tailored carbon additives to meet requirements for high...

AABC Europe 2017January 31, Mainz

Carbon

-

Lead

-Pb -

-

Pb2+

Pb2+

Pb2+

Pb2+

Pb2+

© Fraunhofer

1

Tailored Carbon Additives to Meet Requirements for High DCA and Low Water Loss – Wish and Reality

J. Settelein1, B. Bozkaya1, G. Sextl1, 2

1 Fraunhofer Institute for Silicate Research ISC, Würzburg, Germany2 University of Würzburg, Germany

© Fraunhofer

2 AABC Europe 2017January 31, Mainz

Center for Applied ElectrochemistryMaterial Development since 1989

Lithium-ion-

technology

▪ Core-shell▪ Polymer & ceramic

electrolytes▪ Binder materials▪ Low cost synthesis

Lead-acid-

technology

▪ Lead/Carbon electrodes

▪ Active material development

▪ Laboratory cells▪ Testing & post-

mortem analysis

Electrochromic

systems

▪ Organic & inorganic films

▪ Process development

▪ Large scale▪ Cost efficient

Analytics

▪ Electrochemical tests

▪ Controlled ageing▪ Failure cause▪ Post-mortem▪ Interface

Process

development

▪ Solid-state-concepts

▪ Semi-automatic electrode & cell manufacturing

© Fraunhofer


Influence of Carbon Additives on Battery PerformanceExamples

1Id from qDCA (EN 50342-6)

Formation Energy Density Charge Acceptance1

Lowering H2-overpotential Increasing energy density at high

rates

Increasing charge

acceptance

© Fraunhofer


Influence of Carbon Additives on Battery Performance

Water Loss

DCA

1.0 1.1 1.2 1.3 1.4 1.5 1.6

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

Pb/PbSO4

PbSO4/Pb

Cu

rre

nt

/ A

Potential vs ? / V

AC-1

AC-2

CB

H2 evolution

© Fraunhofer


Electrochemical Investigation of Negative ElectrodesProduction of Laboratory Electrodes

Paste Components Electrode Paste Laboratory Electrodes

© Fraunhofer


Electrochemical Investigation of Negative ElectrodesSetup of Laboratory Cells

EFB1 battery of C20 = 1 Ah

PE separator

1 negative electrode

2 positive electrodes

Ag/Ag2SO4 reference electrode

Container formation

Separator

Pos. Electrodes

Neg.

Electrode

1 enhanced flooded battery

Test of different negative active

material (NAM) variants

© Fraunhofer


Current Potential Relationship of Negative ElectrodesElectrochemical Fundamentals

Hydrogen

evolution

PbSO4

Pb

ORR

2 mA/Ah

Cyclic Voltammetry

Hydrogen Evolution

Oxygen

Reduction

PbSO4 Pb

Mass transport limitation

Tafel Plot

Charge

Discharge

© Fraunhofer


Improved mass transport

Increasing porosity of electrode

Improved diffusion between electrode

interior and bulk electrolyte

Higher exchange current densities

Larger contact area between electrolyte and electrode

Increased lead surface

Additional carbon surface (micro pores)

Increasing amount of sulfate crystals

Smaller more reversible sulfate crystals

Current Potential Relationship of Negative ElectrodesElectrochemical Activation due to Carbon Additives

Hydrogen Evolution

PbSO4 Pb

Tafel Plot

Mass transport limitation

Oxygen

Reduction

© Fraunhofer


Electrochemical Investigation of Negative ElectrodesTesting of the Dynamic Charge Acceptance DCA

Dynamic charge acceptance test on laboratory

cell level

Adaption test from EN 50342-6 norm

Determination of charge acceptance

after charge history Ic

after discharge history Id

at simulated real world conditions Ir

Reasonable results on laboratory cell level

Most distinct differences between NAM variants can be observed for Ir

© Fraunhofer


Electrochemical Investigation of Negative ElectrodesPolarography/Cyclic Voltammetry

Potential range between

Open circuit potential: -1.0 V vs. Ag/Ag2SO4

Hydrogen evolution: -1.5 V vs. Ag/Ag2SO4

Evaluation of

Hydrogen evolution current @ -1.5 V

Double-layer capacity @ -1.2 V

Hydrogen

EvolutionOn-Set

Double-Layer

Capacity

Can we directly correlate DCA with

electrochemical activity of the negative electrode?

