2012 storage symposium - columbia...
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Scaled Electrochemical Cells for Scaled Stationary Energy Storage: A Case Study
2012 Energy Storage Symposium
Jay WhitacreCarnegie Mellon University
Large Format High Voltage Aqueous Polyionic Devices for Low Cost Scaled
Energy Storage
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J.F. Whitacre1,2, S. Shanbhag2, W. Yang2, A. Mohamed,1,2 E. Weber2
1Carnegie Mellon University, Department of Materials Science and Engineering, Department of Engineering and Public Policy, 5000 Forbes Ave, Pittsburgh PA 15213
2Aquion Energy 32 39th Street, Pittsburgh PA 15201
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SUPPORTED BY
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THE ECONOMIC REALITY OF ENERGY STORAGE – SPECIFIC COST
• First key ‐ capital cost: Specific cost = $/kWh
• Simple linear relationship between cost of good sold (COGS) and energy density
• Another key ‐ cycle life:• Issue: typically energy
density and cycle life are inversely correlated
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THE ECONOMIC REALITY OF ENERGY STORAGE – CYCLE LIFE
• Another key ‐ cycle life:• Issue: typically energy density and cycle life are
inversely correlated• Important metric: levelized cost of stored energy as
amortized over the lifetime of the system
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SOLUTION: LOW COST AND HIGH ENOUGH ENERGY DENSITY
• Goal was to identify the “sweet spot” between specific cost, energy density, and cycle life
• Significant testing yielded a finding:
• Aqueous electrolyte sodium ion functional materials and battery structures
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THE HYBRID ENERGY STORAGE DEVICE
• Anode is low cost activated carbon– Electrochemical Double Layer Capacitor Effect
• Cathode is Na0.44MnO2– Alkali ion intercalation material
• Electrolyte is Na2SO4 in water (~1 M)
Activated carbon NaMnO2
‐ +
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STABILITY/CAPACITY OF FIRST GENERATION CHEMISTRY
•Significant energy present, •BUT, using costing rules, materials have to be under $2/kg all in to compete•Very difficult to do!
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CYCLE LIFE/COLUMBIC EFFICIENCY
0
0.5
1
1.5
2
0 200 400 600 800 1000
Q charge/mA.hQ discharge/mA.h
Spe
cific
Cap
acitr
y (m
Ah/
g)
Cycle Number
Optimized Solid State Na0.44
MnO2
Cycled at 4C rate, 0.4 to 1.8 V, Cell Capacity ~1.8 mAh1 M Na2SO4, Kuraray RP-20
1000 cycles, negligible loss in capacity, 100% Columbic efficiency
5 C charge/discharge rate
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• – MnO2 has over 2 times the capacity and 3 times the energy of Na4Mn9O18,
• Rate capability also found to be very good.
Lambda MnO2 in Na2SO4
SECOND GENERATION CHEMISTRY: LAMBDA‐MNO2
• Much higher specific capacity compared to Na4Mn9O18
• In balanced device, over 100 Wh/kg (cathode) at lower rates
• Still extremely stable
• Added cost of using Li2CO3 to template material is justified.
SECOND GENERATION CHEMISTRY: ELECTRODE THICKNESS
• In thin format cells, the material displays excellent rate capability
• However, these cells are far too costly to scale with these dimensions . . .
• 3 different species are functional:– Lithium – cathode materials templating, extracted into electrolyte during first charge, remains functional
– Sodium – electrolyte cation, intercalates into MnO2 of cathode and also performs EDLC function at anode
– and Hydrogen. . . .
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POLYIONIC FUNCTIONALITY
• At the anode: as the potential of hydrogen evolution is reached, local OH‐ species are generated, and are not extracted rapidly
• This increases the pH inside the negative electrode, and subsequently re‐stabilizes the local water. There is also the natural overpotential of water splitting on Carbon
• So minimum stable anode potential is ‐0.9 V (vs. NHE) at local pH of 14 plus ~0.2 to 0.4 V of over potential.
• If cathode is pinned at ~+1 V, then, we have a cell voltage of over 2 V • BUT hydrogen is evolved during this process – what of it?
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ANODIC POURBAIX SHIFT AT ANODE ENABLES HIGH CELL V
ACVmax
*Nature Chemistry, 2, 2010, pg 760
*
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• At increasingly anodic potentials more and more hydrogen is reversibly stored inside the electrode
• Some carbons more amenable to this than others
• Cost benefit assessment necessary!
