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NELLHI Report Summary

Project ID: 621227
Funded under: FP7-JTI
Country: Italy

Periodic Report Summary 1 - NELLHI (New all-European high-performance stack: design for mass production)

Project Context and Objectives:
NELLHI combines European know-how in single cells, coatings, sealing, stack designs and manufacturing technology to produce an innovative and modular 1 kW SOFC stack. In this project, improvements over the state of the art in cost, performance, efficiency, and reliability will be proven, as a combined result of high-performance cells and manufacturability designed for mass production at high yield. The NELLHI stack operates at reduced temperature, with unprecedented performance. Within the project, the stack module will be developed over 3 successive generations according to system integrators’ requirements guided by an industrial advisory group. The target application of the development is stationary and residential combined heat and power production based on natural gas, and will form the basis for Elcogen Oy’s commercial SOFC stack technology as well as enforce market penetration for component manufacturers Elcogen AS, Sandvik, Borit and Flexitallic. All manufacturing methods, stack designs, and materials are tailored to mass production to enable 1000 €/kW profitable stack price.

To achieve this high-level objective, a systematic approach is undertaken, focusing on each key component of the stack assembly and establishing sub-objectives for each part:
• Cell development
o Upscale the unit cell from 100x100 mm2 size to 120x120 mm2 to increase yield rate and specific performance
o Tailor and improve the production process to achieve unit cells capable of reaching 900 mV cell voltage with 0.4 Acm-2 current density at 650 ºC operating temperature and 75% fuel utilization in a stack environment.
o Achieve robust cell structures with less than 0.5% degradation per 1000h and 1% per 10 thermal cycles
o Validate cell performances and investigate cell processes in situ for analysis of critical conditions and parameters
• Interconnect development
o Consolidate the once-through roll-to-roll process of pre-coated steel sheets for massive supply of ready material for interconnect manufacturing without further surface treatment
o Select the optimal substrate and coating combination for the NELLHI stack in terms of operating performance and cost
o Design and optimize interconnect geometry for the NELLHI stack assembly focusing on minimizing leakage and weight
o Consolidate the hydroforming process for rapid shaping of the interconnect from supplied pre-coated steel sheets, based on optimized design
o Adapt cutting and welding techniques for maximum manufacturing effectiveness and speed
• Sealing development
o Develop and optimize gasket material, thickness and composition based on the hybrid sealing concept
o Validate sealing performance in terms of leakage and conformability in stack environment
o Improve sealing designs for quick manufacturing and easy handling in stack assembly line
• Stack integration
o Incorporate the successive improvements of above components in 2 design-freezes before confirming the optimal design, assembly and integration
o Validate stack performance in representative and aggravated test conditions

Project Results:
The first reporting period has seen excellent collaboration and progress taking place in all 4 lines of activity. The overall objective was to finalize the component development for the 2nd generation stack. This has been achieved, with a final quality check outstanding for the interconnect plates (see Section 1.2.4).
Cell manufacturing is a key process in terms of ultimate stack performance, especially in the tape-casting process. Elcogen AS has been able to focus on this line of activity exclusively, with important achievements in terms of slurry composition, sintering response, porosity tailoring and substrate finish.
Sandvik has perfected the production line for coil-to-coil rolling of a commercial steel (cheaper than high-grade, special steel like Crofer or Sanergy) and PVD coating of Cerium-Cobalt for corrosion and chromium evaporation protection. Characterization (also long-term) is ongoing, but the specs achieved so far are the best available on the market.
Borit has upscaled their production line to process more interconnects per day and have consolidated robotic welding of the shaped interconnect plates, being able to handle the latest design supplied by Elcogen. With this new design, some issues emerged regarding efficient leak testing of the plates, which are being tackled for production line Quality Assurance.
Flexitallic has successfully collaborated with Elcogen to resolve unforeseen contamination issues in the sealing production line, as well as tailor the composition of seals to enable high conformability and excellent hermetic qualities, improve the design for one-step shaping and cutting of seals, and maintain easy handling capability. These results are being brought together for the next generation of the NELLHI stack.
Elcogen have overseen all progress and carried out contemporaneous systematic evaluation of the different parts to ensure quick feedback to the different partners in charge of component development.
ENEA has assisted Elcogen AS in cell characterization and validation, VTT has done in-depth analysis of interconnect material behaviour, and CUTEC has validated Elcogen’s integrated stack in a dedicated test bench for the full range of operation.

Potential Impact:
All expected impacts as specified in section 3.1 of the DoW are retained at this stage of the project. Improved electrical efficiency is being achieved already with Elcogen’s 1st generation 15-cell stack, with the targeted performance of the 2nd generation stack already achieved. Improved robustness is being pursued, thanks to better design of the stack assembly components which will improve uniformity of stack conditions. The current degradation rate is already below MAWP targets (<1%/1000h) and the leakage rate after thermal cycling is already beyond the targets for the 2nd year. Considerable cost reductions are foreseeable thanks to the strong focus on mass-production manufacturing techniques in the project, cutting process steps, employing cheaper materials, reducing material expenditure and improving design to allow lower tolerances of parts.
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