Meaning
Phase transition in layered transition metal oxide cathodes to a cubic rock salt structure represents a serious mode of performance degradation. This process, referred to as rock salt phase transformation, occurs primarily at the surface of cathode particles during high voltage charging. It involves the migration of transition metal ions into the lithium layers, leaving a disordered, electrochemically inactive phase that blocks ion transport.
Battery design teams analyze this surface layer to optimize protective coatings and improve the long-term stability of the cell.
Atomic Restructuring
Oxygen loss from the cathode lattice during high voltage cycles triggers the transition to the inactive phase. This surface reconstruction creates a barrier that raises the charge transfer resistance and reduces the output power of the cell. Over multiple cycles, the inactive layer grows thicker and leads to accelerated capacity fade.
Supplier Compliance
Quality agreements for active cathode materials often specify surface coating and doping requirements to suppress this transformation. Sourcing departments of cell manufacturers require raw material suppliers to provide transition electron microscopy data of the particle surfaces after cycling. These audits ensure that the supplier has implemented surface stabilization techniques.
Testing Procedure
Evaluation of the transformed surface layer relies on high resolution microscopy and surface-sensitive spectroscopy. Diagnostic laboratories measure the thickness of the inactive layer to determine the efficacy of the surface protection. These results help manufacturers decide the upper voltage limits of their cell designs.
