Solid electrolyte separator bonding agent

An electrochemical stack, comprising:

• a lithium metal negative electrode, a positive electrode, an electrolyte separator film comprising a lithium-stuffed garnet, and a bonding layer;
• wherein the bonding layer comprises a lithium salt and two or more solvents,
• wherein the lithium salt in the bonding layer is selected from LiPF6, LiBOB, LiBETI, LiTFSi, LiBF4, LiCO4, LiAsF6, LiFSI, LiI, and combinations thereof;
• wherein the lithium salt in the bonding layer is at a concentration of 0.5 M to 2 M;
• wherein the bonding layer has a vapor pressure less than about 80 Torr at 20° C.;
• wherein the bonding layer has a boiling point above 80° C. at 1 atmosphere;
• wherein a water content in the two or more solvents is less than 200 ppm;
• wherein the bonding layer has a lithium ion conductivity of greater than 10−5 S/cm at room temperature;
• wherein the bonding layer is characterized by a thickness of about 1 nm to about 5 μm;
• wherein the bonding layer contacts, and is positioned between, the electrolyte separator film and the positive electrode;
• wherein the electrolyte separator film is characterized by a thickness of about 0.1 μm to about 50 μm;
• wherein the electrolyte separator has a density greater than 95% of its theoretical density as determined by scanning electron microscopy.