production and characterization of carbon-free bi- functional … 2014 wagner.pdf · 2014. 10....

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

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


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

(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

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|



Frequency f / Hz

Curren

tI / mA

Volta

geU / mV

Electrochemical Model of Li-S Battery


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

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

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

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


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

Manufactoring of bifunctional gas diffusion electrodes


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

Rhodius substrate with APS

Rhodius substrate

Catalyst layer


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


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


Electrode Model with cylindrical , homogeneouspores and complex Faraday-impedance

Zq=


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


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


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

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


-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 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


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


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


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


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)


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 2 (low pressure) 50c

R5 OER (oxide layer)


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


• 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


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- functional … 2014 wagner.pdf · 2014. 10....

Documents