Intrinsic origin of intra-granular cracking in Ni-rich layered oxide cathode material
Journal
PCCP (Physical Chemistry Chemical Physics)
Date
2017.12.14
Abstract
Mechanical degradation phenomena in layered oxide cathode materials during electrochemical cycling have limited their long-term usage because they deteriorate structural stability and result in poor capacity retention rate. Among them, intra-granular cracking inside primary particle progressively degrades performance of the cathode but comprehensive understanding on its intrinsic origin is still lacking. In this study, the mechanical properties of the primary particle in Ni-rich layered oxide cathode material (LiNi0.8Co0.1Mn0.1O2) are investigated under tensile and compressive deformation to both of in-plane and out-of-plane direction within the density functional theory framework. Young’s modulus and maximum strength values indicate that the pristine structure is more vulnerable to the tensile deformation than then compression. In addition, delithiation significantly deteriorates the mechanical properties regardless directions of the deformation. In particular, substantial degree of anisotropy is observed, indicating that the mechanical properties in the out-of-plane direction are much weaker than those in the in-plane. Particular weakness in that direction is further confirmed from using heterogeneously delithiated structures as well as calculating the accumulated mechanical stress values inside during delithiation. The comparison with the mechanical properties of the structure with lower Ni content (Ni=33 ％) demonstrates that the Ni-rich material is slightly weaker and hence; its intra-granular cracking could become accelerated during cycling.