 3.49 DPropylene, 3.56 DPyrene, 3.42 D

XRD of carbon samples derived from the “templating” method

High resolution TEM of a carbon sample

synthesized using PILC/pyrene

Energy, eV

280 290 300 310 320

Re

lativ

e In

ten

sity

Carbon from pyreneCarbon from styreneCarbon from propyleneCarbon from trioxane

B*1 (C=C)C-H*

F* C-C F* C=C

B*2

C K-edge of different carbon samples

Energy, eV520 540 560 580

Re

lativ

e In

ten

sity

1.1

1.2

1.3

1.4

1.5

1.6

1.7

PyreneStyrenePropyleneTrioxane

O K-edge of different carbon samples

Energy, eV280 290 300 310 320

Rel

ativ

e In

tens

ityCarbon from pyreneCarbon from styreneCarbon from trioxane

292 eV

B*

302 eVF*

C K-edge of different carbon electrodes

1/

q-df

1/r

Log Q ()Lo

g S

(Q

)

Theory of Freltoft, Kjems, and Sinha (Phys. Rev. B. 1986)

SANS Analysis

Where:df = fractal dimensionr = hole radius = cutoff length

Q (D)-10.01 0.1 1

I(Q

) cm

-1

0.01

0.1

1

10

100

1000

10000

PILCPILC/pyreneCarbon

Sample r (Å) (Å) df

PILC 3.7 ± 0.3 876 ± 400 2.47 ± 0.01

Carbon fromPILC/pyrene

11.4 ± 0.3 1380 ± 320 2.68 ± 0.02

Carbon fromPILC/styrene

10.9 ± 0.2 806 ± 54 2.88 ± 0.01

Carbon fromPILC/ethylene

4.0 ± 0.6 112 ± 0.6 2.74 ± 0.02

Carbon fromPILC/propylene

4.0 ± 0.1 364 ± 4 2.86 ± 0.01

Carbon fromPILC/trioxane

2.3 ± 0.4 161 ± 1 2.77 ± 0.01

Experimental parameters calculated from SANS data

15 År0

3.7 Å

Al2O3

Al2O3

N2, 700 °C

HF, HCl

r0

11.4 Å

Schematic representation of the mechanism of formation of porous carbon using PILC/pyrene

Coin cell used to test the electrochemical performance

Electrodes were prepared using:90% m/m carbon5% m/m carbon black5% m/m binder (PVDF in NMP)

t

t

dtIech0

arg

ech

edischefficiency

IfordtIech

IfordtIedisch

cycle

cycle

arg

arg

0arg

0arg

Where:charge is the charge capacityt0 is the starting timet is the current timeI is the current value measuredfor this data point

Applied current for 20 hrs (C/20):

I20h = 18.6 (mA) x Wact (g)

Electrochemical parameters

Capacity, mAh/g

0 200 400 600 800 1000 1200 1400 1600 1800

Vo

ltag

e, V

0.0

0.5

1.0

1.5

2.0

2.5

Carbon from pyreneCarbon from styreneCarbon from propyleneCarbon from trioxane

Voltage profiles of the second cycle of various C/Li cells

Number of cycles

0 20 40 60 80 100

Cou

lom

bic

effic

ienc

y, %

50

60

70

80

90

100

110

StyreneTrioxanePyrenePropylene

Coulombic efficiencies obtained for C/Li coin cells cycled between 0 and 2.5 V

Carbonfrom

Averagespecific

capacity,mAh/g

Standarddeviation,mAh/g

Irreversiblecapacity,mAh/g

Pyrene 720 60 62

Styrene 730 45 177

Propylene 794 91 180

Trioxane 675 75 165

Effect of different carbon precursors on the performance of Li/C coin cells

Role of curved vs. planar carbon

lattices in the lithium uptakeInfluence of a curved lattice (C60) on the nature of lithium bonding and spacing in endohedral lithium complexes

Interior of the C60 is large enough to easilyaccommodate two or three lithium atoms

The curved ring structure of theC60 facilitated theclose approach ofthe lithiums (2.96 Å),even in the trilithiatedspecies

Role of curved vs. planar carbon

lattices in the lithium uptake…..Implications: 2.96 Å is closer than the interlithium distance in the stage-one

LiC6 complex Lithium anode capacities may be improved over graphitic

carbon by synthesizing carbons with curved lattices such as corannulene

Concept was experimentally tested using corannulene as a model electrode material

