Meaning
Crystallographic transformations that occur within layered oxide materials as lithium ions are removed. These high-nickel cathode phase transitions are characterized by the movement between hexagonal and monoclinic structures during charging. Controlling these shifts is necessary to prevent structural collapse in energy-dense cells.
Mechanical Stress
Volume changes associated with the transition between the H2 and H3 phases induce micro-cracking in the primary particles. These high-nickel cathode phase transitions result in the exposure of fresh surfaces to the electrolyte, which leads to secondary reactions. Coating the particles with protective layers helps mitigate the impact of these physical shifts.
Cracks often form at the grain boundaries when the material undergoes rapid contraction at the top of the charge cycle. This degradation path allows the electrolyte to penetrate the core of the particles.
Thermal Stability
Heat release increases when the material reaches high states of delithiation. At the conclusion of the high-nickel cathode phase transitions, the lattice becomes unstable and may release oxygen. This gas evolution creates pressure within the cell housing and requires durable venting designs.
Life Cycle
Repeatability of the structural change determines the long-term capacity retention of the battery. Irreversible high-nickel cathode phase transitions cause the material to lose its ability to host lithium ions efficiently. Optimising the dopant levels in the crystal structure can stabilise the phases and extend the operational life.
