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Novel Carbon Materials for Electrochemical Applications. Giselle Sandí. Chemistry 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

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slide2

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
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
slide5

Comparison of the energy density of the

most common rechargeable batteries

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

slide6

Problems with metallic Li

Cathode

Li = Anode

e-

e-

the rocking chair model
The Rocking Chair Model

Charge

Li+

Li+

Cathode

Electrolyte

Anode

Li+

Li+

Discharge

types of electrodes
Types of Electrodes

Anode materials

Cathode materials

  • Pitches
  • Cokes
  • Natural graphite
  • Fullerenes
  • Synthetic carbons
  • Transition metal oxides
  • and chalcogenides
  • Uni-dimensional structures: TiS3, NbSe3
  • Bi-dimensional structures
  • Metal sulfides of Ti, Nb, Ta, Mo, and W
  • Metal oxides of V, Cr, Fe, Co, Ni and Mn
  • Three-dimensional structure
  • Manganese oxides: -MnO2 (Mn2O4)
  • Organic molecules
  • Polymers
slide9

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 area

of the carbon

the novel approach
The Novel Approach

At the beginning….

Intercalation

+

+

Silicate layer

Pore

+

+

-nH2O

+

+

+

+

Hydroxyl cation

Pillared clay (PILC)

carbon precursors
Carbon Precursors

Linear

polymer

Condensation

polymer similar

to phenoplasts

O

O

O

Mechanism similar to Schll

reaction: 2 ArH Ar-Ar + H2

Incorporation of liquid monomer

followed by low temperature

polymerization reaction

AlCl3

H+

H

H

H

C

C

C

H

H

H

Gaseous hydrocarbon is deposited in the PILC

layers and pyrolized

loading methods

Pyrene

Loading Methods

pyrolize at 700 °C

under N2, dissolve

in HF, and reflux in

HCl

overnight

dry

Styrene

N2

Wash out excess and dry

To vacuum

C2H4 or C3H6

PILC

Styrene

C2H4 or

C3H6

N2

characterization techniques
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
slide19

SANS Analysis

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

q-df

Log S (Q)

1/

1/r

Log Q ()

Where:

df = fractal dimension

r = hole radius

 = cutoff length

slide21

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

Al2O3

15 Å

r0

N2, 700 °C

r0

3.7 Å

11.4 Å

HF, HCl

Al2O3

slide22

Coin cell used to test the electrochemical performance

Electrodes were prepared using:

90% m/m carbon

5% m/m carbon black

5% m/m binder (PVDF in NMP)

slide23

Electrochemical parameters

Where:

charge is the charge capacity

t0 is the starting time

t is the current time

I is the current value measured

for this data point

Applied current for 20 hrs (C/20):

I20h = 18.6 (mA) x Wact (g)

slide27

Role of curved vs. planar carbon lattices in the lithium uptake

Influence of a curved lattice (C60) on the nature of lithium

bonding and spacing in endohedral lithium complexes

The curved ring

structure of the

C60 facilitated the

close approach of

the lithiums (2.96 Å),

even in the trilithiated

species

Interior of the C60 is large enough to easily

accommodate two or three lithium atoms

slide28

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

slide30

Electrochemical NMR

  • Uses:
  • 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

Potentiostat

Working Electrode

Counter Electrode

NMR Spectrometer

slide31

Electrochemical NMR…New approach

The “old” cell

The “new” toroid

cavity coin cell

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

Carbon sample

Celgard separator

Lithium

Copper mesh

 Standard 2032 size

 In situ NMR detector

 Imaging capability

slide32

Electrochemical NMR…Spectra obtained using the new cell

A) Li intercalated into graphite, Li:C 0.8:6

B) Li-corannulene complex, Li:C  1.8:6

slide33

An advanced synthetic route to produce

high performance carbons…..sepiolite clay

A= Two tetrahedral sheets and a central magnesium octahedral sheet

N= neutral sites

B= cross section of an ideal fiber

P= charged adsorption sites

slide34

XRD of sepiolite, sepiolite/propylene composite,

and carbon obtained after removal of the template

slide35

TEM of sepiolite, sepiolite/propylene composite,

and carbon obtained after removal of the template

slide36

Voltage profile and efficiency of carbon

electrodes derived from sepiolite/propylene

slide37

Electrochemical NMR…Spectra

obtained using the new cell

slide38

Cu mesh

Cu mesh

Polypropylene bag

Electrolyte

Separator

Carbon

Li

Pouch electrochemical cell for in situ SAXS experiments

slide39

In situ SAXS results of a carbon electrodes a) derived

from sepiolite and b) commercial graphite

a

Lattice expansion upon

Li incorporation

b

There are no changes in the

structure upon Li incorporation

slide40

Changes in the power law slope

with discharge from 2.6 to 0 V

slide41

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 SAXS

and NMR experiments to elucidate the Li “location”

upon charging and discharging electrochemical

cells

slide42

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)

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