Highly conductive lithium aluminum germanium phosphate solid electrolyte prepared by sol-gel method and hot-pressing

摘要

A hot-pressing process is applied to improve sinterbility of NASICON (Na ion conductor)-type of Li1.5Al0.5Ge1.5(PO4)(3) (LAGP) solid electrolyte prepared by sol-gel method. During the hot-pressing process, amorphilization caused by Li loss and reduction of LAGP is observed due to a contact with a carbon mold. To compensate the Li loss, addition of 15% LiNO3 into LAGP powder before the hot-pressing is needed. By the hot-pressing, the porosity of the LAGP pellet is decreased from 12% to 4%. The grain boundary conductivity of hot-pressed LAGP pellet is 5 times higher than that of conventional atmospheric sintered LAGP pellet. Contrary, bulk conductivities are almost same, indicating that the hot-pressing affects only grain boundaries, not crystal structure. The highest conductivity is obtained in the hot-pressed LAGP pellet with 15% LiNO3 addition and bulk, grain boundary and total conductivities are 3.22 x 10(-4), 1.69 x 10(-3), 2.7 x 10(-3) S cm(-1), respectively. The activation energy is 0.31 eV, which is comparable to that prepared by conventional melt-quenching method.