Lithium-ion conductive garnet and method of making membranes thereof
A gallium doped garnet composition of the formula: Li 7−3y La 3 Zr 2 Ga y O 12 where y is from 0.4 to 2.0, and as defined herein. Also disclosed is a method for making a dense Li-ion conductive cubic garnet membrane, comprising one of two alternative lower temperature routes, as defined herein.
1. A method of making a Li-ion conductive cubic garnet, comprising:
forming a nitrate source aqueous solution comprising a first nitrate source and a nitrate dopant source;
contacting the nitrate source aqueous solution and a carbohydrate source and heating in a first heating step to form a nano-particle ash;
a second heating step of the nano-particle ash to produce a garnet nanoprecursor;
pelletizing the garnet nanoprecursor to form a Li-ion conductive cubic garnet pellet; and
a third heating step of the garnet pellet to form a dense Li-ion conductive cubic garnet membrane.
2. The method of claim 1 , wherein:
the first nitrate source comprises a mixture of LiNO 3 , La(NO 3 ) 3 , and ZrN 2 O 7 ;
the nitrate dopant source is at least one element from Groups IIA to VIIA, and IIIB to IVB;
the carbohydrate source has from 5 to 10 carbon atoms; and
the nano-particle ash has a size in a range of 10 nm to 50 nm.
3. The method of claim 1 , wherein the dense Li-ion conductive cubic garnet membrane has a Li-ion conductivity in a range of 0.2×10 −3 S/cm to 2.0×10 −3 S/cm.
4. The method of claim 1 , wherein the third heating step is conducted in a closed platinum vessel, and wherein the garnet pellet is a pellet surrounded in a garnet burying powder comprising at least one micrometer sized Li-oxide garnet.
5. The method of claim 1 , wherein the nitrate dopant source is at least one of a metal nitrate, or a mixture of at least two different metal nitrates.
6. The method of claim 1 , further comprising: adding from 1 wt. % to 20 wt. % excess of a nitrate source containing Li to compensate for Li losses during the third heating step.
7. The method of claim 1 , wherein a mole ratio of the nitrate source aqueous solution to the carbohydrate source in the contacting step is in a range of 1:1 to 1:4.
8. The method of claim 7 , wherein the first heating step is conducted at a temperature in a range of 200° C. to 550° C.
9. The method of claim 1 , wherein the second heating step is conducted at a temperature in a range of 650° C. to 700° C. to form nano-sized garnet nanoprecursor particles having a size in a range of 10 nm to 100 nm.
10. The method of claim 1 , wherein the third heating step is conducted at a temperature in a range of 950° C. to 1200° C. for a time in a range of 0.5 hr to 30 hrs.
11. The method of claim 10 , wherein the third heating step is held at 800° C. for a time in a range of 2 hrs to 6 hrs to form and stabilize a pure cubic garnet phase.
12. A method of making a Li-ion conductive cubic garnet, comprising:
forming a nitrate source aqueous solution comprising of a first nitrate source and a nitrate dopant source;
contacting the nitrate source aqueous solution and a carbohydrate source and heating in a first heating step to form a nano-particle ash;
a second heating step of the nano-particle ash to produce a Li-ion conductive pure cubic garnet powder;
milling the cubic garnet powder to produce a sub-micron powder;
pelletizing the sub-micron powder to form a garnet pellet; and
a third heating step of the garnet pellet to form a dense Li-ion conductive cubic garnet membrane.
13. The method of claim 12 wherein:
the first nitrate source comprises a mixture of LiNO 3 , La(NO 3 ) 3 , and ZrN 2 O 7 ;
the nitrate dopant source is at least one element from Groups IIA to VIIA, and IIIB to IVB;
the carbohydrate source has from 5 to 10 carbon atoms;
the cubic garnet powder comprises irregularly-shaped, porous particles before milling;
the sub-micron powder comprises sub-micron-sized particles having a size in a range of 100 nm to 1000 nm after milling.
14. The method of claim 12 , further comprising: adding from 1 wt. % to 20 wt. % excess of a nitrate source containing Li to compensate for Li losses during the third heating step.
15. The method of claim 12 , wherein the dense Li-ion conductive cubic garnet membrane has a Li-ion conductivity in a range of 0.2×10 −3 S/cm to 2.0×10 −3 S/cm.
16. The method of claim 12 , wherein a mole ratio of the nitrate source aqueous solution to the carbohydrate source in the contacting step is in a range of 1:1 to 1:4.
17. The method of claim 16 , wherein the first heating step is conducted at a temperature in a range of 200° C. to 550° C.
18. The method of claim 12 , wherein the second heating step is conducted at a temperature in a range of 775° C. to 1000° C. to form Li-ion conductive pure cubic garnet powder having irregularly-shaped micron-sized particles.
19. The method of claim 12 , wherein the third heating step is conducted at a temperature in a range of 950° C. to 1200° C.