Electrolyte-resistant epoxy for bonding batteries based on sandwich structures

Adhesives that are stable in Li-ion battery electrolytes are required to realize the potential of new battery designs that integrate structural elements with energy storage. Here, several polymers, commercial adhesives, and sealants were investigated to bond and seal a Li-ion battery sandwich panel. Gravimetric electrolyte uptake measurements were compared with Hansen solubility parameters to predict long-term durability of the materials exposed to battery electrolyte. The durability of adhesively bonded joints with an epoxy adhesive, which was selected as the lowest electrolyte uptake material, was examined using single lap shear strength tests and three-point bending tests in a fabricated sandwich panel. The strength of the epoxy decreased after exposure to battery electrolyte due to solvent uptake in the bond. The addition of lithium hexafluorophosphate to the ethylene carbonate/dimethyl carbonate mixture severely decreased the strength with respect to the pure solvents. In device testing, the sandwich panel did not show any visible damage or leakage when loaded to above 1000 N during three-point bending tests. Using sol extraction measurements and differential scanning calorimetry analyses, the optimized curing temperature for the epoxy adhesive ranged from 80 to 100 °C. At these temperatures, the cured adhesive had a highly crosslinked structure with low sol extraction.