Probing the thermal degradation mechanism of polycrystalline and single-crystal Li(Ni0.8Co0.1Mn0.1)O2 cathodes from the perspective of oxygen vacancy diffusion

The Ni-rich cathode is one of the most promising materials for application in high-energy-density lithium-ion batteries. However, the inherent thermal instability of this material raises the risk of thermal runaway, which presents a significant obstacle to its eventual commercialization. At present, the in-depth mechanism of how grain structure affects the thermal stability of Ni-rich cathodes remains unclear. In this work, we study the thermal degradation behavior of polycrystalline and single-crystal NCM811 cathodes from multiple dimensions based on a series of state-of-the-art physicochemical characterization tools combined with theoretical calculations, report different degradation pathways of polycrystalline and single-crystal cathodes, and investigate the enhancement mechanism of single-crystal structure on the thermal stability of cathodes from the atomic scale. The larger grain size and better integrity of single-crystal NCM811 particle effectively retard the oxygen vacancy formation and increase oxygen vacancy diffusion paths at high temperatures. As a result, the diffusion of oxygen vacancies is kinetically unfavorable during heating, which delays the degradation of its lattice structure and the release of oxygen. This work provides insight into the thermal failure mechanisms of Ni-rich cathode materials with different grain structures and offers an essential theoretical basis for designing future thermally stable cathode materials.