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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
| / °
Impe
dance|Z| / m
Ω Z01 Impedance |Z|Z01 Phase |ϕ|
Z02 Impedance |Z|Z02 Phase |ϕ|
Z03 Impedance |Z|Z03 Phase |ϕ|
Z07 Impedance |Z|Z07 Phase |ϕ|
Frequency f / Hz
Curren
tI / mA
Volta
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
7
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
www.DLR.de • Chart 8 10. EIA, Borovetz 2014, Norbert Wagner
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
www.DLR.de • Chart 9 10. EIA, Borovetz 2014, Norbert Wagner
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
www.DLR.de • Chart 10 10. EIA, Borovetz 2014, Norbert Wagner
Architectures of Li-air Batteries
www.DLR.de • Chart 11 10. EIA, Borovetz 2014, Norbert Wagner
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
Lith
ium
Fest
körp
er L
i+ -Le
iter
Reaktions -produkte
Wässrige Elektrolyt -lösung
O2-R
eduk
tion
Lith
ium
Solid
Li+
--c
ondu
ctor
Reaction -products
Aqueouselectroytesolution O
2-Red
uctio
n
Interlayer
10. EIA, Borovetz 2014, Norbert Wagnerwww.DLR.de • Chart 12
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-…
GDE
M eta l net
Addit ives Ca talysts
Reac tive Mixing
10. EIA, Borovetz 2014, Norbert Wagnerwww.DLR.de • Chart 14
Production Techniques
-Dry Spraying Technique-Wet Spraying Techniquen- Reactive Mixing and Rolling (RMR)-Screen printing-…
GDE
M eta l net
Addit ives Ca talysts
Reac tive Mixing
10. EIA, Borovetz 2014, Norbert Wagnerwww.DLR.de • Chart 15
Dry Powder Spraying Technique
Nitrogen
coating nozzle
roller
membrane
catalystadditive
powder supporter
RMR(Substrat)
Dry sprayed layer
Top view
10. EIA, Borovetz 2014, Norbert Wagnerwww.DLR.de • Chart 16
N. Wagner, T. Kaz, DE 101 12 232 A1, 2002
10. EIA, Borovetz 2014, Norbert Wagnerwww.DLR.de • Chart 17
O2
O O
NaOH 30%(H2O)
NaOH 32%
Na+
Na+
Na+
Na+
NaOH2 H2O
4 NaOHNaOH
e-
OH-
e-
e-
e-
e-
Electrical Circuit
OH-
O2
O O
O
Net AgMembrane
Silver GDE (ODC)
O-2
OH
H
NaCl solution(Brine)
Na+
Cl2
Cl-
e-
Anode
10. EIA, Borovetz 2014, Norbert Wagnerwww.DLR.de • Chart 18
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
O2
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
10. EIA, Borovetz 2014, Norbert Wagnerwww.DLR.de • Chart 22
PTFE-bounded Carbon Powder: SEM- picture
10. EIA, Borovetz 2014, Norbert Wagnerwww.DLR.de • Chart 23
VPS coated cathode for Li-air battery
Cro‐Fer netcoated one side with
Ag+LSCFother side with C+PTFE
10. EIA, Borovetz 2014, Norbert Wagnerwww.DLR.de • Chart 24
Picture of APS-coated porous substrate with 50 vol. % Ag+50 vol. % LSCF, gas side C/PTFE (dry sprayed)
10. EIA, Borovetz 2014, Norbert Wagnerwww.DLR.de • Chart 25
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
0
-40
-20
20
Potential / mV
Current / mA
CV 1 mV/s Air, RTCV 1 mV/s O2, RT
10. EIA, Borovetz 2014, Norbert Wagnerwww.DLR.de • Chart 26
Atmospheric Plasma Spraying (APS)
www.DLR.de • Chart 27 10. EIA, Borovetz 2014, Norbert Wagner
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
www.DLR.de • Chart 28 10. EIA, Borovetz 2014, Norbert Wagner
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
www.DLR.de • Chart 29 10. EIA, Borovetz 2014, Norbert Wagner
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
www.DLR.de • Chart 30 10. EIA, Borovetz 2014, Norbert Wagner
• 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
www.DLR.de • Chart 31 10. EIA, Borovetz 2014, Norbert Wagner
• 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
500m
1
2
1.5
5
|Z| /
0
15
30
45
60
75
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
0
-3
-3.5
-2
-2.5
-1
-1.5
-0.5
1
0.5
1.5
Z' /
Z'' /
50 mA
45 mA40 mA
35 mA30 mA
25 mA20mA
15 mA10 mA
5 mA
Bode representation Nyquist representation
10. EIA, Borovetz 2014, Norbert Wagnerwww.DLR.de • Chart 32
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
600m
800m
1
2
1.5
|Z| /
0
15
30
45
60
75
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
0
-1
-0.5
0.5
Z' /
Z'' /
500 mA
450 mA400 mA350 mA300 mA250 mA200 mA
150 mA 100 mA 50 mA
10. EIA, Borovetz 2014, Norbert Wagnerwww.DLR.de • Chart 33
Electrode Model with cylindrical , homogeneouspores and complex Faraday-impedance
Zq=
10. EIA, Borovetz 2014, Norbert Wagnerwww.DLR.de • Chart 34
Evaluation of EIS measured during ORREquivalent circuit and Rad = f(i)
0
2
4
6
-100 -80 -60 -40 -20current/mA
R /
Rad Cad
Rct
Cdl
Rpor
Rel
L
10. EIA, Borovetz 2014, Norbert Wagnerwww.DLR.de • Chart 35
Current density dependency of the charge transfer resitance Rct
1
0.6
0.8
1.2
1.4
1.6
-100 -80 -60 -40 -20current/mA
Rct /
10. EIA, Borovetz 2014, Norbert Wagnerwww.DLR.de • Chart 36
Current density dependency of electrolyte resistance inside the pore
1
2
1.5
2.5
-500 -450 -400 -350 -300 -250 -200 -150 -100 -50current/mA
pore electrolyte res. /
10. EIA, Borovetz 2014, Norbert Wagnerwww.DLR.de • Chart 37
U-i characteristic and current density dependencyof impedance elements Rad and Rct
0,9
0,92
0,94
0,96
0,98
1
1,02
1,04
1,06
1,08
1,1
-0,10 -0,08 -0,06 -0,04 -0,02 0,00
Current density / Acm-2
iR-c
orr.
