NanoscaleNanoscale Materials: Exploring Materials: Exploring the Energy Frontierthe Energy Frontier

PrashantPrashant N. N. KumtaKumtaDepartment of Materials Science and Engineering,Department of Materials Science and Engineering,

Biomedical EngineeringBiomedical EngineeringCarnegie Mellon University,Carnegie Mellon University,

Pittsburgh, PA 15213Pittsburgh, PA 15213

Hybrid Electric Vehicle

Backup Power Source

Telecommunication

Electronic Devices

Laser

Military Use

Particle Accelerator

Nissan DieselSizuki ElectricPower Systems

www.hondacorporate.com

www.maxwell.com

www.nissandiesel.co.jp

www.nissandiesel.co.jp

www.maxwell.com

Need for Energy Storage SystemsNeed for Energy Storage Systems

Potential Energy Storage SystemsPotential Energy Storage Systems

LiLi--ion Batteriesion Batteries**

SuperSuper--capacitorscapacitors**

Direct Methanol Fuel CellsDirect Methanol Fuel Cells**

Hydrogen StorageHydrogen Storage

*Focus of the current presentation

LithiumLithium--Ion Systems: Anodes and CathodesIon Systems: Anodes and Cathodes

Comparison of Battery Energy Density(gravimetric and volumetric)

Considerable improvement in area of cathodes with identification of newlayered compounds, LiFePO4 and LiNi0.5Mn0.5O2, LiMn1/3Ni1/3Co1/3O2.Improvements in the anode area are still warranted.

° Li-alloy (LixM) : Anodes for Li ion cells- Intermetallic phases containing lithium

LixM xLi+ + xe- + M

(M = Mg, Ca, Al, Si, Ge, Sn, Sb, Bi, Zn, etc)1

- Higher theoretical capacity than graphite

(LiC6 : 372 mAh/g, 832 Ah/L,

Li22Sn5 : 990 mAh/g, 14780 Ah/L

Li22Si5 : 4000 mAh/g, 10997 Ah/L)1, 2

° Major problems of Li-alloys for use as anodes- Poor reversibility caused by large volume changes

(Sn: 593%, Si: 412% volume change)

- Cracking or crumbling during cycling1. M. Winter & J. O. Besenhard, Electrochimica Acta, 1999, 45, 31.

2. B. A. Boukamp & R. A. Huggins, J. Electrochemical Soc., 1981, 128, 729.

Introduction and Background3

3. L.Y. Beaulieu, K.W. Eberman, R.L. Turner, L.J. Krause and J.R. Dahn, Elect. Sol. St. Lett. 2001, A137.

- No secondary phase observed at the interface

Si/Transition metal non-oxide system is stable during HEMM.

20nm 20nm

Bright Field Dark Field

Nanoscale structureis the key to attainingthe high capacity

2 nm

Amorphous active phase

- Theoretical Capacity = 636 mAh/g- Higher capacity than graphite (~480mAh/g or 1450Ah/l) with stability (0.15%loss/cycle).

Electrochemical Response(Sn:C=1:1)

(Tetraethyl tin+Ps-resin powder heat-treated at 600 oC for 5h in UHP-Ar, current rate = 100µA/cm2 )

0

100

200

300

400

500

600

700

800

0 5 10 15 20 25 30

Cycle Number

Sp.C

apac

ity (m

Ah/

g)

0

500

1000

1500

2000

2500

Vol.C

apac

ity (A

h/l)

Graphite

-5000

-4000

-3000

-2000

-1000

0

1000

2000

3000

0 0.5 1 1.5 2 2.5 3

Cell Potential (V)dQ

/dV

(mA

h/g.

V)

Cycle between 0.02 and 1.2V

HEMM derived Si-C nanocompositesNanostructured inactive matrix can endurelarge volumetric stresses of the active material due to possiblesuperplastic deformation that can provide compressive stresses to accommodate large strains*.

