solid oxide fuel cell manufacturing overview · solid oxide fuel cell manufacturing overview ......

Solid Oxide Fuel CellManufacturing Overview

Hydrogen and Fuel Cell TechnologiesManufacturing R&D Workshop

August 11-12, 2011Washington, DC

Mark Richards, Eric Tang, Randy Petri

Copyright © 2011 Versa Power Systems. All Rights Reserved. 2

Contents

Manufacturing development dependencies SOFC elements Cell manufacturing processes

– Materials– Forming– Conditioning

Stack assembly Quality control and testing VPS projected cost reductions in SECA


The Solid Oxide Fuel Cell Electrochemistry


Cell

Seal

Interconnect

Contacts

Current Collection

ComponentDevelopment

TechnologyDevelopment

Flow Management

Thermal Management

Manufacturability

Repeatability

Tolerance

Stack Manufacturing Development

Stack EngineeringIntegration

Process Development and Piloting


Influencing Factors

Manufacturing– Selection of fabrication process– Evolution of desired microstructure– Cell-to-cell variability as manufactured

(high yields necessary)– Stack (cell-to-cell variation)

Design– Cell architecture– Stack design– Material stability

• Oxidation behavior of steels• Sintering at operating conditions• Interdiffusion of cations• Phase changes/phase separation• Creep warpage

Operation– Fuel composition (Uf, H/C ratio,

contaminants, f(t))– Oxidant (Uo, contaminants, pO2)– Temperature (max)– Temperature gradient (°C/cm)– Temperature variation: x, y, z

Design

OperationManufacturing

MaterialsProcess

Microstructure


SOFC Elements: Independent of Construction

Need to create and join the electrochemical elements (cells)– Anode, cathode, electrolyte– Ceramics

Need to bring reactants to (and from) the cells and keep them where they belong– Flow fields, seals, manifolds– Ceramics or metallics

Need to move electricity from cells– Interconnects, current collection– Ceramics or metallics

Need to move heat from cells and stacks– Active and passive thermal management


SOFC Stack Elements

Fuel cell– Electrolyte, cathode,

anode Interconnects

– Deliver gases, transfer electrons, mechanically support cell

Seals– Keeps gases where they

belong Compression system

– Hold it all in place Current collection

– Get the electrons out

Anode Substrate

Anode Functional LayerElectrolyte

Cathode Functional Layer

Current Collection Layer

Cell

Cathode Flow Field/Contact

Interconnect

Interconnect

Anode Flow Field/Contact

StackRepeat

Unit


Common Ceramic Manufacturing Steps

Raw material preparation– Powder production– Powder preparation– Sizing

Forming– Tape casting, slip casting, pressing, extrusion, calendaring,

dispensing… – Printing, dip coating, spraying, vapor deposition…

Conditioning – Drying, bisqueing, sintering


Ceramic Raw Material Preparation

Generally, most powders will be procured from suppliers– May require in-house processing such as sizing or purification– Inbound quality control

Further preparation prior to forming or deposition– Additional functional materials may be added as well as binders or

slurry agents– Milling is commonly used to refine and mix materials


Ceramic Forming: Primary Layer

Extrusion– Ceramic with a binder is forced through a mandrel forming the desired

green shape (which can be closed at the leading end) Tape Casting

– Ceramic tape is made by uniformly spreading slurry onto a smooth surface

Drying– Both extrusions and tapes need to be dried to allow for handling and

application of other functional elements prior to sintering Cutting

– With extrusions, cutting may result in nearly no loss of material– In a planar cell, tape lost to cutting is a function of cell geometry and

tape size– Recycling of tape lost to cutting is possible


Anode Tape

Tape Casting


Ceramic Forming: Additional Layers

In either a planar or tubular configuration, additional layers are applied to the primary (usually support) layer

Screen printing– Thickness can be limited, reasonable cycle times and cost, planar only

Thermal spraying– Typically uses a flame or plasma, can provide thick coatings, higher depositions

rates than vapor deposition Vapor deposition

– Chemical processes use a fluid precursor which undergoes a chemical change at a solid surface, leaving a solid layer

– Physical processes tend to require a low-pressure vapor environment to function properly

Dip coating– Coating thickness a function of coated surface characteristics, ceramic paint

properties, and number of applications– Equipment is inexpensive but cycle times can be relatively long


Unfired Cell

Screen Printing


Ceramic Conditioning

Drying– Typically done at temperatures up to a few hundred C– Yields a flexible green ceramic

Bisque firing– 300 to 500 C– Yields a stable but brittle shape

Sintering– Ceramic powders are partially melted allowing particles to partially fuse– Time and temperature dependent

Co-firing is possible but varying shrinkage rates make it challenging Low volume production tends to use batch furnaces, continuous

furnaces are available for high volume firing


Loading Conveyor Unloading Conveyor

Exit Chamber

EntranceCross pusher

Entrance Chamber

Main PusherEntrance Door Entrance Door

Exit Cross Pusher

Discharge Pusher

Fired Cell

High Temperature Firing


Common Metallic Manufacturing Steps

Metallic fabrication processes are well established and not unique to SOFC manufacturing– Stamping, punching, rolling, brazing, welding– Powder metallurgy, casting

