Microstructure Informed Mechanical Properties and Chemomechanical Degradation of Battery Cathode Particles

Abstract Background Mechanical degradation of electrodes driven by electrochemical reactions limits battery performance and longevity. While various microstructures of LiNi x Mn y Co z O 2 (NMC) cathodes have been developed, their comparative mechanical properties and chemomechanical degradation are unknown. Objective This study measures the mechanical properties of NMC cathode particles of three different microstructures: gravel-type NMC of large grains, gravel NMC of small grains, and rod-shaped NMC. Damage evolution in the NMC particles is simulated using finite element modeling. Methods We use flat punch indentation to measure the particle strength, contact modulus, and fracture energy of NMC particles of different microstructures. We also assess the effect of voids on the mechanical properties and damage generation in NMC particles upon cycles. Results The particle strength dictated by grain boundaries is measured to be ~ 200 MPa in the three NMC microstructures. The contact modulus changes nonlinearly during mechanical load. The fracture energy of gravel NMC particles is ~ 0.5 J/m 2 . The presence of voids compromises the mechanical properties of NMC particles, but it helps delocalize stress within the particles and reduces damage generation upon electrochemical cycles. Conclusions The combined experiments and modeling provide a comprehensive analysis of the mechanical behaviors and their implications on chemomechanical degradation of NMC cathode particles of various microstructures.