* M.J. Mayo, Nanostructured Materials, Vol. 9 (1997) 717)Q/RTexp(Ddε op-n −=

•

σ

XTEM of sputter deposited XTEM of sputter deposited SiSi film film (250 nm as(250 nm as--deposited film)deposited film)

100 nm

Si

Cu2 nm

Conventional XTEM High Resolution XTEM

Galvanostatic Cycling of 250 nm Si Thin Film (C/2.5 and 2C rates)High Capacity and Excellent Rate Capability of 250 nm Silicon Thin Film Anode (Area = 1 cm2)

0

500

1000

1500

2000

2500

3000

3500

4000

4500

0 5 10 15 20 25 30 35

Cycle Number

Spec

ific

Cap

acity

(mA

h/g)

C/2.5 ChargeC/2.5 Discharge2C Charge2C Discharge

C/2.5 rate (100uA/cm2)

2C rate (500uA/cm2)

372 mAh/g : Theoretical Capacity of Conventional Graphite Anode Material Used in Commercial Lithium-Ion Batteries

4199 mAh/g : Theoretical Capacity of Pure Silicon Anode Material

SEM : C/2.5 rate – 30 cycles2 µm 2 µm

Si EDAX : C/2.5 rate – 30 cycles

2 µm

Also note low irreversible loss ~14% and 0.1 % loss per cycle.Increase of capacity with cycle # for the 2C sample may be due to kinetic limitation of the amorphous Si sample in the initial cycles, which is mitigated gradually in later cycles by morphological changes in the electrode, decreasing the effective diffusion distance for the lithium ions from the electrolyte.

As-Deposited

Multilayer Film SchematicMultilayer Film Schematic

Silicon (250 nm)Carbon (50nm)

Cr (10 nm)

Copper Foil (25 µm)

Note: Drawing not to scale

Note: Ecarbon ~ 50 – 500 GPa

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

0 5 10 15 20 25 30 35 40 45 50

Cycle Number

Spec

ific

Cap

acity

(mA

h/g-

Si)

dischargecharge

Cycling of Multilayer Film, C/2.5 rate

-160000

-140000

-120000

-100000

-80000

-60000

-40000

-20000

0

20000

40000

0 0.2 0.4 0.6 0.8 1 1.2

Cell Potential (V)

dQ/d

V (m

Ah/

gV)

SEM image of a 500°C-4h annealed 250 nm Si/50nm C/10 nm Cr/Cu multilayer thin film cycled at 0.4 C after 75 cycles, 5000x.

Interface dynamics control of the nanoscalefilms is the key to improved electrochemical performance

Energy Density (Wh/kg)

Pow

er D

ensi

ty (W

/kg)

1 h

6 min40s4s

10 h

100 h

1000 h

10

100

1000

10000

10 100 1000 100001

Pb/Acid

Supercapacitor

Ni-Cd

NiMH

Primary Li

Li-ion

Leclanche

Alkaline

Zinc-Air

Fuel Cell

Electrochemical Capacitor

“Ultracapacitor”“Supercapacitor”

Primary Battery

• Leclanche• Primary Li • Alkaline

Secondary Battery

• Pb/Acid• Zinc-Air• Ni-Cd• NiMH• Li-ion

Fuel Cell

Ragone Plot

Supercapacitors: Potential Energy Storage Systems

Gouy-ChapmanDiffuse Layer

Stern Layer

+

_

-

-

-

-

-

-

Cation

Anion

Neutral Molecule

+

-

1/k

ψ0 ψd

Inner Helmholtz Layer

Outer Helmholtz Layer

(≈ ζ )

H2O (Solvent)

+_

−−−+

=)exp(1)exp(1ln

2xx

zeTkB

κγκγψ

=

Tkze

B

o

4tanh ϕγ

KB : Boltzmann constant ϕ0 : Potential at (x=0)z : Ion valency x : Distance from the surface T : Temperature εo : Permittivity of free spaceεr : Solvent dielectric constantCo : Electrolyte concentration

Non-Faradaic : No electron transfer

Ex) Dielectric CapacitorElectric Double Layer Capacitor

= ∗

TkzeTckB

orooB 2

sinh)8( 2/1 ϕεεσ

θB= f (V)

Cφ

Cφ∆V0.5

∆V0.5

θA= f (V)

θ

Cφ

(= q

·dθ/

dV)

(g = 0) (g > 0)

)exp(exp1

θθ

θ gRTVFK ±

=

−

2

exp1

exp

+

⋅=≈

RTVFK

RTVFK

RTF

dVdC θ

φ

1θ

2θ

Faradaic : electron transfer

Ex) Battery, Pseudocapacitor

θ : CoverageV : VoltageK : Reaction rate constantg : Adsorption isotherm constantF : Faraday constant

dzeOx Re↔+

Lin Lin et al. et al. 5050--1.1 1.1 −− 0.80.81M KOH1M KOH291291Co(OH)Co(OH)22 XerogelXerogel

Prasad Prasad et al.et al.2002000 0 −− 0.750.751M LiClO1M LiClO44 in PCin PC650~1300650~1300Polyaniline (PANI) Polyaniline (PANI) on Stainless Steelon Stainless Steel

