Production and Characterization of carbon-free bi- … air battery Wagner.pdfProduction and...

Production and Characterization of carbon-free bi-functional cathodes for the use in lithium-air batteries with an aqueous alkaline electrolyte

Norbert Wagner, Dennis Wittmaier, K. Andreas FriedrichGerman Aerospace Center (DLR)Pfaffenwaldring 38-49, 70569 Stuttgart, Germany

www.DLR.de • Chart 1 10. EIA, Borovetz 2014, Norbert Wagner

Presentation outline

• Application of EIS in battery research at DLR• Motivation Li-air batteries

• Electrode production techniques at the DLR• Cathode for the Li-air battery

• Catalyst screening of bifunctional cathodes (ORR and OER)

• Conclusion and outlook

10. EIA, Borovetz 2014, Norbert Wagnerwww.DLR.de • Chart 2

Production and Characterisationof cathodes forLithium-Sulfur andLithium-air batteries

Characterisation ofLi-ion batteries within-situ and ex-situ-methods

Activities of the „Batterietechnik“ team

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

(NMC 2,25 Ah)

(LiFePO4 1,1Ah)

EIS measurement at

different SOC

Discharge at 1C

Discrimination of SOC and SOH of serial connected batteries

Z02Z01 Z07

02I‐Sens01 07

itotal (t)

Serial connection V2

Z01 U=3,25V SoH100

Z02 U=3,25V SoH100

Z07 U=3,25V SoH60

û‐Z01û‐Z02û‐Z07î‐Z01î‐Z02î‐Z07

Frequency f / Hz

Phase angle |ϕ

| / °

dance|Z| / m

Ω Z01 Impedance |Z|Z01 Phase |ϕ|

Z02 Impedance |Z|Z02 Phase |ϕ|

Frequency f / Hz

Curren

tI / mA

geU / mV

In-situ XRD and EIS measurements during discharging

Li-S batteries

N. A. Cañas, S. Wolf, N. Wagner, K. A. Friedrich. J. of Power Sources, 226 (2013) 313-319.

Electrochemical Model of Li-S Battery

Equivalent circuit

Model Chemical and physical cause

R0 Ohmic resistance

R1-CPE1 Anode charge transfer

R2-CPE2 Cathode process: charge transfer of sulfur intermediates

R3-CPE3 Cathode process: reaction and formation of S8 and Li2S

R4-CPE4 Diffusion

Presentation August 2013www.DLR.de • Chart 7

Motivation

Why Li-air batteries?• Highest theoretical specific energy density (11.425 Wh/kg)

Cathodic reactant, O2 from air, does not have to be stored• Environmental friendliness• Higher safety than Li-ion batteries

(only one of the reactants contained in the battery)• Potentially longer cycle and shelf lives

Motivation

G. Girishkumar et al., J. Phys. Chem. Lett., 2010, 1, 2193‐2203

Why Li-air batteries?• Highest theoretical specific energy density (11.425 Wh/kg).

Cathodic reactant, O2 from air, does not have to be stored• Environmental friendliness• Higher safety than Li-ion batteries

(only one of the reactants contained in the battery)• Potentially longer cycle and shelf lives

Schematically representation of a Li-air battery

Architectures of Li-air Batteries

2Li+ + O2 + 2e‐ Li2O2 Erev= 2,959 V2Li++2e‐ + (1/2) O2 Li2O Erev= 2,913 V

4Li + O2 + 2H2O 4LiOH (alkaline media) Erev= 3,446 V4Li + O2 + 4H+ 2H2O + 4Li+(acidic media) Erev= 4,274 V

Non-aqueous electrolyte: Aqueous electrolyte:

Schematically representation of Lithium-Air Battery with Aqueous Electrolyte

Reaction equation (alkaline Electrolyte):4 Li + O2 + 2H2O ↔ 4LiOH; E = 3,45 V

i+ -Le

Reaktions -produkte

Wässrige Elektrolyt -lösung

Reaction -products

Aqueouselectroytesolution O

Interlayer

Bi-functional Oxygen-Electrodes: Design

• Bi-functional Oxygen-Electrodes = catalizes ORR and OER

• Depending on manufactoring process every electrode consists of:

