production and characterization of carbon-free bi

Production and Characterization of Carbon-Free Bi-Functional Cathodes for the use in Lithium-Air Batteries with an Aqueous Alkaline Electrolyte

www.DLR.de • Folie 1

Norbert Wagner, Dennis Wittmaier, K. Andreas FriedrichInstitute of Engineering Thermodynamics| Electrochemical Energy Technology | Pfaffenwaldring 38-40 | 70569 Stuttgart | Germany

GDCh - Electrochemistry, 22.-24.09.2014, Mainz


Preparation methods

Characterization methods

Carbon-free electrodes

Conclusion

Outline

Activities Battery-Group (DLR)


11 Scientists, 2 Technicians, 6 Students

Activities:Characterization of state of the art Li

- Ion Batteries (in- and ex-situ)Generation 4 batteries:Lithium - SulfurLithium - Air

Preparation andcharacterization

Source: N AT U R E | VO L 5 0 7 | 6 M A R C H 2 0 1 4

Basic Concept Li-Air Battery


Highly porous, 3-dimensional bi-functional gas diffusion electrode(cathode)Bi-functional cathode catalizes

battery reactions: ORR = Oxygen reduction

reaction – dischargingOER = Oxygen evolution

reaction - charging

Anode: Metallic lithiumCathode: Porous gas diffusion

electrode (catalyst(s), binder, substrate and conductive agent)Battery reaction for aqueous alkaline

Li-air battery: 4 Li + O2 + 2 H2O ↔ 4 LiOH;

E0=3,45V Ref.: G. Girishkumar, B. McCloskey, A. C. Luntz, S. Swanson, W. Wilcke, J. Phys. Chem. Lett. (2010) 1, 2193

Sketch of gas diffusion electrode

Catalyst layer

Substrate

Electrolyte Concepts Li-Air Battery


3 Basic electrolyte concepts :

Aprotic electrolyte (water free)Aqueous electrolyteSolid stateMixed aqueous/aprotic hybrid

DLR Activities:

Bi-functional cathodesAqueous alkaline electrolyte e.g.

LiOH(aq.)Ref.: G. Girishkumar, B. McCloskey, A. C. Luntz, S. Swanson, W. Wilcke, J. Phys. Chem. Lett. (2010) 1, 2193

Preparation methods


Lab-scale Mid-scale Large-scale

Colloidal Supension Spraying

Hydraulic Pressing

Nitrogen

coating nozzle

roller

membrane

catalystadditive

powder supporter

Dry Powder Spraying

Reactive Rolling andMixing

Atmospheric Plasma Spraying(APS)

Preparation methods I: Hydraulic pressing


Hydraulic Pressing:Simple and fast process

Dry process

Solvent free

Almost every powder processible

Any shape of electrode

Variable thickness

Suitable for carbon-free electrodes

d

Preparation methods II: Dry spraying


Dry Spraying:

Dry process

Solvent free

Coated substrates e.g. macroporous

Rhodius metal mesh, metal foams

Variable thickness

Especially suitable for carbon

contenting

Nitrogen

coating nozzle

roller

membrane

catalystadditive

powder supporter

Catalyst layer = catalyst+carbon/graphite+binder

Various substrate

Preparation methods III: APS


Atmosheric Plasma Spraying (APS):

Synthesis of catalysts via nitrate

solution

Oxide catalysts e.g. Co3O4, Mn3O4,

NiO

Coated substrates e.g. macroporous

Rhodius metal mesh, metal foams

Thin catalyst layer possible

Characterization methods: In- and Ex-Situ


SEM XRD/XPS ElectricConductivity

EISCV

ElectrochemicalCharacterization

Electrolyte

Carbon-Free Bi-functional Electrodes


! Problem of carbon material ! :High carbon corrosion at potentials> 1.35V vs. RHE resulting in structuraldecomposition of electrodes anddecreasing current densities due to theloss of active material !

Carbon is inexpensive, available, non-toxic, catalytic active for ORR and elec. conductiveMost reported electrodes based on

carbon material due to properties

DLR goal: Complete substitution of carbonmaterials to enhance stability ofelectrodes !

