The Study On Structure And Ionic Conductance Of Na₃Zr₂Si₂PO₁₂ Ceramic

Sodium batteries are most suitable unit for energy storage stations because of abundant resource reserves and excellent performance.However,sodium batteries now have only a small amount of applications for their high operating temperature and the difficulty of preparing the ?? alumina which is the solid electrolyte of sodium batteries.The synthesis temperature and preparation difficulty of sodium super ionic conductor(NASICON)are lower than ?? alumina,which will be more advantageous in decreasing the temperature and promoting the application of sodium batteries.The main difficulty of NASICON applied in sodium batteries is that the crystalline structure of NASICON will transform when temperature raised,which would lead to batteries are damaged.The crystalline structure of NASICON has a relatively stable structure when synthesized at a temperature lower than 1100?.However,the synthesis temperature of NASICON is higher than 1200? with conventional sintering which is widely used in preparing NASICON,so,it's necessary to decrease the synthesis temperature of NASICON by improving the preparation.In this paper,four methods that conventional sintering,one-step solid sintering,hot-pressing sintering and glass-phase-assisted hot-pressing sintering were used.Dense and free of impurities NASICON ceramics were prepared by conventional sintering at 1250?,and the upper limit on conductivity of NASICON samples prepared by conventional sintering was analyzed by combined with literatures.The basic sintering process and mechanism of one-step solid sintering in preparing NASICON were studied,the NASICON samples with high purity and density were prepared at 1000~1250?,and higher purity and density NASICON samples obtained by solid phase one-step sintering after process optimization.NASICON samples with a density close to 98% and a very low impurity content were prepared at 1160? and 1000? by hot-pressing sintering and glass-phase-assisted hot-pressing sintering,respectively.The changes on the conductivity of NASICON samples with temperature were studied when the purity and density were basically stabilized.By comparing the XRD patterns of NASICON prepared at 950~1250? for 4 hours and 1100? for various holding times,it is found that the crystalline structure of NASICON at room temperature changes with the increase of synthesis temperature.The samples obtained by conventional sintering and hot-pressing sintering were compared,and the changing rule between the conductivity of NASICON and purity,density and crystalline structure of samples with the increase of sintering temperature was analyzed.The main results obtained as follows:(1)Through comparing the densification temperature of one-step solid sintering and glass-phase-assisted hot-pressing sintering,it is determined that the densification temperature of the glass phase is around 850?.(2)The crystalline structure of NASICON at room temperature changes from trigonal phase to monoclinic phase when the sintering temperature is higher than 1000?,and the crystalline structure of monoclinic NASICON changed with the increase of sintering temperature between 1000? and 1200?.(3)Because of the changing of the crystalline structure in NASICON,the conductivity of NASICON at room temperature climb up and then decline with the rising of sintering temperature between 1000? and 1200?,and the maximum value obtained at 1100?.