In order to improve the ionic conductivity of NASICON-type lithium ion conductor, Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP), lithium ion conductive composites have been prepared to disperse the perovskite-type lithium ion conductor, Li 0.348 La 0.55 TiO 3 (LLTO), in the LATP matrix. X-ray powder diffraction revealed that the added LLTO has reacted with LATP to form some LaPO 4 derivatives after the sintering at 1000°C. The measured conductivity of the composite increases with the amount of added LLTO up to 4 wt% showing the highest value of 7.6 × 10 −4 S cm, which is approximately three times larger than that of pristine LATP. Further amount of LLTO addition gives gradual decrease in conductivity due to the deterioration of sintered density. It is also confirmed that the transport number of lithium ion is almost unity for the LATP-LLTO composite from the DC conduction experiments using blocking electrode.

We have previously reported that a three-fold increase in lithium-ion conduction can be achieved on LATP (Li1.3Al0.3Ti1.7(PO4)3) by dispersing LaPO4 particles through the co-sintering of LATP with 4wt% of LLTO (Li0.348La0.55TiO3). However, the LaPO4 formation during sintering has been detected only by means of XRD and back-scattered SEM, and precise morphology of LaPO4 particles as well as LATP / LaPO4 interface have still been uncertain. In the present study, we carried out TEM experiments on the LaPO4-dispersed LATP composite to investigate the detailed microstructure and compositions of the dispersed LaPO4 particles and surrounding LATP matrix. HR-TEM coupled with EDS reveals that LaPO4 particle attains an intimate contact with the LATP matrix, which would allow the formation of space charge layer at the interface to enhance the conductivity.