To determine optimum conditions for the synthesis of LiNiO 2 by the combustion method, syntheses were carried out in air and under oxygen at various calcination temperatures and for different times. The electrochemical properties of the prepared samples were then investigated. The optimum conditions are preheating at 400°C for 30 min in air in the mole ratio of urea to nitrate 3.6 and calcination at 750°C for 36 h under O 2 . The LiNiO 2 synthesized under these conditions had a first discharge capacity of 189 mAh g )1 at 0.1 C-rate and relatively good cycling performance. This sample has a larger value of I 003 /I 104 (smaller cation mixing) and a smaller R-factor (larger hexagonal ordering). Cycling performance was investigated in various voltage ranges. The first discharge capacity increased as the upper limit of the voltage range rose. The first discharge capacity was small but cycling performance was good when the sample was cycled in the voltage range with the lowest upper limit.
For the syntheses of LiNi 1-y Fe y O 2 (0.000 B y B 0.300), mixtures of the starting materials with the desired compositions were preheated in an air atmosphere at 400°C for 30 min and calcined in air at 700°C for 48 h. The phases appearing in the intermediate reaction steps for the formation of lithium nickel oxide are deduced from the DTA analysis. XRD analysis, FE-SEM observation, FTIR analysis and electrochemical measurement were performed for the synthesized Li 1-z (Ni 1-y Fe y ) 1?z O 2 (0.000 B y B 0.300) samples. The samples of Li 1-z (Ni 1-y Fe y ) 1?z O 2 with y = 0.025 and 0.050 have higher first discharge capacities than Li 1-z (Ni 1-y Fe y ) 1?z O 2 with y = 0.000 and better or similar cycling performance at the 0.1 C rate in the voltage range of 2.7-4.2 V. Similar results have not previously been reported except for Co-substituted LiNiO 2 . The sample Li 1-z (Ni 0.975 Fe 0.025 ) 1?z O 2 has the highest first discharge capacity (176.5 mAh g -1 ). Rietveld refinement of the XRD patterns of LiNi 1-y Fe y O 2 (0.000 \ y B 0.100) from a starting structure model [Li,Ni] 3b [Li,Ni,Fe] 3a [O 2 ] 6c showed that cation disordering occurred in the samples.
Growth of an oxide layer between the metallic interconnect and cathode leads to undesirable increases in contact resistance across the interface. It is particularly important to minimize the interfacial resistance by using suitable electrical contact layer between cathode and interconnect. In order to develop ideal electrical contact layer, fundamental mechanism of the evolution of interface between electrical contact and metallic interconnect in SOFC cathode environment was studied. ASR evolution of LaNi0.6Fe0.4O3 (1) and Pt contact layer/Pt sheet interface was evaluated. It was found that interdiffusion plays a key role in ASR increase. Particle sintering was minimal after 200 hours. Smaller particle size of LNF electrical contact layer enhanced diffusion rate to the scale. ASR of growing oxide was measured with Pt and LNF electrode. Interdiffusion between electrical contact material and growing oxide was observed and contributed to ASR increase rate. It seems that development of electrical contact material that reacts with oxide scale and forms the phase that has low resistance is a direction to pursue.
One of the candidates for metallic interconnects of solid oxide fuel cells is a ferritic stainless steel, Crofer22 APU. Ferritic stainless steel Crofer22 APU samples with different roughness were prepared by grinding with SiC grinding papers of various grits, and a polished Crofer22 APU sample was also prepared. The prepared samples were then thermally cycled. The variations of their oxidation behavior with surface roughness and the number of thermal cycles were investigated. After 120 thermal cycles (a total 3000 h of exposure at 800 °C), the polished Crofer22 APU had a relatively flat, continuous Cr2O3 layer (thickness, ~ 1 µm), while the Crofer22 APU ground with 80 grit showed an undulating, continuous Cr2O3 layer (thickness, ~ 2 µm). For the samples that were thermally cycled 4 times (at 800 °C for 100 h total), the area specific resistance (ASR) increased as grit number increased for all measured temperatures (600 -850 °C). Generally, for the samples that were thermally cycled 20 times, the ASR decreased slowly as the grit number increased. For the samples thermally cycled 40 times, the ASR decreased in general at all the measuring temperatures as the number of grit increased, indicating that the polished Crofer22 APU is better than those with rougher surfaces for the application of Crofer22 APU to an interconnect of SOFC.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.