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
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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
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3 AABC Europe 2017January 31, Mainz
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
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4 AABC Europe 2017January 31, Mainz
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
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5 AABC Europe 2017January 31, Mainz
Electrochemical Investigation of Negative ElectrodesProduction of Laboratory Electrodes
Paste Components Electrode Paste Laboratory Electrodes
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6 AABC Europe 2017January 31, Mainz
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
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7 AABC Europe 2017January 31, Mainz
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
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8 AABC Europe 2017January 31, Mainz
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
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9 AABC Europe 2017January 31, Mainz
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
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10 AABC Europe 2017January 31, Mainz
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
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11 AABC Europe 2017January 31, Mainz
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
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12 AABC Europe 2017January 31, Mainz
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
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13 AABC Europe 2017January 31, Mainz
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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14 AABC Europe 2017January 31, Mainz
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
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15 AABC Europe 2017January 31, Mainz
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
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16 AABC Europe 2017January 31, Mainz
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
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Jochen Setteleinphone: +49 (0)931 4100 916e-mail: [email protected]: fzeb.fraunhofer.de
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18 AABC Europe 2017January 31, Mainz
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
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19 AABC Europe 2017January 31, Mainz
Electrochemical investigation of negative electrodesCorrelation between Formation Voltage and DCA