Ni Migration-Induced Strain and Phase Segregation in LiNiO₂ Cathodes

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• High-nickel layered oxides offer high energy density for next-generation lithium-ion batteries.
• Structural instability at high voltages limits the practical application of these advanced cathode materials.

Purpose of the Study:

• To investigate the influence of nickel (Ni) migration on phase segregation, Li/Ni antisite defects, and mechanical degradation in LiNiO₂ (LNO).
• To link atomic-scale lattice distortions to long-term performance limitations in high-Ni cathodes.

Main Methods:

• Combined experimental techniques: Synchrotron X-ray Diffraction (XRD), Extended X-ray Absorption Fine Structure (EXAFS), Transmission Electron Microscopy (TEM).
• Computational analysis: Density Functional Theory (DFT) calculations.

Main Results:

• At high voltages, Ni migrates to tetrahedral sites, forming coexisting R3̅m phases with differing lattice behaviors.
• Phase segregation results in inhomogeneous lithium distribution, internal stress, strain accumulation, microcracking, and accelerated degradation.
• Continuous cycling leads to irreversible Li/Ni antisite defect accumulation, hindering Li-ion transport and destabilizing the structure.

Conclusions:

• Bulk Ni migration is a key factor driving phase segregation and structural degradation in high-Ni cathodes.
• Understanding Ni migration mechanisms provides insights for developing strategies, like selective doping, to enhance structural stability and battery performance.