| Eletrolyte has always been an important part of lithium-ion battery. In order to solve the safety problem during the application of conventional lithium-ion battery, people started to pay a lot of attention to inorganic solid electrolyte. Glass-ceramic solid electrolyte LATP(Li1+xAlxTi2-x(PO4)3) which possesses the NASICON structure has a great prospect in application because of its high lithium-ion conductivity and good chemical stability. This paper selected LATP as objects for research, discussed the impact of different kinds of preparation methods on LATP’s composition, structure and ion conductivity. On the basis of the result, the possibility of the LATP’s application in lithium-air battery which was prepared by optimized preparation methods was discussed.LATP solid electrolyte was prepared by using sintering of powder method. The samples’ composition, structure and ion conductivity are characterized by XRD, SEM and AC impedance measurements. With the sintering temperature ranges from 600℃ to 950℃, LATP has the highest ion conductivity which can reach 4×10-5S/cm. The reason why the conductivity of samples prepared by sintering of powder method turns out low is the binding phase can not bind all the particles in samples. The gaps between particles affect the migration of the Li-ion which caused the impedance of grain interface rises and sample’s conductivity drops.We prepared LATP by doping MgO, CaO and reducing the content of TiO2. The generating temperature of bindering phase drops after doping Ca2+ and Mg2+. Samples’ viscous flow during sintering is enhanced. But when the sintering temperature rises, masses of AlPO4 crystallizes which reduces the binding phase. When masses of solid particles crystallize, the samples can not fill the gap and hole caused by the change of volume. Therefore the samples’ shape changes which caused bubbles in the electrolyte. The masses of gaps in samples impede the migration of Li+ and the highest conductivity of electrolyte can only reach 6.3×10-7S/cm which is relatively low.Two-times sintering method was used to prepare LATP which was doped with MgO and CaO. The results show that two-times sintering method can eliminate gaps caused by crystallization during sintering. Density and ion conductivity are improved. The conductivity of samples prepared at 800℃ rises from 6.3×10-7S/cm to 2.05×10-6S/cm compared to the ones prepared by one-time sintering method. Because masses of AlPO4 crystallizes during sintering which reduces the binding phase, lots of gaps are still between particles in samples. The electrolyte’s conductivity remains low.We prepared LATP with different content of Al2O3 by using two-times sintering method. The results show that Al, Ti have competing relationships for PO43-. When the content of Al is high(Al:Ti>0.39), lots of AlPO4 will crystallize and reduce the binding phase which caused gaps in samples after the samples are sintered. Therefore the conductivity of samples is low(2.23×10-7S/cm). As for the LATP which does not contain Al2O3, the density will rise after sintering. But the conductivity of samples is still low(1.27×10-5S/cm) which indicates that the doping of Al3+ improves the ion conducting properties of grain interface and binding phase.We prepared LAGTP by doping GeO2 and using two-times sintering method. Compared to Ti, Ge is more effective in improving viscous flow properties of the binding phase which can result in large area of glass-ceramic phase in samples. Among all samples, LAGP has the highest conductivity(4.21×10-4S/cm) at room temperature. When sintering temperature rises to 900℃ and 950℃, the size of the grain rises and the volume of LAGP electrolyte changes. Because lots of AlPO4 starts to crystallize during high temperature sintering which reduces the binding phase, caused gaps in the LAGP electrolyte and affects LAGP’s ion-conducting properties. When the sintering time of two-times mothod is above 6h, prolonging the sintering time has little effect on grain size and binding phase. Therefore the conductivity does not chage much.Finally we applied the LAGP to lithium-air battery to achieve double liquid electrolyte system. After reviewing battery’s cycling performace, we concluded that the proposed Li-air battery has sustained repeated cycling for 35 cycles in 700 h. The cycling performance of the proposed Li-air battery improves significantly compared to the Li-air battery using single liquid electrolyte. The LAGP displays reliable mechanical stablity and sound chemical durability. The result shows the broad prospect of the applications of the LAGP solid electrolyte. |
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