Time (h)0 10 20 30 40 50 60 70 80 90 100 110

Vo

ltag

e (

V)

0.0

0.5

1.0

1.5

Time (h)0 50 100 150 200 250 300 350 400

Vol

tage

(V

)

0.0

0.5

1.0

1.5

Voltage profile of an electrode made of corannulene vs. Li

Potentiostat

NMR Spectrometer

Working Electrode

Counter Electrode

Electrochemical NMRUses: Near electrode chemistry

Electrode-electrolyte interface Electrolyte depletion zone

Transport properties of battery materials Electrolyte penetration Redox chemistry at the SEI Li “location” and chemical nature

Carbon sampleCelgard separator

LithiumCopper mesh

Working electrode (current collector) and NMR detector (central conductor)

Electrochemical NMR…New approach

The “old” cell

Standard 2032 size In situ NMR detector Imaging capability

The “new” toroid cavity coin cell

7Li Chemical Shift (PPM)-2000-1000010002000

-300-200-1000100200300

A

B Graphite

Corannulene

Electrochemical NMR…Spectra obtained using the new cell

A) Li intercalated into graphite, Li:C 0.8:6B) Li-corannulene complex, Li:C 1.8:6

A= Two tetrahedral sheets and a central magnesium octahedral sheet

N= neutral sites

B= cross section of an ideal fiber

P= charged adsorption sites

An advanced synthetic route to produce high performance carbons…..sepiolite clay

Degrees 220 10 20 30 40

Rel

ativ

e In

tens

itySepioliteSepiolite/propyleneCarbon

3.57 Å

XRD of sepiolite, sepiolite/propylene composite,and carbon obtained after removal of the template

TEM of sepiolite, sepiolite/propylene composite,and carbon obtained after removal of the template

0

0.5

1

1.5

2

0 1000 2000 3000 4000 5000 6000

Capacity (mAh/g)

Vo

ltag

e (V

)

Cycle number0 10 20 30 40 50

Effi

cie

ncy

50

100

300

Voltage profile and efficiency of carbon electrodes derived from sepiolite/propylene

7Li Chemical Shift (PPM)

-300-200-1000100200300

sepiolite-derived carbon

sepiolite-derived carbon

Graphite

Delithiated

Lithiated

Lithiated

LiC6

Electrochemical NMR…Spectra obtained using the new cell

Separator

Cu meshCu mesh

Polypropylene bag

LiCarbon

Electrolyte

Pouch electrochemical cell for in situ SAXS experiments

10-7

10-6

10-5

10-4

10-3

Inte

nsi

ty (

cm)-1

3 4 5 6 7 8 90.1

2 3 4 5 6 7 8 9

q (Å)-1

2.95 V 2.41 V 1.71 V 1.11 V 0.41 V 0.00 V 0.60 V

2

4

6

810

-5

2

4

6

810

-4

2

4

6

Inte

nsi

ty (

cm)-1

3 4 5 6 7 8 90.1

2 3 4 5 6 7

q (Å)-1

2.60 V 2.06 V 1.46 V 0.86 V 0.22 V 0.00 V 0.35 V

There are no changes in thestructure upon Li incorporation

Lattice expansion uponLi incorporation

In situ SAXS results of a carbon electrodes a) derived from sepiolite and b) commercial graphite

a

b

Voltage/V

0.00.61.21.82.4

Po

wer

Law

Slo

pe

1.9

2.0

2.1

2.2

2.3

2.4

2.5

2.6

GraphiteTemplated carbon

Changes in the power law slope with discharge from 2.6 to 0 V

Summary

The novel approach for synthesizing carbon produced good candidates for electrochemical applications

Understanding the performance of these carbons as a function of structure has been a main goal of this research

More efforts will be dedicated to conducting in situ SAXSand NMR experiments to elucidate the Li “location”upon charging and discharging electrochemicalcells

ACKNOWLEDGMENTS

This work was performed under the auspices of the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, under contract number W-31-109-ENG-38.

Randy Winans (CHM)Kathleen Carrado (CHM)Christopher Johnson (CMT)Rex Gerald and Robert Klingler (CMT)P. Thiyagarajan (IPNS)Sönke Seifert (CHM, APS)Roseann Csencsits (MSD)Lawrence Scanlon (Wright Patterson AFB)Lawrence Scott (Boston College)