Deciphering the synergistic mechanism for thermal stability improvement in Ni-rich single-crystal cathode materials <i>via</i> LiNbO<sub>3</sub> coating and Nb<sup>5+</sup> surface doping

<p>Ni-rich cathode materials are highly regarded for their potential in high-energy density lithium-ion batteries (LIBs). Nonetheless, their intrinsic thermal instability poses a significant risk of thermal runaway, which is a major obstacle to their commercial application. This study presents a novel approach to enhancing the thermal stability of Ni-rich cathode materials for LIBs through a synergistic modification strategy combining LiNbO<sub>3</sub> coating and Nb<sup>5+</sup> surface doping. By applying particle atomic layer deposition and high-temperature sintering, the modified cathode material Nb@SC-NCM811 shows better electrochemical performance. Thermal analysis reveals that Nb@SC-NCM811 has a higher thermal decomposition temperature, generates less heat, and releases less oxygen under thermal induction, indicating enhanced thermal stability. The microscopic mechanisms underlying the improvement of thermal stability are further revealed through aberration-corrected transmission electron microscopy and density functional theory calculations, which shows that the enhancement in thermal stability is due to the increased formation energy of oxygen vacancies and the raised energy barrier for interlayer migration of transition metal cations. This work provides insight into the Nb-modified mechanism of Ni-rich cathode materials and offers a promising avenue for designing safer, high-energy density LIBs.</p>