Strain Mechanism Study on Li-rich Layered Cathode Materials Li-Ni-Mn-O for Li-ion Batteries

Lithium-rich layered oxides (LLOs) has attracted the attention of scientists due to its theoretical specific capacity exceeding 250 mAh center dot g(-1). It is considered the most promising new generation of lithium-ion battery cathode materials. However, the aggregation of Li2MnO3 domains and the release of lattice oxygen in LLOs can lead to severe capacity/voltage degradation, hindering their commercial applications. This work adopts a manganese-based lithium-rich layered Li1.17Ni0.165Co0.165Mn0.5O2 (Li-Ni-Co-Mn-O) model with C2/m symmetry. Select a 2x2x1 supercell with a total of 96 atoms, namely Li28Ni4Co4Mn12O48. Construct two systems, one with Co permeation into Li2MnO3 domain (LNCMO-P) and the other without (LNCMO-nP), to investigate the effect of Co permeation on the redox process and delithiation structure stability of Li2MnO3 domain and O. The spin-polarized generalized gradient approximation (GGA) method with PBE (Perdew Burke Ernzerhof) exchange-correlation function is adopted, and the projected augmented wave (PAW) potential function is selected to describe the interaction between ions and electrons to complete all calculations. The research results indicate that by regulating the concentration of oxygen vacancies, Co can penetrate Li2MnO3 domains. The permeation of Co alleviates the stress distortion between Li2MnO3 and LiTMO2 phases and suppresses the lattice strain caused by uneven electrochemical activity and structural evolution. The study on the geometry and electronic structure of the Li1.17Ni0.165Co0.165Mn0.5O2 system found that Co-Ni aggregation caused the appearance of high-spin Co electronic states, which alleviated the volume expansion caused by charging. The permeation of Co activates more interfacial oxygen, and oxygen at the interface participates in charge compensation and disperses oxygen oxidation, thereby sharing the oxidation pressure of oxygen in the Li-O-Li configuration, which is beneficial for suppressing the release of lattice oxygen and improving the problem of irreversible oxygen evolution caused by lattice oxygen reactions. This study provides a theoretical basis for designing lithium-rich cathode materials with high-performance structural stability.