• Catalyst(s)• Conductive agent (C, Graphit…)• Binder (PTFE, PVdF…)• Substrate (Metal mesh,…)

Function BOE

Catalyst

Active Surface

Cond. agent

Electrolyte

Pore-structure

Design

• Different manufactoring processes used at DLR: Dry Powder Spraying, Reactive Rolling an Mixing, Pressing and APS

Production Techniques

-Dry Spraying Technique-Wet Spraying Techniquen- Reactive Mixing and Rolling (RMR)-Screen printing-…

M eta l net

Addit ives Ca talysts

Reac tive Mixing

Production Techniques

-Dry Spraying Technique-Wet Spraying Techniquen- Reactive Mixing and Rolling (RMR)-Screen printing-…

M eta l net

Addit ives Ca talysts

Reac tive Mixing

Dry Powder Spraying Technique

Nitrogen

coating nozzle

roller

membrane

catalystadditive

powder supporter

RMR(Substrat)

Dry sprayed layer

Top view

N. Wagner, T. Kaz, DE 101 12 232 A1, 2002

NaOH 30%(H2O)

NaOH 32%

NaOH2 H2O

4 NaOHNaOH

Electrical Circuit

Net AgMembrane

Silver GDE (ODC)

NaCl solution(Brine)

Chlorine production with ODC (Oxygen Depolarised Cathode)

10. EIA, Borovetz 2014, Norbert Wagner

Chlorine productionunit with ODC techniqueat Bayer in Ürdingen(20,000 t/y) since May 2011

www.DLR.de • Chart 19

CT picture of a Silver gas diffusion electrode

FIB-TEM picture of a Silver gas diffusion electrode

Possible production options for multilayer electrodes

Li+‐conductingMembrane

electr. contact(metal net, foam, porous substrate, etc.)

Catalyst layer 1(Changed composition, production conditions and techniques)Catalyst Layer 2hydrophobic barrier layer (C‐PTFE)

Catalyst layer 1(Changed composition, production conditions and techniques) Catalyst layer 2 hydrophobic barrier layer

Composition:• chemical composition (metals and metal oxides) • structure

PTFE-bounded Carbon Powder: SEM- picture

VPS coated cathode for Li-air battery

Cro‐Fer netcoated one side with

Ag+LSCFother side with C+PTFE

Picture of APS-coated porous substrate with 50 vol. % Ag+50 vol. % LSCF, gas side C/PTFE (dry sprayed)

CV: with Ag+LSCF (APS, electrolyte side) and PTFE+C (Dry Powder Spraying, gas side) coated Rhodius-Net in 1 N LiOH, Reference electrode: Hg/HgO

-600 -400 -200 0 200 400 600 800

Potential / mV

Current / mA

CV 1 mV/s Air, RTCV 1 mV/s O2, RT

Atmospheric Plasma Spraying (APS)

0.3Mnitrate solution

for injection

SEM of catalyst layer and cross section

plasma sprayed at DLR

P. Fauchais, J. Phys. D: Appl. Phys. 37 (2004) R86–R108

Manufactoring of bifunctional gas diffusion electrodes

Electrodes with noble metal and other catalysts can be made with dry power spraying technique

Oxide catalysts (La0.6Ca0.4CoO3…) can be sprayed on for example a

Rhodius substrate with APS

Rhodius substrate

Catalyst layer

Catalyst layer = catalyst+carbon/graphite+binder

Graphite GDE substrate

or by pressing the catalyst layer on for example a Sigracet® GDL 35 DC with a hydraulic press

Catalyst layer = catalyst+carbon/graphite+binder

Sigracet® GDL35 DC

Screening of bifunctional catalysts

Experimental

• Thin catalyst layers reduce the influence of the electrode structure

• Cyclic Voltammetrie was carried out at a half cell with 1M LiOH (aq.) and25°C and 50°C

• Gas O2, platinum counter electrode (CE), reversible hydrogen reference electrode (RE)

Potential range 0.1V - 1.8V vs. RHE

Noble metal catalystconfiguration

Electrode

80 wt % graphite + 20 wt % PTFE +

catalyst

Oxide catalyst configuration

Electrode + Sigracet® GDL35 DC

100 wt % catalystGas Gas

Experimental results

• Polarization curves with 1mV s-1

• Noble metal catalysts show good activity towards oxygen reduction reaction (ORR) but poor activity towards oxygen evolution reaction (OER)

• Increasing the temperature shows a significant improvment of activity

Experimental results

• Polarization curves with 1mV s-1

• Oxide catalysts show more balanced characteristics towards ORR and OER than noble metal catalysts. Compared to their activity in ORR they show a high activity in OER.