Clement Clement et al.et al.50500 0 −− 1.21.2Poly(methylmethacrylate) Poly(methylmethacrylate) –– PMMAPMMA2525Polyaniline (PANI)Polyaniline (PANI)

Arbizzani Arbizzani et al.et al.50500 0 −− 0.30.3Poly(ethylene oxide) Poly(ethylene oxide) –– PEOPEO1515Poly(dithienothiophene)Poly(dithienothiophene)--pDTTpDTT

Searson Searson et al.et al.2525--2 2 −− 00Poly(acrylonitrile)Poly(acrylonitrile)23 ~ 30mAh/g23 ~ 30mAh/gPoly3Poly3--(3,5(3,5--difluorophenylthiophene)difluorophenylthiophene)Polym

erPolym

er

Wu Wu et al.et al.22--1.2 1.2 −− 1.21.21M Na1M Na22SOSO443838FeFe33OO44

Liu Liu et alet al. . 1010--0.4 0.4 –– 0.50.51M KOH1M KOH260260NiONiOxx

Lee Lee et alet al..10100.1 0.1 −− 0.850.851M KCl1M KCl153153Amorphous MnOAmorphous MnO22⋅⋅HH22OO

Long Long et al. et al. 220.2 0.2 −− 0.70.70.5M H0.5M H22SOSO44900900RuORuO2 2 on Carbon Tapeon Carbon Tape

Zheng Zheng et alet al. . 2250500 0 −− 110.5M H0.5M H22SOSO44

720 ~ 760720 ~ 760250250RuORuO22··xHxH22OO

Raistrick Raistrick et al.et al.1001000 0 −− 110.5M H0.5M H22SOSO44350350RuORuO22Transition Metal O

xideTransition M

etal Oxide

Zhou Zhou et al.et al.550.75 0.75 –– 3.753.751M LiPF1M LiPF669595MesoporousMesoporous CarbonCarbon

Ma Ma et al.et al.10mA10mA0 0 −− 0.90.938wt% H38wt% H22SOSO4415 ~ 2515 ~ 25Carbon nanoCarbon nano--tubestubes

Niu Niu et alet al. . --0038wt% H38wt% H22SOSO44113113MultiMulti--walled carbon walled carbon nanonano--tubestubes

Carbon

Carbon

ReferenceReferenceScan rateScan rate(mV/s)(mV/s)

Potential Potential WindowWindow

(V)(V)ElectrolyteElectrolyte

Gravimetric Gravimetric Capacitance Capacitance

(F/g)(F/g)MaterialMaterial

Competitive Systems

Good Electrical Conductivity

• High rate electrochemical response of the capacitor depends onelectrical conductivity of the electrode and the ionic conductivity of the electrolyte

Chemical Stability

• The electrolyte widely used are corrosive (H2SO4 or KOH)

Cost

High Mass Density (g/cm3)

• To increase volumetric capacitance (F/cc)

High Specific Surface Area (m2/g )

• To increase the electrode-electrolyte interface area for charge storage

Transition Metal Nitrides: Novel Capacitor Materials

194.96194.965.555.55××10104414.114.1Cubic (Fm3m)Cubic (Fm3m)TaNTaN

612.87612.87< 10< 10--44Orthorhombic Orthorhombic (Cmcm)(Cmcm)TaTa33NN55

197.89197.8912.1212.12Cubic (Pn3m)Cubic (Pn3m)WNWN

205.88205.885.055.05××1010448.48.4Cubic (Pm3m)Cubic (Pm3m)MoMo22NN

106.91106.911.281.28××1010448.38.3Cubic (Fm3m)Cubic (Fm3m)NbNNbN

105.23105.235.555.55××1010447.097.09Cubic (Fm3m)Cubic (Fm3m)ZrNZrN

64.9564.951.671.67××1010446.046.04Cubic (Fm3m)Cubic (Fm3m)VNVN

61.9161.912.52.5××1010445.435.43Cubic (Fm3m)Cubic (Fm3m)TiNTiN

12.0012.00< 4< 4××101044< 1< 1--CarbonCarbon

133.07133.0722××1010666.976.97Tetragonal Tetragonal (P4(P422/mnm)/mnm)RuORuO22

M.W.M.W.Electronic ConductivityElectronic Conductivityσ×σ×1010--22ΩΩ--11mm--11

DensityDensity(g/cm(g/cm33))

