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

ABSTRACT

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.