• Increasing the temperature shows a significant improvment of activity

Impedance Measurements during ORR in 10 N NaOH, on Silver Electrodes at Different CurrentDensities, i< -50 mAcm-2

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

90|phase| / o

frequency / Hz

453 50 mA453 45 mA

453 40 mA453 35 mA

453 30 mA453 25 mA

453 20 mA453 15 mA

453 10 mA453 5 mA

1 2 3 4 5

45 mA40 mA

35 mA30 mA

25 mA20mA

15 mA10 mA

Bode representation Nyquist representation

Impedance Measurements during ORR in 10 N NaOH, on Silver Electrodes at Different CurrentDensities, i> -50 mAcm-2

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

90|phase| / o

frequency / Hz

453 500 mA453 450 mA

453 400 mA453 350 mA453 300 mA453 250 mA

453 200 mA

453 150 mA

453 100 mA

453 50 mA

0.6 0.8 1 1.2 1.4 1.6 1.8 2

500 mA

450 mA400 mA350 mA300 mA250 mA200 mA

150 mA 100 mA 50 mA

Electrode Model with cylindrical , homogeneouspores and complex Faraday-impedance

Evaluation of EIS measured during ORREquivalent circuit and Rad = f(i)

-100 -80 -60 -40 -20current/mA

Rad Cad

Current density dependency of the charge transfer resitance Rct

-100 -80 -60 -40 -20current/mA

Current density dependency of electrolyte resistance inside the pore

-500 -450 -400 -350 -300 -250 -200 -150 -100 -50current/mA

pore electrolyte res. /

U-i characteristic and current density dependencyof impedance elements Rad and Rct

-0,10 -0,08 -0,06 -0,04 -0,02 0,00

Current density / Acm-2

Current density dependency of kad, Rad and Rct, determined from EIS evaluation

-0.100 -0.080 -0.060 -0.040 -0.020 0.000

Current density / Acm-2

kad=1/CadRad

Influence of compacting pressure: Evaluation of EIS measured during OCR, 100 mA, 80°C, 10 N NaOH

0.6 0.8 1 1.2 1.4 1.6 1.8

Z'' / m

aaaaaaaaaaaaaaaaaaaaaaaaa bbbb

bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb

48 100 mA49 100 mA

100m 1 3 10 30 100 300 1K 3K 10K

|phase| / o

frequency / Hz

a a a a a a aa

aaa a a a a a a a a a a aa a a a a a a a a aa

b bb b bb b b bb b bbb

b bb b b bb b b bb b b bb b bb

a a a a a a a a a a aa a a a a a a a a a aa a a a a a a a a a a aa a a a a a a a a aab bb b bb b b bb b b bb b b bb b b bb b b bb b b bb b b bb b b bb b b bb b bb

48 100 mA

49 100 mA

Sample Rct Rpor Rel

48 (High pressure) 940 287m 524m

49 (Low pressure) 534 727m 577m

Overview EIS measurement points and CV with 1 mV/s at RT, 1 N LiOH , Ag-GDE

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

Potential vs. RHE / V

Electrode 1 (high pressure) 25c

Electrode 2 (low pressure) 50c

EIS measurement point

Impedance measurements during Oxygen evolution on Ag-GDE (high pressure), 1 N LiOH, 25°C

1 100 10K

frequency / Hz

a a a a a a a a a a a a a a a a aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa

b b b b b b b b b b b b b b b b bbbbbbbbbbbbbbbbbbbbbbbbbbb

c c c c c c c c c c c c c c c c cccccccccccccccccccccccccccccccccccccc

d d d d d d d d d d d d d d d d ddddddddddddddddddddddddddddddddddddddddd

a a a a a a a a a a a a a a a a aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa

b b b b b b b b b b b b b b b b bbbbbbbbbbbbbbbbbbbbbbb

c c c c c c c c c c c c c c c c cccccccccccccccccccccccccccccccccccccc

d d d d d d d d d d d d d d d d dddddddddddddddddddddddddddddddddddddddddddd

OCV+100 mV

OCV+300 mV

OCV+500 mVOCV+700 mV

10 20 30 40 50

aaaaaaaaaaaaaaaaaaaaaaaa

bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb

cccccccccccccccccccccccccccccccccccccccddddddddddddddddddddddddddddddddddddddddddddddd

