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