StructureStructureMaterialMaterial

Ref: 1) J. P. Zheng, P. J. Cygan, and T. R. Jow, J. Electrochem. Soc., 142(8), (1995) p.26992) M. Wixom, L. Owens, J. Parker, J. Lee, I. Song, and L. Thompson, Electrochem. Soc. Proc., 96 (25) (1999)

p. 633) P. T. Shaffer, Handbook of High-Temperature Materials, Vol.1, pp.292-92. Plenum Press, New York, (1964)

VN-400oC

VN500o C

TEM Analysis: Morphology of the Nanocrystalline Nitirdes

-45-40-35-30-25-20-15-10-505

1015202530354045

100mV/s 50mV/s 25mV/s

10mV/s

-1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0

2mV/s

Gra

vim

etric

Cur

rent

(I/g

)

Potential V (vs. Hg/HgO)

1 10 1000

200

400

600

800

1000

1200

1400 0.25mg/cm3

0.28mg/cm3

0.44mg/cm3

0.67mg/cm3

0.99mg/cm3

Gra

vim

etric

Cap

acita

nce

(F/g

)

Scan Rate (mV/s)

Figure 2 The (a) cyclic voltammogram of nanocrystallites synthesized at 400oC and (b) gravimetric capacitance (F/g) versus VN nanocrystallites loading scanned at various rates (2~100mV/s) in 1M KOH electrolyte.

Electrochemical Response of the Nanocrystalline Nitrides

4000 3500 3000 2500 2000 1500 1000 500

V=O

-OH stretching

V-O

3535

3047

3423

798

970

VN 400oC cycled 10times at 2mV/s

Wavenumber (cm-1)

(a)

(b)

VN 400oC

(c)

VN 400oC in 1M KOH for 24h

Tran

smitt

ance

(%)

1

x 103

5

10

15

20

25

Cou

nts

540 535 530 525 520 515 510 505Binding Energy (eV)

O 1s

V 2p1

V 2p3

(a)

1

x 103

4

6

8

10

12

14

16

18

20

22

Cou

nts

540 535 530 525 520 515 510 505Binding Energy (eV)

O 1s

V 2p1

V 2p3

(b)

The FTIR spectra of (a) VN powder, immersed in 1M KOH solution for 24h and cycled 200 times and XPS spectra of VN powder (b) before and (c) after electrochemically cycled for 200 times.

Controlled oxidation is the keyminimal reduction in electronicconductivity

XPS: Presence of V2O5before cycling

XPS: Formation of V2O3 after 200 cycles

Major Benefits of Direct Methanol Fuel CellsMajor Benefits of Direct Methanol Fuel Cells

High Efficiency of Energy ConversionHigh Efficiency of Energy Conversion•• Enhanced utilization of fuelEnhanced utilization of fuel•• Lower carbon dioxide emissionsLower carbon dioxide emissions

Direct Generation of Electrical EnergyDirect Generation of Electrical Energy•• Losses in mechanical to electrical energy Losses in mechanical to electrical energy

conversion is avoidedconversion is avoided

Low temperature operationLow temperature operation•• Low emissions of nitrogen oxides, carbon Low emissions of nitrogen oxides, carbon

monoxide and particulatesmonoxide and particulates

Potential solution for portable applicationsPotential solution for portable applications

Near Ambient temperature operationNear Ambient temperature operationHigh energy density required High energy density required Easy to handle fuelEasy to handle fuel

2W 20W 50-100W 500W 1-5kW

DIRECT METHANOL FUEL CELL SYSTEM

METHANOL FUEL CELL

G. Cacciola et al. J. Power Sources 100 (2001) 67-79

CO2 Emissions and Efficiency for Traditional ICE

and methanol or hydrogen fed Fuel Cells

DrawbacksDrawbacks

Expensive materialsExpensive materials•• Platinum catalysts, Platinum catalysts, fluoropolymersfluoropolymersComponents that are expensive to Components that are expensive to manufacturemanufactureLack of fuel flexibilityLack of fuel flexibilityRequires clean fuel; Requires clean fuel; e.g.e.g. sulfur free sulfur free Electrochemical reactions are sensitive to Electrochemical reactions are sensitive to poisons in the environmentpoisons in the environment

PROTON EXCHANGE MEMBRANE (PEM)

CO2

<3% Methanol / water

- Electrode (Anode) + Electrode (Cathode)

LOAD +-

OXIDANT

CO2

3% Methanol / water

FUEL

6H+

+ H20, N2, O2

Air (O2)

3H2O

6H+

+3/2 O2

6e-6e-

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H2O+

CH3OH

Direct Methanol Fuel Cell Concept

Cathode (Pt)

6H+ + 1.5 O2 + 6e- 3H2O

Anode (Pt-Ru)

