  The recycling of lithium ion batteries has been mentioned as one of the
near-future waste management necessities. In order for recycling to be
economically viable, straightforward and cost effective techniques need to be
developed to separate the individual materials in a composite electrode.
Ultrasonic separation might be such a technique, provided that lithium ion
battery microparticles respond predictably to a sound field. Lithium ion
battery cathodes contain hydrophobic carbon. Owing to the incompressibility of
a solid, the thin gaseous layer surrounding these hydrophobic particles must
oscillate asymmetrically, when subjected to ultrasound. Consequently, the
harmonic content of the ultrasound signal radiated from hydrophobic
microparticles must be higher than that from hydrophilic microparticles with
the same size. The question of whether the harmonic signal response generated
by physical hydrophobic microparticles present in lithium ion battery cathodes
is higher than the harmonic response of other component materials in the
cathode is the focus of this paper. The scattering response of cathode
materials subjected to 1-MHz ultrasound was measured and compared. The cathode
materials C65, PVDF, and NMC respond differently to 1-MHz ultrasound. The
superharmonic response of C65 has been attributed to asymmetric oscillations
owing to its hydrophobicity. In addition, C65 hydrophobic microparticles might
be suitable candidates for harmonic imaging.