Decreasingcurrentdensity

Carbon-Free Bi-functional Electrodes


Substitution of carbon byelectrochem. stable, elec. conductive+ catalytic active material to supportCo3O4 + maintain elec. conductivityPossible materials due to alk. elec-

trolyte: Ag and NiCombinations Ag/Co3O4 and

Ni/Co3O4

IrO2, Co3O4, Mn3O4 andLa0.6Ca0.4CoO3 are most promising bi-functional catalysts

Further investigations: Co3O4 mostpromising oxide catalyst, comp-arable results to high cost catalystIrO2D. Wittmaier, T. Danner, N. Wagner, K. A. FriedrichScreening and further investigations on promising bi-functional catalysts for lithium-air batteries with an aqueous alkaline electrolyte, Journal of Applied Electrochemistry (2014)

0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8-6

-4

-2

0

2

4

6

8

10

12 La0.6Ca0.4CoO3 La0.8Ca0.2CoO3 LaCoO3 Co3O4 Mn3O4

Cur

rent

den

sity

/ m

A c

m-1

mg-1

Potential vs. RHE / V

0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8

-2

0

2

4

6

8

10

La0.6Ca0.4CoO3 La0.8Ca0.2CoO3 LaCoO3 Co3O4 Mn3O4

Cur

rent

den

sity

/ m

A c

m-1

mg-1


25°C

50°C

Basic concept Li-air battery: Type I (Ag)


High current densities + synergeticeffect of Ag and Co3O4 leads tohigher current densities for ORR + OER compared to pure Ag or Co3O4electrodes (not completelyunderstood yet) D. Wittmaier, N. Wagner, K. A. Friedrich, H. M. A. Amin, H. BaltruschatModified carbon-free silver electrodes for the use as cathodes in lithium-air batteries with an aqueous alkaline electrolyte, Journal of Power Sources (2014)D. Wittmaier, N. Wagner, H. M. A. Amin, H. BaltruschatBifunktioneller Katalysator als Kathodenmaterial für die Metall-Luft-Batterie, Patentnummer 10 2014 102 304.8 (2014)

Combination exhibits high currentdensities

Variation of Ag/Co3O4 ratio to find optimum composition; Binder content 10 wt.-% constant

20 wt.-% Co3O4 optimum catalystcontent

32,83

43,9

48,5551,43

50,0347,5

20

25

30

35

40

45

50

55

60

0 302010 40C

urre

nt d

ensit

y / m

A c

m-2

Content Co3O4 / Gew.-%5

115,27

119,5 119,5120,5 120,15

108,65

105

110

115

120

125

Cur

rent

den

sity

/ m

A c

m-2

Content Co3O4 / Gew.-%0 5 10 20 30 40

ORR

OER

Carbon-Free Bi-functional Electrodes: Type I (Ag)


FIB-SEM Ag / Co3O4, 20 wt.-% [University of Ulm]

SEM Ag / Co3O4, 20 wt.-% [DLR]

Ag Co3O4 Ag

Co3O4

Carbon-Free Bi-functional Electrodes: Type I (Ag)


Comparision of Ag/Co3O4 electrodesto high cost Ag/ IrO2 combination(benchmark)

20 wt.-% IrO2 also highest currentdensity

High improvement over pure Ag; Ag/Co3O4 combination improves

ORR activity Comparison shows only slight

advantage of Ag/ IrO2 electrodes (in OER) but much higher costs

Ag/Co3O4 most promising combination for future investigations

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

-120

-100

-80

-60

-40

-20

0

20

40

60

Cur

rent

den

sity

/ m

A c

m-2


20 wt.% Co3O4 20 wt.% IrO2 Pure Ag

D. Wittmaier, N. Wagner, K. A. Friedrich, H. M. A. Amin, H. BaltruschatModified carbon-free silver electrodes for the use as cathodes in lithium-air batteries with an aqueous alkaline electrolyte, Journal of Power Sources (2014)

ORR

OER

Carbon-Free Bi-functional Electrodes: EIS, Type I (Ag)


Recorded impedance spectra weremodeled with equivalent circuitmodel

Different models for ORR and OER

OER model takes into accountgrowing oxide layer on surface ofelectrode while electrode operating in OER mode

Evaluation of important resistancesRtotal for ORR and OER and R5 (oxidelayer)

R1 R4R2 R5

CPE2

CPE1

L1

CPE3

R3

ORR

OER

100m 1 3 10 30 100 1K 3K 10K 100K

2

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2.5

5

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10

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90

135

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Carbon-Free Bi-functional Electrodes: EIS, Type I (Ag)


Resistances gained fromsimulation of impedance model:

