Fracture mechanisms of NCM polycrystalline particles in lithium-ion batteries: A review

The development of high-energy LiNixCoyMnzO2 (NCM) cathode materials for lithium-ion batteries (LIBs) is central to many emerging technologies in the fields of power and energy storage. However, the limited cycle life of batteries caused by electrochemical and mechanical damage of NCM polycrystalline particles remains a crucial barrier to their applications. During the charging and discharging of batteries, the insertion and extraction of lithium-ions within the active particles induce diffusion-induced stresses, resulting in the fracture of NCM particles, which ultimately leads to a decline in the overall battery performance. In this review, the fracture mechanisms of NCM polycrystalline particles are systematically summarized, and the internal and intergranular defects in primary particles are comprehensively discussed, including dislocations, nanoscale pores, cation mixing oxygen vacancies grain boundaries and porosity. The influences of stress concentration, which occurs due to phase transitions, changes in the crystal structure and anisotropic volume variations during the insertion and extraction of lithium-ions, are also summarized in this work. These factors are the key to the initiation and propagation processes of intergranular and intragranular cracks in NCM polycrystalline particles. Finally, this review also aims to address the observation methods and existing research gaps related to the fracture damage mechanisms of NCM polycrystalline particles, which provide further assistance for the optimization design of NCM cathode materials and the precise prediction of battery performance degradation.