Pote
ntia
l vs.
NH
E / V
0,00
1,00
2,00
3,00
4,00
5,00
6,00
7,00
8,00
R ad;
Rct
/ Ohm
10. EIA, Borovetz 2014, Norbert Wagnerwww.DLR.de • Chart 38
Current density dependency of kad, Rad and Rct, determined from EIS evaluation
0
1
2
3
4
5
6
7
8
-0.100 -0.080 -0.060 -0.040 -0.020 0.000
Current density / Acm-2
R ad;
Rct
/ O
hm
0
10
20
30
40
50
60
70
80
Reac
tion
rate
con
stan
te /
s-1
kad=1/CadRad
10. EIA, Borovetz 2014, Norbert Wagnerwww.DLR.de • Chart 39
Influence of compacting pressure: Evaluation of EIS measured during OCR, 100 mA, 80°C, 10 N NaOH
www.DLR.de • Chart 40 10. EIA, Borovetz 2014, Norbert Wagner
0.6 0.8 1 1.2 1.4 1.6 1.8
0
-500
Z' /
Z'' / m
aaa
aa
aa
aa
aaaaa
aa
aa
aa
aaaaaaaaaaaaaaaaaaaaaaaaa bbbb
bbbbb
bb
bbb
bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
48 100 mA49 100 mA
100m 1 3 10 30 100 300 1K 3K 10K
600m
800m
1
1.5
|Z| /
0
45
90
135
|phase| / o
frequency / Hz
a a a a a a aa
aa
aa
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
bb
bb
bb
bb
bb
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
www.DLR.de • Chart 41 10. EIA, Borovetz 2014, Norbert Wagner
-0,3
-0,25
-0,2
-0,15
-0,1
-0,05
0
0,05
0,1
0,15
0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 2
Cur
rent
den
sity
/ A
cm
-2
Potential vs. RHE / V
Electrode 1 (high pressure) 25c
Electrode 1 (high pressure) 50c
Electrode 2 (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
5
10
20
15
50
|Z| /
0
15
30
45
60
75
90
|pha
se| /
o
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
bb
b
b
b
b
b
b
b
bb
bbbbb
b
c c c c c c c c c c c c c c c c cccccccccccccccccccccccccccccccccccccc
cc
c
cc
c
d d d d d d d d d d d d d d d d ddddddddddddddddddddddddddddddddddddddddd
dd
d
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
bb
bb
bb
bb
bbbb
b
b
b
bb
bbbb
c c c c c c c c c c c c c c c c cccccccccccccccccccccccccccccccccccccc
ccc
cc
c
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
www.DLR.de • Chart 42 10. EIA, Borovetz 2014, Norbert Wagner
10 20 30 40 50
0
-30
-20
-10
10
Z' /
Z'' /
aaaaaaaaaaaaaaaaaaaaaaaa
bbbbb
bb
bbbb
bb
bb
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
www.DLR.de • Chart 43 10. EIA, Borovetz 2014, Norbert Wagner
Potential dependency of total resistance duringORR at different electrodes, 1 N LiOH
www.DLR.de • Chart 44 10. EIA, Borovetz 2014, Norbert Wagner
1
10
100
0 200 400 600 800 1000
Res
ista
nce
/ Ω
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
www.DLR.de • Chart 45 10. EIA, Borovetz 2014, Norbert Wagner
0,01
0,1
1
10
100
100 200 300 400 500 600 700 800
Res
ista
nce
/ Ω
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)
www.DLR.de • Chart 46 10. EIA, Borovetz 2014, Norbert Wagner
0
0,5
1
1,5
2
2,5
3
3,5
4
100 200 300 400 500 600 700 800
Res
ista
nce
/ Ω
Potential OCV plus x / mV
Electrode 1 (high pressure) 25c
Electrode 1 (high pressure) 50c
Electrode 2 (high pressure) 25c
Electrode 2 (low pressure) 50c
R5 OER (oxide layer)
CV of a polished Ag electrode, 25% KOH, O2 sat.
10. EIA, Borovetz 2014, Norbert Wagnerwww.DLR.de • Chart 47
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
-100
-50
0
50
100
Cu
rren
t d
ensi
ty [
mA
cm
-2]
Voltage vs. RHE [V]
Co3O
4/Ag
IrO2/Ag
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 !
www.DLR.de • Chart 50 10. EIA, Borovetz 2014, Norbert Wagner
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
10. EIA, Borovetz 2014, Norbert Wagnerwww.DLR.de • Chart 51
SEM pictures of Ag-GDE, produced by the RMR technique (Ag2O+PTFE)
Ag-GDE, unused part Ag-GDE, used
10. EIA, Borovetz 2014, Norbert Wagnerwww.DLR.de • Chart 52