HYDROGEN STORAGE AT ANODE
• We have excess cathode material to pin the positive electrode potential below the point of oxygen evolution
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THREE – ELECTRODE DATA:
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• Na functional in cubic spinel ‐ different recipe is optimal •>40 Wh/kg specific capacity, same long term stability• >90% round trip energy efficiency
0
0.5
1
1.5
2
0 10 20 30 40
Cel
l P
oten
tial
(V)
Energy (Wh/kg or Wh/Liter)
Wh/kg (active material)
Wh/liter(Electrode Volume)
MNO2 – BASED CELLS: ENERGY DENSITY
MANUFACTURING PROCESS AND FLOW
SEMI‐AUTOMATED MANUFACTURING IN PLACE; FULLY AUTOMATED IS DESIGNED
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TECHNOLOGY: CYCLE LIFE
5000 rapid cycles on Indicative Test Cell
Large Format Cycle Profile: +/‐ 1.5 Amps
• Chemistry stable over broad voltage range• Symmetric charge/discharge profile• >5000 Cycles shown at high rates, (100% DoD)• >800 cycles over 15 months; ~ 6 hour rate• Near perfect coulombic efficiency• Application specific tests performed (backup
slides)
0
20
40
60
80
100
120
0 1000 2000 3000 4000 5000
Charge CapacityDischarge Capacity
Cap
acity
(%
of
initi
al C
apac
ity)
Cycle #
> 1 year constant cycling6 hour rate, 100% DoD
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TECHNOLOGY: DURABLE MANUFACTURED BATTERIES
Voltage vs. Capacity
• Chemistry locked down and scaling; In‐house large format industrial production demonstrated
• > 30 Wh prototype batteries in production
• Industry‐proven polypropylene casing and sealing technologies
• Multiple 3rd party verification tests completed by industry experts
“Battery 0”
Energy Density of Electrode Stack
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TECHNOLOGY: HIGH VOLTAGE STRINGS
• >100 V strings in use currently• High tolerance to cell‐to‐cell mismatch• Minimal or no BMS required• Anodic hydrogen mechanism is self‐
balancing mechanism
String 10 Batteries
String of 60 Batteries
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TECHNOLOGY: HIGH TEMPERATURE ABUSE TESTING
• Testing performed of exposure to 60˚C for 850 hours while deep cycling• Open Circuit Stand at 75% DoD for 40 hours• No self discharge observed• No loss in capacity/function as a result of stand
Test cycle
• 6 A constant current baseline test on 4 Aquion batteries in series before and after 3176 Sandia PSoC test cycles.
• 0 capacity fade observed. Battery is unaltered by PSOC cycling
• PbA loses over half it’s capacity after this kind of use
APPLICATION DATA: PSOC CYCLING (REF. BASELINE CYCLE TESTING)
Rapid PSoC Tesing around 50% SoC Benchmark Discharge Before/after >3000 Cycles
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TECHNOLOGY: TESTING AT KEMA
• Fully sensored Aquion Energy 1 Wh units in environmental test chamber at KEMA
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• 1 Wh units tested; wind typified power vs. time duty cycle imparted on battery
• Charge/discharge rates range from 1C discharge to 1.5 C charge
• Battery easily supports signal, very
APPLICATION ANALYSIS: WIND SUPPORT/MICRO CYCLE
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APPLICATION ANALYSIS: PEAK SHAVING
• 8 hour charge, 16 hour discharge• Constant current conditions used• Energy taken/given very consistent through many cycles
• “250 Ah” Hoppecke OPxV 2 V deep cycle “solar.power” battery. Rated (20 hr) capacity is 500 Wh, cost is ~$150
• ~18 hour cycle: ~6 hour constant current charge, ~6 hour constant current discharge, 6 hour stand at discharge, repeat
– Using mfg. spec on safe V window (2.25 to 1.85 V)– After only 14 cycles, Battery is giving less than half of the rated 250 Ah (about 100 Ah).
• 15 V, 24 Ah Aquion Energy Battery under same testing protocol.
205 Wh
OFF GRID SOLAR CYCLE (W/OUT TRICKLE CONDITIONING)
• Very stable performance, even with batteries in series
OFF GRID SOLAR/DIESEL HYBRID SYSTEM CYCLE
• “250 Ah” Hoppecke OPxV 2 V deep cycle “solar.power” battery. Rated (20 hr) capacity is 500 Wh, cost is ~$150
• ~18 hour cycle: ~6 hour constant current charge, ~6 hour constant current discharge, 6 hour stand at discharge, repeat
–Using mfg. spec on safe V window (2.25 to 1.85 V)–After only 14 cycles, Battery is giving less than half of the rated 250 Ah (about 100 Ah).
• 15 V, 24 Ah Aquion Energy Battery under same testing protocol.
Lead acid unable to handle long stands at partial SOC without frequent “top off” trickle events:
IMPACT OF STANDING AT PSOC ON BATTERY LIFE
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1000 VOLTAGE SYSTEM
540 batteries connected in a single string
NO BMS used. Reliance on anodic hydrogen reaction for self balancing to occur
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1000 VOLT SYSTEM: DATA
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1000 VOLT SYSTEM: DATA
• Off‐grid diesel hybrid support cycle run on 1000 V system after 2 months of testing/break‐in.
COMMERCIAL PRODUCTS: TIMING AND FORM FACTOR
In pilot production now: 8V cells Fundamental system building block
Q412 Early Customer Demo/Validation: Individual 48V, 1kWh modules
Q113 Early Customer Demo/Validation: Large format, palletized 48 V, 12kWh Modules
Q212 Q312 Q412 Q113 Q213 Q313 Q413 Q114 Q214 Q314 Q414
B1 Containerized Solutions
B1 Bulk Solutions
B1 Stacks
B1 Pallets
AHI COMMERCIALIZATION TIMELINE
DISCUSSION ON ECONOMICS
• Expected cost of battery and and system as function of time
• The entry strategy
• Path to grid‐scale disruption.
2012 Energy Storage Symposium
Wednesday, May 2 – Thursday, May 3, 2012Columbia University