From Brittle to Damage‐Tolerant: Particle‐Level Mechanical Reinforcement Enables High‐Voltage Stability in Ni‐Rich Cathodes

Mechanical degradation driven by stress accumulation and particle fracture is a critical barrier to the high-voltage operation of Ni-rich layered oxide cathodes, yet particle-level mechanical design strategies remain underdeveloped. Here, we demonstrate that coupling particle-level mechanical reinforcement with electrochemical stabilization enables a transition from brittle to damage-tolerant behavior in high-Ni cathodes. The mechanically reinforced material exhibits a nearly fivefold increase in single-particle crushing strength (from 9.52 to 45.50 MPa) compared with the undoped counterpart, despite a reduced Young's modulus, indicating a shift toward a more compliant and fracture-resistant mechanical response. Finite-element simulations incorporating experimentally measured mechanical parameters reveal substantially reduced internal stress accumulation and stress heterogeneity during electrochemical cycling, with the peak mean von Mises stress decreasing from ∼6.0 to <3.6 GPa at high states of charge. This stress mitigation suppresses crack initiation and propagation during the anisotropic lattice contraction associated with the H2-H3 phase transition, as further confirmed by in situ x-ray diffraction. As a result, the cathode delivers markedly enhanced electrochemical durability under harsh high-voltage conditions, retaining 81.0% of its capacity after 400 cycles at 1C between 3.0 and 4.6 V, compared to only 36.5% for the undoped material, alongside improved rate capability and reduced impedance growth. This work establishes particle-level mechanical robustness as a decisive parameter governing high-voltage stability and provides a generalizable, mechanics-informed design principle for developing damage-tolerant Ni-rich cathodes.