Lithium Clustering during the Lithiation/Delithiation Process in LiFePO₄ Olivine-Structured Materials

Olivine-structured LiFePO₄ is one of the most popular cathode materials in lithium-ion batteries (LIBs) for sustainable applications. Significant attention has been paid to investigating the dynamics of the lithiation/delithiation process in Li FePO₄ (0 ≤ x ≤ 1), which is crucial for the development of high-performance LiFePO₄ material. Various macroscopic models based on experimental evidence have been proposed to explain the mechanism of phase transition from LiFePO₄ to FePO₄, such as the shrinking core (i.e., core-shell) model, Laffont's (i.e., new core-shell) model, domino-cascade model, phase transformation wave, solid solution model, many-particle models, etc. However, these models, unfortunately, contradict each other and their validity is still under debate. An atomistic model is urgently required to depict the lithiation/delithiation process in Li FePO₄. In this article, we reveal the lithiation/delithiation process in LiFePO₄ simulated by a computational model using the generalized gradient approximation (GGA + U) method. We find that the clustered configuration is the most energetically favorable, leading to co-operative Jahn-Teller distortion among the inter-polyhedrons that can be observed clearly from the bond patterns. This atomistic model not only offers answers to experimental results obtained at moderate or high rates but also gives the direction to further improve the rate capability of LiFePO₄ cathode material for high-power LIBs.