| Sodium-sulfur batteries are a kind of energy storage device with broad potential applications thank to their high thermal stability,high reliability,long service life and variable shapes.As a core component of batteries,?"-Al2O3 serves both as the electrolyte material and the separator in the whole battery system.At present,the conductivity of ?"-Al2O3 prepared by traditional methods is poor because of the low content and density of ?"-Al2O3 phase and the existence of a large number of grain boundaries that make the ion migration paths tortuous.In this thesis,?-AlOOH precursor with controlled morphology was prepared by hydrothermal reaction method and used to fabricate?"-Al2O3 electrolyte material for aluminum source.This was used as a way to explore the preparation process of highly oriented.highly dense and highly conductive ?"-Al2O3.The main research work includes the following three aspects:First,the one-dimensional rod-like ?-AlOOH precursor was prepared by the hydrothermal reaction method.After pre-sintered at 1100?,the precursor,as the aluminum source and Na2CO3 were wet-mixed to ensure the Na:Al=1:5.33.to the mixture MgO was added as a stabilizer.The resulting mixture was first calcined in a high-temperature sintering furnace at 1300? and then sintered in a spark plasma sintering(SPS)furnace to study how the sintering temperature(1200?1500 ?),heating rate,pressure(20?50 MPa),and holding time(0?20 min)influence the electrolyte density,phase content,and orientation degree.The results show that the ?"-A12O3 sample sintered at 40 MPa with a holding temperature of 1300? and holding time of 10 minutes provided the best performance,with a phase content of 87.2%,a density of 98.4%,and an orientation degree of0.74.In addition,to further study the effect of orientation structure on the performance of electrolyte material,the morphology of ?-AlOOH precursor was changed by changing the pH value of the hydrothermal reaction.As a result,one-dimensional rod-like and two-dimensional flake-like ?-AlOOH were obtained,respectively.The results show that SPS sintering can result in ?"-Al2O3 electrolyte material with high density and high degree of orientation at lower temperatures.The degree of orientation of the sample resulted from rod-like y-AlOOH(0.74)is higher than that of the flake-like counterpart(0.46).At 350??the conductivity of sample from rod-like ?"-Al2O3 that is perpendicular to the uniaxial pressure direction is 1.83×10-1 S·cm-1,and the bending strengths of both rod-like and flake-like ?"-Al2O3 samples are 250 MPa.Finally,freeze-drying was combined with SPS sintering approach in order to obtain ?"-Al2O3 electrolyte materials with better electrical properties.The results show that this combination can give rise to higher phase content of ?"-Al2O3 but lower density and conductivity as well as the degree of orientation.The content of ?"-Al2O3 phase increased by about 6%,however when the sample was subject to a secondary treatment at 1600?.Further,the conductivity of the sample after secondary treatment at 1600? is greatly increased to 2.34×10-1 S·cm-1 when the SPS sintering temperature was lowered to 1100?. |
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