CH3OH + H2O CO2 + 6H+ + 6e-

Synthesis of Catalysts

• Most synthetic approaches in the literature are based on the reduction of Halide precursors of Pt and Ru

• Limitations:

—Need for several washing steps to eliminate unwanted by-products

—Tedious process leading to loss of active material

— Poisoning of the catalyst

• Need for improved catalyst using non-halogen containing precursors

• Objective: Develop novel sol-gel based methods using non-halogen precursors for generating Pt-Ru catalysts— High surface area— Pt to Ru ratio close to unity— High electrochemical activity — (low polarization of the electrode)

Morphology Characterization Transmission Electron Microscopy (TEM)

•TEM micrographs of the powder possessing the highest surface area (120-160 m2/g) with the best electrochemical activity (optimized sample)

—Diffraction pattern indicates single phase Pt-Ru composition

—HRTEM images show 2-4 nm sized crystallites

•Results of electrochemical tests conducted on the powders derived using a large excess of

tetramethylammonium hydroxide [TMAH : (Pt-acac+Ru-acac) = 1.75:1 and Pt:Ru = 1:1]

Electrochemical CharacterizationAnode polarization data

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 2 4 6 8 10

E (25oC, measured)E' (25oC, corrected)E (60oC, measured)E' (60oC, corrected)

y = 0.28913 + 0.014178x R= 0.95483

y = 0.19655 + 0.01602x R= 0.95062 Pote

ntia

l vs

H2/H

+

Ln(mA/g)

SSA = 97.9 m2/g

(a) Two step heat treatment of

400/3h/1%O2 (3 g) (0.5g)300/3h/1%O2

IV-1-1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 2 4 6 8 10

1214.10E (25oC, measured)E' (25oC, corrected)E (60oC, measured)E' (60oC, corrected)

y = 0.26396 + 0.014772x R= 0.97508

y = 0.18419 + 0.013872x R= 0.95196 Pote

ntia

l vs

H2/H

+

Ln(mA/g)

SSA = 139.6 m2/g

(b) Two step heat treatment of

300/2h/1%O2 (3 g) (0/5g)300/4h/1%O2

IV-1-2

Comparison of catalytic activity

Sample Specific

surface area (m2/g)

Intercept on y axis in polarization

curve

Slope in polarization

curve

Cell potential (V) at ln(mA/g)=8

(60°C)

25°C 60°C 25°C 60°C JPL 49.5 0.305 0.182 0.0216 0.0193 0.336

Giner 94.2 0.269 0.177 0.0273 0.0306 0.422 Johnson-Matthey

71.3 0.298 0.173 0.0127 0.0163 0.304

1208.12 94.2 0.214 0.155 0.0284 0.0231 0.340 TMAH:acac=1.25:1 Pt:Ru = 1:1

1212.03 95.9 0.322 0.217 0.0169 0.0194 0.372 TMAH:acac=1.25:1 Pt:Ru = 1:1.25

1214.03 97.9 0.289 0.197 0.0142 0.0160 0.325 TMAH:acac=1.25:1 Pt:Ru = 1:1.5

1214.10 139.6 0.264 0.184 0.0148 0.0139 0.295 TMAH:acac=1.75:1 Pt:Ru = 1:1

330.38590.3859Pt(RuPt(Ru) + C) + C158158Sample BSample B(Sample A: (Sample A:

30030000C/2h in ArC/2h in Ar--1% O2)1% O2)

000.38590.3859Pt(RuPt(Ru))120120Sample CSample C(Sample B: (Sample B:

30030000C/2h in ArC/2h in Ar--1% O1% O22))

63630.38610.3861Pt(RuPt(Ru) + C) + C11Sample ASample A(500(50000C/6h in C/6h in ArAr))

000.38580.3858Pt(RuPt(Ru) +) +RuRu--JM catalystJM catalyst--(600(600ooC/6h in C/6h in ArAr))

000.38660.3866Pt(RuPt(Ru))7070JM catalystJM catalyst

Carbon Carbon content content

(%)(%)

Lattice Lattice parameter parameter

(nm)(nm)

Phase/phases Phase/phases presentpresent

Surface Surface area(marea(m22/g)/g)

Sample Sample identificationidentification

Prospects for FutureProspects for Future

NanomaterialsNanomaterials show potential for energy show potential for energy storage storage NanoscaleNanoscale phenomena in batteries, fuel phenomena in batteries, fuel cells and cells and supercapacitorssupercapacitors still need to be still need to be studiedstudiedConsiderable potential for integration, Considerable potential for integration, theoretical and experimental studiestheoretical and experimental studies