Rock-Salt Phase

Meaning

Structural arrangement of atoms mimics the face-centered cubic lattice found in sodium chloride. Formation of a rock-salt phase in lithium ion battery cathodes often indicates the irreversible migration of transition metals into the lithium layers. This structural transformation leads to a significant loss of capacity because the metal ions block the pathways for lithium movement.

Cation Ordering

Degree of organization between different metal ions determines the stability of the lattice. In a rock-salt phase, the random distribution of nickel or manganese atoms replaces the layered structure of the original cathode. This transition usually occurs during high voltage cycling or exposure to extreme heat.

The resulting structure is electrochemically inactive and highly resistive.

Transition Metal

Concentration of nickel in the original material influences the speed of the phase change. High nickel contents are more prone to forming a rock-salt phase due to the similar size of nickel and lithium ions. This similarity allows the ions to swap positions easily under stress.

Cycle Life

Accumulated structural damage limits the number of times a battery can be recharged. Monitoring the growth of the rock-salt phase through x-ray diffraction provides a measure of the health of the electrode. Prevention strategies include doping the lattice with larger ions to lock the structure in place.

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High voltage thermal cycling accelerates cathode surface reconstruction and metal dissolution, doubling impedance and driving capacity fade.

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Surface Phase Transformations in High Nickel Lithium Cathodes

Surface phase transitions from layered to rock-salt structures drive impedance growth and oxygen release, requiring targeted surface modifications to preserve cycle life.

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