LITHIUM ION-CONDUCTING OXIDE
A lithium ion-conducting oxide including at least lithium, tantalum, M1, phosphorus, and oxygen as constituent elements. M1 is at least one metal element selected from elements of the Group 4, the Group 5, the Group 6, the Group 13, and the Group 14 (provided that tantalum is excluded), a ratio of number of atoms of each constituent element of lithium, tantalum, M1, phosphorus, and oxygen is 1:2−x:x:1:8, wherein x is more than 0 and less than 1, and the lithium ion-conducting oxide contains a monoclinic crystal. Also disclosed is a lithium-ion secondary battery including the lithium ion-conducting oxide.
1 . A lithium ion-conducting oxide, comprising at least lithium, tantalum, M1, phosphorus, and oxygen as constituent elements,
wherein M1 is at least one metal element selected from the group consisting of elements of the Group 4, the Group 5, the Group 6, the Group 13, and the Group 14 and M1 is other than tantalum,
a ratio of number of atoms of each constituent element of lithium, tantalum, M1, phosphorus, and oxygen is 1:2−x:x: 1 : 8 ,
wherein x is more than 0 and less than 1, and
the lithium ion-conducting oxide comprising a monoclinic crystal.
2 . The lithium ion-conducting oxide according to claim 1 , wherein M1 is any one or more metal elements selected from the group consisting of Nb, Zr, Ga, Sn, Hf, W, and Mo.
3 . The lithium ion-conducting oxide according to claim 1 , wherein a total content rate of the monoclinic crystal is 70% or more.
4 . The lithium ion-conducting oxide according to claim 1 , wherein a lithium ion conductivity δ gb (25° C.) at a grain boundary measured at 25° C. is 1.90×10 −4 S/cm or more.
5 . A lithium-ion secondary battery comprising the lithium ion-conducting oxide according to claim 1 as a solid electrolyte.