Current densities for ORR onlyslight difference, thiscorresponds to values for Rtotal, ORRCurrent densities for pure Ag

electrodes in OER much lowerthan for also corresponds toRtotal, OERBest combintion for OER

exhibits lowest resistance R5 foroxide layerAg electrodes have highest

resistances for OER0 10 20 30 40 50 60 70 80

0.01

0.1

1

10

Res

ista

nce

R5 (O

xide

Lay

er) /

Current density / mA cm-2

Co3O4 20 wt.% IrO2 20 wt.% pure Ag

0 10 20 30 40 50 60 70 801

10

100

1000 Co3O4 20 wt.%

Res

ista

nce

tota

l /


IrO2 20 wt.%

pure Ag

0 10 20 30 40 50 60 70 80 90 1001

10

100

1000 Co3O4 20 wt.%

Res

ista

nce

tota

l /


IrO2 20 wt.%

pure Ag

Rtotal, ORR

Rtotal, OER R5


16,14

25,7530,58

44,76

37,69 36,71

0

10

20

30

40

50

60

Cur

rent

den

sity

/ m

A c

m-2

Electrode Co3O4 content / wt. %

Pure nickel 5 wt.-% Co3O4

10 wt.-% Co3O4

20 wt.-% Co3O4

30 wt.-% Co3O4

40 wt.-% Co3O4

0 % 5 % 10 % 20 % 30 % 40 %

3,01

15,1717,94

33,97

18,85 20,17

0

10

20

30

40

50

60

40 %10 %5 % 30 %20 %

Cur

rent

den

sity

/ m

A c

m-2

Electrode Co3O4 content / wt.-%

Pure nickel 5 wt.-% Co3O4

10 wt.-% Co3O4

20 wt.-% Co3O4

30 wt.-% Co3O4

40 wt.-% Co3O4

0 %

ORR

OER

Carbon-Free Bi-functional Electrodes: Type II (Ni)


High current densities + synergeticeffect of Ni + Co3O4 leads to highercurrent densities for ORR + OER compared to pure Ni or Co3O4electrodes (not completely understoodyet) Higher current densities for OER than

ORR but lower than Ag/Co3O4D. Wittmaier, S. Aisenbrey, N. Wagner, K. A. FriedrichCarbon-free nickel/cobalt-oxide cathodes for lithium-air batteries with an aqueous alkaline electrolyte, Electrochim. Acta (2014), submittedD. Wittmaier, N. WagnerBifunktioneller Katalysator und Leitzusatz als Kathodenmaterial für die Metall-Luft-Batterie, Patentnummer 10 2014 111 701.8 (2014)

Combination exhibits high currentdensities and high stability

Variation of Ni/Co3O4 ratio to find optimum composition; Binder content 10 wt.-% constant

20 wt.-% Co3O4 optimum catalystcontent (as for Ag and IrO2)

Publications


Peer-reviewed publications:

D. Wittmaier, T. Danner, N. Wagner, K. A. FriedrichScreening and further investigations on promising bi-functional catalysts for lithium-air batteries with an aqueous alkaline electrolyte, Journal of Applied Electrochemistry (2014)


D. Wittmaier, S. Aisenbrey, N. Wagner, K. A. FriedrichCarbon-free nickel/cobalt-oxide cathodes for lithium-air batteries with an aqueous alkaline electrolyte, Electrochim. Acta(2014), submitted

T. Danner, B. Horstmann, D. Wittmaier, N. Wagner, W. G. BesslerReaction and transport in Ag/Ag2O gas diffusion electrodes of aqueous Li-O2 batteries; Experiments and modeling, Journal of Power Sources (2014)

H. M. A. Amin, H. Baltruschat, D. Wittmaier, K.A. FriedrichHighly efficient bifunctional catalyst for alkaline oxygen-electrodes based on a Ag and spinel Co3O4 hybrid: RRDE and online DEMS insights, Angewandte Chemie (2014) submitted

Patents:

D. Wittmaier, N. Wagner, H. M. A. Amin, H. BaltruschatBifunktioneller Katalysator als Kathodenmaterial für die Metall-Luft-Batterie, Patentnummer 10 2014 102 304.8 (2014)

D. Wittmaier, N. WagnerBifunktioneller Katalysator und Leitzusatz als Kathodenmaterial für die Metall-Luft-Batterie, Patentnummer 10 2014 111 701.8 (2014)


Thank you for yourattention!

Most promising bi-functional catalysts Co3O4 and IrO2

Due to carbon corrosion carbon-free electrodes promise higher (long-term) stability

Substituion of carbon by Ag and Ni. Electrodes prepared with in comparision to IrO2 low cost Co3O4

20 wt.-% Co3O4 carbon-free electrodes show highest current densities

Conclusion


Thank you to

and our project partners of

production and characterization of carbon-free bi

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