Garnet-mgo composite thin membrane and method of making

A sintered composite ceramic, comprising:

• a lithium-garnet major phase;
• and
• a grain growth inhibitor minor phase,
• wherein:
• the lithium-garnet major phase comprises:
• Li7-cLa3(Zr2-c, Nc)O12, with N=Ta, Mg, or combinations thereof, and 0<c<1, and
• the grain growth inhibitor minor phase comprises MgO in a range of 0.1 wt. % to 10 wt. % based on the total weight of the sintered composite ceramic.

A sintered composite ceramic, comprising:

• a lithium-garnet major phase;
• and
• a grain growth inhibitor minor phase, wherein the sintered composite ceramic comprises at least one of:
• a Li-ion conductivity of at least 10−4 S/cm;
• and
• a relative density of at least 90% of a theoretical maximum density of the membrane.

A method, comprising:

• a first mixing of inorganic source materials to form a mixture, including a lithium source compound and at least one transition metal compound;
• a first calcining conducted at a first temperature range of 800° C. to 1200° C.;
• a second calcining conducted at a second temperature range of 1000° C. to 1300° C.;
• a milling step of the mixture to reduce particle size;
• a sieving step to obtain a powder having at least one dimension in a range of 0.01 μm to 1 μm.

A method of forming a composite ceramic, comprising:

• forming a garnet powder including a lithium source compound and at least one transition metal compound;
• passivating the garnet powder by at least one of air carbonation and acid treatment;
• heating a metal oxide at a first temperature range of 500° C. to 1500° C.;
• forming a slip composition comprising the passivated garnet powder and metal oxide;
• tape casting the slip composition to form a green tape;
• sintering the green tape at a second temperature range of 950° C. to 1500° C. to form the composite ceramic.