Understanding the Origin of Voltage Hysteresis in Disordered Rocksalt Cathodes

Lithium-rich cathodes are regarded as promising energy storage materials due to their high energy densities. However, voltage hysteresis presents challenges to maximizing their energy efficiency and practical implementation. Voltage hysteresis has generally been associated with transition metal migration and oxygen dimer formation within the structure. To understand the contribution of specific structural disorder to voltage hysteresis, one needs to consider the kinetics of the formation and recovery of each of these. In this work, we clarified the mechanism by which oxygen dimerization and transition metal migration induce voltage hysteresis using lithium-rich disordered rocksalt cathodes as a model compound. We identify the type of structural transformations that occur at an exceptionally rapid rate, potentially saturating during room-temperature ab-initio molecular dynamics simulations lasting several hundred picoseconds. This clarification indicates that the formation of certain structural disorder is not always directly linked to hysteresis. Furthermore, we confirm a correlation between oxygen dimerization and transition metal migration, demonstrating that they mutually promote each other. Our work provides a mechanistic understanding of how structural disorder induces voltage hysteresis in lithium-rich cathodes, thereby reconciling the debate over the cause of hysteresis.