Our ultrasonic system was validated using 250 mAh battery pouch cells that were machinemade (Li-Fun) with lithium manganese iron phosphate (LMFP) cathodes and copper current collectors as the bare anode, and shipped to us dry. All fabrication steps were carried out in an inert atmosphere glove box (Argon, O2 < 0.5 ppm, H2O < 0.1 ppm). Electrolyte was prepared by making a 1:1 volume/volume (v/v) mixture of diethyl carbonate (DEC) (Acros Organics) and fluoroethylene carbonate (FEC) (TCI). Lithium difluoro(oxalato)borate (LiDFOB) (Sigma Aldrich) powder was weighed and then dissolved in the 1:1 (v/v) DEC:FEC solvent at a 2 M concentration by overnight stirring. The dry pouch cells were cut open in the glovebox and further dried in the glovebox antechamber under vacuum and at 120 ºC to remove residual moisture. 1.00 mL of the 2 M LiDFOB in 1:1 (v/v) DEC:FEC was added to the cell. The pouch was then vacuum sealed at -90 kPa and immediately removed from the glovebox for ultrasonic testing.