Li-ion conductivity of NASICON-type Li1+2xZr2−xCax(PO4)3 solid electrolyte prepared by spark plasma sintering

Abstract

In order to improve Li-ion conductivity of Li 1+2x Ca x Zr 2−x (PO 4 ) 3 (x = 0.05–0.3) solid electrolytes, the Spark Plasma Sintering technique is applied. High conductive rhombohedral phase is obtained in x = 0.1–0.3, while at x = 0.05, both triclinic and rhombohedral phases are formed. The samples sintered by the Spark Plasma Sintering technique show higher density than conventionally sintered samples. Elemental distributions of Ca and Zr are overlapped each other, indicating that Ca is incorporated into the LiZr 2 (PO 4 ) 3 lattice, while the Ca-rich grain boundary phase is observed in conventionally sintered Li 1+2x Ca x Zr 2−x (PO 4 ) 3 . This would be attributed to suppression of Ca diffusion into the grain boundary region due to low temperature and short time of the Spark Plasma Sintering process. The highest bulk conductivity of 5.8 × 10 −4 S cm −1 is achieve at x = 0.1. With further Ca substitution, the bulk conductivity is decreased. This is consistent with theoretical calculation which reveals Li-ion is trapped near Ca ion in higher concentration of Ca. The highest total conductivity is 1.0 × 10 −4 S cm −1 at x = 0.15 which is higher than that of conventionally sintered samples. The spark plasma sintering technique is useful to obtain well sintered Li 1+2x Ca x Zr 2−x (PO 4 ) 3 pellets with high Li-ion conductivity. • Li 1+2x Ca x Zr 2−x (PO 4 ) 3 (x = 0.05~0.3) was sintered by spark plasma sintering (SPS) • High conductive rhombohedral phase was obtained in x = 0.1~0.3 • The SPS-sintered samples showed higher conductivity than conventional sintered ones • Highest total conductivity of 1.0 × 10 −4 S cm −1 was obtained at x = 0.15 • SPS suppressed formation of Ca-rich grain boundary phase with low conductivity