OCV+100 mV

OCV+300 mVOCV+500 mV

OCV+700 mV

Equivalent circuit used for evaluation of EIS during OCR and OER at different electrodes for Lithium-Air batteries

Potential dependency of total resistance duringORR at different electrodes, 1 N LiOH

0 200 400 600 800 1000

Potential OCV minus x / mV

Electrode 1 (high pressure) 25cElectrode 1 (high pressure) 50cElectrode 2 (low pressure) 25cElectrode 2 (low pressure) 50c

Rtotal ORR

Potential dependency of charge transferresistance during OER

100 200 300 400 500 600 700 800

Potential OCV plus x / mV

Electrode 1 (high pressure) 25cElectrode 1 (high pressure) 50cElectrode 2 (high pressure) 25cElectrode 2 (low pressure) 50c

R2 OER (charge transfer)

Potential dependency of charge transferresistance in oxide layer potential region (OER)

100 200 300 400 500 600 700 800

Potential OCV plus x / mV

Electrode 2 (low pressure) 50c

R5 OER (oxide layer)

CV of a polished Ag electrode, 25% KOH, O2 sat.

Bi-functional Oxygen-Electrodes: IrO2/- and Co3O4/Ag-electrodes

www.DLR.de • Folie 48

• CV´s electrodes 20 wt. % catalyst (IrO2, Co3O4

• Improved cyclingperformance due touse of IrO2 and Co3O4compared to pure Ag

0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0-150

Voltage vs. RHE [V]

IrO2/Ag

No IR corr.

max. overpotential 1.5V

2.6V vs. Li/Li+

Current density @ 2.6V vs. Li/Li+ [mA cm-2]

IrO2/Ag 99,7Co3O4/Ag 107

N. Wagner et al., German Patent Application, 2014

• From the catalyst screening, a new bifunctionall catalysts systemfor the cathode of a Li-air battery was found

• From the evaluation of the measured impedance spectra one canpropose a reaction mechanism for the ORR:

• Adsorptions- / heterogeneous reactions and charge transferreaction are consecutive reactions

• Reaction mechanism and rate determining step is changing athigher current densities at ca. 20 mAcm-2

• Production parameters, composition and structure have a strong influence on electrode reactivity

• Change of reaction zone with current density• Silver electrodes are not stable during OER

10. EIA, Borovetz 2014, Norbert Wagner

Conclusion

www.DLR.de • Chart 49

Thank you for yourAttention !

Acknowledgment

Reactions pathways for the cathodic oxygenreduction in alkaline solution

Direct-X 4e- - path: 2H2O + O2 + 4e- → 4OH-

O2 + 2M ↔ 2M…O2 (M…O + e- → MO-)2 (MO- + H2O ↔ MOH + OH-)2 (MOH + e- ↔ OH- + M)

Peroxid - Path: H2O + O2 + 2e- ↔ HO2- + OH-

O2 + M ↔ M…O2M…O2 + e- → MO2

MO2- + H2O ↔ MHO2 + OH-

MHO2 + e- ↔ HO2- + M

Peroxid-Reduction: HO2- + H2O + 2e- → 3OH-

HO2- + M ↔ MHO2

MHO2- + H2O ↔ MH2O2 + OH-

MH2O2 + e- → MOH + OH-

MOH + e- ↔ M + OH-

Catalytically Peroxid-decomposition: 2HO2- → O2 + 2OH-

HO2- + M ↔ MHO2

MHO2- → MO + OH-

MO + HO2- → O2 + OH- + M

SEM pictures of Ag-GDE, produced by the RMR technique (Ag2O+PTFE)

Ag-GDE, unused part Ag-GDE, used

Production and Characterization of carbon-free bi- … air battery Wagner.pdfProduction and...

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