Oct 20, 2011 - The work presented here deals with the Advanced Battery, where carbon has been added to the negative acti
Carbon-Enhanced VRLA Batteries October 20th, 2011 David G. Enos, Summer R. Ferreira, Wes E. Baca Sandia National Laboratories Rod Shane East Penn Manufacturing
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
The Advanced VRLA Battery • Recently, there are several manners in which carbon has been added to a Pb-Acid battery The work presented here deals with the Advanced Battery, where carbon has been added to the negative active material Advanced VRLA Battery PbO2
Pb
Lead-Acid Cell
Ultrabattery
PbO2
Carbon
Asymmetric Supercapacitor
PbO2 PbO2
Separator
Pb + C
Why add excess carbon to the NAM? • Carbon additions to the negative active material (NAM) can substantially reduce hard sulfation
Fernandez, 2010*
Standard
Carbon Addition
*M.Fernandez, J.Valenciano, F.Trinidad, N. Munoz, Journal of Power Sources, Vol. 195 (2010), pp. 4458-4469.
Research Goals • The overall goal of this work is to quantitatively define the role that carbon plays in the electrochemistry of a VRLA battery. What reactions/changes take place on the surface of the carbon particles? What processes govern the increase and then eventual decrease in capacity with increasing # of cycles? Are the kinetics of the charge/discharge process different when carbon is present vs. when it is not? Why are some carbons effective additions while others are not? Are there any distinguishing characteristics of effective additions? Is the effectiveness controlled by aspects of the plate production method? etc.
Constituent Material Analysis • Given the limited understanding of what characteristics yield an effective carbon addition, a broad spectrum approach is being taken to quantify the carbon particle properties. Carbon Black
Graphite
Actetylene Black
Activated Carbon
20 nm
20+ µm
20 nm
100+ µm
75 m2/g
6 m2/g
75 m2/g
>2000 m2/g
Structure (XRD)
Semicrystalline
Crystalline
Semicrystalline
Amorphous
Acid Soluble Contamination
Clean
Clean
Very Clean
Na, PO4
Particle size Effective surface area (BET)
Performance Testing Shows Some Differentiation between Control and Carbon Modified Batteries 1.0
1.0
0.8
Cumulative Probability
0.8
Cumulative Probability
Impedance
Control Carbon Black + Graphite Acetylene Black Activated Carbon
Capacity
0.6
0.4
0.6
0.4
0.2
0.2
0.0 1950
0.0 9.5
10.0
10.5
11.0
11.5
12.0
12.5
2000
Capacity (Ah)
2100
2150
Alber Impedance ()
250
1.0
Float Current
Self Discharge
200
0.8
Cumulative Probability
Float Current (mA)
2050
150
100
50
0 2.26
0.6
0.4
0.2
2.28
2.30
2.32
2.34
2.36
2.38
Float Voltage (V)
2.40
2.42
2.44
2.46
0.0 0
10
20
30
6 Month Self Dischage (%)
40
Performance Testing Shows Similarities Between Control and Carbon Modified Batteries HPPC Discharge Capacity
HPPC Charge Capacity 320
300
300
260
Pulse Power Capacity (W)
Pulse Power Capacity (W)
280
240 220 200 180 160 Control Carbon Black + Graphite Acetylene Black Activated Carbon
140 120
280 260 240 220 200 180 160
100 0
20
40
60
Depth of Discharge (%)
80
100
0
20
40
60
Depth of Discharge (%)
Note: These HPPC data are for new cells
80
100
More Dramatic Differentiation Observed as the Batteries are Cycled • Comparable behavior observed for all four battery types at 1k cycles • At 10k cycles, capacity loss was evident in the control, acetylene black, and activated carbon batteries (but not in the carbon black + graphite cell) • Control battery failed at 11,292 cycles Failure defined as a capacity loss of greater than 20% after three discharge/charge cycles in an attempt to recover.
Log Differential Intrusion (mL/g)
Porosity and Pore Size Distribution 0.30 0.25 0.20 0.15 0.10 0.05 0.00 0.01
Log Differential Intrusion (mL/g)
Raw
Control Carbon Black + Graphite Acetylene Black Activated Carbon
0.1
0.5
1
10
Pore Size Diameter (m)
100
Formed
0.4
0.3
0.2
0.1
0.0 0.01
0.1
1
Pore Size Diameter (m)
10
100
Log Differential Intrusion (mL/g)
0.6
Log Differential Intrusion (mL/g)
Porosity and Pore Size Distribution
0.6
0.5 0.4
1k Cycles
Control Carbon Black + Graphite Acetylene Black Activated Carbon
0.3 0.2 0.1 0.0 0.01
0.1
1
10
100
10k Cycles
Pore Size Diameter (m) 0.5 0.4 0.3 0.2 0.1 0.0 0.01
0.1
1
Pore Size Diameter (m)
10
100
Minimal Sulfation at 1k Cycles Control
Activated Carbon
Acetylene Black
Carbon Black + Graphite
100 microns
Significant Sulfation at 10k Cycles for Two of the Batteries Control
20% Capacity Loss
Acetylene Black
15% Capacity Loss
100 microns
Activated Carbon
15% Capacity Loss
Carbon Black + Graphite
4% Capacity Gain
250 microns
Summary/Conclusions to Date •
Battery performance Pb-C batteries had lower initial capacity, higher initial internal resistance, higher float current, comparable HPPC performance, and superior HRPSoC cycling performance
•
Material Characterization Pore structure in Pb-C batteries notably smaller (order of
magnitude), but comparable in overall volume Hard sulfation becoming significant after 10k cycles with the control battery and activated carbon battery
Future Tasks • Cycle testing will continue 50k and 100k cycles Cycle to end of life Analysis of cycled battery materials
• Program will conclude in August 2012
