The nature of irreversible phase transformation propagation in nickel-rich layered cathode for lithium-ion batteries

Ni-rich layered cathode is regarded as one of the most promising candidates to achieve lithium-ion batteries (LIBs) with high energy density. However, due to the irreversible phase transformation (IPT) and its eventual propagation from surface to the bulk of the material, Ni-rich layered cathode typically suffers from severe capacity fading, structure failure, and thermal instability, which greatly hinders its mass adoption. Hence, achieving an in-depth understanding of the IPT propagation mechanism in Ni-rich layered cathode is crucial in addressing these issues. Herein, the triggering factor of IPT propagation in Ni-rich cathode is verified to be the initial surface disordered cation mixing domain covered by a thin rock-salt phase, instead of the rock-salt phase itself. According to the density functional theory (DFT) results, it is further illustrated that the metastable cation mixing domain possesses a lower Ni migration energy barrier, which facilitates the migration of Ni ions towards the Li slab, and thus driving the propagation of IPT from surface to the bulk of the material. This finding clarifies a prevailing debate regarding the surface impurity phases of Ni-rich cathode material and reveals the origin of IPT propagation, which implies the principle and its effectiveness of tuning the surface microstructure to address the structural and thermal instability issue of Ni-rich layered cathode materials. CO 2021 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.

Automated summary

Ni-rich layered cathode is a promising candidate for high energy density lithium-ion batteries, but suffers from capacity fading, structure failure, and thermal instability due to irreversible phase transformation (IPT). Understanding the IPT propagation mechanism is crucial, with research showing that the triggering factor is the initial surface disordered cation mixing domain, rather than the rock-salt phase itself. This finding clarifies the debate on surface impurity phases and reveals the origin of IPT propagation, suggesting the importance of tuning the surface microstructure to address the instability issues.