Cu

rre

nt

/ m

A

© Fraunhofer


Electrochemical Investigation of Negative ElectrodesCorrelation between Double-Layer Capacity and DCA

Comparison of

Simulated real world dynamic chargeacceptance Ir

Differential double-layer capacity@ -1.2 V vs. Ag/Ag2SO4

Linear relationship between double-layer

capacity and recuperation current Ir

For high dynamic charge acceptance a large

double-layer capacity is favored

© Fraunhofer


Electrochemical Investigation of Negative ElectrodesPolarography/Cyclic Voltammetry

Potential range between

Open circuit potential: -1.0 V vs. Ag/Ag2SO4

Hydrogen evolution: -1.5 V vs. Ag/Ag2SO4

Evaluation of

Hydrogen evolution current @ -1.5 V

Double-layer capacity @ -1.2 V

Hydrogen

EvolutionOn-Set

Double-Layer

Capacity

Can we directly correlate DCA with

electrochemical activity of the negative electrode?

Cu

rre

nt

/ m

A

© Fraunhofer


Electrochemical Investigation of Negative ElectrodesCorrelation between Hydrogen Evolution Overpotential and DCA

Comparison of

real world dynamic charge acceptance Ir

gassing current at 500 mV polarization ofnegative electrode

In general: linear relationship between Ir and

gassing current

Activation of DCA and HER in parallel

But: possibility to influence this ratio

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Electrochemical Investigation of Negative ElectrodesSummary

Two Correlations between laboratory half cell tests and DCA tests could be established

1. Correlation between double-layer capacity and DCA

The higher the double-layer capacity the higher the dynamic charge acceptance

2. Correlation between DCA and hydrogen evolution

Activation of DCA and HER occurs mostly in parallel

In general: Higher DCA leads to higher gassing currents

But: The ratio between gassing currents and DCA can be controlled

© Fraunhofer


Future Prospects

Water Loss

DCA

1.0 1.1 1.2 1.3 1.4 1.5 1.6

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

Pb/PbSO4

PbSO4/Pb

Cu

rre

nt

/ A

Potential vs ? / V

AC-1

AC-2

CB

H2 evolution

© Fraunhofer


Future ProspectsWays to Overcome the Water Loss – DCA Dilemma for EFB

1. Redefiningoverchargespecifications for„High DCA“-batteries

e.g. gas evolution / weight

loss during real worldconditions

2. Further optimization ofnegative activematerial mixture

Adjustment of

Organic expander

Additive types

3. Tailored additives toincrease DCA withoutincreasing hydrogen evolution

Adjustment of

Pore size distribution

Surface chemistry

© Fraunhofer


Tailored Carbon AdditivesNecessary Steps in the Future

Oxidation of carbon surfaces increasesH2 overpotential

Increasing activity of carbon surface byreduction

-2.5-2.0-1.5-1.0-0.50.00.51.01.5

-14

-12

-10

-8

-6

-4

-2

0

2

4

Cu

rren

t de

nsity

/ mA

/cm

2

Potential vs. Hg/Hg2SO4 / V

30 mV/s

Cycle 1

Cycle 20

Are carbon surface oxides stable in battery?

-1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2

-22

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

Cycle 1

Cycle 40

Cycle 80

Cycle 120

Cycle 170

Cu

rre

nt

de

nsity /

mA

/cm

2

Potential vs. Hg/Hg2SO

4 / V

tailored carbon additives to meet requirements for high...

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