Lithium-garnet solid electrolyte composite, tape articles, and methods thereof

1. A composite ceramic comprising:

a lithium garnet major phase; and

a grain growth inhibitor minor phase positioned between grains of the lithium garnet major phase,

wherein the grain growth inhibitor minor phase is MgO and comprises from 3 to 9 wt % based on the total weight of the composite ceramic.

2. The ceramic of claim 1 , wherein the ceramic has an average grain size of from 3 to 7 microns.

3. The ceramic of claim 1 , wherein the ceramic has a mechanical strength of from 100 to 180 MPa.

4. The ceramic of claim 1 , wherein the ceramic has an ion conductivity of from 1×10 −4 S/cm to 6×10 −4 S/cm.

5. The ceramic of claim 1 , wherein the density of the ceramic is at least 95 to 98% of a theoretical maximum density of the ceramic.

6. A ceramic electrolyte comprising at least the ceramic of claim 1 .

7. A method of making the composite ceramic of claim 1 comprising:

a first mixing of inorganic source materials to form a mixture, including a lithium source compound, and other inorganic source materials to make the desired garnet composition;

a first milling of the mixture to reduce the particle site of the precursors;

calcining the milled mixture to form a garnet oxide at from 800 to 1200° C.;

a second mixing of the milled and calcined garnet oxide and a second additive to provide a second mixture;

a second milling of the second mixture to reduce the particle site of constituents of the second mixture;

compacting the second milled second mixture into a compact; and

sintering the compact at from 600 to 1300° C.

wherein the second additive is MgO.

8. The method of claim 7 wherein the lithium source compound is present in a stoichiometric excess.

9. The method of claim 7 wherein the sintering is accomplished in air, in an inert atmosphere, or first in air then in an inert atmosphere.

10. The method of claim 7 wherein the sintering is accomplished in air at from 1000 to 1300° C.

11. The method of claim 7 wherein the sintering is accomplished in an inert atmosphere at from 800 to 1200° C.

12. The method of claim 7 wherein the particle size of the first milling is from 0.3 to 4 microns and the particle size of the second milling is from 0.15 to 2 microns.

13. An electrochemical device comprising: a negative electrode; a positive electrode; and an interposed solid electrolyte material, wherein the interposed solid electrolyte material comprises the composite ceramic of claim 1 having at least one grain growth inhibitor comprising magnesia in an amount of from 3 to 9 wt. % based on the total weight of the solid electrolyte.

14. A composite electrolyte comprising:

a lithium garnet ceramic, having a lithium garnet major phase and a grain growth inhibitor minor phase positioned between grains of the lithium garnet major phase, of the formula:

Li 7-x La 3 (Zr 2-x ,M x )O 12 -SA,

where

M is selected from the group Al, Ga, In, Si, Ge, Sn, Sb, Bi, Sc, Y, Ti, Hf, V, Nb, Ta, W, or a mixture thereof; and

“SA” comprises a second additive oxide selected from the group MgO, CaO, ZrO 2 , HfO 2 , or a mixture thereof, present in from 3 to 9 wt % based on the total amount of the ceramic; and x is greater than 0 and less than 1.

15. A method of making a tape of the composite electrolyte of claim 14 , comprising:

thoroughly mixing, wet or dry, a lithium garnet batch including oxide precursors to form a batch mixture powder;

calcining the batch mixture powder in a platinum container to form a calcined powder;

milling the calcined powder to form a milled powder;

tape casting the milled powder to form a green tape; and

sintering the green tape to form the tape of the composite electrolyte.

16. The method of claim 15 further comprising classifying the milled powder to a mono-modal distribution having a particle size of from 0.3 to 0.7 microns.

17. The composite electrolyte of claim 14 , wherein:

M is Ta;

SA comprises MgO; and

the lithium garnet major phase comprises between 91 to 97 wt % of the composite ceramic.