Meaning
Internal transformation of the atomic arrangement within an electrode material during ion insertion or extraction. High nickel cathodes undergo a microstructural phase transition when lithium levels drop below a certain point. This change often results in a shift from a hexagonal to a monoclinic lattice structure.
Lattice Transformation
Reversible shifts in atomic positions allow the battery to function through many cycles. However, the microstructural phase transition at high voltage can become irreversible if the cell stays in a charged state for too long. Capacity fading occurs as a direct result of these structural changes.
Loss of available lithium sites follows the permanent collapse of the host structure.
Cycle Consequence
Mechanical strain develops as the material expands and contracts at different rates during the shift. This strain causes cracking within the secondary particles of the electrode. Electrolyte then penetrates these cracks and reacts with the newly exposed surfaces.
Thick layers of decomposition products form and increase the internal resistance of the cell.
Structural Stability
Doping the material with elements like aluminum or magnesium can suppress the microstructural phase transition. These additives act as pillars that hold the lattice together even when lithium ions are removed. Stable materials exhibit much better capacity retention over thousands of cycles.
Thermal runaway risks are also lower when the crystal structure remains intact under stress. Designers select these stabilized chemistries for long range electric vehicles where reliability is paramount.
