Trace Element Impurity Limits in Recycled Battery Precursor Hydroxides
Recycled precursor hydroxides demand strict trace impurity limits below 100 ppm total metals to prevent cathode microcracking and rapid cell capacity fade.
Lattice Distortion
Meaning
Atomic displacement within a crystal structure alters the spacing between planes and affects the mobility of charge carriers. When foreign ions are substituted into a cathode framework, lattice distortion occurs due to the difference in ionic radii. This phenomenon can either improve the structural stability of the material or hinder the diffusion of lithium ions.
Structural Strain
Misalignment of the atomic layers creates internal stress that can lead to the formation of microcracks during repeated charging and discharging. If lattice distortion becomes excessive, the crystal structure may eventually collapse into a different phase with lower capacity. Researchers use x-ray diffraction to measure the degree of this strain in new battery chemistries.
Charge Transport
Changes in the distance between atoms directly influence the energy barriers that an ion must overcome to move through the solid. Controlled lattice distortion can be used to widen the pathways for lithium ions, which increases the power density of the battery. However, if the distortion is too great, the pathways may become blocked by displaced atoms.
Phase Stability
Doping a material with elements like aluminum or magnesium is a common strategy to mitigate the volume changes that occur during cycling. Because lattice distortion anchors the structure in place, the material is less likely to undergo a parasitic reaction with the electrolyte. This improves the cycle life of the battery by preventing the loss of active lithium sites over time.
Final performance depends on the balance between atomic strain and chemical bonding.