Preparation And Modification Of Lithium Aluminum Titanium Phosphate-based Solid-state Electrolyte And Thin Films

NASICON-type solid electrolyte Li_1.3Al_0.3Ti_1.7（PO₄）₃（LATP）has attracted much attention of researchers because of its considerable ionic conductivity(～10^-3S/cm)at room temperature and excellent chemical stability.The application of LATP in all solid-state lithium battery and electrochromic device faces some problems.Firstly,LATP sintering performance is poor and sintering temperature is too high.In the application of lithium-ion battery,high-temperature sintering will cause element diffusion or thermal activation reaction between electrode and solid electrolyte interface.Secondly,the ionic conductivity of LATP films deposited by magnetron sputtering is low(～10^-7S/cm),which cannot meet its application in electrochromic devices.In this study,LATP solid electrolyte powder was synthesized by using（NH₄PO₃）_n（n>1500）as the phosphorus source.In order to improve the sintering characteristics of LATP,Li₂CO₃·Bi₂O₃was introduced as a sintering agent,and the influence of Li₂CO₃·Bi₂O₃on the structure and properties of LATP ceramic sheet was systematically investigated.Secondly,Nitrogen and sulfur ions were introduced into the LATP films by changing the sputtering atmosphere and using powder targets.The effects of nitrogen and sulfur ions on the ionic conductivity and visible light transmission rate of LATP films were investigated.In addition,the effects of annealing temperature on LATP films was also systematically investigated.The main results of this study are as follows:1.LATP solid electrolyte powders were successfully synthesized with（NH₄PO₃）_n（n>1500）as the phosphorus source.The replacement of the phosphorus source solved the problem of the raw material powder sticking to the corundum crucible after calcination.The comparison experiments of sintering temperature showed that the LATP ceramic pellets sintered at 1050℃for 6 h had the highest total ionic conductivity and relative density,reaching 0.622 m S/cm and 90.27%,respectively.The sintering aid Li₂CO₃·Bi₂O₃（LB）can obviously improve the sinterability of LATP.After adding 2 wt%Li₂CO₃·Bi₂O₃（LB）,the relative density and total ionic conductivity of LATP ceramic pellets sintered at 900℃increased from 77.16%and 0.15 m S/cm to 95.28%and 0.673 m S/cm,respectively.2.The LATP-x N（x=0,15,30,45）films were prepared by sputtering LATP ceramic targets under different argon/nitrogen gas flow ratios（70:0,70:15,70:30,70:45）by RF magnetron sputtering.The prepared films are all amorphous.The ionic conductivity of LATP films increased with the increase of nitrogen content in the sputtering atmosphere,and the highest ionic conductivity of 3.69μS/cm was achieved for the LATP-45N film.The average visible transmittance of LATP-x N（x=0,15,30,45）films was maintained at about 83%.The LATP-45N films annealed at different temperatures remained amorphous.Annealing temperature has little effect on the ionic conductivity of LATP-45N films,and the ionic conductivity of LATP-45N films annealed at 400°C only reached 4.88μS/cm.The annealing treatment improved the average visible transmittance of LATP-45N film.3.The LATP-x S（x=0,2,4,6）thin films were prepared by sputtering LATP-x wt%Li₂S（x=0,2,4,6）powder targets under 70 sccm argon atmosphere by RF magnetron sputtering.The prepared films are all amorphous.The ionic conductivity of LATP films increased with the increase of Li₂S content in the powder target,and the ionic conductivity of LATP-6S films was the largest is 3.23μS/cm.With the increase of Li₂S content in the powder target,the average visible transmittance of LATP films showed a decreasing trend,and the average visible transmittance of LATP-6S films was 81.23%.The LATP-6S films annealed at different temperatures remained amorphous.The improvement of the ionic conductivity of LATP-6S films by annealing treatment was not obvious,but annealing treatment increases the average visible light transmittance of LATP-6s films,and the average visible light transmittance of 400℃samples is the highest,which is 83.63%.