In some instances, coatings are applied to metallic stack components to improve oxidation characteristics


Assembly

Planar– Layering of cells, flow fields, interconnects, seals, etc. bounded by end

plates/manifolds and compressed– Leak check and initial conditioning

Tubular– Tubes and interconnects assembled with manifolds and enclosed– Leak check and initial conditioning

Automated assembly equipment can require significant volumes to justify its development and expense

Conditioning and test equipment are nearly like full-featured development test stands


Quality Control

Physical properties – Dimensions– Density or porosity– Flatness– Uniformity– Discontinuity

Chemical properties– Compositions– Phases– Impurities

Electrochemical properties

Some QC activities are amenable to automation on non-operating parts, others are not to either or both

Peeling

Voids (Air Holes)

Chipped

Z Average

Y Average

X Average

Surface Flaws

Low Temp Cracks

Misprint

AlignmentOther

LeakDebris

BrokenZ Variation

High Temp Cracks

Tape Inconsistencies

1 2 2 3 3 3 3 4 10 12 14 22 34 61 77112146 0 0 0 1 1 1 1 1 2 2 3 4 712152229

100100 99 99 98 98 97 97 96 94 92 89 84 78 66 51 29

500

400

300

200

100

0

100

80

60

40

20

0

DefectCount

PercentCum %

Perc

ent

Coun

t

Pareto Chart for Failure Reas

Process Capability - 28 Cell StacksBased on 102 Stacks (2856 Cells)

0

100

200

300

400

500

600

0.762

5

0.767

5

0.772

5

0.777

5

0.782

5

0.787

5

0.792

5

0.797

5

0.802

5

0.807

5

0.812

5

0.817

5

0.822

5

0.827

5

0.832

5

0.837

5

0.842

5

0.847

5

0.852

5

0.857

5

0.862

5

0.867

5

0.872

5

0.877

5

0.882

5

0.887

5

0.892

5

Cell Voltage

Freq

uenc

y

28 Cell Stacks x 121 cm2 active area60A (0.50 A/cm2), after 1 thermal cycle42 slpm H2, 37.8 slpm N2, 84 slpm air725°C Furnace Temperature

Sample N = 2856Sample Mean = 0.8613Sample Median= 0.8633Std Dev = 0.0137Minimum = 0.7600Maximum = 0.8949Variance = 0.0002


Cell Manufacturing Process Development


SECA Projected Stack Cost Reduction

Cost Reduction Focus Areas1. Stack Performance Increase

• Peak Power Increase Resolved thermal management issues

2. Material Reduction:• Thinner stack components• Interconnect material reduction• Reduced number of intermediate

plates3. Manufacturing Process Changes

• Interconnect manufacturing development

• Improved material utilization4. Process Optimization

• Automation• Elimination of process steps

SOFC Stack Block Cost Reduction

$197

$119

$210

$153

$85

$108

$0

$50

$100

$150

$200

$250

Phase I Factory CostEst. (2002 USD)

2009 Interim(2002 USD)

Phase II FactoryCost Est. (2000 USD)

$/kW net AC$/kW gross DC

The fuel cell stack cost has decreased substantially mainly due to the R&D activities in the SECA project


Stack Cost by Components and Category

$0/kW

$10/kW

$20/kW

$30/kW

$40/kW

$50/kW

$60/kW

$70/kW

$80/kW

$90/kW

RepeatComponents

Stack

Cathode ShimsBuilding CostBlock AssemblyInstrumentation Plate(s)End PlatesRepeat Comp. TotalInterconnectsCathode Flow FieldCathode SealsAnode Flow FieldAnode SealsShimsCell HolderCell FabricationCell

The majority of stack cost is driven by the cost of materials The relatively low labor cost is attributed partly to the fact that cells and seals

are produced by VPS in-house

96-cell Stack: $2,658 (2000 USD)

Labor$19/kW

22%

Non-Repeat Components

Material$4/kW

5% Repeat Components

Material$62/kW

73%


Manufacturing Automation Strategies

Manual operation– Production volumes from 5 MW to 25 MW– Use manual equipment with longer cycle times and smaller batch size

Semi-automatic operation– Production volumes from 25 MW to ~100 MW– Use medium size equipment and has partial automation in key stations

Automatic operation– High volume production from ~100 MW to 250 MW– Workstations and material handling system are automated


Cost and Manufacturing Initiatives

Materials– Materials reduction in cell and stack– Low cost materials– Interconnect coating

Fabrication and assembly– Cell co-sintering– Sealing technology

Quality control and testing– On-line QA/QC with real time feedback– Stack conditioning


Questions?

Portions of this material are based upon work supported by theDepartment of Energy under Award Number

DE-FC26-04NT41837

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned

rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and

opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

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