Unrecoverable Lattice Rotation Governs Structural Degradation of Single-Crystalline Cathodes

Transitioning from polycrystalline to single-crystalline LiNi_xMn_yCo_zO₂ (NMC) cathodes has garnered considerable attention in both academia and industry, driven by many advantages such as high tap density and enhanced mechanical properties. While these metrics have facilitated the rapid commercialization of medium Ni content NMC, cathodes with higher nickel content (Ni > 70%) suffer from significant capacity degradation, posing a challenge to their commercial viability. The underlying cause of single crystal cathode’s failure that may differ inherently from polycrystalline remains elusive. Herein, leveraging novel multiscale spatial resolution diffraction and imaging techniques, we unveil that lattice rotations, a hidden factor that was overlooked due to the previous technique limitation, occurs universally in single-crystalline cathodes and plays a pivotal role in the structure degradation. Unlike the seemingly reversible structure evolution observed at macroscale, these lattice rotations prove unrecoverable and govern the accumulation of adverse lattice distortions over repeated cycles. This ultimately contributes to exacerbating structural and mechanical degradation, serving as the root cause of fast capacity fade. These findings bridge the previous knowledge gap that exists in the mechanistic link between fast performance failure and tiny atomic-scale structure degradation, thereby closing the loop on single-crystal cathodes degradation mechanism. We anticipate that this fundamental understanding will inspire compelling strategies in developing high performance cathode materials for next generation advanced batteries.