Unveiling the thermal decomposition mechanism of high-nickel cathode with loaded nano-Al₂O₃ on conductive carbon for safe lithium-ion batteries

High-nickel single-crystal LiNixCoyMnzO2 (NCM) has become the preferred cathode candidate for nextgeneration lithium-ion batteries because of its high capacity and great structural stability. Its thermal decomposition process and thermal stability enhancement strategies, however, require in-depth research before largescale implementation. In this work, atomic layer deposition (ALD) technique is used to uniformly load Al2O3 nanoparticles on acetylene black (AB). The modified AB was used as the conductive agent for single crystal LiNi0.87Co0.05Mn0.08O2 composite cathode to fabricate the electrode. It shows that the thermal stability of the delithiated composite cathodes with electrolytes is significantly improved such as the 44 % drop in maximum heat flow from 5.59 mW mg-1 to 3.15 mW mg-1 and the phase transition from spinel to rock salt is delayed with comparable electrochemical performance. Furthermore, the thermal decomposition mechanism of the delithiated composite cathodes with electrolytes was carefully investigated by ex-situ MS, XPS, DRIFT and TG-MS. Our results disclose that the nano-Al2O3 particles could catalyze the dehydrogenation reaction of solvent on the surface of cathode. If the cathode is consumed in such a more moderate way in advance, the heavy heat release due to the oxidation of solvents by active oxygen species will be reduced significantly, thus improving the thermal stability of the cathode and the safety of the battery.