Role of Exposure Atmospheres on Particle Coarsening and Phase Transformation of LiAlO₂

Abstract

The phase transformation and particle coarsening of lithium aluminate (α-LiAlO 2 ) in electrolyte are the major causes of degradation affecting the performance and the lifetime of the molten carbonate fuel cell (MCFC). The stability of LiAlO 2 has been studied in Li 2 CO 3 -Na 2 CO 3 electrolyte under accelerated conditions in reducing and oxidizing gas atmospheres at temperatures of 650 and 750 for up to 500 hours. X-ray diffraction analyses show that the progressive transformation of α-LiAlO 2 to γ-LiAlO 2 phase proceeds with increasing temperature in lower P CO 2 and lower P O 2 environments. Spherical LiAlO 2 particles were transformed to coarsened pyramid-shape particles in 4% H 2 -3% H 2 O-N 2 and 100% N 2 (∼10 ppm P O 2 ) atmospheres. Under CO 2 -rich atmospheres (4% H 2 -30% CO 2 -N 2 and 70% air-30% CO 2 ), both phase and particle size remained unchanged at 650 and 750 • C. Selected area electron diffraction (SAED) pattern analysis indicated that the large pyramidal shape particles (∼30 μm) were γ-LiAlO 2 phase. Experimental observations and related simulation results pertaining to particle coarsening and phase transformation behavior of Molten carbonate fuel cell (MCFC) power generation systems are currently being developed and commercialized because of their demonstrated high electrical efficiency (>45% net electrical AC and >90% combined heat and electric), multi-fuel operational flexibility (pipeline natural gas, bio-gases from farm waste and wastewater treatment), pollution-free operation (no NO x , SO x , PM's, VOC) and reduced CO 2 foot print.1-3 A large number of MCFC power plants in multi -MWe class have been successfully installed and operated in North America, Europe and Asia demonstrating the technology and systems engineering robustness. 4 Over the last decade, optimization of cell and stack operating conditions, materials chemistry and fabrication processes have resulted in significant improvement of the cell life and performance making it possible to obtain long life (>50,000 hrs.) of MWe class systems.5 A need to increase the system life time to >80,000 hours has been identified as next steps for increased market penetration and cost reduction. 6 For the state of the art MCFC's, the electrical performance degradation is commonly assigned to cell and stack component corrosion, structural changes, and electrolyte loss. Although effective mitigation strategies for a number of materials related degradation issues (anode creep, cathode dissolution, current collectors and bipolar plate corrosion) have been developed and implemented, 7,8 challenge with matrix coarsening beyond 60,000 hours remains.The lithium aluminate (LiAlO 2 ) is the state-of-the-art ceramic constituent material in the electrolyte matrix. It effectively retains the liquid electrolyte and prevents gas crossover with sufficient finepore structure stability.9 LiAlO 2 exists in three different allotropic forms which are hexagonal α-LiAlO 2 (ρ = 3.401 g/cm 3 ), monoclinic β-LiAlO 2 (ρ = 2.615 g/cm 3 ), and tetragonal γ-LiAlO 2 (ρ...

Role of interfaces in damage process of irradiated lithium aluminate nanocrystals

“…For example, in MCFCs, the pore size of the LiAlO 2 matrix is a key to maintain an appropriate amount of electrolyte in the matrix. However, during a prolonged operation, particle growth and phase transformation occurs and results in pore coarsening, which poses an important challenge to develop long‐life commercial components . In nuclear applications, LiAlO 2 is subjected to neutron irradiation which causes transmutation and atomic displacement damage.…”

A review on MCFC matrix: State-of-the-art, degradation mechanisms and technological improvements

“…1 ), the state-of-the-art material consists of lithium aluminate LiAlO 2 reinforced by Al agents. Among three allotropic forms, α -LiAlO 2 hexagonal structure, β-LiAlO 2 monoclinic structure and γ -LiAlO 2 tetragonal structure [ 38 ], α-phase [ [39] , [40] , [41] ] and γ -phase [ 28 , 29 , 33 , 40 , 42 ] are mainly used as MCFC matrices.

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“…The addition of reinforcing elements permits to overcome these issues and increase the mechanical strength by improving the structural stability and hindering the crack propagation. Several alternatives have been proposed starting from metal and ceramic particles in different shapes and amounts [ 36 , [38] , [39] , [40] ] to metallic mesh integration [ 26 ], Al 2 O 3 and LiAlO 2 fibers [ 36 , 41 ] and more recently high performing Al foam based matrix [ 69 , 72 ], looking for a compromise between an effective increase of the mechanical strength and the hindering of unwanted degradation processes due to the addition of further elements within the matrix. Fig.…”

Corrosion of AISI 310 and 316 in Molten Hydroxide Under Steam Electrolysis Conditions

“…Exposures to high temperatures in the presence of hydroxides can be detrimental to the durability of the fuel cell components. Commonly used metallic components/current collectors/separators such as Ni and AISI steel grades on the anode and cathode side, respectively, can be quite vulnerable to accelerated corrosion attack in the presence of molten electrolyte [6], [7], [8], [9], [10]. Tzvetkoff and Girginov examined corrosion of Ni at 200 °C and reported porous nickelates compound/NiO formation on the Ni surface [11].…”