Impact of lithium diffusion paths on electrochemical behavior of LiNi_0.6Co_0.2Mn_0.2O₂ cathode for lithium-ion batteries

Severe microcracks of polycrystal LiNi_xCo_yMn_zO₂ cathodes during cycling have led to increasing attention to the development of single-crystal cathodes. The single-crystal cathode particle is considered to induce a straight Li-ion diffusion through two-dimensional pathways in bulk compared with the pathways of grain boundary and cracks inside polycrystal particles. However, the effect of different paths on diffusion kinetics and the resulting electrochemical properties still needs to be better understood. In this work, the electrochemical performance of polycrystal and single-crystal cathodes caused by different diffusion paths was compared in detail. The results showed that grain boundaries and cracks of polycrystalline cathodes facilitate Li-ion diffusion. In contrast, relatively slow Li-ion diffusion occurs in the single-crystal cathode particles due to long diffusion paths. Moreover, the single-crystal cathode particles experience severe structural inhomogeneity due to the slow diffusion kinetics and inhomogeneous Li concentrations, resulting in structural distortion and localized strain increasing during cycling.