Production and Characterization of carbon-free bi- functional … 2014 Wagner.pdf · 2014. 10....
Transcript of Production and Characterization of carbon-free bi- functional … 2014 Wagner.pdf · 2014. 10....
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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
7th International Workshop on Impedance Spectroscopy (IWIS)September 24-26 2014, ChemnitzGermany
www.DLR.de • Chart 1 7th IWIS 2014, Norbert Wagner
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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
• Influence of production parameter on electrode performance
• Conclusion and outlook
www.DLR.de • Chart 2 7th IWIS 2014, Norbert Wagner
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Characterisation ofLi-ion batteries within-situ and ex-situ-methods
Production and Characterisationof cathodes forLithium-Sulfur andLithium-air batteries
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
www.DLR.de • Folie 3 7th IWIS 2014, Norbert Wagner
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(NMC 2,25 Ah)
(LiFePO4 1,1Ah)
EIS measurement at
different SOC
Discharge at 1C
www.DLR.de • Folie 4 7th IWIS 2014, Norbert Wagner
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Discrimination of SOC and SOH of serial connected batterieswww.DLR.de • Folie 5 7th IWIS 2014, Norbert Wagner
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
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Electrochemical Model of Li-S Battery
www.DLR.de • Chart 6 7th IWIS 2014, Norbert Wagner
6
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
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Motivation
www.DLR.de • Chart 7
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
7th IWIS 2014, Norbert Wagner
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Motivation
www.DLR.de • Chart 8
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
7th IWIS 2014, Norbert Wagner
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Schematically representation of a Li-air battery
www.DLR.de • Chart 9 7th IWIS 2014, Norbert Wagner
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Architectures of Li-air Batteries
www.DLR.de • Chart 10
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:
7th IWIS 2014, Norbert Wagner
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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
www.DLR.de • Chart 11 7th IWIS 2014, Norbert Wagner
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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
www.DLR.de • Folie 12
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Manufactoring of bifunctional gas diffusion electrodes
www.DLR.de • Chart 13
Oxide catalysts (La0.6Ca0.4CoO3…) can be sprayed on for example a
Rhodius substrate with APS
Rhodius substrate
Catalyst layer
7th IWIS 2014, Norbert Wagner
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Manufactoring of bifunctional gas diffusion electrodes
www.DLR.de • Chart 14
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
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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
www.DLR.de • Chart 15 7th IWIS 2014, Norbert Wagner
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Electrode Model with cylindrical , homogeneouspores and complex Faraday-impedance
Zq=
www.DLR.de • Chart 16 7th IWIS 2014, Norbert Wagner
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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
www.DLR.de • Chart 17 7th IWIS 2014, Norbert Wagner
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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
www.DLR.de • Chart 18 7th IWIS 2014, Norbert Wagner
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Influence of compacting pressure: Evaluation of EIS measured during OCR, -100 mA, 80°C, 10 N NaOH
www.DLR.de • Chart 19
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
7th IWIS 2014, Norbert Wagner
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Overview EIS measurement points and CV with 1 mV/s at RT, 1 N LiOH , Ag-GDE
www.DLR.de • Chart 20
-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
7th IWIS 2014, Norbert Wagner
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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 21
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
7th IWIS 2014, Norbert Wagner
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Equivalent circuit used for evaluation of EIS during OCR and OER at different electrodes for Lithium-Air batteries
www.DLR.de • Chart 22 7th IWIS 2014, Norbert Wagner
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Potential dependency of total resistance duringORR at different electrodes, 1 N LiOH
www.DLR.de • Chart 23
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
7th IWIS 2014, Norbert Wagner
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Potential dependency of charge transferresistance during OER
www.DLR.de • Chart 24
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)
7th IWIS 2014, Norbert Wagner
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Potential dependency of charge transferresistance in oxide layer potential region (OER)
www.DLR.de • Chart 25
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)
7th IWIS 2014, Norbert Wagner
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CV of a polished Ag electrode, 25% KOH, O2 sat.
www.DLR.de • Chart 26 7th IWIS 2014, Norbert Wagner
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• 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
Conclusion
www.DLR.de • Chart 27 7th IWIS 2014, Norbert Wagner
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Thank you for yourAttention !
www.DLR.de • Chart 28
Acknowledgment
7th IWIS 2014, Norbert Wagner
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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
www.DLR.de • Chart 29 7th IWIS 2014, Norbert Wagner
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SEM pictures of Ag-GDE, produced by the RMR technique (Ag2O+PTFE)
Ag-GDE, unused part Ag-GDE, used
www.DLR.de • Chart 30 7th IWIS 2014, Norbert Wagner