low-cost fabrication processes for solid oxide fuel cells
TRANSCRIPT
LowLow--Cost Fabrication Processes Cost Fabrication Processes for Solid Oxide Fuel Cellsfor Solid Oxide Fuel Cells
M.M. Seabaugh, S.L. Swartz, W.J. Dawson, K. Hasinska and B.E. McCormick
NEXTECH
MATERIALS
NexTech Materials, Ltd. 720-I Lakeview Plaza BoulevardWorthington, OH 43085
Colloidally Deposited Nanoscale YSZ Electrolytes for Tubular SOFCs
• Objective: Low-cost YSZ membrane fabrication process to replace EVD in the Siemens-Westinghouse tubular SOFC.
• Approach: Deposition of YSZ films from colloidal suspensions onto pre-sintered, porous LSM cathode tubes, followed by sintering.
Stresses and Constrained Sintering
20 µµmRigid Substrate Creates Tensile Stresses in Drying and Sintering Films
Porous Substrate Creates Unsupported Regions of Intense Stress in Coating
Microcracking in Mismatched Coating(Sintered 1250°C, 3 hours)
Nanoscale Porosity in Drying Film Creates Extremely High Capillary Tensile Stresses
Management of stresses is essential to the deposition of defect free electrolytes
20 µµm
20 µµm
Control of binder content, particle size, and solvent surface tension allows the deposition of continuous green films
Sintering at 1400°C, 1h results in continuous, dense films.
Crack Free Deposition of Electrolyte Films on LSM Tubes
Cathode-Supported Thin-Film SOFCs with Low Operating Temperatures
• Objective: Establish feasibility of a low-cost tape casting and colloidal deposition processes for cathode-supported thin-film SOFCs
• Approach: Develop ceramic fabrication methods for LSM cathode substrates with high porosity (40 to 50 vol%) after sintering at 1300°C. Deposit ceria interlayer and YSZ electrolyte films on the LSM substrates. Co-sinter the coated substrates to obtain dense and defect-free YSZ films on porous LSM substrates at temperatures of 1200 to 1300°C.
Colloidal Depositionof Interfacial and Electrolyte Films
Dried Electrolyte Film on Porous LSM Support
Co-sintering
Green LSM Support
Tape
FugitivesBinderSolvent
CastingLSM
Thin-Film SOFC Processing Route
Electrolyte Film• Thickness: ~10-15 ìm
• Composition: YSZ
• Density: ~100%
Cathode Substrate• Structural Support,
Gas Transport via Pores
• Thickness: ~1 mm
• Composition: LSM
• Density: 60~65%
• Pore Size: 5~20 ìm
Cathode/ElectrolyteBi-Layer Elements• Area: 10 ×× 10 cm
• Substrate Calcined Priorto Electrolyte Deposition
• Co-sintered to Densify Electrolyte Layers
Interlayer Film• Diffusion Barrier, Enhance
Cathode Performance
• Thickness: 5~10 ìm
• Composition: SDC/PSM
• Density: 80~100%
Thin-Film SOFC Architecture
Cathode Tape ProductionA slurry containing cathode powder, fugitive and binder is cast in sheets. The slurry must be highly pseudoplastic to retain its dimensions during drying.
The tape is calcined prior to electrolyte deposition. This removes the binder and fugitive phases, creating interconnected porosity. This porosity will serve as air channels in the finished cell.
As the tape dries, it shrinks in the thickness direction. The powder, fugitive, and binder form a flexible, leathery film that can be cut and laminated to form more intricate parts.
After calcination, the interfacial and electrolyte layers are applied by aerosol spray coating. The trilayer is cosintered at high temperature to simultaneously densify the cathode and electrolyte layers.
T = ~600ºCt = 2-12 h
T = 1300ºCt = 1-4 h
Shrinkage < 5%
Shrinkage 10-20%
Shrinkage 20-30%
20 µm
20 µm
20 µm
Refinement of Substrate Densification
Initial attempts to densify LSM substrates resulted in good densification and shrinkage, but inappropriate pore morphology. Adjustments to particle size distribution and liquid phase sintering aids improved microstructure development.
Sintered Morphology of Initial Substrates
Sintered Substrate with Modified PSD Liquid Phase Sintered Substrate with Modified PSD
0
20
40
60
80
100
120
140
160
0 1 2 31000/T
S/c
m
LSM + 0.5 % Liquid Phase Former
LSM + 1% Liquid Phase Former
LSM
30%
40%
50%
60%
70%
80%
90%
100%
950 1050 1150 1250 1350 1450Temperature
Per
cen
t Th
eore
tical
Den
sity LSM + Liq. Phase Former
LSM + Liq. Phase + 50% Fugitive
LSM + Liq. Phase + 25% Fugitive
Control of Cathode PorosityThe graph at right shows the effect of fugitive addition on the sintered density of a liquid phase sintered LSM powder. The data shows that sintering can be performed at high temperature to obtain good strength, while maintaining high porosity.
