Ion trapping agent, separator for lithium ion battery, and lithium ion secondary battery
An ion trapping agent which is a layered phosphate compound that includes a proton as an ion exchange group, that supports lithium ions in excess of a theoretical exchange capacity of the layered phosphate compound, and that has no water of crystallization; and a separator for a lithium ion battery or a lithium ion secondary battery containing the ion trapping agent.
1. An ion trapping agent which is a layered phosphate compound that comprises a proton as an ion exchange group, that supports lithium ions in excess of a theoretical exchange capacity of the layered phosphate compound, and that has no water of crystallization,
wherein the layered phosphate compound is α-zirconium phosphate or α-titanium phosphate, and
wherein the α-zirconium phosphate is a compound represented by the following formula (1):
ZrO 2 .n P 2 O 5 .x Li 2 O (1)
wherein, in Formula (1), n is a positive number of from 0.5 to 1.5, x is a positive number of from 0.8 to 2.2, and n is equal to or smaller than x; and
wherein the α-titanium phosphate is a compound represented by the following Formula (2):
TiO 2 .x P 2 O 5 .n Li 2 O (2)
wherein, in Formula (2), n is a positive number of from 0.5 to 1.5, x is a positive number of from 0.8 to 2.2, and n is equal to or smaller than x.
2. The ion trapping agent according to claim 1 , wherein a mass ratio (Li/PO 4 ) of lithium atoms with respect to phosphate groups PO 4 contained in the layered phosphate compound is 0.07 or more.
3. The ion trapping agent according to claim 1 , wherein a specific surface area of the layered phosphate compound is 15 m 2 /g or more.
4. The ion trapping agent according to claim 1 , wherein a moisture content of the layered phosphate compound is 1% by mass or less.
5. A separator for a lithium ion battery, the separator comprising an ion trapping layer that contains the ion trapping agent according to claim 1 .
6. A lithium ion secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, the lithium ion secondary battery containing the ion trapping agent according to claim 1 .
7. The ion trapping agent according to claim 1 , wherein a mass ratio (Li/PO 4 ) of lithium atoms with respect to phosphate groups PO 4 contained in the layered phosphate compound is from 0.10 to 0.33.
8. The ion trapping agent according to claim 1 , wherein an amount of lithium ions substituted with respect to the compound of Formula (1) is from 7.5 to 15 meq/g.
9. The ion trapping agent according to claim 1 , wherein an amount of lithium ions substituted with respect to the compound of Formula (1) is from 8 to 12 meq/g.
10. The ion trapping agent according to claim 1 , wherein an amount of lithium ions substituted with respect to the compound of Formula (2) is from 7.5 to 15 meq/g.
11. The ion trapping agent according to claim 1 , wherein an amount of lithium ions substituted with respect to the compound of Formula (2) is from 8 to 12 meq/g.