Electrical Properties of Liquid Phase Sintered LSMThe graph at left shows the effect of liquid phase addition on the electrical conductivity of sintered LSM powder. The data shows that the addition of liquid phase sintering can be used improve densification without severely affecting electrical performance.
Spray Suspension Synthesis Process
Metal Salts, Alkali,Coprecipitation
Temperature < 300°CPressure < 15 MPaBatch or Continuous
Dewatering, Dispersion
FEED PREPARATION
HYDROTHERMALTREATMENT
PRODUCTCOLLECTION
SUSPENSIONMODIFICATION
AEROSOL SPRAY ORDIP COATING
DeagglomerationAddition of Organics
Drying, Calcination, Sintering
HEAT TREATMENT
02468
101214161820
8.5 14.4
24.6
41.9
71.5 12
220
835
4.760
4.9
1031
.6
Size (nm)
Wei
gh
t Per
cen
t
Particle Size Distribution of Nanoscale YSZ
Design Specifications of Spray SuspensionAqueous Solvent: Inexpensive
Direct Processing of Product Safe, and Environmentally Friendly
High Solids Content: Low Shrinkage During DryingFast Drying
Optimized Particle Size: Minimize Drying StressMinimize Sintering Shrinkage/StressLower Sintering Temperature
Optimized Organic Content: Increase Film StrengthLower Drying Stresses
Laboratory Scale Application of Spray Suspension on an
LSM Cathode Tube
Co-Sintered YSZ/LSM Bilayers
←← Calcined 1000°C
Sintered 1350°C →→
←← 20 µµm →→
←← 20 µµm →→
LSM
YSZ
Low-Cost Manufacturing of Multilayer Ceramic Fuel Cells
Program Partners
NexTech Materials, Ltd. Adaptive Materials, Inc.Oak Ridge National Laboratory Institute of Gas Technology University of Missouri-Rolla Northwestern UniversityMichael A. Cobb & Company Ohio State UniversityAdvanced Materials Technology, Inc. Iowa State UniversityEdison Materials Technology Center U.S. Air Force
To meet market needs, solid oxide fuel cells must be:• Widely available at much lower cost (<400 $/kW)• Manufacturable by high volume processes• Have demonstrated long life• Have acceptable reliability, maintainability
Our challenge is to define and develop new manufacturing approaches to make solid oxide fuel cells
Multilayer SOFC Program
• Low-Cost, High Volume ManufacturingReduce Stack Cost to $100/kWDesign for Manufacture/Volumetric EfficiencyLow Operating Temperature (600 to 800ºC)
• Performance TestingSingle-Cell SOFC TestingLong-Term SOFC TestingNon-Destructive TestingMechanical Properties
OperatingTemperature
ProcessYields
Cost ofRaw Materials atLarge Volumes Cathode or
Anode as Support Electrode
Thicknessof SupportElectrode
Internalor ExternalReforming
Laminationof Tape-Cast
Layers
Aqueous versusNon-Aqueous
Processes
Cost Drivers
Low-TemperatureCathode Materials
Integrationof Fabrication
Processes
Gas Diffusion and Interface
Reactions Defect-Free and High-Density
YSZ Films
Robustness ofPorous Electrode
Support
Co-SinteringShrinkage
Mismatches
ThermalExpansion
Mismatches
InternallyReforming
Anodes
Performance Drivers
Summary of Cost/Design Analysis
Configuration & Track Leader
Manufacturing Methods
Stack Cost ($/kW)
Active Volume
(Liter/kW)
Active Volume (kg/kW)
Cathode Supported Planar Cell (NexTech)
Tape Casting of LSM Cathode
Colloidal Deposition of YSZ Electrolyte Co-sintering of Tri-Layers
Screen Printing of Ni-YSZ Anode
139
2.13
7.18
Cathode Supported Planar Cell (UM-Rolla)
Tape Casting of LSM Cathode
Sintering of LSM Substrates
Spin-Coating of YSZ Electrolyte Films Screen Printing of Ni-YSZ Anode
179
2.63
8.98
Anode Supported Planar Cell (ORNL)
Tape Casting of Ni-YSZ Anode Screen Printing of YSZ Electrolyte
Co-sintering of Bi-Layers Screen Printing of LSM Cathode
150
2.13
7.21
Anode Supported Planar Cell (AMI)
Co-Extrusion and Co-Sintering of Anode/Electrolyte/Cathode
Multilayer Plates
145
2.13
7.22
Proprietary Cell A Proprietary 94 0.83 1.92
020406080
100120140160180200
$/kW
NexTech ORNL AMI UMR ProprietaryDesign
Manufacturing Cost Comparison
Cost of CapitalIndirect CostDirect LaborMaterial
Research Supported by:
National Energy Technology Laboratory
Ohio Department of Development
U.S. Department of Energy